JP7589604B2 - Pressure-sensitive adhesive sheet, its manufacturing method, and laminate manufacturing method - Google Patents

Description

The present invention relates to a pressure-sensitive adhesive sheet and a method for manufacturing the same, as well as a method for manufacturing a laminate.

It is known that crosslinking of adhesives improves their cohesive strength at room temperature and at high temperatures, as well as their resistance to solvents and oils. Generally, crosslinking of adhesives is performed by incorporating a crosslinking agent such as an isocyanate-based curing agent into the adhesive layer and crosslinking the adhesive by heat, or by polymerizing a polyfunctional monomer with ultraviolet light (see, for example, Patent Document 1 and Patent Document 2).

Patent Document 1 discloses the production of an 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 relative to all monomer units, and a crosslinking agent. In addition, Patent Document 2 discloses the formation of an adhesive layer using a composition containing a thermally crosslinkable adhesive having a weight average molecular weight of less than 300,000 and a thermal crosslinking agent.

International Publication No. 2018/235217 JP 2017-197604 A

When attaching an adhesive sheet to a textile fabric or attaching a decorative sheet to an article, the adherend may have large surface irregularities. However, as in Patent Documents 1 and 2, adhesive sheets with crosslinked adhesive layers cannot conform to the uneven shape of an adherend with large surface irregularities, and are prone to peeling in harsh environments such as high temperatures, raising concerns about poor adhesion (particularly unevenness-following ability and high-temperature adhesion). In addition, one of the properties required of the adhesive layer is high solvent resistance.

The present invention was made in consideration of the above circumstances, and its main objective is to provide an adhesive sheet that has excellent conformability, solvent resistance, and high-temperature adhesion.

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 focus, they have discovered that the adhesive sheet's unevenness-following ability, solvent resistance, and high-temperature adhesion can be improved by incorporating a specific component into the adhesive layer, and have completed the present invention. Specifically, the present invention provides the following means.

[1] An adhesive sheet having an adhesive layer, the adhesive layer containing an acrylic adhesive polymer (A) and a thermal polymerization initiator, the acrylic adhesive polymer (A) having a structural unit derived from an (meth)acrylic acid alkoxyalkyl ester, the gel fraction of the adhesive layer based on the acrylic adhesive polymer (A) being less than 20%, and the gel fraction of the adhesive layer based on the acrylic adhesive polymer (A) after heat treatment being 20% or more.

[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] A method for producing a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, comprising: irradiating with active energy rays a layer made of a pressure-sensitive adhesive composition containing an acrylic adhesive polymer syrup, a photopolymerization initiator, and a thermal polymerization initiator, to form the pressure-sensitive adhesive layer containing an acrylic adhesive polymer (A) and a thermal polymerization initiator, wherein the acrylic adhesive polymer syrup contains a (meth)acrylic acid alkoxyalkyl ester, the pressure-sensitive adhesive layer has a gel fraction based on the acrylic adhesive polymer (A) of less than 20 mass%, and the pressure-sensitive adhesive layer after heat treatment has a gel fraction based on the acrylic adhesive polymer (A) of 20% or more.
[5] A method for producing a laminate, comprising the steps of laminating the pressure-sensitive adhesive sheet according to any one of [1] to [3] above to an adherend, and then carrying out a heat treatment to cure the pressure-sensitive adhesive layer.

According to the present invention, it is possible to obtain an adhesive sheet that has excellent conformability, solvent resistance, and high-temperature adhesion.

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

<Adhesive sheet>
The pressure-sensitive adhesive sheet of the present invention (hereinafter also referred to as "the pressure-sensitive adhesive sheet") is a sheet having a pressure-sensitive adhesive layer containing an acrylic adhesive polymer (A) and a thermal polymerization initiator. The pressure-sensitive adhesive sheet is a thermally reactive pressure-sensitive adhesive sheet that is used by laminating the pressure-sensitive adhesive layer and an adherend together, and then applying heat to the laminate to cure the pressure-sensitive adhesive layer.

Here, in this adhesive sheet, the crosslinking reaction proceeds by performing a heat treatment after laminating the adhesive layer and the adherend. This forms a crosslinked structure, and excellent adhesive performance and solvent resistance are expressed. The mechanism is speculated as follows. When the adhesive layer and the adherend are laminated and then heated, radicals are generated by the thermal polymerization initiator in the adhesive layer, and hydrogen is extracted from the side chain portion of the acrylic acid alkoxyalkyl ester constituting the acrylic adhesive polymer (A), and a peroxy radical is generated by bonding with oxygen (see the scheme below). After that, a hydrogen abstraction reaction occurs again, and the generated radicals are coupled with each other to form a crosslinked structure. Therefore, according to this adhesive sheet, even if the 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 adhesive layer and the adherend and performing a heat treatment. In addition, when the adhesive layer of this adhesive sheet is attached to an adherend, the adhesive layer is flexible because the crosslinked structure has not yet been formed, and the adhesive layer can be attached to an adherend that has a large surface irregularity by following the irregularities of the surface. This is thought to result in an adhesive sheet that has good irregularity-following properties.

Next, we will explain the acrylic adhesive polymer (A) and the thermal polymerization initiator contained in the adhesive layer of this adhesive sheet.

<Acrylic adhesive polymer (A)>
The acrylic adhesive polymer (A) is a polymer mainly composed of structural units derived from (meth)acrylic monomers, and has adhesiveness.In this specification, the acrylic adhesive polymer (A) is "mainly composed" of (meth)acrylic monomers, and the ratio of the structural units derived from (meth)acrylic monomers to all structural units derived from the 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.

