JP7804436B2 - Optical adhesive tape - Google Patents

Description

The present invention relates to an optical adhesive tape. In particular, it relates to an optical adhesive tape suitable for manufacturing a tiling display in which multiple image display devices are arranged in a tiled pattern.

With the trend toward higher image quality, such as 4K and 8K, demand for larger-screen image display devices is growing. Large-screen image display devices are also increasingly being used for signage, such as advertising displays and bulletin boards, outdoors and in public facilities. However, manufacturing large-screen image display devices poses problems, such as lower yields and higher manufacturing costs. To manufacture large-screen image display devices at lower cost, tiling displays, in which multiple image display devices are arranged in a tiled pattern, are being considered (see, for example, Patent Document 1).

JP 2017-161634 A

In a tiling display, the gaps between multiple image display devices must be narrow (for example, 100 μm or less) to make them less noticeable, but the image display devices may shrink or expand under usage conditions, creating small gaps or slight overlaps between the image display devices, making the gaps more noticeable and further reducing transparency and deteriorating the appearance. Another problem is that the adhesive layer that bonds the optical components that make up the image display device cannot keep up with the shrinkage and expansion of the image display device, causing lifting and peeling at the edges and deteriorating the appearance.

The present invention was conceived in light of the above circumstances, and its object is to provide an optical adhesive tape that, in a tiling display in which multiple image display devices are arranged in a tiled pattern, makes the gaps between the multiple image display devices less noticeable, maintains transparency, and maintains a good appearance even under certain usage conditions.

That is, the first aspect of the present invention provides an optical pressure-sensitive adhesive tape having a laminated structure in which a substrate has a first side and a second side, and a pressure-sensitive adhesive layer is laminated on the first side of the substrate.

The optical pressure-sensitive adhesive tape of the first aspect of the present invention exhibits an average dimensional change rate of ±0.15% or less in the width direction and machine direction when heated for 500 hours in an environment of 60°C and 90% relative humidity. The average dimensional change rate of ±0.15% is advantageous in that, in a tiling display in which a plurality of image display devices each having the optical pressure-sensitive adhesive tape of the first aspect of the present invention laminated thereon are arranged, shrinkage or expansion in the usage environment of the image display devices is suppressed, gaps between the image display devices are suppressed from becoming noticeable, a good appearance is maintained, and transparency can be maintained unchanged with little shrinkage or expansion. The average dimensional change rate is preferably within ±0.1%, and may be within ±0.05%, in terms of suppressing gaps between the image display devices from becoming noticeable, little shrinkage or expansion, and transparency can be maintained unchanged.

In the optical pressure-sensitive adhesive tape according to the first aspect of the present invention, the pressure-sensitive adhesive layer has a recovery rate determined in the following shear test of 95% or less.
<Shear test>
A disc-shaped pressure-sensitive adhesive layer having a thickness of 2 mm and a diameter of 7.9 mm was subjected to a torsional shear force of 500 Pa at 60°C from above and below for 600 seconds, and the amount of distortion A (%) was measured. The amount of distortion B (%) was then measured when the layer was held at a shear force of 0 Pa for 1,800 seconds, and the recovery rate (%) was calculated using the following formula.
Recovery rate (%) = (strain amount A - strain amount B) / strain amount A x 100

In this specification, unless otherwise specified, the terms "strain amount A," "strain amount B," and "recovery rate" refer to the "strain amount A," "strain amount B," and "recovery rate" determined in the shear test described above.

A configuration in which the recovery rate of the pressure-sensitive adhesive layer is 95% or less is preferable in that the pressure-sensitive adhesive layer can adequately adapt to contraction or expansion in the usage environment of an image display device to which the optical pressure-sensitive adhesive tape of the first aspect of the present invention is laminated, thereby preventing lifting or peeling, and maintaining transparency unchanged. It is also preferable in that, when an adherend such as an image display panel has uneven steps due to wiring or the like, the pressure-sensitive adhesive layer can adequately conform to the steps and fill them without leaving any air bubbles. In terms of preventing lifting or peeling of the optical pressure-sensitive adhesive tape of the first aspect of the present invention, maintaining transparency unchanged, and being able to conform to the steps, the recovery rate of the pressure-sensitive adhesive layer is preferably 94% or less, and may be 93.5% or less.

The average dimensional change rate in the width direction and the machine direction when the optical pressure-sensitive adhesive tape according to the first aspect of the present invention is heated for 500 hours in an environment of 60°C and 90% relative humidity is defined as C [%],
The pressure-sensitive adhesive layer of the optical pressure-sensitive adhesive tape is attached to a PET film having a thickness of 50 μm, and then cut into a 10 cm square. When the laminate is heated for 500 hours in an environment of 60°C and a relative humidity of 90%, the maximum curl amount D [mm] preferably satisfies the following formula:

|C×D|≦3

Maximum curl amount: The laminate was placed on a horizontal surface with the convex curled surface facing downwards, and the maximum curl amount D [mm] was the largest of the warps at the four corners. The maximum curl amount measured when the laminate was placed on a horizontal surface with the PET film side facing downwards was designated as "+," and the maximum curl amount measured when the laminate was placed on a horizontal surface with the substrate side facing downwards was designated as "-."

The configuration in which the absolute value |C×D| of the product of the average dimensional change rate C [%] and the maximum curl amount D [mm] is 3 or less is advantageous in that, in a tiling display in which a plurality of image display devices, each having the optical adhesive tape of the first aspect of the present invention laminated thereon, changes in the gap between the image display devices are less visible and the image display devices can be accurately bonded to the film substrate. In order to make changes in the gap between the image display devices less visible and to enable the image display devices to be accurately bonded to the film substrate, |C×D| is preferably 2.5 or less, more preferably 2.4 or less, and may be 2.3 or less, or 2.2 or less.

In the optical pressure-sensitive adhesive tape of the first aspect of the present invention, the strain amount A of the pressure-sensitive adhesive layer determined in the shear test described above is not particularly limited, but is preferably 3% or more. A configuration in which the strain amount A of the pressure-sensitive adhesive layer is 3% or more is preferable in that the pressure-sensitive adhesive layer can sufficiently adapt to contraction or expansion in the usage environment of an image display device to which the optical pressure-sensitive adhesive tape of the first aspect of the present invention is laminated, thereby preventing lifting or peeling. It is also preferable in that, when an adherend such as an image display panel has uneven steps due to wiring or the like, the pressure-sensitive adhesive layer can sufficiently adapt to the steps and fill them without leaving any air bubbles. In terms of preventing lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and being able to adapt to the steps, the strain amount A of the pressure-sensitive adhesive layer of the present invention is preferably 4% or more, and may be 5% or more.

In the optical pressure-sensitive adhesive tape of the first aspect of the present invention, the strain amount B of the pressure-sensitive adhesive layer determined in the shear test described above is not particularly limited, but is preferably 0.1% or more. A configuration in which the strain amount B of the pressure-sensitive adhesive layer is 0.1% or more is preferable in that the pressure-sensitive adhesive layer can sufficiently follow contraction or expansion in the usage environment of an image display device to which the optical pressure-sensitive adhesive tape of the first aspect of the present invention is laminated, thereby preventing lifting or peeling. It is also preferable in that, when an adherend such as an image display panel has uneven steps due to wiring or the like, the pressure-sensitive adhesive layer can sufficiently follow the steps and fill them without leaving any air bubbles. In terms of preventing lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and being able to follow the steps, the strain amount B of the pressure-sensitive adhesive layer of the present invention is preferably 0.2% or more, and may be 0.3% or more.

In the optical pressure-sensitive adhesive tape of the first aspect of the present invention, the glass transition point (Tg) of the substrate is preferably 60°C or higher. The configuration in which the glass transition point of the substrate is 60°C or higher is preferable in that, in a tiling display in which a plurality of image display devices, each having the optical pressure-sensitive adhesive tape of the first aspect of the present invention laminated thereon, are arranged, the mechanical properties of the image display device are stable in the usage environment. From the viewpoint of the stability of the mechanical properties of the image display device, the glass transition point of the substrate may be 63°C or higher, or 65°C or higher.

In the optical pressure-sensitive adhesive tape of the first aspect of the present invention, the glass transition point (Tg) of the pressure-sensitive adhesive layer is preferably -10°C or lower. The configuration in which the Tg of the pressure-sensitive adhesive layer is -10°C or lower is preferable in that the stress relaxation properties of the pressure-sensitive adhesive layer are maintained even in low-temperature environments, the pressure-sensitive adhesive layer can sufficiently follow contraction or expansion in the usage environment of an image display device to which the optical pressure-sensitive adhesive tape of the first aspect of the present invention is laminated, lifting or peeling can be suppressed, and sufficient adhesion to the adherend can be ensured. In terms of suppressing lifting or peeling in the image display device and ensuring good adhesion to the adherend, the glass transition point of the pressure-sensitive adhesive layer is preferably -15°C or lower, and may be -20°C or lower.

The optical pressure-sensitive adhesive tape of the first aspect of the present invention preferably has a humidity expansion coefficient of 0.1% or less when humidified from 60°C and 30% relative humidity to 60°C and 60% relative humidity. The humidity expansion coefficient of 0.1% or less is advantageous in a tiling display in which a plurality of image display devices, each having the optical pressure-sensitive adhesive tape of the first aspect of the present invention laminated thereon, in that it suppresses expansion of the image display devices due to moisture absorption, prevents gaps between the image display devices from becoming noticeable, and minimizes shrinkage or expansion, thereby maintaining transparency unchanged. From the viewpoint of suppressing expansion of the image display devices due to moisture absorption, minimizing shrinkage or expansion, and maintaining transparency unchanged, the humidity expansion coefficient is preferably 0.08% or less, and may be 0.06% or less.

In the optical pressure-sensitive adhesive tape according to the first aspect of the present invention, the substrate preferably has a humidity expansion coefficient of 5×10 ⁻⁵ /% RH or less. The humidity expansion coefficient of the substrate of 5×10 ⁻⁵ /% RH or less improves the dimensional stability of the substrate against humidity changes, and in a tiling display in which a plurality of image display devices, each having the optical pressure-sensitive adhesive tape according to the first aspect of the present invention laminated thereon, the humidity expansion coefficient of the substrate is preferably 5×10 ⁻⁵ /% RH or less, and may be 5×10 ⁻⁵ /% RH or less ...

In the optical pressure-sensitive adhesive tape according to the first aspect of the present invention, the second surface of the substrate is preferably anti-reflection and/or anti-glare treated. The configuration in which the second surface of the substrate is anti-reflection and/or anti-glare treated is preferable in that it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display device. It is also preferable in that in a tiled display in which a plurality of image display devices, each having the optical pressure-sensitive adhesive tape according to the first aspect of the present invention stacked thereon, are arranged, the gaps between the image display devices are less visible.

In the optical pressure-sensitive adhesive tape of the first aspect of the present invention, the pressure-sensitive adhesive layer is preferably an acrylic pressure-sensitive adhesive layer containing an acrylic polymer. This configuration is advantageous for adjusting the above-mentioned properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, and recovery rate).

A second aspect of the present invention provides an image display device in which the optical pressure-sensitive adhesive tape according to the first aspect of the present invention and an image display panel are laminated together. A third aspect of the present invention provides a tiling display in which a plurality of image display devices according to the second aspect of the present invention are arranged side by side.
The image display device according to the second aspect of the present invention has the optical pressure-sensitive adhesive tape according to the first aspect of the present invention in its laminated structure, and therefore is able to suppress shrinkage or expansion under usage conditions. Furthermore, even if the image display device according to the second aspect of the present invention shrinks or expands to a certain extent, the pressure-sensitive adhesive layer sufficiently follows the shrinkage or expansion of the image display device, making it less likely to lift or peel off. Therefore, in the tiling display according to the third aspect of the present invention, which is produced by arranging a plurality of image display devices according to the second aspect of the present invention, gaps between the image display devices are less noticeable under usage conditions, and a good appearance can be maintained. Furthermore, transparency can be maintained unchanged.

By using the optical adhesive tape of the present invention in the manufacture of a tiling display in which multiple image display devices are arranged, it is possible to suppress shrinkage or expansion in the environment in which the image display devices are used, making gaps between the image display devices less noticeable and maintaining a good appearance. Transparency can also be maintained unchanged. Furthermore, even if the image display devices expand or contract to a certain extent, the adhesive layer is less likely to lift or peel off, making it possible to efficiently manufacture high-performance tiling displays.

1A and 1B are schematic diagrams showing an embodiment of the optical pressure-sensitive adhesive tape of the present invention, in which (a) is a cross-sectional view and (b) is a top view. FIG. 2 is a schematic diagram (cross-sectional view) showing another embodiment of the optical pressure-sensitive adhesive tape of the present invention. FIG. 3 is a schematic diagram (cross-sectional view) showing one embodiment of the image display device of the present invention in which the optical pressure-sensitive adhesive tape of FIG. 2 is laminated. FIG. 4 is a schematic diagram (perspective view) showing one embodiment of the tiling display of the present invention. FIG. 5 is a schematic diagram (perspective view) for explaining the shear test.

A first aspect of the present invention provides an optical pressure-sensitive adhesive tape having a laminated structure in which a substrate having a first surface and a second surface and a pressure-sensitive adhesive layer are laminated on the first surface of the substrate.
In this specification, the optical pressure-sensitive adhesive tape according to the first aspect of the present invention may be referred to as the "optical pressure-sensitive adhesive tape of the present invention." Furthermore, in this specification, the substrate and pressure-sensitive adhesive layer constituting the optical pressure-sensitive adhesive tape of the present invention may be referred to as the "substrate of the present invention" and the "pressure-sensitive adhesive layer of the present invention," respectively. Furthermore, the term "pressure-sensitive adhesive tape" includes the meaning of "pressure-sensitive adhesive sheet." In other words, the optical pressure-sensitive adhesive tape of the present invention may be a pressure-sensitive adhesive sheet having a sheet-like form.

A second aspect of the present invention provides an image display device in which the optical pressure-sensitive adhesive tape according to the first aspect of the present invention and an image display panel are laminated together. In this specification, the image display device according to the second aspect of the present invention may be referred to as the "image display device of the present invention."
A third aspect of the present invention provides a tiling display in which a plurality of image display devices of the present invention are arranged. The tiling display of the third aspect of the present invention may be referred to as the "tiling display of the present invention" in this specification.

Embodiments of the optical adhesive tape of the present invention will be described below with reference to the drawings, but the present invention is not limited to these and is merely an example.

1A and 1B are schematic diagrams showing an embodiment of the optical pressure-sensitive adhesive tape of the present invention, in which (a) is a cross-sectional view and (b) is a top view.
1( a), an optical pressure-sensitive adhesive tape 10A has a laminated structure in which a substrate 1 and a pressure-sensitive adhesive layer 2 are laminated. The substrate 1 has a first surface 1 a and a second surface 1 b, and the pressure-sensitive adhesive layer 2 is laminated on the first surface 1 a of the substrate 1.
In FIG. 1( b ), the width direction (TD) and machine direction (MD) of the optical pressure-sensitive adhesive tape 10</b>A are determined to correspond to the width direction (TD) and machine direction (MD) of the substrate 1 .

In Figure 2, optical adhesive tape 10B has a laminated structure in which substrate 1 and adhesive layer 2 are laminated. Substrate 1 has a first surface 1a and a second surface 1b, and adhesive layer 2 is laminated on first surface 1a of substrate 1. Second surface 1b of substrate 1 has been subjected to anti-reflection treatment and/or anti-glare treatment 3.

Figure 3 is a schematic diagram (cross-sectional view) showing one embodiment of an image display device of the present invention. In Figure 3, the image display device 20 has an image display panel 4 laminated on the adhesive layer 2 of the optical adhesive tape 10B.

4 is a schematic diagram (perspective view) showing one embodiment of a tiling display of the present invention. In Fig. 4, the tiling display 30 is formed by arranging nine image display devices 20 (the stacked structure is not shown) in a 3 x 3 array in a tiled pattern on a support substrate 31, with the image display devices 20 adjacent to each other with gaps 32 between them.
Each component will be described below.

<Optical adhesive tape>
The term "optical" in the optical pressure-sensitive adhesive tape of the present invention means that it is used for optical applications, and more specifically, that it is used in the manufacture of products (optical products) that use optical members. Examples of optical products include image display devices and input devices such as touch panels, and the optical pressure-sensitive adhesive tape of the present invention can be suitably used in the manufacture of liquid crystal image display devices and self-luminous image display devices (e.g., organic EL (electroluminescence) image display devices and LED image display devices). In particular, the optical pressure-sensitive adhesive tape of the present invention is suitable for the manufacture of tiling displays in which multiple image display devices are arranged in a tiled pattern.

The optical pressure-sensitive adhesive tape of the present invention is not particularly limited in its form, so long as the pressure-sensitive adhesive layer of the present invention is laminated on the first surface of the substrate of the present invention. For example, it may be a single-sided pressure-sensitive adhesive tape in which only one surface is adhesive, or a double-sided pressure-sensitive adhesive tape in which both surfaces are adhesive. Furthermore, when the optical pressure-sensitive adhesive tape of the present invention is a double-sided pressure-sensitive adhesive tape, the optical pressure-sensitive adhesive tape of the present invention may have a form in which both adhesive surfaces are provided by the pressure-sensitive adhesive layer of the present invention, or a form in which one adhesive surface is provided by the pressure-sensitive adhesive layer of the present invention and the other adhesive surface is provided by a pressure-sensitive adhesive layer other than the pressure-sensitive adhesive layer of the present invention (another pressure-sensitive adhesive layer). When the optical pressure-sensitive adhesive tape of the present invention forms the outermost surface of an optical product, a single-sided pressure-sensitive adhesive tape is preferred, and when adherends (optical components) are to be bonded together, a double-sided pressure-sensitive adhesive tape is preferred.

In addition to the substrate and the pressure-sensitive adhesive layer of the present invention, the optical pressure-sensitive adhesive tape of the present invention may also have other layers on the surface or between any of the layers, such as substrates other than the substrate of the present invention, pressure-sensitive adhesive layers other than the pressure-sensitive adhesive layer of the present invention, intermediate layers, undercoat layers, antistatic layers, separators, surface protection films, etc., as long as the effects of the present invention are not impaired.

The optical pressure-sensitive adhesive tape of the present invention has an average dimensional change rate of within ±0.15% in the width direction and machine direction when heated for 500 hours in an environment of 60°C and 90% relative humidity. The dimensional change rates in the width direction and machine direction are the percentage (%) of the amount of change in dimension after heating for 500 hours in an environment of 60°C and 90% relative humidity, with the initial dimensions in the width direction and machine direction, respectively, being 100%, and are calculated using the following formula.

Dimensional change rate (%) = [(dimension after heating for 500 hours in an environment of 60°C and 90% relative humidity) - (initial dimension)] / (initial dimension) x 100

For the dimensional change rate (%), "+" indicates expansion and "-" indicates contraction. The average dimensional change rate in the width direction and machine direction is the average value of the dimensional change rate in the width direction and the dimensional change rate in the machine direction, and is calculated using the following formula.

Average dimensional change rate (%) = [(dimensional change rate in the cross direction (%)) + (dimensional change rate in the machine direction (%))] / 2

The dimensions of the optical adhesive tape of the present invention are not particularly limited, but can generally be determined by measuring the lengths of the ends of the optical adhesive tape in the width direction and machine direction.

The configuration in which the average dimensional change rate is within ±0.15% is advantageous in the tiling display of the present invention in that it suppresses shrinkage or expansion in the usage environment of the image display device of the present invention, prevents gaps between the image display devices from becoming noticeable, maintains a good appearance, and minimizes shrinkage or expansion, maintaining transparency unchanged. In terms of preventing gaps between the image display devices from becoming noticeable, minimizes shrinkage or expansion, and maintaining transparency unchanged, the average dimensional change rate is preferably within ±0.1%, and may be within ±0.05%.

Specifically, the average dimensional change rate in the optical pressure-sensitive adhesive tape of the present invention can be measured by the method described in the Examples below. The average dimensional change rate in the optical pressure-sensitive adhesive tape of the present invention can be adjusted by adjusting the type and thickness of the resin constituting the substrate of the present invention, the humidity expansion coefficient and glass transition point of the substrate, the type of resin constituting the pressure-sensitive adhesive layer of the present invention, the monomer composition, degree of crosslinking, modulus of elasticity, glass transition point, etc.

The average dimensional change rate in the width direction and the machine direction when the optical pressure-sensitive adhesive tape of the present invention is heated for 500 hours in an environment of 60°C and 90% relative humidity is defined as C [%].
The pressure-sensitive adhesive layer of the optical pressure-sensitive adhesive tape is attached to a PET film having a thickness of 50 μm, and then cut into a 10 cm square. When the laminate is heated for 500 hours in an environment of 60°C and a relative humidity of 90%, the maximum curl amount D [mm] preferably satisfies the following formula:

|C×D|≦3

Maximum curl amount: The laminate was placed on a horizontal surface with the convex curled surface facing downwards, and the maximum curl amount D [mm] was the largest of the warps at the four corners. The maximum curl amount measured when the laminate was placed on a horizontal surface with the PET film side facing downwards was designated as "+," and the maximum curl amount measured when the laminate was placed on a horizontal surface with the substrate side facing downwards was designated as "-."

The configuration in which the absolute value |C×D| of the product of the average dimensional change rate C [%] and the maximum curl amount D [mm] is 3 or less is preferable in that, in a tiling display in which a plurality of image display devices, each having the optical pressure-sensitive adhesive tape of the present invention laminated thereon, are arranged, changes in the gap between the image display devices are difficult to visually recognize, and the image display devices can be bonded to the film substrate with high precision. In order to make changes in the gap between the image display devices difficult to visually recognize, and to allow the image display devices to be bonded to the film substrate with high precision, |C×D| is preferably 2.5 or less, more preferably 2.4 or less, and may be 2.3 or less, or 2.2 or less.
The lower limit of |C×D| is not particularly limited, and the lower the value, the better, but it may be 0.001 or more.

The absolute value of the maximum curl amount |D| [mm] is not particularly limited, but in a tiling display in which multiple image display devices each having the optical adhesive tape of the present invention laminated thereon are arranged, it is preferably 60 mm or less, more preferably 55 mm or less, and even more preferably 50 mm or less, so that the image display devices can be accurately attached to the film substrate.
The lower limit of |D| is not particularly limited, and the lower the better, but it may be 0.1 mm or more.

The |C×D| and |D| in the optical pressure-sensitive adhesive tape of the present invention can be specifically measured by the method described in the Examples below. The |C×D| and |D| in the optical pressure-sensitive adhesive tape of the present invention can be adjusted by adjusting the type and thickness of the resin constituting the substrate of the present invention, the humidity expansion coefficient and glass transition point of the substrate, the type of resin constituting the pressure-sensitive adhesive layer of the present invention, the monomer composition, degree of crosslinking, modulus of elasticity, glass transition point, etc.

The optical pressure-sensitive adhesive tape of the present invention preferably has a humidity expansion coefficient of 0.1% or less when humidified from 60°C and 30% relative humidity to 60°C and 60% relative humidity. A humidity expansion coefficient of 0.1% or less is advantageous in the tiling display of the present invention in that it suppresses expansion of the image display device of the present invention due to moisture absorption, prevents gaps between the image display devices from becoming noticeable, and minimizes shrinkage or expansion, thereby maintaining transparency unchanged. From the perspective of suppressing expansion of the image display device of the present invention due to moisture absorption, minimizes shrinkage or expansion, and maintains transparency unchanged, the humidity expansion coefficient is preferably 0.08% or less, and may be 0.06% or less.

