Optical pressure-sensitive adhesive sheet

Abstract

This pressure-sensitive adhesive sheet (10) comprises a base polymer, a polyfunctional monomer, and a photopolymerization initiator. The base polymer is a photopolymerization product of a polymerizable component comprising a monofunctional monomer and a photopolymerizable polyfunctional compound. The polyfunctional monomer includes a polyfunctional monomer containing a cyclic structure.

Description

Optical adhesive sheet

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

[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 the display panel, for example, an optically transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure. Optical adhesive sheets for display panel applications are described in, for example, Patent Document 1 listed below.

[0003] JP 2010-97070 A

[0004] The laminated structure of a display panel includes elements having 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. The printed layer is provided, for example, around the entire edge of the cover glass. This printed layer has a predetermined thickness. Therefore, on the pixel panel side of the cover glass, there is a step (printed step) between the cover glass surface and the printed layer surface. Therefore, optical adhesive sheets used for display panels are required to be soft enough to follow the printed step (step-following ability). Insufficient step-following ability of the optical adhesive sheet can, for example, cause air bubbles to form along the printed layer between the optical 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, the softer a conventional optical pressure-sensitive adhesive sheet is, the lower its cohesiveness is, and therefore bubbles are likely to form at the interface between the adherend and the optical pressure-sensitive adhesive sheet to which the optical pressure-sensitive adhesive sheet is attached (the bubbles are formed, for example, by foreign matter as a nucleus).

[0006] Therefore, from the viewpoint of suppressing bubbles, high elasticity is required for the optical adhesive sheet (i.e., the adhesive that forms the optical adhesive sheet). However, the higher the elasticity of a conventional optical adhesive sheet, the more likely stress is concentrated at the interface between the optical adhesive sheet and the adherend to which the optical adhesive sheet is bonded. When such stress is concentrated on the optical adhesive sheet, the optical adhesive sheet is likely to peel off from the adherend, which is undesirable (reduced bonding reliability). For example, in the manufacturing process of a display panel, when the above-mentioned stress is concentrated on the adhesive sheet after bonding two components with the optical adhesive sheet, physical stimulation to the edge of the adhesive sheet may trigger peeling between the components, which is undesirable.

[0007] Optical pressure-sensitive adhesive sheets are required to have a pressure-sensitive adhesive design that not only has good conformability to unevenness when bonding adherends, but also has high elasticity to suppress bubbles at the interface with the adherend and stress relaxation properties to suppress peeling at the interface. The inventors have considered optical pressure-sensitive adhesive sheets in this way and have arrived at the present invention.

[0008] The present invention provides an optical pressure-sensitive adhesive sheet that achieves good conformability to unevenness when bonding adherends together, and is suitable for both suppressing air bubbles and ensuring bonding reliability after bonding between adherends.

[0009] The present invention [1] includes an optical adhesive sheet comprising a base polymer, a polyfunctional monomer, and a photopolymerization initiator, wherein the base polymer is a photopolymer of a polymerizable component comprising a monofunctional monomer and a photopolymerizable polyfunctional compound, and the polyfunctional monomer comprises a cyclic structure-containing polyfunctional monomer.

[0010] The present invention [2] includes the optical pressure-sensitive adhesive sheet according to the above [1], wherein the cyclic structure-containing polyfunctional monomer includes an alicyclic polyfunctional monomer.

[0011] The present invention [3] includes an optical adhesive sheet described in [1] or [2] above, in which the cyclic structure-containing polyfunctional monomer is at least one selected from the group consisting of tricyclodecane dimethanol diacrylate, tricyclodecane dimethanol dimethacrylate, and tris(2-acryloyloxyethyl) isocyanurate.

[0012] The present invention [4] includes an optical adhesive sheet described in any one of [1] to [3] above, in which the content of the cyclic structure-containing polyfunctional monomer per 100 mass parts of the base polymer is 5 mass parts or more and 50 mass parts or less.

[0013] As described above, the optical adhesive sheet of the present invention contains a base polymer, a polyfunctional monomer, and a photopolymerization initiator. Such an optical adhesive sheet can be attached to the stepped surface of an adherend in a soft state before being cured by light irradiation (photocuring) (it can be photocured after attachment). Therefore, the optical adhesive sheet is suitable for achieving good step-following ability when attached to an adherend having a stepped surface.

[0014] Furthermore, in the optical pressure-sensitive adhesive sheet of the present invention, as described above, the base polymer is a photopolymer of a polymerizable component containing a monofunctional monomer and a photopolymerizable polyfunctional compound. Such a base polymer has a network structure in which linear units derived from the monofunctional monomer are connected by the photopolymerizable polyfunctional compound. When the optical pressure-sensitive adhesive sheet is irradiated with light, a photopolymerization reaction of a polyfunctional monomer (including a cyclic structure-containing polyfunctional monomer) proceeds around the base polymer of such a network structure. Therefore, the photopolymerization product of the polyfunctional monomer is formed while forming an interpenetrating polymer network (IPN) with the network-structured base polymer. This increases the elasticity of the optical pressure-sensitive adhesive sheet. Furthermore, a cyclic structure-containing polyfunctional monomer is bulkier than a polyfunctional monomer not containing a cyclic structure. Therefore, the network structure formed by the polymerization reaction of a polyfunctional monomer containing a cyclic structure-containing polyfunctional monomer has a larger mesh size than the network structure formed by the polymerization reaction of a polyfunctional monomer not containing a cyclic structure-containing polyfunctional monomer. This is suitable for achieving both high elasticity and stress relaxation properties in the optical pressure-sensitive adhesive sheet after photocuring. Furthermore, the combination of high elasticity and stress relaxation properties in the optical pressure-sensitive adhesive sheet after photocuring that bonds adherends helps to achieve both the above-mentioned bubble suppression and bonding reliability.

[0015] Therefore, the optical pressure-sensitive adhesive sheet of the present invention achieves good conformability to unevenness when bonding adherends together, and is suitable for both suppressing air bubbles and ensuring bonding reliability after bonding between adherends.

[0016] 1 is a cross-sectional schematic diagram of an embodiment of the optical adhesive sheet of the present invention. It shows an example of a method for producing the optical adhesive sheet shown in FIG. 1. FIG. 2A shows a process for forming a coating film of a pressure-sensitive adhesive composition, FIG. 2B shows a process for forming a base adhesive sheet, FIG. 2C shows a process for peeling one of the release liners, FIG. 2D shows a process for supplying a post-added component to the base adhesive sheet, and FIG. 2E shows a process for laminating a release liner to an adhesive sheet. It shows an example of a method for using the optical adhesive sheet shown in FIG. 1. FIG. 3A shows a process for laminating an optical adhesive sheet to a member (adherend), FIG. 3B shows a process for joining members together via the optical adhesive sheet, and FIG. 3C shows a process for photocuring the optical adhesive sheet between members. It shows the positional relationship between the glass plate and the adhesive sheet in the laminate used to evaluate the step-following ability of the examples and comparative examples.

[0017] As shown in Figure 1, a pressure-sensitive adhesive sheet 10 according to one embodiment of the present invention has a sheet shape of a predetermined thickness and extends in a direction (plane direction) perpendicular to the thickness direction H. The pressure-sensitive adhesive sheet 10 has an adhesive surface 11 (first adhesive surface) and an adhesive surface 12 (second adhesive surface) opposite to the adhesive surface 11. Figure 1 exemplarily shows a state in which release liners 21 and 22 are bonded to the adhesive surfaces 11 and 12 of the pressure-sensitive adhesive sheet 10. The release liner 21 is in releasable contact with the adhesive surface 11. The release liner 22 is in releasable contact with the adhesive surface 12.

[0018] The adhesive sheet 10 is an optically transparent adhesive sheet (optical adhesive sheet). The adhesive sheet 10 contains a base polymer, a polyfunctional monomer, and a photopolymerization initiator, and is photocurable. Such an 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.

[0019] The base polymer in the pressure-sensitive adhesive sheet 10 is a photopolymer of a polymerizable component containing a monofunctional monomer and a photopolymerizable multifunctional compound. Photopolymerization is a polymerization method in which the polymerization reaction of the polymerizable component is promoted by irradiation with active energy rays such as ultraviolet light. A photopolymer is a product formed by such a polymerization method. Such a base polymer has a network structure in which linear units derived from the monofunctional monomer are linked by the photopolymerizable multifunctional compound as a crosslinking agent.

[0020] The base polymer is preferably an acrylic polymer. The acrylic polymer is a copolymer of polymerizable components containing 50% by mass or more of a (meth)acrylic acid alkyl ester. That is, the monofunctional monomer preferably contains a (meth)acrylic acid alkyl ester. "(Meth)acrylic" means acrylic and / or methacrylic.

[0021] The (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms. Examples of such (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, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and (meth)acrylic acid. Examples of the alkyl (meth)acrylate include nonyl, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, n-octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate. The alkyl (meth)acrylate may be used alone or in combination of two or more. The alkyl (meth)acrylate is preferably at least one selected from the group consisting of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

[0022] The proportion of the (meth)acrylic acid alkyl ester in the monofunctional monomer is preferably 60% by mass or more, more preferably 62% by mass or more, more preferably 64% by mass or more, more preferably 65% ​​by mass or more, more preferably 67% by mass or more, more preferably 68% by mass or more, and more preferably 70% 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, 99.9% by mass or less, 99.5% by mass or less, or 99% by mass or less.

[0023] The monofunctional monomer may include a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. 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 ensuring the cohesive strength of the acrylic polymer. The polar group-containing monomer is preferably at least one selected from the group consisting of hydroxy group-containing monomers and monomers having a nitrogen atom-containing ring.

[0024] 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 (2HEA) and 4-hydroxybutyl acrylate (4HBA).

[0025] The proportion of the hydroxy group-containing monomer in the monofunctional monomer is preferably 1% by mass or more, more preferably 2% by mass or more, more preferably 3% by mass or more, more preferably 5% by mass or more, more preferably 6% by mass or more, more preferably 7% by mass or more, and more preferably 8% 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 relates to the compatibility between the acrylic polymer and various additive components in the pressure-sensitive adhesive sheet 10), this proportion is preferably 30% by mass or less, more preferably 28% by mass or less, more preferably 26% by mass or less, more preferably 24% by mass or less, more preferably 22% by mass or less, more preferably 20% by mass or less, more preferably 18% by mass or less, more preferably 16% by mass or less, and more preferably 15% by mass or less.

[0026] 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.

[0027] From the viewpoint of avoiding the risk of corrosion of the adherend by acid, the proportion of the carboxyl group-containing monomer in the monofunctional monomer is preferably 3 mass % or less, more preferably 1 mass % or less, even more preferably 0.5 mass % or less, and even more preferably 0.1 mass % or less.

[0028] 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 (NVP) and acryloylmorpholine (ACMO).

[0029] The proportion of the monomer having a nitrogen atom-containing ring in the monofunctional monomer is preferably 1% by mass or more, more preferably 2% by mass or more, more preferably 3% by mass or more, more preferably 5% by mass or more, more preferably 6% by mass or more, more preferably 7% by mass or more, and more preferably 8% by mass or more, from the viewpoints of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10 and ensuring the adhesion to the adherend in the pressure-sensitive adhesive sheet 10. 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 pressure-sensitive adhesive sheet), this proportion is preferably 30% by mass or less, more preferably 28% by mass or less, more preferably 26% by mass or less, more preferably 24% by mass or less, more preferably 22% by mass or less, and more preferably 20% by mass or less.

