Heat-peelable pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

Abstract

To provide a heat-peelable adhesive composition that exhibits strong adhesiveness when in use, but becomes weakly adhesive when heated.SOLUTION: A heat-peelable adhesive composition contains an acrylic resin (A), a compound with an ethylenically unsaturated group (B), an epoxy-based crosslinker (C), and a thermal polymerization initiator (D).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-peelable pressure-sensitive adhesive composition that has sufficient peel strength within the range of normal use and whose peel strength decreases only upon heat treatment, and to a pressure-sensitive adhesive sheet having an adhesive layer formed by crosslinking the pressure-sensitive adhesive composition. [Background technology]

[0002] In recent years, there has been an increasing trend to improve the recycling rate of home appliances, various plastic products, metal products, etc. Since these products are usually manufactured by joining or gluing together many parts, in order to improve the recycling rate, it is important to separate and disassemble each joined or glued part at the time of recycling, and separate them by material.

[0003] To bond these parts, adhesive sheets are often used to simplify the bonding process. Generally, such adhesive sheets have strong adhesive properties to ensure reliable bonding of parts. However, this means that strong force must be applied during disassembly, which can lead to various undesirable behaviors, such as damage to the parts rather than the adhesive bonded portions, or adhesive residue remaining on the parts, hindering recycling of the parts.

[0004] From this perspective, proposals have been made for adhesives that become easily peelable when a specific trigger is activated during recycling. For example, Patent Document 1 proposes an adhesive that uses a photoresponsive compound to become easily peelable when treated with UV light, and Patent Document 2 proposes a resin that is peeled by heat using a compound with a structure that can be decomposed and recombined. Furthermore, Patent Document 3 proposes a resin that is peeled by heat by combining a resin having an amino group and a compound having an ethylenically unsaturated group. Furthermore, Patent Document 4 proposes using a composition of an acrylic resin and a urethane (meth)acrylate compound crosslinked with an isocyanate crosslinking agent, and then using the resulting resin that peels by heat in an adhesive sheet for protecting chemical solutions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-70558 [Patent Document 2] Special Publication No. 2013-519764 [Patent Document 3] Japanese Patent Application Publication No. 2019-156919 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-204617 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the adhesive of Patent Document 1 cannot be used to bond opaque parts such as colored or metallic materials, and is therefore limited in the types of adherends that can be used. Furthermore, the adhesive using the resin of Patent Document 2 is, in principle, prone to leaving adhesive residue due to decomposition products, posing a problem in terms of recyclability. Furthermore, the resin composition of Patent Document 3 has limitations, such as the need for increased adhesion during normal use and difficulty in adjusting the heating temperature and heating time during disassembly, and further improvements are needed.

[0007] The present inventors then conducted a detailed study of the adhesive composition of Patent Document 4 and found that there was a problem with the holding power as an adhesive, and that further improvement was required for use in more general-purpose applications.

[0008] Therefore, under these circumstances, an object of the present invention is to provide a heat-peelable pressure-sensitive adhesive composition that exhibits excellent adhesiveness during use and changes to weak adhesiveness upon heating, and a pressure-sensitive adhesive sheet comprising an adhesive layer formed by crosslinking the pressure-sensitive adhesive composition. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems, and have found that the above problems can be achieved by using an adhesive composition having a specific composition, thereby completing the present invention. That is, the gist of the present invention is as follows: [1] to [7] [1] A heat-peelable pressure-sensitive adhesive composition comprising an acrylic resin (A), a compound having an ethylenically unsaturated group (B), an epoxy crosslinking agent (C), and a thermal polymerization initiator (D). [2] The heat-peelable pressure-sensitive adhesive composition according to [1], wherein the acrylic resin (A) contains a carboxyl group-containing monomer as a copolymerization component. [3] The heat-peelable pressure-sensitive adhesive composition according to [2], wherein the carboxy group-containing monomer is an acrylic acid monomer. [4] The heat-peelable pressure-sensitive adhesive composition according to any one of [1] to [3], wherein the compound (B) having an ethylenically unsaturated group is a urethane (meth)acrylate compound. [5] The heat-peelable pressure-sensitive adhesive composition according to any one of [1] to [4], wherein the thermal polymerization initiator (D) has a 10-hour half-life temperature of 80 to 130°C. [6] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed by crosslinking the heat-peelable pressure-sensitive adhesive composition according to any one of [1] to [5]. [7] The pressure-sensitive adhesive sheet according to [6], wherein the 180° peel strength measured using a SUS-BA plate as an adherend according to the method described in JIS Z0237:2009 is 10 N / 25 mm or more after treatment at 60°C and 90% RH for 24 hours, and 2 N / 25 mm or less after treatment at 150°C for 2 hours. [Effects of the Invention]

[0010] The heat-peelable pressure-sensitive adhesive composition of the present invention can provide a pressure-sensitive adhesive layer that has excellent adhesive strength and holding power during use and can be easily peeled off by heating. This pressure-sensitive adhesive layer can be used to provide a product in which multiple parts are bonded and adhered together. When the product is collected and recycled, it can be easily separated and disassembled into individual parts under specified heating conditions. This can greatly contribute to improving the recycling rate of various plastic products, metal products, etc.