Specifically, the humidity expansion coefficient of the optical pressure-sensitive adhesive tape of the present invention can be measured by the method described in the Examples below. The humidity expansion coefficient of the optical pressure-sensitive adhesive tape of the present invention can be adjusted by adjusting the type and thickness of the resin constituting the substrate of the present invention, the humidity expansion coefficient and glass transition point of the substrate, the type of resin constituting the pressure-sensitive adhesive layer of the present invention, the monomer composition, degree of crosslinking, modulus of elasticity, glass transition point, etc.

When the optical pressure-sensitive adhesive tape of the present invention is heated for 500 hours in an environment of 60°C and 90% relative humidity, the ratio of the dimensional change rate in the machine direction to the dimensional change rate in the width direction (machine direction dimensional change rate/width direction dimensional change rate) is not particularly limited, but is preferably 0.5 or more and 2.0 or less. Having this ratio within this range reduces the difference in dimensional change rate between the width direction and the machine direction in the usage environment of the image display device of the present invention in the tiling display of the present invention, which is advantageous in that it reduces the visibility of gaps between image display devices, maintains a good appearance, minimizes shrinkage or expansion, and maintains transparency without change. From the viewpoints of reducing the visibility of gaps between image display devices, minimizes shrinkage or expansion, and maintains transparency without change, the ratio is preferably 0.6 or more and 1.8 or less, and may be 0.7 or more and 1.5 or less.

The above ratio (machine direction dimensional change rate/width direction dimensional change rate) in the optical pressure-sensitive adhesive tape of the present invention can be adjusted by adjusting the type and thickness of the resin constituting the substrate of the present invention, the humidity expansion coefficient and glass transition point of the substrate, the manufacturing conditions of the substrate (e.g., extrusion molding temperature and speed), the type, monomer composition, degree of crosslinking, modulus of elasticity, glass transition point, etc. of the resin constituting the pressure-sensitive adhesive layer of the present invention.

The haze of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but is preferably 5% or more. A haze of 5% or more for the optical pressure-sensitive adhesive tape of the present invention is preferable because it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display panel in the image display device of the present invention, and because it makes gaps between image display devices in the tiling display of the present invention less visible. The haze is more preferably 6% or more, and may be 7% or more. The upper limit of the haze of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but from the viewpoint of visibility of the tiling display of the present invention, it is preferably 50% or less, and may be 40% or less, or 30% or less.

The haze of the optical pressure-sensitive adhesive tape of the present invention can be measured in accordance with JIS K 7136, specifically by the method described in the Examples below. The haze of the optical pressure-sensitive adhesive tape of the present invention can be adjusted by the type and thickness of the resin constituting the substrate of the present invention, the type and thickness of the resin constituting the pressure-sensitive adhesive layer of the present invention, or by applying an anti-reflection treatment and/or an anti-glare treatment to the substrate surface.

The reflectance of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but is preferably 5% or less. A configuration in which the reflectance of the optical pressure-sensitive adhesive tape of the present invention is 5% or less is preferable because it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display panel in the image display device of the present invention, and because it makes gaps between image display devices in the tiling display of the present invention less visible. The reflectance is more preferably 3% or less, and may be 1.5% or less. The lower limit of the reflectance of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but may be 0.1% or more, or 0.3% or more.

The reflectance of the optical pressure-sensitive adhesive tape of the present invention can be measured in accordance with JIS K7361-1, specifically by the method described in the Examples below. The reflectance of the optical pressure-sensitive adhesive tape of the present invention can be adjusted by adjusting the type and thickness of the resin constituting the substrate of the present invention, the type and thickness of the resin constituting the pressure-sensitive adhesive layer of the present invention, and applying an anti-reflection treatment and/or anti-glare treatment to the substrate surface.

The total light transmittance of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but is preferably 85% or more. A total light transmittance of 85% or more is preferred in that it allows for excellent transparency and an excellent appearance to be obtained in the image display device of the present invention, and is more preferably 88% or more, and may even be 90% or more. The upper limit of the total light transmittance of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but may be 95% or less.

The total light transmittance of the optical pressure-sensitive adhesive tape of the present invention can be measured in accordance with JIS K7361-1. The total light transmittance of the optical pressure-sensitive adhesive tape of the present invention can be adjusted by adjusting the type and thickness of the resin constituting the substrate of the present invention, the type and thickness of the resin constituting the pressure-sensitive adhesive layer of the present invention, and applying an anti-reflection treatment and/or an anti-glare treatment to the substrate surface.

The thickness of the optical pressure-sensitive adhesive tape of the present invention is not particularly limited, but taking into consideration factors such as dimensional stability, strength, workability (e.g., ease of handling), and thin layer properties, it is preferably in the range of 10 to 500 μm, more preferably in the range of 20 to 300 μm, and optimally in the range of 30 to 200 μm.

<Base material>
Examples of materials constituting the substrate of the present invention include glass and plastic films. Examples of the plastic film include polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), cyclic olefin polymers (COP) (for example, trade name "Arton" (manufactured by JSR Corporation) and trade name "ZEONOR" (manufactured by Zeon Corporation), acrylic resins such as polymethyl methacrylate (PMMA), and plastic materials such as polycarbonate (PC), triacetyl cellulose (TAC), polysulfone, polyarylate, polyether ether ketone (PEEK), polyimide (PI), transparent polyimide (CPI), polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, and ethylene-propylene copolymer. Polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), which have excellent dimensional stability and are resistant to shrinkage, cyclic olefin polymers (COP), polycarbonate (PC), polyether ether ketone (PEEK), and transparent polyimide (CPI) are preferred. These plastic materials can be used alone or in combination of two or more. The substrate of the present invention is the part that is attached to an adherend together with the pressure-sensitive adhesive layer when the optical pressure-sensitive adhesive tape of the present invention is attached to an adherend (such as an image display panel). The release liner that is peeled off when the optical pressure-sensitive adhesive tape of the present invention is used (applied) is not included in the "substrate".

The substrate of the present invention has a film-like (substrate-like) form having a first surface and a second surface. The width direction (TD) and machine direction (MD) of the substrate of the present invention are determined in the manufacturing process of the substrate. For example, the machine direction (MD) refers to the direction in which the film-like extruded body flows after extrusion molding of the raw resin material, and the width direction (TD) is the direction perpendicular to the machine direction.

The substrate of the present invention is not particularly limited as long as it is an optical component that constitutes the optical product, and examples thereof include various optical films such as cover members, polarizing plates, and retardation plates, and is preferably used as a cover member. When the substrate of the present invention is a cover member, the second surface becomes, for example, the outermost surface of the optical product.

The glass transition point (Tg) of the substrate of the present invention is not particularly limited, but is preferably 60°C or higher. A configuration in which the glass transition point of the substrate of the present invention is 60°C or higher is preferred in the tiling display of the present invention, as it stabilizes the mechanical properties of the image display device of the present invention under the usage environment. From the perspective of the stability of the mechanical properties of the image display device of the present invention, the glass transition point of the substrate may be 63°C or higher, or 65°C or higher. Furthermore, while the upper limit of the glass transition point of the substrate is not particularly limited, from the perspective of simplifying the substrate molding process, the glass transition point of the substrate is preferably 350°C or lower, and may be 250°C or lower, 200°C or lower, 140°C or lower, 130°C or lower, or 125°C or lower.

The glass transition point (Tg) of the substrate of the present invention can be measured in accordance with JIS K 7121. The glass transition point (Tg) of the substrate of the present invention can be adjusted by, for example, the type of resin that constitutes the substrate of the present invention.

The humidity expansion coefficient of the substrate of the present invention is not particularly limited, but is preferably 5×10 ⁻⁵ /% RH or less. A configuration in which the humidity expansion coefficient of the substrate of the present invention is 5×10 ⁻⁵ /% RH or less improves the dimensional stability of the substrate of the present invention against humidity changes, and in the tiling display of the present invention, it is preferable in that it suppresses shrinkage or expansion of the image display device of the present invention under the usage environment, suppresses gaps between the image display devices from becoming noticeable, maintains a good appearance, and can maintain transparency without change with little shrinkage or expansion. In terms of the dimensional stability of the substrate of the present invention, little shrinkage or expansion, and can maintain transparency without change, the humidity expansion coefficient of the substrate of the present invention is preferably 3×10 ⁻⁵ /% RH or less, and may be 2×10 ⁻⁵ /% RH or less.
The lower limit of the humidity expansion coefficient of the substrate of the present invention is not particularly limited, and the lower the better, but it may be 0.001×10 ⁻⁵ /% RH or more.

Specifically, the humidity expansion coefficient of the substrate of the present invention can be measured by the method described in the Examples below. The humidity expansion coefficient of the substrate of the present invention can be adjusted by the type of resin that constitutes the substrate of the present invention and the conditions during substrate production (temperature, extrusion speed, etc.).

The haze of the substrate of the present invention is not particularly limited, but is preferably 5% or more. A haze of 5% or more for the substrate of the present invention is preferred because it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display panel in the image display device of the present invention, and because it makes gaps between image display devices less visible in the tiling display of the present invention. It is more preferred that the haze be 6% or more, and may be 7% or more. The upper limit of the haze of the substrate of the present invention is not particularly limited, but from the viewpoint of visibility in the tiling display of the present invention, it is preferably 50% or less, and may be 40% or less, or 30% or less.

The haze of the substrate of the present invention can be measured in accordance with JIS K 7136. The haze of the substrate of the present invention can be adjusted by the type and thickness of the resin constituting the substrate of the present invention, or by applying an anti-reflection treatment and/or anti-glare treatment to the substrate surface.

The reflectance of the substrate of the present invention is not particularly limited, but is preferably 5% or less. A configuration in which the reflectance of the substrate of the present invention is 5% or less is preferable in that it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display panel in the image display device of the present invention, and in that it makes gaps between image display devices in the tiling display of the present invention less visible. The reflectance is more preferably 3% or less, and may be 1.5% or less. The lower limit of the reflectance of the substrate of the present invention is not particularly limited, but may be 0.1% or more, or 0.3% or more.

The reflectance of the substrate of the present invention can be measured in accordance with JIS K7361-1. The reflectance of the substrate of the present invention can be adjusted by the type and thickness of the resin constituting the substrate of the present invention, or by applying an anti-reflection treatment and/or anti-glare treatment to the substrate surface.

The thickness of the substrate of the present invention is not particularly limited, but taking into consideration factors such as dimensional stability, strength, workability (e.g., ease of handling), and thin layer properties, it is preferably in the range of 10 to 500 μm, more preferably 20 to 300 μm, and optimally 30 to 200 μm. The refractive index of the substrate of the present invention is not particularly limited, but is, for example, in the range of 1.30 to 1.80, preferably 1.40 to 1.70.

The second surface of the substrate of the present invention is preferably subjected to a reflective surface treatment and/or an anti-glare treatment. A configuration in which the second surface of the substrate of the present invention is subjected to a reflective surface treatment and/or an anti-glare treatment is preferable in that it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display device of the present invention. It is also preferable in that it makes gaps between image display devices less visible in the tiling display of the present invention.

The anti-reflection treatment can be any known anti-reflection treatment without any particular limitations, and examples include anti-reflection (AR) treatment.

The anti-reflection (AR) treatment can be any known AR treatment, with no particular restrictions. Specifically, it can be achieved by forming an optical thin film with strictly controlled thickness and refractive index on the second surface of the substrate of the present invention, or an anti-reflection layer (AR layer) consisting of two or more layers of such optical thin films. The AR layer exhibits anti-reflection function by utilizing the optical interference effect to cancel out the reversed phases of incident light and reflected light. The wavelength range of visible light that exhibits anti-reflection function is, for example, 380 to 780 nm, with the wavelength range of 450 to 650 nm having particularly high luminosity. It is preferable to design the AR layer to minimize the reflectance at the center wavelength of 550 nm.

The AR layer is typically a multilayer anti-reflection layer constructed by stacking two to five optically thin layers (thin films with strictly controlled thickness and refractive index). Forming multiple layers of components with different refractive indexes to a specified thickness increases the degree of freedom in the optical design of the AR layer, further improving the anti-reflection effect and making it possible to achieve uniform (flat) spectral reflectance characteristics across the visible light range. Because high thickness accuracy is required for these optical thin films, each layer is generally formed using dry methods such as vacuum deposition, sputtering, or CVD.

The AR layer can also be formed from a coating liquid for forming an anti-reflection layer. The coating liquid for forming an anti-reflection layer may contain, for example, a resin, a fluorine-containing additive, hollow particles, solid particles, a dilution solvent, etc., and can be produced, for example, by mixing these.

Examples of the resin include thermosetting resins and ionizing radiation curable resins that are cured by ultraviolet light or light. Commercially available thermosetting resins and ultraviolet curable resins can also be used as the resin.

The thermosetting resin or UV-curable resin can be, for example, a curable compound having at least one of an acrylate group and a methacrylate group that is cured by heat, light (UV light, etc.), or electron beams, etc. Examples include silicone resin, polyester resin, polyether resin, epoxy resin, urethane resin, alkyd resin, spiroacetal resin, polybutadiene resin, polythiolpolyene resin, and oligomers or prepolymers of acrylates or methacrylates of polyfunctional compounds such as polyhydric alcohols. These may be used alone or in combination of two or more types.

The resin may also contain a reactive diluent having at least one of an acrylate group and a methacrylate group. Examples of the reactive diluent include those described in JP 2008-88309 A, including monofunctional acrylates, monofunctional methacrylates, polyfunctional acrylates, and polyfunctional methacrylates. Trifunctional or higher acrylates and trifunctional or higher methacrylates are preferred as the reactive diluent. This is because they can enhance the hardness of the second surface of the substrate of the present invention. Examples of the reactive diluent include butanediol glycerin ether diacrylate, acrylate of isocyanuric acid, and methacrylate of isocyanuric acid. These may be used alone or in combination. The weight-average molecular weight of the resin before curing may be, for example, 100 or more, 300 or more, 500 or more, 1,000 or more, or 2,000 or more, or 100,000 or less, 70,000 or less, 50,000 or less, 30,000 or less, or 10,000 or less. If the weight-average molecular weight before curing is high, the hardness decreases, but cracking tends to be less likely to occur when bent. On the other hand, if the weight-average molecular weight before curing is low, the intermolecular crosslink density increases, and the hardness tends to increase.

The resin preferably contains a polyfunctional acrylate (e.g., pentasritol triacrylate).

To harden the curable resin, for example, a curing agent may be added. The curing agent is not particularly limited, and for example, known polymerization initiators (e.g., thermal polymerization initiators, photopolymerization initiators, etc.) can be used as appropriate. The amount of the curing agent added is not particularly limited, and may be, for example, 0.5 parts by weight or more, 1.0 parts by weight or more, 1.5 parts by weight or more, 2.0 parts by weight or more, or 2.5 parts by weight or more, or 15 parts by weight or less, 13 parts by weight or less, 10 parts by weight or less, 7 parts by weight or less, or 5 parts by weight or less, relative to 100 parts by weight of the resin in the coating liquid for forming the anti-reflection layer.

The fluorine-containing additive is not particularly limited, but may be, for example, an organic or inorganic compound containing fluorine in its molecule. The organic compound is not particularly limited, but examples include fluorine-containing antifouling coating agents, fluorine-containing acrylic compounds, and fluorine- and silicon-containing acrylic compounds. Specific examples of the organic compound include "KY-1203" manufactured by Shin-Etsu Chemical Co., Ltd. and "Megafac" manufactured by DIC Corporation. The inorganic compound is also not particularly limited. The amount of the fluorine-containing additive added is not particularly limited, but for example, the weight of fluorine in the solid content of the anti-reflection layer-forming coating solution may be, for example, 0.05 wt% or more, 0.1 wt% or more, 0.15 wt% or more, 0.20 wt% or more, or 0.25 wt% or more, or 20 wt% or less, 15 wt% or less, 10 wt% or less, 5 wt% or less, or 3 wt% or less, relative to the total weight of the solid content. Furthermore, for example, the weight of the fluorine-containing additive may be, for example, 0.05% by weight or more, 0.1% by weight or more, 0.15% by weight or more, 0.20% by weight or more, or 0.25% by weight or more, or 20% by weight or less, 15% by weight or less, 10% by weight or less, 5% by weight or less, or 3% by weight or less, relative to 100 parts by weight of the resin in the coating liquid for forming an anti-reflection layer.

The hollow particles are not particularly limited and may be, for example, silica particles, acrylic particles, acrylic-styrene copolymer particles, etc. Examples of the silica particles include products manufactured by JGC Catalysts and Chemicals Industries, Ltd., such as "Suluria 5320" and "Suluria 4320." The weight-average particle diameter of the hollow particles is not particularly limited and may be, for example, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, or 70 nm or more, or 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, or 110 nm or less. The shape of the hollow particles is not particularly limited and may be, for example, approximately spherical like beads or irregular shapes such as powder. However, approximately spherical particles are preferred, more preferably approximately spherical particles with an aspect ratio of 1.5 or less, and most preferably spherical particles. The addition of the hollow particles can, for example, achieve a low refractive index and excellent anti-reflection properties for the anti-reflection layer. The amount of hollow particles added is not particularly limited, and may be, for example, 30 parts by weight or more, 50 parts by weight or more, 70 parts by weight or more, 90 parts by weight or more, or 100 parts by weight or more, or 300 parts by weight or less, 270 parts by weight or less, 250 parts by weight or less, 200 parts by weight or less, or 180 parts by weight or less, relative to 100 parts by weight of the resin in the coating liquid for forming an antireflection layer. From the viewpoint of lowering the refractive index of the antireflection layer, it is preferable that the amount of hollow particles added is not too small, and from the viewpoint of ensuring the mechanical properties of the antireflection layer, it is preferable that the amount of hollow particles added is not too large.

The solid particles are not particularly limited, but may be, for example, silica particles, zirconium oxide particles, titanium-containing particles (e.g., titanium oxide particles), etc. Examples of the silica particles include products manufactured by Nissan Chemical Industries, Ltd., such as "MEK-2140Z-AC," "MIBK-ST," and "IPA-ST." The weight-average particle diameter of the solid particles is not particularly limited, but may be, for example, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, or 25 nm or more, or 300 nm or less, 250 nm or less, 200 nm or less, 150 nm or less, or 100 nm or less. The shape of the solid particles is not particularly limited, and may be, for example, approximately spherical in shape like beads or irregular in shape such as powder. However, approximately spherical particles are preferred, more preferably approximately spherical particles with an aspect ratio of 1.5 or less, and most preferably spherical particles. By adding the solid particles, for example, the fluorine-containing additive is more likely to be unevenly distributed on the surface of the applied coating liquid for forming an antireflection layer, thereby achieving excellent scratch resistance, a low refractive index, and good antireflection properties in the antireflection layer. The amount of the solid particles added is not particularly limited, and may be, for example, 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, or 25 parts by weight or more, or 150 parts by weight or less, 120 parts by weight or less, 100 parts by weight or less, or 80 parts by weight or less, relative to 100 parts by weight of the resin in the coating liquid for forming an antireflection layer.

The dilution solvent may be, for example, a mixed solvent containing MIBK (methyl isobutyl ketone) and PMA (propylene glycol monomethyl ether acetate). In this case, the mixing ratio is not particularly limited, but if the weight of MIBK is taken as 100% by weight, the weight of PMA may be, for example, 20% by weight or more, 50% by weight or more, 100% by weight or more, 150% by weight or more, or 200% by weight or more, or 400% by weight or less, 350% by weight or less, 300% by weight or less, or 250% by weight or less.

The dilution solvent may be a mixed solvent containing, for example, MIBK, PMA, and TBA (tertiary butyl alcohol). In this case, the mixing ratio is not particularly limited. However, when the weight of MIBK is taken as 100% by weight, the weight of PMA may be, for example, 10% by weight or more, 30% by weight or more, 50% by weight or more, 80% by weight or more, or 100% by weight or more, and may be 200% by weight or less, 180% by weight or less, 150% by weight or less, 130% by weight or less, or 110% by weight or less. Furthermore, when the weight of MIBK is taken as 100% by weight, the weight of TBA may be, for example, 10% by weight or more, 30% by weight or more, 50% by weight or more, 80% by weight or more, or 100% by weight or more, and may be 200% by weight or less, 180% by weight or less, 150% by weight or less, 130% by weight or less, or 110% by weight or less.

The amount of dilution solvent added is not particularly limited, and may be, for example, such that the weight of solids relative to the total weight of the anti-reflection layer-forming coating liquid is, for example, 0.1 wt % or more, 0.3 wt % or more, 0.5 wt % or more, 1.0 wt % or more, or 1.5 wt % or more, or 20 wt % or less, 15 wt % or less, 10 wt % or less, 5 wt % or less, or 3 wt % or less. From the perspective of ensuring coatability (wetting and leveling), it is preferable that the solids content is not too high, and from the perspective of preventing poor appearance due to drying, such as uneven air-drying and whitening, it is preferable that the solids content is not too low.

Next, the anti-reflection layer-forming coating liquid is applied to the second surface of the substrate of the present invention (the coating step). The coating method is not particularly limited, and known coating methods such as fountain coating, die coating, spin coating, spray coating, gravure coating, roll coating, and bar coating can be used as appropriate. The amount of the anti-reflection layer-forming coating liquid applied is also not particularly limited, and the thickness of the formed anti-reflection layer may be, for example, 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, 1.0 μm or more, or 2.0 μm or more, or 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less.

Next, the applied anti-reflection layer-forming coating liquid is dried to form a coating film (the coating film formation step). The drying temperature is not particularly limited, but may be, for example, in the range of 30 to 200°C. The drying temperature may be, for example, 40°C or higher, 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, 90°C or higher, or 100°C or higher, and may be 190°C or lower, 180°C or lower, 170°C or lower, 160°C or lower, 150°C or lower, 140°C or lower, 135°C or lower, 130°C or lower, 120°C or lower, or 110°C or lower. The drying time is not particularly limited, but may be, for example, 30 seconds or higher, 40 seconds or higher, 50 seconds or higher, or 60 seconds or higher, or 150 seconds or lower, 130 seconds or lower, 110 seconds or lower, or 90 seconds or lower.

Furthermore, the coating film may be cured (curing step). The curing can be carried out, for example, by heating, light irradiation, or the like. The light is not particularly limited, but may be, for example, ultraviolet light. The light source for the light irradiation is also not particularly limited, but may be, for example, a high-pressure mercury lamp. The irradiation dose of the energy ray source in the ultraviolet curing is preferably 50 to 500 mJ/ ^cm2 as the cumulative exposure dose at an ultraviolet wavelength of 365 nm. If the irradiation dose is 50 mJ/ ^cm2 or more, the curing proceeds sufficiently, and the hardness of the formed antireflection layer is likely to be high. Furthermore, if the irradiation dose is 500 mJ/ ^cm2 or less, coloration of the formed antireflection layer can be prevented.

