Optical adhesive sheet with release liner

Abstract

An optical adhesive sheet (X) with a release liner according to the present invention comprises: an adhesive sheet (10) (optical adhesive sheet); a release liner (20) (tight release liner) that releasably contacts a first surface (11) of the adhesive sheet (10); and a release liner (30) (easy release liner) that releasably contacts a second surface (12) of the adhesive sheet (10). The adhesive sheet (10) contains a base polymer, a photopolymerizable polyfunctional compound and a photopolymerization initiator. In a probe tack test under predetermined conditions for the second surface (12) after peeling off the release liner (30) from the adhesive sheet (10), the probe peeling distance when the stress becomes 0 gf during the probe peeling process is 200-900 μm inclusive.

Description

Optical adhesive sheet with release liner

[0001] The present invention relates to an optical pressure-sensitive adhesive sheet with a release liner.

[0002] A display panel has a laminated structure including elements such as a pixel panel, a polarizing film, and a cover glass. In the manufacturing process of a display panel, for example, an optically transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure. The optical adhesive sheet is manufactured, for example, as an optical adhesive sheet with a release liner, in which release liners are bonded to both sides of the optical adhesive sheet. In an optical adhesive sheet with a release liner, a heavy release liner is bonded to one side of the optical adhesive sheet, and a light release liner is bonded to the other side of the optical adhesive sheet. Such optical adhesive sheets for display panel applications are described, for example, in Patent Document 1 listed below.

[0003] Japanese Patent Application Laid-Open No. 2020-122140

[0004] The laminated structure of a display panel includes elements with surface steps. For example, a decorative or light-shielding printed layer is provided on the edge of the pixel panel side surface of the cover glass, resulting in a step (printed step) between the cover glass surface and the printed layer surface. Therefore, optical pressure-sensitive adhesive sheets for display panel applications require not only reliable bonding between adherends, but also flexibility (step-following ability) sufficient to follow the printed step. Insufficient step-following ability of an optical pressure-sensitive adhesive sheet can, for example, cause air bubbles to form along the printed layer between the optical pressure-sensitive adhesive sheet bonded to the printed layer surface of the cover glass and the cover glass, which is undesirable.

[0005] From the viewpoint of conformability to unevenness, a softer optical pressure-sensitive adhesive sheet is preferable. However, in an optical pressure-sensitive adhesive sheet with a release liner, the softer the optical pressure-sensitive adhesive sheet, the more likely it is that the heavy release liner will unintentionally peel off when the light release liner is peeled off from the optical pressure-sensitive adhesive sheet.

[0006] The present invention provides an optical pressure-sensitive adhesive sheet with a release liner that is suitable for achieving both suppression of peeling of a heavy release liner when a light release liner is peeled off and conformability to unevenness.

[0007] The present invention [1] provides an optical adhesive sheet with a release liner, comprising an optical adhesive sheet having a first surface and a second surface opposite to the first surface, a heavy release liner releasably contacting the first surface, and a light release liner releasably contacting the second surface, wherein the optical adhesive sheet contains a base polymer, a photopolymerizable multifunctional compound, and a photopolymerization initiator, and in a probe tack test under the following conditions on the second surface after the light release liner has been peeled from the optical adhesive sheet, the probe peel distance when the stress becomes 0 gf during the probe peel process is 200 μm or more and 900 μm or less.

[0008] [Conditions] Temperature: 25°C Probe diameter: 2.5 mm Pressing load: 1000 gf Pressing time: 30 seconds Peeling speed: 0.08 mm / second

[0009] The present invention [2] includes the optical pressure-sensitive adhesive sheet with a release liner according to the above [1], wherein the photopolymerizable polyfunctional compound includes a photopolymerizable polyfunctional compound having an aromatic ring.

[0010] The present invention [3] includes the optical pressure-sensitive adhesive sheet with a release liner according to the above [1] or [2], wherein the photopolymerizable polyfunctional compound has a weight-average molecular weight of 1,000 or less.

[0011] The present invention [4] includes the optically adhesive sheet with a release liner according to any one of the above [1] to [3], which has a gel fraction of 50% by mass or more.

[0012] As described above, the optical adhesive sheet of the release liner-equipped optical adhesive sheet of the present invention contains a base polymer, a photopolymerizable multifunctional compound, and a photopolymerization initiator. In such an optical adhesive sheet, the softness of the optical adhesive sheet can be ensured when bonding adherends together using the optical adhesive sheet (before photocuring), and after bonding, the photopolymerizable multifunctional compound can be photopolymerized to increase the elasticity of the adhesive sheet. Such an optical adhesive sheet is suitable for ensuring conformability to unevenness on the adherend surface when bonding adherends together and for ensuring bonding reliability after bonding between the adherends. Furthermore, in a probe tack test under specified conditions on the second surface of the release liner-equipped optical adhesive sheet after peeling the light release liner from the optical adhesive sheet, the probe peel distance when the stress reaches 0 gf during the probe peel process is 200 μm or more and 900 μm or less. Such an optical adhesive sheet with a release liner is suitable for suppressing unintended peeling of the heavy release liner when peeling the light release liner from the optical adhesive sheet.

[0013] 4A and 4B are cross-sectional schematic diagrams of an embodiment of the optical pressure-sensitive adhesive sheet with a release liner of the present invention. A probe tack test is shown schematically. An example of a stress-peel distance curve obtained in a probe tack test is shown. An example of a method for producing the optical pressure-sensitive adhesive sheet with a release liner shown in FIG. 1 is shown. FIG. 4A shows a process for forming a coating film of a pressure-sensitive adhesive composition, FIG. 4B shows a sheet-forming process, FIG. 4C shows a process for peeling a light release liner, FIG. 4D shows a process for supplying post-added components to a base pressure-sensitive adhesive sheet, and FIG. 4E shows a process for laminating another light release liner to the sheet. An example of a method for using the optical pressure-sensitive adhesive sheet shown in FIG. 1 is shown. FIGS. 5A and 5B show a process for bonding a first adherend and a second adherend via the optical pressure-sensitive adhesive sheet, and FIG. 5C shows an aging process. A stress-peel distance curve obtained by a probe tack test of the optical pressure-sensitive adhesive sheet with a release liner of Example 1 is shown. Figure 1 shows a stress-peel distance curve obtained by a probe tack test on the optical pressure-sensitive adhesive sheet with a release liner of Example 2. Figure 2 shows a stress-peel distance curve obtained by a probe tack test on the optical pressure-sensitive adhesive sheet with a release liner of Example 3. Figure 3 shows a stress-peel distance curve obtained by a probe tack test on the optical pressure-sensitive adhesive sheet with a release liner of Comparative Example 1. Figure 4 shows the positional relationship between the glass plate and the optical pressure-sensitive adhesive sheet in the bonded structure used to evaluate the step-conformability for the Examples and Comparative Examples.

[0014] As shown in Figure 1, an optical adhesive sheet X with a release liner according to one embodiment of the present invention comprises an adhesive sheet 10, a release liner 20, and a release liner 30. The adhesive sheet 10 has a first surface 11 and a second surface 12 opposite the first surface 11. The first surface 11 and the second surface 12 are adhesive surfaces. The release liner 20 has a release surface 21. The release liner 20 is in releasable contact with the first surface 11 of the adhesive sheet 10 on the release surface 21 side. The release liner 30 has a release surface 31. The release liner 30 is in releasable contact with the second surface 12 of the adhesive sheet 10 on the release surface 31 side. That is, the optical adhesive sheet X with a release liner comprises, in order in the thickness direction H, the release liner 20, the adhesive sheet 10, and the release liner 30. The optical pressure-sensitive adhesive sheet X with release liner extends in a direction perpendicular to the thickness direction H (plane direction).

[0015] The adhesive sheet 10 is an optically transparent adhesive sheet (optical adhesive sheet). The adhesive sheet 10 is a sheet-like pressure-sensitive adhesive. The adhesive sheet 10 contains a base polymer, a photopolymerizable multifunctional compound, and a photopolymerization initiator, and is photocurable. The adhesive sheet 10 is, for example, an optical adhesive sheet that is disposed at a light passage location in a display panel. Examples of display panels include liquid crystal display panels and organic EL display panels. The display panel has a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover glass. The adhesive sheet 10 is used, for example, to bond elements included in the laminated structure during the manufacturing process of the display panel.

