Copolymer, adhesive composition, and adhesive

Abstract

To provide a (meth) acrylic copolymer capable of forming an adhesive excellent in adhesive force and holding force.SOLUTION: The (meth) acrylic copolymer contains a constituent unit derived from a monomer (a) represented by formula (I) and is a block copolymer or a graft copolymer. In Formula (I), R1 represents H, methyl, or ethyl, R2 represents an alkylene group having 1 to 2 carbon atoms or an alkylene group having 3 to 5 carbon atoms, R3 and R4 independently represent an alkyl group having 1 to 2 carbon atoms or an alkyl group having 3 to 5 carbon atoms, and R3 and R4 may be bonded to each other to form a ring.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a pressure-sensitive adhesive composition, and a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition. [Background technology]

[0002] Acrylic adhesives are used in a wide range of applications, including stickers, labels, adhesive tapes, bonding of display peripheral films, optically clear adhesives (OCA), and tapes used in semiconductor manufacturing processes. These adhesives are required to have both excellent adhesive strength and holding power, and improvements in the design of acrylic polymers and the formulation of adhesive compositions are being investigated to achieve these performances.

[0003] For example, Patent Document 1 discloses that a pressure-sensitive adhesive composition containing a graft copolymer obtained by polymerizing a structural unit derived from a macromonomer and a benzophenone derivative having a (meth)acryloyloxy group can provide a pressure-sensitive adhesive with excellent coating properties, adhesive strength, and holding power. Patent Document 2 discloses that a pressure-sensitive adhesive composition containing an acrylic resin having a structural moiety derived from a (meth)acrylate having an intramolecular cleavage-type active group can provide a pressure-sensitive adhesive with good adhesive strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 158475 [Patent Document 2] Japanese Patent Publication No. 2022-51554 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the adhesive described in Patent Document 1 has insufficient adhesive strength, and the adhesive described in Patent Document 2 has insufficient holding strength, so these methods cannot achieve both adhesive strength and holding strength. The present invention aims to provide a (meth)acrylic copolymer that can provide a pressure-sensitive adhesive having excellent adhesive strength and holding power, a pressure-sensitive adhesive composition using the same, and a pressure-sensitive adhesive obtained by crosslinking such a pressure-sensitive adhesive composition. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A (meth)acrylic copolymer which contains a structural unit derived from a monomer (a) represented by general formula (I) and is a block copolymer or a graft copolymer.

[0007] [ka]

[0008] [In the formula, R 1 represents a hydrogen atom, a methyl group, or an ethyl group, and R 2 represents an alkylene group having 1 to 2 carbon atoms or a linear or branched alkylene group having 3 to 5 carbon atoms; R 3 , R 4 each independently represents an alkyl group having 1 to 2 carbon atoms or a linear or branched alkyl group having 3 to 5 carbon atoms; R 3 and R 4 may be bonded to each other to form a ring. [2] The (meth)acrylic copolymer according to [1], further comprising a structural unit derived from a (meth)acrylic acid alkyl ester (b) having an alkyl group having 1 to 30 carbon atoms. [3] The (meth)acrylic copolymer according to [1] or [2], which has a structural unit derived from the macromonomer (M) and a structural unit derived from the first vinyl radical polymerizable monomer (m1). [4] The (meth)acrylic copolymer according to [3], wherein the macromonomer (M) has a number average molecular weight of 1,000 to 30,000. [5] The (meth)acrylic copolymer according to [3] or [4], wherein the macromonomer (M) contains, as a constituent unit, a constituent unit derived from a second vinyl radically polymerizable monomer (m2). [6] A pressure-sensitive adhesive composition containing the (meth)acrylic copolymer according to any one of [1] to [5]. [7] A pressure-sensitive adhesive obtained by crosslinking a pressure-sensitive adhesive composition containing the (meth)acrylic copolymer according to any one of [1] to [5]. [Effects of the Invention]

[0009] According to the present invention, there are provided a pressure-sensitive adhesive composition which can provide a pressure-sensitive adhesive having excellent adhesive strength and holding power, and a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] Several embodiments of the present invention will be described below, but these are representative examples of implementation and the present invention is not limited to these. Furthermore, the present invention can be implemented with any modifications within the scope of the gist thereof. The meanings of the terms are as follows: "(Meth)acrylate" is a general term for acrylate and methacrylate. The same applies to "(meth)acryloyl group," "(meth)acrylic acid," "(meth)acrylonitrile," and "(meth)acrylamide." "(Meth)acrylic copolymer" refers to a copolymer having structural units derived from (meth)acrylic monomers. (Meth)acrylic copolymers may also have structural units derived from monomers other than (meth)acrylic monomers (e.g., styrene). "(Meth)acrylic monomer" refers to a monomer having a (meth)acryloyl group. "Vinyl radically polymerizable monomer" refers to a compound having an ethylenically unsaturated bond (polymerizable carbon-carbon double bond). The "to" symbol indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. The number-average molecular weight and mass-average molecular weight of macromonomers and (meth)acrylic copolymers are molecular weights measured by gel permeation chromatography (GPC) using polystyrene as a standard.