The anti-glare (AG) treatment can be any known AG treatment without any particular restrictions, and can be performed, for example, by forming an anti-glare layer on the second surface of the substrate of the present invention. Any known anti-glare layer can be used without any restrictions, and is generally formed as a layer in which inorganic or organic particles are dispersed as an anti-glare agent in a resin.

The anti-glare layer is not particularly limited, but may be formed, for example, using an anti-glare layer-forming material containing resin, particles, and a thixotropy-imparting agent, and convex portions are formed on the surface of the anti-glare layer as the particles and the thixotropy-imparting agent aggregate. This configuration allows the anti-glare layer to have excellent display characteristics, combining anti-glare properties with prevention of white blur. Furthermore, despite the anti-glare layer being formed using particle aggregation, it is possible to prevent the occurrence of protrusions on the surface of the anti-glare layer, which can be a visual defect, thereby improving product yield.

Examples of the resin include thermosetting resins and ionizing radiation curable resins that are cured by ultraviolet light or light. Commercially available thermosetting resins and ultraviolet curable resins can also be used as the resin.

The thermosetting resin or UV-curable resin can be, for example, a curable compound having at least one of an acrylate group and a methacrylate group that is cured by heat, light (UV light, etc.), or electron beams, etc. Examples include silicone resin, polyester resin, polyether resin, epoxy resin, urethane resin, alkyd resin, spiroacetal resin, polybutadiene resin, polythiolpolyene resin, and oligomers or prepolymers of acrylates or methacrylates of polyfunctional compounds such as polyhydric alcohols. These may be used alone or in combination of two or more types.

The resin may also contain a reactive diluent having at least one of an acrylate group and a methacrylate group. Examples of the reactive diluent include those described in JP 2008-88309 A, including monofunctional acrylates, monofunctional methacrylates, polyfunctional acrylates, and polyfunctional methacrylates. Trifunctional or higher functional acrylates and trifunctional or higher functional methacrylates are preferred as the reactive diluent. This is because they can improve the hardness of the anti-glare layer. Examples of the reactive diluent include butanediol glycerin ether diacrylate, acrylate of isocyanuric acid, and methacrylate of isocyanuric acid. These may be used alone or in combination.

The resin preferably contains a urethane acrylate resin, and more preferably is a copolymer of a curable urethane acrylate resin and a polyfunctional acrylate (e.g., pentasthitol triacrylate).

The particles used to form the anti-glare layer primarily function to impart anti-glare properties to the surface of the resulting anti-glare layer by creating an irregular shape and to control the haze value of the anti-glare layer. The haze value of the anti-glare layer can be designed by controlling the difference in refractive index between the particles and the resin. Examples of the particles include inorganic and organic particles. The inorganic particles are not particularly limited, and examples include silicon oxide particles, titanium oxide particles, aluminum oxide particles, zinc oxide particles, tin oxide particles, zirconium oxide particles, calcium carbonate particles, barium sulfate particles, talc particles, kaolin particles, and calcium sulfate particles. The organic particles are not particularly limited, and examples include polymethyl methacrylate resin powder (PMMA fine particles), silicone resin powder, polystyrene resin powder, polycarbonate resin powder, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyethylene fluoride resin powder. These inorganic particles and organic particles may be used alone or in combination of two or more types.

The weight-average particle size (D) of the particles is preferably in the range of 2.5 to 10 μm. By setting the weight-average particle size of the particles in this range, for example, excellent anti-glare properties can be achieved and white blur can be prevented. The weight-average particle size of the particles is more preferably in the range of 3 to 7 μm. The weight-average particle size of the particles can be measured, for example, by the Coulter count method. For example, a particle size distribution measuring device using the pore electrical resistance method (product name: Coulter Multisizer, manufactured by Beckman Coulter) is used to measure the electrical resistance of the electrolyte, which corresponds to the volume of the particles when they pass through the pores, to measure the number and volume of the particles and calculate the weight-average particle size.

The shape of the particles is not particularly limited and may be, for example, roughly spherical like beads or irregularly shaped like powder, but roughly spherical particles are preferred, more preferably roughly spherical particles with an aspect ratio of 1.5 or less, and most preferably spherical particles.

The ratio of the particles in the anti-glare layer is preferably in the range of 0.2 to 12 parts by weight, more preferably 0.5 to 12 parts by weight, and even more preferably 1 to 7 parts by weight, per 100 parts by weight of the resin. By keeping the ratio in this range, for example, excellent anti-glare properties can be achieved and white blur can be prevented.

The anti-glare layer may contain a thixotropy-imparting agent. By including the thixotropy-imparting agent, it is possible to easily control the aggregation state of the particles. Examples of thixotropy-imparting agents used to form the anti-glare layer include organic clay, polyolefin oxide, and modified urea.

The organoclay is preferably clay that has been organically treated to improve its affinity with the resin. Examples of organoclay include layered organoclay. The organoclay may be homemade or commercially available. Examples of the commercially available products include Lucentite SAN, Lucentite STN, Lucentite SEN, Lucentite SPN, Somasif ME-100, Somasif MAE, Somasif MTE, Somasif MEE, and Somasif MPE (trade names, all manufactured by Co-op Chemical Co., Ltd.); Esben, Esben C, Esben E, Esben W, Esben P, Esben WX, Esben N-400, Esben NX, Esben NX80, Esben NO12S, Esben NEZ, Esben NO12, Esben NE, Esben NZ, Esben NZ70, Organite, Organite D, and Organite T (trade names, all manufactured by Hojun Co., Ltd.); Kunipia F, Kunipia G, and Kunipia G4 (trade names, all manufactured by Kunimine Industries Co., Ltd.); Thixogel VZ, Clayton HT, and Clayton 40 (trade names, all manufactured by Rockwood Chemical Co., Ltd.). Examples include Additives.

The oxidized polyolefin may be prepared in-house or a commercially available product may be used. Examples of commercially available products include Disparlon 4200-20 (trade name, manufactured by Kusumoto Chemical Co., Ltd.) and Flonon SA300 (trade name, manufactured by Kyoeisha Chemical Co., Ltd.).

The modified urea is a reaction product of an isocyanate monomer or its adduct with an organic amine. The modified urea may be prepared in-house or a commercially available product may be used. Examples of commercially available products include BYK410 (manufactured by BYK-Chemie).

The thixotropy-imparting agents may be used alone or in combination of two or more.

The height of the convex ridge portion from the roughness mean line of the anti-glare layer is preferably less than 0.4 times the thickness of the anti-glare layer. More preferably, it is in the range of 0.01 to less than 0.4 times, and even more preferably, it is in the range of 0.01 to less than 0.3 times. This range effectively prevents the formation of protrusions on the convex ridge portion that could cause appearance defects. Having convex ridge portions of this height makes the anti-glare layer less likely to cause appearance defects. Here, the height from the mean line can be measured, for example, by the method described in JP 2017-138620 A.

The proportion of the thixotropy-imparting agent in the anti-glare layer is preferably in the range of 0.1 to 5 parts by weight, and more preferably in the range of 0.2 to 4 parts by weight, per 100 parts by weight of the resin.

The thickness (d) of the anti-glare layer is not particularly limited, but is preferably in the range of 3 to 12 μm. By setting the thickness (d) of the anti-glare layer within this range, for example, it is possible to prevent curling of the optical pressure-sensitive adhesive tape of the present invention, and to avoid problems such as poor transportability and reduced productivity. Furthermore, when the thickness (d) is within this range, the weight-average particle size (D) of the particles is preferably in the range of 2.5 to 10 μm, as described above. The combination of the thickness (d) of the anti-glare layer and the weight-average particle size (D) of the particles described above can achieve even better anti-glare properties. The thickness (d) of the anti-glare layer is more preferably in the range of 3 to 8 μm.

The relationship between the thickness (d) of the anti-glare layer and the weight average particle size (D) of the particles is preferably within the range of 0.3≦D/d≦0.9. This relationship results in an anti-glare layer with superior anti-glare properties, prevention of white blur, and no appearance defects.

As described above, in the optical pressure-sensitive adhesive tape of the present invention, the particles and the thixotropy-imparting agent aggregate to form convex portions on the surface of the anti-glare layer. In the aggregates that form the convex portions, the particles are present in a state of being aggregated in the surface direction of the anti-glare layer. This gives the convex portions a gentle shape. By having convex portions of this shape, the anti-glare layer can maintain anti-glare properties, prevent white blurring, and reduce the likelihood of appearance defects.

The surface shape of the anti-glare layer can be designed as desired by controlling the aggregation state of the particles contained in the anti-glare layer-forming material. The aggregation state of the particles can be controlled, for example, by the material of the particles (e.g., the chemical modification state of the particle surface, affinity for solvents or resins, etc.), the type and combination of resins (binders) or solvents, etc. Here, the aggregation state of the particles can be controlled by a thixotropy-imparting agent contained in the anti-glare layer-forming material. As a result, the aggregation state of the particles can be controlled as described above, and the convex portions can be made to have a smooth shape.

When the substrate of the optical pressure-sensitive adhesive tape of the present invention is formed from a resin or the like, it is preferable that a permeation layer be present at the interface between the substrate of the present invention and the anti-glare layer. The permeation layer is formed when the resin component contained in the material forming the anti-glare layer permeates into the substrate of the present invention. The formation of the permeation layer is preferable because it can improve the adhesion between the substrate of the present invention and the anti-glare layer. The permeation layer preferably has a thickness in the range of 0.2 to 3 μm, more preferably 0.5 to 2 μm. For example, when the substrate of the present invention is a polyester resin and the resin contained in the anti-glare layer is an acrylic resin, the permeation layer can be formed. The permeation layer can be confirmed, and its thickness can be measured, for example, by observing a cross-section of the optical pressure-sensitive adhesive tape of the present invention with a transmission electron microscope (TEM).

Even when applied to the optical pressure-sensitive adhesive tape of the present invention having such a permeation layer, it is possible to easily form the desired smooth surface irregularities that combine anti-glare properties with prevention of white blur. The permeation layer is preferably formed thicker for substrates that have poorer adhesion to the anti-glare layer in order to improve adhesion.

In the anti-glare layer, it is preferable that the number of appearance defects having a maximum diameter of 200 μm or more is one or less per m ² of the anti-glare layer. More preferably, there are no appearance defects.

In the uneven shape of the surface of the anti-glare layer, the average tilt angle θa (°) is preferably in the range of 0.1 to 5.0, more preferably in the range of 0.3 to 4.5, even more preferably in the range of 1.0 to 4.0, and particularly preferably in the range of 1.6 to 4.0. Here, the average tilt angle θa is a value defined by the following mathematical formula (1). The average tilt angle θa is a value measured, for example, by the method described in JP 2017-138620 A.
Average inclination angle θa=tan-1Δa (1)

In the above formula (1), Δa is the value obtained by dividing the sum (h1 + h2 + h3 ... + hn) of the differences (heights h) between the peaks of adjacent peaks and the lowest points of adjacent valleys in the reference length L of a roughness curve defined in JIS B 0601 (1994 edition) by the reference length L, as shown in the following formula (2): The roughness curve is a curve obtained by removing surface waviness components longer than a predetermined wavelength from a profile curve using a phase difference compensation high-pass filter. The profile curve is the outline that appears at the cut surface when the target surface is cut by a plane perpendicular to the target surface.
Δa=(h1+h2+h3...+hn)/L (2)

When θa is within the above range, the anti-glare properties are superior and white blur can be prevented.

When forming the anti-glare layer, it is preferable that the prepared anti-glare layer-forming material (coating liquid) exhibits thixotropy, and the Ti value, as defined below, is preferably in the range of 1.3 to 3.5, more preferably in the range of 1.3 to 2.8.
Ti value = β1/β2
Here, β1 is the viscosity measured using a HAAKE RheoStress 6000 at a shear rate of 20 (1/s), and β2 is the viscosity measured using a HAAKE RheoStress 6000 at a shear rate of 200 (1/s).

If the Ti value is less than 1.3, defects in appearance are more likely to occur, and anti-glare properties and white blur characteristics will deteriorate. Furthermore, if the Ti value exceeds 3.5, the particles will be less likely to aggregate and will be more likely to remain dispersed.

The anti-glare layer can be manufactured by any method without particular limitations. For example, the anti-glare layer can be manufactured by preparing an anti-glare layer-forming material (coating liquid) containing the resin, particles, thixotropy-imparting agent, and solvent, applying the anti-glare layer-forming material (coating liquid) to the second surface of the substrate of the present invention to form a coating film, and curing the coating film to form the anti-glare layer. Methods for imparting a textured shape using a mold transfer method or an appropriate method such as sandblasting or an embossing roll can also be used in combination.

The solvent is not particularly limited, and various solvents can be used. One type may be used alone, or two or more types may be used in combination. The optimal solvent type and solvent ratio depend on the composition of the resin, the type and content of the particles and the thixotropy-imparting agent, etc. The solvent is not particularly limited, but examples include alcohols such as methanol, ethanol, isopropyl alcohol, butanol, and 2-methoxyethanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclopentanone; esters such as methyl acetate, ethyl acetate, and butyl acetate; ethers such as diisopropyl ether and propylene glycol monomethyl ether; glycols such as ethylene glycol and propylene glycol; cellosolves such as ethyl cellosolve and butyl cellosolve; aliphatic hydrocarbons such as hexane, heptane, and octane; and aromatic hydrocarbons such as benzene, toluene, and xylene.

When a polyester resin is used as the substrate of the present invention to form the permeation layer, a good solvent for the polyester resin can be suitably used. Examples of such solvents include ethyl acetate, methyl ethyl ketone, and cyclopentanone.

By appropriately selecting the solvent, the thixotropy-imparting agent can effectively impart thixotropy to the anti-glare layer-forming material (coating liquid). For example, when using an organoclay, toluene and xylene can be used alone or in combination. For example, when using an oxidized polyolefin, methyl ethyl ketone, ethyl acetate, and propylene glycol monomethyl ether can be used alone or in combination. For example, when using a modified urea, butyl acetate and methyl isobutyl ketone can be used alone or in combination.

Various leveling agents can be added to the anti-glare layer-forming material. For example, fluorine-based or silicone-based leveling agents can be used as the leveling agent to prevent coating unevenness (uniformity of the coated surface). An appropriate leveling agent can be selected depending on whether antifouling properties are required on the surface of the anti-glare layer, or whether an anti-reflection layer (low refractive index layer) or a layer containing an interlayer filler is formed on the anti-glare layer. For example, adding the thixotropy-imparting agent can impart thixotropy to the coating liquid, making coating unevenness less likely to occur. This has the advantage of broadening the options for the leveling agent, for example.

The amount of the leveling agent added is, for example, 5 parts by weight or less, preferably in the range of 0.01 to 5 parts by weight, per 100 parts by weight of the resin.

If necessary, pigments, fillers, dispersants, plasticizers, UV absorbers, surfactants, antifouling agents, antioxidants, etc. may be added to the anti-glare layer-forming material, provided that the additives do not impair performance. These additives may be used alone or in combination of two or more.

The anti-glare layer-forming material can be a conventionally known photopolymerization initiator, such as that described in JP-A-2008-88309.

Examples of methods that can be used to coat the anti-glare layer-forming material on the second surface of the substrate of the present invention include fountain coating, die coating, spin coating, spray coating, gravure coating, roll coating, and bar coating.

The anti-glare layer-forming material is applied to the substrate of the present invention to form a coating film, and the coating film is then cured. Prior to the curing, it is preferable to dry the coating film. The drying may be, for example, natural drying, air drying by blowing air, heat drying, or a combination of these methods.

The means for curing the coating film of the anti-glare layer-forming material is not particularly limited, but ultraviolet curing is preferred. The irradiation dose of the energy ray source is preferably 50 to 500 mJ/ ^cm2 as the cumulative exposure dose at an ultraviolet wavelength of 365 nm. If the irradiation dose is 50 mJ/ ^cm2 or more, curing will be more sufficient, and the hardness of the formed anti-glare layer will also be more sufficient. Furthermore, if the irradiation dose is 500 mJ/ ^cm2 or less, coloration of the formed anti-glare layer can be prevented.

In this manner, the anti-glare layer can be formed on the second surface of the substrate of the present invention. It should be noted that the anti-glare layer may also be formed by a manufacturing method other than the method described above. The hardness of the anti-glare layer is preferably a pencil hardness of 2H or more, although this is also affected by the thickness of the layer.

The anti-glare layer may have a multi-layer structure in which two or more layers are stacked.

The above-mentioned AR layer (low refractive index layer) may be disposed on top of the anti-glare layer. For example, when optical adhesive tape is attached to an image display device, one of the factors that reduces image visibility is light reflection at the interface between air and the anti-glare layer. The AR layer reduces this surface reflection. Note that the anti-glare layer and anti-reflection layer may each have a multi-layer structure in which two or more layers are stacked.

In addition, to prevent adhesion of contaminants and to improve ease of removal of adhered contaminants, it is preferable to laminate an anti-contamination layer formed from a fluorine group-containing silane compound or a fluorine group-containing organic compound on the anti-reflection layer and/or anti-glare layer.

It is preferable to perform a surface treatment on at least one of the substrate of the present invention and the anti-glare layer. By performing a surface treatment on the surface of the substrate of the present invention, adhesion to the anti-glare layer is further improved. Furthermore, by performing a surface treatment on the surface of the anti-glare layer, adhesion to the AR layer is further improved.

To prevent curling of the substrate of the present invention, the other surface of the anti-glare layer may be subjected to a solvent treatment. Furthermore, to prevent curling, a transparent resin layer may be formed on the other surface of the anti-glare layer.

<Adhesive Layer>
The pressure-sensitive adhesive layer of the present invention may be a pressure-sensitive adhesive layer that does not have a substrate (substrate layer), or may be a pressure-sensitive adhesive layer of a type that has a substrate. In this specification, a pressure-sensitive adhesive layer that does not have a substrate (substrate layer) may be referred to as a "substrate-less pressure-sensitive adhesive layer," and a pressure-sensitive adhesive layer of a type that has a substrate may be referred to as a "substrate-attached pressure-sensitive adhesive layer." Examples of the substrate-less pressure-sensitive adhesive layer include a single-layer pressure-sensitive adhesive layer consisting of only the pressure-sensitive adhesive layer of the present invention, and a pressure-sensitive adhesive layer consisting of the pressure-sensitive adhesive layer of the present invention and another pressure-sensitive adhesive layer (a pressure-sensitive adhesive layer other than the pressure-sensitive adhesive layer of the present invention). Examples of the substrate-attached pressure-sensitive adhesive layer include a pressure-sensitive adhesive layer having the pressure-sensitive adhesive layer of the present invention on both sides of the substrate, and a pressure-sensitive adhesive layer having the pressure-sensitive adhesive layer of the present invention on one side of the substrate and another pressure-sensitive adhesive layer on the other side. The "substrate (substrate layer)" constituting the "substrate-attached pressure-sensitive adhesive layer" can be a plastic film similar to the substrate of the present invention.

The recovery rate of the pressure-sensitive adhesive layer of the present invention is 95% or less as determined by the shear test described below.
<Shear test>
A disc-shaped pressure-sensitive adhesive layer having a thickness of 2 mm and a diameter of 7.9 mm was subjected to a torsional shear force of 500 Pa at 60°C from above and below for 600 seconds, and the amount of distortion A (%) was measured. The amount of distortion B (%) was then measured when the layer was held at a shear force of 0 Pa for 1,800 seconds, and the recovery rate (%) was calculated using the following formula.
Recovery rate (%) = (strain amount A - strain amount B) / strain amount A x 100

The above-mentioned "shear test" will be explained with reference to the drawings. Fig. 5 is a schematic diagram for explaining the shear test, in which 40 indicates a pressure-sensitive adhesive layer, and 41 and 42 indicate parallel plates.
The adhesive layer 40 is a disc-shaped adhesive layer having a thickness of 2 mm and a diameter of 7.9 mm, and is made of the adhesive layer of the present invention. The parallel plates 41 and 42 each have a top and bottom surface with a diameter of 7.9 mm and are made of, for example, stainless steel ( FIG. 5( a) ). The top surface of the parallel plate 41 and the bottom surface of the parallel plate 42 are aligned and abutted against the bottom and top surfaces of the adhesive layer 40, respectively ( FIG. 5( b) ). Next, the ambient temperature is set to 60° C., and a torsional shear force F of 500 Pa is applied to the adhesive layer 40 for 600 seconds ( FIG. 5( c) ). Next, the shear force of the parallel plates 41 and 42 is released, and the adhesive layer 40 is left at a shear force of 0 Pa for 1,800 seconds ( FIG. 5( d) ). "Strain A" is the percentage (%) of the amount of change in the torsional direction at the time point (FIG. 5(c)) when shear force F is applied for 600 seconds relative to the outer periphery (100%) of the pressure-sensitive adhesive layer 40 initially (FIG. 5(b)). "Strain B" is the percentage (%) of the amount of change in the torsional direction at the time point (FIG. 5(d)) when shear force F is applied for 600 seconds and then left at a shear force of 0 Pa for 1800 seconds relative to the outer periphery (100%) of the pressure-sensitive adhesive layer 40 initially (FIG. 5(b)). The recovery rate (%) is calculated using the following formula.
Recovery rate (%) = (strain amount A - strain amount B) / strain amount A x 100

A configuration in which the pressure-sensitive adhesive layer of the present invention has a recovery rate of 95% or less is preferable because the pressure-sensitive adhesive layer can adequately adapt to contraction or expansion in the usage environment of the image display device of the present invention, suppress lifting or peeling, and maintain transparency without change. It is also preferable because, when an adherend such as an image display panel has uneven surfaces due to wiring or the like, the pressure-sensitive adhesive layer can adequately conform to the uneven surfaces and fill them without leaving any air bubbles. In order to suppress lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention, maintain transparency without change, and conform to uneven surfaces, the recovery rate of the pressure-sensitive adhesive layer of the present invention is preferably 94% or less, and may be 93.5% or less. The lower limit of the recovery rate of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the viewpoint of processability, such as reducing the risk of problems such as the pressure-sensitive adhesive layer protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, it is preferably 70% or more, and may be 80% or more, or 85% or more.

The strain amount A of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but is preferably 3% or more. A configuration in which the strain amount A of the pressure-sensitive adhesive layer of the present invention is 3% or more is preferred because the pressure-sensitive adhesive layer can adequately adapt to contraction or expansion in the usage environment of the image display device of the present invention, thereby suppressing lifting or peeling. This is also preferred because, when an adherend such as an image display panel has unevenness due to wiring or the like, the pressure-sensitive adhesive layer can adequately conform to the unevenness and fill it without leaving any air bubbles. In order to suppress lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and to be able to conform to the unevenness, the strain amount A of the pressure-sensitive adhesive layer of the present invention is preferably 4% or more, and may be 5% or more. The upper limit of the strain amount A of the present invention is not particularly limited, but from the viewpoints of processability, such as reducing the risk of problems such as the pressure-sensitive adhesive layer protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, and maintaining transparency without change, the strain amount A is preferably 25% or less, and may be 20% or less, or 15% or less.