[0016] Release liner 20 is a heavy release liner that requires a relatively large force to be peeled from PSA sheet 10, and release liner 30 is a light release liner that requires a relatively small force to be peeled from PSA sheet 10. Specifically, in a peel test in which release liner 20 is peeled from PSA sheet 10 under conditions of 25°C, a peel angle of 180°, and a tensile speed of 300 mm / min, release liner 20 has a greater release force than release liner 30. More specifically, the method for measuring this release force is as described below in connection with the Examples. Release liner 30 (light release liner) and release liner 20 (heavy release liner) are peeled from PSA sheet 10 in that order when PSA sheet 10 is used.

[0017] In a probe tack test under the following conditions on the second surface 12 after the release liner 30 has been peeled off from the adhesive sheet 10, the probe peel distance d when the stress becomes 0 gf during the probe peeling process is 200 μm or more and 900 μm or less.

[0018] [Conditions] Temperature: 25°C Probe diameter: 2.5 mm Pressing load: 1000 gf Pressing time: 30 seconds Peeling speed: 0.08 mm / second

[0019] Before the probe tack test, as shown in Figure 2, the pressure-sensitive adhesive sheet 10 with release liner 20 is set on the measurement table W of the tack tester as a test piece Z. Specifically, first, the release liner 20 side of the release-liner optical adhesive sheet X is fixed to the measurement table W via an adhesive (not shown). Then, the release liner 30 is peeled off from the pressure-sensitive adhesive sheet 10 of the release-liner optical adhesive sheet X on the measurement table W.

[0020] The probe tack test under the above conditions is specifically as follows: A cylindrical stainless steel probe with a tip diameter (probe diameter) of 2.5 mm is used as the probe P. The area of ​​the tip Pa of this probe P is 19.63 mm ２ After the ambient temperature and the temperature of the probe P are brought to 25°C, the tip Pa of the probe P (diameter 2.5 mm) is pressed perpendicularly against the adhesive sheet 10 from above at a pressing speed of 0.08 mm / sec until a pressing load of 1000 gf is reached. The pressing load of the probe P of 1000 gf is then maintained for 30 seconds. The probe P is then peeled upward from the second surface 12 of the adhesive sheet 10 at a peeling speed of 0.08 mm / sec (peeling process). During this time, the load acting on the probe P is measured as the stress of the adhesive sheet 10. The method of the probe tack test is specifically as described below in the examples.

[0021] FIG. 3 shows an example of a stress-peel distance curve indicating the stress (load acting downward on the probe P) after the start of peeling of the probe P. In the graph of FIG. 3, the horizontal axis represents the peel distance (μm) of the probe P, and the vertical axis represents the stress (gf). The peel distance of the probe P is the distance the tip Pa of the probe P rises during the peeling process of the probe P (the distance moved in the height direction from the position of the second surface 12 at the start of peeling). During the probe peeling process, first, the pressure-sensitive adhesive sheet 10 elastically deforms and the stress increases. Next, after the stress reaches the maximum stress Smax, the pressure-sensitive adhesive sheet 10 plastically deforms and the stress decreases. The stress of the pressure-sensitive adhesive sheet 10 decreases to 0 gf. The probe peel distance when the stress is 0 gf is shown as distance d in FIG. 3. Methods for adjusting the peel distance d when the stress is 0 gf include, for example, selecting the type of base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. Selection of the type of base polymer includes adjustment of the composition of the monomers that form the base polymer. Methods for adjusting the peel distance d also include selection of the type, adjustment of the molecular weight, and adjustment of the blending amount of components other than the base polymer in the PSA sheet 10. Examples of such components include photopolymerizable multifunctional compounds and silane coupling agents.

[0022] As described above, the adhesive sheet 10 of the optical adhesive sheet X with release liner contains a base polymer, a photopolymerizable multifunctional compound, and a photopolymerization initiator. Such an adhesive sheet 10 can ensure the softness of the adhesive sheet 10 when bonding adherends together using the adhesive sheet 10 (before photocuring), and after bonding, the photopolymerizable multifunctional compound can be photopolymerized to increase the elasticity of the adhesive sheet 10. Such an adhesive sheet 10 is suitable for ensuring conformability to unevenness on the surfaces of adherends when bonding the adherends together, and for ensuring bonding reliability after bonding the adherends together.

[0023] Furthermore, in a probe tack test under the above conditions on the second surface 12 of the release liner-equipped optical adhesive sheet X after peeling the release liner 30 (light release liner) from the pressure-sensitive adhesive sheet 10, the probe peel distance d when the stress becomes 0 gf during the probe peeling process is 200 μm or more and 900 μm or less. An optical adhesive sheet with a release liner having a peel distance d of 900 μm or less is suitable for suppressing unintended peeling of the release liner 20 as a heavy release liner when peeling the release liner 30 as a light release liner from the pressure-sensitive adhesive sheet 10. Furthermore, an optical adhesive sheet with a release liner having a peel distance d of 200 μm or more is suitable for ensuring the viscosity of the surface of the pressure-sensitive adhesive sheet 10 and ensuring bonding reliability after bonding between adherends by the pressure-sensitive adhesive sheet 10.

[0024] As described above, the optical adhesive sheet X with release liner is suitable for achieving both prevention of peeling of the release liner 20 (heavy release liner) when the release liner 30 (light release liner) is peeled off and conformability to unevenness.

[0025] From the viewpoint of suppressing peeling as described above, the peel distance d (stress 0 gf) is preferably 250 μm or more, more preferably 300 μm or more, even more preferably 400 μm or more, and is preferably 850 μm or less, more preferably 750 μm or less, even more preferably 650 μm or less.

[0026] The gel fraction of the pressure-sensitive adhesive sheet 10 (before photocuring) is preferably 50% by mass or more, more preferably 53% by mass or more, from the viewpoint of improving the storage stability of the release liner-attached optical adhesive sheet X or the pressure-sensitive adhesive sheet 10. If the storage stability of the pressure-sensitive adhesive sheet 10 is poor, for example, the flow of the pressure-sensitive adhesive sheet 10 during storage of the release liner-attached optical adhesive sheet X is likely to cause changes in the product shape, and dents or the like are likely to occur in the pressure-sensitive adhesive sheet 10 when stored in a stacked state. From the viewpoint of ensuring the above-mentioned conformability to uneven surfaces, the gel fraction of the pressure-sensitive adhesive sheet 10 (before photocuring) is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less. Methods for adjusting the gel fraction of the pressure-sensitive adhesive sheet 10 include, for example, selecting the type of base polymer in the pressure-sensitive 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.

[0027] The peel force F1 for peeling the release liner 20 (heavy release liner) from the pressure-sensitive adhesive sheet 10 (before photocuring) is preferably 0.1 N / 25 mm or more, more preferably 0.3 N / 25 mm or more, and even more preferably 0.5 N / 25 mm or more, from the viewpoint of preventing unintended peeling of the release liner 20 from the pressure-sensitive adhesive sheet 10. From the viewpoint of ensuring ease of peeling of the release liner 20 from the pressure-sensitive adhesive sheet 10, the peel force F1 is preferably 3.0 N / 25 mm or less, more preferably 2.0 N / 25 mm or less, and even more preferably 1.0 N / 25 mm or less. The peel force F1 is a value measured by conducting a peel test in which the release liner 20 is peeled from the pressure-sensitive adhesive sheet 10 under conditions of a measurement temperature of 25°C, a peel angle of 180°, and a pulling speed of 300 mm / min. Specific methods for measuring the peel force F1 are as described below in connection with the Examples. Methods for adjusting the release force F1 include, for example, selecting the type of base polymer in the PSA sheet 10, adjusting the molecular weight, and adjusting the blending amount. Methods for adjusting the release force F1 also include selecting the type of components other than the base polymer in the PSA sheet 10 and adjusting the blending amount of those components. Examples of such components include photopolymerizable multifunctional compounds and silane coupling agents. These adjustment methods also apply to the release force F2 described below. Another method for adjusting the release force F1 is selecting the type of material that forms the release surface 21 of the release liner 20.

[0028]

[0033] The peel force F2 for peeling the release liner 30 (light release liner) from the PSA sheet 10 is preferably 0.001 N / 25 mm or more, more preferably 0.01 N / 25 mm or more, and even more preferably 0.015 N / 25 mm or more, from the viewpoint of preventing unintended peeling of the release liner 30 from the PSA sheet 10. From the viewpoint of ensuring the light releasability of the release liner 30 as a light release liner, the peel force F2 is preferably 1.0 N / 25 mm or less, more preferably 0.1 N / 25 mm or less, and even more preferably 0.05 N / 25 mm or less. The peel force F2 is a value measured by conducting a peel test in which the release liner 30 is peeled from the PSA sheet 10 under conditions of a measurement temperature of 25°C, a peel angle of 180°, and a pulling speed of 300 mm / min. Specific methods for measuring the peel force F2 are as described below in connection with the Examples. The release force F2 can be adjusted by selecting the type of material that forms the release surface 31 of the release liner 30.

