Adhesive composition and adhesive sheet

Abstract

SOLUTION: To provide an adhesive composition comprising a (meth)acrylic polymer (A) which is a polymer of a monomer component containing 0.5 to 89.8 mass% of a cyclic polymerizable monomer, 10.1 to 90.0 mass% of a (meth)acrylic acid alkyl ester having an alkyl group having 4 to 18 carbon atoms and 0.1 to 9.5 mass% of a crosslinkable functional group-containing monomer and has a glass transition temperature of less than 0°C and a crosslinking agent (B).EFFECT: There are provided an adhesive composition and an adhesive sheet excellent in heat resistance. The adhesive composition is excellent in adhesiveness especially to a polyimide base material and a polytetrafluoroethylene base material.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet, and more particularly to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet having excellent heat resistance. [Background technology]

[0002] 2. Description of the Related Art Adhesive tapes have been used for fixing or bonding components in electronic components, vehicles, houses, building materials, and the like. Adhesive tapes are required to have various performance characteristics depending on the environment and location of use. For example, when used in a high-temperature environment or when bonded parts are exposed to a high-temperature environment during transportation, the adhesive tape is required to not peel off from the adherend even in the high-temperature environment, and the adhesive layer of the adhesive tape is required not to lose adhesion to the substrate.

[0003] Although there has been much research and development into improving the heat resistance of adhesive tapes, in recent years there has been a demand for even better heat resistance. Cited Document 1 discloses a resin composition for optical tapes that can form an adhesive layer with excellent transparency and adhesive properties. The composition is characterized by containing a resin obtained by polymerizing a monomer composition containing an α-allyloxymethylacrylic acid monomer (AMA monomer) and a crosslinking agent.

[0004] Cited Document 2 discloses a pressure-sensitive adhesive composition and a pressure-sensitive adhesive product. The pressure-sensitive adhesive composition is characterized by comprising a polymer obtained by polymerizing a monomer composition containing a (meth)acrylic acid ester having an alkyl group having 2 to 18 carbon atoms and a monomer having a specific structure, and a crosslinking agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-3960 A [Patent Document 2] JP 2015-3959 A Summary of the Invention [Problem to be solved by the invention]

[0006] Although cited documents 1 and 2 describe the adhesive strength of each composition at 23°C, they make no mention of the adhesive strength in a high temperature environment, and no knowledge regarding heat resistance was obtained from cited documents 1 and 2.

[0007] An object of the present invention is to provide a pressure-sensitive adhesive having excellent heat resistance. [Means for solving the problem]

[0008] The present invention has been made in consideration of the above circumstances, and has been completed based on the discovery that a pressure-sensitive adhesive sheet having excellent heat resistance can be obtained by using a pressure-sensitive adhesive composition containing a polymer obtained from a monomer component including a cyclopolymerization monomer.

[0009] The present invention relates to, for example, the following [1] to [5]. [1] A (meth)acrylic polymer (A) which is a polymer of monomer components including 0.5 to 89.8% by mass of a cyclopolymerization monomer, 10.1 to 90.0% by mass of a (meth)acrylic acid alkyl ester having an alkyl group of 4 to 18 carbon atoms, and 0.1 to 9.5% by mass of a crosslinkable functional group-containing monomer, and has a glass transition temperature of less than 0°C; Crosslinker (B) A pressure-sensitive adhesive composition comprising: [2] The pressure-sensitive adhesive composition according to [1], wherein the (meth)acrylic polymer (A) is a polymer of monomer components including 10.5 to 79.5 mass % of the cyclic polymerization monomer, 20.0 to 84.0 mass % of the (meth)acrylic acid alkyl ester, and 0.5 to 5.5 mass % of the crosslinkable functional group-containing monomer. [3] The pressure-sensitive adhesive composition according to [1] or [2], wherein the cyclopolymerizable monomer is a monomer represented by the following formula (1) or formula (2): [ka] (In the formula, R 1 is an alkyl group having 1 to 18 carbon atoms. [ka] (In the formula, R 2 is an alkyl group having 1 to 18 carbon atoms. [4] R in the above formula (1) 1 and R in Eq. (2) 2 is an alkyl group having 6 to 18 carbon atoms. [5] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer produced from the pressure-sensitive adhesive composition according to any one of [1] to [4] provided on a polyimide substrate or a polytetrafluoroethylene substrate. Effect of the Invention

[0010] The pressure-sensitive adhesive sheet obtained by the present invention has excellent heat resistance. In addition, the pressure-sensitive adhesive layer obtained by the present invention can maintain a low haze regardless of the amount of the cyclopolymerization monomer used by appropriately selecting the cyclopolymerization monomer, and can maintain adhesive strength even when exposed to a humid and hot environment. Furthermore, the pressure-sensitive adhesive composition of the present invention has excellent adhesion, particularly to polyimide substrates and polytetrafluoroethylene substrates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet of the present invention will be described below. In the present invention, acrylic and methacrylic are also collectively referred to as "(meth)acrylic", and acrylate and methacrylate are also collectively referred to as "(meth)acrylate".