The strain amount B of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but is preferably 0.1% or more. A configuration in which the strain amount B of the pressure-sensitive adhesive layer of the present invention is 0.1% or more is preferred because the pressure-sensitive adhesive layer can adequately follow contraction or expansion in the usage environment of the image display device of the present invention, thereby suppressing lifting or peeling. This is also preferred because, when an adherend such as an image display panel has unevenness due to wiring or the like, the pressure-sensitive adhesive layer can adequately follow the unevenness and fill it without leaving any air bubbles. In order to suppress lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and to be able to follow the unevenness, the strain amount B of the pressure-sensitive adhesive layer of the present invention is preferably 0.2% or more, and may be 0.3% or more. The upper limit of the strain amount B of the present invention is not particularly limited, but from the viewpoints of processability, such as reducing the risk of problems such as the pressure-sensitive adhesive layer protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, and maintaining transparency without change, the strain amount B is preferably 10% or less, and may be 8% or less, or 5% or less.

The strain amount A, strain amount B, and recovery rate of the pressure-sensitive adhesive layer of the present invention are measured by a shear test in the Examples described below. The strain amount A, strain amount B, and recovery rate of the present invention can be adjusted by the composition of the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer of the present invention (e.g., the type and molecular weight of the base polymer, the amount used, the monomer composition, the type and amount of functional groups, and the type and amount of the crosslinking agent), the curing conditions (heating conditions, radiation exposure conditions), etc.

The pressure-sensitive adhesive layer of the present invention preferably has a glass transition point (Tg) of -10°C or lower. The pressure-sensitive adhesive layer of the present invention having a Tg of -10°C or lower is preferable because it maintains the stress relaxation properties of the pressure-sensitive adhesive layer even in low-temperature environments, allows the pressure-sensitive adhesive layer to adequately follow contraction or expansion in the usage environment of the image display device of the present invention, suppresses lifting or peeling, and ensures sufficient adhesion to the adherend. From the viewpoint of suppressing lifting or peeling in the image display device of the present invention and maintaining good adhesion to the adherend, the pressure-sensitive adhesive layer of the present invention preferably has a glass transition point of -15°C or lower, and may also have a glass transition point of -20°C or lower. The lower limit of the Tg of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the viewpoint of processability, such as preventing problems such as the pressure-sensitive adhesive layer from protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, it is preferably -50°C or higher, and may also have a glass transition point of -40°C or higher.

The glass transition temperature (Tg) of the pressure-sensitive adhesive layer of the present invention is measured by dynamic viscoelasticity measurement in the Examples below. The glass transition temperature (Tg) of the pressure-sensitive adhesive layer of the present invention can be adjusted by the composition of the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer of the present invention (e.g., the type and molecular weight of the base polymer, the amount used, the monomer composition, the type and amount of functional groups, and the type and amount of the crosslinking agent) and the curing conditions (heating conditions, radiation exposure conditions), etc.

The storage modulus of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is not particularly limited, but is preferably 80 kPa or less. A configuration in which the storage modulus of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is 80 kPa or less is preferred because the pressure-sensitive adhesive layer of the present invention can adequately adapt to contraction or expansion in the usage environment of the image display device of the present invention, thereby preventing lifting or peeling. This is also preferred because, when an adherend such as an image display panel has uneven surfaces due to wiring or other irregularities, the pressure-sensitive adhesive layer can adequately conform to the uneven surfaces and fill them without leaving any air bubbles. In terms of preventing lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and being able to conform to the uneven surfaces, the storage modulus of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is more preferably 70 kPa or less, and may be 60 kPa or less, or even 50 kPa or less. The lower limit of the storage modulus at 70°C and 1 Hz of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the viewpoint of processability, such as preventing problems such as the pressure-sensitive adhesive layer from protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, it is preferably 1 kPa or more, and may be 5 kPa or more.

The loss tangent of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is not particularly limited, but is preferably 0.15 or greater. A configuration in which the loss tangent of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is 0.15 or greater is preferred because the pressure-sensitive adhesive layer of the present invention can adequately adapt to contraction or expansion in the usage environment of the image display device of the present invention, thereby suppressing lifting or peeling. This is also preferred because, when an adherend such as an image display panel has unevenness due to wiring or other factors, the pressure-sensitive adhesive layer can adequately conform to the unevenness and fill it without leaving any air bubbles. In order to suppress lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and to be able to conform to the unevenness, the loss tangent of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is preferably 0.2 or greater, and may be 0.25 or greater, or even 0.3 or greater. The upper limit of the loss tangent of the pressure-sensitive adhesive layer of the present invention at 70°C and 1 Hz is not particularly limited, but from the viewpoint of processability, such as reducing the risk of the pressure-sensitive adhesive layer protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, the loss tangent is preferably 1 or less, and may be 0.8 or less.

The storage modulus and loss tangent at 70°C and 1 Hz of the pressure-sensitive adhesive layer of the present invention are measured by dynamic viscoelasticity measurement in the Examples described below. The storage modulus and loss tangent at 70°C and 1 Hz of the pressure-sensitive adhesive layer of the present invention can be adjusted by the composition of the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer of the present invention (e.g., the type and molecular weight of the base polymer, the amount used, the monomer composition, the type and amount of functional groups, and the type and amount of crosslinking agent) and the curing conditions (heating conditions, radiation exposure conditions), etc.

The shear force when a pressure-sensitive adhesive layer of the present invention having an adhesive area of 1 ^cm2 is attached to a resin plate and pulled in the shear direction at a tensile speed of 0.06 mm/min at 23°C is not particularly limited, but is preferably 20 N/ ^cm2 or less. In this specification, unless otherwise specified, the term "shear force" refers to "the shear force when a pressure-sensitive adhesive layer having an adhesive area of 1 ^cm2 is attached to a resin plate and pulled in the shear direction at a tensile speed of 0.06 mm/min at 23°C."

The shear strength of the pressure-sensitive adhesive layer of the present invention is preferably 20 N/cm ² or less, since the pressure-sensitive adhesive layer of the present invention can sufficiently follow contraction or expansion in the usage environment of the image display device of the present invention, thereby suppressing lifting or peeling. Furthermore, when an adherend such as an image display panel has unevenness due to wiring or the like, the pressure-sensitive adhesive layer can sufficiently follow the unevenness and fill it without leaving any air bubbles. In order to suppress lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and to be able to follow the unevenness, the shear strength of the pressure-sensitive adhesive layer of the present invention is more preferably 15 N/cm ² or less, and may be 13 N/cm ² or less. The lower limit of the shear strength of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the viewpoint of processability, such as preventing problems such as the pressure-sensitive adhesive layer from protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, it is preferably 5 N/cm ² or more, and may be 7 N/cm ² or more.

The shear strength of the pressure-sensitive adhesive layer of the present invention is measured by the shear force measurement method described in the Examples below. The shear strength of the pressure-sensitive adhesive layer of the present invention can be adjusted by the composition of the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer of the present invention (e.g., the type and molecular weight of the base polymer, the amount used, the monomer composition, the type and amount of functional groups, and the type and amount of crosslinking agent) and the curing conditions (heating conditions, radiation exposure conditions), etc.

The 300% tensile residual stress value of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but is preferably 10 N/ ^cm2 or less. A configuration in which the 300% tensile residual stress value of the pressure-sensitive adhesive layer of the present invention is 10 N/ ^cm2 or less is preferred in that the pressure-sensitive adhesive layer of the present invention can sufficiently follow contraction or expansion in the usage environment of the image display device of the present invention, thereby suppressing lifting or peeling. It is also preferred in that, when an adherend such as an image display panel has uneven steps due to wiring or the like, the pressure-sensitive adhesive layer can sufficiently follow the steps and fill them without leaving any air bubbles. In terms of suppressing lifting or peeling of the optical pressure-sensitive adhesive tape of the present invention and being able to follow the steps, the 300% tensile residual stress value of the pressure-sensitive adhesive layer of the present invention is more preferably 7 N/ ^cm2 or less, and may be 5 N/ ^cm2 or less. The lower limit of the 300% tensile residual stress value of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the viewpoint of processability, such as preventing problems such as the pressure-sensitive adhesive layer from protruding from the edges during storage of the optical pressure-sensitive adhesive tape of the present invention, it is preferably 1 N/ ^cm2 or more, and may be 1.5 N/ ^cm2 or more.

The 300% tensile residual stress value of the pressure-sensitive adhesive layer of the present invention is measured by the 300% tensile residual stress value measurement in the Examples below. The 300% tensile residual stress value of the pressure-sensitive adhesive layer of the present invention can be adjusted by the composition of the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer of the present invention (e.g., the type and molecular weight of the base polymer, the amount used, the monomer composition, the type and amount of functional groups, the type and amount of crosslinking agent) and the curing conditions (heating conditions, radiation exposure conditions), etc.

The adhesive that constitutes the adhesive layer of the present invention is not particularly limited, but examples include acrylic adhesives, rubber adhesives, vinyl alkyl ether adhesives, silicone adhesives, polyester adhesives, polyamide adhesives, urethane adhesives, fluorine-based adhesives, and epoxy adhesives. Among these, acrylic adhesives are preferred as the adhesive that constitutes the adhesive layer in terms of transparency, adhesion, weather resistance, cost, and ease of adhesive design. In other words, the adhesive layer of the present invention is preferably an acrylic adhesive layer composed of an acrylic adhesive. The above adhesives can be used alone or in combination of two or more.

The acrylic pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer. The acrylic polymer is a polymer containing an acrylic monomer (a monomer having a (meth)acryloyl group in the molecule) as a monomer component constituting the polymer. The acrylic polymer is preferably a polymer containing a (meth)acrylic acid alkyl ester as a monomer component constituting the polymer. The acrylic polymers can be used alone or in combination of two or more types.

The pressure-sensitive adhesive composition forming the pressure-sensitive adhesive layer of the present invention may be in any form. For example, the pressure-sensitive adhesive composition may be an emulsion type, a solvent type (solution type), an active energy ray curable type, a hot melt type, or the like. Among these, solvent-type and active energy ray curable pressure-sensitive adhesive compositions are preferred from the standpoint of productivity and the ease with which a pressure-sensitive adhesive layer with excellent optical properties and appearance can be obtained. In particular, active energy ray curable pressure-sensitive adhesive compositions are preferred from the standpoint of ease in controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition point, etc.) within specified ranges.

In other words, the pressure-sensitive adhesive layer of the present invention is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer, and is preferably formed from an active energy ray-curable acrylic pressure-sensitive adhesive composition.

Examples of the active energy rays include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. In other words, the active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable pressure-sensitive adhesive composition.

Examples of the adhesive composition (acrylic adhesive composition) that forms the acrylic adhesive layer include an acrylic adhesive composition containing an acrylic polymer as an essential component, and an acrylic adhesive composition containing a mixture of monomers (sometimes referred to as a "monomer mixture") that constitute an acrylic polymer or a partially polymerized product thereof as an essential component. Examples of the former include so-called solvent-based acrylic adhesive compositions. Examples of the latter include so-called active energy ray-curable acrylic adhesive compositions. The "monomer mixture" refers to a mixture containing the monomer components that constitute the polymer. The "partially polymerized product" is sometimes referred to as a "prepolymer" and refers to a composition in which one or more of the monomer components in the monomer mixture are partially polymerized.

The acrylic polymer is a polymer constituted (formed) using an acrylic monomer as an essential monomer component. The acrylic polymer is preferably a polymer constituted (formed) using a (meth)acrylic acid alkyl ester as an essential monomer component. That is, the acrylic polymer preferably contains a (meth)acrylic acid alkyl ester as a structural unit. In this specification, "(meth)acrylic" refers to "acrylic" and/or "methacrylic" (either one or both of "acrylic" and "methacrylic"), and similarly applies to other terms. The acrylic polymer is constituted by one or more monomer components.

Preferred examples of the (meth)acrylic acid alkyl ester as an essential monomer component include (meth)acrylic acid alkyl esters having a linear or branched alkyl group. These (meth)acrylic acid alkyl esters can be used alone or in combination of two or more.

Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and nonaphthalene (meth)acrylate. [0043] Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 1 to 20 carbon atoms include alkyl (meth)acrylates such as methyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate), isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, the (meth)acrylic acid alkyl ester having a linear or branched alkyl group is preferably a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 4 to 18 carbon atoms, and more preferably 2-ethylhexyl acrylate (2EHA), isostearyl acrylate (ISTA), lauryl acrylate (LA), or butyl acrylate (BA). Furthermore, the above-mentioned (meth)acrylic acid alkyl esters having a linear or branched alkyl group can be used alone or in combination of two or more types.

The proportion of the (meth)acrylic acid alkyl ester in all monomer components (100% by weight) constituting the acrylic polymer is not particularly limited, but is preferably 50% by weight or more (e.g., 50 to 100% by weight), more preferably 53 to 90% by weight, and even more preferably 55 to 85% by weight.

The acrylic pressure-sensitive adhesive composition may also contain the above-mentioned (meth)acrylic acid alkyl ester in addition to the above-mentioned acrylic polymer. When the acrylic pressure-sensitive adhesive composition contains the (meth)acrylic acid alkyl ester in addition to the acrylic polymer, the content (blended amount) of the (meth)acrylic acid alkyl ester is preferably 10 parts by weight or more (e.g., 10 to 100 parts by weight), more preferably 20 to 90 parts by weight, and even more preferably 30 to 80 parts by weight, per 100 parts by weight of the acrylic polymer.

The acrylic polymer may contain a copolymerizable monomer in addition to the alkyl (meth)acrylate ester as a monomer component constituting the polymer. That is, the acrylic polymer may contain a copolymerizable monomer as a structural unit. The copolymerizable monomer may be used alone or in combination of two or more types.

The copolymerizable monomer is not particularly limited, but from the viewpoints of easily controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges, suppressing clouding in high-humidity environments and improving durability, adhesive reliability, compatibility with various additives such as UV absorbers, and transparency, preferred examples include monomers having a nitrogen atom in the molecule and monomers having a hydroxyl group in the molecule. In other words, the acrylic polymer preferably contains, as a structural unit, a monomer having a nitrogen atom in the molecule. Furthermore, the acrylic polymer preferably contains, as a structural unit, a monomer having a hydroxyl group in the molecule.

The above-mentioned monomer having a nitrogen atom in its molecule is a monomer having at least one nitrogen atom in its molecule (per molecule). In this specification, the above-mentioned "monomer having a nitrogen atom in its molecule" may be referred to as a "nitrogen atom-containing monomer." The above-mentioned nitrogen atom-containing monomer is not particularly limited, but preferred examples include cyclic nitrogen-containing monomers and (meth)acrylamides. The nitrogen atom-containing monomers can be used alone or in combination of two or more types.

The cyclic nitrogen-containing monomer is not particularly limited as long as it has a polymerizable functional group with an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and a cyclic nitrogen structure. The cyclic nitrogen structure preferably has a nitrogen atom within the cyclic structure.

Examples of the cyclic nitrogen-containing monomer include N-vinyl cyclic amides (lactam vinyl monomers) and vinyl monomers having nitrogen-containing heterocycles.

Examples of the N-vinyl cyclic amide include N-vinyl cyclic amides represented by the following formula (1):
(In formula (1), ^R1 represents a divalent organic group.)

R ¹ in the above formula (1) is a divalent organic group, preferably a divalent saturated or unsaturated hydrocarbon group, and more preferably a divalent saturated hydrocarbon group (for example, an alkylene group having 3 to 5 carbon atoms).

Examples of N-vinyl cyclic amides represented by the above formula (1) include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, and N-vinyl-3,5-morpholinedione.

Examples of the vinyl monomer having a nitrogen-containing heterocycle include acrylic monomers having a nitrogen-containing heterocycle such as a morpholine ring, piperidine ring, pyrrolidine ring, or piperazine ring.

The vinyl monomer having the nitrogen-containing heterocycle is not particularly limited, but examples include (meth)acryloylmorpholine, N-vinylpiperazine, N-vinylpyrrole, N-vinylimidazole, N-vinylpyrazine, N-vinylmorpholine, N-vinylpyrazole, vinylpyridine, vinylpyrimidine, vinyloxazole, vinylisoxazole, vinylthiazole, vinylisothiazole, vinylpyridazine, (meth)acryloylpyrrolidone, (meth)acryloylpyrrolidine, and (meth)acryloylpiperidine.

Among the vinyl monomers having a nitrogen-containing heterocycle, acrylic monomers having a nitrogen-containing heterocycle are preferred, with (meth)acryloylmorpholine, (meth)acryloylpyrrolidine, and (meth)acryloylpiperidine being more preferred.

Examples of the (meth)acrylamides include (meth)acrylamide, N-alkyl(meth)acrylamide, and N,N-dialkyl(meth)acrylamide. Examples of the N-alkyl(meth)acrylamide include N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide, and N-octyl(meth)acrylamide. Furthermore, the N-alkyl(meth)acrylamides also include (meth)acrylamides having an amino group, such as dimethylaminoethyl(meth)acrylamide, diethylaminoethyl(meth)acrylamide, and dimethylaminopropyl(meth)acrylamide. Examples of the N,N-dialkyl(meth)acrylamides include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide.

The above-mentioned (meth)acrylamides also include, for example, various N-hydroxyalkyl(meth)acrylamides. Examples of the above-mentioned N-hydroxyalkyl(meth)acrylamides include N-methylol(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, N-(4-hydroxybutyl)(meth)acrylamide, and N-methyl-N-2-hydroxyethyl(meth)acrylamide.

The above-mentioned (meth)acrylamides also include, for example, various N-alkoxyalkyl(meth)acrylamides. Examples of the above-mentioned N-alkoxyalkyl(meth)acrylamides include N-methoxymethyl(meth)acrylamide and N-butoxymethyl(meth)acrylamide.

Furthermore, examples of nitrogen atom-containing monomers other than the above-mentioned cyclic nitrogen-containing monomers and the above-mentioned (meth)acrylamides include amino group-containing monomers, cyano group-containing monomers, imide group-containing monomers, and isocyanate group-containing monomers. Examples of the amino group-containing monomers include aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate. Examples of the cyano group-containing monomers include acrylonitrile and methacrylonitrile. Examples of the imide group-containing monomer include maleimide monomers (e.g., N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc.), itaconimide monomers (e.g., N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-laurylitaconimide, N-cyclohexylitaconimide, etc.), and succinimide monomers (e.g., N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth)acryloyl-8-oxyoctamethylenesuccinimide, etc.). Examples of the isocyanate group-containing monomer include 2-(meth)acryloyloxyethyl isocyanate.

Among these, cyclic nitrogen-containing monomers are preferred as the nitrogen atom-containing monomers, and N-vinyl cyclic amides are more preferred. More specifically, N-vinyl-2-pyrrolidone (NVP) is particularly preferred.

When the acrylic polymer contains the nitrogen-containing monomer as a monomer component constituting the polymer, the proportion of the nitrogen-containing monomer in the total monomer components (100% by weight) constituting the acrylic polymer is not particularly limited, but is preferably 1% by weight or more, more preferably 3% by weight or more, and even more preferably 5% by weight or more. A proportion of 1% by weight or more is preferable because it further suppresses clouding in high-humidity environments, improves durability, and provides high adhesive reliability. Furthermore, the upper limit of the proportion of the nitrogen-containing monomer is preferably 30% by weight or less, more preferably 25% by weight or less, and even more preferably 20% by weight or less, from the viewpoints of obtaining a pressure-sensitive adhesive layer with appropriate flexibility, obtaining a pressure-sensitive adhesive layer with excellent transparency, and easily controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges.

The monomer having a hydroxyl group in its molecule is a monomer having at least one hydroxyl group in its molecule (within one molecule), and is preferably one having a polymerizable functional group with an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and also having a hydroxyl group. However, the monomer having a hydroxyl group in its molecule does not include the nitrogen-containing monomer. In other words, in this specification, a monomer having both a nitrogen atom and a hydroxyl group in its molecule is included in the "nitrogen-containing monomer." In this specification, the "monomer having a hydroxyl group in its molecule" may be referred to as a "hydroxyl-containing monomer." The hydroxyl-containing monomers can be used alone or in combination of two or more.

Examples of the hydroxyl group-containing monomer include hydroxyl group-containing (meth)acrylic acid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and 4-hydroxymethylcyclohexyl (meth)acrylate; vinyl alcohol; and allyl alcohol.

Among these, the hydroxyl group-containing monomer is preferably a hydroxyl group-containing (meth)acrylic acid ester, more preferably 2-hydroxyethyl acrylate (HEA) or 4-hydroxybutyl acrylate (4HBA).

When the acrylic polymer contains the hydroxyl group-containing monomer as a monomer component constituting the polymer, the proportion of the hydroxyl group-containing monomer in the total monomer components (100% by weight) constituting the acrylic polymer is not particularly limited, but is preferably 0.5% by weight or more, more preferably 0.8% by weight or more, and even more preferably 1% by weight or more, from the viewpoints of suppressing clouding in high-humidity environments, improving durability, and achieving high adhesive reliability. Furthermore, the upper limit of the proportion of the hydroxyl group-containing monomer is preferably 30% by weight or less, more preferably 25% by weight or less, and even more preferably 20% by weight or less, from the viewpoint of easily controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges.

In addition, to further enhance the effects of the hydroxyl group-containing monomer, the acrylic pressure-sensitive adhesive composition may contain a hydroxyl group-containing monomer in addition to the acrylic polymer. When the acrylic pressure-sensitive adhesive composition contains a hydroxyl group-containing monomer in addition to the acrylic polymer, the content (amount) of the hydroxyl group-containing monomer is preferably 1 part by weight or more, more preferably 3 parts by weight or more, and even more preferably 5 parts by weight or more, per 100 parts by weight of the acrylic polymer. A content of 5 parts by weight or more is preferable because it further suppresses clouding in high-humidity environments, improves durability, and provides higher adhesive reliability. Furthermore, the upper limit of the content (amount) of the hydroxyl group-containing monomer is preferably 30 parts by weight or less, more preferably 25 parts by weight or less, even more preferably 20 parts by weight or less, and particularly preferably 17 parts by weight or less, in terms of cohesive strength, adhesiveness, ease of achieving adhesive reliability, and ease of controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges.

The total proportion of the nitrogen-containing monomer and the hydroxyl-containing monomer in all monomer components (100% by weight) constituting the acrylic polymer is not particularly limited, but is preferably 5% by weight or more, more preferably 10% by weight or more, and even more preferably 15% by weight or more, in order to suppress clouding in high-humidity environments, improve durability, and achieve high adhesive reliability. Furthermore, the upper limit of the total proportion is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 35% by weight or less, in order to obtain a pressure-sensitive adhesive layer with appropriate flexibility, excellent transparency, and ease of controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges.

Further examples of copolymerizable monomers other than nitrogen atom-containing monomers and hydroxyl group-containing monomers include alicyclic structure-containing monomers. The alicyclic structure-containing monomers are not particularly limited as long as they have a polymerizable functional group with an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and an alicyclic structure. For example, alkyl (meth)acrylates having a cycloalkyl group are included in the alicyclic structure-containing monomers. The alicyclic structure-containing monomers can be used alone or in combination of two or more.

The alicyclic structure in the above alicyclic structure-containing monomer is a cyclic hydrocarbon structure, preferably having 5 or more carbon atoms, more preferably 6 to 24 carbon atoms, even more preferably 6 to 15 carbon atoms, and particularly preferably 6 to 10 carbon atoms.

