Pressure-sensitive adhesive composition, pressure-sensitive adhesive layer, and pressure-sensitive adhesive film

Abstract

To provide an adhesive composition which exhibits excellent optical transparency, high adhesive strength, and foaming resistance even under a high temperature / high humidity environment and a high temperature water immersion environment.SOLUTION: Provided is an adhesive composition, comprising an acrylic polymer (A), a crosslinking agent (B), and an acrylic polymer (C). The acrylic polymer (A) contains a unit derived from an alkyl (meth)acrylate monomer (a1) having a C1-4 alkyl group, a unit derived from a monomer (a2) having a nitrogen atom, and a unit derived from at least one selected from the group consisting of a monomer (a3) having an acidic group and a monomer (a4) having a hydroxyl group. The acrylic polymer (C) contains a unit derived from a (meth)acrylic monomer (c1) having an alicyclic structure and a unit derived from an alkyl (meth)acrylate monomer (c2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive film. [Background technology]

[0002] Acrylic adhesives have been used in a variety of fields for a long time, but in recent years they have been in particularly high demand in IT-related products such as smartphones, which require higher performance and functionality due to their product characteristics.

[0003] As an example of an acrylic adhesive used in IT-related products, there is a demand for a heat-sensitive adhesive that is weakly adhesive at room temperature but develops strong adhesiveness upon heating, and that maintains adhesiveness even after heating is removed. Specific examples include an adhesive containing an acrylic low-molecular-weight polymer with a weight-average molecular weight of 2,000 to 9,000 (see, for example, Patent Document 1). Another proposed adhesive contains a polymer with a glass transition temperature of less than 0°C and a polymer with a weight-average molecular weight of 10,000 or more but less than 100,000, which contains, as monomer units, a monomer having a polyorganosiloxane skeleton and a monomer with a glass transition temperature of 40°C or higher (see, for example, Patent Document 2).

[0004] High optical transparency is essential for protective films and components attached to the display surfaces of IT-related products with display functions, such as televisions, PCs, mobile devices, office automation equipment, car navigation systems, game consoles, and electronic organizers, to ensure visibility. Furthermore, they must quickly develop strong adhesive strength after application to the housing or display device, and maintain their adhesive strength even after endurance testing. While metal or glass was traditionally used for the surface panels of housings and display devices, plastic materials such as acrylic and polycarbonate have recently been used to reduce weight and provide design features such as 3D molding. Conventional adhesives have faced challenges when subjected to harsh conditions, such as high temperature and humidity, or immersion in hot water, due to the formation of bubbles between the substrate or adherend and the adhesive surface, resulting in loss of optical transparency, reduced visibility, and difficulty in maintaining high adhesive strength due to foaming.

[0005] It is also used in automobile exteriors and outdoor advertising materials as a replacement for paint or as a printed film applied over paint, which is then replaced after a certain period of time. In these applications, as with the above, it is required that the film has excellent optical transparency to impart high design appeal, and that its adhesive strength does not decrease even after being subjected to durable environments, regardless of the type of substrate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6618522 [Patent Document 2] Japanese Patent Application Publication No. 2019-123884 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive film that exhibit excellent optical transparency, high adhesive strength, and foaming resistance even in a high-temperature, high-humidity environment or a high-temperature, hot water immersion environment. [Means for solving the problem]

[0008] The pressure-sensitive adhesive composition of the present invention comprises an acrylic polymer (A), a crosslinking agent (B), and an acrylic polymer (C), wherein the acrylic polymer (A) comprises units derived from an alkyl (meth)acrylate monomer (a1) having an alkyl group having 1 to 4 carbon atoms; units derived from a monomer (a2) having a nitrogen atom; and units derived from at least one monomer selected from the group consisting of a monomer (a3) having an acid group and a monomer (a4) having a hydroxyl group, wherein the glass transition temperature of the acrylic polymer (A) is −20° C. or lower, and the weight average molecular weight of the acrylic polymer (A) is The acrylic polymer (C) has a glass transition temperature of 50°C or higher and a weight average molecular weight of less than 100,000. The content of units derived from the alkyl (meth)acrylate monomer (a1) having an alkyl group of 1 to 4 carbon atoms in the acrylic polymer (A) is 50 mass% or higher and less than 97 mass%. The acrylic polymer (C) contains units derived from the alicyclic structure-containing (meth)acrylate monomer (c1) and units derived from the alkyl (meth)acrylate monomer (c2). The acrylic polymer (C) has a glass transition temperature of 50°C or higher and a weight average molecular weight of less than 100,000. [Effects of the Invention]

[0009] The pressure-sensitive adhesive composition of the present invention exhibits excellent optical transparency, high adhesive strength and foaming resistance even in high-temperature, high-humidity environments and high-temperature, hot-water immersion environments, and can therefore be suitably used for protective films for IT-related products with display functions such as televisions, personal computers, mobile terminals, office automation equipment, car navigation systems, game consoles and electronic notebooks; paint protection films used on automobile exteriors; and protective films for outdoor advertising materials and indoor / outdoor building materials. DETAILED DESCRIPTION OF THE INVENTION

[0010] The pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A), a crosslinking agent (B), and an acrylic polymer (C).

[0011] The acrylic polymer (A) contains units derived from an alkyl (meth)acrylate monomer (a1) having an alkyl group with 1 to 4 carbon atoms; units derived from a monomer (a2) having a nitrogen atom; and units derived from at least one monomer selected from the group consisting of a monomer (a3) having an acid group and a monomer (a4) having a hydroxyl group.

