Pressure-sensitive adhesive composition for optical member, pressure-sensitive adhesive layer, and optical member with pressure-sensitive adhesive layer

Abstract

To provide a pressure-sensitive adhesive composition for an optical member capable of forming a pressure-sensitive adhesive layer excellent in durability and curved surface adhesiveness under a high-temperature environment, and to provide the pressure-sensitive adhesive layer and an optical member with the pressure-sensitive adhesive layer.SOLUTION: A structural unit (a1) derived from an alkyl (meth)acrylate monomer containing at least methyl (meth)acrylate and a structural unit (a2) derived from a monomer having a hydroxyl group, wherein the content of the structural unit derived from methyl (meth)acrylate is from 15.0 mass% to 40.0 mass% with respect to the total structural units, and the content of the structural unit (a2) is in a range of more than 0 mass% and less than 0.3 mass% with respect to the total structural units; The pressure-sensitive adhesive composition for an optical member contains a (meth)acrylic copolymer having Mw of 1,800,000-2,500,000 and Mw / Mn of 3.0-5.0, an aromatic isocyanate-based crosslinking agent, and a crosslinking catalyst, wherein the content of the crosslinking agent is 0.05-0.4 parts by mass based on 100 parts by mass of the copolymer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a pressure-sensitive adhesive composition for an optical member, a pressure-sensitive adhesive layer, and an optical member with a pressure-sensitive adhesive layer. [Background technology]

[0002] Optical films such as polarizing plates are used as components in image display devices such as smartphones, tablet terminals, and televisions (e.g., liquid crystal display devices and organic EL (Electro Luminescence) display devices). These optical films are often bonded to image display elements (e.g., liquid crystal display elements and organic EL display elements) via a pressure-sensitive adhesive layer. To ensure visibility, (meth)acrylic pressure-sensitive adhesive compositions are often used to form the pressure-sensitive adhesive layer used to bond the optical film to the image display element.

[0003] Optical films such as polarizing plates are usually constructed by laminating multiple components with different shrinkage rates, and are therefore prone to dimensional changes due to temperature changes. When dimensional changes occur in the optical film, stress is generated in the optical film due to the dimensional changes, which places a load on the pressure-sensitive adhesive layer. Therefore, when an optical film bonded to an image display element via the pressure-sensitive adhesive layer is exposed to a high-temperature environment, wrinkles may form in the pressure-sensitive adhesive layer and / or the optical film, or foaming and / or peeling may occur at the interface between the pressure-sensitive adhesive layer and the optical film and / or the image display element. Under these circumstances, pressure-sensitive adhesive compositions used for optical members are required to be capable of forming pressure-sensitive adhesive layers having excellent durability and capable of effectively suppressing wrinkles, foaming, and peeling that may occur when exposed to a high-temperature environment. In particular, image display devices such as car navigation systems and liquid crystal digital meters installed in automobiles and the like are sometimes exposed to extremely high-temperature environments, and therefore the pressure-sensitive adhesive layers are required to have durability at extremely high temperatures.

[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 polarized films has been reported, which contains, as essential components, (B) 0.3 to 3 parts by mass of a polyisocyanate compound, and (C) 0.05 to 5 parts by mass of a mercapto group- or alicyclic epoxy group-containing silane coupling agent, based on 100 parts by mass of (A) an acrylic copolymer (where the mass of the acrylic copolymer is taken as 100% by mass) containing 0.1 to 1% by mass of repeating units having a carboxy group in the molecule and 0.01 to 0.5% by mass of repeating units having a hydroxy group, and having a weight-average molecular weight (Mw) of 800,000 or more and a glass transition temperature (Tg) of −40° C. or less (see, for example, Patent Document 1). Also reported is a pressure-sensitive adhesive composition for polarizing plates, which contains a (meth)acrylic copolymer including structural units formed from a (meth)acrylic acid alkyl ester, at least one structural unit selected from the group consisting of structural units formed from a monomer having a hydroxyl group, and structural units formed from a monomer having a carboxy group, and a tolylene diisocyanate crosslinking agent, in which the total content of structural units formed from the monomer having a hydroxyl group and structural units formed from the monomer having a carboxy group in the (meth)acrylic copolymer is greater than 0 mass% and 0.45 mass% or less, based on all structural units, and the ratio of the number of moles of isocyanate groups in the tolylene diisocyanate crosslinking agent to the total number of moles of the hydroxyl groups and the carboxy groups is 3.0 to 22.0 (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-224873 [Patent Document 2] Japanese Patent Publication No. 2020-129103 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been an increasing demand for display devices with curved surfaces to improve design and operability. When an optical film with a pressure-sensitive adhesive layer is attached to a display device with a curved surface, the optical film attempts to return to its original shape, causing a load on the pressure-sensitive adhesive layer. Therefore, in a high-temperature environment, in addition to the load caused by dimensional changes in the optical film due to heat, the pressure-sensitive adhesive layer is also subjected to a load caused by the shape recovery of the optical film attached to the curved surface. In order for the pressure-sensitive adhesive layer to withstand the load caused by dimensional changes in the optical film, it is necessary to increase the cohesive strength of the pressure-sensitive adhesive layer. However, a pressure-sensitive adhesive layer with high cohesive strength cannot flexibly conform to a curved surface when attached, and is prone to peeling.

[0007] Therefore, pressure-sensitive adhesive compositions used for optical members are required to be capable of forming pressure-sensitive adhesive layers that have high cohesive strength capable of withstanding the loads that arise due to dimensional changes in the optical film, and sufficient flexibility to conform to curved surfaces.

[0008] 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 members, which can form a pressure-sensitive adhesive layer that is excellent in durability under high-temperature environments and in curved surface adhesion. Another problem to be solved by another embodiment of the present disclosure is to provide a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for optical members, and an optical member with a pressure-sensitive adhesive layer including the pressure-sensitive adhesive layer. [Means for solving the problem]

[0009] Specific means for solving the problems include the following aspects. <1> a (meth)acrylic copolymer comprising structural units (a1) derived from a (meth)acrylic acid alkyl ester monomer containing at least methyl (meth)acrylate and structural units (a2) derived from a monomer having a hydroxyl group, wherein the content of the structural units derived from methyl (meth)acrylate is in the range of 15.0% by mass or more and 40.0% by mass or less, based on all structural units, and the content of the structural units (a2) is in the range of more than 0% by mass and less than 0.3% by mass, based on all structural units; and wherein the weight average molecular weight is in the range of 1,800,000 or more and 2,500,000 or less, and the molecular weight distribution is in the range of 3.0 or more and 5.0 or less; an aromatic isocyanate-based crosslinking agent; a crosslinking catalyst; Including, A pressure-sensitive adhesive composition for optical members, wherein the content of the aromatic isocyanate crosslinking agent is in the range of 0.05 parts by mass or more and 0.4 parts by mass or less per 100 parts by mass of the (meth)acrylic copolymer. <2> the (meth)acrylic copolymer further contains a structural unit (a3) ​​derived from a monomer having a carboxy group; <1> The pressure-sensitive adhesive composition for optical members according to claim 1. <3> the content of the structural unit (a3) ​​in the (meth)acrylic copolymer is in the range of more than 0% by mass and less than 0.3% by mass, based on all structural units; <2> The pressure-sensitive adhesive composition for optical members according to claim 1. <4> The (meth)acrylic copolymer has a glass transition temperature in the range of −45° C. or higher and −20° C. or lower. <1> ~ <3> 10. The pressure-sensitive adhesive composition for optical members according to any one of the above items. <5> The gel fraction after crosslinking is in the range of 50% by mass or more and 85% by mass or less. <1> ~ <4> 10. The pressure-sensitive adhesive composition for optical members according to any one of the above items. <6> the (meth)acrylic copolymer further contains a structural unit (a4) derived from a (meth)acrylate having an aromatic ring; <1> ~ <5> 10. The pressure-sensitive adhesive composition for optical members according to any one of the above items. <7> the content of the structural unit (a4) in the (meth)acrylic copolymer is in the range of 15.0% by mass or more and 20.0% by mass or less, based on all structural units; <6> The pressure-sensitive adhesive composition for optical members according to claim 1. <8> <1> ~ <7> 1. A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for optical members according to any one of 1 to 8. <9> an optical member; <8> the pressure-sensitive adhesive layer according to An optical member with a pressure-sensitive adhesive layer comprising: [Effects of the Invention]

[0010] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition for optical members, which can form a pressure-sensitive adhesive layer that is excellent in durability under high-temperature environments and in curved surface adhesion. According to another embodiment of the present disclosure, there are provided a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for an optical member, and an optical member with a pressure-sensitive adhesive layer including the pressure-sensitive adhesive layer. DETAILED DESCRIPTION OF THE INVENTION

[0011] The pressure-sensitive adhesive composition for optical members, the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer-attached optical member of the present disclosure will be described in detail below. The following description of the requirements 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.

