Adhesive composition and adhesive film

Abstract

To express high adhesive strength by sensing heat while maintaining optical transparency.SOLUTION: The adhesive composition of the present invention includes: an acrylic polymer (A); a crosslinking agent (B); and an acrylic polymer (C). The acrylic polymer (A) includes: a unit derived from a (meth)acrylate monomer (al); a unit derived from a nitrogen-containing monomer (a2); and a unit derived from at least one selected from the group consisting of a monomer (a3) having an acid group, and a monomer (a4) having a hydroxyl group. The weight average molecular weight of the acrylic polymer (A) is 100,000 or more. The acrylic polymer (C) includes: a unit derived from an alicyclic structure-having (meth)acrylate monomer (c1); and a unit derived from alkyl(meth)acrylate monomer (c2). The content of the unit derived from the alicyclic structure-having (meth)acrylate monomer (c1) is 35 mass% or more and less than 95 mass% in the acrylic polymer (C). The glass transition point of the acrylic polymer (C) is 50°C or higher, and the weight average molecular weight of the acrylic polymer (C) is less than 100,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to adhesive compositions and adhesive films. [Background technology]

[0002] Acrylic adhesives have long been used in various fields, but in recent years, demand has been particularly high for IT-related products such as smartphones. These IT-related products, due to their characteristics, require higher performance and functionality.

[0003] As an example of an acrylic adhesive used in IT-related products, there is a demand for a heat-sensitive adhesive that is slightly tacky at room temperature but becomes strongly tacky upon heating and retains its tackiness even after deheating. Specific examples include adhesives containing acrylic low molecular weight polymers with a weight-average molecular weight of 1,000 to 50,000 (see, for example, Patent Document 1). Furthermore, adhesives have been proposed that include polymers with a glass transition temperature of less than 0°C and polymers containing monomers having a polyorganosiloxane skeleton and monomers with a glass transition temperature of 40°C or higher as monomer units, with a weight-average molecular weight of 10,000 or more and less than 100,000 (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2008-222814 [Patent Document 2] Japanese Patent Publication No. 2019-123884 [Overview of the project] [Problems that the invention aims to solve]

[0005] In IT-related products, high optical transparency (transparent coating) is a crucial requirement. However, conventional adhesives have sometimes made it difficult to achieve both slight tackiness at room temperature and strong tackiness after heating (hereinafter, slight tackiness at room temperature and strong tackiness after heating may be collectively referred to as "high adhesive strength due to heat sensitivity") while maintaining optical transparency.

[0006] This invention has been made in view of the above circumstances, and aims to achieve high adhesive strength through heat sensitivity while maintaining optical transparency. [Means for solving the problem]

[0007] The 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 (meth)acrylate monomer (a1), units derived from nitrogen-containing monomer (a2), and units derived from at least one selected from the group consisting of monomers having acid groups (a3) ​​and monomers having hydroxyl groups (a4), and the weight-average molecular weight of the acrylic polymer (A) is 100,000 or more; the acrylic polymer (C) comprises units derived from alicyclic structure-containing (meth)acrylate monomer (c1) and units derived from alkyl (meth)acrylate monomer (c2), the content of units derived from alicyclic structure-containing (meth)acrylate monomer (c1) is 35% by mass or more and less than 95% by mass of the acrylic polymer (C); the glass transition temperature of the acrylic polymer (C) is 50°C or higher; and the weight-average molecular weight of the acrylic polymer (C) is less than 100,000. [Effects of the Invention]

[0008] By using the adhesive composition of the present invention, it is possible to achieve high adhesive strength through heat sensitivity while maintaining optical transparency. [Modes for carrying out the invention]

[0009] The adhesive composition of the present invention comprises an acrylic polymer (A), a crosslinking agent (B), and an acrylic polymer (C).

[0010] The acrylic polymer (A) comprises units derived from (meth)acrylate monomer (a1); units derived from nitrogen-containing monomer (a2); and units derived from at least one selected from the group consisting of monomers having an acid group (a3) ​​and monomers having a hydroxyl group (a4).