[0012] Examples of the alkyl(meth)acrylate monomer (a1) having an alkyl group having 1 to 4 carbon atoms include methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, t-butyl(meth)acrylate, etc. These alkyl(meth)acrylate monomers (a1) can be used alone or in combination of two or more, but it is preferable to contain n-butyl acrylate because it is easy to balance the development of cohesive strength and flexibility, and the content of n-butyl acrylate in the alkyl(meth)acrylate monomer (a1) is more preferably 25% by mass or more, and even more preferably 30% by mass or more.

[0013] The nitrogen atom-containing monomer (a2) is a monomer having a nitrogen atom and a polymerizable double bond in the molecule, and is preferably a monomer having an amide bond and a polymerizable double bond in the molecule, and examples thereof include lactam compounds having a vinyl group; (meth)acrylamide monomers; and (meth)acrylate compounds having a nitrogen atom-containing functional group (e.g., amino group, mono-substituted amino group, di-substituted amino group, nitrile group, etc.). These nitrogen atom-containing monomers (a2) can be used alone or in combination of two or more.

[0014] Examples of the lactam compound having a vinyl group include N-vinylpyrrolidone and N-vinylcaprolactam.

[0015] Examples of the (meth)acrylamide monomer include compounds in which a hydrogen atom or a hydrocarbon group (preferably an aliphatic hydrocarbon group, provided that -CH- contained in the hydrocarbon may be replaced with -CO-, and a hydrogen atom contained in the hydrocarbon group may be replaced with a hydroxyl group) is bonded to the nitrogen atom of (meth)acrylamide. When two or more groups (the hydrocarbon groups) are substituted to the nitrogen atom of (meth)acrylamide, the groups may be bonded to each other to form a ring containing the nitrogen atom.

[0016] The hydrocarbon group (preferably an aliphatic hydrocarbon group) substituting the nitrogen atom contained in the amide bond preferably has 1 or more carbon atoms, preferably 10 or less, and more preferably 6 or less carbon atoms.

[0017] The (meth)acrylamide monomer may be one or more of the following: (meth)acrylamide, an N-1 substituted (meth)acrylamide compound, or an N,N-2 substituted (meth)acrylamide compound.

[0018] The (meth)acrylamide compound may be used alone or in combination of two or more thereof. Examples of the (meth)acrylamide compound include (meth)acrylamide; N-1-substituted (meth)acrylamide compounds such as N-isopropyl(meth)acrylamide, N-(1,1-dimethyl-3-oxobutyl)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-(2-hydroxymethyl)acrylamide, and N-(2-hydroxyethyl)acrylamide; N- Examples of N-2 substituted (meth)acrylamide compounds include (meth)acryloylmorpholine, N-(meth)acryloylpiperidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloyl-4-piperidone, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-methylenebis(meth)acrylamide, and N,N-dimethylaminopropyl(meth)acrylamide.

[0019] Among these, the (meth)acrylamide monomer preferably contains a monomer represented by formula (1).

[0020] [ka] [In formula (1), R 1 represents a hydrogen atom or a methyl group. 2 and R 3 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, -CH2- contained in the hydrocarbon group may be replaced by -CO- or -O-, and a hydrogen atom contained in the hydrocarbon group may be replaced by a hydroxyl group; R 2 and R 3 may be bonded to each other to form a ring containing the nitrogen atom.

[0021] R 2 and R 3The hydrocarbon group represented by R may be one or more types, and examples thereof include linear or branched saturated aliphatic hydrocarbon groups; linear or branched unsaturated aliphatic hydrocarbon groups, etc. Among these, linear or branched saturated aliphatic hydrocarbon groups are preferred, and branched saturated aliphatic hydrocarbon groups are more preferred. 2 and R 3 At least one of these is preferably a hydrogen atom.

[0022] The (meth)acrylamide monomer is R 2 and R 3 It is also preferable to include a (meth)acrylamide monomer in which both of the R 2 and R 3 and (b) are the hydrocarbon groups, the content of units derived from the monomer in the acrylic polymer (A) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less.

[0023] In the nitrogen atom-containing monomer (a2), the content of units derived from the acrylamide monomer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, with the upper limit being 100% by mass.

[0024] Examples of the (meth)acrylate compound having a functional group containing a nitrogen atom (for example, an amino group, a mono-substituted amino group, a di-substituted amino group, a nitrile group, etc.) include (meth)acrylonitrile, t-butylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate.

[0025] The monomer (a3) having an acid group includes a monomer having an acid group and a polymerizable double bond, preferably a monomer having a carboxyl group or a monomer having a sulfo group, and more preferably a monomer having a carboxyl group.

[0026] The monomer having a carboxyl group can be used alone or in combination of two or more kinds, and examples thereof include (meth)acrylic acid; carboxyalkyl (meth)acrylates such as carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and β-carboxyethyl (meth)acrylate; and unsaturated carboxylic acids such as itaconic acid, itaconic anhydride, maleic acid, maleic anhydride, fumaric acid, and crotonic acid.

[0027] The content of the carboxyl group-containing monomer in the acid group-containing monomer (a3) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, with the upper limit being 100% by mass.

[0028] The hydroxyl group-containing monomer (a4) may be a monomer having a hydroxyl group and a polymerizable double bond. The hydroxyl group-containing (meth)acrylic monomer may be a hydroxyalkyl (meth)acrylate or a polyalkylene glycol (meth)acrylate, and is preferably a hydroxyalkyl (meth)acrylate.