Examples of the alicyclic structure-containing monomer include (meth)acrylic monomers such as cyclopropyl (meth)acrylate, cyclobutyl (meth)acrylate, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, HPMPA represented by the following formula (2), TMA-2 represented by the following formula (3), and HCPA represented by the following formula (4). In formula (4), the bonding position between the cyclohexyl ring connected by a line and the structural formula in parentheses is not particularly limited. Among these, cyclohexyl (meth)acrylate and isobornyl (meth)acrylate are preferred.

When the acrylic polymer contains the alicyclic structure-containing monomer as a monomer component constituting the polymer, the proportion of the alicyclic structure-containing monomer in all monomer components (100% by weight) constituting the acrylic polymer is not particularly limited, but is preferably 10% by weight or more in terms of improving durability and achieving high adhesive reliability. Furthermore, the upper limit of the proportion of the alicyclic structure-containing monomer is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less, in terms of obtaining a pressure-sensitive adhesive layer with appropriate flexibility and making it easy to control the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges.

Further examples of copolymerizable monomers include polyfunctional monomers. Examples of polyfunctional monomers include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, and urethane acrylate. The polyfunctional monomers can be used alone or in combination of two or more.

When the acrylic polymer contains the polyfunctional monomer as a monomer component constituting the polymer, the proportion of the polyfunctional monomer in all monomer components (100% by weight) constituting the acrylic polymer is not particularly limited, but from the viewpoint of easily controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition point, etc.) within predetermined ranges, it is preferably 0.5% by weight or less (e.g., greater than 0% by weight and less than 0.5% by weight), and more preferably 0.2% by weight or less (e.g., greater than 0% by weight and less than 0.2% by weight).

The polyfunctional monomer may be blended into the acrylic pressure-sensitive adhesive composition in addition to the acrylic polymer. When the acrylic pressure-sensitive adhesive composition contains a polyfunctional monomer in addition to the acrylic polymer, the content (blended amount) of the polyfunctional monomer is preferably 0.5 parts by weight or less (e.g., more than 0 parts by weight and 0.5 parts by weight or less) and more preferably 0.2 parts by weight or less (e.g., more than 0 parts by weight and 0.2 parts by weight or less) per 100 parts by weight of the acrylic polymer, from the viewpoint of easily controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition point, etc.) within predetermined ranges.

Furthermore, the copolymerizable monomer includes an alkoxyalkyl (meth)acrylate. The alkoxyalkyl (meth)acrylate is not particularly limited, but examples include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, and 4-ethoxybutyl (meth)acrylate. Among these, the alkoxyalkyl (meth)acrylate is preferably an alkoxyalkyl acrylate, and more preferably 2-methoxyethyl acrylate (MEA). The alkoxyalkyl (meth)acrylates can be used alone or in combination of two or more.

When the acrylic polymer contains the (meth)acrylic acid alkoxyalkyl ester as a monomer component constituting the polymer, the ratio of the (meth)acrylic acid alkyl ester to the (meth)acrylic acid alkoxyalkyl ester is not particularly limited, but is preferably greater than 100:0 and less than 25:75 (former:latter) by weight, and more preferably greater than 100:0 and less than 50:50.

Other examples of the copolymerizable monomer include carboxyl group-containing monomers, epoxy group-containing monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, (meth)acrylic acid esters having aromatic hydrocarbon groups, vinyl esters, aromatic vinyl compounds, olefins or dienes, vinyl ethers, and vinyl chloride. Examples of the carboxyl group-containing monomers include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. The carboxyl group-containing monomers also include acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride. Examples of the epoxy group-containing monomers include glycidyl (meth)acrylate and methyl glycidyl (meth)acrylate. Examples of the sulfonic acid group-containing monomers include sodium vinyl sulfonate. Examples of the phosphate group-containing monomers include 2-hydroxyethyl acryloyl phosphate. Examples of the (meth)acrylic acid ester having an aromatic hydrocarbon group include phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate. Examples of the vinyl esters include vinyl acetate and vinyl propionate. Examples of the aromatic vinyl compounds include styrene and vinyl toluene. Examples of the olefins or dienes include ethylene, propylene, butadiene, isoprene, and isobutylene. Examples of the vinyl ethers include vinyl alkyl ethers.

In order to obtain an acrylic pressure-sensitive adhesive layer with excellent corrosion resistance, the acrylic polymer preferably does not contain or substantially does not contain acidic group-containing monomers as monomer components constituting the polymer, and it is particularly preferable that the acrylic polymer does not contain or substantially does not contain carboxyl group-containing monomers. Examples of acidic group-containing monomers include carboxyl group-containing monomers, sulfonic acid group-containing monomers, and phosphate group-containing monomers. Specifically, the acrylic polymer can be said to be substantially free of acidic group-containing monomers when the proportion of the acidic group-containing monomers in the total monomer components (100% by weight) constituting the acrylic polymer is 0.05% by weight or less (preferably 0.01% by weight or less).

The content of the base polymer (particularly the acrylic polymer) in the pressure-sensitive adhesive layer of the present invention is not particularly limited, but is preferably 50% by weight or more (e.g., 50 to 100% by weight), more preferably 80% by weight or more (e.g., 80 to 100% by weight), and even more preferably 90% by weight or more (e.g., 90 to 100% by weight), relative to 100% by weight of the total weight of the pressure-sensitive adhesive layer of the present invention.

The weight-average molecular weight (Mw) of the acrylic polymer is 100,000 to 5,000,000, preferably 500,000 to 4,000,000, and more preferably 750,000 to 3,000,000. An acrylic polymer with a weight-average molecular weight of 100,000 or more is preferred in that it improves adhesive strength and foaming-peeling resistance. On the other hand, an acrylic polymer with a weight-average molecular weight of 5,000,000 or less is preferred in that it makes it easier to increase adhesive strength and improves foaming-peeling resistance.

The weight average molecular weight (Mw) of the acrylic polymer can be determined in terms of polystyrene by GPC, for example, using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions:
Column: TSKgel Super HZM-H/HZ4000/HZ3000/HZ2000
Solvent: tetrahydrofuran Flow rate: 0.6 ml/min

The glass transition temperature (Tg) of the acrylic polymer is not particularly limited, but is preferably -70 to -10°C, more preferably -65 to -15°C, and even more preferably -60 to -20°C. Having an acrylic polymer with a glass transition temperature of -70°C or higher is preferable because it improves cohesive strength and foaming/peeling resistance. Furthermore, having an acrylic polymer with a glass transition temperature of -10°C or lower is preferable because it maintains the stress relaxation properties of the pressure-sensitive adhesive layer even in low-temperature environments, allows the pressure-sensitive adhesive layer to fully adapt to contraction or expansion in the usage environment of the image display device of the present invention, prevents lifting or peeling, and ensures sufficient adhesion to the adherend.

The glass transition temperature (Tg) of the acrylic polymer is a theoretical value represented by the following FOX formula:
1/Tg = W ₁ /Tg ₁ +W ₂ /Tg ₂ +...+W _n /Tg _n
In the above formula, Tg represents the glass transition temperature (unit: K) of the acrylic polymer, Tg _i represents the glass transition temperature (unit: K) when monomer i forms a homopolymer, and W _i represents the weight fraction of monomer i in the total amount of monomer components (i = 1, 2, ... n).
The following values can be used as the Tg of the homopolymer of the monomer that constitutes the acrylic polymer.
2-Ethylhexyl acrylate -70℃
n-Hexyl acrylate -65℃
n-Octyl acrylate -65℃
Isononyl acrylate -60℃
n-Nonyl acrylate -58℃
n-Butyl acrylate -55°C
Ethyl acrylate -20℃
Lauryl acrylate 0℃
2-Ethylhexyl methacrylate -10℃
Methyl acrylate 8℃
n-Butyl methacrylate 20℃
Methyl methacrylate 105℃
Acrylic acid 106℃
Methacrylic acid 228℃
Vinyl acetate 32℃
Styrene 100℃

The Tg of a homopolymer of a monomer not listed above can be determined from the values listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). Furthermore, the Tg of a homopolymer of a monomer not listed in the above literature can be determined from the value obtained by the measurement method described above (the peak top temperature of tan δ measured by a viscoelasticity test).

The base polymer, such as the acrylic polymer, contained in the pressure-sensitive adhesive layer of the present invention is obtained by polymerizing monomer components. The polymerization method is not particularly limited, but examples include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization by active energy ray irradiation (active energy ray polymerization). Among these, from the standpoints of the transparency and cost of the pressure-sensitive adhesive layer, solution polymerization and active energy ray polymerization are preferred, with active energy ray polymerization being more preferred.

In addition, various common solvents may be used when polymerizing the above-mentioned monomer components. Examples of such solvents include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. These solvents can be used alone or in combination.

When polymerizing the above-mentioned monomer components, a polymerization initiator such as a thermal polymerization initiator or a photopolymerization initiator (photoinitiator) may be used depending on the type of polymerization reaction. The polymerization initiators may be used alone or in combination of two or more types.

The thermal polymerization initiator is not particularly limited, but examples include azo polymerization initiators, peroxide polymerization initiators (e.g., dibenzoyl peroxide, tert-butyl permaleate, etc.), and redox polymerization initiators. Among these, the azo polymerization initiators disclosed in JP-A-2002-69411 are preferred. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile (hereinafter sometimes referred to as "AIBN"), 2,2'-azobis-2-methylbutyronitrile (hereinafter sometimes referred to as "AMBN"), 2,2'-azobis(2-methylpropionate)dimethyl, and 4,4'-azobis-4-cyanovaleric acid. The thermal polymerization initiators can be used alone or in combination of two or more.

When the azo polymerization initiator is used during polymerization of the acrylic polymer, the amount of the azo polymerization initiator used is not particularly limited, but is, for example, preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, and preferably 0.5 parts by weight or less, more preferably 0.3 parts by weight or less, per 100 parts by weight of all monomer components constituting the acrylic polymer.

The photopolymerization initiator is not particularly limited, but examples thereof include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. Other examples include acylphosphine oxide-based photopolymerization initiators and titanocene-based photopolymerization initiators. Examples of the benzoin ether-based photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethan-1-one, and anisole methyl ether. Examples of the acetophenone-based photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of the α-ketol-based photopolymerization initiator include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of the aromatic sulfonyl chloride-based photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the photoactive oxime-based photopolymerization initiator include 1-phenyl-1,1-propanedione-2-(O-ethoxycarbonyl)-oxime. Examples of the benzoin-based photopolymerization initiator include benzoin. Examples of the benzyl-based photopolymerization initiator include benzyl. Examples of the benzophenone-based photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, and α-hydroxycyclohexylphenyl ketone. Examples of the ketal-based photopolymerization initiator include benzyl dimethyl ketal. Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone. Examples of the acylphosphine oxide-based photopolymerization initiator include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of the titanocene photopolymerization initiator include bis(η ⁵ -2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium. The photopolymerization initiators can be used alone or in combination of two or more.

When the photopolymerization initiator is used during polymerization of the acrylic polymer, the amount of the photopolymerization initiator used is not particularly limited, but is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, and preferably 3 parts by weight or less, more preferably 1.5 parts by weight or less, per 100 parts by weight of all monomer components constituting the acrylic polymer.

The acrylic pressure-sensitive adhesive composition preferably contains, in addition to the acrylic polymer, an acrylic oligomer having a weight-average molecular weight of 1,000 to 30,000. The inclusion of an acrylic oligomer improves the adhesion of the optical pressure-sensitive adhesive tape of the present invention to an adherend at the interface, making it easier to achieve strong adhesion and excellent resistance to foaming and peeling. In this specification, "an acrylic oligomer having a weight-average molecular weight of 1,000 to 30,000" may be simply referred to as "acrylic oligomer."

Preferred examples of the acrylic oligomer include acrylic polymers composed of a (meth)acrylic acid ester having a cyclic structure within the molecule as an essential monomer component, and more preferred examples of the acrylic polymers composed of a (meth)acrylic acid ester having a cyclic structure within the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group as essential monomer components. That is, preferred examples of the acrylic oligomer include acrylic polymers containing a (meth)acrylic acid ester having a cyclic structure within the molecule as a monomer unit, and more preferred examples of the acrylic polymers containing a (meth)acrylic acid ester having a cyclic structure within the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group as monomer units.

The cyclic structure (ring) of the (meth)acrylic acid ester having a cyclic structure within the molecule (within one molecule) (hereinafter sometimes referred to as a "ring-containing (meth)acrylic acid ester") may be either an aromatic ring or a non-aromatic ring, and is not particularly limited. Examples of the aromatic ring include aromatic carbocycles [for example, monocyclic carbocycles such as a benzene ring, and fused carbocycles such as a naphthalene ring], various aromatic heterocycles, and the like. Examples of the non-aromatic ring include non-aromatic aliphatic rings (non-aromatic alicyclic rings) [for example, cycloalkane rings such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; cycloalkene rings such as cyclohexene], non-aromatic bridged rings [for example, bicyclic hydrocarbon rings such as pinane, pinene, bornane, norbornane, and norbornene; tricyclic or higher aliphatic hydrocarbon rings (bridged hydrocarbon rings) such as adamantane], and non-aromatic heterocycles [for example, epoxy rings, oxolane rings, and oxetane rings].

Examples of the tricyclic or higher aliphatic hydrocarbon ring (tricyclic or higher bridged hydrocarbon ring) include a dicyclopentanyl group represented by the following formula (5a), a dicyclopentenyl group represented by the following formula (5b), an adamantyl group represented by the following formula (5c), a tricyclopentanyl group represented by the following formula (5d), and a tricyclopentenyl group represented by the following formula (5e).

That is, examples of the ring-containing (meth)acrylic acid esters include (meth)acrylic acid cycloalkyl esters such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate; (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamanyl (meth)acrylate, and the like. and (meth)acrylic acid esters having an aromatic ring such as (meth)acrylic acid aryl esters such as phenyl (meth)acrylate, (meth)acrylic acid aryloxyalkyl esters such as phenoxyethyl (meth)acrylate, and (meth)acrylic acid arylalkyl esters such as benzyl (meth)acrylate. Of these, the ring-containing (meth)acrylic acid esters are particularly preferably non-aromatic ring-containing (meth)acrylic acid esters, more preferably cyclohexyl acrylate (CHA), cyclohexyl methacrylate (CHMA), dicyclopentanyl acrylate (DCPA), and dicyclopentanyl methacrylate (DCPMA), and even more preferably dicyclopentanyl acrylate (DCPA) and dicyclopentanyl methacrylate (DCPMA). The ring-containing (meth)acrylic acid esters may be used alone or in combination of two or more.

Among the above non-aromatic ring-containing (meth)acrylic acid esters, (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring (particularly a tricyclic or higher bridged hydrocarbon ring) are preferred because they are less likely to cause polymerization inhibition. Furthermore, when a (meth)acrylic acid ester having a dicyclopentanyl group represented by formula (5a), an adamantyl group represented by formula (5c), or a tricyclopentanyl group represented by formula (5d) that does not have an unsaturated bond is used, foaming and peeling resistance can be further improved, and adhesion to low-polarity substrates such as polyethylene and polypropylene can be significantly improved.

The content (ratio) of the ring-containing (meth)acrylic ester in all monomer units of the acrylic oligomer (total amount of monomer components constituting the acrylic oligomer) is not particularly limited, but is preferably 10 to 90 parts by weight, and more preferably 20 to 80 parts by weight, relative to the total amount (100 parts by weight) of monomer components constituting the acrylic oligomer. A content of 10 parts by weight or more of the ring-containing (meth)acrylic ester is preferred because it tends to improve foaming and peeling resistance. Furthermore, a content of 90 parts by weight or less is preferred because it tends to provide the pressure-sensitive adhesive layer with appropriate flexibility and improve adhesive strength, bump absorbency, etc.

Furthermore, examples of (meth)acrylic acid alkyl esters having the above-mentioned linear or branched alkyl group as monomer units of acrylic oligomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of suitable (meth)acrylic acid alkyl esters include those having an alkyl group containing 1 to 20 carbon atoms, such as xyl, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, methyl methacrylate (MMA) is preferred due to its good compatibility with acrylic polymers. The above alkyl (meth)acrylates may be used alone or in combination of two or more.

The content (ratio) of the (meth)acrylic acid alkyl ester having the above-mentioned linear or branched alkyl group in all monomer units of the acrylic oligomer (total amount of monomer components constituting the acrylic oligomer) is not particularly limited, but from the viewpoint of foaming and peeling resistance, it is preferably 10 to 90 parts by weight, more preferably 20 to 80 parts by weight, and even more preferably 20 to 60 parts by weight, relative to the total amount (100 parts by weight) of monomer components constituting the acrylic oligomer. A content of 10 parts by weight or more is preferred, as it tends to improve adhesive strength, particularly to adherends made of acrylic resin or polycarbonate.

In addition to the above-mentioned ring-containing (meth)acrylic acid ester and (meth)acrylic acid alkyl ester having a linear or branched alkyl group, the monomer units of the acrylic oligomer may also include a monomer (copolymerizable monomer) that is copolymerizable with these monomers. The content (ratio) of the above copolymerizable monomer in all monomer units of the acrylic oligomer (total amount of monomer components constituting the acrylic oligomer) is not particularly limited, but is preferably 49.9 parts by weight or less (e.g., 0 to 49.9 parts by weight), and more preferably 30 parts by weight or less, relative to the total amount (100 parts by weight) of monomer components constituting the acrylic oligomer. The copolymerizable monomers may be used alone or in combination of two or more types.

Examples of the copolymerizable monomers as monomer units of the acrylic oligomer (the copolymerizable monomers constituting the acrylic oligomer) include, for example, (meth)acrylic acid alkoxyalkyl esters [e.g., 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxytriethylene glycol (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, etc.]; hydroxyl group (hydroxyl group)-containing monomers [e.g., hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, etc.]; vinyl alcohol; alcohol, etc.); amide group-containing monomers [e.g., (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, etc.]; amino group-containing monomers [e.g., aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, etc.]; cyano group-containing monomers [e.g., acrylonitrile, methacrylonitrile, etc.]; sulfonic acid group-containing monomers [e.g., sodium vinyl sulfonate, etc.]; phosphate group-containing monomers [e.g., 2-hydroxyethyl acryloyl phosphate, etc.]; isocyanate group-containing monomers [e.g., 2-methacryloyloxyethyl isocyanate, etc.]; imide group-containing monomers [cyclohexylmaleimide, isopropylmaleimide, etc.], etc.

As described above, the acrylic oligomer is preferably an acrylic polymer containing, as monomer units, a (meth)acrylic acid ester having a cyclic structure within the molecule and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group. Of these, an acrylic polymer containing, as monomer units, a ring-containing (meth)acrylic acid ester and the above-mentioned (meth)acrylic acid alkyl ester having a linear or branched alkyl group is preferred. In the acrylic polymer containing, as monomer units, a ring-containing (meth)acrylic acid ester and a (meth)acrylic acid alkyl ester having a linear or branched alkyl group, the amount of the ring-containing (meth)acrylic acid ester relative to the total amount (100 parts by weight) of the monomer components constituting the acrylic oligomer is not particularly limited, but is preferably 10 to 90 parts by weight, more preferably 20 to 80 parts by weight. Furthermore, the content of the (meth)acrylic acid alkyl ester having a linear or branched alkyl group is not particularly limited, but is preferably 10 to 90 parts by weight, more preferably 20 to 80 parts by weight, even more preferably 20 to 60 parts by weight.

Furthermore, a particularly preferred specific configuration of the acrylic oligomer is an acrylic polymer containing, as monomer units, (1) at least one monomer selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and (2) methyl methacrylate. In the acrylic oligomer of the particularly preferred specific configuration described above, the content of (1) dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate (the total amount when two or more types are included) in all monomer units of the acrylic oligomer is preferably 30 to 70 parts by weight, and the content of (2) methyl methacrylate is preferably 30 to 70 parts by weight, relative to the total amount (100 parts by weight) of the monomer components constituting the acrylic oligomer. However, the acrylic oligomer is not limited to the specific configuration described above.

The acrylic oligomer can be obtained by polymerizing the above-mentioned monomer components using a known or conventional polymerization method. Examples of polymerization methods for the acrylic oligomer include solution polymerization, emulsion polymerization, bulk polymerization, and polymerization using active energy ray irradiation (active energy ray polymerization). Of these, bulk polymerization and solution polymerization are preferred, with solution polymerization being more preferred.

A variety of common solvents may be used during the polymerization of acrylic oligomers. Examples of such solvents include organic solvents such as esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. These solvents may be used alone or in combination of two or more.

Furthermore, when polymerizing the acrylic oligomer, known or commonly used polymerization initiators (e.g., thermal polymerization initiators, photopolymerization initiators, etc.) may be used. These polymerization initiators may be used alone or in combination of two or more.

Examples of thermal polymerization initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis-2-methylbutyronitrile (AMBN), 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1- Examples of suitable initiators include azo initiators such as 2,2'-azobis(2,4,4-trimethylpentane) and 2,2'-azobis(2,4,4-trimethylpentane); and peroxide initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane. When solution polymerization is performed, it is preferable to use an oil-soluble polymerization initiator. Thermal polymerization initiators may be used alone or in combination of two or more.

The amount of the thermal polymerization initiator used is not particularly limited, but is, for example, 0.1 to 15 parts by weight per 100 parts by weight of all monomer units of the acrylic oligomer (total amount of monomer components constituting the acrylic oligomer).

The photopolymerization initiator is not particularly limited, but examples include the same photopolymerization initiators as those used in the polymerization of the acrylic polymers listed above. The amount of the photopolymerization initiator used is not particularly limited and may be selected appropriately.

During polymerization of the acrylic oligomer, a chain transfer agent may be used to adjust the molecular weight (specifically, to adjust the weight average molecular weight to 1,000 to 30,000). Examples of chain transfer agents include 2-mercaptoethanol, α-thioglycerol, 2,3-dimercapto-1-propanol, octyl mercaptan, t-nonyl mercaptan, dodecyl mercaptan (lauryl mercaptan), t-dodecyl mercaptan, glycidyl mercaptan, thioglycolic acid, methyl thioglycolate, ethyl thioglycolate, propyl thioglycolate, butyl thioglycolate, t-butyl thioglycolate, 2-ethylhexyl thioglycolate, octyl thioglycolate, isooctyl thioglycolate, decyl thioglycolate, dodecyl thioglycolate, thioglycolic acid esters of ethylene glycol, thioglycolic acid esters of neopentyl glycol, thioglycolic acid esters of pentaerythritol, and α-methylstyrene dimer. Of these, from the viewpoint of suppressing whitening of the optical pressure-sensitive adhesive tape of the present invention due to humidification, α-thioglycerol and methyl thioglycolate are preferred, with α-thioglycerol being particularly preferred. Chain transfer agents may be used alone or in combination of two or more.

The content (amount used) of the chain transfer agent is not particularly limited, but is preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by weight, and even more preferably 0.3 to 10 parts by weight, per 100 parts by weight of all monomer units of the acrylic oligomer (total amount of monomer components constituting the acrylic oligomer). By keeping the content (amount used) of the chain transfer agent within the above range, it is possible to easily obtain an acrylic polymer with a weight-average molecular weight controlled to 1,000 to 30,000.

