Pressure-sensitive adhesive sheet and method for manufacturing the same, and method for manufacturing laminate

Abstract

To provide an adhesive sheet having excellent unevenness followability, solvent resistance and high-temperature adhesion.SOLUTION: An adhesive sheet has an adhesive layer. The adhesive layer has an acrylic adhesive polymer (A) and a photopolymerization initiator but is free of a compound having a reactive unsaturated bond. The acrylic adhesive polymer (A) has a (meth)acrylic acid alkoxyalkyl ester-derived constitutional unit. The gel fraction based on the acrylic adhesive polymer (A) of the adhesive layer is less than 20%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet, a method for producing the same, and a method for producing a laminate. [Background technology]

[0002] It is known that crosslinking of pressure-sensitive adhesives improves their cohesive strength at room temperature and at high temperatures, and improves their solvent resistance and oil resistance. Generally, pressure-sensitive adhesives are crosslinked by incorporating a crosslinking agent such as an isocyanate curing agent into the pressure-sensitive adhesive layer and crosslinking the adhesive by heat, or by polymerizing a polyfunctional monomer with ultraviolet light (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses the production of a pressure-sensitive adhesive sheet using an acrylic resin composition containing a polymer having 40 to 99 mass% of structural units derived from (meth)acrylic acid alkoxyalkyl ester based on all monomer units and a crosslinking agent. Patent Document 2 discloses the formation of a pressure-sensitive adhesive layer using a composition containing a thermally crosslinkable pressure-sensitive adhesive having a weight-average molecular weight of less than 300,000 and a thermal crosslinking agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 235217 [Patent Document 2] Japanese Patent Application Publication No. 2017-197604 Summary of the Invention [Problem to be solved by the invention]

[0005] When adhering a pressure-sensitive adhesive sheet to a textile fabric or a decorative sheet to an article, the adherend may have a large surface irregularity. However, as in Patent Documents 1 and 2, pressure-sensitive adhesive sheets having a crosslinked pressure-sensitive adhesive layer cannot conform to the irregular shapes of adherends with large surface irregularities, and are prone to peeling under harsh environments such as high temperatures, raising concerns about poor adhesion (particularly, ability to conform to irregularities and high-temperature adhesion). Furthermore, one of the properties required of a pressure-sensitive adhesive layer is high solvent resistance.

[0006] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a pressure-sensitive adhesive sheet that is excellent in conformability to irregularities, solvent resistance, and high-temperature adhesion. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and have focused on minimizing the amount of crosslinking agent used or on forming crosslinks without using a crosslinking agent. Based on this finding, they have discovered that the adhesive sheet can be improved in terms of conformability to uneven surfaces, solvent resistance, and high-temperature adhesion by incorporating a specific component into the adhesive layer, and have completed the present invention. Specifically, the present invention provides the following means.

[0008] [1] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive polymer (A) and a photopolymerization initiator, and does not contain a compound having a reactive unsaturated bond, the acrylic pressure-sensitive adhesive polymer (A) has a structural unit derived from a (meth)acrylic acid alkoxyalkyl ester, and the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20%.

[0009] [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the content of structural units derived from an alkoxyalkyl (meth)acrylate in the acrylic pressure-sensitive adhesive polymer (A) is 20 mass% or more based on all structural units derived from monomers constituting the acrylic pressure-sensitive adhesive polymer (A). [3] The pressure-sensitive adhesive sheet according to the above [1] or [2], wherein the glass transition temperature of the acrylic pressure-sensitive adhesive polymer (A) is -80°C to 10°C. [4] The pressure-sensitive adhesive sheet of [1] or [2] above, wherein the acrylic pressure-sensitive adhesive polymer (A) is a block copolymer having a polymer block M and an acrylic polymer block N, and the glass transition temperature of the acrylic polymer block N is -80°C to 10°C. [5] The pressure-sensitive adhesive sheet according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer has a gel fraction of 20% or more based on the acrylic pressure-sensitive adhesive polymer (A) after the pressure-sensitive adhesive layer is cured by irradiation with active energy rays. [6] The pressure-sensitive adhesive sheet according to any one of the above [1] to [5], wherein the photopolymerization initiator is a hydrogen abstraction photopolymerization initiator.

[0010] [7] A method for producing a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, comprising: forming the pressure-sensitive adhesive layer using a pressure-sensitive adhesive composition containing an acrylic pressure-sensitive adhesive polymer (A), a photopolymerization initiator, and a solvent; the acrylic pressure-sensitive adhesive polymer (A) has a structural unit derived from a (meth)acrylic acid alkoxyalkyl ester; the pressure-sensitive adhesive composition does not contain a compound having a reactive unsaturated bond; and the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20 mass%. [8] A method for producing a laminate, comprising the steps of laminating the pressure-sensitive adhesive sheet according to any one of [1] to [6] above to an adherend, and then irradiating the pressure-sensitive adhesive layer with active energy rays to cure the pressure-sensitive adhesive layer. [Effects of the Invention]

[0011] According to the present invention, a pressure-sensitive adhesive sheet having excellent conformability to irregularities, solvent resistance, and high-temperature adhesion can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. In this specification, "(meth)acrylic" means acrylic and / or methacrylic, and "(meth)acrylate" means acrylate and / or methacrylate.

[0013] <Adhesive sheet> The pressure-sensitive adhesive sheet of the present invention (hereinafter also referred to as "the pressure-sensitive adhesive sheet") is a sheet comprising a pressure-sensitive adhesive layer containing an acrylic pressure-sensitive adhesive polymer (A) having a structural unit derived from a (meth)acrylic acid alkoxyalkyl ester and a photopolymerization initiator. The pressure-sensitive adhesive sheet is a photoreactive pressure-sensitive adhesive sheet that is used by laminating the pressure-sensitive adhesive layer to an adherend and then irradiating the resulting laminate with active energy rays to cure the pressure-sensitive adhesive layer.

[0014] In this pressure-sensitive adhesive sheet, a crosslinking reaction occurs when the pressure-sensitive adhesive layer is irradiated with active energy rays after lamination between the pressure-sensitive adhesive layer and the adherend. This forms a crosslinked structure, resulting in excellent adhesive performance and solvent resistance. The mechanism is presumed to be as follows: When the pressure-sensitive adhesive layer is irradiated with active energy rays after lamination between the pressure-sensitive adhesive layer and the adherend, radicals are generated by the photopolymerization initiator in the pressure-sensitive adhesive layer. Hydrogen is abstracted from the side chain of the alkoxyalkyl acrylate constituting the acrylic adhesive polymer (A), and peroxy radicals are generated by bonding with oxygen (see the scheme below). It is believed that a hydrogen abstraction reaction then occurs again, and the generated radicals couple with each other to form a crosslinked structure. Therefore, with this pressure-sensitive adhesive sheet, even if the pressure-sensitive adhesive layer does not contain a crosslinking agent or a compound having a reactive unsaturated bond (specifically, a monomer or a polyfunctional (meth)acrylic compound), a crosslinked structure can be formed by laminating the pressure-sensitive adhesive layer to the adherend and then irradiating with active energy rays. Furthermore, when the pressure-sensitive adhesive layer of this pressure-sensitive adhesive sheet is attached to an adherend, the crosslinked structure has not yet been formed, so the pressure-sensitive adhesive layer is flexible and can be attached to an adherend with large surface irregularities, following the irregularities of the surface. This is presumably why a pressure-sensitive adhesive sheet with good conformability to irregularities can be obtained.

[0015] [ka]

[0016] Next, the acrylic adhesive polymer (A) and the photopolymerization initiator contained in the adhesive layer of the present adhesive sheet will be described.

[0017] <Acrylic adhesive polymer (A)> The acrylic adhesive polymer (A) is a polymer mainly composed of structural units derived from (meth)acrylic monomers and has adhesive properties. In this specification, the term "the acrylic adhesive polymer (A) is "mainly composed of" (meth)acrylic monomers" means that the proportion of structural units derived from (meth)acrylic monomers relative to all structural units derived from monomers constituting the acrylic adhesive polymer (A) (hereinafter also referred to as "total monomer units") is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0018] The acrylic adhesive polymer (A) has structural units derived from an alkoxyalkyl (meth)acrylate. The alkoxyalkyl (meth)acrylate constituting the acrylic adhesive polymer (A) preferably has an alkoxyalkyl group having 2 to 12 carbon atoms. Specific examples thereof include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, n-propoxyethyl (meth)acrylate, n-butoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, n-propoxypropyl (meth)acrylate, n-butoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, n-propoxybutyl (meth)acrylate, and n-butoxybutyl (meth)acrylate.

[0019] From the viewpoint of versatility, the (meth)acrylic acid alkoxyalkyl ester constituting the acrylic adhesive polymer (A) is preferably a (meth)acrylic acid alkoxyalkyl ester having an alkoxyalkyl group having 2 to 8 carbon atoms, and more preferably at least one selected from the group consisting of methoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, and ethoxyethyl (meth)acrylate. The (meth)acrylic acid alkoxyalkyl ester constituting the acrylic adhesive polymer (A) may be one type or two or more types.

[0020] In the acrylic adhesive polymer (A), the proportion of structural units derived from (meth)acrylic acid alkoxyalkyl ester is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the total monomer units of the acrylic adhesive polymer (A), from the viewpoint of forming a crosslinked structure by utilizing the reaction caused by the coexistence of the (meth)acrylic acid alkoxyalkyl ester and oxygen radicals, and improving the adhesiveness, solvent resistance, and unevenness conformability of the pressure-sensitive adhesive sheet. In the acrylic adhesive polymer (A), the upper limit of the proportion of structural units derived from (meth)acrylic acid alkoxyalkyl ester is not particularly limited, but from the viewpoint of improving adhesive performance, it is preferably 99% by mass or less, more preferably 95% by mass or less, based on the total monomer units of the acrylic adhesive polymer (A).

[0021] The monomer constituting the acrylic adhesive polymer (A) may be only a (meth)acrylic acid alkoxyalkyl ester, or may contain a monomer different from a (meth)acrylic acid alkoxyalkyl ester (hereinafter also referred to as "other monomer").

