Release Adhesive Composition and Adhesive Sheet

Abstract

An object of the present invention is to provide a pressure-sensitive adhesive composition for re-peeling, which is excellent in high-temperature re-peelability and re-stickability. 【Means for solving the problem】 A pressure-sensitive adhesive composition for re-peeling, comprising a (meth)acrylic copolymer (A) containing 2-octyl (meth)acrylate in an amount of 31 to 89% by mass and a carboxyl group-containing monomer in an amount of 0.6 to 4.9% by mass, and containing 0 to 10 parts by mass of a tackifier resin (B) with respect to 100 parts by mass of the (meth)acrylic copolymer (A).

Description

Technical Field

[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 adhesion to the substrate and 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] In order to achieve the object of the present invention, the pressure-sensitive adhesive composition for re-peeling of the present invention has the following constitution. That is, it comprises a (meth)acrylic copolymer (A) containing 2-octyl (meth)acrylate at 31 to 89% by mass and a carboxyl group-containing monomer at 0.6 to 4.9% by mass. With respect to 100 parts by mass of the (meth)acrylic copolymer (A), it contains 0 to 10 parts by mass of a tackifier resin (B) and further contains a curing agent (C). The curing agent (C) contains at least one of an isocyanate-based curing agent and a metal chelate-based curing agent. The (meth)acrylic copolymer (A) further contains, as a structural unit, a (meth)acrylic monomer having an alkyl group having 4 to 12 carbon atoms other than 2-octyl (meth)acrylate. - wo and other than 2-octyl (meth)acrylate the (meth)acrylic monomer having an alkyl group having 4 to 12 carbon atoms - wa includes at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The (meth)acrylic copolymer (A) contains 91.7 to 98.4% by mass of a (meth)acrylic monomer (a1) having an alkyl group having 4 to 12 carbon atoms, which includes the 2-octyl (meth)acrylate and the (meth)acrylic monomer having an alkyl group having 4 to 12 carbon atoms other than the 2-octyl (meth)acrylate. - to

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition for re-peeling that is excellent in high-temperature re-peelability and re-stickability.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the embodiments will be described in detail. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the invention. Two or more of the plurality of features described in the embodiments may be arbitrarily combined.

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

[0010] In this specification, "(meth)acryl" means both "acryl" and "methacryl". Also, "(meth)acrylate" means both "acrylate" and "methacrylate".

[0011] In this specification, "mass%" represents the blending amounts of the respective components of (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 blending amounts of the respective components of (B) and (C) described below, relative to 100 parts by mass of the (meth)acrylic copolymer (A).

[0012] In this specification, "high-temperature re-peelability" means the property that when an adhesive sheet having an adhesive layer composed of a re-peeling adhesive composition is attached to an adherend and a certain period of time has elapsed in a high-temperature environment, it is difficult for adhesive residue to remain on the adherend when the adhesive sheet is peeled off.

[0013] In this specification, "re-stickability" means the property that an adhesive sheet having an adhesive layer composed of a re-peeling adhesive composition can be re-attached to an adherend.

[0014] <Re-peeling adhesive composition> The re-peeling adhesive composition is used, for example, as the adhesive layer and adhesive of the adhesive sheet described below. The re-peeling adhesive composition contains a (meth)acrylic copolymer (A) and a curing agent (C), and may optionally contain a tackifier resin (B).

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

[0016] <(Meth)acrylic monomer (a1)> (Meth)acrylic monomer (a1) is a (meth)acrylic acid alkyl ester monomer having an alkyl group with 1 to 18 carbon atoms. Examples of (meth)acrylic monomer (a1) include linear or branched alkyl group-containing (meth)acrylic acid alkyl esters such as 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, 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, 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 with 4 to 12 carbon atoms. Examples of the alkyl (meth)acrylate 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] (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 with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate includes at least one of a monomer having a homopolymer Tg comparable to that of the homopolymer of 2-octyl acrylate and a monomer having a homopolymer Tg lower than that of the homopolymer of 2-octyl acrylate. The (meth)acrylic monomer (a1) having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate can further include 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 into the (meth)acrylic copolymer (A), the balance between high-temperature re-peelability and re-stickability 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, both high-temperature re-peelability and re-stickability can be achieved. 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 pressure-sensitive adhesive layer to the substrate deteriorates, and the high-temperature re-peelability deteriorates.

