JP5982068B2 - Composition for pressure-sensitive adhesive, pressure-sensitive adhesive, and pressure-sensitive adhesive sheet - Google Patents

Description

  The present invention provides a pressure-sensitive adhesive composition containing a (meth) acrylic acid ester polymer obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization and an isocyanate compound, a pressure-sensitive adhesive formed from the composition, And a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the composition.

  In recent years, in the field of pressure-sensitive adhesives, stable performance and handling properties under more severe durability conditions are being demanded. For example, in the field of protective films, balancing adhesive strength at low and high peel speeds, durability and re-peelability under high temperature and high humidity conditions, low contamination to adherends when peeling adhesive sheets Etc.

  As a conventional adhesive composition for a protective film, an acrylic polymer is used from the viewpoint of weather resistance and transparency. Acrylic polymers are generally synthesized by so-called free radical polymerization. However, the acrylic polymer obtained by free radical polymerization produces a low molecular weight component and a polymer component having no functional group, and these components are deteriorated in removability or adherend when the adhesive sheet is peeled off. It was difficult to satisfy the required performance required for the pressure-sensitive adhesive layer for the protective film at the same time.

  On the other hand, not only the field of pressure-sensitive adhesives but also acrylic polymers obtained by various production methods have been proposed.

  In Patent Document 1, RAFT obtained by subjecting a vinyl monomer to RAFT polymerization using a RAFT polymerization agent obtained by a RAFT polymerization method using a dibenzyltrithiocarbonate derivative having a hydroxyl group at both ends as a starting material. Polymers are described. Moreover, the polymer obtained by making a diisocyanate compound react with the hydroxyl group which this RAFT polymer has is described.

  However, Patent Document 1 does not particularly examine the use of a polymer obtained by reacting a diisocyanate compound with the hydroxyl group of the RAFT polymer as an adhesive.

  Patent Document 2 discloses a pressure-sensitive adhesive containing a (meth) acrylic acid ester copolymer having a weight average molecular weight of 200,000 to 2,000,000 and a molecular weight distribution of less than 2.5 obtained by living radical polymerization, and a crosslinking agent. A protective film having a pressure-sensitive adhesive layer formed by the composition is described.

  Patent Document 3 discloses that a weight average molecular weight obtained by copolymerizing a (meth) acrylic acid alkyl ester and a vinyl monomer having a reactive functional group by a living radical polymerization method using an organic tellurium compound is 300,000 to A pressure-sensitive adhesive obtained by blending 2 million copolymers and a crosslinking agent is described.

  However, in order to form an adhesive that maintains excellent adhesive properties even when exposed to heat-resistant conditions and reduces the degree of contamination of the adherend when the adhesive sheet is peeled off, an acrylic polymer, a crosslinking agent Further improvements are needed for other configurations.

JP 2011-052057 A JP 2011-074380 A International Publication No. 2007/119884 Pamphlet

  An object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive that exhibits excellent adhesive properties even when exposed to heat-resistant conditions and that reduces the degree of contamination of the adherend when the pressure-sensitive adhesive sheet is peeled off. To provide things.

  The present inventors diligently studied to solve the above problems. As a result, the inventors found that the above-mentioned problems can be solved by a composition for pressure-sensitive adhesives containing a specific (meth) acrylic acid ester polymer and an isocyanate compound having 3 or more isocyanate groups in one molecule, and the present invention is completed. It came to.

  The present invention includes, for example, the following [1] to [4].

  [1] (A) The weight average molecular weight (Mw) obtained by RAFT polymerization and measured by gel permeation chromatography is 60,000 to 200,000, and the molecular weight distribution (Mw / Mn) is 3.0. The composition for adhesives which is the following and contains the (meth) acrylic acid ester polymer which has a structural unit derived from a hydroxyl-containing monomer, and (B) the isocyanate compound in which the number of isocyanate groups in 1 molecule is 3 or more.

  [2] The isocyanate compound (B) is contained in a range of 0.1 to 50 parts by mass in solid content ratio with respect to 100 parts by mass of the (meth) acrylic acid ester polymer (A). Composition for pressure-sensitive adhesives.

  [3] A pressure-sensitive adhesive formed from the composition according to [1] or [2].

  [4] A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer formed from the composition according to [1] or [2].

  ADVANTAGE OF THE INVENTION According to this invention, the composition for adhesives which can form the adhesive which shows the outstanding adhesion characteristic when exposed to heat-resistant conditions, and the contamination degree with respect to the adherend at the time of adhesive sheet peeling is reduced is formed. Things can be provided. Moreover, the said composition can form the adhesive with a small raise with time of adhesive force, and low peeling rate dependence and peeling temperature dependence of adhesive force.

  Hereinafter, the composition for pressure-sensitive adhesives, the pressure-sensitive adhesive, and the pressure-sensitive adhesive sheet of the present invention will be described.

  In the present specification, “polymer” is used to include homopolymers and copolymers, and “polymerization” is used to include homopolymerization and copolymerization. The compound represented by formula (i) (i is a formula number) is also simply referred to as “compound (i)”.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present invention has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) obtained by RAFT polymerization of 60,000 to 200,000, and a molecular weight distribution (Mw / Mn) is 3.0 or less, a (meth) acrylic acid ester polymer (A) having a structural unit derived from a hydroxyl group-containing monomer, an isocyanate compound (B) having 3 or more isocyanate groups in one molecule, and Containing. Hereinafter, the components are also referred to as “RAFT polymer (A)” and “polyfunctional isocyanate compound (B)”, respectively.