[0012] <Adhesive composition> The pressure-sensitive adhesive composition of the present invention contains a (meth)acrylic polymer (A) and a crosslinking agent (B).

[0013] [(Meth)acrylic polymer (A)] The (meth)acrylic polymer (A) is a polymer of monomer components including a cyclopolymerization monomer, a (meth)acrylic acid alkyl ester having an alkyl group with a carbon number of 4 to 18, and a crosslinkable functional group-containing monomer. The monomer components may further include other monomers (other monomers).

[0014] The (meth)acrylic polymer (A) contains a cyclic structural unit formed by polymerization of a cyclopolymerization monomer, and this structural unit enables the pressure-sensitive adhesive sheet obtained from the pressure-sensitive adhesive composition of the present invention to exhibit good heat resistance and adhesive properties.

[0015] (Cyclopolymerization monomer) The cyclopolymerization monomer is not particularly limited as long as it is polymerizable with the (meth)acrylic acid alkyl ester and the crosslinkable functional group-containing monomer, and suitable examples of the cyclopolymerization monomer include the monomers represented by the following formulae (1) to (7): From the viewpoint of achieving both the heat resistance and adhesive properties of the pressure-sensitive adhesive sheet, the monomer represented by the following formula (1) or (2) is preferred, and from the viewpoint of the heat resistance of the pressure-sensitive adhesive sheet, the monomer represented by the following formula (1) is particularly preferred.

[0016] In the present invention, good heat resistance means that there is no significant difference between the initial adhesive strength of the adhesive sheet and the adhesive strength after being left in a thermal environment, and that the adhesive sheet does not peel off from the adherend, etc., during a heat resistance test.

[0017] [ka]

[0018] [ka]

[0019] [ka]

[0020] [ka]

[0021] [ka]

[0022] [ka]

[0023] [ka] R in formula (1), formula (2), formula (3), formula (5), and formula (6) 1 , R 2 , R 3 , R 7 , and R 10 is an alkyl group having 1 to 18 carbon atoms.

[0024] Examples of the alkyl group having 1 to 18 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an isooctyl group, a 2-ethylhexyl group, an n-nonyl group, an isononyl group, an n-decyl group, an isodecyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, and an isooctadecyl group.

[0025] R in formula (1), formula (2), formula (3), formula (5), and formula (6) 1 , R 2 , R 3 , R 7 , and R 10 It is more preferable that the alkyl group has 6 to 18 carbon atoms, since the resulting pressure-sensitive adhesive layer has low haze and excellent heat resistance.

[0026] R in formula (3), formula (4), formula (5) and formula (7) 4 , R 6 , R 8 , and R 12 is an alkyl group having a number of 1 to 18. Among them, from the viewpoint of suppressing the gelation reaction in the cyclopolymerization, R 4 , R 6 , R 8 , and R 12 is more preferably an alkyl group having 3 to 12 carbon atoms.

[0027] R in Equation (4), Equation (6) and Equation (7) 5 , R 9 , and R 11 is hydrogen or an alkyl group having 1 to 6 carbon atoms. Among them, from the viewpoint of increasing the degree of polymerization of the polymer, R 5 , R 9 , and R 11 is more preferably hydrogen or a methyl group.

[0028] Specific examples of the monomer represented by formula (1) include methyl α-allyloxymethylacrylate, ethyl α-allyloxymethylacrylate, n-propyl α-allyloxymethylacrylate, isopropyl α-allyloxymethylacrylate, n-butyl α-allyloxymethylacrylate, sec-butyl α-allyloxymethylacrylate, isobutyl α-allyloxymethylacrylate, tert-butyl α-allyloxymethylacrylate, n-pentyl α-allyloxymethylacrylate, n-hexyl α-allyloxymethylacrylate, n-heptyl α-allyloxymethylacrylate, n-octyl α-allyloxymethylacrylate, isooctyl α-allyloxymethylacrylate, and α-allyloxymethylacrylate. Examples of the acrylates include 2-ethylhexyl α-allyloxymethylacrylate, n-nonyl α-allyloxymethylacrylate, isononyl α-allyloxymethylacrylate, n-decyl α-allyloxymethylacrylate, isodecyl α-allyloxymethylacrylate, n-undecyl α-allyloxymethylacrylate, n-dodecyl α-allyloxymethylacrylate, n-tridecyl α-allyloxymethylacrylate, n-tetradecyl α-allyloxymethylacrylate, n-pentadecyl α-allyloxymethylacrylate, n-hexadecyl α-allyloxymethylacrylate, n-heptadecyl α-allyloxymethylacrylate, n-octadecyl α-allyloxymethylacrylate, and isooctadecyl α-allyloxymethylacrylate.