[0011] Examples of (meth)acrylate monomers (a1) include alkyl (meth)acrylate monomers in which an alkyl group is esterified, cyclic ether-containing (meth)acrylate monomers, alicyclic structure-containing (meth)acrylate monomers, aromatic ring-containing (meth)acrylate monomers, and alkylene oxide structure-containing (meth)acrylate monomers.

[0012] Examples of alkyl groups in the alkyl (meth)acrylate monomer include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, lauryl, and stearyl groups; and branched alkyl groups such as isopropyl, isobutyl, t-butyl, isopentyl, neopentyl, isohexyl, isoheptyl, isooctyl, 2-ethylhexyl, isononyl, isodecyl, and isostearyl groups. The number of carbon atoms in the alkyl group is preferably 1 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less.

[0013] Examples of the alkyl (meth)acrylate monomers 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, 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, isostearyl (meth)acrylate, and the like.

[0014] Furthermore, examples of the (meth)acrylate monomer (a1) include cyclic ether-containing (meth)acrylate monomers such as glycidyl (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; and alkylene oxide-containing (meth)acrylate monomers such as 2-methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate.

[0015] The alkyl (meth)acrylate monomer (a1) includes a low-Tg monomer (a1-1) whose homopolymer has a glass transition temperature (Tg) of less than -15°C, and a high-Tg monomer (a1-2) whose homopolymer has a glass transition temperature (Tg) of -15°C or higher.

[0016] The glass transition temperature (Tg) of the low-Tg monomer (a1-1) is less than -15°C, preferably -20°C or lower, more preferably -25°C or lower, and the lower limit may be, for example, -100°C or higher.

[0017] The content rate of the low-Tg monomer (a1-1) is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 44% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less in the alkyl (meth)acrylate monomer.

[0018] The glass transition temperature of the high-Tg monomer (a1-2) is -15°C or higher, preferably -10°C or higher, more preferably -5°C or higher, and the upper limit may be, for example, 150°C or lower, 100°C or lower.

[0019] The content of the high-Tg monomer (a1-2) is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 25 parts by mass or more, and preferably 50 parts by mass or less, more preferably 45 parts by mass or less, still more preferably 40 parts by mass or less with respect to 100 parts by mass of the low-Tg monomer (a1-1).

[0020] The unit derived from the high-Tg monomer (a1-2) is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less in the acrylic polymer (A).

[0021] One or more of the (meth)acrylate monomers (a1) can be used, and an alkyl acrylate or a (meth)acrylate monomer containing an alicyclic structure is preferable because it can impart flexibility and cohesion in a well-balanced manner.

[0022] The content rate of the unit derived from the (meth)acrylate monomer (a1) in the acrylic polymer (A) is preferably 50% by mass or more, more preferably 70% by mass or more, and preferably 97% by mass or less, more preferably 95% by mass or less.

[0023] The nitrogen-containing monomer (a2) is a monomer having a nitrogen atom and a polymerizable double bond in its molecule, and is preferably a monomer having an amide bond and a polymerizable double bond in its molecule. Examples include lactam compounds having a vinyl group; (meth)acrylamide monomers; and (meth)acrylate compounds having a functional group containing a nitrogen atom (e.g., an amino group, a monosubstituted amino group, a disubstituted amino group, a nitrile group, etc.).

[0024] Examples of lactam compounds having a vinyl group include N-vinylpyrrolidone and N-vinylcaprolactam.

[0025] The (meth)acrylamide monomers include compounds in which a hydrogen atom or a hydrocarbon group (preferably an aliphatic hydrocarbon group; however, the -CH2- contained in the hydrocarbon may be replaced with -CO-, and the hydrogen atom contained in the hydrocarbon group may be substituted with a hydroxyl group) is bonded to the nitrogen atom of (meth)acrylamide. Furthermore, when two or more groups (the hydrocarbon groups) are substituted to the nitrogen atom of (meth)acrylamide, these groups may be bonded to each other to form a ring containing the nitrogen atom.

[0026] The number of carbon atoms in the hydrocarbon group (preferably an aliphatic hydrocarbon group) that substitutes for the nitrogen atom in the amide bond is preferably 1 or more, preferably 10 or less, and more preferably 6 or less.

[0027] The (meth)acrylamide monomer (a2) can be one or more types. The (meth)acrylamide monomer may be (meth)acrylamide, an N-1 substituted (meth)acrylamide compound, or an N,N-2 substituted (meth)acrylamide compound.