[(Meth) acrylic acid ester polymer (A)]
The weight average molecular weight (Mw) measured by the GPC method of the RAFT polymer (A) is 60,000 to 200,000, preferably 70,000 to 180,000, more preferably 80,000 to 160, 000. By using the RAFT polymer (A) having Mw in the above range, it is easy to balance the adhesive force. When Mw exceeds the above range, the adhesive strength greatly increases with time under heat-resistant conditions, and the dependency of the adhesive strength on the peeling rate and the peeling temperature increases. When Mw is less than the above range, the adherend is contaminated when the pressure-sensitive adhesive sheet is peeled off.

  “Peeling speed dependency of adhesive strength” refers to the degree to which the adhesive strength (peeling strength) is influenced by the peeling speed when peeling the adhesive sheet. “Peeling temperature dependence of adhesive strength” refers to the degree to which the adhesive strength (peeling strength) is affected by the peeling temperature when peeling an adhesive sheet.

  The molecular weight distribution (Mw / Mn) measured by the GPC method of the RAFT polymer (A) is 3.0 or less, preferably 2.8 or less, more preferably 2.5 or less. Since the RAFT polymer (A) having Mw / Mn in the above range has a uniform molecular weight and a small amount of low molecular weight components, the resulting pressure-sensitive adhesive sheet is excellent in heat resistance and is attached by a low molecular weight material when the pressure-sensitive adhesive sheet is peeled off. It can reduce body contamination. When Mw / Mn exceeds the above range, the adherence to the adherend under heat resistant conditions increases, and the dependency of the adhesive force on the peeling rate and the peeling temperature increases.

  Moreover, in the conventional composition for adhesives, in order to ensure cohesion force, it is required that Mw of a polymer is about 250,000 or more. On the other hand, in the composition for pressure-sensitive adhesives of the present invention, the polymer exhibits excellent cohesive force despite the polymer Mw being 200,000 or less, and low molecular weight components adhere to the adherend even under heat resistant conditions. This prevents contamination of the adherend.

  The RAFT polymer (A) has a small molecular weight distribution, and the RAFT polymer (A) contains a number of hydroxyl groups derived from a hydroxyl group-containing monomer that serves as a crosslinking point with the polyfunctional isocyanate compound (B). It is considered that a highly cohesive pressure-sensitive adhesive layer can be formed. For this reason, by using the composition for pressure-sensitive adhesives of the present invention, it has excellent adhesive performance that suppresses an increase in adhesive strength over time even under heat-resistant conditions, and also depends on the peeling speed dependence and peeling temperature dependence of adhesive strength. It is possible to form an adhesive having excellent re-peeling performance such as low property.

  In the RAFT polymer (A), the hydroxyl group that the structural unit derived from the hydroxyl group-containing monomer has becomes a crosslinking point that is crosslinked by the polyfunctional isocyanate compound (B). In the RAFT polymer (A), the content of the structural unit derived from the hydroxyl group-containing monomer is usually 0.1 to 30% by mass, preferably 0.5 to 20% by mass, more preferably based on the total structural unit amount. Is 1-10 mass%. When this content is in the above range, it is preferable from the viewpoint of crosslinkability of the RAFT polymer (A).

  Content of RAFT polymer (A) in the composition for adhesives of this invention is 50-99.9 mass% normally in 100 mass% of solid content except the solvent of a composition, More preferably, it is 70-99. It is 9 mass%, Most preferably, it is 80-99.9 mass%. When the content of the RAFT polymer (A) is in the above range, the performance as an adhesive is balanced and the adhesive properties are excellent.

  The (meth) acrylic acid ester polymer (A) is obtained, for example, by RAFT polymerization using at least a hydroxyl group-containing monomer as a raw material monomer. The RAFT polymerization method is a method of polymerizing a radically polymerizable compound as a raw material monomer in the presence of a RAFT agent. The whole amount of the raw material monomers may be batch charged and polymerized, or after a part of the raw material monomers are polymerized, the remaining monomer components may be added continuously or intermittently for polymerization.

<RAFT agent>
As the RAFT agent, a conventionally known compound can be used and is not particularly limited. Examples of the RAFT agent include thiocarbonylthio compounds such as dithioesters, trithiocarbonates, dithiocarbamates, and xanthates. Specifically, the dithioesters represented by the formula (a1-1) and the formula (a1-2) ) Or a trithiocarbonate represented by the formula (a1-2 ′), a dithiocarbamate represented by the formula (a1-3), and a xanthate represented by the formula (a1-4).

  The meanings of the symbols in formulas (a1-1) to (a1-4) are as follows.

Z ¹ is an aryl group or an alkyl group, for example, an aryl group having 6 to 8 carbon atoms such as a phenyl group or a cyanophenyl group, or an alkyl group having 2 to 8 carbon atoms such as an ethyl group. Z ² is an alkyl group, for example, an alkyl group having 2 to 18 carbon atoms such as a dodecyl group. Z ³ and Z ⁴ are each independently an alkyl group, an aryl group or a 4-pyridyl group, for example, an alkyl group having 1 to 8 carbon atoms such as a methyl group, or an aryl group having 6 to 8 carbon atoms such as a phenyl group. . Z ³ and Z ⁴ may be bonded to each other to form a heterocyclic ring such as a pyrrole ring or a pyrrolidone ring together with the N atom in formula (a1-3). Z ⁵ is an alkyl group, for example, an alkyl group having 1 to 8 carbon atoms such as an ethyl group.