[0030] Examples of the photopolymerizable polyfunctional compound include polyfunctional oligomers and polyfunctional monomers.

[0031] 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.

[0032] From the viewpoint of compatibility between the monofunctional monomer and the polyfunctional oligomer, 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. The weight average molecular weight is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0033] Examples of polyfunctional monomers include polyfunctional (meth)acrylates containing two or more ethylenically unsaturated double bonds in one molecule. Polyfunctional (meth)acrylates are preferred as polyfunctional monomers because they facilitate the introduction of crosslinked structures by photopolymerization. Examples of polyfunctional (meth)acrylates include bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

[0034] 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, and di(meth)acryloyl isocyanurate.

[0035] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0036] 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.

[0037] The photopolymerizable polyfunctional compound may be used alone or in combination of two or more kinds. The photopolymerizable polyfunctional compound is preferably a polyfunctional oligomer, more preferably a urethane acrylate oligomer.

[0038] The amount of the photopolymerizable polyfunctional compound per 100 parts by mass of the monofunctional monomer is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of realizing good bonding reliability in the adhesive sheet 10 after photocuring that bonds adherends. The amount of the photopolymerizable polyfunctional compound per 100 parts by mass of the monofunctional monomer is preferably 2.0 parts by mass or less, more preferably 1.8 parts by mass or less, more preferably 1.6 parts by mass or less, more preferably 1.4 parts by mass or less, more preferably 1.2 parts by mass or less, more preferably 1.0 parts by mass or less, and more preferably 0.8 parts by mass or less, from the viewpoint of ensuring softness and realizing good step-following ability in the adhesive sheet 10 before photocuring.

[0039] The base polymer can be formed by photopolymerizing a polymerizable component containing a monofunctional monomer and a photopolymerizable multifunctional compound. Examples of photopolymerization include photopolymerization by ultraviolet irradiation. The polymerizable components (monofunctional monomer, photopolymerizable multifunctional compound) may be polymerized in one step or in multiple steps. In the multistep polymerization method, the monofunctional monomer is first polymerized (prepolymerization), thereby preparing a prepolymer composition containing a partial polymer (a mixture of a low-polymerization polymer and unreacted monofunctional monomer). Next, the photopolymerizable multifunctional compound is added to the prepolymer composition, and a polymerization reaction is then carried out in a reaction system containing the partial polymer and the photopolymerizable multifunctional compound (main polymerization). A photopolymerization initiator is used as the polymerization initiator.

[0040] Examples of the photopolymerization initiator include a radical photopolymerization initiator, a cationic photopolymerization initiator, and an anionic photopolymerization initiator.

[0041] 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.

[0042] 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-2-phenylacetophenone. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 1-hydroxycyclohexylphenyl 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 benzil. Examples of benzophenone photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. Examples of ketal photopolymerization initiators include benzil dimethyl ketal. Examples of the thioxanthone photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone. The photopolymerization initiators may be used alone or in combination of two or more.The photopolymerization initiator is preferably at least one selected from the group consisting of bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2-dimethoxy-2-phenylacetophenone, and 1-hydroxycyclohexyl phenyl ketone.

[0043] The amount of the photopolymerization initiator (first photopolymerization initiator) used in the preliminary polymerization (the total amount of the photopolymerization initiators when multiple photopolymerization initiators are used) is, relative to 100 parts by mass of the monofunctional monomer, for example, 0.02 parts by mass or more, preferably 0.04 parts by mass or more, and more preferably 0.06 parts by mass or more, and is, for example, 1.0 part by mass or less, preferably 0.8 parts by mass or less, more preferably 0.6 parts by mass or less, more preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, more preferably 0.3 parts by mass or less, more preferably 0.2 parts by mass or less, and more preferably 0.1 parts by mass or less. The amount of the photopolymerization initiator (second photopolymerization initiator) used in the main polymerization (the total amount of the photopolymerization initiators when multiple photopolymerization initiators are used) is, relative to 100 parts by mass of the polymerizable component (monofunctional monomer, photopolymerizable polyfunctional compound), for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more, and is, for example, 2.0 parts by mass or less, preferably 1.8 parts by mass or less, more preferably 1.6 parts by mass or less, more preferably 1.4 parts by mass or less, more preferably 1.2 parts by mass or less, more preferably 1.0 part by mass or less, and more preferably 0.8 parts by mass or less.

[0044] The weight average molecular weight (Mw) of the base polymer is preferably 500,000 or more, more preferably 600,000 or more, and even more preferably 800,000 or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet 10. The weight average molecular weight of the base polymer is preferably 1,200,000 or less, more preferably 1,100,000 or less, and even more preferably 1,000,000 or less, from the viewpoint of ensuring the step-conforming ability of the pressure-sensitive adhesive sheet 10. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in polystyrene equivalent terms.

[0045] From the viewpoint of ensuring sufficient flexibility in the pressure-sensitive adhesive sheet 10 before photocuring, the glass transition temperature (Tg) of the base polymer is preferably 10°C or lower, more preferably 8°C or lower, more preferably 6°C or lower, more preferably 4°C or lower, more preferably 2°C or lower, more preferably 0°C or lower, more preferably -2°C or lower, more preferably -4°C or lower, more preferably -6°C or lower, more preferably -8°C or lower, more preferably -10°C or lower, more preferably -12°C or lower, more preferably -14°C or lower, more preferably -16°C or lower, more preferably -18°C or lower, more preferably -20°C or lower, more preferably -22°C or lower, more preferably -24°C or lower, more preferably -26°C or lower, more preferably -28°C or lower, more preferably -30°C or lower, more preferably -32°C or lower, more preferably -34°C or lower, more preferably -36°C or lower, more preferably -38°C or lower, more preferably -40°C or lower. The glass transition temperature is, for example, -80°C or higher.

[0046] The glass transition temperature of the base polymer may be determined using the theoretical glass transition temperature (Tg) calculated based on the Fox formula below. The Fox formula is a relationship between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of a homopolymer of the monomers constituting the polymer. In the Fox formula below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of the monomer i constituting the polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from the monomer i. Literature values ​​can be used for the glass transition temperature of the homopolymer. For example, the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) lists the glass transition temperatures of various homopolymers. Meanwhile, 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 formula: 1 / (273 + Tg) = Σ[Wi / (273 + Tgi)]

[0047] The polyfunctional monomer in the pressure-sensitive adhesive sheet 10 includes a cyclic structure-containing polyfunctional monomer. Examples of cyclic structure-containing polyfunctional monomers include alicyclic polyfunctional monomers and aromatic ring-containing polyfunctional monomers. The cyclic structure of the alicyclic polyfunctional monomer may be a single ring, a condensed ring of multiple rings, or a crosslinked ring structure. That is, the alicyclic polyfunctional monomer may be a single ring alicyclic polyfunctional monomer with or without a crosslinked structure, or a condensed ring alicyclic polyfunctional monomer with or without a crosslinked structure. Examples of the cyclic structure of the alicyclic polyfunctional monomer include norbornane, tricyclodecane, tetracyclododecane, pentacyclopentadecane, adamantane, and diamantane. The cyclic structure of the aromatic ring-containing polyfunctional monomer may be a single ring, a condensed ring of multiple rings, or a crosslinked ring structure. That is, the aromatic ring-containing polyfunctional monomer may be a monocyclic aromatic ring-containing polyfunctional monomer with or without a crosslinked structure, or a fused ring aromatic ring-containing polyfunctional monomer with or without a crosslinked structure. The cyclic structure-containing polyfunctional monomer may be a bifunctional monomer or a trifunctional or higher functional monomer.

[0048] Examples of the alicyclic polyfunctional monomer include tricyclodecane dimethanol diacrylate, tricyclodecane dimethanol dimethacrylate, tris(2-acryloyloxyethyl) isocyanurate, and bis(vinylsulfone)tricyclo[5.2.1.0 2,6 ]decane. An example of an aromatic ring-containing polyfunctional monomer is ethoxylated bisphenol A diacrylate (BPAEODE). The cyclic structure-containing polyfunctional monomer is preferably an alicyclic polyfunctional monomer, more preferably a fused ring alicyclic polyfunctional monomer, even more preferably a fused ring alicyclic polyfunctional monomer having a crosslinked structure, and even more preferably at least one selected from the group consisting of tricyclodecane dimethanol diacrylate and tricyclodecane dimethanol dimethacrylate.

[0049] The entanglement point molecular weight Me of the homopolymer of the cyclic structure-containing polyfunctional monomer is preferably 10 or more, more preferably 20 or more, more preferably 40 or more, more preferably 60 or more, more preferably 80 or more, more preferably 100 or more, from the viewpoint of the balance between the high elasticity and stress relaxation properties of the optical adhesive sheet after photocuring. Also, preferably 400,000 or less, more preferably 380,000 or less, more preferably 360,000 or less, more preferably 340,000 or less, more preferably 320,000 or less, more preferably 300,000 or less, more preferably 270,000 or less, more preferably 250,000 or less, more preferably 230,000 or less, more preferably 200,000 or less, more preferably 170,000 or less, more preferably 150,000 or less, more preferably 130,000 or less, more preferably 100,000 or less, more preferably 80,000 or less, more preferably 60,000 or less, more preferably 50,000 or less.

[0050] The content of the cyclic structure-containing polyfunctional monomer per 100 parts by mass of base polymer in the pressure-sensitive adhesive sheet 10 is preferably 5 parts by mass or more, more preferably 5.5 parts by mass or more, more preferably 6 parts by mass or more, more preferably 6.5 parts by mass or more, more preferably 7 parts by mass or more, more preferably 8 parts by mass or more, more preferably 9 parts by mass or more, and more preferably 10 parts by mass or more, from the viewpoint of increasing the elasticity of the pressure-sensitive adhesive sheet 10 after photocuring. The content of the cyclic structure-containing polyfunctional monomer per 100 parts by mass of base polymer in the pressure-sensitive adhesive sheet 10 is preferably 50 parts by mass or less, more preferably 48 parts by mass or less, more preferably 46 parts by mass or less, more preferably 45 parts by mass or less, more preferably 43 parts by mass or less, more preferably 41 parts by mass or less, and more preferably 40 parts by mass or less, from the viewpoint of the stress relaxation properties of the pressure-sensitive adhesive sheet 10 after photocuring.

[0051] The polyfunctional monomer may include a polyfunctional monomer that does not contain a cyclic structure (a polyfunctional monomer that does not contain a cyclic structure). Examples of such polyfunctional monomers include the polyfunctional monomers described above as polyfunctional monomers that serve as photopolymerizable polyfunctional compounds. From the viewpoint of the stress relaxation properties of the pressure-sensitive adhesive sheet 10 after photocuring, the pressure-sensitive adhesive sheet 10 preferably does not include a polyfunctional monomer that does not contain a cyclic structure.

