JP7793343B2 - Optical adhesive sheet with release liner - Google Patents

Description

The present invention relates to an optically adhesive sheet with a release liner.

Display panels have a laminated structure that includes elements such as a pixel panel, polarizing plate, touch panel, and cover film. During the manufacturing process of such display panels, for example, a transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure.

Meanwhile, progress is being made in the development of display panels that can be repeatedly bent (foldable), for example, for smartphones and tablet devices. Specifically, foldable display panels can be repeatedly deformed between a bent shape and a flat, unbent shape. In such foldable display panels, each element in the laminated structure is made to be repeatedly bendable, and a thin optical adhesive sheet is used to bond these elements together. Optical adhesive sheets for flexible devices such as foldable display panels are described, for example, in Patent Document 1 below.

Japanese Patent Application Laid-Open No. 2018-111754

Optical adhesive sheets for flexible devices are conventionally manufactured, for example, as follows:

First, as shown in Figure 6A, a laminate sheet 60 is prepared as a long raw material sheet. The laminate sheet 60 includes a release liner 61, an adhesive layer 62, and a release liner 63, arranged in that order in the thickness direction H. The release liner 61 is releasably attached to one side of the adhesive layer 62. The release liner 63 is releasably attached to the other side of the adhesive layer 62.

Next, as shown in FIG. 6B , the adhesive layer 62 of the laminate sheet 60 is punched to form multiple individual optical adhesive sheets 62A (punching process). Specifically, a cutting blade (not shown) is inserted into the adhesive layer 62 on the release liner 61 from the release liner 63 side to the release liner 61, forming an optical adhesive sheet 62A with a predetermined planar shape (the cut area by the cutting blade is schematically represented by a thick line). A peripheral portion 62a is formed around the optical adhesive sheet 62A in the adhesive layer 62. In this process, the release liner 63 is also punched to form a release liner 63A with the same planar shape as the adhesive layer 62A, and a peripheral portion 63a is formed around the release liner 63A. Also, in this process, as shown in FIG. 7 , a cut groove 65 is formed in the release liner 61 by the cutting blade. The cut groove 65 has a wedge shape corresponding to the sharp cutting edge of the cutting blade.

Next, as shown in Figure 6C, the peripheral portions 62a and 63a are removed from the release liner 61.

Then, as shown in Figure 6D, the long release liner 61 is cut into sheet-like release liners 61A. This results in sheet-like optical adhesive sheets with release liners (release liner 61A/optical adhesive sheet 62A/release liner 63A).

However, in the above-described manufacturing method, after the punching process (FIG. 6B), as shown in FIG. 7, a break B is likely to occur in the release liner 61, starting from the tip of the bottom of the cut groove 65 (the lower end in FIG. 7). Breaking of the release liner 61 reduces the manufacturing yield of the release-liner-attached optical adhesive sheet, and is therefore undesirable.

In addition, optical adhesive sheets for flexible devices are required to be highly flexible so that they can conform sufficiently to the adherend (each element in the laminate structure) when the device is bent, and have excellent stress relaxation properties. As flexible devices become thinner, optical adhesive sheets are also required to be thin. However, in the above-mentioned manufacturing method, the softer and thinner the adhesive layer 62, the more likely it is that deep cut grooves 65 will be formed in the release liner 61 during the punching process (Figure 6B). The deeper the cut grooves 65, the more likely it is that the release liner 61 will break after the punching process.

The present invention provides an optical pressure-sensitive adhesive sheet with a release liner that is suitable for preventing tearing of the release liner.

The present invention [1] relates to an optically adhesive sheet with a release liner, the optically adhesive sheet having a first surface and a second surface opposite the first surface, a first release liner releasably contacting the first surface, and a second release liner releasably contacting the second surface, wherein the first release liner has an extended end portion that extends outward from the sheet end surface of the optically adhesive sheet in a surface direction perpendicular to the thickness direction, and the first release liner has a half-cut groove having a depth in the thickness direction along the sheet end surface of the optically adhesive sheet, the half-cut groove having a first inner wall surface flush with the sheet end surface, a second inner wall surface facing the first inner wall surface in the surface direction, and a rounded bottom with a curvature radius of 1 μm or more between the first inner wall surface and the second inner wall surface in the surface direction.

The present invention [2] includes the optical pressure-sensitive adhesive sheet with release liner described in [1] above, in which the ratio of the depth of the half-cut groove to the thickness of the first release liner is 0.5 or less.

The present invention [3] includes the optical pressure-sensitive adhesive sheet with release liner described in [1] or [2] above, in which the peel force required to peel the first release liner from the optical pressure-sensitive adhesive sheet is greater than the peel force required to peel the second release liner from the optical pressure-sensitive adhesive sheet.

The present invention [4] includes the optical pressure-sensitive adhesive sheet with release liner described in any one of [1] to [3] above, wherein the optical pressure-sensitive adhesive sheet has a shear storage modulus of 10 kPa or more and 1,000 kPa or less at 25°C.

The present invention [5] includes an optically adhesive sheet with a release liner according to any one of [1] to [4] above, wherein the optically adhesive sheet has a gel fraction of 40% or more and 80% or less.

The present invention [6] includes the optically adhesive sheet with a release liner described in any one of [1] to [5] above, wherein the first release liner has a first protrusion that protrudes toward the optically adhesive sheet in the thickness direction, and the first protrusion extends along the second inner wall surface of the half-cut groove.

The present invention [7] includes the optically adhesive sheet with a release liner described in [6] above, in which the second release liner has a liner end surface that is flush with the sheet end surface and a second protrusion that protrudes on the opposite side of the optically adhesive sheet in the thickness direction, and the second protrusion extends along the liner end surface.

The present invention [8] includes the optically adhesive sheet with release liner described in [7] above, in which the distance between the outer end of the first protrusion portion of the first release liner in the surface direction and the inner end of the second protrusion portion of the second release liner in the surface direction is 20 μm or more and 300 μm or less.

The present invention [9] includes the optical pressure-sensitive adhesive sheet with a release liner described in [6] above, in which the second release liner has an extending end portion that extends outward beyond the end surface of the sheet in a plane direction perpendicular to the thickness direction.

The present invention [10] includes the optical pressure-sensitive adhesive sheet with release liner described in [9] above, in which the distance between the outer end of the first protrusion portion of the first release liner in the surface direction and the inner end of the sheet end surface of the optical pressure-sensitive adhesive sheet in the surface direction is 20 μm or more and 300 μm or less.

In the optical adhesive sheet with release liner of the present invention, as described above, the half-cut groove in the first release liner along the sheet edge surface of the optical adhesive sheet has a rounded bottom with a curvature radius of 1 μm or more. This configuration is more suitable for preventing breakage of the release liner (first release liner) than conventional optical adhesive sheets with release liner that have wedge-shaped cut grooves in the release liner.

1 is a cross-sectional schematic diagram of one embodiment of an optical pressure-sensitive adhesive sheet with a release liner of the present invention. FIG. 2 is a partially enlarged cross-sectional view of the end portion of the optical pressure-sensitive adhesive sheet with release liner shown in FIG. 1 . 3 shows a method for producing the optical pressure-sensitive adhesive sheet with release liner shown in Fig. 1. Fig. 3A shows the laminated sheet production process, Fig. 3B shows the first contour processing process, Fig. 3C shows the removal process, and Fig. 3D shows the second contour processing process. 2 shows a modified example of the optical pressure-sensitive adhesive sheet shown in Fig. 1. In this modified example, one release liner does not have an extended end portion that extends outward from the end face of the optical pressure-sensitive adhesive sheet. FIG. 5 is a partially enlarged cross-sectional view of the end portion of the optical pressure-sensitive adhesive sheet with release liner shown in FIG. 4. 6A shows an example of a conventional method for producing an optical pressure-sensitive adhesive sheet with a release liner, in which Fig. 6A shows a laminated sheet production process, Fig. 6B shows a punching process, Fig. 6C shows a removal process, and Fig. 6D shows a cutting process. FIG. 10 is a partially enlarged schematic cross-sectional view of a cut portion after a punching process.