[0012] 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 this disclosure, the upper or lower limit value described in one 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.

[0013] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0014] In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified.

[0015] 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 only solvent contained in the composition is water, the solid content refers to the components other than water contained in the composition; when the only solvent contained in the composition is an organic solvent, the solid content refers to the components other than the organic solvent contained in the composition; and when the solvents contained in the composition are water and an organic solvent, the solid content refers to the components other than water and the organic solvent contained in the composition.

[0016] In the present disclosure, the term "(meth)acrylic copolymer" refers to a copolymer 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. In the present disclosure, the term "(meth)acrylic monomer" means a monomer having a (meth)acryloyl group.

[0017] 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."

[0018] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0019] In the present disclosure, the terms "monomer" and "monomer compound" are synonymous, and the terms "polymer" and "polymeric compound" are synonymous.

[0020] In the present disclosure, "% by mass" and "% by weight" are synonymous, and "parts by mass" and "parts by weight" are synonymous.

[0021] In the present disclosure, the term "structural unit derived from a monomer" refers to a structural unit formed by addition polymerization of a monomer.

[0022] 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.

[0023] [Adhesive composition for optical members] The pressure-sensitive adhesive composition for optical members of the present disclosure (hereinafter also simply referred to as "pressure-sensitive adhesive composition") comprises a (meth)acrylic copolymer that contains structural units (a1) derived from a (meth)acrylic acid alkyl ester monomer containing at least methyl (meth)acrylate and structural units (a2) derived from a monomer having a hydroxyl group, the content of the structural units derived from methyl (meth)acrylate being in the range of 15.0 to 40.0 mass% of all structural units, the content of the structural units (a2) being in the range of more than 0 mass% and less than 0.3 mass% of all structural units, the weight-average molecular weight being in the range of 1.8 million to 2.5 million and the molecular weight distribution being in the range of 3.0 to 5.0, an aromatic isocyanate-based crosslinking agent, and a crosslinking catalyst, the content of the aromatic isocyanate-based crosslinking agent being in the range of 0.05 to 0.4 parts by mass per 100 parts by mass of the (meth)acrylic copolymer.

[0024] The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that is excellent in durability in high-temperature environments and in adhesiveness to curved surfaces. 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.

[0025] Copolymers containing structural units derived from (meth)acrylic acid alkyl ester monomers with short side chains, such as methyl (meth)acrylate, tend to exhibit strong interactions and entanglements between copolymers, which can enhance the cohesive strength of the pressure-sensitive adhesive layer that is formed. Furthermore, the higher the molecular weight of a copolymer, the stronger the entanglement between copolymers, which can enhance the cohesive strength of the pressure-sensitive adhesive layer that is formed. Furthermore, when comparing copolymers with similar weight-average molecular weights but different molecular weight distributions, copolymers with narrow molecular weight distributions are more likely to enhance the cohesive strength of the pressure-sensitive adhesive layer that is formed than copolymers with broad molecular weight distributions. Furthermore, the greater the amount of crosslinking agent in the pressure-sensitive adhesive composition and the greater the amount of groups in the copolymer that react with the crosslinking agent (so-called reactive groups), the denser the crosslinked structure that is formed, which tends to enhance the cohesive strength of the pressure-sensitive adhesive layer. On the other hand, the higher the cohesive strength of the pressure-sensitive adhesive layer, the harder it becomes and the lower its flexibility tends to be.

[0026] In the pressure-sensitive adhesive composition of the present disclosure, by adjusting the content of the structural unit derived from methyl (meth)acrylate and the structural unit (a2) derived from a monomer having a hydroxyl group in the (meth)acrylic copolymer, the weight-average molecular weight and molecular weight distribution of the (meth)acrylic copolymer, and the content of the aromatic isocyanate-based crosslinking agent, the pressure-sensitive adhesive layer formed is imparted with a good balance of cohesive strength capable of withstanding loads arising from dimensional changes in the optical film and flexibility to conform to curved surfaces, and it is presumed that this makes it possible to achieve both excellent durability and curved surface adhesion in high-temperature environments. It should be noted that although the pressure-sensitive adhesive composition of the present disclosure has a relatively small content of aromatic isocyanate-based crosslinking agent and a relatively low content of the structural unit (a2) in the (meth)acrylic copolymer, the crosslinking reaction between the (meth)acrylic copolymer and the aromatic isocyanate-based crosslinking agent is thought to proceed quickly because the pressure-sensitive adhesive composition contains a crosslinking catalyst.

[0027] In contrast to the pressure-sensitive adhesive composition of the present disclosure, a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition described in Patent Document 1 (JP 2004-224873 A; the same applies hereinafter) is said to be excellent in durability and does not peel even in a high-temperature environment of 100°C. Furthermore, a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition described in Patent Document 2 (JP 2020-129103 A; the same applies hereinafter) is said to be excellent in durability and does not foam even in a high-temperature environment of 115°C. However, neither the pressure-sensitive adhesive composition described in Patent Document 1 nor the pressure-sensitive adhesive composition described in Patent Document 2 is intended for use in bonding optical films to curved surfaces, and is not designed to balance the cohesive strength and flexibility of the layer formed. Therefore, when the formed layer is used to bond an optical film to a curved surface, there is a risk of the layer peeling.

[0028] In the present disclosure, "a (meth)acrylic copolymer comprising structural units (a1) derived from a (meth)acrylic acid alkyl ester monomer containing at least methyl (meth)acrylate and structural units (a2) derived from a monomer having a hydroxyl group, wherein the content of the structural units derived from the methyl (meth)acrylate is in the range of 15.0% by mass or more and 40.0% by mass or less with respect to all structural units, and the content of the structural units (a2) is in the range of more than 0% by mass and less than 0.3% by mass with respect to all structural units, and wherein the weight-average molecular weight is in the range of 1.8 million or more and 2.5 million or less, and the molecular weight distribution is in the range of 3.0 or more and 5.0 or less" is also referred to as a "specific (meth)acrylic copolymer."

[0029] [Specific (meth)acrylic copolymer] The pressure-sensitive adhesive composition of the present disclosure comprises a (meth)acrylic copolymer (i.e., a specific (meth)acrylic copolymer) that includes structural units (a1) derived from a (meth)acrylic acid alkyl ester monomer containing at least methyl (meth)acrylate and structural units (a2) derived from a monomer having a hydroxyl group, wherein the content of the structural units derived from methyl (meth)acrylate is in the range of 15.0% by mass or more and 40.0% by mass or less, based on all structural units, and the content of the structural units (a2) is in the range of more than 0% by mass and less than 0.3% by mass, based on all structural units, and that has a weight-average molecular weight of 1,800,000 or more and 2,500,000 or less and a molecular weight distribution of 3.0 or more and 5.0 or less. The pressure-sensitive adhesive composition of the present disclosure may contain one type of specific (meth)acrylic copolymer alone, or may contain two or more types.

[0030] <Constituent unit (a1)> The specific (meth)acrylic copolymer contains structural units (a1) derived from a (meth)acrylic acid alkyl ester monomer containing at least methyl (meth)acrylate, and the content of the structural units derived from methyl (meth)acrylate is in the range of 15.0 mass% or more and 40.0 mass% or less of all structural units.

[0031] The structural unit (a1) is only required to contain a structural unit derived from methyl (meth)acrylate, and may be a structural unit derived from methyl (meth)acrylate, or may contain a structural unit derived from methyl (meth)acrylate and a structural unit derived from a (meth)acrylic acid alkyl ester monomer other than methyl (meth)acrylate. In the present disclosure, "(meth)acrylic acid alkyl ester monomers other than methyl (meth)acrylate" is also referred to as "other (meth)acrylic acid alkyl ester monomers."

[0032] 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 a hydroxyl group and a carboxyl 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 number of carbon atoms in the alkyl moiety of the other (meth)acrylic acid alkyl ester monomer is, for example, preferably 2 to 18, more preferably 2 to 12, even more preferably 2 to 8, and particularly preferably 2 to 4.