[0028] The (meth)acrylamide compound can be one or more types, for example, (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, N-(2-hydroxyethyl)acrylamide; N- Examples include N-2 substituted (meth)acrylamide compounds such as (meth)acrylloylmorpholine, N-(meth)acrylloylpiperidone, N-(meth)acrylloylpiperidine, N-(meth)acrylloylpyrrolidine, N-(meth)acrylloyl-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.

[0029] In particular, the (meth)acrylamide monomer is preferably one that contains the monomer represented by formula (1).

[0030] [ka] [In formula (1), R 1 R represents a hydrogen atom or a methyl group. 2 and R 3 Each of these independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and the -CH2- contained in the hydrocarbon group may be replaced with -CO- or -O-, and the hydrogen atom contained in the hydrocarbon group may be replaced with a hydroxyl group, R 2 and R 3 These atoms may be bonded to each other to form a ring containing nitrogen atoms.

[0031] The aforementioned R 2 and R 3The hydrocarbon group represented by may be one or more, and examples thereof include a linear or branched saturated aliphatic hydrocarbon group; a linear or branched unsaturated aliphatic hydrocarbon group and the like. Among them, a linear or branched saturated aliphatic hydrocarbon group is preferable, and a branched saturated aliphatic hydrocarbon group is more preferable. R 2 and R 3 It is preferable that at least one of is a hydrogen atom.

[0032] The (meth)acrylamide monomer preferably contains a (meth)acrylamide monomer in which both R 2 and R 3 are the hydrocarbon groups. When the (meth)acrylamide monomer in which both R 2 and R 3 are the hydrocarbon groups is included, the content ratio of the unit derived from the monomer is preferably 0.5% by mass or more, more preferably 1% by mass or more, preferably 20% by mass or less, and more preferably 15% by mass or less in the acrylic polymer (A).

[0033] In the nitrogen-containing monomer (a2), the content ratio of the unit derived from the acrylamide monomer is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and the upper limit is 100% by mass.

[0034] 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, diethylaminoethyl (meth)acrylate and the like.

[0035] In the acrylic polymer (A), the content ratio of the unit derived from the nitrogen-containing monomer (a2) is preferably 0.5% by mass or more, more preferably 1% by mass or more, preferably 20% by mass or less, and more preferably 15% by mass or less.

[0036] Examples of the aforementioned monomer having an acid group (a3) ​​include monomers having an acid group and a polymerizable double bond, preferably monomers having a carboxyl group and monomers having a sulfo group, with monomers having a carboxyl group being preferred.

[0037] One or more monomers having a carboxyl group can be used, for example, (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.

[0038] In the monomer (a3) ​​having an acid group, the content of monomers having a carboxyl group is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, with an upper limit of 100% by mass.

[0039] In the acrylic polymer (A), the content of units derived from the monomer (a3) ​​having the acid group is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0040] The monomer (a4) having a hydroxyl group includes monomers having a hydroxyl group and a polymerizable double bond. Examples of the (meth)acrylic monomer having a hydroxyl group include hydroxyalkyl (meth)acrylate, hydroxyalkyl (meth)acrylamide, and polyalkylene glycol (meth)acrylate, with hydroxyalkyl (meth)acrylate being preferred.

[0041] Examples of monomers having a hydroxyl group (a4) include hydroxyalkyl(meth)acrylates with 2 to 10 carbon atoms in the alkyl group (alkylene group), 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; hydroxyalkyl(meth)acrylamides with 2 to 8 carbon atoms in the alkyl group (alkylene group), such as 2-hydroxyethyl(meth)acrylamide, 4-hydroxyethyl(meth)acrylamide, 6-hydroxyhexyl(meth)acrylamide, and 8-hydroxyoctyl(meth)acrylamide; and polyalkylene glycol(meth)acrylates such as polyethylene glycol(meth)acrylate.

[0042] The content of units derived from the monomer (a4) having a hydroxyl group 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, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, in the acrylic monomer (A).

[0043] The total amount of units derived from the monomer having an acid group (a3) ​​and the monomer having a hydroxyl group (a4) in the acrylic polymer (A) is 0.5% by mass or more, preferably 1.5% by mass or more, more preferably 2% by mass or more, preferably 30% by mass or less, more preferably 22% by mass or less, and even more preferably 17% by mass or less.