[0011] [(Meth)acrylic copolymer] The (meth)acrylic copolymer of the present invention contains a structural unit derived from a monomer (a) (hereinafter also referred to as component (a)) represented by general formula (I). Furthermore, if necessary, it may contain a structural unit derived from (b) (hereinafter also referred to as component (b)) alkyl (meth)acrylate ester (also referred to as “alkyl (meth)acrylate”) having an alkyl group having 1 to 30 carbon atoms, and a structural unit derived from (c) (hereinafter also referred to as component (c)) (meth)acrylate compound other than the components (a) and (b). Furthermore, other than the components (a), (b), and (c), a structural unit derived from a vinyl radical polymerizable monomer (d) (hereinafter also referred to as component (d)) may be contained.

[0012] The (meth)acrylic copolymer is a block copolymer or a graft copolymer. A block copolymer is a copolymer having a plurality of segments each composed of a constituent unit derived from the same type of monomer, the constituent units of which have different chemical structures from one another, and the plurality of segments bonded in a linear chain. In a (meth)acrylic copolymer that is a block copolymer, it is preferred that some of the segments have a constituent unit derived from a macromonomer. A graft copolymer refers to a polymer in which a side chain polymer structure (branch polymer structure) is connected (graft polymerized) to a main chain polymer structure (trunk polymer structure). The main chain polymer and the side chain polymer structures may be different or the same. The side chain polymer structure of the graft copolymer is preferably a structural unit derived from a macromonomer.

[0013] <Monomer (a)> The component (a) has a structure represented by the following general formula (I): When irradiated with active energy rays, the component (a) is easily cleaved to generate radicals.

[0014] [ka]

[0015] In formula (I), R 1 is a hydrogen atom, a methyl group, or an ethyl group. Among these, a hydrogen atom or a methyl group is preferred, and a methyl group is particularly preferred. R 2 is an alkylene group having 1 to 2 carbon atoms or a linear or branched alkylene group having 3 to 5 carbon atoms, preferably an ethylene group, a propane-1,3-diyl group, a butane-1,3-diyl group or a butane-1,4-diyl group, more preferably an ethylene group. R 3 , R 4 R are each independently an alkyl group having 1 to 2 carbon atoms or a linear or branched alkyl group having 3 to 5 carbon atoms. 3 and R 4 may be bonded to each other to form a ring. 3 and R 4 The number of carbon atoms in the ring formed by R is preferably 5 to 8, and more preferably 6. 3 , R 4 , or R 3 and R 4 The cyclic group formed by R is preferably a methyl group, an ethyl group, or a cyclohexyl group, more preferably a methyl group. 3 and R 4 More preferably, all of are methyl groups. The component (a) may be used alone or in combination of two or more.

[0016] The content of component (a) is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 15% by mass or less, and even more preferably 0.1% by mass or more and 10% by mass or less, relative to 100% by mass of the total mass of the monomers constituting the (meth)acrylic copolymer, in order to improve the holding power.

[0017] <(Meth)acrylic acid alkyl ester (b) having an alkyl group having 1 to 30 carbon atoms> Component (b) does not include component (a). That is, component (b) has an alkyl group having 1 to 30 carbon atoms and does not have the structure represented by general formula (I). Component (b) has one (meth)acryloyl group. The alkyl group has 1 to 30 carbon atoms, preferably 1 to 13, and more preferably 1 to 8. The alkyl group may be linear, branched, or cyclic. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, s-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-undecyl (meth)acrylate, n-dodecyl (meth)acrylate, and Examples of the acrylate include tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, i-amyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, i-nonyl (meth)acrylate, i-decyl (meth)acrylate, 3-i-propylheptyl (meth)acrylate, i-undecyl (meth)acrylate, 2-t-butylheptyl (meth)acrylate, i-dodecyl (meth)acrylate, i-tridecyl (meth)acrylate, and i-tetradecyl (meth)acrylate.

[0018] Among the above, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, s-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, with methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate being more preferred, and methyl (meth)acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate being more preferred. One type of component (b) may be used alone, or two or more types may be used in combination.

[0019] The content of component (b) is preferably 30% by mass or more and 99.9% by mass or less, more preferably 40% by mass or more and 99.5% by mass or less, and even more preferably 50% by mass or more and 99.0% by mass or less, relative to 100% by mass of the total mass of the monomers constituting the (meth)acrylic copolymer, in order to obtain good adhesive strength.