R is a monovalent organic group, for example
(I) an alkyl group, and (ii) one or more hydrogen atoms of the alkyl group are a phenyl group, a cyano group, a hydroxyl group, a carboxyl group, an alkoxycarbonyl group having 1 to 4 carbon atoms, a phenoxycarbonyl group, an acetoxy It includes at least one substituted group with a group selected from the group R _s consisting of groups and below g1 to g4.

  In formula (a1-2 '), two Rs may be the same or different.

  Carbon number of the alkyl group in R is 1-18 normally, Preferably it is 2-12.

  The above formulas g1 to g4 and * represent bonding positions. In said formula g2, A is a C2-C5 alkylene group, n is an integer of 10-300.

In particular, from the viewpoint of a homolytic leaving group, R is a hydrogen atom bonded to a carbon atom bonded to S, which (I) the carbon bonded to S has a tertiary carbon alkyl group and (II) the alkyl group has A group in which one or two or more are substituted with at least one group selected from the group R _s is preferable.

  Examples of the dithioester (a1-1) include the following compounds.

  Examples of trithiocarbonates (a1-2) and (a1-2 ′) include the following compounds.

  In the formula, n is an integer of 10 to 300.

  Examples of the dithiocarbamate (a1-3) include the following compounds.

  Examples of xanthate (a1-4) include the following compounds.

  Examples of trithiocarbonate also include a compound represented by the formula (a1-2 ″).

In formula (a1-2 ″), each R ¹ is independently a divalent organic group.

  The compound (a1-2 ″) has a trithiocarbonate structure near the center or the center of the molecule and has hydroxyl groups at both ends of the molecule. The compound (a1-2 ″) is, for example, JP-A-2007-230947. It can synthesize | combine according to the method of gazette publication.

  By conducting RAFT polymerization using the compound (a1-2 ″) as the RAFT agent, structural units derived from the radical polymerizable compound are bonded almost uniformly on both sides of the trithiocarbonate structure in the center of the molecule or in the vicinity of the center. A highly symmetrical chain polymer having hydroxyl groups bonded to both ends of the molecule can be obtained.

  Examples of the compound (a1-2 ″) include a compound represented by the formula (a1-2 ″ -1) and a compound represented by the formula (a1-2 ″ -2).

  Compound (a1-2 ″ -1) has a trithiocarbonate structure in the vicinity of the center or center of the molecule, and has one hydroxyl group at each end of the molecule.

In formula (a1-2 ″ -1), each X is independently —COO—, —CONR ³ — or a direct bond, R ³ is each independently an alkyl group, and the number of carbon atoms of the alkyl group is preferably 1 to 4, more preferably 1 to 3; each R ² is independently an alkylene group, and the alkylene group preferably has 1 to 4, more preferably 1 to 3 carbon atoms; Ar is each independently Are groups in which at least one of the aromatic ring hydrogen contained in the phenylene group, naphthylene group, phenylene group, or naphthylene group is substituted with a substituent, such as an alkyl group or an alkoxy group. , X represents a carbonyl group in —COO— and —CONR ³ — bonded to Ar. Two Xs are preferably the same group, and two R ² are The same group is preferable, and two R ³ are preferably the same group, and two Ar are preferably the same group.

  Compound (a1-2 ″ -2) has a trithiocarbonate structure in the vicinity of the center or the center of the molecule, and has two hydroxyl groups at both ends of the molecule.

In formula (a1-2 ″ -2), X and Ar have the same meanings as the same symbols in formula (a1-2 ″ -1); each R ⁴ is independently an alkylene group, and each R ⁵ is independently It is a direct bond or an alkylene group, and the carbon number of these alkylene groups is preferably 1 to 4, more preferably 1 to 3. Two X are preferably the same group, two R ⁴ are preferably the same group, two R ⁵ are preferably the same group, and two Ar are the same group It is preferable.

  Examples of trithiocarbonate (a1-2 ″) include the following compounds.

<< Amount of RAFT agent used >>
The amount of the RAFT agent used is usually 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the total amount of raw material monomers. If the amount of RAFT agent used is not less than the lower limit of the above range, the reaction control is easy, and if it is not more than the upper limit of the above range, it is easy to adjust the weight average molecular weight of the resulting polymer to the above range. .

<Raw monomer>
In RAFT polymerization, it is preferable to use at least a hydroxyl group-containing monomer as a raw material monomer. Moreover, it is preferable to use (meth) acrylic acid ester other than a hydroxyl-containing monomer as a raw material monomer. In addition, functional group-containing monomers other than hydroxyl group-containing monomers and other copolymerizable monomers can be used.

<< Hydroxyl group-containing monomer >>
Examples of the hydroxyl group-containing monomer include a hydroxyl group-containing (meth) acrylate, specifically, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate. , Hydroxyalkyl (meth) acrylates such as 6-hydroxyhexyl (meth) acrylate and 8-hydroxyoctyl (meth) acrylate. Carbon number of the alkyl group in hydroxyalkyl (meth) acrylate is 2-8 normally, Preferably it is 2-6.

