Adhesive composition for flexible adherend, and product

Abstract

Provided is an adhesive composition for a flexible adherend that is used for bonding flexible adherends together (however, said bonding excludes bonding fiber fabrics together, bonding conductive sheets together, bonding fiber fabric and a conductive sheet together, and bonding fiber fabric and an elastomer base material together). The adhesive composition contains a (meth)acrylic polymer (A) having a weight average molecular weight of 100,000 or more and a glass transition temperature of -80°C to 10°C, and the storage elastic modulus of the adhesive layer at 23°C is 1.0 MPa or less.

Description

Adhesive compositions and products for flexible adherends

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to Japanese Patent Application No. 2023-131481, filed on August 10, 2023, the entire contents of which are incorporated herein by reference. The present disclosure relates to a pressure-sensitive adhesive composition for flexible substrates and a product thereof.

[0002] When manufacturing products in a wide range of fields, such as clothing including fashion accessories, daily necessities, sporting goods, electronic components, and automotive interior parts, flexible adherends such as fabrics, resin sheets, resin films, leather, rubber sheets, rubber films, and metal foils are bonded together by adhesive processing. Various techniques have been proposed for bonding such flexible adherends together by adhesive processing. For example, one technique for bonding fiber fabrics by adhesive processing is a method using a urethane-based hot melt adhesive (see, for example, Patent Document 1 and Patent Document 2).

[0003] JP 2016-74996 A JP 2017-78232 A

[0004] Flexible adherends (hereinafter also referred to as "flexible adherends") are soft and pliable, and so are often used in parts that require repeated bending and returning to their original shape, taking advantage of these properties. However, when flexible adherends are bonded together using conventional urethane-based hot melt adhesives, the bonded area is hard, causing the texture and flexibility of the materials to be lost, and when the flexible adherend is bent and stretched, the bonded area cannot follow the bending and stretching of the flexible adherend, resulting in peeling of the flexible adherend.

[0005] The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a pressure-sensitive adhesive composition for flexible substrates that can form a pressure-sensitive adhesive layer having good adhesive properties when bonding flexible substrates together while maintaining good flexibility and texture at the bonded portion.

[0006]

[0009] As a means for solving the above-mentioned problems, the present inventors have focused on using a (meth)acrylic polymer as a polymer component of a pressure-sensitive adhesive layer used when bonding flexible adherends together, and as a result of extensive investigation, have found that the above-mentioned problems can be solved. Specifically, the present disclosure provides the following pressure-sensitive adhesive composition for flexible adherends and product.

[0007] [1] A pressure-sensitive adhesive composition for flexible substrates, for forming a pressure-sensitive adhesive layer used for bonding flexible substrates together (excluding bonding of fiber fabrics together, bonding of conductive sheets together, bonding of a fiber fabric to a conductive sheet, and bonding of a fiber fabric to an elastomer substrate), the pressure-sensitive adhesive composition for flexible substrates comprising a (meth)acrylic polymer (A) having a weight-average molecular weight of 100,000 or more and a glass transition temperature of -80°C or more and 10°C or less, the pressure-sensitive adhesive layer having a storage modulus at 23°C of 1.0 MPa or less. [2] The pressure-sensitive adhesive composition for flexible substrates according to [1] above, wherein the (meth)acrylic polymer (A) is a block copolymer having a polymer block (C) having a glass transition temperature of 10°C or more and 250°C or less and a (meth)acrylic polymer block (D) having a glass transition temperature of -80°C or more and less than 10°C. [3] The pressure-sensitive adhesive composition for flexible substrates according to the above [2], wherein the glass transition temperature of the polymer block (C) is 10° C. or higher and 90° C. or lower. [4] The pressure-sensitive adhesive composition for flexible substrates according to the above [2] or [3], wherein the polymer block (C) comprises a structural unit (U1) derived from an imide group-containing vinyl monomer and a structural unit (U2) derived from a (meth)acrylic monomer, and the total content of the structural unit (U1) and the structural unit (U2) is 80 mass % or higher, based on all structural units of the polymer block (C). [5] The pressure-sensitive adhesive composition for flexible substrates according to any of the above [2] to [4], wherein the (meth)acrylic polymer block (D) comprises a structural unit derived from a (meth)acrylic acid ester compound having a hydrocarbon group having 3 or more carbon atoms, in an amount of 20 mass % or higher, based on all structural units of the (meth)acrylic polymer block (D). [6] The pressure-sensitive adhesive composition for flexible substrates according to any one of [1] to [5] above, wherein the (meth)acrylic polymer (A) comprises a structural unit derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters. [7] The pressure-sensitive adhesive composition for flexible substrates according to any one of [1] to [6] above, further comprising a vinyl polymer (B) having a glass transition temperature of 30°C or higher and 200°C or lower and a number average molecular weight of 500 or higher and 10,000 or lower.[8] The pressure-sensitive adhesive composition for flexible substrates according to [7] above, wherein the vinyl polymer (B) contains a structural unit derived from an aliphatic cyclic vinyl monomer. [9] The pressure-sensitive adhesive composition for flexible substrates according to [7] or [8] above, wherein the content of the vinyl polymer (B) is 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A).

[10] The pressure-sensitive adhesive composition for flexible substrates according to any of [1] to [9] above, further comprising a silane coupling agent.

[11] The pressure-sensitive adhesive composition for flexible substrates according to

[10] above, wherein the silane coupling agent has at least one selected from the group consisting of an epoxy group, a (meth)acryloyl group, an isocyanate group, and a blocked isocyanate group.

[12] The pressure-sensitive adhesive composition for flexible substrates according to any of [1] to

[11] above, further comprising an isocyanate-based crosslinking agent.

[13] The pressure-sensitive adhesive composition for flexible substrates according to any one of [1] to

[12] above, further comprising fine particles.

[14] A product comprising a first adherend, a second adherend, and a pressure-sensitive adhesive layer, the first adherend and the second adherend are bonded together by the pressure-sensitive adhesive layer, the first adherend and the second adherend are flexible adherends (excluding, however, fiber fabrics, conductive sheets, a combination of a fiber fabric and a conductive sheet, and a combination of a fiber fabric and an elastomer substrate), and the pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition for flexible substrates according to any one of [1] to

[13] above.

[0008] According to the pressure-sensitive adhesive composition for flexible substrates of the present disclosure, when flexible adherends are bonded together, a pressure-sensitive adhesive layer can be formed that exhibits excellent adhesiveness while maintaining the flexibility and texture of the bonded portion. Furthermore, by bonding flexible adherends together via a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition for flexible adherends of the present disclosure, a product can be obtained that exhibits good flexibility and texture at the bonded portion and high adhesive strength.

[0009] The present disclosure will be described in detail below. In this specification, "(meth)acrylic" means acrylic and / or methacrylic. "(meth)acrylate" means acrylate and / or methacrylate. "(meth)acrylo" means acrylo and / or methacrylo.

[0010] The pressure-sensitive adhesive composition for flexible substrates of the present disclosure (hereinafter also referred to as "the composition") is a (meth)acrylic pressure-sensitive adhesive used to form a pressure-sensitive adhesive layer for bonding flexible substrates together. Hereinafter, the flexible substrate will be described first, followed by the composition.

[0011] <Flexible Adherend> Flexible adherends to be bonded using the present composition include those that are flexible and do not break or crack when bent. Specifically, it is preferable that a 50 mm x 100 mm piece of the adherend can be bent so that the short sides of the adherend pieces are in contact with each other, and that the adherend pieces do not break or crack when bent. In addition, the bending stiffness of the flexible adherend is 0.01 N m ２ / m or more 10N・m ２ For example, cowhide and artificial leather generally have a strength of 0.3 N·m ２ / m to 10N・m ２ Fabrics generally have a stiffness of 0.01 N·m ２ / m to 0.5 N·m ２ In this specification, the bending rigidity of the flexible adherend is a value measured using a bending tester (for example, pure bending tester KES-FB2, FB2-L manufactured by Kato Tech Co., Ltd.).

[0012] The thickness of the flexible adherend can be appropriately set depending on the application. The thickness of the flexible adherend is, for example, 0.01 mm or more and 15.0 mm or less. The thickness of the flexible adherend is preferably 10.0 mm or less, more preferably 5.0 mm or less, even more preferably 2.0 mm or less, and even more preferably 1.0 mm or less, in view of the high effect of improving the flexibility and texture of the bonded portion by applying the present composition.

[0013] Specific examples of flexible adherends include textile fabrics; leather; conductive substrates; film-, sheet-, or sponge-shaped resin substrates; and film-, sheet-, or sponge-shaped elastomer substrates. Hereinafter, a film-shaped substrate having a thickness of less than 200 μm is referred to as a film-shaped substrate, and a thin plate-shaped substrate having a thickness of 200 μm or more is referred to as a sheet-shaped substrate. The flexible adherend may be formed from only one of the above types, or from two or more types. Furthermore, the two flexible adherends bonded together using the present composition may be of the same type or different types.

[0014] Examples of fiber fabrics include synthetic fibers such as polyester, polyamide, polyurethane, 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. Examples of leather include synthetic leather, artificial leather, fur, and natural leather (cowhide, pigskin, sheepskin, etc.). Examples of conductive substrates include metal foil (i.e., metal film), metal foil composite film, and conductive sheet. A metal foil composite film is a laminate comprising a metal foil and a film formed from a material other than metal. A metal foil composite film may be composed only of a metal foil and a film formed from a material other than metal, or may further comprise another layer (e.g., an adhesive layer, etc.). Examples of metals forming the metal foil of metal foil and metal foil composite film include pure metals such as copper, silver, gold, aluminum, titanium, and magnesium, as well as alloys thereof. In a metal foil composite film, the film formed from a material other than metal is preferably a resin film. Examples of materials for the resin film include polyester resins such as polyethylene terephthalate (PET), polyethersulfone resins, polyimide resins, acetate resins, polycarbonate resins, and polyolefin resins.

[0015] A conductive sheet is a biosensor that acquires biometric information such as heart rate, body temperature, and blood pressure by receiving electrical signals from a living body. The conductive sheet includes an insulator layer and a conductor layer. One example of a conductive sheet is a laminate in which a first insulator layer, a conductor layer, and a second insulator layer are stacked in this order. The insulator layer is formed, for example, from a stretchable resin material (such as urethane resin). The conductor layer is formed, for example, from a conductive material such as a pure metal, such as copper, silver, gold, aluminum, titanium, or magnesium, or an alloy thereof. The conductor layer is preferably stretchable, and is formed, for example, by kneading conductive particles and a flexible resin and forming it into a film. A portion of the conductor layer serves as an electrode that comes into contact with the skin of the subject. Note that the conductor layer of the conductive sheet differs from a metal film, whose entire substrate is made of metal.

[0016] Examples of the film-, sheet- or sponge-like resin substrate include those formed from polyester resins such as polyethylene terephthalate (PET), polyethersulfone resins, polyimide resins, acetate resins, polycarbonate resins, polyolefin resins, etc.

[0017] The film-, sheet-, or sponge-like elastomer substrate may be formed from a thermoplastic elastomer or a thermosetting elastomer. It is also possible to use a material that combines a thermoplastic elastomer and a thermosetting elastomer. Specific examples of thermoplastic elastomers include styrene-based thermoplastic elastomers (TPS), polyolefin-based thermoplastic elastomers (TPO), polyester-based thermoplastic elastomers (TPEE), vinyl chloride-based thermoplastic elastomers (TPVC), polyurethane-based thermoplastic elastomers (TPU), and polyamide-based thermoplastic elastomers (TPA). Specific examples of thermosetting elastomers include urethane rubber, silicone rubber, isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), nitrile rubber (NBR), ethylene-propylene rubber (EPM), acrylic rubber (ACM), and fluororubber.

[0018] The flexible adherend is preferably at least one selected from the group consisting of a fiber fabric, a resin substrate, a conductive substrate, leather, and an elastomer substrate, and more preferably at least one selected from the group consisting of a synthetic fiber, a film-like resin substrate, a sheet-like resin substrate, synthetic leather, a film-like elastomer substrate, a metal foil, and a metal foil composite film. The flexible adherend may be in a mesh shape (network shape) having a large number of holes penetrating in the thickness direction, or the surface of the flexible adherend may have metal wiring formed thereon, or may have been subjected to a surface treatment such as a roughening or water-repellent finish.

[0019] The combination of flexible adherends to be bonded with the pressure-sensitive adhesive layer formed from the present composition may be any combination other than bonding of fiber fabrics together, bonding of conductive sheets together, bonding of fiber fabrics to a conductive sheet, and bonding of fiber fabrics to an elastomer substrate. Specific examples of combinations of flexible adherends to be bonded with the pressure-sensitive adhesive layer formed from the present composition include a combination of fiber fabrics and a resin substrate, a combination of metal films, a combination of metal foil composite films, a combination of leather and a resin substrate, a combination of a conductive substrate and a resin substrate, a combination of resin substrates, and a combination of leather and an elastomer substrate.