As shown in Figures 1 and 2, optical adhesive sheet X with a release liner, which is one embodiment of the optical adhesive sheet with a release liner of the present invention, comprises an optical adhesive sheet 10, a release liner 20 (first release liner), and a release liner 30 (second release liner). The optical adhesive sheet 10 has a first surface 11 and a second surface 12 opposite the first surface 11. The release liner 20 has a release surface 20a. The release liner 20 releasably contacts the first surface 11 on the release surface 20a side. The release liner 30 has a release surface 30a. The release liner 30 releasably contacts the second surface 12 on the release surface 30a side. In other words, optical adhesive sheet X with a release liner comprises, in order in the thickness direction H, a release liner 20, an optical adhesive sheet 10, and a release liner 30. The optical adhesive sheet X with release liner extends in a plane direction D that is perpendicular to the thickness direction H.

The optical adhesive sheet 10 is a transparent adhesive sheet that is placed at a location in a flexible device where light passes through. An example of a flexible device is a flexible display panel. A flexible display panel has a laminated structure that includes elements such as a pixel panel, a polarizing plate, a touch panel, and a cover film. The optical adhesive sheet 10 is used, for example, to bond elements included in the laminated structure during the display panel manufacturing process. The release liners 20, 30 are peeled off from the optical adhesive sheet 10 as needed when using the optical adhesive sheet 10.

The optical adhesive sheet 10 has a sheet end surface 13 that defines the outer shape of the sheet in a plan view. In this embodiment, the sheet end surface 13 is an inclined end surface that is inclined with respect to the first surface 11.

The release liner 20 has an extending end portion 20A. The extending end portion 20A is a portion that extends outward beyond the sheet end surface 13 in the planar direction D.

The release liner 20 has a half-cut groove 21 (not shown in Figure 1) on the release surface 20a side, along the sheet end surface 13 of the optical adhesive sheet 10. The half-cut groove 21 has a depth in the thickness direction H. The half-cut groove 21 has an inner wall surface 21a (first inner wall surface), an inner wall surface 21b (second inner wall surface), and a rounded bottom 21c. The inner wall surface 21a is located on the inside of the half-cut groove 21 in the planar direction D (toward the optical adhesive sheet 10). The inner wall surface 21a is flush with the sheet end surface 13. The inner wall surface 21b is located on the outside of the half-cut groove 21 in the planar direction D. The inner wall surface 21b is spaced apart from the inner wall surface 21a in the planar direction D and faces the inner wall surface 21a in the planar direction D. The rounded bottom 21c is located between the inner wall surfaces 21a and 21b in the planar direction D. In a cross section (Figure 2) perpendicular to the extension direction of the half-cut groove 21 that extends along the sheet end surface 13 in a plan view, the rounded bottom 21c has a convex curved shape with a radius of curvature (curvature radius R) of 1 μm or more.

In the optical adhesive sheet X with release liner, as described above, the half-cut grooves 21 in the release liner 20 along the sheet edge surface 13 of the optical adhesive sheet 10 have rounded bottoms 21c with a radius of curvature of 1 μm or more. This configuration is more suitable for preventing breakage of the release liner 20 than conventional optical adhesive sheets with release liner that have wedge-shaped cut grooves in the release liner (the rounded bottoms 21c are less likely to be the starting point for breakage of the release liner 20). To reduce the sharpness of the bottom shape of the half-cut grooves 21 and prevent breakage of the release liner 20, the radius of curvature R is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. In the release liner 20, to reduce the groove width of the half-cut grooves 21 and ensure the strength of the areas where the half-cut grooves 21 are formed, the radius of curvature R is preferably 120 μm or less, more preferably 100 μm or less, and even more preferably 90 μm or less.

As described above, the half-cut groove 21 in the optical adhesive sheet X with release liner has an inner wall surface 21a that is flush with the sheet end surface 13, an inner wall surface 21b that faces the inner wall surface 21a in the planar direction D, and a rounded bottom 21c (with a curvature radius of 1 μm or more) between the inner wall surface 21a and the inner wall surface 21b in the planar direction D. Such a half-cut groove 21 can be formed by laser processing the contour of the optical adhesive sheet 10 on the release liner 20, as described below.

The ratio ( _d1 / _d0 ) of the depth _d1 of the half-cut grooves 21 to the thickness _d0 of the release liner 20 is preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less. This configuration is preferable for ensuring the strength of the portion of the release liner 20 where the half-cut grooves 21 are formed. Ensuring the strength of the release liner 20 helps to prevent the release liner 20 from breaking.

The release liner 20 has protrusions 22 (first protrusions) on the release surface 20a. The protrusions 22 are arranged along the inner wall surfaces 21b of the half-cut grooves 21. The protrusions 22 protrude from the release surface 20a toward the optical adhesive sheet 10. The protrusion height _h1 of the protrusions 22 from the release surface 20a is, for example, 0.1 μm or more and, for example, 20 μm or less. Such protrusions 22 can be used as marks (alignment marks for edge detection) for detecting the edge of the release-liner-attached optical adhesive sheet X, or as part thereof. Furthermore, the ratio ( _h1 / _d1 ) of the protrusion height _h1 of the protrusions 22 to the depth _d1 of the half-cut grooves 21 is preferably 0.1 or less, more preferably 0.2 or less, and even more preferably 0.3 or more, from the viewpoint of ensuring the strength of the portion of the release liner 20 where the half-cut grooves 21 are formed.

The distance (edge width _W1 ) between the outer end of the protrusion 22 of the release liner 20 in the plane direction D and the inner end of the sheet end surface 13 of the optical adhesive sheet 13 in the plane direction D is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. Such a configuration is preferable for appropriately detecting the mark with a detection camera when the region of edge width _W1 (the region between the outer end of the protrusion 22 and the inner end of the sheet end surface 13) is used as an edge detection alignment mark, and is also preferable for accurately measuring the dimensions of the release liner-attached optical adhesive sheet X using the region of edge width _W1 . The edge width _W1 is preferably 300 μm or less, more preferably 250 μm or less, even more preferably 200 μm or less, and particularly preferably 150 μm or less. Such a configuration is preferable for suppressing erroneous detection by a detection camera when the area of edge width _W1 is used as an edge detection alignment mark, and is also preferable for suppressing measurement errors when the area of edge width _W1 is used to measure the dimensions of the optical adhesive sheet X with release liner.

In the release liner-attached optical adhesive sheet X, as described above, the release liner 20 has an extended end portion 20A that extends outward from the sheet end surface 13 of the optical adhesive sheet 10 in the planar direction D. This configuration is suitable for preventing the ends of the optical adhesive sheets 10 from adhering to each other (blocking) when multiple release liner-attached optical adhesive sheets X are stacked in the thickness direction H. From the viewpoint of preventing blocking, the extension length _L1 of the extended end portion 20A from the sheet end surface 13 in the planar direction D is preferably 0.1 mm or more, more preferably 0.5 mm or more, even more preferably 1 mm or more, and particularly preferably 1.5 mm or more. From the viewpoint of efficient production of the release liner-attached optical adhesive sheet X, the extension length _L1 is preferably 20 mm or less, more preferably 15 mm or less, and even more preferably 10 mm or less.

