Removable adhesive composition and adhesive sheet

Abstract

The present invention aims to provide a repositionable adhesive composition that exhibits excellent high-temperature repositionability and repositionability. [Solution] A repositionable adhesive composition comprising a (meth)acrylic copolymer (A) containing 31 to 89% by mass of 2-octyl (meth)acrylate and 0.6 to 4.9% by mass of a carboxyl group-containing monomer, wherein the composition contains 0 to 10 parts by mass of a tackifying resin (B) per 100 parts by mass of the (meth)acrylic copolymer (A).

Description

Technical Field

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[0005]

[0001] The present invention relates to an adhesive composition for re-peeling and an adhesive sheet.

Background Art

[0002] There is a market demand for adhesives and adhesive sheets that are excellent in both high-temperature re-peelability and re-stickability. Conventionally, as an adhesive layer with good high-temperature re-peelability, 2EHA: 2-ethylhexyl acrylate and / or BA: n-butyl acrylate have been used as main monomers in order to emphasize the adhesion to the substrate and the wettability to the adherend (Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in Patent Documents 1 and 2, since 2EHA is used as the main monomer, there is a problem that the re-stickability deteriorates. On the other hand, in Patent Document 3, since BA is used as the main monomer, there is a problem that the high-temperature re-peelability deteriorates. Thus, it has been difficult to realize an adhesive composition for re-peeling that is excellent in both high-temperature re-peelability and re-stickability.

[0005] Therefore, an object of the present invention is to provide an adhesive composition for re-peeling that is excellent in high-temperature re-peelability and re-stickability.

Means for Solving the Problems

[0006] To achieve the objectives of the present invention, the re-peelable adhesive composition of the present invention comprises the following: a (meth)acrylic copolymer (A) containing 31 to 89% by mass of 2-octyl (meth)acrylate and 0.6 to 4.9% by mass of a carboxyl group-containing monomer, and containing 0 to 10 parts by mass of tackifying resin (B) per 100 parts by mass of the (meth)acrylic copolymer (A). [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a repositionable adhesive composition that exhibits excellent high-temperature repositionability and repositionability. [Modes for carrying out the invention]

[0008] The embodiments will be described in detail below. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined in any way.

[0009] In this specification, the notation "A~B" representing a numerical range is synonymous with "greater than or equal to A" and "less than or equal to B," and includes the lower limit A and the upper limit B.

[0010] In this specification, "(meth)acrylic" means both "acrylic" and "methacrylic." Similarly, "(meth)acrylate" means both "acrylate" and "methacrylate."

[0011] In this specification, "mass%" represents the amount of each of the components (a1), (a2), and (a3) ​​described below contained in 100 mass% of the monomer mixture constituting the (meth)acrylic copolymer (A). In this specification, "parts by mass" represents the amount of each of the components (B) and (C) described below contained in 100 parts by mass of the (meth)acrylic copolymer (A).

[0012] In this specification, "high-temperature re-peelability" refers to the property of an adhesive sheet having an adhesive layer made of a re-peelable adhesive composition that, when applied to a substrate and peeled off after a certain period of time in a high-temperature environment, leaves little adhesive residue on the substrate.

[0013] In this specification, "repositionability" means the property of an adhesive sheet having an adhesive layer made of a repositionable adhesive composition that allows it to be repositioned onto an adherend.

[0014] <Removable adhesive composition> The removable adhesive composition is used, for example, as the adhesive layer and adhesive of the adhesive sheet described later. The removable adhesive composition comprises a (meth)acrylic copolymer (A) and a curing agent (C), and optionally contains a tackifying resin (B).

[0015] <(meth)acrylic copolymer (A)> The (meth)acrylic copolymer (A) comprises a (meth)acrylic monomer (a1) and a functional group-containing monomer (a2) as constituent units, and optionally further comprises a vinyl monomer (a3) ​​as a constituent unit.

[0016] <(meth)acrylmonomer(a1)> (Meth)acrylic monomer (a1) is an alkyl ester monomer of (meth)acrylate having an alkyl group with 1 to 18 carbon atoms. Examples of (meth)acrylic monomer (a1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, and isooctyl (meth)acrylate. Examples of alkyl (meth)acrylates having linear or branched alkyl groups include 2-ethylhexyl (meth)acrylate, 2-octyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-undecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, cetyl (meth)acrylate, and stearyl (meth)acrylate. These may be used alone or in combination of two or more.

