JP7696381B2 - Pressure-sensitive adhesive layer, its manufacturing method, pressure-sensitive adhesive sheet, optical film with pressure-sensitive adhesive layer, and image display device - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive layer and a method for producing the same. The present invention also relates to a pressure-sensitive adhesive sheet and a pressure-sensitive adhesive layer-attached optical film having the pressure-sensitive adhesive layer. The present invention further relates to an image display device using these.

For example, in a display device such as a liquid crystal display device or an organic EL display device, a pressure-sensitive adhesive composition is used to bond a polarizing film, a retardation film, a transparent cover member such as a cover glass, or various other optical films to other optical films. In this way, an optical film laminate having the two optical films is formed by disposing an adhesive layer between the two optical films. In a display device, an optical film laminate having such a configuration is disposed, for example, such that the optical film side is the viewing side. In this configuration, when external light is incident from the optical film on the viewing side, there is a problem that the incident light is reflected at the interface between the adhesive layer and the optical film on the non-viewing side and returns to the viewing side. This problem is particularly noticeable when the angle of incidence of the external light is shallow.

On the other hand, for example, it has been proposed to use a light-diffusing adhesive composition containing a (meth)acrylic polymer as the base polymer and light-diffusing fine particles in the backlight unit of an image display device (Patent Document 1).

JP 2014-224964 A

The above problems are thought to be caused by the difference in refractive index between the adhesive layer and the adherend. For example, between the adhesive layer and an optical component (e.g., anti-reflection film, light diffusion film, light guide film, prism film, lens film, Fresnel lens, lenticular lens, or microlens film) using a material with a low refractive index such as a fluorine-based resin, polysiloxane, low-refractive-index inorganic particle, porous material, or hollow material, a problem occurs in visibility due to the influence of internal reflection of incident light at the interface. Since the problem is thought to be caused by the refractive index of the optical film being lower than that of the adhesive layer, it is thought that the problem can be solved by using an adhesive layer with a low refractive index. For example, a method of forming an adhesive layer with a low refractive index using an acrylic adhesive can be considered to use a fluoroalkyl acrylate (refractive index of about 1.38) as a monomer unit in a general acrylic polymer (refractive index is usually 1.47 to 1.52) that is the base polymer. However, an adhesive layer with a low refractive index that uses a base polymer containing the fluoroalkyl acrylate as a monomer unit has high surface tension and it is difficult to ensure adhesion. Thus, it was extremely difficult to create an adhesive layer with a low refractive index (e.g., a refractive index of 1.40 or less) while still ensuring the adhesiveness of the adhesive layer.

On the other hand, the adhesive layer formed from the light-diffusing adhesive composition of Patent Document 1 has a light-diffusing function, but since the light-diffusing fine particles are dispersed throughout the entire adhesive layer, it is difficult to ensure sufficient adhesion to optical films, etc.

The present invention aims to provide a pressure-sensitive adhesive layer that can effectively suppress internal reflection and has good adhesion, even when applied to optical components with low refractive index such as anti-reflection films, light diffusion films, lens films, Fresnel lenses, lenticular lenses, or microlens films, and a method for producing the same.

Another object of the present invention is to provide a pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer, and further to provide an optical film with a pressure-sensitive adhesive layer having the pressure-sensitive adhesive layer, and further to provide an image display device having the pressure-sensitive adhesive layer or the optical film with a pressure-sensitive adhesive layer.

As a result of extensive research into solving the above problems, the inventors discovered the adhesive layer and other components shown below, and completed the present invention.

That is, the present invention provides a pressure-sensitive adhesive layer having a first surface and a second surface opposite to the first surface,
the pressure-sensitive adhesive layer has a base formed of a pressure-sensitive adhesive composition containing a base polymer,
The first surface has a first refractive index based on the pressure-sensitive adhesive composition, while the second refractive index of the second surface is lower than the first refractive index of the first surface.

In the pressure-sensitive adhesive layer, it is preferable that the difference between the first refractive index of the first surface and the second refractive index of the second surface is 0.02 to 0.45.

In the pressure-sensitive adhesive layer, it is preferable that the second refractive index of the second surface is 1.45 or less.

The pressure-sensitive adhesive layer may have a low refractive index material dispersed on the second surface, the low refractive index material having a refractive index lower than that of the base polymer.

In the pressure-sensitive adhesive layer, it is preferable that the thickness of the region in which the low refractive index material is dispersed is 600 nm or less in the thickness direction from the second surface side of the pressure-sensitive adhesive layer.

In the pressure-sensitive adhesive layer, it is preferable that the refractive index of the base polymer is 1.40 to 1.55, and the refractive index of the low refractive index material is 1.10 to 1.45. It is also preferable that the difference between the refractive index of the base polymer and the refractive index of the low refractive index material is 0.07 to 0.45.

The low refractive index material may be particles with an average particle size of 10 nm to 150 nm.

The low refractive index material includes at least one inorganic particle selected from _the group consisting of _MgF2 , _CaF2 , and _Na3AlF6 , porous silica particles, hollow nanosilica particles, and hollow polymer particles.

The adhesive layer preferably has a total light transmittance of 85% or more.

It is preferable that the reflectance of the second surface of the adhesive layer is 0.5 to 3.5%.

It is preferable that the difference in reflectance between the first and second surfaces of the pressure-sensitive adhesive layer is 0.1 to 3.5%.

The pressure-sensitive adhesive layer preferably has a gel fraction of 30 to 95% by weight.

The pressure-sensitive adhesive layer preferably has a storage modulus G' of 0.05 to 0.50 MPa at 25°C.

The pressure-sensitive adhesive layer preferably has a tan δ peak value of -5 to -50°C when dynamic viscoelasticity is measured at 1 Hz.

The present invention also provides a method for producing the pressure-sensitive adhesive layer, comprising the steps of:
A step (1) of forming a base adhesive layer on a support using an adhesive composition containing a base polymer;
A step (2) of preparing a dispersion liquid in which a low refractive index material having a refractive index lower than that of the base polymer is dispersed;
a step (3) of applying the dispersion or solution to a second surface of the base pressure-sensitive adhesive layer opposite to the first surface on the support side, and allowing the low refractive index material contained in the dispersion or solution to permeate the base pressure-sensitive adhesive layer in a thickness direction from the second surface; and a step (4) of drying the pressure-sensitive adhesive layer permeated with the low refractive index material.
The present invention relates to a method for producing a pressure-sensitive adhesive layer, comprising the steps of:

The present invention also relates to an adhesive sheet having the above-mentioned adhesive layer and a support on one or both sides of the adhesive layer.

The present invention also provides an optical film with a pressure-sensitive adhesive layer, comprising an optical film and a pressure-sensitive adhesive layer provided on one or both sides of the optical film,
The present invention relates to an optical film with a pressure-sensitive adhesive layer, characterized in that the pressure-sensitive adhesive layer on one or both sides is the pressure-sensitive adhesive layer, and a first surface side of the pressure-sensitive adhesive layer is provided on the optical film.

In the optical film with the pressure-sensitive adhesive layer, a polarizing film is preferably used as the optical film.

The present invention also relates to an optical laminate comprising the optical film with a pressure-sensitive adhesive layer and an optical member with a low refractive index bonded to the pressure-sensitive adhesive layer of the optical film with a pressure-sensitive adhesive layer.

The present invention also relates to an image display device having the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer-attached optical film, or the optical laminate.

Unlike a diffusion adhesive layer in which fine particles are uniformly diffused in the adhesive layer, the adhesive layer of the present invention has different refractive indices on both sides of a single adhesive layer having a first surface and a second surface, and has a first refractive index based on the adhesive composition that forms the base of the entire adhesive layer on the first surface side, and a second refractive index lower than the first refractive index of the first surface on the other side of the second surface side. In this way, the adhesive layer of the present invention has an adhesive surface controlled to a lower refractive index than the refractive index based on the adhesive layer, so that the refractive index difference between the adhesive layer and an optical member (e.g., an anti-reflection film, a light diffusion film, a light guide film, a prism film, a lens film, a Fresnel lens, a lenticular lens, or a microlens film, etc.) formed of a material with a low refractive index can be adjusted, which can suppress reflection at the interface between the adhesive layer and the optical member and contribute to improving the light extraction efficiency. When the second surface of the pressure-sensitive adhesive layer of the present invention is applied to a surface uneven portion such as a microlens, the pressure-sensitive adhesive layer can fill the surface uneven portion to protect the surface uneven portion. Compared to the case where a void layer is provided on the surface uneven portion, the void can be filled without impairing the light extraction efficiency, and scratches and damage to the shape due to vibration during handling and transportation can be suppressed. In addition, the second surface of the pressure-sensitive adhesive layer of the present invention has a refractive index adjustment region adjusted to a low refractive index, but the total light transmittance is high and a low refractive index region can be formed without increasing the haze value. In addition, since the first surface of the pressure-sensitive adhesive layer of the present invention maintains the adhesive force that the pressure-sensitive adhesive layer originally has, the adhesion to a general optical film (e.g., a polarizing film, etc.) is also good, and on the other hand, since the pressure-sensitive adhesive composition forms the base even on the second surface of the pressure-sensitive adhesive layer controlled to a low refractive index, adhesion to an optical film formed of a material with a low refractive index can be ensured.

