KR20190036526A - (Meth) acrylic copolymer and a process for producing the same, a pressure-sensitive adhesive composition, and a pressure- - Google Patents

Abstract

[assignment]
The pressure-sensitive adhesive composition containing the (meth) acrylic copolymer obtained by the RAFT polymerization using the RAFT agent is further improved in storage stability and adhesion reliability to various adherends.
[Solution]
(Meth) acrylic 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 copolymer and a process for producing the same, a pressure-sensitive adhesive composition, and a pressure-

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

There is a demand for a pressure-sensitive adhesive composition having excellent durability such that the pressure-sensitive adhesive sheet is not peeled off even under harsh conditions, in the field of pressure-sensitive adhesives. Patent Documents 1 and 2 disclose a pressure-sensitive adhesive composition containing a (meth) acrylic copolymer obtained by RAFT polymerization using various reversible addition-cleft chain transfer (RAFT) agents. However, a pressure-sensitive adhesive composition containing such a copolymer needs further improvement in terms of storage stability and adhesive reliability for various adherends.

Japanese Patent Application Laid-Open No. 2003-041224 Japanese Patent Laid-Open Publication No. 2014-208762

It is an object of the present invention to further improve the storage stability, the removability in static load for various adherends, and the reliability of the adhesive for a pressure-sensitive adhesive composition containing a (meth) acrylic copolymer obtained by RAFT polymerization using a RAFT agent.

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 copolymer having the following constitution, and the present invention has been completed.

The present invention is, for example, the following [1] to [5].

[1] A (meth) acrylic 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.]

[2] A (meth) acrylic copolymer (A) having a group represented by the formula (a2) at the molecular end.

[In the formula (a2), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group.]

[3] A pressure-sensitive adhesive composition comprising the (meth) acrylic copolymer (A), the curing agent (B) and the tackifier resin (C) described in the above [1] or [2].

[4] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to [3].

[5] A process for producing a (meth) acrylic copolymer (A) having a step of polymerizing a (meth) acrylic acid ester 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.]

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a pressure-sensitive adhesive composition which is obtained by RAFT polymerization using a RAFT agent and which is excellent in storage stability and pressure-sensitive adhesiveness to a (meth) acrylic copolymer and various adherends.

Hereinafter, the (meth) acrylic 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 copolymer (A)]

The (meth) acrylic copolymer (A) according to the first aspect of the present invention can be obtained by RAFT polymerization using the RAFT agent represented by the formula (a1), specifically RAFT polymerization of a polymerizable double bond- 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). Therefore, the copolymer can improve the storage stability of the copolymer solution, the pressure-sensitive adhesive composition containing the copolymer and the pressure-sensitive adhesive formed from the composition, since the copolymer does not have a highly reactive molecular end functional 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 become a liquid at room temperature, and thus has excellent handling properties. However, acyl group, acyloxy group and acyloxyalkyl group are preferred because excellent adhesion reliability to various kinds of 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.

In the RAFT polymerization, polymerization is carried out by reacting to introduce a polymerizable double bond-containing monomer containing a (meth) acrylic acid ester between a sulfur atom in the RAFT agent and a methylene group adjacent to the sulfur atom. The copolymer (A) includes, for example, a copolymer represented by the following formula.

(Wherein R is the same as defined in the formula (a1), and Ap is independently a divalent group derived from a polymer of a polymerizable double bond-containing monomer containing a (meth) acrylic acid ester Polymer chains of monomers).

The Ap may be either a random copolymer structure of a polymerizable double bond-containing monomer or a block copolymer structure. The block copolymer structure may be obtained by, for example, adding a polymerizable double bond-containing monomer to the RAFT agent to perform a first RAFT polymerization, and adding to the resulting polymer a polymerizable double bond-containing monomer having a composition different from that of the monomer And then performing a second RAFT polymerization.

The (meth) acrylic copolymer (A) according to the second aspect of the present invention has a group represented by the formula (a2) at the molecular end, and in one embodiment, the trivalent tri Thiocarbonate structure.