[0033] Specific examples of other (meth)acrylic acid alkyl ester monomers include 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.

[0034] The structural unit (a1) preferably contains a structural unit derived from methyl (meth)acrylate and a structural unit derived from n-butyl acrylate, more preferably contains a structural unit derived from methyl acrylate and a structural unit derived from n-butyl acrylate, and even more preferably contains a structural unit derived from methyl acrylate and a structural unit derived from n-butyl acrylate.

[0035] The specific (meth)acrylic copolymer may contain one type of structural unit (a1) alone, or may contain two or more types. However, when the specific (meth)acrylic copolymer contains one type of structural unit (a1), the structural unit (a1) is a structural unit derived from methyl acrylate or a structural unit derived from methyl methacrylate. When the specific (meth)acrylic copolymer contains two or more types of structural units (a1), the structural unit (a1) may be a structural unit derived from methyl acrylate or a structural unit derived from methyl methacrylate, or may be a combination of at least one of a structural unit derived from methyl acrylate or a structural unit derived from methyl methacrylate with one or more other (meth)acrylic acid alkyl ester monomers.

[0036] The content of structural units derived from methyl (meth)acrylate in the specific (meth)acrylic copolymer is in the range of 15.0% by mass to 40.0% by mass based on the total structural units of the specific (meth)acrylic copolymer. When the specific (meth)acrylic copolymer contains a structural unit derived from methyl (meth)acrylate, the interaction and entanglement between the specific (meth)acrylic copolymers becomes stronger, and the cohesive strength of the pressure-sensitive adhesive layer formed tends to increase. When the content of structural units derived from methyl (meth)acrylate in the specific (meth)acrylic copolymer is 15.0% by mass or more relative to the total structural units of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have excellent durability in high-temperature environments. This is presumably because the pressure-sensitive adhesive layer has sufficient cohesive strength and can withstand the load caused by dimensional changes in the optical film. The content of structural units derived from methyl (meth)acrylate in the specific (meth)acrylic copolymer is preferably 18.0 mass% or more, and more preferably 20.0 mass% or more, based on the total structural units of the specific (meth)acrylic copolymer. When the content of structural units derived from methyl (meth)acrylate in the specific (meth)acrylic copolymer is 40.0 mass% or less relative to all structural units of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have excellent curved surface adhesion in high-temperature environments. This is presumably because the cohesive strength of the pressure-sensitive adhesive layer does not become excessively high, allowing the pressure-sensitive adhesive layer to have the flexibility to conform to curved surfaces. The content of structural units derived from methyl (meth)acrylate in the specific (meth)acrylic copolymer is preferably 35.0 mass% or less, and more preferably 30.0 mass% or less, based on the total structural units of the specific (meth)acrylic copolymer. In one embodiment, the content of structural units derived from methyl (meth)acrylate in the specific (meth)acrylic copolymer may be in the range of 15.0% by mass or more and 35.0% by mass or less, or in the range of 18.0% by mass or more and 35.0% by mass or less, or in the range of 20.0% by mass or more and 30.0% by mass or less.

[0037] The content of the structural unit (a1) in the specific (meth)acrylic copolymer is, for example, preferably in the range of 50.0 mass% or more and 99.7 mass% or less, more preferably in the range of 60.0 mass% or more and 99.0 mass% or less, even more preferably in the range of 70.0 mass% or more and 90.0 mass% or less, and particularly preferably in the range of 80.0 mass% or more and 84.0 mass% or less, relative to all structural units of the specific (meth)acrylic copolymer. The content of the structural unit (a1) in the specific (meth)acrylic copolymer being 50.0 mass% or more relative to all structural units of the specific (meth)acrylic copolymer means that the structural unit (a1) is contained as a main component of the structural units of the specific (meth)acrylic copolymer.

[0038] <Constituent unit (a2)> The specific (meth)acrylic copolymer contains a structural unit (a2) derived from a monomer having a hydroxyl group, and the content of the structural unit (a2) is in the range of more than 0 mass % and less than 0.3 mass % of all structural units. The hydroxyl group of the structural unit (a2) contributes to the crosslinking reaction between the specific (meth)acrylic copolymer and the aromatic isocyanate crosslinking agent described below. When the specific (meth)acrylic copolymer contains the structural unit (a2), the specific (meth)acrylic copolymer and the aromatic isocyanate crosslinking agent described below form a crosslinked structure.

[0039] 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.

[0040] 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.

[0041] The structural unit (a2) preferably contains a structural unit derived from a hydroxyalkyl (meth)acrylate, more preferably contains a structural unit derived from 2-hydroxyethyl (meth)acrylate, even more preferably contains a structural unit derived from 2-hydroxyethyl acrylate, and is particularly preferably a structural unit derived from 2-hydroxyethyl acrylate.

[0042] The specific (meth)acrylic copolymer may contain one type of structural unit (a2) alone, or may contain two or more types.

[0043] The content of the structural unit (a2) in the specific (meth)acrylic copolymer is in the range of more than 0 mass % and less than 0.3 mass % based on all structural units of the specific (meth)acrylic copolymer. The content of the structural unit (a2) in the specific (meth)acrylic copolymer exceeding 0% by mass relative to all structural units of the specific (meth)acrylic copolymer means that the specific (meth)acrylic copolymer actively contains the structural unit (a2). When the specific (meth)acrylic copolymer contains the structural unit (a2), the durability of the pressure-sensitive adhesive layer in high-temperature environments tends to improve. This is presumably because the formation of a crosslinked structure between the specific (meth)acrylic copolymer and the aromatic isocyanate-based crosslinking agent described below imparts cohesive strength to the pressure-sensitive adhesive layer. The content of the structural unit (a2) in the specific (meth)acrylic copolymer is preferably 0.03 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.1 mass% or more, based on the total structural units of the specific (meth)acrylic copolymer. When the content of the structural unit (a2) in the specific (meth)acrylic copolymer is less than 0.3% by mass relative to all structural units of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have excellent curved surface adhesion in high-temperature environments. This is presumably because the crosslink density in the pressure-sensitive adhesive layer does not become excessively high, allowing the pressure-sensitive adhesive layer to have the flexibility to conform to curved surfaces. The content of the structural unit (a2) in the specific (meth)acrylic copolymer is preferably 0.25 mass % or less based on the total mass of all structural units in the specific (meth)acrylic copolymer. In one embodiment, the content of the structural unit (a2) in the specific (meth)acrylic copolymer may be in the range of 0.03% by mass or more and less than 0.3% by mass, 0.05% by mass or more and less than 0.3% by mass, 0.1% by mass or more and less than 0.3% by mass, or 0.1% by mass or more and 0.25% by mass or less, based on all structural units of the specific (meth)acrylic copolymer.

[0044] <Constituent unit (a3)> The specific (meth)acrylic copolymer preferably further contains a structural unit (a3) ​​derived from a monomer having a carboxy group.

[0045] 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).

[0046] The structural unit (a3) ​​preferably contains a structural unit derived from (meth)acrylic acid, more preferably contains a structural unit derived from acrylic acid, and even more preferably is a structural unit derived from acrylic acid.

[0047] When the specific (meth)acrylic copolymer contains the structural unit (a3), it may contain either one type of structural unit (a3) ​​alone, or two or more types of structural unit (a3).

[0048] When the specific (meth)acrylic copolymer contains the structural unit (a3), the content of the structural unit (a3) ​​in the specific (meth)acrylic copolymer is not particularly limited, but for example, it is preferably in the range of more than 0 mass% and less than 0.3 mass%, more preferably in the range of 0.05 mass% or more and less than 0.3 mass%, and even more preferably in the range of 0.1 mass% or more and less than 0.3 mass%, relative to all structural units of the specific (meth)acrylic copolymer. The content of the structural unit (a3) ​​in the specific (meth)acrylic copolymer being greater than 0% by mass relative to all structural units of the specific (meth)acrylic copolymer means that the specific (meth)acrylic copolymer actively contains the structural unit (a3). When the specific (meth)acrylic copolymer contains the structural unit (a3), for example, when the pressure-sensitive adhesive composition of the present disclosure further contains a silane coupling agent described below and the adherend is glass, the pressure-sensitive adhesive layer tends to have excellent durability in high-temperature environments. The alkoxy groups of the silane coupling agent hydrolyze to form silanol groups, which react with hydroxyl groups on the surface of the adherend. When the specific (meth)acrylic copolymer contains the structural unit (a3), the hydrolysis of the alkoxy groups is promoted, increasing the number of silanol groups, improving the adhesion between the adherend and the pressure-sensitive adhesive layer, and it is presumed that this allows the pressure-sensitive adhesive layer to withstand loads arising from dimensional changes in the optical film. Metals such as copper and metal oxides such as indium tin oxide (ITO) are often used in image display devices. Components containing a carboxyl group have relatively high acidity and can corrode metals and metal oxides. When the content of the structural unit (a3) ​​in the specific (meth)acrylic copolymer is less than 0.3 mass% of the total structural units of the specific (meth)acrylic copolymer, corrosion of metals and metal oxides by the pressure-sensitive adhesive layer tends to be less likely to occur.