The acrylic adhesive polymer (A) has a structural unit derived from an alkoxyalkyl ester of (meth)acrylic acid. The alkoxyalkyl ester of (meth)acrylic acid constituting the acrylic adhesive polymer (A) preferably has an alkoxyalkyl group having 2 to 12 carbon atoms. Specific examples of these 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.

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.

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 (meth)acrylic acid alkoxyalkyl ester and oxygen radicals, and improving the adhesiveness, solvent resistance, and step-following ability of the 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).

The monomer constituting the acrylic adhesive polymer (A) may be only an alkoxyalkyl ester (meth)acrylate, but may also contain a monomer different from the alkoxyalkyl ester (meth)acrylate (hereinafter also referred to as "other monomer").

From the viewpoint of achieving excellent adhesive performance, it is preferable that the acrylic adhesive polymer (A) 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.

Specific examples of alkyl (meth)acrylates 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.

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 portion has 1 to 8 carbon atoms are preferred, and (meth)acrylic acid alkyl esters in which the alkyl portion has 1 to 4 carbon atoms are more preferred.

Specific examples of hydroxyalkyl (meth)acrylates 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.

In the acrylic adhesive polymer (A), the proportion of structural units derived from (meth)acrylic acid alkyl esters 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 esters is not particularly limited, but from the viewpoint of sufficient crosslinking formation by (meth)acrylic acid alkoxyalkyl esters, 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).

In the acrylic adhesive polymer (A), the proportion of structural units derived from (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 (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 sufficient crosslinking formation by the (meth)acrylic acid alkoxyalkyl ester.

In addition to the above, the acrylic adhesive polymer (A) may also use a monomer that is copolymerizable with the above monomer, as long as 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.

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.

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.

Examples of polyalkylene glycol mono(meth)acrylate compounds 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, nonylphenoxypolyethylene glycol mono(meth)acrylate, and nonylphenoxypolyethylene glycol-polypropylene glycol mono(meth)acrylate.

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, p-t-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, etc.

Examples of imide group-containing vinyl compounds 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 citraconimide 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.

Examples of amino group-containing unsaturated compounds 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, 3-(di-n-propylamino)propyl (meth)acrylate, etc.

Examples of amide group-containing unsaturated compounds 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.

Examples of nitrile group-containing unsaturated compounds 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, α-fluoroacrylonitrile, etc.

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.

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

When using solution polymerization, the manufacturing method involves charging an organic solvent and monomers into a reactor, adding a polymerization initiator, and heating to 50 to 300°C to polymerize.

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 fed continuously into the reactor, or a continuous polymerization method in which all raw materials are fed continuously and the resulting resin is simultaneously continuously withdrawn from the reactor.

Examples of organic solvents used in the solution polymerization method 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, for example, an amount such that the total amount of monomers used in polymerization is 1 to 50% by mass relative to the total amount of organic solvent and monomers.

As the polymerization initiator, known radical polymerization initiators such as azo compounds, organic peroxides, and inorganic peroxides can be used, and are not particularly limited. Among these, azo compounds are preferred because they are safe and easy to handle, and side reactions are unlikely to occur during radical polymerization. Azo compounds are preferred. As the polymerization initiator, a redox type polymerization initiator consisting of a known oxidizing agent and a known reducing agent may also be used. Furthermore, a known chain transfer agent can be used in combination with the polymerization initiator.

Specific examples of polymerization initiators 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).

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.

Examples of inorganic peroxides include potassium persulfate and sodium persulfate. Examples of redox type 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. When producing the acrylic adhesive polymer (A), the amount of polymerization initiator used is, for example, 0.01 to 20 parts by mass per 100 parts by mass of the total monomers used in the polymerization.

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, it is preferable in that the cohesive strength of the adhesive layer can be sufficiently increased and sufficient adhesion can be ensured. From this perspective, 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.

On the other hand, if the Tg of the acrylic adhesive polymer (A) is 10°C or less, it is preferable because it is possible to ensure sufficient adhesion under low-temperature conditions, and 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. 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, even more preferably -5°C or less, and particularly preferably -10°C or less. The range of the Tg of the acrylic adhesive polymer (A) is more preferably from -60°C to 5°C, and even more preferably from -50°C to 0°C.

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.

(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 force 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.

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 further ensuring ease of manufacture, 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).

For the acrylic adhesive polymer (A), the molecular weight distribution (Mw/Mn), 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 adhesion 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.

<Thermal Polymerization Initiator>
The adhesive layer of the present pressure-sensitive adhesive sheet contains a thermal polymerization initiator. The thermal polymerization initiator is a compound that generates radicals when heat is applied. As the thermal polymerization initiator, a known thermal-start radical polymerization initiator can be used. Among them, organic peroxides and azo compounds are preferable as the thermal polymerization initiator contained in the adhesive layer of the present pressure-sensitive adhesive sheet.

Specific examples of organic peroxides include 1,1-bis(t-butylperoxy)2-methylcyclohexane, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(4,4-di-butylperoxycyclohexyl)propane, 1,1 -Bis(t-butylperoxy)cyclododecane, t-hexylperoxyisopropyl monocarbonate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxylaurate, 2,5-dimethyl-2,5-di(m-toluoylperoxy)hexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate t, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxyacetate, 2,2-bis(t-butylperoxy)butane, t-butylperoxybenzoate, n-butyl-4,4-bis(t-butylperoxy)valerate, di-t-butylperoxyisophthalate, α,α'-bis(t-butylperoxy)diisopropylbenzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t -butylcumyl peroxide, di-t-butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, diisopropylbenzene hydroperoxide, t-butyltrimethylsilyl peroxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide, and t-butyl hydroperoxide.

