Adhesive composition and adhesive sheet using the adhesive composition

Abstract

The present invention provides a pressure-sensitive adhesive composition combining adhesive force with light-releasing properties so that the pressure-sensitive adhesive composition has excellent adhesive force in application to adherends even at high temperatures and, after brought into contact with warm water for removal, can be removed with low peel force without leaving any adhesive residue. This pressure-sensitive adhesive composition comprises: an acrylic polymer comprising a structural unit of a (meth)acrylate monomer containing an alkoxy group, as a main component, and a structural unit of a polymerizable monomer, the homopolymer of which has a Tg of 0°C or higher, the amount of the latter structural unit being 1-40 parts by mass per 100 parts by mass of all the structural monomer units; and a surfactant.

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition. [Background Art]

[0002] Conventionally, pressure-sensitive adhesive sheets such as pressure-sensitive adhesive tapes and pressure-sensitive adhesive labels have been used in various fields. For example, when heat treatment is performed in the manufacture of various industrial products, a pressure-sensitive adhesive sheet is attached to a portion where direct heating is desired to be avoided, and the pressure-sensitive adhesive sheet is peeled off from the surface of an adherend after the heat treatment.

[0003] As a conventional pressure-sensitive adhesive sheet used for such heat-resistant masking, those containing a carbon-based polymer in the pressure-sensitive adhesive layer are used. However, when the pressure-sensitive adhesive sheet is heated together with an adherend such as glass or metal at a high temperature of 130°C or higher, the intermolecular attraction of carbon becomes strong, the pressure-sensitive adhesive layer adsorbs to the surface of the adherend, and it may become difficult to peel off the pressure-sensitive adhesive sheet.

[0004] On the other hand, hot water is used for peeling the pressure-sensitive adhesive sheet, and various pressure-sensitive adhesive compositions that can be peeled with hot water have been proposed. For example, Patent Document 1 discloses that an acrylic pressure-sensitive adhesive mainly composed of a (meth)acrylic acid alkyl ester resin contains a macromonomer of N-mono- or di-C2-C4 alkyl-substituted acrylamide having a viscosity average molecular weight of 250 to 1000. An adhesive composition containing the same has been proposed. Further, Patent Document 2 proposes a hot water peelable adhesive resin composition containing an epoxy resin and a compound having two or more mercapto groups and a molecular weight of 800 or less. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 2006-241264 [Patent Document 2] Japanese Unexamined Patent Publication No. 2011-057870 [Summary of the Invention] [Problems that the invention aims to solve]

[0006] However, the hot water-removable adhesive compositions described in Patent Documents 1 and 2 are not intended to be subjected to high-temperature heating, and their adhesive strength and peelability during heat treatment are unknown. Adhesive sheets used in heat treatment require both heat resistance and easy peelability after heat treatment. Therefore, the object of the present invention is to provide an adhesive composition that has excellent adhesion to the adherend even at high temperatures, and can be peeled off with light peeling force without leaving any adhesive residue when brought into contact with warm water. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have discovered that an adhesive composition containing an acrylic polymer of a specific structure and a surfactant possesses heat resistance, excellent adhesion to the adherend, and superior peelability after hot water treatment, thus completing the present invention.

[0008] In other words, the present invention relates to the following (1) to (7). (1) An adhesive composition comprising an acrylic polymer containing structural units of an alkoxy group-containing (meth)acrylate monomer as the main component, and 1 to 40 parts by mass of polymerizable monomer structural units having a homopolymer Tg of 0°C or higher, per 100 parts by mass of the total structural units of the monomer, and a surfactant. (2) The adhesive composition according to (1), wherein the surfactant is a nonionic surfactant. (3) The adhesive composition according to (1) or (2), wherein the alkoxy group-containing (meth)acrylate monomer is at least one selected from the group consisting of methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol acrylate, and polypropylene glycol acrylate. (4) The adhesive composition according to any one of (1) to (3) above, wherein the contact angle with water when the adhesive composition is cured is 80 degrees or less. (5) An adhesive sheet comprising an adhesive layer made of the adhesive composition described in any one of (1) to (4) above. (6) A method for peeling off an adhesive sheet as described in (5) above, which has been bonded to a substrate, comprising the step of bringing the substrate to which the adhesive sheet is bonded, which has been heat-treated at 130 to 250°C, into contact with warm water at 40 to 90°C to peel it off at the interface between the substrate and the adhesive sheet. (7) The method for peeling off the adhesive sheet according to (6), wherein the object to which the adhesive sheet is attached is brought into contact with the hot water for one minute or more. [Effects of the Invention]

[0009] The adhesive composition of the present invention has excellent heat resistance and adhesive strength, and its adhesive strength decreases when it comes into contact with hot water after heating. Therefore, an adhesive sheet equipped with an adhesive layer formed by the adhesive composition of the present invention has excellent adhesion to the adherend, and can be peeled off from the adherend with light peeling force by coming into contact with hot water after heat treatment. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described in more detail below, but the present invention is not limited in any way to the embodiments described below. In this specification, "(meth)acrylate" means acrylate and / or methacrylate. Furthermore, in this specification, "mass" is synonymous with "weight."

