KR20190036527A - (Meth) acrylic triblock copolymer and a process for producing the same, a pressure-sensitive adhesive composition, and a pressure- - Google Patents

Abstract

[assignment]
(Meth) acrylic block copolymer, the adhesive properties to various adherends are further improved.
[Solution]
(Meth) acrylic triblock copolymer (A) obtained by RAFT polymerization using RAFT agent represented by the formula (a1). [In the formula (a1), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group, and two R groups may be the same or different.]

Description

(Meth) acrylic triblock copolymer and a process for producing the same, a pressure-sensitive adhesive composition, and a pressure-

The present invention relates to a (meth) acrylic triblock copolymer, a process for producing the same, a pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet.

In the field of pressure-sensitive adhesives, a pressure-sensitive adhesive composition having good adhesive properties to a holding force, a tack, and the like is required. Patent Documents 1 to 4 disclose a pressure-sensitive adhesive composition containing a (meth) acrylic block copolymer obtained by living radical polymerization. In particular, Patent Document 1 discloses a pressure-sensitive adhesive composition containing a (meth) acrylic block copolymer obtained by RAFT polymerization using a reversible addition-cleaving chain transfer (RAFT) agent. However, the pressure-sensitive adhesive composition containing such a block copolymer needs further improvement in terms of adhesive properties to various adherends.

Japanese Patent Laid-Open Publication No. 2014-208762 Japanese Patent Publication No. 10-008013 Japanese Patent Application Laid-Open No. 2001-348553 Japanese Patent Application Laid-Open No. 2016-023237

An object of the present invention is to further improve the adhesive properties to various adherends for a pressure-sensitive adhesive composition containing a (meth) acrylic block copolymer.

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above problems. As a result, it has been found that the above problems can be solved by the (meth) acrylic triblock copolymer having the following constitution, and the present invention has been accomplished.

The present invention is, for example, the following [1] to [11].

[1] A (meth) acrylic triblock copolymer (A) obtained by RAFT polymerization using a RAFT agent represented by the formula (a1).

[In the formula (a1), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group, and two R groups may be the same or different.]

[2] The (meth) acrylic triblock copolymer (A) according to the above [1], wherein R in the formula (a1) is a hydrocarbon group, an acyl group, an acyloxy group or an acyloxyalkyl group.

[3] The (meth) acrylic tri-block copolymer according to [1] or [2], which has a weight average molecular weight (Mw) measured by GPC of 30,000 to 600,000 and a molecular weight distribution (Mw / Mn) Coalescence (A).

[4] Block A-block B-A block having a tri-block structure of block A, wherein the block B has a bivalent structure represented by -SC (= S) -S-, (Meth) acrylic triblock copolymer (A) according to any one of the above [1] to [3], wherein the total content of the block A is 5 to 40 mass% and the content of the block B is 95 to 60 mass%.

[5] The positive resist composition according to any one of [1] to [5], wherein the content of the structural unit derived from the reactive functional group-containing monomer is 0.5 to 15% by mass and the 95% by mass or more of the total structural units derived from the reactive functional group- (Meth) acrylic triblock copolymer (A) according to the above-mentioned [4].

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

[7] The pressure-sensitive adhesive composition according to the above-mentioned [6], further comprising a curing agent (B).

[8] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to [6] or [7].

[9] A method for producing a polymerizable double bond-containing monomer, comprising the steps of: (1) polymerizing a polymerizable double bond-containing monomer using the RAFT agent represented by the formula (a1) (Meth) acrylic triblock copolymer (A) containing one or both of the above-mentioned monomers used in step 1 and the above-mentioned monomers to be added in step 2 is a (meth) acrylic acid ester ).

[10] The process for producing a (meth) acrylic triblock copolymer (A) according to the above [9], wherein the polymer obtained in the step 1 has a weight average molecular weight (Mw) measured by GPC method of 3,000 to 40,000.

[11] A process for producing a (meth) acrylic tri-block copolymer (1) as described in the above [9] or [10], wherein 95% by mass or more of the above monomers in 100% by mass of the reactive functional group- (A).

According to the present invention, it is possible to provide a pressure-sensitive adhesive composition having excellent adhesive properties to various adherends, and to provide a (meth) acrylic triblock copolymer suitable as a component contained in the composition.

Hereinafter, the (meth) acrylic triblock copolymer of the present invention, the production method thereof, the pressure-sensitive adhesive composition, and the pressure-sensitive adhesive sheet will be described in detail, including a preferred embodiment.

In the present specification, the term " polymer " is used to mean a homopolymer and a copolymer, and the term " polymerization " is used to mean homopolymerization and copolymerization. Further, acrylic and methacrylic are collectively referred to as " (meth) acrylic ".

In the present specification, a copolymer having at least a constituent unit derived from a (meth) acrylic acid ester is also referred to as a " (meth) acrylic copolymer ". In the copolymer, 70 mass % Or more is preferably a (meth) acrylic acid ester.

In the present specification, the reversible adduct cleavage chain transfer is also referred to as " RAFT ".

[( Meta ) Acrylic try  Block Copolymer (A)]

The (meth) acrylic triblock copolymer (A) of the present invention is obtained by RAFT polymerization using the RAFT agent represented by the formula (a1), specifically, RAFT polymerization of a polymerizable double bond-containing monomer containing at least a (meth) Lt; / RTI >

In formula (a1), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group. The two Rs may be the same or different, and preferably the same group in terms of synthesis.

The resulting copolymer does not have the above-mentioned functional groups at the molecular end derived from the RAFT agent, since R does not have the above-mentioned functional groups (hydroxyl group, carboxyl group and amino group).

As the monovalent organic group for example an alkyl group, an aryl group, an aralkyl group such as a hydrocarbon ^{group, R 1 -C (= O)} - represented by the group O, R ¹ -C (= O) acyl represented by -O- And an acyloxyalkyl group represented by R < ^{1 >} -C (= O) -OR < ² > -. R ¹ is an alkyl group, and R ² is an alkylene group. Of these, the RAFT agent tends to be a liquid at room temperature, and therefore has excellent handling properties. However, acyl group, acyloxy group and acyloxyalkyl group are preferable because excellent adhesion properties to various adherends having high or low polarity can be obtained Do.

