Adhesive composition for optical film, adhesive sheet, optical member, and display device

Abstract

To provide an adhesive composition for optical film or the like by which an adhesive layer showing excellent durability and whitening defect occurrence inhibiting property can be formed even in the case of being used for a polarizer with TAC on one side.SOLUTION: An adhesive composition for optical film contains (meth)acrylic polymer (A) and crosslinking agent, where the polymer (A) contains a constitutional unit (a1) derived from (meth)acrylic acid ester monomer having an aromatic ring, a constitutional unit (a2) derived from an acrylic acid alkyl ester monomer in which the carbon number of an alkyl group is 1 to 2, a constitutional unit (a3) derived from a carboxyl group-containing monomer, and a constitutional unit (a4) derived from a hydroxy group-containing monomer, the content ratio of the constitutional unit (a1) is 16.0 to 20.0 mass% for the total constitutional unit, the content ratio of the constitutional unit (a3) is 0.1 to 3.0 mass% for the total constitutional unit, a molar ratio between the content of the constitutional unit (a1) and the content of the constitutional unit (a2) is 1.15 to 4.10, and Mw is 1,500,000 to 2,500,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a pressure-sensitive adhesive composition for optical films, a pressure-sensitive adhesive sheet, an optical member, and a display device. [Background technology]

[0002] A liquid crystal display device generally includes a liquid crystal cell in which a liquid crystal layer is sandwiched between two support substrates, and optical films such as a polarizing plate, a retardation film, and a brightness enhancement film. When a liquid crystal display device is manufactured by laminating a liquid crystal cell and an optical film, or by laminating optical films together, these components are bonded together via a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition. In liquid crystal display devices, (meth)acrylic pressure-sensitive adhesive compositions are often used to ensure visibility.

[0003] Optical films such as polarizing plates are usually constructed by laminating multiple components with different shrinkage rates, and therefore are prone to dimensional changes due to temperature changes. For this reason, for example, when an optical film bonded to a liquid crystal cell via a pressure-sensitive adhesive layer is placed in a high-temperature environment, foaming and / or peeling may occur at the interface between the pressure-sensitive adhesive layer and the optical film and / or the liquid crystal cell, or wrinkles may occur in the pressure-sensitive adhesive layer and / or the optical film. Therefore, pressure-sensitive adhesive compositions used in optical films are required to be able to form a pressure-sensitive adhesive layer with excellent durability that can effectively suppress foaming, wrinkles, and peeling that may occur when placed in a high-temperature environment.

[0004] As a (meth)acrylic pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer with excellent durability, for example, a pressure-sensitive adhesive composition for polarizing plates has been reported (see, for example, Patent Document 1), which contains a (meth)acrylic copolymer (A) obtained by copolymerizing monomer components including 10 to 30 mass% of a (meth)acrylic acid alkyl ester (a1) having a homopolymer glass transition temperature of 0°C or higher and 0.1 to 5 mass% of a crosslinkable functional group-containing monomer (a2) including a hydroxyl group-containing monomer and a carboxyl group-containing monomer, and which has a weight-average molecular weight measured by gel permeation chromatography of 600,000 or less and a glass transition temperature of -80 to 0°C, and an isocyanate-based crosslinking agent (B), in which the crosslinking agent (B) is contained in an amount of 10 to 40 parts by mass per 100 parts by mass of the copolymer (A).

[0005] Furthermore, polarizing plates have a film-type polarizer (so-called polarizing film) made of polyvinyl alcohol (PVA) or the like, and a stretched film may be used for this polarizing film. A polarizing film made of a stretched film is prone to dimensional changes due to shrinkage when placed in a high-temperature environment. Dimensional changes in the polarizing film cause stress to be generated in the polarizing plate. If this generated stress is not alleviated by a pressure-sensitive adhesive layer disposed between the polarizing plate and the liquid crystal cell, residual stress will be generated unevenly in the polarizing plate. As a result, a phase shift occurs between two polarizing plates disposed on the front and back surfaces of a liquid crystal panel so that the stretching axes of the polarizing films intersect with each other, resulting in unevenness known as "white spots" (more specifically, light leakage). Therefore, pressure-sensitive adhesive compositions used in optical films are also required to be capable of forming pressure-sensitive adhesive layers that are excellent in suppressing the occurrence of white spots and can effectively suppress white spots that may occur when placed in a high-temperature environment.

[0006] Examples of (meth)acrylic pressure-sensitive adhesive compositions capable of forming a pressure-sensitive adhesive layer excellent in suppressing the occurrence of white voids include those comprising at least (meth)acrylic acid alkyl ester monomer units (a) having 1 to 18 carbon atoms, copolymerizable monomer units (b) having an aromatic ring, and copolymerizable monomer units (c) having a carboxy group and / or a hydroxyl group, wherein the units (c) are 0.1 to 4 parts by mass per 100 parts by mass of the total of the units (a) and the units (b), the units (a) are in an amount of 40 to 80% by mass in 100% by mass of the total of the units (a) and the units (b), and the units (b) are in an amount of 20 to 60% by mass in 100% by mass of the total of the units (a) and the units (b), and the copolymer (A) has a weight-average molecular weight of 1,000,000 to 2,000,000, and a crosslinking agent (B), wherein the content of the crosslinking agent (B) is such that the 90°C viscosity coefficient of the pressure-sensitive adhesive layer to be formed is 0.5×10 7 Pa·s~10×10 7 An optical pressure-sensitive adhesive composition in which the amount is such that the viscosity becomes Pa·s has been reported (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 072197 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-169329 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, attempts have been made to reduce the thickness of polarizing plates in line with the trend toward thinner liquid crystal display devices. One such attempt involves changing the design of a conventional polarizing plate (hereinafter also referred to as a "double-sided TAC polarizing plate") that has a protective layer such as a triacetyl cellulose (TAC) film on both sides of a polarizer to a polarizing plate (hereinafter also referred to as a "single-sided TAC polarizing plate") that has a protective layer such as a TAC film on only one side of a polarizer. However, when a single-sided TAC polarizing plate that has a protective layer on only one side of a polarizer is placed in a high-temperature environment while being bonded to a glass substrate of a liquid crystal cell via a pressure-sensitive adhesive layer, it is more susceptible to bubbling, wrinkling, peeling, and white spots than a double-sided TAC polarizing plate. Therefore, there is a need for a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that exhibits excellent durability and white spot suppression not only when used in a double-sided TAC polarizing plate but also when used in a single-sided TAC polarizing plate.

[0009] Regarding the above-mentioned point, neither of the pressure-sensitive adhesive compositions described in Patent Document 1 nor Patent Document 2 is intended to be used in a single-sided TAC polarizing plate.

[0010] The present disclosure has been made in light of the above-mentioned circumstances. An object of one embodiment of the present disclosure is to provide a pressure-sensitive adhesive composition for optical films that can form a pressure-sensitive adhesive layer that exhibits excellent durability and suppression of white voids even when used in a single-sided TAC polarizing plate. Another problem to be solved by another embodiment of the present disclosure is to provide a pressure-sensitive adhesive sheet, an optical member, and a display device that include a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for optical films. [Means for solving the problem]

[0011] Specific means for solving the problems include the following aspects. <1> The composition comprises a (meth)acrylic polymer (A) and a crosslinking agent, the (meth)acrylic polymer (A) comprises a structural unit (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring, a structural unit (a2) derived from an acrylate alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety, a structural unit (a3) ​​derived from a monomer having a carboxy group, and a structural unit (a4) derived from a monomer having a hydroxyl group, wherein the content of the structural unit (a1) is 16.0% by mass to 20.0% by mass, based on all structural units, and the content of the structural unit (a3) ​​is 0.1% by mass to 3.0% by mass, based on all structural units, the molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) [content of structural unit (a1) / content of structural unit (a2)] is 1.15 to 4.10, and the weight-average molecular weight is 1.5 million to 2.5 million. <2> The (meth)acrylic acid ester monomer having an aromatic ring includes at least one selected from phenoxyethyl acrylate and benzyl acrylate. <1> The pressure-sensitive adhesive composition for optical films according to claim 1. <3> The crosslinking agent includes an isocyanate-based crosslinking agent. <1> or <2> The pressure-sensitive adhesive composition for optical films according to claim 1. <4> Further containing a silane coupling agent <1> ~ <3> 10. The pressure-sensitive adhesive composition for use on an optical film according to any one of the above items. <5> The composition further contains a (meth)acrylic polymer (B) having a glass transition temperature of 100°C or higher and a weight average molecular weight of 100,000 to 300,000. <1> ~ <4> 10. The pressure-sensitive adhesive composition for use on an optical film according to any one of the above items. <6> <1> ~ <5> 10. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for use on an optical film according to any one of the above items. <7> an optical film; and a protective film provided on at least one surface of the optical film, <1> ~ <5> and a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for an optical film according to any one of the above items. <8> The optical film is a polarizing plate. <7> The adhesive sheet according to claim 1. <9> A glass substrate; <1> ~ <5> 1. An optical member comprising, in this order, a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for an optical film according to any one of 1 to 8 above, and an optical film. <10> <9> A display device comprising the optical member according to claim 1. [Effects of the Invention]

[0012] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition for optical films that can form a pressure-sensitive adhesive layer that exhibits excellent durability and suppression of white voids even when used in a single-sided TAC polarizing plate. According to another embodiment of the present disclosure, there are provided a pressure-sensitive adhesive sheet, an optical member, and a display device, each of which includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for an optical film. DETAILED DESCRIPTION OF THE INVENTION

[0013] The pressure-sensitive adhesive composition for optical films, the pressure-sensitive adhesive sheet, the optical member, and the display device of the present disclosure will be described in detail below. The explanation of the requirements described below may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

[0014] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0015] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0016] In the present disclosure, when the PSA composition contains a plurality of substances corresponding to each component, the amount of each component in the PSA composition means the total amount of the plurality of substances present in the PSA composition, unless otherwise specified.

[0017] In the present disclosure, unless otherwise specified, "solid content" means components other than the solvent contained in the composition, and "solvent" means water and organic solvents. For example, when the solvent contained in the composition is only an organic solvent, the solid content refers to the components contained in the composition other than the organic solvent, and when the solvent contained in the composition is water and an organic solvent, the solid content refers to the components contained in the composition other than water and the organic solvent.