[0011] [Adhesive composition] The adhesive composition according to an embodiment of the present invention comprises an acrylic polymer containing structural units of an alkoxy group-containing (meth)acrylate monomer as the main component, and 1 to 40 parts by mass of polymerizable monomer structural units having a homopolymer Tg of 0°C or higher, per 100 parts by mass of the total monomer structural units, and a surfactant.

[0012] (Acrylic polymer) The acrylic polymer contained in the pressure-sensitive adhesive composition according to an embodiment of the present invention is obtained by polymerizing a monomer component containing an alkoxy group-containing (meth)acrylate monomer and a polymerizable monomer having a glass transition temperature (Tg) of 0°C or higher for a homopolymer thereof.

[0013] The alkoxy group-containing (meth)acrylate monomer is a monomer containing an alkoxy group in its structure, and examples thereof include compounds represented by the following formula (1).

[0014]

Chemical Formula

[0015] In general formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 represents an alkylene group having 2 to 5 carbon atoms, R 3 represents an alkyl group having 1 to 12 carbon atoms, a benzyl group or a biphenyl group, and n represents an integer of 1 to 12.

[0016] Specific examples of the alkoxy group-containing (meth)acrylate monomer include methoxyethyl acrylate, ethoxyethoxyethyl acrylate, methoxy-triethylene glycol acrylate, 2-ethylhexyl diglycol acrylate, methoxy-polyethylene glycol acrylate, methoxydipropylene glycol acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxy-polyethylene glycol acrylate, ethoxylated O-phenylphenol acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, and the like. One type of the alkoxy group-containing (meth)acrylate monomer may be used alone, or two or more types may be used in combination. Among these, from the viewpoint of adhesiveness, it is preferable to use at least one selected from the group consisting of methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol acrylate, and polypropylene glycol acrylate.

[0017] The alkoxy group-containing (meth)acrylate monomer is contained as a main component in the acrylic polymer. In this specification, unless otherwise specified, the term "main component" refers to a component contained in an amount exceeding 50% by mass, preferably 60% by mass or more, and more preferably 70% by mass or more.

[0018] The structural unit of the alkoxy group-containing (meth)acrylate monomer is preferably contained in an amount ranging from 50 to 99 parts by mass based on 100 parts by mass of all structural units of the monomers. When the content of the structural unit of the alkoxy group-containing (meth)acrylate monomer is 50 parts by mass or more, the pressure-sensitive adhesive composition can exhibit heat resistance; when the content is 99 parts by mass or less, the cohesive force of the pressure-sensitive adhesive can be increased by adding a high-Tg monomer, and adhesive residue can be reduced. The content of the structural unit of the alkoxy group-containing (meth)acrylate monomer is more preferably 60 parts by mass or more, further preferably 70 parts by mass or more, based on 100 parts by mass of all structural units of the monomers, and is more preferably 97 parts by mass or less, further preferably 95 parts by mass or less.

[0019] The polymerizable monomer having a homopolymer with a Tg of 0°C or higher is a monomer having at least one polymerizable unsaturated double bond in one molecule. The acrylic polymer of the present invention obtained by using, as a component, a polymerizable monomer whose homopolymer has a Tg of 0°C or higher has the characteristic that it can increase the cohesive force of the pressure-sensitive adhesive and reduce adhesive residue, and therefore the pressure-sensitive adhesive composition containing the acrylic polymer of the present invention is prone to swelling in warm water.

[0020] Polymerizable monomers with a homopolymer Tg of 0°C or higher include, for example, N-vinyl-2-pyrrolidone, acrylic acid, methyl (meth)acrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptade Examples include syl(meth)acrylate, stearyl(meth)acrylate, isostearyl(meth)acrylate, nonadecyl(meth)acrylate, eicosylacrylate, dicyclopentanyl methacrylate, β-carboxyethyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, acrylonitrile, acrylamide, dimethylacrylamide, isopropylacrylamide, hydroxyethylacrylamide, hydroxymethylacrylamide, hydroxybutylacrylamide, acryloylmorpholine, and 1-vinylimidazole. Polymerizable monomers may be used individually or in combination of two or more. In order to better exhibit the effects of the present invention, the polymerizable monomer is preferably at least one selected from acrylic acid and N-vinyl-2-pyrrolidone.

[0021] The polymerizable monomer structural units, with a Tg of 0°C or higher, are contained in an amount of 1 to 40 parts by mass per 100 parts by mass of the total structural units of the monomer. If the polymerizable monomer structural units are 1 part by mass or more, the cohesive force of the adhesive can be increased and adhesive residue can be reduced, while if they are 40 parts by mass or less, the adhesive function of the adhesive is not impaired. The content of polymerizable monomer structural units is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, per 100 parts by mass of the total structural units of the monomer.