[0052] Examples of the photopolymerization initiator (third photopolymerization initiator) in the adhesive sheet 10 include radical photopolymerization initiators, cationic photopolymerization initiators, and anionic photopolymerization initiators, and specifically include the photopolymerization initiators described above with respect to the photopolymerization of the base polymer.

[0053] From the viewpoint of ensuring good photocurability in the pressure-sensitive adhesive sheet 10, the content of the photopolymerization initiator (third photopolymerization initiator) in the pressure-sensitive adhesive sheet 10 is, per 100 parts by mass of the base polymer, preferably 0.1 parts by mass or more, more preferably 0.15 parts by mass or more, more preferably 0.18 parts by mass or more, more preferably 0.2 parts by mass or more, more preferably 0.22 parts by mass or more, more preferably 0.24 parts by mass or more, more preferably 0.25 parts by mass or more, and is also preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less, more preferably 2.6 parts by mass or less, more preferably 2.4 parts by mass or less, more preferably 2.2 parts by mass or less, more preferably 2.0 parts by mass or less, more preferably 1.9 parts by mass or less, more preferably 1.8 parts by mass or less, more preferably 1.7 parts by mass or less, more preferably 1.6 parts by mass or less, more preferably 1.5 parts by mass or less, more preferably 1.3 parts by mass or less, and more preferably 1.0 parts by mass or less.

[0054] The pressure-sensitive adhesive sheet 10 may contain other components, such as an oligomer, an ultraviolet absorber, an antioxidant, a silane coupling agent, and a rust inhibitor.

[0055] When the base polymer is an acrylic polymer, the oligomer is preferably an acrylic oligomer, which is a copolymer of polymerizable components containing 50% by mass or more of a (meth)acrylic acid ester and has a weight-average molecular weight of, for example, 1,000 to 30,000.

[0056] The acrylic oligomer is preferably a polymer of polymerizable 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 described above as the polymerizable component of the acrylic polymer.

[0057] As the chain alkyl (meth)acrylate, methyl methacrylate is preferred because of its high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. That is, the acrylic oligomer is preferably a polymer of a polymerizable component containing methyl methacrylate and one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate.

[0058] The proportion of alicyclic alkyl (meth)acrylate in the polymerizable component of the acrylic oligomer is preferably 10% by mass or more, more preferably 12% by mass or more, more preferably 14% by mass or more, more preferably 16% by mass or more, more preferably 18% by mass or more, more preferably 20% by mass or more, more preferably 22% by mass or more, more preferably 24% by mass or more, more preferably 26% by mass or more, more preferably 28% by mass or more, more preferably 30% by mass or more, and is preferably 90% by mass or less, more preferably 88% by mass or less, more preferably 86% by mass or less, more preferably 84% by mass or less, more preferably 82% by mass or less, more preferably 80% by mass or less, more preferably 78% by mass or less, more preferably 76% by mass or less, more preferably 74% by mass or less, more preferably 72% by mass or less, and more preferably 70% by mass or less. The proportion of chain alkyl (meth)acrylate in the polymerizable component of the acrylic oligomer is preferably 90% by mass or less, more preferably 88% by mass or less, more preferably 86% by mass or less, more preferably 84% by mass or less, more preferably 82% by mass or less, more preferably 80% by mass or less, more preferably 78% by mass or less, more preferably 76% by mass or less, more preferably 74% by mass or less, more preferably 72% by mass or less, and more preferably 70% by mass or less. The proportion is preferably 10% by mass or more, more preferably 12% by mass or more, more preferably 14% by mass or more, more preferably 16% by mass or more, more preferably 18% by mass or more, more preferably 20% by mass or more, more preferably 22% by mass or more, more preferably 24% by mass or more, more preferably 26% by mass or more, more preferably 28% by mass or more, and more preferably 30% by mass or more.

[0059] The acrylic oligomer is obtained by polymerizing the polymerizable components of the acrylic oligomer. Examples of polymerization methods include solution polymerization, bulk polymerization, and emulsion polymerization. The acrylic oligomer is preferably formed by solution polymerization. Examples of solvents used in solution polymerization include toluene and ethyl acetate. Polymerization of the acrylic oligomer may use a thermal polymerization initiator, or a chain transfer agent for the purpose of adjusting the molecular weight. In this embodiment, after the acrylic oligomer is formed, low-molecular-weight components and the solvent are volatilized and removed from the reaction system, such as the reaction solution, by heating. Examples of low-molecular-weight components include unreacted monomers, chain transfer agents, thermal polymerization initiators, and their decomposition products (residues).

[0060] 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, and 2,2'-azobis(2-methylpropionate)dimethyl. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

[0061] 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.

[0062] From the viewpoint of ensuring the adhesive strength of the pressure-sensitive adhesive sheet 10, the weight average molecular weight (Mw) of the oligomer is preferably 1000 or more, more preferably 1200 or more, more preferably 1400 or more, more preferably 1500 or more, more preferably 1700 or more, more preferably 1800 or more, more preferably 2000 or more, and also preferably 30,000 or less, more preferably 27,000 or less, more preferably 25,000 or less, more preferably 23,000 or less, more preferably 20,000 or less, more preferably 17,000 or less, more preferably 15,000 or less, more preferably 13,000 or less, more preferably 10,000 or less, more preferably 8,000 or less. The weight average molecular weight of the oligomer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene. The method for measuring the Mw of the oligomer is specifically described below in the examples.

[0063] The content of the oligomer in the pressure-sensitive adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, more preferably 0.09 parts by mass or more, more preferably 0.1 parts by mass or more, more preferably 0.12 parts by mass or more, more preferably 0.14 parts by mass or more, more preferably 0.16 parts by mass or more, more preferably 0.18 parts by mass or more, and more preferably 0.2 parts by mass or more, per 100 parts by mass of the base polymer, from the viewpoint of ensuring the adhesive strength of the pressure-sensitive adhesive sheet 10. The content of the oligomer in the pressure-sensitive adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4.7 parts by mass or less, more preferably 4.5 parts by mass or less, more preferably 4.3 parts by mass or less, more preferably 4 parts by mass or less, more preferably 3.7 parts by mass or less, more preferably 3.6 parts by mass or less, and more preferably 3.5 parts by mass or less, per 100 parts by mass of the base polymer, from the viewpoint of ensuring the transparency of the pressure-sensitive adhesive sheet 10.

[0064] 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 nm to 370 nm and excellent compatibility with acrylic polymers. The ultraviolet absorbers may be used alone or in combination of two or more.

[0065] 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).

[0066] The content of the UV absorber in the pressure-sensitive adhesive sheet 10 is preferably 0.5 parts by mass or more, more preferably 0.6 parts by mass or more, more preferably 0.7 parts by mass or more, more preferably 0.8 parts by mass or more, more preferably 0.85 parts by mass or more, more preferably 0.9 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the base polymer, and is also preferably 15 parts by mass or less, more preferably 13 parts by mass or less, more preferably 11 parts by mass or less, more preferably 10 parts by mass or less, more preferably 8 parts by mass or less, more preferably 6 parts by mass or less, more preferably 5 parts by mass or less, more preferably 4 parts by mass or less, more preferably 3 parts by mass or less, more preferably 2 parts by mass or less, more preferably 1.8 parts by mass or less, more preferably 1.6 parts by mass or less, and more preferably 1.5 parts by mass or less. Such a configuration is preferable from the viewpoint of achieving both UV-blocking function for device protection and photocurability in the pressure-sensitive adhesive sheet 10.

[0067] 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.

[0068] 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).

[0069] 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.

[0070] 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.

[0071] Examples of the rust inhibitor include benzotriazole compounds, such as 1,2,3-benzotriazole, 5-methylbenzotriazole, 4-methylbenzotriazole, and carboxybenzotriazole.

[0072] The content of the rust inhibitor in the adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.15 parts by mass or more, per 100 parts by mass of the base polymer, and is preferably 2 parts by mass or less, more preferably 1.7 parts by mass or less, more preferably 1.5 parts by mass or less, more preferably 1.2 parts by mass or less, more preferably 1 part by mass or less, more preferably 0.8 parts by mass or less, more preferably 0.7 parts by mass or less, more preferably 0.6 parts by mass or less, and more preferably 0.5 parts by mass or less.

[0073] From the viewpoint of ensuring sufficient adhesiveness to the adherend, the thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. From the viewpoint of the ease of handling and cutting of the pressure-sensitive adhesive sheet 10, the thickness of the pressure-sensitive adhesive sheet 10 is preferably 300 μm or less, more preferably 280 μm or less, more preferably 260 μm or less, more preferably 240 μm or less, more preferably 220 μm or less, more preferably 200 μm or less, more preferably 180 μm or less, more preferably 160 μm or less, more preferably 150 μm or less, more preferably 140 μm or less, more preferably 130 μm or less, more preferably 120 μm or less, and more preferably 115 μm or less. In particular, when the thickness of the adhesive sheet 10 is 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm or 115 μm, the coatability of the adhesive composition for forming the adhesive sheet 10 and the diffusibility of the later-added components within the adhesive sheet 10 are favorable, enabling stable production, which is preferred.

[0074] The light transmittance of the pressure-sensitive adhesive sheet 10 at a wavelength of 380 nm is preferably 10% or less, more preferably 9% or less, more preferably 8% or less, more preferably 7% or less, more preferably 6.5% or less, more preferably 6% or less, more preferably 5.5% or less, more preferably 5% or less, and is, for example, 0.05% or more. When the pressure-sensitive adhesive sheet 10 is used for a display panel, by having the light transmittance of the pressure-sensitive adhesive sheet 10 at a wavelength of 380 nm be equal to or less than the above upper limit, the pressure-sensitive adhesive sheet 10 can ensure the protection function of the display panel by blocking ultraviolet rays. Methods for adjusting the light transmittance of the pressure-sensitive adhesive sheet 10 at a wavelength of 380 nm include, for example, selecting the type and adjusting the amount of ultraviolet absorber added to the pressure-sensitive adhesive sheet 10.

[0075] Shear storage modulus G of adhesive sheet 10 at 25 ° C. １From the viewpoint of the step-following ability of the pressure-sensitive adhesive sheet 10 before photocuring, the shear storage modulus G is preferably 0.3 MPa or less, more preferably 0.25 MPa or less, more preferably 0.2 MPa or less, more preferably 0.18 MPa or less, more preferably 0.16 MPa or less, more preferably 0.15 MPa or less, more preferably 0.14 MPa or less, more preferably 0.12 MPa or less, more preferably 0.10 MPa or less, and more preferably 0.09 MPa or less. １ From the viewpoint of ensuring ease of handling of the pressure-sensitive adhesive sheet 10 before photocuring, the shear storage modulus G is preferably 0.03 MPa or more, and more preferably 0.04 MPa or more. １ Examples of methods for adjusting the shear storage modulus G include selecting the type of base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount (the shear storage modulus G ２ ,G ３ The same applies to the methods for adjusting the shear storage modulus G.) The selection of the type of base polymer involves adjusting the composition of the monomers that form the base polymer. １ The method for measuring is as described below in the examples.