Specific examples of azo compounds include 1,1'-azobis(cyclohexane-1-carbonitrile), 2-(carbamoylazo)isobutyronitrile, 2-phenylazo-4-methoxy-2,4-dimethylvaleronitrile, azodi-t-octane, azodi-t-butane, etc. As the thermal polymerization initiator, one type may be used alone, or two or more types may be used in combination. When an organic peroxide is used, it is also possible to use it in combination with a reducing agent to cause a redox reaction.

The content of the thermal polymerization initiator in the adhesive layer is preferably 0.05 parts by mass or more relative to 100 parts by mass of the acrylic adhesive polymer (A). When the content of the thermal polymerization initiator is 0.05 parts by mass or more, it is preferable in that a crosslinked structure can be formed using an acrylic acid alkoxyalkyl ester by the radicals generated in the adhesive layer by the heat treatment. From this viewpoint, the amount of the thermal polymerization initiator contained in the adhesive layer is more preferably 0.08 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). In addition, from the viewpoint of suppressing a decrease in adhesive properties due to excessive formation of a crosslinked structure after the heat treatment, the amount of the thermal polymerization initiator contained in the 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 content of the thermal polymerization initiator referred to here is the amount of the thermal polymerization initiator in the adhesive layer before the adhesive sheet is subjected to a heat treatment and cured.

<Manufacturing of adhesive sheets>
The pressure-sensitive adhesive sheet can be produced by applying the pressure-sensitive adhesive composition to a substrate such as a separator to form a pressure-sensitive adhesive layer. There are no particular limitations on the form of the pressure-sensitive adhesive composition, but an active energy ray-curable pressure-sensitive adhesive composition containing an acrylic pressure-sensitive adhesive polymer syrup (hereinafter also referred to as "polymer syrup (Ac)"), a photopolymerization initiator, and a thermal polymerization initiator can be preferably used.

Polymer syrup (Ac)
The active energy ray curable adhesive composition is a so-called syrup type adhesive composition that is cured by active energy rays such as ultraviolet rays and electron beams. The polymer syrup (Ac) contained in the active energy ray curable adhesive composition (hereinafter also simply referred to as the "adhesive composition") is a component that can obtain the acrylic adhesive polymer (A) that constitutes the adhesive layer by irradiation with active energy rays. The polymer syrup (Ac) contains a polymer component that constitutes a part of the acrylic adhesive polymer (A) contained in the adhesive layer and a (meth)acrylic monomer component that constitutes the remainder. Specific embodiments of the polymer syrup (Ac) include, for example, the following embodiments (1) to (3).

(1) A mixture of a polymer component and a (meth)acrylic monomer component obtained by partially polymerizing all of the monomers constituting the acrylic adhesive polymer (A).
(2) A mixture of a polymer component and a monomer component obtained by adding a (meth)acrylic monomer component of the same or different type as the monomer constituting the acrylic adhesive polymer (A) to the mixture (1) above.
(3) A mixture of a polymer component and a (meth)acrylic monomer component, which is obtained by previously preparing a polymer component by a known polymerization method and mixing this polymer component with a desired (meth)acrylic monomer component.

The mixture of the polymer component and the (meth)acrylic monomer component exemplified in (1) to (3) above can generally take the form of a solution in which the polymer component is dissolved in the (meth)acrylic monomer component. That is, the mixture of the polymer component and the (meth)acrylic monomer component is liquid before irradiation with active energy rays, while polymerization proceeds upon irradiation with active energy rays to produce the acrylic adhesive polymer (A).

The polymer component in the polymer syrup (Ac) (i.e., the monomer constituting the acrylic adhesive polymer (A)) and the (meth)acrylic monomer component (i.e., the (meth)acrylate compound) may be of the same type, or at least a part of them may be different types. From the viewpoint of increasing the compatibility between the acrylic adhesive polymer (A) and the (meth)acrylate compound and increasing the transparency of the adhesive layer, it is preferable that the (meth)acrylate compound in the polymer syrup (Ac) is at least a part of the same as the monomer constituting the acrylic adhesive polymer (A), more preferably the same type as the monomer constituting the acrylic adhesive polymer (A), and even more preferably the same composition as the monomer constituting the acrylic adhesive polymer (A). That is, the (meth)acrylate compound contained in the present adhesive composition is preferably the same type as the monomer constituting the acrylic adhesive polymer (A), and more preferably the same composition.

In the polymer syrup (Ac), the ratio of the (meth)acrylic monomer component to the polymer component is not particularly limited as long as the viscosity required for forming a coating film and handling can be obtained. The ratio of the (meth)acrylic monomer component is, for example, 10 parts by mass or more, preferably 20 parts by mass or more, and more preferably 30 parts by mass or more, per 100 parts by mass of the total of the polymer component and the (meth)acrylic monomer component. The upper limit of this ratio is, for example, 99 parts by mass or less, preferably 97 parts by mass or less, and more preferably 95 parts by mass or less, per 100 parts by mass of the total of the polymer component and the (meth)acrylic monomer component.

The weight average molecular weight (Mw) of the polymer component in the polymer syrup (Ac) is preferably 100,000 or more, more preferably 120,000 or more, even more preferably 150,000 or more, and even more preferably 200,000 or more, from the viewpoint of exhibiting good adhesiveness and sufficient cohesive strength. The upper limit of Mw of the polymer component in the polymer syrup (Ac) is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less, from the viewpoint of ease of production. The range of Mw 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.

The molecular weight distribution (Mw/Mn) of the polymer component in the polymer syrup (Ac), expressed as the ratio of Mw to Mn, is preferably 10.0 or less, more preferably 9.5 or less, and even more preferably 9.0 or less, in that good adhesion is easily obtained. The lower limit of Mw/Mn of the polymer syrup (Ac) is not particularly limited, and can be 1.0 or more.