[0020] Further specific examples of combinations of flexible adherends to be bonded with a pressure-sensitive adhesive layer formed from the present composition include, for example, a combination of a textile fabric and a resin film, a combination of a textile fabric and a resin sheet, a combination of leather and a resin film, a combination of leather and a resin sheet, a combination of a metal film and a resin film, a combination of a metal film and a resin sheet, a combination of a metal film and a metal film, a combination of a metal foil composite film and a metal foil composite film, a combination of a resin film and a resin film, a combination of a resin film and a resin sheet, a combination of a resin sheet and a resin sheet, a combination of a metal foil composite film and a resin film, a combination of a metal foil composite film and a resin sheet, and a combination of leather and a film-like elastomer substrate.

[0021] <<Adhesive Composition for Flexible Adherends>> The composition contains a (meth)acrylic polymer (A) having a weight-average molecular weight of 100,000 or more and a glass transition temperature of −80° C. or more and 10° C. or less. The adhesive layer formed from the composition has a storage modulus of 1.0 MPa or less at 23° C. The adhesive layer formed from the composition is easily stretchable and has excellent adhesive properties, making it suitable for use in bonding flexible adherends together. First, the (meth)acrylic polymer (A) blended into the composition and the components blended as needed will be described in detail below.

[0022] <(Meth)acrylic polymer (A)> The (meth)acrylic polymer (A) is a polymer having a weight average molecular weight (Mw) of 100,000 or more. If the Mw of the (meth)acrylic polymer (A) is less than 100,000, the cohesive strength and adhesiveness also tend to be poor. From the viewpoint of obtaining a polymer that exhibits sufficient cohesive strength and good adhesiveness, the Mw of the (meth)acrylic polymer (A) is preferably 150,000 or more, more preferably 200,000 or more, and even more preferably 250,000 or more.

[0023] On the other hand, if the Mw of the (meth)acrylic polymer (A) is too large, the flexibility of the (meth)acrylic polymer (A) and the pressure-sensitive adhesive layer may decrease, or the viscosity of the pressure-sensitive adhesive composition may become too high, resulting in deterioration of coatability and handleability. Therefore, the Mw of the (meth)acrylic polymer (A) is preferably 2,000,000 or less, more preferably 1,500,000 or less, even more preferably 1,200,000 or less, and even more preferably 1,000,000 or less. The Mw of the (meth)acrylic polymer (A) is preferably in the range of 100,000 or more and 2,000,000 or less, more preferably 150,000 or more and 1,500,000 or less, and even more preferably 200,000 or more and 1,200,000 or less.

[0024] From the viewpoint of exhibiting sufficient cohesive strength and good adhesiveness, the Mn of the (meth)acrylic polymer (A) is preferably 60,000 or more, more preferably 80,000 or more, and even more preferably 100,000 or more. From the viewpoint of ease of production, the upper limit of the Mn of the (meth)acrylic polymer (A) is preferably 500,000 or less, more preferably 400,000 or less, and even more preferably 300,000 or less. The Mn of the (meth)acrylic polymer (A) is preferably in the range of 60,000 or more and 500,000 or less, more preferably 80,000 or more and 400,000 or less.

[0025] The molecular weight distribution (Mw / Mn) of the (meth)acrylic polymer (A), expressed as the ratio of Mw to Mn, is preferably 10.0 or less, more preferably 8.0 or less, even more preferably 6.0 or less, even more preferably 5.0 or less, and still more preferably 4.0 or less, from the viewpoint of easily obtaining good adhesive strength and suppressing an increase in viscosity of the pressure-sensitive adhesive composition. The lower limit of Mw / Mn of the (meth)acrylic polymer (A) is not particularly limited and can be 1.0 or more. In this specification, the Mw and Mn of the polymer are values ​​calculated in terms of standard polystyrene obtained using gel permeation chromatography (GPC).

[0026] The glass transition temperature (Tg) of the (meth)acrylic polymer (A) is −80° C. or higher and 10° C. or lower. If the Tg of the (meth)acrylic polymer (A) is lower than −80° C., the cohesive strength of the pressure-sensitive adhesive layer obtained from the composition tends to be insufficient, resulting in poor adhesiveness. Furthermore, if the Tg of the (meth)acrylic polymer (A) exceeds 10° C., the resulting (meth)acrylic polymer tends to be poor in adhesiveness and to be unable to ensure sufficient adhesiveness. From these viewpoints, the Tg of the (meth)acrylic polymer (A) is preferably −70° C. or higher, more preferably −60° C. or higher. The upper limit of the Tg of the (meth)acrylic polymer (A) is preferably 0° C. or lower, more preferably −10° C. or lower, and even more preferably −15° C. or lower, from the viewpoint of enhancing the adhesiveness of the (meth)acrylic polymer (A). The Tg of the (meth)acrylic polymer (A) is preferably in the range of −70° C. or higher and 0° C. or lower, more preferably −60° C. or higher and −10° C. or lower.

[0027] In this specification, the glass transition temperature (Tg) of a polymer is a value measured by differential scanning calorimetry (DSC). Details of the measurement method follow the method described in the Examples below. In this specification, when the (meth)acrylic polymer (A) is a block copolymer, the Tg of each polymer block is a value determined by synthesizing a polymer composed of monomers constituting the polymer block to be measured and measuring the Tg of the polymer by DSC. The Tg of the polymer can be selected arbitrarily by changing the type and composition of the constituent monomers, etc.

[0028] The (meth)acrylic polymer (A) is a polymer containing a (meth)acrylic monomer as a main structural unit. The (meth)acrylic monomer constituting the (meth)acrylic polymer (A) is not particularly limited as long as it is a monomer having a (meth)acryloyl group as a group participating in polymerization. Examples of the (meth)acrylic monomer include unsaturated carboxylic acids, unsaturated acid anhydrides, (meth)acrylic acid alkyl esters, (meth)acrylic acid aliphatic cyclic esters, (meth)acrylic acid aromatic esters, (meth)acrylic acid alkoxyalkyl esters, (meth)acrylic acid hydroxyalkyl esters, polyalkylene glycol mono(meth)acrylates, epoxy group-containing (meth)acrylic acid esters, silyl group-containing (meth)acrylic acid esters, amino group-containing (meth)acrylic acid esters, (meth)acrylamide or derivatives thereof, nitrile group-containing (meth)acrylic acid esters, and (meth)acrylimide compounds.

[0029] Specific examples of these include unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, cinnamic acid, and monoalkyl esters of unsaturated dicarboxylic acids (monoalkyl esters of maleic acid, fumaric acid, itaconic acid, citraconic acid, etc.), etc. Specific examples of unsaturated acid anhydrides include maleic anhydride, itaconic anhydride, citraconic anhydride, etc.

[0030] Specific examples of the (meth)acrylic acid alkyl ester include (meth)acrylic acid alkyl esters having an alkyl group having 1 to 12 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, and lauryl (meth)acrylate.

[0031] Specific examples of aliphatic cyclic esters of (meth)acrylic acid include cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, etc. Specific examples of aromatic esters of (meth)acrylic acid include phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxymethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, 3-phenoxypropyl (meth)acrylate, etc.

[0032] Specific examples of the (meth)acrylic acid alkoxyalkyl ester include 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.

[0033] 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, etc. Specific examples of polyalkylene glycol mono(meth)acrylates include polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and polyethylene glycol-polypropylene glycol mono(meth)acrylate, etc.

[0034] Specific examples of epoxy group-containing (meth)acrylic acid esters include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, etc. Specific examples of silyl group-containing (meth)acrylic acid esters include trimethoxysilylpropyl (meth)acrylate, triethoxysilylpropyl (meth)acrylate, methyldimethoxysilylpropyl (meth)acrylate, and dimethylmethoxysilylpropyl (meth)acrylate.

[0035] Specific examples of the amino group-containing (meth)acrylic acid ester 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.

[0036] Specific examples of (meth)acrylamide or a derivative thereof include (meth)acrylamide, 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.

[0037] Specific examples of the nitrile group-containing (meth)acrylic acid ester 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, and 8-cyanooctyl (meth)acrylate.

[0038] Specific examples of the (meth)acrylimide compound include 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.

[0039] The (meth)acrylic polymer (A) preferably contains a structural unit derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters among the above-mentioned (meth)acrylic monomers. When the (meth)acrylic polymer (A) contains a structural unit derived from these monomers, the Tg of the (meth)acrylic polymer (A) becomes relatively low, and a polymer exhibiting sufficient adhesiveness can be obtained.

[0040] In the (meth)acrylic polymer (A), the content of structural units derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters is preferably 20 mass% or more, more preferably 30 mass% or more, even more preferably 50 mass% or more, even more preferably 60 mass% or more, and even more preferably 70 mass% or more, based on the total structural units of the (meth)acrylic polymer (A). By setting the content of structural units derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters within the above range, the adhesive strength and initial adhesive strength (tack) of the pressure-sensitive adhesive composition can be sufficiently increased.

[0041] In the (meth)acrylic polymer (A), the content of structural units derived from (meth)acrylic monomers is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, based on the total structural units of the (meth)acrylic polymer (A). When producing the (meth)acrylic polymer (A), one type of (meth)acrylic monomer may be used alone, or two or more types may be used in combination.

[0042] The (meth)acrylic polymer (A) may further contain a structural unit derived from a monomer copolymerizable with the (meth)acrylic monomer and different from the (meth)acrylic monomer (hereinafter also referred to as "other monomer"), within a range that does not impair the action of the (meth)acrylic polymer (A). Specific examples of the other monomer constituting the (meth)acrylic polymer (A) include, for example, an aromatic vinyl compound and an imide group-containing vinyl monomer.

[0043] 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-tert-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, as well as vinylnaphthalene. Of these, styrene-based compounds are preferred as aromatic vinyl compounds. One or more of these can be used as the aromatic vinyl compound.

[0044] Examples of the imide group-containing vinyl monomer 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; and citraconic compounds such as N-methylcitraconimide, N-ethylcitraconimide, N-butylcitraconimide, N-octylcitraconimide, N-2-ethylhexylcitraconimide, N-cyclohexylcitraconimide, and N-laurylcitraconimide. Of these, maleimide compounds are preferably used as the imide group-containing vinyl compound.

[0045] As the maleimide compound, at least one selected from the group consisting of maleimide and N-substituted maleimide compounds can be preferably used. Examples of the N-substituted maleimide compound include N-alkyl-substituted maleimide compounds such as N-methylmaleimide, N-ethylmaleimide, N-n-propylmaleimide, N-isopropylmaleimide, N-n-butylmaleimide, N-isobutylmaleimide, N-tert-butylmaleimide, N-pentylmaleimide, N-hexylmaleimide, N-heptylmaleimide, N-octylmaleimide, N-laurylmaleimide, and N-stearylmaleimide; N-cyclopentylmaleimide and N-cyclopentylmaleimide; Examples of such compounds include N-cycloalkyl-substituted maleimide compounds such as cyclohexylmaleimide; N-aralkyl-substituted maleimide compounds such as N-benzylmaleimide; and N-aryl-substituted maleimide compounds such as N-phenylmaleimide, N-(4-hydroxyphenyl)maleimide, N-(4-acetylphenyl)maleimide, N-(4-methoxyphenyl)maleimide, N-(4-ethoxyphenyl)maleimide, N-(4-chlorophenyl)maleimide, and N-(4-bromophenyl)maleimide. One or more of these compounds can be used as the imide group-containing vinyl monomer.

[0046] In addition to the above, other monomers constituting the (meth)acrylic polymer (A) include, for example, aliphatic vinyl compounds such as ethylene and propylene; amide group-containing vinyl compounds such as N-vinylacetamide; polyfunctional alkenyl compounds such as trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, and pentaerythritol diallyl ether; etc. As other monomers constituting the (meth)acrylic polymer (A), only one type may be used, or two or more types may be used.

[0047] Furthermore, in producing the (meth)acrylic polymer (A), a monomer having a crosslinkable functional group (hereinafter also referred to as a "crosslinkable group-containing monomer") may be used to make the (meth)acrylic polymer (A) a polymer having a crosslinkable structural unit. The (meth)acrylic polymer (A) having a crosslinkable structural unit is preferable in that it can provide a product that maintains flexibility while providing excellent adhesion when bonding flexible adherends together.

[0048] The crosslinkable group-containing monomer used in the production of the (meth)acrylic polymer (A) is not particularly limited. The crosslinkable group-containing monomer is preferably at least one selected from the group consisting of (meth)acrylic acid, a hydroxyalkyl (meth)acrylate compound, an epoxy group-containing (meth)acrylic acid ester, and a silyl group-containing (meth)acrylic acid ester. From the viewpoint of adhesive performance, the hydroxyalkyl (meth)acrylate is preferably a compound having a hydroxyalkyl group having 2 to 8 carbon atoms, more preferably a compound having a hydroxyalkyl group having 2 to 4 carbon atoms.

[0049] The (meth)acrylic polymer (A) may have a main chain, in part or in whole, composed of a polymer chain mainly composed of structural units derived from a (meth)acrylic monomer. Examples of the (meth)acrylic polymer (A) include random copolymers, block copolymers, alternating copolymers, and graft copolymers. Among these, block copolymers and / or random copolymers are preferred because the (meth)acrylic polymer (A) can be synthesized relatively easily and can sufficiently improve various performances. Specifically, the (meth)acrylic polymer (A) is preferably a block copolymer (hereinafter also referred to as "block copolymer (A)") containing [1] a polymer block (C) and a (meth)acrylic polymer block (D) composed of a polymer chain mainly composed of structural units derived from a (meth)acrylic monomer, and / or a random copolymer (hereinafter also referred to as "random copolymer (A)") composed of [2] a polymer chain mainly composed of structural units derived from a (meth)acrylic monomer.