[0022] In this specification, the Tg of a polymer refers to either the nominal value stated in literature or catalogs, or the Tg (also called calculated Tg) determined by Fox's formula based on the composition of the monomer components used in the preparation of the polymer. Fox's formula is a relationship between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg = Σ(Wi / Tgi)

[0023] In Fox's equation above, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the monomer i homopolymer (unit: K). If the polymer for which Tg is to be specified is a homopolymer, the Tg of the homopolymer and the Tg of the target polymer are the same.

[0024] The glass transition temperature (Tg) of homopolymers used in calculating Tg shall be the value specified in publicly available documents. Specifically, the values ​​are given in the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are listed in the Polymer Handbook, the highest value shall be adopted.

[0025] For monomers whose glass transition temperature for homopolymers is not listed in the above-mentioned literature "Polymer Handbook," the values ​​obtained by the following measurement method shall be used. Specifically, 100 parts by mass of monomer, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as the polymerization solvent are added to a reactor equipped with a thermometer, stirrer, nitrogen inlet tube, and reflux condenser, and the mixture is stirred for 1 hour while flowing nitrogen gas through it. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is carried out for 10 hours. Then, it is cooled to room temperature to obtain a homopolymer solution with a solid content of 33% by mass. Next, this homopolymer solution is cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. This test sample is punched out into a 7.9 mm diameter disc shape, sandwiched between parallel plates, and measured using a viscoelasticity tester (manufactured by T.A. Instruments Japan, model name "ARES") in shear mode while applying a shear strain of 1 Hz at a frequency of 1 Hz, in a temperature range of -70°C to 150°C, with a heating rate of 5°C / min. The temperature corresponding to the peak top temperature of tanδ is defined as the Tg of the homopolymer.

[0026] Acrylic polymers may also contain monomer components other than the alkoxy group-containing (meth)acrylate monomers and polymerizable monomers whose Tg of the homopolymer is 0°C or higher. Examples of other monomer components include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, s-butyl acrylate, t-butyl acrylate, pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl methacrylate, tetradecyl methacrylate, and the like.

[0027] In the production of acrylic polymers, it is preferable to carry out a polymerization reaction in the presence of a polymerization initiator using an alkoxy group-containing (meth)acrylate monomer, a polymerizable monomer whose homopolymer Tg is 0°C or higher, and optionally other monomer components.

[0028] Suitable polymerization initiators include, for example, hydrogen peroxide; persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; azo compounds such as dimethyl 2,2'-azobis(2-methylpropionate) and 2,2'-azobis(isobutyronitrile); and organic peroxides such as benzoyl peroxide, peracetic acid, and di-t-butyl peroxide. These polymerization initiators may be used individually or in combination of two or more.

[0029] The amount of polymerization initiator used is preferably 0.05 to 0.5 parts by mass, more preferably 0.1 to 0.4 parts by mass, and even more preferably 0.2 to 0.5 parts by mass, per 100 parts by mass of the total structural units of the monomer.

[0030] Such acrylic polymers can be produced using known methods such as solution polymerization, bulk polymerization, emulsion polymerization, and various radical polymerizations, which can be selected as appropriate. Furthermore, the resulting acrylic polymer may be a random copolymer, block copolymer, graft copolymer, or any other type.

[0031] In solution polymerization, for example, ethyl acetate and toluene are used as polymerization solvents. In a specific example of solution polymerization, the reaction is carried out under conditions of adding a polymerization initiator under an inert gas stream such as nitrogen, at a temperature of approximately 50-80°C for 1-8 hours.

[0032] The acrylic polymer used in this invention preferably has a weight-average molecular weight (Mw) of 200,000 to 3,000,000. Considering durability, particularly heat resistance, a weight-average molecular weight (Mw) of 400,000 to 2,500,000 is more preferable, and 500,000 to 2,000,000 is even more preferable. A weight-average molecular weight (Mw) less than 200,000 is undesirable in terms of heat resistance. Furthermore, if the weight-average molecular weight (Mw) exceeds 3,000,000, the adhesive layer tends to harden, making peeling more likely. The weight-average molecular weight (Mw) is determined by measuring it using GPC (gel permeation chromatography) and calculating the value in terms of polystyrene equivalent.

[0033] Furthermore, the acrylic polymer preferably has a glass transition temperature (Tg) of 0°C or lower (usually -100°C or higher), more preferably -5°C or lower, and even more preferably -10°C or lower. If the glass transition temperature is higher than 0°C, the cohesive force increases, reducing fluidity, which may prevent a sufficient adhesive area from being obtained, making it impossible to fix the adherend. In particular, a Tg of -5°C or lower is preferable because it makes the acrylic polymer softer, allowing for sufficient peeling force. The glass transition temperature of the acrylic polymer can be adjusted within the above range by appropriately changing the monomer components and composition ratio used. In this invention, the glass transition temperature of the acrylic polymer can be measured using a dynamic viscoelastic device or calculated using the FOX formula.

