Pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, optical member

Abstract

To provide an adhesive composition excellent in processability, transparency and reworkability, and to provide an adhesive sheet, an optical member and a display device.SOLUTION: A (meth) acrylic polymer (A) having a reactive functional group and having a weight average molecular weight of 650,000 or more and less than 1.5 million, and a constituent unit derived from t-butyl methacrylate at a ratio of 15% by mass or more and 87% by mass or less with respect to all constituent units, A (meth) acrylic polymer (B) having a glass transition temperature of 105 °C or higher and 150 °C or lower and a weight average molecular weight of 100,000 or more and less than 500,000, and a crosslinking agent, in which a content of the (meth) acrylic polymer (B) is 1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the (meth) acrylic polymer (A), and applications thereof.SELECTED DRAWING: None

Description

[Technical Field]

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

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

[0003] For example, Patent Document 1 discloses a pressure-sensitive adhesive composition for optical films, which comprises: a (meth)acrylic polymer (A) having a weight-average molecular weight of 1,000,000 or more; a (meth)acrylic polymer (B) containing structural units derived from a monomer having a hydroxyl group, having a hydroxyl group content of 0.0007 mmol / g to 0.22 mmol / g, having a glass transition temperature of 0°C or higher, and having a weight-average molecular weight of 30,000 to 500,000; and a crosslinking agent, wherein the content of the (meth)acrylic polymer (B) is 1 part by mass to 30 parts by mass per 100 parts by mass of the (meth)acrylic polymer (A). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-145213 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, growing concern about the environment has led to a demand for a reduction in the amount of organic solvent used. When the content of organic solvent in a pressure-sensitive adhesive composition is reduced, the viscosity of the pressure-sensitive adhesive composition increases, thereby impairing the coatability of the pressure-sensitive adhesive composition. In order to reduce the content of organic solvent in the pressure-sensitive adhesive composition without increasing the viscosity of the pressure-sensitive adhesive composition, it is conceivable to reduce the weight-average molecular weight of the base resin used in the pressure-sensitive adhesive composition. When the weight-average molecular weight of the base resin is low, there is no need to use a large amount of organic solvent to adjust the viscosity of the pressure-sensitive adhesive composition.

[0006] Optical films, such as polarizing plates used in liquid crystal displays, are used with a pressure-sensitive adhesive layer attached. Such pressure-sensitive adhesive-coated optical films are typically produced in wide widths and then punched to a predetermined size using a cutting blade. If the pressure-sensitive adhesive layer protrudes from the cut surface during this process, the protruding pressure-sensitive adhesive layer may adhere to other optical films during the overlapping process, potentially contaminating the optical films. For this reason, pressure-sensitive adhesive layers are required to have excellent processability, such as preventing protrusion from the cut surface during cutting. One possible method for improving the processability of a pressure-sensitive adhesive layer is to add a low-molecular-weight resin with a relatively high glass transition temperature to a base resin. For example, Patent Document 1 discloses a pressure-sensitive adhesive layer with excellent processability achieved by adding a resin with a glass transition temperature of 0°C or higher and a weight-average molecular weight of 30,000 to 500,000 to a base resin with a weight-average molecular weight of 1,000,000 or higher. However, with the recent increase in the size of optical displays, the area of ​​optical films such as polarizing plates has also increased, making it easier for the pressure-sensitive adhesive layer to protrude from the cut surface. Therefore, pressure-sensitive adhesive layers are required to have better processability than ever before. To further improve the processability of pressure-sensitive adhesive layers, it is conceivable to increase the glass transition temperature of the low-molecular-weight resin added to the base resin (e.g., 105°C or higher). However, if the weight-average molecular weight of the base resin is lowered to a certain extent (e.g., less than 1.5 million) in order to reduce the amount of organic solvent used, the compatibility between the base resin and the added resin may decrease, resulting in a problem of impaired transparency of the pressure-sensitive adhesive layer. As described above, it has been difficult to form a pressure-sensitive adhesive layer that combines high levels of processability and transparency in a pressure-sensitive adhesive composition in which the weight-average molecular weight of the base resin is set to a certain low level in order to reduce the amount of organic solvent used.

[0007] Furthermore, when the optical film with a pressure-sensitive adhesive layer is attached to a liquid crystal cell, if foreign matter gets caught between the pressure-sensitive adhesive layer and the liquid crystal cell or if misalignment occurs due to an incorrect attachment position, the optical film with a pressure-sensitive adhesive layer is peeled off from the liquid crystal cell and reattached. Since the liquid crystal cell is reused after the optical film with a pressure-sensitive adhesive layer is peeled off, the pressure-sensitive adhesive layer is required to have excellent reworkability so that the pressure-sensitive adhesive layer can be easily peeled off from the liquid crystal cell without damaging the liquid crystal cell or leaving adhesive residue on the attachment surface to the liquid crystal cell.

[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 capable of forming a pressure-sensitive adhesive layer that is excellent in processability, transparency, and reworkability. Another problem to be solved by another embodiment of the present disclosure is to provide a pressure-sensitive adhesive sheet, an optical member, and a display device that include a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. [Means for solving the problem]

[0009] Specific means for solving the problems include the following aspects. <1> a (meth)acrylic polymer (A) having a reactive functional group and a weight average molecular weight of 650,000 or more but less than 1,500,000; a (meth)acrylic polymer (B) containing structural units derived from t-butyl methacrylate in a proportion of 15% by mass or more and 87% by mass or less of all structural units, having a glass transition temperature of 105°C or more and 150°C or less, and having a weight average molecular weight of 100,000 or more and less than 500,000; a cross-linking agent; Including, The pressure-sensitive adhesive composition, wherein the content of the (meth)acrylic polymer (B) is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A). <2> The glass transition temperature of the (meth)acrylic polymer (A) is -60°C or higher and -30°C or lower. <1> The pressure-sensitive adhesive composition according to claim 1. <3> The reactive functional group contains at least one of a carboxy group and a hydroxyl group. <1> or <2> The pressure-sensitive adhesive composition according to claim 1. <4> <1> ~ <3> 1. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of the above items. <5> An optical film; provided on at least one surface of the optical film, and <1> ~ <3> a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of the above items; An adhesive sheet comprising: <6> The optical film is a polarizing plate. <5> The adhesive sheet according to claim 1. <7> A glass substrate; <1> ~ <3> a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of the above items; An optical film; An optical element comprising the above in this order. <8> <7> A display device comprising the optical member according to claim 1. [Effects of the Invention]

[0010] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer that is excellent in processability, transparency, and reworkability. According to another embodiment of the present disclosure, there are provided a pressure-sensitive adhesive sheet, an optical member, and a display device, each comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition. DETAILED DESCRIPTION OF THE INVENTION

[0011] The pressure-sensitive adhesive composition, pressure-sensitive adhesive sheet, optical member, and display device of the present disclosure are 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 the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

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

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

[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, "(meth)acrylic polymer" means a polymer that contains structural units derived from (meth)acrylic monomers and in which the proportion of structural units derived from (meth)acrylic monomers is 50 mass % or more. 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] The pressure-sensitive adhesive composition of the present disclosure comprises: a (meth)acrylic polymer (A) having a reactive functional group and having a weight-average molecular weight of 650,000 or more and less than 1,500,000; a (meth)acrylic polymer (B) containing structural units derived from t-butyl methacrylate in a proportion of 15% by mass or more and 87% by mass or less of all structural units, and having a glass transition temperature of 105°C or more and 150°C or less and a weight-average molecular weight of 100,000 or more and less than 500,000; and a crosslinking agent, wherein the content of the (meth)acrylic polymer (B) is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A). The pressure-sensitive adhesive composition of the present disclosure has the above-described configuration, and thus can form a pressure-sensitive adhesive layer that is excellent in processability, transparency, and reworkability.

[0024] In the present disclosure, "a (meth)acrylic polymer (A) having a reactive functional group and a weight-average molecular weight of 650,000 or more and less than 1,500,000" is also referred to as "a specific (meth)acrylic polymer (A)." In addition, in the present disclosure, "a (meth)acrylic polymer (B) containing structural units derived from t-butyl methacrylate in a proportion of 15% by mass or more and 87% by mass or less of all structural units, having a glass transition temperature of 105°C or more and 150°C or less, and having a weight-average molecular weight of 100,000 or more and less than 500,000" is also referred to as "a specific (meth)acrylic polymer (B)." In the present disclosure, the "specific (meth)acrylic polymer (A) and the specific (meth)acrylic polymer (B)" may be collectively referred to as the "specific (meth)acrylic polymer."

[0025] [Specific (meth)acrylic polymer (A)] The pressure-sensitive adhesive composition of the present disclosure contains a (meth)acrylic polymer (A) having a reactive functional group and a weight-average molecular weight of 650,000 or more and less than 1,500,000 [i.e., specific (meth)acrylic polymer (A)]. The pressure-sensitive adhesive composition of the present disclosure may contain one type of specific (meth)acrylic polymer (A) alone, or may contain two or more types.