[0011] The pressure-sensitive adhesive sheet of the present invention has the advantage that the joining and bonding of parts can be carried out efficiently using the pressure-sensitive adhesive layer. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments for carrying out the present invention will be specifically described, but the present invention is not limited to these specific descriptions.

[0013] In the present invention, "(meth)acrylic" means acrylic or methacrylic, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylate" means acrylate or methacrylate, respectively. In the present invention, the term "sheet" is not particularly distinguished from "film" or "tape," but is used to include these terms. In the present invention, when an expression "X to Y" (X and Y are any numbers) is used, it means "X or more and Y or less" unless otherwise specified, and also includes the meaning of "preferably larger than X" or "preferably smaller than Y."

[0014] <Heat-peelable pressure-sensitive adhesive composition> First, the heat-peelable pressure-sensitive adhesive composition of the present invention (hereinafter, sometimes simply referred to as "the pressure-sensitive adhesive composition") will be described. The pressure-sensitive adhesive composition contains an acrylic resin (A), a compound having an ethylenically unsaturated group (B), an epoxy crosslinking agent (C), and a thermal polymerization initiator (D). Each component will be described below.

[0015] [Acrylic resin (A)] The acrylic resin (A) used in the present pressure-sensitive adhesive composition contains a (meth)acrylic acid alkyl ester monomer (a1) as a main polymerization component, preferably a functional group-containing monomer (a2) as a copolymerization component, and may optionally contain a carboxylic acid vinyl ester monomer (a3) ​​or other copolymerizable monomer (a4) as a copolymerization component. When the acrylic resin (A) contains a functional group-containing monomer (a2) as a copolymerization component, this serves as a crosslinking point for the acrylic resin (A), further improving adhesion to the substrate or adherend. Furthermore, when a carboxylic acid vinyl ester monomer (a3) ​​is used as a copolymerization component, this serves as a crosslinking point for the acrylic resin (A), further improving adhesion to the substrate or adherend. Furthermore, when a carboxylic acid vinyl ester monomer (a3) ​​is used, this is preferred in terms of improving adhesion to the adherend and adhesive strength.

[0016] The (meth)acrylic acid alkyl ester monomer (a1) preferably has an alkyl group having a carbon number of usually 1 to 20, preferably 1 to 12, more preferably 1 to 8, and even more preferably 4 to 8. If the number of carbon atoms is too large, the adherend tends to be easily stained. Specific examples include aliphatic (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, n-propyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and i-stearyl (meth)acrylate; Alicyclic (meth)acrylic acid esters such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate: Examples include: These may be used alone or in combination of two or more.

[0017] Among the above (meth)acrylic acid alkyl ester monomers (a1), n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate are preferably used in terms of copolymerizability, adhesive properties, ease of handling, and availability of raw materials.

[0018] The content of the (meth)acrylic acid alkyl ester monomer (a1) in the copolymerization components is preferably 30 to 99 mass%, particularly preferably 40 to 98 mass%, and even more preferably 50 to 95 mass%. If the content of the (meth)acrylic acid alkyl ester monomer (a1) is too low, the adhesive strength tends to decrease, and if it is too high, the adhesive strength tends to become too high.

[0019] The functional group-containing monomer (a2) may be any monomer containing a functional group that can become a crosslinking point by reacting with the epoxy-based crosslinking agent (C) described below, and examples thereof include hydroxyl group-containing monomers, carboxyl group-containing monomers, amino group-containing monomers, acetoacetyl group-containing monomers, isocyanate group-containing monomers, and glycidyl group-containing monomers. Among these, hydroxyl group-containing monomers and carboxyl group-containing monomers are preferably used because they can efficiently crosslink and, in the present invention, reduce acid-resistant chemicals and adhesive residue. In particular, carboxyl group-containing monomers are more preferably used because of their effectiveness.

[0020] Examples of the hydroxyl group-containing monomer include hydroxyalkyl acrylates such as 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth)acrylate; oxyalkylene-modified monomers such as diethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate. hydroxyalkyl acrylate esters such as 2-hydroxypropyl (meth)acrylate and 2-hydroxybutyl (meth)acrylate, and secondary hydroxyl group-containing monomers such as 3-chloro 2-hydroxypropyl (meth)acrylate; Tertiary hydroxyl group-containing monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate: Examples include:

[0021] Among the above hydroxyl group-containing monomers, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferably used because of their excellent reactivity with crosslinking agents.

[0022] When a hydroxyl group-containing monomer is used in the present invention, it is preferable to use one having a content of di(meth)acrylate as an impurity of 0.5% by mass or less, more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less. Specifically, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate are preferred.