  The amount of the hydroxyl group-containing monomer used in the RAFT polymerization is usually 0.1 to 30% by mass, preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, based on the total mass of all raw material monomers. . When the amount of the hydroxyl group-containing monomer is within the above range, it is preferable from the viewpoint of crosslinkability of the resulting RAFT polymer (A).

  The hydroxyl group-containing monomer can be used alone or in combination of two or more.

<< (Meth) acrylic acid ester >>
Examples of the (meth) acrylic acid ester include alkyl (meth) acrylate, alkoxyalkyl (meth) acrylate, alkoxypolyalkylene glycol mono (meth) acrylate, alicyclic group, and aromatic ring-containing (meth) acrylate. However, functional group-containing (meth) acrylates such as hydroxyl group-containing (meth) acrylate; carboxyl group-containing (meth) acrylate and amino group-containing (meth) acrylate are excluded from (meth) acrylic acid esters.

  It is preferable that carbon number of the alkyl group in alkyl (meth) acrylate is 1-20. Examples of the alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, n-butyl (meth) acrylate, and iso-butyl ( (Meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, Decyl (meth) acrylate, undeca (meth) acrylate, lauryl (meth) acrylate, oleyl (meth) acrylate, n-stearyl (meth) acrylate, iso-stearyl (meth) acrylate, dide (Meth) acrylate.

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

  Examples of the alkoxypolyalkylene glycol mono (meth) acrylate include methoxydiethylene glycol mono (meth) acrylate, methoxydipropylene glycol mono (meth) acrylate, ethoxytriethylene glycol mono (meth) acrylate, ethoxydiethylene glycol mono (meth) acrylate, And methoxytriethylene glycol mono (meth) acrylate.

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

  The total amount of (meth) acrylic acid ester used in RAFT polymerization is usually 70 to 99.9% by mass, preferably 80 to 99.5% by mass, more preferably 89.95 to the total mass of all raw material monomers. It is 98.95 mass%.

  The (meth) acrylic acid ester can be used alone or in combination of two or more.

《Functional group-containing monomer》
Examples of the functional group-containing monomer include an acid group-containing monomer, an amino group-containing monomer, an amide group-containing monomer, a nitrogen-based heterocyclic ring-containing monomer, and a cyano group-containing monomer. Examples of the acid group include a carboxyl group, an acid anhydride group, a phosphoric acid group, and a sulfuric acid group.

  Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth) acrylate, 5-carboxypentyl (meth) acrylate, mono (meth) acryloyloxyethyl ester succinate, and ω-carboxypolycaprolactone mono (meth) acrylate. Carboxyl group-containing (meth) acrylates such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid. Examples of the acid anhydride group-containing monomer include maleic anhydride. Examples of the phosphate group-containing monomer include (meth) acrylic monomers having a phosphate group in the side chain, and examples of the sulfate group-containing monomer include (meth) acrylic monomers having a sulfate group in the side chain.

  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, and N-hexyl (meth) acrylamide. Examples of the nitrogen heterocycle-containing monomer include vinyl pyrrolidone, acryloyl morpholine, and vinyl caprolactam. Examples of the cyano group-containing monomer include cyano (meth) acrylate and (meth) acrylonitrile.

  The total amount of the functional group-containing monomer used in the RAFT polymerization is preferably 0 to 10% by mass, more preferably 0.05 to 5% by mass, based on the total mass of all raw material monomers.

  The functional group-containing monomer can be used alone or in combination of two or more.

《Copolymerizable monomer》
Examples of copolymerizable monomers include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, octyl styrene, and other alkyl styrenes, fluorostyrene, chlorostyrene, bromostyrene, dibromo. Examples thereof include styrene monomers such as styrene, iodinated styrene, nitrostyrene, acetylstyrene, and methoxystyrene, and vinyl acetate.

  The copolymerizable monomer can be used alone or in combination of two or more.

<Polymerization initiator>
RAFT polymerization is preferably performed in the presence of a polymerization initiator. As the polymerization initiator, for example, include conventional organic-based polymerization initiator, specifically, benzoyl peroxide, peroxides such as Lau Royle, 2,2' A azobisisobutyronitrile An azo compound such as Among these, an azo compound is preferable.

Examples of the azo compound include 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), and 2,2′-azobis (2-cyclopropyl). Propionitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile) 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis ( N, N'-dimethylene isobutyl amidine), 2, 2'-azobis (isobutyramide) dihydrate, 4,4'-azobis (4-cyano pentanoic acid), 2 , 2′-azobis (2-cyanopropanol), dimethyl-2,2′-azobis (2-methylpropionate), 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide ].

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

  The amount of the polymerization initiator used is usually 0.001 to 2 parts by mass, preferably 0.002 to 1 part by mass with respect to 100 parts by mass of the raw material monomer. Moreover, the usage-amount of a polymerization initiator is 0.1-3000 mol normally with respect to 1 mol of RAFT agents, Preferably it is 1-10000 mol.