[0017] In one embodiment, the (meth)acrylic monomer (a1) is preferably an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms. Examples of alkyl(meth)acrylates having an alkyl group with 4 to 12 carbon atoms include n-butyl(meth)acrylate, isobutyl(meth)acrylate, tert-butyl(meth)acrylate, sec-butyl(meth)acrylate, n-amyl(meth)acrylate, isoamyl(meth)acrylate, n-hexyl(meth)acrylate, n-heptyl(meth)acrylate, n-octyl(meth)acrylate, isooctyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, 2-octyl(meth)acrylate, n-nonyl(meth)acrylate, isononyl(meth)acrylate, n-decyl(meth)acrylate, isodecyl(meth)acrylate, n-undecyl(meth)acrylate, and n-lauryl(meth)acrylate.

[0018] The (meth)acrylic monomer (a1) contains at least 2-octyl (meth)acrylate, preferably at least 2-octyl acrylate. In this case, the (meth)acrylic monomer (a1) having an alkyl group having 4 to 12 carbon atoms other than 2-octyl (meth)acrylate contains at least one monomer having a homopolymer Tg similar to that of the homopolymer Tg of 2-octyl acrylate, and one monomer having a homopolymer Tg lower than that of the homopolymer Tg of 2-octyl acrylate. The (meth)acrylic monomer (a1) having an alkyl group having 4 to 12 carbon atoms other than 2-octyl (meth)acrylate may further contain at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, but is not limited thereto. By further blending a predetermined amount of monomers other than 2-octyl (meth)acrylate, as described later, into the (meth)acrylic copolymer (A), the balance between high-temperature re-peelability and re-adhesionability can be adjusted.

[0019] In one embodiment, the (meth)acrylic copolymer (A) contains 2-octyl (meth)acrylate in an amount of 31 to 89% by mass, more preferably 50 to 89% by mass, and still more preferably 65 to 89% by mass, based on 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A). When the content of 2-octyl (meth)acrylate is in the range of 31 to 89% by mass, high-temperature re-peelability and re-stickability can be achieved simultaneously. When the content of 2-octyl (meth)acrylate is less than 31% by mass, the re-stickability deteriorates. When the content of 2-octyl (meth)acrylate exceeds 89% by mass, the adhesion of the adhesive layer to the substrate deteriorates and the high-temperature re-peelability deteriorates.

[0020] In addition, 2-octyl acrylate, which is an essential component constituting the (meth)acrylic copolymer (A), can be obtained from biomass-derived materials, so the dependence on monomers derived from fossil resources can be reduced. Since the re-peelable adhesive composition of the present invention contains 2-octyl acrylate, it is excellent in terms of being friendly to both humans and the environment.

[0021] ingredient constituting the (meth)acrylic copolymer (A), further contains n-octyl acrylate in an amount of 8 to 18% by mass, preferably 8 to 17.2% by mass. Hereinafter, the blending amount of monomers other than 2-octyl (meth)acrylate for adjusting the balance between high-temperature re-peelability and re-stickability will be described. The monomers other than 2-octyl (meth)acrylate are, as described above, for example, at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. In one embodiment, the (meth)acrylic copolymer (A) contains n-octyl acrylate in an amount of 8 to 18% by mass, preferably 8 to 17.2% by mass, based on 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A).

[0022] In one embodiment, the (meth)acrylic copolymer (A) contains n-butyl acrylate in an amount of 9 to 27% by mass, preferably 9.8 to 26.1% by mass, based on 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A).

[0023] In one embodiment, the (meth)acrylic copolymer (A) further contains 1 to 61% by mass, preferably 1.8 to 60.7% by mass of 2-ethylhexyl acrylate in 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A).

[0024] The (meth)acrylic monomer (a1) may further contain monomers other than the (meth)acrylic acid alkyl ester monomers having an alkyl group with 1 to 18 carbon atoms described above. Examples of the (meth)acrylic monomer (a1) other than the (meth)acrylic acid alkyl ester monomers having an alkyl group with 1 to 18 carbon atoms include (meth)acrylic acid esters having an alicyclic hydrocarbon group such as cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; (meth)acrylic acid alkoxyalkyl esters such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, and 2-phenoxyethyl (meth)acrylate; (meth)acrylic acid aralkyl esters such as benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and naphthylmethyl (meth)acrylate; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate, tolyl (meth)acrylate, and naphthyl (meth)acrylate; and the like. These may be used alone or in combination of two or more.

[0025] <Functional group-containing monomer (a2)> The (meth)acrylic copolymer (A) contains the functional group-containing monomer (a2) as a structural unit. The functional group-containing monomer (a2) includes at least one of a carboxy group-containing monomer, a hydroxy group-containing monomer, and an amide group-containing monomer. The functional group-containing monomer (a2) preferably contains at least a carboxy group-containing monomer and may optionally further contain a hydroxy group-containing monomer.