[0050] [1] Block Copolymer (A) The polymer block (C) and the (meth)acrylic polymer block (D) contained in the block copolymer (A) are segments having different monomer compositions. It is preferable to make the Tg of the polymer block (C) higher than that of the (meth)acrylic polymer block (D), thereby making the polymer block (C) a segment having a relatively high Tg and the (meth)acrylic polymer block (D) a segment having a relatively low Tg. When the block copolymer (A) contains such polymer block (C) and (meth)acrylic polymer block (D), pseudo-crosslinking is formed between or within molecules due to a microphase separation structure or the like, which is thought to result in improved cohesive strength.

[0051] Polymer Block (C) The Tg of the polymer block (C) is preferably 10°C or higher and 250°C or lower. When the Tg of the polymer block (C) is 10°C or higher, the cohesive strength can be sufficiently improved by pseudo-crosslinking formed by the microphase-separated structure of the block copolymer (A), etc., and the adhesiveness of the pressure-sensitive adhesive layer can be sufficiently ensured. From this viewpoint, the Tg of the polymer block (C) is preferably 15°C or higher, more preferably 20°C or higher, even more preferably 25°C or higher, and even more preferably 30°C or higher. The upper limit of the Tg of the polymer block (C) is preferably 250°C or lower, from the viewpoint of ease of availability of raw materials, etc. From the viewpoint of sufficiently increasing the peel strength when various flexible adherends are bonded together and maintaining good flexibility and texture of the bonded portion, the Tg of the polymer block (C) is preferably 200°C or lower, more preferably 150°C or lower, even more preferably 100°C or lower, even more preferably 90°C or lower, even more preferably 85°C or lower, and even more preferably 80°C or lower. In particular, it is preferable that the Tg of the polymer block (C) is 90°C or less, since this ensures flexibility of the pressure-sensitive adhesive layer even when the ratio of the polymer block (C) in the block copolymer (A) is increased or the molecular weight of the block copolymer (A) is increased in order to ensure good adhesive strength.

[0052] The polymer block (C) preferably has a structural unit derived from a vinyl monomer. From the viewpoint of obtaining a polymer with excellent adhesive properties, the polymer block (C) preferably contains a structural unit (U1) derived from an imide group-containing vinyl monomer and a structural unit (U2) derived from a (meth)acrylic monomer. When the block copolymer (A) contains such a polymer block (C), a pressure-sensitive adhesive layer exhibiting excellent adhesive properties can be formed. Specific examples of the imide group-containing vinyl monomer and the (meth)acrylic monomer include the same compounds as those exemplified as the monomers constituting the (meth)acrylic polymer (A).

[0053] In terms of being able to provide the block copolymer (A) with better adhesiveness, the imide group-containing vinyl monomer used to produce the block copolymer (A) is preferably a compound represented by the following general formula: (In the formula, R ４ represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a cyclohexyl group, a phenyl group, or a group in which a hydroxy group, an alkyl group having 1 to 2 carbon atoms, an alkoxy group having 1 to 2 carbon atoms, an acetyl group, or a halogen atom is bonded to any position of a cyclohexyl group or a phenyl group.

[0054] From the viewpoint of ensuring flexibility and texture at the bonded portion when flexible adherends are bonded together, the structural unit (U2) is preferably a structural unit derived from a compound represented by the following formula (1): CH ２ =CR １ -C(=O)O(R ２ O) ｎ -R ３ ...(1) (In formula (1), R １ represents a hydrogen atom or a methyl group, R ２ represents a linear or branched alkylene group having 2 to 6 carbon atoms; R ３ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and n represents an integer of 0 to 100.

[0055] In the above formula (1), R １is preferably a hydrogen atom in that it is easy to adjust the Tg of the polymer block (C) to the above range. n is preferably 0 to 50, more preferably 0 to 20, from the viewpoints of easy availability of raw materials and adhesiveness.

[0056] In the polymer block (C), the total content of the structural unit (U1) and the structural unit (U2) is preferably 80% by mass or more, based on all structural units in the polymer block (C). By making the total content of the structural unit (U1) and the structural unit (U2) 80% by mass or more, based on all structural units in the polymer block (C), a pressure-sensitive adhesive layer exhibiting excellent adhesiveness can be formed. From the viewpoint of achieving excellent adhesiveness when bonding flexible adherends together, the total content of the structural unit (U1) and the structural unit (U2) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on all structural units in the polymer block (C).

[0057] The ratio of the structural unit (U1) to the structural unit (U2) in the polymer block (C) can be appropriately selected depending on the desired Tg. From the viewpoint of preventing the Tg of the polymer block (C) from becoming too high and further improving the adhesiveness of the pressure-sensitive adhesive layer, the ratio of the structural unit (U2) to the total amount of the structural unit (U1) and the structural unit (U2) is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more.

[0058] In producing the polymer block (C), a crosslinkable group-containing monomer may be used to give the polymer block (C) a structure having a crosslinkable structural unit. Having the crosslinkable structural unit in the polymer block (C) is preferable in that it allows for obtaining a product that maintains flexibility while providing excellent adhesiveness when bonding flexible adherends together.

[0059] The crosslinkable group-containing monomer used to produce polymer block (C) is not particularly limited, but is preferably at least one selected from the group consisting of (meth)acrylic acid, a hydroxyalkyl (meth)acrylate compound, an epoxy group-containing (meth)acrylic acid ester, and a silyl group-containing (meth)acrylic acid ester. Among these, a structural unit derived from a hydroxyalkyl (meth)acrylate is particularly preferred because it is easy to control the Tg of polymer block (C) within the above range. From the viewpoint of adhesive performance, the hydroxyalkyl (meth)acrylate is preferably a compound having a hydroxyalkyl group having 2 to 8 carbon atoms, and more preferably a compound having a hydroxyalkyl group having 2 to 4 carbon atoms.

[0060] When a crosslinkable structural unit is introduced into the polymer block (C), the content of the crosslinkable structural unit in the polymer block (C) is preferably 1% by mass or more, more preferably 2% by mass or more, based on the total structural units of the polymer block (C). From the viewpoint of ensuring flexibility at the bonded portion, the upper limit of the content of the crosslinkable structural unit in the polymer block (C) is preferably 30% by mass or less, more preferably 20% by mass or less, based on the total structural units of the polymer block (C).

[0061] The polymer block (C) may further contain a structural unit derived from a monomer copolymerizable with at least one of an imide group-containing vinyl monomer and a (meth)acrylic monomer, and which is different from the imide group-containing vinyl monomer and the (meth)acrylic monomer, to the extent that the effect of the block copolymer (A) is not impaired. Examples of the monomer constituting the polymer block (C) and different from the imide group-containing vinyl monomer and the (meth)acrylic monomer include the aromatic vinyl compounds exemplified as other monomers in the description of the acrylic polymer (A).

[0062] However, from the viewpoint of achieving better adhesion when flexible adherends are bonded together, it is preferable to minimize the amount of structural units derived from aromatic vinyl compounds in polymer block (C). Specifically, the content of structural units derived from aromatic vinyl compounds in polymer block (C) is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total structural units of polymer block (C).

[0063] The number average molecular weight (Mn) of the polymer block (C) is preferably in the range of 1,000 to 70,000. When the Mn of the polymer block (C) is 1,000 or more, the cohesive strength of the block copolymer (A) can be sufficiently ensured, and when it is 70,000 or less, the peel strength from the adherend can be sufficiently increased while maintaining the elasticity of the pressure-sensitive adhesive layer. The Mn of the polymer block (C) is preferably 2,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and still more preferably 7,000 or more. The upper limit of the Mn of the polymer block (C) is preferably 65,000 or less, more preferably 60,000 or less, and even more preferably 55,000 or less.

[0064] Furthermore, from the viewpoints of ensuring sufficient cohesive strength of the block copolymer (A), maintaining the flexibility of the pressure-sensitive adhesive layer, and sufficiently increasing the peel strength from the adherend, the weight average molecular weight (Mw) of the polymer block (C) is preferably in the range of 1,000 to 100,000. From the above viewpoints, the Mw of the polymer block (C) is preferably 2,000 or more, more preferably 3,000 or more, even more preferably 6,000 or more, and still more preferably 9,000 or more. The upper limit of the Mw of the polymer block (C) is preferably 90,000 or less, more preferably 85,000 or less, even more preferably 80,000 or less, and still more preferably 75,000 or less.

[0065] When block copolymer (A) has a plurality of polymer blocks (C) in one molecule, the terms "Mn of polymer block (C)" and "Mw of polymer block (C)" refer to the Mn and Mw, respectively, of all of the polymer blocks (C) in one molecule of block copolymer (A). For example, when block copolymer (A) is a (CDC) type triblock copolymer consisting of polymer block (C)-(meth)acrylic polymer block (D)-polymer block (C), the Mn of polymer block (C) in the triblock copolymer is the sum of the Mn of the two polymer blocks (C).

[0066] (Meth)acrylic Polymer Block (D) The (meth)acrylic polymer block (D) preferably has a Tg of −80° C. or higher and lower than 10° C. When the (meth)acrylic polymer block (D) has a Tg of −80° C. or higher, the cohesive strength of the pressure-sensitive adhesive layer obtained from the composition can be sufficiently ensured, and a pressure-sensitive adhesive layer exhibiting excellent adhesive properties can be formed. Furthermore, when the (meth)acrylic polymer block (D) has a Tg of less than −10° C., the adhesive properties of the block copolymer (A) can be sufficiently ensured. From the viewpoint of increasing the cohesive strength of the pressure-sensitive adhesive layer and improving the adhesive properties, the Tg of the (meth)acrylic polymer block (D) is preferably −70° C. or higher, more preferably −60° C. or higher. With regard to the upper limit of the Tg of the (meth)acrylic polymer block (D), from the viewpoint of improving the adhesive properties and flexibility of the block copolymer (A), it is preferably 0° C. or lower, more preferably −5° C. or lower, even more preferably −10° C. or lower, and even more preferably −20° C. or lower. The Tg range of the (meth)acrylic polymer block (D) is preferably in the range of -70°C or more and 0°C or less, and more preferably in the range of -60°C or more and -5°C or less.

[0067] The preferred ranges of Tg of the polymer block (C) and the (meth)acrylic polymer block (D) in the block copolymer (A) can be set by appropriately combining the preferred ranges of Tg of each block described above. Specifically, in the block copolymer (A), it is preferred that the Tg of the polymer block (C) is 10°C or more and 250°C or less, and the Tg of the (meth)acrylic polymer block (D) is -80°C or more and less than 10°C. It is more preferable that the Tg of the polymer block (C) is 10°C or more and 150°C or less, and the Tg of the (meth)acrylic polymer block (D) is -80°C or more and less than 10°C; it is even more preferable that the Tg of the polymer block (C) is 10°C or more and 90°C or less, and the Tg of the (meth)acrylic polymer block (D) is -80°C or more and less than 10°C; and it is even more preferable that the Tg of the polymer block (C) is 10°C or more and 90°C or less, and the Tg of the (meth)acrylic polymer block (D) is -70°C or more and 0°C or less.

[0068] The (meth)acrylic polymer block (D) is a polymer containing a (meth)acrylic monomer as a main structural unit. Examples of the (meth)acrylic monomer constituting the (meth)acrylic polymer block (D) include the same compounds as those exemplified as the (meth)acrylic monomer constituting the (meth)acrylic polymer (A).

[0069] From the viewpoint of obtaining a pressure-sensitive adhesive layer having excellent adhesive strength between flexible adherends, the (meth)acrylic polymer block (D) preferably contains a structural unit derived from a (meth)acrylic acid ester having a hydrocarbon group having 3 or more carbon atoms. As the (meth)acrylic acid ester having a hydrocarbon group having 3 or more carbon atoms, a (meth)acrylic acid alkyl ester, an aliphatic cyclic ester of (meth)acrylic acid, an aromatic ester of (meth)acrylic acid, an alkoxyalkyl (meth)acrylic acid ester, or a mixture of two or more of these can be preferably used. Specific examples of the (meth)acrylic acid alkyl ester, aliphatic cyclic ester of (meth)acrylic acid, an aromatic ester of (meth)acrylic acid, and an alkoxyalkyl (meth)acrylic acid ester include compounds having a hydrocarbon group having 3 or more carbon atoms among the compounds exemplified in the description of the (meth)acrylic monomer constituting the (meth)acrylic polymer (A).

[0070] A compound represented by the following formula (2) can be preferably used as the (meth)acrylic acid ester having a hydrocarbon group having 3 or more carbon atoms, in that it can improve the adhesive strength between flexible adherends while ensuring the adhesive properties of the (meth)acrylic polymer block (D). ２ =CR ５ -C(=O)O-R ６ ...(2) (In formula (2), R ５ represents a hydrogen atom or a methyl group, R ６ represents an alkyl group having 3 to 20 carbon atoms, an alkoxyalkyl group having 4 to 20 carbon atoms and having an alkoxy group having 3 or more carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 6 to 20 carbon atoms.