[0076] The adhesive sheet 10 has an accumulated irradiation light amount of 3000 mJ / cm ２ Shear storage modulus G at 25°C after curing by light irradiation ２ From the viewpoint of suppressing the formation of bubbles between the adherend and the pressure-sensitive adhesive sheet 10 when the adherends are bonded by the pressure-sensitive adhesive sheet 10 after photocuring (from the viewpoint of suppressing bubbles), the shear storage modulus G is preferably 0.5 MPa or more, more preferably 0.55 MPa or more, more preferably 0.6 MPa or more, more preferably 0.65 MPa or more, more preferably 0.7 MPa or more, more preferably 0.8 MPa or more, more preferably 0.9 MPa or more, more preferably 1 MPa or more, more preferably 1.1 MPa or more, and more preferably 1.2 MPa or more. ２is preferably 12 MPa or less, more preferably 8 MPa or less, even more preferably 5 MPa or less, and even more preferably 3.5 MPa or less, from the viewpoint of suppressing peeling from the adherend due to the above-mentioned stress concentration in the pressure-sensitive adhesive sheet 10 attached to the adherend. ２ The method for measuring is as described below in the examples.

[0077] Shear storage modulus G １ Shear storage modulus G ２ The ratio (G ２ / G １ ) is preferably 3 or more, more preferably 5 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 100 or less, still more preferably 60 or less, and still more preferably 40 or less, from the viewpoint of the balance between the conformability to unevenness and bubble suppression.

[0078] The adhesive sheet 10 has an accumulated irradiation light amount of 3000 mJ / cm ２ Shear storage modulus G at 70 ° C after curing by light irradiation ３ is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, from the viewpoint of suppressing the formation of bubbles between the adherend and the pressure-sensitive adhesive sheet 10 in a high temperature environment in a state where the adherends are bonded together by the pressure-sensitive adhesive sheet 10 after photocuring. ３ is preferably 3 MPa or less, more preferably 2.7 MPa or less, more preferably 2.4 MPa or less, more preferably 2.1 MPa or less, more preferably 1.8 MPa or less, and more preferably 1.6 MPa or less, from the viewpoint of suppressing peeling from the adherend due to the above-mentioned stress concentration in a high-temperature environment when the pressure-sensitive adhesive sheet 10 is attached to the adherend. ３ The method for measuring is as described below in the examples.

[0079] The adhesive sheet 10 has an accumulated irradiation light amount of 3000 mJ / cm ２After curing by light irradiation, the breaking strain Bs in a tensile test under conditions of 23°C and a tensile speed of 300 mm / min is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 3.0 or more, and even more preferably 3.5 or more, from the viewpoint of ensuring stress relaxation in the pressure-sensitive adhesive sheet 10. From the viewpoint of suppressing excessive deformation of the pressure-sensitive adhesive sheet 10, the breaking strain Bs is preferably 30 or less, more preferably 28 or less, more preferably 26 or less, more preferably 24 or less, more preferably 22 or less, more preferably 20 or less, more preferably 18 or less, more preferably 16 or less, more preferably 14 or less, more preferably 12 or less, and more preferably 10 or less. The breaking strain Bs is the ratio of the initial length L of the test piece of the pressure-sensitive adhesive sheet 10 in the tensile test to the initial length L of the test piece of the pressure-sensitive adhesive sheet 10. ０ The ratio of the elongation length ΔL of the test piece at the time when the test piece broke to the elongation length ΔL (ΔL / L ０ The elongation length ΔL is the initial length L of the test piece. ０ The breaking strain Bs of the pressure-sensitive adhesive sheet 10 is the amount of elongation from the breaking strain Bs. The method for measuring the breaking strain Bs of the pressure-sensitive adhesive sheet 10 is as described below in the examples. The thickness of the pressure-sensitive adhesive sheet 10 when measuring the breaking strain Bs of the pressure-sensitive adhesive sheet 10 is 420 μm±80 μm. As long as the thickness of the pressure-sensitive adhesive sheet 10 is within the above range, an equivalent evaluation can be obtained. Alternatively, multiple pressure-sensitive adhesive sheets 10 can be manufactured separately and laminated together to make the thickness of the pressure-sensitive adhesive sheet 10 within the above range.

[0080] Shear storage modulus G ２ The ratio of the breaking strain Bs to the ２ ) is preferably 0.2 or more, more preferably 0.5 or more, more preferably 0.7 or more, more preferably 0.8 or more, more preferably 0.9 or more, more preferably 1.0 or more, more preferably 1.2 or more, more preferably 1.4 or more, more preferably 1.5 or more, more preferably 1.7 or more, more preferably 1.8 or more, more preferably 1.9 or more, from the viewpoint of the balance between the stress relaxation property and bubble suppression. Also, it is preferably 12 or less, more preferably 10 or less, more preferably 9.0 or less, more preferably 8.0 or less.

[0081] From the viewpoint of the above-mentioned bonding reliability, the adhesive sheet 10 preferably has an adhesive strength F of 2.0 N / 10 mm or more, more preferably 2.5 N / 10 mm or more, more preferably 3.0 N / 10 mm or more, more preferably 3.5 N / 10 mm or more, more preferably 4.0 N / 10 mm or more, more preferably 4.5 N / 10 mm or more, more preferably 5.0 N / 10 mm or more, more preferably 5.5 N / 10 mm or more, and more preferably 6.0 N / 10 mm or more in the peel test described below. The adhesive strength F is the adhesive strength to alkali glass (adhesion strength to alkali glass).

[0082] Peel test: First, a 100 mm long x 10 mm wide adhesive sheet piece of the adhesive sheet 10 is attached to an alkali glass plate produced by the float method to obtain a laminate. The adhesive sheet piece is attached to the air side (non-tin side) of the alkali glass plate. The air side is the exposed surface of the alkali glass plate (the surface opposite to the surface in contact with the molten metal) when the alkali glass plate flows over the molten metal in the manufacturing process of the alkali glass plate. Next, the laminate is subjected to a heat and pressure treatment under conditions of 50°C, 0.5 MPa, and 15 minutes. Next, the adhesive sheet piece in the laminate is irradiated from the alkali glass plate side with an accumulated light dose of 3000 mJ / cm. ２ The adhesive sheet piece is then irradiated with ultraviolet light under the conditions of 23°C, a peel angle of 180°, and a pulling speed of 300 mm / min, thereby peeling the adhesive sheet piece from the alkali glass plate and measuring the adhesive strength F. The method for measuring the adhesive strength F is described more specifically below in the examples.

[0083] Methods for adjusting the adhesive strength F include, for example, selecting the type of base polymer in the pressure-sensitive adhesive sheet 10, adjusting the molecular weight, adjusting the degree of crosslinking, and adjusting the blending amount. Selecting the type of base polymer includes adjusting the composition of the monomers that form the base polymer. Methods for adjusting the adhesive strength F also include selecting the types of components other than the base polymer in the pressure-sensitive adhesive sheet 10 and adjusting the blending amounts of these components. Examples of these components include photopolymerizable multifunctional compounds, photopolymerization initiators, silane coupling agents, and oligomers.

[0084] The release liner 21 is, for example, a flexible, transparent resin film. Examples of materials for the release liner 21 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, the material for the release liner 21 is preferably polyester resin, and more preferably PET.

[0085] The surface of release liner 21 facing the PSA sheet 10 may be 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 PSA sheet 10, silicone release treatments are preferred as the release treatment.

[0086] The thickness of release liner 21 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 PSA sheet 10. The thickness of release liner 21 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.

[0087] The release liner 22 is a flexible, transparent resin film. Examples of materials for the release liner 22 include the materials described above as the materials for the release liner 21. From the viewpoints of transparency and strength, the material for the release liner 22 is preferably a polyester resin, and more preferably PET.

[0088] In this embodiment, the surface of the release liner 22 facing the PSA sheet 10 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.

[0089] The thickness of the release liner 22 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 22 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.

[0090] The pressure-sensitive adhesive sheet 10 can be produced, for example, as follows.

[0091] First, a prepolymer composition is prepared. Specifically, a mixture (liquid) containing the monofunctional monomer for forming the base polymer and a photopolymerization initiator (first photopolymerization initiator) is prepared (prepolymer composition preparation step). 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 ２ The 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 and a monofunctional monomer that has not undergone a polymerization reaction (residual monomer). The prepolymer composition does not contain a solvent.

[0092] Next, a photopolymerizable polyfunctional compound (crosslinking agent), a photopolymerization initiator (second 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 oligomers, antioxidants, silane coupling agents, and rust inhibitors. This pressure-sensitive adhesive composition does not contain a solvent. That is, the pressure-sensitive adhesive composition prepared in this step is a solventless pressure-sensitive adhesive composition.

[0093] Next, as shown in Figure 2A, a coating film 10A is formed between release liners 21 and 22' (coating film forming step). Specifically, first, a pressure-sensitive adhesive composition is applied to the release surface of release liner 21 to form coating film 10A. 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. Next, the release surface of release liner 22' is laminated onto coating film 10A on release liner 21. For example, the same release liner as release liner 22 can be used as release liner 22.

[0094] Next, as shown in Figure 2B, ultraviolet light is irradiated onto the coating film 10A between the release liners 21 and 22' to form a base adhesive sheet 10B (base adhesive sheet formation step). Upon exposure to ultraviolet light, a photopolymerization reaction occurs in the coating film in a reaction system containing a monofunctional monomer (residual monomer) and a photopolymerizable multifunctional compound (crosslinking agent), forming a base polymer. Such a base polymer has a network structure in which linear units derived from the monofunctional monomer are linked by the photopolymerizable multifunctional compound.

[0095] Next, as shown in FIG. 2C, release liner 22' (FIG. 2B) is peeled off from base adhesive sheet 10B (peeling step).

[0096] Next, as shown in FIG. 2D , a later-added component is supplied to the base adhesive sheet 10B (later-added component supplying step). Specifically, 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 cyclic structure-containing polyfunctional monomer and a photopolymerization initiator (third photopolymerization initiator) described above, and may also contain other additives. Examples of other additives include an ultraviolet absorber and an antioxidant. In this step, the later-added component is allowed to penetrate the base adhesive sheet 10B from the surface thereof, and the solvent is evaporated by heating as necessary. 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 result in the formation of an orange peel surface on the base adhesive sheet 10B (it is virtually not formed). Furthermore, the base adhesive sheet 10B and the later-added component form a photocurable adhesive sheet 10. As described above, the amount of the cyclic structure-containing polyfunctional monomer added in this step is, per 100 parts by mass of the base polymer, preferably 5 parts by mass or more, more preferably 5.5 parts by mass or more, more preferably 6 parts by mass or more, more preferably 6.5 parts by mass or more, more preferably 7 parts by mass or more, more preferably 8 parts by mass or more, more preferably 9 parts by mass or more, more preferably 10 parts by mass or more, and is also preferably 50 parts by mass or less, more preferably 48 parts by mass or less, more preferably 46 parts by mass or less, more preferably 45 parts by mass or less, more preferably 43 parts by mass or less, more preferably 41 parts by mass or less, and more preferably 40 parts by mass or less.

[0097] Next, as shown in FIG. 2E, another release liner 22 is attached to the pressure-sensitive adhesive sheet 10 (attaching step).