[0026] Examples of carboxyl group-containing monomers include (meth)acrylic acid esters having a carboxyl group, such as 2-carboxyethyl (meth)acrylate; and unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, maleic acid, itaconic acid, fumaric acid, citraconic acid, and mesaconic acid. These may be used individually or in combination of two or more. The carboxyl group-containing monomer is preferably acrylic acid. By using a carboxyl group-containing monomer, good adhesion and cohesive force can be achieved with various substrates (especially substrates made of highly polar materials).

[0027] The content of carboxyl group-containing monomers is preferably 0.6 to 4.9% by mass, more preferably 0.6 to 2.4% by mass, and even more preferably 0.6 to 1.2% by mass, of 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A). A carboxyl group-containing monomer content in the range of 0.6 to 4.9% by mass allows for both high-temperature re-peelability and repositionability. On the other hand, if the carboxyl group-containing monomer content is less than 0.6% by mass, repositionability deteriorates. If the carboxyl group-containing monomer content exceeds 4.9% by mass, adhesive residue tends to remain, and high-temperature re-peelability deteriorates.

[0028] Examples of hydroxyl group-containing monomers include hydroxyl group-containing (meth)acrylic acid esters (hydroxyalkyl (meth)acrylates) such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These may be used individually or in combination of two or more. The hydroxyl group-containing monomer is preferably 2-hydroxyethyl acrylate. By using a hydroxyl group-containing monomer, it becomes a reaction site with the isocyanate-based curing agent described later, and good high-temperature re-peelability can be imparted to the adhesive even under high-temperature conditions.

[0029] The content of hydroxyl group-containing monomers is 0.1 to 2% by mass of 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A).

[0030] Examples of monomers having an amide group include (meth)acrylamide, isopropyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, and hydroxyethyl(meth)acrylamide. These may be used individually or in combination of two or more. The monomer having an amide group is preferably (meth)acrylamide.

[0031] <Vinyl monomer (a3)> The (meth)acrylic copolymer (A) may optionally contain a vinyl monomer (a3) ​​as a constituent unit. Examples of vinyl monomers (a3) ​​include monomers such as styrene, α-methylstyrene, vinyltoluene, divinylbenzene, vinylpyridine, vinylpyrrolidone, vinylcarbazole, vinyl acetate and acrylonitrile, butadiene, isoprene and chloroprene, vinyl halides such as vinyl chloride and vinyl bromide, and vinylidenes such as vinylidene chloride. These may be used alone or in combination of two or more. The vinyl monomer (a3) ​​is preferably vinyl acetate.

[0032] In one embodiment, the (meth)acrylic copolymer (A) further contains 0.4 to 5% by mass, preferably 0.5 to 4.9% by mass, of vinyl monomer (a3) ​​in 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A). By having the content of vinyl monomer (a3) ​​in the range of 0.4 to 5% by mass, the balance between high-temperature re-peelability and re-adhesionability can be controlled.

[0033] <Tackifying resin (B)> The repositionable adhesive composition may optionally further contain a tackifying resin (B). The tackifying resin (B) may be any of the tackifying resins conventionally used in adhesives, or it may be a novel tackifying resin. From the viewpoint of improving the biomass content of the repositionable adhesive composition, the tackifying resin (B) preferably contains at least one of a rosin-based resin and a terpene-based resin.

[0034] The tackifying resin (B) can be used by any method, such as by incorporating it during solution polymerization or by incorporating it into the (meth)acrylic copolymer (A). When used during solution polymerization, the tackifying resin (B) acts as a chain transfer agent, making it easier to adjust the molecular weight of the (meth)acrylic copolymer (A). Furthermore, the tackiness can be further improved by incorporating a predetermined amount of the tackifying resin (B), as described later, into the (meth)acrylic copolymer (A).

[0035] Examples of rosin-based resins include natural rosin, rosin esters, hydrogenated rosin, hydrogenated rosin esters, polymerized rosin, polymerized rosin esters, disproportionated rosin, and disproportionated rosin esters. These may be used individually or in combination of two or more. The rosin-based resin is preferably polymerized rosin ester.

[0036] Examples of terpene resins include α-pinene resin, β-pinene resin, terpene resin, hydrogenated terpene resin, aromatically modified terpene resin, and terpene phenol resin. These may be used individually or in combination of two or more. The terpene resin is preferably a terpene phenol resin.