[0020] <(c) (meth)acrylate compound other than components (a) and (b)> Component (c) has one (meth)acryloyl group. Examples of component (c) include alkyl (meth)acrylates having a carboxy group, such as 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, 2-(meth)acryloyloxyethyl phthalate, and 2-(meth)acryloyloxyethyl hexahydrophthalate; cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, and 4-t-butylcyclohexyl (meth)acrylate. ) acrylate, and other alkyl (meth)acrylates having a cyclic alkyl group; alkyl (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, ethylene glycol mono(meth)acrylate, and propylene glycol mono(meth)acrylate; phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, nonylphenoxypolyethylene glycol (meth)acrylate, phenoxypolypropylene glycol (meth)acrylate, phenylphenyl (meth)acrylate, phenylphenoxyethyl (meth)acrylate, phenoxybenzyl (meth)acrylate, and phenylbenzyl Alkyl (meth)acrylates having an aromatic ring structure, such as (meth)acrylate, naphthyl (meth)acrylate, and (1-naphthyl)methyl (meth)acrylate; alkyl (meth)acrylates having a heterocyclic structure, such as tetrahydrofurfuryl (meth)acrylate, glycidyl (meth)acrylate, and (meth)acryloylmorpholine; alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and butoxyethyl (meth)acrylate;Examples of such compounds include 4-(meth)acryloyloxybenzophenone, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 2-(meth)acryloyloxyethyl acid phosphate, trifluoroethyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and (meth)acrylamide. Two or more of these compounds may be used in combination.

[0021] <Other vinyl radical polymerizable monomers (d)> The (meth)acrylic copolymer may contain a structural unit derived from a vinyl radical-polymerizable monomer (d) other than components (a), (b), and (c). Component (d) has one ethylenically unsaturated bond. Examples of the component (d) include styrene, α-methylstyrene, pt-butylstyrene, vinyltoluene, vinyl acetate, and (meth)acrylic acid.

[0022] <Macromonomer (M)> The (meth)acrylic copolymer may contain a structural unit derived from a macromonomer (M) (hereinafter also referred to as the (M) component) and a structural unit derived from a first vinyl radical polymerizable monomer (m1) (hereinafter also referred to as the (m1) component).

[0023] Examples of the component (m1) include the compounds exemplified as the component (a), the component (b), and the component (d). In view of excellent radical polymerizability, it is preferable to contain a (meth)acrylate compound as the component (m1). In view of good adhesive strength, it is preferable to contain one or more compounds selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, n-octyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate as the component (m1). One type of the component (m1) may be used alone, or two or more types may be used in combination.

[0024] In order to increase adhesive strength, the content of the (m1) component is preferably 50% by mass or more and 99.9% by mass or less, more preferably 60% by mass or more and 99.5% by mass or less, and even more preferably 70% by mass or more and 99.0% by mass or less, relative to 100% by mass of the total mass of the monomers constituting the (meth)acrylic copolymer.

[0025] The macromonomer (M) is not particularly limited as long as it is a compound having a radical polymerizable group and a repeating structure. Examples include compounds in which the terminals of polyalkylsiloxane, polyisobutylene, or hydrogenated polybutadiene are modified with a vinyl radical polymerizable group, and compounds containing two or more structural units derived from a monomer (m2) (hereinafter also referred to as "component (m2)") having a second vinyl radical polymerizable group and having a radical polymerizable group at the terminal. From the perspective of high designability, compounds containing two or more structural units of component (m2) and having a radical polymerizable group at the terminal are preferred. Two or more types of macromonomer (M) may be used in combination.

[0026] Examples of the (m2) component include the compounds listed as the (a), (b), and (d) components. From the viewpoint of excellent radical polymerizability, it is preferable that the (m2) component contains a (meth)acrylate compound. Furthermore, from the viewpoint of good holding power, it is preferable that the (m2) component contains methyl (meth)acrylate. The (m2) component may be used alone or in combination of two or more types.

[0027] In order to increase the holding power, the content of the (M) component is preferably 0.1% by mass or more and 50% by mass or less, more preferably 0.5% by mass or more and 40% by mass or less, and even more preferably 1% by mass or more and 30% by mass or less, relative to 100% by mass of the total mass of the monomers constituting the (meth)acrylic copolymer.

[0028] From the viewpoint of radical polymerizability, the macromonomer (M) is preferably a compound represented by the following formula (II):

[0029] [ka]

[0030] (In the formula, X 1 ~X n-1 each independently represents a hydrogen atom, a methyl group, or CHOH; Y 1 ~Y n are each independently an X bonded to a vinyl group of a vinyl radical polymerizable monomer (m2) constituting the macromonomer (M). 1 ~X n-1 Z represents a terminal group, and n represents an integer of 2 to 10,000.

[0031] X 1 ~X n-1 and Y 1 ~Y n are each independently a substituent bonded to the vinyl group of component (m2). Y 1 ~Y n For example, OR 11 , halogen atoms, COR 12 , COOR 13 ,CN,CONR 14 R 15 , NHCOR 16 , or R 17 indicates R 11 ~R 17 each independently represents a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, or the like. The terminal group Z may be a hydrogen atom or a group derived from a radical polymerization initiator, similar to the terminal groups of polymers obtained by known radical polymerization.