Photopolymerization initiator As the photopolymerization initiator contained in the pressure-sensitive adhesive composition, known polymerization initiators such as photoinitiators can be used. Specific examples of the photopolymerization initiator include benzoin and its alkyl ethers, acetophenones, anthraquinones, thioxanthones, ketals, benzophenones and xanthones, acylphosphine oxides, α-diketones, and α-hydroxyketones. In addition, in order to improve the sensitivity to the active energy rays irradiated to polymerize the polymer syrup (Ac) to obtain the acrylic pressure-sensitive adhesive polymer (A), a benzoic acid-based or amine-based photosensitizer may be used in combination, if necessary.

The content of the photopolymerization initiator in the pressure-sensitive adhesive composition can be, for example, 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polymer syrup (Ac). From the viewpoint of sufficiently progressing the polymerization reaction by irradiation with active energy rays, the content of the photopolymerization initiator is preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more with respect to 100 parts by mass of the polymer syrup (Ac). In addition, the upper limit is preferably 3 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less, in order to prevent the gel fraction of the pressure-sensitive adhesive layer from becoming too high. The content range of the photopolymerization initiator is preferably 0.03 parts by mass or more and 5 parts by mass or less, more preferably 0.05 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the polymer syrup (Ac).

Thermal polymerization initiator The content of the thermal polymerization initiator in the present adhesive composition is preferably 0.05 parts by mass or more relative to 100 parts by mass of the acrylic adhesive polymer (A). If the content of the thermal polymerization initiator is 0.05 parts by mass or more, it is preferable that a sufficient amount of radicals can be generated in the adhesive layer, and the crosslinking structure can be sufficiently formed using the acrylic acid alkoxyalkyl ester. From this viewpoint, the content of the thermal polymerization initiator in the present adhesive composition is more preferably 0.08 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). In addition, from the viewpoint of suppressing the deterioration of adhesive performance due to excessive crosslinking density, the content of the thermal polymerization initiator in the present 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).

Other Components The pressure-sensitive adhesive composition may further contain components other than the polymer syrup (Ac), the photopolymerization initiator, and the thermal polymerization initiator (hereinafter also referred to as "other components"), as long as the effects of the present invention are not impaired. Examples of other components include crosslinkers, tackifiers, plasticizers, antioxidants, UV absorbers, anti-aging agents, flame retardants, antifungal agents, silane coupling agents, fillers, colorants, etc. The content of each of these components can be appropriately set according to the various compounds, as long as the effects of the present invention are not impaired.

The adhesive composition may contain a solvent such as an organic solvent as another component, but it is preferable to use it as a solvent-free type that does not contain any solvents. A solvent-free curable adhesive composition is advantageous in that it is easy to thicken the adhesive layer.

When a crosslinking agent is blended into the adhesive composition, examples of the crosslinking agent (curing agent) include an epoxy compound having two or more epoxy 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, a polyfunctional (meth)acrylic compound, and the like. However, from the viewpoint of improving the step-following ability of the adhesive sheet, it is preferable that the adhesive composition does not contain a crosslinking agent, or, even if a crosslinking agent is blended, the amount is a very small amount.

Specifically, the content of the crosslinking agent in the adhesive composition is preferably 0 to 0.5 parts by mass, and more preferably 0 to 0.3 parts by mass, per 100 parts by mass of the acrylic adhesive polymer (A), from the viewpoint of improving the step-following ability of the adhesive sheet.

<Formation of Pressure-Sensitive Adhesive Layer>
When a pressure-sensitive adhesive layer is produced using the present pressure-sensitive adhesive composition, the method is not particularly limited. For example, the pressure-sensitive adhesive layer can be produced by applying the present pressure-sensitive adhesive composition to a separator or the like, and then irradiating the pressure-sensitive adhesive composition with active energy rays to cure the pressure-sensitive adhesive composition.

As the separator, a resin film made of various resin materials can be used. Examples of the resin material constituting the resin film include polyester-based resins such as polyethylene terephthalate, polyethersulfone-based resins, acetate-based resins, polycarbonate-based resins, polyolefin-based resins, etc.

The coating method can be appropriately selected depending on the purpose, and examples of the coating method include a bar coater, applicator, doctor blade, dip coater, roll coater, spin coater, flow coater, knife coater, comma coater, reverse coater, die coater, lip coater, gravure coater, microgravure coater, and ink jet. The amount of the adhesive composition to be applied can be appropriately selected depending on the application, etc., so that the thickness of the adhesive layer after irradiation with active energy rays is within the desired range.

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

For example, when ultraviolet light is used as the active energy ray, the wavelength is, for example, 250 to 400 nm. Examples of ultraviolet light irradiation devices include high-pressure mercury lamps, metal halide lamps, ultraviolet electrodeless lamps, and ultraviolet light-emitting diodes (UV-LEDs). The integrated light amount is preferably 500 mJ/cm2 or ^more , more preferably 1,000 mJ/cm2 or ^more , and even more preferably 1,500 mJ/cm2 or ^more . In addition, the upper limit of the integrated light amount is preferably 100,000 mJ/cm2 or ^less , and more preferably 50,000 mJ/cm2 or ^less , from the viewpoint of minimizing the influence on each component in the pressure-sensitive adhesive composition and from the viewpoint of reducing energy.

The illuminance and irradiation time of the ultraviolet light can be appropriately set so that the integrated light amount is the desired amount. For example, the illuminance is preferably 0.5 mW/cm2 or ^more , more preferably 1.0 mW/cm2 or ^more , and even more preferably 2.0 mW/ ^cm2 or more. The upper limit of the illuminance is preferably 100 mW/cm2 or ^less , more preferably 80 mW/cm2 or ^less , and even more preferably 50 mW/cm2 or ^less .