<Polymerization conditions>
The reaction temperature in the RAFT polymerization method is usually 60 to 120 ° C., preferably 80 to 110 ° C., and is usually carried out in an inert gas atmosphere such as nitrogen, argon or helium. The reaction can be performed under any of the conditions of reduced pressure and reduced pressure, and is usually performed at normal pressure. Moreover, reaction time is 1 to 14 hours normally, Preferably it is 2 to 12 hours. Regarding polymerization conditions, for example, JP-A-2007-230947 and JP-A-2011-52057 can be referred to.

  In RAFT polymerization, the reaction is usually carried out without using a reaction solvent, but a reaction solvent may be used if necessary. Examples of the reaction solvent include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; cyclopentane, cyclohexane and cycloheptane. Cycloaliphatic hydrocarbons such as cyclooctane; ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, diphenyl ether; chloroform, carbon tetrachloride, Halogenated hydrocarbons such as 1,2-dichloroethane and chlorobenzene; esters such as ethyl acetate, propyl acetate, butyl acetate and methyl propionate; acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, cyclohexane Ketones such as non; amides such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; sulfoxides such as dimethyl sulfoxide and sulfolane Can be mentioned. These solvents can be used alone or in combination of two or more.

[Polyfunctional isocyanate compound (B)]
The polyfunctional isocyanate compound (B) is an isocyanate compound having 3 or more isocyanate groups in one molecule. A crosslinked body (network polymer) can be formed by crosslinking the polymer (A) with the compound (B).

  The number of isocyanate groups in the polyfunctional isocyanate compound (B) is 3 or more, preferably 3 to 6, and more preferably 3 to 4. It is preferable for the number of isocyanate groups to be in the above range from the viewpoint of the crosslinking reaction efficiency between the polymer (A) and the compound (B) and the flexibility of the pressure-sensitive adhesive.

  The molecular weight of the polyfunctional isocyanate compound (B) is usually 200 to 2,000, preferably 350 to 1,000. Since the cross-linking agent having a molecular weight of 350 or more has low volatility, the odor derived from the cross-linking agent can be reduced.

  Examples of the polyfunctional isocyanate compound (B) include multimers (for example, dimers or trimers, isocyanurates) and derivatives (for example, polyhydric alcohols and 3 or more molecules) of difunctional or trifunctional isocyanates. Product of addition reaction with diisocyanate) and polymer. Moreover, aromatic polyisocyanate, aliphatic polyisocyanate, and alicyclic polyisocyanate having 3 or more isocyanate groups can also be mentioned.

  Examples of the diisocyanate in the multimer, the derivative and the polymer include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, and 3-methyl-1,5. -C4-C30 aliphatic diisocyanates such as pentane diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate; isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diene 7-30 carbon atoms such as isocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate Alicyclic diisocyanate; phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and aromatic diisocyanates having 8 to 30 carbon atoms, such as diphenyl propane diisocyanate.

  Examples of the polyhydric alcohol in the above derivative include trivalent or higher alcohols such as trimethylolpropane, glycerin, and pentaerythritol as low molecular weight polyhydric alcohols; examples of high molecular weight polyhydric alcohols include polyether polyols, A polyester polyol is mentioned.

  Specific examples of the polyfunctional isocyanate compound (B) include a trimer of diphenylmethane diisocyanate, a polymethylene polyphenyl polyisocyanate, an isocyanurate of hexamethylene diisocyanate, a reaction product of trimethylolpropane and tolylene diisocyanate (for example, triethylene diisocyanate). Diisocyanate trimer adducts), reaction products of trimethylolpropane and hexamethylene diisocyanate (eg, trimer adducts of hexamethylene diisocyanate), polyether polyisocyanates, polyester polyisocyanates, 2,4,6- Examples include triisocyanate toluene, 1,3,5-triisocyanatebenzene, and 4,4 ′, 4 ″ -triphenylmethane triisocyanate.

  As a commercial item of a polyfunctional isocyanate compound (B), the brand name "L-45" by Soken Chemical Co., Ltd., the brand name "Duranate TPA-100" by Asahi Kasei Chemicals, the brand name by Nippon Polyurethane Industry Co., Ltd. "Coronate L", "Coronate HL", "Coronate HK", "Coronate HX", "Coronate 2096", and "Millionate MR200".

  Content of the polyfunctional isocyanate compound (B) in the composition for adhesives of this invention is 0.1-50 mass parts normally with respect to 100 mass parts of RAFT polymer (A) by solid content ratio, Preferably Is 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass.

  When content of a compound (B) exists in the said range, the cohesiveness of the composition obtained will not fall and it is excellent in the balance of adhesive physical property. In particular, when the compound (B) is used at the above lower limit or more, the reaction rate between the hydroxyl group and the isocyanate group is improved. If it is less than the above lower limit value, curing may be insufficient and adhesive performance may not be exhibited.

  In addition, in the range which does not impair the balance of adhesive physical properties, the composition of the present invention may contain an isocyanate compound having 2 isocyanate groups in one molecule in addition to the polyfunctional isocyanate compound (B). Examples thereof include diisocyanates such as aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate.

[Additive]
The composition for pressure-sensitive adhesives of the present invention is an organic solvent, an antistatic agent, an ultraviolet absorber, an antioxidant, a tackifying resin, in addition to the above components, as long as the transparency, visibility and effects of the present invention are not impaired. 1 type (s) or 2 or more types selected from a plasticizer, a filler, a stabilizer, a softening agent, and a wettability adjusting agent may be contained.

