Removable adhesive composition and adhesive sheet

Abstract

To provide a removable adhesive composition excellent in balance of adhesive force, tackiness, and removability.SOLUTION: The removable adhesive composition contains: an acrylic copolymer which contains at least a (meth)acrylic monomer and a functional group-containing monomer as constituent units; and a curing agent. The (meth)acrylic monomer contains at least lauryl acrylate. The acrylic copolymer contains 1-5 pts.mass of the functional group-containing monomer based on 100 pts.mass of the (meth)acrylic monomer. The removable adhesive composition contains 0.4-4 pts.mass of the curing agent based on 100 pts.mass of the acrylic copolymer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a removable pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. [Background technology]

[0002] Adhesives are used in various applications and fields, such as adhesive labels, adhesive tapes, and adhesive sheets. The materials of the adherends to which the adhesives are attached include a wide range of materials, such as plastics, metals, glass, paper, and cloth. Some adhesives are used in a manner that they are attached to an adherend and then peeled off from the adherend after a certain period of time has passed. In this case, the use of an adhesive with excellent removability (removable adhesive) has been proposed so that adhesive labels, adhesive tapes, adhesive sheets, and the like can be easily peeled off from the adherend. Here, "removability" refers to the property that, when peeling an adhesive product such as an adhesive label from an adherend, the adhesive product can be peeled off without destroying the substrate (also called the support) that supports the adhesive of the adhesive product and without leaving the adhesive on the surface of the adherend.

[0003] Conventionally, 2-ethylhexyl acrylate and butyl acrylate have been used as components of removable adhesives. However, in conventional removable adhesives, the gel fraction was reduced to obtain high tackiness. On the other hand, reducing the gel fraction increases the adhesive strength and tackiness, but there is a problem that the removable property deteriorates. Here, the gel fraction generally indicates the degree of hardening of the polymer, i.e., the degree of crosslinking.

[0004] In consideration of the above problems, Patent Document 1 discloses a removable pressure-sensitive adhesive composition having good adhesive strength and tackiness by maintaining a high gel fraction. Patent Document 2 discloses a masking pressure-sensitive adhesive having excellent thermal stability and good adhesive strength by maintaining a high gel fraction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7151926 [Patent Document 2] JP 2023-024312 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the techniques of Patent Documents 1 and 2 have too high a gel fraction and therefore cannot realize a removable pressure-sensitive adhesive composition that has an excellent balance between adhesive strength, tackiness, and removability.

[0007] Therefore, an object of the present invention is to provide a removable pressure-sensitive adhesive composition that has an excellent balance between adhesive strength, tackiness, and removable properties. [Means for solving the problem]

[0008] In order to achieve the object of the present invention, the removable pressure-sensitive adhesive composition of the present invention is a removable pressure-sensitive adhesive composition comprising an acrylic copolymer containing, as constituent units, at least a (meth)acrylic monomer and a monomer having a functional group, and a curing agent, wherein the (meth)acrylic monomer comprises at least lauryl acrylate, the acrylic copolymer comprises 1 to 5 parts by mass of the monomer having the functional group per 100 parts by mass of the (meth)acrylic monomer, and the removable pressure-sensitive adhesive composition comprises 0.4 to 4 parts by mass of the curing agent per 100 parts by mass of the acrylic copolymer. Effect of the Invention

[0009] According to the present invention, it is possible to provide a removable pressure-sensitive adhesive composition that has an excellent balance of adhesive strength, tackiness, and removable properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The following embodiments are described in detail. Note that the following embodiments do not limit the scope of the invention, and not all of the 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 combination.

[0011] In this specification, any numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range.

[0012] <Removable Adhesive Composition> The removable adhesive composition according to one embodiment includes an acrylic copolymer including at least a (meth)acrylic monomer and a monomer having a functional group as structural units, and a curing agent. Here, in this specification, the "structural unit" means a unit of a polymerizable monomer that forms the acrylic copolymer (resin).

[0013] The (meth)acrylic monomer according to one embodiment includes at least lauryl acrylate.