FIG. 1 is a cross-sectional view showing one embodiment of a pressure-sensitive adhesive layer of the present invention. FIG. 2 is a plan view showing the state of a second surface of the pressure-sensitive adhesive layer of the present invention. FIG. 2 is a schematic diagram showing the steps for producing the pressure-sensitive adhesive layer of the present invention. 1 is a cross-sectional view showing one embodiment of a pressure-sensitive adhesive sheet of the present invention. 1 is a cross-sectional view showing one embodiment of a pressure-sensitive adhesive layer-attached optical film of the present invention. 1 is a cross-sectional view showing one embodiment of an optical laminate of the present invention.

The adhesive layer of the present invention will be described below with reference to the drawings.

<Adhesive Layer>
As shown in Fig. 1, the pressure-sensitive adhesive layer 1 of the present invention has a first surface f1 and a second surface f2 on the opposite side of the first surface f1. In addition, in the pressure-sensitive adhesive layer 1, a base (matrix) 1a of the entire pressure-sensitive adhesive layer 1 is formed by a pressure-sensitive adhesive composition containing a base polymer. The first surface f1 has a first refractive index n1, and the second refractive index n2 of the second surface f2 is designed to be lower than the first refractive index n1. Fig. 1 illustrates a case in which a low refractive index material 2 having a refractive index lower than the refractive index of the base polymer is dispersed (distributed unevenly) on the second surface f2 side of the base 1a.

The first refractive index n1 of the first surface f1 corresponds to the refractive index of the adhesive layer obtained from the adhesive composition forming the base 1a in the adhesive layer 1 of the present invention. Therefore, the first refractive index n1 is determined by the adhesive composition forming the base 1a. Since the refractive index of the base polymer is substantially the same as the refractive index of the adhesive layer 1 of the entire adhesive layer 1, the first refractive index n1 of the first surface f1 is generally determined by the refractive index of the base polymer. The adhesive composition forming the adhesive layer will be described later, but for example, the refractive index of an adhesive layer formed from a typical acrylic adhesive is generally about 1.47 to 1.52. The refractive index of an adhesive layer formed from a silicone adhesive is generally about 1.40.

On the other hand, the second refractive index n2 of the second surface f2 is not particularly limited as long as it satisfies n1>n2 in relation to the first refractive index n1 on the first surface f1 side, and is appropriately determined taking into consideration the refractive index of the low refractive index optical film to be adhered. However, if the difference (n1-n2) between the first refractive index n1 and the second refractive index n2 becomes too large, internal reflection may occur within the pressure-sensitive adhesive layer 1, so it is preferable to adjust the difference (n1-n2) to 0.02 to 0.45. The difference (n1-n2) is more preferably 0.03 to 0.35, and even more preferably 0.03 to 0.25.

The second refractive index n2 of the second surface f2 is preferably 1.45 or less, for example, from the viewpoint of effectively suppressing internal reflection, more preferably 1.4 or less, more preferably 1.35 or less, and even more preferably 1.3 or less. If the second refractive index n2 is 1.4 or less, it is also possible to use the second surface side of the adhesive layer 1 of the present invention as an alternative to an air layer. On the other hand, from the viewpoint of maintaining adhesive strength, the second refractive index n2 is preferably 1.25 or more, and even more preferably 1.28 or more. The range of the second refractive index n2 is a range lower than the lower limit of the refractive index (generally about 1.47 to 1.52) of an adhesive layer formed from a typical acrylic adhesive.

In addition, in the adhesive layer 1, when the low refractive index material 2 is dispersed on the second surface f2 side as shown in FIG. 1, it is preferable that the refractive index of the base polymer in the adhesive composition forming the substrate 1a is 1.40 to 1.55, and the refractive index of the low refractive index material 2 dispersed on the second surface f2 side in the substrate 1a is 1.10 to 1.45. It is preferable that the difference in refractive index between the base polymer and the low refractive index material 2 is 0.07 to 0.45. The refractive index of the base polymer is more preferably 1.40 to 1.52, and more preferably 1.40 to 1.50. The refractive index of the low refractive index material 2 is more preferably 1.14 to 1.42, and more preferably 1.18 to 1.40. The difference in refractive index between the base polymer and the low refractive index material 2 is more preferably 0.07 to 0.35, and more preferably 0.10 to 0.30. The lower the refractive index of the low refractive index material 2, the lower the amount of addition, but on the other hand, the larger the difference between the refractive index of the base polymer (adhesive layer 1a) and the refractive index of the low refractive index material 2, and the more likely scattering (haze) will occur. Therefore, it is preferable to adjust the refractive index difference so that it is not too large. The refractive index can be expressed as the refractive index value of the D line measured by spectroscopic ellipsometry in an environment of 23°C when the material is made into a single layer film.

The low refractive index material 2 can be particles having an average particle size of 10 nm to 150 nm. Particles with an average particle size in this range are preferable in terms of keeping the haze of the adhesive layer 1 low and maintaining a high total light transmittance even when dispersed on the second surface f2 side of the adhesive layer 1. The average particle size is preferably 20 nm to 100 nm, and more preferably 20 nm to 90 nm. The average particle size of the particles is a value measured by a particle size distribution size measuring device using a dynamic light scattering method.

Examples of the low refractive index material 2 include _MgF2 (refractive index 1.38), _CaF2 (refractive index 1.43: fluorite), _Na3AlF (refractive index 1.34: sodium hexafluoroaluminate (cryolite)), etc. These materials (e.g., particles) can be used alone or in combination of two or more kinds.

As the low refractive index material 2, for example, hollow particles can be used. The hollow particles may be either inorganic particles or polymer particles. Since hollow particles have a void space with a low refractive index within the particle, the refractive index of the hollow particles is lower than the refractive index of the components that form the hollow particles. For example, the refractive index of silica is 1.46, but hollow nanosilica particles (refractive index 1.24, product name: Sururia 5320, particle size 75 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) and porous silica particles can be used as low refractive index materials. Other examples include hollow polymer fine particles (refractive index 1.32, product name: Techpolymer NH, product number XX-255AA, particle size 80 nm, hollow rate 39%, manufactured by Sekisui Chemical Co., Ltd.). When hollow particles are provided in a low refractive index surface treatment layer, there are issues with strength and scratch resistance due to the hollow material, but the hollow particles (low refractive index material 2) in the present invention are added (impregnated) into the adhesive layer 1, so they can be applied without having to consider issues with strength and scratch resistance.

The low refractive index material 2 may be an oligomer containing a fluoroalkyl group, an oligomer of a polysiloxane resin, or the like.

The thickness of the adhesive layer 1 is not particularly limited, but is usually 5 μm to 500 μm, preferably 10 μm to 400 μm, and more preferably 10 μm to 350 μm. In addition, in FIG. 1, the region in which the low refractive index material 2 is dispersed in the adhesive layer 1 is represented by a thickness T from the second surface f2 side. The thickness T is appropriately designed according to the thickness of the adhesive layer, but is usually preferably 600 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less. In order to effectively suppress internal reflection when applied to an optical film with a low refractive index, the thickness T is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more.

The area in the adhesive layer 1 where the low refractive index material 2 having a thickness T is dispersed has an irregular uneven shape in relation to the base (matrix) 1a, but in the present invention, the thickness T is determined by averaging the measured values of the depth of the uneven shape.

The low refractive index material 2 is distributed on the side of the second surface f2 in an individually dispersed state or in a partially aggregated state. The boundary between the region in which the low refractive index material 2 is dispersed and the substrate 1a in which the low refractive index material 2 is not dispersed has an irregular uneven shape as described in relation to FIG. 1, but when measuring the thickness T, the depth range in which 90% of the low refractive index material 2 is present at each measurement position is taken as the measured value of the thickness T at that measurement position, and the measured values at multiple measurement positions are averaged.

Figure 2 is a plan view showing the state of the second surface f2 of the adhesive layer 1. As shown in Figure 2, the low refractive index material 2 is dispersed in the form of islands on the base 1a, forming an island-like structure, with a portion of the base 1a and a portion of the low refractive index material 2. The area ratio of the low refractive index material 2 on the second surface f2 is preferably in the range of 30 to 99%. The area ratio is the ratio of the area occupied by the low refractive index material 2 to the total area of a square region with one side measuring 10 μm to 200 μm, and is determined by measuring multiple square regions and averaging the measured values.

The proportion of the low refractive index material 2 in the adhesive layer 1 is not particularly limited as long as the first refractive index n1 on the first surface f1 side and the second refractive index n2 on the second surface f2 satisfy the relationship n1>n2.