Specific examples of each group in the monovalent organic group are as follows. The number of carbon atoms in the alkyl group is usually 1 to 12, preferably 1 to 6, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group and a hexyl group. The carbon number of the aryl group is usually 6 to 18, preferably 6 to 12, and examples thereof include a phenyl group and a naphthyl group. The carbon number of the aralkyl group is usually 7 to 18, preferably 7 to 12, and examples thereof include a benzyl group and a phenethyl group. The acyl group and the acyloxy group usually have 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms, and examples thereof include an acetyl group and an acetyloxy group. The number of carbon atoms of the acyloxyalkyl group is usually 3 to 8, preferably 3 to 6, and examples thereof include acetyloxymethyl group.

Examples of the RAFT agent represented by the formula (a1) include the following compounds.

The RAFT agent has a trithiocarbonate structure in the molecule, and does not have a hydroxyl group, a carboxyl group and an amino group in the R. The RAFT agent can be synthesized according to the method described in, for example, Japanese Patent Application Laid-Open No. 2007-230947.

The copolymer (A) preferably has a tri-block structure of the block A-block B-block A. Wherein the block B has a bivalent structure represented by -S-C (= S) -S-. In such a case, for example, it is possible to form a sea-island structure, a gyroid structure or a cylinder structure in which the block A becomes an island and the block B becomes a sea, and a cohesive force .

The total content of the block A in 100 mass% of the copolymer (A) is preferably 5 to 40 mass%, more preferably 10 to 30 mass%, and the content of the block B is preferably 95 to 60 mass% And preferably 90 to 70 mass%.

The content of the structural unit derived from the reactive functional group-containing monomer in the 100% by mass of the total constituent units of the copolymer (A) is preferably 0.5 to 15% by mass, more preferably 0.8 to 12% by mass, 10% by mass. The constituent unit amount can be calculated from, for example, the amount of each monomer used and the residual amount of each monomer based on gas chromatographic analysis of the polymer solution after polymerization. In such a case, the pressure-sensitive adhesive is preferable because it can take a proper cross-linking form and is excellent in various adhesive properties. The total constituent unit of the copolymer (A) is the entire constituent unit derived from the raw material monomer.

In the copolymer (A), 95% by mass or more of the 100% by mass of all the structural units derived from the reactive functional group-containing monomer is preferably present in the block A, more preferably 98% by mass or more. In such a case, since the reactive functional group is localized in the block A, the curing is quick and the aging period of the pressure-sensitive adhesive composition can be shortened.

The copolymer (A) is represented by the following formula, for example.

(Wherein R is the same as that in formula (a1), and Ap is independently a divalent group derived from the polymer of the polymerizable double bond-containing monomer (polymer chain of the polymerizable double bond-containing monomer), and Bp Are each independently a divalent group derived from the polymer of the polymerizable double bond-containing monomer (polymer chain of the polymerizable double bond-containing monomer).

In the above formula, Ap corresponds to the above-described block A, and -Bp-S-C (= S) -S-Bp- corresponds to the above-described block B. At least one block of blocks A and B preferably also has a block-derived constituent unit derived from a (meth) acrylic acid ester.

By using the copolymer (A) of the present invention, it is possible to obtain a pressure-sensitive adhesive composition having good adhesion properties (e.g., retention force, tack) to various adherends such as high polarity materials and polyolefin low polarity materials.

" Polymerizable  Double bond containing monomer "

The raw material monomer of the copolymer (A) is a polymerizable double bond-containing monomer containing at least a (meth) acrylic acid ester. Examples of the polymerizable double bond-containing monomer include (meth) acrylic acid ester having no reactive functional group, a monomer having at least one of the following reactive functional groups (hereinafter also referred to as "reactive functional group-containing monomer"), Monomers. Examples of the reactive functional group include an acid group, a hydroxyl group, an amino group, an amide group, a cyano group, and a nitrogen-based heterocyclic ring.

Examples of the (meth) acrylate ester having no reactive functional group include alkyl (meth) acrylates, alkoxyalkyl (meth) acrylates, alkoxypolyalkyleneglycolmono (meth) acrylates, alicyclic groups, Metha) acrylate.

The alkyl group in the alkyl (meth) acrylate preferably has 1 to 20 carbon atoms. Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl Octyl (meth) acrylate, iso-octyl (meth) acrylate, nonyl (meth) acrylate, iso-nonyl (meth) acrylate, decyl (Meth) acrylate, stearyl (meth) acrylate and isostearyl (meth) acrylate.

Examples of the alkoxyalkyl (meth) acrylate include methoxymethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3- Acrylate, 3-ethoxypropyl (meth) acrylate, 4-methoxybutyl (meth) acrylate and 4-ethoxybutyl (meth) acrylate.

Examples of the alkoxypolyalkylene glycol mono (meth) acrylate include methoxy diethylene glycol mono (meth) acrylate, methoxy dipropylene glycol mono (meth) acrylate, ethoxy triethylene glycol (Meth) acrylate, methoxy (meth) acrylate, ethoxy diethylene glycol mono (meth) acrylate, and methoxy triethylene glycol mono (meth) acrylate.

Examples of the alicyclic group or aromatic ring-containing (meth) acrylate include cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl , Benzyl (meth) acrylate, and phenyl (meth) acrylate.

The (meth) acrylic acid esters may be used singly or in combination of two or more.

The amount of the (meth) acrylic ester having no reactive functional group is usually 70 mass% or more, preferably 80 mass% or more, more preferably 80 mass% or more, in 100 mass% of the total polymerizable double bond- Is at least 90 mass%.

Examples of the reactive functional group-containing monomer include acid group-containing monomers, hydroxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, cyano group-containing monomers and nitrogen-containing heterocyclic groups-containing monomers.