The peel force F1 for peeling the release liner 20 from the optical adhesive sheet 10 is preferably greater than the peel force F2 for peeling the release liner 30 from the optical adhesive sheet 10. This configuration is preferable for first peeling the release liner 30 as a light release liner from the optical adhesive sheet 10, and then enjoying the above-mentioned blocking suppression effect of the extended end portion 20A of the release liner 20 as a heavy release liner. The peel forces F1 and F2 are each measured in a peel test to peel the release liner from the optical adhesive sheet 10 under conditions of a measurement temperature of 25°C, a peel angle of 180°, and a tensile speed of 300 mm/min.

The shear storage modulus of the optical adhesive sheet 10 at 25°C is preferably 10 kPa or more and 1000 kPa or less. Such a configuration is preferable for achieving the softness required of optical adhesive sheets for flexible device applications in the optical adhesive sheet 10. From the viewpoint of ensuring the softness of the optical adhesive sheet 10, the shear storage modulus of the optical adhesive sheet 10 at 25°C is more preferably 15 kPa or more, even more preferably 20 kPa or more, particularly preferably 25 kPa or more, and more preferably 700 kPa or less, even more preferably 500 kPa or less, particularly preferably 300 kPa or less. Methods for adjusting the shear storage modulus include, for example, selecting the type of base polymer in the optical adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. The method for measuring the shear storage modulus is as described below in the examples.

The gel fraction of the optical adhesive sheet 10 is preferably 40% or more and 80% or less. This configuration is preferable for ensuring ease of processing the contour of the optical adhesive sheet 10 during the manufacturing process of the optical adhesive sheet X with a release liner (the manufacturing method of the optical adhesive sheet X with a release liner will be described later). From the viewpoint of ensuring ease of processing the contour of the optical adhesive sheet 10, the gel fraction of the optical adhesive sheet 10 is more preferably 50% or more, even more preferably 55% or more, particularly preferably 60% or more, and is more preferably 78% or less, even more preferably 75% or less. Methods for adjusting the gel fraction include, for example, selecting the type of base polymer in the optical adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. The method for measuring the gel fraction is as described below in the examples.

In the optical adhesive sheet 10, the inclination angle α of the sheet end surface 13 relative to the first surface 11 is preferably 85 degrees or less. Having the sheet end surface 13 inclined inward to a degree that the inclination angle α is 85 degrees or less is suitable for suppressing outward deformation of the sheet end surface 13 and suppressing blocking at the edge of the sheet after the contour processing of the optical adhesive sheet 10 in the manufacturing process described below, and is therefore suitable for producing optical adhesive sheets X with release liners with high yields. From this perspective, the inclination angle α is more preferably 83 degrees or less, even more preferably 80 degrees or less, and particularly preferably 78 degrees or less. Furthermore, the inclination angle α is preferably 45 degrees or greater. Having the sheet end surface 13 not inclined too far inward to a degree that the inclination angle α is 45 degrees or greater is suitable for ensuring an effective area of a predetermined thickness in the optical adhesive sheet 10. From this perspective, the inclination angle α is more preferably 50 degrees or greater, even more preferably 55 degrees or greater, even more preferably 60 degrees or greater, and particularly preferably 63 degrees or greater. When the optical adhesive sheet 10 is contoured by laser processing, one method for adjusting the inclination angle α is to adjust the laser irradiation conditions during laser processing. Examples of laser irradiation conditions include the laser pulse width, pulse frequency, laser output, and laser beam spot diameter. Another method for adjusting the inclination angle α is to adjust the thickness of the optical adhesive sheet 10.

The surface roughness Ra of the sheet end surface 13 is preferably 0.25 μm or less, preferably 0.22 μm or less, more preferably 0.2 μm or less, and even more preferably 0.18 μm or less, from the viewpoint of suppressing light scattering at the sheet end surface 13 and ensuring good optical properties at the edge of the optical adhesive sheet 10 (at and near the sheet end surface 13). The surface roughness Ra is, for example, 0.01 μm or more. The surface roughness Ra is the arithmetic mean surface roughness in accordance with JIS B 0601-2001. When the optical adhesive sheet 10 is contoured by laser processing, methods for adjusting the surface roughness Ra include, for example, adjusting the laser irradiation conditions during laser processing. Examples of laser irradiation conditions include the laser pulse width, pulse frequency, and laser output.

The surface roughness Rz of the sheet end surface 13 is preferably 1.5 μm or less, more preferably 1.2 μm or less, even more preferably 1 μm or less, and even more preferably 0.9 μm or less, from the viewpoint of suppressing light scattering at the sheet end surface 13 and ensuring good optical properties at the edge of the optical adhesive sheet 10 (at and near the sheet end surface 13). The surface roughness Rz is, for example, 0.02 μm or more. The surface roughness Rz is the maximum height in accordance with JIS B 0601-2001. When the optical adhesive sheet 10 is contoured by laser processing, methods for adjusting the surface roughness Rz include, for example, adjusting the laser irradiation conditions during laser processing. Examples of laser irradiation conditions include the laser pulse width, pulse frequency, and laser output.

In this embodiment, the release liner 30 has an extending end portion 30A. The extending end portion 30A extends outward in the planar direction D beyond the sheet end surface 13 of the optical adhesive sheet 10. Such a configuration is suitable for suppressing blocking in the release-liner optical adhesive sheet X. From the viewpoint of suppressing blocking, the extending length _L2 of the extending end portion 30A from the sheet end surface 13 in the planar direction D is preferably 0.1 mm or more, more preferably 0.5 mm or more, even more preferably 1 mm or more, and particularly preferably 1.5 mm or more. From the viewpoint of efficient production of the release-liner optical adhesive sheet X, the extending length _L2 is preferably 20 mm or less, more preferably 15 mm or less, and even more preferably 10 mm or less. The extending length _L2 and the above-mentioned extending length _L1 may be the same or different.

The optical adhesive sheet 10 is a sheet-like pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition. The optical adhesive sheet 10 (pressure-sensitive adhesive composition) contains at least a base polymer.

The base polymer is an adhesive component that imparts adhesiveness to the optical adhesive sheet 10. Examples of base polymers include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymers may be used alone or in combination of two or more. From the viewpoint of ensuring good transparency and adhesiveness in the optical adhesive sheet 10, acrylic polymers are preferably used as the base polymer.

Acrylic polymers are copolymers of monomer components containing 50% or more by weight of (meth)acrylic acid esters. "(Meth)acrylic" refers to acrylic and/or methacrylic.

As the (meth)acrylic acid ester, preferably, a (meth)acrylic acid alkyl ester is used, and more preferably, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms. The (meth)acrylic acid alkyl ester may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, Examples include nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (i.e., lauryl acrylate), isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

As the (meth)acrylic acid alkyl ester, an acrylic acid alkyl ester having an alkyl group having 3 to 15 carbon atoms is preferably used, and more preferably at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate is used.

From the viewpoint of properly exhibiting basic properties such as adhesiveness in the optical adhesive sheet 10, the proportion of (meth)acrylic acid alkyl ester in the monomer components is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 92% by mass or more. This proportion is, for example, 99% by mass or less.

The monomer component may include a copolymerizable monomer that is copolymerizable with the (meth)acrylic acid alkyl ester. Examples of copolymerizable monomers include monomers having polar groups. Examples of polar group-containing monomers include hydroxy group-containing monomers, carboxy group-containing monomers, and monomers having nitrogen atom-containing rings. Polar group-containing monomers are useful for modifying acrylic polymers, such as by introducing crosslinking points into the acrylic polymer and ensuring the cohesive strength of the acrylic polymer.

Examples of hydroxy group-containing monomers include 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, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. The hydroxy group-containing monomer is preferably at least one selected from the group consisting of 4-hydroxybutyl acrylate and 2-hydroxyethyl acrylate.

The proportion of hydroxy group-containing monomers in the monomer components is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoints of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive strength in the PSA sheet. From the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility of the acrylic polymer with various additive components in the PSA sheet), this proportion is preferably 20% by mass or less, and more preferably 10% by mass or less.

Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

The proportion of carboxyl group-containing monomer in the monomer components is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, from the viewpoints of introducing a crosslinked structure into the acrylic polymer, ensuring the cohesive strength of the PSA sheet, and ensuring the adhesive strength of the PSA sheet to the adherend. This proportion is preferably 10% by mass or less, more preferably 5% by mass or less, from the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid.

Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole. Of the monomers having a nitrogen atom-containing ring, N-vinyl-2-pyrrolidone is preferred.

The proportion of the monomer having a nitrogen atom-containing ring in the monomer components is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, from the viewpoint of ensuring the cohesive strength of the PSA sheet and the adhesive strength of the PSA sheet to the adherend. This proportion is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (which is related to the compatibility of the acrylic polymer with various additive components in the PSA sheet).

The monomer component may contain other copolymerizable monomers. Examples of other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used alone or in combination of two or more.

The base polymer preferably has a crosslinked structure. Methods for introducing a crosslinked structure into the base polymer include a method (first method) in which a base polymer having functional groups reactive with the crosslinking agent and the crosslinking agent are blended into an adhesive composition and the base polymer and crosslinking agent are reacted in the adhesive sheet, and a method (second method) in which a polyfunctional monomer is included in the monomer components forming the base polymer and a base polymer having a branched structure (crosslinked structure) introduced into the polymer chain is formed by polymerization of the monomer components. These methods may be used in combination.

Examples of crosslinking agents used in the first method include compounds that react with functional groups (such as hydroxy groups and carboxy groups) contained in the base polymer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. A single crosslinking agent may be used, or two or more types may be used in combination. Isocyanate crosslinking agents, peroxide crosslinking agents, and epoxy crosslinking agents are preferred because they are highly reactive with the hydroxy groups and carboxy groups in the base polymer and facilitate the introduction of crosslinked structures.

Examples of isocyanate crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenylisocyanate. Also included as isocyanate crosslinking agents are derivatives of these isocyanates. Examples of such isocyanate derivatives include isocyanurate-modified derivatives and polyol-modified derivatives. Commercially available isocyanate crosslinking agents include, for example, Coronate L (a trimethylolpropane adduct of tolylene diisocyanate, manufactured by Tosoh), Coronate HL (a trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), Coronate HX (an isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh), Takenate D110N (a trimethylolpropane adduct of xylylene diisocyanate, manufactured by Mitsui Chemicals), and Takenate 600 (1,3-bis(isocyanatomethyl)cyclohexane, manufactured by Mitsui Chemicals).

Peroxide crosslinking agents include dibenzoyl peroxide, di(2-ethylhexyl) peroxydicarbonate, di(4-t-butylcyclohexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, and t-butyl peroxypivalate.

Epoxy crosslinkers include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

Isocyanate crosslinking agents (especially bifunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferred from the viewpoint of ensuring the flexibility of the optical adhesive sheet 10. Isocyanate crosslinking agents (especially trifunctional isocyanate crosslinking agents) are preferred from the viewpoint of ensuring the durability of the optical adhesive sheet 10. In the base polymer, bifunctional isocyanate crosslinking agents and peroxide crosslinking agents form more flexible two-dimensional crosslinks, whereas trifunctional isocyanate crosslinking agents form stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the optical adhesive sheet 10, it is preferable to use a trifunctional isocyanate crosslinking agent in combination with a peroxide crosslinking agent and/or a bifunctional isocyanate crosslinking agent.

From the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10, the amount of crosslinking agent blended per 100 parts by mass of base polymer is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more. From the viewpoint of ensuring good tackiness in the optical adhesive sheet 10, the amount of crosslinking agent blended per 100 parts by mass of base polymer is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

In the second method, the monomer components (including a multifunctional monomer for introducing a crosslinked structure and other monomers) may be polymerized in one step or in multiple steps. In the multi-step polymerization method, first, a monofunctional monomer for forming the base polymer is polymerized (preliminary polymerization), thereby preparing a prepolymer composition containing a partial polymer (a mixture of a low-polymerization polymer and unreacted monomer). Next, a multifunctional monomer is added to the prepolymer composition, and then the partial polymer and the multifunctional monomer are polymerized (main polymerization).

Examples of polyfunctional monomers include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. Polyfunctional acrylates are preferred as polyfunctional monomers because they can introduce crosslinked structures by active energy ray polymerization (photopolymerization).

Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid-modified pentaerythritol di(meth)acrylate, dicyclopentenyl diacrylate, di(meth)acryloyl isocyanurate, and alkylene oxide-modified bisphenol di(meth)acrylate.

Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl) isocyanurate.

Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa(meth)acrylate.

The molecular weight of the polyfunctional monomer is preferably 1,500 or less, more preferably 1,000 or less. Furthermore, the functional group equivalent (g/eq) of the polyfunctional monomer is preferably 50 or more, more preferably 70 or more, and even more preferably 80 or more. The functional group equivalent is preferably 500 or less, more preferably 300 or less, and even more preferably 200 or less. These configurations are preferred from the perspective of appropriately adjusting the viscoelasticity (e.g., shear storage modulus and loss tangent) by introducing a crosslinked structure into the base polymer.

Acrylic polymers can be formed by polymerizing the above-mentioned monomer components. Polymerization methods include, for example, solution polymerization, solvent-free photopolymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. Ethyl acetate and toluene are used as solvents for solution polymerization. Thermal polymerization initiators and photopolymerization initiators are used as polymerization initiators. The amount of polymerization initiator used is, for example, 0.05 parts by mass or more and, for example, 1 part by mass or less per 100 parts by mass of the monomer components.

Examples of thermal polymerization initiators include azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionate)dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine)disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine)dihydrochloride. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

Examples of photopolymerization initiators 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, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators.

In the polymerization, a chain transfer agent and/or a polymerization inhibitor (polymerization retarder) may be used for purposes such as molecular weight adjustment. Examples of chain transfer agents include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene dimer.

The molecular weight of the base polymer can be adjusted by adjusting the type and/or amount of polymerization initiator. For example, in radical polymerization, the greater the amount of polymerization initiator, the higher the radical concentration in the reaction system, which results in a higher density of reaction initiation points and a lower molecular weight of the base polymer formed. In contrast, the smaller the amount of polymerization initiator, the lower the density of reaction initiation points, which results in easier polymer chain elongation and a higher molecular weight of the base polymer formed.

From the viewpoint of ensuring cohesive strength in the optical adhesive sheet 10, the weight average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and even more preferably 500,000 or more. The weight average molecular weight is preferably 5,000,000 or less, more preferably 3,000,000 or less, and even more preferably 2,000,000 or less. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in polystyrene equivalent terms.

The glass transition temperature (Tg) of the base polymer is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. The glass transition temperature is, for example, -80°C or higher.

The glass transition temperature (Tg) of the base polymer can be determined using the theoretical glass transition temperature (theoretic value) calculated using the Fox equation below. The Fox equation relates the glass transition temperature (Tg) of a polymer to the glass transition temperature (Tgi) of the homopolymer of the monomers that make up that polymer. In the Fox equation below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of monomer i that makes up that polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from monomer i. Literature values can be used for the glass transition temperature of homopolymers. For example, the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Paints" (Kyozo Kitaoka, Polymer Publishing Association, 1995) list the glass transition temperatures of various homopolymers. On the other hand, the glass transition temperature of a homopolymer of a monomer can also be determined using the method specifically described in JP 2007-51271 A.