[0018] In the present disclosure, the term "(meth)acrylic monomer" means a monomer having a (meth)acryloyl group. In the present disclosure, "(meth)acrylic polymer" means a polymer that contains structural units derived from (meth)acrylic monomers and in which the proportion of structural units derived from (meth)acrylic monomers is 50 mass % or more.

[0019] In the present disclosure, "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic," "(meth)acrylate" is a term that encompasses both "acrylate" and "methacrylate," and "(meth)acryloyl" is a term that encompasses both "acryloyl" and "methacryloyl."

[0020] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0021] In the present disclosure, "% by mass" and "% by weight" are synonymous, and "parts by mass" and "parts by weight" are synonymous.

[0022] In the present disclosure, the terms "monomer" and "monomer" are synonymous, and the terms "polymer" and "polymeric polymer" and "copolymer" are synonymous.

[0023] In the present disclosure, the term "structural unit derived from a monomer" refers to a structural unit formed by addition polymerization of a monomer.

[0024] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0025] [Adhesive composition for optical films] The pressure-sensitive adhesive composition for optical films of the present disclosure (hereinafter also simply referred to as "pressure-sensitive adhesive composition") comprises a (meth)acrylic polymer (A) and a crosslinking agent, and the (meth)acrylic polymer (A) comprises a structural unit (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring, a structural unit (a2) derived from an acrylic acid alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety, a structural unit (a3) ​​derived from a monomer having a carboxy group, and a structural unit (a4) derived from a hydroxyl group. The polymer contains a structural unit (a4) derived from a monomer having a group, the content of the structural unit (a1) is 16.0% by mass to 20.0% by mass of all structural units, the content of the structural unit (a3) ​​is 0.1% by mass to 3.0% by mass of all structural units, the molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) [content of the structural unit (a1) / content of the structural unit (a2)] is 1.15 to 4.10, and the weight average molecular weight is 1.5 million to 2.5 million. According to the pressure-sensitive adhesive composition of the present disclosure, a pressure-sensitive adhesive layer that exhibits excellent durability and suppression of white voids can be formed even when used in a single-sided TAC polarizing plate. The reason why the PSA composition of the present disclosure can exhibit such effects is unclear, but the present inventors speculate as follows: However, the following speculation is not intended to limit the PSA composition of the present disclosure, but is provided as an example.

[0026] A single-sided TAC polarizer is a polarizer that has a protective layer such as TAC on only one side of the polarizer. The adhesive layer that bonds such a single-sided TAC polarizer to the glass substrate of a liquid crystal cell is provided on the protective layer side of the single-sided TAC polarizer. When a single-sided TAC polarizer is placed in a high-temperature environment while bonded to a glass substrate via the adhesive layer, it is more likely to develop bubbling, wrinkles, peeling, and white spots than a double-sided TAC polarizer. The following is thought to be the cause of this. In the case of a double-sided TAC polarizer, the protective layer is present on both sides of the polarizer, so when the polarizer shrinks, the adhesive layer acts in a horizontal direction relative to the glass surface. On the other hand, in the case of a single-sided TAC polarizer, the protective layer is present only on one side of the polarizer, so when the polarizer shrinks, the adhesive layer acts in a vertical direction in addition to a horizontal force relative to the glass surface, resulting in three-dimensional deformation of the adhesive layer.

[0027] In the pressure-sensitive adhesive composition of the present disclosure, the (meth)acrylic polymer (A) contains structural units (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring and structural units (a2) derived from an acrylic acid alkyl ester monomer having an alkyl moiety with 1 to 2 carbon atoms in a specific ratio, and it is believed that in the pressure-sensitive adhesive layer, the aromatic rings of structural units (a1) and the alkyl moieties of structural units (a2) interact in such a way that the aromatic rings sandwich the alkyl moieties, forming a pseudo-crosslinked structure. Because the alkyl moieties of structural units (a2) have 1 to 2 carbon atoms and short side chains, the degree of freedom of the side chains is low and they are unlikely to easily come off the sandwiched position by the aromatic rings. On the other hand, the pressure-sensitive adhesive composition of the present disclosure comprises a (meth)acrylic polymer (A) and a crosslinking agent. The (meth)acrylic polymer (A) comprises a structural unit (a3) ​​derived from a monomer having a carboxy group and a structural unit (a4) derived from a monomer having a hydroxy group. Therefore, in the pressure-sensitive adhesive layer, the carboxy group of the structural unit (a3) ​​and the hydroxy group of the structural unit (a4) undergo a crosslinking reaction with the crosslinking agent, forming a crosslinked structure. It is believed that a pressure-sensitive adhesive layer with high cohesive strength is formed by the pseudo-crosslinking based on interactions in addition to crosslinking based on chemical bonds. Because the pseudo-crosslinking based on interactions is recombinable and relatively flexible, the pressure-sensitive adhesive layer formed has high cohesive strength without being excessively hard. It is believed that the pressure-sensitive adhesive layer exhibits sufficient wettability to the adherend, thereby providing sufficient adhesion to the adherend. Furthermore, it is believed that the interaction of the carboxy group of the structural unit (a3) ​​with the adherend causes the pressure-sensitive adhesive layer formed to exhibit excellent adhesion to the adherend. Furthermore, the alkyl moiety of the structural unit (a2) has 1 to 2 carbon atoms, and the side chain moiety is short, which facilitates entanglement. When the (meth)acrylic polymer (A) contains the structural unit (a2), entanglement of the (meth)acrylic polymer (A) occurs easily, which is thought to impart sufficient elasticity to the pressure-sensitive adhesive layer. Furthermore, when the (meth)acrylic polymer (A) has a specific weight-average molecular weight, entanglement of the (meth)acrylic polymer (A) occurs appropriately, which is thought to impart just the right amount of elasticity and flexibility to the pressure-sensitive adhesive layer.Therefore, according to the pressure-sensitive adhesive composition of the present disclosure, crosslinking based on chemical bonds and pseudo-crosslinking based on interactions increases the cohesive strength of the pressure-sensitive adhesive layer without impairing the adhesion of the pressure-sensitive adhesive layer to the adherend, the interaction between the pressure-sensitive adhesive layer and the adherend increases the adhesion of the pressure-sensitive adhesive layer to the adherend, and polymer entanglement increases the elasticity of the pressure-sensitive adhesive layer, and as a result, it is presumed that the pressure-sensitive adhesive layer will exhibit high durability even when used in a single-sided TAC polarizing plate. Furthermore, according to the pressure-sensitive adhesive composition of the present disclosure, the (meth)acrylic polymer (A) contains the structural unit (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring in a specific ratio, thereby suppressing birefringence derived from the pressure-sensitive adhesive layer. Therefore, it is presumed that the pressure-sensitive adhesive layer exhibits high suppression of white voids even when used in a single-sided TAC polarizing plate.

[0028] In the present disclosure, "a (meth)acrylic polymer (A) which comprises structural units (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring, structural units (a2) derived from an acrylate alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety, structural units (a3) ​​derived from a monomer having a carboxy group, and structural units (a4) derived from a monomer having a hydroxyl group, wherein the content of structural units (a1) is 16.0% to 20.0% by mass with respect to all structural units, the content of structural units (a3) ​​is 0.1% to 3.0% by mass with respect to all structural units, the molar ratio of the content of structural units (a1) to the content of structural units (a2) [content of structural units (a1) / content of structural units (a2)] is 1.15 to 4.10, and the weight-average molecular weight is 1.5 million to 2.5 million" is also referred to as the "specific (meth)acrylic polymer (A)."

[0029] [Specific (meth)acrylic polymer (A)] The pressure-sensitive adhesive composition of the present disclosure comprises a (meth)acrylic polymer (A) [i.e., specific (meth)acrylic polymer (A)] that includes structural units (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring, structural units (a2) derived from an acrylate alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety, structural units (a3) ​​derived from a monomer having a carboxy group, and structural units (a4) derived from a monomer having a hydroxyl group, wherein the content of structural units (a1) is 16.0% by mass to 20.0% by mass, based on all structural units, and the content of structural units (a3) ​​is 0.1% by mass to 3.0% by mass, based on all structural units, the molar ratio of the content of structural units (a1) to the content of structural units (a2) [content of structural units (a1) / content of structural units (a2)] is 1.15 to 4.10, and the weight-average molecular weight is 1.5 million to 2.5 million. The pressure-sensitive adhesive composition of the present disclosure may contain only one type of specific (meth)acrylic polymer (A), or may contain two or more types.

[0030] <Constituent unit (a1)> The specific (meth)acrylic polymer (A) contains structural units (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring in a proportion of 16.0% by mass to 20.0% by mass based on all structural units.

[0031] The type of the (meth)acrylic acid ester monomer having an aromatic ring is not particularly limited. Examples of the (meth)acrylic acid ester monomer having an aromatic ring include a monomer having at least one aromatic ring and a (meth)acryloyl group in one molecule. The aromatic ring may or may not have a substituent. The aromatic ring may be an aromatic hydrocarbon ring, an aromatic heterocyclic ring, or a condensed ring thereof. Specific examples of the aromatic hydrocarbon ring include a benzene ring, a naphthalene ring, and an anthracene ring. Specific examples of the aromatic heterocycle include an imidazole ring, an oxazole ring, a thiazole ring, a pyridine ring, a pyrazine ring, a pyrrole ring, a furan ring, a thiophene ring, a pyrazole ring, an isoxazole ring, an isothiazole ring, a pyridazine ring, and a pyrimidine ring.

[0032] Specific examples of the (meth)acrylic acid ester monomer having an aromatic ring include phenoxybutyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate. The (meth)acrylic acid ester monomer having an aromatic ring preferably includes at least one selected from phenoxyethyl acrylate and benzyl acrylate, and more preferably at least one selected from phenoxyethyl acrylate and benzyl acrylate.

[0033] The specific (meth)acrylic polymer (A) may contain only one type of structural unit (a1), or may contain two or more types.