[0037] Among these tackifying resins (B), natural rosin and ester resins derived from rosin (rosin esters, water-added rosin esters), etc., are more preferred. In this case, the form of the tackifying resin (B) is preferably solid.

[0038] In one embodiment, the re-peelable adhesive composition contains, preferably, 0 to 10 parts by mass or 1.5 to 10 parts by mass, more preferably 0 to 5 parts by mass, and even more preferably 0 to 2.5 parts by mass of tackifying resin (B) per 100 parts by mass of (meth)acrylic copolymer (A). If the content of tackifying resin (B) is 10 parts by mass or less, the adhesive strength can be improved without degrading high-temperature re-peelability. On the other hand, if the content of tackifying resin (B) exceeds 10 parts by mass, the adhesive strength improves, but the high-temperature re-peelability deteriorates due to the increase in low molecular weight substances.

[0039] <Hardening agent (C)> A removable adhesive composition according to one embodiment contains a curing agent (C). By using the curing agent (C), the cohesive force of the (meth)acrylic copolymer (A) is increased, and the high-temperature removable properties are improved.

[0040] The curing agent (C) according to one embodiment comprises at least one of an isocyanate-based curing agent, an epoxy-based curing agent, a metal chelate-based curing agent, and an aziridine-based curing agent. These may be used individually or in combination of two or more.

[0041] Examples of isocyanate-based curing agents include isocyanate compounds such as toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethyl xylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate, and adducts of polyol compounds such as trimethylolpropane, as well as their burettes and isocyanurates, and adducts of the above isocyanate compounds with any polyol such as polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol, which have three or more isocyanate groups in their molecules; or compounds such as allophanates thereof that have two isocyanate groups in their molecules. These may be used individually or in combination of two or more. The isocyanate-based curing agent can exhibit appropriate tackiness and cohesiveness by forming crosslinking points with carboxyl group-containing monomers and / or hydroxyl group-containing monomers contained in the (meth)acrylic copolymer (A).

[0042] The content of the isocyanate-based curing agent is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A). Sufficient cohesive force can be obtained when the content of the isocyanate-based curing agent is 0.1 parts by mass or more.

[0043] Examples of epoxy curing agents include epoxy resins obtained from the reaction of bisphenol A and epichlorohydrin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, N,N-diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane. These may be used individually or in combination of two or more.

[0044] Examples of metal chelating curing agents include aluminum alkoxides such as aluminum isopropylate, monosec-butoxyaluminum diisopropylate, aluminum sec-butyrate, and aluminum ethylacetate aluminum diisopropylate, aluminum tris(ethylacetate), alkylacetate aluminum diisopropylate, aluminum monoacetylacetate bis(ethylacetate), and aluminum tris(acetylacetonate), as well as titanium tetraisopropoxide, titanium tetran-butoxide, titanium butoxide dimer, and titanium tetra- Examples include titanium alkoxides such as 2-ethylhexoxide, titanium diisopropoxybis(acetylacetonate), titanium tetraacetylacetonate, titanium diisopropoxybis(ethylacetoacetate), titanium phosphate ester complexes, titanium octylene glycolate, and other titanium chelates; zirconium alkoxides such as zirconium tetran-n-propoxide and zirconium tetran-n-butoxide; zirconium chelates such as zirconium tetraacetylacetonate, zirconium triputoxymonoacetylacetonate, and zirconium dibutoxybis(ethylacetoacetate); and zirconium acylates such as zirconium stearate. These may be used individually or in combination of two or more. From the viewpoint of crosslinking properties, tackiness, transparency, and storage stability, aluminum tris(acetylacetonate) is preferred as the metal chelating curing agent.

[0045] The content of the metal chelating curing agent is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and more preferably 0.01 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic copolymer (A). Sufficient cohesive force can be obtained if the content of the metal chelating curing agent is 0.01 parts by mass or more.

[0046] Examples of aziridine curing agents include N,N'-(4,4'-methylenediphenyl)bis(aziridine-1-carboxamide), 1,1'-isophthaloylbis(2-methylaziridine), tris(1-aziridinyl)phosphine oxide, 1,1'-hexamethylenebis(iminocarbonyl)bisaziridine, trimethylolpropane-tris(2-aziridinylpropionate), and 2,4,6-tris(1-aziridinyl)-1,3,5-triazine. These may be used individually or in combination of two or more.

[0047] <Other additives> The repositionable adhesive composition of the present invention may contain various additives, provided that they do not affect the required performance specified in the present invention. Examples of additives include antistatic agents, antioxidants, silane coupling agents, heat or light stabilizers, ultraviolet absorbers, leveling agents, defoamers, antibacterial agents, humectants, pigments, dyes, and fragrances. These may be used individually or in combination of two or more.