[0014] The acrylic copolymer according to one embodiment contains 1 to 5 parts by mass of a monomer having a functional group relative to 100 parts by mass of a (meth)acrylic monomer.

[0015] The removable pressure-sensitive adhesive composition according to one embodiment contains 0.4 to 4 parts by mass of a curing agent based on 100 parts by mass of the acrylic copolymer.

[0016] The acrylic copolymer according to one embodiment contains preferably 1 to 5 parts by mass, more preferably 1.5 to 5 parts by mass, of a monomer having a functional group relative to 100 parts by mass of the (meth)acrylic monomer. For example, when the acrylic copolymer contains less than 1 part by mass of a monomer having a functional group relative to 100 parts by mass of the (meth)acrylic monomer, the cohesive strength of the removable adhesive composition is low, and the removable properties are not good. On the other hand, when the acrylic copolymer contains more than 5 parts by mass of a monomer having a functional group relative to 100 parts by mass of the (meth)acrylic monomer, the cohesive strength of the removable adhesive composition is high, and the removable adhesive composition becomes too hard, resulting in reduced tackiness.

[0017] The removable pressure-sensitive adhesive composition according to one embodiment preferably contains 0.4 to 4 parts by mass, more preferably 0.5 to 3 parts by mass, and even more preferably 0.5 to 2.2 parts by mass of a curing agent relative to 100 parts by mass of the acrylic copolymer. For example, when the removable pressure-sensitive adhesive composition contains less than 0.4 parts by mass or more than 4 parts by mass of a curing agent relative to 100 parts by mass of the acrylic copolymer, at least one of the adhesive strength, tackiness, and removability is reduced. On the other hand, when the removable pressure-sensitive adhesive composition contains the above-mentioned predetermined amount of a curing agent, the gel fraction of the removable pressure-sensitive adhesive composition can be controlled to a predetermined value.

[0018] (Acrylic copolymer) The acrylic copolymer according to one embodiment contains at least a (meth)acrylic monomer and a monomer having a functional group as constituent units, and may contain other monomers as necessary.

[0019] The following describes polymerizable monomers (monomers, also simply called monomers), curing agents, tackifier resins, polymerization initiators, etc. that can be used in the method for producing the acrylic copolymer of the present invention. Note that the term "(meth)acrylic" in this specification means both "acrylic" and "methacrylic", and the term "(meth)acrylate" means both "acrylate" and "methacrylate".

[0020] Polymerizable monomers that can be used to prepare the acrylic copolymer are listed below as examples, but are not limited to these monomers. The following monomers can be used alone or in combination of two or more.

[0021] ((Meth)acrylic monomer) The (meth)acrylic monomer according to one embodiment includes at least one of a (meth)acrylic acid alkyl ester and a (meth)acrylic acid ester.

[0022] The (meth)acrylic monomer according to one embodiment further includes at least one of lauryl methacrylate, 2-ethylhexyl acrylate, and butyl acrylate.

[0023] The acrylic copolymer according to one embodiment preferably contains 5 to 100 parts by mass of lauryl acrylate in 100 parts by mass of the (meth)acrylic monomer. When the acrylic copolymer contains the above-mentioned predetermined amount of lauryl acrylate, the tackiness of the removable pressure-sensitive adhesive composition is improved.

[0024] An acrylic copolymer according to one embodiment contains 0 to 10 parts by mass of lauryl methacrylate, 0 to 70 parts by mass of 2-ethylhexyl acrylate, and 0 to 50 parts by mass of butyl acrylate in 100 parts by mass of a (meth)acrylic monomer.

[0025] Examples of (meth)acrylic acid alkyl esters 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 (meth)acrylic acid alkyl esters having a linear or branched alkyl group include (meth)acrylic acid alkyl esters having a linear or branched alkyl group, such as n-ethylhexyl (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, stearyl (meth)acrylate, and behenyl (meth)acrylate. In particular, as the (meth)acrylic acid alkyl ester, n-lauryl acrylate is preferred from the viewpoint of improving the tackiness of the removable pressure-sensitive adhesive composition.