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

[0021] 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. As described above, the monomers other than 2-octyl (meth)acrylate are, for example, at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. In one embodiment, 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, based on 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A).

[0022] In one embodiment, the (meth)acrylic copolymer (A) further 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] In addition, the (meth)acrylic monomer (a1) can 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 can 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) contains 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 can optionally further contain a hydroxy group-containing monomer.

[0026] Examples of the carboxy group-containing monomer include (meth)acrylic acid esters having a carboxy group such as 2-carboxyethyl (meth)acrylate; 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 alone or in combination of two or more. The carboxy group-containing monomer is preferably acrylic acid. By using the carboxy group-containing monomer, good adhesiveness and cohesive force can be exhibited with respect to various adherends (particularly, adherends made of highly polar materials).

[0027] The content of the carboxy group-containing monomer is preferably 0.6 to 4.9% by mass, more preferably 0.6 to 2.4% by mass, still more preferably 0.6 to 1.2% by mass in 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A). By the content of the carboxy group-containing monomer being in the range of 0.6 to 4.9% by mass, both high-temperature re-peelability and re-stickability can be achieved. On the other hand, when the content of the carboxy group-containing monomer is less than 0.6% by mass, the re-stickability deteriorates. When the content of the carboxy group-containing monomer exceeds 4.9% by mass, it is likely to leave glue and the high-temperature re-peelability deteriorates.

[0028] Examples of the hydroxy group-containing monomer include (meth)acrylic acid esters 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 (hydroxyalkyl (meth)acrylate). These may be used alone or in combination of two or more. The hydroxy group-containing monomer is preferably 2-hydroxyethyl acrylate. By using the hydroxy group-containing monomer, it becomes a reaction point 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 the hydroxy group-containing monomer is 0.1 to 2% by mass in 100% by mass of the monomer mixture constituting the (meth)acrylic copolymer (A).

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

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

[0032] In one embodiment, (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 the content of the vinyl monomer (a3) being in the range of 0.4 to 5% by mass, the balance between high-temperature re-peelability and re-stickability can be controlled.

[0033] <Tackifying resin (B)> The pressure-sensitive adhesive composition for re-peeling may further optionally contain a tackifier resin (B). The tackifier resin (B) may be any of the tackifier resins conventionally used in pressure-sensitive adhesives, or may be a novel tackifier resin. From the viewpoint of improving the biomass degree of the pressure-sensitive adhesive composition for re-peeling, the tackifier resin (B) preferably contains at least one of a rosin resin and a terpene resin.

[0034] The tackifier resin (B) can be used by any method such as a method of blending during solution polymerization and a method of blending with the (meth)acrylic copolymer (A). When the tackifier resin (B) is used during solution polymerization, it acts as a chain transfer agent, facilitating the adjustment of the molecular weight of the (meth)acrylic copolymer (A). Also, when a predetermined amount of the tackifier resin (B) described below is blended with the (meth)acrylic copolymer (A), the adhesive strength can be further improved.

[0035] Examples of the rosin resin include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, disproportionated rosin, and disproportionated rosin ester, etc. These can be used alone or in combination of two or more. The rosin resin is preferably a polymerized rosin ester.

[0036] Examples of the terpene resin include α-pinene resin, β-pinene resin, terpene resin, hydrogenated terpene resin, aromatic-modified terpene resin, and terpene phenol resin, etc. These can be used alone or in combination of two or more. The terpene resin is preferably a terpene phenol resin.

[0037] Among these tackifier resins (B), natural rosin and ester resins derived from such rosin (rosin ester, hydrogenated rosin ester) are more preferable. In this case, the form of the tackifier resin (B) is preferably solid.

[0038] In one embodiment, the pressure-sensitive adhesive composition for re-peeling contains, with respect to 100 parts by mass of the (meth)acrylic copolymer (A), preferably 0 to 10 parts by mass or 1.5 to 10 parts by mass, more preferably 0 to 5 parts by mass, and still more preferably 0 to 2.5 parts by mass of the tackifier resin (B). If the content of the tackifier resin (B) is 10 parts by mass or less, the tack can be improved without deteriorating the high-temperature re-peelability. On the other hand, when the content of the tackifier resin (B) exceeds 10 parts by mass, the tack is improved, but the high-temperature re-peelability deteriorates due to an increase in low-molecular-weight substances.