[0029] The difference F1-F2 between the release forces F1 and F2 is preferably 0.1 N / 25 mm or more, more preferably 0.3 N / 25 mm or more, and even more preferably 0.5 N / 25 mm or more, from the viewpoint of suppressing peeling of the release liner 20 when peeling the release liner 30. From the viewpoint of ensuring a balanced releasability of the release liners 20, 30 from the PSA sheet 10, the difference F1-F2 is preferably 2.0 N / 25 mm or less, more preferably 1.0 N / 25 mm or less, and even more preferably 0.6 N / 25 mm or less.

[0030] The ratio (F1 / F2) of the release force F1 to the release force F2 is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more, from the viewpoint of suppressing peeling of the release liner 20 when peeling the release liner 30. From the viewpoint of ensuring a balanced releasability of the release liners 20, 30 from the PSA sheet 10, the ratio (F1 / F2) is preferably 100 or less, more preferably 60 or less, and even more preferably 40 or less.

[0031] In this embodiment, the base polymer in the pressure-sensitive adhesive sheet 10 is a polymer obtained by photopolymerization of a polymerizable component containing a monofunctional monomer and a crosslinking agent. Photopolymerization is a polymerization method in which a polymerization reaction of a polymerizable component is promoted by irradiation with active energy rays such as ultraviolet light. The base polymer is, for example, a polymer obtained by photopolymerization of a partial polymer obtained by photopolymerization of a monofunctional monomer (a mixture of a polymer of the monofunctional monomer and unreacted monofunctional monomer) and a crosslinking agent.

[0032] Such a base polymer includes a photopolymerized polymer (first photopolymerized polymer) having a photocrosslinked structure. The photocrosslinked structure is a structure in which linear structures formed by units derived from monofunctional monomers are crosslinked by units derived from a crosslinking agent. The base polymer may also include a photopolymerized polymer (second photopolymerized polymer) that does not have such a photocrosslinked structure. The second photopolymerized polymer is a polymer of a monofunctional monomer. The base polymer is preferably an acrylic polymer. The acrylic polymer is a copolymer of polymerizable components containing 50% or more by mass of alkyl (meth)acrylate esters. "(Meth)acrylic" means acrylic and / or methacrylic.

[0033] The monofunctional monomer is preferably a monofunctional (meth)acrylic acid alkyl ester, more preferably a (meth)acrylic acid alkyl ester having an alkyl group having 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 (alicyclic alkyl group).

[0034] Examples of linear or branched (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-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, and isooctyl (meth)acrylate. (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)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.

[0035] Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid alkyl esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid alkyl 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 alkyl esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid alkyl 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.

[0036] The monofunctional monomer may be used alone or in combination of two or more kinds. The monofunctional monomer is preferably an alkyl acrylate ester having an alkyl group having 3 to 12 carbon atoms, and more preferably at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate.

[0037] The proportion of the monofunctional monomer in the polymerizable components forming the base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 75% by mass or more, from the viewpoint of appropriately exhibiting basic properties such as adhesiveness in the pressure-sensitive adhesive sheet 10. This proportion is, for example, 99% by mass or less.

[0038] The polymerizable component may contain a copolymerizable monomer copolymerizable with the monofunctional (meth)acrylic acid alkyl ester as a monofunctional monomer. Examples of the copolymerizable monomer include polar group-containing monomers. Examples of the polar group-containing monomer include hydroxy group-containing monomers, carboxy group-containing monomers, and monomers having a nitrogen atom-containing ring. The polar group-containing monomer is useful for modifying the acrylic polymer, such as by ensuring the cohesive strength of the acrylic polymer.

[0039] 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, and 12-hydroxylauryl (meth)acrylate. The hydroxy group-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

[0040] The proportion of the hydroxy group-containing monomer in the polymerizable component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of ensuring cohesive strength in the pressure-sensitive adhesive sheet 10. 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 pressure-sensitive adhesive sheet 10), this proportion is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0041] Examples of carboxy group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0042] The proportion of the carboxy group-containing monomer in the polymerizable component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoints of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10 and ensuring the adhesive strength to the adherend in the pressure-sensitive adhesive sheet 10. This proportion is preferably 20% by mass or less, more preferably 10% 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.

[0043] 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, N-vinylisothiazole, and acryloylmorpholine. The monomer having a nitrogen atom-containing ring is preferably at least one selected from the group consisting of N-vinyl-2-pyrrolidone and acryloylmorpholine.

[0044] The proportion of the monomer having a nitrogen atom-containing ring in the polymerizable component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoints 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 viewpoints 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).

[0045] Examples of crosslinking agents include polyfunctional oligomers and polyfunctional monomers.

[0046] Examples of polyfunctional oligomers include urethane acrylate oligomers (oligomers having a urethane backbone and two or more acryloyl groups), epoxy acrylate oligomers (oligomers having an epoxy backbone and two or more acryloyl groups), and silicone acrylate oligomers (oligomers having a siloxane backbone and two or more acryloyl groups). Commercially available urethane acrylate oligomers include Art Resin UN-333, UN-350, UN-353, UN-5500, and UN-5590 manufactured by Negami Chemical Industrial Co., Ltd.

[0047] The weight average molecular weight (Mw) of the polyfunctional oligomer is preferably 5,000 or more, and preferably 20,000 or less, more preferably 15,000 or less, from the viewpoint of appropriately adjusting the gel fraction of the PSA sheet 10. The weight average molecular weight is measured by gel permeation chromatography (GPC) and calculated in polystyrene equivalent terms.

[0048] Examples of the polyfunctional monomer include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. As the polyfunctional monomer, polyfunctional (meth)acrylates are preferred from the viewpoint of easily introducing a crosslinked structure by photopolymerization (active energy ray polymerization). Examples of the polyfunctional (meth)acrylate include the polyfunctional (meth)acrylates described below in relation to the photopolymerizable polyfunctional compound.

[0049] The crosslinking agent may be used alone or in combination of two or more kinds. The crosslinking agent is preferably a polyfunctional oligomer, more preferably a urethane acrylate oligomer.

[0050] The proportion of the crosslinking agent in the polymerizable component is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and even more preferably 0.7% by mass or more. Such a configuration is preferable for maintaining the sheet shape of the pressure-sensitive adhesive sheet 10 before photocuring, and therefore is preferable for ensuring the handleability of the pressure-sensitive adhesive sheet 10. The proportion of the crosslinking agent in the polymerizable component is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and even more preferably 1% by mass or less. Such a configuration is preferable for ensuring a high degree of softness in the pressure-sensitive adhesive sheet 10 before photocuring, and for achieving good step-conforming ability. Furthermore, this configuration is preferable for suppressing unintended peeling of the heavy-duty release liner when the light-duty release liner is peeled off.

[0051] Examples of the photopolymerizable polyfunctional compound include polyfunctional monomers and polyfunctional oligomers.

[0052] Examples of polyfunctional monomers include polyfunctional (meth)acrylates, such as difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

[0053] 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 ethoxylated bisphenol A diacrylate (BPAEODE).

[0054] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0055] 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.

[0056] Examples of polyfunctional oligomers include those polyfunctional oligomers described above with respect to the crosslinking agent.

[0057] The photopolymerizable polyfunctional compounds may be used alone or in combination of two or more kinds.

[0058] From the viewpoint of adjusting the peel distance d to 200 to 900 μm, the photopolymerizable multifunctional compound preferably includes a photopolymerizable multifunctional compound having an aromatic ring (first photopolymerizable multifunctional compound), and more preferably includes a first photopolymerizable multifunctional compound and a photopolymerizable multifunctional compound without an aromatic ring (second photopolymerizable multifunctional compound). Since the first photopolymerizable multifunctional compound has an aromatic ring within its molecular structure, the molecular motion of the compound itself is restricted, and the compounds may be π-conjugated with each other. It is presumed that such a first photopolymerizable multifunctional compound tends to have a high viscosity and therefore has a small plasticizing effect on the PSA sheet 10, which helps prevent the peel distance d from becoming excessive.