[0026] Examples of (meth)acrylic acid esters 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; and (meth)acrylic acid aryl esters, such as phenyl (meth)acrylate, tolyl (meth)acrylate, and naphthyl (meth)acrylate.

[0027] (Monomers with functional groups) The monomer having a functional group according to one embodiment includes at least one of a monomer having a hydroxy group, a monomer having a carboxy group, and a monomer having an amide group.

[0028] The acrylic copolymer according to one embodiment contains, as structural units, 0 to 4.0 parts by mass of a monomer having a hydroxy group and 0 to 4.6 parts by mass of a monomer having a carboxy group, relative to 100 parts by mass of a (meth)acrylic monomer.

[0029] The monomer having a functional group according to one embodiment includes at least one of 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and acrylic acid.

[0030] Examples of monomers having a hydroxy group include (meth)acrylic acid esters (hydroxyalkyl (meth)acrylates) having a hydroxy group, 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. In particular, from the viewpoints of reactivity with an isocyanate-based curing agent and improvement of the cohesive strength of the removable pressure-sensitive adhesive composition, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred as monomers having a hydroxy group.

[0031] Examples of the monomer having a carboxy group include (meth)acrylic acid esters having a carboxy 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. In particular, the monomer having a carboxy group is preferably acrylic acid, from the viewpoints of reactivity with an isocyanate-based curing agent and improvement of the cohesive strength of the removable pressure-sensitive adhesive composition.

[0032] Examples of the monomer having an amide group include (meth)acrylamide, isopropyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, and hydroxyethyl(meth)acrylamide.

[0033] (Other monomers) The acrylic copolymer may contain a vinyl monomer as a constituent unit in addition to the (meth)acrylic monomer and the monomer having a functional group.

[0034] Examples of vinyl monomers include styrene, α-methylstyrene, vinyltoluene, divinylbenzene, vinylpyridine, vinylpyrrolidone, vinylcarbazole, vinyl acetate, acrylonitrile, butadiene, conjugated diene monomers such as isoprene and chloroprene, vinyl halides such as vinyl chloride and vinyl bromide, and vinylidene halides such as vinylidene chloride.

[0035] The acrylic copolymer according to one embodiment preferably contains 0 to 15 parts by mass of a vinyl monomer relative to 100 parts by mass of a (meth)acrylic monomer from the viewpoint of improving cohesive strength and adhesive strength. Here, the vinyl monomer does not need to be an essential component of the acrylic copolymer, and may be blended according to the desired adhesive performance. For example, when the acrylic copolymer contains more than 15 parts by mass of a vinyl monomer relative to 100 parts by mass of a (meth)acrylic monomer, the cohesive strength of the removable adhesive composition increases, and the removable adhesive composition becomes too hard, resulting in a decrease in tackiness.

[0036] (hardening agent) The curing agent according to one embodiment includes 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. As the curing agent, it is preferable to use one or more of these. In particular, the isocyanate-based curing agent can impart high cohesive strength to the removable pressure-sensitive adhesive composition by forming a crosslinking point with a monomer having at least one of a hydroxy group, a carboxy group, and an amide group that constitutes an acrylic copolymer.

[0037] Examples of the isocyanate-based curing agent include compounds having three or more isocyanate groups in the molecule, such as adducts of isocyanate compounds such as toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate with polyol compounds such as trimethylolpropane, as well as biuret forms and isocyanurates thereof, and adducts of the above-mentioned isocyanate compounds with any of polyols such as polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, and polyisoprene polyols; or compounds having two isocyanate groups in the molecule, such as allophanate forms thereof.

[0038] Examples of epoxy curing agents include epoxy resins obtained by reacting bisphenol A with 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.