[0026] The specific (meth)acrylic polymer (A) may be a homopolymer or a copolymer. The specific (meth)acrylic polymer (A) may be, for example, a homopolymer or copolymer of a (meth)acrylic monomer having no reactive functional group into which a reactive functional group has been introduced by substitution, or a copolymer of a (meth)acrylic monomer having no reactive functional group and a monomer having no reactive functional group but other than the (meth)acrylic monomer, into which a reactive functional group has been introduced by substitution. The specific (meth)acrylic polymer (A) may be, for example, a copolymer of a (meth)acrylic monomer having a reactive functional group and a (meth)acrylic monomer not having a reactive functional group, a copolymer of a (meth)acrylic monomer having a reactive functional group and a monomer not having a reactive functional group but a monomer other than the (meth)acrylic monomer, or a copolymer of a (meth)acrylic monomer not having a reactive functional group and a monomer having a reactive functional group but a monomer other than the (meth)acrylic monomer.

[0027] The specific (meth)acrylic polymer (A) has a reactive functional group. In the present disclosure, the term "reactive functional group" refers to a functional group that can react with a crosslinking agent to form a crosslinked structure. The specific (meth)acrylic polymer (A) has reactive functional groups, and thus forms a crosslinked structure by reaction of the reactive functional groups with a crosslinking agent described below. The formation of the crosslinked structure imparts cohesive strength to the pressure-sensitive adhesive layer. When the cohesive strength of the pressure-sensitive adhesive layer is increased, the adhesion between the pressure-sensitive adhesive layer and the substrate is improved, suppressing protrusion of the pressure-sensitive adhesive layer from the cut surface and improving the processability of the pressure-sensitive adhesive layer. Furthermore, when the cohesive strength of the pressure-sensitive adhesive layer is increased, cohesive failure of the pressure-sensitive adhesive layer is less likely to occur, improving the reworkability of the pressure-sensitive adhesive layer. Specific examples of reactive functional groups include a hydroxyl group, a carboxyl group, and an amino group. In the present disclosure, the term "amino group" encompasses primary amino groups, secondary amino groups, and tertiary amino groups. The reactive functional group preferably contains at least one of a hydroxyl group and a carboxyl group, and more preferably contains both a hydroxyl group and a carboxyl group.

[0028] A preferred embodiment of the specific (meth)acrylic polymer (A) is an embodiment in which the specific (meth)acrylic polymer (A) has a reactive functional group by containing a structural unit derived from a monomer having a reactive functional group, which will be described later.

[0029] <Structural Units Derived from Monomers Having Reactive Functional Groups> The type of the monomer having a reactive functional group is not particularly limited. Examples of the monomer having a reactive functional group include a monomer having at least one reactive functional group and an ethylenically unsaturated group in one molecule. Specific examples of the reactive functional group are as described above. Examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, and a (meth)acryloyl group.

[0030] Examples of the monomer having a reactive functional group include a monomer having a carboxy group, a monomer having a hydroxyl group, and a monomer having an amino group.

[0031] The type of the monomer having a carboxy group is not particularly limited. Specific examples of the monomer having a carboxy group include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≒2) monoacrylate], and succinic acid derivatives (e.g., 2-acryloyloxyethyl-succinic acid). The monomer having a carboxy group preferably includes acrylic acid, and more preferably is acrylic acid.

[0032] The type of the hydroxyl group-containing monomer is not particularly limited. Specific examples of monomers 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, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate. The monomer having a hydroxyl group preferably includes a hydroxyalkyl (meth)acrylate, more preferably includes 2-hydroxyethyl (meth)acrylate, even more preferably includes 2-hydroxyethyl acrylate, and particularly preferably includes 2-hydroxyethyl acrylate.

[0033] The type of the monomer having an amino group is not particularly limited. Specific examples of the monomer having an amino group include 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2-diisopropylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylamide.

[0034] The monomer having a reactive functional group preferably includes at least one of a monomer having a carboxy group and a monomer having a hydroxyl group, and more preferably includes a monomer having a carboxy group.

[0035] When the specific (meth)acrylic polymer (A) contains a structural unit derived from a monomer having a reactive functional group, it may contain one type of structural unit derived from a monomer having a reactive functional group alone, or may contain two or more types of structural units derived from a monomer having a reactive functional group.

[0036] When the specific (meth)acrylic polymer (A) contains a structural unit derived from a monomer having a reactive functional group, the content of the structural unit derived from the monomer having a reactive functional group in the specific (meth)acrylic polymer (A) is not particularly limited, but, for example, from the viewpoint of further improving the processability and reworkability of the pressure-sensitive adhesive layer, it is preferably from 0.5% by mass to 9% by mass, more preferably from 1% by mass to 7% by mass, and even more preferably from 2% by mass to 7% by mass, based on the total structural units of the specific (meth)acrylic polymer (A).

[0037] <Structural Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The specific (meth)acrylic polymer (A) preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer. The type of (meth)acrylic acid alkyl ester monomer is not particularly limited. The (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent (excluding reactive functional groups), but is preferably unsubstituted. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The alkyl moiety of the (meth)acrylic acid alkyl ester monomer preferably has 1 to 18 carbon atoms, more preferably 1 to 12 carbon atoms, further preferably 1 to 8 carbon atoms, and particularly preferably 1 to 4 carbon atoms.

[0038] Specific examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. The (meth)acrylic acid alkyl ester monomer preferably contains at least one selected from the group consisting of n-butyl acrylate, methyl acrylate, and methyl methacrylate, more preferably contains n-butyl acrylate, and even more preferably is n-butyl acrylate.

[0039] When the specific (meth)acrylic polymer (A) contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, it may contain one type of structural unit derived from a (meth)acrylic acid alkyl ester monomer alone, or may contain two or more types of structural units derived from a (meth)acrylic acid alkyl ester monomer.

[0040] When the specific (meth)acrylic polymer (A) contains structural units derived from a (meth)acrylic acid alkyl ester monomer, the content of the structural units derived from a (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic polymer (A) is not particularly limited, but, for example, is preferably 50 mass% or more, more preferably 50 mass% or more and 99.5 mass% or less, even more preferably 60 mass% or more and 99.0 mass% or less, and particularly preferably 70 mass% or more and 98.0 mass% or less, relative to all structural units of the specific (meth)acrylic polymer (A). The content of structural units derived from (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic polymer (A) being 50 mass% or more relative to all structural units of the specific (meth)acrylic polymer (A) means that structural units derived from (meth)acrylic acid alkyl ester monomers are contained as a main component of the structural units of the specific (meth)acrylic polymer (A).

[0041] <Constituent units derived from other monomers> The specific (meth)acrylic polymer (A) may contain a structural unit derived from a monomer (so-called other monomer) that does not fall into either the category of a monomer having a reactive functional group or a (meth)acrylic acid alkyl ester monomer.

[0042] Examples of structural units derived from other monomers include structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; 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.

[0043] From the viewpoint of suppressing white spots, the specific (meth)acrylic polymer (A) preferably contains, as a constituent unit derived from another monomer, a constituent unit derived from a (meth)acrylate having an aromatic ring, more preferably at least one selected from the group consisting of benzyl (meth)acrylate and phenoxyethyl (meth)acrylate, even more preferably a constituent unit derived from phenoxyethyl (meth)acrylate, and particularly preferably a constituent unit derived from phenoxyethyl acrylate. Here, "white spots" refers to, for example, a phenomenon in which light leakage occurs in a liquid crystal display device, resulting in a white appearance.

[0044] When the specific (meth)acrylic polymer (A) contains a structural unit derived from another monomer, it may contain one type of structural unit derived from the other monomer alone, or may contain two or more types of structural units derived from the other monomer.

[0045] When the specific (meth)acrylic polymer (A) contains a structural unit derived from another monomer, the content of the structural unit derived from the other monomer in the specific (meth)acrylic polymer (A) can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0046] <<Glass transition temperature of specific (meth)acrylic polymer (A)>> The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic polymer (A) is not particularly limited, but is preferably, for example, -60°C or higher and -30°C or lower, more preferably -55°C or higher and -35°C or lower, and even more preferably -50°C or higher and -40°C or lower. When the glass transition temperature of the specific (meth)acrylic polymer (A) is −60° C. or higher, the reworkability of the pressure-sensitive adhesive layer tends to be improved. When the glass transition temperature of the specific (meth)acrylic polymer (A) is −30° C. or lower, the reworkability and transparency of the pressure-sensitive adhesive layer tend to be improved.

[0047] The glass transition temperature of the specific (meth)acrylic polymer (A) 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)

[0048] In formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk respectively represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific (meth)acrylic polymer (A) is made into a homopolymer. m1, m2, . . . , m(k-1), and mk respectively represent the molar fractions of each monomer constituting the specific (meth)acrylic polymer (A), 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.