[0029] Specific examples of the monomer represented by formula (2) include dimethyl-2,2'-[oxybis(methylene)]bis-2-propenoate, diethyl-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-propyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(isopropyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-butyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, bis-2-propenoate, and di(sec-butyl)-2,2'-[oxybis(methylene)]bis-2-propenoate. di(isobutyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(tert-butyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-pentyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-hexyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-heptyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-octyl)-2,2'-[oxybis(methylene)]bis-2-propenoate di(isooctyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(2-ethylhexyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-nonyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(isononyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-decyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(isodecyl)-2,2'-[oxy bis(methylene)]bis-2-propenoate, di(n-undecyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-dodecyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-tridecyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-tetradecyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-pentadecyl)-2,2'-[oxybis(methylene)]bis-2-propenoate, di(n-hexadecyl)-2,Examples of the bis(oxybis(methylene)] bis-2-propenoate include 2'-[oxybis(methylene)] bis-2-propenoate, di(n-heptadecyl)-2,2'-[oxybis(methylene)] bis-2-propenoate, di(n-octadecyl)-2,2'-[oxybis(methylene)] bis-2-propenoate, and di(isooctadecyl)-2,2'-[oxybis(methylene)] bis-2-propenoate.

[0030] The monomer represented by formula (3) can be obtained by the synthesis method disclosed in the following document 1, the monomer represented by formula (4) by the synthesis method disclosed in the following document 2, the monomer represented by formula (5) by the synthesis method disclosed in the following document 3, the monomer represented by formula (6) by the synthesis method disclosed in the following document 4, and the monomer represented by formula (7) by the synthesis method disclosed in the following document 5.

[0031] Reference 1: Lon J. Mathias et al., Journal of Polymer Science Part A: Polymer Chemistry, Vol. 35, pp2111―2121, 1997 Reference 2: Toshiyuki Kodaira et al., Journal of Polymer Science: Polymer Chemistry Edition, Vol. 14, pp1107―1115, 1976 Reference 3: Toshiyuki Kodaira et al., Macromolecules, Vol. 29, 484-485, 1996 Reference 4: Akira Matsumoto et al., Journal of Polymer Science: Polymer Chemistry Edition, Vol. 21, pp609―613, 1983 Reference 5: Toshiyuki Kodaira et al., Journal of Polymer Science: Polymer Chemistry Edition, Vol. 12, pp897―910, ​​1974 These cyclopolymerization monomers may be used alone or in combination of two or more.

[0032] When the monomer component contains the cyclopolymerizable monomer, the pressure-sensitive adhesive sheet obtained from the pressure-sensitive adhesive composition of the present invention, which contains the (meth)acrylic polymer (A) obtained by polymerization of the monomer component, has improved heat resistance.

[0033] The ratio of the cyclopolymerization monomer in the monomer components is from 0.5 to 89.8% by mass, preferably from 10.5 to 79.5% by mass, and more preferably from 20.0 to 70.0% by mass. By setting the ratio of the cyclopolymerization monomer within the above range, a pressure-sensitive adhesive sheet with excellent heat resistance can be obtained.

[0034] ((Meth)acrylic acid alkyl esters having an alkyl group with 4 to 18 carbon atoms) Examples of (meth)acrylic acid alkyl esters having an alkyl group with 4 to 18 carbon atoms include n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, n-heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca(meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, and isooctadecyl (meth)acrylate. Among these, n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferred, and n-butyl (meth)acrylate, which allows the (meth)acrylic polymer (A) to be easily made into a high molecular weight, is more preferred.

[0035] The (meth)acrylic acid alkyl esters having an alkyl group with 4 to 18 carbon atoms may be used alone or in combination of two or more kinds. The proportion of the (meth)acrylic acid alkyl ester having an alkyl group with 4 to 18 carbon atoms in the monomer components is 10.1 to 90.0 mass %, preferably 20.0 to 84.0 mass %, and more preferably 26.0 to 79.0 mass %.

[0036] By setting the ratio of the (meth)acrylic acid alkyl ester having an alkyl group with 4 to 18 carbon atoms within the above range, the molecular weight of the (meth)acrylic polymer can be improved, and a pressure-sensitive adhesive sheet with excellent heat resistance retention can be obtained.

[0037] (Crosslinkable functional group-containing monomer) The crosslinkable functional group-containing monomer is preferably a monomer having at least one of a hydroxy group and a carboxy group as a crosslinkable functional group, and more preferably at least one monomer selected from a hydroxy group-containing monomer and a carboxy group-containing monomer.

[0038] Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, chloro-2-hydroxypropyl acrylate, diethylene glycol mono(meth)acrylate, and allyl alcohol, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred. The hydroxyl group-containing monomer may be used alone or in combination of two or more.

[0039] Examples of the carboxyl group-containing monomer include (meth)acrylic acid, 2-carboxyethyl (meth)acrylate, 3-carboxypropyl (meth)acrylate, 4-carboxybutyl (meth)acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, and maleic anhydride, and (meth)acrylic acid is preferred. The carboxyl group-containing monomer may be used alone or in combination of two or more.

[0040] The proportion of the crosslinkable functional group-containing monomer in the monomer components is from 0.1 to 9.5% by mass, preferably from 0.5 to 5.5% by mass, and more preferably from 1.0 to 4.0% by mass. By setting the ratio of the crosslinkable functional group-containing monomer within the above range, a pressure-sensitive adhesive sheet that is less likely to leave adhesive residue when peeled off from an adherend and has excellent heat resistance can be obtained.