[0034] The content of the structural unit (a1) in the specific (meth)acrylic polymer (A) is 16.0% by mass to 20.0% by mass, based on all structural units of the specific (meth)acrylic polymer (A). When the content of the structural unit (a1) in the specific (meth)acrylic polymer (A) is within this range, the formed pressure-sensitive adhesive layer tends to be better able to suppress the occurrence of white spots. This is thought to be because, when the content of the structural unit (a1) in the specific (meth)acrylic polymer (A) is within this range, based on all structural units of the specific (meth)acrylic polymer (A), the positive birefringence caused by the structural unit (a1) having an aromatic ring and the negative birefringence caused by structural units other than the structural unit (a1) that do not have an aromatic ring cancel each other out, thereby suppressing the birefringence of the pressure-sensitive adhesive layer as a whole. The content of the structural unit (a1) in the specific (meth)acrylic polymer (A) may be, for example, 18.0 mass% to 20.0 mass%, 17.0 mass% to 19.0 mass%, or 16.0 mass% to 18.0 mass%, relative to all structural units of the specific (meth)acrylic polymer (A).

[0035] <Constituent unit (a2)> The specific (meth)acrylic polymer (A) contains a structural unit (a2) derived from an acrylate alkyl ester monomer in which the alkyl moiety has 1 to 2 carbon atoms. In the present disclosure, the "acrylate alkyl ester monomer in which the alkyl moiety has 1 to 2 carbon atoms" is also referred to as the "specific acrylate alkyl ester monomer."

[0036] The alkyl group in the specific acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent (excluding groups having an aromatic ring, a carboxy group, and a hydroxyl group), but is preferably unsubstituted. Note that, in the present disclosure, the number of carbon atoms in the alkyl moiety of the specific acrylic acid alkyl ester monomer, which is 1 to 2, does not include the number of carbon atoms in the substituent.

[0037] Specific examples of the specific acrylic acid alkyl ester monomer include methyl acrylate and ethyl acrylate. The specific acrylic acid alkyl ester monomer is preferably at least one selected from methyl acrylate and ethyl acrylate, more preferably methyl acrylate or ethyl acrylate, and even more preferably methyl acrylate.

[0038] The specific (meth)acrylic polymer (A) may contain only one type of structural unit (a2), or may contain two or more types.

[0039] The molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) in the specific (meth)acrylic polymer (A) [content of the structural unit (a1) / content of the structural unit (a2)] is 1.15 to 4.10. When the molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) [content of the structural unit (a1) / content of the structural unit (a2)] is 1.15 or more, the durability of the pressure-sensitive adhesive layer formed tends to be improved. The reason for this is thought to be that, since the proportion of the specific acrylic acid alkyl ester monomer with short side chains is not too high, an increase in the elasticity of the pressure-sensitive adhesive layer due to entanglement of the side chains of the specific acrylic acid alkyl ester monomer is unlikely to occur, and the pressure-sensitive adhesive layer does not become excessively hard. The molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) in the specific (meth)acrylic polymer (A) [content of the structural unit (a1) / content of the structural unit (a2)] is preferably 1.34 or more, and more preferably 1.61 or more. When the molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) [content of the structural unit (a1) / content of the structural unit (a2)] is 4.10 or less, the durability of the formed adhesive layer tends to improve. The reason for this is thought to be that, since the proportion of alkyl moieties interacting with the aromatic ring is not too small, relatively flexible pseudo-crosslinking based on the interaction between the (meth)acrylic acid ester monomer having an aromatic ring and the specific acrylic acid alkyl ester monomer occurs appropriately, and the adhesive layer does not become excessively hard. The molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) in the specific (meth)acrylic polymer (A) [content of the structural unit (a1) / content of the structural unit (a2)] is preferably 3.22 or less, and more preferably 2.69 or less. In one embodiment, the molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) in the specific (meth)acrylic polymer (A) [content of structural unit (a1) / content of structural unit (a2)] may be 1.34 to 3.22, 1.34 to 2.69, 1.61 to 3.22, or 1.61 to 2.69.

[0040] <Constituent unit (a3)> The specific (meth)acrylic polymer (A) contains structural units (a3) ​​derived from a monomer having a carboxy group in a proportion of 0.1% by mass to 3.0% by mass based on all structural units. The carboxy group of the structural unit (a3) ​​contributes to the crosslinking reaction with the crosslinking agent described below.

[0041] The type of the monomer having a carboxy group is not particularly limited. Examples of the monomer having a carboxy group include a monomer having at least one carboxy group and an ethylenically unsaturated group in one molecule. Examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group. Specific examples of the monomer having a carboxy group include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≒2) monoacrylate], and succinic acid derivatives (e.g., 2-acryloyloxyethyl-succinic acid). The monomer having a carboxy group is preferably acrylic acid.

[0042] The specific (meth)acrylic polymer (A) may contain only one type of structural unit (a3), or may contain two or more types.

[0043] The content of the structural unit (a3) ​​in the specific (meth)acrylic polymer (A) is 0.1% by mass to 3.0% by mass based on all structural units of the specific (meth)acrylic polymer (A). When the content of the structural unit (a3) ​​in the specific (meth)acrylic polymer (A) is 0.1 mass% or more relative to all structural units of the specific (meth)acrylic polymer (A), the durability of the pressure-sensitive adhesive layer formed tends to improve. This is thought to be because the cohesive strength of the pressure-sensitive adhesive layer is sufficiently increased and the interaction at the interface between the pressure-sensitive adhesive layer and the adherend is sufficiently strengthened. The content of the structural unit (a3) ​​in the specific (meth)acrylic polymer (A) is preferably 0.3 mass% or more, and more preferably 0.5 mass% or more, based on all structural units of the specific (meth)acrylic polymer (A). When the content of the structural unit (a3) ​​in the specific (meth)acrylic polymer (A) is 3.0 mass% or less based on all structural units of the specific (meth)acrylic polymer (A), the durability of the formed pressure-sensitive adhesive layer tends to improve. This is thought to be because the cohesive strength of the pressure-sensitive adhesive layer does not become too high, which makes it less likely that a decrease in stress relaxation, which causes wrinkling and peeling, occurs, and the interaction at the interface between the pressure-sensitive adhesive layer and the adherend does not become excessively strong. The content of the structural unit (a3) ​​in the specific (meth)acrylic polymer (A) is preferably 2.5 mass % or less, and more preferably 2.0 mass % or less, based on all structural units of the specific (meth)acrylic polymer (A). In one embodiment, the content of the structural unit (a3) ​​in the specific (meth)acrylic polymer (A) may be 0.3 to 2.5% by mass, 0.3 to 2.0% by mass, 0.5 to 2.5% by mass, or 0.5 to 2.0% by mass, relative to all structural units of the specific (meth)acrylic polymer (A).

[0044] <Constituent unit (a4)> The specific (meth)acrylic polymer (A) contains a structural unit (a4) derived from a monomer having a hydroxyl group. The hydroxyl group of the structural unit (a4) contributes to a crosslinking reaction with the crosslinking agent described below.

[0045] The type of the hydroxyl group-containing monomer is not particularly limited. Examples of the monomer having a hydroxyl group include a monomer having at least one hydroxyl group and an ethylenically unsaturated group in one molecule. Examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group.

[0046] Specific examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, butyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate. The monomer having a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate, more preferably 2-hydroxyethyl acrylate.

[0047] The specific (meth)acrylic polymer (A) may contain only one type of structural unit (a4), or may contain two or more types.

[0048] The content of the structural unit (a4) in the specific (meth)acrylic polymer (A) is not particularly limited, but for example, it is preferably 0.1% by mass to 1.0% by mass, more preferably 0.15% by mass to 0.8% by mass, even more preferably 0.2% by mass to 0.6% by mass, and particularly preferably 0.3% by mass to 0.5% by mass, relative to all structural units of the specific (meth)acrylic polymer (A). When the content of the structural unit (a4) in the specific (meth)acrylic polymer (A) is 0.1 mass% or more relative to all structural units of the specific (meth)acrylic polymer (A), the durability of the pressure-sensitive adhesive layer formed tends to be improved. This is thought to be because sufficient three-dimensional crosslinking is formed, imparting sufficient cohesive strength to the pressure-sensitive adhesive layer. When the content of the structural unit (a4) in the specific (meth)acrylic polymer (A) is 1.0 mass% or less based on all structural units of the specific (meth)acrylic polymer (A), the durability of the pressure-sensitive adhesive layer formed tends to be improved. This is thought to be because excessive formation of three-dimensional crosslinks is suppressed, making the pressure-sensitive adhesive layer less likely to become excessively hard.

[0049] <Constituent unit (a5)> The specific (meth)acrylic polymer (A) preferably contains structural units derived from an acrylic acid alkyl ester monomer other than the specific acrylic acid alkyl ester monomer and a methacrylic acid alkyl ester monomer. In the present disclosure, "acrylic acid alkyl ester monomers and methacrylic acid alkyl ester monomers other than the specific acrylic acid alkyl ester monomers" are also referred to as "other (meth)acrylic acid alkyl ester monomers." Furthermore, in the present disclosure, "structural units derived from other (meth)acrylic acid alkyl ester monomers" are also referred to as "structural unit (a5)."

[0050] The type of other (meth)acrylic acid alkyl ester monomer is not particularly limited. The other (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer. The alkyl group contained in the other (meth)acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent (excluding groups having an aromatic ring, a carboxy group, and a hydroxyl group), but is preferably unsubstituted. The alkyl group contained in the other (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The alkyl moiety of the other (meth)acrylic acid alkyl ester monomer preferably has 3 to 18 carbon atoms, more preferably 3 to 12 carbon atoms, and even more preferably 3 to 8 carbon atoms, for example.

[0051] Specific examples of other (meth)acrylic acid alkyl ester monomers include methyl methacrylate, ethyl methacrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. The other (meth)acrylic acid alkyl ester monomer is preferably at least one selected from n-butyl acrylate and 2-ethylhexyl acrylate, and more preferably n-butyl acrylate.

[0052] When the specific (meth)acrylic polymer (A) contains the structural unit (a5), it may contain only one type of structural unit (a5), or may contain two or more types of structural unit (a5).

[0053] When the specific (meth)acrylic polymer (A) contains the structural unit (a5), the content of the structural unit (a5) in the specific (meth)acrylic polymer (A) is not particularly limited, but, for example, it is preferably 50% by mass or more, more preferably 50% by mass to 82% by mass, even more preferably 60% by mass to 82% by mass, and particularly preferably 70% by mass to 82% by mass, relative to all structural units of the specific (meth)acrylic polymer (A). Here, the content of the structural unit (a5) in the specific (meth)acrylic polymer (A) being 50 mass% or more relative to all structural units of the specific (meth)acrylic polymer (A) means that the structural unit (a5) is contained as a main component of the structural units of the specific (meth)acrylic polymer (A).