[0049] In the present disclosure, the "glass transition temperature when converted into a homopolymer" refers to a value described in a publicly known document or a value measured using a differential scanning calorimeter (DSC). The specific value to be used is as follows:

[0050] 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).

[0051] 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.

[0052] 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.

[0053] The glass transition temperature of the specific (meth)acrylic polymer (A) can be adjusted to a desired value, for example, by appropriately selecting the types and ratios of the monomers that are polymerization components of the specific (meth)acrylic polymer (A).

[0054] <<Weight-average molecular weight of specific (meth)acrylic polymer (A)>> The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic polymer (A) is 650,000 or more and less than 1,500,000. When the weight-average molecular weight of the specific (meth)acrylic polymer (A) is 650,000 or more, entanglement of the polymers occurs to a moderate extent, and localization of the specific (meth)acrylic polymer (B) at the interface of the pressure-sensitive adhesive layer is suppressed, so that the transparency of the pressure-sensitive adhesive layer tends to be excellent. The weight average molecular weight of the specific (meth)acrylic polymer (A) is preferably 700,000 or more, more preferably 750,000 or more, and even more preferably 850,000 or more. When the weight-average molecular weight of the specific (meth)acrylic polymer (A) is less than 1,500,000, even if the amount of organic solvent used is reduced to some extent, the viscosity of the pressure-sensitive adhesive composition does not become excessively high, and the pressure-sensitive adhesive composition tends to have excellent coatability. The weight average molecular weight of the specific (meth)acrylic polymer (A) is preferably 1,400,000 or less, more preferably 1,300,000 or less, and even more preferably 1,200,000 or less. In one embodiment, the weight average molecular weight of the specific (meth)acrylic polymer (A) may be 700,000 or more and 1,400,000 or less, 750,000 or more and 1,300,000 or less, or 850,000 or more and 1,200,000 or less.

[0055] The weight average molecular weight of the specific (meth)acrylic polymer (A) is a value measured by the following method, specifically, according to the following (1) to (3). (1) A solution of the specific (meth)acrylic polymer (A) is applied to a release paper and then dried at 100° C. for 1 minute to obtain a film of the specific (meth)acrylic polymer (A). (2) Using the film-like specific (meth)acrylic polymer (A) obtained in (1) above and tetrahydrofuran, a sample solution having a solids concentration of 0.2% by mass is obtained. Here, the "solids concentration" refers to the mass proportion of the specific (meth)acrylic polymer (A) in the sample solution. (3) The weight average molecular weight of the specific (meth)acrylic polymer (A) is determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) under the following conditions.

[0056] ~Conditions~ Measurement equipment: High-speed GPC [Model: HLC-8420 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [built into HLC-8420, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Two Tosoh products are used. Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0057] The weight average molecular weight of the specific (meth)acrylic polymer (A) 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.

[0058] <<Content of specific (meth)acrylic polymer (A)>> The content rate of the specific (meth)acrylic polymer (A) in the adhesive composition of the present disclosure is not particularly limited, but for example, it is preferably 73.5 mass% to 99.0 mass%, more preferably 75.5 mass% to 98.0 mass%, and even more preferably 76.0 mass% to 96.5 mass% with respect to the total solid content in the adhesive composition.

[0059] 〔Specific (meth)acrylic polymer (B)〕 The adhesive composition of the present disclosure contains a (meth)acrylic polymer (B) [i.e., specific (meth)acrylic polymer (B)] having a glass transition temperature of 105°C or higher and 150°C or lower and a weight average molecular weight of 100,000 or higher and less than 500,000, containing structural units derived from t-butyl methacrylate at a ratio of 15 mass% or more and 87 mass% or less with respect to all the structural units. The adhesive composition of the present disclosure may contain the specific (meth)acrylic polymer (B) alone or in combination of two or more kinds.

[0060] <Structural units derived from t-butyl methacrylate> The specific (meth)acrylic polymer (B) contains structural units derived from t-butyl methacrylate at a ratio of 15 mass% or more and 87 mass% or less with respect to all the structural units. In the adhesive composition of the present disclosure, as one method for improving the processability of the adhesive layer, the cohesive force of the adhesive layer is increased by combining the specific (meth)acrylic polymer (A) as the base resin and the specific (meth)acrylic polymer (B) having a relatively high glass transition temperature of 105°C or higher. In order to increase the glass transition temperature of the specific (meth)acrylic polymer (B) to 105°C or higher, it is conceivable to select, for example, a methacrylic acid alkyl ester monomer having a relatively short alkyl chain (in other words, a small number of carbon atoms in the alkyl moiety) as the monomer component of the specific (meth)acrylic polymer (B). Methacrylic acid alkyl ester monomers having a relatively short alkyl chain tend to have a high glass transition temperature when formed into a homopolymer. However, if the content of structural units derived from methacrylic acid alkyl ester monomers having a short alkyl chain in the specific (meth)acrylic polymer (B) increases, it becomes difficult for the specific (meth)acrylic polymer (B) to form an entangled structure with the specific (meth)acrylic polymer (A). This makes the specific (meth)acrylic polymer (B) more likely to localize at the interface of the pressure-sensitive adhesive layer, impairing the transparency of the pressure-sensitive adhesive layer. Furthermore, in order to increase the glass transition temperature of the specific (meth)acrylic polymer (B) to 105°C or higher, it is possible to select, for example, a methacrylic acid alkyl ester monomer having a cyclic structure as the monomer component of the specific (meth)acrylic polymer (B). Methacrylic acid alkyl ester monomers having a cyclic structure also tend to have a high glass transition temperature when formed into a homopolymer. However, since methacrylic acid alkyl ester monomers having a cyclic structure have a very bulky structure, if the specific (meth)acrylic polymer (B) contains a large number of structural units derived from methacrylic acid alkyl ester monomers having a cyclic structure, the compatibility between the specific (meth)acrylic polymer (A) and the specific (meth)acrylic polymer (B) decreases, and the transparency of the pressure-sensitive adhesive layer is likely to be impaired. In contrast, the specific (meth)acrylic polymer (B) contains structural units derived from t-butyl methacrylate, which has a glass transition temperature of 118°C when made into a homopolymer, in a proportion of 15% by mass or more relative to all structural units, so that the glass transition temperature can be adjusted to 105°C or higher without containing a large amount of structural units derived from methacrylic acid alkyl ester monomers with relatively short alkyl chains and / or structural units derived from methacrylic acid alkyl ester monomers having a cyclic structure. Furthermore, the specific (meth)acrylic polymer (B) contains structural units derived from t-butyl methacrylate having a t-butyl group that relatively easily entangles with the specific (meth)acrylic polymer (A), in a proportion of 15% by mass or more relative to all structural units, so that the specific (meth)acrylic polymer (B) can sufficiently form an entangled structure with the specific (meth)acrylic polymer (A), making it less likely to localize at the interface of the pressure-sensitive adhesive layer. Therefore, when the content of structural units derived from t-butyl methacrylate in the specific (meth)acrylic polymer (B) is 15 mass% or more relative to the total structural units of the specific (meth)acrylic polymer (B), the pressure-sensitive adhesive layer tends to have excellent processability as well as transparency. On the other hand, when the content of structural units derived from t-butyl methacrylate in the specific (meth)acrylic polymer (B) is 87% by mass or less relative to the total structural units of the specific (meth)acrylic polymer (B), the transparency of the pressure-sensitive adhesive layer tends to be excellent. The reason for this is presumably that, since the proportion of structural units derived from t-butyl methacrylate, which has bulky t-butyl groups and a relatively high glass transition temperature when made into a homopolymer, is not excessively high, the specific (meth)acrylic polymer (B) is suitably compatible with the specific (meth)acrylic polymer (A), and the formation of a phase-separated structure with a size larger than several hundred nanometers, which is the wavelength range of light, is unlikely to occur. The content of the structural units derived from t-butyl methacrylate in the specific (meth)acrylic polymer (B) is preferably 17% by mass or more, more preferably 19% by mass or more, and even more preferably 30% by mass or more, based on the total structural units of the specific (meth)acrylic polymer (B). The content of the structural units derived from t-butyl methacrylate in the specific (meth)acrylic polymer (B) is preferably 85% by mass or less, more preferably 83% by mass or less, and even more preferably 80% by mass or less, based on the total structural units of the specific (meth)acrylic polymer (B). In one embodiment, the content of structural units derived from t-butyl methacrylate in the specific (meth)acrylic polymer (B) may be 17% by mass or more and 85% by mass or less, 19% by mass or more and 83% by mass or less, or 30% by mass or more and 80% by mass or less, relative to all structural units of the specific (meth)acrylic polymer (B).

[0061] <Other Structural Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The specific (meth)acrylic polymer (B) preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer other than t-butyl methacrylate (so-called other (meth)acrylic acid alkyl ester monomer).

[0062] 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, but is preferably 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 reactive functional groups), 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 1 to 18, more preferably 1 to 12, even more preferably 1 to 8, and particularly preferably 1 to 4.