[0034] (Surfactants) The surfactant contained in the adhesive composition according to the embodiment of the present invention can be any nonionic surfactant, anionic surfactant, cationic surfactant, amphoteric surfactant, etc. By including a surfactant in the adhesive composition, peeling after contact with warm water can be done with light force, improving peelability.

[0035] Examples of nonionic surfactants include polyoxyalkylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether; polyoxyethylene alkylphenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, and polyoxyethylene sorbitan monolaurate; polyoxyethylene glyceryl ether fatty acid esters; and polyoxyalkylenes such as polyoxyethylene-polyoxypropylene block copolymer, polyoxyethylene, polyoxypropylene, and polyoxybutylene.

[0036] Examples of anionic surfactants include alkyl sulfates such as lauryl sulfate and octadecyl sulfate; fatty acid salts; alkylbenzene sulfonates such as nonylbenzenesulfonate and dodecylbenzenesulfonate; naphthalene sulfonates such as dodecylnaphthalenesulfonate; alkyldiphenyl ether disulfonates such as dodecyldiphenyl ether disulfonate; polyoxyethylene alkyl ether sulfates such as polyoxyethylene octadecyl ether sulfate and polyoxyethylene lauryl ether sulfate; polyoxyethylene alkylphenyl ether sulfates such as polyoxyethylene laurylphenyl ether sulfate; polyoxyethylene styrene phenyl ether sulfate; sulfosuccinates such as lauryl sulfosuccinate and polyoxyethylene lauryl sulfosuccinate; polyoxyethylene alkyl ether phosphates; and polyoxyethylene alkyl ether acetates.

[0037] Examples of cationic surfactants include alkyldimethylbenzylammonium chloride, alkyltrimethylammonium chloride, alkyldimethylethylammonium ethyl sulfate, higher alkylamine salts (such as acetates and hydrochlorides), ethylene oxide adducts to higher alkylamines, condensates of higher fatty acids and polyalkylene polyamines, salts of esters of higher fatty acids and alkanolamines, salts of higher fatty acid amides, imidazoline-type cationic surfactants, and alkylpyridinium salts.

[0038] Examples of amphoteric surfactants include amino acid-type amphoteric surfactants such as alkali metal alkylaminopropionates, betaine-type amphoteric surfactants such as alkyldimethylbetaine, and imidazoline-type amphoteric surfactants.

[0039] Surfactants may be used individually or in combination of two or more. Among these, nonionic surfactants are preferred in terms of their miscibility with the adhesive composition, and sorbitan fatty acid esters, polyoxyalkylene alkyl ethers, and polyoxyalkylenes are more preferred.

[0040] The surfactant content is preferably 0.3 to 10 parts by mass per 100 parts by mass of acrylic polymer. When the surfactant content is 0.3 parts by mass or more per 100 parts by mass of acrylic polymer, the resin composition swells easily when in contact with hot water, allowing for peeling with light force. When it is 10 parts by mass or less, a high initial peeling force can be maintained. The surfactant content is more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less.

[0041] (Crosslinking agent) In this embodiment, the adhesive composition may contain a crosslinking agent. The type of crosslinking agent is not particularly limited and can be appropriately selected from conventionally known crosslinking agents. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. Among these, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, and isocyanate-based crosslinking agents and epoxy-based crosslinking agents are more preferred. The use of isocyanate-based crosslinking agents tends to provide better impact resistance than other crosslinking agents while obtaining cohesive force in the adhesive layer. Furthermore, the use of isocyanate-based crosslinking agents is advantageous in terms of improving adhesion to adherends made of polyester resin such as PET. The crosslinking agent may be used alone or in combination of two or more types.

[0042] As an isocyanate-based crosslinking agent, polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used.

[0043] Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; and 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

[0044] Specific examples of alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0045] Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Examples include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropanediisocyanate, m-phenylenediisocyanate, p-phenylenediisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0046] As an isocyanate-based crosslinking agent, commercially available products such as "Coronate L," "Coronate HL," and "Coronate HX" manufactured by Nippon Polyurethane Industries Co., Ltd. can be used.

[0047] Examples of epoxy crosslinking agents include polyfunctional epoxy compounds having two or more epoxy groups in one molecule. The epoxy groups of the epoxy crosslinking agent may also be glycidyl groups. Examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycidyl adipate ester, diglycidyl o-phthalate ester, triglycidyl-tris(2-hydroxyethyl) isocyanurate, resorcinol diglycidyl ether, and bisphenol-S-diglycidyl ether.

[0048] As epoxy crosslinking agents, commercially available products such as "Denacol" from Nagase ChemteX Corporation, and "Tetrad-X" and "Tetrad-C" from Mitsubishi Gas Chemical Company, Inc. can be used.