[0098] In this manner, a pressure-sensitive adhesive sheet 10 whose adhesive surface is covered and protected by release liners 21, 22 can be produced. In the above-described production method, the pressure-sensitive adhesive sheet 10 can be produced from a solvent-free pressure-sensitive adhesive composition. Such a pressure-sensitive adhesive sheet 10 does not require the solvent to be volatilized and removed from the coating film during the sheeting process, and the occurrence of orange peel-like irregularities on the surface of the pressure-sensitive adhesive sheet 10 can be suppressed. Furthermore, by controlling the occurrence of irregularities, good visibility can be achieved. Furthermore, for example, when the pressure-sensitive adhesive sheet 10 is bonded to a printed unevenness on a display cover, the thicker the pressure-sensitive adhesive sheet 10, the easier it is to fill the printed unevenness and maintain a smooth surface (excellent unevenness absorption). However, a pressure-sensitive adhesive sheet 10 made from a solvent-free pressure-sensitive adhesive composition does not thin due to solvent evaporation during the sheeting process, and therefore a uniform, thick pressure-sensitive adhesive sheet 10 can be easily produced. Furthermore, such a pressure-sensitive adhesive sheet 10 has excellent unevenness absorption. Furthermore, a pressure-sensitive adhesive sheet 10 made from a solvent-free pressure-sensitive adhesive composition is suitable for reducing environmental impact. That is, the pressure-sensitive adhesive sheet 10 formed from a solvent-free pressure-sensitive adhesive composition is environmentally friendly and is preferable from the perspective of sustainable development.

[0099] In this method, a network-structured base polymer is formed from the solventless pressure-sensitive adhesive composition in the base adhesive sheet forming step, and a photopolymerization reaction of a polyfunctional monomer (including a cyclic structure-containing polyfunctional monomer) proceeds around the network-structured base polymer in the post-addition component supplying step. Therefore, the photopolymerized product of the polyfunctional monomer is formed while forming an interpenetrating polymer network (IPN) with the network-structured base polymer. This increases the elasticity of the optical pressure-sensitive adhesive sheet.

[0100] On the other hand, for example, when a base polymer is formed from a solvent-based pressure-sensitive adhesive composition, and then a polyfunctional monomer is blended into a solution containing the base polymer and the polyfunctional monomer is photopolymerized, some of the monofunctional monomer remains in the solution containing the base polymer. Therefore, the interpenetrating polymer network structure (IPN) cannot be sufficiently formed from the beginning, and the optical pressure-sensitive adhesive sheet cannot be made highly elastic. In addition, the remaining monofunctional monomer polymerizes over time, and the elasticity also changes over time.

[0101] When the adhesive sheet 10 is used, the release liners 21 and 22 are each peeled off from the adhesive sheet 10 at a predetermined timing.

[0102] 3A to 3C show an example of how the adhesive sheet 10 is used.

[0103] In this method, first, as shown in FIG. 3A , a pressure-sensitive adhesive sheet 10 is bonded to a cover glass 31 (first adherend). The cover glass 31 has a first surface 31a and a second surface 31b opposite the first surface 31a. A decorative or light-blocking printed layer 32 is formed on the edge of the first surface 31a. The printed layer 32 is provided, for example, around the entire edge of the cover glass 31. The cover glass 31 has a step (printed step) between the first surface 31a and the surface of the printed layer 32. In other words, the cover glass 31 is a stepped adherend having a step on its surface. Specifically, in this process, a pressure-sensitive adhesive sheet 10 before photo-curing is bonded to a region of the surface 31a of the cover glass 31 that includes the printed layer 32. FIG. 3A exemplarily illustrates a case in which the pressure-sensitive adhesive sheet 10 before photo-curing is bonded to the entire surface 31a of the cover glass 31.

[0104] 3B , the cover glass 31 and a member 33 are bonded via the adhesive sheet 10 before photo-curing on the cover glass 31. The member 33 is, for example, a pixel panel for a display panel, a polarizing film, or a touch panel.

[0105] Next, as shown in FIG. 3C , the adhesive sheet 10 between the member 33 and the cover glass 31 is photocured by ultraviolet irradiation. The ultraviolet irradiation causes a photopolymerization reaction of the polyfunctional monomer, including the cyclic structure-containing polyfunctional monomer, in the adhesive sheet 10, forming a photopolymerized product of the polyfunctional monomer. Because the photopolymerization reaction proceeds around the base polymer, the photopolymerized product of the polyfunctional monomer is formed while forming an interpenetrating polymer network (IPN) with the base polymer. This increases the elasticity of the adhesive sheet 10 (photocuring of the adhesive sheet 10). Examples of light sources for ultraviolet irradiation include ultraviolet LED lights, black lights, 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 during ultraviolet irradiation. The illuminance of the ultraviolet irradiation is, for example, 5 to 600 mW / cm. ２ The cumulative irradiation amount is, for example, 50 to 15,000 mJ / cm ２ is.

[0106] The adhesive sheet 10 is used, for example, as described above. In the above-described method of use, two members (in the above-described use example, the cover glass 31 and the member 33) are joined together by the adhesive sheet 10, and then the adhesive sheet 10 is photocured. Alternatively, an adhesive sheet 10 (uncured) with a release liner on one side may be attached to one member, the adhesive sheet 10 may be photocured, the release liner may be peeled off from the cured adhesive sheet 10, and then the cured adhesive sheet 10 may be used to join the one member to the other member.

[0107] As described above, the pressure-sensitive adhesive sheet 10 contains a base polymer, a polyfunctional monomer, and a photopolymerization initiator (third photopolymerization initiator). As shown in Fig. 3A, such a pressure-sensitive adhesive sheet 10 can be attached to the stepped surface of an adherend in a soft state before photocuring. Therefore, the pressure-sensitive adhesive sheet 10 is suitable for achieving good step-conforming properties when attached to an adherend having a stepped surface.

[0108] Furthermore, in the pressure-sensitive adhesive sheet 10, as described above, the base polymer is a photopolymer of a polymerizable component containing a monofunctional monomer and a photopolymerizable polyfunctional compound. Such a base polymer has a network structure in which linear units derived from the monofunctional monomer are linked by the photopolymerizable polyfunctional compound. When the pressure-sensitive adhesive sheet 10 is irradiated with light, a photopolymerization reaction of a polyfunctional monomer (including a cyclic-structure-containing polyfunctional monomer) proceeds around the base polymer of such a network structure. As a result, the photopolymerization product of the polyfunctional monomer forms an interpenetrating polymer network (IPN) with the network-structured base polymer. This increases the elasticity of the pressure-sensitive adhesive sheet 10. Furthermore, cyclic-structure-containing polyfunctional monomers are bulkier than polyfunctional monomers that do not contain a cyclic structure. Therefore, the network structure formed by the polymerization reaction of a polyfunctional monomer containing a cyclic-structure-containing polyfunctional monomer has a larger mesh size than the network structure formed by the polymerization reaction of a polyfunctional monomer that does not contain a cyclic-structure-containing polyfunctional monomer. This is suitable for achieving both high elasticity and stress relaxation properties in the photocured pressure-sensitive adhesive sheet 10. Furthermore, the combination of high elasticity and stress relaxation properties in the photocured pressure-sensitive adhesive sheet 10 that bonds adherends together helps to achieve both the above-mentioned bubble suppression and bonding reliability.

[0109] Therefore, the pressure-sensitive adhesive sheet 10 achieves good conformability to unevenness when bonding adherends together, and is suitable for both suppressing air bubbles and ensuring bonding reliability after bonding the adherends together.

[0110] 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."

[0111] Preparation of Acrylic Oligomer: First, in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture containing 60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (MMA), 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a polymerization solvent was stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added to the mixture to prepare a reaction solution. This was reacted under a nitrogen atmosphere at 70°C for 2 hours and then at 80°C for 2 hours (polymerization reaction). Next, the reaction solution was heated to 130°C to volatilize and remove the toluene, chain transfer agent, and unreacted monomer. This resulted in a solid acrylic oligomer. The weight-average molecular weight of this acrylic oligomer was 5100.

[0112] Example 1 Preparation of Prepolymer Composition In a flask, a monomer mixture of 71 parts by weight of n-butyl acrylate (BA), 13 parts by weight of 4-hydroxybutyl acrylate (4HBA), 13 parts by weight of N-vinyl-2-pyrrolidone (NVP), and 3 parts by weight of acryloylmorpholine (ACMO) was added with 0.062 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 polymerizable components in the mixture, yielding a prepolymer composition. The first photoinitiators used were 0.031 parts by weight of BASF's "Omnirad 184" (1-hydroxycyclohexyl phenyl ketone) and 0.031 parts by weight of BASF's "Omnirad 651" (2,2-dimethoxy-2-phenylacetophenone). UV irradiation was continued until the viscosity of the composition reached approximately 20 Pa s. This viscosity is a value measured using a Brookfield viscometer with a rotor No. 5 at a rotor rotation speed of 10 rpm and a temperature of 30° C. The obtained prepolymer composition is a partial polymer containing a photopolymerized product (photopolymerized polymer P1a) and a polymerizable component (residual monomer) that has not undergone a polymerization reaction.

[0113] <Preparation of Pressure-Sensitive Adhesive Composition> Next, 100 parts by mass of the prepolymer composition, 3 parts by mass of the acrylic oligomer, 0.6 parts by mass of a urethane acrylate oligomer (UAO) (trade name "UN-350", manufactured by Negami Chemical Industrial Co., Ltd.) as a photopolymerizable polyfunctional compound, 0.4 parts by mass of a second photopolymerization initiator (trade name "Omnirad 819", bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by BASF), 0.5 parts by mass of an antioxidant (trade name "Irganox 1010", manufactured by BASF), 0.2 parts by mass of a rust inhibitor (trade name "BT-120", 1,2,3-benzotriazole, manufactured by Johoku Chemical Industry Co., Ltd.), and 0.3 parts by mass of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a pressure-sensitive adhesive composition.

[0114] <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 MRF", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) 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) 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 and form a 90 μm thick pressure-sensitive adhesive layer (ultraviolet light irradiation step). The ultraviolet light irradiation step includes a first step and a subsequent second step. In the first step of ultraviolet light irradiation, a black light lamp (wavelength 320 nm to 400 nm, 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 ２ In the second step of ultraviolet irradiation, an ultraviolet LED light (wavelength 365 nm, manufactured by Quark Technology) was used, and the illuminance was 90 mW / cm. ２ The cumulative irradiation light amount was 1800 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 and photopolymerizable polyfunctional compound, forming a photopolymerized polymer P1b having a crosslinked structure. Furthermore, since the photopolymerization reaction proceeds around the 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 polymer P1. In this manner, a base pressure-sensitive adhesive sheet with a release liner (first release liner / base pressure-sensitive adhesive sheet (thickness 90 μm) / second release liner) was produced.

[0115] Preparation of Later-Added Component Solution A later-added component solution was prepared by mixing 27.8 parts by mass of a bifunctional acrylate monomer (trade name "Light Acrylate DCP-A", tricyclodecane dimethanol diacrylate (CAS No. 42594-17-2), Kyoeisha Chemical) as a polyfunctional monomer, 1.2 parts by mass of a third photopolymerization initiator (trade name "Omnirad 819", manufactured by BASF), 3.6 parts by mass of an ultraviolet absorber (trade name "Tinosorb S", manufactured by BASF), and 67.4 parts by mass of ethyl acetate as a solvent (everything in the solution other than the solvent is a later-added component). The composition of the later-added component solution is shown in Table 1. In Table 1, the unit of the amount of each component is relative "parts by mass."