[0039] <Curing agent (C)> The pressure-sensitive adhesive composition for re-peeling 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 re-peelability is improved.

[0040] The curing agent (C) according to one embodiment contains 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 alone or in combination of two or more.

[0041] Examples of the isocyanate-based curing agent include 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 their burette forms, isocyanurate forms, and adducts of the above isocyanate compounds with any of the polyols such as polyether polyol, polyester polyol, acrylic polyol, polybutadiene polyol, and polyisoprene polyol, etc., which are compounds having three or more isocyanate groups in the molecule; or compounds having two isocyanate groups in the molecule such as their allophanate forms, etc. These may be used alone or in combination of two or more. The isocyanate-based curing agent can exhibit appropriate adhesive force and cohesive force by forming crosslinking points with the carboxy group-containing monomer and / or the hydroxy group-containing monomer 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 still more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer (A). When the content of the isocyanate-based curing agent is 0.1 part by mass or more, sufficient cohesive force can be obtained.

[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, etc. These may be used alone or in combination of two or more kinds.

[0044] Examples of the metal chelate-based curing agent include aluminum alkoxides such as aluminum isopropylate, mono-sec-butoxyaluminum diisopropylate, aluminum sec-butyrate, 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 alkoxides such as titanium tetraisopropoxide, titanium tetra-n-butoxide, titanium butoxide dimer, and titanium tetra-2-ethylhexoxide; titanium chelates such as titanium diisopropoxide bis(acetylacetonate), titanium tetraacetylacetonate, titanium diisopropoxide bis(ethyl acetoacetate), phosphate ester titanium complex, and titanium octylene glycolate; zirconium alkoxides such as zirconium tetra-n-propoxide and zirconium tetra-n-butoxide; zirconium chelates such as zirconium tetraacetylacetonate, zirconium tributoxymonoacetylacetonate, and zirconium dibutoxybis(ethyl acetoacetate); and zirconium acylates such as zirconium stearate. These may be used alone or in combination of two or more. From the viewpoints of crosslinkability, adhesiveness, transparency, and storage stability, the metal chelate-based curing agent is preferably aluminum tris(acetylacetonate).

[0045] The content of the metal chelate-based curing agent is preferably 0.01 to 10 parts by mass, more preferably 0.01 to 5 parts by mass, and still more preferably 0.01 to 3 parts by mass with respect to 100 parts by mass of the (meth)acrylic copolymer (A). When the content of the metal chelate-based curing agent is 0.01 part by mass or more, sufficient cohesive force can be obtained.

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

[0047] <Other Additives> The pressure-sensitive adhesive composition for re-peeling of the present invention may contain various additives as long as they do not affect the required performance defined in the present invention. Examples of the additives include antistatic agents, antioxidants, silane coupling agents, heat or light stabilizers, ultraviolet absorbers, leveling agents, defoaming agents, antibacterial agents, moisturizing agents, pigments, dyes, and fragrances. These may be used alone or in combination of two or more.

[0048] <Method for Producing (Meth)acrylic Copolymer (A)> (Meta)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 preferably produced by solution polymerization. Specifically, it is common to heat a solvent, a monomer, a 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 in 4 to 12 hours. The solvent used in solution polymerization can be appropriately selected in consideration of the leveling property during coating, the drying property, the environment, and the influence on the human body. The solvent is preferably at least one of aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, esters, ketones, and alcohols. Examples of the solvent 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 normal hexane, and alcohol solvents such as methanol, ethanol, normal propanol, and isopropanol. These can be used alone or in combination of two or more kinds.

[0049] The polymerization initiator is not particularly limited, and any conventionally known one can be used. For example, polymerization initiators generally used for radical polymerization as listed below can be appropriately used.

[0050] Examples of the polymerization initiator include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; oil-soluble azo compounds 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; water-soluble azo compounds such as 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, 2,2'-azobis(2-methylpropynamidine) and its salts, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] and its salts; organic peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxy-2-ethylhexanoate, and t-butyl peroxyisobutyrate. These may be used alone or in combination of two or more kinds.