[0049] <Constituent unit (a4)> The specific (meth)acrylic copolymer preferably further contains a structural unit (a4) derived from a (meth)acrylate having an aromatic ring. Optical films such as polarizing plates are prone to dimensional changes due to shrinkage when exposed to high-temperature environments. For example, dimensional changes in a polarizing plate 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 light leakage (unevenness known as "white spots"). In contrast, the pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that can effectively suppress light leakage because the specific (meth)acrylic copolymer further contains the structural unit (a4).

[0050] The type of (meth)acrylate having an aromatic ring is not particularly limited. Specific examples of (meth)acrylates having an aromatic ring include benzyl (meth)acrylate and phenoxyethyl (meth)acrylate.

[0051] The structural unit (a4) preferably includes at least one structural unit selected from the group consisting of structural units derived from benzyl (meth)acrylate and structural units derived from phenoxyethyl (meth)acrylate, more preferably includes a structural unit derived from phenoxyethyl acrylate, and even more preferably is a structural unit derived from phenoxyethyl acrylate.

[0052] When the specific (meth)acrylic copolymer contains the structural unit (a4), it may contain either one type of structural unit (a4) alone, or two or more types of structural unit (a4).

[0053] When the specific (meth)acrylic copolymer contains the structural unit (a4), the content of the structural unit (a4) in the specific (meth)acrylic copolymer is not particularly limited, but is preferably, for example, in the range of 12.0 mass % or more and 24.0 mass % or less, and more preferably in the range of 15.0 mass % or more and 20.0 mass % or less, relative to all structural units of the specific (meth)acrylic copolymer. When the content of the structural unit (a4) in the specific (meth)acrylic copolymer is within the above range, the pressure-sensitive adhesive layer that is formed tends to be able to more effectively suppress light leakage.

[0054] <Other structural units> The specific (meth)acrylic copolymer may, as necessary, contain a structural unit that does not fall into any of the structural units (a1), (a2), (a3), and (a4) (so-called other structural units), as long as the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired.

[0055] Other structural units 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 copolymer contains other structural units, it may contain one type of other structural unit alone, or two or more types of other structural units.

[0057] When the specific (meth)acrylic copolymer contains other structural units, the content of the other structural units in the specific (meth)acrylic copolymer can be set appropriately 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 copolymer>> The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic copolymer is in the range of 1.8 million to 2.5 million. When the weight-average molecular weight of the specific (meth)acrylic copolymer is 1.8 million or more, the pressure-sensitive adhesive layer tends to have excellent durability in high-temperature environments. This is presumably because the pressure-sensitive adhesive layer has sufficient cohesive strength and can withstand the load caused by dimensional changes in the optical film. When the weight-average molecular weight of the specific (meth)acrylic copolymer is 2.5 million or less, the pressure-sensitive adhesive layer tends to have excellent curved surface adhesion in high-temperature environments. This is presumably because the cohesive strength of the pressure-sensitive adhesive layer does not become excessively high, allowing the pressure-sensitive adhesive layer to have the flexibility to conform to curved surfaces. The weight average molecular weight of the specific (meth)acrylic copolymer is, for example, preferably in the range of 1.8 million to 2.3 million, and more preferably in the range of 1.8 million to 2 million.

[0059] <<Molecular weight distribution of specific (meth)acrylic copolymers>> The molecular weight distribution of the specific (meth)acrylic copolymer is in the range of 3.0 to 5.0. The molecular weight distribution of the specific (meth)acrylic copolymer is an index showing the proportion of specific (meth)acrylic copolymers with different molecular weights present. When the molecular weight distribution of the specific (meth)acrylic copolymer is 3.0 or more, the pressure-sensitive adhesive layer tends to have excellent curved surface adhesion in high-temperature environments. This is presumably because the cohesive strength of the pressure-sensitive adhesive layer does not become excessively high, allowing the pressure-sensitive adhesive layer to have the flexibility to conform to curved surfaces. When the molecular weight distribution of the specific (meth)acrylic copolymer is 5.0 or less, the pressure-sensitive adhesive layer tends to have excellent durability in high-temperature environments. This is presumably because the pressure-sensitive adhesive layer has sufficient cohesive strength and can withstand the load caused by dimensional changes in the optical film. The molecular weight distribution of the specific (meth)acrylic copolymer is preferably in the range of 3.0 or more and 4.5 or less, and more preferably in the range of 3.0 or more and 4.0 or less.

[0060] The molecular weight distribution of a specific (meth)acrylic copolymer is determined from the weight average molecular weight (Mw) and number average molecular weight (Mn), and is expressed as the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn).

[0061] As an embodiment of the specific (meth)acrylic copolymer, for example, a preferred embodiment is one in which the weight average molecular weight is in the range of 1.8 million to 2.3 million and the molecular weight distribution is in the range of 3.0 to 4.5, and a more preferred embodiment is one in which the weight average molecular weight is in the range of 1.8 million to 2.0 million and the molecular weight distribution is in the range of 3.0 to 4.0.

[0062] The weight-average molecular weight and number-average molecular weight of the specific (meth)acrylic copolymer are values ​​measured by the following method, specifically, according to the following (1) to (3). (1) A solution of the specific (meth)acrylic copolymer is applied to a release paper and then dried at 100° C. for 1 minute to obtain a film of the specific (meth)acrylic copolymer. (2) Using the film-like specific (meth)acrylic copolymer obtained in (1) above and tetrahydrofuran, a sample solution having a solids concentration of 0.2% by mass is obtained. Note that the "solids concentration" here refers to the mass proportion of the specific (meth)acrylic copolymer in the sample solution. (3) The weight average molecular weight and number average molecular weight of the specific (meth)acrylic copolymer are determined as values ​​converted into standard polystyrene by gel permeation chromatography (GPC) under the following conditions.

[0063] ~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 GMHXL Two columns (7.8mmφ×30cm, manufactured by Tosoh Corporation) were used. Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min Injection amount: 100μm

[0064] The weight average molecular weight of the specific (meth)acrylic copolymer can be adjusted to a desired value by 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. The number average molecular weight of the specific (meth)acrylic copolymer can be adjusted to a desired value by adjusting the type of organic solvent, the concentration of the monomer, the amount of polymerization initiator used, etc. when polymerizing the monomer.

[0065] <<Glass transition temperature of specific (meth)acrylic copolymers>> The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic copolymer is not particularly limited, but is preferably in the range of -45°C or higher and -20°C or lower, more preferably in the range of -40°C or higher and -25°C or lower, and even more preferably in the range of -40°C or higher and -30°C or lower. When the glass transition temperature of the specific (meth)acrylic copolymer is -45°C or higher, the durability of the pressure-sensitive adhesive layer in high-temperature environments tends to be improved. This is presumably because the increased cohesive strength of the pressure-sensitive adhesive layer allows the pressure-sensitive adhesive layer to better withstand the load caused by dimensional changes in the optical film. When the glass transition temperature of the specific (meth)acrylic copolymer is −20° C. or lower, the adhesiveness of the pressure-sensitive adhesive layer to curved surfaces in high-temperature environments tends to be improved. This is presumably because the cohesive force of the pressure-sensitive adhesive layer is suppressed, allowing the pressure-sensitive adhesive layer to have flexibility that allows it to conform better to curved surfaces.

[0066] The glass transition temperature of the specific (meth)acrylic copolymer 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)

[0067] In formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific (meth)acrylic copolymer is made into a homopolymer. m1, m2, . . . , m(k-1), and mk represent the mole fractions of each monomer constituting the specific (meth)acrylic copolymer, respectively, 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.