The weight-average molecular weight (Mw) of the acrylic oligomer is 1,000 to 30,000, preferably 1,000 to 20,000, more preferably 1,500 to 10,000, and even more preferably 2,000 to 8,000. Because the weight-average molecular weight of the acrylic oligomer is 1,000 or more, adhesive strength and retention properties are improved, and foaming and peeling resistance is improved. On the other hand, because the weight-average molecular weight of the acrylic oligomer is 30,000 or less, adhesive strength can be easily increased, and foaming and peeling resistance is improved.

The weight average molecular weight (Mw) of the acrylic oligomer can be determined in terms of polystyrene by GPC, for example, using a high-speed GPC device "HPLC-8120GPC" manufactured by Tosoh Corporation under the following conditions:
Column: TSKgel Super HZM-H/HZ4000/HZ3000/HZ2000
Solvent: tetrahydrofuran Flow rate: 0.6 ml/min

The glass transition temperature (Tg) of the acrylic oligomer is not particularly limited, but is preferably 20 to 300°C, more preferably 30 to 300°C, and even more preferably 40 to 300°C. An acrylic oligomer with a glass transition temperature of 20°C or higher is preferred as it tends to improve foaming and peeling resistance. Furthermore, an acrylic oligomer with a glass transition temperature of 300°C or lower is preferred as it tends to provide the pressure-sensitive adhesive layer with adequate flexibility, making it easier to achieve good adhesive strength and good level difference absorbency, and therefore excellent adhesive reliability.

The glass transition temperature (Tg) of the acrylic oligomer is the glass transition temperature (theoretical value) represented by the above FOX formula.
The Tg of a homopolymer of a monomer constituting the acrylic oligomer may be a value shown in Table 1 below. Furthermore, the Tg of a homopolymer of a monomer not shown in Table 1 may be a value shown in "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). Furthermore, the Tg of a homopolymer of a monomer not shown in the above literature may be a value obtained by the above-mentioned measurement method (peak top temperature of tan δ measured by a viscoelasticity test).

In Table 1, the copolymer "DCPMA/MMA=60/40" means a copolymer of 60 parts by weight of DCPMA and 40 parts by weight of MMA.

When the acrylic pressure-sensitive adhesive composition contains an acrylic polymer and an acrylic oligomer, the content of the acrylic oligomer is not particularly limited, but is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, and even more preferably 2 to 10 parts by weight, per 100 parts by weight of the acrylic polymer. That is, the content of the acrylic oligomer in the pressure-sensitive adhesive composition is not particularly limited, but is preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, and even more preferably 2 to 10 parts by weight, per 100 parts by weight of all monomer units of the acrylic polymer. The content of the acrylic oligomer in the acrylic pressure-sensitive adhesive composition is not particularly limited, but is, for example, preferably 1 to 30 parts by weight, more preferably 2 to 20 parts by weight, and even more preferably 2 to 10 parts by weight, per 100 parts by weight of the monomer mixture. An acrylic oligomer content of 1 part by weight or more is preferred, as it facilitates achieving excellent adhesion and excellent foaming/peeling resistance. Furthermore, an acrylic oligomer content of 30 parts by weight or less is preferred, as it facilitates achieving excellent transparency and adhesive reliability. Furthermore, from the viewpoint of making it easier to control the above-mentioned various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition temperature, etc.) within specified ranges, the acrylic oligomer content is preferably 10 parts by weight or less, and more preferably 8 parts by weight or less.

There are no particular limitations on the method for preparing the above-mentioned pressure-sensitive adhesive composition containing an acrylic polymer and an acrylic oligomer. For example, the composition can be prepared by adding an acrylic oligomer, additives, etc., as needed to a mixture of monomer components that constitute the acrylic polymer or a partial polymer of a mixture of monomer components that constitute the acrylic polymer (a monomer mixture that forms the acrylic polymer or a partial polymer thereof), and mixing the mixture.

The pressure-sensitive adhesive layer of the present invention is not particularly limited, but preferably contains an ultraviolet absorber (UVA). When the pressure-sensitive adhesive layer of the present invention contains an ultraviolet absorber, it is preferable in that damage to the image display panel caused by ultraviolet rays can be suppressed. The ultraviolet absorbers can be used alone or in combination of two or more types.

The above-mentioned UV absorbers are not particularly limited, but examples include benzotriazole-based UV absorbers, hydroxyphenyltriazine-based UV absorbers, benzophenone-based UV absorbers, salicylic acid ester-based UV absorbers, cyanoacrylate-based UV absorbers, and oxybenzophenone-based UV absorbers.

Examples of benzotriazole-based ultraviolet absorbers (benzotriazole-based compounds) include 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (trade name "TINUVIN PS", manufactured by BASF), an ester compound of benzenepropanoic acid and 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy (C7-9 side chain and linear alkyl) (trade name "TINUVIN 384-2", manufactured by BASF), and a mixture of octyl 3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate and 2-ethylhexyl-3-[3-tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl]propionate (trade name "TINUVIN 109" (manufactured by BASF Corporation), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (trade name "TINUVIN 900" (manufactured by BASF Corporation), 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (trade name "TINUVIN 928" (manufactured by BASF Corporation), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate/polyethylene glycol 300 (trade name "TINUVIN 1130" (manufactured by BASF Corporation), 2-(2H-benzotriazol-2-yl)-p-cresol (trade name "TINUVIN P”, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (trade name “TINUVIN 234”, manufactured by BASF), 2-[5-chloro-2H-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (trade name “TINUVIN 326”, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (trade name “TINUVIN 328”, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (trade name “TINUVIN 329" (manufactured by BASF Corporation), 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol] (trade name "TINUVIN 360" (manufactured by BASF Corporation), reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate and polyethylene glycol 300 (trade name "TINUVIN 213" (manufactured by BASF Corporation), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (trade name "TINUVIN 571" (manufactured by BASF Corporation), 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole (trade name "Sumisorb 250" manufactured by Sumitomo Chemical Co., Ltd.), 2,2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol] (trade name "ADK STAB LA-31" manufactured by ADEKA Corporation), etc.

Examples of hydroxyphenyltriazine-based ultraviolet absorbers (hydroxyphenyltriazine-based compounds) include a reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(C10-C16 (mainly C12-C13) alkyloxy)methyl]oxirane (trade name "TINUVIN 400", manufactured by BASF), 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-[3-(dodecyloxy)-2-hydroxypropoxy]phenol, and a reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine with (2-ethylhexyl)-glycidic acid ester (trade name "TINUVIN 405" manufactured by BASF), 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (trade name "TINUVIN 460" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol (trade name "TINUVIN 1577" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol (trade name "ADK STAB LA-46, manufactured by ADEKA Corporation), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (trade name "TINUVIN 479", manufactured by BASF), etc. Other examples include the compound represented by the following formula (6) (trade name "TINUVIN 477", manufactured by BASF):

Examples of benzophenone-based UV absorbers (benzophenone-based compounds) and oxybenzophenone-based UV absorbers (oxybenzophenone-based compounds) include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (anhydrous and trihydrate), 2-hydroxy-4-octyloxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 4-benzyloxy-2-hydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone (trade name "KEMISORB 111", manufactured by Chemipro Chemical Co., Ltd.), 2,2',4,4'-tetrahydroxybenzophenone (trade name "SEESORB 106", manufactured by Shipro Chemical Co., Ltd.), and 2,2'-dihydroxy-4,4'-dimethoxybenzophenone.

Examples of salicylate ester-based UV absorbers (salicylate ester-based compounds) include phenyl 2-acryloyloxybenzoate, phenyl 2-acryloyloxy-3-methylbenzoate, phenyl 2-acryloyloxy-4-methylbenzoate, phenyl 2-acryloyloxy-5-methylbenzoate, phenyl 2-acryloyloxy-3-methoxybenzoate, phenyl 2-hydroxybenzoate, phenyl 2-hydroxy-3-methylbenzoate, phenyl 2-hydroxy-4-methylbenzoate, phenyl 2-hydroxy-5-methylbenzoate, phenyl 2-hydroxy-3-methoxybenzoate, and 2,4-di-tert-butylphenyl 3,5-di-tert-butyl-4-hydroxybenzoate (trade name "TINUVIN 120", manufactured by BASF).

Examples of cyanoacrylate-based ultraviolet absorbers (cyanoacrylate-based compounds) include alkyl 2-cyanoacrylate, cycloalkyl 2-cyanoacrylate, alkoxyalkyl 2-cyanoacrylate, alkenyl 2-cyanoacrylate, and alkynyl 2-cyanoacrylate.

As the UV absorber, at least one UV absorber selected from the group consisting of benzotriazole-based UV absorbers, benzophenone-based UV absorbers, and hydroxyphenyltriazine-based UV absorbers is preferred, as they have high UV absorption while further improving corrosion resistance (particularly UV resistance), excellent optical properties, ease of obtaining a pressure-sensitive adhesive layer with high transparency, and excellent photostability. Benzotriazole-based UV absorbers and benzophenone-based UV absorbers are more preferred. In particular, benzotriazole-based UV absorbers in which a phenyl group having a group with 6 or more carbon atoms and a hydroxyl group as substituents is bonded to the nitrogen atom constituting the benzotriazole ring are preferred.

In addition, the ultraviolet absorber preferably has an absorbance A of 0.5 or less, as determined below, in order to obtain higher ultraviolet absorption and further improve corrosion resistance (particularly UV resistance).
Absorbance A: The absorbance measured when a 0.08% toluene solution of the ultraviolet absorber is irradiated with light having a wavelength of 400 nm.

When the pressure-sensitive adhesive layer of the present invention contains an ultraviolet absorber, the content of the ultraviolet absorber in the pressure-sensitive adhesive layer of the present invention (particularly an acrylic pressure-sensitive adhesive layer) is not particularly limited, but in order to further improve corrosion resistance (particularly UV resistance), it is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and even more preferably 0.1 parts by weight or more, per 100 parts by weight of base polymer. Furthermore, in order to suppress the yellowing of the pressure-sensitive adhesive that occurs with the addition of an ultraviolet absorber and to obtain excellent optical properties, high transparency, and excellent appearance properties, the upper limit of the content of the ultraviolet absorber is preferably 10 parts by weight or less, more preferably 9 parts by weight or less, and even more preferably 8 parts by weight or less, per 100 parts by weight of base polymer.

The pressure-sensitive adhesive layer of the present invention may contain a light stabilizer. When the pressure-sensitive adhesive layer of the present invention contains a light stabilizer, it is particularly preferable to contain the light stabilizer together with the above-mentioned UV absorber. The light stabilizer can capture radicals generated by photooxidation, thereby improving the resistance of the pressure-sensitive adhesive layer to light (particularly UV light). The light stabilizers can be used alone or in combination of two or more types.

The light stabilizer is not particularly limited, but examples include phenol-based light stabilizers (phenol-based compounds), phosphorus-based light stabilizers (phosphorus-based compounds), thioether-based light stabilizers (thioether-based compounds), and amine-based light stabilizers (amine-based compounds) (particularly hindered amine-based stabilizers (hindered amine-based compounds)).

Examples of the phenolic light stabilizers (phenolic compounds) include 2,6-di-tert-butyl-4-methylphenol, 4-hydroxymethyl-2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-ethylphenol, butylated hydroxyanisole, n-octadecyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate, distearyl (4-hydroxy-3-methyl-5-tert-butyl)benzyl malonate, tocopherol, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 4,4'-methylenebis(2,6-di-tert-butylphenol) ), 4,4'-butylidenebis(6-tert-butyl-m-cresol), 4,4'-thiobis(6-tert-butyl-m-cresol), styrenated phenol, N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamide, bis(3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid ethyl ester)calcium, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane, 1,6-hexamethylenebis(3,5-di-tert-butyl-4-hydroxybenzyl)methyl Sandiol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-methylenebis(4-methyl-6-cyclohexylphenol), 2,2'-methylenebis[6-(1-methylcyclohexyl)-p-cresol], 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, triethylene glycol bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2'-oxamidobis[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate nate], 6-(4-hydroxy-3,5-di-tert-butylanilino)-2,4-dioctylthio-1,3,5-triazine, bis[2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl]terephthalate, 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, 3,9-bis{2-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, etc.

Examples of phosphorus-based light stabilizers (phosphorus compounds) include trisnonylphenyl phosphite, tris(2,4-di-tert-butylphenyl) phosphite, tris[2-tert-butyl-4-(3-tert-butyl-4-hydroxy-5-methylphenylthio)-5-methylphenyl]phosphite, tridecyl phosphite, octyldiphenyl phosphite, di(decyl)monophenyl phosphite, di(tridecyl)pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, di(nonylphenyl)pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, bis( Examples include 2,4,6-tri-tert-butylphenyl)pentaerythritol diphosphite, tetra(tridecyl)isopropylidenediphenol diphosphite, tetra(tridecyl)-4,4'-n-butylidenebis(2-tert-butyl-5-methylphenol)diphosphite, hexa(tridecyl)-1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane triphosphite, tetrakis(2,4-di-tert-butylphenyl)biphenylene diphosphonite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and tris(2-[(2,4,8,10-tetrakis-tert-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]ethyl)amine.

Examples of thioether-based light stabilizers (thioether-based compounds) include dialkyl thiodipropionate compounds such as dilauryl, dimyristyl, and distearyl thiodipropionate; and β-alkyl mercaptopropionate ester compounds of polyols such as tetrakis[methylene(3-dodecylthio)propionate]methane.

Examples of amine-based light stabilizers (amine compounds) include a polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol (trade name "TINUVIN 622", manufactured by BASF), a 1:1 reaction product of a polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol with N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine (trade name "TINUVIN 119" manufactured by BASF), polycondensate of dibutylamine/1,3-triazine/N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine (trade name "TINUVIN 2020" manufactured by BASF), poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2-4-diyl}{2,2,6,6-tetramethyl-4-piperidyl}imino]hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino} (trade name "TINUVIN 944" manufactured by BASF), a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidylsebacate (trade name "TINUVIN 765" manufactured by BASF), bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (trade name "TINUVIN 770" manufactured by BASF), decanedioic acid bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl)ester, reaction product of 1,1-dimethylethyl hydroperoxide and octane (trade name "TINUVIN 123" (manufactured by BASF Corporation), bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate (trade name "TINUVIN 144" (manufactured by BASF Corporation), reaction product of cyclohexane and N-butyl 2,2,6,6-tetramethyl-4-piperidinamine-2,4,6-trichloro-1,3,5-triazine peroxide with 2-aminoethanol (trade name "TINUVIN 152" (manufactured by BASF Corporation), mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidylsebacate (trade name "TINUVIN 292, manufactured by BASF), and a mixed ester of 1,2,3,4-butanetetracarboxylic acid with 1,2,2,6,6-pentamethyl-4-piperidinol and 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (trade name "ADK STAB LA-63P", manufactured by ADEKA Corporation). Among amine-based stabilizers, hindered amine-based stabilizers are particularly preferred.

When the pressure-sensitive adhesive layer of the present invention contains a light stabilizer, the content of the light stabilizer in the pressure-sensitive adhesive layer of the present invention (particularly an acrylic pressure-sensitive adhesive layer) is not particularly limited, but in order to facilitate the development of light resistance, it is preferably 0.1 parts by weight or more, and more preferably 0.2 parts by weight or more, per 100 parts by weight of base polymer. Furthermore, in order to prevent discoloration due to the light stabilizer itself, to facilitate the achievement of high transparency, and to improve optical properties, the upper limit of the content is preferably 5 parts by weight or less, and more preferably 3 parts by weight or less, per 100 parts by weight of base polymer.

A crosslinking agent may be used to form the pressure-sensitive adhesive layer of the present invention, although this is not particularly limited. For example, the acrylic polymer in the acrylic pressure-sensitive adhesive layer can be crosslinked to control the gel fraction. The crosslinking agents may be used alone or in combination of two or more.

The crosslinking agent is not particularly limited, but examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Of these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred, and isocyanate-based crosslinking agents are more preferred.

Examples of the above-mentioned isocyanate-based crosslinking agents (polyfunctional isocyanate compounds) include lower aliphatic polyisocyanates such as 1,2-ethylene diisocyanate, 1,4-butylene diisocyanate, and 1,6-hexamethylene diisocyanate; alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated xylene diisocyanate; and aromatic polyisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate. Examples of the isocyanate crosslinking agent include commercially available products such as trimethylolpropane/tolylene diisocyanate adduct (trade name "Coronate L", manufactured by Nippon Polyurethane Industry Co., Ltd.), trimethylolpropane/hexamethylene diisocyanate adduct (trade name "Coronate HL", manufactured by Nippon Polyurethane Industry Co., Ltd.), and trimethylolpropane/xylylene diisocyanate adduct (trade name "Takenate D-110N", manufactured by Mitsui Chemicals, Inc.).

Examples of the epoxy-based crosslinking agent (polyfunctional epoxy compound) include N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycol Examples of suitable crosslinking agents include diglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether, as well as epoxy resins having two or more epoxy groups in the molecule. Examples of the epoxy crosslinking agent include commercially available products such as "Tetrad C" (manufactured by Mitsubishi Gas Chemical Company, Inc.).

When a crosslinking agent is used to form the pressure-sensitive adhesive layer of the present invention, the amount of the crosslinking agent used is not particularly limited, but from the viewpoint of obtaining sufficient adhesive reliability, it is preferably 0.001 parts by weight or more, and more preferably 0.01 parts by weight or more, per 100 parts by weight of base polymer. Furthermore, from the viewpoint of obtaining appropriate flexibility in the pressure-sensitive adhesive layer and improving adhesive strength, and from the viewpoint of easily controlling the various properties of the pressure-sensitive adhesive layer (particularly, strain amount A, strain amount B, recovery rate, glass transition point, etc.) within specified ranges, the upper limit of the amount used is preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of base polymer.

The pressure-sensitive adhesive layer (particularly the acrylic pressure-sensitive adhesive layer) of the present invention may contain a silane coupling agent to improve adhesion reliability under humid conditions, particularly to improve adhesion reliability to glass. Silane coupling agents can be used alone or in combination of two or more. When the pressure-sensitive adhesive layer contains a silane coupling agent, adhesion under humid conditions, particularly adhesion to glass, can be improved.

The silane coupling agent is not particularly limited, but examples include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-phenyl-aminopropyltrimethoxysilane. Furthermore, examples of silane coupling agents include commercially available products such as "KBM-403" (manufactured by Shin-Etsu Chemical Co., Ltd.). Of these, γ-glycidoxypropyltrimethoxysilane is preferred as the silane coupling agent.

When the pressure-sensitive adhesive layer of the present invention contains a silane coupling agent, the content of the silane coupling agent in the pressure-sensitive adhesive layer of the present invention (particularly the acrylic pressure-sensitive adhesive layer) is not particularly limited, but is preferably 0.01 parts by weight or more, and more preferably 0.02 parts by weight or more, per 100 parts by weight of the base polymer. Furthermore, the upper limit of the content of the silane coupling agent is preferably 1 part by weight or less, and more preferably 0.5 parts by weight or less, per 100 parts by weight of the base polymer.

The pressure-sensitive adhesive layer of the present invention may contain an antistatic agent. These antistatic agents may be used alone or in combination of two or more. When the pressure-sensitive adhesive layer contains an antistatic agent, damage to the adherend, such as an image display panel, can be prevented.

Examples of the antistatic agent include cationic antistatic agents having cationic functional groups such as quaternary ammonium salts, pyridinium salts, and primary, secondary, and tertiary amino groups; anionic antistatic agents having anionic functional groups such as sulfonates, sulfate ester salts, phosphonates, and phosphate ester salts; amphoteric antistatic agents such as alkylbetaine and its derivatives, imidazoline and its derivatives, and alanine and its derivatives; nonionic antistatic agents such as aminoalcohols and their derivatives, glycerin and its derivatives, and polyethylene glycol and its derivatives; and ionic conductive polymers obtained by polymerizing or copolymerizing monomers having the above-mentioned cationic, anionic, or amphoteric ionic conductive groups.

When the pressure-sensitive adhesive layer of the present invention contains an antistatic agent, the content of the antistatic agent in the pressure-sensitive adhesive layer of the present invention is not particularly limited, but is preferably 0.01 parts by weight or more, and more preferably 0.02 parts by weight or more, per 100 parts by weight of the base polymer. The upper limit of the content of the antistatic agent is preferably 1 part by weight or less, and more preferably 0.5 parts by weight or less, per 100 parts by weight of the base polymer.

The pressure-sensitive adhesive layer of the present invention may contain a colorant. The colorants may be used alone or in combination of two or more. It is preferable for the pressure-sensitive adhesive layer to contain a colorant, as this can prevent reflections from metal wiring, ITO wiring, and the like arranged on the substrate of the image display device of the present invention.

The colorant may be either a dye or a pigment, as long as it is soluble or dispersible in the pressure-sensitive adhesive layer of the present invention. Dyes are preferred because they can achieve low haze even with a small amount added, do not settle like pigments, and are easily distributed uniformly. Pigments are also preferred because they provide high color expression even with a small amount added. When using a pigment as the colorant, it is preferable that it has low or no conductivity. When using a dye, it is preferable to use it in combination with the above-mentioned light stabilizers, etc.

As long as the colorant absorbs visible light (wavelengths 400-700 nm), any colorant that is transparent to ultraviolet light (wavelengths 330-400 nm) or absorbs ultraviolet light can be used. However, colorants that absorb visible light and are transparent to ultraviolet light are preferred. That is, the colorant is preferably one whose maximum transmittance at wavelengths of 330-400 nm is greater than its maximum transmittance at wavelengths of 400-700 nm. It is also preferable for the colorant to have an average transmittance at wavelengths of 330-400 nm greater than its average transmittance at wavelengths of 400-700 nm. The transmittance of the colorant is measured using a solution or dispersion diluted with an appropriate solvent or dispersion medium (an organic solvent with low absorption in the wavelength range of 330-700 nm) such as tetrahydrofuran (THF) so that the transmittance at a wavelength of 400 nm is approximately 50-60%.

Carbon black and titanium black, commonly used black colorants, absorb more ultraviolet light than visible light (their ultraviolet transmittance is lower than their visible light transmittance). Therefore, when a colorant such as carbon black is added to an active energy ray-curable acrylic adhesive composition, much of the ultraviolet light irradiated for photocuring is absorbed by the colorant, reducing the amount of light absorbed by the photopolymerization initiator and resulting in longer photocuring times (increasing the cumulative amount of light irradiated). Furthermore, when the adhesive layer is thick, less ultraviolet light reaches the surface opposite the light-irradiated surface, which tends to result in insufficient photocuring even with extended light irradiation. In contrast, using a colorant with a higher ultraviolet transmittance than visible light can suppress curing inhibition caused by the colorant.

Examples of UV-transmitting black pigments include Tokushiki's "9050BLACK" and "UVBK-0001." Examples of UV-absorbing black dyes include Orient Chemical Industries' "VALIFAST BLACK 3810" and "NUBIAN Black PA-2802." Examples of UV-absorbing black pigments include carbon black and titanium black.

The content of the colorant in the pressure-sensitive adhesive layer of the present invention is, for example, approximately 0.01 to 20 parts by weight per 100 parts by weight of the base polymer, and may be set appropriately depending on the type of colorant, the color tone and light transmittance of the pressure-sensitive adhesive layer, etc. The colorant may be added to the composition as a solution or dispersion dissolved or dispersed in an appropriate solvent.