  As the organic solvent, the reaction solvent described in the column of RAFT polymerization can be used. For example, the polymer solution containing the RAFT polymer (A) and the reaction solvent obtained by RAFT polymerization and the polyfunctional isocyanate compound (B) can be mixed to prepare a pressure-sensitive adhesive composition. In the pressure-sensitive adhesive composition of the present invention, the content of the organic solvent is usually 0 to 90% by mass, preferably 10 to 80% by mass.

[Adhesive]
The pressure-sensitive adhesive and pressure-sensitive adhesive layer of the present invention are formed from the above-described pressure-sensitive adhesive composition.

  For example, the pressure-sensitive adhesive and pressure-sensitive adhesive layer of the present invention can be prepared by, for example, advancing the crosslinking reaction in the above-described pressure-sensitive adhesive composition, thereby specifically converting the (meth) acrylic acid ester polymer (A) to a polyfunctional isocyanate compound ( Obtained by crosslinking in B). The pressure-sensitive adhesive and pressure-sensitive adhesive layer thus obtained are excellent in, for example, pressure-sensitive adhesive strength under heat resistance and stability over time, and have a low degree of contamination to the adherend when peeling the pressure-sensitive adhesive sheet. It has a function that the dependence and the peeling temperature dependence are small.

  The pressure-sensitive adhesive composition is applied by a known method such as knife coating method, roll coating method, bar coating method, blade coating method, die coating method, gravure coating method, etc. -A drying method can be used.

  The conditions for forming the pressure-sensitive adhesive and the pressure-sensitive adhesive layer are as follows. For example, the pressure-sensitive adhesive composition of the present invention is applied onto a support, and is usually dried at 60 to 120 ° C., preferably 70 to 110 ° C., usually for 1 to 5 minutes, preferably 2 to 4 minutes. Form. The film thickness of the dried coating film is usually 3 to 100 μm, preferably 5 to 50 μm.

  The pressure-sensitive adhesive and the pressure-sensitive adhesive layer are preferably formed under the following conditions. After apply | coating the composition for adhesives of this invention on a support body and sticking a cover film on the coating film formed on the said conditions, it is normally 3 days or more, Preferably it is 7-10 days, Usually 5-60 degreeC. , Preferably under an environment of 15 to 40 ° C. When crosslinking is performed under the aging conditions as described above, a crosslinked body (network polymer) can be efficiently formed.

  Examples of the support and the cover film include polyester films such as polyethylene terephthalate; plastic films such as polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer.

  The gel fraction of the pressure-sensitive adhesive and pressure-sensitive adhesive layer of the present invention is preferably 50 to 99% by mass, more preferably 70 to 98% by mass. When the gel fraction is within the above range, it is preferable in terms of low contamination to the adherend.

[Adhesive sheet]
The adhesive sheet of this invention has a base material and the adhesive layer formed from the above-mentioned composition for adhesives. This pressure-sensitive adhesive sheet may have a protective film on the pressure-sensitive adhesive layer.

  Examples of the base material and the protective film include polyester films such as polyethylene terephthalate; plastic films such as polyolefin films such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer.

  The thickness of the pressure-sensitive adhesive layer is usually 3 to 100 μm, preferably 5 to 50 μm. Although the film thickness of a base material and a protective film is not specifically limited, Usually, 10-100 micrometers, Preferably it is 25-50 micrometers.

  The pressure-sensitive adhesive sheet of the present invention has a good balance of pressure-sensitive adhesive performance, and has a feature that the adherend is less contaminated when it is peeled off after being affixed to the adherend. For example, even when the pressure-sensitive adhesive sheet of the present invention is placed under a heat resistant condition of about 150 ° C., an increase in pressure-sensitive adhesive force with time can be suppressed.

  In addition, when the pressure-sensitive adhesive sheet of the present invention is applied to an adherend and then peeled off, the pressure difference between the case where the pressure-sensitive adhesive sheet is peeled off at a low speed and the case where the pressure-sensitive adhesive sheet is peeled off at a high speed is small. The difference in peeling force between the case where it peels off and the case where it peels off in a low temperature environment is small.

  Accordingly, the pressure-sensitive adhesive sheet of the present invention can be widely used as an industrial pressure-sensitive adhesive sheet, but can be used as a heat-resistant protective film, particularly as a re-peeling protective film or an optical protective film.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples. In the following description of Examples and the like, “part” means “part by mass” unless otherwise specified.

  Each measured value in the examples was determined by the following method.

[(Meth) acrylic acid ester polymer (acrylic polymer)]
<1. Molecular weight and molecular weight distribution>
About the (meth) acrylic acid ester polymer, the weight average molecular weight (Mw) and number average molecular weight (Mn) by standard polystyrene conversion were calculated | required by the gel permeation chromatography (GPC) method on the following conditions.
・ Measurement device: HLC-8120GPC (manufactured by Tosoh Corporation)
-GPC column configuration: 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: As will be 1.0 mg / cm ^3, diluting and mobile phase solvent with tetrahydrofuran: tetrahydrofuran Flow rate: 1.0 cm ³ / min
-Column temperature: 40 ° C
<2. Viscosity measurement>
For acrylic polymer solution obtained in Examples and the like, said solution containing a 500ml bottle 12 hours after standing immersed in 25 ° C. water bath, in accordance with the measuring method of the type B viscometer, the viscosity was measured at 25 ° C. .