[0068] In the present disclosure, the "glass transition temperature when converted into a homopolymer" refers to a value disclosed in a publicly known document or a value measured using a differential scanning calorimeter (DSC). The specific value to be used is as follows:

[0069] 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 (-65°C), Cyclohexyl methacrylate (104°C), isobornyl acrylate (94°C), isobornyl methacrylate (180°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).

[0070] 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.

[0071] 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.

[0072] The glass transition temperature of the specific (meth)acrylic copolymer can be adjusted to a desired value, for example, by appropriately selecting the types and ratios of monomers that are polymerization components of the specific (meth)acrylic copolymer.

[0073] <<Specific (meth)acrylic copolymer content>> The content of the specific (meth)acrylic copolymer in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably in the range of 70.0 mass % or more and 99.9 mass % or less, more preferably in the range of 80.0 mass % or more and 99.8 mass % or less, and even more preferably in the range of 90.0 mass % or more and 99.7 mass % or less, relative to the total solid content in the pressure-sensitive adhesive composition.

[0074] 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.

[0075] [Method for producing specific (meth)acrylic copolymer] The method for producing the specific (meth)acrylic copolymer is not particularly limited. The specific (meth)acrylic copolymer can be produced by polymerizing the above-mentioned monomers by a known polymerization method, such as solution polymerization, emulsion polymerization, suspension polymerization, or bulk polymerization. As the polymerization method, solution polymerization is preferred because the processing steps are relatively simple and can be completed in a short time when preparing the pressure-sensitive adhesive composition of the present disclosure after production.

[0076] In the solution polymerization method, a predetermined organic solvent, a monomer, 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, the monomer, the polymerization initiator, and the optional chain transfer agent may be added sequentially. Alternatively, the reaction may be carried out in a nitrogen gas stream.

[0077] 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.

[0078] In producing the specific (meth)acrylic copolymer, 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 ethyl acetate from the viewpoints of the solubility of the specific (meth)acrylic copolymer, ease of the polymerization reaction, etc.

[0079] During the polymerization reaction, one type of organic solvent may be used alone, or two or more types may be used.

[0080] 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.

[0081] During the polymerization reaction, one type of polymerization initiator may be used alone, or two or more types may be used.

[0082] 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 copolymer.

[0083] In producing the specific (meth)acrylic copolymer, a chain transfer agent may be used as needed. 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.

[0084] When a chain transfer agent is used in producing the specific (meth)acrylic copolymer, 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 copolymer.

[0085] From the viewpoint of achieving a molecular weight distribution in the range of 3.0 or more and 5.0 or less, it is preferable not to use a chain transfer agent when producing the pressure-sensitive adhesive composition of the present disclosure.

[0086] 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 copolymer.

[0087] [Aromatic isocyanate crosslinking agent] The pressure-sensitive adhesive composition of the present disclosure contains an aromatic isocyanate-based crosslinking agent. In the present disclosure, the term "aromatic isocyanate crosslinking agent" refers to a compound having one or more aromatic structures and two or more isocyanate groups in one molecule (so-called aromatic polyisocyanate compound).

[0088] The type of aromatic isocyanate crosslinking agent is not particularly limited. Examples of aromatic isocyanate crosslinking agents include aromatic polyisocyanate compounds, polymers of aromatic polyisocyanate compounds, adducts of aromatic polyisocyanate compounds and polyol compounds, and biuret compounds of aromatic polyisocyanate compounds. Specific examples of aromatic polyisocyanate compounds include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate.

[0089] The aromatic isocyanate crosslinking agent is preferably a tolylene diisocyanate compound. The tolylene diisocyanate compounds include, 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 (so-called TMP adduct of TDI) is preferred.

[0090] As the aromatic isocyanate-based crosslinking agent, commercially available products can be used. Commercially available examples of aromatic isocyanate crosslinking agents include "Coronate 2031," "Coronate 2037," "Coronate 4370," and "Millionate MR-100" (all manufactured by Tosoh Corporation), as well as "Takenate D-101E," "Takenate D-110N," "Takenate D-120N," and "Takenate D-262" (all manufactured by Mitsui Chemicals, Inc.). The above "Coronate," "Millionate," and "Takenate" are all registered trademarks.

[0091] The pressure-sensitive adhesive composition of the present disclosure may contain one type of aromatic isocyanate crosslinking agent alone, or may contain two or more types.

[0092] The content of the aromatic isocyanate crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is in the range of 0.05 parts by mass or more and 0.4 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic copolymer. When the content of the aromatic isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 0.05 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have excellent durability in high-temperature environments. This is presumably because the pressure-sensitive adhesive layer has sufficient cohesive strength and can withstand loads caused by dimensional changes in the optical film. The content of the aromatic isocyanate crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is preferably 0.1 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic copolymer. When the content of the aromatic isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 0.4 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic copolymer, the pressure-sensitive adhesive layer tends to have excellent curved surface adhesion in high-temperature environments. This is presumably because the cohesive strength of the pressure-sensitive adhesive layer does not become excessively high, allowing the pressure-sensitive adhesive layer to have the flexibility to conform to curved surfaces. The content of the aromatic isocyanate crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is preferably 0.3 parts by mass or less, and more preferably 0.2 parts by mass or less, per 100 parts by mass of the specific (meth)acrylic copolymer. In an embodiment, the content of the aromatic isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure may be in the range of 0.05 parts by mass or more and 0.3 parts by mass or less, or may be in the range of 0.05 parts by mass or more and 0.2 parts by mass or less, or may be in the range of 0.1 parts by mass or more and 0.3 parts by mass or less, or may be in the range of 0.1 parts by mass or more and 0.2 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic copolymer.

[0093] [Crosslinking catalyst] The pressure-sensitive adhesive composition of the present disclosure contains a crosslinking catalyst. The pressure-sensitive adhesive composition of the present disclosure has a relatively small content of aromatic isocyanate-based crosslinking agent and a relatively low content of the structural unit (a2) in the (meth)acrylic copolymer. However, by including a crosslinking catalyst, the crosslinking reaction between the specific (meth)acrylic copolymer and the aromatic isocyanate-based crosslinking agent can proceed quickly.

[0094] The type of crosslinking catalyst is not particularly limited. Examples of crosslinking catalysts include imidazole compounds such as 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, and 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, organometallic compounds such as dioctyltin dilaurate and 1,3-diacetoxytetrabutylstannoxane, and tertiary amine compounds such as triethylenediamine and N-methylmorpholine.

[0095] As the crosslinking catalyst, commercially available products can be used. Examples of commercially available crosslinking catalysts include "Curesol 1B2MZ," "Curesol 1B2PZ," "Curesol TBZ," and "Curesol 1,2DMZ" (all trade names) manufactured by Shikoku Chemicals Corporation. The above "Curezol" is a registered trademark.

[0096] The pressure-sensitive adhesive composition of the present disclosure may contain one type of crosslinking catalyst alone, or may contain two or more types.

[0097] The content of the crosslinking catalyst in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably in the range of 0.01 parts by mass or more and 1.0 parts by mass or less, more preferably in the range of 0.05 parts by mass or more and 0.7 parts by mass or less, and even more preferably in the range of 0.1 parts by mass or more and 0.5 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic copolymer. When the content of the crosslinking catalyst in the pressure-sensitive adhesive composition of the present disclosure is 0.01 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic copolymer, the crosslinking reaction between the specific (meth)acrylic copolymer and the aromatic isocyanate-based crosslinking agent tends to be favorably promoted. When the content of the crosslinking catalyst in the pressure-sensitive adhesive composition of the present disclosure is 1.0 part by mass or less relative to 100 parts by mass of the specific (meth)acrylic copolymer, the crosslinking catalyst is not excessively localized at the interface between the pressure-sensitive adhesive layer and the substrate, and therefore the adhesion between the pressure-sensitive adhesive layer and the substrate tends not to be impaired.

[0098] [Silane coupling agent] The pressure-sensitive adhesive composition of the present disclosure may contain 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 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 in high-temperature environments.

[0099] 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).

[0100] 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.

[0101] When the pressure-sensitive adhesive composition of the present disclosure contains a silane coupling agent, it may contain one type of silane coupling agent alone, or may contain two or more types of silane coupling agents.

[0102] When the pressure-sensitive adhesive composition of the present disclosure contains a silane coupling agent, the content of the silane coupling agent is not particularly limited, but from the viewpoint of durability of the pressure-sensitive adhesive layer in a high-temperature environment, for example, the content is 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 0.6 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic polymer.