The pressure-sensitive adhesive layer of the present invention may further contain additives such as crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), antioxidants, fillers, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, etc., as needed, provided that the effects of the present invention are not impaired. These additives may be used alone or in combination of two or more.

The haze of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the standpoints of appearance characteristics, transparency, and optical properties, it is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. In this specification, the haze of the pressure-sensitive adhesive layer can be measured, for example, using a haze meter in accordance with JIS K 7136.

The total light transmittance of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the standpoints of appearance characteristics, transparency, and optical properties, it is preferably 85% or more, more preferably 90% or more, and even more preferably 92% or more. In this specification, the total light transmittance of the pressure-sensitive adhesive layer can be measured, for example, using a haze meter in accordance with JIS K 7361-1. The total light transmittance is the transmittance of light (visible light) with a wavelength of 400 to 780 nm.

The thickness of the pressure-sensitive adhesive layer of the present invention is not particularly limited, but from the viewpoint of obtaining sufficient adhesive reliability, it is preferably 12 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and particularly preferably 70 μm or more. A thickness of 12 μm or more is preferable because the pressure-sensitive adhesive layer can adequately follow the contraction or expansion in the usage environment of the image display device of the present invention and can suppress lifting or peeling. Furthermore, from the viewpoint of optical properties, the thickness is preferably 500 μm or less, preferably 300 μm or less, and even more preferably 200 μm or less.

<Production of optical adhesive tape>
The optical pressure-sensitive adhesive tape of the present invention can be prepared by laminating the pressure-sensitive adhesive layer of the present invention on the first surface of the substrate of the present invention.

The method for laminating the pressure-sensitive adhesive layer of the present invention on the first surface of the substrate of the present invention is not particularly limited, and can be carried out, for example, by applying (coating) the pressure-sensitive adhesive composition on a separator and drying and curing the resulting pressure-sensitive adhesive composition layer, or by applying (coating) the pressure-sensitive adhesive composition on a separator and irradiating the resulting pressure-sensitive adhesive composition layer with active energy rays to cure it, thereby forming a sheet-like pressure-sensitive adhesive layer on the separator, and then laminating the pressure-sensitive adhesive layer on the first surface of the substrate of the present invention. Furthermore, if necessary, the pressure-sensitive adhesive layer may be further dried by heating.
When curing is performed by irradiation with active energy rays, it is preferable to further attach a separator to the surface of the coating film and irradiate the active energy rays while the pressure-sensitive adhesive composition is sandwiched between the two separators, thereby preventing polymerization inhibition by oxygen.

Another method for laminating the pressure-sensitive adhesive layer of the present invention on the first surface of the substrate of the present invention can be, for example, by applying (coating) the pressure-sensitive adhesive composition on the first surface of the substrate of the present invention and drying and curing the resulting pressure-sensitive adhesive composition layer, or by applying (coating) the pressure-sensitive adhesive composition on the first surface of the substrate of the present invention and irradiating the resulting pressure-sensitive adhesive composition layer with active energy rays to cure it. Furthermore, if necessary, the resulting pressure-sensitive adhesive composition may be further dried by heating.
When curing is performed by irradiation with active energy rays, it is preferable to attach a separator to the surface of the coating film and irradiate the active energy rays while the pressure-sensitive adhesive composition is sandwiched between the substrate of the present invention and the separator, thereby preventing polymerization inhibition by oxygen.

Prior to irradiation with active energy rays, the sheet-like coating film may be heated to remove the solvent, etc. If the solvent, etc. is to be removed by heating, it is preferable to do so before attaching the separator.

Examples of the active energy rays include ionizing radiation such as α rays, β rays, γ rays, neutron rays, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. Furthermore, there are no particular limitations on the irradiation energy, irradiation time, and irradiation method of the active energy rays.

The above-mentioned pressure-sensitive adhesive composition can be prepared by known or conventional methods. For example, a solvent-based acrylic pressure-sensitive adhesive composition can be prepared by mixing an additive (e.g., an ultraviolet absorber) with a solution containing the above-mentioned acrylic polymer, as needed. For example, an active energy ray-curable acrylic pressure-sensitive adhesive composition can be prepared by mixing an additive (e.g., an ultraviolet absorber) with a mixture of the above-mentioned acrylic monomers or a partially polymerized product thereof, as needed.

The adhesive composition may be applied (coated) using a known coating method. For example, a coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater may be used.

In particular, when a pressure-sensitive adhesive layer is formed using an active energy ray-curable pressure-sensitive adhesive composition, the active energy ray-curable pressure-sensitive adhesive composition preferably contains a photopolymerization initiator. Furthermore, when the active energy ray-curable pressure-sensitive adhesive composition contains an ultraviolet absorber, the photopolymerization initiator preferably contains at least a photopolymerization initiator that has absorption properties over a wide wavelength range. For example, it is preferable to contain at least a photopolymerization initiator that has absorption properties for visible light as well as ultraviolet light. This is because, while there is a concern that the action of an ultraviolet absorber may inhibit curing by active energy rays, the inclusion of a photopolymerization initiator that has absorption properties over a wide wavelength range makes it easier to achieve high photocurability in the pressure-sensitive adhesive composition.

<Antistatic Layer>
The optical pressure-sensitive adhesive tape of the present invention may have an antistatic layer on the surface or between any layers. By having the antistatic layer, the optical pressure-sensitive adhesive tape of the present invention can prevent damage to an adherend such as an image display panel. The antistatic layer is preferably formed between the substrate of the present invention and the pressure-sensitive adhesive layer of the present invention.

The antistatic layer is not particularly limited, but may be, for example, an antistatic layer formed by coating a separator with a conductive coating liquid containing a conductive polymer. Specifically, it may be, for example, an antistatic layer formed by coating the first surface of the substrate of the present invention with a conductive coating liquid containing a conductive polymer. Specific coating methods include roll coating, bar coating, and gravure coating.

Examples of the conductive polymer include conductive polymers in which a π-conjugated conductive polymer is doped with a polyanion. Examples of π-conjugated conductive polymers include chain-like conductive polymers such as polythiophene, polypyrrole, polyaniline, and polyacetylene. Examples of polyanions include polystyrene sulfonic acid, polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylate ethyl sulfonic acid, and polymethacrylic carboxylic acid.

The thickness of the antistatic layer is preferably 1 nm to 1,000 nm, and more preferably 5 nm to 900 nm. The antistatic layer may consist of a single layer or two or more layers.

<Separator>
In the optical pressure-sensitive adhesive tape of the present invention, the surface of the pressure-sensitive adhesive layer of the present invention (the adhesive surface of the pressure-sensitive adhesive layer of the present invention) may be protected by a separator until use. The separator is used as a protective material for the pressure-sensitive adhesive layer and is peeled off when the optical pressure-sensitive adhesive tape of the present invention is attached to an adherend.

Conventional release paper can be used as the separator. Specific examples include substrates having a release treatment layer made from a release agent on at least one surface, low-adhesion substrates made from fluorine-based polymers (e.g., polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chlorofluoroethylene-vinylidene fluoride copolymer, etc.), and low-adhesion substrates made from non-polar polymers (e.g., olefin-based resins such as polyethylene and polypropylene).

As the separator, for example, a separator having a release treatment layer formed on at least one surface of the separator substrate can be suitably used. Examples of such separator substrates include plastic substrate films (synthetic resin films) such as polyester films (polyethylene terephthalate film, etc.), olefin resin films (polyethylene film, polypropylene film, etc.), polyvinyl chloride film, polyimide film, polyamide film (nylon film), and rayon film; papers (high-quality paper, Japanese paper, kraft paper, glassine paper, synthetic paper, top-coated paper, etc.); and composites (2- to 3-layer composites) made by laminating or co-extruding these materials.

The release agent constituting the release treatment layer is not particularly limited, but examples include silicone-based release agents, fluorine-based release agents, and long-chain alkyl-based release agents. Release agents can be used alone or in combination of two or more.

The thickness of the separator is not particularly limited and may be selected appropriately from the range of 5 to 100 μm.

The separator may have an antistatic layer formed on at least one surface of the separator substrate to prevent damage to the adherend, such as an image display panel. The antistatic layer may be formed on one surface of the separator (the release-treated surface or the untreated surface), or on both surfaces of the separator (the release-treated surface and the untreated surface).

The antistatic layer is not particularly limited, but may be, for example, an antistatic layer formed by coating a separator with a conductive coating liquid containing a conductive polymer. Specifically, it may be, for example, an antistatic layer formed by coating a separator (release-treated surface and/or untreated surface) with a conductive coating liquid containing a conductive polymer. Specific coating methods include roll coating, bar coating, and gravure coating.

The conductive polymer can be the same as the conductive polymer that constitutes the antistatic layer of the optical pressure-sensitive adhesive tape of the present invention.

The thickness of the antistatic layer is preferably 1 nm to 1000 nm, and more preferably 5 nm to 900 nm. The antistatic layer may consist of a single layer or two or more layers.

<Surface protection film>
In the optical pressure-sensitive adhesive tape of the present invention, the second surface of the substrate of the present invention may be protected by a surface protective film. The surface protective film is used as a protective material for the second surface of the substrate of the present invention during production or transportation of the optical pressure-sensitive adhesive tape of the present invention, the image display device of the present invention, or the tiling display of the present invention.

Examples of materials for forming the surface protection film include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins of these. Ester resins (particularly polyethylene terephthalate resins) are preferred.

The thickness of the surface protection film is typically 20 μm to 250 μm, and preferably 30 μm to 150 μm.

The surface protection film is releasably bonded to the second surface of the substrate of the present invention via any suitable adhesive. Preferably, a surface protection film having an adhesive layer formed thereon is formed and then bonded to the second surface of the substrate of the present invention of the optical adhesive tape of the present invention. Examples of adhesives used to laminate the surface protection film include adhesive compositions containing a base resin such as an acrylic resin, a styrene resin, or a silicone resin, blended with a crosslinking agent selected from an isocyanate compound, an epoxy compound, an aziridine compound, or a silane coupling agent. The thickness of the adhesive layer is typically 1 μm to 60 μm, preferably 3 μm to 30 μm. If the adhesive layer is too thin, problems such as reduced adhesion and increased likelihood of air bubbles being trapped may occur. If the adhesive layer is too thick, problems such as the adhesive overflowing may occur. Acrylic adhesives are preferably used from the standpoints of chemical resistance and adhesion.

<Image display device>
The image display device of the present invention has a laminated structure in which the optical pressure-sensitive adhesive tape of the present invention and an image display panel are laminated together. In Fig. 3, an image display device 20 has an image display panel 4 laminated on the pressure-sensitive adhesive layer 1 of the optical pressure-sensitive adhesive tape 10B.

The image display device of the present invention has the optical pressure-sensitive adhesive tape of the present invention in its laminated structure, which prevents shrinkage or expansion under usage conditions and maintains its transparency. Furthermore, the pressure-sensitive adhesive layer of the present invention adequately conforms to the shrinkage or expansion of the image display device, making it less likely to lift or peel off. Furthermore, if the image display panel has uneven surfaces due to wiring or other factors, the pressure-sensitive adhesive layer of the present invention adequately conforms to these surfaces and can fill them without leaving any air bubbles.

The image display panel is not particularly limited, but examples include liquid crystal image display panels, self-luminous image display panels (e.g., organic EL (electroluminescence) image display panels, LED image display panels), etc.

The image display panel is formed by arranging RGB elements alternately, and it is preferable that the spaces between the RGB elements be filled with a black matrix (BM) to improve contrast.

The image display device of the present invention may include optical components other than the optical pressure-sensitive adhesive tape of the present invention and the image display panel on the surface or between any of the layers. Examples of such optical components include, but are not limited to, polarizing plates, retardation plates, anti-reflection films, viewing angle adjustment films, and optical compensation films. The optical components also include components that provide decoration or protection while maintaining the visibility of the image display device or input device (such as design films, decorative films, and surface protection plates).

The image display device of the present invention can be produced by bonding the image display panel and the adhesive layer of the optical adhesive tape of the present invention together.

Specifically, the optical pressure-sensitive adhesive tape of the present invention can be attached to the image display panel by laminating them under heat and/or pressure. After laminating them under heat and/or pressure, they may be cured by irradiating them with active energy rays. The irradiation of active energy rays can be carried out in the same manner as in forming the pressure-sensitive adhesive layer of the present invention.

<Tiling display>
The tiling display of the present invention is formed by arranging a plurality of image display devices of the present invention. In Fig. 4, the tiling display 30 is formed by arranging nine image display devices 20 (the stacked structure is not shown) in a 3 x 3 array in a tiled pattern on a support substrate 31, with the image display devices 20 contacting each other with gaps 32. The support substrate can be a glass plate or a plastic film similar to the base material of the present invention.

The image display device of the present invention is suppressed from shrinking or expanding under usage conditions, so gaps or overlaps are less likely to occur between multiple image display devices in the tiling display of the present invention, making gaps less noticeable and maintaining a good appearance. Furthermore, with little shrinkage or expansion, transparency can be maintained unchanged. Furthermore, the pressure-sensitive adhesive layer of the present invention adequately follows the shrinkage or expansion of the image display device, preventing problems caused by lifting or peeling.

Furthermore, in the tiling display of the present invention, if the second surface of the base material of the present invention is subjected to an anti-reflection treatment and/or an anti-glare treatment, this is preferable in that it can prevent reflections from metal wiring, ITO wiring, etc. arranged on the substrate of the image display device of the present invention. Furthermore, this is also preferable in that it makes gaps between the image display devices of the present invention less visible in the tiling display.

The tiling display of the present invention may include components other than the image display device of the present invention and the support substrate. Such components include, but are not limited to, a backlight, a touch sensor, etc.

The tiling display of the present invention can be produced by arranging multiple image display devices of the present invention on the support substrate without any gaps and fixing them together by sealing the outermost surface with glass, for example.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

Production Example 1
(Preparation of Anti-Glare Film 1)
[Preparation of Coating Solution for Forming Antiglare Layer 1]
The resin contained in the anti-glare layer forming material is a UV-curable urethane acrylate resin (manufactured by Shin-Nakamura Chemical Co., Ltd., product name "NK Oligo"). The mixture contained 40 parts by weight of a diluent for an optical adjustment layer ("Opstar Z7540" manufactured by JSR Corporation) containing zirconia particles and an ultraviolet-curable resin, 57.5 parts by weight of a polyfunctional acrylate containing pentaerythritol triacrylate as a main component (manufactured by Osaka Organic Chemical Industry Ltd., trade name "Viscoat #300"); 2.5 parts by weight of a diluent for an optical adjustment layer containing zirconia particles and an ultraviolet-curable resin ("Opstar Z7540" manufactured by JSR Corporation); 2.8 parts by weight of silicone particles (manufactured by Momentive Performance Materials Japan LLC, trade name "Tospearl 130ND"); 2.5 parts by weight of a synthetic smectite (manufactured by Kunimine Industries Co., Ltd., trade name "Sumecton SAN") which is an organic clay as a thixotropy-imparting agent; 3 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "OMNIRAD907"); and fine particles of a cross-linked acrylic styrene copolymer resin (manufactured by Sekisui Plastics Co., Ltd.). 6.5 parts by weight of an organic clay (trade name "SSX-103DXE") and 0.1 parts by weight of a leveling agent (trade name "LE-303", manufactured by Kyoeisha Chemical Co., Ltd.) were mixed. The organic clay was diluted with toluene to a solids content of 6% by weight before use. This mixture was diluted with a toluene/cyclopentanone (CPN) mixed solvent (weight ratio 64/36) to a solids concentration of 38% by weight, and an antiglare layer-forming material (coating liquid) was prepared using an ultrasonic disperser.

[Formation of Antiglare Layer 1]
A transparent plastic film substrate (PET film, manufactured by Toray Industries, Inc., product name "38U413", thickness: 38 μm) was prepared as the substrate. The antiglare layer-forming material (coating liquid) was applied to one side of the transparent plastic film substrate using a wire bar to form a coating film (coating process). The coating film was then dried by heating at 95°C for 1 minute (drying process). Thereafter, the coating film was cured by irradiating it with ultraviolet light at an integrated light intensity of 300 mJ/ ^cm2 using a high-pressure mercury lamp to form an antiglare layer with a thickness of 6.5 μm. In this way, a laminate of the light-transmitting substrate and the antiglare layer 1 was obtained.

[Preparation of Coating Solution for Forming Antireflection Layer 1]
100 parts by weight of a polyfunctional acrylate containing pentaerythritol triacrylate as a main component (manufactured by Osaka Organic Chemical Industry Ltd., trade name "Viscoat #300"), 100 parts by weight of hollow nanosilica particles (manufactured by JGC Catalysts and Chemicals Industries, Ltd., trade name "Sururia 5320"), 40 parts by weight of solid nanosilica particles (manufactured by Nissan Chemical Industries, Ltd., trade name "MIBK-ST", solid content 30 wt%, weight average particle size 10 nm), 12 parts by weight of a fluorine-containing additive (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KY-1203"), 5 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "OMNIRAD907"), and 5 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "OMNIRAD2959") were mixed together. To the mixture was added a mixed solvent of MIBK (methyl isobutyl ketone) and PMA (propylene glycol monomethyl ether acetate) in a weight ratio of 70:30 as a dilution solvent, so that the total solid content was 1.5 wt %, and the mixture was stirred to prepare a coating liquid for forming an antireflection layer.
[Formation of Antireflection Layer 1]
The anti-reflection layer-forming coating liquid was applied to the anti-glare layer surface of the laminate of the light-transmitting substrate and the anti-glare layer 1 using a wire bar (coating step). The applied coating liquid was heated at 80°C for 1 minute and dried to form a coating film (drying step). The dried coating film was irradiated with ultraviolet light from a high-pressure mercury lamp at an integrated light intensity of 300 mJ/ ^cm2 for a curing treatment (curing step). This cured the coating film, forming an anti-reflection layer 1 with a thickness of 0.1 µm (anti-reflection layer forming step). In this manner, an anti-glare film 1 of this Production Example 1 was produced.

Production Example 2
(Preparation of Antiglare Film 2)
[Formation of Antiglare Layer 2]
A laminate of the light-transmitting substrate and the antiglare layer 2 was produced in the same manner as in Production Example 1, except that in preparing the coating liquid for forming the antiglare layer, the amount of the polyfunctional acrylate containing pentaerythritol triacrylate as a main component was changed to 60 parts by weight, the amount of the silicone particles was changed to 0.9 parts by weight, the amount of synthetic smectite, which is an organic clay, used as a thixotropy-imparting agent was changed to 1.5 parts by weight, and the diluted solution of the composition for the optical adjustment layer containing zirconia particles and an ultraviolet-curable resin and the fine particles of cross-linked acrylic-styrene copolymer resin were not used.
[Formation of Antireflection Layer 2]
An anti-reflection layer 2 was formed in the same manner as in Production Example 1, except that in preparing the coating solution for forming an anti-reflection layer, the blending amount of the hollow nanosilica particles was changed to 240 parts by weight. In this manner, an anti-glare film 2 of Production Example 2 was produced.

Production Example 3
(Preparation of Antiglare Film 3)
Antiglare film 3 of Production Example 3 was produced in the same manner as Production Example 1, except that in forming the antiglare layer, a transparent plastic film substrate (COP film, manufactured by Zeon Corporation, trade name "ZF14", thickness: 50 μm) was used as the substrate.

Production Example 4
(Preparation of Antiglare Film 4)
Antiglare film 4 of Production Example 4 was produced in the same manner as Production Example 1, except that in forming the antiglare layer, a transparent plastic film substrate (PEN film, manufactured by Toyobo Co., Ltd., product name "Q51", thickness: 25 μm) was used as the substrate.

Production Example 5
(Preparation of Antiglare Film 5)
Anti-glare film 5 of Production Example 5 was produced in the same manner as in Production Example 1, except that in forming the anti-glare layer, a transparent plastic film substrate (PEEK film, manufactured by Kurabo Industries, Ltd., trade name "EXPEEK", thickness: 50 μm) was used as the substrate.

Production Example 6
(Manufacturing transparent plastic film substrate)
A reaction vessel was charged with 81.98 parts by mass of isosorbide (hereinafter sometimes abbreviated as "ISB"), 47.19 parts by mass of tricyclodecane dimethanol (hereinafter sometimes abbreviated as "TCDDM"), 175.1 parts by mass of diphenyl carbonate (hereinafter sometimes abbreviated as "DPC"), and 0.979 parts by mass of a 0.2% by mass aqueous solution of cesium carbonate as a catalyst, and in a nitrogen atmosphere, the heating bath temperature was heated to 150°C as the first step of the reaction, and the raw materials were dissolved (approximately 15 minutes) with stirring as necessary. Next, the pressure was increased from atmospheric pressure to 13.3 kPa, and the heating bath temperature was increased to 190°C over 1 hour, while the generated phenol was discharged out of the reaction vessel. After the entire reaction vessel was held at 190 ° C for 15 minutes, in the second step, the pressure inside the reaction vessel was set to 6.67 kPa, the heating bath temperature was increased to 230 ° C over 15 minutes, and the generated phenol was removed from the reaction vessel. As the stirring torque of the agitator increased, the temperature was increased to 250 ° C in 8 minutes, and the pressure inside the reaction vessel was reduced to 0.200 kPa or less to remove the generated phenol. After reaching a predetermined stirring torque, the reaction was terminated, and the resulting reaction product was extruded into water to obtain polycarbonate resin pellets. The obtained polycarbonate resin was vacuum-dried at 80 ° C for 5 hours, and then a transparent plastic film substrate composed of a 40 μm thick polycarbonate resin was produced using a film-forming device equipped with a single-screw extruder (Shibaura Machine Co., Ltd., cylinder setting temperature: 250 ° C), a T-die (width 300 mm, setting temperature: 250 ° C), a chill roll (setting temperature: 120-130 ° C), and a winder.
(Preparation of Antiglare Film 6)
An anti-glare film 6 of Production Example 6 was produced in the same manner as in Production Example 1, except that in forming the anti-glare layer, a transparent plastic film substrate made of the polycarbonate resin obtained above was used as the substrate.

Production Example 7
(Preparation of Antiglare Film 7)
Antiglare film 7 of Production Example 7 was produced in the same manner as in Production Example 1, except that in forming the antiglare layer, a transparent plastic film substrate (CPI film, manufactured by KOLON Corporation, product name "C_50_D", thickness: 50 μm) was used as the substrate.

Production Example 8
(Preparation of Antiglare Film 8)
Antiglare film 8 of Production Example 8 was produced in the same manner as in Production Example 1, except that in forming the antiglare layer, a transparent plastic film substrate (TAC film, manufactured by Fujifilm Corporation, product name "TD80UL", thickness: 80 μm) was used as the substrate.

Production Example 9
(Preparation of Acrylic Pressure-Sensitive Adhesive Composition 1)
[Preparation of Acrylic Oligomer]
60 parts by weight of dicyclopentanyl methacrylate (DCPMA) and 40 parts by weight of methyl methacrylate (MMA) as monomer components, 3.5 parts by weight of α-thioglycerol as a chain transfer agent, and 100 parts by weight of toluene as a polymerization solvent were mixed and stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator, and the mixture was reacted at 70°C for 2 hours, then heated to 80°C and reacted for 2 hours. The reaction solution was then heated to 130°C, and the toluene, chain transfer agent, and unreacted monomer were dried and removed to obtain a solid acrylic oligomer (acrylic oligomer A). The weight-average molecular weight of acrylic oligomer A was 5100 and the glass transition temperature (Tg) was 130°C.