In the formula (a2), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group. Specific examples and examples of the organic group are the same as the organic groups described with respect to formula (a1).

In the following description, the term "(meth) acrylic copolymer (A)" or "(meth) acrylic copolymer (of the invention)" is used unless otherwise specified for the (meth) acrylic copolymer (A) " of the present invention (hereinafter referred to as " copolymer (A) "

By using the copolymer (A) of the present invention, it is possible to obtain a pressure-sensitive adhesive composition that exhibits excellent peel resistance (adhesive reliability) that is excellent in storage stability and does not peel off from an adherend even in a severe environment.

" 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 a (meth) acrylic acid ester having no functional group, a monomer having at least one of the following functional groups (hereinafter also referred to as "functional group-containing monomer"), and a copolymerizable monomer other than these monomers . Examples of the 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) acrylic esters having no functional group include alkyl (meth) acrylates, alkoxyalkyl (meth) acrylates, alkoxypolyalkyleneglycolmono (meth) acrylates, alicyclic groups or aromatic rings ) 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 acid ester having no functional group is usually 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, based on 100% by mass of the total polymerizable double bond- Mass% or more.

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

The amount of the functional group-containing monomer to be used is usually 0.1 to 10% by mass, preferably 0.5 to 8% by mass, and more preferably 1 to 5% by mass, based on 100% by mass of the total 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 first invention, preferably in the second invention, also 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 (meth) acrylic copolymer (A) of the present invention has a step of polymerizing (meth) acrylic acid ester by, for example, RAFT polymerization using the RAFT agent represented by the formula (a1). Other polymerizable double bond-containing monomers may be used together with the (meth) acrylic acid ester.

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. The polymerization conditions can be found, for example, in Japanese Patent Application Laid-Open Nos. 2007-230947 and 2011-52057.

[Physical Properties of Copolymer (A)] [

The weight average molecular weight (Mw) of the copolymer (A) measured by gel permeation chromatography (GPC) is preferably 50,000 to 1,000,000, more preferably 100,000 to 900,000, and even more preferably 150,000 to 800,000 to be. Such a structure is preferable from the viewpoint of improving the durability under high temperature and high humidity conditions because it is given high cohesive strength to the pressure-sensitive adhesive composition.

The molecular weight distribution (Mw / Mn) of the copolymer (A) is preferably 1.5 to 6.0, more preferably 1.5 to 5.0, and still more 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).

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 a heat change. A graph of "heat absorption amount" 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 copolymer (A). The pressure-sensitive adhesive composition of the present invention may further contain a curing agent (B); And may further contain a tackifier resin (C).

[( Meta ) Acrylic copolymer (A)]

The content of the (meth) acrylic copolymer (A) in the solid content of the pressure-sensitive adhesive composition is usually 60 mass% or more, preferably 65 to 99 mass%, more preferably 70 to 97 mass% Is 70 to 95% by mass. Such a solar cell is preferable in that the adhesive force to various adherends can be arbitrarily adjusted. 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 functional group that can be introduced into the copolymer (A) and the curing system of the pressure-sensitive adhesive composition. For example, when the acrylic copolymer (A) has a 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.

As the isocyanate compound, for example, there can be mentioned a multimer (for example, a dimer or a trimer, a burette, an 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.

[Adhesion-imparting resin (C)]

The pressure-sensitive adhesive composition of the present invention preferably contains a tackifier resin (C). In this case, a pressure-sensitive adhesive layer having a better adhesive strength, specifically, a pressure-sensitive adhesive layer exhibiting a high static-load-peeling property can be obtained not only for a high polarity material such as an SUS substrate, but also for a polyolefin low-polarity material such as polyethylene or polypropylene .

Examples of the tackifying resin (C) include rosin-based tackifying resins such as rosin ester-based resins, terpene-based tackifying resins such as a terpene phenol-based resin, styrene-based tackifying resins and alicyclic saturated hydrocarbon resins. Rosin ester-based resins are preferable.