[0023] Examples of the carboxy group-containing monomer include (meth)acrylic acid, acrylic acid dimer, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, acrylamido-N-glycolic acid, and cinnamic acid, and among these, (meth)acrylic acid is preferably used.

[0024] Examples of the amino group-containing monomer include t-butylaminoethyl (meth)acrylate, ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate.

[0025] Examples of the acetoacetyl group-containing monomer include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate.

[0026] Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and alkylene oxide adducts thereof.

[0027] Examples of the glycidyl group-containing monomer include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate.

[0028] These functional group-containing monomers (a2) may be used alone or in combination of two or more.

[0029] The content of the functional group-containing monomer (a2) in the copolymerization components is preferably 0.1 to 30 mass%, particularly preferably 0.5 to 20 mass%, and further preferably 1 to 15 mass%. If the content of the functional group-containing monomer (a2) is too high, the viscosity of the acrylic resin (A) tends to be too high and the adhesive strength immediately after application tends to be too high, while if the content is too low, the degree of crosslinking tends to be low and the adherend tends to be easily stained.

[0030] Examples of the vinyl carboxylic acid ester monomer (a3) ​​include vinyl acetate, vinyl propionate, vinyl stearate, and vinyl benzoate. Among these, vinyl acetate is preferred in terms of adhesion and cohesive strength to the adherend. These vinyl carboxylic acid ester monomers (a3) ​​may be used alone or in combination of two or more.

[0031] The content of the carboxylic acid vinyl ester monomer (a3) ​​is preferably 0 to 20 mass%, more preferably 0 to 10 mass%, and particularly preferably 0 to 7 mass%, based on the total mass of the copolymerization components. If the content of the carboxylic acid vinyl ester monomer (a3) ​​is too high, it tends to elute upon immersion in hydrofluoric acid. Therefore, in applications where chemical resistance is required, it is preferable that the carboxylic acid vinyl ester monomer (a3) ​​is not contained.

[0032] Examples of the other copolymerizable monomer (a4) include: Monomers containing one aromatic ring, such as phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyldiethylene glycol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, styrene, α-methylstyrene, etc.; (meth)acrylic acid ester monomers containing a biphenyloxy structure, such as biphenyloxyethyl (meth)acrylate; (meth)acrylamide-based monomers such as ethoxymethyl (meth)acrylamide, n-butoxymethyl (meth)acrylamide, (meth)acryloylmorpholine, dimethyl (meth)acrylamide, diethyl (meth)acrylamide, dimethylaminopropyl acrylamide, and (meth)acrylamide N-methylol (meth)acrylamide; Monomers containing an alkoxy group or an oxyalkylene group, such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and polypropylene glycol mono(meth)acrylate; Acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, allyl trimethyl ammonium chloride, dimethyl allyl vinyl ketone, etc. Examples include:

[0033] The content of the other copolymerizable monomer (a4) in the copolymerization components is preferably 0 to 40% by mass, particularly preferably 0 to 30% by mass, and further preferably 0 to 25% by mass. If the content of the other copolymerizable monomer (a4) is too high, the adhesive properties tend to be easily reduced.

[0034] In the present invention, the (meth)acrylic resin (A) is produced by polymerizing the above-mentioned (meth)acrylic acid alkyl ester monomer (a1), preferably the functional group-containing monomer (a2), and, if necessary, other copolymerizable monomers (a4), etc., as copolymerization components. Such polymerization can be carried out by a conventionally known method such as solution radical polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc., and can be appropriately selected. Among these, production by solution radical polymerization is preferred in that it allows the (meth)acrylic resin (A) to be produced safely and stably with any monomer composition.

[0035] In the solution radical polymerization, for example, monomer components such as the (meth)acrylic acid alkyl ester monomer (a1), the functional group-containing monomer (a2), and other copolymerizable monomers (a4), and a polymerization initiator are mixed or dropped into an organic solvent, and polymerization is carried out under reflux or generally at 50 to 98°C for about 0.1 to 20 hours.

[0036] Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as n-propyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. These organic solvents can be used alone or in combination of two or more.

[0037] Among these organic solvents, from the viewpoints of ease of polymerization reaction, chain transfer effect, ease of drying when applying the pressure-sensitive adhesive composition, and safety, esters such as ethyl acetate and butyl acetate, and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone are preferred, and in particular, it is preferred to include ethyl acetate.

[0038] Examples of polymerization initiators used in such solution radical polymerization include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 4,4'-azobis(4-cyanovaleric acid), and 2,2'-azobis(methylpropionic acid), which are common radical polymerization initiators, and organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide, and cumene hydroperoxide, and can be appropriately selected and used depending on the monomer used. These polymerization initiators can be used alone or in combination of two or more.

[0039] In this manner, the acrylic resin (A) used in the present invention can be obtained.