[0049] The crosslinking agent content is preferably 0.01 to 10 parts by mass per 100 parts by mass of acrylic polymer. If the crosslinking agent content is 0.01 parts by mass or more per 100 parts by mass of acrylic polymer, the cohesive force of the adhesive can be improved, and if it is 10 parts by mass or less, a high peeling force before heating can be maintained. The crosslinking agent content is more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, even more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less.

[0050] (Thermal polymerization initiator) The adhesive composition of the present invention may contain a thermal polymerization initiator that generates radicals upon heating. Examples of such thermal polymerization initiators include peroxides, azo compounds, dihalogen compounds, alkylphenone compounds, and acylphosphine oxide compounds. Among these, peroxides and azo compounds are preferred from the viewpoint of durability and cost. A single thermal polymerization initiator may be used, or two or more may be used in combination.

[0051] Examples of peroxides include benzoyl peroxide, 1,1-bis(t-hexyl peroxy)cyclohexane, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(t-butyl peroxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butyl peroxy)cyclohexane, n-butyl-4,4-bis(t-butyl peroxy) valerate, cumene hydroperoxide, and 2,5-dimethylhexane-2,5-dimethylhexane. Examples include hydroperoxide, 1,3-bis(t-butylperoxy)-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, diisopropylbenzene peroxide, t-butylcumyl peroxide, decanoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide, bis(t-butylcyclohexyl)peroxydicarbonate, t-butylperoxybenzoate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane.

[0052] Examples of azo compounds include 2,2'-azobis(isobutyronitrile), 1,1-azobis(cyclohexane-1-carbonnitrile), azocumene, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisdimethylvaleronitrile, 4,4'-azobis(4-cyanovaleric acid), 2-(tert-butylazo)-2-cyanopropane, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), and dimethyl-2,2'-azobis(2-methylpropionate).

[0053] The thermal polymerization initiator is preferably contained in an amount of 1.2 to 10 parts by mass per 100 parts by mass of all components excluding the thermal polymerization initiator. If the thermal polymerization initiator content is 1.2 parts by mass or more per 100 parts by mass of all components excluding the thermal polymerization initiator, a rapid increase in adhesive strength after heat treatment can be suppressed, and if it is 10 parts by mass or less, a high initial peeling force can be maintained. The thermal polymerization initiator content is preferably 1.7 parts by mass or more, more preferably 2.0 parts by mass or more, even more preferably 2.5 parts by mass or more, and also preferably 7 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less.

[0054] Furthermore, the adhesive composition of the present invention may contain other known additives, such as polyether compounds of polyalkylene glycols such as polypropylene glycol, powders such as colorants and pigments, dyes, plasticizers, silane coupling agents, tackifiers, surface lubricants, leveling agents, softeners, anti-aging agents, antioxidants, light stabilizers, ultraviolet absorbers, polymerization inhibitors, inorganic or organic fillers, metal powders, particulate matter, foil-like materials, etc., which can be added as appropriate depending on the application.

[0055] The adhesive composition of the present invention is obtained by mixing an acrylic polymer, a surfactant, and an optional component.

[0056] The adhesive composition according to the embodiment of the present invention preferably has a contact angle with water of 80 degrees or less when it is cured. A contact angle of 80 degrees or less with water of the cured film reduces the peeling force when peeling the adhesive sheet by bringing it into contact with warm water. The contact angle is more preferably 60 degrees or less, even more preferably 50 degrees or less, and although there is no particular lower limit, it is preferably 10 degrees or more.

[0057] [Adhesive sheet] The adhesive sheet of the present invention comprises an adhesive layer formed by the above-described adhesive composition on at least one side of a support substrate. Methods for forming the adhesive layer include, for example, applying the adhesive composition to a peelable liner or the like, drying and removing the polymerization solvent, etc. to form the adhesive layer, and then transferring it to the support substrate, or applying the adhesive composition to the support substrate, drying and removing the polymerization solvent, etc. to form the adhesive layer on the support substrate. When applying the adhesive, one or more solvents other than the polymerization solvent may be added as appropriate.

[0058] The substrate supporting (backing) the adhesive layer is not particularly limited, but for example, resin films, paper, cloth, rubber sheets, foam sheets, metal foils, and composites thereof can be used. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; and cellophane. Examples of paper include Japanese paper, kraft paper, glassine paper, fine paper, synthetic paper, and topcoat paper. Examples of cloth include woven and nonwoven fabrics made from various fibrous materials individually or in blends. Examples of the above fibrous materials include cotton, rayon, Manila hemp, pulp, rayon, acetate fibers, polyester fibers, polyvinyl alcohol fibers, polyamide fibers, and polyolefin fibers. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foamed sheets include foamed polyurethane sheets and foamed polychloroprene rubber sheets. Examples of metal foils include aluminum foil and copper foil.

[0059] The term "nonwoven fabric" as used herein primarily refers to nonwoven fabrics used for adhesive sheets, particularly in the field of adhesive tapes and other adhesive sheets. Typically, this refers to nonwoven fabrics produced using general-purpose paper machines (sometimes referred to simply as "paper"). Furthermore, the term "resin film" as used herein typically refers to a non-porous resin sheet and is distinct from, for example, nonwoven fabric (i.e., it does not include nonwoven fabric). The resin film may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film.