Fox equation: 1/(273 + Tg) = Σ[Wi/(273 + Tgi)]

The PSA composition may contain one or more oligomers in addition to the base polymer. When an acrylic polymer is used as the base polymer, an acrylic oligomer is preferably used as the oligomer. The acrylic oligomer is a copolymer of monomer components containing 50% or more by mass of alkyl (meth)acrylate ester, and has a weight-average molecular weight of, for example, 1,000 or more and 30,000 or less.

The glass transition temperature of the acrylic oligomer is preferably 60°C or higher, more preferably 80°C or higher, even more preferably 100°C or higher, and particularly preferably 110°C or higher. The glass transition temperature of the acrylic oligomer is, for example, 200°C or lower, preferably 180°C or lower, and more preferably 160°C or lower. The combined use of a low-Tg acrylic polymer (base polymer) into which a crosslinked structure has been introduced and a high-Tg acrylic oligomer increases the adhesive strength of the optical adhesive sheet 10, particularly at high temperatures. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula above.

Acrylic oligomers with a glass transition temperature of 60°C or higher are preferably polymers of monomer components containing a (meth)acrylic acid alkyl ester having a chain alkyl group (chain alkyl (meth)acrylate) and a (meth)acrylic acid alkyl ester having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate). Specific examples of these (meth)acrylic acid alkyl esters include the (meth)acrylic acid alkyl esters listed above as monomer components for acrylic polymers.

As a chain alkyl (meth)acrylate, methyl methacrylate is preferred due to its high glass transition temperature and excellent compatibility with the base polymer. As an alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. In other words, the acrylic oligomer is preferably a polymer of monomer components containing methyl methacrylate and one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate.

The proportion of alicyclic alkyl (meth)acrylate in the monomer components of the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. This proportion is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The proportion of chain alkyl (meth)acrylate in the monomer components of the acrylic oligomer is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. This proportion is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more.

The weight-average molecular weight of the acrylic oligomer is preferably 1,000 or more, more preferably 1,500 or more, and even more preferably 2,000 or more. The molecular weight is preferably 30,000 or less, more preferably 10,000 or less, and even more preferably 8,000 or less. This molecular weight range of the acrylic oligomer is preferable for ensuring the adhesive strength and adhesive retention of the optical adhesive sheet 10.

Acrylic oligomers are obtained by polymerizing the monomer components of the acrylic oligomer. Polymerization methods include, for example, solution polymerization, bulk polymerization, and emulsion polymerization. In polymerizing the acrylic oligomer, a polymerization initiator may be used, and a chain transfer agent may also be used to adjust the molecular weight.

In order to sufficiently increase the adhesive strength of the optical adhesive sheet 10, the content of the acrylic oligomer in the optical adhesive sheet 10 is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the base polymer. On the other hand, from the perspective of ensuring the transparency of the optical adhesive sheet 10, the content of the acrylic oligomer in the optical adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the base polymer. If the content of the acrylic oligomer in the optical adhesive sheet 10 is too high, the compatibility of the acrylic oligomer will decrease, which will tend to increase haze and reduce transparency.

The PSA composition may contain a silane coupling agent. The content of the silane coupling agent in the PSA composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, per 100 parts by mass of the base polymer. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The pressure-sensitive adhesive composition may contain other components as needed. Examples of other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents. Examples of solvents include polymerization solvents used as needed during the polymerization of the acrylic polymer, and solvents added to the polymerization reaction solution after polymerization. Examples of such solvents include ethyl acetate and toluene.

From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the optical adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more. From the viewpoint of the handleability of the optical adhesive sheet 10, the thickness of the optical adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

The haze of the optical adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and more preferably 1% or less. The haze of the optical adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of haze meters include the "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and the "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.

The release liner 20 can be, for example, a flexible plastic film. Examples of such plastic films include polyethylene terephthalate film, polyethylene film, polypropylene film, and polyester film. The thickness of the release liner 20 is preferably 5 μm or more, more preferably 10 μm or more, and preferably 200 μm or less, more preferably 150 μm or less. The surface of the release liner 20 is preferably release-treated. Examples of release treatments include silicone release treatments and fluorine release treatments (the same applies to the release treatments described below). The adhesive force F1 for peeling the release liner 20 from the optical pressure-sensitive adhesive sheet 10 can be adjusted by selecting the presence or absence of a release treatment, the type of release treatment, and adjusting the conditions.

The release liner 30 can be, for example, the plastic film described above for the release liner 20. The thickness of the release liner 30 is preferably 5 μm or more, more preferably 10 μm or more, and preferably 200 μm or less, more preferably 150 μm or less. The surface of the release liner 30 is preferably release-treated. The adhesive strength F2 described above for the release of the release liner 30 from the optical adhesive sheet 10 can be adjusted by selecting the presence or absence of release treatment, the type of treatment, and adjusting the conditions.

The optical adhesive sheet X with release liner can be manufactured, for example, as follows.

First, as shown in Figure 3A, a long laminate sheet Y is prepared (laminate sheet preparation process). The laminate sheet Y comprises a long adhesive layer 101, a long release liner 102 covering one side of the adhesive layer 101 in the thickness direction H, and a long release liner 103 covering the other side. The laminate sheet Y can be produced, for example, by applying the above-described adhesive composition to the release liner 102 to form a coating film, laminating the release liner 103 onto the coating film, drying the coating film, and optionally irradiating it with light. Examples of methods for applying the adhesive composition include 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, and die coating. The drying temperature for the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

Next, as shown in FIG. 3B , the adhesive layer 101 on the release liner 102 is laser-processed to form multiple sheet-like optical adhesive sheets 10 (first contour processing step). Specifically, a laser is applied to the laminated sheet Y in the thickness direction H from the release liner 103 side along the planned cutting line of the laminated sheet Y, thereby cutting the adhesive layer 101 and release liner 103 on the release liner 102. As a result, the optical adhesive sheet 10 (having a sheet end surface 13) is formed in the adhesive layer 101, and a peripheral portion 101a is generated around the optical adhesive sheet 10. The release liner 103 is formed in the release liner 103, and a peripheral portion 103a is generated around the release liner 103A. The release liner 102 is formed with the above-mentioned half-cut groove 21 (not shown). Furthermore, by fusing the release liner 102 with laser irradiation, the release liner 102 also has the above-mentioned protrusions 22 (not shown in Figures 3B to 3D) formed along the inner wall surfaces 21b of the half-cut grooves 21. The release liner 102 may also have protrusions (not shown) formed along the inner wall surfaces 21a of the half-cut grooves 21.

Examples of lasers used for laser processing include gas lasers, solid-state lasers, and semiconductor lasers. Examples of gas lasers include excimer lasers and _CO2 lasers (10.6 μm) (the numbers in parentheses indicate the laser wavelength; the same applies below for lasers). Examples of excimer lasers include _F2 excimer lasers (157 nm), ArF excimer lasers (193 nm), KrF excimer lasers (248 nm), and XeCl excimer lasers (308 nm). Examples of solid-state lasers include Nd:YAG lasers (1064 nm), the second harmonic of Nd:YAG lasers (532 nm), the third harmonic of Nd:YAG lasers (355 nm), and the fourth harmonic of Nd:YAG lasers (266 nm). Examples of semiconductor lasers include semiconductor lasers with a wavelength of 405 nm. In laser processing, the pulse width of the irradiated laser is, for example, 0.5 to 50 μsec, the pulse frequency is, for example, 1 to 200 kHz, and the laser output is, for example, 2 to 250 W.