[Preparation of prepolymer and acrylic pressure-sensitive adhesive composition 1]
As monomer components for forming a prepolymer, 60 parts by weight of lauryl acrylate (LA), 22 parts by weight of 2-ethylhexyl acrylate (2EHA), 8 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 10 parts by weight of N-vinyl-2-pyrrolidone (NVP) were blended, and as photopolymerization initiators, 0.1 parts by weight of "Omnirad 184" manufactured by BASF and 0.1 parts by weight of "Omnirad 651" manufactured by BASF were blended, and polymerization was carried out by irradiation with ultraviolet light to obtain a prepolymer composition. To 100 parts by weight of the above prepolymer composition, 37 parts by weight of 2-ethylhexyl acrylate (2EHA), 0.08 part by weight of 1,6-hexanediol diacrylate (trade name "A-HD-N", manufactured by Shin-Nakamura Chemical Co., Ltd.), 6 parts by weight of the above acrylic oligomer A, and 0.3 part by weight of a silane coupling agent ("KBM403" manufactured by Shin-Etsu Chemical Co., Ltd.) were added as post-added components, and then these were mixed uniformly to prepare acrylic pressure-sensitive adhesive composition 1.

Production Example 10
(Preparation of prepolymer and acrylic pressure-sensitive adhesive composition 2)
As monomer components for forming a prepolymer, 67 parts by weight of butyl acrylate (BA), 14 parts by weight of cyclohexyl acrylate (Viscoat #155 manufactured by Osaka Organic Chemical Industry Ltd.), and 19 parts by weight of 4-hydroxybutyl acrylate (4HBA) were blended, as well as 0.09 parts by weight of Omnirad 184 manufactured by BASF and 0.09 parts by weight of Omnirad 651 manufactured by BASF as photopolymerization initiators, and polymerization was carried out by irradiation with ultraviolet light to obtain a prepolymer composition. To 100 parts by weight of the above prepolymer composition, 9 parts by weight of hydroxylethyl acrylate (HEA), 8 parts by weight of 4-hydroxybutyl acrylate (4HBA), 0.02 parts by weight of dipentaerythritol hexaacrylate (DPHA), 0.3 parts by weight of a photopolymerization initiator ("Omnirad 651" manufactured by BASF) and 0.35 parts by weight of a silane coupling agent ("KBM403" manufactured by Shin-Etsu Chemical Co., Ltd.) were added as post-addition components, and then these were mixed uniformly to prepare acrylic pressure-sensitive adhesive composition 2.

Production Example 11
(Preparation of prepolymer and acrylic pressure-sensitive adhesive composition 3)
As monomer components for forming a prepolymer, 78 parts by weight of 2-ethylhexyl acrylate (2EHA), 4 parts by weight of hydroxylethyl acrylate (HEA), and 18 parts by weight of N-vinyl-2-pyrrolidone (NVP) were blended, and as photopolymerization initiators, 0.035 parts by weight of "Omnirad 184" manufactured by BASF and 0.035 parts by weight of "Omnirad 651" manufactured by BASF were blended, and polymerization was carried out by irradiation with ultraviolet light to obtain a prepolymer composition. To 100 parts by weight of the above prepolymer composition, 17.6 parts by weight of hydroxyl ethyl acrylate (HEA), 0.294 parts by weight of 1,6-hexanediol diacrylate (trade name "A-HD-N", manufactured by Shin-Nakamura Chemical Co., Ltd.), 11.8 parts by weight of the above acrylic oligomer A, and 0.35 parts by weight of a silane coupling agent ("KBM403" manufactured by Shin-Etsu Chemical Co., Ltd.) were added as post-added components, and then these were mixed uniformly to prepare acrylic pressure-sensitive adhesive composition 3.

Example 1
(Preparation of substrate-less pressure-sensitive adhesive layer 1)
A 75 μm thick polyethylene terephthalate (PET) film ("Diafoil MRF75" manufactured by Mitsubishi Chemical) having a silicone release layer on its surface was used as a substrate (double-duty release film), and the above-mentioned acrylic pressure-sensitive adhesive composition 1 was applied to the release layer of the substrate to a thickness of 25 μm to form a coating layer. On this coating layer, a release layer of a 75 μm thick PET film ("Diafoil MRE75" manufactured by Mitsubishi Chemical) having one side treated with silicone release was attached as a cover sheet (double-duty release film). This laminate was photocured by irradiating ultraviolet light from the cover sheet side using a black light adjusted so that the irradiation intensity at the irradiation surface directly below the lamp was 5 mW/cm ² , to obtain a 25 μm thick substrateless pressure-sensitive adhesive layer 1.
(Preparation of Adhesive Tape 1)
One release film was peeled off from the substrate-less adhesive layer 1 obtained above, and the exposed adhesive surface was attached to the non-antiglare layer surface of the anti-glare film 1 shown in Production Example 1, thereby obtaining an adhesive tape 1 consisting of anti-glare film 1/adhesive layer 1/release film.

Example 2
(Preparation of Adhesive Tape 2)
An adhesive tape 2 consisting of an anti-glare film 2/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the anti-glare film 2 described above was used.

Example 3
(Preparation of substrate-less pressure-sensitive adhesive layer 2)
A substrate-less pressure-sensitive adhesive layer 2 having a thickness of 25 μm was obtained in the same manner as in Example 1, except that the acrylic pressure-sensitive adhesive composition 2 described above was used.
(Preparation of Adhesive Tape 3)
An adhesive tape 3 consisting of an anti-glare film 1/adhesive layer 2/release film was obtained in the same manner as in Example 1, except that the substrate-less adhesive layer 2 obtained above was used.

Example 4
(Preparation of Adhesive Tape 4)
An adhesive tape 4 consisting of an anti-glare film 3/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the above-described anti-glare film 3 was used.

Example 5
(Preparation of Adhesive Tape 5)
An adhesive tape 5 consisting of an anti-glare film 4/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the anti-glare film 4 described above was used.

Example 6
(Preparation of Adhesive Tape 6)
An adhesive tape 6 consisting of an anti-glare film 5/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the above-described anti-glare film 5 was used.

Example 7
(Preparation of Adhesive Tape 7)
An adhesive tape 7 consisting of an anti-glare film 6/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the above-described anti-glare film 6 was used.

Example 8
(Preparation of Adhesive Tape 8)
An adhesive tape 8 consisting of an anti-glare film 7/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the anti-glare film 7 described above was used.

Comparative Example 1
(Preparation of Adhesive Tape 9)
An adhesive tape 9 consisting of an anti-glare film 8/adhesive layer 1/release film was obtained in the same manner as in Example 1, except that the anti-glare film 8 described above was used.

Comparative Example 2
(Preparation of substrate-less pressure-sensitive adhesive layer 3)
A substrate-less pressure-sensitive adhesive layer 3 having a thickness of 25 μm was obtained in the same manner as in Example 1, except that the acrylic pressure-sensitive adhesive composition 3 described above was used.
(Preparation of Adhesive Tape 10)
An adhesive tape 10 consisting of an antiglare film 8/adhesive layer 3/release film was obtained in the same manner as in Example 1, except that the antiglare film 8 and substrate-less adhesive layer 3 described above were used.

(evaluation)
The pressure-sensitive adhesive tapes obtained in the above Examples and Comparative Examples were evaluated as follows. The evaluation methods are shown below. The results are shown in Table 2.

(1) Average dimensional change rate The pressure-sensitive adhesive tapes prepared in each Example and Comparative Example were cut into a roughly square shape in plan view, measuring 100 mm in MD x 100 mm in TD, and cross-pattern scratches were made in each of the four corners to prepare test pieces.
The distance (length) between scratches (cross pattern centers) in the MD direction and the distance (length) between scratches in the TD direction were measured at room temperature (25°C) using a CNC three-dimensional measuring machine (Mitutoyo Corporation, "LEGEX774") to obtain the pre-heating lengths in both the MD and TD directions.
Next, the test piece was heated for 500 hours in an environment of 60°C and 90% relative humidity, and then allowed to cool at room temperature (25°C) for 1 hour. The distance between scratches in the MD direction and the distance between scratches in the TD direction were then measured using a CNC coordinate measuring machine. This resulted in the length after heating in each of the MD and TD directions. Next, the dimensional change rates A1 and A2 were calculated in each of the MD and TD directions using the following formula, and their average values were used as the average dimensional change rate (%). The ratio of the dimensional change rate in the MD direction to the dimensional change rate in the TD direction (A1/A2) was also calculated.

Dimensional change rate (%) = [length after heating (mm) - length before heating (mm)] / length before heating (mm) × 100

Average dimensional change rate (%) = [dimensional change rate in MD direction + dimensional change rate in TD direction] / 2

(2) Maximum curl amount The release film of the pressure-sensitive adhesive tape prepared in each Example and Comparative Example was peeled off, and a PET film (manufactured by Mitsubishi Chemical Corporation, product name "Diafoil T100E50") was attached, and the resulting laminate was cut into a 100 mm x 100 mm approximately square shape in plan view to prepare a test piece.
The test piece was then heated for 500 hours in an environment of 60°C and 90% relative humidity, and then allowed to cool at room temperature (25°C) for 1 hour. Thereafter, the test piece was placed on a horizontal surface with the curled convex side facing downwards, and the distances from the horizontal surface to the four corner points were measured, and the distance from the horizontal surface to the longest point was taken as the maximum curl amount (mm).
The maximum curl amount measured by placing the laminate on a horizontal surface with the PET film side facing downward was defined as +, and the maximum curl amount measured by placing the laminate on a horizontal surface with the substrate side (the side opposite the PET film) facing downward was defined as −.

(3) Reflectance The adhesive surface of each adhesive tape obtained in each Example and Comparative Example was attached to a black acrylic plate to prepare a test piece. The test piece obtained was placed in a spectrophotometer U4100 (manufactured by Hitachi High-Technologies Corporation) with the adhesive tape side facing the light source, and the reflectance (%) of the visible light region at 5° regular reflection was measured.

(4) Haze The pressure-sensitive adhesive tapes obtained in each Example and Comparative Example were measured at room temperature (23° C.) using a haze measuring device (HR-100 manufactured by Murakami Color Research Institute). The measurement was repeated three times, and the average value was taken as the measured value.

(5) Strain Amount A, Strain Amount B, and Recovery Rate The separator was peeled from the pressure-sensitive adhesive layer obtained in each Example and Comparative Example, and multiple pressure-sensitive adhesive layers were laminated to prepare a test sample with a thickness of approximately 2 mm. This test sample was then punched into a disk shape with a diameter of 7.9 mm to obtain the test specimen. The shear test to determine "Strain Amount A,""StrainB," and "Recovery Rate" was carried out in the format shown in Figure 5. Specifically, using an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific, Inc., having parallel plates 41 and 42 with a diameter of 7.9 mm, the top surface of parallel plate 41 and the bottom surface of parallel plate 42 were aligned and brought into contact with the bottom and top surfaces of the pressure-sensitive adhesive layer of the sample, respectively (Figure 5(b)). Next, dynamic viscoelasticity measurement was performed under the following measurement conditions. The strain amount A at 500 Pa and 600 seconds (FIG. 5(c)) and the strain amount B at 0 Pa and 1800 seconds (FIG. 5(d)) were read, and the recovery rate was calculated using the following formula.
(Measurement conditions)
Deformation mode: torsion Measurement program: 500 Pa, held for 600 seconds, then 0 Pa, held for 1800 seconds.
Measurement temperature: 60℃
Axial Force: 0.2N
Recovery rate: (strain A - strain B) / strain A x 100

(6) Storage Modulus, Loss Tangent, and Glass Transition Temperature of the Pressure-Sensitive Adhesive Layer The separator was peeled off from the pressure-sensitive adhesive layer obtained in each Example and Comparative Example, and multiple pressure-sensitive adhesive layers were laminated to prepare a test sample with a thickness of approximately 2 mm. This test sample was punched into a disk with a diameter of 7.9 mm, sandwiched between parallel plates, and dynamic viscoelasticity measurement was performed under the following conditions using an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific. The storage modulus G' and loss tangent tanδ at each temperature were read from the measurement results. The temperature at which tanδ was maximized was determined as the glass transition temperature of the pressure-sensitive adhesive layer.
(Measurement conditions)
Deformation mode: Torsion Measurement frequency: 1 Hz
Measurement temperature: -70℃~150℃

(7) Shear strength of adhesive layer The adhesive tapes obtained in each example and comparative example were cut to a size of 10 mm wide and 100 mm long, and after peeling off the separator, the adhesive tape was attached to an acrylic resin plate (Acrylite, manufactured by Mitsubishi Chemical) so that the adhesive (bonding) area of the adhesive layer of the adhesive tape was ¹ cm2.The tape was then pulled in the shear direction at 23°C and a peeling rate of 0.06 mm/min, and the maximum load (N/ ^cm2 ) at that time was taken as the shear force.

(8) 300% Tensile Residual Stress Value of Pressure-Sensitive Adhesive Layer The pressure-sensitive adhesive layer obtained in each Example and Comparative Example was cut to a size of 40 mm x 40 mm, the separator on one side was peeled off, and the cut was folded once so that the adhesive surfaces were bonded together. The separator on one side was peeled off again, and the adhesive surfaces were bonded together again to prepare a pressure-sensitive adhesive layer sample having a size of approximately 10 mm x 40 mm and a thickness of approximately 400 μm. The pressure-sensitive adhesive layer sample was placed in a tensile tester with a chuck distance set to 20 mm and pulled 60 mm (300%) at a pulling speed of 200 mm/min (the chuck distance after pulling was 80 mm). The sample was held fixed at the 60 mm pull position for 300 seconds, after which the stress value was measured, and the "300% tensile residual stress value" was calculated using the following formula:

300% tensile residual stress value (N/cm ² )=stress value after holding for 300 seconds (N)/(4×adhesive sheet thickness (mm)/10)

(9) Humidity Expansion Coefficient The pressure-sensitive adhesive tapes obtained in each of the Examples and Comparative Examples were cut into a size of 2 mm width in the TD direction and 20 mm length in the MD direction, and measurement was carried out under the following conditions using a HC-TMA4000SA model manufactured by Bruker AXS Corporation.
(Measurement conditions)
Deformation mode: Tensile Load: 2g
Holding time: 5 hours Temperature increase rate: 5% RH/min
Measurement atmosphere: maintained at 60°C and 30% relative humidity until saturated, then controlled to 60°C and 60% relative humidity

(10) Humidity Expansion Coefficient of Substrate The humidity expansion coefficient was determined by measuring the elongation of each film when the humidity was changed from 30% RH to 60% RH at 60°C using a Bruker AXS HC-TMA4000SA model (unit: /RH%).
The humidity expansion coefficient (α) was calculated using the following formula:
α=ΔL/{(T2-T1)×L}
T1: Low humidity (% RH) for calculating the coefficient of humidity expansion
T2: High humidity side humidity (% RH) for calculating the humidity expansion coefficient
ΔL: Difference in length between T1 and T2 for the test piece (μm)
L: length of test piece at room temperature (60°C) (µm)

(11) Glass transition temperature (Tg) of the substrate
Approximately 8 mg of a sample was collected and placed in an aluminum container, and then subjected to DSC measurement.
Apparatus: TA Instruments Q-2000
Container: Aluminum container Temperature program: -30°C → 300°C
Temperature increase rate: 10°C/min
Atmospheric gas: _N2 (50 ml/min)

(12) Checking Gaps Between Adhesive Tapes Four pieces of the adhesive tapes obtained in the Examples and Comparative Examples were cut into 5 cm x 5 cm pieces and attached tightly to glass, and then heated in an environment of 60°C and 90% relative humidity for 500 hours, and then allowed to cool at room temperature (25°C) for 1 hour. Thereafter, the glass was placed over a backlight, and the gaps between the adhesive tapes when irradiated with light from the backlight were visually observed and evaluated according to the following criteria.
◯: No gaps were observed between the adhesive tapes.
×: Gaps were found between the adhesive tapes

(13) Confirmation of peeling of adhesive The edge of the adhesive tape of the sample heated at 60°C and 90% relative humidity for 500 hours used in the confirmation of gaps between the adhesive tapes was observed with an optical microscope and evaluated according to the following criteria.
◯: No peeling of the adhesive tape was observed.
×: Peeling of adhesive tape was confirmed

Variations of the present invention are listed below.
[Appendix 1] An optical pressure-sensitive adhesive tape having a laminated structure in which a substrate having a first surface and a second surface and a pressure-sensitive adhesive layer are laminated on the first surface of the substrate,
the average dimensional change rate in the width direction and the machine direction when the optical pressure-sensitive adhesive tape is heated for 500 hours in an environment of 60°C and 90% relative humidity is within ±0.15%,
An optical pressure-sensitive adhesive tape, characterized in that the pressure-sensitive adhesive layer has a recovery rate of 95% or less as determined in the following shear test.
<Shear test>
The amount of distortion A (%) was measured when a shear force of 500 Pa in the torsional direction was applied to the top and bottom of a disc-shaped pressure-sensitive adhesive layer having a thickness of 2 mm and a diameter of 7.9 mm at 60°C for 600 seconds, and the amount of distortion B (%) was measured when the layer was then held at a shear force of 0 Pa for 1,800 seconds, and the recovery rate (%) was calculated using the following formula.
Recovery rate (%) = (strain amount A - strain amount B) / strain amount A x 100
[Appendix 2] The average dimensional change rate in the width direction and the machine direction when the optical pressure-sensitive adhesive tape is heated for 500 hours in an environment of 60°C and 90% relative humidity is defined as C [%],
The optical adhesive tape described in Appendix 1, wherein the adhesive layer of the optical adhesive tape is bonded to a 50 μm thick PET film, and then cut into 10 cm squares to form a laminate. When the laminate is heated for 500 hours in an environment of 60°C and 90% relative humidity, the maximum curl amount D [mm] satisfies the following formula:

|C×D|≦3

Maximum curl amount: The laminate was placed on a horizontal surface with the convex curled surface facing downwards, and the maximum curl amount D [mm] was the largest of the warps at the four corners. The maximum curl amount measured when the laminate was placed on a horizontal surface with the PET film side facing downwards was designated as "+," and the maximum curl amount measured when the laminate was placed on a horizontal surface with the substrate side facing downwards was designated as "-."
[Appendix 3] The optical pressure-sensitive adhesive tape according to appendix 1 or 2, wherein the pressure-sensitive adhesive layer has a distortion amount A of 3% or more.
[Appendix 4] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 3, wherein the pressure-sensitive adhesive layer has a distortion amount B of 0.1% or more.
[Appendix 5] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 4, wherein the glass transition point (Tg) of the substrate is 60°C or higher.
[Appendix 6] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 5, wherein the pressure-sensitive adhesive layer has a glass transition temperature (Tg) of −10° C. or lower.
[Appendix 7] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 6, wherein the optical pressure-sensitive adhesive tape has a humidity expansion coefficient of 0.1% or less when humidified from a relative humidity of 30% at 60°C to a relative humidity of 60% at 60°C.
[Appendix 8] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 7, wherein the humidity expansion coefficient of the substrate is 5×10 ⁻⁵ /% RH or less.
[Appendix 9] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 8, wherein the second surface of the substrate is subjected to an anti-reflection treatment and/or an anti-glare treatment.
[Appendix 10] The optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 9, wherein the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer.
[Appendix 11] An image display device in which the optical pressure-sensitive adhesive tape according to any one of Appendices 1 to 10 and an image display panel are laminated together.
[Appendix 12] A tiling display in which a plurality of image display devices according to appendix 11 are arranged side by side.

10A, 10B Optical adhesive tape 1 Substrate 1a First surface 1b of substrate Second surface 2 Adhesive layer 3 Anti-reflection treatment and/or anti-glare treatment 20 Image display device 4 Image display panel 30 Tiling display 31 Support substrate 40 Adhesive layers 41, 42 Parallel plate

Claims (10)

An optical pressure-sensitive adhesive tape having a laminated structure in which a substrate having a first surface and a second surface and a pressure-sensitive adhesive layer are laminated on the first surface of the substrate,
the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer,
the average dimensional change rate in the width direction and the machine direction when the optical pressure-sensitive adhesive tape is heated for 500 hours in an environment of 60°C and 90% relative humidity is within ±0.15%,
an optical pressure-sensitive adhesive tape, characterized in that the pressure-sensitive adhesive layer has a recovery rate of 95% or less as determined in the following shear test;
an image display panel;
An image display device bonded to the optical pressure-sensitive adhesive tape at the pressure-sensitive adhesive layer.
<Shear test>
The amount of distortion A (%) was measured when a shear force of 500 Pa in the torsional direction was applied to the top and bottom of a disc-shaped pressure-sensitive adhesive layer having a thickness of 2 mm and a diameter of 7.9 mm at 60°C for 600 seconds, and the amount of distortion B (%) was measured when the layer was then held at a shear force of 0 Pa for 1,800 seconds, and the recovery rate (%) was calculated using the following formula.
Recovery rate (%) = (strain amount A - strain amount B) / strain amount A x 100 The average dimensional change rate in the width direction and the machine direction when the optical pressure-sensitive adhesive tape is heated for 500 hours in an environment of 60°C and 90% relative humidity is defined as C [%].
2. The image display device according to claim 1, wherein the pressure-sensitive adhesive layer of the optical pressure-sensitive adhesive tape is attached to a 50 μm-thick PET film, and then cut into a 10 cm square. When the laminate is heated for 500 hours in an environment of 60°C and 90% relative humidity, the following formula is satisfied when the maximum curl amount is D [mm]:

|C×D|≦3

Maximum curl amount: The laminate was placed on a horizontal surface with the convex curled surface facing downwards, and the maximum curl amount D [mm] was the largest of the warps at the four corners. The maximum curl amount measured when the laminate was placed on a horizontal surface with the PET film side facing downwards was designated as "+," and the maximum curl amount measured when the laminate was placed on a horizontal surface with the substrate side facing downwards was designated as "-." The image display device described in claim 1 or 2, wherein the strain amount A of the adhesive layer is 3% or more. The image display device described in any one of claims 1 to 3, wherein the strain amount B of the adhesive layer is 0.1% or more. The image display device according to any one of claims 1 to 4, wherein the glass transition temperature (Tg) of the substrate is 60°C or higher. The image display device according to any one of claims 1 to 5, wherein the glass transition temperature (Tg) of the adhesive layer is -10°C or lower. The image display device described in any one of claims 1 to 6, wherein the optical pressure-sensitive adhesive tape has a humidity expansion coefficient of 0.1% or less when humidified from 60°C and 30% relative humidity to 60°C and 60% relative humidity. 8. The image display device according to claim 1, wherein the humidity expansion coefficient of the substrate is 5×10 ⁻⁵ /% RH or less. The image display device described in any one of claims 1 to 8, wherein the second surface of the substrate is subjected to anti-reflection and/or anti-glare treatment. A tiling display comprising a plurality of image display devices according to any one of claims 1 to 9 arranged side by side.