[0116] <Post-Added Component Supply Process> First, the second release liner was peeled from the above-mentioned release-liner-attached base adhesive sheet, and then the post-added component solution was applied to a thickness of 30 μm on the exposed surface of the base adhesive sheet. An R.D. SPECIALTIES RDS No. 14 bar coater was used for application. Next, the base adhesive sheet was dried for 3 minutes in a 110°C dryer. The application and drying processes allowed the post-added components (multifunctional monomer, third photopolymerization initiator, and UV absorber) to penetrate into the base adhesive sheet, and the solvent was evaporated. A photocurable optical adhesive sheet was formed by the penetration of the post-added components into the base adhesive sheet. The addition of the post-added components to the base adhesive sheet resulted in the optical adhesive sheet being thicker than the base adhesive sheet (this also applies to the examples and comparative examples described below). The thickness of the formed adhesive sheet is shown in Table 2. The amount of polyfunctional monomer (DCP-A) added per 100 parts by mass of base polymer (100 parts by mass of the above prepolymer composition and photopolymerizable polyfunctional compound combined) was 8.5 parts by mass, the amount of third photopolymerization initiator (Omnirad 819) added was 0.4 parts by mass, and the amount of ultraviolet absorber (Tinosorb S) added was 1.1 parts by mass. Next, the release-treated surface of a third release liner (trade name "Diafoil MRE", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was bonded to the pressure-sensitive adhesive sheet on the first release liner.

[0117] In this manner, a pressure-sensitive adhesive sheet with release liner (first release liner / pressure-sensitive adhesive sheet (thickness 103 μm) / third release liner) of Example 1 was produced. The pressure-sensitive adhesive sheet was a photocurable optical pressure-sensitive adhesive sheet containing a base polymer, a polyfunctional monomer (DCP-A), and a third photopolymerization initiator.

[0118] Example 2 A release-liner-attached PSA sheet of Example 2 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, the composition of the post-addition component solution was changed as shown in Table 1. The thickness of the PSA sheet formed by adding the post-addition component was 104 μm.

[0119] Example 3 A release-liner-attached PSA sheet of Example 3 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, the composition of the post-addition component solution was changed as shown in Table 1. The thickness of the PSA sheet formed by the addition of the post-addition component was 106 μm.

[0120] Example 4 The release-lined PSA sheet of Example 4 was produced in the same manner as the release-lined PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, the composition of the post-addition component solution was changed as shown in Table 1. In the post-addition component supplying step, a bar coater RDS No. 20 manufactured by R.D. SPECIALTIES was used, and the post-addition component solution was applied to a thickness of 44 μm. The thickness of the PSA sheet formed by the addition of the post-addition component was 112 μm.

[0121] Example 5 The release-liner-attached PSA sheet of Example 5 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, the composition of the post-addition component solution was changed as shown in Table 1. In the post-addition component supplying step, a bar coater RDS No. 24 manufactured by R.D. SPECIALTIES was used, and the post-addition component solution was applied to a thickness of 50 μm. The thickness of the PSA sheet formed by the addition of the post-addition component was 121 μm.

[0122] Example 6 The release-liner-attached PSA sheet of Example 6 was prepared in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In the ultraviolet irradiation step for preparing the base PSA sheet, the second step (irradiation with an ultraviolet LED light) was not performed. This ultraviolet irradiation step resulted in the formation of a base polymer P2 having a weight-average molecular weight (Mw) greater than that of base polymer P1. In preparing the post-addition component solution, the composition of the post-addition component solution was changed as shown in Table 1. In the post-addition component supply step, a bar coater RDS No. 10 manufactured by R.D. SPECIALTIES was used, and the post-addition component solution was applied to a thickness of 23 μm. The PSA sheet formed by the addition of the post-addition component had a thickness of 106 μm.

[0123] Example 7 The release-liner-attached PSA sheet of Example 7 was produced in the same manner as the release-liner-attached PSA sheet of Example 6, except for the following: In preparing the post-addition component solution, 23.8 parts by mass of a bifunctional acrylate monomer, tricyclodecane dimethanol dimethacrylate (CAS No. 43048-08-4) manufactured by Osaka Organic Chemical Industry Ltd. (hereinafter sometimes referred to as DCP-DMA), was used instead of DCP-A as the polyfunctional monomer, and the composition of the other components was changed as shown in Table 1. Furthermore, in the post-addition component supplying step, a bar coater RDS No. 16 manufactured by R.D. SPECIALTIES was used, and the post-addition component solution was applied to a thickness of 37 μm. The thickness of the PSA sheet formed by the addition of the post-addition components was 103 μm.

[0124] Example 8 The PSA sheet with release liner of Example 8 was produced in the same manner as the PSA sheet with release liner of Example 7, except for the following: In preparing the post-addition component solution, the composition of each component was changed as shown in Table 1. The thickness of the PSA sheet formed by adding the post-addition components was 104 μm.

[0125] Comparative Example 1 A release-liner-attached PSA sheet of Comparative Example 1 was produced in the same manner as the release-liner-attached PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, 44.1 parts by mass of trimethylolpropane triacrylate (TMPTA) (CAS No. 15625-89-5) (product name "Viscoat #295", manufactured by Osaka Organic Chemical Industry Ltd.) was blended in place of DCP-A as the polyfunctional monomer, and the composition of the other components was changed as shown in Table 1. The thickness of the PSA sheet formed by the addition of the post-addition components was 106 μm.

[0126] Comparative Example 2 A release-lined PSA sheet of Comparative Example 2 was produced in the same manner as the release-lined PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, 43.6 parts by mass of TMPTA (Viscoat #295) was blended in place of DCP-A as the polyfunctional monomer, and the composition of the other components was changed as shown in Table 1. In the post-addition component supply step, a bar coater RDS No. 20 manufactured by R.D. SPECIALTIES was used, and the post-addition component solution was applied to a thickness of 44 μm. The PSA sheet formed by the addition of the post-addition components had a thickness of 111 μm.

[0127] Comparative Example 3 A release-lined PSA sheet of Comparative Example 3 was produced in the same manner as the release-lined PSA sheet of Example 1, except for the following: In preparing the post-addition component solution, 56.5 parts by mass of TMPTA (Viscoat #295) was blended in place of DCP-A as the polyfunctional monomer, and the composition of the other components was changed as shown in Table 1. In the post-addition component supply step, a bar coater RDS No. 24 manufactured by R.D. SPECIALTIES was used, and the post-addition component solution was applied to a thickness of 50 μm. The PSA sheet formed by the addition of the post-addition components had a thickness of 122 μm.

[0128] Comparative Example 4 A release-lined PSA sheet of Comparative Example 4 (first release liner / PSA sheet / second release liner) was produced in the same manner as the release-lined PSA sheet of Example 1, except for the following: No post-addition component solution was prepared, and no post-addition component supplying step was carried out.

[0129] <Measurement of Weight-Average Molecular Weight> The weight-average molecular weight (Mw) of the above acrylic oligomer was measured by gel permeation chromatography (GPC) under the following measurement conditions and calculated as a polystyrene equivalent value. A GPC measurement device (product name "HLC-8120GPC", manufactured by Tosoh Corporation) was used for the measurement. A sample solution was prepared as follows. First, a tetrahydrofuran (THF) solution (salt added) with a sample concentration of 0.15% by mass was prepared using the acrylic oligomer as a sample, and the THF solution was then left to stand for 20 hours. Next, the THF solution was filtered through a membrane filter with an average pore size of 0.45 μm, and the filtrate was obtained as a sample solution for molecular weight measurement.

[0130] [GPC measurement conditions] Column: G7000H ＸＬ +GMH ＸＬ +GMH ＸＬ , TSKgel (manufactured by Tosoh) Column temperature: 40°C Eluent: THF solution Flow rate: 0.8 mL / min Sample injection volume: 100 μL Standard sample: polystyrene (manufactured by Agilent) Detector: differential refractometer (RI)

[0131] <Light Transmittance> The light transmittance of each of the PSA sheets of Examples 1 to 8 and Comparative Examples 1 to 4 was measured using a spectrophotometer (product name "U4100", manufactured by Hitachi High-Technologies Corporation). In this measurement, a sample piece (first release liner / PSA sheet / third release liner (second release liner for Comparative Example 4 only)) was cut out from the PSA sheet, and then the sample piece was irradiated with ultraviolet light through the first release liner. For ultraviolet irradiation, a metal halide lamp was used as the light source, and the illuminance was 300 mW / cm. ２ The cumulative irradiation dose was 3000 mJ / cm ２ Next, the release liners were peeled off from both sides of the pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive sheet was fixed to a measurement jig of a spectrophotometer so as not to deform. In Comparative Example 4, ultraviolet irradiation was not performed. In addition, in this measurement, the temperature condition was 23°C, and the measurement wavelength range was 300 nm to 800 nm. The measured light transmittance (%) at a wavelength of 380 nm is shown in Table 2.

[0132] <Adhesive Strength> The adhesive strength of each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4 was measured by the following peel test.

[0133] First, a test specimen was prepared for each PSA sheet. To prepare the test specimens, the third release liner (second release liner only in Comparative Example 4) was peeled from the PSA sheet, and a PET film (50 μm thick) was attached to the exposed surface of the PSA sheet to obtain a laminate film (first release liner / PSA sheet / PET film). Next, a test specimen (length 100 mm x width 10 mm) was cut out from the laminate film. Next, in an environment of 23°C and 50% relative humidity, the first release liner was peeled from the PSA sheet of the test specimen, and the exposed surface of the PSA sheet was attached to the air side (non-tin side) of an alkali glass plate (blue plate glass, manufactured by Matsunami Glass Industry Co., Ltd.) prepared by the float method to obtain a laminate (alkali glass plate / PSA sheet / PET film). For attachment, the test specimen was pressure-bonded to the alkali glass plate by rolling a 2 kg roller back and forth once. The laminate was then autoclaved. The autoclave treatment was carried out at a temperature of 50°C, a pressure of 0.5 MPa, and a treatment time of 15 minutes. Next, the pressure-sensitive adhesive sheet in the laminate was irradiated with ultraviolet light from the alkali glass plate side (photo-curing treatment). For ultraviolet irradiation, a metal halide lamp was used as the light source, and the illuminance was 300 mW / cm. ２ The cumulative irradiation dose was 3000 mJ / cm ２ The laminate was then left to stand for 15 hours in an environment of 23°C and 50% relative humidity. A test was then conducted to peel the test piece from the alkali glass plate in an environment of 23°C and 50% relative humidity to measure the peel strength. A tensile tester (product name "Autograph AG-Xplus 200N", manufactured by Shimadzu Corporation) was used for this measurement. In this measurement, the peel angle of the test piece relative to the adherend was 180°, the tensile speed of the test piece was 300 mm / min, and the peel length was 50 mm (peel test measurement conditions). The arithmetic mean values ​​of the peel strengths from three measurements (n = 3) for each type of pressure-sensitive adhesive sheet are shown in Table 2 as the adhesive strength F (N / 10 mm) after photocuring to an alkali glass plate prepared by the float method.