[0051] <Adhesive sheet> The pressure-sensitive adhesive sheet includes a base material and a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition for re-peeling of the present invention provided on at least one surface of the base material. The pressure-sensitive adhesive sheet can be manufactured, for example, by applying the pressure-sensitive adhesive composition for re-peeling on the base material and drying it. The pressure-sensitive adhesive layer may be provided on at least one surface of the base material according to the use of the pressure-sensitive adhesive sheet. Further, a release sheet may be provided on the adhesive surface of the pressure-sensitive adhesive layer.

[0052] The pressure-sensitive adhesive sheet of the present invention can be attached to an adherend such as paper, cloth, non-woven fabric, plastic products, glass products, metal products such as stainless steel, and rubber products as an adherend.

[0053] Since the pressure-sensitive adhesive sheet has both high-temperature re-peelability and re-stickability, it can be suitably used in various applications such as label applications, seal applications, tape applications, building material applications, packaging material applications, and applications for electronic products.

[0054] In one embodiment, the 180-degree peel strength with respect to a stainless steel plate is 9.0 N / 25 mm or less. From the viewpoint of facilitating peeling of the pressure-sensitive adhesive sheet from the adherend, the 180-degree peel strength is preferably 9.0 N / 25 mm or less.

[0055] In one embodiment, in the J.Dow method inclined ball tack test, the maximum diameter of the steel ball stopped on the adhesive surface of the pressure-sensitive adhesive layer is 9 / 32 inch or less. The numerical value for evaluating the tack of the pressure-sensitive adhesive sheet is preferably 9 or less from the viewpoint of facilitating re-stickability to the adherend.

[0056] Examples of the liquid medium used when applying the pressure-sensitive adhesive composition for release 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 organic solvents such as hydrocarbon solvents. These may be used alone or in combination of two or more. Any liquid medium can be added to the pressure-sensitive adhesive composition for release to adjust the viscosity. Also, the viscosity of the pressure-sensitive adhesive composition for release can be reduced by heating.

[0057] Examples of the base material include paper, cellophane, plastic sheet, rubber, foam, fabric, rubber cloth, resin-impregnated cloth, glass plate, and wood. The base material may be in the form of a plate or a film. Further, the base material may be composed of a single material, or may be a multilayer base material formed by laminating base materials of a plurality of materials. Furthermore, a base material with its surface subjected to a release treatment can also be used.

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

[0059] As a release sheet (separator) for protecting the adhesive surface of the adhesive layer, a resin film such as a polyester film or paper can be used. The surface of the release sheet on the side that comes into contact with the adhesive surface of the adhesive layer can be subjected to a release treatment with a silicone-based or fluorine-based release agent or the like.

[0060] Examples of the coating method of the re-peelable adhesive composition include a Meyer bar, an applicator, a brush, a spray, a roller, a gravure coater, a die coater, a lip coater, a comma coater, a knife coater, a reverse coater, and a spin coater. Examples of the drying method include hot air drying, infrared rays, and a reduced pressure method. The drying conditions can be appropriately changed according to the curing form, film thickness, and type of solvent of the re-peelable 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 re-peelable adhesive composition> The definitions of the abbreviations in Tables 1 and 2 are as follows. Definition of Abbreviations 2OA: 2-octyl acrylate NOAA: n-octyl acrylate BA: n-butyl acrylate 2EHA: 2-ethylhexyl acrylate VAC: Vinyl acetate AAc: Acrylic acid HEA: 2-hydroxyethyl acrylate Adhesion resin A: Arakawa Chemical Industries, Ltd. Pencil D-135 (polymerized rosin ester) Adhesion resin B: Yasuhara Chemical Co., Ltd. YS Polyster T130 (terpene phenol resin) Hardener A: Mitsui Chemicals, Inc. Takenate D101E (45EA) (adduct of toluene diisocyanate and polyol compound) Hardener B: Aluminum chelate A (aluminum trisacetylacetonate) manufactured by Kawaken Fine Chemicals Co., Ltd. (a1): (Meth)acrylic monomer (a1) (a2): Functional group-containing monomer (a2) (a3): Vinyl monomer (a3) (B): Tackifier resin (B) (C): Hardener (C) Adhesive strength: Refer to Test 1 described below Ball tack, re-stickability: Refer to Test 2 described below High-temperature re-peelability: Refer to Test 3 described below

[0063] Table 1 shows the raw material formulations of the re-peelable adhesive compositions of Examples 1 to 9. Table 2 shows the raw material formulations of the re-peelable adhesive compositions of Comparative Examples 1 to 8. The unit of the numerical values described in the categories (a1) to (C) in Tables 1 and 2 is "parts".