[0059] The first photopolymerizable polyfunctional compound is preferably a polyfunctional monomer having an aromatic ring, more preferably BPAEODE. The molecular weight of the first photopolymerizable polyfunctional compound is preferably 1,000 or less, more preferably 700 or less, even more preferably 500 or less, and is preferably 300 or more, more preferably 400 or more, even more preferably 450 or more, from the viewpoint of adjusting the peel distance d to 200 to 900 μm.

[0060] The second photopolymerizable polyfunctional compound is preferably a polyfunctional monomer having no aromatic ring, more preferably trimethylolpropane triacrylate (TMPTA). The molecular weight of the second photopolymerizable polyfunctional compound is preferably 1,000 or less, more preferably 700 or less, even more preferably 500 or less, and is preferably 200 or more, more preferably 250 or more, even more preferably 280 or more, from the viewpoint of adjusting the peel distance d to 200 to 900 μm.

[0061] The content of the photopolymerizable multifunctional compound in the pressure-sensitive adhesive sheet 10 (the total content when the pressure-sensitive adhesive sheet 10 contains multiple photopolymerizable multifunctional compounds) is preferably 1.2 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 2.5 parts by mass or more per 100 parts by mass of the base polymer, from the viewpoint of ensuring good bonding reliability after photocuring in the pressure-sensitive adhesive sheet 10. The content of the photopolymerizable multifunctional compound in the pressure-sensitive adhesive sheet 10 is preferably 7 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3.5 parts by mass or less per 100 parts by mass of the base polymer, from the viewpoint of adjusting the peel distance d to 200 to 900 μm. The content of the first photopolymerizable multifunctional compound in the pressure-sensitive adhesive sheet 10 is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, and even more preferably 0.5 parts by mass or more per 100 parts by mass of the base polymer, from the viewpoint of ensuring good bonding reliability after photocuring in the pressure-sensitive adhesive sheet 10. The content of the first photopolymerizable multifunctional compound in the pressure-sensitive adhesive sheet 10 is preferably 2 parts by mass or less, more preferably 1.5 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the base polymer, from the viewpoint of adjusting the above-mentioned peel distance d to 200 to 900 μm. The content of the second photopolymerizable multifunctional compound in the pressure-sensitive adhesive sheet 10 is preferably 1 part by mass or more, more preferably 1.6 parts by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the base polymer, from the viewpoint of ensuring good bonding reliability after photocuring in the pressure-sensitive adhesive sheet 10. The content of the second photopolymerizable multifunctional compound in the pressure-sensitive adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 3.5 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the base polymer, from the viewpoint of adjusting the above-mentioned peel distance d to 200 to 900 μm.

[0062] Examples of the photopolymerization initiator in the pressure-sensitive adhesive sheet 10 include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator.

[0063] Examples of the radical photopolymerization initiator include an acylphosphine oxide photopolymerization initiator, a benzoin ether photopolymerization initiator, an acetophenone photopolymerization initiator, an α-ketol photopolymerization initiator, an aromatic sulfonyl chloride photopolymerization initiator, a photoactive oxime photopolymerization initiator, a benzoin photopolymerization initiator, a benzyl photopolymerization initiator, a benzophenone photopolymerization initiator, a ketal photopolymerization initiator, and a thioxanthone photopolymerization initiator.

[0064] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin photopolymerization initiators include benzoin. Examples of benzyl photopolymerization initiators include benzyl. Examples of benzophenone photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. Examples of ketal photopolymerization initiators include benzyl dimethyl ketal. Examples of thioxanthone photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.The photopolymerization initiator may be used alone or in combination of two or more kinds. The photopolymerization initiator is preferably an acylphosphine oxide photopolymerization initiator, and more preferably at least one selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-dimethoxy-1,2-diphenylethan-1-one, and 1-hydroxycyclohexyl phenyl ketone.

[0065] The content of the photopolymerization initiator in the pressure-sensitive adhesive sheet 10 is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.25 parts by mass or more, even more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more per 100 parts by mass of the base polymer. Such a configuration is preferable for forming a crosslinked network with sufficient crosslinking density within the pressure-sensitive adhesive sheet 10 through a photopolymerization reaction upon light irradiation of the pressure-sensitive adhesive sheet 10, thereby significantly changing the viscoelasticity of the pressure-sensitive adhesive sheet 10. The content of the photopolymerization initiator in the pressure-sensitive adhesive sheet 10 is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less per 100 parts by mass of the base polymer. Such a configuration is preferable for suppressing excessive generation of the polymerization initiator upon light irradiation of the pressure-sensitive adhesive sheet 10, and for forming a long-distance and continuous crosslinked network through the photopolymerization reaction.

[0066] The pressure-sensitive adhesive sheet 10 may contain other components, such as an ultraviolet absorber, an antioxidant, a silane coupling agent, and a rust inhibitor.

[0067] Examples of ultraviolet absorbers include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. As ultraviolet absorbers, triazine-based ultraviolet absorbers are preferred because they have high absorption of ultraviolet light in the wavelength range of 320 to 370 nm and excellent compatibility with acrylic polymers. The ultraviolet absorbers may be used alone or in combination of two or more.

[0068] Commercially available triazine-based ultraviolet absorbers include, for example, bisethylhexyloxyphenol methoxyphenyl triazine (trade name "Tinosorb S", manufactured by BASF), a reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(alkyloxy)methyl]oxirane (trade name "TINUVIN 400", manufactured by BASF), a reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine with (2-ethylhexyl)-glycidic acid ester (trade name "TINUVIN 405", manufactured by BASF), and (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (trade name "TINUVIN Examples of suitable phenols include 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol (trade name "TINUVIN 577", manufactured by BASF), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (trade name "TINUVIN 479", manufactured by BASF), and 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol (trade name "ADK STAB LA-46", manufactured by ADEKA).

[0069] The content of the ultraviolet absorber in the pressure-sensitive adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less, per 100 parts by mass of the base polymer. Such a configuration is preferable from the viewpoint of achieving both an ultraviolet blocking function for device protection and photocurability in the pressure-sensitive adhesive sheet 10.

[0070] Examples of antioxidants include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and amine-based antioxidants. The antioxidants may be used alone or in combination of two or more.

[0071] As the antioxidant, a phenol-based antioxidant is preferably used, and more preferably a hindered phenol-based antioxidant is used. Examples of the hindered phenol-based antioxidant include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (product name "Irganox 1010", manufactured by BASF) and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (product name "Irganox 1076", manufactured by BASF).

[0072] The content of the antioxidant in the pressure-sensitive adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less, per 100 parts by mass of the base polymer. Such a configuration is preferable from the viewpoint of achieving both suppression of oxidative degradation of the pressure-sensitive adhesive sheet 10 and photocurability.

[0073] Examples of silane coupling agents include silane coupling agents containing an epoxy group. Examples of epoxy group-containing silane coupling agents include 3-glycidoxydialkyldialkoxysilane and 3-glycidoxyalkyltrialkoxysilane. Examples of 3-glycidoxydialkyldialkoxysilane include 3-glycidoxypropylmethyldimethoxysilane and 3-glycidoxypropylmethyldiethoxysilane. Examples of 3-glycidoxyalkyltrialkoxysilane include 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane. As the silane coupling agent, preferably 3-glycidoxyalkyltrialkoxysilane is used, and more preferably 3-glycidoxypropyltrimethoxysilane is used. The silane coupling agents may be used alone or in combination of two or more. The content of the silane coupling agent in the adhesive sheet 10 is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of the base polymer.

[0074] The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoint of ensuring sufficient adhesiveness to the adherend. The thickness of the pressure-sensitive adhesive sheet 10 is preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, still more preferably 200 μm or less, and even more preferably 150 μm or less, from the viewpoint of ease of handling and cutting of the pressure-sensitive adhesive sheet 10.

[0075] The total light transmittance of the pressure-sensitive adhesive sheet 10 is preferably 90% or more, more preferably 92% or more. Such a configuration is preferable for ensuring the transparency required of the pressure-sensitive adhesive sheet 10 for use in display panels. The total light transmittance of the pressure-sensitive adhesive sheet 10 is, for example, 100% or less. The total light transmittance can be measured in accordance with JIS K 7375 (2008).