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 in 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.

One embodiment of the adhesive sheet thus obtained is a so-called substrate-less embodiment in which the adhesive layer is sandwiched between two separators with different peel strengths. The adhesive sheet may also have a configuration in which a substrate is disposed on one side of the adhesive layer and a separator is disposed on the other side. There are no particular limitations on the shape of the adhesive sheet, and it may be appropriately set depending on the mode of use. The adhesive sheet may be, for example, in the form of a sheet, in the form of a roll, or cut into strips. It may also have any shape depending on the adhesion location.

<Gel fraction (before curing)>
The adhesive layer of the present adhesive sheet has a gel fraction based on the acrylic adhesive polymer (A) of less than 20%. By making the gel fraction of the adhesive layer less than 20%, an adhesive sheet exhibiting good step conformability can be obtained. The gel fraction referred to here is the gel fraction before the adhesive layer is cured (i.e., before the adhesive sheet is subjected to a heat treatment). From the viewpoint of making the adhesive sheet excellent in step conformability, the gel fraction of the 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 adhesive layer is the ratio of the mass W2 of the adhesive layer remaining after immersion in a solvent to the initial mass W1 of the adhesive layer. Details are as follows in the measurement method of the examples described later.

<Method of manufacturing laminate>
The pressure-sensitive adhesive sheet is laminated to an adherend and then heat-treated to harden the pressure-sensitive adhesive layer, thereby improving the adhesion to the adherend. For example, to bond a first adherend and a second adherend with the pressure-sensitive adhesive sheet, the first adherend and the second adherend are first arranged to sandwich the pressure-sensitive adhesive layer, forming a laminate consisting of the first adherend/pressure-sensitive adhesive layer/second adherend. Then, heat is applied to this laminate to harden the pressure-sensitive adhesive layer (hardening step). This allows a laminate to be obtained in which the first adherend and the second adherend are bonded with high adhesive strength via the adhesive layer.

In the heat treatment after laminating the pressure-sensitive adhesive sheet to the adherend, the heating temperature is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 120°C or higher, and even more preferably 130°C or higher, from the viewpoint of sufficiently improving the cohesive strength and solvent resistance by forming a crosslinked structure. The upper limit of the heating temperature is preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower, from the viewpoint of suppressing the effects of heat. The heating time is preferably 0.1 to 60 minutes, and more preferably 0.1 to 30 minutes.

<Gel fraction (after curing)>
The adhesive layer of the present adhesive sheet is cured by applying heat, thereby improving the cohesive force, and improving the solvent resistance and oil resistance. After the adhesive layer is cured by applying heat, the gel fraction of the adhesive layer based on the acrylic adhesive polymer (A) is 20% or more. If the gel fraction of the adhesive layer based on the acrylic adhesive polymer (A) after heat treatment is less than 20%, the adhesive performance is insufficient and the solvent resistance tends to be poor. From the viewpoint of improving the cohesive force to improve the adhesive performance and improving the solvent resistance, the gel fraction of the 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. The gel fraction based on the acrylic adhesive polymer (A) of the adhesive layer after heat treatment here is the gel fraction when the adhesive layer is heated under heating conditions that decompose the thermal polymerization initiator, and the specific heating conditions can be, for example, the heat treatment 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 an alkoxyalkyl (meth)acrylate in the acrylic pressure-sensitive adhesive polymer (A).

The adhesive sheet thus obtained can be used as an adhesive in a wide range of applications. Specifically, it can be used as an adhesive in a variety of applications, such as clothing (including clothing accessories), sports goods (e.g., sportswear, sports shoes, sports gloves, bat and racket grips, etc.), medical supplies (e.g., supports and corsets, etc.), automotive interior and exterior parts, outdoor goods, handicraft supplies, toys, daily goods, household goods, furniture, etc.

For example, when the adhesive sheet is used as an adhesive for bonding textile fabrics together, the textile fabrics to which it is applied are not particularly limited, and examples thereof 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, hemp, and wool. Furthermore, the textile products manufactured using the adhesive sheet are also not particularly limited, and the sheet can be used as an adhesive for the manufacture of a wide range of clothing items, such as everyday Western and Japanese clothing, ethnic clothing, underwear (e.g., seamless lingerie products and innerwear products), jackets, tops, bottoms, outdoor equipment, work clothes, uniforms, formal wear, swimsuits, sportswear, socks, hats, shoes, etc., as well as for handicrafts.

In addition, when the 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 bonnets; various miscellaneous items such as household goods and daily miscellaneous goods; electronic parts; nursing care and medical products; interior and exterior components of ships and aircraft, etc.

The present invention will be specifically explained 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 analysis methods for the polymers used in the examples and comparative examples are as follows.

<Molecular Weight Measurement>
Using a gel permeation chromatograph (model name "HLC-8320", manufactured by Tosoh Corporation), the number average molecular weight (Mn) and weight average molecular weight (Mw) were measured in terms of polystyrene 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°C
Eluent: Tetrahydrofuran Detector: RI
Flow rate: 600μL/min

<Measurement of Glass Transition Temperature (Tg)>
The glass transition temperature (Tg) of the polymer was determined from the intersection of the baseline of the heat flux curve obtained using a differential scanning calorimeter and the tangent at the inflection point. The heat flux curve was obtained under the following conditions: about 10 mg of a sample was cooled to -50°C, held for 5 minutes, heated to 300°C at 10°C/min, cooled to -50°C, held for 5 minutes, and heated to 350°C at 10°C/min.
Measuring equipment: SII NanoTechnology DSC6220
Measurement atmosphere: Nitrogen atmosphere

<Calculation of Monomer Composition of Polymer>
The monomer composition of the resulting polymer was calculated from the charged amounts and the consumed amounts of monomers measured by gas chromatography (GC).