[0071] In the above formula (2), R ５ is preferably a hydrogen atom, since it is easy to adjust the Tg of the (meth)acrylic polymer block (D) to fall within the above range. ６ is preferably an alkyl group having 3 to 20 carbon atoms, more preferably an alkyl group having 4 to 12 carbon atoms, in that the adhesiveness of the (meth)acrylic polymer block (D) can be further increased.

[0072] In the (meth)acrylic polymer block (D), the content of structural units derived from a (meth)acrylic acid ester having a hydrocarbon group with 3 or more carbon atoms is preferably 20% by mass or more relative to all structural units in the (meth)acrylic polymer block (D). By setting the content of structural units derived from a (meth)acrylic acid ester having a hydrocarbon group with 3 or more carbon atoms to 20% by mass or more, a pressure-sensitive adhesive layer with higher adhesive strength between flexible adherends can be obtained. From this perspective, the content of structural units derived from a (meth)acrylic acid ester having a hydrocarbon group with 3 or more carbon atoms in the (meth)acrylic polymer block (D) is more preferably 25% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, and even more preferably 50% by mass or more.

[0073] The monomer constituting the (meth)acrylic polymer block (D) preferably contains at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters, since this allows for the production of a polymer block having a relatively low Tg and exhibiting sufficient tackiness, adhesiveness, and flexibility. Specific examples of the (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters include the same compounds as those exemplified in the description of the polymer block (C).

[0074] In the (meth)acrylic polymer block (D), the content of structural units derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters is preferably 30 mass % or more, more preferably 50 mass % or more, even more preferably 70 mass % or more, still more preferably 80 mass % or more, and still more preferably 90 mass % or more, based on the total structural units of the (meth)acrylic polymerizable block (D).

[0075] In particular, from the viewpoint of obtaining a pressure-sensitive adhesive layer having high cohesive strength while maintaining flexibility, the (meth)acrylic polymer block (D) preferably contains structural units derived from (meth)acrylic acid alkoxyalkyl ester. Specifically, the content of structural units derived from (meth)acrylic acid alkoxyalkyl ester is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total structural units of the (meth)acrylic polymer block (D). The upper limit of the content of structural units derived from (meth)acrylic acid alkoxyalkyl ester in the (meth)acrylic polymer block (D) is not particularly limited, but is preferably 80% by mass or less, more preferably 75% by mass or less, based on the total structural units of the (meth)acrylic polymer block (D).

[0076] As the (meth)acrylic acid alkoxyalkyl ester constituting the (meth)acrylic polymer block (D), from the viewpoint of obtaining a pressure-sensitive adhesive layer that is flexible and has high cohesive strength, a (meth)acrylic acid alkoxyalkyl ester having an alkoxy group having 1 or 2 carbon atoms can be preferably used.

[0077] In producing the (meth)acrylic polymer block (D), a crosslinkable group-containing monomer may be used to introduce a crosslinkable structural unit into the (meth)acrylic polymer block (D). When the (meth)acrylic polymer block (D) has a crosslinkable structural unit, the adhesive strength can be improved while maintaining good flexibility and texture at the bonded portion.

[0078] The crosslinkable group-containing monomer used in the production of the (meth)acrylic polymer block (D) is not particularly limited. From the viewpoint of enhancing the adhesiveness of the (meth)acrylic polymer block (D), the crosslinkable group-containing monomer used in the production of the (meth)acrylic polymer block (D) is preferably at least one selected from the group consisting of (meth)acrylic acid, a hydroxyalkyl (meth)acrylate compound, an epoxy group-containing (meth)acrylic acid ester, and a silyl group-containing (meth)acrylic acid ester. Among these, at least one selected from the group consisting of (meth)acrylic acid and a hydroxyalkyl (meth)acrylate compound is particularly preferred because it tends to be more effective in enhancing the adhesive strength of the (meth)acrylic polymer block (D).

[0079] When the (meth)acrylic polymer block (D) has a crosslinkable structural unit, the content of the crosslinkable structural unit is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, relative to the total structural units of the (meth)acrylic polymer block (D). By setting the content of the crosslinkable structural unit in the (meth)acrylic polymer block (D) to 0.1% by mass or more, a good crosslinked structure can be formed, and the adhesive strength can be further improved. The upper limit of the content of the crosslinkable structural unit is not particularly limited, but from the viewpoint of improving the flexibility of the obtained pressure-sensitive adhesive layer, it is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, relative to the total structural units of the (meth)acrylic polymer block (D). In addition, when producing the (meth)acrylic polymer block (D), one type of crosslinkable-containing monomer may be used alone, or two or more types may be used in combination.

[0080] In producing the (meth)acrylic polymer block (D), in addition to the above-mentioned monomers, monomers copolymerizable with the above-mentioned monomers may be used to the extent that the adhesive performance is not impaired. Examples of the monomers constituting the (meth)acrylic polymer block (D) include, in addition to the above, aliphatic vinyl compounds, amino group-containing vinyl compounds, amide group-containing vinyl compounds, polyfunctional alkenyl compounds, and nitrile group-containing unsaturated compounds.

[0081] The polymer block (C) may have the property of phase separation from the (meth)acrylic polymer block (D). Such a property is advantageous in that it facilitates the formation of a microphase-separated structure in the block copolymer (A). Based on the common technical knowledge at the time of filing, a person skilled in the art can easily design a polymer block (C) that phase separates from the (meth)acrylic polymer block (D). For example, the difference ΔSP (absolute value) between the SP value of the polymer block (C) calculated by a known method for calculating the SP value, which is a solubility parameter (e.g., the Fedors method), and the SP value of the (meth)acrylic polymer block (D) may be 0.01 or more. The difference ΔSP is, for example, 0.05 or more, or may be 0.1 or more, or may be 0.5 or more. When using the Fedors method, the SP value is calculated by the R.F. The phase separation property between the blocks can be easily estimated by observing the structure of the intended block copolymer (A) using an electron microscope, a scanning probe microscope, small-angle X-ray scattering, or the like.

[0082] The number and arrangement of blocks of the block copolymer (A) are not particularly limited, as long as the block copolymer (A) has the polymer block (C) and the (meth)acrylic polymer block (D). Specific examples of the block copolymer (A) include a (CD) type diblock copolymer consisting of the polymer block (C) and the (meth)acrylic polymer block (D); a (CDC) type triblock copolymer consisting of the polymer block (C)-(meth)acrylic polymer block (D)-polymer block (C); and a (DCD) type triblock copolymer consisting of the (meth)acrylic polymer block (D)-polymer block (C)-(meth)acrylic polymer block (D). The block copolymer (A) may further have a polymer block other than the polymer block (C) and the (meth)acrylic polymer block (D). Of these, the block copolymer (A) preferably contains a triblock copolymer of the polymer block (C)-(meth)acrylic polymer block (D)-polymer block (C). In this structure, the block copolymer (A) is likely to form a pseudo-crosslinked structure via the polymer block (C), and the effect of improving adhesive strength as well as adhesive performance can be sufficiently obtained. The content of the triblock copolymer in the block copolymer (A) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0083] The ratio of the polymer block (C) to the (meth)acrylic polymer block (D) in the block copolymer (A) (hereinafter also referred to as the "block ratio"), expressed as polymer block (C) / (meth)acrylic polymer block (D), is preferably 3 / 97 to 30 / 70 by mass. When the block ratio is within this range, the block copolymer (A) has the polymer block (C) that constitutes a hard segment and can serve as a pseudo-crosslinking point, and the (meth)acrylic polymer block (D) that can serve as a soft segment, making it possible to obtain a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer with excellent adhesiveness while maintaining flexibility. Furthermore, by lowering the Tg of the polymer block (C), for example, to 100°C or less, preferably 90°C or less, the block copolymer (A) is less likely to harden even when the ratio of the polymer block (C) is relatively high. This makes it possible to maintain the flexibility and texture of the bonded portion while increasing the adhesive strength. From these viewpoints, the block ratio is more preferably 6 / 94 to 30 / 70, even more preferably 7 / 93 to 30 / 70, and still more preferably 8 / 92 to 30 / 70. The block ratio can be calculated from the monomers and / or polymer blocks used in the polymerization and the amount of monomer consumed measured by gas chromatography (GC). Details of the calculation method follow the method described in the Examples below.

[0084] -Method for producing block copolymer (A) The block copolymer (A) is not particularly limited in terms of production method, and can be produced by any known production method, as long as a polymer having the polymer block (C) and the (meth)acrylic polymer block (D) can be obtained. Examples of methods for producing the block copolymer (A) include methods that utilize various controlled polymerization methods, such as living radical polymerization and living anionic polymerization, and methods of coupling polymers having functional groups together. Among these, living radical polymerization is preferred because it is easy to operate and can be applied to a wide range of monomers.

[0085] 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.

[0086] 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 method), nitroxy radical method (NMP method), atom transfer radical polymerization (ATRP method), polymerization method using an organotellurium compound (TERP method), polymerization method using an organoantimony compound (SBRP method), polymerization method using an organobismuth compound (BIRP method), and iodine transfer polymerization. Among these, the RAFT method, the NMP method, and the ATRP method are preferred from the viewpoints of controllability of polymerization and ease of implementation.

[0087] 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 as the RAFT agent, such as dithioester compounds, xanthate compounds, trithiocarbonate compounds, and dithiocarbamate compounds. As the RAFT agent, a monofunctional compound having only one active site may be used, or a bifunctional or higher functional compound may be used. In terms of efficiently obtaining a block copolymer having three or more blocks, it is preferable to use a bifunctional RAFT agent. The amount of the RAFT agent used is appropriately adjusted depending on the type of monomer and RAFT agent, etc.

[0088] As the polymerization initiator used in polymerization by the RAFT method, known radical polymerization initiators such as azo compounds, organic peroxides, and persulfates can be used. Of 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 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis[N-(2-propenyl)-2-methylpropionamide], and 2,2'-azobis(N-butyl-2-methylpropionamide). Only one type of polymerization initiator may be used, or two or more types may be used in combination. The proportion of the polymerization initiator used is not particularly limited, but from the viewpoint of stably carrying out the polymerization reaction and obtaining a polymer with a narrower molecular weight distribution, the amount of the polymerization initiator used is preferably 0.01 mol or more and 0.5 mol or less, and more preferably 0.01 mol or more and 0.2 mol or less, relative to 1 mol of the RAFT agent.

[0089] In the polymerization reaction by the RAFT method, the reaction temperature 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 in that the polymerization reaction can proceed smoothly. A reaction temperature of 100° C. or lower is preferred in that side reactions can be suppressed and restrictions on usable polymerization initiators and solvents are relaxed.

[0090] 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. In producing the block copolymer (A), the type of nitroxide radical is not particularly limited, and commercially available nitroxide polymerization initiators can be used. From the viewpoint of polymerization controllability when polymerizing a monomer containing an acrylate, it is preferable to use a compound represented by the following formula (3) as the nitroxide compound: (In formula (3), R ８ represents a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, and R ９ represents an alkyl group having 1 to 2 carbon atoms or a nitrile group, and R １０ Ha-(CH ２ ) r-, r represents an integer of 0 to 2, R １１ and R １２ Each of R independently represents an alkyl group having 1 to 4 carbon atoms. １１ may be the same or different, and multiple R １２ may be the same or different.)

[0091] The nitroxide compound represented by formula (3) 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 polymerization precursor is then subjected to secondary dissociation under heating, resulting in living polymerization of the vinyl monomer. In this case, the polymerization precursor has two or more active sites in its molecule, allowing for the production of a polymer with a narrower molecular weight distribution. In terms of the ease of efficiently obtaining block copolymer (A), it is preferable to use a bifunctional polymerization precursor having two active sites in its molecule. The amount of the nitroxide compound used is adjusted appropriately depending on the type of monomer and nitroxide compound, among other factors.

[0092] When the block copolymer (A) is produced by the NMP method, polymerization may be carried out by adding 0.001 to 0.2 moles of a nitroxide radical represented by the following formula (4) relative to 1 mole of the nitroxide compound represented by the above formula (3). (In formula (4), R １３ and R １４ Each of R independently represents an alkyl group having 1 to 4 carbon atoms. １３ may be the same or different, and multiple R １４ may be the same or different.)

[0093] Adding 0.001 moles or more of the nitroxide radical represented by formula (4) above can shorten 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.

[0094] 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, and even more preferably 70° C. or higher and 120° C. or lower. By setting the reaction temperature to 50° C. or higher, the polymerization reaction can proceed smoothly. Furthermore, by setting the reaction temperature to 140° C. or lower, side reactions such as radical chain transfer tend to be suppressed.

[0095] In the ATRP method, a polymerization reaction is generally carried out using an organic halide as a polymerization initiator and a transition metal complex as a catalyst. The organic halide used as the polymerization initiator may be a monofunctional compound or a bifunctional or higher functional compound. In terms of efficiently obtaining the block copolymer (A), it is preferable to use a bifunctional compound. As the type of halogen, bromides and chlorides are preferred. 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 that the polymerization reaction can proceed smoothly.