[0044] In the acrylic polymer (A), the total amount of units derived from the alkyl (meth)acrylate monomer (a1), the nitrogen-containing monomer (a2), the monomer having an acid group (a3), and the monomer having a hydroxyl group (a4) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, with an upper limit of 100% by mass.

[0045] The acrylic polymer (A) may have units derived from monomers (ax) other than the alkyl (meth)acrylate monomer (a1), nitrogen-containing monomer (a2), monomer having an acid group (a3), and monomer having a hydroxyl group (a4).

[0046] The aforementioned other monomers (ax) can be one or more, and examples 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, ethyl vinylbenzene, 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.

[0047] In the acrylic polymer (A), the content of units derived from other monomers (ax) is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, with a lower limit of 0% by mass.

[0048] 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, preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less.

[0049] In this specification, the number-average molecular weight and weight-average molecular weight of the acrylic polymer (A) represent converted values ​​measured using gel permeation chromatography (GPC) with polystyrene as the standard sample.

[0050] In the adhesive composition of the present invention, the content of the acrylic polymer (A) 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, in the nonvolatile content.

[0051] In this specification, the non-volatile content of the adhesive composition refers to the portion excluding the solvent components that may be included in the adhesive composition as needed.

[0052] The acrylic polymer (A) can be produced by copolymerizing the alkyl (meth)acrylate monomer (a1), nitrogen-containing monomer (a2), monomer having an acid group (a3), monomer having a hydroxyl group (a4), and other monomers (ax) as needed, in the presence of a polymerization initiator.

[0053] Examples of the polymerization initiators include one or more thermal polymerization initiators, such as peroxide initiators like benzoyl peroxide and lauroyl peroxide; and azo initiators like azobismethylbutyronitrile and azobisisobutylnitrile.

[0054] The adhesive composition of the present invention contains a crosslinking agent (B). One or more types of crosslinking agents can be used, and examples 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, glycidyl(alkoxy)epoxysilane crosslinking agents, and the like.

[0055] Among these, isocyanate crosslinking agents, epoxy 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.

[0056] The content of the epoxy crosslinking agent is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and preferably 100% by mass or less in the crosslinking agent (B).

[0057] The content of the crosslinking agent (B) 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, preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, per 100 parts by mass of the acrylic polymer (A).

[0058] The acrylic polymer (C) comprises units derived from an alicyclic structure-containing (meth)acrylate monomer (c1) and units derived from an alkyl (meth)acrylate monomer (c2).

[0059] The alicyclic structure-containing (meth)acrylate monomer (c1) (hereinafter sometimes simply referred to as "(meth)acrylate (c1)") represents an alicyclic structure-containing (meth)acrylate monomer in its molecule. The alicyclic hydrocarbon group may be a monocyclic or a cross-linked ring, and the number of alicyclic hydrocarbon groups contained in the (meth)acrylate (c1) may be one or two or more.

[0060] Examples of alicyclic hydrocarbon groups contained in the (meth)acrylate (c1) include monocyclic alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, and cycloheptyl groups; and bridged ring alicyclic hydrocarbon groups such as norbornyl, isobornyl, and dicyclopentanyl groups.

[0061] The number of carbon atoms in the alicyclic hydrocarbon group contained in the (meth)acrylate (c1) is 3 or more, preferably 5 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less.

[0062] The alicyclic structure-containing (meth)acrylate monomer (c1) contained in the (meth)acrylate (c1) can be specifically one or more types, for example, monocyclic alicyclic structure-containing (meth)acrylate monomers such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and cycloheptyl (meth)acrylate; and cross-linked ring alicyclic structure-containing (meth)acrylate monomers such as norbornyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0063] The content of units derived from the (meth)acrylate (c1) is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 92% by mass or less in the acrylic polymer (C).

[0064] The alkyl (meth)acrylate monomer (c2) (hereinafter sometimes simply referred to as "(meth)acrylate (c2)") represents a (meth)acrylate monomer having an alkyl group.