[0039] Examples of the metal chelate curing agent include aluminum alkoxides such as aluminum isopropylate, mono sec-butoxy aluminum diisopropylate, aluminum sec-butylate, and aluminum ethylate; aluminum chelates such as ethyl acetoacetate aluminum diisopropylate, aluminum tris(ethyl acetoacetate), alkyl acetoacetate aluminum diisopropylate, aluminum monoacetylacetate bis(ethyl acetoacetate), and aluminum tris(acetylacetonate); titanium tetraisopropoxide, titanium tetra-n-butoxide, titanium butoxide dimer, and titanium tetra- Examples of the titanium alkoxide include titanium alkoxides such as 2-ethylhexoxide; titanium diisopropoxybis(acetylacetonate), titanium tetraacetylacetonate, titanium diisopropoxybis(ethylacetoacetate), phosphate titanium complexes, titanium chelates such as titanium octylene glycolate; zirconium alkoxides such as zirconium tetra-normal-propoxide and zirconium tetra-normal-butoxide; zirconium chelates such as zirconium tetraacetylacetonate, zirconium tributoxy monoacetylacetonate, and zirconium dibutoxybis(ethylacetoacetate); and zirconium acylates such as zirconium stearate.

[0040] 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.

[0041] (tackifier resin) The removable pressure-sensitive adhesive composition according to one embodiment further contains 0 to 7 parts by mass of a tackifier resin relative to 100 parts by mass of the acrylic copolymer.

[0042] The removable adhesive composition according to one embodiment preferably contains 0 to 7 parts by mass, more preferably 0 to 5 parts by mass, and even more preferably 0 to 4 parts by mass of a tackifier resin relative to 100 parts by mass of the acrylic copolymer. Here, the tackifier resin may not be an essential component of the removable adhesive composition, and may be blended according to the desired adhesive performance. For example, when the removable adhesive composition contains a small amount of a tackifier resin, there is an advantage that the adhesive performance of the removable adhesive composition can be easily controlled. On the other hand, when the removable adhesive composition contains more than 7 parts by mass of a tackifier resin, the adhesive strength of the removable adhesive composition becomes too high, and the removable property becomes poor.

[0043] The tackifier resin according to one embodiment includes at least one of a rosin-based resin and a terpene-based resin.

[0044] As the tackifier resin, any tackifier resin that has been used in conventional pressure sensitive adhesives can be used, and a new tackifier resin can also be used. As the tackifier resin, rosin-based resins and terpene-based resins can be mentioned, since they lead to an improvement in the biomass degree of the removable pressure sensitive adhesive composition, and it is preferable to use one or more of these.

[0045] Examples of rosin-based resins include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, disproportionated rosin, and disproportionated rosin ester.

[0046] Examples of terpene resins include α-pinene resins, β-pinene resins, terpene resins, hydrogenated terpene resins, aromatic modified terpene resins, and terpene phenol resins. Among these tackifier resins, natural rosin and ester resins derived from the rosin (rosin esters, water-added rosin esters), etc., are more preferred. In this case, the form of the tackifier resin is preferably an aqueous dispersion or a solid.

[0047] (Polymerization initiator) The polymerization initiator is not particularly limited, and any of those known in the art can be used. For example, the following polymerization initiators generally used in radical polymerization can be appropriately used.

[0048] Examples of the polymerization initiator include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; 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-imidazolin-2-yl) propane] and its salts, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] and its salts, 2,2'-azobis[2-(3,4,5,6-tetrahydropyrimidin-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 of the water-soluble azo compounds include 2,2'-azobis(2-methylpropynamidine) and its salts, and 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.

[0049] (solvent) The removable pressure-sensitive adhesive composition according to an embodiment may include a solvent. Here, the solvent is used during the preparation of the acrylic copolymer. In addition, the solvent may be used as a dilution solvent for adjusting the viscosity during the preparation of the removable pressure-sensitive adhesive composition.

[0050] The solvent may be appropriately selected in consideration of leveling properties during application, drying properties, effects on the environment and the human body, etc. The solvent is preferably an aliphatic hydrocarbon, an alicyclic hydrocarbon, an aromatic hydrocarbon, an ester, a ketone, an alcohol, or the like.

[0051] Examples of the solvent include ester-based solvents such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; ketone-based solvents such as acetone, methyl ethyl ketone, methyl butyl ketone, and cyclohexanone; hydrocarbon-based solvents such as toluene, xylene, and normal hexane; and alcohol solvents such as methanol, ethanol, normal propanol, and isopropanol.