[0096] For example, when a (CDC) triblock copolymer consisting of polymer block (C)-(meth)acrylic polymer block (D)-polymer block (C) is obtained by living radical polymerization, the target block copolymer may be obtained by sequentially polymerizing each block. In this case, first, in the first polymerization step, the constituent monomers of polymer block (C) are polymerized to obtain polymer block (C), and then, in the second polymerization step, the constituent monomers of (meth)acrylic polymer block (D) are polymerized to obtain (meth)acrylic polymer block (D). Furthermore, in the third polymerization step, the constituent monomers of polymer block (C) are polymerized. This allows the (CDC) triblock copolymer to be obtained. As the polymerization initiator, it is preferable to use the above-mentioned monofunctional polymerization initiator or polymerization precursor.

[0097] Furthermore, when a (CDC) triblock copolymer is produced using a bifunctional polymerization initiator or polymerization precursor and the two-stage polymerization process shown below, the target product can be obtained more efficiently. First, in the first polymerization process, the constituent monomers of the polymer block (C) are polymerized to obtain the polymer block (C), and then in the second polymerization process, the constituent monomers of the (meth)acrylic polymer block (D) are polymerized. This allows the production of a (CDC) triblock copolymer. This method simplifies the process compared to when each block is produced by sequentially polymerizing it.

[0098] The polymerization of the block copolymer (A) 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 can be used as the chain transfer agent.

[0099] When producing the block copolymer (A), 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.In addition, bulk polymerization or the like may be used without using a polymerization solvent.

[0100] [2] Random Copolymer (A) The above-mentioned explanation for the (meth)acrylic polymer block (D) applies to specific examples and preferred examples of the Tg and constituent monomers of the random copolymer (A). However, from the viewpoint of ensuring the flexibility of the pressure-sensitive adhesive layer, in the random copolymer (A), the structural units derived from a (meth)acrylic acid ester having a hydrocarbon group having 3 or more carbon atoms preferably account for 80 mass% or less, more preferably 70 mass% or less, even more preferably 60 mass% or less, and even more preferably 50 mass% or less of the total structural units of the random copolymer (A).

[0101] Similarly to the (meth)acrylic polymer block (D), the random copolymer (A) preferably contains a structural unit derived from a crosslinkable group-containing monomer, since this can improve the adhesive strength between flexible adherends. Specific examples and preferred examples of the crosslinkable group-containing monomer used in producing the random copolymer (A) are the same as those for the (meth)acrylic polymer block (D).

[0102] The content of the crosslinkable structural units in the random copolymer (A) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the total structural units of the random copolymer (A). From the viewpoint of ensuring the flexibility of the pressure-sensitive adhesive layer, the upper limit of the content of the crosslinkable structural units is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total structural units of the random copolymer (A).

[0103] The random copolymer (A) can be obtained by polymerizing the monomers using a known radical polymerization method such as solution polymerization. When producing the random copolymer (A) by solution polymerization, 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 copolymerize, thereby obtaining the desired random copolymer (A). The method for charging the raw materials including the monomers may be a batch-type initial lump-sum charge in which all raw materials are charged at once, a semi-continuous charge 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 the produced resin is continuously withdrawn from the reactor at the same time.

[0104] 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, for example, 1 to 50% by mass of the total amount of monomers used in polymerization relative to the total amount of the organic solvent and the monomers.

[0105] 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. Alternatively, a redox polymerization initiator consisting of a known oxidizing agent and a known reducing agent may be used. Furthermore, a known chain transfer agent may be used in combination with the polymerization initiator.

[0106] 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).

[0107] 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.

[0108] 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, or the like as a reducing agent and potassium peroxodisulfate, hydrogen peroxide, tert-butyl hydroperoxide, or the like as an oxidizing agent. In producing the random copolymer (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.

[0109] The (meth)acrylic polymer (A) to be blended in the present composition is preferably a block copolymer (A) in that a pressure-sensitive adhesive layer having excellent adhesive properties can be obtained.

[0110] From the viewpoint of ensuring sufficient adhesiveness of the pressure-sensitive adhesive layer obtained using the composition, the content of the (meth)acrylic polymer (A) in the composition is preferably 70% by mass or more, based on the total amount of polymers contained in the composition, more preferably 80% by mass or more, and even more preferably 85% by mass or more, based on the total amount of polymers contained in the composition.

[0111] <Other Components> The present composition may contain only the (meth)acrylic polymer (A), or may further contain, as necessary, various components (hereinafter also referred to as "other components") such as polymers other than the (meth)acrylic polymer (A), additives, solvents, etc. The other components that may be blended in the present composition will be described below.

[0112] Vinyl Polymer (B) The composition may further contain, in addition to the (meth)acrylic polymer (A), a vinyl polymer (hereinafter also referred to as "vinyl polymer (B)") having a glass transition temperature (Tg) of 30°C or higher and 200°C or lower and a number average molecular weight (Mn) of 500 or higher and 10,000 or lower. By forming a pressure-sensitive adhesive layer using a pressure-sensitive adhesive composition containing such a vinyl polymer (B) together with the (meth)acrylic polymer (A), it is possible to cause partial segregation of the vinyl polymer (B) in the surface layer portion of the pressure-sensitive adhesive layer. This allows the Tg of the surface layer portion of the pressure-sensitive adhesive layer to be sufficiently high, thereby improving adhesion when bonding flexible adherends together.

[0113] When the Tg of the vinyl polymer (B) is 30°C or higher, when a pressure-sensitive adhesive layer is formed from the pressure-sensitive adhesive composition, the Tg of the surface layer of the pressure-sensitive adhesive layer can be increased, thereby ensuring sufficient adhesiveness. On the other hand, due to restrictions on raw material monomers, the Tg of the vinyl polymer (B) is generally 200°C or lower. The Tg of the vinyl polymer (B) is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, still more preferably 70°C or higher, and even more preferably 75°C or higher. From the viewpoint of ensuring the stretchability of the pressure-sensitive adhesive layer, the upper limit of the Tg of the vinyl polymer (B) is preferably 150°C or lower, more preferably 130°C or lower, even more preferably 120°C or lower, and even more preferably 110°C or lower.

[0114] The preferred range of Tg of the vinyl polymer (B) can be determined by appropriately combining the above-mentioned upper and lower limits of Tg. The range of Tg of the vinyl polymer (B) is preferably 40°C or higher and 150°C or lower, more preferably 40°C or higher and 130°C or lower, even more preferably 50°C or higher and 120°C or lower, and still more preferably 60°C or higher and 110°C or lower.

[0115] Various radically polymerizable vinyl monomers can be used as the monomer constituting the vinyl polymer (B). Examples of such vinyl monomers include the same compounds as those exemplified as the constituent monomers of the (meth)acrylic polymer (A). Among these, it is preferable that the vinyl polymer (B) contains a structural unit derived from a hydrocarbon-based vinyl monomer, in terms of having suitable compatibility with the (meth)acrylic polymer (A). Specific examples of hydrocarbon-based vinyl monomers include (meth)acrylic acid alkyl esters, aliphatic cyclic esters of (meth)acrylic acid, aromatic esters of (meth)acrylic acid, and aromatic vinyl compounds. These compounds may be used alone or in combination of two or more.

[0116] In the vinyl polymer (B), the content of structural units derived from hydrocarbon vinyl monomers is preferably in the range of 30% by mass or more and 100% by mass or less, based on all structural units contained in the vinyl polymer (B), more preferably 50% by mass or more, even more preferably 70% by mass or more, and still more preferably 80% by mass or more, based on all structural units contained in the vinyl polymer (B).

[0117] In producing the vinyl polymer (B), an aliphatic cyclic vinyl monomer can be preferably used because it can relatively increase Tg and enhance the effect of improving adhesiveness. The aliphatic cyclic vinyl monomer is preferably an aliphatic cyclic ester of (meth)acrylic acid, and specific examples thereof include the same compounds as the aliphatic cyclic ester of (meth)acrylic acid exemplified in the description of the (meth)acrylic polymer (A).

[0118] In the vinyl polymer (B), the content of structural units derived from alicyclic vinyl monomers is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, based on the total structural units contained in the vinyl polymer (B). The upper limit of the content of structural units derived from alicyclic vinyl monomers is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less, based on the total structural units contained in the vinyl polymer (B). The content range of structural units derived from alicyclic vinyl monomers is preferably 1% by mass or more to 90% by mass or less, more preferably 10% by mass or more to 80% by mass or less, and even more preferably 15% by mass or more to 70% by mass or less.

[0119] Among the above, at least one selected from the group consisting of tert-butyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, cyclohexyl (meth)acrylate and adamantyl (meth)acrylate is preferably used as the monomer constituting the vinyl polymer (B), since this allows the Tg of the vinyl polymer (B) to be set high, the vinyl polymer (B) is likely to segregate at the surface when a pressure-sensitive adhesive layer is formed, and good heat resistance tends to be obtained.

[0120] The Mn of the vinyl polymer (B) is preferably 500 or more and 10,000 or less. By setting the Mn of the vinyl polymer (B) to 10,000 or less, sufficient segregation of the vinyl polymer (B) occurs in the pressure-sensitive adhesive layer, and the adhesiveness can be sufficiently improved. Furthermore, compatibility with the (meth)acrylic polymer (A) can be sufficiently ensured. By setting the Mn of the vinyl polymer (B) to 500 or more, the amounts of polymerization initiator and chain transfer agent used during polymer production can be appropriate, and a decrease in productivity can be avoided.

[0121] The Mn of the vinyl polymer (B) is more preferably 1,000 or more, even more preferably 1,500 or more, still more preferably 2,000 or more, and even more preferably 3,000 or more. The upper limit of the Mn of the vinyl polymer (B) is more preferably 9,500 or less, even more preferably 9,000 or less, still more preferably 7,000 or less, and even more preferably 5,000 or less. The Mn of the vinyl polymer (B) is more preferably in the range of 1,000 or more to 9,500 or less, even more preferably 1,000 or more to 9,000 or less, still more preferably 1,500 or more to 7,000 or less, and even more preferably 2,000 or more to 5,000 or less.

[0122] In the vinyl polymer (B), the molecular weight distribution (Mw / Mn), which is the ratio of Mw to Mn, is preferably 3.0 or less, since good adhesive strength is easily obtained. Mw / Mn is more preferably 2.5 or less, and even more preferably 2.0 or less. The lower limit of Mw / Mn of the vinyl polymer (B) is not particularly limited, and is 1.0 or more.

[0123] The vinyl polymer (B) is not particularly limited in its production method and can be obtained by a known production method, such as solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization, by polymerizing the above-mentioned monomers.

[0124] When a vinyl polymer (B) is blended into the pressure-sensitive adhesive composition, the content of the vinyl polymer (B) is preferably in the range of 0.5 to 15 parts by mass, calculated as solids, per 100 parts by mass of the (meth)acrylic polymer (A). When the content of the vinyl polymer (B) is 0.5 parts by mass or more, a sufficient amount of the vinyl polymer (B) is present in the surface layer portion of the pressure-sensitive adhesive layer, thereby achieving a sufficient effect of improving adhesiveness. Furthermore, when the content of the vinyl polymer (B) is 15 parts by mass or less, the flexibility of the pressure-sensitive adhesive layer can be maintained at a high level, and good adhesiveness can be maintained. From this perspective, the lower limit of the content of the vinyl polymer (B) is more preferably 1 part by mass or more, and even more preferably 1.5 parts by mass or more, per 100 parts by mass of the (meth)acrylic polymer (A). The upper limit of the content of the vinyl polymer (B) is more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the (meth)acrylic polymer (A).

[0125] When the present composition contains a vinyl polymer (B), a preferred range of the content of the vinyl polymer (B) can be determined by appropriately combining the above-mentioned upper and lower limits of the content of the vinyl polymer (B). Specifically, the content of the vinyl polymer (B) is preferably 0.5 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the (meth)acrylic polymer (A).

[0126] Crosslinking Agent When the (meth)acrylic polymer (A) has a crosslinkable functional group, a crosslinking agent capable of reacting with the crosslinkable functional group may be blended into the pressure-sensitive adhesive composition. By blending a crosslinking agent into this composition, the adhesive strength of the pressure-sensitive adhesive layer can be further improved. This makes it possible to improve the adhesive strength of the pressure-sensitive adhesive layer while maintaining the flexibility and texture of the flexible adherends, even when various flexible adherends are bonded together.

[0127] Examples of the crosslinking agent (curing agent) include an epoxy-based crosslinking agent having two or more glycidyl groups, an isocyanate-based crosslinking agent having two or more isocyanate groups, an aziridine-based crosslinking agent having two or more aziridinyl groups, an oxazoline-based crosslinking agent having an oxazoline group, a metal chelate compound, a butylated melamine compound, etc. Among these, at least one selected from the group consisting of an epoxy-based crosslinking agent, an isocyanate-based crosslinking agent, and an aziridine-based crosslinking agent is preferred in that it allows for easy adjustment of the cohesive strength and adhesiveness of the pressure-sensitive adhesive layer, and an isocyanate-based crosslinking agent is preferred in that it allows for the formation of a pressure-sensitive adhesive layer with excellent cohesive strength.

[0128] Specific examples of the crosslinking agent include epoxy-based crosslinking agents, such as polyfunctional glycidyl compounds 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.

[0129] Examples of isocyanate crosslinking agents 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; 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.