The total light transmittance of the entire pressure-sensitive adhesive layer 1 of the present invention is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. The higher the total light transmittance of the pressure-sensitive adhesive layer 1, the better. The haze value is preferably 1.5% or less, more preferably 1% or less, and even more preferably 0.8% or less. The lower the haze value of the pressure-sensitive adhesive layer 1, the better. The total light transmittance and haze value of the entire pressure-sensitive adhesive layer 1 are values measured in accordance with JIS K7361.

The reflectance of the second surface of the pressure-sensitive adhesive layer 1 of the present invention is preferably 0.5 to 3.5%. The reflectance of the second surface of the pressure-sensitive adhesive layer 1 of the present invention is lower than the reflectance of the first surface, and the internal reflection can be controlled to be small even in relation to the low refractive index material. The reflectance of the second surface is preferably 0.5 to 3.0%, and more preferably 0.5 to 2.5%. The difference in reflectance between the first surface and the second surface of the pressure-sensitive adhesive layer 1 of the present invention is preferably 0.1 to 3.5%.

The above description of the adhesive layer 1 of the present invention is based on the premise that the second refractive index n2 of the second surface f2 is designed to be lower than the first refractive index n1. However, the adhesive layer 1 of the present invention can be considered as an invention that can be specified by the relationship between the refractive indices of both surfaces, and is characterized in that the reflectance of the second surface f2 is lower than the reflectance of the first surface f1.

The adhesive layer 1 of the present invention preferably has a gel fraction of 30 to 95% by weight. The gel fraction is preferably 30 to 90% by weight, more preferably 35 to 90% by weight, and even more preferably 40 to 90% by weight. When the gel fraction of the adhesive layer 1 is within the above range, it is a preferred embodiment in terms of having stress relaxation properties and ensuring conformability to unevenness. Note that the gel fraction relates to the base 1a in the adhesive layer 1 and does not include the low refractive index material 2.

<Measurement of Gel Fraction of Pressure-Sensitive Adhesive Layer>
About 0.2 g was scraped off from the adhesive layer (before the low refractive index material was permeated) and used as sample 1. Sample 1 was wrapped in a Teflon (registered trademark) film (trade name "NTF1122", manufactured by Nitto Denko Corporation) having a diameter of 0.2 μm, and then tied with a kite string, which was used as sample 2. The weight of sample 2 before being subjected to the following test was measured and this was used as weight A. The weight A is the total weight of sample 1 (adhesive layer), the Teflon (registered trademark) film, and the kite string. The total weight of the Teflon (registered trademark) film and the kite string was used as weight B. Next, sample 2 was placed in a 50 ml container filled with ethyl acetate and left to stand at 23° C. for one week. Thereafter, sample 2 was taken out of the container and dried in a dryer at 130° C. for 2 hours to remove the ethyl acetate, and the weight of sample 2 was measured. The weight of sample 2 after being subjected to the above test was measured and used as weight C. The gel fraction (% by weight) was calculated from the following formula:
Gel fraction (wt%)=(C−B)/(A−B)×100

The pressure-sensitive adhesive layer 1 of the present invention preferably has a storage modulus G' at 25°C of 0.05 to 0.50 MPa. The storage modulus G' is preferably 0.06 to 0.45 MPa, more preferably 0.07 to 0.40 MPa, and even more preferably 0.08 to 0.35 MPa. When the storage modulus G' of the pressure-sensitive adhesive layer 1 is within the above range, it is preferable for protecting image display devices (LCD, OLED terminals, etc.) that are becoming thinner and for ensuring dimensional stability during cutting processing.

The pressure-sensitive adhesive layer 1 of the present invention preferably has a tan δ peak value (glass transition temperature) of -5 to -50°C when dynamic viscoelasticity is measured at 1 Hz. The tan δ peak value is preferably -7 to -50°C, more preferably -9 to -45°C, and even more preferably -10 to -40°C. If the tan δ peak value of the pressure-sensitive adhesive layer 1 is within the above range, this is a preferred embodiment in terms of ensuring resistance to drop impact of an image display device (mobile terminal, etc.).

<Measurement of storage modulus G′ and peak tan δ value of pressure-sensitive adhesive layer>
A test sample having a thickness of about 2 mm was prepared by laminating a plurality of pressure-sensitive adhesive layers. The test sample was punched out into a disk having a diameter of 7.9 mm, sandwiched between parallel plates, and subjected to dynamic viscoelasticity measurement under the following conditions using an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific. From the measurement results, the storage modulus G' and tan δ peak value of the pressure-sensitive adhesive layer at 25°C were read.
(Measurement conditions)
Frequency: 1Hz
Deformation mode: Torsion Measurement temperature: -70℃ to 150℃
Heating rate: 5° C./min

Next, the method for producing the adhesive layer of the present invention will be explained with reference to Figure 3.

First, in step (1), a base adhesive layer 1' is formed on a support S using an adhesive composition containing a base polymer. The base adhesive layer 1' forms the base 1a of the resulting adhesive layer 1. In the base adhesive layer 1', the support 1 side is the first surface f1', and the opposite side is the second surface f2'. The method for forming the base adhesive layer 1' is not particularly limited, and it can be formed by a method usually used in this field. Specifically, the adhesive composition is applied to one side of the support S, and the coating film formed from the adhesive composition is dried to form the base adhesive layer, or it can be formed by irradiating it with active energy rays such as ultraviolet rays.

The support S is not particularly limited, and various substrates such as release films and transparent resin film substrates can be used.

Examples of materials constituting the release film include resin films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films; porous materials such as paper, cloth, and nonwoven fabric; nets, foam sheets, metal foils, and appropriate thin sheets such as laminates of these; however, resin films are preferably used because of their excellent surface smoothness. The release film can also be subjected to release and antifouling treatments and antistatic treatments as necessary.

Meanwhile, in step (2), a dispersion liquid 10 is prepared in which a low refractive index material 2 having a refractive index lower than that of the base polymer used in the adhesive composition is dispersed (not shown). The dispersion medium used in the dispersion liquid is one that can disperse the low refractive index material 2 and can penetrate into the base adhesive layer 1', and is selected appropriately depending on the type of low refractive index material and the type of adhesive composition that forms the base adhesive layer. The concentration of the low refractive index material in the dispersion medium is preferably adjusted to, for example, 0.1 to 10% by weight.

Examples of the dispersion medium include alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, n-butanol, 2-butanol, cyclohexanol, t-butyl alcohol, glycerin, ethylene glycol, 2-methyl-2,4-pentadiol, phenol, and parachlorophenol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pentanone, 2-hexanone, and 2-heptanone; ethers such as diethyl ether, tetrahydrofuran, dioxane, and anisole; esters such as ethyl acetate, butyl acetate, and methyl lactate; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-hexane and cyclohexane, amides such as dimethylformamide and dimethylacetamide; and cellosolves such as methyl cellosolve, ethyl cellosolve, and methyl cellosolve acetate. These dispersion media can be used alone or in combination of two or more types. The above solvents are merely examples, and the solvents used in the present invention are not limited to these.

Next, in step (3), the dispersion liquid 10 is applied to the second surface f2' of the base adhesive layer 1', and the low refractive index material 2 contained in the dispersion liquid 10 is allowed to permeate in the thickness direction from the second surface f2' of the base adhesive layer 1'. In FIG. 3, (3)-1 shows the state immediately after the dispersion liquid 10 is applied to the base adhesive layer 1', and (3)-2 shows the state in which the low refractive index material 2 has permeated into the base adhesive layer 1'. The second surface f2' side of the base adhesive layer 1' is swollen by the dispersion medium of the dispersion liquid 10, and in the process, the low refractive index material 2 in the dispersion liquid 10 permeates into the base adhesive layer 1'.

Next, in step (4), the base adhesive layer 1' permeated with the low refractive index material 2 is dried. The drying step evaporates the dispersion medium of the dispersion liquid 10 that has permeated the base adhesive layer 1', thereby obtaining the adhesive layer 1 shown in FIG. 1. This state is shown in FIG. 3 (4). The conditions for the drying step are determined according to the type of dispersion medium.

The region (thickness T) in which the low refractive index material 2 is dispersed in the adhesive layer 1 is determined by the relationship between the adhesive composition forming the base adhesive layer 1' and the dispersion medium of the dispersion liquid 10. The dispersion medium can be appropriately selected so that the penetration depth is the value described above. In addition, the coating amount of the dispersion liquid is appropriately set so that the desired thickness T is obtained.

The above-mentioned dispersion can be applied by any suitable method, such as roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, etc. The thickness T can be controlled by the method of application of the dispersion, the concentration of the dispersion, the amount of application, etc.

<Adhesive composition>
The pressure-sensitive adhesive composition containing a base polymer that forms the matrix 1a of the pressure-sensitive adhesive layer 1 of the present invention will be described.