[0040] The weight-average molecular weight (Mw) of the acrylic resin (A) is preferably 100,000 to 3,000,000, particularly preferably 150,000 to 1,000,000, and even more preferably 200,000 to 800,000. If the weight-average molecular weight is too small, the toughness and cohesive strength of the resulting adhesive layer tend to decrease, and the transferability, holding power, and shear strength after curing tend to decrease. On the other hand, if the weight-average molecular weight is too large, the viscosity tends to be too high, resulting in increased scaling during polymerization, reduced compatibility with other components, and reduced handleability.

[0041] The dispersity of the acrylic resin (A) [weight average molecular weight (Mw) / number average molecular weight (Mn)] is preferably 10 or less, particularly preferably 7 or less, and even more preferably 5.5 or less. If the dispersity is too high, the cohesive strength tends to decrease. The lower limit of the dispersity is usually 1.

[0042] The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight converted into the molecular weight of standard polystyrene. The weight-average molecular weight was measured by a high-performance liquid chromatograph (Waters Japan, "Waters 2695 (main body)" and "Waters 2414 (detector)") using a Shodex GPC KF-806L column (exclusion limit molecular weight: 2 × 10 7Separation range: 100 to 2 × 10 7 The measurement is performed using three tubes connected in series (theoretical plate number: 10,000 / tube, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm), and the number average molecular weight can also be measured in a similar manner. The dispersity can be determined from the measured values ​​of the weight average molecular weight and number average molecular weight.

[0043] The glass transition temperature (Tg) of the acrylic resin (A) is preferably −70 to 10° C., more preferably −60 to 0° C., and particularly preferably −50 to −10° C. If the glass transition temperature of the acrylic resin (A) is too low, the adhesive strength after heating tends not to decrease sufficiently, and if it is too low, the adherend tends to be more susceptible to contamination.

[0044] The glass transition temperature (Tg) is a value calculated by applying the glass transition temperature and weight fraction of each of the monomers constituting the acrylic resin (A) as a homopolymer to the following Fox's formula. Here, the glass transition temperature when the monomers constituting the acrylic resin (A) are made into a homopolymer is usually measured by a differential scanning calorimeter (DSC), and can be measured by a method in accordance with JIS K 7121-1987 or JIS K 6240.

[0045]

number

[0046] [Compound (B) having an ethylenically unsaturated group] The compound (B) having an ethylenically unsaturated group (hereinafter sometimes simply referred to as "ethylenically unsaturated compound") used in the present pressure-sensitive adhesive composition is not particularly limited as long as it has an ethylenically unsaturated group, but to obtain a composition with excellent peeling properties after heating, the number of ethylenically unsaturated groups per molecule is usually preferably 2 to 15, more preferably 3 to 12, and particularly preferably 4 to 10. If the number of ethylenically unsaturated groups is too high, the crosslinking density after heating will tend to be too high, making the pressure-sensitive adhesive layer more susceptible to cracking, while if the number is too low, sufficient crosslinking density will not be obtained, making peeling after heating more difficult.

[0047] The ethylenically unsaturated compound (B) is preferably a (meth)acrylate compound in terms of compatibility with the acrylic resin (A), and is particularly preferably a urethane (meth)acrylate compound (B1).

[0048] The urethane (meth)acrylate compound (B1) may be a urethane (meth)acrylate compound (b1*2) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1) and a polyvalent isocyanate compound (b2), or a urethane (meth)acrylate compound (b1*2*3) which is a reaction product of a hydroxyl group-containing (meth)acrylate compound (b1), a polyvalent isocyanate compound (b2), and a polyol compound (b3). Among these, in the present invention, it is preferable to use the urethane (meth)acrylate compound (b1*2) in terms of releasability after heating.

[0049] Examples of the ethylenically unsaturated compound (B2) other than the urethane (meth)acrylate compound (B1) include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene oxide-modified bisphenol A di(meth)acrylate, propylene oxide-modified bisphenol A di(meth)acrylate, cyclohexane dimethacrylate, methyl ... compounds having two ethylenically unsaturated groups, such as ethanol di(meth)acrylate, ethoxylated cyclohexanedimethanol di(meth)acrylate, dimethyloldicyclopentane di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol di(meth)acrylate, ethylene glycol diglycidyl ether di(meth)acrylate, diethylene glycol diglycidyl ether di(meth)acrylate, phthalic acid diglycidyl ester di(meth)acrylate, hydroxypivalic acid-modified neopentyl glycol di(meth)acrylate, and isocyanuric acid ethylene oxide-modified diacrylate; compounds having three ethylenically unsaturated groups, such as trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tri(meth)acryloyloxyethoxytrimethylolpropane, ethylene oxide-modified isocyanuric acid triacrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, and ethoxylated glycerin triacrylate; compounds having four or more ethylenically unsaturated groups, such as pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, glycerin polyglycidyl ether poly(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, caprolactone-modified pentaerythritol tetra(meth)acrylate, ethylene oxide-modified dipentaerythritol penta(meth)acrylate, ethylene oxide-modified dipentaerythritol hexa(meth)acrylate, and ethylene oxide-modified pentaerythritol tetra(meth)acrylate; etc.