[0022] From the viewpoint of achieving excellent adhesive performance, the acrylic adhesive polymer (A) preferably has, as another monomer, a structural unit derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid hydroxyalkyl esters.

[0023] Specific examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate.

[0024] From the viewpoint of increasing the elastic modulus of the acrylic adhesive polymer (A) and improving the heat resistance, among these, (meth)acrylic acid alkyl esters in which the alkyl moiety has 1 to 8 carbon atoms are preferred, and (meth)acrylic acid alkyl esters in which the alkyl moiety has 1 to 4 carbon atoms are more preferred.

[0025] Specific examples of the (meth)acrylic acid hydroxyalkyl ester include 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.

[0026] In the acrylic adhesive polymer (A), the proportion of structural units derived from (meth)acrylic acid alkyl ester is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total monomer units of the acrylic adhesive polymer (A), from the viewpoint of improving adhesive performance. In the acrylic adhesive polymer (A), the upper limit of the proportion of structural units derived from (meth)acrylic acid alkyl ester is not particularly limited, but from the viewpoint of sufficient crosslinking by the (meth)acrylic acid alkoxyalkyl ester, it is preferably 90% by mass or less, more preferably 80% by mass or less, based on the total monomer units of the acrylic adhesive polymer (A).

[0027] In the acrylic adhesive polymer (A), the proportion of structural units derived from a (meth)acrylic acid hydroxyalkyl ester is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, based on the total monomer units of the acrylic adhesive polymer (A), from the viewpoint of improving the cohesive strength of the adhesive layer and enhancing adhesive performance. The upper limit of the proportion of structural units derived from a (meth)acrylic acid hydroxyalkyl ester in the acrylic adhesive polymer (A) is preferably 10% by mass or less, more preferably 7% by mass or less, based on the total monomer units of the acrylic adhesive polymer (A), from the viewpoint of sufficiently carrying out crosslinking by the (meth)acrylic acid alkoxyalkyl ester.

[0028] In addition to the above, the acrylic adhesive polymer (A) may contain a monomer copolymerizable with the above monomers, provided that the adhesive performance is not impaired. Examples of such other monomers include alicyclic ester compounds of (meth)acrylic acid, aromatic ester compounds of (meth)acrylic acid, polyalkylene glycol mono(meth)acrylate compounds, aromatic vinyl compounds, imide group-containing vinyl compounds, amino group-containing unsaturated compounds, amide group-containing unsaturated compounds, and nitrile group-containing unsaturated compounds.

[0029] Specific examples of these include alicyclic ester compounds of (meth)acrylic acid, such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, 1-adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

[0030] Examples of aromatic ester compounds of (meth)acrylic acid include phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxymethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and 3-phenoxypropyl (meth)acrylate.

[0031] Examples of the polyalkylene glycol mono(meth)acrylate compound include polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol-polypropylene glycol mono(meth)acrylate, polyethylene glycol-polytetraethylene glycol mono(meth)acrylate, methoxypolyethylene glycol mono(meth)acrylate, lauroxypolyethylene glycol mono(meth)acrylate, stearoxypolyethylene glycol mono(meth)acrylate, octoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, phenoxypolyethylene glycol mono(meth)acrylate, phenoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate, nonylphenoxypolyethylene glycol mono(meth)acrylate, nonylphenoxypolypropylene glycol mono(meth)acrylate, and nonylphenoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate.

[0032] Examples of aromatic vinyl compounds include styrene, α-methylstyrene, β-methylstyrene, vinylxylene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, p-n-butylstyrene, p-isobutylstyrene, pt-butylstyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-hydroxystyrene, m-hydroxystyrene, o-hydroxystyrene, p-isopropenylphenol, m-isopropenylphenol, o-isopropenylphenol, o-vinylbenzoic acid, m-vinylbenzoic acid, p-vinylbenzoic acid, and styrene-based compounds such as divinylbenzene; vinylnaphthalene, and the like.

[0033] Examples of the imide group-containing vinyl compound include maleimide compounds such as maleimide and N-substituted maleimide compounds; itaconimide compounds such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide; N-methylcitraconimide, N-ethylcitraconimide, N-butylcitraconimide, N-octylcitraconimide, N-2-ethylhexylcitraconimide, and N-cyclohexylitaconimide; Examples of the imide group-containing vinyl compound include citraconic acid compounds such as cyclohexylcitraconimide and N-laurylcitraconimide; and (meth)acrylimide compounds such as N-(2-(meth)acryloyloxyethyl)succinimide, N-(2-(meth)acryloyloxyethyl)maleimide, N-(2-(meth)acryloyloxyethyl)phthalimide, N-(4-(meth)acryloyloxybutyl)succinimide, N-(4-(meth)acryloyloxybutyl)maleimide, and N-(4-(meth)acryloyloxybutyl)phthalimide. Of these, maleimide compounds are preferably used as the imide group-containing vinyl compound.

[0034] Examples of the amino group-containing unsaturated compound include dimethylaminomethyl (meth)acrylate, diethylaminomethyl (meth)acrylate, 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2-(di-n-propylamino)ethyl (meth)acrylate, 2-dimethylaminopropyl (meth)acrylate, 2-diethylaminopropyl (meth)acrylate, 2-(di-n-propylamino)propyl (meth)acrylate, 3-dimethylaminopropyl (meth)acrylate, 3-diethylaminopropyl (meth)acrylate, and 3-(di-n-propylamino)propyl (meth)acrylate.

[0035] Examples of the amide group-containing unsaturated compound include (meth)acrylamide, (meth)acrylamide derivatives, and N-vinylamide monomers. Specific examples of (meth)acrylamide derivatives include tert-butyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, and (meth)acryloylmorpholine. Specific examples of N-vinylamide monomers include N-vinylacetamide, N-vinylformamide, and N-vinylisobutylamide.

[0036] Examples of the nitrile group-containing unsaturated compound include cyanomethyl (meth)acrylate, 1-cyanoethyl (meth)acrylate, 2-cyanoethyl (meth)acrylate, 1-cyanopropyl (meth)acrylate, 2-cyanopropyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, 4-cyanobutyl (meth)acrylate, 6-cyanohexyl (meth)acrylate, 2-ethyl-6-cyanohexyl (meth)acrylate, 8-cyanooctyl (meth)acrylate, (meth)acrylonitrile, α-ethylacrylonitrile, α-isopropylacrylonitrile, α-chloroacrylonitrile, and α-fluoroacrylonitrile.

[0037] The proportion of the other monomers constituting the acrylic adhesive polymer (A) can be appropriately selected within a range that does not impair the effects of the present invention. As the other monomers, one type may be used alone, or two or more types may be used in combination.

[0038] (Method for producing acrylic adhesive polymer (A)) The acrylic adhesive polymer (A) is not particularly limited in its production method and can be obtained by a known production method, for example, by polymerizing the above-mentioned monomers using a known radical polymerization method such as solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization.

[0039] In the case of the solution polymerization method, an organic solvent and monomers are charged into a reactor, a polymerization initiator is added, and the mixture is heated to 50 to 300° C. to polymerize.

[0040] The method of feeding each raw material including the monomer may be a batch-type initial lump-sum feeding in which all raw materials are fed at once, a semi-continuous feeding in which at least some of the raw materials are continuously fed into the reactor, or a continuous polymerization method in which all raw materials are continuously fed and at the same time the produced resin is continuously withdrawn from the reactor.

[0041] Examples of organic solvents used in solution polymerization include cyclic ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbon compounds such as benzene, toluene, and xylene, esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, and alcohols such as methyl orthoformate, methyl orthoacetate, methanol, ethanol, and isopropanol. One or more of these organic solvents can be used. The amount of organic solvent used is such that the total amount of monomers used in polymerization is, for example, 1 to 50% by mass relative to the total amount of the organic solvent and the monomers.

[0042] The polymerization initiator may be any known radical polymerization initiator, such as an azo compound, an organic peroxide, or an inorganic peroxide, and is not particularly limited. Among these, an azo compound is preferred because it is easy to handle safely and is less likely to cause side reactions during radical polymerization. An azo compound is preferred. Alternatively, a redox polymerization initiator consisting of a known oxidizing agent and a known reducing agent may be used as the polymerization initiator. Furthermore, a known chain transfer agent may be used in combination with the polymerization initiator.

[0043] Specific examples of the polymerization initiator include azo compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4-cyanovaleric acid), 2-(tert-butylazo)-2-cyanopropane, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), and dimethyl 2,2'-azobis(2-methylpropionate).

[0044] Examples of organic peroxides include cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane.

[0045] Examples of inorganic peroxides include potassium persulfate and sodium persulfate. Examples of redox polymerization initiators include those using sodium sulfite, sodium thiosulfate, sodium formaldehyde sulfoxylate, ascorbic acid, ferrous sulfate, etc. as a reducing agent and potassium peroxodisulfate, hydrogen peroxide, tert-butyl hydroperoxide, etc. as an oxidizing agent. In producing the acrylic adhesive polymer (A), the amount of the polymerization initiator used is, for example, 0.01 to 20 parts by mass per 100 parts by mass of all monomers used in the polymerization.

[0046] The glass transition temperature (Tg) of the acrylic adhesive polymer (A) is preferably in the range of -80°C or higher and 10°C or lower. If the Tg of the acrylic adhesive polymer (A) is -80°C or higher, the cohesive strength of the adhesive layer can be sufficiently increased, and adhesiveness can be sufficiently ensured, which is preferable. From this viewpoint, the Tg of the acrylic adhesive polymer (A) is more preferably -60°C or higher, even more preferably -50°C or higher, and even more preferably -45°C or higher.

[0047] On the other hand, if the Tg of the acrylic adhesive polymer (A) is 10°C or less, sufficient adhesion can be ensured under low-temperature conditions, and the adhesive sheet can conform well to the adherend, which is preferable in that an adhesive sheet with high durability under high temperature or high-temperature and high-humidity conditions can be obtained. The upper limit of the Tg of the acrylic adhesive polymer (A) is more preferably 5°C or less, even more preferably 0°C or less, still more preferably -5°C or less, and particularly preferably -10°C or less. The Tg range of the acrylic adhesive polymer (A) is more preferably -60°C or more and 5°C or less, even more preferably -50°C or more and 0°C or less.