[0041] (Other Monomers) Examples of other monomers that can be included in the monomer component include (meth)acrylic acid alkyl esters having an alkyl group with 1 to 3 carbon atoms, alicyclic hydrocarbon group-containing (meth)acrylates, nitrogen atom-containing monomers, alkoxyalkyl (meth)acrylates, epoxy group-containing (meth)acrylates, acetoacetyl group-containing (meth)acrylates, aromatic ring-containing monomers, methacryloxypropyl methoxysilane, vinyl acetate, vinyl chloride, and (meth)acrylonitrile.

[0042] Examples of the (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 3 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate.

[0043] Examples of the alicyclic hydrocarbon group-containing (meth)acrylate include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate.

[0044] The nitrogen atom-containing monomer includes a monomer having at least one functional group of an amide group or an amino group. Specific examples of the nitrogen atom-containing monomer include amide group-containing monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, acryloylmorpholine, N-vinylacetamide, diacetone(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, vinylpyrrolidone, methylol(meth)acrylamide, and methoxyethyl(meth)acrylamide; and amino group-containing monomers such as N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, and aminoethyl(meth)acrylate.

[0045] Examples of the alkoxyalkyl (meth)acrylate include methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate. An example of the epoxy group-containing (meth)acrylate is glycidyl (meth)acrylate.

[0046] An example of the acetoacetyl group-containing (meth)acrylate is acetoacetoxyethyl (meth)acrylate. Examples of the aromatic ring-containing monomer include benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, styrene, methylstyrene, and vinyltoluene.

[0047] The other monomers may be used alone or in combination of two or more. When the monomer component contains the other monomer, the ratio of the other monomer in the monomer component is preferably 0.1 to 30% by mass, and more preferably 0.2 to 25% by mass.

[0048] The (meth)acrylic polymer (A) has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of usually 100,000 to 2,000,000, and from the viewpoint of the coatability of the pressure-sensitive adhesive composition and the particularly excellent high-temperature properties of the resulting pressure-sensitive adhesive sheet, it is preferably 200,000 to 1,800,000, and more preferably 300,000 to 1,500,000.

[0049] The glass transition temperature (Tg) of the (meth)acrylic polymer (A) measured by a differential scanning calorimeter (DSC) is usually 0° C. or lower, preferably −80 to 0° C., and more preferably −60 to −10° C. If the Tg is within the above range, it is preferable from the viewpoint of the adhesion of the pressure-sensitive adhesive layer to the adherend. On the other hand, if the Tg is equal to or higher than the above lower limit, it is preferable from the viewpoint of excellent cohesive force of the pressure-sensitive adhesive layer and improved durability.

[0050] (Method for producing (meth)acrylic polymer (A)) The (meth)acrylic polymer (A) can be obtained by polymerizing the monomer components by a conventionally known polymerization method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method, or a suspension polymerization method. Among these, the solution polymerization method is preferable. The (meth)acrylic polymer (A) may be obtained as a polymer solution comprising the polymer and an organic solvent.

[0051] For example, a polymerization solvent and monomer components are charged into a reaction vessel, a polymerization initiator is added under an inert gas atmosphere such as nitrogen gas, the reaction initiation temperature is set to usually 40 to 100°C, preferably 50 to 90°C, and the reaction system is maintained at a temperature of usually 50 to 90°C, preferably 60 to 90°C, and the reaction is carried out for 3 to 20 hours to obtain the (meth)acrylic polymer (A).

[0052] Examples of the polymerization initiator include a peroxide-based polymerization initiator and an azo-based polymerization initiator. Examples of the peroxide-based polymerization initiator include t-butyl hydroperoxide, cumene hydroxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propionate, and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propionate. peroxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane.

[0053] Examples of the azo initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 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- azo compounds such as 2,2'-azobis(N,N'-amidinopropane) dihydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 2,2'-azobis(isobutylamide) dihydrate, 4,4'-azobis(4-cyanopentanoic acid), 2,2'-azobis(2-cyanopropanol), dimethyl-2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide).

[0054] The polymerization initiator may be used alone or in combination of two or more kinds. In addition, there is no restriction on adding the polymerization initiator multiple times during the polymerization. The polymerization initiator is used in an amount of usually 0.001 to 5 parts by mass, preferably 0.005 to 3 parts by mass, based on 100 parts by mass of the monomer components forming the (meth)acrylic polymer (A). In addition, during the polymerization reaction, the polymerization initiator, the chain transfer agent, the polymerizable monomer, and the polymerization solvent may be appropriately added.

[0055] Examples of the polymerization solvent used in the solution polymerization 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; ethers such as diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, and diphenyl ether; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1,2-dichloroethane, and chlorobenzene; 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; and sulfoxides such as dimethyl sulfoxide and sulfolane. The polymerization solvent may be used alone or in combination of two or more kinds.

[0056] [Crosslinking agent (B)] The crosslinking agent (B) is not particularly limited as long as it can crosslink the (meth)acrylic polymer (A). As the crosslinking agent (B), for example, a crosslinking agent capable of reacting with the crosslinkable functional group of the (meth)acrylic polymer (A), such as an isocyanate compound, an epoxy compound, or a metal chelate compound, can be used. The crosslinking agent (B) may be used alone or in combination of two or more kinds.