[0060] The thickness of the support substrate is not particularly limited, but it is preferably 5 to 200 μm from the viewpoint of avoiding the adhesive sheet becoming excessively thick. When the thickness of the support substrate is 5 μm or more, the handling and processability of the adhesive sheet are excellent. Furthermore, when the thickness of the support substrate is 200 μm or less, the adhesive sheet can be made lighter and thinner. The thickness of the support substrate is more preferably 7 μm or more, even more preferably 10 μm or more, even more preferably 100 μm or less, and even more preferably 50 μm or less.

[0061] A silicone release liner is preferably used as the release liner. In the step of applying and drying the adhesive composition of the present invention onto such a liner to form an adhesive layer, an appropriate method can be used for drying the adhesive, depending on the purpose. Preferably, a method of heating and drying the coated film is used. The heating and drying temperature is preferably 60 to 150°C, more preferably 70 to 140°C, and particularly preferably 80 to 130°C. By setting the heating temperature within the above range, an adhesive with excellent adhesive properties can be obtained.

[0062] The drying time can be set to an appropriate time as needed. The drying time is preferably 1 to 10 minutes, more preferably 2 to 7 minutes, and particularly preferably 3 to 5 minutes.

[0063] Furthermore, an anchor layer or surface treatment layer can be formed on the surface of the substrate, or various easy-adhesion treatments such as corona treatment or plasma treatment can be applied before forming the adhesive layer. Additionally, an easy-adhesion treatment may be applied to the surface of the adhesive layer.

[0064] Various methods are used to form the adhesive layer. Specifically, examples include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and extrusion coating methods using die coaters, etc.

[0065] The thickness of the adhesive layer is not particularly limited, but it is preferably 2 to 200 μm from the viewpoint of avoiding the adhesive sheet becoming excessively thick. When the thickness of the adhesive layer is 2 μm or more, adhesion to the adherend is ensured and impact resistance is easily obtained. Furthermore, when the thickness of the adhesive layer is 200 μm or less, the adhesive sheet can be made lighter and thinner. The thickness of the adhesive layer is more preferably 5 μm or more, even more preferably 10 μm or more, even more preferably 100 μm or less, and even more preferably 50 μm or less.

[0066] If the adhesive layer is exposed after forming it on the support substrate, the adhesive layer may be protected with a peeled sheet (separator) until it is ready for practical use.

[0067] [Method for removing adhesive sheets] Adhesive sheets can be used for a variety of purposes, such as heat-resistant masking tape, heat-resistant adhesive tapes for industrial use, heat-resistant adhesive tapes for semiconductors, and heat-resistant adhesive tapes for optical applications.

[0068] Examples of adherends include optical glass plates such as anhydrous alkali glass, metal layers such as ITO layers, metal plates, constituent resin plates, synthetic resin films, and synthetic resin sheets, but are not particularly limited.

[0069] The adhesive sheet of the present invention is attached to an object, and after the object is heat-treated at 130-250°C, the adhesive sheet is peeled off the object. In this invention, the object to which the adhesive sheet is attached is brought into contact with hot water at 40-90°C to peel it off at the interface between the object and the adhesive sheet. By bringing the object to which the adhesive sheet is attached into contact with hot water, the adhesive layer of the adhesive sheet swells due to the hot water, allowing the adhesive sheet to be peeled off the object with little force. Therefore, when heat treatment is performed at temperatures of 130°C or higher in the manufacture of various industrial products, if the adhesive sheet of the present invention is attached to the part where direct heating should be avoided, the object will be protected during the heat treatment, and when peeling off the adhesive sheet, it can be peeled off from the surface of the object with little force by bringing it into contact with hot water.

[0070] The heat treatment temperature of the adherend is more preferably 150 to 250°C, even more preferably 170 to 200°C, and the heat treatment time is more preferably 5 minutes to 5 hours, even more preferably 10 minutes to 3 hours.

[0071] There are no particular limitations on the method for bringing an object to which an adhesive sheet is attached into contact with hot water, but examples include immersing the object with the adhesive sheet in hot water, pouring hot water over the object with the adhesive sheet, or spraying hot water onto the object with the adhesive sheet. Among these, immersion in hot water using a constant temperature water bath or the like is preferred from the viewpoint of making it easier to keep the temperature of the hot water constant.

[0072] The water temperature of the hot water is 40 to 90°C. If the water temperature is 40°C or higher, the adhesive composition will swell more easily, making it easier to peel off. If the water temperature is 90°C or lower, there is no need to excessively heat the water, resulting in better manufacturing efficiency. The water temperature of the hot water is preferably 50°C or higher, more preferably 60°C or higher, preferably 85°C or lower, and more preferably 80°C or lower.