[0048] In this specification, the Tg of a polymer is a value determined from the intersection of the baseline of a heat flux curve obtained using a differential scanning calorimeter (DSC) and the tangent point at the inflection point. Details of the measurement conditions are as described in the Examples below. The Tg of a polymer can be selected arbitrarily by changing the type and composition of the constituent monomers.

[0049] (Block copolymer) The acrylic adhesive polymer (A) may be a block copolymer having two or more polymer blocks (hereinafter also referred to as "block copolymer BL"). The block copolymer BL preferably has a polymer block M and an acrylic polymer block N.

[0050] The polymer block M of the block copolymer BL is preferably a segment having a higher glass transition temperature (Tg) than the acrylic polymer block N. Specifically, the Tg (hereinafter also referred to as "TgM") of the polymer block M is preferably 50°C or higher. A TgM of 50°C or higher is preferred because it can impart good heat resistance to the block copolymer BL. It is also preferred because the block copolymer BL can form pseudo-crosslinks by forming a microphase separation structure, for example. When the polymer constituting the pressure-sensitive adhesive layer forms a pseudo-crosslinked structure, the cohesive force tends to improve, and the adhesive strength tends to increase.

[0051] In this specification, the Tg of the polymer block M and the acrylic polymer block N is a value determined by producing a polymer comprising the polymer block M and a polymer comprising the acrylic polymer block N, and then measuring each polymer using DSC. Details of the measurement method follow the procedures described in the Examples below.

[0052] When the acrylic adhesive polymer (A) is a block copolymer BL, the glass transition temperature (hereinafter also referred to as "TgN") of the acrylic polymer block N is preferably in the range of -80°C or higher and 10°C or lower. When TgN is -80°C or higher, the cohesive strength of the adhesive layer can be sufficiently increased, and sufficient adhesiveness tends to be ensured. When TgN is 10°C or lower, sufficient adhesiveness under low-temperature conditions tends to be ensured. In addition, the adhesive sheet has good conformability to the adherend, and an adhesive sheet with high durability under high temperature or high-temperature and high-humidity conditions can be obtained. TgN is more preferably -60°C or higher, even more preferably -50°C or higher, and even more preferably -45°C or higher. Furthermore, TgN is more preferably 5°C or lower, even more preferably 0°C or lower, still more preferably -5°C or lower, and particularly preferably -10°C or lower. The range of TgN is more preferably -60°C or higher and 5°C or lower, even more preferably -50°C or higher and 0°C or lower.

[0053] The types of monomers constituting the acrylic polymer block N and the content of each monomer are the same as the compounds exemplified as the monomers constituting the acrylic adhesive polymer (A) and the content thereof.

[0054] The polymer block M preferably has a structural unit (hereinafter also referred to as "structural unit U1") derived from at least one compound selected from the group consisting of imide group-containing vinyl compounds, styrene-based compounds, (meth)acrylic acid alkyl esters, and amide group-containing vinyl compounds. When the polymer block M has the structural unit U1, a block copolymer BL having superior heat resistance and adhesiveness can be obtained. The polymer block M preferably has a structural unit derived from at least one compound selected from the group consisting of imide group-containing vinyl compounds and styrene-based compounds.

[0055] From the viewpoint of copolymerizability with styrene-based compounds, the imide group-containing vinyl compound used in the production of polymer block M is preferably a maleimide compound. Among the above-mentioned maleimide compounds, the compound represented by the following formula (1) is preferred, since it can provide block copolymer BL with better heat resistance and adhesiveness: [ka] (In formula (1), R 1 represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a cyclohexyl group, a phenyl group, or a substituted phenyl group in which a hydroxy group, an alkoxy group having 1 to 2 carbon atoms, an acetyl group, or a halogen atom is bonded to any position of the phenyl group.

[0056] When an imide group-containing vinyl compound is used as a monomer constituting the polymer block M, the proportion of the imide group-containing vinyl compound is preferably 10 to 95 mass %, more preferably 25 to 80 mass %, based on the total monomer units of the polymer block M. A block copolymer BL containing a structural unit derived from an imide group-containing vinyl compound is preferred in terms of excellent heat resistance and adhesiveness.

[0057] Styrenic compounds are thought to have the property of improving the polymerizability of maleimide compounds. Therefore, when a maleimide compound is used as a monomer constituting polymer block M, it is preferable to improve the polymerizability of the maleimide compound by using a styrene compound in combination. When a maleimide compound and a styrene compound are used in combination in producing polymer block M, the ratio of structural units derived from the styrene compound to 1 part by mass of structural units derived from the maleimide compound is preferably 0.01 to 100 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.2 to 5 parts by mass, and particularly preferably 0.5 to 1.5 parts by mass.

[0058] When a styrene-based compound is used as the monomer constituting the polymer block M, the proportion of the styrene-based compound is preferably 5 to 90% by mass, and more preferably 20 to 75% by mass, based on all the monomer units of the polymer block M. The proportion of the structural unit U1 in the polymer block M is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on all the constituent monomer units of the polymer block M.

[0059] In order to impart good heat resistance to the block copolymer BL, the Tg (TgM) of the polymer block M is preferably 50° C. or higher, more preferably 60° C. or higher, even more preferably 80° C. or higher, and particularly preferably 90° C. or higher. In addition, in order to provide a high degree of freedom in the monomers that can be used as the monomers constituting the acrylic pressure-sensitive adhesive polymer (A) and to enable a low temperature during lamination, TgM is preferably 350° C. or lower, more preferably 280° C. or lower, even more preferably 270° C. or lower, and particularly preferably 260° C. or lower.

[0060] The number and structure of the polymer blocks contained in the block copolymer BL are not particularly limited. Specific examples of the block copolymer BL include a diblock copolymer with an MN structure composed of a polymer block M and an acrylic polymer block N, a triblock copolymer with an MNM structure composed of polymer block M / acrylic polymer block N / polymer block M, and a triblock copolymer with an NMN structure composed of an acrylic polymer block N / polymer block M / acrylic polymer block N. The block copolymer BL may also contain a polymer block other than the polymer block M and the acrylic polymer block N. Of these, the block copolymer BL is preferably a triblock copolymer with an MNM structure. With such a structure, the polymer block M and the acrylic polymer block N are likely to form a pseudo-crosslinked structure, thereby improving the physical properties of the pressure-sensitive adhesive.

[0061] The molar ratio of polymer block M to acrylic polymer block N in the block copolymer BL (polymer block M / acrylic polymer block N) is preferably 1 / 99 to 25 / 75. A molar ratio within this range is preferred because a polymer having polymer block M, which constitutes a hard segment and can serve as a crosslinking point, and acrylic polymer block N, which serves as a soft segment, can easily produce a pressure-sensitive adhesive exhibiting excellent adhesive properties, and can also adequately maintain flexibility at the bonded portion. The molar ratio of polymer block M to acrylic polymer block N is more preferably 1 / 99 to 23 / 77, even more preferably 1 / 99 to 20 / 80, even more preferably 1 / 99 to 15 / 85, and particularly preferably 1 / 99 to 10 / 90.

[0062] ·Method of manufacturing block copolymer BL The block copolymer BL can be produced by any known production method without any particular limitations. Examples of production methods for the block copolymer BL include methods that utilize various controlled polymerization methods such as living radical polymerization and living anionic polymerization, and methods that involve coupling polymers having functional groups together. Among these, living radical polymerization is preferred from the viewpoints of ease of operation and applicability to a wide range of monomers.

[0063] The living radical polymerization may be any of a batch process, a semi-batch process, a dry continuous polymerization process, a continuous stirred tank process (CSTR), etc. The polymerization method may be applied to various modes such as bulk polymerization without using a solvent, solvent-based solution polymerization, aqueous emulsion polymerization, mini-emulsion polymerization, or suspension polymerization.

[0064] There are no particular limitations on the type of living radical polymerization method, and various polymerization methods can be used, such as reversible addition-fragmentation chain transfer polymerization (RAFT), nitroxy radical polymerization (NMP), atom transfer radical polymerization (ATRP), polymerization using an organotellurium compound (TERP), polymerization using an organoantimony compound (SBRP), polymerization using an organobismuth compound (BIRP), and iodine transfer polymerization. Among these, the RAFT, NMP, and ATRP methods are preferred from the viewpoints of polymerization controllability and ease of implementation.

[0065] In the RAFT method, controlled polymerization proceeds via a reversible chain transfer reaction in the presence of a specific polymerization control agent (RAFT agent) and a general free radical polymerization initiator. Various known RAFT agents can be used, such as dithioester compounds, xanthate compounds, trithiocarbonate compounds, and dithiocarbamate compounds. The RAFT agent may be monofunctional, having only one active site, or bifunctional or higher functional. Bifunctional RAFT agents are preferred because they facilitate efficient production of block copolymers with an MNM structure. The amount of RAFT agent used is adjusted appropriately depending on the type of monomer and RAFT agent used.

[0066] As the polymerization initiator used in the RAFT polymerization, known radical polymerization initiators such as azo compounds, organic peroxides, and persulfates can be used. Among these, azo compounds are preferred because they are safe and easy to handle and are less likely to cause side reactions during radical polymerization. Specific examples of azo compounds include the azo compounds exemplified in the description of the acrylic adhesive polymer (A). Only one type of radical polymerization initiator may be used, or two or more types may be used in combination. The proportion of the radical polymerization initiator used is not particularly limited. However, in order to stably carry out the polymerization reaction and obtain a polymer with a narrower molecular weight distribution, the amount of radical polymerization initiator used per mole of the RAFT agent is preferably 0.01 mol to 0.5 mol, and more preferably 0.01 mol to 0.2 mol.