[0054] <Constituent units derived from other monomers> The specific (meth)acrylic polymer (A) may contain, as necessary, a constituent unit derived from a monomer that does not fall into any of the following categories: a (meth)acrylic acid ester monomer having an aromatic ring, a specific acrylic acid alkyl ester monomer, a monomer having a carboxy group, a monomer having a hydroxyl group, and other (meth)acrylic acid alkyl ester monomers (so-called other monomers), within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0055] Examples of structural units derived from other monomers include structural units derived from alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; structural units derived from aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; structural units derived from vinyl cyanides, such as acrylonitrile and methacrylonitrile; and structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0056] When the specific (meth)acrylic polymer (A) contains a structural unit derived from another monomer, it may contain only one type of structural unit derived from the other monomer, or may contain two or more types of structural units derived from the other monomer.

[0057] When the specific (meth)acrylic polymer (A) contains structural units derived from other monomers, the proportion of the structural units derived from other monomers contained in the specific (meth)acrylic polymer (A) can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0058] <<Weight-average molecular weight of specific (meth)acrylic polymer (A)>> The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic polymer (A) is 1.5 million to 2.5 million, preferably 1.7 million to 2.3 million, and more preferably 1.9 million to 2.1 million. When the weight-average molecular weight of the specific (meth)acrylic polymer (A) is 1,500,000 or more, the durability of the pressure-sensitive adhesive layer formed tends to be improved. This is thought to be because the entanglement of the specific (meth)acrylic polymers (A) becomes appropriately strong, imparting sufficient elasticity to the pressure-sensitive adhesive layer. When the weight-average molecular weight of the specific (meth)acrylic polymer (A) is 2,500,000 or less, the durability of the pressure-sensitive adhesive layer formed tends to be improved. This is thought to be because the entanglement of the specific (meth)acrylic polymers (A) with each other is not excessively strong, and the flexibility of the pressure-sensitive adhesive layer is sufficiently maintained.

[0059] The weight average molecular weight of the specific (meth)acrylic polymer (A) is a value measured by the following method, specifically, according to the following (1) to (3). (1) A solution of the specific (meth)acrylic polymer (A) is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the specific (meth)acrylic polymer (A). (2) Using the film-like specific (meth)acrylic polymer (A) obtained in (1) above and tetrahydrofuran, a sample solution having a solids concentration of 0.2% by mass is obtained. Here, the "solids concentration" refers to the mass proportion of the specific (meth)acrylic polymer (A) in the sample solution. (3) The weight average molecular weight of the specific (meth)acrylic polymer (A) is determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) under the following conditions.

[0060] ~Conditions~ Measurement equipment: High-speed GPC [Model: HLC-8420 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [built into HLC-8420, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Two Tosoh products are used. Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0061] The weight average molecular weight of the specific (meth)acrylic polymer (A) can be adjusted to a desired value by, for example, adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. when polymerizing the monomers.

[0062] <<Content of specific (meth)acrylic polymer (A)>> The content of the specific (meth)acrylic polymer (A) in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably 50.0 mass % to 99.8 mass %, more preferably 60.0 mass % to 99.0 mass %, and even more preferably 70.0 mass % to 98.0 mass %, relative to the total solid content in the pressure-sensitive adhesive composition.

[0063] In the present disclosure, the "total solid content in the PSA composition" means the total mass of the PSA composition when the PSA composition does not contain a solvent, and means the mass of the residue remaining after removing the solvent from the PSA composition when the PSA composition contains a solvent.

[0064] [Method for producing specific (meth)acrylic polymer (A)] The method for producing the specific (meth)acrylic polymer (A) is not particularly limited. The specific (meth)acrylic polymer (A) can be produced by polymerizing the above-mentioned monomers using a known polymerization method, typically a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, or a bulk polymerization method. As a polymerization method, solution polymerization is preferred in that the processing steps for preparing the pressure-sensitive adhesive composition of the present disclosure after production are relatively simple and can be carried out in a short time.

[0065] In the solution polymerization method, a predetermined organic solvent, monomers, a polymerization initiator, and an optional chain transfer agent are generally charged into a polymerization vessel and reacted by heating for several hours with stirring, for example, at the reflux temperature of the organic solvent. In this case, at least a portion of the organic solvent, monomers, polymerization initiator, and optional chain transfer agent may be added sequentially. Alternatively, the reaction may be carried out in a nitrogen gas stream.

[0066] Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. More specifically, examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine; ester compounds such as methyl acetate, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone; Examples of the alcohol compounds include ketone compounds typified by ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether compounds typified by ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; and alcohol compounds typified by methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

[0067] In producing the specific (meth)acrylic polymer (A), it is preferable to use an organic solvent that is unlikely to cause chain transfer during the polymerization reaction, such as an aromatic hydrocarbon compound, an ester compound, or a ketone compound. In particular, it is preferable to use methyl acetate and / or ethyl acetate from the viewpoints of the solubility of the specific (meth)acrylic polymer (A), ease of the polymerization reaction, etc.

[0068] During the polymerization reaction, only one type of organic solvent may be used, or two or more types may be used.

[0069] Examples of the polymerization initiator include organic peroxides and azo compounds that are used in ordinary solution polymerization methods. Specific examples of organic peroxides include t-butyl peroxy-2-ethylhexanoate, t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxysilane), peroxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane. Specific examples of azo compounds include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(isobutyrate) dimethyl.

[0070] In the polymerization reaction, only one type of polymerization initiator may be used, or two or more types may be used.

[0071] The amount of the polymerization initiator used is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer (A).

[0072] In producing the specific (meth)acrylic polymer (A), a chain transfer agent may be used, if necessary. Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, aromatic compounds such as α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds such as p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives such as benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives such as tributylborane, carbon tetrabromide, tetrabromide, tetrachloromethane, benzoquinone derivatives such as benzoquinone ... Examples of such compounds include halogenated hydrocarbon compounds such as carbon chloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene, aldehyde compounds such as chloral and furaldehyde, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds such as thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds such as pinene and terpinolene.

[0073] When a chain transfer agent is used in producing the specific (meth)acrylic polymer (A), the amount of the chain transfer agent used is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer (A).

[0074] The polymerization temperature is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer (A).

[0075] [Crosslinking agent] The pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent. The type of crosslinking agent is not particularly limited. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, a metal chelate-based crosslinking agent, an epoxy-based crosslinking agent, and an aziridine-based crosslinking agent. The crosslinking agent preferably contains at least one selected from the group consisting of an isocyanate-based crosslinking agent and a metal chelate-based crosslinking agent, more preferably contains an isocyanate-based crosslinking agent, and even more preferably is an isocyanate-based crosslinking agent.

[0076] In this disclosure, "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate-based compound). Furthermore, "metal chelate-based crosslinking agent" refers to a metal chelate-based compound that functions as a crosslinking agent. Furthermore, "epoxy-based crosslinking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher epoxy-based compound). Furthermore, "aziridine-based crosslinking agent" refers to a compound having two or more aziridine groups in one molecule (so-called polyaziridine-based compound).

[0077] Examples of polyisocyanate compounds include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, and aromatic polyisocyanate compounds. "Aliphatic polyisocyanate compounds" include, for example, aliphatic polyisocyanate compounds, polymers of aliphatic polyisocyanate compounds, adducts of aliphatic polyisocyanate compounds and polyol compounds (e.g., trimethylolpropane (TMP); the same applies hereinafter), and biuret compounds of aliphatic polyisocyanate compounds. Specific examples of aliphatic polyisocyanate compounds include hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. The "alicyclic polyisocyanate compound" includes, for example, an alicyclic polyisocyanate compound, a polymer of an alicyclic polyisocyanate compound, an adduct of an alicyclic polyisocyanate compound and a polyol compound, and a biuret of an alicyclic polyisocyanate compound. Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. The "aromatic polyisocyanate compound" includes, for example, an aromatic polyisocyanate compound, a polymer of an aromatic polyisocyanate compound, an adduct of an aromatic polyisocyanate compound and a polyol compound, and a biuret of an aromatic polyisocyanate compound. Specific examples of the aromatic polyisocyanate compound include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate.

[0078] The polyisocyanate compound is preferably an aromatic polyisocyanate compound, and more preferably at least one selected from the group consisting of tolylene diisocyanate compounds and xylylene diisocyanate compounds. The "tolylene diisocyanate compound" includes, for example, TDI, TDI polymers, adducts of TDI and polyol compounds, and biuret compounds of TDI. As the tolylene diisocyanate compound, an adduct of TDI and TMP is preferred. The "xylylene diisocyanate compound" includes, for example, XDI, XDI polymers, adducts of XDI and polyol compounds, and biuret compounds of XDI. The xylylene diisocyanate compound is preferably an adduct of XDI and TMP.

[0079] As the isocyanate-based crosslinking agent, commercially available products can be used. Commercially available examples of isocyanate crosslinking agents include "Coronate HX," "Coronate HL-S," "Coronate L," "Coronate L-45E," "Coronate 2031," "Coronate 2037," "Coronate 2234," "Coronate 2785," "Aquanate 200," and "Aquanate 210" (all manufactured by Tosoh Corporation), "Sumidur N3300," "Desmodur N3400," and "Sumidur N75" (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate D201," "Duranate E405-70B," "Duranate E405-80T," "Duranate AE700-100," "Duranate 24A-100," and "Duranate TSE-100" (all manufactured by Asahi Kasei Corporation), and "Takenate Examples of such compounds include "Takenate D-110N," "Takenate D-101E," "Takenate D-120N," "Takenate D-140N," "Takenate M-631N," "MT-Olestar NP1200," and "Stabio XD-340N" (all manufactured by Mitsui Chemicals, Inc.). The above-mentioned "Coronate," "Aquanate," "Sumidur," "Desmodur," "Duranate," "Takenate," "Olestar," and "Stabio" are all registered trademarks.

[0080] Examples of metal chelate compounds include aluminum chelate compounds, titanium chelate compounds, zirconium chelate compounds, and cobalt chelate compounds. The metal chelate crosslinking agent is preferably an aluminum chelate compound. Specific examples of aluminum chelate compounds include aluminum tris(acetylacetonate), aluminum alkylacetoacetate diisopropylate, aluminum monoacetylacetonate bis(ethylacetoacetate), and aluminum tris(ethylacetoacetate).