[0048] <Meth)acrylic copolymer (A) manufacturing method> The (meth)acrylic copolymer (A) is not particularly limited and can be produced by polymerizing the monomer mixture described above by a known radical polymerization reaction, but it is preferable to produce it by solution polymerization. Specifically, it is common to heat a solvent, monomer, polymerization initiator, etc., to a reaction temperature of about 50 to 90°C in an inert gas atmosphere such as nitrogen gas and carry out the polymerization reaction for 4 to 12 hours. The solvent used in solution polymerization can be appropriately selected considering the leveling properties during coating, drying properties, and effects on the environment and human health. The solvent is preferably at least one of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, esters, ketones, and alcohols. Examples of solvents include ester solvents such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone, methyl butyl ketone, and cyclohexanone; hydrocarbon solvents such as toluene, xylene, and n-hexane; and alcohol solvents such as methanol, ethanol, n-propanol, and isopropanol. These may be used individually or in combination of two or more.

[0049] The polymerization initiator is not particularly limited, and any conventionally known one can be used. For example, polymerization initiators commonly used in radical polymerization, such as those listed below, can be used as appropriate.

[0050] Examples of polymerization initiators include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; and oils such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile. Soluble azo compounds; 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxyethyl)]propionamide}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamide}, 2,2'-azobis[2-(5-methyl-2-imidazoline-2-yl) 2,2'-Azobis[2-(2-imidazolin-2-yl)propane] and its salts, 2,2'-Azobis[2-(3,4,5,6-tetrahydropyrimidine-2-yl)propane] and its salts, 2,2'-Azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} and its salts, 2,2'-Azobis(2-methylpropionamidine) and its salts, Examples include water-soluble azo compounds such as 2,2'-azobis(2-methylpropyneamidine) and its salts, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] and its salts; and organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxyisobutyrate. These may be used individually or in combination of two or more.

[0051] <Adhesive sheet> The adhesive sheet comprises a substrate and an adhesive layer made of the re-peelable adhesive composition of the present invention, provided on at least one surface of the substrate. The adhesive sheet can be manufactured, for example, by coating the re-peelable adhesive composition onto the substrate and drying it. The adhesive layer may be provided on at least one surface of the substrate depending on the application of the adhesive sheet. A release sheet may also be provided on the adhesive surface of the adhesive layer.

[0052] The adhesive sheet of the present invention can be attached to various substrates, such as paper, cloth, nonwoven fabric, plastic products, glass products, metal products such as stainless steel, and rubber products.

[0053] Since the adhesive sheet possesses both high-temperature re-peelability and repositionability, it can be suitably used in a variety of applications, such as labels, seals, tapes, building materials, packaging materials, and electronic products.

[0054] In one embodiment, the 180-degree peel strength to a stainless steel plate is 9.0 N / 25 mm or less. A 180-degree peel strength of 9.0 N / 25 mm or less is preferable from the viewpoint of making it easier to peel the adhesive sheet from the adherend.

[0055] In one embodiment, in the J. Dow inclined ball tack test, the maximum diameter of the steel ball that stops on the adhesive surface of the adhesive layer is 9 / 32 inches or less. The numerical value used to evaluate the tack of the adhesive sheet is preferably 9 or less, from the viewpoint of facilitating repositioning to the adherend.

[0056] Examples of liquid media used when applying the repositionable adhesive composition include hydrocarbon solvents such as toluene, xylene, hexane, and heptane; ester solvents such as methyl acetate, ethyl acetate, and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; halogenated hydrocarbon solvents such as dichloromethane and chloroform; ether solvents such as diethyl ether, methoxytoluene, and dioxane; and other hydrocarbon solvents. These may be used individually or in combination of two or more. The viscosity can be adjusted by adding any liquid media to the repositionable adhesive composition. The viscosity can also be reduced by heating the repositionable adhesive composition.

[0057] Examples of substrates include paper, cellophane, plastic sheets, rubber, foam, cloth, rubber cloth, resin-impregnated cloth, glass plates, and wood. The substrate may be in the form of a plate or a film. Furthermore, the substrate may be composed of a single material or a multilayer substrate formed by laminating multiple substrates of different materials. In addition, a substrate with a peeled surface may be used.