The inclination angle α of the sheet end surface 13 formed in this process is preferably 85 degrees or less, more preferably 83 degrees or less, even more preferably 80 degrees or less, and particularly preferably 78 degrees or less. Having the sheet end surface 13 tilted inward to a degree such that the inclination angle α is 85 degrees or less is suitable for suppressing outward deformation of the sheet end surface 13 after this process and preventing blocking at the edge of the optical adhesive sheet 10, and is therefore suitable for producing optical adhesive sheets X with release liners with high yields. The inclination angle α is preferably 45 degrees or more, more preferably 50 degrees or more, even more preferably 55 degrees or more, even more preferably 60 degrees or more, and particularly preferably 63 degrees or more. Having the sheet end surface 13 not tilted too far inward to a degree such that the inclination angle α is 45 degrees or more is suitable for ensuring an effective area of a predetermined thickness in the optical adhesive sheet 10. Furthermore, the surface roughness Ra of the sheet end surface 13 is preferably 0.25 μm or less, more preferably 0.22 μm or less, even more preferably 0.2 μm or less, and particularly preferably 0.18 μm or less. The surface roughness Rz of the sheet end surface 13 is preferably 1.5 μm or less, more preferably 1.2 μm or less, even more preferably 1 μm or less, and even more preferably 0.9 μm or less. These configurations regarding the surface roughness of the sheet end surface 13 are suitable for suppressing light scattering at the sheet end surface 13 and ensuring good optical properties at the edge of the optical adhesive sheet 10 (the sheet end surface 13 and its vicinity). By adjusting the above conditions for laser processing, the above-mentioned inclination angle α, surface roughness Ra, and surface roughness Rz of the sheet end surface 13 can be adjusted.

Next, as shown in Figure 3C, the peripheral portions 101a and 103a are removed from the release liner 102 (removal process).

Next, as shown in Figure 3D, the long release liner 102 is cut into individual release liners 20 (second contour processing step). Examples of cutting methods include cutting by laser irradiation and cutting by punching.

Next, the release liner 103A on the optical adhesive sheet 10 is peeled off, and then the release liner 30 is attached to the exposed surface of the optical adhesive sheet 10 (re-attachment process). This results in an optical adhesive sheet X with a release liner.

As shown in Figures 4 and 5, the optical adhesive sheet X with a release liner may include a release liner 30 that does not have an extended end portion 30A. Such an optical adhesive sheet X with a release liner can be manufactured, for example, by not performing the above-mentioned re-attachment process after the second contour processing process (Figure 3D). In this case, release liner 103A (Figure 3D) becomes the release liner 30 as the second release liner. From the perspective of protecting the end portion of the optical adhesive sheet 10, it is preferable that the release liner 30 have an extended end portion 30A as described above.

The release liner 30 in this modified example has a liner end surface 31 that defines the outer shape of the liner in a plan view. The liner end surface 31 is flush with the sheet end surface 13. In this embodiment, the liner end surface 31 is an inclined end surface that is inclined in the same manner as the sheet end surface 13.

The release liner 30 also has a protrusion 32 (second protrusion) on the release surface 30a side. The protrusion 32 is arranged along the liner end surface 31. The protrusion 32 protrudes from the release surface 30a toward the opposite side of the optical adhesive sheet 10. The protrusion height _h2 of the protrusion 32 from the release surface 30a is, for example, 0.1 μm or more and, for example, 20 μm or less. The protrusion 32 can be used as a mark for detecting the edge of the release liner-attached optical adhesive sheet X (an alignment mark for edge detection) or as part thereof. Such a protrusion 32 is formed along the liner end surface 31 of the release liner 30 by fusing the release liner 103 with laser irradiation in the first contour processing step ( FIG. 3B ) using laser processing.

The distance (edge width _W2 ) between the outer end of the protrusion 22 of the release liner 20 in the surface direction D and the inner end of the protrusion 32 of the release liner 30 in the surface direction D is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and particularly preferably 25 μm or more. Such a configuration is preferable for appropriately detecting an edge detection alignment mark with a detection camera when the region of edge width _W2 (the region between the outer end of the protrusion 22 and the inner end of the protrusion 32) is used as an edge detection alignment mark, and is also preferable for accurately measuring the dimensions of the release liner-attached optical adhesive sheet X using the region of edge width _W2 . Edge width _W2 is preferably 300 μm or less, more preferably 250 μm or less, even more preferably 200 μm or less, and particularly preferably 150 μm or less. Such a configuration is preferable for suppressing erroneous detection by a detection camera when the area of edge width _W2 is used as an edge detection alignment mark, and is also preferable for suppressing measurement errors when the area of edge width _W2 is used to measure the dimensions of the optical adhesive sheet X with release liner.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to these examples. Furthermore, the specific numerical values of the compounding amounts (contents), physical properties, parameters, etc. described below can be substituted for the upper limits (numerical values defined as "equal to or less than") or lower limits (numerical values defined as "equal to or greater than") of the corresponding compounding amounts (contents), physical properties, parameters, etc. described in the "Description of the Invention" above.

Example 1
<Preparation of Pressure-Sensitive Adhesive Composition>
First, a mixture containing 50 parts by mass of 2-ethylhexyl acrylate (2EHA), 40 parts by mass of lauryl acrylate (LA), 2 parts by mass of n-butyl acrylate (BA), 6 parts by mass of 4-hydroxybutyl acrylate (4HBA), 2 parts by mass of N-vinyl-2-pyrrolidone (NVP), and 0.015 parts by mass of a photopolymerization initiator (trade name "Omnirad 184", manufactured by IGM Resins) was irradiated with ultraviolet light (polymerization reaction) to obtain a prepolymer composition (polymerization rate: approximately 10%) (the prepolymer composition contains monomer components that have not undergone the polymerization reaction). Next, 100 parts by mass of the prepolymer composition, 0.08 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a polyfunctional acrylate monomer, and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a pressure-sensitive adhesive composition C1.

<Preparation of Laminated Sheet>
First, a coating film was formed by applying the PSA composition C1 to the release-treated surface of a first release liner, one side of which had been silicone-release-treated. The first release liner was prepared as described below. Next, the release-treated surface of a second release liner, one side of which had been silicone-release-treated, was bonded to the coating film on the first release liner. The second release liner was prepared as described below. Next, the coating film was irradiated with ultraviolet light through the second release liner to UV-cure the coating film and form a 100 μm-thick PSA layer (PSA A1). This resulted in a laminate sheet (first release liner/adhesive layer/second release liner) as the base sheet for the optical PSA sheet with release liner. For UV irradiation, a black light was used as the irradiation light source, and the irradiation intensity was 5 mW/ ^cm2 (the same applies to the UV irradiation described below).

(Preparation of First Release Liner)
First, 90 parts by mass of a silicone-based release treatment agent (product name "KE-3703", a 28.5% by mass toluene solution of an addition-type silicone-based release treatment agent containing a polyorganosiloxane having hexenyl groups in the molecule and a polyorganosiloxane crosslinker having hydrosilyl groups in the molecule, manufactured by Shin-Etsu Chemical Co., Ltd.), 0.9 parts by mass of a silicone-based release control agent (product name "KS-3800", manufactured by Shin-Etsu Kogyo Chemical Co., Ltd.), 0.3 parts by mass of a platinum catalyst for silicone curing (product name "CAT-PL-50T", manufactured by Shin-Etsu Kogyo Chemical Co., Ltd.), and a solvent were mixed to prepare a release treatment agent solution with a silicone solids concentration of 0.7% by mass. The solvent was a mixed solvent of toluene and hexane in a volume ratio of 1:1. Next, a biaxially oriented polyester film (product name "Lumirror XD500P", thickness 75 μm, manufactured by Toray Advanced Materials Korea Co., Ltd.) was subjected to a release treatment as a substrate film. Specifically, the release treatment agent solution described above was first applied to one side of the substrate film to form a coating film. A wire bar #9 was used for application. Next, the coating film on the substrate film was heated and dried at 130°C for 1 minute using a hot air dryer. This formed a 0.1 µm-thick silicone release layer on the substrate film (release treatment). In this way, a first release liner having a release-treated surface on one side was produced.