[0064]

Table 1

[0065]

Table 2

[0066] <Example 1: (Meth)acrylic copolymer (A) and manufacturing method of re-peelable 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 part of 2-hydroxyethyl acrylate, 65 parts of ethyl acetate, 10 parts of acetone, and 0.08 part of polymerization initiator (azobisisobutyronitrile) were charged into a reaction apparatus equipped with a stirrer, a thermometer, and a reflux condenser. While stirring the reaction apparatus, it was heated to 85°C to initiate the reaction, and a polymerization reaction was carried out at the reflux temperature for 7 hours. After the reaction was completed, it was cooled and diluted by adding 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 part of Takenate D101E(45EA) (trade name, manufactured by Mitsui Chemicals, Inc.) as an isocyanate curing agent was added in terms of solid content, and they were sufficiently mixed to obtain a pressure-sensitive adhesive composition for re-peeling.

[0068] <Examples 2 to 9: Manufacturing method of (meth)acrylic copolymer (A) and pressure-sensitive adhesive composition for re-peeling> Based on the raw material formulations in Table 1 and the same manufacturing method as in Example 1, the (meth)acrylic copolymers (A) and pressure-sensitive adhesive compositions for re-peeling in Examples 2 to 9 were manufactured, and thus detailed descriptions are omitted.

[0069] <Comparative Examples 1 to 8: Manufacturing method of (meth)acrylic copolymer (A) and pressure-sensitive adhesive composition for re-peeling> Based on the raw material formulations in Table 2 and the same manufacturing method as in Example 1, the (meth)acrylic copolymers (A) and pressure-sensitive adhesive compositions for re-peeling in Comparative Examples 1 to 8 were manufactured, and thus detailed descriptions are omitted.

[0070] <Example 1: Manufacturing method of adhesive sheet> The pressure-sensitive adhesive composition for re-peeling in Example 1 was coated on the release-treated surface of a release sheet so that the dried thickness would be 30 μm, and dried in a hot air circulation dryer at 100 °C for 1 minute to form an adhesive layer. The adhesive layer was laminated on 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 an adhesive sheet A.

[0071] <Examples 2 to 9, Comparative Examples 1 to 8: Manufacturing method of adhesive sheet> Based on the same manufacturing method as in Example 1, the adhesive sheets in Examples 2 to 9 and Comparative Examples 1 to 8 were manufactured, and thus detailed descriptions are omitted.

[0072] <Test method> The following Tests 1 to 3 were conducted using the adhesive sheets in Examples 1 to 9 and Comparative Examples 1 to 8.

[0073] (Test 1: Measurement of adhesive force) The adhesive sheet A was cut into pieces with a width of 25 mm and a length of 70 mm to obtain test pieces. The release sheet was peeled off from the test pieces (adhesive sheet A), and they were adhered to the surface of a stainless steel plate (SUS304) as the adherend, and a 2 kg roll was reciprocated once for pressure bonding. Then, they were left for 20 minutes in an atmosphere of 23°C and 50%. After leaving, in accordance with JIS Z-0237:2000, using a tensile testing machine (Tensilon: manufactured by A&D), the adhesive strength of the test pieces was measured under the conditions of a tensile speed of 300 mm / min and a peeling angle of 180°. The evaluation criteria are as follows. [Evaluation Criteria] 〇 (Good): The adhesive strength is 9.0 N / 25 mm or less. × (Poor): The adhesive strength exceeds 9.0 N / 25 mm.

[0074] (Test 2: Evaluation of Re-stickability) The adhesive sheet A was cut into pieces with a width of 70 mm and a length of 100 mm to obtain test pieces. The release sheet was peeled off from the test pieces (adhesive sheet A), and they were fixed to an inclined plate with an inclination angle of 30 degrees with the adhesive surface facing up. Then, in accordance with the J. Dow method, in an atmosphere of 23°C and 50%, a steel ball was rolled on a sample with a running start of 10 cm and an adhesive surface of 10 cm, and the number of the diameter of the steel ball that stopped near the center of the adhesive surface was recorded. The evaluation criteria are as follows. [Evaluation Criteria] 〇 (Good): Ball tack (No.) ≤ 9 × (Poor): Ball tack (No.) > 9