[0057] (Isocyanate compounds) As the isocyanate compound, for example, an isocyanate compound having 2 or more isocyanate groups in one molecule is usually used, and the number of isocyanate groups in one molecule is preferably 2 to 8, and more preferably 3 to 6. When the number of isocyanate groups is within the above range, it is preferable in terms of the efficiency of the crosslinking reaction between the (meth)acrylic polymer (A) and the isocyanate compound, and in terms of maintaining the flexibility of the pressure-sensitive adhesive layer.

[0058] Examples of diisocyanate compounds having two isocyanate groups per molecule include aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates. Examples of aliphatic diisocyanates include aliphatic diisocyanates having 4 to 30 carbon atoms, such as ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Examples of the alicyclic diisocyanate include alicyclic diisocyanates having 7 to 30 carbon atoms, such as isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylene diisocyanate. Examples of the aromatic diisocyanate include aromatic diisocyanates having 8 to 30 carbon atoms, such as phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate.

[0059] Examples of isocyanate compounds 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.

[0060] Examples of the isocyanate compound include multimers (e.g., dimers or trimers, biuret bodies, isocyanurates), derivatives (e.g., addition reaction products of polyhydric alcohols and two or more molecules of diisocyanate compounds), and polymers of the above isocyanate compounds having two or more isocyanate groups. Examples of the polyhydric alcohol in the derivative include low molecular weight polyhydric alcohols such as trihydric or higher alcohols, such as trimethylolpropane, glycerin, and pentaerythritol, and high molecular weight polyhydric alcohols such as polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols.

[0061] Examples of such isocyanate compounds include a trimer of diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, a biuret or isocyanurate of hexamethylene diisocyanate or tolylene diisocyanate, a reaction product of trimethylolpropane and tolylene diisocyanate or xylylene diisocyanate (for example, a trimole adduct of tolylene diisocyanate or xylylene diisocyanate), a reaction product of trimethylolpropane and hexamethylene diisocyanate (for example, a trimole adduct of hexamethylene diisocyanate), polyether polyisocyanate, and polyester polyisocyanate.

[0062] Among isocyanate compounds, xylylene diisocyanate and hexamethylene diisocyanate crosslinking agents are preferred from the viewpoint of yellowing resistance, and tolylene diisocyanate crosslinking agents are preferred from the viewpoint of stress relaxation. Examples of xylylene diisocyanate crosslinking agents include xylylene diisocyanate and its multimers, derivatives, and polymers, examples of hexamethylene diisocyanate crosslinking agents include hexamethylene diisocyanate and its multimers, derivatives, and polymers, and examples of tolylene diisocyanate crosslinking agents include tolylene diisocyanate and its multimers, derivatives, and polymers.

[0063] (Epoxy compounds) Examples of epoxy compounds 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, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N'-diamine glycidylaminomethyl).

[0064] (Metal chelate compounds) Examples of metal chelate compounds include compounds in which polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium are coordinated with alkoxides, acetylacetone, ethyl acetoacetate, etc. Specific examples include aluminum isopropylate, aluminum secondary butylate, aluminum ethyl acetoacetate diisopropylate, aluminum trisethyl acetoacetate, and aluminum trisacetylacetonate.

[0065] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition is usually 0.05 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 0.3 to 2.5 parts by mass, relative to 100 parts by mass of the (meth)acrylic polymer (A). In such an embodiment, a crosslinked structure is sufficiently and appropriately formed, and a pressure-sensitive adhesive having high cohesive strength, excellent balance of adhesive properties, and excellent durability can be obtained.

[0066] [Organic solvent (C)] The pressure-sensitive adhesive composition may contain an organic solvent (C) in order to adjust the coatability. Examples of the organic solvent (C) include the organic solvents mentioned in the above-mentioned method for producing the (meth)acrylic polymer (A). The organic solvent used in producing the (meth)acrylic polymer (A) and the organic solvent (C) contained in the pressure-sensitive adhesive composition may be the same type of organic solvent or different types of organic solvents. The organic solvent may be used alone or in combination of two or more types. When the pressure-sensitive adhesive composition contains an organic solvent (C), the content of the organic solvent (C) is usually 30 to 90 mass %, preferably 40 to 90 mass %, in 100 mass % of the pressure-sensitive adhesive composition.

[0067] [Additives (D)] The pressure-sensitive adhesive composition may contain, in addition to the above components (A) to (C), an additive (D) within a range that does not impair the effects of the present invention. Examples of additives (D) include tackifier resins, silane coupling agents, antistatic agents, antioxidants, light stabilizers, metal corrosion inhibitors, plasticizers, crosslinking accelerators, and rework agents. The additives (D) may be used alone or in combination of two or more. When the pressure-sensitive adhesive composition contains additives (D), the content of additives (D) varies depending on the type of additive (D) and is not particularly limited, but is usually 0.01 to 10% by mass, preferably 0.1 to 5% by mass, based on 100% by mass of the pressure-sensitive adhesive composition.