[0032] The number average molecular weight (Mn) of the component (M) measured by GPC is preferably from 500 to 100,000, more preferably from 600 to 50,000, and even more preferably from 1,000 to 30,000, in order to achieve good retention. The component (M) may be produced by a known method or may be commercially available. Examples of methods for producing the component (M) include a method using a cobalt chain transfer agent (U.S. Pat. No. 4,680,352), a method using an α-substituted unsaturated compound such as α-bromomethylstyrene as a chain transfer agent (WO 88 / 04304), a method of chemically bonding a polymerizable group (JP-A No. 60-133007 and U.S. Pat. No. 5,147,952), and a method using thermal decomposition (JP-A No. 11-240854).

[0033] The method using a cobalt chain transfer agent is preferred in terms of the number of production steps and the use of a catalyst with a high chain transfer constant. Because the cobalt chain transfer agent has a high chain transfer constant, a macromonomer with a controlled molecular weight can be obtained by adding a small amount. As the cobalt chain transfer agent, a known cobalt complex can be used. The amount of the cobalt chain transfer agent is preferably 0.00001 to 0.1 parts by mass, more preferably 0.00005 to 0.05 parts by mass, and particularly preferably 0.0001 to 0.02 parts by mass, per 100 parts by mass of the component (m2).

[0034] <Physical properties of (meth)acrylic copolymer> The (meth)acrylic copolymer has a mass average molecular weight (Mw) measured by GPC of preferably 10,000 to 2,000,000, more preferably 50,000 to 1,500,000, and even more preferably 100,000 to 1,000,000, in order to improve compatibility with the (B) component and hot melt processability.

[0035] The glass transition temperature (Tg) of the (meth)acrylic copolymer is preferably 0° C. or lower, more preferably −5° C. or lower, even more preferably −10° C. or lower, and particularly preferably −15° C. or lower, in order to improve adhesive strength.

[0036] <Method of producing (meth)acrylic copolymer> The (meth)acrylic copolymer can be produced by a known method using a known polymerization initiator, such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, or an emulsion polymerization method, and among these, the solution polymerization method is preferred.

[0037] The polymerization initiator is preferably a radical polymerization initiator such as a peroxide or an azo compound.

[0038] Examples of the solvent for solution polymerization include organic solvents such as acetone, toluene, xylene, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, methyl isobutyl ketone, methyl ethyl ketone, ethyl acetate, n-butyl acetate, n-propyl acetate, i-propyl acetate, ethyl 3-ethoxypropionate, and isopropyl alcohol.

[0039] The (meth)acrylic copolymer may be a graft copolymer. There are no particular limitations on the method for producing the graft copolymer. Examples include a method in which a macromonomer having a radically polymerizable double bond at its terminal is produced as a side chain polymer structure, and then the macromonomer is radically polymerized with a monomer that will become a structural unit of the main chain polymer; a method in which a main chain polymer having a reactive site and a macromonomer having a reactive site are produced in advance, and then the two are reacted; and a method in which, after the main chain polymer is produced, a radical is generated on the main chain polymer using an initiator having hydrogen abstraction ability, and then a monomer that will become a structural unit of the side chain polymer is reacted with the main chain polymer to produce a side chain polymer structure.

[0040] [Adhesive composition / adhesive] The pressure-sensitive adhesive composition of the present invention contains the (meth)acrylic copolymer. The content of the (meth)acrylic copolymer in the pressure-sensitive adhesive composition is 50 to 100% by mass, preferably 60 to 99% by mass, based on the total pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition of the present invention may further contain other components, such as a photopolymerization initiator, a crosslinking agent, a tackifier, a solvent, a filler, an antioxidant, an ultraviolet absorber, a light stabilizer, a metal deactivator, an antioxidant, a moisture absorbent, a rust inhibitor, a hydrolysis inhibitor, and a reaction catalyst.

[0041] Examples of the photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-(2-hydroxyethoxy)phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-[4-{4-(2-hydroxy-2-methyl-propionyl)benzyl}phenyl]-2-methyl-propan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), phenylglyoxylyl Examples of the photopolymerization initiator include methyl acrylate, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3'-dimethyl-4-methoxybenzophenone, 4-(1,3-acryloyl-1,4,7,10,13-pentaoxotridecyl)benzophenone, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide. Each of the photopolymerization initiators may be used alone, or two or more may be mixed and used.

[0042] When the pressure-sensitive adhesive composition contains a photopolymerization initiator, the content thereof is preferably 0.1 to 2.0 mass %, more preferably 0.1 to 1.0 mass %, and even more preferably 0.1 to 0.5 mass %, relative to the total mass of the pressure-sensitive adhesive composition (excluding the mass of the solvent if a solvent is contained).