[0081] As the metal chelate crosslinking agent, commercially available products can be used. Examples of commercially available metal chelate crosslinking agents include Aluminum Chelate A (trade name, chemical name: aluminum tris(acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.), Aluminum Chelate D (trade name, chemical name: aluminum monoacetylacetonate bis(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.), Aluminum Chelate M (trade name, chemical name: aluminum alkylacetoacetate diisopropylate, manufactured by Kawaken Fine Chemicals Co., Ltd.), and ALCH-TR (trade name, chemical name: aluminum tris(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.).

[0082] The pressure-sensitive adhesive composition of the present disclosure may contain only one type of crosslinking agent, or may contain two or more types.

[0083] The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably 0.05 to 3.0 parts by mass, more preferably 0.1 to 2.0 parts by mass, and even more preferably 0.1 to 1.0 part by mass, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0084] [Silane coupling agent] The pressure-sensitive adhesive composition of the present disclosure preferably further contains a silane coupling agent. The alkoxy groups of the silane coupling agent are converted by hydrolysis into silanol groups, which react with hydroxyl groups on the surface of the adherend (e.g., glass). When the pressure-sensitive adhesive composition of the present disclosure further contains a silane coupling agent, the interaction at the interface between the pressure-sensitive adhesive layer and the adherend becomes stronger, and the adhesion between the pressure-sensitive adhesive layer and the adherend increases, which tends to further improve the durability of the pressure-sensitive adhesive layer formed.

[0085] The type of silane coupling agent is not particularly limited. Examples of silane coupling agents include polymerizable unsaturated group-containing silane compounds typified by vinyltrimethoxysilane, vinyltriethoxysilane, and 3-methacryloxypropyltrimethoxysilane; thiol group-containing silane compounds typified by 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane; epoxy group-containing silane compounds typified by 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane compounds typified by 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; and tris-(3-trimethoxysilylpropyl)isocyanurate. Examples of the silane coupling agent include silane compounds having a plurality of reactive functional groups such as polymerizable unsaturated groups, thiol groups, epoxy groups, and amino groups (so-called polyfunctional silane compounds).

[0086] As the silane coupling agent, commercially available products can be used. Examples of commercially available silane coupling agents include "X-41-1053," "X-41-1056," "X-41-1805," "X-41-1810," "X-41-1811," "X-41-1818," "KBE-402," "KBE-403," "KBE-9007N," "KBM-303," "KBM-402," "KBM-403," "KBM-573," "KBM-802," "KBM-803," and "KBM-9659" (all trade names) manufactured by Shin-Etsu Chemical Co., Ltd.

[0087] When the pressure-sensitive adhesive composition of the present disclosure contains a silane coupling agent, it may contain only one type of silane coupling agent, or may contain two or more types of silane coupling agents.

[0088] The content of the silane coupling agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably 0.1 to 1.0 parts by mass, more preferably 0.1 to 0.8 parts by mass, and even more preferably 0.1 to 0.5 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0089] [Specific (meth)acrylic polymer (B)] The pressure-sensitive adhesive composition of the present disclosure preferably further contains a (meth)acrylic polymer (B) having a glass transition temperature of 100° C. or higher and a weight-average molecular weight of 100,000 to 300,000. In the present disclosure, "a (meth)acrylic polymer (B) having a glass transition temperature of 100° C. or higher and a weight average molecular weight of 100,000 to 300,000" is also referred to as "specific (meth)acrylic polymer (B)." When the pressure-sensitive adhesive composition of the present disclosure further contains the specific (meth)acrylic polymer (B), the durability of the pressure-sensitive adhesive layer formed tends to be improved. This is thought to be because the addition of a component with a high glass transition temperature increases the elasticity of the pressure-sensitive adhesive layer, and the addition of a component with a low weight-average molecular weight increases the stress relaxation property of the pressure-sensitive adhesive layer.

[0090] The specific (meth)acrylic polymer (B) has a glass transition temperature of 100°C or higher, preferably 100 to 150°C, and more preferably 100 to 140°C. The specific (meth)acrylic polymer (B) has a glass transition temperature of 100° C. or higher, and thus can impart high elasticity to the pressure-sensitive adhesive layer to be formed.

[0091] The glass transition temperature of the specific (meth)acrylic polymer (B) is a value obtained by converting the absolute temperature (unit: K) calculated from the following formula 1 into Celsius temperature (unit: ° C.). 1 / Tg=m1 / Tg1+m2 / Tg2+ +m(k-1) / Tg(k-1)+mk / Tgk (Formula 1)

[0092] In formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk respectively represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific (meth)acrylic polymer (B) is made into a homopolymer. m1, m2, . . . , m(k-1), and mk respectively represent the molar fractions of each monomer constituting the specific (meth)acrylic polymer (B), and the equation is m1 + m2 + . . . + m(k-1) + mk = 1. Note that absolute temperatures can be converted to Celsius degrees by subtracting 273 from the absolute temperature, and Celsius degrees can be converted to absolute temperatures by adding 273 to the Celsius degrees.

[0093] In the present disclosure, the "glass transition temperature when converted into a homopolymer" refers to a value described in a publicly known document or a value measured using a differential scanning calorimeter (DSC). The specific value to be used is as follows:

[0094] For the "glass transition temperature when made into a homopolymer" of the monomers shown below, the value in parentheses is used. Methyl acrylate (10°C), methyl methacrylate (105°C), ethyl acrylate (-22°C), ethyl methacrylate (65°C), n-butyl acrylate (-54°C), n-butyl methacrylate (20°C), i-butyl methacrylate (53°C), t-butyl acrylate (43°C), t-butyl methacrylate (118°C), 2-ethylhexyl acrylate (-70°C), 2-ethylhexyl methacrylate (-10°C), n-octyl acrylate (-65°C), stearyl acrylate (30°C), stearyl methacrylate (38°C), lauryl acrylate (-3°C), lauryl methacrylate acrylate (-65°C), cyclohexyl methacrylate (104°C), isobornyl acrylate (94°C), benzyl acrylate (6°C), phenoxyethyl acrylate (-22°C), 2-methoxyethyl acrylate (-50°C), glycidyl methacrylate (74°C), 2-hydroxyethyl acrylate (-15°C), 2-hydroxyethyl methacrylate (85°C), 4-hydroxybutyl acrylate (-80°C), acrylic acid (106°C), methacrylic acid (228°C), dimethylaminoethyl methacrylate (18°C), ω-carboxy-polycaprolactone (n≒2) monoacrylate (-30°C).

[0095] Regarding the "glass transition temperature when made into a homopolymer" of a monomer other than the above-mentioned monomers, the value described in the Polymer Handbook (4th edition, Wiley-Interscience; the same applies hereinafter) is adopted. If there is no description in the Polymer Handbook, the value of the glass transition temperature of the homopolymer obtained by the following measurement method is adopted.

[0096] Specifically, a differential scanning calorimeter (DSC) is used to measure 10 mg of a measurement sample (i.e., homopolymer) in a nitrogen gas flow at a temperature increase rate of 10°C / min, and the inflection point of the obtained DSC curve is taken as the glass transition temperature of the homopolymer. As a differential scanning calorimeter, for example, a differential scanning calorimeter (trade name: Discovery DSC 2500) manufactured by TA Instruments Japan Co., Ltd. can be suitably used. However, the differential scanning calorimeter is not limited to this.

[0097] The glass transition temperature of the specific (meth)acrylic polymer (B) can be adjusted to a desired value, for example, by appropriately selecting the types and ratios of the monomers that are polymerization components of the specific (meth)acrylic polymer (B).

[0098] The specific (meth)acrylic polymer (B) has a weight average molecular weight of 100,000 to 300,000, and preferably 100,000 to 200,000. When the weight average molecular weight of the specific (meth)acrylic polymer (B) is within the above range, it can impart stress relaxation properties to the pressure-sensitive adhesive layer that is formed.

[0099] The weight average molecular weight of the specific (meth)acrylic polymer (B) is a value measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic polymer (A) described above.

[0100] The weight average molecular weight of the specific (meth)acrylic polymer (B) can be adjusted to a desired value by, for example, adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. when polymerizing the monomers.

[0101] The specific (meth)acrylic polymer (B) may be a homopolymer or a copolymer, and is not particularly limited. The structural units that the specific (meth)acrylic polymer (B) may contain will be described below.

[0102] The specific (meth)acrylic polymer (B) preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer. In the present disclosure, the "structural unit derived from a (meth)acrylic acid alkyl ester monomer" that the specific (meth)acrylic polymer (B) may contain is also referred to as the "structural unit (b1)." The type of (meth)acrylic acid alkyl ester monomer is not particularly limited. The (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer, but is preferably a methacrylic acid alkyl ester monomer. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent (excluding a hydroxyl group), but is preferably unsubstituted. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The alkyl moiety of the (meth)acrylic acid alkyl ester monomer preferably has 1 to 18 carbon atoms, more preferably 1 to 12 carbon atoms, further preferably 1 to 8 carbon atoms, and particularly preferably 1 to 4 carbon atoms.

[0103] Specific examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. The (meth)acrylic acid alkyl ester monomer can be appropriately selected depending on, for example, the desired glass transition temperature of the specific (meth)acrylic polymer (B). The (meth)acrylic acid alkyl ester monomer preferably includes at least one selected from methyl methacrylate and t-butyl methacrylate, for example, in that the glass transition temperature of the polymer can be easily adjusted to 100°C or higher.

[0104] When the specific (meth)acrylic polymer (B) contains the structural unit (b1), it may contain only one type of structural unit (b1), or may contain two or more types of structural unit (b1).

[0105] When the specific (meth)acrylic polymer (B) contains the structural unit (b1), the content of the structural unit (b1) in the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably 50% by mass or more, more preferably 70% by mass to 95% by mass, and even more preferably 80% by mass to 95% by mass, relative to all structural units of the specific (meth)acrylic polymer (B). Here, the content of the structural unit (b1) in the specific (meth)acrylic polymer (B) being 50 mass% or more relative to all structural units of the specific (meth)acrylic polymer (B) means that the structural unit (b1) is contained as a main component of the structural units of the specific (meth)acrylic polymer (B).