[0063] Specific examples of other (meth)acrylic acid alkyl ester monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. The other (meth)acrylic acid alkyl ester monomer preferably includes at least one selected from the group consisting of methyl methacrylate, i-butyl methacrylate, and isobornyl methacrylate, more preferably includes methyl methacrylate, and even more preferably is methyl methacrylate.

[0064] When the specific (meth)acrylic polymer (B) contains a structural unit derived from another (meth)acrylic acid alkyl ester monomer, it may contain one type of structural unit derived from another (meth)acrylic acid alkyl ester monomer alone, or may contain two or more types of structural units derived from another (meth)acrylic acid alkyl ester monomer.

[0065] When the specific (meth)acrylic polymer (B) contains structural units derived from other (meth)acrylic acid alkyl ester monomers, the content of the structural units derived from other (meth)acrylic acid alkyl ester monomers in the specific (meth)acrylic polymer (B) is not particularly limited, but is, for example, preferably from 13% by mass to 85% by mass, more preferably from 17% by mass to 85% by mass, and even more preferably from 19% by mass to 85% by mass, relative to all structural units of the specific (meth)acrylic polymer (B).

[0066] <Structural Units Derived from Monomers Having Reactive Functional Groups> The specific (meth)acrylic polymer (B) may contain a structural unit derived from a monomer having a reactive functional group. The type of the monomer having a reactive functional group is not particularly limited. Examples of the monomer having a reactive functional group include a monomer having at least one reactive functional group and an ethylenically unsaturated group in one molecule. Specific examples of the reactive functional group are as described above. Examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, and a (meth)acryloyl group.

[0067] Examples of the monomer having a reactive functional group include a monomer having a carboxy group, a monomer having a hydroxyl group, and a monomer having an amino group. Specific examples of these monomers having a reactive functional group are the same as those explained in the specific (meth)acrylic polymer (A). The monomer having a reactive functional group is preferably a monomer having a hydroxyl group. A hydroxyl group is preferred in that the crosslinking reaction proceeds more slowly than other reactive functional groups such as a carboxyl group and therefore tends to be less likely to inhibit the reaction between the specific (meth)acrylic polymer (A) and the crosslinking agent.

[0068] When the specific (meth)acrylic polymer (B) contains a structural unit derived from a monomer having a reactive functional group, it may contain one type of structural unit derived from a monomer having a reactive functional group alone, or may contain two or more types of structural units derived from a monomer having a reactive functional group.

[0069] From the viewpoint of further improving the reworkability of the pressure-sensitive adhesive layer, for example, the specific (meth)acrylic polymer (B) preferably does not contain any structural units derived from monomers having a reactive functional group, or the content of structural units derived from monomers having a reactive functional group is more than 0 mass% and 1.0 mass% or less, relative to all structural units of the specific (meth)acrylic polymer (B); more preferably, it does not contain any structural units derived from monomers having a reactive functional group, or the content of structural units derived from monomers having a reactive functional group is more than 0 mass% and 0.5 mass% or less, relative to all structural units of the specific (meth)acrylic polymer (B); and even more preferably, it does not contain any structural units derived from monomers having a reactive functional group.

[0070] <Constituent units derived from other monomers> The specific (meth)acrylic polymer (B) may contain a structural unit derived from a monomer (so-called other monomer) that does not fall under any of t-butyl methacrylate, a monomer having a reactive functional group, and other (meth)acrylic acid alkyl ester monomers.

[0071] Examples of structural units derived from other monomers include structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; 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.

[0072] When the specific (meth)acrylic polymer (B) contains a structural unit derived from another monomer, it may contain one type of structural unit derived from the other monomer alone, or may contain two or more types of structural units derived from the other monomer.

[0073] When the specific (meth)acrylic polymer (B) contains a structural unit derived from another monomer, the content of the structural unit derived from another monomer in the specific (meth)acrylic polymer (B) can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0074] <<Glass transition temperature of specific (meth)acrylic polymer (B)>> The glass transition temperature (Tg) of the specific (meth)acrylic polymer (B) is 105°C or higher and 150°C or lower. When the glass transition temperature of the specific (meth)acrylic polymer (B) is 105° C. or higher, the pressure-sensitive adhesive layer formed tends to have excellent processability since it is endowed with appropriate elasticity. The glass transition temperature of the specific (meth)acrylic polymer (B) is preferably 107°C or higher, more preferably 110°C or higher, and even more preferably 113°C or higher. In order to increase the glass transition temperature of the specific (meth)acrylic polymer (B) to a temperature exceeding 150° C., it is conceivable to select, for example, a methacrylic acid alkyl ester monomer having a cyclic structure as the monomer component of the specific (meth)acrylic polymer (B). However, since a methacrylic acid alkyl ester monomer having a cyclic structure has an extremely bulky structure, if the specific (meth)acrylic polymer (B) contains a structural unit derived from a methacrylic acid alkyl ester monomer having a cyclic structure, its compatibility with the specific (meth)acrylic polymer (A) decreases, and the transparency of the pressure-sensitive adhesive layer is likely to be impaired. In contrast, when the glass transition temperature of the specific (meth)acrylic polymer (B) is 150°C or lower, the specific (meth)acrylic polymer (B) does not need to contain an excessive amount of structural units derived from a methacrylic acid alkyl ester monomer having a cyclic structure in order to adjust the glass transition temperature, and therefore the compatibility between the specific (meth)acrylic polymer (A) and the specific (meth)acrylic polymer (B) is less likely to decrease, and the transparency of the pressure-sensitive adhesive layer tends not to be impaired. The glass transition temperature of the specific (meth)acrylic polymer (B) is preferably 140°C or lower, more preferably 135°C or lower. In one embodiment, the glass transition temperature of the specific (meth)acrylic polymer (B) may be 105°C or higher and 140°C or lower, 107°C or higher and 140°C or lower, 110°C or higher and 135°C or lower, or 113°C or higher and 135°C or lower.

[0075] The glass transition temperature of the specific (meth)acrylic polymer (B) is determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic polymer (A) described above.

[0076] The glass transition temperature of the specific (meth)acrylic polymer (B) can be adjusted to a desired value, for example, by appropriately selecting the types and ratios of the monomers that are polymerization components of the specific (meth)acrylic polymer (B).

[0077] <<Weight-average molecular weight of specific (meth)acrylic polymer (B)>> The weight average molecular weight (Mw) of the specific (meth)acrylic polymer (B) is 100,000 or more and less than 500,000. When the weight average molecular weight of the specific (meth)acrylic polymer (B) is 100,000 or more, the pressure-sensitive adhesive layer formed tends to have excellent processability because an appropriate cohesive force is imparted to the pressure-sensitive adhesive layer. The weight average molecular weight of the specific (meth)acrylic polymer (B) is preferably 130,000 or more, more preferably 200,000 or more, and even more preferably 250,000 or more. When the weight-average molecular weight of the specific (meth)acrylic polymer (B) is less than 500,000, the specific (meth)acrylic polymer (A) and the specific (meth)acrylic polymer (B) having a small weight-average molecular weight are likely to form an entangled structure, and the transparency of the pressure-sensitive adhesive layer tends to be excellent. The weight average molecular weight of the specific (meth)acrylic polymer (B) is preferably 470,000 or less, more preferably 440,000 or less, and even more preferably 400,000 or less. In one embodiment, the weight average molecular weight of the specific (meth)acrylic polymer (B) may be 130,000 or more and 470,000 or less, 200,000 or more and 440,000 or less, or 250,000 or more and 400,000 or less.

[0078] The weight average molecular weight of the specific (meth)acrylic polymer (B) is measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic polymer (A) described above.

[0079] The weight average molecular weight of the specific (meth)acrylic polymer (B) 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.

[0080] <<Content of specific (meth)acrylic polymer (B)>> The content of the specific (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition of the present disclosure is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the specific (meth)acrylic polymer (A). When the content of the specific (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition of the present disclosure is 1 part by mass or more per 100 parts by mass of the specific (meth)acrylic polymer (A), the pressure-sensitive adhesive layer formed is imparted with appropriate elasticity, and the pressure-sensitive adhesive layer tends to have excellent processability. The content of the specific (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition of the present disclosure is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 6 parts by mass or more, per 100 parts by mass of the specific (meth)acrylic polymer. When the content of the specific (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition of the present disclosure is 40 parts by mass or less relative to 100 parts by mass of the specific (meth)acrylic polymer (A), the pressure-sensitive adhesive layer formed does not have excessively high elasticity, and the pressure-sensitive adhesive layer can appropriately relieve stress generated in the pressure-sensitive adhesive layer when peeled from an adherend, and therefore the pressure-sensitive adhesive layer tends to have excellent reworkability. The content of the specific (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition of the present disclosure is preferably 35 parts by mass or less, more preferably 32 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the specific (meth)acrylic polymer. In an embodiment, the content of the specific (meth)acrylic polymer (B) in the pressure-sensitive adhesive composition of the present disclosure may be 2 parts by mass or more and 35 parts by mass or less, 4 parts by mass or more and 35 parts by mass or less, 6 parts by mass or more and 32 parts by mass or less, or 6 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic polymer (A).