[0029] Specific examples of the hydroxyl group-containing monomer (a4) include hydroxyalkyl (meth)acrylates in which the alkyl group (alkylene group) has 2 to 10 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; and polyalkylene glycol (meth)acrylates, such as polyethylene glycol (meth)acrylate.

[0030] The acrylic polymer (A) may contain units derived from other monomers (a5) besides the above-mentioned monomers (a1) to (a4). Examples of the other monomers (a5) include alkyl (meth)acrylates having an alkyl group having 5 or more carbon atoms, such as pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate; glycols; Cyclic ether-containing (meth)acrylate monomers such as cyclohexyl (meth)acrylate and tetrahydrofurfuryl (meth)acrylate; alicyclic structure-containing (meth)acrylate monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylate monomers such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; alkylene oxide structure-containing (meth)acrylate monomers such as 2-methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate; Examples of suitable monomers include vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl versatate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, amyl vinyl ether, and hexyl vinyl ether; aromatic vinyl monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylvinylbenzene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and parahydroxystyrene; and isoprene, chloroprene, butadiene, ethylene, tetrafluoroethylene, and vinylidene fluoride. Among these, (meth)acrylate monomers, vinyl ester monomers, and vinyl ether monomers are preferred because they allow for easy adjustment of the balance of various properties, such as adhesiveness. These other monomers (a5) can be used alone or in combination of two or more.

[0031] In the acrylic polymer (A), the content of units derived from the alkyl (meth)acrylate monomer (a1) is 45% by mass or more and less than 97% by mass, preferably 55% by mass or more, more preferably 70% by mass or more, and preferably 95% by mass or less.

[0032] In the acrylic polymer (A), the content of units derived from the nitrogen atom-containing monomer (a2) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.

[0033] In the acrylic polymer (A), the content of units derived from the monomer (a3) having an acid group is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0034] The content of units derived from the monomer (a4) having a hydroxyl group in the acrylic monomer (A) is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, even more preferably 0.05% by mass or more, and is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less.

[0035] The total content of units derived from the monomer (a3) having an acid group and the monomer (a4) having a hydroxyl group in the acrylic polymer (A) is 0.5% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, and is preferably 30% by mass or less, more preferably 22% by mass or less, and even more preferably 17% by mass or less.

[0036] In the acrylic polymer (A), the total content of units derived from the alkyl(meth)acrylate monomer (a1), the nitrogen atom-containing monomer (a2), the acid group-containing monomer (a3), and the hydroxyl group-containing monomer (a4) is preferably 50 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more, with the upper limit being 100 mass %.

[0037] In the acrylic polymer (A), the content of units derived from the other monomer (a5) is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0038] The acid value of the acrylic polymer (A) is preferably 5 mgKOH / g or more, and more preferably 20 mgKOH / g or more, and is preferably 200 mgKOH / g or less, and more preferably 100 mgKOH / g or less, because this further improves the cohesive strength effective in suppressing foaming and the adhesion to the adherend.

[0039] The acid value of the polymer in the present invention is a calculated value calculated from the raw material composition.

[0040] The weight average molecular weight of the acrylic polymer (A) is 100,000 or more, preferably 200,000 or more, more preferably 300,000 or more, and is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less.

[0041] In this specification, the number average molecular weight and weight average molecular weight of a polymer represent converted values measured by gel permeation chromatography (GPC) using polystyrene as a standard sample.

[0042] The glass transition temperature of the acrylic polymer (A) is -20°C or lower, preferably -60°C or higher, more preferably -50°C or higher, and even more preferably -50°C or higher and -25°C or lower.

[0043] The glass transition temperature Tga (K) of the acrylic polymer (A) can be calculated based on the following FOX equation. 1 / Tga=Σ(Wi / Tgi)

[0044] In the FOX formula, Wi represents the content of units derived from each monomer in the acrylic polymer (A), and Tgi (K) represents the glass transition temperature (unit: absolute temperature) of a homopolymer formed from only each monomer. Details of the FOX formula are described in Bulletin of the American Physical Society, Series 2, Vol. 1, No. 3, p. 123 (1956). The glass transition temperature (Tgi) of a homopolymer of each monomer can be, for example, the value described in Paints and Coatings (Paint Publishing Co., Ltd., Vol. 10 (No. 358), 1982).

[0045] The acrylic polymer (A) can be produced by copolymerizing the alkyl(meth)acrylate monomer (a1), the nitrogen atom-containing monomer (a2), the acid group-containing monomer (a3), the hydroxyl group-containing monomer (a4), and other monomers (a5) used as needed in the presence of a polymerization initiator.

[0046] As the polymerization initiator, for example, one or more thermal polymerization initiators can be used, and examples thereof include peroxide initiators such as benzoyl peroxide and lauroyl peroxide; and azo initiators such as azobismethylbutyronitrile and azobisisobutylnitrile.

[0047] The pressure-sensitive adhesive composition of the present invention contains a crosslinking agent (B). One or more crosslinking agents can be used, and examples thereof include isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, polyvalent metal salt crosslinking agents, metal chelate crosslinking agents, ketohydrazide crosslinking agents, oxazoline crosslinking agents, carbodiimide crosslinking agents, silane crosslinking agents, and glycidyl(alkoxy)epoxysilane crosslinking agents.

[0048] Among these, isocyanate crosslinking agents, epoxy crosslinking agents, metal chelate crosslinking agents, oxazoline crosslinking agents, and carbodiimide crosslinking agents are preferred, isocyanate crosslinking agents, epoxy crosslinking agents, and carbodiimide crosslinking agents are more preferred, and epoxy crosslinking agents are particularly preferred.