[0058] Examples of plastic sheets include polyvinyl alcohol film, triacetylcellulose film, polyolefin resin films such as polypropylene, polyethylene, polycycloolefin, and ethylene-vinyl acetate copolymer; polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; vinyl resin films such as polyvinyl chloride; polycarbonate resin films; polynorbornene resin films; polyarylate resin films; acrylic resin films; polyphenylene sulfide resin films; polystyrene resin films; polyamide resin films; polyimide resin films; and epoxy resin films. These may be used individually or in combination of two or more types.

[0059] As a release sheet (separator) to protect the adhesive surface of the adhesive layer, a resin film such as polyester film or paper can be used. The surface of the release sheet that comes into contact with the adhesive surface of the adhesive layer may be treated with a release agent such as a silicone-based or fluorine-based release agent.

[0060] Methods for applying the repositionable adhesive composition include, for example, a Meyer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, and spin coater. Methods for drying include, for example, hot air drying, infrared drying, and reduced pressure drying. Drying conditions can be appropriately changed depending on the curing form, film thickness, and type of solvent of the repositionable adhesive composition, but for example, hot air drying at 60 to 130°C may be used.

[0061] The thickness of the adhesive layer is not particularly limited, but is 1 to 200 μm, preferably 3 to 100 μm.

[0062] <Method for producing a removable adhesive composition> The definitions of the abbreviations in Tables 1 and 2 are as follows: Definition of an abbreviation 2OA:2-Octylacrylate NOAA: n-Octylacrylate BA: n-butyl acrylate 2EHA:2-Ethylhexylacrylate VAC: Vinyl acetate AAc: Acrylic acid HEA: 2-hydroxyethyl acrylate Tackifying resin A: Arakawa Chemical Industries, Ltd. Pencel D-135 (polymerized rosin ester) Tackifying resin B: Yasuhara Chemical Co., Ltd. YS Polystar T130 (terpene phenol resin) Curing agent A: Mitsui Chemicals, Inc. Takenate D101E (45EA) (Adduct of toluene diisocyanate and polyol compound) Hardener B: Kawaken Fine Chemical Co., Ltd. Aluminum Chelate A (Aluminum Trisacetylacetonate) (a1): (meth)acrylic monomer (a1) (a2): Functional group-containing monomer (a2) (a3): Vinyl monomer (a3) (B): Tackifying resin (B) (C): Hardener (C) Adhesion: See Test 1 below. Ball tack, repositionability: See Test 2 below. High-temperature re-peeling: See Test 3 below.

[0063] Table 1 shows the raw material formulations of the repositionable adhesive compositions of Examples 1 to 9. Table 2 shows the raw material formulations of the repositionable adhesive compositions of Comparative Examples 1 to 8. The units of the numerical values ​​listed in sections (a1) to (C) of Tables 1 and 2 are "parts".

[0064] [Table 1]

[0065] [Table 2]

[0066] <Example 1: Method for producing (meth)acrylic copolymer (A) and repositionable adhesive composition> Based on the raw material formulation of Example 1 in Table 1, 89.0 parts of 2-octyl acrylate, 8.0 parts of n-octyl acrylate, 2.9 parts of acrylic acid, 0.1 parts of 2-hydroxyethyl acrylate, 65 parts of ethyl acetate, 10 parts of acetone, and 0.08 parts of polymerization initiator (azobisisobutyronitrile) were charged into a reactor equipped with a stirrer, thermometer, and reflux condenser. The reactor was heated to 85°C while stirring to initiate the reaction, and the polymerization reaction was carried out at reflux temperature for 7 hours. After the reaction was complete, the mixture was cooled and diluted with ethyl acetate to obtain a (meth)acrylic copolymer (A) with a solid content of 45% by mass.

[0067] To 100 parts of the obtained (meth)acrylic copolymer (A), 0.4 parts in solid content of Takenate D101E (45EA) (trade name, manufactured by Mitsui Chemicals, Inc.) was added as an isocyanate curing agent and thoroughly mixed to obtain a re-peelable adhesive composition.

[0068] <Examples 2-9: Method for producing (meth)acrylic copolymer (A) and repositionable adhesive composition> Since the (meth)acrylic copolymer (A) and re-peelable adhesive compositions of Examples 2 to 9 were manufactured based on the raw material formulations in Table 1 and the same manufacturing method as in Example 1, a detailed explanation is omitted.

[0069] <Comparative Examples 1-8: Method for producing (meth)acrylic copolymer (A) and repositionable adhesive composition> Since the (meth)acrylic copolymer (A) and re-peelable adhesive compositions of Comparative Examples 1 to 8 were manufactured based on the raw material formulations in Table 2 and the same manufacturing method as in Example 1, a detailed explanation is omitted.