[0081] 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.

[0082] [Method for producing specific (meth)acrylic polymer] The method for producing the specific (meth)acrylic polymer (A) and the specific (meth)acrylic polymer (B) (i.e., the specific (meth)acrylic polymer) is not particularly limited. The specific (meth)acrylic polymer 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.

[0083] 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 the mixture is heated and reacted 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.

[0084] 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.

[0085] In producing the specific (meth)acrylic polymer, 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 polymer, ease of the polymerization reaction, etc.

[0086] During the polymerization reaction, one type of organic solvent may be used alone, or two or more types may be used.

[0087] 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.

[0088] During the polymerization reaction, one type of polymerization initiator may be used alone, or two or more types may be used.

[0089] The amount of the polymerization initiator used is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer.

[0090] In producing the specific (meth)acrylic polymer, 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, α-methylstyrene, aromatic compounds such as anthracene, phenanthrene, fluorene, and 9-phenylfluorene, p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, aromatic nitro compounds such as 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, ... Examples of suitable mercaptan 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.

[0091] When a chain transfer agent is used in producing the specific (meth)acrylic polymer, the amount of the chain transfer agent used is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer.

[0092] The polymerization temperature is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer.

[0093] [Crosslinking agent] The pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent. The type of crosslinking agent is not particularly limited. Examples of the crosslinking agent include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, a metal chelate-based crosslinking agent, and an aziridine-based crosslinking agent.

[0094] In this disclosure, "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate-based compound). Also, "epoxy-based crosslinking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher epoxy-based compound). Also, "metal chelate-based crosslinking agent" refers to a metal chelate-based compound that functions as a crosslinking agent. Also, "aziridine-based crosslinking agent" refers to a compound having two or more aziridine groups in one molecule (so-called polyaziridine-based compound).

[0095] The crosslinking agent preferably contains at least one selected from the group consisting of an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent, more preferably contains an isocyanate-based crosslinking agent, and even more preferably is an isocyanate-based crosslinking agent.

[0096] Examples of the isocyanate crosslinking agent include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, and aromatic polyisocyanate compounds. "Aliphatic polyisocyanate compounds" include, for example, aliphatic polyisocyanate compounds, polymers of aliphatic polyisocyanate compounds, adducts of aliphatic polyisocyanate compounds and polyol compounds (e.g., trimethylolpropane (TMP); the same applies hereinafter), and biuret compounds of aliphatic polyisocyanate compounds. Specific examples of aliphatic polyisocyanate compounds include hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. The "alicyclic polyisocyanate compound" includes, for example, an alicyclic polyisocyanate compound, a polymer of an alicyclic polyisocyanate compound, an adduct of an alicyclic polyisocyanate compound and a polyol compound, and a biuret of an alicyclic polyisocyanate compound. Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. The "aromatic polyisocyanate compound" includes, for example, an aromatic polyisocyanate compound, a polymer of an aromatic polyisocyanate compound, an adduct of an aromatic polyisocyanate compound and a polyol compound, and a biuret of an aromatic polyisocyanate compound. Specific examples of the aromatic polyisocyanate compound include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate.

[0097] The isocyanate-based crosslinking agent is preferably an aromatic polyisocyanate-based compound, more preferably at least one selected from the group consisting of tolylene diisocyanate-based compounds and xylylene diisocyanate-based compounds, and even more preferably a tolylene diisocyanate-based compound. The "tolylene diisocyanate compound" includes, for example, TDI, TDI polymers, adducts of TDI and polyol compounds, and biuret compounds of TDI. As the tolylene diisocyanate compound, an adduct of TDI and TMP is preferred. The "xylylene diisocyanate compound" includes, for example, XDI, XDI polymers, adducts of XDI and polyol compounds, and biuret compounds of XDI. The xylylene diisocyanate compound is preferably an adduct of XDI and TMP.

[0098] As the isocyanate-based crosslinking agent, commercially available products can be used. Examples of commercially available isocyanate crosslinking agents include "Coronate HX," "Coronate HK," "Coronate HL," "Coronate HL-S," "Coronate 2031," "Coronate 2037," "Coronate 2234," "Coronate 2770," "Coronate 2785," "Coronate 2793," "Aquanate 200," and "Aquanate 210" (all manufactured by Tosoh Corporation), "Sumidur N75," "Sumidur N3300," "Desmodur N75 MPA / X," "Desmodur N100," "Desmodur N3200," and "Desmodur N3400" (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate D201," "Duranate E405-70B," "Duranate E405-80T," "Duranate AE700-100," and "Duranate 24A-100," "Duranate TSE-100," and "Duranate TMA-100" (all manufactured by Asahi Kasei Corporation), as well as "Takenate D-101E," "Takenate D-110N," "Takenate D-120N," "Takenate D-140N," "Takenate D-160N," "Takenate D-172N," "Takenate M-631N," "MT-Olestar NP1200," and "Stabio XD-340N" (all manufactured by Mitsui Chemicals, Inc.). The above-mentioned "Coronate," "Aquanate," "Sumidur," "Desmodur," "Duranate," "Takenate," "Olestar," and "Stabio" are all registered trademarks.

[0099] Examples of bifunctional or higher functional epoxy compounds include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and resol. Examples of suitable glycidyl ethers include lucine diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris(glycidyl)isocyanurate, tris(glycidoxyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine), and 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate.

[0100] As the epoxy-based crosslinking agent, commercially available products can be used. Examples of commercially available epoxy crosslinking agents include "TETRAD-X" and "TETRAD-C" (both manufactured by Mitsubishi Gas Chemical Company, Inc.), "Denacol EX-201" and "Denacol EX-931" (both manufactured by Nagase ChemteX Corporation), and Celloxide 2021P (manufactured by Daicel Corporation). The above "TETRAD," "Denacol," and "Celloxide" are all registered trademarks.

[0101] The pressure-sensitive adhesive composition of the present disclosure may contain one type of crosslinking agent alone, or may contain two or more types of crosslinking agents.

[0102] The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably 0.05 to 15 parts by mass, more preferably 0.07 to 10 parts by mass, and even more preferably 0.1 to 8 parts by mass, relative to 100 parts by mass of the specific (meth)acrylic polymer (A). The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure being 0.05 parts by mass or more per 100 parts by mass of the specific (meth)acrylic polymer (A) means that the pressure-sensitive adhesive composition of the present disclosure actively contains a crosslinking agent. When the pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent, the crosslinking reaction of the specific (meth)acrylic polymer (A) proceeds, and cohesive strength is imparted to the pressure-sensitive adhesive layer formed. This tends to result in excellent processability of the pressure-sensitive adhesive layer. Furthermore, the pressure-sensitive adhesive layer is less susceptible to cohesive failure due to the imparted cohesive strength. This tends to result in excellent reworkability of the pressure-sensitive adhesive layer. When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is 15 parts by mass or less per 100 parts by mass of the specific (meth)acrylic polymer (A), a decrease in transparency due to excess crosslinking agent tends to be less likely to occur.

[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. Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the above-mentioned specific (meth)acrylic polymer.

[0104] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvents.

[0105] 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.

[0106] [Other ingredients] The pressure-sensitive adhesive composition of the present disclosure may contain components other than the components described above (so-called other components) as needed, provided that the effects of the composition are not impaired. Examples of other components include various additives such as polymers other than the specific (meth)acrylic polymer, silane coupling agents, release adjusters (e.g., silicone oils), crosslinking catalysts, antioxidants, colorants (e.g., dyes and pigments), light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[0107] 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.

[0108] <<Applications of adhesive compositions>> The use of the pressure-sensitive adhesive composition of the present disclosure is not particularly limited. The pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that is excellent in processability, transparency, and reworkability, and is therefore suitable, for example, as a pressure-sensitive adhesive composition to be used in optical films (i.e., a pressure-sensitive adhesive composition for optical films), and among optical films, is particularly suitable as a pressure-sensitive adhesive composition to be used in polarizing plates (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.

[0109] [Adhesive sheet] The pressure-sensitive adhesive sheet of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive sheet of the present disclosure also includes a sheet-like pressure-sensitive adhesive layer itself formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present disclosure contains a cured product of the pressure-sensitive adhesive composition of the present disclosure. The cured product includes, for example, a crosslinked product of the specific (meth)acrylic polymer (A) obtained by crosslinking and curing with a crosslinking agent. The pressure-sensitive adhesive sheet of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and therefore tends to have excellent processability, transparency, and reworkability.

[0110] The thickness of the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited. The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 30 μm.

[0111] 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.