[0052] (Physical Properties of Removable Adhesive Composition) The gel fraction of the removable pressure-sensitive adhesive composition according to one embodiment is preferably 40 to 80%, more preferably 40 to 75%. The gel fraction can be controlled by adjusting the amount of the curing agent. For example, when the gel fraction of the removable pressure-sensitive adhesive composition is less than 40%, the crosslinking of the acrylic copolymer is weak, so the cohesive force is low and the removable properties are not good. On the other hand, when the gel fraction of the removable pressure-sensitive adhesive composition is more than 80%, the crosslinking of the acrylic copolymer is too advanced, so the cohesive force is high, and the removable pressure-sensitive adhesive composition becomes too hard and cannot exhibit its adhesive performance (i.e., the tackiness is reduced). The method of calculating the gel fraction will be described later in Test Example 1.

[0053] <Adhesive sheet> The pressure-sensitive adhesive sheet according to one embodiment comprises a substrate and a pressure-sensitive adhesive layer made of a removable pressure-sensitive adhesive composition provided on at least one surface of the substrate. The pressure-sensitive adhesive layer can be formed on one or both surfaces of the substrate. If necessary, the exposed surface of the pressure-sensitive adhesive layer can be covered with a release sheet (release paper). Furthermore, the release sheet is peeled off when the pressure-sensitive adhesive sheet is attached to an adherend. Note that the removable pressure-sensitive adhesive composition of the present invention described above can be used as the removable pressure-sensitive adhesive composition of the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet, and therefore a detailed description of the removable pressure-sensitive adhesive composition will be omitted.

[0054] Examples of the substrate include resin sheets, paper, and metal foils. The substrate may have a laminated structure of one or more of these substrates. The surface of the substrate on which the adhesive layer is formed may be subjected to a corona discharge treatment and an easy-adhesion treatment such as application of an anchor coating agent, if necessary.

[0055] Examples of resin sheets include ester-based resins such as polyethylene terephthalate (PET), olefin-based resins such as polyethylene (PE) and polypropylene (PP), vinyl-based resins such as polyvinyl chloride, amide-based resins such as nylon 66, urethane-based resins (including foams), etc. The resin sheet may be one or a combination of two or more of these.

[0056] Examples of the paper include plain paper, coated paper, and art paper. Examples of the metal of the metal foil include aluminum, copper, and combinations thereof.

[0057] As the release sheet, a known release sheet can be used, which is obtained by subjecting the surface of a base sheet such as a resin sheet or paper to a known release treatment such as coating with a release agent.

[0058] The pressure-sensitive adhesive sheet can be manufactured by a known method. The following is an outline of the method for manufacturing the pressure-sensitive adhesive sheet. First, the removable pressure-sensitive adhesive composition of the present invention is applied to the surface of the substrate. The method for applying the removable pressure-sensitive adhesive composition is a known method, and examples of such methods include a roll coater method, a comma coater method, a die coater method, a reverse coater method, a silk screen method, and a gravure coater method. Next, the coated surface of the substrate is dried, and the removable pressure-sensitive adhesive composition is cured to form a pressure-sensitive adhesive layer made of the removable pressure-sensitive adhesive composition of the present invention. The heating and drying temperature is, for example, 60 to 150°C. The thickness of the pressure-sensitive adhesive layer (thickness after drying) varies depending on the application, but is preferably 0.1 to 200 μm. Next, if necessary, a release sheet is attached to the exposed surface of the pressure-sensitive adhesive layer by a known method. Through the above manufacturing steps, a single-sided pressure-sensitive adhesive sheet can be manufactured. It should be noted that a double-sided pressure-sensitive adhesive sheet can be manufactured by applying the above manufacturing steps to the other surface of the substrate.

[0059] Contrary to the above-mentioned manufacturing method, the removable adhesive composition of the present invention may be applied to the surface of a release sheet, followed by drying and curing to form an adhesive layer consisting of the removable adhesive composition of the present invention, and then a substrate may be attached to the exposed surface of the adhesive layer.