(Preparation of second release liner)
First, 30 parts by mass of a silicone-based release treatment agent (product name "LTC761", a 30% by mass toluene solution of an addition-type silicone-based release treatment agent containing a polyorganosiloxane having hexenyl groups in the molecule and a polyorganosiloxane crosslinker having hydrosilyl groups in the molecule, manufactured by Dow Corning Toray Co., Ltd.), 0.9 parts by mass of a silicone dispersion (product name "BY 240-850", manufactured by Dow Corning Toray Co., Ltd.), 2 parts by mass of a platinum catalyst for silicone curing (product name "SRX 212"), and a solvent were mixed to prepare a release treatment agent solution with a silicone solids concentration of 0.7% by mass. The solvent was a mixed solvent of toluene and hexane in a volume ratio of 1:1. Next, a biaxially oriented polyester film (product name "Lumirror XD500P", thickness 75 μm, manufactured by Toray Advanced Materials Korea Co., Ltd.) was subjected to a release treatment as a substrate film. Specifically, the release treatment solution described above was first applied to one side of the substrate film to form a coating film. A wire bar #9 was used for application. Next, the coating film on the substrate film was heated and dried at 130°C for 1 minute using a hot air dryer. This formed a 0.1 μm-thick silicone release layer on the substrate film (release treatment). In this way, a second release liner having a release-treated surface on one side was produced.

<First external shape processing>
Next, the pressure-sensitive adhesive layer of the laminate sheet was contoured (first contouring process). Specifically, a _CO2 laser was irradiated from the second release liner side along the first planned cutting line of the laminate sheet in the thickness direction to cut the pressure-sensitive adhesive layer on the first release liner and the second release liner in the thickness direction (laser processing). For laser irradiation, a first laser processing device (product name "LC500", manufactured by Takei Electric Co., Ltd.) was used, and the irradiated laser pulse width was 3.3 μs, the pulse frequency was 15 kHz, and the laser output was 20 W. In this process, an optical pressure-sensitive adhesive sheet with a predetermined planar shape and a first peripheral portion around it were formed in the pressure-sensitive adhesive layer, and a second peripheral portion was formed on the first peripheral portion in the second release liner. In addition, a half-cut groove was formed on the pressure-sensitive adhesive layer side of the first release liner along the cutting line for the pressure-sensitive adhesive layer.

<Removal of peripheral parts, second external processing>
After the first contour processing step, the first and second peripheral portions were removed from the first release liner. The first release liner was then contour processed (second contour processing step). Specifically, a CO2 _laser was irradiated in the thickness direction of the first release liner along the second planned cutting line of the first release liner, thereby cutting the first release liner into a predetermined shape in a plan view. The second planned cutting line was 3 mm outward in the planar direction from the first planned cutting line. Furthermore, the laser irradiation in this step was performed using a first laser processing device (product name "LC500", manufactured by Takei Electric Co., Ltd.), with a laser pulse width of 3.3 μs, a pulse frequency of 15 kHz, and a laser output of 40 W.

In this manner, the optically adhesive sheet with release liner of Example 1 (first release liner/optical adhesive sheet (thickness 100 μm)/second release liner) was prepared.

Example 2
The optical adhesive sheet with a release liner of Example 2 was produced in the same manner as the optical adhesive sheet with a release liner of Example 1, except for the following: In the laminate sheet production step, the thickness of the pressure-sensitive adhesive layer formed was 50 μm, and in the contour processing step, the pulse frequency of the irradiated laser was 30 kHz.

Example 3
The optical adhesive sheet with release liner of Example 3 was produced in the same manner as the optical adhesive sheet with release liner of Example 1, except for the following: In the contour processing step, a second laser processing device (product name "LC750", manufactured by Takei Electric Co., Ltd.) was used instead of the first laser processing device, and the pulse width of the irradiated laser was set to 0.83 μs, the pulse frequency to 100 kHz, and the laser output to 20 W.

Example 4
The optical adhesive sheet with a release liner of Example 4 was produced in the same manner as the optical adhesive sheet with a release liner of Example 1, except for the following: In the laminate sheet production step, the thickness of the pressure-sensitive adhesive layer formed was 50 μm, and in the contour processing step, the pulse frequency of the irradiated laser was 100 kHz.

Example 5
An optical adhesive sheet with a release liner of Example 5 was produced in the same manner as the optical adhesive sheet with a release liner of Example 1, except for the following: In the contour processing step, the pulse frequency of the irradiated laser was set to 100 kHz.

Example 6
First, a mixture containing 45 parts by mass of 2-ethylhexyl acrylate (2EHA), 42 parts by mass of lauryl acrylate (LA), 2 parts by mass of n-butyl acrylate (BA), 4 parts by mass of 4-hydroxybutyl acrylate (4HBA), 7 parts by mass of N-vinyl-2-pyrrolidone (NVP), and 0.015 parts by mass of a photopolymerization initiator (trade name "Omnirad 184", manufactured by IGM Resins) was irradiated with ultraviolet light (polymerization reaction) to obtain a prepolymer composition (polymerization rate: approximately 10%) (the prepolymer composition contains monomer components that have not undergone the polymerization reaction). Next, 100 parts by mass of the prepolymer composition, 0.08 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a polyfunctional acrylate monomer, and 0.3 parts by mass of a silane coupling agent (trade name "KBM-403", 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a pressure-sensitive adhesive composition C2. The release-liner optical adhesive sheet of Example 6 was produced in the same manner as the release-liner optical adhesive sheet of Example 1, except that this pressure-sensitive adhesive composition C2 was used instead of pressure-sensitive adhesive composition C1 to form a 50 μm thick pressure-sensitive adhesive layer (pressure-sensitive adhesive A2).

Comparative Example 1
The optical adhesive sheet with a release liner of Comparative Example 1 was produced in the same manner as the optical adhesive sheet with a release liner of Example 1, except for the following: In the laminate sheet production process, the thickness of the adhesive layer formed was 50 μm. In the contour processing process, press processing was performed instead of laser processing. Specifically, a first press processing blade was inserted into the adhesive layer on the first release liner in the thickness direction from the second release liner side to the first release liner, thereby forming an optical adhesive sheet with a predetermined shape in a planar view. The first press processing blade had a cutting edge with a cutting angle of 80 degrees.

Comparative Example 2
The optical pressure-sensitive adhesive sheet with a release liner of Comparative Example 2 was produced in the same manner as the optical pressure-sensitive adhesive sheet with a release liner of Comparative Example 1, except for the following: In the press working of the contour working step, a second press working blade was used instead of the first press working blade. The second press working blade had a cutting edge with a cutting edge angle of 30 degrees.

Comparative Example 3
The optical adhesive sheet with a release liner of Comparative Example 3 was produced in the same manner as the optical adhesive sheet with a release liner of Example 6, except for the following: In the contour processing step, press processing was performed instead of laser processing. Specifically, a second press processing blade (blade angle 30 degrees) was inserted into the pressure-sensitive adhesive layer on the first release liner in the thickness direction from the second release liner side to the first release liner, thereby forming an optical adhesive sheet with a predetermined planar shape.

<Gel fraction>
The gel fraction of each of the optical pressure-sensitive adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 3 was measured. Specifically, the measurement was as follows.

First, approximately 0.1 g (mass: W ₁ mg) of a PSA sample was collected from the PSA sheet. Next, the PSA sample was wrapped in a purse-shaped tetrafluoroethylene resin porous membrane (mass: W ₂ mg) with an average pore size of 0.2 μm, and the opening was tied with kite string (mass: W ₃ mg) to obtain a package. The tetrafluoroethylene resin porous membrane used was a porous membrane manufactured by Nitto Denko Corporation (product name: "Nitoflon NTF1122"). Next, the package containing the PSA sample was placed in a 50 mL container, which was then filled with ethyl acetate (one container was used for each package). This was left to stand at 23°C for 7 days, after which the package was removed from the container and dried at 130°C for 2 hours. The mass (W ₄ mg) of the package was then measured. The values of W ₁ to W ₄ were then substituted into the following formula to calculate the gel fraction of the PSA layer. The values are shown in Tables 1 and 2.