[0067] The reaction temperature during the polymerization reaction by the RAFT method is preferably 40°C or higher and 100°C or lower, more preferably 45°C or higher and 90°C or lower, and even more preferably 50°C or higher and 80°C or lower. A reaction temperature of 40°C or higher is preferred because it allows the polymerization reaction to proceed smoothly. A reaction temperature of 100°C or lower is also preferred because it can suppress side reactions and alleviates restrictions on the initiators and solvents that can be used.

[0068] In the NMP method, a specific alkoxyamine compound having a nitroxide is used as a living radical polymerization initiator, and polymerization proceeds via the nitroxide radical derived from the living radical polymerization initiator. There are no particular limitations on the type of nitroxide radical used in producing the block copolymer BL, and commercially available nitroxide-based polymerization initiators can be used. From the viewpoint of polymerization controllability when polymerizing monomers containing acrylate, it is preferable to use a compound represented by the following formula (2) as the nitroxide compound.

[0069] [ka] (In formula (2), R 1 is an alkyl group having 1 to 2 carbon atoms or a hydrogen atom, and R 2 is an alkyl group or a nitrile group having 1 to 2 carbon atoms, and R 3 is -(CH2)m-, m is an integer of 0 to 2, and R 4 and R 5 are each independently an alkyl group having 1 to 4 carbon atoms. 4 may be the same or different.)

[0070] The nitroxide compound represented by the formula (2) undergoes primary dissociation upon heating at approximately 70 to 80°C and undergoes an addition reaction with a vinyl monomer. In this case, a polyfunctional polymerization precursor can be obtained by adding the nitroxide compound to a vinyl monomer having two or more vinyl groups. The vinyl monomer can then be subjected to living polymerization by secondary dissociation of the polymerization precursor under heating. In this case, since the polymerization precursor has two or more active sites in its molecule, a polymer with a narrower molecular weight distribution can be obtained. From the viewpoint of efficiently obtaining a block copolymer with an MNM structure, it is preferable to use a bifunctional polymerization precursor having two active sites in its molecule. The amount of the nitroxide compound used can be adjusted appropriately depending on the type of monomer and nitroxide compound used, etc.

[0071] When the block copolymer BL is produced by the NMP method, polymerization may be carried out by adding 0.001 to 0.2 moles of the nitroxide radical represented by the following formula (3) to 1 mole of the nitroxide compound represented by the above formula (2).

[0072] [ka] (In formula (3), R 6 and R 7 are each independently an alkyl group having 1 to 4 carbon atoms. 6 may be the same or different, and multiple R 7 may be the same or different.)

[0073] Adding 0.001 moles or more of the nitroxide radical represented by formula (3) shortens the time it takes for the nitroxide radical concentration to reach a steady state. This allows for more precise control of the polymerization, which is advantageous in that it allows for the production of a polymer with a narrower molecular weight distribution. On the other hand, if the amount of nitroxide radical added is too large, the polymerization may not proceed. The amount of nitroxide radical added per mole of nitroxide compound is more preferably in the range of 0.01 to 0.5 moles, and even more preferably in the range of 0.05 to 0.2 moles.

[0074] The reaction temperature in the NMP method is preferably 50°C or higher and 140°C or lower, more preferably 60°C or higher and 130°C or lower, even more preferably 70°C or higher and 120°C or lower, and particularly preferably 80°C or higher and 120°C or lower. If the reaction temperature is 50°C or higher, the polymerization reaction can proceed smoothly. On the other hand, if the reaction temperature is 140°C or lower, side reactions such as radical chain transfer tend to be suppressed.

[0075] In the ATRP method, a polymerization reaction is generally carried out using an organic halide as an initiator and a transition metal complex as a catalyst. The organic halide initiator may be monofunctional or bifunctional or higher. The use of a bifunctional compound is preferred in terms of the ease with which a block copolymer having an MNM structure can be efficiently obtained. Preferred types of halogen are bromides and chlorides. The reaction temperature in the ATRP method is preferably 20°C or higher and 200°C or lower, more preferably 50°C or higher and 150°C or lower. A reaction temperature of 20°C or higher is preferred in terms of the smooth progress of the polymerization reaction.

[0076] When a triblock copolymer consisting of polymer block M / acrylic polymer block N / polymer block M is obtained by living radical polymerization, the target block copolymer may be obtained, for example, by sequentially polymerizing each block. In this case, first, in the first polymerization step, polymer block M is obtained using the constituent monomers of polymer block M. Then, in the second polymerization step, acrylic polymer block N is obtained using the constituent monomers of acrylic polymer block N. Furthermore, in the third polymerization step, a triblock copolymer having an MNM structure can be obtained by polymerization using the constituent monomers of polymer block M. As the polymerization initiator, it is preferable to use the monofunctional polymerization initiator or polymerization precursor described above.

[0077] A production method including the following two-stage polymerization process is preferred because it allows for more efficient production of the target product. That is, in the first polymerization process, polymer block M is obtained using constituent monomers of polymer block M, and then in the second polymerization process, constituent monomers of acrylic polymer block N are polymerized to obtain acrylic polymer block N. This allows for the production of a triblock copolymer with an MNM structure consisting of polymer block M, acrylic polymer block N, and polymer block M. In this case, it is preferable to use a bifunctional polymerization initiator or polymerization precursor as the polymerization initiator. This method allows for a simplification of the process compared to production by sequentially polymerizing each block.

[0078] The polymerization of the block copolymer BL may be carried out in the presence of a chain transfer agent, if necessary. Known chain transfer agents can be used. Specific examples include alkylthiol compounds having an alkyl group having 2 to 20 carbon atoms, such as ethanethiol, 1-propanethiol, 2-propanethiol, 1-butanethiol, 2-butanethiol, 1-hexanethiol, 2-hexanethiol, 2-butylbutane-1-thiol, 1,1-dimethyl-1-pentanethiol, 1-dodecanethiol, tert-tetradecanethiol, 1-hexadecanethiol, and 1-octadecanethiol, as well as mercaptoacetic acid, mercaptopropionic acid, and 2-mercaptoethanol. One or more of these chain transfer agents can be used.

[0079] When producing the block copolymer BL, a polymerization solvent known in living radical polymerization can be used. Specific examples include aromatic compounds such as benzene, toluene, xylene, and anisole; ester compounds such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; ketone compounds such as acetone and methyl ethyl ketone; dimethylformamide, acetonitrile, dimethyl sulfoxide, alcohol, and water. Alternatively, bulk polymerization or other methods may be used without using a polymerization solvent.

[0080] (Molecular weight characteristics of acrylic adhesive polymer (A)) The Mw of the acrylic adhesive polymer (A) is preferably 100,000 or more from the viewpoint of exhibiting sufficient cohesive strength and good adhesiveness. When the Mw of the acrylic adhesive polymer (A) is 100,000 or more, sufficient adhesiveness and solvent resistance can be ensured. The Mw of the acrylic adhesive polymer (A) is more preferably 120,000 or more, even more preferably 150,000 or more, and even more preferably 200,000 or more.

[0081] The upper limit of the Mw of the acrylic adhesive polymer (A) is not particularly limited, but from the viewpoint of ensuring good coating and handling properties when forming an adhesive sheet and ensuring ease of production, it is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. The Mw range of the acrylic adhesive polymer (A) is preferably 100,000 or more and 3,000,000 or less, more preferably 150,000 or more and 2,000,000 or less, and even more preferably 200,000 or more and 1,500,000 or less. In this specification, the molecular weight of the polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0082] The molecular weight distribution (Mw / Mn) of the acrylic adhesive polymer (A), which is expressed as the ratio of Mw to Mn, is preferably 10.0 or less, more preferably 9.0 or less, from the viewpoint of easily obtaining good adhesiveness and suppressing the increase in viscosity of the adhesive composition. The lower limit of Mw / Mn of the acrylic adhesive polymer (A) is not particularly limited, and can be 1.0 or more.

[0083] <Photopolymerization initiator> The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet contains a photopolymerization initiator. The photopolymerization initiator is a compound that generates radicals when irradiated with active energy rays. Examples of active energy rays include ultraviolet rays, visible light, and electron beams, and ultraviolet rays or electron beams are preferred.

[0084] As the photopolymerization initiator, a known photoinitiated radical polymerization initiator can be used, including an intramolecular cleavage type radical polymerization initiator that generates radicals by molecular decomposition, and a hydrogen abstraction type radical polymerization initiator that generates radicals by abstracting hydrogen from other molecules.

[0085] Specific examples of the intramolecular cleavage type radical polymerization initiator include acetophenones such as diethoxyacetophenone, 1-hydroxycyclohexyl-phenyl ketone, 2-hydroxy-2-methylpropiophenone, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 2-methyl-2-morpholino(4-methylthiophenyl)propan-1-one, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone; benzoins such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; and acylphosphine oxides such as 2,4,6-trimethylbenzoin diphenylphosphine oxide.

[0086] Examples of hydrogen abstraction type radical polymerization initiators include benzophenone, 2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 4-(methylphenylthio)phenylphenylmethane, methyl-2-benzophenone, 1-[4-(4-benzoylphenylsulfanyl)phenyl]-2-methyl-2-(4-methylphenylsulfonyl)propan-1-one, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, and 4-methoxy-4' benzophenones such as 1-dimethylaminobenzophenone; thioxanthones such as thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, isopropylthioxanthone, 1-chloro-4-propylthioxanthone, 3-[3,4-dimethyl-9-oxo-9H-thioxanthone-2-yl-oxy]-2-hydroxypropyl-N,N,N-trimethylammonium chloride, and fluorothioxanthone; as well as benzil ketal, anthraquinone, ethyl anthraquinone, phenanthrenequinone, xanthone, and hydroxyacetophenone.

[0087] As the photopolymerization initiator to be contained in the pressure-sensitive adhesive layer of the present pressure-sensitive adhesive sheet, a hydrogen abstraction type radical polymerization initiator can be preferably used, since it can further promote the crosslinking reaction using the (meth)acrylic acid alkoxyalkyl ester by irradiation with active energy rays. Note that, in order to improve the sensitivity of the present pressure-sensitive adhesive sheet to the active energy rays, a benzoic acid-based or amine-based photosensitizer may be used in combination, if necessary. Note that, as the photopolymerization initiator, one type may be used alone, or two or more types may be used in combination.