[0130] Examples of the aziridine crosslinking agent 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).

[0131] When a crosslinking agent is blended into the composition, the content of the crosslinking agent in the composition is not particularly limited. The content of the crosslinking agent is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 5 parts by mass, and even more preferably 0.05 to 2 parts by mass, per 100 parts by mass of the (meth)acrylic polymer (A). By setting the content of the crosslinking agent within the above range, it is possible to sufficiently obtain the effect of improving adhesive strength by forming a crosslinked structure, while ensuring the flexibility of the pressure-sensitive adhesive layer.

[0132] Silane Coupling Agent The present composition may further contain a silane coupling agent. A pressure-sensitive adhesive composition containing a silane coupling agent in addition to the (meth)acrylic polymer (A) can provide a pressure-sensitive adhesive layer with even better adhesion to flexible substrates. Examples of the silane coupling agent include silane coupling agents having one or more functional groups such as an epoxy group, a (meth)acryloyl group, an amino group, a vinyl group, a thiol group, an isocyanate group, or a blocked isocyanate group.

[0133] Specific examples of the silane coupling agent include silane coupling agents having an epoxy group, such as oxiranyl group-containing silane coupling agents, such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 8-glycidoxyoctyltriethoxysilane; and oxetanyl group-containing silane coupling agents, such as 2-(3,4-oxetanylcyclohexyl)ethyltrimethoxysilane, 3-oxetanylpropyltrimethoxysilane, 3-oxetanylpropylmethyldiethoxysilane, 3-oxetanylpropyltriethoxysilane, and 8-oxetanyloctyltriethoxysilane.

[0134] Specific examples of silane coupling agents having a (meth)acryloyl group include 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, 6-(meth)acryloyloxyhexyltrimethoxysilane, and 8-(meth)acryloyloxyoctyltrimethoxysilane.

[0135] Specific examples of silane coupling agents having an amino group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-(3-cyclohexylamino)propyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane.

[0136] Specific examples of the silane coupling agent having a thiol group include 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane.

[0137] Specific examples of silane coupling agents having a vinyl group include vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, vinyl(trimethoxysilyl) ether, vinyl(methyldiethoxysilyl) ether, and vinyl(triethoxysilyl) ether.

[0138] Specific examples of silane coupling agents having an isocyanate group or a blocked isocyanate group include isocyanatoalkyltrialkoxysilane compounds such as isocyanatomethyltrimethoxysilane, 3-isocyanatopropyltrimethoxysilane, 6-isocyanatohexyltrimethoxysilane, 8-isocyanatooctyltrimethoxysilane, isocyanatomethyltriethoxysilane, 3-isocyanatopropyltriethoxysilane, 6-isocyanatohexyltriethoxysilane, and 8-isocyanatooctyltriethoxysilane; isocyanatomethylmethyldimethoxysilane, 3-isocyanatopropylmethyldimethoxysilane, 6-isocyanatohexylmethyldimethoxysilane, 8-isocyanatooctylmethyldimethoxysilane, isocyanatomethylmethyldiethoxysilane, 3-isocyanatopropylmethyldiethoxysilane, 6-isocyanatohexylmethyldiethoxysilane, isocyanatoalkyl monoalkyl dialkoxysilane compounds such as isocyanatomethyl dimethyl methoxysilane, 3-isocyanatopropyl dimethyl methoxysilane, 6-isocyanatohexyl dimethyl methoxysilane, 8-isocyanatooctyl dimethyl methoxysilane, isocyanatomethyl dimethyl ethoxysilane, 3-isocyanatopropyl dimethyl ethoxysilane, 6-isocyanatohexyl dimethyl ethoxysilane, and isocyanatooctyl dimethyl ethoxysilane; isocyanatoalkyl trialkoxysilane compounds, blocked isocyanatoalkyl alkoxysilane compounds in which the isocyanate group of an isocyanatoalkyl monoalkyl dialkoxysilane compound or an isocyanatoalkyl dialkyl alkoxysilane compound is protected; and the like.

[0139] Regarding the blocked isocyanatoalkylalkoxysilane compound, the protecting agent for protecting the isocyanate group is not particularly limited, and known compounds can be used as appropriate. Examples of protecting agents include alcohols (ethanol, etc.), caprolactams, dimethylpyrazole, and methyl ethyl ketone oxime. Commercially available blocked isocyanatoalkylalkoxysilane compounds can also be used. Commercially available blocked isocyanatoalkylalkoxysilane compounds include Shin-Etsu Silicone X-12-1195, X-12-1293, and X-12-1308ES (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0140] The silane coupling agent to be blended in the present composition is particularly preferably a silane coupling agent having at least one selected from the group consisting of an epoxy group, a (meth)acryloyl group, an isocyanate group, and a blocked isocyanate group, and more preferably a silane coupling agent having at least one selected from the group consisting of an isocyanate group and a blocked isocyanate group, because of its high effect of improving peel strength when a fiber fabric and a film-like resin material are bonded together.

[0141] When a silane coupling agent is blended in the present composition, the content of the silane coupling agent in the present composition is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the content of (meth)acrylic polymer (A).In addition, the content of the silane coupling agent is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the content of (meth)acrylic polymer (A).By making the content of the silane coupling agent within the above range, the addition of the silane coupling agent can sufficiently obtain the effect of improving adhesive strength while ensuring the elasticity of the pressure-sensitive adhesive layer.

[0142] The composition may further contain fine particles. By blending fine particles together with the (meth)acrylic polymer (A) to form a pressure-sensitive adhesive composition, it is possible to obtain a pressure-sensitive adhesive layer with further improved adhesive strength to various flexible adherends.

[0143] The microparticles are not particularly limited as long as the effects of the present disclosure can be obtained. The microparticles incorporated into the composition may be inorganic or organic. Examples of inorganic materials constituting the inorganic microparticles include silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, titanium dioxide, talc, glass (soda glass, float glass, etc.), or a combination of two or more of these. Examples of organic materials constituting the organic microparticles include (meth)acrylic resins, polystyrene resins, polyurethane resins, polyolefin resins (e.g., polyethylene, polypropylene, etc.), silicone resins, epoxy resins, nylon resins, or a combination of two or more of these. Examples of (meth)acrylic resins include homopolymers of methyl methacrylate, copolymers of methyl methacrylate with other monomers (e.g., styrene, vinyl acetate, methyl acrylate, ethyl acrylate, etc.), and crosslinked polymers of these homopolymers or copolymers. The microparticles may be hot-melt powders.

[0144] Among these, the fine particles are preferably organic fine particles, and more preferably fine particles formed using one or more selected from the group consisting of (meth)acrylic resin, polyurethane resin, and nylon resin. When the fine particles are formed using one or more resins selected from the group consisting of (meth)acrylic resin, polyurethane resin, and nylon resin, the resin may be a hot melt resin. The shape of the fine particles is not particularly limited, but spherical ones can be preferably used.

[0145] The volume average particle diameter of the microparticles can be appropriately selected depending on the thickness of the pressure-sensitive adhesive layer, etc. Specifically, the volume average particle diameter of the microparticles is preferably 5 to 200 μm, more preferably 5 to 100 μm, and even more preferably 10 to 70 μm. The volume average particle diameter of the microparticles is a value measured using a laser diffraction / scattering particle size distribution analyzer.

[0146] When microparticles are blended in this composition, the content of microparticles in this composition is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the content of (meth)acrylic polymer (A).In addition, the content of microparticles is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the content of (meth)acrylic polymer (A).By making the content of microparticles within the above range, it can ensure the elasticity and adhesiveness of the pressure-sensitive adhesive layer.

[0147] Tackifier The composition may 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 based on 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% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, relative to the content of the (meth)acrylic polymer (A).

[0148] The 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% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, based on the content of the (meth)acrylic polymer (A).

[0149] Examples of additives that may be blended into the composition include the above-mentioned vinyl polymer (B), crosslinking agent, silane coupling agent, fine particles, tackifier, and plasticizer, as well as, for example, antioxidants, ultraviolet absorbers, antiaging agents, flame retardants, mildew inhibitors, fillers, colorants, and antistatic agents. The content of the additives can be appropriately set depending on the various additives within a range that does not impair the effects of the present disclosure.

[0150] Solvent: The present composition may be a solution-type PSA composition in which the (meth)acrylic polymer (A) and optional components are dissolved in a solvent. When the present composition is a solution-type PSA composition, the solvent used to prepare the PSA composition may be an organic solvent capable of dissolving the (meth)acrylic 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 mixture of two or more of these solvents. For example, a solvent-type PSA composition can be obtained by dissolving the (meth)acrylic polymer (A) in one or more organic solvents selected from the group consisting of ethyl acetate, butyl acetate, ethyl methyl ketone, and toluene. Furthermore, when preparing the present composition, an aqueous medium capable of dispersing the (meth)acrylic polymer (A) may be used as the solvent, and the (meth)acrylic polymer (A) may be dispersed in the aqueous medium to form an emulsion-type PSA composition.

[0151] The present composition may contain a (meth)acrylic polymer (A), and there are no particular limitations on the form of the composition. For example, in addition to the (meth)acrylic polymer (A), the composition may contain a monofunctional and / or polyfunctional (meth)acrylic monomer, a photopolymerization initiator, and the like, thereby constituting a so-called syrup-type photocurable pressure-sensitive adhesive composition that is cured by active energy rays such as ultraviolet light. In the case of a photocurable pressure-sensitive adhesive composition, the composition may contain a solvent such as an organic solvent, but is usually prepared and used as a solventless type that does not contain a solvent. Alternatively, the present composition may be a solid or semi-solid pressure-sensitive adhesive composition containing the (meth)acrylic polymer (A) and components blended as necessary.

[0152] In the case of a solution-type PSA composition, the solids concentration in the composition (i.e., the ratio of the mass of components other than the solvent in the PSA composition to the total mass of the PSA composition) is not particularly limited, but is preferably 1 to 70 mass%. When the solids concentration is 1 mass% or more, a PSA layer with sufficient thickness can be formed. When the solids concentration is 70 mass% or less, good coatability can be ensured and a PSA layer with uniform thickness can be easily formed. The solids concentration in the PSA composition is more preferably 5 to 60 mass%, and even more preferably 10 to 50 mass%.

[0153] <Production of Pressure-Sensitive Adhesive Layer> The pressure-sensitive adhesive layer can be formed by applying the composition to a separator or the like and drying as necessary. Resin films made of various resin materials can be used as the separator. Examples of such resin materials include polyester resins such as polyethylene terephthalate, polyethersulfone resins, acetate resins, polycarbonate resins, and polyolefin resins. For example, to form a pressure-sensitive adhesive layer using a liquid pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition is applied to a separator by a known coating method, and the solvent is 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 duration that can remove the solvent, and can be appropriately set depending on the type of solvent, solids concentration, and the like.

[0154] <Characteristics of the Pressure-Sensitive Adhesive Layer> Storage Modulus The pressure-sensitive adhesive layer formed using the present composition has a storage modulus (G') at 23°C of 1.0 MPa or less. If the storage modulus at 23°C exceeds 1.0 MPa, when flexible adherends are bonded together, the flexibility and texture of the bonded portion cannot be sufficiently ensured. From the viewpoint of ensuring sufficient flexibility and texture of the bonded portion, the storage modulus of the pressure-sensitive adhesive layer at 23°C is preferably 0.8 MPa or less, more preferably 0.6 MPa or less, even more preferably 0.5 MPa or less, and even more preferably 0.4 MPa or less.

[0155] In this specification, the storage modulus of the pressure-sensitive adhesive layer at 23°C is a value obtained by measuring the shear viscoelasticity of an 800 µm thick pressure-sensitive adhesive layer under conditions of a heating rate of 2°C / min, a strain of 0.1%, and a measurement frequency of 1 Hz. Details of the method for measuring the storage modulus are as described in the Examples below. The storage modulus of the pressure-sensitive adhesive layer can be adjusted as desired by adjusting the composition and degree of crosslinking of the (meth)acrylic polymer (A), the Tg and the amount of addition of optional components (e.g., the vinyl polymer (B) and tackifier described below). For example, the storage modulus of the pressure-sensitive adhesive layer can be adjusted by using one or more of alkyl (meth)acrylates having an alkyl group with 1 to 4 carbon atoms and alkoxyalkyl (meth)acrylates having an alkoxy group with 1 to 4 carbon atoms as constituent monomers of the (meth)acrylic polymer (A), and adjusting the type and amount of these monomers used.

[0156] Gel Fraction The gel fraction of the pressure-sensitive adhesive layer made of the composition is preferably 90% or less. By setting the gel fraction to 90% or less, both adhesion and stretchability can be achieved when bonding flexible adherends together. From this perspective, the gel fraction of the pressure-sensitive adhesive layer is more preferably 80% or less, even more preferably 70% or less, and particularly preferably 60% 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 (= (W2 / W1) × 100 [%]). Details will be determined according to the measurement method described in the Examples below.