[0065] Examples of alkyl groups included in the (meth)acrylate (c2) are linear alkyl groups such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, lauryl group, and stearyl group; and branched alkyl groups such as isopropyl group, isobutyl group, t-butyl group, isopentyl group, neopentyl group, isohexyl group, isoheptyl group, isooctyl group, 2-ethylhexyl group, isononyl group, isodecyl group, and isostearyl group.

[0066] The number of carbon atoms in the alkyl group contained in the (meth)acrylate (c2) is preferably 1 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less.

[0067] The (meth)acrylate (c2) can be one or more types, such as 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, isostearyl (meth)acrylate, etc.

[0068] The content of units derived from the (meth)acrylate (c2) is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less in the acrylic polymer (C).

[0069] The content ratio ((c1) / (c2)) of units derived from (meth)acrylate (c1) to units derived from (meth)acrylate (c2) is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 0.7 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less, on a mass basis.

[0070] 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).

[0071] Examples of the aforementioned other monomers (c3) include the cyclic ether-containing (meth)acrylate monomer, the aromatic ring-containing (meth)acrylate monomer, the alkylene oxide structure-containing (meth)acrylate monomer, and other (meth)acrylate monomers; and the nitrogen-containing monomer.

[0072] The content of the other monomer (c3) is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less in the acrylic polymer (C), with a lower limit of 0% by mass.

[0073] 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, preferably 120°C or lower, and more preferably 110°C or lower.

[0074] The glass transition temperature Tga(K) of the acrylic polymer (C) can be calculated based on the following FOX equation. 1 / Tga = Σ(Wi / Tgi)

[0075] In the FOX formula, Wi represents the content of units derived from each monomer in the acrylic polymer (C), and Tgi(K) represents the glass transition temperature (in absolute temperature) of the homopolymer formed solely from each monomer. Details of the FOX formula are described in the Bulletin of the American Physical Society, Series 2, Volume 1, Number 3, Page 123 (1956). Furthermore, the glass transition temperature (Tgi) of the homopolymer of each monomer can be taken from values ​​such as those described in "Coatings and Paints" (Paints Publishers, 10 (No. 358), 1982).

[0076] 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, preferably 1,000 or more, more preferably 1,500 or more, and even more preferably 2,500 or more.

[0077] In this specification, the number-average molecular weight and weight-average molecular weight of the acrylic polymer (C) represent converted values ​​measured using gel permeation chromatography (GPC) with polystyrene as the standard sample.

[0078] In the adhesive composition of the present invention, the content of 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, preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, based on the nonvolatile content.

[0079] In the adhesive composition of the present invention, the content of the acrylic polymer (C) is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, based on 100 parts by mass of the acrylic polymer (A).

[0080] 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) as needed, in the presence of a polymerization initiator.

[0081] Examples of the polymerization initiators include one or more thermal polymerization initiators, such as peroxide initiators like benzoyl peroxide and lauroyl peroxide; and azo initiators like azobismethylbutyronitrile and azobisisobutylnitrile.

[0082] The adhesive composition of the present invention preferably contains a solvent (D). One or more types of solvents (D) can be used, and examples 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, the inclusion of an ester solvent is preferred.

[0083] The content of the ester solvent is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and preferably 100% by mass or less, in the solvent (D).

[0084] The content of the solvent (D) in the adhesive composition is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less.

[0085] In the adhesive composition of the present invention, the content of the tackifying resin is preferably reduced in order to maintain low yellowing, 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 parts by mass, per 100 parts by mass of the acrylic polymer.

[0086] The adhesive composition of the present invention may contain, as additives, bases (such as aqueous ammonia) or acids for adjusting pH; foaming agents; plasticizers; softeners; antioxidants; fillers such as glass or plastic fibers, balloons, beads, and metal powders; colorants such as pigments and dyes; pH adjusters; film-forming aids; leveling agents; thickeners; water repellents; defoaming agents; acid catalysts; acid generators, etc.

[0087] An adhesive layer can be formed by applying the adhesive composition onto a support and drying it. The support may be any substrate such as a release sheet or an adhesive sheet.

[0088] As the coating method, methods such as knife coater, reverse coater, die coater, lip die coater, slot die coater, gravure coater, and curtain coater can be used.

[0089] 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, preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 75 μm or less.