[0075] (Test 3: Evaluation of High-temperature Re-peelability) The adhesive sheet A was cut into pieces with a width of 25 mm and a length of 70 mm to obtain test pieces. The release sheet was peeled off from the test pieces (adhesive sheet A), and they were adhered to the surface of a stainless steel plate (SUS304) as the adherend, and a 2 kg roll was reciprocated once for pressure bonding. Then, they were stored in an environment of 70°C for 3 days. After 3 days, the test pieces were taken out and left at 23°C and 50% for 1 hour, and the state of the adhesive residue on the stainless steel plate (SUS304) after manually peeling off the adhesive sheet A was observed. The evaluation criteria are as follows. [Evaluation Criteria] ○: No adhesive adheres to the stainless steel plate, or the adhesive adhesion on the stainless steel plate is 5% or less of the sticking area. △: The adhesive adhesion on the stainless steel plate exceeds 5% and is 30% or less of the sticking area. ×: The adhesive adhesion on the stainless steel plate exceeds 30% of the sticking area.

[0076] <Test Results> Referring to Tables 1 and 2, the test results of Examples 1 to 9 and Comparative Examples 1 to 8 will be described.

[0077] As shown in the results of Tests 2 and 3, Examples 1 to 9 were excellent in both high-temperature peelability and re-stickability. The reason is presumably that at least one of the factors that the side chain of 2-octyl acrylate has a structure as long as that of 2-ethylhexyl acrylate and the Tg of the homopolymer of 2-octyl acrylate is comparable to the Tg of the homopolymer of n-butyl acrylate enables adjustment of the substrate adhesion and Tg of the adhesive layer. On the other hand, Comparative Examples 1 to 8 were not excellent in both high-temperature peelability and re-stickability. Hereinafter, the reasons why Comparative Examples 1 to 8 could not achieve both high-temperature peelability and re-stickability will be described.

[0078] In Comparative Example 1, since it contains 2-octyl acrylate exceeding the upper limit content defined in the present invention, the adhesion of the adhesive layer to the substrate deteriorated, and the high-temperature peelability deteriorated.

[0079] In Comparative Examples 2 to 4, since they do not contain 2-octyl acrylate as the main monomer, the re-stickability and / or high-temperature peelability deteriorated. Comparative Examples 2 to 4 correspond to the prior art in which n-butyl acrylate, 2-ethylhexyl acrylate, or n-octyl acrylate is blended as the main monomer as described at the beginning of this specification.

[0080] In Comparative Example 5, since it contains a carboxyl group-containing monomer exceeding the upper limit content defined in the present invention, it is likely to leave glue, and the high-temperature peelability deteriorated.

[0081] In Comparative Example 6, since it contains a tackifying resin (B) exceeding the upper limit content defined in the present invention, it is likely to leave residue and the high-temperature releasability deteriorates. In addition, Comparative Example 6 is not suitable for re-peeling applications because the adhesive strength is too high.

[0082] In Comparative Example 7, since it contains 2-octyl acrylate less than the lower limit content defined in the present invention, the re-stickability deteriorates.

[0083] In Comparative Example 8, since it contains a carboxyl group-containing monomer less than the lower limit content defined in the present invention, the re-stickability deteriorates.

[0084] As described above, the pressure-sensitive adhesive composition for re-peeling of the present invention has remarkable effects such as excellent high-temperature releasability and re-stickability.

[0085] In addition, since the present invention can provide an environmentally and user-friendly pressure-sensitive adhesive composition for re-peeling using biomass-derived raw materials with a low dependence on fossil resources, it is possible to contribute to Goal 12, "Responsible Production and Consumption," of the Sustainable Development Goals (SDGs) led by the United Nations.

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

Claims

1. Comprising a (meth)acrylic copolymer (A) containing 2-octyl (meth)acrylate at 31 to 89% by mass and a carboxyl group-containing monomer at 0.6 to 4.9% by mass, containing 0 to 10 parts by mass of a tackifier resin (B) with respect to 100 parts by mass of the (meth)acrylic copolymer (A), further comprising a curing agent (C), the curing agent (C) containing at least one of an isocyanate-based curing agent and a metal chelate-based curing agent, the (meth)acrylic copolymer (A) further containing, as a constituent unit, a (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate, the (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate including at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, the (meth)acrylic copolymer (A) containing 91.7 to 98.4% by mass of a (meth)acrylic monomer (a1) having an alkyl group with 4 to 12 carbon atoms, which includes the 2-octyl (meth)acrylate and the (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than the 2-octyl (meth)acrylate, A pressure-sensitive adhesive composition for re-peeling.