1. Synthesis of acrylic adhesive polymer (A) [Synthesis Example 1] Polymer A-1 used in Examples 1 to 6
Into a 3-liter four-neck flask, 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) were charged. This mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, and 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 so that the solid content was 30% by mass, and an ethyl acetate solution of polymer A-1 was obtained. The obtained polymer A-1 was composed of 80 mass % of MEA, 15 mass % of BA, and 5 mass % of HEA, and had Mn of 92,000, Mw/Mn of 8.7, and Tg of -35°C.

[Synthesis Example 2] Polymer A-2 used in Examples 2 to 7 and Comparative Examples 1 and 3
In a 3-liter four-neck flask, MEA (336 parts by mass), HEA (30 parts by mass), BA (144 parts by mass), methyl acrylate (hereinafter also referred to as "MA") (90 parts by mass), and ethyl acetate (890 parts by mass) were charged. This mixture was thoroughly degassed by bubbling nitrogen gas, the internal temperature of the mixture was raised to 75°C, V-65 (0.12 parts by mass) was charged, and polymerization was carried out for 5 hours. Ethyl acetate was added so that the solid content concentration was 30%, and an ethyl acetate solution of polymer A-2 was obtained. The obtained polymer A-2 consisted of 52% by mass of MEA, 21% by mass of MA, 22% by mass of BA, and 5% by mass of HEA, and had Mn 155,000, Mw / Mn 6.1, and Tg = -27 ° C.

[Synthesis Example 3] Polymer A-3 used in Example 8
In a 3-liter four-neck flask, MEA (104 parts by mass), HEA (21 parts by mass), BA (309 parts by mass), and ethyl acetate (770 parts by mass) were charged. 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 so that the solid content was 30% by mass, and an ethyl acetate solution of polymer A-3 was obtained. The obtained polymer A-3 consisted of 20% by mass of MEA, 75% by mass of BA, and 5% by mass of HEA, and had Mn 92,000, Mw/Mn 8.1, and Tg = -40°C.

[Synthesis Example 4] Polymer A-4 used in Example 9
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 so that the solid content became 30% by mass, and an ethyl acetate solution of polymer A-4 was obtained. The obtained polymer A-4 consisted of 80% by mass of EEA, 15% by mass of BA, and 5% by mass of HEA, and had Mn of 89,000, Mw/Mn of 8.7, and Tg of -56°C.

[Synthesis Example 5] Polymer A-5 used in Example 10
In a 3-liter four-neck flask, MEA (182 parts by mass), HEA (21 parts by mass), MA (312 parts by mass), and ethyl acetate (770 parts by mass) were charged. 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 so that the solid content was 30% by mass, and an ethyl acetate solution of polymer A-5 was obtained. The obtained polymer A-5 consisted of 60% by mass of MA and 35% by mass of MEA, and had Mn 90,000, Mw/Mn 8.4, and Tg = -10°C.

[Synthesis Example 6] Polymer A-6 used in Comparative Example 2
HEA (24 parts by mass), BA (506 parts by mass), and ethyl acetate (974 parts by mass) were charged into a 3-liter four-neck flask. 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 so that the solid content became 30% by mass, and an ethyl acetate solution of polymer A-6 was obtained. The obtained polymer A-6 was composed of 95% by mass of BA and 5% by mass of HEA, and had Mn of 87,000, Mw/Mn of 5.4, and Tg of −41° C.

The abbreviations in Table 1 represent the following names (same for Table 2).
MEA: 2-methoxyethyl acrylate EEA: 2-ethoxyethyl acrylate MA: methyl acrylate BA: n-butyl acrylate HEA: 2-hydroxyethyl acrylate

2. Preparation of acrylic syrup [Formulation example 1] Preparation of syrup Ac-1 used in Example 1 MEA (68.0 parts by mass), BA (12.7 parts by mass), and HEA (4.3 parts by mass) were added to the isolated polymer A-1 (15 parts by mass), and stirred until homogenous to obtain syrup Ac-1. The composition of syrup Ac-1 is shown in Table 2.

[Formulation Example 2] Preparation of Syrup Ac-2 used in Examples 2 to 7 and Comparative Examples 1 and 3 MEA (44.2 parts by mass), MA (17.8 parts by mass), BA (18.7 parts by mass), and HEA (4.3 parts by mass) were added to the isolated polymer A-2 (15 parts by mass) and stirred until homogenous, to obtain syrup Ac-2. The composition of syrup Ac-2 is shown in Table 2.

[Formulation Example 3] Preparation of Syrup Ac-3 used in Example 8 MEA (17.0 parts by mass), BA (63.7 parts by mass), and HEA (4.3 parts by mass) were added to the isolated polymer A-3 (15 parts by mass), and stirred until homogenous to obtain syrup Ac-3. The composition of syrup Ac-3 is shown in Table 2.

[Formulation Example 4] Preparation of Syrup Ac-4 used in Example 9 EEA (68.0 parts by mass), BA (12.7 parts by mass), and HEA (4.3 parts by mass) were added to the isolated polymer A-4 (15 parts by mass), and stirred until homogenous, to obtain syrup Ac-4. The composition of syrup Ac-4 is shown in Table 2.

[Formulation Example 5] Preparation of Syrup Ac-5 used in Example 10 MEA (29.7 parts by mass), MA (51.0 parts by mass), and HEA (4.3 parts by mass) were added to the isolated polymer A-5 (15 parts by mass), and stirred until homogenous to obtain syrup Ac-5. The composition of syrup Ac-5 is shown in Table 2.