[0112] The pressure-sensitive adhesive sheet of the present disclosure may be a substrate-free pressure-sensitive adhesive sheet that does not have a substrate, or may be a substrate-containing pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one or both sides of a substrate. When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-free type pressure-sensitive adhesive sheet that does not have a substrate, or when it is a substrate-containing type pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one side of a substrate, the exposed surface of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet of the present disclosure may be protected by a release sheet. Generally, the release sheet protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is put to practical use, and is peeled off at the time of use.

[0113] 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.

[0114] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed thereon. Examples of the substrate include films containing resins such as polyolefin resins (e.g., polyethylene (PE) and polypropylene (PP)), polyester resins (e.g., polyethylene terephthalate (PET)), acetate resins (e.g., triacetyl cellulose), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyurethane resins, (meth)acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins.

[0115] The surface of the substrate on which the adhesive layer is provided may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment (so-called easy-adhesion treatment) in order to improve the adhesion between the substrate and the adhesive layer.

[0116] The substrate may contain various additives such as plasticizers, colorants (eg, dyes and pigments), heat stabilizers, light stabilizers, antistatic agents, flame retardants, antioxidants, fillers, and the like. The substrate may be partially or entirely patterned.

[0117] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is preferably an optical film. In this case, a preferred embodiment of the pressure-sensitive adhesive sheet of the present disclosure includes an optical film and a pressure-sensitive adhesive layer provided on at least one surface of the optical film and formed from the pressure-sensitive adhesive composition of the present disclosure.

[0118] The type of optical film is not particularly limited. Specific examples of optical films include polarizing plates, AG (Anti-Glare) polarizing plates, wave plates (e.g., half-wave plates and quarter-wave plates), retardation films including the wave plates, viewing angle compensation films, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, prism sheets, lens sheets, diffusion plates, and transparent conductive films.

[0119] The optical film is preferably a polarizing plate (so-called polarizing film). The polarizing plate is configured to include at least a polarizer, and may be a polarizer alone or a laminate of a polarizer and a protective film. 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.

[0120] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate and the substrate is a polarizing plate, examples of the layer configuration include pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer], pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer / protective film], pressure-sensitive adhesive layer / polarizing plate [retardation film / polarizer], pressure-sensitive adhesive layer / polarizing plate [retardation film / polarizer / protective film], pressure-sensitive adhesive layer / polarizing plate [retardation film / protective film / polarizer / protective film], pressure-sensitive adhesive layer / polarizing plate [polarizer / brightness-enhancing film], pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer / brightness-enhancing film], pressure-sensitive adhesive layer / polarizing plate [polarizer / protective film / brightness-enhancing film], and pressure-sensitive adhesive layer / polarizing plate [protective film / polarizer / protective film / brightness-enhancing film].

[0121] 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).

[0122] The thickness of the substrate (preferably, the optical film) is not particularly limited, but is, for example, preferably 10 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 10 μm to 100 μm.

[0123] In this disclosure, "thickness of the substrate" means the average thickness of the substrate. The average thickness of the substrate is a value determined by the following method. The thickness of the substrate is measured at 10 randomly selected locations in the thickness direction using a film thickness meter. The arithmetic mean of the measured values ​​is calculated and this value is taken as the average thickness of the substrate.

[0124] [How to make adhesive sheets] The method for producing the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited. The pressure-sensitive adhesive sheet of the present disclosure can be produced by a known method. The pressure-sensitive adhesive sheet of the present disclosure can be produced, for example, by the following method.

[0125] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-free type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present disclosure is applied to the easily peelable surface of the release sheet to form a coating film on the release sheet. The formed coating film is then dried to form an adhesive film on the release sheet. Next, the exposed surface of the formed adhesive film is laminated onto the easily peelable surface of a separately prepared release sheet, and then cured as necessary, thereby producing a pressure-sensitive adhesive sheet of the present disclosure having a laminated structure of release sheet / pressure-sensitive adhesive layer / release sheet.

[0126] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present disclosure is applied to one surface of the substrate (preferably the surface treated for easy adhesion) to form a coating film on the substrate. The formed coating film is then dried to form a pressure-sensitive adhesive film on the substrate. Next, the exposed surface of the formed pressure-sensitive adhesive film is laminated onto the surface of a release sheet treated for easy release, and then cured as necessary to produce a pressure-sensitive adhesive sheet of the present disclosure having a laminate structure of substrate / pressure-sensitive adhesive layer / release sheet.

[0127] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-containing pressure-sensitive adhesive sheet, another method may be mentioned, for example, as follows. The pressure-sensitive adhesive composition of the present disclosure is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet. The formed coating film is then dried to form a pressure-sensitive adhesive film on the release sheet. Next, the exposed surface of the formed pressure-sensitive adhesive film is laminated to one surface of the substrate (preferably the easy-adhesion treated surface), and then cured as necessary, thereby producing a pressure-sensitive adhesive sheet of the present disclosure having a laminated structure of substrate / pressure-sensitive adhesive layer / release sheet.

[0128] 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.

[0129] The method for drying the coating film is not particularly limited. Examples of methods for drying the coating film include natural drying, heat drying, hot air drying, and vacuum drying. The drying temperature and drying time of the coating film are not particularly limited, and are set appropriately depending on the thickness of the coating film, the amount of solvent contained in the coating film, and the like. Drying conditions include, for example, using a hot air circulation dryer to blow air at 60°C to 130°C at a speed of 3 m / sec to 5 m / sec for 30 seconds to 300 seconds.

[0130] The curing method may involve leaving the product to stand for 2 to 7 days in an environment with an ambient temperature of 20°C to 35°C and a relative humidity of 45% to 65%, for example.

[0131] [Optical components] The optical member of the present disclosure includes, in this order, a glass substrate, a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure, and an optical film. In the optical member of the present disclosure, the pressure-sensitive adhesive layer is unlikely to cause a decrease in transparency, and the optical film can be easily peeled off from the glass substrate without leaving any adhesive residue.

[0132] The thickness of the glass substrate is not particularly limited, but is generally 0.3 mm to 0.7 mm, and preferably 0.3 mm to 0.5 mm.

[0133] 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.

[0134] The pressure-sensitive adhesive layer and optical film in the optical member of the present disclosure have the same meaning as the pressure-sensitive adhesive layer and optical film in the pressure-sensitive adhesive sheet of the present disclosure, and preferred embodiments are also the same, so description thereof will be omitted here.

[0135] The optical member of the present disclosure can be suitably used, for example, as a member of a display device. Examples of display devices include liquid crystal displays and organic EL (Electro-Luminescence) displays.

[0136] The method for producing the optical member of the present disclosure is not particularly limited. The optical member of the present disclosure can be produced, for example, by using an optical film as a substrate, preparing a pressure-sensitive adhesive sheet of the present disclosure by the method described above, and then bonding the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet to a glass substrate.

[0137] [Display device] The display device of the present disclosure includes the optical member of the present disclosure. In the display device of the present disclosure, a decrease in transparency due to the pressure-sensitive adhesive layer is unlikely to occur.

[0138] Specific examples of the display device are as described above. [Example]

[0139] The pressure-sensitive adhesive composition of the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as they do not depart from the gist of the disclosure.

[0140] [Production of (meth)acrylic polymer (A)] [Manufacturing example A-1] A reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser was charged with 77.7 parts by weight of n-butyl acrylate (n-BA), 18.0 parts by weight of phenoxyethyl acrylate (PHEA), 1.5 parts by weight of acrylic acid (AA), 2.8 parts by weight of 2-hydroxyethyl acrylate (2HEA), 110.0 parts by weight of ethyl acetate (organic solvent), and 20.0 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, 0.01 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile) (ABVN; polymerization initiator) and 30.0 parts by weight of ethyl acetate were sequentially added to the mixture in the reactor, and the mixture was then maintained for 6 hours to complete the polymerization reaction. Next, the solution obtained upon completion of the polymerization reaction was diluted with ethyl acetate to a solid content concentration of 25.0% by mass, and then cooled to obtain a solution of (meth)acrylic polymer A-1.

[0141] The term "solid content concentration" used herein refers to the mass proportion of the (meth)acrylic polymer A-1 in the solution of the (meth)acrylic polymer A-1. The same applies to the solutions of the (meth)acrylic polymers A-2 to A-11 produced below.

[0142] [Manufacturing examples A-2 to A-5] In Production Examples A-2 to A-5, the same operations as in Production Example A-1 were carried out, except that at least one of the amount of organic solvent used and the amount of polymerization initiator used was adjusted to make the weight average molecular weight of the (meth)acrylic polymer (A) the weight average molecular weight shown in Table 1, to obtain solutions of (meth)acrylic polymers A-2 to A-5 each having a solid content concentration of 25.0 mass%.