[0049] The content of the epoxy crosslinking agent in the crosslinking agent (B) is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, and is preferably 100% by mass or less.

[0050] The acrylic polymer (C) contains units derived from an alicyclic structure-containing (meth)acrylate monomer (c1) and units derived from an alkyl (meth)acrylate monomer (c2).

[0051] The alicyclic structure-containing (meth)acrylate monomer (c1) (hereinafter sometimes simply referred to as "(meth)acrylate (c1)") represents a (meth)acrylate monomer containing an alicyclic structure in the molecule. The alicyclic hydrocarbon group may be a monocyclic ring or a bridged ring, and the number of alicyclic hydrocarbon groups contained in the (meth)acrylate (c1) may be one or two or more.

[0052] Examples of the alicyclic hydrocarbon group contained in the (meth)acrylate (c1) include monocyclic alicyclic hydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group; and bridged ring alicyclic hydrocarbon groups such as a norbornyl group, an isobornyl group, and a dicyclopentanyl group.

[0053] The alicyclic hydrocarbon group contained in the (meth)acrylate (c1) has 3 or more, preferably 5 or more, and preferably 20 or less, more preferably 15 or less, and further preferably 10 or less, carbon atoms.

[0054] The alicyclic structure-containing (meth)acrylate monomer (c1) contained in the (meth)acrylate (c1) may specifically be one or more of different monomers, and examples thereof include monocyclic alicyclic structure-containing (meth)acrylate monomers such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate; and bridged ring alicyclic structure-containing (meth)acrylate monomers such as norbornyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0055] The content of units derived from the (meth)acrylate (c1) in the acrylic polymer (C) is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and is preferably 95% by mass or less, more preferably 92% by mass or less, even more preferably 90% by mass or less.

[0056] The alkyl (meth)acrylate monomer (c2) (hereinafter, may be simply referred to as "(meth)acrylate (c2)") represents a (meth)acrylate monomer having an alkyl group.

[0057] Examples of the alkyl group contained in the (meth)acrylate (c2) include linear alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, a lauryl group, and a stearyl group; and branched alkyl groups such as an isopropyl group, an isobutyl group, a t-butyl group, an isopentyl group, a neopentyl group, an isohexyl group, an isoheptyl group, an isooctyl group, a 2-ethylhexyl group, an isononyl group, an isodecyl group, and an isostearyl group.

[0058] The alkyl group contained in the (meth)acrylate (c2) preferably has 1 or more carbon atoms, and preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less carbon atoms.

[0059] The (meth)acrylate (c2) may be used alone or in combination of two or more thereof, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate.

[0060] The content of units derived from the (meth)acrylate (c2) in the acrylic polymer (C) is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less.

[0061] The content ratio ((c1) / (c2)) of the units derived from the (meth)acrylate (c1) to the units derived from the (meth)acrylate (c2) is, on a mass basis, preferably 0.1 or more, more preferably 0.5 or more, even more preferably 0.7 or more, and is preferably 20 or less, more preferably 15 or less, even more preferably 12 or less.

[0062] The acrylic polymer (C) may contain units derived from other monomers (c3) in addition to the alicyclic structure-containing (meth)acrylate monomer (c1) and the alkyl (meth)acrylate monomer (c2).

[0063] Examples of the other monomer (c3) include a monomer having an acid group, a monomer having a hydroxyl group, a monomer having a nitrogen atom, a monomer having a cyclic ether, a monomer having an aromatic ring, and a monomer having an alkylene oxide structure.

[0064] The content of the other monomer (c3) in the acrylic polymer (C) is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less, with the lower limit being 0% by mass.

[0065] The glass transition temperature of the acrylic polymer (C) is 50°C or higher, preferably 55°C or higher, more preferably 60°C or higher, and is preferably 120°C or lower, more preferably 110°C or lower.

[0066] The glass transition temperature Tga (K) of the acrylic polymer (C) can be calculated based on the FOX equation, similarly to the above-described acrylic polymer (A).

[0067] The weight average molecular weight of the acrylic polymer (C) is less than 100,000, preferably 80,000 or less, more preferably 60,000 or less, and preferably 1,000 or more, more preferably 1,500 or more, and even more preferably 2,500 or more.

[0068] The acrylic polymer (C) can be produced by copolymerizing the alicyclic structure-containing (meth)acrylate monomer (c1), the alkyl (meth)acrylate monomer (c2), and other monomers (c3) used as needed in the presence of a polymerization initiator.

[0069] As the polymerization initiator, for example, one or more thermal polymerization initiators can be used, and examples thereof include peroxide initiators such as benzoyl peroxide and lauroyl peroxide; and azo initiators such as azobismethylbutyronitrile and azobisisobutylnitrile.

[0070] In the pressure-sensitive adhesive composition of the present invention, the content of the acrylic polymer (A) in the nonvolatile matter is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 99% by mass or less.

[0071] In this specification, the non-volatile content of the PSA composition refers to the portion excluding the solvent component that may be contained as needed in the PSA composition.

[0072] In the pressure-sensitive adhesive composition of the present invention, the content of the crosslinking agent (B) relative to 100 parts by mass of the acrylic polymer (A) is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 2 parts by mass or less.

[0073] In the pressure-sensitive adhesive composition of the present invention, the content of the acrylic polymer (C) in the nonvolatile matter is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.