[0068] [Preparation of Adhesive Composition] The pressure-sensitive adhesive composition can be prepared, for example, by mixing the above-mentioned components by a conventionally known method. For example, the pressure-sensitive adhesive composition can be prepared by mixing a solution containing the (meth)acrylic polymer (A), the crosslinking agent (B), and other components such as additives used as necessary.

[0069] <Adhesive sheet> A pressure-sensitive adhesive sheet can be obtained from the pressure-sensitive adhesive composition of the present invention. The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer made from the pressure-sensitive adhesive composition of the present invention. Examples of the pressure-sensitive adhesive sheet include a pressure-sensitive adhesive sheet formed only from a pressure-sensitive adhesive layer, a double-sided pressure-sensitive adhesive sheet having a substrate and pressure-sensitive adhesive layers formed on both sides of the substrate, at least one of the pressure-sensitive adhesive layers being formed from the pressure-sensitive adhesive composition of the present invention, a single-sided pressure-sensitive adhesive sheet having a substrate and a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention formed on one side of the substrate, and a pressure-sensitive adhesive sheet in which substrates are disposed on both sides of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention.

[0070] The substrate is not particularly limited, and examples thereof include plastic substrates, nonwoven fabrics, woven fabrics, paper, metals, glass, ceramics, foams, etc. The thickness of the substrate varies depending on the application, etc., and is not particularly limited, but is usually 5 to 200 μm.

[0071] Examples of the plastic substrate include polyethylene terephthalate, polyvinyl chloride, polyolefin, polypropylene, polymethyl methacrylate, polycarbonate, polyphenylene sulfide, polyether ether ketone, polyethylene naphthalate, polyimide, polytetrafluoroethylene, and ABS. Among these, polyphenylene sulfide, polyether ether ketone, polyethylene naphthalate, polyimide, and polytetrafluoroethylene are preferred, and polyimide and polytetrafluoroethylene are particularly preferred. The adhesive sheet obtained from the adhesive composition of the present invention has excellent heat resistance, and is therefore suitable for use in heat-resistant masking applications used for protecting the soldering process. In addition, copolymerization of the cyclic polymerization monomer improves the thermal decomposition temperature of the polymer, and suppresses the generation of oligomers that cause deterioration of substrate adhesion during heating. Therefore, the adhesive composition of the present invention also has excellent adhesion to polyimide and polytetrafluoroethylene used in heat-resistant masking applications.

[0072] In order to improve the polarity of the surface, more specifically the wettability and chemical affinity for the pressure-sensitive adhesive composition, the surface of the substrate may be pretreated, for example, by sodium treatment, corona treatment, primer treatment, flame treatment, fluorination or plasma treatment, before forming the adhesive layer. When the substrate is polytetrafluoroethylene, it is preferable to pretreat the surface of the substrate, and particularly preferable to perform sodium treatment, corona treatment or plasma treatment.

[0073] The substrate may be a substrate that has been subjected to a release treatment. When the pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet in which substrates are disposed on both sides of the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present invention, at least one of the substrates is a substrate that has been subjected to a release treatment, and the substrate that has been subjected to the release treatment is removed when the pressure-sensitive adhesive sheet is adhered to the adherend.

[0074] The thickness of the adhesive layer is usually 5 to 200 μm, preferably 10 to 100 μm, from the viewpoint of maintaining adhesive performance. The pressure-sensitive adhesive layer may be at least partially crosslinked by reaction between the (meth)acrylic polymer (A) and the crosslinking agent (B) in the pressure-sensitive adhesive composition during the production process.

[0075] The method for producing the pressure-sensitive adhesive sheet is not particularly limited, but for example, is as follows. The pressure-sensitive adhesive composition described above is applied onto a substrate. When the pressure-sensitive adhesive composition contains a solvent, the composition is dried, usually at 50 to 150°C, preferably 60 to 100°C, for usually 1 to 10 minutes, preferably 2 to 7 minutes, to remove the solvent and form a coating film. Then, another substrate is attached to the surface of the coating film on the side where there is no substrate. Then, the composition is aged, usually for one day or more, preferably for 3 to 10 days, usually in an environment of 5 to 60°C, preferably 15 to 40°C, usually 30 to 70% RH, preferably 40 to 70% RH, to produce a pressure-sensitive adhesive sheet. The aging is also called aging. When the composition is aged under the above conditions, crosslinking proceeds during aging, and a crosslinked body can be efficiently formed.

[0076] The pressure-sensitive adhesive composition can be applied by a known method, such as spin coating, knife coating, roll coating, bar coating, blade coating, die coating, gravure coating, or doctor blade method, followed by coating and drying to a predetermined thickness. EXAMPLES

[0077] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these. In the following Production Examples, the weight average molecular weight (Mw) and the glass transition temperature (Tg) were measured by the following methods.