[0060] <Method of producing removable adhesive composition> Tables 1 to 5 show the raw material blends and test results of Examples 1 to 18 and Comparative Examples 19 to 30. The numbers for the raw material blend amounts in Tables 1 to 5 represent parts by mass as solid content. The abbreviations in Tables 1 to 5 are explained as follows. LA: Lauryl acrylate LMA: Lauryl methacrylate 2-EHA: 2-Ethylhexyl acrylate BA: Butyl acrylate AAC: Acrylic acid HEA: 2-hydroxyethyl acrylate 4-HBA: 4-hydroxybutyl acrylate VAC: Vinyl acetate Tackifying resin: Arakawa Chemical Industries, Ltd. Pencel D-135 (polymerized rosin ester) Hardener: Mitsui Chemicals Takenate D101E (45EA) (adduct of toluene diisocyanate and polyol compound)

[0061] [Table 1]

[0062] [Table 2]

[0063] [Table 3]

[0064] [Table 4]

[0065] [Table 5]

[0066] Example 1: Preparation of removable adhesive composition and adhesive sheet Based on the raw material composition of Example 1 in Table 1, 65.0 parts of 2-ethylhexyl acrylate, 30.0 parts of butyl acrylate, 5.0 parts of lauryl acrylate, 3.0 parts of acrylic acid, 100 parts of ethyl acetate, 10 parts of acetone, and 0.05 parts of a polymerization initiator (azobisisobutyronitrile) were charged into a reactor equipped with a stirrer, a thermometer, and a reflux condenser. The reactor was heated to 85°C while stirring to start the reaction, and the polymerization reaction was carried out at the reflux temperature for 7 hours. After the reaction was completed, the mixture was cooled and diluted with ethyl acetate to obtain an acrylic copolymer with a solid content of 45% by mass.

[0067] To 100 parts of the obtained acrylic copolymer, 0.5 parts in solid content of Takenate D101E (45EA) (product name, manufactured by Mitsui Chemicals) as an isocyanate curing agent was added and thoroughly mixed to obtain a removable pressure-sensitive adhesive composition.

[0068] The removable adhesive composition was applied onto the release-treated surface of a release paper so that the thickness after drying would be 25 μm, and the applied adhesive layer was dried for 1 minute in a hot air circulation dryer at 100° C. An adhesive layer was prepared. This was laminated onto a 25 μm-thick substrate (made of polyethylene terephthalate) and aged for 7 days at 23° C. and 50% humidity to obtain an adhesive sheet A.

[0069] <Examples 2 to 18 and Comparative Examples 19 to 30: Production of removable adhesive compositions and adhesive sheets> The removable adhesive compositions and adhesive sheets of Examples 2 to 18 and Comparative Examples 19 to 30 were prepared and produced based on the raw material compositions in Tables 1 to 5 and the same production methods as in Example 1, so detailed explanations are omitted.

[0070] <Test Method> The removable pressure-sensitive adhesive compositions of Examples 1 to 18 and Comparative Examples 19 to 30 were used to carry out the tests of the following Test Examples 1 to 4 to evaluate their performance.

[0071] (Test Example 1: Measurement of gel fraction) The removable adhesive composition obtained in Example 1 and the like was applied onto the release-treated surface of a 38 μm-thick release sheet (made of polyethylene terephthalate) so that the thickness after drying was 25 μm, and the coating was dried for 1 minute in a hot air circulation dryer at 100° C. to prepare an adhesive layer. This was laminated onto the release-treated surface of another 38 μm-thick release sheet (made of polyethylene terephthalate), and aged for 7 days at 23° C. and 50%, to obtain adhesive sheet B. After aging for 7 days, the release sheet was peeled off from adhesive sheet B, and about 0.3 g of the adhesive layer was peeled off. The weight (W1) of the peeled adhesive layer was accurately measured, and the adhesive layer was immersed in 50 g of ethyl acetate. The mixture of the adhesive layer and ethyl acetate was left for 24 hours, and then the mixture was filtered through a 200-mesh wire mesh (W2) of known weight. The 200 mesh wire netting after filtration was dried in a hot air circulating dryer at 100° C. for 1 hour, and then the weight (W3) of the 200 mesh wire netting was measured. The gel fraction of the pressure-sensitive adhesive layer was calculated based on the following formula 1. Gel fraction (%)=(W3-W2) / W1×100 (Equation 1) W1: Weight of adhesive layer W2: Weight of 200 mesh wire netting W3: Weight of the 200 mesh wire screen after filtering and drying the mixture