Examples of the acid group in the acid group-containing monomer include a carboxyl group, an acid anhydride group, a phosphoric acid group and a sulfuric acid group. Examples of the acid group-containing monomer include (meth) acrylic acid? -Carboxyethyl, (meth) acrylic acid 5-carboxypentyl, succinic acid mono (meth) acryloyloxyethyl ester,? -Carboxypolycaprolactone mono Containing unsaturated carboxylic acids such as (meth) acrylate, (meth) acrylic acid, itaconic acid, crotonic acid, fumaric acid and maleic acid; Monomers containing acid anhydride groups such as maleic anhydride; Monomers containing phosphoric acid groups such as (meth) acrylic monomers having a phosphoric acid group in the side chain; And (meth) acrylic monomers having a sulfate group in the side chain.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (Meth) acrylate, and 8-hydroxyoctyl (meth) acrylate.

Examples of the amino group-containing monomer include amino group-containing (meth) acrylates such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate.

Examples of the amide group-containing monomer include (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N-hexyl (Meth) acrylic amide. Examples of the cyano group-containing monomer include cyano (meth) acrylate and (meth) acrylonitrile. Examples of the nitrogen-containing heterocyclic ring-containing monomer include vinyl pyrrolidone, (meth) acryloylmorpholine, and vinyl caprolactam.

Among the reactive functional group-containing monomers, at least one member selected from a carboxyl group-containing monomer and a hydroxyl group-containing monomer is preferable from the viewpoint of the crosslinking reactivity with the crosslinking agent (B1) described later.

The reactive functional group-containing monomers may be used alone or in combination of two or more.

The amount of the reactive functional group-containing monomer to be used is usually 0.5 to 15% by mass, preferably 0.8 to 12% by mass, and more preferably 1 to 10% by mass, based on 100% by mass of the entire polymerizable double bond-containing monomer. When at least one kind selected from a carboxyl group-containing monomer and a hydroxyl group-containing monomer is used, the total amount thereof is preferably in the above range.

Examples of the copolymerizable monomer include styrene-based monomers and vinyl-based monomers. Examples of the styrene-based monomer include styrene,? -Methylstyrene; Alkylstyrene such as methylstyrene, dimethylstyrene and octylstyrene; Halogenated styrene such as fluorostyrene, chlorostyrene and bromostyrene; Other examples include nitrostyrene, acetylstyrene, and methoxystyrene. The vinyl-based monomer includes, for example, vinyl acetate.

The copolymerizable monomers may be used singly or in combination of two or more.

" RAFT "

In the RAFT polymerization, the polymerizable double bond-containing monomer is polymerized in the presence of the RAFT agent represented by the formula (a1). The amount of the RAFT agent represented by formula (a1) is usually 0.05 to 20 parts by mass, preferably 0.05 to 10 parts by mass, based on 100 parts by mass of the total amount of the polymerizable double bond-containing monomers. In such a case, reaction control is easy, and it is easy to adjust the weight average molecular weight of the resulting copolymer to the range described below.

"polymerization Initiator "

The RAFT polymerization is preferably carried out in the presence of a polymerization initiator. Examples of the polymerization initiator include conventional organic polymerization initiators. Specific examples thereof include azo compounds such as peroxides such as benzoyl peroxide and lauroyl peroxide, and 2,2'-azobisisobutyronitrile . Of these, azo compounds are preferred.

Examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azo Azo compounds such as bis (2-cyclopropylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2-methylbutyronitrile) Azobis (cyclohexane-1-carbonitrile), 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, Azo compounds such as 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutylamidine) Amide) dihydrate, 4,4'-azobis (4-cyanopentophosphoric acid), 2,2'-azobis (2 -cyanopropanol), dimethyl-2,2'-azobis Propionate) and 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide].

The polymerization initiator may be used alone or in combination of two or more.

The amount of the polymerization initiator to be used is usually 0.001 to 2 parts by mass, preferably 0.002 to 1 part by mass based on 100 parts by mass of the total amount of the polymerizable double bonds-containing monomers. In such a case, it is easy to adjust the weight average molecular weight of the resulting copolymer to the range described later.

The term "polymerization solvent"

The RAFT polymerization may be a bulk polymerization without using a polymerization solvent. In the RAFT polymerization, a polymerization solvent may be used if necessary.

Examples of the polymerization solvent include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; Alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane and cyclooctane; Halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,2-dichloroethane and chlorobenzene; Ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenyl ethyl ether, diphenyl ether; Esters such as ethyl acetate, propyl acetate, butyl acetate and methyl propionate; Ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and cyclohexanone; Amides such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone; Nitriles such as acetonitrile and benzonitrile; Dimethyl sulfoxide, sulfolane, and the like.

The polymerization solvent may be used alone or in combination of two or more.

&Quot; Polymerization conditions &

The process for producing the copolymer (A) of the present invention comprises a step 1 (first RAFT polymerization) of polymerizing a polymerizable double bond-containing monomer using the RAFT agent represented by formula (a1) And a step 2 (second RAFT polymerization) in which the resultant polymer is further polymerized by further adding a polymerizable double bond-containing monomer different from the monomer composition in Step 1. It is preferable that one or both of the monomer used in Step 1 and the monomer added in Step 2 include a (meth) acrylic acid ester, and all of them contain a (meth) acrylic acid ester.

The polymerizable double bond-containing monomer which is different from the monomer composition in the step 1 is a monomer composition in which the monomer composition to be added in the step 2 is different from the monomer composition used in the step 1, The same shall apply). For example, the monomer used in Step 1 and the monomer added in Step 2 may be included. In addition, even if the used monomer in Step 1 and the added monomer in Step 2 are the same, plural kinds of monomers are used and added, and the ratio in the used monomer in Step 1 (e.g., methyl acrylate 90 wt% Rate 10 wt%) and the ratio in the added monomer in Step 2 (e.g., methyl acrylate 10 wt%, butylacrylate 90 wt%).

In the RAFT polymerization, polymerization is carried out by reacting between the sulfur atom in the RAFT agent represented by the formula (a1) and the methylene group adjacent to the sulfur atom, so that the polymerizable double bond-containing monomer as the raw material monomer is inserted.