[0076] The shear storage modulus of the pressure-sensitive adhesive sheet 10 (before photocuring) at 25°C is preferably 1 MPa or less, more preferably 500 kPa or less, even more preferably 300 kPa or less, even more preferably 200 kPa or less, even more preferably 180 kPa or less, and particularly preferably 150 kPa or less, from the viewpoint of ensuring the flexibility of the pressure-sensitive adhesive sheet 10. The shear storage modulus of the pressure-sensitive adhesive sheet 10 at 25°C is preferably 5 kPa or more, more preferably 10 kPa or more, even more preferably 15 kPa or more, and particularly preferably 20 kPa or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10. The shear storage modulus of the pressure-sensitive adhesive sheet can be measured using a dynamic viscoelasticity measuring device. As a dynamic viscoelasticity measuring device, for example, the "Advanced Rheometric Expansion System" manufactured by Rheometric Scientific can be used. In the measurement, the measurement mode is shear mode, the measurement temperature range is -50°C to 150°C, the heating rate is 5°C / min, and the frequency is 1 Hz. The specific method for measuring the shear storage modulus is as will be described later in the examples.

[0077] The release liner 20 is, for example, a flexible, transparent resin film. Examples of materials for the release liner 20 include polyester resin, polyolefin resin, polycarbonate resin, polyethersulfone resin, polyarylate resin, melamine resin, polyamide resin, cellulose resin, and polystyrene resin. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer (COP). From the viewpoints of transparency and strength, polyester resin is preferably used as the material for the release liner 20, and PET is more preferably used.

[0078] The release surface 21 of the release liner 20 may be subjected to a release treatment with a release treatment agent. Examples of release treatments include silicone release treatments, long-chain alkyl acrylate release treatments, and fluorine release treatments. From the viewpoint of ease of adjusting the release force from the PSA sheet 10, silicone release treatments are preferred as the release treatment.

[0079] The thickness of the release liner 20 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, from the viewpoint of ensuring the protective function for the PSA sheet 10. The thickness of the release liner 20 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less, from the viewpoint of handleability.

[0080] The release liner 30 is a flexible, transparent resin film. Examples of materials for the release liner 30 include the materials described above as the materials for the release liner 20. From the viewpoints of transparency and strength, the material for the release liner 30 is preferably a polyester resin, and more preferably PET.

[0081] In this embodiment, the release surface 31 of the release liner 30 is release-treated with a release treatment agent. Examples of release treatments include silicone release treatments, long-chain alkyl acrylate release treatments, and fluorine release treatments. From the viewpoint of ease of adjusting the release force from the PSA sheet 10, silicone release treatments are preferred as the release treatment. The release treatment of the release liner 30 is carried out so that the release force F2 of the release liner 30 is smaller than the release force F1 of the release liner 20.

[0082] The thickness of the release liner 30 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, from the viewpoint of ensuring the protective function for the PSA sheet 10. The thickness of the release liner 30 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less, from the viewpoint of handleability.

[0083] The optical pressure-sensitive adhesive sheet X with a release liner can be produced, for example, as follows.

[0084] First, a prepolymer composition is prepared (prepolymer composition preparation step). Specifically, first, a mixture (liquid) containing the above-mentioned monofunctional monomer for forming the base polymer and a photopolymerization initiator is prepared. Next, the mixture is irradiated with ultraviolet light to photopolymerize a portion of the monofunctional monomer in the mixture, thereby obtaining a prepolymer composition. Examples of light sources for ultraviolet irradiation include ultraviolet LED lights, black light lamps, high-pressure mercury lamps, and metal halide lamps. Furthermore, in ultraviolet irradiation, a wavelength cut filter for cutting a portion of the wavelength range of light emitted from the light source may be used as needed. In ultraviolet irradiation, the illuminance is, for example, 5 to 200 mW / cm. ２ The cumulative irradiation amount is, for example, 100 to 5000 mJ / cm ２The ultraviolet irradiation is preferably continued until the viscosity of the composition reaches approximately 15 to 25 Pa·s. This viscosity is measured using a Brookfield viscometer with a No. 5 rotor at a rotor rotation speed of 10 rpm and a temperature of 30°C. The prepolymer composition contains a photopolymerized product of a monofunctional monomer (the second photopolymerized polymer) and a monofunctional monomer that has not undergone a polymerization reaction (residual monomer). The prepolymer composition does not contain a solvent.

[0085] Next, a crosslinking agent, a photopolymerization initiator, and other components, if necessary, are added to the prepolymer composition to prepare a pressure-sensitive adhesive composition (pressure-sensitive adhesive composition preparation step). Examples of other components include additional monofunctional monomers (additional monomers), antioxidants, silane coupling agents, and rust inhibitors. The pressure-sensitive adhesive composition does not contain a solvent, and is therefore a solventless pressure-sensitive adhesive composition.

[0086] 4A, a coating film 10A is formed between release liners 20, 30 (coating film forming step). Specifically, first, a pressure-sensitive adhesive composition is applied to release surface 21 of release liner 20 to form coating film 10A. Next, release surface 31 of release liner 30 is laminated onto coating film 10A on release liner 20. Examples of methods for applying the pressure-sensitive 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.

[0087] Next, as shown in Figure 4B, ultraviolet light is irradiated onto the coating film 10A (Figure 4A) between the release liners 20 and 30 to form a base adhesive sheet 10B (base adhesive sheet formation step). Upon irradiation with ultraviolet light, a photopolymerization reaction proceeds in the coating film in a reaction system containing monofunctional monomers (residual monomers, additional monomers) and a crosslinking agent, forming a base polymer.

[0088] Next, as shown in FIG. 4C, release liner 30 is peeled off from base adhesive sheet 10B (peeling step).

[0089] Next, as shown in FIG. 4D , a later-added component is supplied to the base adhesive sheet 10B (later-added component supplying step). For example, a later-added component solution (not shown) containing the later-added component and a solvent is applied to the exposed surface of the base adhesive sheet 10B. The later-added component includes the photopolymerizable multifunctional compound and the photopolymerization initiator described above, and may also contain additives such as an ultraviolet absorber and an antioxidant. Next, the later-added component is allowed to penetrate the base adhesive sheet 10B from the surface thereof, while the solvent is evaporated, if necessary, by heating. Prior to this step, the base polymer already has a crosslinked structure, forming the base adhesive sheet 10B. Therefore, evaporation of the solvent in this step is unlikely to (or does not substantially) form an orange peel surface on the base adhesive sheet 10B. Furthermore, the photocurable adhesive sheet 10 is formed by the base adhesive sheet 10B and the later-added component. As described above, the amount of the photopolymerizable polyfunctional compound added in this step is preferably 1.2 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 2.5 parts by mass or more per 100 parts by mass of the base polymer, and is preferably 7 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3.5 parts by mass or less.

[0090] Next, as shown in FIG. 4E, another release liner 30 is attached to the pressure-sensitive adhesive sheet 10 (attaching step).

[0091] In this manner, it is possible to produce a pressure-sensitive adhesive sheet 10 whose adhesive surface is covered and protected by release liners 20, 30. A pressure-sensitive adhesive sheet 10 formed from a solvent-free pressure-sensitive adhesive composition is suitable for reducing the environmental load.

[0092] 5A to 5C show an example of a method of using the pressure-sensitive adhesive sheet 10 of the optical pressure-sensitive adhesive sheet X with a release liner.

[0093] In this method, first, as shown in FIGS. 5A and 5B , a member 51 and a cover glass 52 are bonded together via an adhesive sheet 10. The member 51 is, for example, a pixel panel for a display panel, a polarizing film, or a touch panel. The cover glass 52 has a first surface 52a on the member 51 side and a second surface 52b opposite the first surface 52a. A decorative or light-blocking printed layer 53 is formed on the edge of the first surface 52a. The printed layer 53 is provided, for example, around the entire edge of the cover glass 52. On the member 51 side of the cover glass 52, there is a step (printed step) between the first surface 52a and the surface of the printed layer 53. The member 51 and the cover glass 52 are bonded together via the adhesive sheet 10. Specifically, the following first or second method is used.

[0094] In the first method, first, the release liner 30 is peeled from the adhesive sheet 10 of the release-liner optical adhesive sheet X ( FIG. 1 ). Next, the adhesive sheet 10 exposed by the peeling is bonded to a member 51 ( FIG. 5A ). Next, the release liner 20 is peeled from the adhesive sheet 10 on the member 51. Next, the adhesive sheet 10 exposed by the peeling is bonded to a first surface 52 a of a cover glass 52. In the second method, first, the release liner 30 is peeled from the adhesive sheet 10 of the release-liner optical adhesive sheet X ( FIG. 1 ). Next, the adhesive sheet 10 exposed by the peeling is bonded to a first surface 52 a of the cover glass 52. Next, the release liner 20 is peeled from the adhesive sheet 10 on the cover glass 52. Next, the adhesive sheet 10 exposed by the peeling is bonded to a member 51.