[0043] Examples of crosslinking agents include polyfunctional (meth)acrylates having two or more (meth)acryloyl groups. Examples of polyfunctional (meth)acrylates include ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, polybutylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, polycarbonate diol di(meth)acrylate, polyester diol di(meth)acrylate, bisphenol A ethylene oxide adduct di(meth)acrylate, bisphenol A dimethacrylate, bisphenol B dimethacrylate, bisphenol C dimethacrylate, bisphenol D dimethacrylate, bisphenol E dimethacrylate, bisphenol G dimethacrylate, bisphenol H ... Examples of suitable (meth)acrylates include difunctional (meth)acrylates such as propylene oxide adduct di(meth)acrylate, polyurethane di(meth)acrylate, and 9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene; trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, and ε-caprolactone-modified tris((meth)acryloxyethyl)isocyanurate; tetrafunctional (meth)acrylates such as ditrimethylolpropane tetra(meth)acrylate; pentafunctional (meth)acrylates such as dipentaerythritol penta(meth)acrylate; and hexafunctional (meth)acrylates such as dipentaerythritol hexa(meth)acrylate. Other examples include urethane (meth)acrylates having 2 to 6 (meth)acryloyl groups. These polyfunctional (meth)acrylates may be used alone or in combination of two or more.

[0044] When the pressure-sensitive adhesive composition contains a crosslinking agent, the content thereof is preferably 0.1 to 10.0 mass %, more preferably 0.1 to 5.0 mass %, and even more preferably 0.1 to 2.0 mass %, relative to the total mass of the pressure-sensitive adhesive composition (excluding the mass of the solvent if a solvent is contained).

[0045] Examples of tackifiers include rosin-based resins (rosin, rosin phenolic resin, rosin ester resin, disproportionated rosin ester resin, hydrogenated rosin ester resin, maleated rosin ester, polymerized rosin ester, etc.), terpene-based resins (terpene resin, terpene phenolic resin, hydrogenated terpene phenolic resin, aromatic modified terpene resin), petroleum resin, coumarone-indene resin, styrene resin, phenolic resin, xylene resin, etc.

[0046] When the pressure-sensitive adhesive composition contains a tackifier, the content thereof is preferably 1 to 30 mass %, more preferably 1 to 20 mass %, and even more preferably 1 to 10 mass %, relative to the total mass of the pressure-sensitive adhesive composition (excluding the mass of the solvent if a solvent is contained).

[0047] Examples of antioxidants include phenol-based, phosphorus-based, hydroxylamine-based, and sulfur-based antioxidants.

[0048] When the pressure-sensitive adhesive composition contains an antioxidant, the content thereof is preferably 0.1 to 3.0 mass %, more preferably 0.1 to 2.0 mass %, and even more preferably 0.1 to 1.0 mass %, relative to the total mass of the pressure-sensitive adhesive composition (excluding the mass of the solvent if a solvent is contained).

[0049] The pressure-sensitive adhesive composition of the present invention may be in the form of a liquid pressure-sensitive adhesive composition containing a solvent, or may be in the form of a hot-melt type pressure-sensitive adhesive composition containing no solvent. The pressure-sensitive adhesive composition of the present invention forms a crosslinked structure upon irradiation with active energy rays. For example, as shown in the following formulas (1) and (2), it is thought that irradiation with active energy rays causes cleavage at the terminals of the structural units derived from the monomer (a) to generate radicals, and the terminal radicals react between molecular chains to form a crosslinked structure (-C(=O)-C(=O)-) as shown in formula (3). Furthermore, when the pressure-sensitive adhesive composition further contains a crosslinking agent, it is thought that a series of reactions occur, for example, as shown in the following formulas (4) to (7), in which cleavage occurs at the terminal of the structural unit derived from monomer (a) to generate a radical, which reacts with the acryloyl group of the crosslinking agent to form a bond as shown in formula (8) (-C(=O)-CH2-CH2-C(=O)-).

[0050] [ka]

[0051] [ka]

[0052] As the active energy ray, ultraviolet rays are preferred from the viewpoint of versatility. Examples of sources of ultraviolet rays include xenon lamps, high-pressure mercury lamps, and metal halide lamps. The crosslinked and cured product of the pressure-sensitive adhesive composition can be used as a pressure-sensitive adhesive. For example, the pressure-sensitive adhesive composition can be applied to a substrate (e.g., a film, a tape, etc.) and crosslinked by irradiating with active energy rays to form a pressure-sensitive adhesive layer (a layer of the cured product). In this manner, a film with a pressure-sensitive adhesive layer, a tape with a pressure-sensitive adhesive layer, etc. can be produced.

[0053] The pressure-sensitive adhesive composition of the present invention contains a structural unit derived from monomer (a) represented by general formula (I) and a (meth)acrylic copolymer that is a block copolymer or a graft copolymer, thereby enabling the production of a pressure-sensitive adhesive with excellent adhesive strength and holding power. Block copolymers and graft copolymers are derived from a structure in which different copolymers are covalently bonded, forming a high-order structure called a microphase-separated structure in which each component is periodically arranged on the nanometer order. Because a microphase-separated structure is a weak structure formed by molecular self-assembly, it does not significantly impair the wettability required for adhesive strength. However, the formation of a microphase-separated structure makes the pressure-sensitive adhesive less susceptible to deformation than a disordered molecular state, which is thought to result in high holding power.