[0106] The specific (meth)acrylic polymer (B) preferably contains a structural unit derived from a monomer having a hydroxyl group. In the present disclosure, the "structural unit derived from a monomer having a hydroxyl group" that the specific (meth)acrylic polymer (B) may contain is also referred to as the "structural unit (b2)".

[0107] Specific examples of the monomer having a hydroxyl group are the same as those described in connection with the specific (meth)acrylic polymer (A). The monomer having a hydroxyl group can be appropriately selected depending on, for example, the desired glass transition temperature of the specific (meth)acrylic polymer (B). The monomer having a hydroxyl group preferably includes, for example, 2-hydroxyethyl methacrylate, in that the glass transition temperature of the polymer can be easily adjusted to 100°C or higher.

[0108] When the specific (meth)acrylic polymer (B) contains the structural unit (b2), it may contain only one type of structural unit (b2), or may contain two or more types of structural unit (b2).

[0109] When the specific (meth)acrylic polymer (B) contains the structural unit (b2), the content of the structural unit (b2) in the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably 0.01% by mass to 3.0% by mass, more preferably 0.1% by mass to 3.0% by mass, and even more preferably 0.1% by mass to 1.5% by mass, relative to all structural units of the specific (meth)acrylic polymer (B).

[0110] When the pressure-sensitive adhesive composition of the present disclosure contains the specific (meth)acrylic polymer (B), it may contain only one type of specific (meth)acrylic polymer (B), or may contain two or more types of specific (meth)acrylic polymer (B).

[0111] When the pressure-sensitive adhesive composition of the present disclosure contains the specific (meth)acrylic polymer (B), the content of the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably 5.0 parts by mass to 30.0 parts by mass, more preferably 5.0 parts by mass to 25.0 parts by mass, and even more preferably 5.0 parts by mass to 20.0 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0112] [Organic solvent] The pressure-sensitive adhesive composition of the present disclosure may contain an organic solvent. When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the coating properties can be improved. Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the specific (meth)acrylic polymer (A) described above.

[0113] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvents.

[0114] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be set appropriately depending on the purpose.

[0115] [Other ingredients] The pressure-sensitive adhesive composition of the present disclosure may contain components other than the components described above (so-called other components) as needed, provided that the effects of the composition are not impaired. Examples of other components include polymers other than the specific (meth)acrylic polymer (A) and the specific (meth)acrylic polymer (B), crosslinking catalysts, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and various additives such as antistatic agents.

[0116] When the pressure-sensitive adhesive composition of the present disclosure contains other components, the content of the other components can be set appropriately within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0117] <<Applications of adhesive compositions>> The pressure-sensitive adhesive composition of the present disclosure is a pressure-sensitive adhesive composition used in optical films, and is particularly suitable as a pressure-sensitive adhesive composition used in polarizing plates (i.e., a pressure-sensitive adhesive composition for polarizing plates).The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that exhibits excellent durability and suppression of white voids even when used in a single-sided TAC polarizing plate, and is therefore particularly suitable as a pressure-sensitive adhesive composition used in polarizing plates, particularly single-sided TAC polarizing plates. Specific applications of the pressure-sensitive adhesive composition of the present disclosure include bonding a polarizing plate (preferably a single-sided TAC polarizing plate) to a glass substrate of a liquid crystal cell, and bonding optical films together.

[0118] [Adhesive sheet] The pressure-sensitive adhesive sheet of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive sheet of the present disclosure also includes a sheet-like pressure-sensitive adhesive layer itself formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present disclosure contains a cured product of the pressure-sensitive adhesive composition of the present disclosure. The cured product includes, for example, a crosslinked product of the specific (meth)acrylic polymer (A) obtained by crosslinking and curing with a crosslinking agent. The pressure-sensitive adhesive sheet of the present disclosure has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore exhibits excellent durability and suppression of white voids even when used in a single-sided TAC polarizing plate.

[0119] The thickness of the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited. The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 30 μm.

[0120] In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" refers to the average thickness of the pressure-sensitive adhesive layer. The average thickness of the pressure-sensitive adhesive layer is a value determined by the following method. The thickness of the adhesive layer is measured at 10 randomly selected locations in the thickness direction using a film thickness meter. The arithmetic mean of the measured values ​​is calculated and this value is taken as the average thickness of the adhesive layer.

[0121] The pressure-sensitive adhesive sheet of the present disclosure may be a substrate-free pressure-sensitive adhesive sheet that does not have a substrate, or may be a substrate-containing pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one or both sides of a substrate. When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-free type pressure-sensitive adhesive sheet that does not have a substrate, or when it is a substrate-containing type pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one side of a substrate, the exposed surface of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet of the present disclosure may be protected by a release sheet. Generally, the release sheet protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is put to practical use, and is peeled off at the time of use.

[0122] The release sheet is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer. Examples of release sheets include resin films, paper, synthetic paper, and composite sheets made by laminating two or more of these, each of which has been surface-treated with a release agent on one or both sides (so-called easy-release treatment). In the present disclosure, a release sheet in an embodiment in which one or both sides of a resin film have been surface-treated with a release treatment agent (so-called easy-release treatment) is also referred to as a "release film." Examples of release agents include silicone-based release agents (such as silicone), wax-based release agents (such as paraffin wax), and fluorine-based release agents (such as fluorine-based resins). Examples of resin films include polyester films such as polyethylene terephthalate (PET) films. Examples of paper include fine paper and coated paper. The thickness of the release sheet is not particularly limited, and is generally 20 μm to 180 μm.

[0123] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed thereon. Examples of the substrate include films containing resins such as polyolefin resins (e.g., polyethylene (PE) and polypropylene (PP)), polyester resins (e.g., polyethylene terephthalate (PET)), acetate resins (e.g., triacetyl cellulose), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyurethane resins, (meth)acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins.

[0124] The surface of the substrate on which the adhesive layer is provided may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment (so-called easy-adhesion treatment) in order to improve the adhesion between the substrate and the adhesive layer.

[0125] The substrate may contain various additives such as plasticizers, colorants (eg, dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants, antioxidants, fillers, and the like. The substrate may be partially or entirely patterned.

[0126] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is preferably an optical film. In this case, a preferred embodiment of the pressure-sensitive adhesive sheet of the present disclosure includes an optical film and a pressure-sensitive adhesive layer provided on at least one surface of the optical film and formed from the pressure-sensitive adhesive composition of the present disclosure.

[0127] The type of optical film is not particularly limited. Specific examples of optical films include polarizing plates, AG (Anti-Glare) polarizing plates, wave plates (e.g., half-wave plates and quarter-wave plates), retardation films including the wave plates, viewing angle compensation films, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, prism sheets, lens sheets, diffusion plates, and transparent conductive films.

[0128] The optical film is preferably a polarizing plate (so-called polarizing film). The polarizing plate is configured to include at least a polarizer, and may be a polarizer alone or a laminate of a polarizer and a protective film. The polarizing plate may have a single-layer structure with a polarizer alone, a two-layer structure with a protective film provided on one side of the polarizer, or a three-layer structure with protective films provided on both sides of the polarizer.

[0129] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate and the substrate is a polarizing plate, examples of the layer configuration include pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer], pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer / protective film], pressure-sensitive adhesive layer / polarizing plate [retardation film / polarizer], pressure-sensitive adhesive layer / polarizing plate [retardation film / polarizer / protective film], pressure-sensitive adhesive layer / polarizing plate [retardation film / protective film / polarizer / protective film], pressure-sensitive adhesive layer / polarizing plate [polarizer / brightness-enhancing film], pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer / brightness-enhancing film], pressure-sensitive adhesive layer / polarizing plate [polarizer / protective film / brightness-enhancing film], and pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer / protective film / brightness-enhancing film].

[0130] The protective film may be a film containing a resin such as triacetyl cellulose (TAC), polycycloolefin (COP), polyethylene terephthalate (PET), or polymethyl methacrylate (PMMA). The polarizer may be, for example, a stretched film of polyvinyl alcohol (PVA) impregnated with iodine. The retardation film may be a film containing a resin such as polycycloolefin (COP).

[0131] The thickness of the substrate is not particularly limited, but is preferably from 10 μm to 500 μm, more preferably from 10 μm to 300 μm, and even more preferably from 10 μm to 200 μm.

[0132] In this disclosure, "thickness of the substrate" means the average thickness of the substrate. The average thickness of the substrate is a value determined by the following method. The thickness of the substrate is measured at 10 randomly selected locations in the thickness direction using a film thickness meter. The arithmetic mean of the measured values ​​is calculated and this value is taken as the average thickness of the substrate.

[0133] [How to make adhesive sheets] The method for producing the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited. The pressure-sensitive adhesive sheet of the present disclosure can be produced by a known method. The pressure-sensitive adhesive sheet of the present disclosure can be produced, for example, by the following method.

[0134] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-free type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present disclosure is applied to the easily peelable surface of the release sheet to form a coating film on the release sheet. The formed coating film is then dried to form an adhesive film on the release sheet. Next, the exposed surface of the formed adhesive film is laminated onto the easily peelable surface of a separately prepared release sheet, and then cured as necessary, thereby producing a pressure-sensitive adhesive sheet of the present disclosure having a laminated structure of release sheet / pressure-sensitive adhesive layer / release sheet.

[0135] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present disclosure is applied to one surface of the substrate (preferably the surface treated for easy adhesion) to form a coating film on the substrate. The formed coating film is then dried to form a pressure-sensitive adhesive film on the substrate. Next, the exposed surface of the formed pressure-sensitive adhesive film is laminated onto the surface of a release sheet treated for easy release, and then cured as necessary to produce a pressure-sensitive adhesive sheet of the present disclosure having a laminate structure of substrate / pressure-sensitive adhesive layer / release sheet.

[0136] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-containing pressure-sensitive adhesive sheet, another method may be mentioned, for example, as follows. The pressure-sensitive adhesive composition of the present disclosure is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet. The formed coating film is then dried to form a pressure-sensitive adhesive film on the release sheet. Next, the exposed surface of the formed pressure-sensitive adhesive film is laminated to one surface of the substrate (preferably the easy-adhesion treated surface), and then cured as necessary, thereby producing a pressure-sensitive adhesive sheet of the present disclosure having a laminated structure of substrate / pressure-sensitive adhesive layer / release sheet.