[0073] Furthermore, it is preferable that the adhesive sheet be in contact with the hot water for at least one minute. By exposing it to hot water for at least one minute, the adhesive layer swells sufficiently, making it easier to peel the adhesive sheet from the substrate. From the viewpoint of processing efficiency, the contact time with hot water is more preferably 1 to 120 minutes, and even more preferably 5 to 60 minutes. [Examples]

[0074] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0075] Acrylic polymers A to E were prepared according to the following procedure. Table 1 shows the amount of monomer used for each polymer.

[0076] <Preparation of acrylic polymer A> In a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirrer, 85 parts by mass of methoxyethyl acrylate (hereinafter referred to as "MEA"), 5 parts by mass of 4-hydroxybutyl acrylate (hereinafter referred to as "4HBA"), 10 parts by mass of n-vinyl-2-pyrrolidone (hereinafter referred to as "NVP"), 0.5 parts by mass of acrylic acid (hereinafter referred to as "AA"), 0.2 parts by mass of benzoyl peroxide, and 65 parts by mass of toluene were added. Polymerization was carried out at 61°C for 6 hours under a nitrogen atmosphere to obtain acrylic polymer A with the structure shown below. In the structure below, k, l, m, and n are the mass ratios of each monomer, with k=84.6, l=9.9, m=5.0, and n=0.5, respectively. The weight-average molecular weight (Mw) of acrylic polymer A was 550,000.

[0077] [ka]

[0078] <Preparation of acrylic polymer B> Acrylic polymer B was obtained by performing the same procedure as for acrylic polymer A, except that MEA was replaced with ethoxyethoxyethyl acrylate (hereinafter referred to as "EEEA"). In the structure below, k, l, m, and n represent the mass ratios of each monomer, with k=84.6, l=9.9, m=5, and n=0.5, respectively. The weight-average molecular weight (Mw) of acrylic polymer B was 410,000.

[0079] [ka]

[0080] <Preparation of acrylic polymer C> In a reaction vessel equipped with a condenser, nitrogen inlet tube, thermometer, and stirring device, 95 parts by mass of MEA, 5 parts by mass of AA, 0.2 parts by mass of benzoyl peroxide, and 65 parts by mass of toluene were added, and polymerization was carried out at 61°C for 6 hours under a nitrogen atmosphere to obtain an acrylic polymer C with the structure shown below. In the structure below, m and n are the mass ratios of each monomer, with m=95 and n=5, respectively. The weight-average molecular weight (Mw) of acrylic polymer C was 800,000.

[0081] [ka]

[0082] <Preparation of acrylic polymer D> Except for replacing MEA with n-butyl acrylate (hereinafter referred to as "BA"), the same procedure as for preparing acrylic polymer C was followed to obtain acrylic polymer D with the structure shown below. In the structure below, m and n represent the mass ratio of each monomer, with m=95 and n=5, respectively. The weight-average molecular weight (Mw) of acrylic polymer D was 650,000.

[0083] [ka]

[0084] <Preparation of acrylic polymer E> Except for changing AA to 4HBA, the same procedure as for the preparation of acrylic polymer C was followed to obtain acrylic polymer E with the structure shown below. In the structure below, m and n represent the mass ratio of each monomer, with m=95 and n=5, respectively. The weight-average molecular weight (Mw) of acrylic polymer E was 460,000.

[0085] [ka]

[0086] [Table 1]

[0087] <Example 1> To 100 parts by mass of acrylic polymer A, 0.5 parts by mass of epoxy crosslinking agent (product name "Tetrad-C", manufactured by Mitsubishi Gas Chemical Co., Ltd.), 1 part by mass of polyisocyanate compound (product name "Coronate L", manufactured by Nippon Polyurethane Industries Co., Ltd.), and 5 parts by mass of polyoxyethylene sorbitan monolaurate (product name "Leodol TW-L120", manufactured by Kao Corporation) as a nonionic surfactant were added to prepare an adhesive solution. The obtained adhesive solution was applied to the silicone-treated surface of a PET release liner and heated at 80°C for 5 minutes to form an adhesive layer with a thickness of 10 μm. Next, a PET film with a thickness of 12 μm was laminated to the adhesive layer. After that, it was stored at 50°C for 24 hours to produce adhesive sheet 1.

[0088] <Example 2> In Example 1, adhesive sheet 2 was prepared in the same manner as in Example 1, except that acrylic polymer A was replaced with acrylic polymer B.

[0089] <Example 3> In Example 1, adhesive sheet 3 was prepared in the same manner as in Example 1, except that the amount of polyoxyethylene sorbitan monolaurate added was changed to 1.5 parts by mass and 1.5 parts by mass of polypropylene glycol (manufactured by Sigma-Aldrich, Mn4000) was added.

[0090] <Example 4> In Example 1, an adhesive sheet 4 was prepared in the same manner as in Example 1, except that acrylic polymer A was replaced with acrylic polymer C.