[0072] (Test Example 2: Measurement of adhesive strength) The adhesive sheet A was cut to a width of 25 mm and a length of 70 mm to obtain a test piece. The release paper was peeled off from the test piece (adhesive sheet), and the test piece was attached to the surface of a stainless steel plate (SUS 304), and pressed by rolling it back and forth with a 2 kg roll once. The test piece was then left for 20 minutes in an atmosphere of 23°C and 50% humidity. After leaving the test piece, the adhesive strength of the test piece was measured in accordance with JIS Z-0237:2000 using a tensile tester (Tensilon: manufactured by A&D) at a tensile speed of 300 mm / min and a peel angle of 180°. From the viewpoint of making it easier to peel the adhesive sheet from the adherend, it is preferable that the adhesive strength is 0.1 to 9.0 (N / 25 mm). (Evaluation Criteria) ○: Adhesive strength is 0.1 to 9.0 (N / 25 mm). ×: The adhesive strength is outside the range of 0.1 to 9.0 (N / 25 mm).

[0073] (Test Example 3: Ball Tack (Evaluation of Tackiness)) Adhesive sheet A was cut to a width of 100 mm and a length of 70 mm to obtain a test specimen. The release paper was removed from the test specimen (adhesive sheet) and the test specimen was fixed with the adhesive side facing up on an inclined plate with an inclination angle of 30 degrees. In an atmosphere of 23°C and 50%, a steel ball was rolled over the sample with a run-up of 10 cm and an adhesive surface of 10 cm, and the diameter number of the ball that stopped near the center of the adhesive surface was recorded. The tackiness of the adhesive sheet is preferably 13 or more from the viewpoint of easy attachment to an adherend with poor wettability. (Evaluation Criteria) Good tackiness: Ball tack (No.) ≧ 13 Insufficient tack: Ball tack (No.) <13

[0074] (Test Example 4: Evaluation of removability) Adhesive sheet A was cut to a width of 25 mm and a length of 70 mm to obtain a test piece. The release paper was removed from the test piece (adhesive sheet) and the test piece was attached to the surface of a stainless steel plate (SUS 304) and pressed with a 2 kg roll once. The test piece was then stored in a 50°C environment for 3 days. After 3 days, the test piece was removed and left at 23°C and 50% humidity for 1 hour, and the adhesive sheet was peeled off by hand and the condition of the adhesive remaining on the stainless steel plate (SUS 304) was observed. The evaluation criteria are as follows. (Evaluation Criteria) ○: No adhesive adhered to the stainless steel plate, or adhesive adhered to the stainless steel plate was less than 5% of the applied area △: Adhesive adhesion on the stainless steel plate is 5% to 30% of the applied area ×: Adhesive adhesion on the stainless steel plate is 30% or more of the adhesion area

[0075] <Test Results> Tables 1 to 5 show the test results of Examples 1 to 18 and Comparative Examples 19 to 30. Examples 1 to 18 showed that the adhesive strength, tackiness, and removability were well balanced. In particular, Examples 1 to 18 showed that the pressure-sensitive adhesive sheets had excellent tackiness. On the other hand, Comparative Examples 19 to 30 showed that at least one of the adhesive strength, tackiness, and removability did not meet the evaluation criteria. Here, Comparative Examples 19 to 22 show cases where the acrylic copolymer does not contain lauryl acrylate. Comparative Examples 23 to 25 show cases where the acrylic copolymer contains a monomer having a functional group that is greater than the amount specified in the present invention. Comparative Examples 26 to 28 show cases where the acrylic copolymer does not contain lauryl acrylate and contains lauryl methacrylate that is greater than the amount specified in the present invention. Comparative Examples 29 to 30 show cases where the removable pressure-sensitive adhesive composition contains a curing agent that is outside the range of the amount specified in the present invention.