[0054] Preferred embodiments of the (meth)acrylic copolymer include the following embodiments (1) and (2). Aspect (1): A (meth)acrylic copolymer in which a side chain polymer derived from the (M) component is graft polymerized onto a main chain polymer structure obtained by polymerizing the (m1) component, wherein a structural unit of the (M) component has a structural unit derived from the (m2) component, and one or both of the (m1) component and the (m2) component contain the (a) component. In embodiment (1), when component (m1) contains component (a), a structural unit derived from component (a) is present in the structural units of the main chain polymer, and when component (m2) contains component (a), a structural unit derived from component (a) is present in the structural units of the side chain polymer. Aspect (2): A (meth)acrylic copolymer having a structure in which a segment consisting of two or more structural units derived from the same type of component (m1) and a segment consisting of two or more structural units derived from the same type of component (M) are bonded in a linear chain, wherein the structural units of the component (M) have structural units derived from the component (m2), and one or both of the component (m1) and the component (m2) contain the component (a).

[0055] The pressure-sensitive adhesive of the present invention can be suitably used for, for example, labels, stickers, adhesive tapes, films for vehicles, films for building materials, films for displays, optically clear adhesives (OCA), tapes for semiconductor manufacturing processes, and the like. [Example]

[0056] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the following, "parts" means "parts by mass." In each example, the following measurement methods were used.

[0057] (Measurement of number average molecular weight (Mn) of macromonomer) A 0.2% by mass solution of the macromonomer in tetrahydrofuran was prepared, and the number average molecular weight (Mn) was determined in terms of standard polystyrene under the following conditions. GPC equipment: Tosoh HLC-8320. Column: The following columns manufactured by Tosoh Corporation were connected in series. The guard column used was a Tosoh "TSKguardcolumn SuperHZ-L" (4.6 mm ID x 2.0 cm L). "TSKgel SuperHZM-M" (4.6mm ID x 15cm L) x 2 bottles. "TSKgel SuperHZ2000" (4.6mm ID x 15cm L) x 1 bottle. ·Injection volume: 10μL. Eluent: tetrahydrofuran (stabilizer BHT). ·Flow rate: 0.35mL / min. · Column temperature: 40℃.

[0058] (Measurement of mass average molecular weight (Mw) of (meth)acrylic copolymer) A tetrahydrofuran solution containing 0.27% by mass of the (meth)acrylic copolymer was prepared, and the weight average molecular weight (Mw) was determined in terms of standard polystyrene under the following conditions. GPC equipment: Tosoh HLC-8320. Column: Two columns, "TSKgel SuperHZM-H" (6.0 mm ID x 15 cm L) manufactured by Tosoh Corporation, were connected in series. The guard column was "TSKguardcolumn SuperHZ-H" (4.6 mm ID x 3.5 cm L) manufactured by Tosoh Corporation. ·Injection volume: 10μL. Eluent: tetrahydrofuran (stabilizer BHT). ·Flow rate: 0.5mL / min. · Column temperature: 40℃.

[0059] (Measurement of Tg of (meth)acrylic copolymer) The glass transition temperature (Tg) was measured using a differential scanning calorimeter (manufactured by Hitachi High-Tech Corporation, product name "NEXTA DSC200") at a heating rate of 10°C / min.

[0060] (Preparation of test specimens) The (meth)acrylic copolymer solution was applied to a 38 μm-thick PET film (substrate film) with an applicator so that the thickness after drying would be 50 μm, and the applied layer was dried at 90°C for 10 minutes to form an uncured pressure-sensitive adhesive layer. A 75 μm-thick release film (a silicone-treated PET film manufactured by Mitsubishi Chemical Corporation) was then laminated on top of the uncured pressure-sensitive adhesive layer. Using a UV irradiation device (I-Graphics, US5-X0402), a high-pressure mercury lamp was used to irradiate ultraviolet light from the release film side at an output of 160 W, thereby curing the adhesive layer. In this way, a test piece was obtained in which the base film and the release film were laminated via the adhesive layer. The irradiation energy was 2000 mJ / cm. 2 (Light meter: UV-351 manufactured by DRC)

[0061] (Glass adhesion measurement) The test piece obtained above was cut into a width of 1 cm, the release film was peeled off, and the piece was attached to a glass plate (manufactured by Matsunami Glass Industry Co., Ltd.) using a 3 kg hand roller. This was then treated in an oven at 40°C for 3 hours to finish the attachment, and a sample for measuring adhesive strength was prepared. The adhesive strength measurement samples were then pulled at an angle of 180° at a peeling speed of 300 mm / min at 23°C, and the adhesive layer was peeled off together with the PET film. The tensile strength (N / cm) was measured with a load cell and used as the adhesive strength to glass. Adhesive layer rupture during pulling was recorded as cohesive failure in Table 1.

[0062] (holding force measurement) The test specimen obtained above was cut to a width of 25 mm. The release film was peeled off at one end of the test specimen to expose the adhesive layer, and the specimen was attached to a 30 mm x 125 mm stainless steel (SUS304, surface BA finish) with a 3 kg hand roller so that the bonded surface was 25 mm x 25 mm. The specimen was then cured for 15 minutes in a constant temperature and humidity tester at 80°C and 35% humidity. Immediately after this, a SUS plate was placed so that a force was applied in the shear direction to the bonded surface, and a 1.0 kg load was applied with the other end of the test specimen facing downward. The time until the test specimen peeled off from the SUS plate was measured and recorded as the holding strength.