<3. Nonvolatile content measurement>
1 g of the acrylic polymer solution obtained in the production example and the like was put into a precisely weighed tin plate (n1), and the total weight (n2) was precisely weighed, followed by heating at 105 ° C. for 3 hours. Thereafter, the tin plate was allowed to stand in a desiccator at room temperature for 1 hour, then weighed again, and the total weight (n3) after heating was measured. Using the obtained weight measurement values (n1 to n3), the nonvolatile content was calculated from the following formula.

Nonvolatile content (%) = 100 x [weight after heating (n3-n1) / weight before heating (n2-n1)]
<4. Production of (meth) acrylic acid ester polymer>
[Production Example 1]
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 18.98 parts of 2-ethylhexyl acrylate, 1.0 part of 2-hydroxyethyl acrylate, 0.02 part of acrylic acid, Bis [4- {ethyl- (2-hydroxyethyl) aminocarbonyl} -benzyl] trithiocarbonate represented by the formula (manufactured by Nippon Terpene Chemical Co., Ltd.) (hereinafter also referred to as “RAFT agent-1”) 4 parts were charged (initial charge), and the contents of the flask were heated to 90 ° C. while introducing nitrogen gas into the flask.

  Next, 0.03 part of 2,2′-azobisisobutyronitrile (hereinafter also referred to as “AIBN”) is added to the flask under stirring so that the temperature of the contents in the flask can be maintained at 90 ° C. Heating and cooling were continued for 6 hours. One hour after the start of the reaction, a mixed solution of 75.92 parts of 2-ethylhexyl acrylate, 4.0 parts of 2-hydroxyethyl acrylate, and 0.08 part of acrylic acid was dropped into the flask over 1 hour ( Additional preparation). Subsequently, 40.0 parts of ethyl acetate was dripped over 1 hour. Further, 6 hours after the start of the reaction, 0.03 part of AIBN was additionally charged.

  As described above, a polymer solution containing the acrylic polymer (1) was obtained.

  The molecular weight measured by GPC for the acrylic polymer (1) contained in the obtained polymer solution was Mn: 53,000, Mw: 90,000, and Mw / Mn: 1.7. The viscosity of the obtained polymer solution at 25 ° C. was 3.4 Pa · s, and the nonvolatile content was 70% by mass.

[Production Examples 2-7, Comparative Example Production Examples 2-4]
In Production Example 1, the same manner as in Production Example 1 except that the type and amount of raw material monomer (initial charge and additional charge of raw material monomer) and the type and amount of RAFT agent were changed as shown in Table 1. A polymer solution containing the polymer (2) to (7) or the acrylic polymer (c2) to (c4) was obtained.

  RAFT agent-2 is dibenzyltrithiocarbonate ("BlocBuilderDB" from Arkema), and RAFT agent-3 is 2-cyano-2-propylbenzodithioate (Aldrich).

[Comparative Production Example 1] In a flask equipped with a free radical polymerization stirrer, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 94.9 parts of 2-ethylhexyl acrylate, 5.0 parts of 2-hydroxyethyl acrylate, 0.1 parts of acrylic acid, 0.25 parts of n-dodecyl mercaptan, and 100 parts of ethyl acetate were charged, and the contents of the flask were heated to 66-67 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part of dimethyl-2,2′-azobis (2-methylpropionate) (V-601; manufactured by Wako Pure Chemical Industries, Ltd.) was added to the flask with stirring. Heating and cooling were performed for 4 hours so that the temperature of the contents in the flask could be maintained at 66-67 ° C. In this way, a polymer solution containing the acrylic polymer (c1) was obtained.

[Production Example 8]
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 94.9 parts of n-butyl acrylate, 5.0 parts of 4-hydroxybutyl acrylate, 0.1 part of acrylic acid, and RAFT Agent-1 0.2 parts and 40 parts of ethyl acetate were charged, and the contents of the flask were heated to 90 ° C. while introducing nitrogen gas into the flask. Next, 0.1 part of dimethyl-2,2′-azobis (2-methylpropionate) (V-601; manufactured by Wako Pure Chemical Industries, Ltd.) was added to the flask with stirring, and the contents in the flask Heating and cooling were continued so that the temperature of the product could be maintained at 90 ° C., and the reaction was performed for 6 hours.

  As described above, a polymer solution containing the acrylic polymer (8) was obtained.

  The molecular weights measured by GPC for the acrylic polymer (8) contained in the obtained polymer solution were Mn: 67,000, Mw: 145,000, and Mw / Mn: 2.2. The resulting polymer solution had a viscosity at 25 ° C. of 7.4 Pa · s and a nonvolatile content of 70% by mass.

  Table 1 shows the evaluation results of the acrylic polymer.

[Example 1]
The polymer solution containing the acrylic polymer (1) obtained in Production Example 1 and L-45 (manufactured by Soken Chemical Co., Ltd.) as the isocyanate compound were blended with L-45 to 100 parts of the acrylic polymer (1). The mixture was mixed at a ratio (solid content ratio) of 9 parts to obtain an adhesive composition.