The adhesive composition is preferably a transparent material having adhesiveness that can be used for optical applications. The adhesive composition can be appropriately selected from, for example, acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. From the viewpoints of transparency, processability, durability, etc., it is preferable to use an acrylic adhesive. A base polymer according to the type of the adhesive composition is used. In the present invention, it is preferable to use an acrylic adhesive containing a (meth)acrylic polymer as a base polymer.

The acrylic adhesive may contain, for example, a partial polymer of a monomer component containing an alkyl (meth)acrylate and/or a (meth)acrylic polymer obtained from the monomer component. The base polymer of the acrylic adhesive may contain a partial polymer of a monomer component containing an alkyl (meth)acrylate and/or a (meth)acrylic polymer obtained from the monomer component.

Examples of the alkyl (meth)acrylate include the linear or branched alkyl (meth)acrylates having 1 to 24 carbon atoms described above, and among these, alkyl (meth)acrylates having 1 to 9 carbon atoms are preferred, and branched alkyl (meth)acrylates having 4 to 9 carbon atoms are preferred. The alkyl (meth)acrylates are preferred because they have a well-balanced adhesive property. Specific examples of branched alkyl (meth)acrylates having 4 to 9 carbon atoms include n-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and isononyl (meth)acrylate, and these can be used alone or in combination of two or more.

In the present invention, the alkyl (meth)acrylate having an alkyl group having 1 to 24 carbon atoms at the ester end is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more, of the total amount of the monofunctional monomer components forming the (meth)acrylic polymer.

The monomer component may contain a copolymerizable monomer other than the alkyl (meth)acrylate as a monofunctional monomer component. The copolymerizable monomer may be used as the remainder of the alkyl (meth)acrylate in the monomer component.

The copolymerization monomer may include, for example, a cyclic nitrogen-containing monomer. As the cyclic nitrogen-containing monomer, a monomer having a polymerizable functional group with an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and having a cyclic nitrogen structure may be used without particular limitation. The cyclic nitrogen structure is preferably one having a nitrogen atom in the cyclic structure. Examples of the cyclic nitrogen-containing monomer include lactam-based vinyl monomers such as N-vinylpyrrolidone, N-vinyl-ε-caprolactam, and methylvinylpyrrolidone; vinyl-based monomers having nitrogen-containing heterocycles such as vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, and vinylmorpholine. In addition, (meth)acrylic monomers containing heterocycles such as morpholine ring, piperidine ring, pyrrolidine ring, and piperazine ring may be used. Specific examples include N-acryloylmorpholine, N-acryloylpiperidine, N-methacryloylpiperidine, and N-acryloylpyrrolidine. Among the cyclic nitrogen-containing monomers, lactam vinyl monomers are preferred.

In the present invention, the amount of the cyclic nitrogen-containing monomer is preferably 0.5 to 50% by weight, more preferably 0.5 to 40% by weight, and even more preferably 0.5 to 30% by weight, based on the total amount of the monofunctional monomer components forming the (meth)acrylic polymer.

The monomer component used in the present invention may contain a hydroxyl group-containing monomer as a monofunctional monomer component. As the hydroxyl group-containing monomer, a monomer having a polymerizable functional group with an unsaturated double bond such as a (meth)acryloyl group or a vinyl group and having a hydroxyl group may be used without any particular limitation. Examples of the hydroxyl group-containing monomer include 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, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; and hydroxyalkyl cycloalkane (meth)acrylates such as (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Other examples include hydroxyethyl (meth)acrylamide, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, etc. These can be used alone or in combination. Among these, hydroxyalkyl (meth)acrylates are preferred.

In the present invention, the hydroxyl group-containing monomer is preferably 1% by weight or more, more preferably 2% by weight or more, and even more preferably 3% by weight or more, based on the total amount of the monofunctional monomer components forming the (meth)acrylic polymer, in order to increase the adhesive strength and cohesive strength. On the other hand, if the amount of the hydroxyl group-containing monomer is too large, the adhesive layer may become hard and the adhesive strength may decrease, and the viscosity of the adhesive composition may become too high or gel. Therefore, the hydroxyl group-containing monomer is preferably 30% by weight or less, more preferably 27% by weight or less, and even more preferably 25% by weight or less, based on the total amount of the monofunctional monomer components forming the (meth)acrylic polymer.

In addition, the monomer components forming the (meth)acrylic polymer may contain other functional group-containing monomers as monofunctional monomers, such as carboxyl group-containing monomers and monomers having a cyclic ether group.

As the carboxyl group-containing monomer, any monomer having a polymerizable functional group with an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and having a carboxyl group can be used without any particular restrictions. Examples of the carboxyl group-containing monomer include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc., which can be used alone or in combination. Anhydrides of itaconic acid and maleic acid can be used. Among these, acrylic acid and methacrylic acid are preferred, and acrylic acid is particularly preferred. Note that any carboxyl group-containing monomer can be used as a monomer component used in the production of the (meth)acrylic polymer of the present invention, and on the other hand, a carboxyl group-containing monomer may not be used.

As the monomer having a cyclic ether group, those having a polymerizable functional group having an unsaturated double bond such as a (meth)acryloyl group or a vinyl group, and having a cyclic ether group such as an epoxy group or an oxetane group, can be used without any particular restrictions. Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, etc. Examples of oxetane group-containing monomers include 3-oxetanylmethyl (meth)acrylate, 3-methyl-oxetanylmethyl (meth)acrylate, 3-ethyl-oxetanylmethyl (meth)acrylate, 3-butyl-oxetanylmethyl (meth)acrylate, 3-hexyl-oxetanylmethyl (meth)acrylate, etc. These can be used alone or in combination.

In the present invention, the amount of the carboxyl group-containing monomer and the monomer having a cyclic ether group is preferably 30% by weight or less, more preferably 27% by weight or less, and even more preferably 25% by weight or less, based on the total amount of the monofunctional monomer components forming the (meth)acrylic polymer.

The monomer components forming the (meth)acrylic polymer of the present invention include, as copolymerizable monomers, alkyl (meth)acrylates represented by CH ₂ ═C(R ¹ )COOR ² (wherein R ¹ represents hydrogen or a methyl group, and R ² represents a substituted alkyl group having 1 to 3 carbon atoms, or a cyclic cycloalkyl group).

Here, the substituent of the substituted alkyl group having 1 to 3 carbon atoms as ^R2 is preferably an aryl group having 3 to 8 carbon atoms or an aryloxy group having 3 to 8 carbon atoms. The aryl group is not limited, but a phenyl group is preferable.

Examples of such monomers represented by CH ₂ ═C(R ¹ )COOR ² include phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc. These can be used alone or in combination.

In the present invention, the (meth)acrylate represented by _CH2 =C( ^R1 ) ^COOR2 can be used in an amount of 50% by weight or less, preferably 45% by weight or less, more preferably 40% by weight or less, and even more preferably 35% by weight or less, based on the total amount of the monofunctional monomer components forming the (meth)acrylic polymer.

Other copolymerizable monomers include vinyl acetate, vinyl propionate, styrene, α-methylstyrene; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; acrylic ester monomers such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, and 2-methoxyethyl acrylate; amide group-containing monomers, amino group-containing monomers, imide group-containing monomers, N-acryloylmorpholine, and vinyl ether monomers. In addition, monomers having a cyclic structure such as terpene (meth)acrylate and dicyclopentanyl (meth)acrylate can be used as copolymerizable monomers.

Further examples include silane-based monomers containing silicon atoms. Examples of silane-based monomers include 3-acryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4-vinylbutyltrimethoxysilane, 4-vinylbutyltriethoxysilane, 8-vinyloctyltrimethoxysilane, 8-vinyloctyltriethoxysilane, 10-methacryloyloxydecyltrimethoxysilane, 10-acryloyloxydecyltrimethoxysilane, 10-methacryloyloxydecyltriethoxysilane, 10-acryloyloxydecyltriethoxysilane, and 10-acryloyloxydecyltriethoxysilane.

In addition to the monofunctional monomers exemplified above, the monomer components forming the (meth)acrylic polymer of the present invention may contain a polyfunctional monomer as necessary to adjust the cohesive strength of the pressure-sensitive adhesive composition.

A polyfunctional monomer is a monomer having at least two polymerizable functional groups having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and examples thereof include (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, and 1,2-ethylene glycol di(meth)acrylate. Examples of suitable polyfunctional monomers include ester compounds of polyhydric alcohols and (meth)acrylic acid, such as 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tetramethylolmethane tri(meth)acrylate; allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl di(meth)acrylate, and hexyl di(meth)acrylate. Among these, trimethylolpropane tri(meth)acrylate, hexanediol di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate can be preferably used. The polyfunctional monomers can be used alone or in combination of two or more.

The amount of polyfunctional monomer used varies depending on its molecular weight, number of functional groups, etc., but is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and even more preferably 1 part by weight or less, per 100 parts by weight of monofunctional monomers in total. The lower limit is not particularly limited, but is preferably 0 parts by weight or more, and more preferably 0.001 parts by weight or more. By keeping the amount of polyfunctional monomer used within the above range, the adhesive strength can be improved.