[0103] [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.

[0104] The type of organic solvent is not particularly limited. Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the above-mentioned specific (meth)acrylic copolymer.

[0105] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain one kind of organic solvent alone, or may contain two or more kinds of organic solvents.

[0106] 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.

[0107] [Other ingredients] The pressure-sensitive adhesive composition of the present disclosure may contain components other than the above-mentioned components (so-called other components) as needed, within the range that does not impair the effects of the composition. Examples of other components include various additives such as polymers other than the specific (meth)acrylic copolymer, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[0108] 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.

[0109] <<Gel fraction after crosslinking>> The gel fraction of the pressure-sensitive adhesive composition of the present disclosure after crosslinking (i.e., the gel fraction of the pressure-sensitive adhesive layer) is not particularly limited, but is preferably in the range of 50% by mass or more and 85% by mass or less, more preferably in the range of 55% by mass or more and 75% by mass or less, and even more preferably in the range of 60% by mass or more and 70% by mass or less. When the pressure-sensitive adhesive composition of the present disclosure has a gel fraction of 50% by mass or more after crosslinking, the pressure-sensitive adhesive layer tends to have better durability in high-temperature environments, presumably because the increased cohesive strength of the pressure-sensitive adhesive layer enables the pressure-sensitive adhesive layer to better withstand loads caused by dimensional changes in the optical film. When the pressure-sensitive adhesive composition of the present disclosure has a gel fraction of 85% by mass or less after crosslinking, the pressure-sensitive adhesive layer tends to have better curved surface adhesion in high-temperature environments, presumably because the suppression of the cohesive force of the pressure-sensitive adhesive layer allows the pressure-sensitive adhesive layer to have flexibility that allows it to better conform to curved surfaces.

[0110] In the present disclosure, the "gel fraction of a pressure-sensitive adhesive composition after crosslinking" refers to the proportion of solvent-insoluble components measured using ethyl acetate as an extraction solvent. Specifically, the gel fraction of a pressure-sensitive adhesive composition after crosslinking is measured according to the following [1] to [4].

[0111] [1] Approximately 0.15 g of the crosslinked adhesive composition (i.e., adhesive layer) is attached to a 250-mesh wire mesh (100 mm × 100 mm) whose mass has been accurately measured using a precision balance, and the wire mesh is folded five times with the attached adhesive layer facing inward to prevent leakage of the gel content, thereby preparing a sample. Next, the mass of the sample is accurately measured using a precision balance. [2] The obtained sample is immersed in 80 mL of ethyl acetate for 3 days. [3] The sample is taken out, washed with a small amount of ethyl acetate, and dried for 24 hours at 120°C. The mass of the dried sample is then accurately measured using a precision balance. [4] Calculate the gel fraction using the following formula: Gel fraction [unit: mass%] = (ZX) / (YX) × ​​100 where X is the mass of the wire mesh (unit: g), Y is the mass of the wire mesh with the adhesive layer attached (unit: g) before immersion, and Z is the mass of the wire mesh with the adhesive layer attached after immersion and drying (unit: g).

[0112] <<Application>> The pressure-sensitive adhesive composition of the present disclosure is a pressure-sensitive adhesive composition used for optical members. The details of the optical members will be described later, and therefore will not be described here. The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that is excellent in durability and curved surface adhesion in high-temperature environments. Specifically, a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of the present disclosure can withstand loads that occur due to dimensional changes in an optical film such as a polarizing plate exposed to a high-temperature environment. Furthermore, a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of the present disclosure can conform to a curved surface and withstand loads that occur due to shape recovery of an optical film attached to the curved surface. For this reason, the pressure-sensitive adhesive composition of the present disclosure is suitable as a pressure-sensitive adhesive composition for use in optical components that may be exposed to a high-temperature environment. The pressure-sensitive adhesive composition of the present disclosure is suitable as a pressure-sensitive adhesive composition to be used in optical films among optical components (i.e., a pressure-sensitive adhesive composition for optical films), and is particularly suitable as a pressure-sensitive adhesive composition to be used in polarizing plates among optical films (i.e., a pressure-sensitive adhesive composition for polarizing plates). Specific applications of the pressure-sensitive adhesive composition of the present disclosure include applications for bonding a polarizing plate to a glass substrate (for example, a glass substrate of a liquid crystal cell) and applications for bonding optical films together. The pressure-sensitive adhesive composition of the present disclosure can be applied to electronic devices equipped with display devices such as liquid crystal displays equipped with polarizing plates and organic EL (Electro Luminescence) displays.

[0113] [Adhesive layer] The pressure-sensitive adhesive layer of the present disclosure is a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive layer of the present disclosure includes a cured product of the pressure-sensitive adhesive composition of the present disclosure, including, for example, a crosslinked product of a specific (meth)acrylic copolymer obtained by crosslinking and curing with an aromatic isocyanate-based crosslinking agent. The pressure-sensitive adhesive layer of the present disclosure is a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore has excellent durability in high-temperature environments and curved surface adhesion.

[0114] The thickness of the pressure-sensitive adhesive layer of the present disclosure is not particularly limited. The thickness of the pressure-sensitive adhesive layer of the present disclosure is set appropriately depending on the material, shape, etc. of the adherend. The thickness of the pressure-sensitive adhesive layer of the present disclosure may be, for example, 1 μm to 100 μm, 10 μm to 30 μm, or 15 μm to 25 μm.

[0115] 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.

[0116] [Optical components with adhesive layers] The pressure-sensitive adhesive layer-attached optical member of the present disclosure includes an optical member and the pressure-sensitive adhesive layer of the present disclosure. That is, the pressure-sensitive adhesive layer-attached optical member of the present disclosure includes an optical member and the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive layer-equipped optical member of the present disclosure has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore tends to be less susceptible to wrinkling, foaming, and peeling even when exposed to a high-temperature environment. Furthermore, the pressure-sensitive adhesive layer-equipped optical member of the present disclosure has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore tends to conform to a curved surface and be less susceptible to peeling.

[0117] The optical member included in the pressure-sensitive adhesive layer-attached optical member of the present disclosure is not particularly limited. Examples of optical components include components constituting devices such as display devices and input devices (so-called optical devices), and components used in these devices. Examples of display devices include liquid crystal displays and organic EL (Electro-Luminescence) displays. Specific examples of optical members include polarizing plates, AG (Anti-Glare) polarizing plates, wave plates (e.g., ½ wave plates and ¼ wave plates), retardation films including the wave plates, viewing angle compensation films, optical compensation films, brightness enhancement films, light guide plates, reflective films, antireflection films, prism sheets, lens sheets, diffusers, and transparent conductive films (e.g., transparent conductive films formed from ITO (indium-doped tin oxide), ATO (antimony-doped tin oxide), FTO (fluorine-doped tin oxide), tin oxide, zinc oxide, etc.), and other optical films.

[0118] The optical member included in the pressure-sensitive adhesive layer-attached optical member of the present disclosure is preferably a polarizing plate. 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. That is, 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. When the optical member is a polarizing plate, examples of the layer structure 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), 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). The number in parentheses indicates the layer structure of the polarizing plate.

[0119] 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).

[0120] In the pressure-sensitive adhesive layer-attached optical member of the present disclosure, the exposed pressure-sensitive adhesive layer 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 layer-attached optical member is put to practical use, and is peeled off when the optical member is used. 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.

[0121] The adherend to which the pressure-sensitive adhesive layer-carrying optical member of the present disclosure is applied is not particularly limited. Examples of the adherend to which the pressure-sensitive adhesive layer-carrying optical member of the present disclosure is applied include glass substrates. 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. The adherend of the pressure-sensitive adhesive layer-carrying optical member of the present disclosure may be an adherend that has been subjected to a curved surface treatment, for example, a glass substrate that has been subjected to a curved surface treatment. The pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive layer-carrying optical member of the present disclosure is a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore, even if the adherend has been subjected to a curved surface treatment, it tends to conform to the curved surface and is less likely to peel off even in a high-temperature environment.

[0122] [Method for producing an optical member with a pressure-sensitive adhesive layer] The method for producing the pressure-sensitive adhesive layer-attached optical member of the present disclosure is not particularly limited. The pressure-sensitive adhesive layer-attached optical member of the present disclosure can be produced by a known method.