[Formulation Example 6]
To the isolated polymer A-6 (15 parts by mass), BA (80.7 parts by mass) and HEA (4.3 parts by mass) were added and stirred until homogenous, to obtain syrup Ac-6. The composition of syrup Ac-6 is shown in Table 2.

3. Preparation of adhesive composition and production of adhesive sheet [Example 1]
Syrup Ac-1 obtained in Formulation Example 1 (100 parts by mass), 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, product name "Omnirad 184") (0.2 parts by mass) as a photopolymerization initiator, and t-butylperoxy-2-ethylhexyl monocarbonate (manufactured by NOF Corporation, product name "Perbutyl E") (0.1 parts by mass) as a thermal polymerization initiator were mixed to obtain a pressure-sensitive adhesive composition.
This adhesive composition was applied onto a 50 μm thick polyethylene terephthalate (hereinafter referred to as "PET") separator. Next, a 38 μm thick PET separator with a different peel strength from the separator was attached, and irradiated with a UV-LED surface irradiation device (model: HLDL-470X370U65PSCSP) manufactured by CCS Co., Ltd. at an illuminance of 3.0 mW/cm ² for 15 minutes to polymerize the monomer in the adhesive composition, thereby obtaining an adhesive sheet sample with a double-sided separator. The polymer obtained at this time is referred to as an acrylic adhesive polymer (A). The thickness of the adhesive layer after UV curing was 100 μm. Using the obtained adhesive sheet sample, various evaluations were performed by the following methods. The evaluation results are shown in Table 3.

<Evaluation method>
- Gel fraction measurement (before heat treatment)
0.2 g of adhesive was taken 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 left at room temperature for 16 hours. Then, it was filtered through a 200 mesh wire net, and the residue remaining on the net was dried at 80 ° C for 3 hours and weighed. From the initial mass and the mass of the residue, the gel fraction based on the acrylic adhesive polymer (A) was calculated by the following formula.
Gel fraction (%)=(mass of residue)/[(initial mass)×(solid content of acrylic adhesive polymer (A))/(solid content of entire adhesive composition)]×100

- Gel fraction measurement (after heat treatment)
The pressure-sensitive adhesive sheet samples were heat-treated under the following heat treatment conditions, and the gel fraction of the heat-treated pressure-sensitive adhesive sheet samples was measured in the same manner as above.
(Heat treatment conditions)
The laminate after pressure bonding was subjected to a heat treatment at 150° C. for 10 minutes using a blower dryer (SPHH202 manufactured by Espec).

Evaluation of conformability to irregularities Two polyester fabrics were laminated together using a pressure-sensitive adhesive sheet sample cut to a width of 10 mm to obtain a laminate consisting of polyester fabric/pressure-sensitive adhesive sheet sample/polyester fabric in this order. The obtained laminate was pressed by heat pressing (conditions: 130°C, 3 kg/ ^cm2 , 10 seconds) and then peeled off by hand. If the laminate broke inside the adhesive while peeling off, it was judged as having good conformability to irregularities on the fabric, as "○", and if the laminate peeled off at the fabric interface, it was judged as having insufficient conformability to irregularities, as "×".

- Evaluation of Solvent Resistance A laminate produced in the same manner as in the evaluation of unevenness conformability and then subjected to heat treatment at 150°C was placed in a 250mL glass bottle, 200mL of perchloroethylene was added thereto and stirred with a MIX rotor for 1 hour, after which the test piece was dried at 130°C for 5 minutes and the presence or absence of peeling of the adhesive portion was evaluated. Those in which no peeling was observed were judged as "○", and those in which peeling was observed were judged as "×".

High-Temperature Peel Test A laminate produced in the same manner as in the evaluation of the conformability to irregularities and then subjected to a heat treatment at 150°C was used as a test piece, and a T-type peel strength was measured using a tensile tester INSTRON 5566A (manufactured by Instron Japan) under conditions of a measurement temperature of 80°C, a test piece width of 10 mm, and a peel speed of 300 mm/min, which was defined as the high-temperature peel strength.

[Example 2]
A pressure-sensitive adhesive composition was produced by the same operation as in Example 1, except that syrup Ac-2 obtained in Blending Example 2 was used instead of syrup Ac-1, and the amount of the thermal polymerization initiator "Perbutyl E" added was 0.1 parts by mass, and various evaluations were performed 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 syrup Ac-2 obtained in Formulation Example 2 was used instead of syrup Ac-1, and various evaluations were carried out in the same manner as in Example 1.
[Example 4]
A pressure-sensitive adhesive composition was produced by the same operation as in Example 1, except that syrup Ac-2 obtained in Blending Example 2 was used instead of syrup Ac-1, and the amount of the thermal polymerization initiator "Perbutyl E" added was 0.6 parts by mass, and various evaluations were performed in the same manner as in Example 1.

[Example 5]
A pressure-sensitive adhesive composition was produced by the same operation as in Example 1, except that syrup Ac-2 obtained in Formulation Example 2 was used instead of syrup Ac-1, and 0.01 parts by mass of a multifunctional acrylate, "Anilox M-309" (manufactured by Toagosei Co., Ltd.), was added, and various evaluations were performed in the same manner as in Example 1.
[Example 6]
A pressure-sensitive adhesive composition was produced by the same operations as in Example 1, except that syrup Ac-2 obtained in Blending Example 2 was used instead of syrup Ac-1, and 0.3 parts by mass of t-hexylperoxyisopropyl monocarbonate (manufactured by NOF Corporation, product name "Perhexyl I"), a thermal polymerization initiator having a lower hydrogen abstraction ability than "Perbutyl E", was added instead of "Perbutyl E". Various evaluations were performed in the same manner as in Example 1.
[Example 7]
A pressure-sensitive adhesive composition was produced by the same operation as in Example 1, except that syrup Ac-2 obtained in Blending Example 2 was used instead of syrup Ac-1, and 0.6 parts by mass of "Perhexyl I" was added instead of "Perbutyl E", and various evaluations were performed in the same manner as in Example 1.