[0090] The adhesive sheet or adhesive tape of the present invention comprises the adhesive layer and the substrate. The substrate may be in the form of a film, sheet, tape, plate, or three-dimensional shape. Examples of materials 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, with plastic being preferred and polyester resin being more preferred. The substrate may have a smooth surface, or it may have an uneven surface, such as a fibrous substrate or a foam substrate.

[0091] The thickness of the substrate is preferably 0.1 μm or more, and preferably 1,000 μm or less. [Examples]

[0092] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0093] [Synthesis Example 1: Synthesis of Acrylic Resin (A1)] In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 200 parts by mass of butyl acrylate (hereinafter abbreviated as "BA"), 277 parts by mass of 2-ethylhexyl acrylate (hereinafter abbreviated as "2EHA"), 400 parts by mass of cyclohexyl acrylate (hereinafter abbreviated as "CHA"), 50 parts by mass of diacetone acrylamide (hereinafter abbreviated as "DAAM"), 70 parts by mass of acrylic acid (hereinafter abbreviated as "AA"), 3 parts by mass of 4-hydroxybutyl acrylate (hereinafter abbreviated as "4HBA"), and 1000 parts by mass of ethyl acetate were charged, and the mixture was heated to 70°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by mass (5% solids) of 2,2'-azobis(2-methylbutyronitrile) solution, which had been previously dissolved in ethyl acetate, was added. Subsequently, the mixture was held at 70°C for 8 hours under stirring, then cooled and filtered through a 200-mesh wire mesh to obtain acrylic resin (A1) with a non-volatile content of 50% by mass, a viscosity of 100,000 mPa·s, and a weight-average molecular weight of 900,000.

[0094] [Synthesis Examples 2-3] Acrylic resins (A2) to (A3) were obtained in the same manner as in Synthesis Example 1, except that the (meth)acrylate monomer (a1), nitrogen-containing monomer (b), monomer with an acid group (c), and monomer with a hydroxyl group (d) were changed as shown in Table 1.

[0095] [Synthesis Example 4: Synthesis of Acrylic Resin (C-1)] 395 parts by mass of methyl ethyl ketone (hereinafter abbreviated as "MEK") were charged into a reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser, and nitrogen gas inlet, and the temperature was raised to 80°C. Next, at the same temperature, a mixture containing 220 parts by mass of cyclohexyl methacrylate (hereinafter abbreviated as "CHMA"), 138 parts by mass of methyl methacrylate (hereinafter abbreviated as "MMA"), 127 parts by mass of butyl methacrylate (hereinafter abbreviated as "BMA"), 38 parts by mass of BA, 28 parts by mass of methacrylic acid (hereinafter abbreviated as "MAA"), 33 parts by mass of MEK, and 55 parts by mass of tert-butyl peroxy-2-ethylhexanoate (hereinafter abbreviated as "TBPEH") was added dropwise to the reaction vessel over 4 hours. After the addition was complete, the mixture was reacted at the same temperature for a further 20 hours to obtain an organic solvent solution of acrylic resin (C-1) with a non-volatile content of 55% by mass and a weight-average molecular weight of 2,500.

[0096] [Synthesis Examples 5-10, Comparative Synthesis Examples 1-4] Acrylic resins (C-2) to (C-7) and comparative acrylic resins (r-1) to (r-4) were obtained in the same manner as in Synthesis Example 4, except that the (meth)acrylate monomer was changed as shown in Tables 2 and 3.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] [Example 1] An acrylic adhesive composition was obtained by uniformly stirring and mixing 100 parts by mass of acrylic resin (A1) obtained in Synthesis Example 1 with 18 parts by mass of acrylic resin (C-1) obtained in Synthesis Example 4 and 0.3 parts by mass of epoxy crosslinking agent (Finetac curing agent EX-50; manufactured by DIC Corporation).

[0101] [Examples 2-13, Comparative Examples 1-5] An acrylic adhesive composition was obtained in the same manner as in Example 1, except that the acrylic resin (A1) obtained in Synthesis Example 1 was replaced with acrylic resins (A2) to (A3) obtained in Synthesis Examples 2 to 3, the acrylic resin (C-1) obtained in Synthesis Example 4 was replaced with acrylic resins (C-2) to (C-7) obtained in Synthesis Examples 5 to 10, and the comparative acrylic resins (r-1) to (r-4) obtained in Comparative Synthesis Examples 1 to 4 were changed as shown in Table 4.