[0088] The content of the photopolymerization initiator in the pressure-sensitive adhesive layer is preferably 0.01 parts by mass or more relative to 100 parts by mass of the acrylic adhesive polymer (A). A photopolymerization initiator content of 0.01 parts by mass or more is advantageous in that radicals generated in the pressure-sensitive adhesive layer upon irradiation with active energy rays can be used to form a crosslinked structure using an alkoxyalkyl acrylate. From this perspective, the amount of photopolymerization initiator contained in the pressure-sensitive adhesive layer is more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the acrylic adhesive polymer (A). Furthermore, from the perspective of suppressing a decrease in adhesive properties due to excessive formation of crosslinked structures after active energy irradiation, the amount of photopolymerization initiator contained in the pressure-sensitive adhesive layer is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the acrylic adhesive polymer (A). The photopolymerization initiator content referred to here refers to the amount of photopolymerization initiator in the pressure-sensitive adhesive layer before the pressure-sensitive adhesive sheet is irradiated with active energy rays.

[0089] (reactive unsaturated compounds) The present pressure-sensitive adhesive sheet does not contain a compound having a reactive unsaturated bond (hereinafter also referred to as "reactive unsaturated compound") in the pressure-sensitive adhesive layer, and in this respect, it differs from pressure-sensitive adhesive sheets in which a pressure-sensitive adhesive layer is formed using an active energy ray-curable pressure-sensitive adhesive composition. Here, the active energy ray-curable pressure-sensitive adhesive composition is a so-called syrup-type curable pressure-sensitive adhesive composition that is cured by active energy rays such as ultraviolet rays. The acrylic adhesive polymer syrup contained in the active energy ray-curable pressure-sensitive adhesive composition produces an acrylic adhesive polymer that constitutes the pressure-sensitive adhesive layer when irradiated with active energy rays. This acrylic adhesive polymer syrup contains a polymer component that will constitute a portion of the acrylic adhesive polymer contained in the pressure-sensitive adhesive layer and a monomer component that will constitute the remainder. Note that this monomer component corresponds to the reactive unsaturated compound of the present invention. Specific examples of the reactive unsaturated compound include the compounds exemplified as monomers that constitute the acrylic adhesive polymer (A) and polyfunctional (meth)acrylic compounds.

[0090] However, in this specification, "free from compounds having reactive unsaturated bonds" means that the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet may contain trace amounts of reactive unsaturated compounds, provided that the effects of the present invention are not impaired. Specifically, the content of reactive unsaturated compounds in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is 0.5% by mass or less, preferably 0.2% by mass or less, and more preferably 0.1% by mass or less, based on the total amount of the pressure-sensitive adhesive layer. Furthermore, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet does not contain a compound having two or more reactive unsaturated bonds in one molecule (e.g., a polyfunctional (meth)acrylic monomer). Specifically, the content of compounds having two or more reactive unsaturated bonds in the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, based on the total amount of the pressure-sensitive adhesive layer.

[0091] <Manufacturing of adhesive sheets> The present pressure-sensitive adhesive sheet can be produced by a method including a step of forming a pressure-sensitive adhesive layer using a pressure-sensitive adhesive composition containing an acrylic pressure-sensitive adhesive polymer (A) and a photopolymerization initiator (hereinafter also referred to as "the present pressure-sensitive adhesive composition"). There are no particular restrictions on the present pressure-sensitive adhesive composition as long as it contains the above-mentioned acrylic pressure-sensitive adhesive polymer (A) and a photopolymerization initiator, but it is preferable that the present pressure-sensitive adhesive composition is a solvent-based pressure-sensitive adhesive composition that further contains a solvent.

[0092] <Adhesive composition> The solvent contained in the present pressure-sensitive adhesive composition is preferably an organic solvent capable of dissolving the acrylic pressure-sensitive adhesive polymer (A). Specific examples of organic solvents include aprotic polar solvents, phenolic solvents, alcoholic solvents, ester solvents, ketone solvents, ether solvents, and hydrocarbon solvents. The organic solvent may be one of these solvents or a mixed solvent of two or more of them. The solvent contained in the present pressure-sensitive adhesive composition is preferably at least one selected from the group consisting of ethyl acetate, butyl acetate, ethyl methyl ketone, and toluene.

[0093] The content of the photopolymerization initiator in the present pressure-sensitive adhesive composition is preferably 0.01 parts by mass or more relative to 100 parts by mass of the acrylic adhesive polymer (A). A photopolymerization initiator content of 0.01 parts by mass or more is advantageous in that a sufficient amount of radicals can be generated in the pressure-sensitive adhesive layer upon irradiation with active energy rays, thereby enabling sufficient formation of a crosslinked structure using the acrylic acid alkoxyalkyl ester. The amount of the photopolymerization initiator contained in the present pressure-sensitive adhesive composition is more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the acrylic adhesive polymer (A). Furthermore, from the viewpoint of preventing a decrease in adhesive performance due to excessive crosslinking, the content of the photopolymerization initiator in the present pressure-sensitive adhesive composition is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the acrylic adhesive polymer (A).

[0094] The present pressure-sensitive adhesive composition may further contain components other than the acrylic pressure-sensitive adhesive polymer (A), the photopolymerization initiator, and the solvent (hereinafter also referred to as "other components"), as long as the effects of the present invention are not impaired. Examples of other components include a crosslinking agent, a tackifier, and a plasticizer.

[0095] (Crosslinking agent) When the acrylic adhesive polymer (A) has a crosslinkable functional group, the gel fraction of the adhesive layer of the present adhesive sheet may be adjusted by blending a crosslinking agent capable of reacting with the crosslinkable functional group into the adhesive composition.

[0096] Examples of the crosslinking agent (curing agent) include a glycidyl compound having two or more glycidyl groups, an isocyanate compound having two or more isocyanate groups, an aziridine compound having two or more aziridinyl groups, an oxazoline compound having an oxazoline group, a metal chelate compound, a butylated melamine compound, etc. Among these, an isocyanate compound is preferred because of its excellent adhesive properties under high temperature conditions.

[0097] Specific examples of the crosslinking agent include glycidyl compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, tetraglycidylxylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and trimethylolpropane polyglycidyl ether.

[0098] Examples of isocyanate compounds include aromatic isocyanate compounds such as diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), naphthalene diisocyanate (NDI), p-phenylene diisocyanate (PPDI), xylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and tolidine diisocyanate (TODI); hexamethylene diisocyanate (HDI), and lysine diisocyanate (LYS); alicyclic isocyanate compounds such as isophorone diisocyanate (IPDI), cyclohexyl diisocyanate (CHDI), hydrogenated XDI (H6XDI), and hydrogenated MDI (H12MDI); and modified isocyanate compounds such as urethane-modified compounds, dimers, trimers, carbodiimide-modified compounds, urea-modified compounds, isocyanurate-modified compounds, oxazolidone-modified compounds, and isocyanate-terminated prepolymers.

[0099] Examples of the aziridine compound include 1,6-bis(1-aziridinylcarbonylamino)hexane, 1,1'-(methylene-di-p-phenylene)bis-3,3-aziridyl urea, ethylene bis-(2-aziridinyl propionate), 2,4,6-triaziridinyl-1,3,5-triazine, and trimethylolpropane-tris(2-aziridinyl propionate).

[0100] The content of the crosslinking agent in the present adhesive composition is preferably 0 to 0.3 parts by mass, more preferably 0 to 0.2 parts by mass, per 100 parts by mass of the acrylic adhesive polymer (A), from the viewpoint of improving the conformability of the present adhesive sheet to irregularities.

[0101] (tackifier) The present pressure-sensitive adhesive composition may further contain a tackifier. Examples of tackifiers include rosin derivatives such as rosin ester, gum rosin, tall oil rosin, hydrogenated rosin ester, maleated rosin, and disproportionated rosin ester; terpene-based resins mainly containing terpene phenol resins, α-pinene, β-pinene, or limonene; coumarone-indene resins, hydrogenated aromatic copolymers, and phenolic resins. One type of tackifier may be used alone, or two or more types may be used in combination. The content of the tackifier is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, and even more preferably 0 to 5 parts by mass, per 100 parts by mass of the acrylic pressure-sensitive adhesive polymer (A).

[0102] (plasticizer) The pressure-sensitive adhesive composition may contain a plasticizer. Examples of the plasticizer include phthalates such as di-n-butyl phthalate, di-n-octyl phthalate, bis(2-ethylhexyl) phthalate, and di-n-decyl phthalate; adipates such as bis(2-ethylhexyl) adipate and di-n-octyl adipate; sebacates; azelaates; paraffins such as chlorinated paraffin; glycols such as polypropylene glycol; epoxy-modified vegetable oils such as epoxidized soybean oil and epoxidized linseed oil; phosphates such as trioctyl phosphate and triphenyl phosphate; phosphites such as triphenyl phosphite; ester oligomers such as esters of adipic acid and 1,3-butylene glycol; low-molecular-weight polymers such as low-molecular-weight polybutene, low-molecular-weight polyisobutylene, and low-molecular-weight polyisoprene; and oils such as process oil and naphthenic oil. The content of the plasticizer is preferably 0 to 20 parts by mass, more preferably 0 to 10 parts by mass, and even more preferably 0 to 5 parts by mass, based on 100 parts by mass of the acrylic adhesive polymer (A).

[0103] Other additives that can be blended into the pressure-sensitive adhesive composition include, for example, antioxidants, ultraviolet absorbers, antiaging agents, flame retardants, mildew inhibitors, silane coupling agents, fillers, colorants, etc. The content of the additives can be appropriately set depending on the various compounds, as long as the effects of the present invention are not impaired.