[0137] The method for applying the pressure-sensitive adhesive composition is not particularly limited. Examples of methods for applying the pressure-sensitive adhesive composition include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, knife coater, spray coater, bar coater, applicator, etc. The amount of the pressure-sensitive adhesive composition to be applied is not particularly limited, and is set appropriately depending on, for example, the thickness of the pressure-sensitive adhesive layer to be formed.

[0138] The method for drying the coating film is not particularly limited. Examples of methods for drying the coating film include natural drying, heat drying, hot air drying, and vacuum drying. The drying temperature and drying time of the coating film are not particularly limited, and are set appropriately depending on the thickness of the coating film, the amount of solvent contained in the coating film, and the like. Drying conditions include, for example, using a hot air circulation dryer to blow air at 60°C to 130°C at a speed of 3 m / sec to 5 m / sec for 30 seconds to 300 seconds.

[0139] As a method for curing, for example, a method of leaving the product to stand in an environment with an atmospheric temperature of 20°C to 35°C and a relative humidity of 45% to 65% for 2 to 7 days can be mentioned.

[0140] [Optical components] The optical member of the present disclosure includes, in this order, a glass substrate, a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure described above, and an optical film. The optical member of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure as described above. Therefore, even if the optical film is a thinner polarizer than conventional ones, such as a single-sided TAC polarizer, foaming is unlikely to occur at the interface between the pressure-sensitive adhesive layer and the glass substrate in a high-temperature environment, wrinkles are unlikely to occur in the pressure-sensitive adhesive layer and / or the optical film, peeling is unlikely to occur at the interface between the pressure-sensitive adhesive layer and the optical film and / or the glass substrate, and white spots are unlikely to occur.

[0141] The thickness of the glass substrate is not particularly limited, but is generally 0.3 mm to 0.7 mm, and preferably 0.3 mm to 0.5 mm.

[0142] Examples of the glass substrate include a soda glass plate, an alkali-free glass plate, and an ITO (Indium Tin Oxide) film-coated glass plate.

[0143] The pressure-sensitive adhesive layer and optical film in the optical member of the present disclosure have the same meaning as the pressure-sensitive adhesive layer and optical film in the pressure-sensitive adhesive sheet of the present disclosure, and preferred embodiments are also the same, so description thereof will be omitted here.

[0144] The optical member of the present disclosure can be suitably used, for example, as a member of a display device. Examples of display devices include liquid crystal displays and organic EL (Electro-Luminescence) displays.

[0145] The method for producing the optical member of the present disclosure is not particularly limited. The optical member of the present disclosure can be produced, for example, by using an optical film as a substrate, preparing a pressure-sensitive adhesive sheet of the present disclosure by the method described above, and then bonding the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet to a glass substrate.

[0146] [Display device] The display device of the present disclosure includes the optical member of the present disclosure described above. Because the display device of the present disclosure includes the optical component of the present disclosure, even if the optical film is a thinner polarizer than conventional ones, such as a single-sided TAC polarizer, in a high-temperature environment, foaming is less likely to occur at the interface between the adhesive layer and the glass substrate, wrinkles are less likely to occur in the adhesive layer and / or the optical film, peeling is less likely to occur at the interface between the adhesive layer and the optical film and / or the glass substrate, and the white void phenomenon is less likely to occur.

[0147] Specific examples of the display device are as described above. [Example]

[0148] The pressure-sensitive adhesive composition of the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure.

[0149] [Production of (meth)acrylic polymer (A)] [Manufacturing example A-1] A reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser was charged with 70.7 parts by weight of n-butyl acrylate (n-BA), 7.5 parts by weight of methyl acrylate (MA), 20.0 parts by weight of phenoxyethyl acrylate (PHEA), 1.5 parts by weight of acrylic acid (AA), 0.3 parts by weight of 2-hydroxyethyl acrylate (2HEA), and 50.0 parts by weight of methyl acetate (organic solvent). The contents of the reactor were then purged with nitrogen. The mixture was then heated to 70°C with stirring, and 0.001 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile) (ABVN; polymerization initiator) and 120.0 parts by weight of ethyl acetate (organic solvent) were added sequentially to the mixture. After the addition was completed, the mixture was held for 6 hours to allow the polymerization reaction to proceed, yielding a polymerization product. The obtained polymerization reaction product was diluted with ethyl acetate to a solid content concentration of 15.0% by mass, and then cooled to obtain a solution of (meth)acrylic polymer A-1.

[0150] The term "solid content" as used herein refers to the mass proportion of the (meth)acrylic polymer A-1 in the solution of the (meth)acrylic polymer A-1. The same applies to the solutions of the (meth)acrylic polymers A-2 to A-32 produced below.

[0151] [Production Examples A-2 to A-12, A-14, A-17 to A-25, and A-29 to A-32] In Production Examples A-2 to A-12, A-14, A-17 to A-25, and A-29 to A-32, the same operation as in Production Example A-1 was carried out, except that the monomer composition of the (meth)acrylic polymer (A) was changed to the monomer composition shown in Table 1, to obtain solutions of (meth)acrylic polymers A-2 to A-12, A-14, A-17 to A-25, and A-29 to A-32 each having a solids concentration of 15.0 mass%.

[0152] [Production Examples A-13 and A-26] In Production Examples A-13 and A-26, the monomer composition of the (meth)acrylic polymer (A) was changed to the monomer composition shown in Table 1, and the weight average molecular weight of the (meth)acrylic polymer (A) was adjusted to the weight average molecular weight shown in Table 1 by adjusting at least one of the amount of organic solvent used and the amount of polymerization initiator used, to obtain solutions of (meth)acrylic polymers A-13 and A-26 each having a solids concentration of 15.0 mass%.

[0153] [Production Examples A-15, A-16, A-27 and A-28] In Production Examples A-15, A-16, A-27, and A-28, the same operation as in Production Example A-5 was carried out, except that the weight average molecular weight of the (meth)acrylic polymer (A) was adjusted to the weight average molecular weight shown in Table 1 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, to obtain solutions of (meth)acrylic polymers A-15, A-16, A-27, and A-28 each having a solids concentration of 15.0 mass%.

[0154] Table 1 shows the monomer compositions (unit: mass %) and weight average molecular weights (denoted as "Mw") of the (meth)acrylic polymers A-1 to A-32.

[0155] The weight average molecular weights of the (meth)acrylic polymers A-1 to A-32 were measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic polymer (A) described above.

[0156] Among the (meth)acrylic polymers A-1 to A-32, the (meth)acrylic polymers A-1 to A-19 correspond to the specific (meth)acrylic polymer (A) of the present disclosure.

[0157] [Table 1]

[0158] Details of each monomer listed in Table 1 are as follows: In Table 1, for the sake of convenience, "a (meth) acrylic acid ester monomer having an aromatic ring" is represented as "(a1)", "an acrylic acid alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety" is represented as "(a2)", "a monomer having a carboxy group" is represented as "(a3)", "a monomer having a hydroxyl group" is represented as "(a4)", and "other (meth) acrylic acid alkyl ester monomer" is represented as "(a5)".

[0159] (a1) Aromatic ring-containing (meth)acrylic acid ester monomer "PHEA": Phenoxyethyl acrylate "BZA": Benzyl acrylate (a2) Acrylic acid alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety "MA": methyl acrylate "EA": Ethyl acrylate (a3) Monomer having a carboxy group "AA": acrylic acid (a4) Monomer having a hydroxyl group "2HEA": 2-hydroxyethyl acrylate (a5) Other (meth)acrylic acid alkyl ester monomers "n-BA": n-butyl acrylate "2EHA": 2-ethylhexyl acrylate "MMA": Methyl methacrylate

[0160] In Table 1, "-" in the column of monomer composition means that the monomer in that column was not used. In Table 1, "molar ratio (a1) / (a2)" means the "molar ratio of the content of structural unit (a1) to the content of structural unit (a2) [content of structural unit (a1) / content of structural unit (a2)]," and "-" in the "molar ratio (a1) / (a2)" column means that there is no applicable data.

[0161] [Production of (meth)acrylic polymer (B)] [Manufacturing example B-1] A reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser was charged with 15.0 parts by weight of methyl methacrylate (MMA), 84.6 parts by weight of t-butyl methacrylate (t-BMA), 0.4 parts by weight of 2-hydroxyethyl methacrylate (2HEMA), and 55.0 parts by weight of ethyl acetate (organic solvent). The mixture was then mixed to obtain a mixture, and the atmosphere inside the reactor was then purged with nitrogen. The mixture inside the reactor was then heated to 85°C while stirring, and 0.013 parts by weight of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator) and 35.0 parts by weight of ethyl acetate (organic solvent) were then sequentially added to the mixture inside the reactor. After the addition was completed, the mixture was held for 6 hours to allow polymerization, yielding a polymerization product. The resulting polymerization product was diluted with ethyl acetate to a solids concentration of 45.0% by weight and then cooled to obtain a solution of (meth)acrylic polymer B-1.

[0162] The term "solids concentration" used herein refers to the mass proportion of the (meth)acrylic polymer B-1 in the solution of the (meth)acrylic polymer B-1. The same applies to the solutions of the (meth)acrylic polymers B-2 and B-3 produced below.

[0163] [Manufacturing example B-2] In Production Example B-2, the same operations as in Production Example B-1 were carried out, except that the weight average molecular weight of the (meth)acrylic polymer (B) was adjusted to the weight average molecular weight shown in Table 2 by adjusting at least one of the amount of the organic solvent used and the amount of the polymerization initiator used, to obtain a solution of (meth)acrylic polymer B-2 having a solid content concentration of 45.0 mass%.

[0164] [Manufacturing example B-3] In Production Example B-3, the same operation as in Production Example B-1 was carried out except that the monomer composition of the (meth)acrylic polymer (B) was changed to the monomer composition shown in Table 2, and a solution of (meth)acrylic polymer B-3 having a solids concentration of 45.0 mass% was obtained.

[0165] Table 2 shows the monomer compositions (unit: mass %), glass transition temperatures (denoted as "Tg"), and weight average molecular weights (denoted as "Mw") of the (meth)acrylic polymers B-1 to B-3.

[0166] The glass transition temperatures of the (meth)acrylic polymers B-1 to B-3 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic polymer (B) described above. The weight average molecular weights of the (meth)acrylic polymers B-1 to B-3 were measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic polymer (A) described above.

[0167] The (meth)acrylic polymers B-1 to B-3 all correspond to the specific (meth)acrylic polymer (B) of the present disclosure.