The (meth)acrylic polymer can be produced by any known production method, such as solution polymerization, radiation polymerization such as ultraviolet (UV) polymerization, bulk polymerization, emulsion polymerization, or other radical polymerization methods. The resulting (meth)acrylic polymer may be any of a random copolymer, a block copolymer, a graft copolymer, and the like.

In addition, in the present invention, partial polymers of the above monomer components can also be suitably used.

The (meth)acrylic polymer can be produced by any known production method, such as solution polymerization, radiation polymerization such as ultraviolet (UV) polymerization, bulk polymerization, emulsion polymerization, or other radical polymerization methods. The resulting (meth)acrylic polymer may be any of a random copolymer, a block copolymer, a graft copolymer, and the like.

When the (meth)acrylic polymer is produced by radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier, etc. used in radical polymerization can be appropriately added to the monomer components to carry out polymerization. The polymerization initiator, the chain transfer agent, the emulsifier, etc. used in the radical polymerization are not particularly limited and can be appropriately selected and used. The weight average molecular weight of the (meth)acrylic polymer can be controlled by the amount of polymerization initiator and the chain transfer agent used and the reaction conditions, and the amount used is appropriately adjusted depending on the type of these.

For example, in solution polymerization, ethyl acetate, toluene, etc., are used as the polymerization solvent. In a specific example of solution polymerization, the reaction is carried out under a stream of inert gas such as nitrogen, with the addition of a polymerization initiator, usually at about 50 to 70°C, for about 5 to 30 hours.

When the (meth)acrylic polymer is produced by radiation polymerization, the monomer component can be polymerized by irradiating it with radiation such as electron beams or ultraviolet (UV) rays. When performing ultraviolet polymerization, it is preferable to include a photopolymerization initiator in the monomer component, since this has the advantage of shortening the polymerization time.

(Silane coupling agent)
Furthermore, the pressure-sensitive adhesive composition of the present invention may contain a silane coupling agent. The amount of the silane coupling agent is preferably 1 part by weight or less, more preferably 0.01 to 1 part by weight, and even more preferably 0.02 to 0.6 parts by weight, per 100 parts by weight of the base polymer (e.g., the above-mentioned (meth)acrylic polymer).

(Crosslinking Agent)
The pressure-sensitive adhesive composition of the present invention may contain a crosslinking agent. Examples of the crosslinking agent include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, silicone-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, silane-based crosslinking agents, alkyl etherified melamine-based crosslinking agents, metal chelate-based crosslinking agents, and peroxide-based crosslinking agents. The crosslinking agents may be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents are preferably used.

The above crosslinking agents may be used alone or in combination of two or more. The total content is preferably 5 parts by weight or less, more preferably 0.01 to 5 parts by weight, even more preferably 0.01 to 4 parts by weight, and particularly preferably 0.02 to 3 parts by weight, relative to 100 parts by weight of the monofunctional monomer component that forms the (meth)acrylic polymer.

(Other additives)
In addition to the above-mentioned components, the pressure-sensitive adhesive composition of the present invention may contain appropriate additives depending on the application, such as viscosity adjusters, release adjusters, tackifiers (e.g., rosin derivative resins, polyterpene resins, petroleum resins, oil-soluble phenolic resins, etc., which are solid, semi-solid, or liquid at room temperature), plasticizers, softeners, pigments, colorants (pigments, dyes, etc.), pH adjusters (acids or bases), rust inhibitors, antiaging agents, antioxidants, light stabilizers, ultraviolet absorbers, etc.

The adhesive sheet of the present invention has the adhesive layer 1 and a support on one or both sides of the adhesive layer 1. FIG. 4 shows a case where the adhesive layer 1 has a support 3a on the first side f1 and a support 3b on the second side f2. The supports 3a and 3b can be the same as the support S used in the adhesive layer 1 shown in FIG. 3. The support 3a can be the support S used in the manufacturing method of the adhesive layer 1 shown in FIG. 3 as it is. The support 3b can be appropriately provided on the second side f2 of the adhesive layer 1 after the adhesive layer 1 is manufactured by the manufacturing method shown in FIG. 3.

The pressure-sensitive adhesive layer-attached optical film A of the present invention has an optical film 4 and a pressure-sensitive adhesive layer 1 provided on one or both sides of the optical film 4. The pressure-sensitive adhesive layer 1 is provided on one or both sides of the optical film 4. The pressure-sensitive adhesive layer 1 is provided on the first surface f1 side of the pressure-sensitive adhesive layer 1 on the optical film 4. When the pressure-sensitive adhesive layer 1 is provided on one side of the optical film 4, a normal pressure-sensitive adhesive layer can also be provided on the other side. Figure 5 shows a case where the pressure-sensitive adhesive layer 1 is provided only on one side of the optical film 4. Figure 5 shows a case where the pressure-sensitive adhesive layer 1 has a support 3b on the second surface f2 of the pressure-sensitive adhesive layer 1.

<Optical film>
The optical film may be, for example, a film used in forming an image display device such as a liquid crystal display device, and the type is not particularly limited. For example, the optical film may be a polarizing film. The polarizing film generally has a transparent protective film on one or both sides of a polarizer.

<Polarizing film>
The polarizing film may include a polarizer having a transparent protective film on at least one surface thereof.

The polarizer is not particularly limited, and various types can be used. Examples of polarizers include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films, which are uniaxially stretched after adsorbing a dichroic substance such as iodine or a dichroic dye, and polyene-based oriented films such as dehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride. Among these, polarizers made of a polyvinyl alcohol film and a dichroic substance such as iodine are preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.

A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and stretching it uniaxially can be produced, for example, by immersing the polyvinyl alcohol-based film in an aqueous solution of iodine to dye it and stretching it to 3 to 7 times its original length. If necessary, it can also be immersed in an aqueous solution of potassium iodide or the like which may contain boric acid, zinc sulfate, zinc chloride, or the like. Furthermore, if necessary, the polyvinyl alcohol-based film can be immersed in water and washed before dyeing. Washing the polyvinyl alcohol-based film with water can wash off dirt and blocking inhibitors on the surface of the polyvinyl alcohol-based film, and also has the effect of preventing unevenness such as uneven dyeing by swelling the polyvinyl alcohol-based film. Stretching can be performed after dyeing with iodine, or it can be stretched while dyeing, or it can be dyed with iodine after stretching. Stretching can be performed in an aqueous solution of boric acid, potassium iodide, or the like, or in a water bath.

In addition, in the present invention, a thin polarizer having a thickness of 10 μm or less can also be used. From the viewpoint of thinning, the thickness is preferably 1 to 7 μm. Such a thin polarizer has little thickness unevenness, excellent visibility, and excellent durability due to little dimensional change, and is also preferable in that the thickness as a polarizing film can be made thin.

Representative examples of thin polarizers include the thin polarizing films described in JP-A-51-069644, JP-A-2000-338329, WO 2010/100917, or Japanese Patent No. 4751481 and JP-A-2012-073563. These thin polarizing films can be obtained by a manufacturing method including a step of stretching a polyvinyl alcohol-based resin (hereinafter also referred to as PVA-based resin) layer and a resin substrate for stretching in a laminated state, and a step of dyeing. With this manufacturing method, even if the PVA-based resin layer is thin, it can be stretched without problems such as breakage due to stretching because it is supported by the resin substrate for stretching.

As the thin polarizing film, among the manufacturing methods including the steps of stretching and dyeing the laminate, those obtained by a manufacturing method including a step of stretching in an aqueous boric acid solution as described in WO 2010/100917, or JP 4751481 and JP 2012-073563 are preferred, because they can be stretched at a high ratio and have improved polarization performance. In particular, those obtained by a manufacturing method including a step of auxiliary air-stretching before stretching in an aqueous boric acid solution as described in JP 4751481 and JP 2012-073563 are preferred.

As a material for forming the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture blocking property, isotropy, etc. is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. A transparent protective film is attached to one side of the polarizer with an adhesive layer, while a thermosetting resin or an ultraviolet-curing resin such as a (meth)acrylic, urethane, acrylic urethane, epoxy, or silicone resin can be used as the transparent protective film on the other side. The transparent protective film may contain one or more suitable additives. Examples of additives include ultraviolet absorbers, antioxidants, lubricants, plasticizers, release agents, coloring inhibitors, flame retardants, nucleating agents, antistatic agents, pigments, colorants, etc. The content of the thermoplastic resin in the transparent protective film is preferably 50 to 100% by weight, more preferably 50 to 99% by weight, even more preferably 60 to 98% by weight, and particularly preferably 70 to 97% by weight. If the content of the thermoplastic resin in the transparent protective film is 50% by weight or less, the inherent high transparency of the thermoplastic resin may not be fully exhibited.