[0095] With the optical adhesive sheet X with release liner, in both the first method and the second method, when the release liner 30 (light release liner) is peeled from the adhesive sheet 10, unintentional peeling of the release liner 20 (heavy release liner) from the adhesive sheet 10 is suppressed. Furthermore, with the optical adhesive sheet X with release liner, in both the first method and the second method, the adhesive sheet 10 is attached to the stepped surface of the adherend (the first surface 52a of the cover glass 52) in a soft state before photo-curing. Therefore, the adhesive sheet 10 of the optical adhesive sheet X with release liner is suitable for achieving good step-conforming properties.

[0096] Next, as shown in FIG. 5C , the adhesive sheet 10 is photocured between the member 51 and the cover glass 52 by UV irradiation (photocuring process). UV irradiation causes a photopolymerization reaction of the photopolymerizable multifunctional compound in the adhesive sheet 10, forming a photopolymerized product of the photopolymerizable multifunctional compound. Because the photopolymerization reaction proceeds around the base polymer (the first photopolymerizable polymer and the second photopolymerizable polymer having a photocrosslinking structure), the photopolymerized product of the photopolymerizable multifunctional compound is formed while forming an interpenetrating polymer network (IPN) with the base polymer. This increases the elasticity of the adhesive sheet 10 and enhances the bonding strength between the member 51 and the cover glass 52. Examples of light sources for UV irradiation include UV LED lamps, black light lamps, high-pressure mercury lamps, and metal halide lamps. Furthermore, a wavelength cut filter may be used to cut out a portion of the wavelength range of the light emitted from the light source. The cumulative irradiation light dose for UV irradiation is, for example, 50 to 10,000 mJ / cm. ２ is.

[0097] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. The specific numerical values ​​of the blending amounts (contents), physical property values, parameters, etc. described below can be substituted with the upper limits (numerical values ​​defined as "equal to or less than") or lower limits (numerical values ​​defined as "equal to or more than") of the corresponding blending amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Description of the Invention."

[0098] Example 1 Preparation of Prepolymer Composition In a flask, a monomer mixture of 78 parts by weight of n-butyl acrylate (BA), 16 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 6 parts by weight of 4-hydroxybutyl acrylate (4HBA) was added with 0.07 parts by weight of two first photoinitiators. The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture, yielding a prepolymer composition. The first photoinitiators used were 0.035 parts by weight of "Omnirad 184" (1-hydroxycyclohexyl phenyl ketone) manufactured by IGM Resins and 0.035 parts by weight of "Omnirad 651" (2,2-dimethoxy-1,2-diphenylethan-1-one) manufactured by IGM Resins. UV irradiation was continued until the viscosity of the composition reached approximately 20 Pa s. This viscosity was measured using a Brookfield viscometer with a No. 5 rotor at a rotor rotation speed of 10 rpm at a temperature of 30° C. (The same applies to the viscosity described below.) The obtained prepolymer composition was a partial polymer containing a photopolymerized product (photopolymerized polymer P1a) and a monomer component that had not undergone a polymerization reaction (residual monomer).

[0099] <Preparation of Pressure-Sensitive Adhesive Composition> Next, 100 parts by mass of the prepolymer composition, 2 parts by mass of acryloylmorpholine (ACMO) as an additional monomer, 8 parts by mass of 4-hydroxybutyl acrylate (4HBA) as another additional monomer, and urethane acrylate oligomer (UAO) (product name "Art Resin UN-350") as a crosslinking agent were mixed. A pressure-sensitive adhesive composition was obtained by mixing 0.8 parts by mass of "NDTN001BA", weight average molecular weight 12500, manufactured by Negami Chemical Industrial Co., Ltd.), 0.4 parts by mass of a second photopolymerization initiator, 0.5 parts by mass of an antioxidant (trade name "Irganox 1010", manufactured by BASF), 0.15 parts by mass of a rust inhibitor (trade name "BT-120", benzotriazole, manufactured by Johoku Chemical Industry Co., Ltd.), and 0.35 parts by mass of a silane coupling agent (trade name "KBM-403", 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.). As the second photopolymerization initiator, "Omnirad 819" (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide) manufactured by IGM Resins was used.

[0100] <Preparation of Base Pressure-Sensitive Adhesive Sheet> Next, a pressure-sensitive adhesive composition was applied to the release-treated surface of a first release liner (trade name "Diafoil MRV", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) as a heavy release liner having a release-treated surface on one side, to form a coating film. Next, the release-treated surface of a second release liner (trade name "Diafoil MRE", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) as a light release liner having a release-treated surface on one side was laminated onto the coating film on the first release liner. Next, ultraviolet light was irradiated from the second release liner side to photocure the coating film, forming a 100 μm thick pressure-sensitive adhesive layer (ultraviolet light irradiation step). For ultraviolet light irradiation, a black light lamp (manufactured by Toshiba) was used as the light source, and the illuminance was 6.5 mW / cm. ２ The cumulative irradiation dose was 1500 mJ / cm ２In the ultraviolet irradiation step, a photopolymerization reaction proceeds in the coating film in a reaction system containing the above-mentioned residual monomer, additional monomer, and crosslinking agent, forming a photopolymerized polymer P1b having a photocrosslinked structure. Furthermore, since the photopolymerization reaction proceeds around the above-mentioned photopolymerized polymer P1a, the photopolymerized polymer P1b is formed around the photopolymerized polymer P1a. The pressure-sensitive adhesive layer formed in this step contains such photopolymerized polymer P1a and photopolymerized polymer P1b as base polymers. In this manner, a base pressure-sensitive adhesive sheet with a release liner (first release liner / base pressure-sensitive adhesive sheet (thickness 100 μm) / second release liner) was produced.

[0101] Preparation of Post-Addition Component Solution 1.8 parts by mass of ethoxylated bisphenol A diacrylate (BPAEODE) (product name "ABE-300", molecular weight: 468.0, manufactured by Shin-Nakamura Chemical Co., Ltd.) as the first photopolymerizable multifunctional compound, 5.7 parts by mass of trimethylolpropane triacrylate (TMPTA) (product name "Viscoat #295", molecular weight: 296.3, manufactured by Osaka Organic Chemical Industry Co., Ltd.) as the second photopolymerizable multifunctional compound, 1.4 parts by mass of a third photopolymerization initiator, 3.5 parts by mass of an ultraviolet absorber (product name "Tinosorb S", manufactured by BASF), and 49.1 parts by mass of ethyl acetate as a solvent were mixed to prepare a post-addition component solution (everything other than the solvent in the solution is a post-addition component). As the third photopolymerization initiator, "Omnirad 819" manufactured by IGM Resins was used. The composition of the post-addition component solution is shown in Table 1. In Table 1, the unit of the amount of each component is relative "parts by mass."

[0102] <Preparation of Optical Adhesive Sheet> After peeling the second release liner from the base adhesive sheet with release liner described above, the post-added component solution was applied to a thickness of 20 μm on the exposed surface of the base adhesive sheet (coating process). A bar coater RDS No. 10 manufactured by R.D. SPECIALTIES was used for the coating. Next, the solution was dried for 60 seconds in a dryer at 110°C. The coating and drying processes allowed the post-added components (photopolymerizable multifunctional compound, third photopolymerization initiator, and ultraviolet absorber) to penetrate into the base adhesive sheet, and also vaporized the solvent. A photocurable optical adhesive sheet was formed by the penetration of the post-added components into the base adhesive sheet. The amount of BPAEODE added per 100 parts by mass of the base polymer (100 parts by mass of the above-mentioned prepolymer composition, additional monomer, and crosslinking agent) was 0.6 parts by mass, the amount of TMPTA added was 2.0 parts by mass, and the amount of the third photopolymerization initiator (Omnirad 819) added was 0.5 parts by mass (in Table 2, the relative amounts of the photopolymerizable multifunctional compound and the third photopolymerization initiator per 100 parts by mass of the base polymer are shown in parentheses next to the components.) Next, the release-treated surface of a third release liner (product name "Diafoil MRQ", thickness 50 μm, manufactured by Mitsubishi Chemical Corporation) serving as a light release liner having a release-treated surface on one side was bonded to the optical pressure-sensitive adhesive sheet on the first release liner.

[0103] In this manner, the optical adhesive sheet with release liner of Example 1 (first release liner / optical adhesive sheet (thickness 100 μm) / third release liner) was produced. The optical adhesive sheet is a photocurable optical adhesive sheet containing a base polymer, a photopolymerizable multifunctional compound, and a third photopolymerization initiator.