[0143] [Manufacturing examples A-6 to A-11] In Production Examples A-6 to A-11, the monomer composition of the (meth)acrylic polymer (A) was changed to the monomer composition shown in Table 1, and at least one of the amount of organic solvent used and the amount of polymerization initiator used was adjusted to make the weight average molecular weight of the (meth)acrylic polymer (A) the weight average molecular weight shown in Table 1. Solutions of (meth)acrylic polymers A-6 to A-11, each having a solids concentration of 25.0 mass%, were obtained by performing the same operation as in Production Example A-1.

[0144] Table 1 shows the monomer compositions (unit: mass %), glass transition temperatures (denoted as "Tg"), and weight average molecular weights (denoted as "Mw") of the (meth)acrylic polymers A-1 to A-11. The glass transition temperatures of the (meth)acrylic polymers A-1 to A-11 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic polymer (A) described above. The weight average molecular weights of the (meth)acrylic polymers A-1 to A-11 were measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic polymer (A) described above.

[0145] Among the (meth)acrylic polymers A-1 to A-11, the (meth)acrylic polymers A-1 to A-4 and A-6 to A-10 correspond to the specific (meth)acrylic polymer (A) in the present disclosure.

[0146] [Table 1]

[0147] Details of each monomer listed in Table 1 are as follows: <Monomers having reactive functional groups> "AA": acrylic acid (reactive functional group: carboxyl group) "2HEA": 2-hydroxyethyl acrylate (reactive functional group: hydroxyl group) <(Meth)acrylic acid alkyl ester monomer> "n-BA": n-butyl acrylate "MA": methyl acrylate "MMA": Methyl methacrylate <Other monomers> "PHEA": Phenoxyethyl acrylate

[0148] In Table 1, "-" in the column of monomer composition means that the monomer in that column was not used.

[0149] [Production of (meth)acrylic polymer (B)] [Manufacturing example B-2] A reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser was charged with 16.9 parts by mass of t-butyl methacrylate (t-BMA), 3.0 parts by mass of methyl methacrylate (MMA), 0.08 parts by mass of 2-hydroxyethyl methacrylate (2HEMA), 0.01 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator), 25.0 parts by mass of ethyl acetate (organic solvent), and 2.5 parts by mass of methyl acetate (organic solvent), and mixed to obtain a mixture. The atmosphere in the reactor was then replaced with nitrogen. The mixture in the reactor was then heated to 70°C while stirring. Next, 67.7 parts by mass of t-butyl methacrylate (t-BMA), 12.0 parts by mass of methyl methacrylate (MMA), 0.32 parts by mass of 2-hydroxyethyl methacrylate (2HEMA), 0.1 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator), 90.0 parts by mass of ethyl acetate (organic solvent), and 10.0 parts by mass of methyl acetate (organic solvent) were successively added to the mixture in the reactor, and the mixture was maintained for 6 hours to complete the polymerization reaction. Next, the solution obtained by the completion of the polymerization reaction was diluted with ethyl acetate to a solids concentration of 35.0% by mass, and then cooled to obtain a solution of (meth)acrylic polymer B-2.

[0150] The term "solid content concentration" used herein refers to the mass proportion of the (meth)acrylic polymer B-2 in the solution of the (meth)acrylic polymer B-2. The same applies to the solutions of the (meth)acrylic polymers B-1 and B-3 to B-18 produced below.

[0151] [Production Examples B-1, B-3 to B-7, B-10 and B-12] In Production Examples B-1, B-3 to B-7, B-10, and B-12, the same operations as in Production Example B-2 were carried out except that the monomer composition of the (meth)acrylic polymer (B) was changed to the monomer composition shown in Table 2, and solutions of (meth)acrylic polymers B-1, B-3 to B-7, B-10, and B-12 each having a solids concentration of 35.0 mass% were obtained.

[0152] [Production Examples B-8, B-9, B-11, B-17 and B-18] In Production Examples B-8, B-9, B-11, B-17, and B-18, the monomer composition of the (meth)acrylic polymer (B) was changed to the monomer composition shown in Table 2, and at least one of the amount of organic solvent used and the amount of polymerization initiator used was adjusted to make the weight average molecular weight of the (meth)acrylic polymer (B) the weight average molecular weight shown in Table 2. Except for this, the same operation as in Production Example B-2 was performed to obtain solutions of (meth)acrylic polymers B-8, B-9, B-11, B-17, and B-18, each having a solids concentration of 35.0 mass%.

[0153] [Manufacturing examples B-13 to B-16] In Production Examples B-13 to B-16, the same operations as in Production Example B-2 were carried out, except that the weight average molecular weight of the (meth)acrylic polymer (B) was adjusted to the weight average molecular weight shown in Table 2 by adjusting at least one of the amount of organic solvent used and the amount of polymerization initiator used, to obtain solutions of (meth)acrylic polymers B-13 to B-16 each having a solids concentration of 35.0 mass%.

[0154] Table 2 shows the monomer compositions (unit: mass %), glass transition temperatures (denoted as "Tg"), and weight average molecular weights (denoted as "Mw") of (meth)acrylic polymers B-1 to B-18. The glass transition temperatures of the (meth)acrylic polymers B-1 to B-18 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic polymer (A) described above. The weight average molecular weights of the (meth)acrylic polymers B-1 to B-18 were measured by the same method as the method for measuring the weight average molecular weight of the specific (meth)acrylic polymer (A) described above.

[0155] Among the (meth)acrylic polymers B-1 to B-18, the (meth)acrylic polymers B-2 to B-6, B-8, B-12, B-14, B-15, and B-17 correspond to the specific (meth)acrylic polymer (B) in the present disclosure.

[0156] [Table 2]

[0157] Details of each monomer listed in Table 2 are as follows: "MMA": Methyl methacrylate "t-BMA": t-butyl methacrylate "n-BMA": n-butyl methacrylate "i-BMA": i-butyl methacrylate "IBXMA": Isobornyl methacrylate "2HEMA": 2-hydroxyethyl methacrylate

[0158] In Table 2, "-" in the column of monomer composition means that the monomer in that column was not used.

[0159] [Preparation of Pressure-Sensitive Adhesive Composition] Example 1 A pressure-sensitive adhesive composition of Example 1 was obtained by thoroughly mixing 400.00 parts by mass (100 parts by mass as solids) of the solution of (meth)acrylic polymer A-1, 25.71 parts by mass (9 parts by mass as solids) of the solution of (meth)acrylic polymer B-2, 0.44 parts by mass (0.20 parts by mass as solids) of Takenate (registered trademark) D-101E (trade name, isocyanate-based crosslinking agent, solids concentration: 45% by mass, manufactured by Mitsui Chemicals, Inc.) as a crosslinking agent, and an appropriate amount of ethyl acetate (organic solvent).

[0160] Examples 2 to 25 In Examples 2 to 25, the same procedure as in Example 1 was carried out except that the formulation of the adhesive composition was changed to the formulation shown in Table 3, to obtain each of the adhesive compositions of Examples 2 to 25.

[0161] Comparative Examples 1 to 13 In Comparative Examples 1 to 13, the same procedure as in Example 1 was carried out except that the formulation of the adhesive composition was changed to the formulation shown in Table 4, to obtain each of the adhesive compositions of Comparative Examples 1 to 13.

[0162] [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 20 μm. Next, the formed coating film was dried by blowing 100°C air at a wind speed of 3 m / s 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 20 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.

[0163] [Measurement and Evaluation] 1. Processability The polarizing plate with the adhesive layer prepared above was cut to prepare test pieces measuring 25 mm (short side) × 70 mm (long side). The prepared test pieces were then continuously cut into 1 mm widths from the short side toward the long side using a super cutter (model number: NC-600, manufactured by Hagino Seiki Co., Ltd.) to obtain 10 cut test pieces. The cut surfaces of the obtained cut test pieces were observed at five points using a digital microscope (model number: VHX7000, magnification: 500x, manufactured by Keyence Corporation), and the percentage of cut test pieces in which the adhesive layer protruded 20 μm or more from the polarizing plate and release film was determined. Evaluation was then performed according to the following evaluation criteria. The evaluation results are shown in Tables 3 and 4. In the following evaluation criteria, "A," "B," and "C" are practically acceptable levels, with "A" being the most preferable.

[0164] -Evaluation criteria- A: The percentage of cut test pieces in which the adhesive layer protrudes 20 μm or more from the polarizing plate and release film is less than 15%. B: The percentage of cut test pieces in which the pressure-sensitive adhesive layer protrudes by 20 μm or more from the polarizing plate and release film is 15% or more and less than 30%. C: The percentage of cut test pieces in which the pressure-sensitive adhesive layer protrudes by 20 μm or more from the polarizing plate and release film is 30% or more and less than 60%. D: The percentage of cut test pieces in which the pressure-sensitive adhesive layer protrudes 20 μm or more from the polarizing plate and release film is 60% or more.