[0050] These ethylenically unsaturated compounds (B) may be used alone or in combination of two or more. The content of the ethylenically unsaturated compound (B) is usually 5 to 100 parts by mass, preferably 10 to 80 parts by mass, and particularly preferably 20 to 60 parts by mass, per 100 parts by mass of the acrylic resin (A). If the content of the ethylenically unsaturated compound (B) is too low, peeling after heating tends to be difficult, while if it is too high, the stain resistance of the adherend after peeling tends to decrease.

[0051] [Epoxy-based crosslinking agent (C)] The epoxy-based crosslinking agent (C) used in the present pressure-sensitive adhesive composition reacts with the functional groups in the acrylic resin (A) to form a crosslinked structure.

[0052] Examples of the epoxy crosslinking agent (C) include bisphenol A-epichlorohydrin epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether, N,N,O-triglycidyl-p-aminophenol, 1,3'-bis(N,N-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

[0053] Among these, epoxy crosslinking agents containing nitrogen atoms, such as N,N,O-triglycidyl-p-aminophenol, 1,3'-bis(N,N-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-m-xylenediamine, are preferred because they facilitate the smooth formation of a crosslinked structure, and 1,3'-bis(N,N-diglycidylaminomethyl)cyclohexane and N,N,N',N'-tetraglycidyl-m-xylenediamine are particularly preferred.

[0054] The epoxy-based crosslinking agent (C) may be used alone or in combination of two or more. The content thereof is usually preferably 0.001 to 30 parts by mass, more preferably 0.01 to 20 parts by mass, and particularly preferably 0.03 to 15 parts by mass, per 100 parts by mass of the acrylic resin (A) and the ethylenically unsaturated compound (B) combined. If the epoxy-based crosslinking agent (C) is too small, the cohesive strength when forming an adhesive layer from the adhesive composition tends to decrease, which can cause adhesive residue. If the epoxy-based crosslinking agent (C) is too large, the flexibility and adhesive strength of the formed adhesive layer tend to decrease, resulting in lift-off from the adherend.

[0055] [Thermal polymerization initiator (D)] The thermal polymerization initiator (D) used in the present pressure-sensitive adhesive composition may be any one that initiates a curing reaction by heating, and examples thereof include methyl ethyl ketone peroxide, cyclohexanone peroxide, methylcyclohexanone peroxide, methylacetoacetate peroxide, acetylacetate peroxide, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)-cyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1 -Bis(t-butylperoxy)-2-methylcyclohexane, 1,1-bis(t-butylperoxy)-cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 1,1-bis(t-butylperoxy)butane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide, t-butyl Hydroperoxide, t-butyl hydroperoxymalonic acid, α,α'-bis(t-butylperoxy)diisopropylbenzene, dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3, isobutyryl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide Side, succinic acid peroxide, m-toluoylbenzoyl peroxide, benzoyl peroxide, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di-2-ethoxyhexyl peroxydicarbonate, di-3-methoxybutyl peroxydicarbonate, di-s-butyl peroxydicarbonate, di(3-methyl-3-methoxybutyl) peroxydicarbonate, α,α'-Bis(neodecanoylperoxy)diisopropylbenzene, cumyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, 1,1,3,3-tetramethyl t-butylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexanoate, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-hexylperoxyisopropyl monocarbonate, t-butylperoxyisobutyrate, t Organic peroxide initiators such as t-butyl peroxymalate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-butylperoxyacetate, t-butylperoxy-m-toluylbenzoate, t-butylperoxybenzoate, bis(t-butylperoxy)isophthalate, 2,5-dimethyl-2,5-bis(m-toluylperoxy)hexane, t-hexyl peroxybenzoate, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-butylperoxyallyl monocarbonate, t-butyltrimethylsilyl peroxide, 3,3',4,4'-tetra(t-butylperoxycarbonyl)benzophenone, and 2,3-dimethyl-2,3-diphenylbutane; 2-Phenylazo-4-methoxy-2,4-dimethylvaleronitrile, 1-[(1-cyano-1-methylethyl)azo]formamide, 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis(2-methyl-N-phenylpropionamidine) dihydrochloride, 2,2'-azobis[N-( 2,2'-Azobis[N-(4-chlorophenyl)-2-methylpropionamidine]dihydride chloride, 2,2'-Azobis[N-(4-hydrophenyl)-2-methylpropionamidine]dihydrochloride, 2,2'-Azobis[2-methyl-N-(phenylmethyl)propionamidine]dihydrochloride, 2,2'-Azobis[2-methyl-N-(2-propenyl)propionamidine]dihydrochloride, 2,2'-Azobis[N-(2-hydroxyethyl)-2-methylpropionamidine]dihydrochloride, 2,2'-Azobis[2-(5-methyl-2-imidazoline 2,2'-Azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-Azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane]dihydrochloride, 2,2'-Azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride, 2,2'-Azobis[2-(5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride, 2,2'-Azobis[2-[ 1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane]dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide], 2,2'-azobis[2-methyl-N-[1,1-bis(hydroxymethyl)ethyl]propionamide], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(2-methylpropionamide), 2,Azo initiators such as 2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), dimethyl-2,2-azobis(2-methylpropionate), 4,4'-azobis(4-cyanopentanoic acid), and 2,2'-azobis[2-(hydroxymethyl)propionitrile]; etc.