[0070] <Example 1: Method for manufacturing an adhesive sheet> The repositionable adhesive composition of Example 1 was applied to the release-treated surface of a release sheet to a dry thickness of 30 μm, and dried in a hot air circulating dryer at 100°C for 1 minute to prepare an adhesive layer. The adhesive layer was laminated to a substrate (made of polyethylene terephthalate) with a thickness of 25 μm, and cured at 23°C and 50% RH for 7 days to obtain adhesive sheet A.

[0071] <Examples 2-9, Comparative Examples 1-8: Methods for Manufacturing Adhesive Sheets> Since the adhesive sheets of Examples 2-9 and Comparative Examples 1-8 were manufactured using the same manufacturing method as in Example 1, a detailed explanation is omitted.

[0072] <Testing Method> The following tests 1 to 3 were performed using the adhesive sheets of Examples 1 to 9 and Comparative Examples 1 to 8.

[0073] (Test 1: Measurement of adhesive strength) Adhesive sheet A was cut to a width of 25 mm and a length of 70 mm to obtain test specimens. The release sheet was peeled off the test specimen (adhesive sheet A), and it was attached to the surface of a stainless steel plate (SUS304) as the adherend. A 2 kg roll was then used to press it down once back and forth. After that, it was left in an atmosphere of 23°C and 50% humidity for 20 minutes. After the period of time, the adhesive strength of the test specimen was measured using a tensile testing machine (Tensilon: manufactured by A&D) in accordance with JIS Z-0237:2000, under conditions of a tensile speed of 300 mm / min and a peel angle of 180°. The evaluation criteria are as follows. [Evaluation Criteria] ○ (Good): Adhesion is 9.0 N / 25 mm or less. × (Defective): Adhesive strength exceeds 9.0 N / 25 mm.

[0074] (Test 2: Evaluation of repositionability) Adhesive sheet A was cut to a width of 70 mm and a length of 100 mm to obtain test specimens. The release sheet was peeled off the test specimen (adhesive sheet A), and it was fixed with the adhesive side facing up on an inclined plate at a 30-degree angle. Then, following the J. Dow method, a steel ball was rolled over the sample with a run-up of 10 cm and an adhesive surface of 10 cm in a 23°C, 50% atmosphere, and the diameter number of the steel ball that stopped near the center of the adhesive surface was recorded. The evaluation criteria are as follows. [Evaluation Criteria] ○ (Good): Ball tack (No.) ≤ 9 ×(Defective): Ball tack (No.) > 9

[0075] (Test 3: Evaluation of high-temperature re-peelability) Adhesive sheet A was cut to a width of 25 mm and a length of 70 mm to obtain test specimens. The release sheet was peeled off the test specimen (adhesive sheet A), and it was attached to the surface of a stainless steel plate (SUS304) as the adherend. A 2 kg roll was then used to press it down once back and forth. After that, it was stored in a 70°C environment for 3 days. After 3 days, the test specimen was removed and left at 23°C and 50% humidity for 1 hour, and the state of adhesive residue on the stainless steel plate (SUS304) after peeling off adhesive sheet A by hand was observed. The evaluation criteria are as follows. [Evaluation Criteria] ○: No adhesive residue on the stainless steel plate, or adhesive residue on the stainless steel plate covers 5% or less of the application area. △: Adhesion of adhesive on the stainless steel plate exceeds 5% but is less than or equal to 30% of the application area. ×: Adhesive adheres to more than 30% of the surface area of ​​the stainless steel plate.

[0076] <Test Results> The test results for Examples 1-9 and Comparative Examples 1-8 will be explained with reference to Tables 1 and 2.

[0077] Examples 1-9 exhibited excellent high-temperature re-peelability and repositionability, as shown in the results of Tests 2 and 3. This is presumed to be because the adhesion and Tg of the adhesive layer to the substrate can be adjusted by at least one of the following factors: the side chain of 2-octyl acrylate has a long structure similar to that of 2-ethylhexyl acrylate, and the homopolymer Tg of 2-octyl acrylate is approximately the same as that of the homopolymer Tg of n-butyl acrylate. On the other hand, Comparative Examples 1-8 did not exhibit excellent high-temperature re-peelability and repositionability. The reasons why Comparative Examples 1-8 could not achieve both high-temperature re-peelability and repositionability are explained below.

[0078] Comparative Example 1 contained 2-octyl acrylate in excess of the upper limit specified in the present invention, resulting in poor adhesion of the adhesive layer to the substrate and poor high-temperature re-peelability.