[0134] <Dynamic Viscoelasticity Measurement> The dynamic viscoelasticity of each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4 was measured (first measurement).

[0135] First, the required number of measurement samples were prepared for each PSA sheet. Specifically, multiple PSA sheet pieces cut from the PSA sheet were laminated together to prepare a sample sheet with a thickness of 0.8 to 1.2 mm. Next, this sheet was punched out to obtain cylindrical pellets (8 mm in diameter) as measurement samples.

[0136] Next, dynamic viscoelasticity measurements were carried out on the measurement sample using a dynamic viscoelasticity measuring device (product name "Advanced Rheometric Expansion System (ARES) G2", manufactured by TA Instruments). Specifically, the measurement sample was fixed to a parallel plate jig with a diameter of 8 mm on the device, and then the measurement was carried out. In this measurement, the measurement mode was shear mode, the measurement temperature was in 5°C increments in the range of -50°C to 150°C, the temperature rise rate was 5°C / min, the frequency was 1 Hz, the set load was 30 g, and the set strain amount was 0.1%. Then, from the measurement results, the shear storage modulus G at 25°C was calculated. １ The values ​​are shown in Table 2.

[0137] On the other hand, the dynamic viscoelasticity after photocuring was measured for each of the PSA sheets of Examples 1 to 8 and Comparative Examples 1 to 3 (second measurement). To prepare the samples for measurement, PSA sheets were used that had been photocured by irradiating the first release liner with ultraviolet light. For ultraviolet irradiation, a metal halide lamp was used, and the illuminance was 300 mW / cm. ２ The cumulative irradiation dose was 3000 mJ / cm ２ The load set during the measurement was 100 g. Other than these, the measurement device and measurement conditions in the second measurement were the same as those in the first measurement. From the measurement results, the shear storage modulus G ２ (MPa) and shear storage modulus G at 70 ° C. ３ The values ​​are shown in Table 2.

[0138] <Break Strain> The amount of strain at break in a tensile break test was examined for each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4. Specifically, the results are as follows.

[0139] First, the pressure-sensitive adhesive sheet with release liner was irradiated with ultraviolet light through the first release liner to photocure the pressure-sensitive adhesive sheet. For ultraviolet irradiation, a metal halide lamp was used as the light source, and the illuminance was 300 mW / cm. ２ The cumulative irradiation dose was 3000 mJ / cm ２ Next, four sheet pieces measuring 30 mm in length and 5 mm in width were cut out from the PSA sheet with release liner. Four of these PSA sheets were stacked together to prepare test pieces (30 mm in length x 5 mm in width). Next, the test pieces were autoclaved. In the autoclaving, the temperature was 50°C, the pressure was 0.5 MPa, and the treatment time was 15 minutes. Next, using a tensile tester (Autograph AGS-50NX, manufactured by Shimadzu Corporation), the test pieces were pulled in the length direction until they broke under conditions of 25°C, an initial chuck distance of 10 mm, and a tensile speed of 300 mm / min (tensile test). In this tensile test, the elongation length ΔL of the test piece at the time it broke was measured. The elongation length ΔL is the difference between the initial length of the test piece between the chucks of 10 mm (L ０ ) and the initial length of 10 mm (L ０ The ratio of the elongation length ΔL to the elongation length ΔL (ΔL / L ０ The arithmetic mean value of the ratios for three tests (n=3) for each type of PSA sheet is shown as the breaking strain Bs in Table 2. In Comparative Example 4, ultraviolet irradiation was not performed.

[0140] <Conformability to unevenness> The conformability to unevenness of each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4 was examined as follows.

[0141] First, a sample sheet (75 mm long x 45 mm wide) was cut out from the pressure-sensitive adhesive sheet with a release liner. Next, the third release liner (only the second release liner in Comparative Example 4) was peeled off from the pressure-sensitive adhesive sheet in the sample sheet, and the exposed surface of the pressure-sensitive adhesive sheet was bonded to the center of a PET film (100 mm long x 50 mm wide, 125 μm thick). A roll laminator was used for bonding, with an inter-roll pressure of 0.2 MPa and a feed rate of 100 mm / min. Next, the first release liner was peeled off from the pressure-sensitive adhesive sheet on the PET film, and the exposed surface of the pressure-sensitive adhesive sheet was bonded to a glass plate (100 mm long x 50 mm wide, 500 μm thick) with a printed layer to obtain a bonded structure (first bonded structure). A roll laminator was used for bonding, with an inter-roll pressure of 0.2 MPa and a feed rate of 100 mm / min. FIG. 4 shows the positional relationship between the glass plate 41 and the adhesive sheet 42 (optical adhesive sheet) in this first bonded assembly. A 45 μm-thick printed layer 43 (black ink layer) is formed on one thickness-wise surface of the glass plate 41, extending along the entire periphery of the edge of the glass plate 41. The printed layer 43 is formed within a range of 15 mm inward from each end of the glass plate 41 in the length direction L1, and within a range of 5 mm inward from each end of the glass plate 41 in the width direction L2 (the printed layer 43 is indicated by hatching in FIG. 4). The adhesive sheet 42 is bonded to the center of one thickness-wise surface of the glass plate 41 and is in contact with the printed layer 43 along the entire periphery of the edge of the sheet. In other words, the printed layer 43 on the glass plate 41 is sandwiched between the glass plate 41 and the adhesive sheet 42 within a range of 2.5 mm outward from the inner edge of the printed layer 43.

[0142] Next, the first bonded body was autoclaved under conditions of 50°C, 0.5 MPa, and 30 minutes. After this, the vicinity of the inner edge of the printed layer 43 in the first bonded body was observed. Specifically, the inside of the inner edge of the printed layer 43 (the area where the adhesive sheet 42 should be in close contact with the glass plate 41) was observed from the PET film side of the first bonded body using a digital microscope at a magnification of 20. The step-conforming ability of each adhesive sheet was evaluated as "good" if no bubbles were observed within the observed area, and as "poor" if bubbles were observed. These results are shown in Table 2.

[0143] <Bonding Reliability> The bonding reliability of each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4 was evaluated as follows.

[0144] First, an evaluation sample was prepared. In preparing the evaluation sample, a retardation layer-attached polarizing film piece (length 28 mm x width 10 mm) was cut out from a retardation layer-attached polarizing film. The retardation layer-attached polarizing film was prepared as described below, and had a first surface (the surface on the retardation layer side) and a second surface (the hard coat layer surface of the TAC film described below) opposite the first surface. Next, a sample sheet (length 25 mm x width 10 mm) was cut out from a pressure-sensitive adhesive sheet with a release liner (first release liner / pressure-sensitive adhesive sheet (uncured) / third release liner (second release liner only in Comparative Example 4)). Next, the third release liner (second release liner only in Comparative Example 4) was peeled from the pressure-sensitive adhesive sheet in the sample sheet, and the exposed surface of the pressure-sensitive adhesive sheet was bonded to the second surface of a retardation layer-attached polarizing film piece. Specifically, one longitudinal end (one short side) of the retardation layer-attached polarizing film piece was aligned with one longitudinal end (one short side) of the adhesive sheet, and the pieces were laminated together using a hand roller. Next, the first release liner was peeled off from the adhesive sheet on the retardation layer-attached polarizing film piece, and the exposed surface of the adhesive sheet was then laminated to an alkali-free glass plate (product name "Eagle XG", manufactured by Corning) using a hand roller. This resulted in a laminate (alkali-free glass plate / adhesive sheet / polarizing film). Next, this laminate was autoclaved for 15 minutes under conditions of 50°C and 0.5 MPa. Next, the adhesive sheet in the laminate was irradiated with ultraviolet light from the alkali-free glass plate side to photocure the adhesive sheet. For ultraviolet irradiation, an LED light with a wavelength of 405 nm was used as the light source, and the illuminance was 400 mW / cm. ２ The cumulative light intensity is 3000 mJ / cm ２ In this manner, an evaluation sample (alkali-free glass plate / photocured pressure-sensitive adhesive sheet / polarizing film piece with retardation layer) was prepared.

[0145] Next, the evaluation sample was heated at 105°C for 1 hour. Next, the evaluation sample was visually observed from the alkali-free glass plate side. Then, with regard to the bonding reliability of the pressure-sensitive adhesive sheet, a sample in which no substantial lifting or peeling was observed between the pressure-sensitive adhesive sheet and the alkali-free glass plate and / or between the pressure-sensitive adhesive sheet and the polarizing film was evaluated as "good," and a sample in which there was obvious lifting or peeling was evaluated as "poor." The results are shown in Table 2.

[0146] As another evaluation condition, the evaluation sample was heated at 105°C for 3 hours, and then visually observed from the alkali-free glass plate side. Regarding the bonding reliability of the pressure-sensitive adhesive sheet, a sample in which no substantial lifting or peeling was observed between the pressure-sensitive adhesive sheet and the alkali-free glass plate and / or between the pressure-sensitive adhesive sheet and the polarizing film was evaluated as "good," while a sample in which there was obvious lifting or peeling was evaluated as "poor." Furthermore, after heating at 115°C for 1 hour, the evaluation sample was again visually observed from the alkali-free glass plate side. Regarding the bonding reliability of the pressure-sensitive adhesive sheet, a sample in which no substantial lifting or peeling was observed between the pressure-sensitive adhesive sheet and the alkali-free glass plate and / or between the pressure-sensitive adhesive sheet and the polarizing film was evaluated as "excellent." The results are shown in Table 2. In Examples 7 and 8 and Comparative Example 4, the bonding reliability after heating at 105°C for 1 hour was not evaluated, and only the bonding reliability after heating at 105°C for 3 hours and then at 115°C for 1 hour was evaluated.

[0147] <Preparation of Polarizing Film with Retardation Layer> A polarizing film with a pressure-sensitive adhesive layer and a retardation film were prepared as follows, and then bonded together (bonding step described below) to prepare a polarizing film with a retardation layer.

[0148] <Preparation of Polarizing Film with Pressure-Sensitive Adhesive Layer> A long polyvinyl alcohol (PVA) film (product name "PE3000", thickness 30 μm, manufactured by Kuraray Co., Ltd.) was subjected to swelling treatment, dyeing treatment, crosslinking treatment, washing treatment, and drying treatment in this order to prepare a polarizer with a thickness of 12 μm. Specifically, the procedures are as follows.

[0149] In the swelling treatment, the PVA film was immersed in a pure water bath at 20° C. and uniaxially stretched in the longitudinal direction using a roll stretching machine (the same applies to the uniaxial stretching described below). The stretching ratio in the swelling treatment was 2.2 times.

[0150] In the dyeing treatment, the PVA film was uniaxially stretched in the longitudinal direction while immersed in a dye bath at 30°C. The dye bath was an aqueous solution containing iodine and potassium iodide at a mass ratio of 1:7. The iodine concentration in the dye bath was adjusted so that the single transmittance of the target polarizer would be 45.0%. The stretching ratio in the dyeing treatment was 1.4 times.