[0046] Based on the above test results, it is presumed that a removable adhesive composition having an excellent balance of adhesive strength, tackiness, and removability can be realized based on the inclusion of lauryl acrylate in the acrylic copolymer and the combination of the monomer having a specified amount of functional group and the curing agent of the present invention.

[0076] As described above, the removable adhesive composition of the present invention has a remarkable effect of being excellent in balance between adhesive strength, tackiness, and removable property. For example, even when a pressure-sensitive adhesive sheet comprising the removable adhesive composition of the present invention is applied to an adherend with poor wettability, the user can easily apply the adhesive sheet to the adherend. In addition, since the adhesive strength of the adhesive sheet is designed to be low, the adhesive sheet is easily peeled off from the adherend even after a certain time has passed since the adhesive sheet was applied. Furthermore, there is no adhesive residue on the adherend after the adhesive sheet is peeled off. Thus, the adhesive sheet comprising the removable adhesive composition of the present invention can be suitably used for temporary fixing applications, for example, as a masking tape and a masking tape.

[0077] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. an acrylic copolymer including, as constituent units, at least a (meth)acrylic monomer and a monomer having a functional group; A removable pressure-sensitive adhesive composition comprising: The (meth)acrylic monomer includes at least lauryl acrylate, The acrylic copolymer contains 1 to 5 parts by mass of the monomer having a functional group relative to 100 parts by mass of the (meth)acrylic monomer, The removable pressure-sensitive adhesive composition contains 0.4 to 4 parts by mass of the curing agent relative to 100 parts by mass of the acrylic copolymer. A removable pressure-sensitive adhesive composition.

2. The monomer having a functional group includes at least one of a monomer having a hydroxy group, a monomer having a carboxy group, and a monomer having an amide group. The removable pressure-sensitive adhesive composition according to claim 1 .

3. The removable pressure-sensitive adhesive composition has a gel fraction of 40 to 80%. The removable pressure-sensitive adhesive composition according to claim 1 .

4. The (meth)acrylic monomer further includes at least one of lauryl methacrylate, 2-ethylhexyl acrylate, and butyl acrylate, The acrylic copolymer contains 5 to 100 parts by mass of the lauryl acrylate in 100 parts by mass of the (meth)acrylic monomer. The removable pressure-sensitive adhesive composition according to claim 1 .

5. The acrylic copolymer contains, in 100 parts by mass of the (meth)acrylic monomer, 0 to 10 parts by mass of the lauryl methacrylate, 0 to 70 parts by mass of the 2-ethylhexyl acrylate, and 0 to 50 parts by mass of the butyl acrylate. The removable pressure-sensitive adhesive composition according to claim 4.

6. The removable pressure-sensitive adhesive composition further contains 0 to 7 parts by mass of a tackifier resin relative to 100 parts by mass of the acrylic copolymer. The removable pressure-sensitive adhesive composition according to claim 1 .

7. The tackifier resin contains at least one of a rosin-based resin and a terpene-based resin. The removable pressure-sensitive adhesive composition according to claim 6 .

8. The curing agent includes 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. The removable pressure-sensitive adhesive composition according to claim 1 .

9. The acrylic copolymer contains, relative to 100 parts by mass of the (meth)acrylic monomer, 0 to 4.0 parts by mass of the monomer having a hydroxy group and 0 to 4.6 parts by mass of the monomer having a carboxy group. The removable pressure-sensitive adhesive composition according to claim 2 .

10. The monomer having a functional group includes at least one of 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and acrylic acid. The removable pressure-sensitive adhesive composition according to claim 1 .

11. The acrylic copolymer further contains a vinyl monomer as a constituent unit. The removable pressure-sensitive adhesive composition according to claim 1 .

12. The acrylic copolymer further contains 0 to 15 parts by mass of the vinyl monomer relative to 100 parts by mass of the (meth)acrylic monomer. The removable pressure-sensitive adhesive composition according to claim 11.

13. A substrate; and a pressure-sensitive adhesive layer comprising the removable pressure-sensitive adhesive composition according to any one of claims 1 to 12 and provided on at least one surface of the substrate. Adhesive sheet.

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