[0078] (Weight average molecular weight (Mw)) The weight average molecular weight (Mw) was measured by gel permeation chromatography (GPC) under the following conditions. Device name: Tosoh Corporation, HLC-8120 Columns: Tosoh Corporation, G7000HXL (7.8 mm ID x 30 cm) x 1, GMHXL (7.8 mm ID x 30 cm) x 2, G2000HXL (7.8 mm ID×30cm) 1 piece Sample concentration: 1.5mg / cm 3 Dilute with tetrahydrofuran to Mobile phase solvent: Tetrahydrofuran Flow rate: 1.0cm 3 / min Column temperature: 40℃

[0079] (Glass transition temperature (Tg)) The polymer was placed in a simple sealed pan and measured using a differential scanning calorimeter (DSC). The temperature was raised from -100°C to 200°C at 10°C / min. under a nitrogen stream, and the heat change was measured. A graph of "amount of heat absorbed and released" versus "temperature" was plotted, and the characteristic inflection observed at this time was taken as Tg. The value obtained from the DSC curve by the midpoint method was used as Tg.

[0080] [Production Example 1] (Synthesis of acrylic polymer (A-1)) A reaction apparatus equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen inlet tube was charged with 8 parts by mass of methyl α-allyloxymethylacrylate, 90 parts by mass of n-butyl acrylate, 2 parts by mass of 4-hydroxybutyl acrylate, and 90 parts by mass of ethyl acetate, and the temperature was raised to 65° C. while introducing nitrogen gas. Next, 0.1 parts by mass of 2,2′-azobisisobutyronitrile was added, and a polymerization reaction was carried out at 65° C. for 8 hours under a nitrogen atmosphere, to obtain an acrylic polymer (A-1) solution. The Mw and Tg of the resulting acrylic polymer (A-1) are shown in Table 1.

[0081] [Manufacturing Examples 2-11] Solutions of acrylic polymers (A-2) to (A-10) and (A'-1) were obtained in the same manner as in Production Example 1, except that the blending composition was changed as shown in Table 1. Table 1 shows the Mw and Tg of the resulting acrylic polymers (A-2) to (A-10) and (A'-1).

[0082] [Table 1] MeAMA: methyl α-allyloxymethylacrylate HxAMA: α-allyloxymethyl hexyl acrylate DdAMA: n-dodecyl α-allyloxymethylacrylate HxED: Di(n-hexyl)-2,2'-[oxybis(methylene)]bis-2-propenoate BA: n-butyl acrylate 4HBA: 4-Hydroxybutyl acrylate AA: Acrylic acid

[0083] [Example 1] (Preparation of Pressure-Sensitive Adhesive Composition) An isocyanate-based crosslinking agent L-45 (manufactured by Soken Chemical Industries, Ltd.) was added in an amount of 2 parts by mass in terms of solid content to an acrylic polymer (A-1) solution (100 parts by mass in terms of solid content (acrylic polymer)), and the mixture was stirred with a glass rod for 5 minutes to obtain a pressure-sensitive adhesive composition.

[0084] (Preparation of adhesive sheet) The obtained adhesive composition was applied onto a polyimide (PI) film using a doctor blade after defoaming so that the thickness after drying would be 25 μm, and the adhesive layer was formed by drying at 90 ° C for 3 minutes to remove the solvent. A release-treated polyethylene terephthalate (PET) film was attached to the surface of the adhesive layer opposite to the surface in contact with the PI film. The adhesive layer was then left to stand for 7 days under conditions of 23 ° C / 50% RH to mature, producing an adhesive sheet having an adhesive layer with a thickness of 25 μm.

[0085] [Examples 2 to 9, Comparative Example 1] Except for changing the blending composition as shown in Table 2, the same procedure as in Example 1 was carried out to obtain pressure-sensitive adhesive compositions and pressure-sensitive adhesive sheets.

[0086] [Example 10] An adhesive composition and an adhesive sheet were obtained in the same manner as in Example 1, except that an acrylic polymer (A-10) solution was used instead of the acrylic polymer (A-1) solution, and further, 1 part by mass, calculated as solid content, of an epoxy-based crosslinking agent E-5C (manufactured by Soken Chemical Industries, Ltd.) was used instead of the isocyanate-based crosslinking agent L-45.

[0087] [Example 11] An adhesive composition and an adhesive sheet were obtained in the same manner as in Example 1, except that the acrylic polymer (A-8) solution was used instead of the acrylic polymer (A-1) solution, and that sodium-treated polytetrafluoroethylene (PTFE) was used instead of the polyimide (PI) film.

[0088] The total light transmittance and haze of the pressure-sensitive adhesive compositions obtained in the Examples and Comparative Examples were measured by the following methods. The initial adhesive strength, heat-resistant adhesive strength, and adhesive strength after moist heat were also measured by the following methods for the pressure-sensitive adhesive sheets obtained in the Examples and Comparative Examples.

[0089] Total light transmittance and haze The obtained adhesive composition was applied to a release-treated polyethylene terephthalate (PET) film after defoaming to a thickness of 25 μm after drying using a doctor blade, and the solvent was removed by drying at 90° C. for 3 minutes to form an adhesive layer. A release-treated film was attached to the surface of the adhesive layer opposite to the surface in contact with the release-treated PET film. Then, the adhesive layer was left to stand for 7 days under conditions of 23° C. / 50% RH to mature, and an adhesive sheet having an adhesive layer with a thickness of 25 μm was produced. The obtained adhesive sheet was cut to a size of 50 mm×50 mm, and one of the release-treated PET films was peeled off, and the exposed adhesive layer was attached to a glass plate with a thickness of 0.5 mm. Then, the other release-treated PET film was peeled off, and the total light transmittance and haze were measured using a haze meter MH-150 (manufactured by Murakami Color Research Laboratory).