[0102] [Method for processing adhesive film] An acrylic adhesive composition obtained in the example was applied to the surface of a 50 μm thick polyethylene terephthalate film (release PET50) that had been treated with a release agent on its surface, such that the film thickness after solvent drying was 25 μm. After the solvent was evaporated in an 80°C dryer for 3 minutes, a PET50 μm film was laminated to it.

[0103] [Method for measuring adhesive strength] The adhesive film prepared using the method described above was cut into 25mm wide strips to serve as test specimens. A glass plate was used as the substrate, and the film was applied to the substrate using a 2kg roll with two passes. After one hour of application, the peel strength at 180 degrees was measured under an atmosphere of 23°C and 50%RH, and this was defined as the adhesive strength.

[0104] [Method for measuring adhesive strength after heat treatment] The adhesive film prepared using the method described above was cut into 25mm wide strips to serve as test specimens. A glass plate was used as the substrate, and the film was applied to the substrate using a 2kg roll with two passes. After application, the specimens were heated in a 120°C dryer for 5 minutes. After removing them from the dryer, the peel strength was measured at 180°C under a 23°C, 50%RH atmosphere for 1 hour, and this was defined as the adhesive strength after heat treatment.

[0105] [Method for measuring retention force after heat treatment] Test specimens were made by cutting the adhesive film prepared using the method described above into 25mm widths. The film was applied to a mirror-finished stainless steel plate using a 2kg roll with two passes, ensuring an adhesive area of ​​25mm x 25mm. After application, the specimens were heated in a 120°C dryer for 5 minutes. After removing them from the dryer, a 1kg load was applied to the test specimens attached to the stainless steel plate in a 70°C atmosphere, at a 0° angle to the stainless steel plate (shear direction). The time it took for the adhesive film to slide off the substrate was measured, and this retention time was defined as the retention force after heat treatment. If the film was still retained after 24 hours, the retention time was defined as 24 hours or longer.

[0106] [Method for measuring the initial number of colors (b*)] A test specimen was prepared by attaching an adhesive film, created using the method described above, to a glass plate. The initial number of colors (b*) of this test specimen was measured in accordance with JIS K 7105 using a light source C, a field of view of 2°, and a spectrophotometer "CM-5000d" (manufactured by Konica Minolta Sensing, Inc.).

[0107] [Method for measuring initial haze and initial light transmittance] A test specimen was prepared by attaching an adhesive film, created using the method described above, to a glass plate. The haze and light transmittance of this test specimen were measured using a turbidimeter "NDH5000" (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1.

[0108] [Measurement method for color number (b*), haze, and light transmittance after heat treatment] The adhesive film prepared using the method described above was attached to a glass plate and heated in a 120°C dryer for 5 minutes to prepare a test specimen. The number of colors (b*) after heat treatment of this test specimen was measured in accordance with JIS K 7105, in the same manner as described above. In addition, the adhesive film prepared using the method described above was attached to a glass plate and heated in a 120°C dryer for 5 minutes to prepare a test specimen. The haze and light transmittance of this test specimen were measured using a turbidimeter "NDH5000" in accordance with JIS K 7361-1, in the same manner as described above.

[0109] In Tables 1-5, each abbreviation represents one of the following compounds. BA: n-butyl acrylate 2EHA: 2-Ethylhexyl acrylate CHA: Cyclohexyl acrylate MA: Methyl acrylate IBXA: Isoboronyl acrylate DMAA: Dimethylacrylamide DAAM: Diacetone acrylamide AA: Acrylic acid HEA: 2-Hydroxyethyl Acrylate 4HBA: 4-hydroxybutyl acrylate CHMA: Cyclohexyl methacrylate MMA: Methyl methacrylate BMA:n-butyl methacrylate MAA: Methacrylic acid TBPEH: tert-butylperoxy-2-ethylhexanoate D-40: Fine Tack Hardener D-40 (Isocyanate-based crosslinking agent: Manufactured by DIC Corporation) EX-50: Fine Tack Hardener EX-50 (Epoxy Crosslinking Agent: Manufactured by DIC Corporation)

[0110] [Table 4]

[0111] [Table 5]

[0112] [Table 6]

[0113] Examples 1 to 13 are embodiments of the present invention. Initially, the adhesive strength exhibited slight tackiness, and after heat treatment, the adhesive strength could be improved while maintaining optical transparency, thus achieving both high transparency and high adhesive strength.