[Example 8]
A pressure-sensitive adhesive composition was produced by carrying out the same operations as in Example 1, except that syrup Ac-3 obtained in Formulation Example 3 was used instead of syrup Ac-1, and various evaluations were carried out 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 syrup Ac-4 obtained in Formulation Example 4 was used instead of syrup Ac-1, and various evaluations were carried out in the same manner as in Example 1.
[Example 10]
A pressure-sensitive adhesive composition was produced by the same procedure as in Example 1, except that syrup Ac-5 obtained in Formulation Example 5 was used instead of syrup Ac-1, and various evaluations were carried out in the same manner as in Example 1.

[Comparative Example 1]
A pressure-sensitive adhesive composition was produced in the same manner as in Example 1, except that syrup Ac-2 obtained in Blending Example 2 was used instead of syrup Ac-1, and the thermal polymerization initiator "Perbutyl E" was not added, 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 syrup Ac-6 obtained in Formulation Example 6 was used instead of syrup Ac-1, 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 syrup Ac-2 obtained in Formulation Example 2 was used instead of syrup Ac-1, and 1.0 part by mass, calculated as solid content, of "Takenate D-110N" (ethyl acetate solution with 75% solid content) manufactured by Mitsui Chemicals, which is an isocyanate-based curing agent, was added. In addition, a pressure-sensitive adhesive sheet sample with a double-sided separator was obtained in the same manner as in Example 1, using the obtained pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet sample was aged at room temperature for one week to promote the reaction of the isocyanate-based curing agent. Various evaluations were performed in the same manner as in Example 1 using the obtained pressure-sensitive adhesive sheet sample.

The compositions of the pressure-sensitive adhesive compositions of Examples 1 to 10 and Comparative Examples 1 to 4, and the evaluation results are shown in Table 3.

The abbreviations in Table 3 represent the following names.
M-309: polyfunctional acrylate, trade name "Anilox M-309", manufactured by Toagosei Co., Ltd. D-110: isocyanate-based curing agent, trade name "Takenate D-110N", manufactured by Mitsui Chemicals, Inc. Omnirad 184: photopolymerization initiator, trade name "Omnirad 184", manufactured by BASF Perbutyl E: thermal polymerization initiator, trade name "Perbutyl E", manufactured by NOF Corporation Perhexyl I: thermal polymerization initiator, trade name "Perhexyl I", manufactured by NOF Corporation The blending amounts of the polyfunctional acrylate, crosslinking agent, photopolymerization initiator, and thermal polymerization initiator are the blending amounts per 100 parts by mass of polymer syrup.

As shown in Table 3, all of the adhesive sheets of Examples 1 to 10, which were produced using an adhesive composition containing a polymer syrup that produces an acrylic adhesive polymer (A) having (meth)acrylic acid alkoxyalkyl ester units and a thermal polymerization initiator, had good conformability, solvent resistance, and high-temperature adhesion. In particular, Examples 1 to 7 and 9, which had a large difference in gel fraction before and after heating after bonding the adherend (polyester fabric) and the adhesive sheet, were rated as "○" for both conformability and solvent resistance, and also showed a high high-temperature peel strength of 1.5 N/10 mm.

In contrast, Comparative Example 1, in which no thermal polymerization initiator was added to the adhesive composition, and Comparative Example 2, in which the adhesive layer contained a polymer that did not have an (meth)acrylic acid alkoxyalkyl ester unit as the acrylic adhesive polymer, were rated as "x" for solvent resistance and had low high-temperature peel strength. Comparative Example 3, in which a crosslinking agent was added to the adhesive composition, had a high gel fraction of 78.3% for the adhesive sheet before it was attached to the adherend (i.e., before it was cured). In this case, the unevenness-following ability and solvent resistance were rated as "x", and the high-temperature peel strength was also low.

Claims (5)

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 thermal polymerization initiator,
The acrylic adhesive polymer (A) has a structural unit derived from an alkoxyalkyl (meth)acrylate,
the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20%,
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 20% or more after heat treatment. The adhesive sheet according to claim 1, wherein the content of structural units derived from an alkoxyalkyl ester of (meth)acrylic acid in the acrylic adhesive polymer (A) is 20% by mass or more relative to the total structural units derived from the monomers constituting the acrylic adhesive polymer (A). The adhesive sheet according to claim 1 or 2, wherein the glass transition temperature of the acrylic adhesive polymer (A) is -80°C to 10°C. A method for producing a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, comprising:
The method includes a step of forming a pressure-sensitive adhesive layer containing an acrylic adhesive polymer (A) and a thermal polymerization initiator by irradiating an active energy ray onto a layer of a pressure-sensitive adhesive composition containing an acrylic adhesive polymer syrup, a photopolymerization initiator, and a thermal polymerization initiator,
The acrylic adhesive polymer syrup contains an alkoxyalkyl (meth)acrylic acid ester,
the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) of less than 20 mass%,
the pressure-sensitive adhesive layer has a gel fraction based on the acrylic pressure-sensitive adhesive polymer (A) after heat treatment of 20% or more;
A method for producing a pressure-sensitive adhesive sheet. A method for producing a laminate, comprising a step of laminating the adhesive sheet according to any one of claims 1 to 3 to an adherend, and then performing a heat treatment to harden the adhesive layer.