The rosin ester-based resin is a resin obtained by esterifying a rosin-based resin with an alcohol. Examples of the rosin-based resin include a rosin resin containing a resin acid such as abietic acid as a main component, a disproportionated rosin resin, and a dimer of resin acid such as hydrogenated rosin resin or abietic acid (polymerized rosin resin) . Examples of the alcohol include polyhydric alcohols such as ethylene glycol, glycerin and pentaerythritol.

Wherein the resin obtained by esterifying the rosin resin is a rosin ester resin, the resin obtained by esterifying the disproportionated rosin resin is a disproportionated rosin ester resin, the resin obtained by esterifying the hydrogenated rosin resin is a hydrogenated rosin ester resin, Is a polymerized rosin ester resin.

The terpene phenol resin is a resin obtained by polymerizing terpene in the presence of phenol.

The softening temperature of the tackifier resin (C) is preferably 70 to 170 占 폚, more preferably 100 to 170 占 폚. With this type of solar cell, the pressure-sensitive adhesive layer has a favorable tackiness, excellent heat resistance, and excellent durability under a high-temperature environment. The softening temperature can be measured by the JIS K2207 ring method.

Examples of the disproportionated rosin ester resin include Super Ester A75 (75 占 폚), Super Ester A100 (100 占 폚), Super Ester A115 (115 占 폚) and Super Ester A125 (125 占 폚). Examples of the hydrogenated rosin ester resin include Fine Crystal KE-359 (100 占 폚) and Esther G (70 占 폚). Examples of the polymerized rosin ester resin include PENCEL D-135 (135 DEG C), PENCEL D-125 (125 DEG C), and PENCEL D-160 (160 DEG C). The above products are manufactured by Arakawa Chemical Industries, Ltd., and the temperature in the parentheses is the softening temperature.

Examples of the terpene tackifier resin include YS Polyster G150 (150 占 폚), YS Polyster T100 (100 占 폚), YS Polyster G125 (125 占 폚), YS Polyster T115 (115 占 폚), YS Polyster T145 145 占 폚) and YS Polystyrene T130 (130 占 폚). The above products are manufactured by Yasuhara Chemical Co., Ltd. The temperature in the parentheses is the softening temperature.

Examples of the styrene-based tackifier resin include FMR-0150 (145 占 폚), FTR-6100 (100 占 폚), FTR-6110 (110 占 폚), FTR-6125 -8120 (120 占 폚), FTR-0100 (100 占 폚), FTR-2120 (120 占 폚) and FTR-2140 (145 占 폚). The above products are manufactured by Mitsui Chemicals, Inc. The temperature in the parentheses is the softening temperature. SX-100 (100 ° C, manufactured by Yasuhara Chemical Co., Ltd.) can also be used.

Examples of the alicyclic saturated hydrocarbon resin include Arcon P-90 (90 占 폚), Arcon P-100 (100 占 폚), Arcon P-115 (115 占 폚), Arcon P- 90 ° C), Arcon M-100 (100 ° C), Arcon M-115 (115 ° C) and Arcon M-135 (135 ° C). The above products are manufactured by Arakawa Chemical Industries, Ltd., and the temperature in the parentheses is the softening temperature.

The tackifier resin (C) may be used alone or in combination of two or more.

The pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition in which the tackifier resin (C) is added in an amount of 5 to 50 parts by mass, preferably 8 to 40 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of the copolymer (A) Lt; / RTI > In such a case, the pressure-sensitive adhesive layer has a favorable tack and is excellent in the peelability in a static load to a polyolefin-based low-polarity material.

[ Light curing Initiator (D)]

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

Examples of the photopolymerization initiator (D) 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 (D) 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 (E)]

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 silane coupling agent, an antistatic agent, an antioxidant, a light stabilizer, a metal corrosion inhibitor, , A crosslinking accelerator, a surfactant, and a reworking agent.

[Organic solvent (F)]

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

The organic solvent (F) 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.