[0104] Example 2 An optical pressure-sensitive adhesive sheet with a release liner of Example 2 was produced in the same manner as the optical pressure-sensitive adhesive sheet with a release liner of Example 1, except for the following.

[0105] In preparing the post-addition component solution, the amount of BPAEODE was 3.0 parts by mass, and the amount of ethyl acetate was 47.9 parts by mass. In the optical adhesive sheet in Example 2, the amount of BPAEODE added as the first photopolymerizable multifunctional compound was 1.0 part by mass, the amount of TMPTA added as the second photopolymerizable multifunctional compound was 2.0 parts by mass, and the amount of the third photopolymerization initiator (Omnirad 819) added was 0.5 parts by mass per 100 parts by mass of the base polymer (shown in Table 2).

[0106] Example 3 An optical pressure-sensitive adhesive sheet with a release liner of Example 3 was produced in the same manner as the optical pressure-sensitive adhesive sheet with a release liner of Example 1, except for the following.

[0107] In preparing the post-addition component solution, the amount of the third photopolymerization initiator (Omnirad 819) added was 1.8 parts by mass, and the amount of ethyl acetate was 49.1 parts by mass. In the optical adhesive sheet in Example 3, the amount of BPAEODE added as the first photopolymerizable multifunctional compound per 100 parts by mass of the base polymer was 0.6 parts by mass, the amount of TMPTA added as the second photopolymerizable multifunctional compound was 2.0 parts by mass, and the amount of the third photopolymerization initiator (Omnirad 819) added was 1.0 part by mass (shown in Table 2).

[0108] Comparative Example 1 An optical pressure-sensitive adhesive sheet with a release liner of Comparative Example 1 was produced in the same manner as the optical pressure-sensitive adhesive sheet with a release liner of Example 1, except for the following.

[0109] In preparing the pressure-sensitive adhesive composition, the amount of crosslinking agent (UAO) was 1.2 parts by mass. In preparing the post-addition component solution, BPAEODE was not added, and the amount of TMPTA (photopolymerizable multifunctional compound) was 16.1 parts by mass, the amount of the third photopolymerization initiator (Omnirad 819) was 0.68 parts by mass, and the amount of ethyl acetate was 39.7 parts by mass. In the optical pressure-sensitive adhesive sheet of Comparative Example 1, the amount of the photopolymerizable multifunctional compound (TMPTA) added per 100 parts by mass of the base polymer was 5.6 parts by mass, and the amount of the third photopolymerization initiator (Omnirad 819) added was 0.24 parts by mass (shown in Table 2).

[0110] Comparative Example 2 An 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 Example 1, except for the following.

[0111] In preparing the pressure-sensitive adhesive composition, the amount of crosslinker (UAO) was 1.2 parts by mass. In preparing the post-addition component solution, BPAEODE was not added, and the amount of TMPTA (photopolymerizable multifunctional compound) was 16.1 parts by mass, and the amount of ethyl acetate was 39.0 parts by mass. In the optical pressure-sensitive adhesive sheet of Comparative Example 2, the amount of photopolymerizable multifunctional compound (TMPTA) added per 100 parts by mass of base polymer was 5.6 parts by mass, and the amount of third photopolymerization initiator (Omnirad 819) added was 0.5 parts by mass (shown in Table 2).

[0112] <Total Light Transmittance> The total light transmittance of each of the optical pressure-sensitive adhesive sheets in Examples 1 to 3 and Comparative Examples 1 and 2 was measured as follows.

[0113] First, a sample for measurement was prepared. Specifically, after peeling off the third release liner from the optical pressure-sensitive adhesive sheet, the exposed surface of the optical pressure-sensitive adhesive sheet was attached to alkali-free glass (manufactured by Matsunami Glass Co., Ltd.), and the first release liner was peeled off from the optical pressure-sensitive adhesive sheet on the glass. This resulted in a sample for measurement. Next, the total light transmittance of the sample was measured in accordance with JIS K7136 (2000) using a haze meter "HM-150N" manufactured by Murakami Color Research Laboratory Co., Ltd. In addition, in this measurement, the measurement results obtained by measuring only the alkali-free glass under the same conditions were used as the baseline. The total light transmittance (%) of each optical pressure-sensitive adhesive sheet is shown in Table 2.

[0114] <Gel Fraction> The gel fraction of each optical pressure-sensitive adhesive sheet in Examples 1 to 3 and Comparative Examples 1 and 2 was measured. Specifically, it is as follows.

[0115] First, about 1 g of a pressure-sensitive adhesive sample was taken from the optical pressure-sensitive adhesive sheet. Next, the mass (W １) was measured. Next, the PSA sample was immersed in 40 g of ethyl acetate in a container for 7 days. Next, all components insoluble in ethyl acetate (insoluble portion) were collected. Next, the insoluble portion was dried at 130°C for 2 hours (removal of ethyl acetate). Next, the mass (W ２ ) was measured. Then, the gel fraction G (mass%) of the optical adhesive sheet after photocuring was calculated based on the following formula. The values ​​are shown in Table 2. The gel fraction G shown in Table 2 for each optical adhesive sheet (having photocurability) in Examples 1 to 3 and Comparative Examples 1 and 2 is the gel fraction of the optical adhesive sheet before photocuring.

[0116] Gel fraction (mass%) = (W ２ / W １ ) x 100

[0117] <Shear storage modulus> Dynamic viscoelasticity was measured for each of the optical pressure-sensitive adhesive sheets in Examples 1 to 3 and Comparative Examples 1 and 2. Specifically, the measurement was as follows.

[0118] First, the required number of measurement samples were prepared for each optical adhesive sheet. Specifically, 20 optical adhesive sheets cut from the optical adhesive sheet were laminated together to prepare a sample sheet with a thickness of approximately 2 mm. Next, this sheet was punched out to obtain cylindrical pellets (diameter 7.9 mm) as measurement samples.

[0119] Then, the measurement sample was 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 then dynamic viscoelasticity measurement was performed. In this measurement, the measurement mode was shear mode, the measurement temperature range was -50 ° C to 150 ° C, the heating rate was 5 ° C / min, and the frequency was 1 Hz. From the measurement results, the shear storage modulus (MPa) at 25 ° C was read. The values ​​are shown in Table 2. The shear storage modulus shown in Table 2 for each optical adhesive sheet (having photocurability) in Examples 1 to 3 and Comparative Examples 1 and 2 is the shear storage modulus of the optical adhesive sheet before photocuring.

[0120] <Release Liner Peel Force> For each of the release-liner optical pressure-sensitive adhesive sheets of Examples 1 to 3 and Comparative Examples 1 and 2, the peel force required to peel the release liner from the optical pressure-sensitive adhesive sheet was measured (first measurement).

[0121] In preparing the test piece for the first measurement, a sample sheet (length 100 mm × width 25 mm) was first cut out from the optical pressure-sensitive adhesive sheet with a release liner. Next, the third release liner (light release liner) was peeled off from the sample sheet, and the exposed surface of the optical pressure-sensitive adhesive sheet was attached to a glass plate to obtain a test piece.

[0122] Next, the test piece was left to stand at 25°C for 60 minutes, and then a peel test was conducted in which the first release liner (heavy release liner) of the test piece was peeled from the PSA sheet, and the force required for peeling was measured as the peel force. In this measurement, a tensile tester (product name "Autograph AG-50NX plus" manufactured by Shimadzu Corporation) was used, and the measurement temperature was 25°C, the peel angle was 180°, and the pulling speed was 300 mm / min (the same applies to the second measurement described below). The measured peel force F1 (N / 25 mm) is shown in Table 2.

[0123] On the other hand, for each of the optical pressure-sensitive adhesive sheets with release liner of Examples 1 to 3 and Comparative Examples 1 and 2, the peel force required to peel the light release liner from the optical pressure-sensitive adhesive sheet was measured (second measurement).

[0124] In preparing the test piece for the second measurement, a sample sheet (length 100 mm × width 25 mm) was first cut out from the optical pressure-sensitive adhesive sheet with a release liner. Next, the first release liner side of the sample sheet (heavy release liner) was bonded to a glass plate with double-sided strong adhesive tape to obtain a test piece.

[0125] Next, the test piece was left to stand at 25°C for 60 minutes, after which a peel test was conducted in which the third release liner (light release liner) of the test piece was peeled from the PSA sheet, and the force required for peeling was measured as the peel force. The measured peel force F2 (N / 25mm) is shown in Table 2. The difference F1-F2 (N / 25mm) between the peel force F1 and the peel force F2, and the ratio of the peel force F1 to the peel force F2 (F1 / F2) are also shown in Table 2.