The thickness of the transparent protective film can be determined as appropriate, but is generally about 1 to 500 μm, taking into consideration strength, ease of handling, thinness, etc.

The surface of the transparent protective film to which the polarizer is not attached can be provided with a functional layer such as a hard coat layer, an anti-reflection layer, or an anti-sticking layer, and may also be treated for the purposes of diffusion or anti-glare.

The adhesive used to bond the polarizer and the transparent protective film is not particularly limited as long as it is optically transparent, and various types of adhesives such as water-based, solvent-based, hot melt, radical curing, and cationic curing types can be used, but water-based or radical curing adhesives are preferred.

Examples of optical films include optical layers that may be used in the formation of liquid crystal displays, such as reflectors, anti-transmitters, retardation films (including 1/2 and 1/4 wavelength plates), visual compensation films, and brightness enhancement films. These may be used alone as optical films, or may be laminated to the polarizing film in practical use to form one or more layers. A retardation film may also be used as the transparent protective film. Retardation films obtained by stretching and shrinking a polymer film or those obtained by aligning and fixing a liquid crystal material may be used as appropriate depending on the purpose.

The optical film in which the optical layer is laminated on the polarizing film can be formed by laminating the layers separately in sequence during the manufacturing process of liquid crystal display devices, etc., but an optical film formed by laminating the layers in advance has the advantage of being excellent in quality stability and assembly work, etc., and can improve the manufacturing process of liquid crystal display devices, etc. For lamination, an appropriate bonding means such as an adhesive layer can be used. When bonding the polarizing film and other optical layers, their optical axes can be arranged at an appropriate angle depending on the desired retardation characteristics, etc.

The optical laminate B of the present invention has an optical film A with a pressure-sensitive adhesive layer and an optical member 5 with a low refractive index laminated to the pressure-sensitive adhesive layer 1 of the optical film A with a pressure-sensitive adhesive layer. The optical member 5 is provided on the second surface f2 side of the pressure-sensitive adhesive layer 1. The optical laminate B shown in FIG. 6 illustrates a case in which the optical member 5 is laminated to the pressure-sensitive adhesive layer 1 after the support 3b (e.g., a release film) is peeled off from the optical film A with a pressure-sensitive adhesive layer shown in FIG. 5. Examples of the optical member 5 include an anti-reflection film, a light diffusion film, a prism film, a light guide film, a lens film, a Fresnel lens, a lenticular lens, or a microlens film.

The pressure-sensitive adhesive layer-attached optical film or optical laminate of the present invention can be preferably used for forming various image display devices such as liquid crystal display devices. The formation of a liquid crystal display device can be carried out in a conventional manner. That is, a liquid crystal display device is generally formed by appropriately assembling a display panel such as a liquid crystal cell and an optical film with a pressure-sensitive adhesive layer, or an optical laminate, and components such as an illumination system as necessary, and incorporating a driving circuit, but in the present invention, there is no particular limitation other than the use of the pressure-sensitive adhesive layer-attached optical film or optical laminate of the present invention, and the formation can be carried out in a conventional manner. As for the liquid crystal cell, any type, such as TN type, STN type, π type, VA type, IPS type, etc., can be used.

It is possible to form suitable liquid crystal display devices, such as a liquid crystal display device in which an optical film or optical laminate with a pressure-sensitive adhesive layer is arranged on one or both sides of a display panel such as a liquid crystal cell, or a display device using a backlight or a reflector as a lighting system. In this case, the optical film or optical laminate with a pressure-sensitive adhesive layer according to the present invention can be placed on one or both sides of a display panel such as a liquid crystal cell. When optical films are provided on both sides, they may be the same or different. Furthermore, when forming a liquid crystal display device, suitable components such as a diffusion layer, an anti-glare layer, an anti-reflection film, a protective plate, a prism array, a lens array sheet, a light diffusion sheet, a backlight, etc. can be arranged in one or more layers at suitable positions.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Note that all parts and percentages in each example are by weight. Unless otherwise specified below, all room temperature storage conditions are 23°C and 65% RH.

(Release film)
A polyester film having a thickness of 38 μm and one side of which had been subjected to a release treatment with silicone (product name: Diafoil MRF, manufactured by Mitsubishi Plastics, Inc.) was used.

Comparative Example 1
(Preparation of Pressure-Sensitive Adhesive Composition (A))
A monomer mixture was prepared by adding 41 parts by weight of 2-ethylhexyl acrylate (2EHA), 41 parts by weight of isostearyl acrylate (ISTA), 14 parts by weight of N-vinyl-2-pyrrolidone (NVP), 4 parts by weight of N-2-hydroxybutyl acrylate (4HBA), 0.035 parts by weight of two kinds of photopolymerization initiators (trade name: Irgacure 184, manufactured by BASF), and 0.035 parts by weight of a photopolymerization initiator (trade name: Irgacure 651, manufactured by BASF) to a four-neck flask. Next, this monomer mixture was exposed to ultraviolet light under a nitrogen atmosphere to be partially photopolymerized, thereby obtaining a partially polymerized product (acrylic polymer syrup) with a polymerization rate of about 10% by weight. To 100 parts by weight of the acrylic polymer syrup thus obtained, 0.025 parts by weight of trimethylolpropane triacrylate (TMPTA) and 0.3 parts of a silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) were added, and then these were uniformly mixed to prepare a pressure-sensitive adhesive composition (A).

(Production of Pressure-Sensitive Adhesive Layer (A))
The pressure-sensitive adhesive composition (A) was applied onto the release-treated surface of a release film so that the thickness of the pressure-sensitive adhesive layer after formation was 100 μm to form a coating layer. Next, another release film was coated on the surface of the coating layer so that the release-treated surface was on the coating layer side. Thereafter, ultraviolet light was irradiated under conditions of illuminance: 6.5 mW/cm ² , light amount: 2000 mJ/cm ² , and peak wavelength: 350 nm to photocure the coating layer to form a pressure-sensitive adhesive layer (A), and a pressure-sensitive adhesive sheet (substrate-less type, pressure-sensitive adhesive layer thickness: 100 μm) in which a release film was provided on both sides of the pressure-sensitive adhesive layer (A) was produced. The refractive index (n _D ) of the pressure-sensitive adhesive layer (A) measured by an Abbe refractometer in an environment of 23 ° C. was 1.48, and the gel fraction was 67%.

Comparative Example 2
(Preparation of Pressure-Sensitive Adhesive Composition (B))
A monomer mixture consisting of 76 parts by weight of 2-ethylhexyl acrylate (2EHA), 18 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 16 parts by weight of 2-hydroxyethyl acrylate (HEA) was mixed with 0.050 parts by weight of 1-hydroxycyclohexyl phenyl ketone (product name: Irgacure 184, having an absorption band at a wavelength of 200 to 370 nm, manufactured by BASF) and 0.050 parts by weight of 2,2-dimethoxy-1,2-diphenylethan-1-one (product name: Irgacure 651, having an absorption band at a wavelength of 200 to 380 nm, manufactured by BASF) as photopolymerization initiators, and then irradiated with ultraviolet light until the viscosity (measurement conditions: BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30° C.) reached about 20 Pa·s, to obtain a prepolymer composition (polymerization rate: 9%) in which a portion of the monomer components was polymerized. Next, 0.060 parts by weight of hexanediol diacrylate (HDDA) and 0.3 parts by weight of a silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to the prepolymer composition and mixed to obtain a pressure-sensitive adhesive composition (b).

(Preparation of Pressure-Sensitive Adhesive Composition (B))
To the adhesive composition (b) obtained above (the monomer component forming the acrylic polymer is taken as 100 parts by weight), 0.8 parts by weight (solid content weight) of 2,4-bis-[{4-(4-ethylhexyloxy)-4-hydroxy}-phenyl]-6-(4-methoxyphenyl)-1,3,5-triazine (trade name: Tinosorb S, absorption maximum wavelength of absorption spectrum: 346 nm, manufactured by BASF Japan) dissolved in butyl acrylate to a solid content of 15% and 0.3 parts by weight of bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (trade name: Irgacure 819, having an absorption band at wavelengths of 200 to 450 nm, manufactured by BASF Japan) were added and stirred to obtain an adhesive composition (B).

(Production of Pressure-Sensitive Adhesive Layer (B))
The pressure-sensitive adhesive composition (B) was applied onto the release-treated surface of a release film so that the thickness after the formation of the pressure-sensitive adhesive layer was 150 μm to form a coating layer. Next, another release film was coated on the surface of the coating layer so that the release-treated surface was on the coating layer side. Thereafter, ultraviolet light was irradiated under conditions of illuminance: 6.5 mW/cm ² , light amount: 2000 mJ/cm ² , and peak wavelength: 350 nm to photocure the coating layer to form a pressure-sensitive adhesive layer (B), and a pressure-sensitive adhesive sheet (substrate-less type, pressure-sensitive adhesive layer thickness: 150 μm) in which a release film was provided on both sides of the pressure-sensitive adhesive layer (B) was produced. The refractive index (n _D ) of the pressure-sensitive adhesive layer (B) measured by an Abbe refractometer in an environment of 23 ° C. was 1.49, and the gel fraction was 88%.