[0104] When the present pressure-sensitive adhesive composition is a solvent-based adhesive, the solids concentration in the pressure-sensitive adhesive composition (i.e., the ratio of the mass of components other than the solvent in the pressure-sensitive adhesive composition to the total mass of the pressure-sensitive adhesive composition) is not particularly limited, but is preferably 1 to 70 mass%. When the solids concentration is 1 mass% or more, a pressure-sensitive adhesive layer with sufficient thickness can be formed. When the solids concentration is 70 mass% or less, good coating properties can be ensured and a pressure-sensitive adhesive layer with uniform thickness can be easily formed. The solids concentration in the pressure-sensitive adhesive composition is more preferably 5 to 50 mass%, and even more preferably 10 to 45 mass%.

[0105] The viscosity of the pressure-sensitive adhesive composition is preferably 500 to 10,000 mPa·s. A viscosity of 10,000 mPa·s or less ensures good coatability. Furthermore, the pressure-sensitive adhesive composition can be used as is without diluting it to a viscosity suitable for coating, resulting in good handleability. From these perspectives, the viscosity of the pressure-sensitive adhesive composition is more preferably 8,000 mPa·s or less, and even more preferably 6,000 mPa·s or less. Furthermore, in order to prevent the film thickness from becoming too thin, the lower limit of the viscosity of the pressure-sensitive adhesive composition is more preferably 1,000 mPa·s or more, and even more preferably 1,500 mPa·s or more. The viscosity of the pressure-sensitive adhesive composition is a value measured at 25°C using a B-type viscometer on a pressure-sensitive adhesive composition with a solids concentration of 25%.

[0106] <Formation of adhesive layer> The pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet can be formed by applying the pressure-sensitive adhesive composition to a separator or the like, and optionally drying the composition. Resin films made of various resin materials can be used as the separator. Examples of resin materials constituting the resin film include polyester resins such as polyethylene terephthalate, polyethersulfone resins, acetate resins, polycarbonate resins, and polyolefin resins.

[0107] When forming a pressure-sensitive adhesive layer using a solvent-based pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition is first applied to a separator by a known coating method, and the solvent is preferably removed by a drying treatment such as heating. The heating temperature and heating time for forming the pressure-sensitive adhesive layer may be any temperature and time that allows for the removal of the solvent, and may be appropriately set depending on the type of solvent contained in the pressure-sensitive adhesive composition, the solids concentration, and the like. The thickness of the pressure-sensitive adhesive layer is, for example, 2 to 200 μm. To achieve the desired thickness of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer may be formed by laminating multiple thin films.

[0108] One embodiment of the present pressure-sensitive adhesive sheet obtained in this manner is a so-called substrate-less embodiment in which the pressure-sensitive adhesive layer is sandwiched between two separators with different peel strengths. The present pressure-sensitive adhesive sheet may also have a configuration in which a substrate is disposed on one side of the pressure-sensitive adhesive layer and a separator is disposed on the other side. The shape of the pressure-sensitive adhesive sheet is not particularly limited and can be appropriately determined depending on the mode of use. The pressure-sensitive adhesive sheet may be, for example, in the form of a sheet, a roll, or cut into strips. It may also have any shape depending on the location of adhesion.

[0109] <Gel fraction (before curing)> The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20%. By making the gel fraction of the pressure-sensitive adhesive layer less than 20%, a pressure-sensitive adhesive sheet exhibiting good conformability to irregularities can be obtained. The gel fraction referred to here is the gel fraction before the pressure-sensitive adhesive sheet is irradiated with active energy rays to cure the pressure-sensitive adhesive layer. From the viewpoint of achieving excellent conformability to irregularities of the pressure-sensitive adhesive sheet, the gel fraction of the pressure-sensitive adhesive layer is preferably 15% or less, more preferably 10% or less, even more preferably 7% or less, even more preferably 5% or less, and even more preferably 2% or less. In this specification, the gel fraction of the pressure-sensitive adhesive layer is the ratio of the mass W2 of the pressure-sensitive adhesive layer remaining after solvent immersion to the initial mass W1 of the pressure-sensitive adhesive layer. Details will be determined according to the measurement method described in the Examples below.

[0110] <Method of manufacturing laminate> After being attached to an adherend, the pressure-sensitive adhesive sheet is irradiated with active energy rays, which cures the pressure-sensitive adhesive layer, thereby improving adhesion to the adherend. For example, to bond a first adherend and a second adherend using the pressure-sensitive adhesive sheet, the first and second adherends are first arranged so as to sandwich the pressure-sensitive adhesive layer, forming a laminate consisting of the first adherend / pressure-sensitive adhesive layer / second adherend. Next, the laminate is irradiated with active energy rays to cure the pressure-sensitive adhesive layer (curing step). This results in a laminate in which the first adherend and the second adherend are bonded with high adhesive strength via the adhesive layer.

[0111] Examples of the active energy ray irradiated to the pressure-sensitive adhesive layer include ultraviolet light, visible light, and electron beams. Of these, ultraviolet light or electron beams are preferred. The active energy ray may be irradiated to only one side or both sides of the substrate coated with the pressure-sensitive adhesive composition. The irradiation energy can be appropriately set depending on the type of active energy ray, the formulation composition of the pressure-sensitive adhesive layer, etc.

[0112] For example, when ultraviolet rays are used as the active energy rays, the wavelength is, for example, 250 to 400 nm. Examples of ultraviolet irradiation devices include high-pressure mercury lamps, metal halide lamps, ultraviolet electrodeless lamps, and ultraviolet light-emitting diodes (UV-LEDs). The cumulative light amount is 500 mJ / cm. 2 More than 1,000mJ / cm is preferable. 2 More preferably, 1,500 mJ / cm 2 The upper limit of the cumulative light amount is preferably 100,000 mJ / cm from the viewpoint of minimizing the influence on each component in the pressure-sensitive adhesive layer and from the viewpoint of reducing energy. 2 Less than 50,000mJ / cm is preferred 2 The following is more preferred:

[0113] The illuminance and irradiation time of the ultraviolet light can be appropriately set so that the integrated light amount is a desired amount. For example, the illuminance is 1.0 mW / cm 2 More than 2.0 mW / cm is preferable. 2 More preferably, 3.0 mW / cm or more 2 More preferably, the upper limit of the illuminance is 150 mW / cm. 2 Less than 120mW / cm is preferable. 2 Less than 100 mW / cm is more preferable. 2 The following is even more preferred:

[0114] When electron beams are used as the active energy rays, the electron beam irradiation device is not particularly limited, but examples include Cockcroft-Walton type, Van de Graaff type, and resonant transformer type devices. The absorbed dose of the electron beam is preferably 1 to 200 kGy, more preferably 10 to 100 kGy. The acceleration voltage of the electron beam may be appropriately set within the range of 80 to 300 kV depending on the film thickness of the substrate. The oxygen concentration of the electron beam irradiation atmosphere is preferably 500 ppm or less, more preferably 300 ppm or less.

[0115] <Gel fraction (after curing)> The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is cured by irradiation with active energy rays, thereby improving cohesive strength and also improving solvent resistance and oil resistance. After the pressure-sensitive adhesive layer is cured by irradiation with active energy rays, the gel fraction of the pressure-sensitive adhesive layer based on the acrylic adhesive polymer (A) is preferably 20% or more. From the viewpoint of improving cohesive strength and adhesive performance as well as improving solvent resistance, the gel fraction of the pressure-sensitive adhesive layer after curing is more preferably 30% or more, even more preferably 50% or more, even more preferably 60% or more, and even more preferably 65% ​​or more. Here, the gel fraction of the pressure-sensitive adhesive layer after curing refers to the gel fraction when irradiated with active energy rays under irradiation conditions that decompose the photopolymerization initiator. Specific irradiation conditions can be, for example, the irradiation conditions described in the Examples below. The gel fraction of the pressure-sensitive adhesive layer after curing can be adjusted by, for example, the content of structural units derived from (meth)acrylic acid alkoxyalkyl ester in the acrylic adhesive polymer (A).

[0116] The PSA sheet thus obtained can be used as a PSA in a wide range of applications, including clothing (including clothing accessories), sports goods (such as sportswear, sports shoes, sports gloves, and bat and racket grips), medical supplies (such as supports and corsets), automotive interior and exterior parts, outdoor goods, handicraft supplies, toys, household goods, household items, and furniture.

[0117] For example, when the present pressure-sensitive adhesive sheet is used as an adhesive for bonding textile fabrics together, the textile fabrics to which it can be applied are not particularly limited, and examples include synthetic fibers such as polyester, polyamide, and acrylic fibers; regenerated fibers such as rayon and cupra; semi-synthetic fibers such as acetate; and natural fibers such as cotton, linen, and wool. Furthermore, the textile products produced using the present pressure-sensitive adhesive sheet are also not particularly limited, and the sheet can be used as an adhesive in the production of a wide range of clothing, such as everyday Western and Japanese clothing, ethnic clothing, underwear (e.g., seamless lingerie and innerwear), outerwear, tops, bottoms, outdoor gear, workwear, uniforms, formal wear, swimwear, sportswear, socks, hats, shoes, and the like, as well as for handicrafts and other purposes.

[0118] Furthermore, when the pressure-sensitive adhesive sheet is used as an adhesive for attaching a decorative film to a molded body, the molded body to which the decorative film is adhered is not particularly limited, and may be any product to which the decorative film can be adhered, such as a resin product, a metal product, a ceramic product, a glass product, etc. Specific examples include various home appliances such as household appliances, kitchen appliances, health appliances, and seasonal appliances; interior and exterior components of housing facilities such as toilets, bathrooms, doors, and walls; automobile interior and exterior components such as bumpers, dashboards, doors, roofs, and hoods; various miscellaneous goods such as household goods and daily necessities; electronic components; nursing care and medical supplies; and interior and exterior components of ships and aircraft. [Example]

[0119] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified. The polymers used in the examples and comparative examples were analyzed as follows.