[0123] Examples of methods for producing an optical member with a pressure-sensitive adhesive layer according to the present disclosure include the following methods. The pressure-sensitive adhesive composition according to the present disclosure is applied to the easily releasable 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. The exposed surface of the formed pressure-sensitive adhesive film is then laminated to one surface of an optical member, followed by curing, to produce an optical member with a pressure-sensitive adhesive layer according to the present disclosure, having a laminate structure of optical member / pressure-sensitive adhesive layer / release sheet.

[0124] Another method for producing an optical member with a pressure-sensitive adhesive layer according to the present disclosure can be, for example, the following method. The pressure-sensitive adhesive composition according to the present disclosure is applied to one surface of the optical member to form a coating film on the optical member. The formed coating film is then dried to form a pressure-sensitive adhesive film on the optical member. The exposed surface of the formed pressure-sensitive adhesive film is then laminated onto the easily releasable surface of a release sheet, followed by curing, thereby producing an optical member with a pressure-sensitive adhesive layer according to the present disclosure having a laminate structure of optical member / pressure-sensitive adhesive layer / release sheet.

[0125] 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.

[0126] 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 type and 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.

[0127] 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. [Example]

[0128] The pressure-sensitive adhesive composition for optical members 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 they do not depart from the gist of the disclosure.

[0129] [Production of (meth)acrylic copolymer] [Manufacturing example A-1] A reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser was charged with 75.10 parts by weight of n-butyl acrylate (n-BA), 24.50 parts by weight of methyl acrylate (MA), 0.20 parts by weight of acrylic acid (AA), 0.20 parts by weight of 2-hydroxyethyl acrylate (2HEA), 25 parts by weight of ethyl acetate (organic solvent), and 50 parts by weight of methyl acetate (organic solvent). The mixture was then mixed and purged with nitrogen. The mixture in the reactor was then heated to 70°C while stirring. Next, 0.035 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile) (ABVN; polymerization initiator) and 276 parts by weight of ethyl acetate were added to the mixture in five stages, and the temperature was maintained at 72°C for a total of 6 hours to allow the polymerization reaction to proceed. The obtained polymerization reaction product was diluted with ethyl acetate to a solid content concentration of 15.5% by mass, and then cooled to obtain a solution of (meth)acrylic copolymer A-1.

[0130] The term "solid content" as used herein refers to the mass proportion of the (meth)acrylic copolymer A-1 in the solution of the (meth)acrylic copolymer A-1. The same applies to the solutions of the (meth)acrylic copolymers A-2 to A-9 produced below.

[0131] [Manufacturing examples A-2 to A-7] In Production Examples A-2 to A-7, the same operations as in Production Example A-1 were carried out except that the monomer composition of the (meth)acrylic copolymer was changed to the monomer composition shown in Table 1, and solutions of (meth)acrylic copolymers A-2 to A-7 each having a solid content of 15.5 mass% were obtained.

[0132] [Manufacturing example A-8] In Production Example A-8, the same operation as in Production Example A-1 was carried out, except that the weight average molecular weight of the (meth)acrylic copolymer 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 a solution of (meth)acrylic copolymer A-8 having a solid content concentration of 15.5 mass%.

[0133] [Manufacturing example A-9] In Production Example A-9, the same operation as in Production Example A-1 was carried out, except that the amount of polymerization initiator used was adjusted to make the molecular weight distribution of the (meth)acrylic copolymer the molecular weight distribution shown in Table 1, to obtain a solution of (meth)acrylic copolymer A-9 with a solid content concentration of 15.5 mass%.

[0134] The monomer composition, weight average molecular weight (represented as "Mw"), molecular weight distribution (represented as "Mw / Mn"), and glass transition temperature (represented as "Tg") of each of the (meth)acrylic copolymers A-1 to A-9 are shown in Table 1.

[0135] The weight average molecular weight and number average molecular weight of the (meth)acrylic copolymers A-1 to A-9 were measured by the same methods as those for measuring the weight average molecular weight and number average molecular weight of the specific (meth)acrylic copolymer described above. The glass transition temperatures of the (meth)acrylic copolymers A-1 to A-9 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic copolymer described above.

[0136] Among the (meth)acrylic copolymers A-1 to A-9, the (meth)acrylic copolymers A-1 to A-4 correspond to the specific (meth)acrylic copolymers of the present disclosure.

[0137] [Table 1]

[0138] In Table 1, "(a1)", "(a2)", "(a3)", and "(a4)" indicate the monomers of "structural unit (a1)", "structural unit (a2)", "structural unit (a3)", and "structural unit (a4)", respectively.

[0139] Details of each monomer listed in Table 1 are as follows: (a1) (Meth)acrylic acid alkyl ester monomer "n-BA": n-butyl acrylate "MA": methyl acrylate (a2) Monomer having a hydroxyl group "2HEA": 2-hydroxyethyl acrylate (a3) Monomer having a carboxy group "AA": acrylic acid (a4) (meth)acrylate having an aromatic ring "PHEA": Phenoxyethyl acrylate

[0140] In Table 1, "-" in the column of monomer composition means that the monomer in that column was not used.

[0141] [Preparation of Pressure-Sensitive Adhesive Composition] Example 1 645.16 parts by mass (100 parts by mass as solid content) of the (meth)acrylic copolymer A-1 solution, 0.11 parts by mass (0.05 parts by mass as solid content) of Takenate (registered trademark) D-101E (trade name, trimethylolpropane (TMP) adduct of tolylene diisocyanate (TDI), solid content concentration: 45% by mass, manufactured by Mitsui Chemicals, Inc.) as an aromatic isocyanate crosslinking agent, and Curesol (registered trademark) as a crosslinking catalyst. 0.20 parts by mass (0.20 parts by mass as solids) of 1B2PZ (trade name, solids concentration: 100% by mass, manufactured by Shikoku Chemical Industry Co., Ltd.), 0.30 parts by mass (0.30 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) were thoroughly mixed to obtain a pressure-sensitive adhesive composition of Example 1.

[0142] Examples 2 to 8 In Examples 2 to 8, the adhesive compositions of Examples 2 to 8 were obtained in the same manner as in Example 1, except that the formulation of the adhesive composition was changed to the formulation shown in Table 2.

[0143] Comparative Examples 1 to 7 In Comparative Examples 1 to 7, 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, and adhesive compositions of Comparative Examples 1 to 7 were obtained.

[0144] [Table 2]

[0145] [Table 3]

[0146] In Tables 2 and 3, the values ​​shown in the "blending amount" column are all solid content converted values. In Tables 2 and 3, "-" in the column for the composition of the adhesive composition means that the component in that column was not blended.

[0147] [Preparation of polarizing plate 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 25 μm. Next, using a hot air circulation dryer (product name: automatic discharge dryer, model: ATO-101, manufactured by Tojo Netsugaku Co., Ltd.), 100°C air was blown onto the formed coating film at a wind speed of 3 m / s for 60 seconds to dry the coating film, forming a 25 μm-thick adhesive film on the release film. Next, the exposed surface of the adhesive film formed on the release film was laminated to one of the TAC layer surfaces of a polarizing plate (thickness: 100 μm) having a triacetyl cellulose (TAC) layer / iodine-containing polyvinyl alcohol (PVA) layer / TAC layer configuration. Next, the laminate obtained by lamination was left to stand for 7 days (so-called curing period) in an environment of an atmospheric temperature of 23°C and 50% RH to cure the adhesive film. In this way, a polarizing plate with an adhesive layer having a structure of release film / adhesive layer / polarizing plate (TAC layer / PVA layer / TAC layer) was produced.

[0148] [Measurement and Evaluation] 1.Durability (1) Preparation of evaluation sample X The polarizing plate with the adhesive layer prepared above was cut into a size of 60.0 mm (short side) × 130.0 mm (long side) so that the long side was at 0° with respect to the absorption axis of the polarizing plate. Next, the release film was peeled off from the cut polarizing plate with the adhesive layer. Hereinafter, this polarizing plate with the adhesive layer from which the release film was peeled off is also referred to as test piece X. Next, the surface of the adhesive layer of test piece X exposed by peeling off the release film was placed in contact with one side of a glass plate (type: soda glass, manufactured by Matsunami Glass Industry Co., Ltd.), and then the test piece X and the glass plate were bonded together using a laminator. In this way, an evaluation sample X having a configuration of glass plate / test piece X [adhesive layer / polarizing plate (TAC layer / PVA layer / TAC layer)] was prepared.