[0056] Among these, it is preferable to use an organic peroxide initiator, since it generates less gas when heated. These thermal polymerization initiators (D) may be used alone or in combination of two or more.

[0057] The reaction temperature and reaction time during curing by heating differ depending on the type of the thermal polymerization initiator (D), and therefore it is generally preferable to use one with a 10-hour half-life temperature of 70 to 150° C., and more preferably one with a 10-hour half-life temperature of 80 to 130° C. That is, one with a 10-hour half-life temperature that is too low tends to be less stable in actual use, while one with a 10-hour half-life temperature that is too high tends to make it difficult to make the material easily peelable by heating. Therefore, for example, it is preferable to use 1,1'-di-(t-hexylperoxy)cyclohexane (87°C), 1,1-di(t-butylperoxy)cyclohexane (91°C), t-hexylperoxyisopropyl monocarbonate (95°C), t-butylperoxymalonate (96°C), t-butylperoxybenzoate (99°C), t-butylperoxyacetate (102°C), t-butylbenzoyl peroxide (104°C), dicumyl peroxide (120°C), di-t-butyl peroxide (128°C), diisopropylbenzene hydroperoxide (145°C), etc. The temperature in parentheses indicates the 10-hour half-life temperature.

[0058] The content of the thermal polymerization initiator (D) is usually preferably 0.01 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and particularly preferably 0.2 to 10 parts by mass, relative to 100 parts by mass of the ethylenically unsaturated compound (B). If the amount of the thermal polymerization initiator (D) is too small, curing tends to be insufficient and the physical properties tend to become unstable, while if the amount is too large, further effects tend not to be obtained.

[0059] [Other ingredients] The present pressure-sensitive adhesive composition may further contain, within the scope of the effects of the present invention, additives such as a resin other than the acrylic resin (A), a photopolymerization initiator, an antistatic agent, an antioxidant, a plasticizer, a filler, a pigment, a diluent, an antioxidant, an ultraviolet absorber, an ultraviolet stabilizer, and a tackifier. These additives may be used alone or in combination of two or more. Antioxidants are particularly effective in maintaining the stability of the pressure-sensitive adhesive layer. When an antioxidant is added, its content is not particularly limited, but is preferably 0.01 to 5% by mass. In addition to the additives, the present pressure-sensitive adhesive composition may also contain small amounts of impurities contained in the raw materials used to produce the components of the pressure-sensitive adhesive composition.

[0060] In this way, the present pressure-sensitive adhesive composition can be obtained by mixing the acrylic resin (A), the ethylenically unsaturated compound (B), the epoxy crosslinking agent (C), the thermal polymerization initiator (D), and, if necessary, appropriate optional components.

[0061] The adhesive composition can then be crosslinked to form an adhesive layer, thereby obtaining the adhesive sheet of the present invention (hereinafter sometimes referred to as "the adhesive sheet"). The adhesive sheet is useful as an adhesive sheet that is intended to be used by bonding various adhesion target members (adherends) together, such as metal plates, plastic plates, and semiconductor wafers, and then peeled off after use. It is also useful as a protective sheet that temporarily covers and protects the surface of a specific member, or as a temporary adhesive sheet for temporarily adhering (sticking) specific parts together during the manufacturing process. The adhesive sheet will be described below.

[0062] The present pressure-sensitive adhesive sheet is generally composed of a substrate sheet, a pressure-sensitive adhesive layer made of the present pressure-sensitive adhesive composition, and a release film. The present pressure-sensitive adhesive sheet can be obtained, for example, as follows. First, the present pressure-sensitive adhesive composition is applied directly onto a release film or a substrate sheet, either as is or after adjusting the concentration with an appropriate organic solvent to increase fluidity. The composition is then dried, for example, by heat treatment at 80 to 105°C for 0.5 to 10 minutes, and integrated with the substrate sheet or release film as an adhesive layer to obtain a pressure-sensitive adhesive sheet. Furthermore, to balance the adhesive properties, further aging may be performed after drying.

[0063] The aging conditions are typically a temperature of room temperature (23°C) to 70°C, and a time of 1 to 30 days. Specifically, the aging may be performed under conditions such as 1 to 20 days at 23°C, 3 to 10 days at 23°C, or 1 to 7 days at 40°C.

[0064] Examples of the material for the base sheet include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymers; Polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; Polyfluoroethylene resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyethylene fluoride; Polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; Cellulose-based resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; Polystyrene, polycarbonate, polyarylate, polyimide: Further examples include metal foils such as aluminum, copper, and iron, paper such as fine paper and glassine paper, and woven and nonwoven fabrics made of glass fiber, natural fiber, synthetic fiber, and the like.