In the present invention, the pressure-sensitive adhesive composition is immediately prepared using the solution containing the synthesized copolymer (A), and the double-sided pressure-sensitive adhesive sheet formed under the conditions described in the examples is subjected to the holding force test described in the embodiment. The initial value and the solution containing the synthesized copolymer (A) were stored in a closed container at 60 DEG C / dry for one month, and the pressure-sensitive adhesive composition was prepared. The value of the displacement distance of the holding force test is usually 0 to 2.0 mm, preferably 0 to 1.5 mm, and more preferably 0 to 1.0 mm. When the result of the holding force test is within this range, the flow in the shearing direction at the time of heating is suppressed and it is judged that the pressure-sensitive adhesive layer has high reliability against heat. Also, the copolymer (A), the pressure-sensitive adhesive composition of the present invention and the pressure-sensitive adhesive formed therefrom are excellent in storage stability.

[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- As for the gel fraction, for example, about 0.1 g of the pressure-sensitive adhesive layer was taken in a sampling bottle, and 30 ml of ethyl acetate was added and shaken for 4 hours. The contents of the sample bottle were then filtered with a 200 mesh stainless steel net, Is dried at 100 DEG C for 2 hours to measure the dry mass, and can be obtained by the following formula.

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

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.

The pressure-sensitive adhesive sheet of the present invention exhibits a high static load peelability for 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]

78 g of n-butyl acrylate (BA), 20 g of 2-ethylhexyl acrylate (2EHA), 2 g of acrylic acid (AA), 20 g of hydroxyethyl acrylate (HEA) and 0.15 g of the RAFT 1st compound represented by the following formula were placed, and the flask contents 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, 60 g of ethyl acetate was added dropwise over 1 hour while maintaining the temperature of the content in the flask at 80 DEG C, and then heating and cooling were carried out for 10 hours so that the temperature of the contents in the flask could be maintained at 80 DEG C. Finally, 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 250,000 and Mw / Mn was 2.1.

[ Example  A2, Comparative Example  A1 to A2]

A polymer solution containing an acrylic polymer (A2), an acrylic polymer (RA1) or an acrylic polymer (RA2) was obtained in the same manner as in Example A1 except that the RAFT agent was changed as shown in Table 1.

≪ Pressure sensitive adhesive composition and pressure sensitive adhesive sheet &

[ Example  B1 to B2 and Comparative Example  B1 to B2]

L-45 (manufactured by Soken Chemical & Engineering Co., Ltd.) was used as an isocyanate crosslinking agent, and PENCEL D-160 (manufactured by Arakawa Chemical Industries, Ltd.) was used as a tackifier resin in Table 1 , And the mixture was appropriately diluted with ethyl acetate to obtain a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition was coated on a paper separator (EKR-78D, thickness: 115 mu m) having been peeled off using a doctor blade after bubbles had been removed to a dry film thickness of 65 mu m and dried at 80 DEG C for 2 minutes to remove the solvent. The resulting pressure-sensitive adhesive coating film was applied to both sides of a nonwoven fabric base material having a thickness of 38 탆 and aged for 7 days under an environment of 23 캜 and 65% RH to obtain a double-faced pressure-sensitive adhesive sheet composed of a paper separator / pressure-sensitive adhesive layer / nonwoven base / pressure-sensitive adhesive layer / paper separator.

<Evaluation>

[ retention  exam〕

One side of the paper separator of the double-sided pressure-sensitive adhesive sheet obtained in Examples and the like was peeled off under conditions of 23 ° C and 50% RH, and a 25 μm thick PET film was laminated on the exposed pressure-sensitive adhesive layer side. Thereafter, another paper separator was peeled off, the pressure-sensitive adhesive layer exposed on the SUS plate was attached, and the 2 kg roller was reciprocated three times. The adhesive area was 20 mm x 20 mm. After 20 minutes from the attachment, a load of 1 kg was applied in parallel to the pressure-sensitive adhesive layer surface at 80 캜 and under drying conditions, and the displacement distance (mm) from the original position after 1 hour from the start of the load portion was measured. Value. Further, the polymer solution obtained in the examples and the like was stored in a closed container at 60 ° C / dry for one month, and then a pressure-sensitive adhesive composition and a pressure-sensitive adhesive double-faced pressure-sensitive adhesive sheet were prepared in the same manner as described above. After the polymer solution was stored at 60 DEG C / dry for one month, the pressure-sensitive adhesive composition thus prepared was added with the same amount of crosslinking agent as that of the pressure-sensitive adhesive composition prepared by the polymer solution which was not stored.