Comparative Example 3
(Preparation of Pressure-Sensitive Adhesive Composition (C))
In a separable flask equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen gas inlet tube, 95 parts by weight of butyl acrylate (BA), 5 parts by weight of acrylic acid (AA), 0.2 parts by weight of azobisisobutyronitrile as a polymerization initiator, and 233 parts by weight of ethyl acetate were added, and nitrogen gas was passed through and substituted with nitrogen for about 1 hour while stirring. The flask was then heated to 60°C and reacted for 7 hours to obtain an acrylic polymer having a weight average molecular weight (Mw) of 1.1 million. The acrylic polymer solution (solid content is 100 parts by weight) was added with 0.8 parts by weight of trimethylolpropane tolylene diisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and 0.1 parts by weight of a silane coupling agent (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) as an isocyanate crosslinking agent to prepare a pressure-sensitive adhesive composition (C: solution).

(Production of Pressure-Sensitive Adhesive Layer (C))
The pressure-sensitive adhesive composition (C: solution) was applied to the release-treated surface of a release film so that the thickness after drying was 23 μm, and then dried at 100 ° C for 3 minutes to remove the solvent, obtaining a pressure-sensitive adhesive layer (C). Then, the adhesive layer was heated at 50 ° C for 48 hours to perform a crosslinking treatment. The exposed surface of the obtained pressure-sensitive adhesive layer (C) was covered with another release film so that the release-treated surface was on the exposed surface side, and a pressure-sensitive adhesive sheet (substrate-less type, thickness of pressure-sensitive adhesive layer: 23 μm) in which a release film was provided on both sides of the pressure-sensitive adhesive layer (C) was produced. The refractive index (n _D ) of the pressure-sensitive adhesive layer (C) measured by an Abbe refractometer in an environment of 23 ° C. was 1.47, and the gel fraction was 82%.

Comparative Example 4
(Preparation of Pressure-Sensitive Adhesive Composition (D))
In a separable flask equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen gas inlet tube, 99 parts by weight of butyl acrylate (BA), 1 part by weight of 4-hydroxybutyl acrylate (4HBA), 0.2 parts by weight of azobisisobutyronitrile as a polymerization initiator and ethyl acetate as a polymerization solvent were added so that the solid content was 30% by weight, and then nitrogen gas was passed through and the mixture was substituted with nitrogen for about 1 hour while stirring. The flask was then heated to 60°C and reacted for 7 hours to obtain an acrylic polymer having a weight average molecular weight (Mw) of 1.1 million. A pressure-sensitive adhesive composition (D: solution) was prepared by adding 0.11 parts of trimethylolpropane xylylene diisocyanate (Mitsui Chemicals, Inc.'s "Takenate D110N") and 0.1 parts of a silane coupling agent (Shin-Etsu Chemical Co., Ltd.'s "KBM-403") to the solution of this acrylic polymer (100 parts of solid content) as an isocyanate crosslinking agent.

(Production of Pressure-Sensitive Adhesive Layer (D))
The pressure-sensitive adhesive composition (D: solution) was applied to the release-treated surface of a release film so that the thickness after drying was 20 μm, and then dried at 120 ° C for 3 minutes to remove the solvent, obtaining a pressure-sensitive adhesive layer (D). Then, the resultant was heated at 50 ° C for 48 hours to perform a crosslinking treatment. The exposed surface of the obtained pressure-sensitive adhesive layer (D) was covered with another release film so that the release-treated surface was on the exposed surface side, and a pressure-sensitive adhesive sheet (substrate-less type, thickness of pressure-sensitive adhesive layer: 23 μm) in which a release film was provided on both sides of the pressure-sensitive adhesive layer (D) was produced. The refractive index (n _D ) of the pressure-sensitive adhesive layer (D) measured by an Abbe refractometer in an environment of 23 ° C. was 1.47, and the gel fraction was 75%.

Example 1
(Preparation of Dispersion Containing Low Refractive Index Particles)
As a dispersion liquid containing low refractive index particles, hollow nanosilica particles (hollow particles, refractive index: 1.24, average primary particle diameter: 75 nm, product name: Sururia 5320, manufactured by JGC Catalysts and Chemicals Co., Ltd.) were diluted with a dispersion medium (methyl ethyl ketone/methyl isobutyl ketone = 9/1: volume ratio) to prepare a dispersion liquid with a particle concentration of 1.5 wt%.

(Production of pressure-sensitive adhesive layer with adjusted refractive index)
One of the release films of the pressure-sensitive adhesive sheet obtained in Comparative Example 1 was peeled off. The above dispersion was applied to the exposed surface of the pressure-sensitive adhesive layer (A) with a bar coater RDS No. 3 so that the thickness of the refractive index adjustment region was about 20 nm to 150 nm, and then dried in a drying oven at 110 ° C. for 180 seconds. Next, a second release film was newly attached to the surface of the pressure-sensitive adhesive layer (A) in which the hollow nanosilica particles were dispersed, to obtain a pressure-sensitive adhesive sheet. The release film on the opposite side to the second release film was referred to as the first release film.

Examples 2 to 8
In Example 1, an adhesive sheet having an adhesive layer with an adjusted refractive index was prepared in the same manner as in Example 1, except that the type of adhesive layer and the type of dispersion liquid (type of low refractive index particles, their average particle size, type of dispersion medium, and particle concentration) were changed as shown in Table 1.
When the target thickness of the refractive index adjustment region after drying was more than 150 to about 300 nm, a bar coater RDS No. 5 was used, and when the target thickness of the refractive index adjustment region after drying was about 20 to 150 nm, a bar coater RDS No. 3 was used.

(evaluation)
The pressure-sensitive adhesive layers (pressure-sensitive adhesive sheets) obtained in the Examples and Comparative Examples were subjected to the following evaluations, and the results are shown in Table 1.

<Measurement of average surface refractive index>
The average surface refractive index of the adhesive layer (refractive index adjustment region side: second surface) obtained in the examples was measured at sodium D line (589 nm) using a spectroscopic ellipsometer (EC-400, manufactured by JA. Woolam). From the adhesive sheets obtained in the examples and comparative examples, the release films on both sides were peeled off, and a blackboard was attached to the surface (first surface) on which the dispersion was not applied, and the average refractive index of the surface (second surface) on which the dispersion was applied was measured. In the adhesive sheet of the comparative example, both release films were peeled off, and a blackboard was attached to one surface, and the average refractive index of the adhesive layer surface was measured. The adhesive layer of the adhesive sheet of the comparative example has the same refractive index on both sides.

<Measurement of thickness of refractive index adjustment region>
The cross section of the pressure-sensitive adhesive layer in the depth direction was adjusted and observed with a TEM. The thickness of the refractive index adjustment region was measured from the obtained TEM image (direct magnification 3000 to 30000 times). The thickness of the refractive index adjustment region was determined as the average value of the unevenness of the interface between the region in which the particles are dispersed and the region in which the particles are not dispersed in the pressure-sensitive adhesive layer. When it was difficult to distinguish the interface, the surface TEM image was binarized using image processing software (ImageJ) and the depth thickness of the region in which 90% (area) of the particles existed was determined as the thickness.

<Total light transmittance, haze>
From the adhesive sheet obtained in the examples, the second release film (the second surface side of the adhesive layer) was peeled off and attached to a slide glass (product name: White Polish No. 1, thickness: 0.8-1.0 mm, total light transmittance: 92%, haze: 0.2%, manufactured by Matsunami Glass Industry Co., Ltd.). The other first release film was further peeled off to prepare a test piece having a layer structure of adhesive layer (refractive index adjustment region on the slide glass side)/slide glass. On the other hand, in the adhesive layer of the comparative example, one release film was peeled off and attached to the same slide glass as above, and the other release film was further peeled off to prepare a test piece having a layer structure of adhesive layer/slide glass. The total light transmittance and haze value in the visible light region of the above test piece were measured using a haze meter (device name: HM-150, manufactured by Murakami Color Research Institute Co., Ltd.).