[0090] ·Initial adhesive strength The obtained adhesive sheet was cut into a size of 25 mm x 100 mm to obtain a test piece. The release-treated PET film of the obtained test piece was peeled off, and the exposed adhesive layer was attached to a SUS plate and pressed with a 2 kg roller three times, and then left in a 23°C / 50% RH environment for 20 minutes. Then, the end of the test piece was pulled at a speed of 300 mm / min in a 180° direction relative to the SUS plate surface to measure the adhesive strength.

[0091] ·Heat-resistant adhesive strength The obtained adhesive sheet was cut into a size of 25 mm x 100 mm to obtain a test piece. The release-treated PET film of the obtained test piece was peeled off, and the exposed adhesive layer was attached to a SUS plate and pressed with a 2 kg roller three times, and then left in a 180°C environment for 2 hours. Then, it was left in a 23°C / 50%RH environment for 20 minutes. The end of the test piece was pulled at a speed of 300 mm / min in a 180° direction relative to the SUS plate surface to measure the adhesive strength. In addition, the rate of change in adhesive strength was calculated from the obtained heat resistant adhesive strength and initial adhesive strength according to the following formula. Adhesive strength change rate [%] = (heat-resistant adhesive strength / initial adhesive strength) x 100

[0092] Adhesive strength after heat and humidity The obtained adhesive sheet was cut into a size of 25 mm x 100 mm to obtain a test piece. The release-treated PET film of the obtained test piece was peeled off, and the exposed adhesive layer was attached to a SUS plate and pressed with a 2 kg roller three times, and then left in a 60°C / 90% RH environment for 24 hours. Then, it was left in a 23°C / 50% RH environment for 20 minutes. The end of the test piece was pulled at a speed of 300 mm / min in a 180° direction relative to the SUS plate surface to measure the adhesive strength. The measurement results are shown in Table 2.

[0093] In the above measurements of initial adhesive strength, heat-resistant adhesive strength, and adhesive strength after wet heat treatment, except for the heat-resistant adhesive strength measurement of Comparative Example 1, interfacial failure (af) occurred at the interface between the adhesive layer of the adhesive sheet and the SUS plate. Therefore, except for the heat-resistant adhesive strength value of Comparative Example 1 shown in Table 2, the adhesive strength between the adhesive sheet and the SUS plate is shown. On the other hand, in the heat-resistant adhesive strength measurement of Comparative Example 1, peeling occurred at the interface between the polyimide (PI) film and the adhesive layer of the adhesive sheet, and the adhesive layer was transferred onto the SUS plate. Therefore, the heat-resistant adhesive strength value of Comparative Example 1 shown in Table 2 does not represent the adhesive strength between the adhesive sheet and the SUS plate.

[0094] [Table 2]

[0095] As shown in Table 2, the adhesive sheets obtained in Examples 1 to 11 had excellent heat resistance, with little difference in adhesive strength between the initial state and after exposure to a heat environment. In particular, when a cyclopolymerization monomer having an alkyl group with 6 or more carbon atoms was used, the adhesive layer obtained could be kept low in haze even by increasing the amount of the cyclopolymerization monomer used, and high adhesive strength was exhibited even when exposed to a humid and hot environment (Examples 4 to 8 and 11). In contrast, the adhesive sheet of Comparative Example 1, which used an acrylic polymer not containing a predetermined amount of cyclopolymerization monomer, had poor adhesion between the adhesive layer and the substrate, and was not excellent in heat resistance.

Claims

1. a (meth)acrylic polymer (A) which is a polymer of monomer components including 10.5 to 89.8% by mass of a cyclopolymerization monomer, 10.1 to 90.0% by mass of a (meth)acrylic acid alkyl ester having an alkyl group of 4 to 18 carbon atoms, and 0.1 to 9.5% by mass of a crosslinkable functional group-containing monomer, and which has a glass transition temperature of less than 0° C.; A crosslinking agent (B); Including, The pressure-sensitive adhesive composition, wherein the cyclopolymerizable monomer is a monomer represented by the following formula (1) or (2): 【Chemistry 1】 (In the formula, R 1 is an alkyl group having 6 to 18 carbon atoms.) 【Chemistry 2】 (In the formula, R 2 is an alkyl group having 6 to 18 carbon atoms.)

2. The pressure-sensitive adhesive composition according to claim 1, wherein the (meth)acrylic polymer (A) is a polymer of monomer components including 10.5 to 79.5% by mass of the cyclopolymerization monomer, 20.0 to 84.0% by mass of the (meth)acrylic acid alkyl ester, and 0.5 to 5.5% by mass of the crosslinkable functional group-containing monomer.

3. 3. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer prepared from the pressure-sensitive adhesive composition according to claim 1 or 2 and provided on a polyimide substrate or a polytetrafluoroethylene substrate.

Images