[0151] The crosslinking treatment included a first stage crosslinking treatment (first crosslinking treatment) and a second stage crosslinking treatment (second crosslinking treatment). In the first crosslinking treatment, the PVA film was uniaxially stretched in the longitudinal direction while immersed in a first crosslinking bath at 40°C. The first crosslinking bath was an aqueous solution containing boric acid and potassium iodide (boric acid concentration: 5.0% by mass, potassium iodide concentration: 3.0% by mass). The stretching ratio in the first crosslinking treatment was 1.2 times. In the subsequent second crosslinking treatment, the PVA film was uniaxially stretched in the longitudinal direction while immersed in a second crosslinking bath at 65°C. The second crosslinking bath was an aqueous solution containing boric acid and potassium iodide (boric acid concentration: 4.3% by mass, potassium iodide concentration: 5.0% by mass). The stretching ratio in the second crosslinking treatment was 1.6 times.

[0152] In the washing treatment, the PVA film was immersed in an aqueous potassium iodide solution (concentration: 2.6% by mass) at 20° C. In the drying treatment, the PVA film was dried at 70° C. for 5 minutes.

[0153] In this manner, a polarizer (thickness: 12 μm) was produced that was uniaxially stretched at a total stretching ratio of 5.9 times.

[0154] Next, a first triacetyl cellulose (TAC) film (trade name "KC2UA", thickness 25 μm, manufactured by Konica Minolta) was bonded to one side of the polarizer using a polyvinyl alcohol adhesive, and a second TAC film (trade name "KC2UA", thickness 25 μm, manufactured by Konica Minolta) with a hard coat layer (thickness 7 μm) was bonded to the other side of the polarizer using a polyvinyl alcohol adhesive. The side of the second TAC film opposite the hard coat layer was bonded to the polarizer. This resulted in a polarized film having a laminated structure of protective layer (with hard coat layer) / polarizer / protective layer (without hard coat).

[0155] Meanwhile, in a reaction vessel equipped with a reflux condenser, a nitrogen inlet tube, a thermometer, and a stirrer, a mixture (reaction solution) containing 79.9 parts by mass of n-butyl acrylate, 15 parts by mass of benzyl acrylate, 5 parts by mass of acrylic acid, 0.1 parts by mass of 4-hydroxybutyl acrylate (4HBA), 0.1 parts by mass of 2,2'-azoisobutyronitrile as a polymerization initiator, and ethyl acetate as a solvent was stirred at 55°C for 7 hours under a nitrogen atmosphere (polymerization reaction). Next, ethyl acetate was added to the reaction solution to adjust the solids concentration to 30% by mass. This yielded a polymer solution containing an acrylic polymer. The weight-average molecular weight of the acrylic polymer in the polymer solution was 2.2 million.

[0156] Next, 0.5 parts by mass of a first crosslinking agent (trade name "Coronate L", trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation), 0.1 parts by mass of a second crosslinking agent (benzoyl peroxide), 0.2 parts by mass of a silane coupling agent (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.5 parts by mass of a polyether compound having a reactive silyl group (trade name "Silyl SAT10", manufactured by Kaneka Corporation) were added to and mixed with the polymer solution per 100 parts by mass of the acrylic polymer, thereby obtaining a pressure-sensitive adhesive composition.

[0157] Next, a pressure-sensitive adhesive composition was applied to the release-treated surface of a 38 μm-thick release film (product name "MRF #38", PET film, manufactured by Mitsubishi Chemical Corporation) with one side treated for release, to form a coating film. Next, this coating film was dried by heating at 155°C for 1 minute. This formed a pressure-sensitive adhesive layer with a thickness of 12 μm on the release film. Next, the pressure-sensitive adhesive layer on the release film was attached to the protective layer side (without hard coat) of the above-mentioned polarizing film. This produced a polarizing film with a pressure-sensitive adhesive layer.

[0158] <Preparation of Retardation Film> First, in a reaction vessel, 26.2 parts by mass of isosorbide (ISB), 100.5 parts by mass of 9,9-[4-(2-hydroxyethoxy)phenyl]fluorene (BHEPF), 10.7 parts by mass of 1,4-cyclohexanedimethanol (1,4-CHDM), 105.1 parts by mass of diphenyl carbonate (DPC), and 0.591 parts by mass of cesium carbonate (0.2% by mass aqueous solution) as a catalyst were mixed and dissolved under a nitrogen atmosphere. At this time, the heat transfer medium temperature in the reaction vessel was set to 150 ° C. Next, the pressure in the reaction vessel was reduced to 13.3 kPa, and the heat transfer medium temperature was increased to 190 ° C. over 1 hour. Phenol generated as the heat transfer medium temperature increased was extracted from the reaction vessel (the same applies to each heat transfer medium temperature increase described below). Next, the temperature inside the reaction vessel was maintained at 190°C for 15 minutes, after which the pressure inside the reaction vessel was changed to 6.67 kPa, and the heat transfer medium temperature was increased to 230°C over 15 minutes. Then, when the stirring torque of the agitator equipped in the reaction vessel began to increase, the heat transfer medium temperature was increased to 250°C over 8 minutes, and the pressure inside the reaction vessel was further reduced to 0.200 kPa or less. After reaching the predetermined stirring torque, the reaction was terminated, and the resulting reaction product was extruded into water and pelletized. In this way, polycarbonate (PC) resin was obtained. The composition of this PC resin was BHEPF / ISB / 1,4-CHDM = 47.4 mol% / 37.1 mol% / 15.5 mol%. The glass transition temperature of the PC resin was 136.6°C, and the reduced viscosity was 0.395 dL / g.

[0159] Next, the PC resin pellets were vacuum-dried at 80°C for 5 hours, and then a long resin film with a thickness of 120 μm was extruded using the pellets as a raw material using a film-forming device. The film-forming device was equipped with a single-screw extruder (screw diameter 25 mm, cylinder temperature setting 220°C) manufactured by Isuzu Chemical Engineering Co., Ltd., a T-die (width 200 mm, temperature setting 220°C), a chill roll (temperature setting 120°C to 130°C), and a winder. Next, the resin film was stretched in the width direction using a tenter stretching machine at a stretching temperature of 137°C to 139°C. The stretching ratio was 2.5 times. As a result, a first retardation film was obtained as the first retardation layer.

[0160] Separately, a liquid crystal composition was prepared by mixing 20 parts by weight of a side-chain liquid crystal polymer (weight average molecular weight 5000) represented by the following chemical formula (1) (where "65" and "35" represent the mol % of each structural unit), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (trade name "Paliocolor LC242"), 5 parts by weight of a photopolymerization initiator (trade name "Irgacure 907", manufactured by Ciba Specialty Chemicals), and 200 parts by weight of cyclopentanone as a solvent. Next, the liquid crystal composition was applied to one side of a norbornene film (trade name "Zeonex", manufactured by Zeon Corporation) as a substrate film using a bar coater to form a coating film. The coating film on the substrate film was then dried by heating at 80°C for 4 minutes to form a liquid crystal layer (the liquid crystal in the coating film was aligned). Next, the liquid crystal layer on the substrate film was photocured by ultraviolet irradiation to form a 0.58 μm thick solidified liquid crystal layer (second retardation layer) as a second retardation film. This solidified liquid crystal layer had an in-plane retardation Re of 0 nm for light with a wavelength of 550 nm, and a thickness direction retardation Rth of −71 nm for light with a wavelength of 550 nm. The solidified liquid crystal layer also exhibited refractive index characteristics of nz > nx = ny (nx = 1.5326, ny = 1.5326, nz = 1.6550).

[0161]

[0162] One surface of the first retardation film (first retardation layer) and a second retardation film (second retardation layer) on a substrate film were bonded via an adhesive to prepare a retardation film with a substrate film (first retardation layer / adhesive layer / second retardation layer).

[0163] <Bonding step> The first retardation layer side of the retardation film was bonded to the pressure-sensitive adhesive layer side of the above-mentioned pressure-sensitive adhesive layer-attached polarizing film. At this time, the pressure-sensitive adhesive layer-attached polarizing film and the retardation film were aligned and bonded so that the angle formed by the slow axis of the first retardation layer and the absorption axis of the polarizing film was 45 degrees counterclockwise when viewed from the first retardation layer side. In this way, a polarizing film with a retardation layer was produced.

[0164] <Bubble-Resistance Reliability> The pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated for bubble-resistance reliability.

[0165] First, a sample sheet (30 mm long x 30 mm wide) was cut out from an uncured PSA sheet with a release liner. Next, the third release liner (only Comparative Example 4, the second release liner) was peeled off from the PSA sheet in the sample sheet, and an alkali-free glass plate (Eagle XG, manufactured by Corning Incorporated) was bonded to the exposed surface of the PSA sheet using a handle roller to produce a laminate. Next, a hard-coated polycarbonate plate (Iupilon MR58, manufactured by Mitsubishi Gas Chemical Company, Inc., thickness 1 mm) was cut out to 40 mm x 40 mm.

[0166] The first release liner was then peeled off from the laminate, and the polycarbonate surface of the hard-coated polycarbonate plate was attached to the exposed surface of the PSA sheet using a handle roller. The laminate was then autoclaved at 50°C and 0.5 MPa for 15 minutes.

[0167] Next, the adhesive sheet in the laminate was irradiated with ultraviolet light from the alkali-free glass plate side to photocure the adhesive sheet. For ultraviolet irradiation, an LED lamp (wavelength 405 nm) was used as the light source, and the illuminance was 400 mW / cm. ２ The cumulative irradiation dose was 3000 mJ / cm２ In this way, an evaluation sample was produced.

[0168] The evaluation sample was then heated at 95°C for 3 hours. The evaluation sample was then visually observed from the alkali-free glass plate side, and the number of bubbles generated in the pressure-sensitive adhesive sheet or at the interface between the pressure-sensitive adhesive sheet and the polycarbonate plate was counted. This operation was performed twice, and the result with the larger number of bubbles was used. Regarding the bubble resistance reliability, a case in which the number of bubbles was less than 20 was evaluated as "excellent," a case in which the number of bubbles was 20 or more but less than 35 was evaluated as "good," and a case in which the number of bubbles was 35 or more was evaluated as "poor." The results are shown in Table 2.

[0169]

[0170]

[0171] 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.

[0172] The optical pressure-sensitive adhesive sheet of the present invention can be suitably used, for example, in the production of display panels.

[0173] 10 Adhesive sheet (optical adhesive sheet) H Thickness direction 21, 22 Release liner 41 Cover glass 43 Printing layer

Claims

1. An optical adhesive sheet comprising a base polymer, a multifunctional monomer, and a photopolymerization initiator, wherein the base polymer is a photopolymer of a polymerizable component comprising a monofunctional monomer and a photopolymerizable multifunctional compound, and the multifunctional monomer comprises a cyclic structure-containing multifunctional monomer.

2. The optical adhesive sheet according to claim 1, wherein the cyclic structure-containing polyfunctional monomer comprises an alicyclic polyfunctional monomer.

3. The optical adhesive sheet according to claim 1, wherein the cyclic structure-containing polyfunctional monomer is at least one selected from the group consisting of tricyclodecane dimethanol diacrylate, tricyclodecane dimethanol dimethacrylate, and tris(2-acryloyloxyethyl)isocyanurate.

4. An optical adhesive sheet described in any one of claims 1 to 3, wherein the content of the cyclic structure-containing polyfunctional monomer per 100 parts by mass of the base polymer is 5 parts by mass or more and 50 parts by mass or less.

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