[0149] (2) Evaluation test The evaluation sample X prepared above was treated at a temperature of 50°C and a pressure of 5 kg / cm 2 After autoclaving for 20 minutes under the conditions above, the sample was left to stand for 500 hours in an environment with an atmospheric temperature of 105°C and 10% RH. After standing for 500 hours, the condition of the evaluation sample X was visually observed and evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 4 and 5. In the following evaluation criteria, "A," "B," and "C" are practically acceptable levels, with "A" being the most preferable.

[0150] -Evaluation criteria- A: No wrinkles, peeling or bubbles were observed on the evaluation sample X. B: At least one of wrinkles, peeling, and bubbles was slightly observed in the evaluation sample X, but was at a level that did not pose any practical problems. C: At least one of wrinkles, peeling, and bubbles was observed in the evaluation sample X, but was at a level acceptable for practical use. D: At least one of wrinkles, peeling, and bubbles was significantly observed in the evaluation sample X, and was at a level that was not acceptable for practical use.

[0151] 2. Light leaks (1) Preparation of evaluation samples (1-1) Evaluation sample X Evaluation sample X was prepared in the same manner as in "(1) Preparation of evaluation sample X" in "1. Durability" above.

[0152] (1-2) Evaluation sample Y The polarizing plate with the adhesive layer prepared as described above was cut into a size of 60.0 mm (short side) × 130.0 mm (long side) so that the short side was at 0° with respect to the absorption axis of the polarizing plate. Next, the release film was peeled off from the cut polarizing plate with the adhesive layer. Hereinafter, this polarizing plate with the adhesive layer from which the release film was peeled off is also referred to as test piece Y. Next, the surface of the adhesive layer of test piece Y exposed by peeling off the release film was placed in contact with one side of a glass plate (type: soda glass, manufactured by Matsunami Glass Industry Co., Ltd.), and then the test piece Y and the glass plate were bonded together using a laminator. In this way, an evaluation sample Y having a configuration of glass plate / test piece Y [adhesive layer / polarizing plate (TAC layer / PVA layer / TAC layer)] was prepared.

[0153] (2) Evaluation test The evaluation samples X and Y prepared above were treated at a treatment temperature of 50°C and a treatment pressure of 5 kg / cm 2 After autoclaving for 20 minutes under the conditions of (1), the samples were left to stand for 168 hours in an environment with an atmospheric temperature of 105°C and 10% RH. Next, after leaving the samples to stand for 168 hours, evaluation sample X and evaluation sample Y were placed one on top of the other in a crossed Nicol position. Next, a light was shone from below the evaluation samples in the stacked state, and the presence and degree of light leakage from the evaluation samples was confirmed, and evaluation was performed according to the following evaluation criteria. The evaluation results are shown in Tables 4 and 5. In the following evaluation criteria, "A" and "B" are practically acceptable levels, with "A" being the most preferable.

[0154] -Evaluation criteria- A: No light leakage was observed. B: Light leakage was observed, but at a level that was not problematic for practical use. C: The degree of light leakage was significant and was at a level that was not acceptable for practical use.

[0155] 3. Gel fraction (1) Preparation of adhesive sheet The pressure-sensitive adhesive composition prepared above was applied to the easily peelable surface of a release film (trade name: Film Byna (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Kogyo Co., Ltd.) that had been surface-treated with a silicone-based release agent (so-called easy-peeling 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 10 μm. Next, the formed coating film was dried by blowing 100°C air at a wind speed of 3 m / s onto it for 60 seconds using a hot air circulation dryer (product name: automatic discharge dryer, model: ATO-101, manufactured by Tojo Netsugaku Co., Ltd.), forming a 10 μm-thick adhesive film on the release film. Next, the exposed surface of the adhesive film formed on the release film was laminated onto the easily peelable surface of a release film (trade name: Film Byna (registered trademark) 100E-0010 No. 23, thickness: 100 μm, manufactured by Fujimori Kogyo Co., Ltd.) that had been surface-treated (so-called easily peelable) with a separately prepared silicone-based release treatment agent. The laminate obtained by lamination was left to stand in an environment of 23°C and 50% RH for 7 days (so-called curing period) to allow the adhesive film to cure. In this way, an adhesive sheet having a release film / adhesive layer / release film configuration was produced.

[0156] (2) Measurement of gel fraction The pressure-sensitive adhesive layer peeled from the pressure-sensitive adhesive sheet prepared above was used to measure the gel fraction according to the following [1] to [4]. The measured values ​​are shown in Tables 4 and 5.

[0157] [1] Approximately 0.15 g of adhesive layer was attached to a 250 mesh wire mesh (100 mm × 100 mm) whose mass was accurately measured using a precision balance, and the wire mesh was folded five times with the attached adhesive layer facing inward to prevent leakage of the gel. The mass of the sample was then accurately measured using a precision balance. [2] The obtained sample was immersed in 80 mL of ethyl acetate for 3 days. [3] The sample was taken out, washed with a small amount of ethyl acetate, and dried for 24 hours at 120° C. The mass of the dried sample was then accurately measured using a precision balance. [4] The gel fraction was calculated using the following formula: Gel fraction [unit: mass%] = (ZX) / (YX) × ​​100 where X is the mass of the wire mesh (unit: g), Y is the mass of the wire mesh with the adhesive layer attached (unit: g) before immersion, and Z is the mass of the wire mesh with the adhesive layer attached after immersion and drying (unit: g).

[0158] [Table 4]

[0159] [Table 5]

[0160] The results shown in Table 4 demonstrate that the pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of Examples 1 to 8 have excellent durability in a high-temperature environment (specifically, a high-temperature, low-humidity environment). Furthermore, a comparison between the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of Example 2 and the pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition of Example 6 demonstrates that the pressure-sensitive adhesive layer formed by further including a structural unit derived from a (meth)acrylate having an aromatic ring can suppress light leakage that may occur in a high-temperature environment. On the other hand, the results shown in Table 5 reveal that the adhesive layers formed using the adhesive compositions of Comparative Examples 1 to 7 have inferior durability in high temperature environments compared to the adhesive layers formed using the adhesive compositions of the Examples.

Claims

1. a (meth)acrylic copolymer comprising a structural unit (a1) derived from a (meth)acrylic acid alkyl ester monomer containing at least methyl (meth)acrylate and a structural unit (a2) derived from a monomer having a hydroxyl group, wherein the content of the structural unit derived from methyl (meth)acrylate is in the range of 15.0 mass% or more and 40.0 mass% or less, based on all structural units, and the content of the structural unit (a2) is in the range of more than 0 mass% and less than 0.3 mass% based on all structural units, and the weight average molecular weight is in the range of 1,800,000 or more and 2,500,000 or less, and the molecular weight distribution is in the range of 3.0 or more and 5.0 or less; an aromatic isocyanate-based crosslinking agent; a crosslinking catalyst; Including, a pressure-sensitive adhesive composition for optical members, wherein the content of the aromatic isocyanate-based crosslinking agent is in the range of 0.05 parts by mass or more and 0.4 parts by mass or less relative to 100 parts by mass of the (meth)acrylic copolymer;

2. The pressure-sensitive adhesive composition for optical members according to claim 1 , wherein the (meth)acrylic copolymer further comprises a structural unit (a3) ​​derived from a monomer having a carboxy group.

3. 3. The pressure-sensitive adhesive composition for optical members according to claim 2, wherein the content of the structural unit (a3) ​​in the (meth)acrylic copolymer is in the range of more than 0 mass% and less than 0.3 mass%, based on all structural units.

4. 2. The pressure-sensitive adhesive composition for optical members according to claim 1, wherein the (meth)acrylic copolymer has a glass transition temperature in the range of −45° C. or higher and −20° C. or lower.

5. The pressure-sensitive adhesive composition for optical members according to claim 1 , wherein a gel fraction after crosslinking is in the range of 50% by mass or more and 85% by mass or less.

6. The pressure-sensitive adhesive composition for optical members according to claim 1 , wherein the (meth)acrylic copolymer further comprises a structural unit (a4) derived from a (meth)acrylate having an aromatic ring.

7. 7. The pressure-sensitive adhesive composition for optical members according to claim 6, wherein the content of the structural unit (a4) in the (meth)acrylic copolymer is in the range of 15.0 mass% or more and 20.0 mass% or less with respect to all structural units.

8. A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for optical members according to any one of claims 1 to 7.

9. an optical member; The pressure-sensitive adhesive layer according to claim 8 ; An optical member with a pressure-sensitive adhesive layer comprising:

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