[0079] Comparative Examples 2-4 did not contain 2-octyl acrylate as the main monomer, resulting in poor repositionability and / or high-temperature re-peelability. Comparative Examples 2-4 are prior art examples that incorporate n-butyl acrylate, 2-ethylhexyl acrylate, or n-octyl acrylate as the main monomer, as described at the beginning of this specification.

[0080] Comparative Example 5 contains a carboxyl group-containing monomer exceeding the upper limit specified in the present invention, resulting in a tendency for adhesive residue to remain and poor high-temperature re-peelability.

[0081] Comparative Example 6 contains tackifying resin (B) in excess of the upper limit specified in the present invention, resulting in a tendency for adhesive residue to remain and poor high-temperature re-peelability. Furthermore, Comparative Example 6 is unsuitable for re-peel applications due to its excessively high adhesive strength.

[0082] Comparative Example 7 contained less 2-octyl acrylate than the lower limit specified in the present invention, resulting in poor repositionability.

[0083] Comparative Example 8 contained a carboxyl group-containing monomer below the lower limit specified in the present invention, resulting in poor repositionability.

[0084] As described above, the repositionable adhesive composition of the present invention has remarkable effects such as excellent high-temperature repositionability and repositionability.

[0085] Furthermore, since the present invention can provide an environmentally and human-friendly repositionable adhesive composition using biomass-derived raw materials that have less reliance on fossil resources, it can contribute to Goal 12 of the United Nations-led Sustainable Development Goals (SDGs), "Responsible Consumption and Production."

[0086] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. The (meth)acrylic copolymer (A) comprises 31 to 89% by mass of 2-octyl (meth)acrylate and 0.6 to 4.9% by mass of a carboxyl group-containing monomer, The (meth)acrylic copolymer (A) is provided with 100 parts by mass of tackifying resin (B) in an amount of 0 to 10 parts by mass. Removable adhesive composition.

2. The (meth)acrylic copolymer (A) further comprises (meth)acrylic monomers (a1) having alkyl groups with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate as constituent units. The re-peelable adhesive composition according to claim 1.

3. The (meth)acrylic copolymer (A) further comprises a vinyl monomer (a3) ​​as a constituent unit. The re-peelable adhesive composition according to claim 1.

4. The (meth)acrylic copolymer (A) further comprises a functional group-containing monomer (a2) other than a carboxyl group-containing monomer, The functional group-containing monomer (a2) includes a hydroxyl group-containing monomer. The re-peelable adhesive composition according to claim 1.

5. The (meth)acrylic copolymer (A) contains 1.5 to 10 parts by mass of tackifying resin (B) per 100 parts by mass, The tackifying resin (B) comprises at least one of a rosin-based resin and a terpene-based resin. The re-peelable adhesive composition according to claim 1.

6. The carboxyl group-containing monomer is acrylic acid. The re-peelable adhesive composition according to claim 1.

7. The (meth)acrylic copolymer (A) further comprises 8 to 18% by mass of n-octyl acrylate. The re-peelable adhesive composition according to claim 1.

8. The (meth)acrylic copolymer (A) further comprises 9 to 27% by mass of n-butyl acrylate. The re-peelable adhesive composition according to claim 1.

9. The (meth)acrylic copolymer (A) further comprises 1 to 61% by mass of 2-ethylhexyl acrylate. The re-peelable adhesive composition according to claim 1.

10. The (meth)acrylic copolymer (A) further contains a vinyl monomer (a3) ​​in an amount of 0.4 to 5% by mass. The re-peelable adhesive composition according to claim 1.

11. The (meth)acrylic copolymer (A) further contains 0.1 to 2% by mass of a hydroxyl group-containing monomer. The re-peelable adhesive composition according to claim 1.

12. The (meth)acrylic monomer (a1) having an alkyl group with 4 to 12 carbon atoms comprises at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The re-peelable adhesive composition according to claim 2.

13. Further containing a hardening agent (C), The curing agent (C) comprises at least one of an isocyanate-based curing agent and a metal chelate-based curing agent. The re-peelable adhesive composition according to claim 1.

14. Substrate and The substrate comprises an adhesive layer provided on at least one surface of the substrate, the adhesive layer being made of the re-peelable adhesive composition according to any one of claims 1 to 13. Adhesive sheet.

15. The 180-degree peel strength for stainless steel sheets is 9.0 N / 25 mm or less. The adhesive sheet according to claim 14.

16. In the J. Dow method inclined ball tack test, the maximum diameter of the steel ball that stops on the adhesive surface of the adhesive layer is 9 / 32 inches or less. The adhesive sheet according to claim 14.

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