The reaction temperature in the RAFT polymerization method is usually 60 to 120 ° C, preferably 70 to 110 ° C, and is usually conducted in an inert gas atmosphere such as nitrogen gas. This reaction can be carried out under atmospheric pressure, under pressure, and under reduced pressure, and is usually conducted at normal pressure. The reaction time is usually 1 to 20 hours, preferably 2 to 14 hours. These conditions can be applied to steps 1 and 2, respectively. The polymerization conditions can be found, for example, in Japanese Patent Application Laid-Open Nos. 2007-230947 and 2011-52057.

The weight average molecular weight (Mw) of the polymer obtained in the step 1 is preferably from 3,000 to 40,000, more preferably from 5,000 to 38,000, and still more preferably from 8,000 to 36,000, as measured by the GPC method.

In addition, it is preferable that 95% by mass or more, particularly preferably 98% by mass or more, of the reactive functional group-containing monomer in 100% by mass of the reactive functional group-containing monomer which can be used in Step 1 and Step 2 is used in Step 1. In such a case, since the reactive functional group is localized in the block A, the curing is quick and the aging period of the pressure-sensitive adhesive composition can be shortened.

The ratio of the monomers used in the step 1 and the step 2 is not particularly limited and is suitably set according to the ratio of the block A and the block B in the target copolymer (A), for example. For example, the amount of the polymerizable double bond-containing monomer added in Step 2 to 100 parts by mass of the polymer obtained in Step 1 is preferably 150 to 1900 parts by mass, and more preferably 233 to 900 parts by mass.

[Physical Properties of Copolymer (A)] [

The weight average molecular weight (Mw) of the copolymer (A) measured by a gel permeation chromatography (GPC) method is preferably 30,000 to 600,000, more preferably 50,000 to 550,000, and still more preferably 80,000 to 500,000 to be. Such a structure is preferable from the viewpoint of improvement in durability under high temperature and high humidity conditions because of high cohesive strength given to the pressure-sensitive adhesive composition.

The molecular weight distribution (Mw / Mn) of the copolymer (A) is preferably 1.5 to 5.0, more preferably 1.5 to 4.8, and further preferably 1.7 to 4.5. In such a case, the obtained crosslinked product and / or the cured product is excellent in heat resistance, and the contamination of the adherend at the peeling of the adhesive sheet can be suppressed.

The molecular weight and the molecular weight distribution can be measured under the conditions described in the examples.

The glass transition temperature (Tg) of the copolymer (A) is preferably less than 0 占 폚, more preferably -70 to -20 占 폚, and still more preferably -60 to -30 占 폚. When the Tg is within the above range, it is preferable from the viewpoint of adhesion to the adherend of the pressure-sensitive adhesive layer. On the other hand, when the Tg is not less than the lower limit, the cohesive force of the pressure-sensitive adhesive layer is excellent and it is preferable from the viewpoint of improvement of durability. The Tg of the copolymer (A) can be calculated from, for example, the Tg of the homopolymer of each monomer and the Fox equation. The Tg of the homopolymer of each monomer can be, for example, a value described in Polymer Handbook Fourth Edition (Wiley-Interscience 2003).

In one embodiment, the Tg of block A is preferably -30 to 150 캜, more preferably -20 to 120 캜, and the Tg of block B is preferably -80 to -40 캜, Is -75 to -50 < 0 > C. The Tg of each block can also be calculated from the Tg of the homopolymer of each monomer and the Fox equation, for example.

For the monomers for which Tg is not described in the above document, the Tg of the homopolymer synthesized under the following conditions is measured under the following conditions, for example. 100 parts by mass of a monomer and 100 parts by mass of an ethyl acetate solvent are placed in a reactor equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet tube, and the temperature is raised to 80 DEG C while nitrogen gas is introduced. Subsequently, 0.1 part by mass of 2,2'-azobisisobutyronitrile was added, and the polymerization reaction was carried out at 80 ° C for 6 hours in a nitrogen gas atmosphere. The obtained homopolymer is sealed in a simple sealed fan. The temperature change was measured at a rate of 10 ° C / min under a nitrogen gas flow using a differential scanning calorimeter (DSC) to measure the heat change. A graph of "heat absorbing heat" and "temperature" was plotted, . Tg is the value obtained by the midpoint method from the DSC curve.

[Pressure sensitive adhesive composition]

The pressure-sensitive adhesive composition of the present invention contains the above-mentioned (meth) acrylic triblock copolymer (A). It is preferable that the pressure-sensitive adhesive composition of the present invention further contains a curing agent (B), depending on the application.

[( Meta ) Acrylic try  Block Copolymer (A)]

The content of the (meth) acrylic triblock copolymer (A) in the pressure-sensitive adhesive composition is usually 60 mass% or more, preferably 65 mass% or more, and more preferably 70 mass% or more, in 100 mass% of the solid content of the pressure-sensitive adhesive composition. Further, the upper limit value of the content of the copolymer (A) may be 100% by mass, and in the case where other components are also included in the solid content, it is determined by the contents of other components. Such a solar cell is preferable in that it can arbitrarily adjust various adhesive properties such as holding power and tack. Solids usually refer to components other than solvents.

[Curing agent (B)]

The pressure-sensitive adhesive composition of the present invention preferably further contains a curing agent (B). The crosslinked product and / or the cured product can be formed by crosslinking the copolymer (A) with the curing agent (B) and / or by curing the composition, and a pressure-sensitive adhesive layer excellent in heat resistance can be obtained.

The pressure-sensitive adhesive composition of the present invention may be either a thermosetting system or an active energy ray curing system.

The kind of the curing agent (B) is appropriately selected by the curing system of the reactive functional group and the pressure-sensitive adhesive composition which can be introduced into the copolymer (A). For example, when the acrylic copolymer (A) has a reactive functional group, a crosslinking agent (B1) capable of undergoing a crosslinking reaction with the functional group such as an isocyanate compound, an epoxy compound or a metal chelate compound can be used. As the curing agent (B), for example, polyfunctional (meth) acrylate (B2) may also be used.