[0120] <Molecular weight measurement> Using a gel permeation chromatograph (model HLC-8320, manufactured by Tosoh Corporation), the polystyrene-equivalent number average molecular weight (Mn) and weight average molecular weight (Mw) were obtained under the following conditions. The molecular weight distribution (Mw / Mn) was calculated from the obtained values. Measurement conditions Column: Tosoh TSKgel SuperMultiporeHZ-M x 4 Column temperature: 40℃ Eluent: tetrahydrofuran Detector: RI Flow rate: 600μL / min

[0121] <Measurement of glass transition temperature (Tg)> The glass transition temperature (Tg) of the polymer was determined from the intersection of the baseline and the tangent at the inflection point of the heat flux curve obtained using a differential scanning calorimeter. The heat flux curve was obtained by cooling approximately 10 mg of a sample to -50°C, holding it for 5 minutes, then heating it at 10°C / min to 300°C, cooling it to -50°C, holding it for 5 minutes, and then heating it at 10°C / min to 350°C. Measuring equipment: SII NanoTechnology DSC6220 Measurement atmosphere: Nitrogen atmosphere The glass transition temperatures of the polymer block M and the acrylic polymer block N were determined by producing a polymer consisting of the polymer block M and a polymer consisting of the acrylic polymer block N, respectively, and performing differential scanning calorimetry (DSC) measurement according to the above-mentioned measurement method.

[0122] <Calculation of the monomer composition of a polymer> The monomer composition of the resulting polymer was calculated from the charged amounts and the amounts of consumed monomers measured by gas chromatography (GC).

[0123] 1. Synthesis of acrylic adhesive polymer (A) [Synthesis Example 1] Polymer A-1 used in Examples 1 to 6 and Comparative Examples 2 and 3 A 3-liter four-neck flask was charged with 2-methoxyethyl acrylate (hereinafter also referred to as "MEA") (421 parts by mass), 2-hydroxyethyl acrylate (hereinafter also referred to as "HEA") (21 parts by mass), n-butyl acrylate (hereinafter also referred to as "BA") (78 parts by mass), and ethyl acetate (770 parts by mass). The mixture was thoroughly degassed by bubbling nitrogen gas, and the internal temperature of the mixture was raised to 75°C. 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as "V-65") (0.35 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-1. The obtained polymer A-1 consisted of 80 mass % of MEA, 15 mass % of BA, and 5 mass % of HEA, and had a Mw of 800,000, a Mw / Mn of 8.7, and a Tg of -35°C.

[0124] [Synthesis Example 2] Polymer A-2 used in Examples 7 to 9 A 1 L flask equipped with a stirrer and thermometer was charged with 3.18 parts by mass of dibenzyl trithiocarbonate (hereinafter also referred to as "DBTTC") as a RAFT agent, 0.51 parts by mass of 2,2'-azobis(2-methylbutyronitrile) (hereinafter also referred to as "ABN-E") as a polymerization initiator, 75 parts by mass of styrene (hereinafter also referred to as "St") and 125 parts by mass of N-phenylmaleimide (hereinafter also referred to as "PhMI") as monomers, and 466 parts by mass of acetonitrile as a solvent. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was initiated in a thermostatic chamber at 70 °C. After 3 hours, the reaction was stopped by cooling to room temperature. The resulting polymerization solution was purified by reprecipitation from methanol and vacuum dried to obtain polymer block M. The resulting polymer block M had an Mn of 10,900 and a Tg of 206 °C. Next, the resulting polymer block M (21.1 parts by mass), ABN-E (0.08 parts by mass) as a polymerization initiator, MEA (234 parts by mass), BA (51 parts by mass), and HEA (15 parts by mass) as monomers, and acetonitrile (107 parts by mass) as a solvent were charged into a 1 L flask equipped with a stirrer and thermometer. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was initiated in a thermostatic bath at 70 °C. After 6 hours, the mixture was cooled to room temperature, and the solids concentration was adjusted to 30% by mass by adding acetonitrile to obtain an acetonitrile solution of an MNM triblock copolymer having polymer block M and acrylic polymer block N (referred to as polymer A-2). The resulting polymer A-2 had an Mw of 280,000 and an Mw / Mn of 1.8. The Tg of the acrylic polymer block N was -34 °C.

[0125] [Synthesis Example 3] Polymer A-3 used in Example 10 A 2-liter four-neck flask was charged with MEA (255 parts by mass), BA (30 parts by mass), HEA (15 parts by mass), and ethyl acetate (520 parts by mass). The mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 40°C, and V-65 (11.4 parts by mass) was charged to initiate polymerization. After 4 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-3. The resulting polymer A-3 consisted of 80% by mass of MEA, 15% by mass of BA, and 5% by mass of HEA, and had a Mw of 520,000, a Mw / Mn of 6.5, and a Tg of -35°C.

[0126] [Synthesis Example 4] Polymer A-4 used in Example 11 A 3-liter four-neck flask was charged with MEA (312 parts by mass), HEA (21 parts by mass), BA (182 parts by mass), and ethyl acetate (770 parts by mass). The mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and V-65 (0.35 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-4. The resulting polymer A-4 consisted of 60% by mass of MEA, 35% by mass of BA, and 5% by mass of HEA, and had a Mw of 800,000, a Mw / Mn of 8.7, and a Tg of -37°C.

[0127] [Synthesis Example 5] Polymer A-5 used in Example 12 A 3-liter four-neck flask was charged with MEA (208 parts by mass), HEA (21 parts by mass), BA (286 parts by mass), and ethyl acetate (770 parts by mass). The mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and V-65 (0.35 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-5. The resulting polymer A-5 consisted of 40% by mass of MEA, 55% by mass of BA, and 5% by mass of HEA, and had an Mw of 730,000, an Mw / Mn of 8.0, and a Tg of -39°C.

[0128] [Synthesis Example 6] Polymer A-6 used in Example 13 A 3-liter four-neck flask was charged with MEA (104 parts by mass), HEA (21 parts by mass), BA (309 parts by mass), and ethyl acetate (770 parts by mass). The mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and V-65 (0.35 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-6. The resulting polymer A-6 consisted of 20% by mass of MEA, 75% by mass of BA, and 5% by mass of HEA, and had a Mw of 750,000, a Mw / Mn of 8.1, and a Tg of -40°C.

[0129] [Synthesis Example 7] Polymer A-7 used in Example 14 A 3-liter four-neck flask was charged with 2-ethoxyethyl acrylate (hereinafter also referred to as "EEA") (420 parts by mass), HEA (21 parts by mass), BA (78 parts by mass), and ethyl acetate (770 parts by mass). This mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and V-65 (0.35 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-7. The resulting polymer A-7 consisted of 80% by mass of EEA, 15% by mass of BA, and 5% by mass of HEA, and had a Mw of 780,000, a Mw / Mn of 8.7, and a Tg of -56°C.

[0130] [Synthesis Example 8] Polymer A-8 used in Example 15 A 3-liter four-neck flask was charged with MEA (182 parts by mass), HEA (21 parts by mass), methyl acrylate (hereinafter also referred to as "MA") (312 parts by mass), and ethyl acetate (770 parts by mass). This mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and V-65 (0.35 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-8. The resulting polymer A-8 consisted of 60% by mass of MA, 35% by mass of MEA, and 5% by mass of HEA, and had a Mw of 760,000, a Mw / Mn of 8.4, and a Tg of -10°C.

[0131] [Synthesis Example 9] Polymer A-9 used in Comparative Example 1 A 3-liter four-neck flask was charged with HEA (24 parts by mass), BA (506 parts by mass), and ethyl acetate (974 parts by mass). The mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and V-65 (0.25 parts by mass) was charged to initiate polymerization. After 5 hours, ethyl acetate was added to adjust the solids content to 30% by mass, yielding an ethyl acetate solution of polymer A-9. The resulting polymer A-9 consisted of 95% by mass of BA and 5% by mass of HEA, and had a Mw of 470,000, a Mw / Mn of 5.4, and a Tg of -41°C.

[0132] 2. Preparation of adhesive composition and production of adhesive sheet [Example 1] A pressure-sensitive adhesive composition was prepared by adding 0.1 parts by mass of the intramolecular cleavage-type photopolymerization initiator "ESACURE ONE" (purchased from DKSH Japan Co., Ltd.) relative to 100 parts by mass of polymer A-1 (equivalent to 100 parts by mass of solids) to an ethyl acetate solution of polymer A-1 obtained in Synthesis Example 1. This pressure-sensitive adhesive composition was applied to a 50 μm-thick polyethylene terephthalate (PET) separator so that the thickness of the pressure-sensitive adhesive layer after drying would be 100 μm. The pressure-sensitive adhesive composition was dried at 100°C for 6 minutes to remove ethyl acetate. After drying, a 38 μm-thick PET separator with a different peel strength from the separator was attached to obtain a pressure-sensitive adhesive sheet sample with a double-sided separator. The resulting pressure-sensitive adhesive sheet sample was subjected to various evaluations using the methods described below. The evaluation results are shown in Table 1.

[0133] <Evaluation method> Gel fraction measurement (before UV irradiation) 0.2 g of adhesive was collected from the adhesive layer of the adhesive sheet sample, and the initial mass of the adhesive was weighed. The adhesive was immersed in 50 g of ethyl acetate and allowed to stand at room temperature for 16 hours. It was then filtered through a 200-mesh wire netting, and the residue remaining on the mesh was dried at 80°C for 3 hours and weighed. The gel fraction based on the acrylic adhesive polymer (A) was calculated from the initial mass and the mass of the residue using the following formula: Gel fraction (%)=(mass of residue) / [(initial mass)×(solid content of acrylic adhesive polymer (A)) / (solid content of entire adhesive composition)]×100

[0134] Gel fraction measurement (after UV irradiation) With a polyester fabric placed on top of the adhesive sheet, UV irradiation treatment was performed through the polyester fabric under the following UV irradiation conditions, and the gel fraction of the adhesive sheet sample after UV irradiation treatment was measured using the same method as above. (UV irradiation conditions) After the bonding, the laminate was irradiated with a UV-LED surface irradiation device (model: HLDL-470X370U65PSCSP) manufactured by CCS Inc. at a wavelength of 365 nm and an illuminance of 50 mW / cm.2 The irradiance and the cumulative light amount were measured using an ultraviolet integrating actinometer "UIT-250" manufactured by Ushio Inc. (center wavelength of the light receiving part: 365 nm).