2. Comprising a (meth)acrylic copolymer (A) containing 2-octyl (meth)acrylate at 31 to 89% by mass and a carboxyl group-containing monomer at 0.6 to 4.9% by mass, containing 0 to 10 parts by mass of a tackifier resin (B) with respect to 100 parts by mass of the (meth)acrylic copolymer (A), further comprising a curing agent (C), the curing agent (C) containing at least one of an isocyanate-based curing agent and a metal chelate-based curing agent, the (meth)acrylic copolymer (A) further containing, as a constituent unit, a vinyl monomer (a3), the (meth)acrylic copolymer (A) further containing, as a constituent unit, a (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate, the (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate including at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, The (meth)acrylic copolymer (A) contains 91.7 to 98.4% by mass of a (meth)acrylic monomer (a1) having an alkyl group with 4 to 12 carbon atoms, which includes the 2-octyl (meth)acrylate and a (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than the 2-octyl (meth)acrylate. Pressure-sensitive adhesive composition for re-peeling.

3. It comprises 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. Based on 100 parts by mass of the (meth)acrylic copolymer (A), it contains 1.5 to 10 parts by mass of a tackifier resin (B). It further contains a curing agent (C). The curing agent (C) contains at least one of an isocyanate-based curing agent and a metal chelate-based curing agent. The tackifier resin (B) contains at least one of a rosin-based resin and a terpene-based resin. The (meth)acrylic copolymer (A) further contains, as a structural unit, a (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate. The (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than 2-octyl (meth)acrylate includes at least one of n-octyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The (meth)acrylic copolymer (A) contains 91.7 to 98.4% by mass of a (meth)acrylic monomer (a1) having an alkyl group with 4 to 12 carbon atoms, which includes the 2-octyl (meth)acrylate and a (meth)acrylic monomer having an alkyl group with 4 to 12 carbon atoms other than the 2-octyl (meth)acrylate. Pressure-sensitive adhesive composition for re-peeling.

4. The (meth)acrylic copolymer (A) further contains a functional group-containing monomer (a2) other than the carboxyl group-containing monomer. The functional group-containing monomer (a2) includes a hydroxy group-containing monomer. The pressure-sensitive adhesive composition for re-peeling according to claim 1.

5. The carboxyl group-containing monomer is acrylic acid. The pressure-sensitive adhesive composition for re-peeling according to any one of claims 1 to 3.

6. The (meth)acrylic copolymer (A) further contains 8 to 18% by mass of n-octyl acrylate. The pressure-sensitive adhesive composition for re-peeling according to claim 1 or 3.

7. The said (meth)acrylic copolymer (A) further contains n-butyl acrylate in an amount of 9 to 27% by mass. The pressure-sensitive adhesive composition for releasability according to any one of claims 1 to 3.

8. The said (meth)acrylic copolymer (A) further contains 2-ethylhexyl acrylate in an amount of 1 to 61% by mass. The pressure-sensitive adhesive composition for releasability according to any one of claims 1 to 3.

9. The said (meth)acrylic copolymer (A) further contains a vinyl monomer (a3) in an amount of 0.4 to 5% by mass. The pressure-sensitive adhesive composition for releasability according to claim 2.

10. The said (meth)acrylic copolymer (A) further contains a hydroxy group-containing monomer in an amount of 0.1 to 2% by mass. The pressure-sensitive adhesive composition for releasability according to any one of claims 1 to 3.

11. A base material, A pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition for releasability according to any one of claims 1 to 3 provided on at least one surface of the said base material. A pressure-sensitive adhesive sheet.

12. The 180-degree peel strength with respect to a stainless steel plate is 9.0 N / 25 mm or less. The pressure-sensitive adhesive sheet according to claim 11.

13. In the J. Dow method inclined ball tack test, the maximum diameter of the steel ball stopped on the adhesive surface of the said pressure-sensitive adhesive layer is (9 / 32)×0.0254 m or less. The pressure-sensitive adhesive sheet according to claim 11.

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