[0065] These substrate sheets can be used as a single layer or as a multi-layered body in which two or more types are laminated together. Among these, synthetic resin sheets are preferred from the viewpoint of weight reduction and the like.

[0066] Furthermore, as the release film, for example, various synthetic resin sheets, paper, woven fabrics, nonwoven fabrics, etc. exemplified above as the base sheet can be used which have been subjected to a release treatment.

[0067] The method for applying the pressure-sensitive adhesive composition is not particularly limited as long as it is a common coating method, and examples thereof include roll coating, die coating, gravure coating, comma coating, and screen printing.

[0068] The thickness of the adhesive layer of the present adhesive sheet is usually preferably 10 to 200 μm, and more preferably 15 to 100 μm.

[0069] This pressure-sensitive adhesive sheet exhibits releasability as it hardens upon heating. The heating conditions are typically a heating temperature of 100 to 250°C, and preferably 130 to 200°C. If the heating temperature is too low, the releasability tends to decrease, while if the heating temperature is too high, no difference in releasability tends to be observed, which is undesirable from the standpoint of energy costs. The heating time is typically 0.25 to 10 hours, and preferably 0.5 to 5 hours. If the heating time is too short, the releasability tends to decrease, while if the heating time is too long, no difference in releasability tends to be observed, which is undesirable from the standpoint of energy costs.

[0070] The adhesive strength of the PSA sheet varies depending on the type of base sheet, the type of adherend, etc., but in order to obtain heat peelability, it is preferable that the 180° peel strength, measured using a SUS-BA plate as the adherend according to the method described in JIS Z0237:2009, be 10 N / 25 mm or more after 24 hours of treatment at 60°C and 90% RH and 2 N / 25 mm or less after 2 hours of treatment at 150°C. Of these, it is more effective for the 180° peel strength to be 20 N / 25 mm or more after 24 hours of treatment at 60°C and 90% RH and 1 N / 25 mm or less after 2 hours of treatment at 150°C.

[0071] The present adhesive sheet has an adhesive layer formed by crosslinking the present adhesive composition, which has excellent heat-peelability. Therefore, by laminating the adhesive sheet to an adherend to temporarily protect the surface of the adherend or to another member, and then heating as necessary, the adhesive layer hardens, reducing the adhesive strength, and the sheet can be easily peeled off from the adherend.

[0072] In particular, when this adhesive sheet is used to bond parts of a product that is made by combining and joining together parts made of different materials with the intention of recycling, when recycling this product, the individual parts can be easily separated, disassembled, and sorted by material simply by heating the bonded parts, making it extremely useful for improving the recycling rate. [Example]

[0073] Examples of the present invention will be specifically described below along with comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "%" and "parts" are by mass.

[0074] First, the following ingredients were prepared:

[0075] [Preparation of acrylic resin (A-1)] A reactor equipped with a temperature controller, thermometer, stirrer, dropping funnel, and reflux condenser was charged with 68 parts of ethyl acetate and heated with stirring. When the internal temperature stabilized at 78°C, a mixture of 70 parts of n-butyl acrylate, 20 parts of methyl methacrylate, 0.1 parts of 2-hydroxyethyl methacrylate, 9.9 parts of acrylic acid, and 0.035 parts of azobisisobutyronitrile (AIBN) as a polymerization catalyst was added dropwise over 2 hours and the reaction was allowed to proceed under reflux. Three hours after the start of the reaction, a solution of 23 parts of ethyl acetate and 0.034 parts of AIBN was added, and five hours after the start of the reaction, 7.6 parts of ethyl acetate was added to terminate the reaction, yielding acrylic resin (A-1) solution (glass transition temperature: -24.2°C, resin content: 35.0%, viscosity: 8,000 mPa·s at 25°C).

[0076] [Ethylenically unsaturated compound (B-1)] Urethane acrylate compound: reaction product of isophorone diisocyanate and dipentaerythritol pentaacrylate [ethylenically unsaturated groups: 10, weight average molecular weight: 2,300]

[0077] [Epoxy-based crosslinking agent (C-1)] Tetrad C (Mitsubishi Gas Chemical Company, Inc.)

[0078] [Thermal polymerization initiator (D-1)] Perbutyl Z (NOF Corporation, 10-hour half-life temperature 104°C)

[0079] [Isocyanate-based crosslinking agent (E-1)] Coronate L (manufactured by Tosoh Corporation)

[0080] Example 1 [Preparation of Pressure-Sensitive Adhesive Composition] A pressure-sensitive adhesive composition was obtained by mixing 67 parts of the above acrylic resin (A-1) in terms of solid content, 33 parts of an ethylenically unsaturated compound (B-1), 0.05 parts of an epoxy-based crosslinking agent (C-1), and 1 part of a thermal polymerization initiator (D-1), and diluting the mixture with ethyl acetate to a solid content of 40%.