[0135] -Unevenness tracking evaluation Two sheets of polyester fabric were bonded together using a pressure-sensitive adhesive sheet sample cut to a width of 10 mm, to obtain a laminate in the order polyester fabric / pressure-sensitive adhesive sheet sample / polyester fabric. The obtained laminate was subjected to a heat press treatment (conditions: 130°C, 3 kg / cm 2 When the laminate was peeled off by hand after pressing, if the adhesive broke inside the adhesive while peeling off, it was judged as "Good" because it had good conformability to the unevenness of the fabric, and if it peeled off at the fabric interface, it was judged as "Poor" because it had insufficient conformability to the unevenness of the fabric.

[0136] Solvent resistance evaluation The laminate was produced using the same procedures as in the evaluation of conformability above, and then irradiated with UV light. It was placed in a 250 mL glass bottle, to which 200 mL of perchloroethylene was added and stirred with a mix rotor for 1 hour. The test piece was then dried at 130°C for 5 minutes and evaluated for peeling of the adhesive. Those that showed no peeling were rated as "Good", and those that showed peeling were rated as "Poor".

[0137] High temperature peel test A laminate was produced using the same procedures as in the evaluation of the conformability of the sample to irregularities, and then irradiated with UV light. The laminate was used as a test piece, and the T-peel strength was measured using an INSTRON 5566A tensile tester (manufactured by Instron Japan) at a measurement temperature of 80°C, a test piece width of 10 mm, and a peel speed of 300 mm / min, to determine the high-temperature peel strength.

[0138] [Example 2] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that the amount of photopolymerization initiator "ESACURE ONE" added was 0.25 parts by mass, and various evaluations were carried out in the same manner as in Example 1. [Example 3] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that the amount of photopolymerization initiator "ESACURE ONE" added was 0.5 parts by mass, and various evaluations were carried out in the same manner as in Example 1. [Example 4] A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that 0.5 parts by mass of the photopolymerization initiator "ESACURE ONE" and 0.1 parts by mass, converted into solids, of the isocyanate-based curing agent "Takenate D-110N" manufactured by Mitsui Chemicals (an ethyl acetate solution with a solids content of 75%) were added. Furthermore, a pressure-sensitive adhesive sheet sample with a double-sided separator was obtained using the obtained pressure-sensitive adhesive composition in the same manner as in Example 1. The pressure-sensitive adhesive sheet sample was aged in an atmosphere of 40°C for 5 days to promote the reaction of the isocyanate-based curing agent, and the obtained pressure-sensitive adhesive sheet sample was subjected to various evaluations in the same manner as in Example 1.

[0139] [Example 5] An adhesive composition was produced by the same procedure as in Example 1, except that 0.1 parts by mass of a hydrogen abstraction type photopolymerization initiator, "SPEEDCURE PBZ" (purchased from DKSH Japan), was added, and various evaluations were carried out in the same manner as in Example 1. [Example 6] A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that 0.3 parts by mass of the photopolymerization initiator "SPEEDCURE PBZ" was added, and various evaluations were carried out in the same manner as in Example 1. [Example 7] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-2 obtained in Synthesis Example 2 was used instead of polymer A-1 and 1.0 part by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were carried out in the same manner as in the examples.

[0140] [Example 8] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-2 obtained in Synthesis Example 2 was used instead of polymer A-1 and 3.0 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1. [Example 9] A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that polymer A-2 obtained in Synthesis Example 2 was used instead of polymer A-1, 3.0 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and 0.1 parts by mass of "Takenate D-110N" manufactured by Mitsui Chemicals, an isocyanate-based curing agent, was added. Furthermore, a pressure-sensitive adhesive sheet sample with a double-sided separator was obtained using the obtained pressure-sensitive adhesive composition in the same manner as in Example 1. The pressure-sensitive adhesive sheet sample was aged in an atmosphere of 40°C for 5 days to promote the reaction of the isocyanate-based curing agent, and the obtained pressure-sensitive adhesive sheet sample was subjected to various evaluations in the same manner as in Example 1.

[0141] [Example 10] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-3 obtained in Synthesis Example 3 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1. [Example 11] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-4 obtained in Synthesis Example 4 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1. [Example 12] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-5 obtained in Synthesis Example 5 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1.

[0142] [Example 13] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-6 obtained in Synthesis Example 6 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1. [Example 14] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-7 obtained in Synthesis Example 7 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1. [Example 15] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-8 obtained in Synthesis Example 8 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1.

[0143] [Comparative Example 1] A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that polymer A-9 obtained in Synthesis Example 9 was used instead of polymer A-1 and 0.25 parts by mass of "ESACURE ONE" was added as a photopolymerization initiator, and various evaluations were performed in the same manner as in Example 1. Comparative Example 2 A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that the photopolymerization initiator "ESACURE ONE" was not added, and various evaluations were carried out in the same manner as in Example 1. Comparative Example 3 A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that "ESACURE ONE" was not added as a photopolymerization initiator to polymer A-1, and 0.5 parts by mass of "Takenate D-110N" manufactured by Mitsui Chemicals, an isocyanate-based curing agent, was added. In addition, a pressure-sensitive adhesive sheet sample with a double-sided separator was obtained using the obtained pressure-sensitive adhesive composition in the same manner as in Example 1, and this pressure-sensitive adhesive sheet sample was used to perform various evaluations in the same manner as in Example 1. Comparative Example 4 A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that polymer A-2 obtained in Synthesis Example 2 was used instead of polymer A-1, and the photopolymerization initiator "ESACURE ONE" was not added, and various evaluations were performed in the same manner as in Example 1.

[0144] The compositions and evaluation results of the pressure-sensitive adhesive compositions of Examples 1 to 15 and Comparative Examples 1 to 4 are shown in Tables 1 and 2. Note that, for the triblock copolymer (polymer A-2) obtained in Synthesis Example 2, the composition *1 The column indicates the monomer composition of the acrylic polymer block N, and the composition *2 The column indicates the monomer composition of the polymer block M.

[0145] [Table 1]

[0146] [Table 2]

[0147] The abbreviations in Tables 1 and 2 represent the following names. MEA: 2-Methoxyethyl acrylate EEA: 2-ethoxyethyl acrylate BA: n-butyl acrylate MA: methyl acrylate HEA: 2-hydroxyethyl acrylate St: styrene PhMI: N-phenylmaleimide D-110: Isocyanate curing agent, product name "Takenate D-110N", manufactured by Mitsui Chemicals ESACURE ONE: Intramolecular cleavage type photopolymerization initiator, product name "ESACURE ONE", purchased from DKSH Japan Co., Ltd. PBZ: Hydrogen abstraction photoinitiator, product name "SPEEDCURE PBZ", purchased from DKSH Japan The amounts of the crosslinking agent and the photopolymerization initiator are based on 100 parts by mass of the acrylic adhesive polymer (A).

[0148] As shown in Tables 1 and 2, all of the pressure-sensitive adhesive sheets of Examples 1 to 15, which were produced using a pressure-sensitive adhesive composition containing an acrylic pressure-sensitive adhesive polymer (A) having (meth)acrylic acid alkoxyalkyl ester units and a photopolymerization initiator, exhibited good conformability, solvent resistance, and high-temperature adhesion. In particular, Examples 1 to 12 and 14, which showed a large difference in gel fraction before and after UV irradiation after bonding the pressure-sensitive adhesive sheet to the adherend (polyester fabric), were rated "Good" for both conformability and solvent resistance, and also showed a high high-temperature peel strength of 1.4 N / 10 mm.

[0149] In contrast, Comparative Example 1, in which a polymer not having a (meth)acrylic acid alkoxyalkyl ester unit was used as the acrylic adhesive polymer, and Comparative Examples 2 to 4, in which no photopolymerization initiator was blended into the adhesive composition, were rated as "x" for solvent resistance and also had low high-temperature peel strength. In Comparative Example 3, in which the blending amount of crosslinking agent in the adhesive composition was increased, the gel fraction of the adhesive sheet before attachment to the adherend was as high as 72.3%, and in this case, the unevenness-following ability was rated as "x".

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive polymer (A) and a photopolymerization initiator, and does not contain a compound having a reactive unsaturated bond; the acrylic adhesive polymer (A) contains structural units derived from an alkoxyalkyl (meth)acrylate in an amount of 20 mass% or more based on all structural units derived from monomers constituting the acrylic adhesive polymer (A); The weight average molecular weight of the acrylic adhesive polymer (A) is 520,000 or more, A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20%.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the acrylic pressure-sensitive adhesive polymer (A) has a glass transition temperature of -80°C to 10°C.

3. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive polymer (A) and a photopolymerization initiator, and does not contain a compound having a reactive unsaturated bond; the acrylic adhesive polymer (A) is a block copolymer having a polymer block M and an acrylic polymer block N, and contains structural units derived from an alkoxyalkyl (meth)acrylate in an amount of 20 mass% or more based on all structural units derived from monomers constituting the acrylic adhesive polymer (A); the glass transition temperature of the acrylic polymer block N is −80° C. to 10° C., A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20%.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of 20% or more after the pressure-sensitive adhesive layer is cured by irradiation with active energy rays.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the photopolymerization initiator is a hydrogen abstraction photopolymerization initiator.

6. a step of laminating a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer to an adherend, and then irradiating the pressure-sensitive adhesive layer with active energy rays to cure the pressure-sensitive adhesive layer; the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive polymer (A) and a photopolymerization initiator, and does not contain a compound having a reactive unsaturated bond; the acrylic adhesive polymer (A) is a block copolymer having a polymer block M and an acrylic polymer block N, the acrylic polymer block N having a glass transition temperature of −80° C. to 10° C., and having structural units derived from an alkoxyalkyl (meth)acrylate in an amount of 20 mass% or more based on all structural units derived from monomers constituting the acrylic adhesive polymer (A); The method for producing a laminate, wherein the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20%.

7. The method for producing a laminate according to claim 6, wherein the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of 20% or more after the pressure-sensitive adhesive layer is cured by irradiation with active energy rays.

8. The method for producing a laminate according to claim 6 or 7, wherein the photopolymerization initiator is a hydrogen abstraction photopolymerization initiator.

Images