[0157] <Product> The product of the present disclosure is obtained by bonding flexible adherends (excluding fiber fabrics, conductive sheets, combinations of fiber fabrics and conductive sheets, and combinations of fiber fabrics and elastomer substrates) together via a pressure-sensitive adhesive layer formed from the composition described above. That is, the product of the present disclosure includes a first adherend, a second adherend, and a pressure-sensitive adhesive layer, and the first and second adherends are bonded together via the pressure-sensitive adhesive layer formed from the composition. However, the first and second adherends are flexible adherends, and the combination is different from fiber fabrics, conductive sheets, combinations of fiber fabrics and conductive sheets, and combinations of fiber fabrics and elastomer substrates. The pressure-sensitive adhesive layer formed from the composition can exhibit excellent adhesiveness while suppressing resistance to bending and stretching of the adherends at the bonded portion and maintaining the texture intact, even when flexible adherends are bonded together.

[0158] The present composition can form a highly adhesive pressure-sensitive adhesive layer while maintaining the flexibility, flexibility, and texture of flexible adherends when they are bonded together. There are no particular limitations on the products that can be produced using the present composition. For example, the present composition can be used as an adhesive for a wide variety of products, including everyday clothing (e.g., decorative items) for the production of clothing for a wide range of uses, such as Western and Japanese clothing, ethnic clothing, underwear, outerwear, tops, bottoms, outdoor gear, workwear, uniforms, formal wear, swimwear, sportswear, socks, hats, shoes, and gloves; handicrafts; clothing accessories (e.g., belts, bags, backpacks, etc.); sporting goods (e.g., bat and racket grips, gloves, etc.); electronic components; automotive interior parts (e.g., car seats and seat belts, etc.); seal packing; tires; furniture; and various daily commodities.

[0159] To obtain the product of the present disclosure, first, flexible adherends are bonded together so that they are in contact with each other via the pressure-sensitive adhesive layer formed from the present composition. Subsequently, temporary pressure-bonding is performed as necessary to obtain a laminate of flexible adherend / pressure-sensitive adhesive layer / flexible adherend. The laminate is then heated (preferably by thermocompression bonding) to obtain a product in which the adherends are bonded together via the pressure-sensitive adhesive layer formed from the present composition.

[0160] When bonding adherends together by thermocompression, the pressure applied during bonding may be appropriately set so as to obtain the desired adhesive strength. The heating temperature is preferably set to the heat resistance temperature or lower of the flexible adherends used.

[0161] The present disclosure will be specifically described below using examples. However, the present disclosure 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 each example were analyzed using the following methods.

[0162] <Molecular weight measurement> Using a gel permeation chromatograph (model "HLC-8320", manufactured by Tosoh Corporation), the number average molecular weight (Mn) and weight average molecular weight (Mw) in terms of polystyrene were obtained under the following conditions. The molecular weight distribution (Mw / Mn) was calculated from the obtained values. Measurement conditions Column: 4 columns of TSKgel SuperMultiporeHZ-M manufactured by Tosoh Corporation Column temperature: 40°C Eluent: Tetrahydrofuran Detector: RI Flow rate: 600 μL / min

[0163] <Monomer composition ratio (mass %) of polymer> The monomer composition ratio (mass %) of the polymer was calculated from the charged amount and the amount of monomer consumed measured by gas chromatography (GC). The GC measurement was carried out under the following conditions: GC: Agilent Technologies (7820A GC System), detector: FID, column: 100% dimethylsiloxane (CP-Sil 5CB), column length: 30 m, column inner diameter: 0.32 mm, calculation method: internal standard method

[0164] <Glass transition temperature (Tg) of polymer> The glass transition temperature (Tg) of the polymer was determined from the intersection of the baseline of a 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: approximately 10 mg of a sample was cooled to -50°C, held for 5 minutes, then heated to 250°C at 10°C / min, subsequently cooled to -50°C, held for 5 minutes, and then heated to 250°C at 10°C / min. Measurement equipment: DSC6220 manufactured by SII Nanotechnology Inc. Measurement atmosphere: nitrogen atmosphere

[0165] 1. Synthesis of Acrylic Polymers [Synthesis Example 1] (Synthesis of Polymer A-1) n-Butyl acrylate (hereinafter also referred to as "BA") (95.5 parts by mass), 2-hydroxyethyl acrylate (hereinafter also referred to as "HEA") (4.5 parts by mass), and ethyl acetate (183.8 parts) were charged into a four-neck flask equipped with a stirrer and a thermometer, and the mixture was thoroughly degassed by bubbling with nitrogen gas, and the internal temperature of the mixture was raised to 75°C. A polymerization initiator, 2,2'-azobis(2,4-dimethylbutyronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-65", hereinafter also referred to as "V-65") (0.0472 parts by mass), was charged thereto, and polymerization was carried out for 5 hours. Ethyl acetate was added so that the solids concentration became 30%, and a pressure-sensitive adhesive solution containing Polymer A-1 was obtained. Polymer A-1 had an Mn of 87,000, an Mw of 468,000, and an Mw / Mn of 5.4. The Tg was −40° C. The analytical results of polymer A-1 are shown in Table 2.

[0166] [Synthesis Example 2] (Synthesis of Polymer A-2) A pressure-sensitive adhesive solution containing Polymer A-2 was obtained by the same operation as in Synthesis Example 1, except that the types and amounts of raw materials charged into the flask were changed as shown in Table 1. The analytical results of the polymer are shown in Table 2.

[0167] Synthesis Example 3 (Synthesis of Polymer Block C-3 and Polymer A-3) A four-neck flask equipped with a stirrer and a thermometer was charged with dibenzyl trithiocarbonate (hereinafter also referred to as "DBTTC") (1.59 parts by mass) as a RAFT agent, 2,2'-azobis(2-methylbutyronitrile) (hereinafter also referred to as "ABN-E") (0.255 parts by mass) as a polymerization initiator, styrene (hereinafter also referred to as "St") (37.5 parts by mass) and N-phenylmaleimide (hereinafter also referred to as "PhMI") (62.5 parts by mass) as monomers, and acetonitrile (233.0 parts by mass) 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 mixture was cooled to room temperature to terminate the reaction. The polymerization solution was purified by reprecipitation from methanol and vacuum dried to obtain polymer block C-3. The resulting polymer block C-3 had an Mn of 10,900, an Mw of 12,700, and an Mw / Mn of 1.2. The glass transition temperature Tg of the polymer block C-3 was 206°C. Next, a 1 L flask equipped with a stirrer and a thermometer was charged with the resulting polymer block C-3 (7.0 parts by mass), ABN-E (0.0267 parts by mass) as a polymerization initiator, BA (17.0 parts by mass), 2-methoxyethyl acrylate (hereinafter also referred to as "MEA") (78.0 parts by mass), and HEA (5.0 parts by mass) as monomers, and acetonitrile (35.7 parts by mass) as a solvent. The mixture was thoroughly degassed by nitrogen bubbling, and polymerization was initiated in a thermostatic oven at 70°C. After 6 hours, the mixture was cooled to room temperature, and ethyl acetate was added to adjust the solids concentration to 30% by mass, yielding a PSA solution containing a (CDC) triblock copolymer A-3 having a polymer block (C) and a (meth)acrylic polymer block (D). The resulting polymer A-3 had an Mn of 160,000, an Mw of 283,000, and an Mw / Mn of 1.8. The glass transition temperature Tg of polymer A-3 was −35° C. Furthermore, the glass transition temperature Tg of a polymer obtained by polymerizing polymer block C-3 and monomers (BA, MEA, HEA) in the same manner as in the synthesis of polymer A-3, except that the same amount of DBTTC as used in the synthesis of polymer block C-1 was used instead of polymer block C-1 (this is referred to as the glass transition temperature of polymer block D-3) was −35° C. The analytical results of polymer A-3 are shown in Table 2.

[0168] In Table 2, "C / D block ratio" represents the ratio (mass ratio) of polymer block (C) to (meth)acrylic polymer block (D) in the acrylic polymer. Using the amount of polymer block (C) charged during the synthesis of the acrylic polymer, the amount of each monomer charged, and the GC reaction rate (=monomer consumption rate determined by GC measurement), the C / D block ratio was expressed as "Q1 / Σ(Q2×γ)." Here, Q1 represents the amount (parts by mass) of polymer block (C) used in the synthesis of the acrylic polymer, Q2 represents the amount (parts by mass) of each monomer charged, and γ represents the GC reaction rate of each monomer.

[0169] Synthesis Examples 4 to 8 (Synthesis of Polymer Blocks C-4 to C-8 and Polymers A-4 to A-8) The same operations as in Synthesis Example 3 were carried out to obtain polymer blocks C-4 to C-8 and PSA solutions containing polymers A-4 to A-8, respectively, except that the types and amounts of raw materials charged into the flask were changed as shown in Table 1 and the reaction time for obtaining polymer blocks C-4 to C-8 was changed to 6 hours. The glass transition temperatures of polymer blocks D-4 to D-8 were determined in the same manner as for polymer D-3. The analytical results for each polymer are shown in Table 2.

[0170]

[0171]

[0172] The abbreviations of the monomers in Tables 1 and 2 are as follows: St: styrene PhMI: N-phenylmaleimide BA: butyl acrylate EA: ethyl acrylate HA: 2-ethylhexyl acrylate HEA: 2-hydroxyethyl acrylate MEA: 2-methoxyethyl acrylate AA: acrylic acid

[0173] 2. Synthesis of Vinyl Polymers [Synthesis Example 9] (Synthesis of Polymer B-1) A four-neck flask equipped with a stirrer and a thermometer was charged with a mixed solution consisting of butyl acetate (200 parts by mass) and dimethyl-2,2'-azobis(2-methylpropionate) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-601", hereinafter also referred to as "V-601") (0.9 parts by mass), and the mixed solution was thoroughly degassed by bubbling nitrogen gas through it, and the internal temperature of the mixed solution was raised to 90°C. Separately, a mixed solution consisting of methyl methacrylate (hereinafter also referred to as "MMA") (165 parts by mass), isobornyl methacrylate (hereinafter also referred to as "IBXMA") (44 parts by mass), V-601 (17 parts by mass), and butyl acetate (90 parts by mass) was added dropwise from a dropping funnel into the flask over 5 hours to carry out polymerization. After completion of the dropwise addition, the polymerization solution was added dropwise to a mixed solution of methanol (4,800 parts by mass) and distilled water (1,200 parts by mass), thereby isolating the vinyl polymer in the polymerization solution to obtain Polymer B-1. The monomer composition of the obtained Polymer B-1 was calculated from the charged amounts and the monomer consumption amounts measured by GC, and was found to be 80% by mass of MMA and 20% by mass of IBXMA, with Mw of 6,700, Mn of 4,370, and Mw / Mn of 1.53. The Tg was 108°C. The composition and analytical results of Polymer B-1 are shown in Table 3.

[0174] Synthesis Example 10 Synthesis of Polymer B-2 A mixed solution consisting of butyl acetate (200 parts by mass) and V-601 (6.2 parts by mass) was placed in a four-neck flask equipped with a stirrer and a thermometer, and the mixed solution was thoroughly degassed by bubbling nitrogen gas through it. The internal temperature of the mixed solution was raised to 90 ° C. Separately, a mixed solution consisting of MMA (100 parts by mass), IBXMA (109 parts by mass), V-601 (20 parts by mass) and butyl acetate (90 parts by mass) was added dropwise from a dropping funnel into the flask over 5 hours to carry out polymerization. After completion of the dropwise addition, the polymerization solution was added dropwise to a mixed solution consisting of methanol (4800 parts by mass) and distilled water (1200 parts by mass), and the vinyl polymer in the polymerization solution was isolated to obtain Polymer B-2. The monomer composition of the obtained polymer B-2 was calculated from the charged amounts and the monomer consumption amounts measured by GC, and was found to be 50% by mass of MMA and 50% by mass of IBXMA, with an Mw of 3,080, an Mn of 5,340, and an Mw / Mn of 1.73. The Tg was 88° C. The composition and analytical results of polymer B-2 are shown in Table 3.

[0175]

[0176] The abbreviations of the monomers in Table 3 are as follows: MMA: methyl methacrylate IBXMA: isobornyl methacrylate

[0177] 3. Production of Pressure-Sensitive Adhesive Layer and Pressure-Sensitive Adhesive Film [Example 1] The pressure-sensitive adhesive solution containing polymer A-1 obtained in Synthesis Example 1 was used as a pressure-sensitive adhesive composition for flexible substrates, and was applied to a 50 μm thick polyethylene terephthalate (hereinafter referred to as "PET") separator so that the thickness after drying would be 100 μm. The pressure-sensitive adhesive composition for flexible substrates was dried at 100°C for 6 minutes to remove volatile components, thereby forming a pressure-sensitive adhesive layer. A 38 μm thick PET separator with a different peel strength from the separator to which the pressure-sensitive adhesive composition for flexible substrates was applied was attached to the surface of the pressure-sensitive adhesive layer, thereby obtaining a pressure-sensitive adhesive film sample with a double-sided separator.

[0178] [Examples 2, 5, 7 to 10 and Comparative Example 1] For Examples 2, 5, 7 to 10 and Comparative Example 1, pressure-sensitive adhesive compositions for flexible substrates were prepared based on the compositions shown in Tables 5 and 6, and pressure-sensitive adhesive film samples were obtained in the same manner as in Example 1.