[0074] In the pressure-sensitive adhesive composition of the present invention, the content of the acrylic polymer (C) relative to 100 parts by mass of the acrylic polymer (A) is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and is preferably 60 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 25 parts by mass or less.

[0075] The pressure-sensitive adhesive composition of the present invention preferably contains a solvent (D). As the solvent (D), one or more solvents can be used, and examples thereof include aromatic hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and aliphatic hydrocarbon solvents such as hexane. Among these, it is preferable to contain an ester solvent.

[0076] The content of the ester solvent in the solvent (D) is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and is preferably 100% by mass or less.

[0077] The content of the solvent (D) in the pressure-sensitive adhesive composition is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and is preferably 90% by mass or less, more preferably 70% by mass or less, even more preferably 65% by mass or less.

[0078] In the pressure-sensitive adhesive composition of the present invention, in order to maintain low yellowing, it is preferable that the content of the tackifier resin is reduced, and is preferably less than 10 parts by mass, more preferably 8 parts by mass or less, even more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and preferably 0 part by mass, relative to 100 parts by mass of the acrylic polymer.

[0079] The pressure-sensitive adhesive composition of the present invention may contain, as additives, bases (such as aqueous ammonia) or acids for adjusting the pH; foaming agents; plasticizers; softeners; antioxidants; fillers such as glass or plastic fibers, balloons, beads, and metal powder; colorants such as pigments and dyes; pH adjusters; film-forming aids; leveling agents; thickeners; water repellents; antifoaming agents; acid catalysts; acid generators, etc.

[0080] The pressure-sensitive adhesive composition can be applied to a support and dried to form a pressure-sensitive adhesive layer. The support may be a base material such as a release sheet or a pressure-sensitive adhesive sheet.

[0081] The coating method may be performed using a knife coater, reverse coater, die coater, lip die coater, slot die coater, gravure coater, curtain coater, or the like.

[0082] The thickness of the adhesive layer is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and is preferably 150 μm or less, more preferably 100 μm or less, even more preferably 75 μm or less.

[0083] The pressure-sensitive adhesive sheet or pressure-sensitive adhesive tape of the present invention comprises the pressure-sensitive adhesive layer and the substrate. The substrate may be in the form of a film, sheet, tape, plate, or three-dimensional shape, and examples of the material for the substrate include plastics such as polyester resin, polypropylene resin, polyethylene resin, polyimide resin, vinyl chloride resin, and urethane resin; rubber; nonwoven fabric; metal foil; and paper, among which plastic is preferred, and polyester resin and thermoplastic urethane resin are more preferred. The substrate may have a smooth surface, or may have an uneven surface such as a fibrous substrate or a foam substrate.

[0084] The thickness of the substrate is preferably 0.1 μm or more and preferably 1,000 μm or less. [Example]

[0085] The present invention will be described in more detail below with reference to specific examples. The weight average molecular weight (Mw) of the resin of the present invention was measured under the following GPC measurement conditions.

[0086] [GPC measurement conditions] Measurement equipment: High-speed GPC equipment (Tosoh Corporation "HLC-8220GPC") Column: The following columns manufactured by Tosoh Corporation were connected in series and used. "TSKgel G5000" (7.8mm I.D. x 30cm) x 1 "TSKgel G4000" (7.8mm I.D. x 30cm) x 1 "TSKgel G3000" (7.8mm I.D. x 30cm) x 1 "TSKgel G2000" (7.8mmI.D. x 30cm) x 1 Detector: RI (differential refractometer) Column temperature: 40℃ Eluent: tetrahydrofuran (THF) Flow rate: 1.0mL / min Injection volume: 100 μL (sample concentration 4 mg / mL in tetrahydrofuran solution) Standard sample: A calibration curve was prepared using the following monodisperse polystyrene.

[0087] (monodisperse polystyrene) Tosoh Corporation's "TSKgel Standard Polystyrene A-500" Tosoh Corporation's "TSKgel Standard Polystyrene A-1000" Tosoh Corporation's "TSKgel Standard Polystyrene A-2500" Tosoh Corporation's "TSKgel Standard Polystyrene A-5000" "TSKgel Standard Polystyrene F-1" manufactured by Tosoh Corporation Tosoh Corporation's "TSKgel Standard Polystyrene F-2" Tosoh Corporation's "TSKgel Standard Polystyrene F-4" Tosoh Corporation's "TSKgel Standard Polystyrene F-10" Tosoh Corporation's "TSKgel Standard Polystyrene F-20" Tosoh Corporation's "TSKgel Standard Polystyrene F-40" Tosoh Corporation's "TSKgel Standard Polystyrene F-80" Tosoh Corporation's "TSKgel Standard Polystyrene F-128" Tosoh Corporation's "TSKgel Standard Polystyrene F-288" Tosoh Corporation's "TSKgel Standard Polystyrene F-550"

[0088] (Synthesis Example 1: Synthesis of acrylic polymer (A-1)) A reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer was charged with 590 parts by mass of butyl acrylate (hereinafter abbreviated as "BA"), 345 parts by mass of methyl acrylate (hereinafter abbreviated as "MA"), 50 parts by mass of diethylacrylamide (hereinafter abbreviated as "DEAA"), 10 parts by mass of acrylic acid (hereinafter abbreviated as "AA"), 5 parts by mass of 4-hydroxybutyl acrylate (hereinafter abbreviated as "4HBA"), and 1,000 parts by mass of ethyl acetate. The mixture was heated to 72°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by mass of a 2,2'-azobis(2-methylbutyronitrile) solution (solids content: 0.5% by mass) previously dissolved in ethyl acetate was added. The mixture was then held at 72°C for 8 hours with stirring, after which the contents were cooled and filtered through a 200-mesh wire net to obtain a 50% by mass solution of acrylic polymer (A-1).