[0168] [Table 2]

[0169] Details of each monomer listed in Table 2 are as follows: In Table 2, for convenience, "(meth)acrylic acid alkyl ester monomer" is represented as "(b1)" and "monomer having a hydroxyl group" is represented as "(b2)".

[0170] (b1) (Meth)acrylic acid alkyl ester monomer "MMA": Methyl methacrylate "i-BMA": i-butyl methacrylate "t-BMA": t-butyl methacrylate (b2) Monomer having a hydroxyl group "2HEMA": 2-hydroxyethyl methacrylate

[0171] In Table 2, "-" in the column of monomer composition means that the monomer in that column was not used.

[0172] [Preparation of Pressure-Sensitive Adhesive Composition] Example 1 A pressure-sensitive adhesive composition of Example 1 was obtained by thoroughly mixing 666.7 parts by mass (100 parts by mass as solids) of the solution of (meth)acrylic polymer A-1, 0.89 parts by mass (0.4 parts by mass as solids) of the isocyanate-based crosslinking agent Takenate D-101E (trade name, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solids concentration: 45% by mass, manufactured by Mitsui Chemicals, Inc.) as a crosslinking agent, 0.3 parts by mass (0.3 parts by mass as solids) of X-41-1810 (trade name, thiol group-containing silane compound, solids concentration: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent, and an appropriate amount of ethyl acetate (organic solvent).

[0173] Examples 2 to 26 In Examples 2 to 26, the same procedure as in Example 1 was carried out except that the formulation of the adhesive composition was changed to the formulation shown in Table 3, to obtain each of the adhesive compositions of Examples 2 to 26.

[0174] Comparative Examples 1 to 14 In Comparative Examples 1 to 14, the same procedure as in Example 1 was carried out except that the formulation of the adhesive composition was changed to the formulation shown in Table 4, to obtain each of the adhesive compositions of Comparative Examples 1 to 14.

[0175] [Preparation of single-sided TAC polarizer with adhesive layer] The pressure-sensitive adhesive composition prepared above was applied to the easily peelable surface of a release film (type: MRF, thickness: 38 μm, manufactured by Mitsubishi Chemical Corporation) that had been surface-treated with a silicone-based release agent (so-called easily peelable treatment) to form a coating film. The amount of pressure-sensitive adhesive composition applied was such that the thickness of the adhesive film described below would be 15 μm. Next, the formed coating film was dried by blowing 100°C air at a wind speed of 3 m / s for 180 seconds using a hot air circulation dryer, thereby forming a 15 μm-thick adhesive film on the release film. Next, the exposed surface of the formed adhesive film was laminated to the TAC layer surface of a single-sided TAC polarizing plate (thickness: 75 μm) having a polyvinyl alcohol (PVA) layer / triacetyl cellulose (TAC) layer structure containing a polarizer. Next, the laminate obtained by lamination was left to stand for 4 days (so-called curing period) in an environment of an atmospheric temperature of 32°C and 65% RH to cure the adhesive film. In this way, a single-sided TAC polarizing plate with an adhesive layer was produced, which had a structure of release film / adhesive layer / polarizing plate (TAC layer / PVA layer).

[0176] [evaluation] 1.Durability (1) Preparation of evaluation samples The single-sided TAC polarizing plate with the adhesive layer prepared above was cut into a size of 66 mm (short side) × 136 mm (long side) so that the long side was at 0° with respect to the absorption axis of the polarizing plate to prepare a test piece. Next, the release film of the prepared test piece was peeled off, and the surface of the adhesive layer exposed by peeling was laminated on one side of a glass plate (type: soda glass, manufactured by Matsunami Glass Industry Co., Ltd.) and pressed using a laminator. In this manner, evaluation sample X having a structure of glass plate / adhesive layer / polarizing plate (TAC layer / PVA layer) was prepared.

[0177] (2) Evaluation test The evaluation sample X prepared above was treated at a temperature of 50°C and a pressure of 5 kg / cm 2After autoclaving for 20 minutes under the above conditions, the sample was left to stand for 24 hours in an environment with an ambient temperature of 23°C and 50% RH. After standing for 24 hours, the evaluation sample X was left to stand for 170 hours in an environment with an ambient temperature of 85°C and 10% RH (a so-called high-temperature, low-humidity environment). After standing for 170 hours, the condition of the evaluation sample X was visually observed, and durability was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 3 and 4. An evaluation result of "A," "B," or "C" is considered passing, with "A" being the most preferable.

[0178] -Evaluation criteria- A: No foaming, wrinkling or peeling was observed. B: At least one of bubbling, wrinkling, and peeling was slightly observed, but was at a level that would not cause any practical problems. C: At least one of bubbling, wrinkling, and peeling was observed, but was at a level acceptable for practical use. D: At least one of bubbling, wrinkling, and peeling was significantly observed, and was at a level that was not acceptable for practical use.

[0179] 2. Suppression of white spots (1) Preparation of evaluation samples The single-sided TAC polarizing plate with adhesive layer prepared as above was cut into two pieces measuring 66 mm (short side) x 136 mm (long side), one so that the long side was at 0° to the absorption axis of the polarizing plate, and the other so that the long side was at 90° to the absorption axis of the polarizing plate, to prepare two test pieces. Next, the release films of the two test pieces prepared were peeled off, and the surfaces of the adhesive layers exposed by the peeling were laminated on both sides of glass plates (type: soda glass, manufactured by Matsunami Glass Industry Co., Ltd.) so that the absorption axes of the test pieces were perpendicular to each other, and the pieces were pressed together using a laminator. In this manner, evaluation sample Y was prepared, which had a structure of polarizing plate (PVA layer / TAC layer) / adhesive layer / glass plate / adhesive layer / polarizing plate (TAC layer / PVA layer).

[0180] (2) Evaluation test The evaluation sample Y prepared above was treated at a temperature of 50°C and a pressure of 5 kg / cm 2 After autoclaving for 20 minutes under these conditions, Sample Y was left to stand for 24 hours in an environment with an ambient temperature of 23°C and 50% RH. After standing for 24 hours, Evaluation Sample Y was left to stand for 170 hours in an environment with an ambient temperature of 85°C and 10% RH (a so-called high-temperature, low-humidity environment). After standing for 170 hours, Evaluation Sample Y was placed on the backlight of an LCD monitor in an environment with an ambient temperature of 23°C and 50% RH, and the state of white spots was visually observed. The ability to suppress the occurrence of white spots was evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 3 and 4. An evaluation result of "A" or "B" is considered a pass, with "A" being the most preferable.

[0181] -Evaluation criteria- A: No white spots were observed, or slight white spots were observed but at a level that would not cause any practical problems. B: White spots were observed, but were at a level acceptable for practical use. C: Significant white spots were observed, and the level was practically unacceptable.

[0182] [Table 3]

[0183] [Table 4]

[0184] Details of the components listed in Tables 3 and 4 are as follows: <Crosslinking agent> -Isocyanate-based crosslinking agent- "Takenate D-101E" (trade name, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), solid content: 45% by mass, manufactured by Mitsui Chemicals, Inc.) "Takenate D-110N" (product name, adduct of xylylene diisocyanate (XDI) and trimethylolpropane (TMP), solid content: 75% by mass, manufactured by Mitsui Chemicals, Inc.) -Metal chelate crosslinking agent- "Aluminum Chelate A" (trade name, aluminum chelate compound, solid content: 100% by mass, manufactured by Kawaken Fine Chemicals Co., Ltd.) <Silane coupling agent> "X-41-1810" (product name, thiol group-containing silane compound, solid content: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.) The above "Takenate" is a registered trademark.

[0185] In Tables 3 and 4, the values ​​shown in the "blending amount" column are all solid content converted values. In Tables 3 and 4, "-" in the column for the composition of the adhesive composition means that the component in that column was not blended.

[0186] As shown in Table 3, it was confirmed that the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Examples 1 to 26 exhibited excellent durability and suppression of white voids even when used in a single-sided TAC polarizing plate. On the other hand, as shown in Table 4, it was confirmed that the adhesive layers formed using the adhesive compositions of Comparative Examples 1 to 14 were inferior to the adhesive layers formed using the adhesive compositions of the Examples in at least one of durability and suppression of white spots when used in a single-sided TAC polarizing plate.

Claims

1. The composition comprises a (meth)acrylic polymer (A) and a crosslinking agent, the (meth)acrylic polymer (A) comprises a structural unit (a1) derived from a (meth)acrylic acid ester monomer having an aromatic ring, a structural unit (a2) derived from an acrylate alkyl ester monomer having 1 to 2 carbon atoms in the alkyl moiety, a structural unit (a3) ​​derived from a monomer having a carboxy group, and a structural unit (a4) derived from a monomer having a hydroxyl group, the content of the structural unit (a1) being 16.0% by mass to 20.0% by mass of all structural units, the content of the structural unit (a3) ​​being 0.1% by mass to 3.0% by mass of all structural units, the molar ratio of the content of the structural unit (a1) to the content of the structural unit (a2) being 1.15 to 4.10, and the weight average molecular weight being 1,500,000 to 2,500,000.

2. The pressure-sensitive adhesive composition for optical films according to claim 1 , wherein the (meth)acrylic acid ester monomer having an aromatic ring comprises at least one selected from the group consisting of phenoxyethyl acrylate and benzyl acrylate.

3. The pressure-sensitive adhesive composition for use on an optical film according to claim 1 , wherein the crosslinking agent comprises an isocyanate-based crosslinking agent.

4. The pressure-sensitive adhesive composition for an optical film according to claim 1 , further comprising a silane coupling agent.

5. 2. The pressure-sensitive adhesive composition for optical films according to claim 1, further comprising a (meth)acrylic polymer (B) having a glass transition temperature of 100° C. or higher and a weight average molecular weight of 100,000 to 300,000.

6. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for use on an optical film according to any one of claims 1 to 5.

7. An optical film; a pressure-sensitive adhesive layer provided on at least one surface of the optical film and formed from the pressure-sensitive adhesive composition for an optical film according to any one of claims 1 to 5; An adhesive sheet comprising:

8. The pressure-sensitive adhesive sheet according to claim 7 , wherein the optical film is a polarizing plate.

9. A glass substrate; A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for an optical film according to any one of claims 1 to 5; An optical film; An optical element comprising the above in this order.

10. A display device comprising the optical member according to claim 9 .

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