<Adhesiveness>
From the adhesive sheets obtained in the Examples and Comparative Examples, sheet pieces having a length of 100 mm and a width of 20 mm were cut out. Next, the first release film (the side of the adhesive layer on which the dispersion liquid was not applied) was peeled off from the sheet pieces obtained from the adhesive sheets of the Examples, and then a PET film (trade name: Lumirror S-10, thickness: 25 μm, manufactured by Toray Industries, Inc.) was attached (backed) to the adhesive layer surface. Next, the second release film was peeled off, and the sheet was pressed onto a glass plate (trade name: soda lime glass #0050, manufactured by Matsunami Glass Industry Co., Ltd.) as a test plate under pressure bonding conditions of a 2 kg roller and one round trip, to prepare a sample consisting of a test plate/adhesive layer (first surface is the PET side)/PET film. On the other hand, the sheet pieces obtained from the adhesive sheets of the Comparative Examples had one release film peeled off, and then a PET film similar to the above attached to the adhesive layer surface, and then the other release film peeled off, and a sample was prepared using the same test plate as above. The obtained sample was subjected to autoclave treatment (50° C., 0.5 MPa, 15 minutes), and then allowed to cool for 30 minutes under an atmosphere of 23° C. and 50% RH. After cooling, the pressure-sensitive adhesive sheet (pressure-sensitive adhesive layer/PET film) was peeled off from the test plate using a tensile tester (apparatus name: Autograph AG-IS, manufactured by Shimadzu Corporation) in accordance with JIS Z0237 under conditions of an atmosphere of 23° C. and 50% RH, a tensile speed of 300 mm/min, and a peel angle of 180°, and the 180° peel adhesion strength (N/20 mm) was measured.

<Measurement of surface reflectance>
The surface (second surface) of the adhesive layer obtained in the examples on which the dispersion liquid was applied was used as the reflectance measurement surface. The first release film (the side of the adhesive layer on which the dispersion liquid was not applied) was peeled off from the adhesive sheet obtained in the examples, and a black acrylic plate (trade name "CLAREX", manufactured by Nitto Resin Industrial Co., Ltd.) was attached thereto, and then the second release film (the side of the adhesive layer on which the dispersion liquid was applied) was peeled off, and the peeled surface was used as a sample for measuring the surface reflectance. On the other hand, for the adhesive layer obtained in the comparative example, one release film was peeled off from the adhesive sheet, and then the sheet was attached to the same black acrylic plate as above, and then the other release film was peeled off, and the peeled surface was used as a sample for measuring the surface reflectance. The surface reflectance (Y value) was measured using a reflective spectrophotometer (U4100, manufactured by Hitachi High-Technologies Corporation).

<Measurement of Internal Reflection Suppression Rate (Effect of Improving Transmittance)>
After peeling off the second release film (the side of the adhesive layer where the dispersion liquid was applied) from the adhesive sheet obtained in the example, the low refractive index layer side of the laminated film in which a low refractive index layer with a refractive index of 1.36 was formed on a triacetyl cellulose film was attached to the adhesive layer surface, and the low refractive index adjustment region of the adhesive layer was laminated so as to contact the low refractive index layer on the laminated film. Next, the first release film was peeled off, and a slide glass (product name: White Polish No. 1, thickness: 0.8 to 1.0 mm, total light transmittance: 92%, haze: 0.2%, manufactured by Matsunami Glass Industry Co., Ltd.) was attached to the adhesive layer surface. In this way, a test piece having a layer structure of triacetyl cellulose film/low refractive index layer/adhesive layer (second surface is the low refractive index layer side)/slide glass was prepared. On the other hand, for the adhesive layer obtained in the comparative example, one of the release films was peeled off from the adhesive sheet, and then a test piece having a layer structure of triacetyl cellulose film/low refractive index layer/adhesive layer/slide glass was prepared in the same manner as described above.

The internal reflection suppression rate (transmittance improvement effect) was calculated by measuring the transmittance of the test piece prepared above and using the following formula. In the formula, the "transmittance (%) in the absence of particles" is the reflectance of the test piece of the comparative example. In other words, the internal reflection suppression effect (transmittance improvement effect) is an index showing the extent to which the internal reflectance can be reduced by having a refractive index adjustment layer.
Internal reflection suppression rate (%) = "Transmittance (%)" - "Transmittance (%) without particles"

In Table 1,
(X1) Hollow nanosilica particles: refractive index 1.24 (product name: Sururia 5320, particle size 75 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.),
(X2) Hollow polymer fine particles: refractive index 1.32 (product name: Techpolymer NH product number XX-255AA, particle size 80 nm, manufactured by Sekisui Plastics Co., Ltd.),
(X3) Hollow polymer fine particles: refractive index 1.33 (product name: Techpolymer NH product number XX-260AA, particle size 60 nm, manufactured by Sekisui Plastics Co., Ltd.),
(Y1) MgF ₂ : 1.38, average primary particle size: 40 nm, manufactured by CIK Nanotech Co., Ltd. (Y2) Na ₃ AlF ₆ : 1.34, average primary particle size: 50 nm, manufactured by CIK Nanotech Co., Ltd.
MEK/MIBK methyl ethyl ketone/methyl isobutyl ketone=9/1 (volume ratio),
Ethanol/MIBK Ethanol/methyl isobutyl ketone=9/1 (volume ratio),
IPA isopropyl alcohol,
Shows.

1: Adhesive layer 1a: Base (matrix) of the entire adhesive layer
2: Low refractive index material f1: First surface of adhesive layer f2: Second surface of adhesive layer T: Thickness S of refractive index adjustment region Support 3a: Support 3b: Support 4: Optical film 5: Low refractive index optical member 10: Dispersion liquid

Claims (17)

A pressure-sensitive adhesive layer having a first surface and a second surface opposite to the first surface,
the pressure-sensitive adhesive layer has a base formed of a pressure-sensitive adhesive composition containing a base polymer,
the first surface has a first refractive index based on the pressure-sensitive adhesive composition, while the second surface has a second refractive index lower than the first refractive index of the first surface;
a low refractive index material having a refractive index lower than a refractive index of the base polymer is dispersed on the second surface side of the pressure-sensitive adhesive layer;
a thickness of the region in which the low refractive index material is dispersed is 600 nm or less in a thickness direction from the second surface side of the pressure-sensitive adhesive layer,
The refractive index of the base polymer is 1.40 to 1.55, and the refractive index of the low refractive index material is 1.10 to 1.45;
A pressure-sensitive adhesive layer for optical films, characterized in that the difference in refractive index between the base polymer and the low refractive index material is 0.07 to 0.45 . The pressure-sensitive adhesive layer for optical films according to claim 1, characterized in that the difference between the first refractive index of the first surface and the second refractive index of the second surface is 0.02 to 0.45. The pressure-sensitive adhesive layer for optical films according to claim 1 or 2, characterized in that the second refractive index of the second surface is 1.45 or less. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 3 , wherein the low refractive index material is particles having an average particle size of 10 nm to 150 nm. The pressure-sensitive adhesive layer for optical films according to any one of _{claims 1} to ₄ , characterized in that the low refractive index material is at least one particle selected from the group consisting of at least one inorganic particle selected from the group consisting of _MgF2 , CaF2 and Na3AlF6 , porous silica particles, hollow nanosilica particles, and hollow polymer particles. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 5 , characterized in that the pressure-sensitive adhesive layer has a total light transmittance of 85% or more. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 6 , wherein the reflectance of the second surface is 0.5 to 3.5%. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 7 , wherein a difference in reflectance between the first surface and the second surface is 0.1 to 3.5%. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 8 , characterized in that the gel fraction is 30 to 95% by weight. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 9 , characterized in that the pressure-sensitive adhesive layer has a storage modulus G' at 25°C of 0.05 to 0.50 MPa. The pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 10 , wherein a tan δ peak value in dynamic viscoelasticity measurement at 1 Hz is -5 to -50°C. A method for producing a pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 11 ,
A step (1) of forming a base adhesive layer on a support using an adhesive composition containing a base polymer;
A step (2) of preparing a dispersion liquid in which a low refractive index material having a refractive index lower than that of the base polymer is dispersed;
a step (3) of applying the dispersion liquid to a second surface of the base pressure-sensitive adhesive layer opposite to the first surface on the support side, and allowing the low refractive index material contained in the dispersion liquid to permeate the base pressure-sensitive adhesive layer in a thickness direction from the second surface; and a step (4) of drying the pressure-sensitive adhesive layer permeated with the low refractive index material.
A method for producing a pressure-sensitive adhesive layer for an optical film, comprising: A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer for an optical film according to any one of claims 1 to 11 and a support on one or both sides of the pressure-sensitive adhesive layer. An optical film with a pressure-sensitive adhesive layer, comprising an optical film and a pressure-sensitive adhesive layer provided on one or both sides of the optical film,
The pressure-sensitive adhesive layer on one or both sides is the pressure-sensitive adhesive layer according to any one of claims 1 to 11 , and a first surface side of the pressure-sensitive adhesive layer is provided on the optical film. The pressure-sensitive adhesive layer-attached optical film according to claim 14 , wherein the optical film is a polarizing film. 16. An optical laminate comprising: the pressure-sensitive adhesive layer-attached optical film according to claim 14 ; and an optical member having a low refractive index laminated to the pressure-sensitive adhesive layer of the pressure-sensitive adhesive layer-attached optical film. An image display device comprising the pressure-sensitive adhesive layer according to any one of claims 1 to 11 , the pressure-sensitive adhesive layer-attached optical film according to claim 14 or 15 , or the optical laminate according to claim 16 .