[0089] (Synthesis Example 2: Synthesis of acrylic polymer (A-2)) A reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer was charged with 250 parts by mass of 2-ethylhexyl acrylate (hereinafter abbreviated as "2EHA"), 509 parts by mass of BA, 25 parts by mass of dimethylacrylamide (hereinafter abbreviated as "DMAA"), 215 parts by mass of AA, 1 part by mass of 2-hydroxyethyl acrylate (hereinafter abbreviated as "HEA"), and 950 parts by mass of ethyl acetate. The mixture was heated to 65°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by mass of a 2,2'-azobis(2-methylbutyronitrile) solution (solids content: 0.5% by mass) previously dissolved in ethyl acetate was added. The mixture was then held at 65°C for 10 hours with stirring, after which the contents were cooled, 50 parts by mass of ethyl acetate was added, and the mixture was filtered through a 200-mesh wire net to obtain a 50% by mass solution of acrylic polymer (A-2).

[0090] (Synthesis Example 3: Synthesis of acrylic polymer (A-3)) A 50% by mass solution of acrylic polymer (A-3) was obtained in the same manner as in Synthesis Example 2, except that the monomer composition was changed as shown in Table 1.

[0091] (Synthesis Examples 4 to 6: Synthesis of acrylic polymers (A-4) to (A-6)) Except for changing the monomer composition as shown in Table 1, the same procedure as in Synthesis Example 1 was carried out to obtain 50% by mass solutions of acrylic polymers (A-4) to (A-6).

[0092] (Synthesis Example 7: Synthesis of acrylic polymer (A-7)) A reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer was charged with 350 parts by weight of 2EHA, 482 parts by weight of BA, 385 parts by weight of MA, 100 parts by weight of DEAA, 3 parts by weight of 4HBA, and 900 parts by weight of ethyl acetate. The mixture was heated to 65°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by weight of a 2,2'-azobis(2-methylbutyronitrile) solution (solids content: 0.5% by weight) previously dissolved in ethyl acetate was added. The mixture was then held at 65°C for 10 hours with stirring, after which the contents were cooled, 100 parts by weight of ethyl acetate was added, and the mixture was filtered through a 200-mesh wire net to obtain a 50% by weight solution of acrylic polymer (A-7).

[0093] (Synthesis Examples 8 and 9: Synthesis of Acrylic Polymers (A-8) and (A-9)) The same procedure as in Synthesis Example 1 was carried out except that the monomer composition was changed as shown in Table 2, to obtain 50% by mass solutions of acrylic polymers (A-8) to (A-9).

[0094] (Synthesis Example 10: Synthesis of acrylic polymer (A-10)) A 50% by mass solution of acrylic polymer (A-10) was obtained in the same manner as in Synthesis Example 3, except that the monomer composition was changed as shown in Table 2.

[0095] (Synthesis Example 11: Synthesis of acrylic polymer (C-1)) A reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser, and nitrogen gas inlet was charged with 75 parts by mass of methyl ethyl ketone (hereinafter abbreviated as "MEK") and heated to 80°C. Next, at the same temperature, a mixture containing 78 parts by mass of cyclohexyl methacrylate (hereinafter abbreviated as "CHMA"), 20 parts by mass of methyl methacrylate (hereinafter abbreviated as "MMA"), 2 parts by mass of methacrylic acid (hereinafter abbreviated as "MAA"), 6.8 parts by mass of MEK, and 5.5 parts by mass of tert-butylperoxy-2-ethylhexanoate (hereinafter abbreviated as "TBPEH") was added dropwise to the reaction vessel over 4 hours. After completion of the addition, the mixture was allowed to react at the same temperature for a further 12 hours to obtain a 55% by mass solution of acrylic polymer (C-1).

[0096] (Synthesis Examples 12 to 14: Synthesis of acrylic polymers (C-2) to (C-4)) Except for changing the monomer composition as shown in Table 3, the same procedure as in Synthesis Example 11 was carried out to obtain 55% by mass solutions of acrylic polymers (C-2) to (C-4).

[0097] (Synthesis Example 15: Synthesis of acrylic polymer (C-5)) A reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser, and nitrogen gas inlet was charged with 75 parts by mass of methyl ethyl ketone (hereinafter abbreviated as "MEK") and heated to 80°C. Next, at the same temperature, a mixture containing 10 parts by mass of CHMA, 76 parts by mass of MMA, 4 parts by mass of 2-ethylhexyl methacrylate (hereinafter abbreviated as "2EHMA"), 9 parts by mass of MAA, 1 part by mass of 2EHA, 6.8 parts by mass of MEK, and 3 parts by mass of TBPEH was added dropwise to the reaction vessel over 4 hours. After completion of the addition, the mixture was allowed to react at the same temperature for a further 12 hours to obtain a 55% by mass solution of acrylic polymer (C-1).

[0098] (Synthesis Examples 16 to 20: Synthesis of acrylic polymers (C-6) to (C-10)) The same procedure as in Synthesis Example 11 was carried out except that the monomer composition was changed as shown in Table 3, to obtain 55% by mass solutions of acrylic polymers (C-6) to (C-10).