As the isocyanate compound, an isocyanate compound having two or more isocyanate groups in one molecule is usually used, and the number of isocyanate groups is preferably 2 to 8, more preferably 3 to 6 . When the number of isocyanate groups is in the above range, the crosslinking reaction efficiency between the copolymer (A) and the isocyanate compound is preferable and flexibility of the pressure-sensitive adhesive layer is maintained.

Examples of the diisocyanate compound having an isocyanate group number of 2 in one molecule include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. Examples of the aliphatic diisocyanate include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate Aliphatic diisocyanates having 4 to 30 carbon atoms such as cyanate, 3-methyl-1,5-pentane diisocyanate and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Cyanate. Examples of the alicyclic diisocyanate include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, Alicyclic diisocyanates having 7 to 30 carbon atoms such as hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethyl xylylene diisocyanate, and the like. Examples of the aromatic diisocyanate include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether isocyanate , Diphenylmethane diisocyanate, diphenyl propane diisocyanate, and other aromatic diisocyanates having 8 to 30 carbon atoms.

Examples of the isocyanate compound having three or more isocyanate groups in one molecule include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Specific examples include 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, and 4,4 ', 4 "-triphenylmethane triisocyanate. have.

Examples of the isocyanate compound include, for example, oligomers (for example, dimer or trimer, burette, isocyanurate) of the above isocyanate compound having an isocyanate group number of 2 or 3 or more, (For example, an addition reaction product of a polyhydric alcohol and two or more molecules of a diisocyanate compound), and a polymer. Examples of the polyhydric alcohol in the derivative include low molecular weight polyhydric alcohols such as trimethylolpropane, glycerin and pentaerythritol; Examples of the high molecular weight polyhydric alcohol include polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol and polyisoprene polyol.

Examples of such an isocyanate compound include a diphenylmethane diisocyanate trimer, a polymethylene polyphenyl polyisocyanate, a hexamethylene diisocyanate or a tolylene diisocyanate The reaction product of burette or isocyanurate, trimethylol propane and tolylene diisocyanate or xylylene diisocyanate (for example, tolylene diisocyanate or xylylene diisocyanate Triamine adduct of hexamethylene diisocyanate), a reaction product of trimethylol propane and hexamethylene diisocyanate, a polyether polyisocyanate (e.g., Cyanate, and polyester polyisocyanate.

Among the isocyanate compounds, a xylylene diisocyanate-based and hexamethylene diisocyanate-based cross-linking agent is preferable in terms of egg yolk denaturation, and a toluylene diisocyanate-based cross-linking agent is preferable from the standpoint of stress relaxation desirable. Examples of the xylylene diisocyanate cross-linking agent include xylylene diisocyanate and its multimers, derivatives and polymers; Examples of the hexamethylene diisocyanate cross-linking agent include hexamethylene diisocyanate and its multimers, derivatives and polymers; Examples of the tolylene diisocyanate cross-linking agent include tolylene diisocyanate and its multimers, derivatives and polymers.

Examples of the epoxy compound include compounds having two or more epoxy groups in the molecule, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, Glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylol propane triglycidyl ether, diglycidyl aniline, diamine glycidyl amine, N, N'- N, N ', N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis (N, N'-diaminoglycidylaminomethyl).

As the metal chelate compound, for example, a compound for feeding an alkoxide, acetylacetone, or ethyl acetoacetate to a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, . Specific examples include aluminum isopropylate, aluminum secondary butylate, aluminum ethyl acetoacetate diisopropylate, aluminum tris ethyl acetoacetate and aluminum tris acetylacetonate.

Examples of the polyfunctional (meth) acrylate (B2) include di-, tri- or polyalkyleneglycol-di (meth) acrylates, alkene diol di (meth) acrylates, bisphenol- , Trifunctional or higher polyol poly (meth) acrylate, polyurethane di (meth) acrylate, and polyurethane poly (meth) acrylate.

The curing agent (B) may be used alone or in combination of two or more.

The pressure-sensitive adhesive composition of the present invention contains the curing agent (B) in an amount of usually 0.01 to 25 parts by mass, preferably 0.05 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, per 100 parts by mass of the copolymer (A) do.

In one embodiment, the composition is used in an amount of preferably 0.01 to 5.0 parts by mass, more preferably 0.05 to 4.0 parts by mass, and still more preferably 0.1 to 4 parts by mass, relative to 100 parts by mass of the copolymer (A) By mass to 3.0 parts by mass. In another embodiment, the composition is used in an amount of preferably 0.01 to 20 parts by mass, more preferably 0.05 to 15 parts by mass (based on 100 parts by mass of the copolymer (A)) of the polyfunctional (meth) acrylate More preferably 0.1 to 10 parts by mass, per 100 parts by mass of the water-soluble polymer. In such a case, it is preferable because appropriate crosslinking degree and hardening degree can be attained and excellent adhesive property can be realized.

[ Light curing Initiator (C)]

The pressure-sensitive adhesive composition of the present invention may further contain a photopolymerization initiator (C). For example, a composition containing at least a multifunctional (meth) acrylate (B2) as a curing agent (B) and further comprising a photopolymerization initiator (C) is preferable as an active energy ray curable pressure sensitive adhesive composition.

Examples of the photopolymerization initiator (C) include benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, thioxanthone photopolymerization initiators and acylphosphine oxide photopolymerization initiators Specific examples of these initiators include the compounds listed in paragraphs [0023] to [0027] of JP-A-2009-013361.

The photopolymerization initiator (C) may be used alone or in combination of two or more.

In one embodiment, the pressure-sensitive adhesive composition of the present invention is used in an amount of 0.1 to 200 parts by mass, preferably 10 to 150 parts by mass, per 100 parts by mass of the polyfunctional (meth) acrylate (B2) , More preferably from 20 to 100 parts by mass.

[Additive (D)]

The pressure-sensitive adhesive composition of the present invention may contain, in addition to the above components, a (meth) acrylic polymer other than the copolymer (A), a tackifier resin, a silane coupling agent, an antistatic agent, an antioxidant, One or more additives selected from metal corrosion inhibitors, plasticizers, crosslinking accelerators, surfactants and reworkers.