[0126] <Probe Tack Test> A probe tack test was carried out on each of the optical pressure-sensitive adhesive sheets with release liners of Examples 1 to 3 and Comparative Examples 1 and 2 as follows.

[0127] First, a 20 mm x 40 mm optical pressure-sensitive adhesive sheet with a release liner was cut out as a test piece from a pressure-sensitive adhesive sheet with a release liner. Next, the test piece was set on the measurement table of a tack tester (product name "TAC-1000", manufactured by Rhesca Co., Ltd.). Specifically, the first release liner side of the test piece was attached to the measurement table via a predetermined strong adhesive. Next, the third release liner was peeled off from the optical pressure-sensitive adhesive sheet of the test piece to expose one side (the second side) of the optical pressure-sensitive adhesive sheet. Then, a probe tack test was performed using the same tester.

[0128] In the probe tack test, a cylindrical stainless steel probe with a tip diameter (probe diameter) of 2.5 mm was used as the probe pressed against the optical pressure-sensitive adhesive sheet. The tip area of ​​this probe was 19.63 mm ２ In this test, the ambient temperature and the probe temperature were 25 ° C., the pressing speed was 0.08 mm / sec, the pressing load was 1000 gf, the pressing time was 30 seconds, and the peeling speed was 0.08 mm / sec. That is, in this test, first, the tip of the probe (diameter 2.5 mm) was pressed perpendicularly to the optical adhesive sheet from above at a pressing speed of 0.08 mm / sec until the pressing load reached 1000 gf. Then, the pressing load of 1000 gf was maintained for 30 seconds. Then, the probe was peeled upward from the optical adhesive sheet at a peeling speed of 0.08 mm / sec (peeling process). During this time, the load acting on the probe was measured as the stress of the optical adhesive sheet.

[0129] The measurement results of Examples 1 to 3 and Comparative Example 1 are shown in Figures 6 to 9. Figure 6 shows a stress-peel distance curve obtained by a probe tack test on the optical adhesive sheet with a release liner of Example 1. In the graph of Figure 6, the horizontal axis represents the probe peel distance (µm), and the vertical axis represents stress (gf) (the same applies to the graphs of Figures 7 to 9). The probe peel distance is the rise distance of the probe tip surface during the probe peeling process (the height-wise movement distance from the position of the second surface of the optical adhesive sheet at the start of peeling). Figure 7 shows a stress-peel distance curve obtained by a probe tack test on the optical adhesive sheet with a release liner of Example 2. Figure 8 shows a stress-peel distance curve obtained by a probe tack test on the optical adhesive sheet with a release liner of Example 3. Figure 9 shows a stress-peel distance curve obtained by a probe tack test on the optical adhesive sheet with a release liner of Comparative Example 1. For the probe tack test of each of the optical pressure-sensitive adhesive sheets with release liner of Examples 1 to 3 and Comparative Examples 1 and 2, the probe peel distance d (μm) when the stress became 0 gf during the probe peeling process is shown in Table 2.

[0130] <Suppression of Peeling of Heavy Release Liner When Peeling Light Release Liner> For each of the release liner-attached optical pressure-sensitive adhesive sheets of Examples 1 to 3 and Comparative Examples 1 and 2, the difficulty of peeling the heavy release liner when peeling the light release liner was examined.

[0131] Specifically, first, 10 evaluation samples were prepared for each optically adhesive sheet with a release liner. Next, the evaluation samples were fixed on a predetermined stage. Specifically, the first release liner (heavy release liner) side of the evaluation sample was fixed to the stage via double-sided adhesive tape (product name "TESA68547", manufactured by TESA). Next, the end of the third release liner (light release liner) of the evaluation sample on the stage was pinched with the fingertips, and the third release liner was peeled off. During the peeling, the peel angle was approximately 45°, and the pulling speed was approximately 300 mm / min. Regarding the prevention of peeling of the first release liner (heavy release liner) when peeling the third release liner (light release liner), if the number of evaluation samples in which only the third release liner could be properly peeled off without peeling of the first release liner was 10, it was evaluated as "A," if it was 7 to 9, it was evaluated as "B," and if it was 0 to 6, it was evaluated as "C." The evaluation results are shown in Table 2.

[0132] <Bump-Conforming Ability Test> The bump-conforming ability of each of the optical pressure-sensitive adhesive sheets in Examples 1 to 3 and Comparative Examples 1 and 2 was examined as follows.

[0133] First, a second sample sheet (75 mm x 45 mm) was cut out from the optical adhesive sheet with a release liner. Next, the third release liner (light release liner) was peeled off from the optical adhesive sheet in the second sample sheet, and the exposed surface of the optical adhesive sheet thus exposed was bonded to the center of a PET film (thickness 125 μm, 100 mm x 50 mm). For bonding, a roll laminator was used, the inter-roll pressure was 0.2 MPa, and the feed rate was 100 mm / min (the same applies to the bonding described below). Next, the first release liner (heavy release liner) was peeled off from the optical adhesive sheet on the PET film, and the exposed surface of the optical adhesive sheet thus exposed was bonded to a glass plate (thickness 500 μm, length 100 mm x width 50 mm) with a printed layer to obtain a bonded structure. Figure 11 shows the positional relationship between the glass plate 71 and the optical adhesive sheet 72 derived from the second sample sheet in the bonded structure. A printed layer 73 (45 μm thick, black ink) is formed on one thickness-wise surface of the glass plate 71 around the entire edge of the glass plate 71. The printed layer 73 is formed in a range of 15 mm inward from each end of the glass plate 71 in the length direction D1, and in a range of 5 mm inward from each end of the glass plate 71 in the width direction D2. The optical adhesive sheet 72 is attached to the center of one thickness-wise surface of the glass plate 71 and is in contact with the printed layer 73 around the entire edge of the sheet. In other words, the printed layer 73 on the glass plate 71 is sandwiched between the glass plate 71 and the optical adhesive sheet 72 within a range of 2.5 mm outward from the inner edge of the printed layer 73.

[0134] Next, the bonded structure was autoclaved for 30 minutes under conditions of 50°C and 0.5 MPa. After this, the vicinity of the inner edge of the printed layer in the bonded structure was observed. Specifically, the inside of the inner edge of the printed layer (the area where the optical pressure-sensitive adhesive sheet should be in close contact with the glass plate) was observed from the PET film side of the bonded structure using a digital microscope at an observation magnification of 20. Then, for the step-conforming ability of the optical pressure-sensitive adhesive sheet, if no bubbles were observed within the observed range, it was evaluated as "A," and if bubbles were observed, it was evaluated as "B." The results are shown in Table 2.

[0135]

[0136]

[0137] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0138] The pressure-sensitive adhesive sheet 10 (optical pressure-sensitive adhesive sheet) of the present invention is suitably used in light-transmitting portions of display panels, such as liquid crystal display panels and organic EL display panels.

[0139] X Optical adhesive sheet with release liner H Thickness direction 10 Adhesive sheet (optical adhesive sheet) 11 First surface 12 Second surface 20 Release liner (heavy release liner) 21, 31 Release surface 30 Release liner (light release liner)

Claims

1. An optically pressure-sensitive adhesive sheet having a first surface and a second surface opposite to the first surface, a release liner that is removably adhered to the first surface, and a light release liner that is removably adhered to the second surface, the optically pressure-sensitive adhesive sheet comprising a base polymer, a photopolymerizable polyfunctional compound, and a photoinitiator, and in a probe tack test under the following conditions on the second surface after peeling the light release liner from the optically pressure-sensitive adhesive sheet, the probe peeling distance at which the stress becomes 0 gf during the probe peeling process is 200 μm or more and 900 μm or less. [Conditions] Temperature: 25°C Probe diameter: 2.5 mm Pressing load: 1000 gf Pressing time: 30 seconds Peeling speed: 0.08 mm / second 2. The optically pressure-sensitive adhesive sheet with a release liner according to claim 1, wherein the photopolymerizable polyfunctional compound contains a photopolymerizable polyfunctional compound having an aromatic ring.

3. The optically pressure-sensitive adhesive sheet with a release liner according to claim 1, wherein the weight average molecular weight of the photopolymerizable polyfunctional compound is 1000 or less.

4. The optically pressure-sensitive adhesive sheet with a release liner according to any one of claims 1 to 3, wherein the gel fraction is 50% by mass or more.

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