[0099] [Table 1]

[0100] [Table 2]

[0101] [Table 3]

[0102] [Table 4]

[0103] In Tables 1 to 4, the abbreviations represent the following compounds. 2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate EA: Ethyl acrylate MA: Methyl acrylate CHA: Cyclohexyl acrylate DEAA: N,N-diethylacrylamide DMAA: N,N-dimethylacrylamide NIPAM: N,N-diisopropylacrylamide DAAM: Diacetone acrylamide AA: acrylic acid 4HBA: 4-hydroxybutyl acrylate HEA: 2-hydroxyethyl acrylate IBXA: Isobornyl acrylate CHMA: Cyclohexyl methacrylate DCP: dicyclopentanyl methacrylate MMA: Methyl methacrylate EMA: Ethyl methacrylate BMA: n-butyl methacrylate 2EHMA: 2-ethylhexyl methacrylate MAA: methacrylic acid IBXMA: Isobornyl methacrylate HEMA: 2-hydroxyethyl methacrylate

[0104] Example 1: Preparation and evaluation of adhesive composition (1) A pressure-sensitive adhesive composition (1) was obtained by mixing 100 parts by mass of a 50% by mass solution of the acrylic polymer (A-1) obtained in Synthesis Example 1, 10 parts by mass of a 55% by mass solution of the acrylic polymer (C-1) obtained in Synthesis Example 4, and 0.05 parts by mass of an epoxy-based crosslinking agent ("Tetrad X" manufactured by Mitsubishi Gas Chemical Company, Inc.; hereinafter abbreviated as "crosslinking agent (B-1)"), with stirring until homogeneous.

[0105] [Adhesive film processing method 1] The adhesive composition obtained in the example was applied to the surface of a 50 μm thick polyethylene terephthalate film (release PET50) with a release-treated surface so that the film thickness after solvent drying would be 25 μm.The solvent was then evaporated in an 80°C dryer for 3 minutes, and a 50 μm thick polyethylene terephthalate film (PET50) was then bonded to the surface.

[0106] [Adhesive film processing method 2] The adhesive composition obtained in the example was applied to the surface of a 50 μm thick polyethylene terephthalate film (release PET50) with a release-treated surface so that the film thickness after solvent drying would be 50 μm.The solvent was then evaporated in an 80°C dryer for 3 minutes, and the release PET50 was then bonded to the film.

[0107] [Evaluation of initial optical properties 1] The adhesive film prepared by the above-mentioned method 2 was attached to a glass plate to prepare a test specimen. The release PET film of the test specimen was peeled off to form a pressure-sensitive adhesive layer and glass plate. The haze was then measured in accordance with JIS K 7361-1 using a turbidity meter "NDH5000" (manufactured by Nippon Denshoku Industries Co., Ltd.). The initial haze of the glass alone was 0.2.

[0108] [Evaluation of initial optical properties 2] The pressure-sensitive adhesive film prepared by Method 2 above was attached to a glass substrate, and then pressure-bonded at a temperature of 50°C and an atmospheric pressure of 0.5 MPa for 20 minutes to prepare a test specimen. The release PET film of the test specimen was peeled off to leave a pressure-sensitive adhesive layer and a glass plate. The initial color number (b*) was measured in accordance with JIS K 7105 using a spectrophotometer CM 5000d (manufactured by Konica Minolta Sensing, Inc.) with a C light source and a 2° field of view. The initial color number (b*) of the glass alone was 0.1.

[0109] [Evaluation of humidity and heat resistance optical properties] The adhesive film prepared by the above-mentioned method 2 was attached to a glass substrate, and then pressed at a temperature of 50°C and an atmospheric pressure of 0.5 MPa for 20 minutes. The test piece was then left to stand in an environment of 85°C and 85% RH for 500 hours. The color number (b*) and haze of the test piece were measured in the same manner as above.

[0110] [Evaluation of foaming resistance] The adhesive film prepared by Method 1 above was cut into a 50 mm wide and 50 mm long specimen. 2 mm thick glass, acrylic plate, and polycarbonate (PC) plate were used as the adherends. After being attached to the adherends, the specimens were pressed at a temperature of 50°C and an atmospheric pressure of 0.5 MPa for 20 minutes. The specimens were then left to stand for a predetermined time in each of the durability test environments (1) to (3), and immediately after removal, their appearance was evaluated according to the following criteria. Durability test environment (1) 100℃ environment for 2 hours Durability test environment (2) 24 hours under 85℃ 85%RH environment Durability test environment (3) 80℃ hot water immersion for 2 hours ◯: No change before and after durability test, △: Surface irregularities occurred, ×: Foaming and whitening occurred

[0111] [Evaluation of initial adhesive strength] The adhesive film prepared by Method 1 above was cut into 25 mm wide pieces to be used as test pieces. The adherend was a polycarbonate plate or a glass plate, and the film was attached to the adherend using a 2 kg roll rolled back and forth twice. Two hours after application, the 180-degree peel strength was measured in an atmosphere of 23°C and 50% RH, and this was taken as the adhesive strength (N / 25 mm).

[0112] [Evaluation of adhesive strength against heat and humidity] The adhesive film prepared by Method 1 above was cut into 25 mm wide pieces to be used as test pieces. The adherend was a polycarbonate plate or a glass plate, and the film was attached to the adherend using a 2 kg roll rolled back and forth twice. 30 minutes after application, the film was left to stand in an 85°C, 85% RH environment for 500 hours. After removal, the film was allowed to cool at room temperature, and the 180° peel strength was measured in an atmosphere of 23°C, 50% RH, and the adhesive strength (N / 25 mm) was calculated.