[0063] <Synthesis Example 1: Synthesis of Chain Transfer Agent (1)> In a synthesis apparatus equipped with a stirrer, 1.00 g of cobalt(II) acetate tetrahydrate, 1.93 g of diphenylglyoxime, and 80 mL of diethyl ether previously deoxygenated by nitrogen bubbling were placed under a nitrogen atmosphere and stirred at room temperature for 30 minutes. Next, 10 mL of boron trifluoride diethyl ether complex was added and stirred for an additional 6 hours. The mixture was filtered, and the solid was washed with diethyl ether and dried in vacuo for 15 hours to obtain 2.12 g of chain transfer agent (1) as a reddish-brown solid.

[0064] <Synthesis Example 2: Synthesis of Dispersant (1)> A polymerization reactor equipped with a stirrer, a condenser, a thermometer, and a nitrogen gas inlet tube was charged with 900 parts of deionized water, 60 parts of 2-sulfoethyl sodium methacrylate, 10 parts of potassium methacrylate, and 12 parts of methyl methacrylate (MMA). The contents were stirred and purged with nitrogen. The temperature was raised to 50°C. 0.08 parts of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was added as a polymerization initiator, and the temperature was further raised to 60°C. After the temperature was raised, MMA was continuously added dropwise at a rate of 0.24 parts / min for 75 minutes using a dropping pump. The reaction solution was maintained at 60°C for 6 hours and then cooled to room temperature to obtain a transparent aqueous solution of dispersant (1) with a solids content of 10% by mass.

[0065] <Synthesis Example 2: Synthesis of HHMPMA> In this example, the component (a) is 2-[4-(2-hydroxy-2-methyl-1-oxopropyl)phenoxy]ethyl methacrylate (R 1 is a methyl group, R 2 is an alkylene group having 2 carbon atoms, R 3 is a methyl group, R 4 We synthesized a compound in which methyl group is used (hereinafter also referred to as HHMPMA). Methacrylic anhydride (manufactured by Tokyo Chemical Industry Co., Ltd.) was distilled under reduced pressure, and fractions with a purity of 99.8% or higher were collected to obtain a distillate of methacrylic anhydride. The distillation was carried out at a pressure of 30 Pa and gradually increasing the temperature from room temperature to 90°C. Separately, 22.4 g (0.1 mol) of 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxymethylpropanone (manufactured by Tokyo Chemical Industry Co., Ltd.) and 30.4 g (0.3 mol) of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in 500 mL of methylene chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) To this solution, 23.1 g (0.15 mol) of the above distillate of methacrylic anhydride was added dropwise at room temperature, and the mixture was stirred for 12 hours. The resulting reaction solution was washed three times with 500 mL of ion-exchanged water, and then the organic phase was concentrated to remove the solvent. The residue was purified by column chromatography (ethyl acetate / hexane = 10 / 90 (volume ratio)) to obtain 21.6 g of the target compound (yield 74%). 1 H-NMR analysis confirmed that the compound obtained was 2-[4-(2-hydroxy-2-methyl-1-oxopropyl)phenoxy]ethyl methacrylate. 1 H-NMR (300MHz, chloroform-d): δ8.06(d,J=9.0Hz,2H),6.96(d,J=9.0Hz,2H),6.13(d,J=0.6Hz,1H),5. 59(s,1H),4.50(d,J=5.1Hz,2H),4.29(dd,J=5.5,4.1Hz,3H),1.94(dd,J=1.6,1.0Hz,3H),1.61(s,6H).

[0066] <Production Example 1> In this example, the macromonomer (1) was synthesized using methyl methacrylate (MMA) as the component (m2) constituting the macromonomer (M). In a polymerization apparatus equipped with a stirrer, a condenser, and a thermometer, 145 parts of deionized water, 0.1 parts of sodium sulfate, and 0.25 parts of dispersant (1) (solid content 10% by mass) were added and stirred to form a uniform aqueous solution. Next, 100 parts of MMA, 0.0035 parts of chain transfer agent (1), and 0.35 parts of Perocta O (manufactured by NOF Corporation) as a polymerization initiator were added to form an aqueous suspension. The atmosphere inside the polymerization apparatus was then purged with nitrogen, the temperature was raised to 80°C, and the reaction was carried out for 1 hour. To further increase the polymerization rate, the temperature was raised to 90°C and maintained for 1 hour. The reaction solution was then cooled to 40°C to obtain an aqueous suspension containing the macromonomer. This aqueous suspension was filtered, and the filtrate was washed with deionized water, dehydrated, and dried at 40°C for 16 hours to obtain macromonomer (1).