[Organic solvent (E)]

The pressure-sensitive adhesive composition of the present invention preferably contains an organic solvent (E) in order to adjust its coating property. In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent (E) is usually 30 to 90% by mass, preferably 40 to 90% by mass. Examples of the organic solvent (E) include the solvents listed above as the polymerization solvent.

The organic solvent (E) may be used alone or in combination of two or more.

[Preparation of pressure-sensitive adhesive composition]

The pressure-sensitive adhesive composition of the present invention can be prepared, for example, by mixing each of the above components by a conventionally known method. For example, a pressure-sensitive adhesive composition can be prepared by mixing a solution containing the copolymer (A) obtained by the synthesis of the copolymer (A) with another component.

[Adhesive sheet]

The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention.

Examples of the pressure sensitive adhesive sheet include a pressure sensitive adhesive double coated sheet having only the pressure sensitive adhesive layer, a substrate, and a pressure sensitive adhesive layer formed on both surfaces of the substrate, wherein at least one pressure sensitive adhesive layer is a pressure sensitive adhesive layer formed from the pressure sensitive adhesive composition of the present invention, A single-sided pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer formed on one side of the substrate, and a pressure-sensitive adhesive sheet in which a release film of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is not adhered to the substrate.

The thickness of the pressure-sensitive adhesive layer is usually from 5 to 200 占 퐉, preferably from 10 to 100 占 퐉, from the viewpoint of maintaining the adhesive performance. The gel fraction of the pressure-sensitive adhesive layer is preferably from 10 to 98% by mass, more preferably from 20 to 95% by mass, and still more preferably from 30 to 90% by mass from the viewpoints of cohesive force, adhesive force and re-

For example, the pressure-sensitive adhesive layer can be obtained by crosslinking the copolymer (A) with the crosslinking agent (B1) in any one embodiment by proceeding the crosslinking and / or curing reaction in the pressure-sensitive adhesive composition of the present invention.

The conditions for forming the pressure-sensitive adhesive layer are as follows, for example. The pressure-sensitive adhesive composition of the present invention is applied onto a base material, a support or a cover film. When the composition contains a solvent, the solvent is usually removed by drying at 50 to 150 ° C, preferably 60 to 100 ° C, usually 1 to 10 minutes, preferably 2 to 7 minutes. A coating film is formed as described above.

The pressure-sensitive adhesive composition may be applied by a known method such as a spin coating method, a knife coating method, a roll coating method, a bar coating method, a blade coating method, a die coating method or a gravure coating method Followed by drying.

In the case of a thermosetting pressure-sensitive adhesive composition, the above-mentioned coating film is usually used for 3 days or more, preferably 7 to 10 days, usually 5 to 60 ° C, preferably 15 to 40 ° C and usually 30 to 70% RH, It may be cured in an environment of 40 to 70% RH. When the crosslinking is carried out under the above aging conditions, a crosslinked product (network polymer) can be efficiently formed.

In the case of the active energy ray-curable pressure-sensitive adhesive composition, the pressure-sensitive adhesive can be obtained by irradiating the coating film with an active energy ray. Examples of the active energy ray include ultraviolet rays, visible rays and electron rays, and ultraviolet rays are preferred. As the irradiation condition of the active energy ray, the accumulated light quantity is usually 300 to 3000 mJ / cm ² .

It is preferable that the aging and active energy ray irradiation is performed in a state in which the coating film is sandwiched by a substrate, a support or a cover film in order to block air contact with the coating film.

Examples of the substrate, the support, and the cover film include a plastic film, a foam substrate, a nonwoven fabric, a paper, and a flat yarn cloth. As the plastic film, for example, a polyester film such as polyethylene terephthalate; And polyolefin films such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer and the like. Examples of the foam substrate include a foam substrate obtained by using an olefin resin such as polyethylene, polypropylene, ethylene-propylene copolymer, or ethylene-vinyl acetate copolymer, a foam substrate obtained by using polystyrene, A foam base obtained using polyvinyl chloride, a foam base obtained using a (meth) acrylic rubber, and a foam base obtained using other elastomers. Examples of the nonwoven fabric include nonwoven fabrics obtained by using chemical fibers such as manila hemp, wood pulp, rayon, acetate fibers, polyester fibers, polyvinyl alcohol fibers and polyamide fibers, and mixtures of two or more thereof. As the flat yarn cloth, for example, a polyethylene flat yarn or a polypropylene yarn is knitted, and a resin film is laminated on the surface. The thickness of the substrate, support and cover film is not particularly limited, but is, for example, 5 to 150 占 퐉.

〔Usage〕

The pressure-sensitive adhesive sheet of the present invention is excellent in balance of adhesive strength and reworkability.

INDUSTRIAL APPLICABILITY The pressure-sensitive adhesive sheet of the present invention has good adhesive properties to the adhesion to a high-polarity material or a polyolefin-based low-polarity material. Examples of the polyolefin low polarity material include polyethylene and polypropylene. Therefore, the pressure-sensitive adhesive sheet of the present invention can be widely used as an industrial pressure-sensitive adhesive sheet, and can be used particularly as a nonwoven double-sided tape used for interior decoration of an automobile or an electronic device,

(Example)

Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. In the following description, " part " refers to " part by mass " unless otherwise specified.

Each measurement value in the examples was obtained by the following method.

〔heating Residue  Measure〕

1 g of the polymer solution was added to the thus-prepared tin-coated pellets (mass: n1), and the total mass (n2) was determined and then heated at 150 ° C for 3 hours. Thereafter, the tin-coated alumina was allowed to stand in a desiccator at room temperature for one hour and then again quenched to measure the total mass (n3) after heating. Using the obtained mass measurement values (n1 to n3), the heating residue was calculated from the following equation.

Heating residue (mass%) = 100 占 [mass after heating (n3-n1) / mass before heating (n2-n1)]

[Weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn)]

(Mw) and Mw / Mn of the (meth) acrylic copolymer in terms of standard polystyrene were determined by the GPC method under the following conditions.