  After removing the foam, the adhesive composition was applied to a polyethylene terephthalate (PET) separator (trade name: Therapy MFA; manufactured by Toray Film Co., Ltd.) using a doctor blade so that the dry film thickness was 25 μm. A coating film was formed on the PET separator by drying at 80 ° C. for 3 minutes. After the drying, a PET film having a thickness of 25 μm is pasted on the surface of the coating film opposite to the PET separator, and left to stand for 7 days under conditions of a room temperature of 23 ° C. and a humidity of 65%, whereby a PET separator / adhesive layer / The adhesive sheet which consists of PET films was obtained.

[Examples 2 to 8, Comparative Examples 1 to 5]
In Example 1, the composition for adhesives and an adhesive sheet were obtained similarly to Example 1 except having changed the kind and compounding quantity of an acrylic polymer and an isocyanate compound as having described in Table 2.

[Gel fraction]
Place 0.1 g of the pressure-sensitive adhesive layer obtained in Examples into a sample bottle, add 30 cc of ethyl acetate and let it infiltrate for 24 hours, and then filter the contents of the sample bottle with a 200-mesh stainless steel wire mesh. The weight of the residue after drying on a wire mesh at 100 ° C. for 2 hours was defined as the dry weight. The gel fraction was computed from the following formula using the obtained weight measurement value.

Gel fraction (%) = 100 x (dry weight / collected pressure-sensitive adhesive layer weight)
[Adhesive sheet]
<1. Heat resistance test>
Under the conditions of 25 ° C./50% RH, the PET separator of the pressure-sensitive adhesive sheet obtained in Examples and the like was peeled off, and the exposed pressure-sensitive adhesive layer surface was pressure-bonded (attached) to a SUS plate using a 2 kg roller.

  (I) After standing for 20 minutes from the pasting, (ii) after standing for 3 hours at 150 ° C. and in dry conditions, and further standing for 20 minutes under conditions of 25 ° C./50% RH, (iii) 150 After standing for 6 hours at 25 ° C. and 50% RH, the plate was further left for 20 minutes under conditions of 25 ° C./50% RH. The film was peeled at a peeling speed of 300 mm / min, and the peel strength (adhesive strength) of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet was measured. The adhesive force after (i) was the initial adhesive force, the adhesive force after (ii) was the adhesive force after 3 hours, and the adhesive force after (iii) was the adhesive force after 6 hours. Moreover, the state of the adherend when peeled after (iii) was visually observed.

<2. Adhesive properties>
Under the conditions of 25 ° C./50% RH, the PET separator of the pressure-sensitive adhesive sheet obtained in Examples and the like was peeled off, and the exposed pressure-sensitive adhesive layer surface was pressure-bonded to a SUS plate using a 2 kg roller.

  20 minutes after sticking, the pressure-sensitive adhesive sheet was peeled from the SUS plate at 25 ° C./50% RH and a peeling angle of 180 ° at a peeling speed of 50 mm / min (A1), 300 mm / min (A2), and 1000 mm / min (A3). It peeled and the peeling force (adhesive force) of the adhesive layer of an adhesive sheet was measured, respectively. In the case of A3, the contamination state of the adherend after peeling was visually observed.

  In addition, 20 minutes after sticking, the pressure-sensitive adhesive sheet was peeled from the SUS plate under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180 °, −20 ° C., dry condition (B1), 25 ° C./50% RH condition (B2). It peeled on 105 degreeC and dry conditions (B3), and the peeling force (adhesive force) of the adhesive layer of an adhesive sheet was measured, respectively. In the case of B3, the contamination state of the adherend after peeling was visually observed.

  The isocyanate compounds used in Examples and the like are as follows.

Claims (6)

(A) The weight average molecular weight (Mw) measured by the gel permeation chromatography method obtained by RAFT polymerization using the RAFT agent represented by the following formula is 60,000 to 200,000, and the molecular weight distribution ( (Mw / Mn) is 3.0 or less, and a (meth) acrylic acid ester polymer having a structural unit derived from a hydroxyl group-containing monomer,
(B) A composition for pressure-sensitive adhesives containing an isocyanate compound having 3 or more isocyanate groups in one molecule.

[Wherein, R is a monovalent organic group, and two Rs may be the same or different. ] The pressure-sensitive adhesive composition according to claim 1, wherein the RAFT agent is represented by the following formula.

[Wherein R ¹ Are each independently a divalent organic group. ] In the RAFT agent, R in the formula is
(I) an alkyl group, or
(Ii) one or more of the hydrogen atoms of the alkyl group is a phenyl group, a cyano group, a hydroxyl group, a carboxyl group, an alkoxycarbonyl group having 1 to 4 carbon atoms, a phenoxycarbonyl group, an acetoxy group and the following g1 to g4 Group R _s A group substituted with at least one group selected from
The composition for pressure-sensitive adhesives according to claim 1.

[In the above formulas g1 to g4, * represents a bonding position. In said formula g2, A is a C2-C5 alkylene group, n is an integer of 10-300. ] Any 1 item | term of Claims 1-3 which contains the said isocyanate compound (B) in 0.1-50 mass parts by solid content ratio with respect to 100 mass parts of (meth) acrylic acid ester polymer (A). The composition for adhesives of claim | item. The adhesive formed from the composition of any one of Claims 1-4 . A substrate;
The adhesive sheet which has an adhesive layer formed from the composition of any one of Claims 1-4 .