[0067] <Production Example 2> In this example, a macromonomer (2) was synthesized using HHMPMA obtained in Synthesis Example 2 and MMA as the component (m2) constituting the macromonomer (M). A four-neck flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet was charged with 80 parts of MMA, 20 parts of HHMPMA, 0.002 parts of chain transfer agent (1), and 58 parts of ethyl acetate. The oxygen was replaced by nitrogen bubbling. Next, 0.4 parts of 2,2'-azobis(2-methylbutyronitrile) (Otsuka Chemical Co., Ltd.) as a polymerization initiator and 2 parts of ethyl acetate were added. The external temperature was then raised to 90°C in a water bath, and the mixture was allowed to react under reflux for 2 hours. Next, 0.2 parts of 2,2'-azobis(2-methylbutyronitrile) and 10 parts of ethyl acetate were added dropwise over 1 hour, and the mixture was then maintained under reflux for another 2 hours. The reaction mixture was then cooled to 40°C, and ethyl acetate was added to obtain an ethyl acetate solution containing 40% by mass of macromonomer (2).

[0068] Example 1 In this example, a graft copolymer was produced by polymerizing the component (m1) with the macromonomer (1) obtained in Production Example 1. As the component (m1), n-butyl acrylate (nBA) and HHMPMA obtained in Synthesis Example 2 were used. A four-neck flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet was charged with 40 parts of ethyl acetate and 1.2 parts of isopropyl alcohol. The external temperature was raised to 85°C in a water bath under nitrogen gas flow. After the reflux condition stabilized, a mixture consisting of 30 parts of ethyl acetate, 94 parts of nBA, 1 part of HHMPMA, 5 parts of macromonomer (1), and 0.13 parts of Niper BK40MT (manufactured by NOF Corporation) as a chain transfer agent was added dropwise over 4 hours. Two more parts of ethyl acetate were then added dropwise. After holding for 1 hour, a mixture consisting of 0.3 parts of Perocta O (manufactured by NOF Corporation) as a polymerization initiator and 15 parts of ethyl acetate was added over 30 minutes. After holding for 2 hours, 0.3 parts of "Irganox 1010" (BASF product name) as an antioxidant and 34.8 parts of ethyl acetate were added, and the mixture was cooled to room temperature to obtain a (meth)acrylic copolymer. The obtained (meth)acrylic copolymer was used to prepare test pieces by the above-mentioned method, and the adhesive strength and holding power were evaluated. The results are shown in Table 1.

[0069] <Comparative Examples 1 and 2> Except for changing the types and composition ratios of the monomers and macromonomers used as shown in Table 1 and adjusting the ratio of ethyl acetate to isopropyl alcohol initially charged, (meth)acrylic copolymers were produced in the same manner as in Example 1, test pieces were prepared, and evaluations of adhesive strength and holding power were carried out. The results are shown in Table 1. In Comparative Example 1, a graft copolymer not containing component (a) was produced by polymerizing component (m1), which was the same as in Example 1 but replaced with 4-methacryloyloxybenzophenone (4MBP), with the macromonomer (1) obtained in Production Example 1. In Comparative Example 2, the components (a) and (b) were polymerized to produce a random copolymer.

[0070] [Table 1]

[0071] As shown in the results in Table 1, a pressure-sensitive adhesive having excellent adhesive strength and holding power was obtained in Example 1. Comparative Example 1, which did not contain component (a), had low adhesive strength. Furthermore, Comparative Example 2, which was not a block copolymer or graft copolymer, had low holding power.

Claims

1. A (meth)acrylic copolymer which contains a structural unit derived from a monomer (a) represented by general formula (I) and is a block copolymer or a graft copolymer. 【Chemistry 1】 [In the formula, R １ represents a hydrogen atom, a methyl group, or an ethyl group; R ２ represents an alkylene group having 1 to 2 carbon atoms or a linear or branched alkylene group having 3 to 5 carbon atoms; R ３ , R ４ each independently represents an alkyl group having 1 to 2 carbon atoms or a linear or branched alkyl group having 3 to 5 carbon atoms; R ３ and R ４ may be bonded to each other to form a ring.

2. The (meth)acrylic copolymer according to claim 1, further comprising a structural unit derived from a (meth)acrylic acid alkyl ester (b) having an alkyl group having 1 to 30 carbon atoms.

3. The (meth)acrylic copolymer according to claim 1 , further comprising a structural unit derived from a macromonomer (M) and a structural unit derived from a first vinyl radically polymerizable monomer (m1).

4. The (meth)acrylic copolymer according to claim 3, wherein the macromonomer (M) has a number average molecular weight of 1,000 to 30,000.

5. The (meth)acrylic copolymer according to claim 3 , wherein the macromonomer (M) contains, as a constituent unit, a constituent unit derived from a second vinyl radically polymerizable monomer (m2).

6. A pressure-sensitive adhesive composition comprising the (meth)acrylic copolymer according to any one of claims 1 to 5.

7. A pressure-sensitive adhesive obtained by crosslinking a pressure-sensitive adhesive composition containing the (meth)acrylic copolymer according to any one of claims 1 to 5.

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