Measurement apparatus: HLC-8120GPC (manufactured by TOSOH CORPORATION)

GPC Column Composition: The following five columns (all manufactured by TOSOH CORPORATION)

(1) TSK-GEL HXL-H (Guard column)

(2) TSK-GEL G7000HXL

(3) TSK-GEL GMHXL

(4) TSK-GEL GMHXL

(5) TSK-GEL G2500HXL

Sample concentration: diluted with tetrahydrofuran to 1.0 mg / cm ³

Mobile phase solvent: tetrahydrofuran

· Flow rate: 1.0 cm ³ / min

Column temperature: 40 ° C

[ Example  A1]

90 g of methyl acrylate (MA), 10 g of acrylic acid (AA), 30 g of ethyl agate and 1.0 g of RAFT 1st as shown in the following formula were placed in a flask equipped with a stirrer, a nitrogen gas introducing tube, a thermometer and a reflux condenser, The contents of the flask were heated to 80 DEG C while nitrogen gas was introduced into the flask.

Subsequently, 0.02 g of 2,2'-azobisisobutyronitrile was added to the flask under stirring, and heating and cooling were performed for one hour so that the temperature of the contents in the flask could be maintained at 80 ° C.

Subsequently, heating and cooling were performed for 10 hours so that the temperature of the contents in the flask could be maintained at 80 DEG C, and finally 20 g of ethyl acetate was added.

Thus, a polymer solution containing an acrylic polymer (A ') was obtained. The heating residue of the obtained polymer solution was about 65 mass%. The Mw of the acrylic polymer (A ') contained in the obtained polymer solution was 25,000.

Separately, a flask equipped with a stirrer, a nitrogen gas introducing tube, a thermometer and a reflux condenser was prepared, and the polymer solution containing the acrylic polymer (A ') was added so that the solid content of the acrylic polymer (A') became 15 g 85 g of n-butyl acrylate (BA) and 50 g of ethyl acetate were charged, and the contents of the flask were heated to 80 캜 while nitrogen gas was introduced into the flask.

Subsequently, 0.02 g of 2,2'-azobisisobutyronitrile was added to the flask under stirring, and heating and cooling were performed for one hour so that the temperature of the contents in the flask could be maintained at 80 ° C.

Subsequently, heating and cooling were performed for 10 hours so that the temperature of the contents in the flask could be maintained at 80 DEG C, and finally 20 g of ethyl acetate was added.

Thus, a polymer solution containing the acrylic polymer (A1) was obtained. The heating residue of the obtained polymer solution was about 52 mass%. With respect to the acrylic polymer (A1) contained in the obtained polymer solution, Mw was 170,000 and Mw / Mn was 2.1.

[ Example  A2]

A polymer solution containing an acrylic polymer (A2) was obtained in the same manner as in Example A1 except that 4-hydroxybutylacrylate (4HBA) was used instead of acrylic acid (AA) shown in Table 1.

[ Comparative Example  A1]

85 g of n-butyl acrylate (BA), 13.5 g of methyl acrylate (MA), 1.5 g of acrylic acid (AA) and 100 g of ethyl acetate were placed in a flask equipped with a stirrer, a nitrogen gas introducing tube, a thermometer and a reflux condenser, The contents of the flask were heated to 80 DEG C while nitrogen gas was introduced into the flask.

Subsequently, 0.05 g of 2,2'-azobisisobutyronitrile was added into the flask with stirring, and heating and cooling were performed for one hour so that the temperature of the contents in the flask could be maintained at 80 ° C.

Subsequently, heating and cooling were performed for 10 hours so that the temperature of the contents in the flask could be maintained at 80 캜, and finally, diluted with ethyl acetate to prepare a copolymer solution containing the copolymer (RA1). The copolymer (RA1) thus obtained had Mw of 240,000 and Mw / Mn of 4.5.

[ Comparative Example  A2]

A polymer solution containing an acrylic polymer (RA2) was obtained in the same manner as in Comparative Example A1 except that 4-hydroxybutylacrylate (4HBA) was used instead of acrylic acid (AA) shown in Table 1.

≪ Pressure sensitive adhesive composition and pressure sensitive adhesive sheet &

[ Example  B1, B2, and Comparative Example  B1, B2]

The polymer solution obtained in Examples and the like was used as an uncrosslinked pressure-sensitive adhesive composition. The polymer solution obtained in the examples and the like and the crosslinking agent M-5A, E-50C or L-45 (both manufactured by Soken Chemical & Engineering Co., Ltd.) were mixed so that the solid content concentration of the crosslinking agent was as shown in Table 1, To obtain a pressure-sensitive adhesive composition for crosslinking.

The pressure-sensitive adhesive composition was applied onto the surface of a polyethylene terephthalate (PET) film having a thickness of 50 탆, which had been subjected to corona treatment, to a dry film thickness of 50 탆 by using a doctor blade and dried at 90 캜 for 5 minutes The solvent was removed. The resulting pressure-sensitive adhesive coating film was applied to a peel-treated PET separator and aged for 7 days at 23 ° C and 65% RH to obtain a pressure-sensitive adhesive sheet.

<Evaluation>

[ retention  exam〕

The PET separator of the pressure-sensitive adhesive sheet obtained in Examples and the like was peeled off under conditions of 23 占 폚 and 50% RH, and the pressure-sensitive adhesive layer exposed on the SUS plate was attached. The adhesive area was 20 mm x 20 mm. After 20 minutes from the attachment, a load of 500 g was applied in the uncrosslinked system at 80 ° C and under the drying condition, and a load of 1 kg in the crosslinked system was applied in the direction parallel to the pressure-sensitive adhesive layer surface. mm) was measured. When the sheet falls within the measuring time, the falling time is described. Further, in the E-50C addition system, a holding force test was also performed on the sheet prepared without the aging period of 7 days, and the sheet after 2 days and 3 days after the aging.