The addition amount of the crosslinking agent is set so that the initial value of the displacement distance in the holding force test in each of the examples and the comparative examples is 0.3 mm. Under these conditions, the values of the holding force test and the static load peeling test were compared.

[ dead load  Peel test]

One side of the paper separator of the double-sided pressure-sensitive adhesive sheet obtained in Examples and the like was peeled off under conditions of 23 ° C and 50% RH, and a 25 μm thick PET film was laminated on the exposed pressure-sensitive adhesive layer side. Thereafter, another paper separator was peeled off and a pressure-sensitive adhesive layer exposed to a polypropylene (PP) plate or an SUS plate having a thickness of 1 mm was stuck thereon, and a 2 kg roller was reciprocated three times. The adhesive area was 20 mm wide x 50 mm. 20 minutes after the application, a load of 200 g in the case of the SUS plate and a load of 100 g in the case of the PP plate were applied in the direction of 90 ° from the surface of the PET film at 80 ° C and under the drying condition, And the length of peeling (mm) after the measurement was measured.

Example A1 Example A2 Comparative Example A1 Comparative Example A2 (Meth) acrylic
Copolymer
(Acrylic polymer) sign A1 A2 RA1 RA2 Monomer composition BA / 2EHA / AA / HEA = 78/20/2 / 0.5 RATF 1st 0.15 RATF 2nd 0.135 RATF 3rd 0.072 RATF Fourth 0.14 Mw 25 million 25 million 25 million 25 million Mw / Mn 2.1 2.1 2.1 2.1 Example B1 Example B2 Comparative Example B1 Comparative Example B2 (Meth) acrylic
Copolymer A1 100 copies A2 100 copies RA1 100 copies RA2 100 copies Cross-linking agent L-45 1.7 part 2.6 parts 2.4 part 1.0 part Tackifying resin D-160 25 25 25 25 Retention force test Early 0.3mm 0.3mm 0.3mm 0.3mm 60 ℃ / 1 month after 0.3mm 0.5mm 0.5mm fall Static load peel test SUS 80 ° C / 200g 3.5mm 1.0 mm 10.0 mm 6.0mm PP 80 ° C / 100g 8.5mm 9.5 mm 17.5 mm 13.0 mm

The double-faced pressure-sensitive adhesive sheets of Examples B1 and B2 had satisfactory results in both the holding force test and the static load peeling test.

The double-sided pressure-sensitive adhesive sheet of Comparative Example B1 was produced from an acrylic polymer prepared using RAFT No. 3 having no group such as an acyl group, an acyloxy group and an acyloxyalkyl group. In the static load peel test on various adherends, The results were less than examples B1 and B2.

The double-sided pressure-sensitive adhesive sheet of Comparative Example B2 prepared from the acrylic polymer prepared using the RAFT No. 4 having a hydroxyl group at the end resulted in a drop in the holding force test after being stored for one month under the condition of 60 ° C / dry. This is because the ester exchange reaction takes place in the system during storage and the hydroxyl groups present at the ends of the polymer migrate into the polymer so that the reactivity with the crosslinking agent is lowered as compared with the polymer before storage and the amount of the crosslinking agent The crosslinking reaction did not proceed sufficiently.

Claims (5)

(Meth) acrylic 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.] A (meth) acrylic copolymer (A) having a group represented by the formula (a2) at the molecular end.

[In the formula (a2), R is a monovalent organic group having neither a hydroxyl group, a carboxyl group nor an amino group.] A pressure-sensitive adhesive composition comprising the (meth) acrylic copolymer (A), the curing agent (B) and the tackifier resin (C) according to claim 1 or 2. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 3. A process for producing a (meth) acrylic copolymer (A) having a step of polymerizing a (meth) acrylic acid ester 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.]