[0113] [Evaluation of hot water resistant adhesive strength] The adhesive film prepared by Method 1 above was cut into 25 mm wide pieces to be used as test pieces. The adherend was a polycarbonate plate or a glass plate, and the film was attached to the adherend using a 2 kg roll rolled back and forth twice. 30 minutes after attachment, the film was immersed in 80°C warm water for 2 hours. After removing from the water, the film was wiped dry and the 180° peel strength was measured in an atmosphere of 23°C and 50% RH, and this was taken as the adhesive strength (N / 25 mm).

[0114] (Examples 2 to 19: Preparation and evaluation of pressure-sensitive adhesive compositions (2) to (19)) Pressure-sensitive adhesive compositions (2) to (19) were obtained in the same manner as in Example 1, except that the acrylic polymer (A-1), crosslinking agent (B-1), and acrylic polymer (C-1) used in Example 1 were changed as shown in Tables 5 to 7, and then various evaluations were performed.

[0115] (Comparative Examples 1 to 4: Preparation and Evaluation of Pressure-Sensitive Adhesive Compositions (R1) to (R4)) Pressure-sensitive adhesive compositions (R1) to (R4) were obtained in the same manner as in Example 1, except that the acrylic polymer (A-1), crosslinking agent (B-1), and acrylic polymer (C-1) used in Example 1 were changed as shown in Table 8, and then various evaluations were performed.

[0116] [Table 5]

[0117] [Table 6]

[0118] [Table 7]

[0119] [Table 8]

[0120] In Tables 5 to 8, the abbreviations represent the following compounds. Crosslinking agent (B-1): Tetrad X (epoxy-based crosslinking agent: manufactured by Mitsubishi Gas Chemical Company, Inc.) Crosslinking agent (B-2): Tetrad C (epoxy-based crosslinking agent: manufactured by Mitsubishi Gas Chemical Company, Inc.) Crosslinking agent (B-3): Burnock D-750 (isocyanate-based crosslinking agent: manufactured by DIC Corporation) Crosslinking agent (B-4): Takenate D-110N (isocyanate-based crosslinking agent: manufactured by Mitsui Chemicals, Inc.) Crosslinking agent (B-5): Burnock DN-980 (isocyanate-based crosslinking agent: manufactured by DIC Corporation)

[0121] It was confirmed that the adhesive films obtained from Examples 1 to 19, which are the adhesive compositions of the present invention, have excellent optical transparency, foaming resistance, and adhesive strength even in a high-temperature, high-humidity environment or a high-temperature, hot water immersion environment.

[0122] Comparative Example 1 is an example that does not contain the acrylic polymer (C), and was inferior in foaming resistance in a high-temperature, high-humidity environment and in a high-temperature, hot water immersion environment.

[0123] Comparative Example 2 is an example in which an acrylic polymer not containing a nitrogen atom-containing monomer (a2) was used instead of the acrylic polymer (A), but the foaming resistance was poor in a high-temperature hot water immersion environment.

[0124] Comparative Example 3 is an example in which an acrylic polymer having a content of units derived from an alkyl (meth)acrylate monomer (a1) having an alkyl group with 1 to 4 carbon atoms of less than 50 mass% was used instead of the acrylic polymer (A), but the foaming resistance was poor in a high-temperature, high-humidity environment and a high-temperature, hot water immersion environment.

[0125] Comparative Example 4 is an example in which an acrylic polymer having a glass transition temperature higher than -20°C was used instead of the acrylic polymer (A), but both the foaming resistance and adhesive strength were poor in a high-temperature, high-humidity environment and a high-temperature, hot water immersion environment.

Claims

1. The composition comprises an acrylic polymer (A), a crosslinking agent (B), and an acrylic polymer (C), the acrylic polymer (A) contains units derived from an alkyl(meth)acrylate monomer (a1) having an alkyl group having 1 to 4 carbon atoms; units derived from a monomer (a2) having a nitrogen atom; units derived from a monomer (a3) having an acid group; and units derived from a monomer (a4) having a hydroxyl group, in the acrylic polymer (A), the content of units derived from the nitrogen atom-containing monomer (a2) is 0.5% by mass or more and 30% by mass or less, and the total content of units derived from the acid group-containing monomer (a3) and the hydroxyl group-containing monomer (a4) is 0.5% by mass or more and 30% by mass or less, the glass transition temperature of the acrylic polymer (A) is −20° C. or lower, the weight average molecular weight of the acrylic polymer (A) is 200,000 or more and 1,500,000 or less, the acid value of the acrylic polymer (A) is 5 mgKOH / g or more and 200 mgKOH / g or less, the content of units derived from the alkyl (meth)acrylate monomer (a1) having an alkyl group having 1 to 4 carbon atoms in the acrylic polymer (A) is 50% by mass or more and less than 97% by mass, the acrylic polymer (C) contains a unit derived from an alicyclic structure-containing (meth)acrylate monomer (c1); and a unit derived from an alkyl (meth)acrylate monomer (c2), the acrylic polymer (C) contains units derived from the (meth)acrylate (c1) in an amount of 20% by mass or more and 95% by mass or less, and contains units derived from the (meth)acrylate (c2) in an amount of 1% by mass or more and 80% by mass or less, the glass transition temperature of the acrylic polymer (C) is 50°C or higher, A pressure-sensitive adhesive composition, characterized in that the weight average molecular weight of the acrylic polymer (C) is 2,500 or more and 80,000 or less.

2. An adhesive layer formed from the adhesive composition according to claim 1.

3. An adhesive film having the adhesive layer according to claim 2.

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