[0114] Comparative Example 1 was an example where the total amount of monomers containing alicyclic alkyl groups was less than 35% by mass, and it showed high initial adhesion. Comparative Example 2 was an example where the total amount of monomers containing alicyclic alkyl groups was 95% by mass or more, and it was confirmed that the haze after heat treatment was high and the transparency was insufficient. Comparative Examples 3 and 4 were examples where the Tg of the acrylic resin for adhesion modification was less than 50°C, and they showed high initial adhesion. Comparative Example 5 was an example that did not contain the acrylic resin for adhesion modification, and it showed high initial adhesion.

Claims

1. It contains an acrylic polymer (A), a crosslinking agent (B), and an acrylic polymer (C), The acrylic polymer (A) comprises units derived from (meth)acrylate monomer (a1); units derived from nitrogen-containing monomer (a2); units derived from monomer having an acid group (a3); and units derived from monomer having a hydroxyl group (a4). The (meth)acrylate monomer (a1) is other than the nitrogen-containing monomer (a2) and the monomer having a hydroxyl group (a4), and includes a low-Tg monomer (a1-1) whose homopolymer glass transition temperature (Tg) is less than -15°C, and a high-Tg monomer (a1-2) whose homopolymer glass transition temperature (Tg) is -15°C or higher. The content of units derived from the high-Tg monomer (a1-2) is 40% by mass or less in the acrylic polymer (A). The content of units derived from the (meth)acrylate monomer (a1) is 70% by mass or more and 97% by mass or less in the acrylic polymer (A). The content of the high-Tg monomer (a1-2) is 100 / 8.45 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the low-Tg monomer (a1-1). The nitrogen-containing monomer (a2) is one or more selected from the group consisting of N-vinylpyrrolidone, N-vinylcaprolactam, monomer represented by formula (1), (meth)acrylonitrile, t-butylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate. The monomer (a3) ​​having the acid group is one or more selected from the group consisting of (meth)acrylic acid, carboxyalkyl (meth)acrylate, and unsaturated carboxylic acid. The content of units derived from the nitrogen-containing monomer (a2) is 1% by mass or more and 20% by mass or less in the acrylic polymer (A). The content of units derived from the monomer (a3) ​​having the acid group is 0.5% by mass or more and 15% by mass or less in the acrylic polymer (A). The content of units derived from the monomer (a4) having a hydroxyl group is 0.01% by mass or more and 5% by mass or less in the acrylic polymer (A). The weight-average molecular weight of the acrylic polymer (A) is 100,000 or more. The aforementioned crosslinking agent (B) is one or more crosslinking agents selected from the group consisting of isocyanate crosslinking agents, epoxy crosslinking agents, and carbodiimide crosslinking agents. The acrylic polymer (C) comprises units derived from an alicyclic structure-containing (meth)acrylate monomer (c1) and units derived from an alkyl (meth)acrylate monomer (c2) other than the (meth)acrylate monomer (c1). The content of units derived from the alicyclic structure-containing (meth)acrylate monomer (c1) is 35% by mass or more and 90% by mass or less in the acrylic polymer (C). The content of units derived from the (meth)acrylate monomer (c2) is 5% by mass or more and 60% by mass or less in the acrylic polymer (C). The glass transition temperature of the acrylic polymer (C) is 50°C or higher. The weight-average molecular weight of the acrylic polymer (C) is less than 100,000. An adhesive composition in which the content of the acrylic polymer (C) is 5 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the acrylic polymer (A). 【Chemistry 1】 (In formula (1), R １ R represents a hydrogen atom or a methyl group. ２ and R ３ Each of these independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and the hydrocarbon group contains -CH ２ The - may be replaced by -CO- or -O-, R ２ and R ３ These atoms may be bonded to each other to form a ring containing nitrogen atoms.

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

3. An adhesive film having the adhesive layer according to claim 1 or 2.

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