[0165] 2.Transparency 2-1. Preparation of samples for transparency evaluation 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 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 40 μm. Next, the formed coating film was dried by blowing 100°C air at a wind speed of 3 m / s 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 40 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 side of a PET film (product name: COSMOSHINE (registered trademark) A4100, thickness: 100 μm, manufactured by Toyobo Co., Ltd.). Next, the laminate obtained by lamination was left to stand in an environment of an atmospheric temperature of 23°C and 50% RH for 7 days (so-called curing period) to cure the adhesive film. In this manner, a sample for evaluating transparency having a structure of release film / adhesive layer / PET film was prepared.

[0166] 2-2.Evaluation test (1) Rating 1 (Transparency) The transparency evaluation sample prepared above was cut to prepare an evaluation adhesive sheet piece measuring 100 mm (short side) × 150 mm (long side). The release film was peeled off from this evaluation adhesive sheet piece to prepare a test piece. The haze was measured at five randomly selected points on the test piece using a haze meter (model: NDH 5000SP, manufactured by Nippon Denshoku Industries Co., Ltd.). The obtained values ​​were arithmetically averaged to obtain the haze value. Evaluation was then performed according to the following evaluation criteria. The haze values ​​and the evaluation results are shown in Tables 3 and 4. In the following evaluation criteria, "A," "B," and "C" are practically acceptable levels, with "A" being the most preferable.

[0167] -Evaluation criteria- A: The haze value is less than 1.0%. B: The haze value is 1.0% or more and less than 3.0%. C: The haze value is 3.0% or more and less than 6.0%. D: The haze value is 6.0% or more.

[0168] (2) Rating 2 The transparency evaluation sample prepared above was cut to prepare a 100 mm (short side) × 150 mm (long side) adhesive sheet strip for evaluation. The release film was peeled off from this prepared adhesive sheet strip for evaluation to prepare a test piece. The haze at 10 randomly selected locations on the test piece was measured using a haze meter (model: NDH 5000SP, manufactured by Nippon Denshoku Industries Co., Ltd.). The obtained values ​​were divided into two groups: Group X, which contained the top five values ​​counting from the largest value, and Group Y, which contained the top five values ​​counting from the smallest value. The five values ​​in Group X and the five values ​​in Group Y were then arithmetically averaged to obtain the haze value (X) and the haze value (Y). The difference in haze value (Z) was calculated from the haze value (X) and the haze value (Y) according to the following formula. Evaluation was then performed according to the following evaluation criteria. The difference in haze value (Z) and the evaluation results are shown in Tables 3 and 4. In the following evaluation criteria, "A," "B," and "C" are practically acceptable levels, with "A" being the most preferable.

[0169] Haze difference (Z) = [Haze value (X) - Haze value (Y)]

[0170] -Evaluation criteria- A: The difference in haze value (Z) is less than 1.0%. B: The difference (Z) in haze value is 1.0% or more and less than 3.0%. C: The difference (Z) in haze value is 3.0% or more and less than 6.0%. D: The difference in haze value (Z) is 6.0% or more.

[0171] In the transparency evaluation test, when the results of the above evaluations 1 and 2 were both "A," "B," or "C," the pressure-sensitive adhesive layer was determined to have excellent transparency.

[0172] 3. Reworkability 3-1. Preparation of samples for reworkability evaluation The polarizing plate with the adhesive layer prepared above was cut to prepare a test piece X1 measuring 25 mm (short side) × 75 mm (long side). Next, the release film was peeled off from the cut test piece X1 [structure: release film / adhesive layer / polarizing plate (TAC layer / PVA layer / TAC layer)] to obtain a test piece X2 [structure: adhesive layer / polarizing plate (TAC layer / PVA layer / TAC layer)]. Next, the exposed adhesive layer surface of test piece X2 was placed on one side of a soda glass plate (manufactured by Matsunami Glass Industry Co., Ltd.) as an adherend, and then pressure-bonded using a laminator. In this manner, a sample for evaluating reworkability was prepared, having a structure of adherend (soda glass plate) / adhesive layer / polarizing plate (TAC layer / PVA layer / TAC layer).

[0173] 3-2.Evaluation test The reworkability evaluation sample prepared above was treated at a temperature of 50°C and a pressure of 5 kg / cm 2 The specimens were autoclaved for 20 minutes under the following conditions: The autoclaved reworkability evaluation samples were then left to stand for 5 hours in an 80°C ambient temperature environment, followed by 30 minutes in an 23°C ambient temperature and 50% RH environment to obtain test specimens. The adhesive strength (unit: N / 25 mm) of the test specimens was measured when test specimen X2 was peeled from the adherend (soda glass plate) at a 90° angle along the long side (75 mm) using a single-column materials testing machine (model number: STA-1225, manufactured by A&D Co., Ltd.) at an ambient temperature of 23°C and 50% RH at a peel speed of 0.3 m / min. Evaluation was then performed according to the following criteria: The measured adhesive strength and evaluation results are shown in Tables 3 and 4. In the following evaluation criteria, "A," "B," and "C" are practically acceptable levels, with "A" being the most preferable.

[0174] -Evaluation criteria- A: The adhesive strength is less than 14N / 25mm. B: The adhesive strength is 14N / 25mm or more and less than 16N / 25mm. C: The adhesive strength is 16N / 25mm or more and less than 18N / 25mm. D: The adhesive strength is 18N / 25mm or more, or adhesive residue is observed on the adherend.

[0175] 4. Coatability The solid content of the pressure-sensitive adhesive composition prepared above was adjusted to 25% by mass with ethyl acetate to prepare a sample for evaluating coatability. The viscosity of this sample for evaluating coatability was measured using a BH-type rotational viscometer (model number: BHII, manufactured by Toki Sangyo Co., Ltd.) at a liquid temperature of 25°C and a rotor rotation speed of 10 rpm (revolutions per minute). The viscosity measurements are shown in Tables 3 and 4. The higher the measured viscosity, the poorer the adhesive composition's coatability.

[0176] [Table 3]

[0177] [Table 4]

[0178] Details of the components listed in Tables 3 and 4 are as follows: <Crosslinking agent> "D-101E" (trade name: Takenate (registered trademark) D-101E, isocyanate-based crosslinking agent, tolylene diisocyanate (TDI) trimethylolpropane (TMP) adduct, solid content: 45% by mass, manufactured by Mitsui Chemicals, Inc.) "D-110N" (trade name: Takenate (registered trademark) D-110N, isocyanate-based crosslinking agent, adduct of xylylene diisocyanate (XDI) and trimethylolpropane (TMP), solid content: 75% by mass, manufactured by Mitsui Chemicals, Inc.) "2021P" (product name: CELLOXIDE (registered trademark) 2021P, epoxy crosslinking agent, 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, solid content: 100% by mass, manufactured by Daicel Corporation) <Other ingredients> "X-41-1810" (product name, silane coupling agent, thiol group-containing silane compound, solid content: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.) "KF-859" (product name, release modifier, silicone oil, amino group-containing silane compound, solid content: 100% by mass, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0179] In Tables 3 and 4, the values ​​shown in the "blending amount" column are all solid content converted values. In Tables 3 and 4, "-" in the column for the composition of the adhesive composition means that the component in that column was not blended. In Table 4, "Adhesive residue" in the "Adhesive strength" column of reworkability means that adhesive residue was confirmed on the adherend after measuring the adhesive strength. Also, "Not rated" in the "Reworkability" column means that the adhesive layer was destroyed when peeling it from the adherend, making it impossible to evaluate.

[0180] As shown in Table 3, it was confirmed that the pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of the examples were excellent in processability, transparency, and reworkability. Furthermore, it is presumed that the pressure-sensitive adhesive compositions of the present disclosure do not have excessively high viscosity and are therefore excellent in coatability. On the other hand, as shown in Table 4, it was confirmed that the adhesive layer formed using the adhesive composition of the comparative example was inferior to the adhesive layer formed using the adhesive composition of the example in at least one of the evaluation items of processability, transparency, and reworkability.

Claims

1. a (meth)acrylic polymer (A) having a reactive functional group and a weight average molecular weight of 650,000 or more but less than 1,500,000; a (meth)acrylic polymer (B) containing structural units derived from t-butyl methacrylate in a proportion of 15% by mass or more and 87% by mass or less of all structural units, having a glass transition temperature of 105°C or more and 150°C or less, and having a weight average molecular weight of 100,000 or more and less than 500,000; a cross-linking agent; Including, The pressure-sensitive adhesive composition, wherein the content of the (meth)acrylic polymer (B) is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A).

2. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic polymer (A) has a glass transition temperature of −60° C. or higher and −30° C. or lower.

3. The pressure-sensitive adhesive composition according to claim 1 , wherein the reactive functional group includes at least one of a carboxy group and a hydroxyl group.

4. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 3.

5. An optical film; a pressure-sensitive adhesive layer provided on at least one surface of the optical film and formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 3; An adhesive sheet comprising:

6. The pressure-sensitive adhesive sheet according to claim 5 , wherein the optical film is a polarizing plate.

7. A glass substrate; A pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 3; An optical film; An optical element comprising the above in this order.

8. A display device comprising the optical member according to claim 7 .

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