[ Probe  Tack test]

The PET separator of the pressure-sensitive adhesive sheet obtained in Examples and the like was peeled off and the probe tack of the exposed pressure-sensitive adhesive layer was measured. The probe was made of SUS with a diameter of 5 mm, the contact time was 1 second, the probe speed was 1 cm / sec, and the load was 20 g.

[Gel fraction]

A PET separator was peeled off from the pressure-sensitive adhesive sheet obtained in the same manner as in Examples and the like except that a PET separator was used instead of the PET film. About 0.1 g of the pressure-sensitive adhesive was taken from the pressure-sensitive adhesive layer thus obtained into a sampling bottle. After shaking for 4 hours, the content of the sample bottle was filtered with a 200 mesh stainless steel net, and the residue on the net was dried at 100 DEG C for 2 hours to measure the dry mass. The gel fraction of the pressure-sensitive adhesive was determined by the following formula. For the E-50C addition system, the gel fraction was determined for the sheet prepared without the aging period of 7 days, and the sheet after 2 days and 3 days after the aging.

Gel fraction (%) = (Dry mass / Adhesive mass obtained) × 100 (%)

Example A1 Example A2 Comparative Example A1 Comparative Example A2 (Meth) acrylic copolymer sign A1 A2 RA1 RA2 Block A MA 13.5wt%
AA 1.5wt%
(Mw: 25,000) MA 13.5wt%
4HBA 1.5wt%
(Mw: 36,000) Block B BA 85wt% BA 85wt% random BA 85wt%
MA 13.5wt%
AA 1.5wt% BA 85wt%
MA 13.5wt%
AA 1.5wt% Mw 170,000 217,000 240,000 270,000 Mw / Mn 2.1 2.3 4.5 4.8 Example B1 Example B2 Comparative Example B1 Comparative Example B2 (Meth) acrylic copolymer A1 A2 RA1 RA2 Uncle retention 0.2mm 1.0 mm Drop immediately Drop immediately Cross-linking agent M-5A (0.2 wt% added) retention 0.25 mm Drop 10 minutes Drop 15 minutes Drop immediately Crosslinking agent E-50C (containing 0.5 wt%) retention 0.1mm 0.05mm Probe pick 16 [N / 5 mmφ] 10.9 [N / 5 mmφ] Crosslinking agent L-45 (0.5 wt% added) retention 0.1mm 0.1mm Probe pick 12 [N / 5 mmφ] 7.4 [N / 5mmφ]

M-5A: Aluminum chelate crosslinking agent

E-50C: Epoxy crosslinking agent

L-45: Isocyanate-based crosslinking agent

Table 2 Example B1, Comparative Example B1 Aging property of the E-50C addition system Immediately after application 2 days 3 days Example B1 Gel fraction 86.6% 86.8% 86.9% retention 0.15mm 0.1mm 0.1mm Comparative Example B1 Gel fraction 0% 64.2% 87.1% retention Drop 13 minutes 0.15mm 0.05mm

※ Immediately after application: Measurement of "application, immediately after drying at 90 ° C for 5 minutes"

Compared to the pressure-sensitive adhesive sheets of Comparative Examples B1 and B2 prepared from the copolymers of Comparative Examples A1 and A2, the pressure-sensitive adhesive sheets of Examples B1 and B2 prepared from the copolymers of Examples A1 and A2 In view of the high cohesive force, the unglazed joint has a sufficient holding force. In addition, the copolymer of Example A1 and Comparative Example A1 had the same monomer composition, but in the case of a structure in which reactive functional groups were localized as in Example A1, a pressure-sensitive adhesive sheet having excellent aging properties was obtained.

Claims (11)

(Meth) acrylic triblock copolymer (A) obtained by RAFT polymerization using RAFT agent represented by the formula (a1).
However,

[In the formula (a1), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group, and two R groups may be the same or different.] The (meth) acrylic triblock copolymer (A) according to claim 1, wherein R in the formula (a1) is a hydrocarbon group, an acyl group, an acyloxy group or an acyloxyalkyl group. The acrylic resin composition according to any one of claims 1 to 3, which has a weight average molecular weight (Mw) of 30,000 to 600,000 and a molecular weight distribution (Mw / Mn) of 1.5 to 5.0 as measured by a GPC method. Copolymer (A). 4. The method according to any one of claims 1 to 3, having a tri-block structure of block A-block B-block A,
The block B has a bivalent structure represented by -SC (= S) -S-,
(Meth) acrylic triblock copolymer (A), wherein the total content of the block A is 5 to 40 mass% and the content of the block B is 95 to 60 mass% in 100 mass% of the copolymer (A). The positive photosensitive resin composition according to claim 4, wherein the content of the structural unit derived from the reactive functional group-containing monomer is 0.5 to 15 mass% and the content of the structural unit derived from the reactive functional group-containing monomer is 100 mass% (A) is present in the block A of the (meth) acrylic triblock copolymer. A pressure-sensitive adhesive composition comprising the (meth) acrylic triblock copolymer (A) according to any one of claims 1 to 5. The pressure-sensitive adhesive composition according to claim 6, further comprising a curing agent (B). A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 6 or 7. A step 1 of polymerizing a polymerizable double bond-containing monomer using the RAFT agent represented by the formula (a1), a step of adding a polymerizable double bond-containing monomer different from the monomer composition in the step 1 to the polymer obtained in the step 1 (Meth) acrylic triblock copolymer (A) having one or both of the above-mentioned monomers used in Step 1 and the above-mentioned monomers to be added in Step 2, wherein the (meth) acrylic triblock copolymer .
[Figure 2]

[In the formula (a1), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group, and two R groups may be the same or different.] The process for producing a (meth) acrylic triblock copolymer (A) according to claim 9, wherein the polymer obtained in the step (1) has a weight average molecular weight (Mw) measured by GPC of 3,000 to 40,000. The method according to claim 9 or 10, wherein 95% by mass or more of the reactive functional group-containing monomer in 100% by mass of the reactive functional group-containing monomer which can be used in Step 1 and Step 2 is used in Step 1, A process for producing an acrylic triblock copolymer (A).