[0081] [Creating adhesive sheets] The obtained pressure-sensitive adhesive composition was applied to a substrate sheet (highly adhesive polyethylene terephthalate film, film thickness 125 μm, manufactured by Toyobo Co., Ltd.: A4360 Cosmoshine) using an applicator, and then dried at 100°C for 2 minutes. After that, the composition was attached to a release film (manufactured by Mitsui Chemicals Tocello Co., Ltd.: SP-PET 38 01-BU) and aged at 40°C for 3 days to obtain a pressure-sensitive adhesive sheet (adhesive layer thickness 25 μm).

[0082] <Example 2> A pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet were obtained in the same manner as in Example 1, except that the amount of the thermal polymerization initiator (D-1) in Example 1 was changed to 2 parts.

[0083] <Comparative Example 1> A pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet were obtained in the same manner as in Example 1, except that the epoxy-based crosslinking agent (C1) in Example 1 was replaced with 2 parts of an isocyanate-based crosslinking agent (E1).

[0084] <Comparative Example 2> A pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet were obtained in the same manner as in Example 1, except that the thermal polymerization initiator (D-1) was not added.

[0085] For each of the adhesive sheets of Examples 1 and 2 and Comparative Examples 1 and 2 obtained in this manner, the 180° peel test strength and holding power of the adhesive layer were measured according to the following procedures, and the results are shown in Table 1 below.

[0086] [180° peel strength] (1) Adhesion of adhesive sheet to SUS-BA plate A 25mm x 100mm test piece was prepared from the obtained adhesive sheet, the release film was peeled off, and the sheet was pressed and attached to a stainless steel plate (SUS304BA plate) by rolling a 2kg rubber roller back and forth twice in an atmosphere of 23°C and 50% relative humidity, and then aged in the same atmosphere for 3 days to obtain adhesive sheet (Q) adhered to the SUS-BA plate. (2) Peel test: 23°C The pressure-sensitive adhesive sheet (Q) was subjected to a 180° peel test in accordance with JIS Z0237:2009 to measure its peel strength. (3) Peel test: 60℃ treatment The pressure-sensitive adhesive sheet (Q) was aged for one day in an environment of 60°C / 90% RH, and then returned to 23°C, and a 180° peel test was carried out to measure the peel strength. (4) Peel test: 150℃ treatment Similarly, the pressure-sensitive adhesive sheet (Q) was aged for 2 hours in an environment at 150°C, and then returned to 23°C, and a 180° peel test was carried out to measure the peel strength. In each peel test, it was visually confirmed whether or not there was any adhesive residue on the SUS-BA plate after peeling.

[0087] [Holding force] The pressure-sensitive adhesive sheet (Q) was subjected to a holding power test in accordance with JIS Z0237:2009 (1 kg load, 40° C.) to measure the holding power of the pressure-sensitive adhesive layer to a SUS-BA plate.

[0088] [Table 1]

[0089] The above results show that the pressure-sensitive adhesive sheets of Examples 1 and 2 both exhibit excellent heat peelability, and the adhesive layer in the bonded state has sufficient holding power. On the other hand, Comparative Example 1, which does not contain the epoxy-based crosslinking agent (C), has a problem with holding power, and Comparative Example 2, which does not contain the thermal polymerization initiator (D), has a problem with not having easy peelability after heating. [Industrial Applicability]

[0090] The present invention can be suitably used as a heat-peelable pressure-sensitive adhesive composition that exhibits strong adhesion when in use and changes to weak adhesion when heated, and as a pressure-sensitive adhesive sheet comprising an adhesive layer formed by crosslinking the pressure-sensitive adhesive composition.

Claims

1. A heat-peelable pressure-sensitive adhesive composition comprising an acrylic resin (A), a compound having an ethylenically unsaturated group (B), an epoxy-based crosslinking agent (C), and a thermal polymerization initiator (D).

2. 2. The heat-peelable pressure-sensitive adhesive composition according to claim 1, wherein the acrylic resin (A) contains a carboxyl group-containing monomer as a copolymerization component.

3. The heat-peelable pressure-sensitive adhesive composition according to claim 2, wherein the carboxyl group-containing monomer is an acrylic acid monomer.

4. The heat-peelable pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the compound (B) having an ethylenically unsaturated group is a urethane (meth)acrylate compound.

5. The heat-peelable pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the thermal polymerization initiator (D) has a 10-hour half-life temperature of 80 to 130°C.

6. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer obtained by crosslinking the heat-peelable pressure-sensitive adhesive composition according to any one of claims 1 to 3.

7. The pressure-sensitive adhesive sheet according to claim 6, wherein the 180° peel strength, measured using an SUS-BA plate as an adherend according to the method described in JIS Z0237:2009, is 10 N / 25 mm or more after treatment at 60°C and 90% RH for 24 hours, and is 2 N / 25 mm or less after treatment at 150°C for 2 hours.

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