Gel fraction (%)=[(W ₄ −W ₂ −W ₃ )/W ₁ ]×100

<Shear storage modulus>
The dynamic viscoelasticity of each of the optical pressure-sensitive adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 3 was measured.

First, the required number of measurement samples were prepared for each adhesive sheet. Specifically, multiple adhesive sheet pieces cut from the adhesive sheet were first glued together to prepare a sample sheet approximately 1.5 mm thick. This sheet was then punched out to obtain cylindrical pellets (7.9 mm in diameter) that served as measurement samples.

The measurement sample was then fixed to a 7.9 mm diameter parallel plate jig using a dynamic viscoelasticity measuring device (product name: "Advanced Rheometric Expansion System (ARES)", manufactured by Rheometric Scientific) and subjected to dynamic viscoelasticity measurement. In this measurement, the measurement mode was shear mode, the measurement temperature range was -40°C to 100°C, the heating rate was 5°C/min, and the frequency was 1 Hz. From the measurement results, the shear storage modulus at 25°C and the maximum shear storage modulus within the measurement temperature range were read. These values are shown in Tables 1 and 2.

<Shape analysis>
For each of the optical adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 3, the inclination angle α of the sheet end surface (sheet end surface in Figures 2 and 5), surface roughness Ra (linear surface roughness and arithmetic mean roughness), surface roughness Rz (maximum height), half-cut groove depth _d1 (μm), curvature radius R (μm) of the bottom of the half-cut groove, and edge width W (μm) were measured using a shape analysis laser microscope (product name "VK-X1000", manufactured by KEYENCE). The edge width W is the edge width _W2 shown in Figure 5. The results are shown in Tables 1 and 2. The ratio ( _d1 / _d0 ) of the half-cut groove depth _d1 to the thickness _d0 (75 μm) of the first release liner is also shown in Tables 1 and 2.

Meanwhile, for each of the optical adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 3, the extension length L ₁ (mm) of the extending end portion of the first release liner (the portion extending outward from the adhesive sheet) was measured using a three-dimensional measuring machine (product name "EXCEL 661UC", manufactured by Micro Vu). The results are shown in Tables 1 and 2.

<Blocking during removal process>
Tables 1 and 2 show the presence or absence of blocking during the removal process in the manufacturing process of each optical pressure-sensitive adhesive sheet in Examples 1 to 6 and Comparative Examples 1 to 3. Blocking during the removal process refers to the situation where, after the contour processing step, the edges of adjacent optical pressure-sensitive adhesive sheets and their surrounding areas come into contact and adhere to each other on the first release liner, causing the edges of the optical pressure-sensitive adhesive sheets to be pulled by the edges of the surrounding areas during the removal process.

<Glue overflow after manufacturing>
The presence or absence of adhesive protrusion (protrusion of the optical adhesive sheet) in each of the optical adhesive sheets of Examples 1 to 6 and Comparative Examples 1 to 3 is shown in Tables 1 and 2. Adhesive protrusion means that at least a portion of the edge of the adhesive sheet sandwiched between the first and second release liners protrudes outside the half-cut groove (formed during the first contour processing described above) of the first release liner.

<First release liner fracture prevention ability>
The optical pressure-sensitive adhesive sheets with release liners of Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated for resistance to tearing of the first release liner when the first release liner was peeled off.

First, an evaluation sample was prepared. Specifically, the second release liner was peeled off from the optical adhesive sheet of the release-liner-attached optical adhesive sheet, and the exposed surface of the optical adhesive sheet was then bonded to a commercially available alkaline glass plate. This yielded an evaluation sample.

Next, a peel test was conducted on each evaluation sample. Specifically, the first release liner was manually and forcefully peeled off from the optical pressure-sensitive adhesive sheet on the alkali glass plate. The first release liner's resistance to tearing (tear suppression) was evaluated as "good" if no cuts, tears, or penetrations occurred in the first release liner during the peel test, and as "poor" if cuts, tears, or penetrations occurred in the first release liner during the peel test. The evaluation results are shown in Tables 1 and 2.

X: Optical adhesive sheet with release liner H: Thickness direction 10: Optical adhesive sheet 11: First surface 12: Second surface 13: Sheet end surface 20: Release liner (first release liner)
20a Peeling surface 20A Extended end portion 21 Half-cut grooves 21a, 21b Inner wall surface 21c Round bottom 22 Protrusion portion (first protrusion portion)
30 Release liner (second release liner)
30a Peel surface 30A Extended end portion 31 Liner end surface 32 Protrusion portion (second protrusion portion)

Claims (10)

an optical pressure-sensitive adhesive sheet having a first surface and a second surface opposite to the first surface;
a first release liner releasably contacting the first surface;
A release liner-attached optical pressure-sensitive adhesive sheet comprising a second release liner releasably contacting the second surface,
The first release liner has an extending end portion, and the extending end portion extends outward from the sheet end surface of the optical adhesive sheet in a plane direction perpendicular to the thickness direction;
The first release liner has a half-cut groove having a depth in the thickness direction along the sheet end surface of the optical pressure-sensitive adhesive sheet,
An optical adhesive sheet with a release liner, wherein the half-cut groove has a first inner wall surface flush with the sheet end surface, a second inner wall surface opposite the first inner wall surface in the surface direction, and a round bottom with a curvature radius of 1 μm or more between the first inner wall surface and the second inner wall surface in the surface direction. The optical pressure-sensitive adhesive sheet with release liner according to claim 1, wherein the ratio of the depth of the half-cut groove to the thickness of the first release liner is 0.5 or less. The optical adhesive sheet with release liner according to claim 1 or 2, wherein the peel force required to peel the first release liner from the optical adhesive sheet is greater than the peel force required to peel the second release liner from the optical adhesive sheet. The optical adhesive sheet with release liner according to any one of claims 1 to 3, wherein the optical adhesive sheet has a shear storage modulus of 10 kPa or more and 1,000 kPa or less at 25°C. The optical adhesive sheet with release liner according to any one of claims 1 to 4, wherein the optical adhesive sheet has a gel fraction of 40% or more and 80% or less. The optical pressure-sensitive adhesive sheet with release liner according to any one of claims 1 to 5, wherein the first release liner has a first protrusion that protrudes toward the optical pressure-sensitive adhesive sheet in the thickness direction, and the first protrusion extends along the second inner wall surface of the half-cut groove. The optical pressure-sensitive adhesive sheet with release liner according to claim 6, wherein the second release liner has a liner end surface flush with the sheet end surface and a second protrusion protruding on the opposite side of the optical pressure-sensitive adhesive sheet in the thickness direction, the second protrusion extending along the liner end surface. The optical pressure-sensitive adhesive sheet with release liner according to claim 7, wherein the distance between the outer end of the first protrusion portion of the first release liner in the surface direction and the inner end of the second protrusion portion of the second release liner in the surface direction is 20 μm or more and 300 μm or less. The optical pressure-sensitive adhesive sheet with release liner according to claim 6, wherein the second release liner has an extending end portion that extends outward beyond the end surface of the sheet in a plane direction perpendicular to the thickness direction. The optical pressure-sensitive adhesive sheet with release liner according to claim 9, wherein the distance between the outer end of the first protrusion portion of the first release liner in the surface direction and the inner end of the sheet end surface of the optical pressure-sensitive adhesive sheet in the surface direction is 20 μm or more and 300 μm or less.