[0179] Example 3 The adhesive solution containing polymer A-2 obtained in Synthesis Example 2 was mixed with a polymer (B-1) solution containing polymer B-1 (4 parts by mass) dissolved in acetonitrile to prepare a solution containing polymer A-2 (100 parts by mass) and polymer B-1 (4 parts by mass) with a solids concentration of 30% by mass, which was used as an adhesive composition for flexible substrates. This adhesive composition for flexible substrates was applied to a 50 μm thick PET separator so that the thickness after drying would be 100 μm. The adhesive composition for flexible substrates was dried at 100°C for 6 minutes to remove volatile components, forming an adhesive layer. A 38 μm thick PET separator with a different peel strength from the separator to which the adhesive composition for flexible substrates was applied was attached to the surface of the adhesive layer to obtain an adhesive film sample with a double-sided separator.

[0180] [Examples 4, 6, 11, 18] For Examples 4, 6, 11, and 18, double-sided separator-attached PSA film samples were obtained using the same procedures as in Example 3 based on the compositions shown in Tables 5 and 6. For Examples 4 and 18, which incorporated the isocyanate-based crosslinking agent "Takenate D-110N" manufactured by Mitsui Chemicals, Inc., a 38 μm-thick PET separator was attached, and then the film was left to stand at 40° C. for 5 days for aging (aging), thereby obtaining double-sided separator-attached PSA film samples. In Tables 5 and 6, the amount of isocyanate-based crosslinking agent (Takenate D-110N) represents the solid content.

[0181] Example 12 A solution of polymer (B-2) with a solids concentration of 30% by mass, prepared by dissolving polymer B-2 (2 parts by mass) in acetonitrile, was mixed with the adhesive solution containing polymer A-4 obtained in Synthesis Example 4 to prepare a solution with a solids concentration of 30% by mass containing polymer A-4 (100 parts by mass) and polymer B-2 (2 parts by mass). An isocyanate group-containing silane coupling agent, "Shin-Etsu Silicone KBE-9007N" (1.0 part by mass), manufactured by Shin-Etsu Chemical Co., Ltd., was added to the resulting solution as an additive to obtain a pressure-sensitive adhesive composition for flexible substrates. This pressure-sensitive adhesive composition for flexible substrates was applied to a 50 μm-thick PET separator to a thickness of 100 μm after drying. The pressure-sensitive adhesive composition for flexible substrates was dried at 100°C for 6 minutes to remove volatile components from the pressure-sensitive adhesive composition for flexible substrates, forming a pressure-sensitive adhesive layer. A 38 μm thick PET separator having a different peel strength from the separator coated with the pressure-sensitive adhesive composition for flexible substrates was attached to the surface of the pressure-sensitive adhesive layer to obtain a pressure-sensitive adhesive film sample with a double-sided separator.

[0182] [Examples 13 to 17] For Examples 13 to 17, adhesive film samples were obtained in the same manner as in Example 12, based on the compositions shown in Tables 5 and 6.

[0183] 4. Evaluation Various measurements and evaluations were carried out using the pressure-sensitive adhesive film sample and a commercially available urethane hot-melt adhesive film (thickness 100 μm). The results are shown in Tables 5 and 6.

[0184] <Gel Fraction> 0.2 g of adhesive was collected from the adhesive film sample, and the initial mass of the adhesive was weighed. The collected adhesive was immersed in 50 g of ethyl acetate and allowed to stand at room temperature for 16 hours. Thereafter, it was filtered through a 200-mesh wire netting, and the residue remaining on the mesh was dried at 80°C for 3 hours and then weighed. The gel fraction (%) was calculated from the initial mass and the mass of the residue.

[0185] <Storage modulus G' at room temperature (23°C)> A pressure-sensitive adhesive layer of a 50 μm thick pressure-sensitive adhesive film sample or a urethane hot melt adhesive film was laminated to prepare a test piece with a pressure-sensitive adhesive layer of 800 μm thick. This test piece was punched into a circle with a diameter of 1 cm, and the dynamic viscoelasticity was measured at a strain of 0.1% and a frequency of 1 Hz using a shear viscoelasticity measuring device Physica MCR301 (manufactured by Anton Paar) while raising the temperature from -50°C to 150°C at a rate of 2°C / min, and the storage modulus G' at 23°C was read. Note that a parallel plate with a diameter of 8 mm was used for the measurement.

[0186] <Evaluation of Peel Strength> The adhesive layer of a pressure-sensitive adhesive film sample or a urethane hot melt adhesive film was sandwiched between the backside of a knitted fabric made of nylon and polyurethane (hereinafter referred to as "nylon / polyurethane knitted fabric", thickness 150 μm) and a PET film (no surface treatment, thickness 50 μm), and temporarily bonded with a hand roller. The temporarily bonded fabric laminate was heat pressed at 120°C and 3 kg / cm. ２ After pressure bonding under conditions of 100°C for 30 seconds, the nylon / polyurethane knit fabric was cut into 25 mm wide pieces along the warp direction to prepare test specimens. The T-peel strength of the prepared test specimens was measured using an INSTRON 5566A tensile tester with a thermostatic bath (manufactured by Instron Japan) at a measurement temperature of 23°C, a test specimen width of 25 mm, and a peel rate of 300 mm / min. The T-peel strength was also measured in the same manner, except that the adherends were changed as shown in Table 4.

[0187]

[0188] <Touch test: texture> Using a laminate prepared in the same manner as in the evaluation of peel strength, the bonded portion was held with both hands and bent, and the bending hardness was evaluated according to the following criteria: ○: No difference in hardness was felt before and after bonding. ×: After bonding, it felt harder than before bonding.

[0189] <Bending Test: Flexibility> Test specimens were prepared in the same manner as in the evaluation of peel strength, except that the cut size was 50 mm x 100 mm. Furthermore, test specimens without a pressure-sensitive adhesive layer were prepared in the same manner as in the evaluation of peel strength, except that the pressure-sensitive adhesive layer of the pressure-sensitive adhesive film sample and the urethane hot-melt adhesive film were not laminated. The prepared test specimens were bent 180° with adherend 1 facing inward so that the short sides were in contact, and the end 1 cm was pinched by hand to observe the change in the radius of curvature of the bent portion. Furthermore, the change in the radius of curvature was observed in the same manner with adherend 2 facing inward. Between bending with adherend 1 facing inward and bending with adherend 2 facing inward, the larger change in the radius of curvature was evaluated according to the following criteria: ○: The radius of curvature of the bent portion was the same as in the case without the adhesive layer; △: The radius of curvature of the bent portion was slightly larger than in the case without the adhesive layer; ×: The radius of curvature of the bent portion was clearly larger than in the case without the adhesive layer.

[0190]

[0191]

[0192] The abbreviations of the additives in Tables 5 and 6 are as follows: KBE-9007N: isocyanate group-containing silane coupling agent, "Shin-Etsu Silicone KBE-9007N", manufactured by Shin-Etsu Chemical Co., Ltd. KBM-403: epoxy group-containing silane coupling agent, "Shin-Etsu Silicone KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd. KBM-503: (meth)acryloyl group-containing silane coupling agent, "Shin-Etsu Silicone KBM-503", manufactured by Shin-Etsu Chemical Co., Ltd. KBM-903: amino group-containing silane coupling agent, "Shin-Etsu Silicone KBM-903", manufactured by Shin-Etsu Chemical Co., Ltd. PMMA microparticles: crosslinked polymethyl methacrylate spherical microparticles, "Techpolymer MBX-50", manufactured by Sekisui Plastics Co., Ltd., average particle size 50 μm Takenate D-110N: isocyanate-based crosslinking agent, "Takenate D-110N", manufactured by Mitsui Chemicals, Inc.

[0193] As shown in Tables 5 and 6, the pressure-sensitive adhesive compositions for flexible substrates of Examples 1 to 18 exhibited high adhesion even when various flexible adherends were bonded together, and were able to form pressure-sensitive adhesive layers with good flexibility and texture at the bonded portions. Among these, the peel strength was particularly high and favorable when a block copolymer was used as the acrylic polymer. Furthermore, Examples 7 to 9 and 11 to 18, which used a block copolymer as the acrylic polymer and in which the Tg of the polymer block (C) was less than 95°C, exhibited higher peel strength while also providing good flexibility and texture at the bonded portions.

[0194] Furthermore, in Examples 12 to 14, which contained an isocyanate group-containing silane coupling agent, an epoxy group-containing silane coupling agent, or a (meth)acryloyl group-containing silane coupling agent as the silane coupling agent, the adhesion when bonding a nylon / polyurethane fabric to a PET film was significantly improved compared to Example 15, which contained an amino group-containing silane coupling agent. Furthermore, in Examples 16 to 18, which used a block copolymer as the acrylic polymer and contained fine particles or a crosslinking agent, the adhesion to various flexible substrates was significantly improved. Furthermore, as shown by comparing Examples 11 to 18 with Example 7, the addition of a vinyl polymer (B) further improved the adhesion to various flexible substrates.

[0195] In contrast, Comparative Example 1, in which the storage modulus at 23° C. of the pressure-sensitive adhesive layer was 2.0 MPa, and Comparative Example 2, in which a urethane hot-melt adhesive film was used, had insufficient texture and flexibility at the bonded portion.

[0196] From the above results, it was revealed that a pressure-sensitive adhesive composition containing a (meth)acrylic polymer (A) having a weight average molecular weight of 100,000 or more and a glass transition temperature of −80° C. or more and 10° C. or less, and in which the pressure-sensitive adhesive layer has a storage modulus at 23° C. of 1.0 MPa or less, can form a pressure-sensitive adhesive layer that exhibits good adhesion when flexible adherends are bonded together, while maintaining good flexibility and texture at the bonded portion.

Claims

1. A pressure-sensitive adhesive composition for flexible substrates for forming a pressure-sensitive adhesive layer used for bonding flexible substrates together (excluding bonding of fiber fabrics together, bonding of conductive sheets together, bonding of a fiber fabric to a conductive sheet, and bonding of a fiber fabric to an elastomer substrate), the pressure-sensitive adhesive composition for flexible substrates comprising a (meth)acrylic polymer (A) having a weight-average molecular weight of 100,000 or more and a glass transition temperature of -80°C or more and 10°C or less, the pressure-sensitive adhesive layer having a storage modulus at 23°C of 1.0 MPa or less.

2. The pressure-sensitive adhesive composition for flexible substrates according to claim 1, wherein the (meth)acrylic polymer (A) is a block copolymer having a polymer block (C) having a glass transition temperature of 10°C or higher and 250°C or lower, and a (meth)acrylic polymer block (D) having a glass transition temperature of -80°C or higher and lower than 10°C.

3. The pressure-sensitive adhesive composition for flexible substrates according to claim 2, wherein the glass transition temperature of the polymer block (C) is 10°C or higher and 90°C or lower.

4. The adhesive composition for flexible substrates according to claim 2, wherein the polymer block (C) comprises a structural unit (U1) derived from an imide group-containing vinyl monomer and a structural unit (U2) derived from a (meth)acrylic monomer, and the total content of the structural unit (U1) and the structural unit (U2) is 80 mass% or more based on the total structural units of the polymer block (C).

5. A pressure-sensitive adhesive composition for flexible substrates as described in claim 2, wherein the (meth)acrylic polymer block (D) contains structural units derived from a (meth)acrylic ester compound having a hydrocarbon group having 3 or more carbon atoms in an amount of 20 mass% or more based on the total structural units of the (meth)acrylic polymer block (D).

6. The pressure-sensitive adhesive composition for flexible substrates according to claim 1, wherein the (meth)acrylic polymer (A) contains a structural unit derived from at least one selected from the group consisting of (meth)acrylic acid alkyl esters and (meth)acrylic acid alkoxyalkyl esters.

7. The pressure-sensitive adhesive composition for flexible substrates according to claim 1, further comprising a vinyl polymer (B) having a glass transition temperature of 30° C. or more and 200° C. or less and a number average molecular weight of 500 or more and 10,000 or less.

8. The pressure-sensitive adhesive composition for flexible substrates according to claim 7, wherein the vinyl polymer (B) contains structural units derived from an aliphatic cyclic vinyl monomer.

9. The pressure-sensitive adhesive composition for flexible substrates according to claim 7, wherein the content of the vinyl polymer (B) is 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the (meth)acrylic polymer (A).

10. The pressure-sensitive adhesive composition for flexible substrates according to claim 1, further comprising a silane coupling agent.

11. The pressure-sensitive adhesive composition for flexible substrates according to claim 10, wherein the silane coupling agent has at least one group selected from the group consisting of an epoxy group, a (meth)acryloyl group, an isocyanate group and a blocked isocyanate group.

12. The pressure-sensitive adhesive composition for flexible substrates according to claim 1, further comprising an isocyanate-based crosslinking agent.

13. The pressure-sensitive adhesive composition for flexible substrates according to claim 1, further comprising fine particles.

14. A product comprising a first adherend, a second adherend, and an adhesive layer, the first adherend and the second adherend being bonded together by the adhesive layer, the first adherend and the second adherend being flexible adherends (excluding, however, fiber fabrics, conductive sheets, a combination of a fiber fabric and a conductive sheet, and a combination of a fiber fabric and an elastomer substrate), and the adhesive layer being formed from the adhesive composition for flexible adherends according to any one of claims 1 to 13.