[0091] <Comparative Example 1> In Example 1, an adhesive sheet 5 was prepared in the same manner as in Example 1, except that acrylic polymer A was replaced with acrylic polymer D.

[0092] <Comparative Example 2> In Example 1, an adhesive sheet 6 was prepared in the same manner as in Example 1, except that acrylic polymer A was replaced with acrylic polymer E.

[0093] <Comparative Example 3> In Example 1, an adhesive sheet 7 was prepared in the same manner as in Example 1, except that a surfactant was not added.

[0094] <Contact angle> Adhesive sheets were cut into strips 20 mm wide and 50 mm long. Under conditions of 25°C and 50% RH, 2 μL of deionized water was dropped onto the adhesive surface of each strip, and the contact angle was measured after 10 seconds. The contact angle was measured by fitting images obtained using a contact angle meter (DMo-501, manufactured by Kyowa Interface Science Co., Ltd.) with Kyowa Interface Science Co., Ltd.'s multi-functional integrated analysis software FAMAS using the "liquid application method" and "θ / 2 method".

[0095] <Evaluation of peeling force> 1. Measurement of initial adhesion strength The adhesive sheet was cut into strips 20 mm wide and 100 mm long, and attached to an alkali glass plate (1.35 mm thick, blue plate with polished edges) manufactured by Matsunami Glass Industry Co., Ltd. using a roller (pressure of 2 kg / 10 mm). This was then autoclaved at 50°C and 5 atmospheres for 30 minutes, and then left to stand at room temperature and atmospheric pressure for 30 minutes to obtain the test sample. The adhesive strength of the test specimen was measured when it was peeled off at a peeling angle of 180 degrees and a peeling speed of 300 mm / min using a tensile testing machine (SHIMAZU "EZ-S 500N") in an environment of 25°C × 50%RH.

[0096] 2. Measurement of adhesive strength after heating The test samples obtained above were heated in an oven at 180°C for 1 hour, then left to stand at room temperature and pressure for 30 minutes, and the adhesive strength was measured using a tensile testing machine in the same manner as above.

[0097] 3. Measurement of adhesive strength after immersion in hot water The test samples obtained as described above were heated in an oven at 180°C for 1 hour, then left to stand at room temperature and pressure for 30 minutes, and then immersed in 60°C warm water for 1 hour. After wiping off the surface moisture with a cloth, the adhesive strength was measured using a tensile testing machine in the same manner as described above.

[0098] <Glue residue evaluation> In "3. Measurement of Adhesion after Hot Water Immersion" above, if no adhesive residue was visible on the glass surface after peeling off the product after hot water immersion, it was judged as "OK (Good)," and if any residue was observed, it was evaluated as "NG (Poor)."

[0099] The results are shown in Table 2.

[0100] [Table 2]

[0101] Examples 1-4 exhibited excellent initial adhesion, and the adhesion tended to increase after heating. However, contact with hot water reduced the adhesion below the initial level, making them easier to peel off. Furthermore, no adhesive residue was observed after peeling, indicating excellent peelability. In contrast, Comparative Example 1 did not decrease in adhesion below the initial level when contacted with hot water, and its adhesion could not be reduced. Comparative Examples 2 and 3 showed a decrease in adhesion upon contact with hot water, but adhesive residue was observed after peeling.

[0102] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2021-160104, filed on 29 September 2021, the contents of which are incorporated herein by reference.

Claims

1. An adhesive composition comprising an acrylic polymer containing structural units of an alkoxy group-containing (meth)acrylate monomer as the main component, and 5 to 20 parts by mass of polymerizable monomer structural units having a homopolymer Tg of 0°C or higher, per 100 parts by mass of the total monomer structural units, and a nonionic surfactant, The alkoxy group-containing (meth)acrylate monomer is at least one selected from the group consisting of methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol acrylate, and polypropylene glycol acrylate. An adhesive composition in which the content of the nonionic surfactant is 3 to 10 parts by mass per 100 parts by mass of the acrylic polymer.

2. The adhesive composition according to claim 1, wherein the nonionic surfactant comprises a sorbitan fatty acid ester.

3. The adhesive composition according to claim 1, wherein the polymerizable monomer having a Tg of 0°C or higher of the homopolymer comprises at least one selected from acrylic acid and N-vinyl-2-pyrrolidone.

4. The adhesive composition according to claim 1, wherein the contact angle with water when the adhesive composition is cured is 80 degrees or less.

5. An adhesive sheet comprising an adhesive layer made of the adhesive composition according to any one of claims 1 to 4.

6. A method for peeling off an adhesive sheet according to claim 5, which has been bonded to an object, A method for peeling off an adhesive sheet, comprising the step of bringing the adherend to which the adhesive sheet is attached, which has been heat-treated at 130 to 250°C, into contact with warm water at 40 to 90°C to peel it off at the interface between the adherend and the adhesive sheet.

7. The method for peeling off an adhesive sheet according to claim 6, wherein the object to which the adhesive sheet is attached is brought into contact with the hot water for one minute or more.

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