adhesive sheet

Abstract

Provided is a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer which can be formed with low heat energy and can exhibit excellent adhesive force.　This pressure-sensitive adhesive sheet comprises a substrate and a pressure-sensitive adhesive layer disposed on at least one side of the substrate, wherein the pressure-sensitive adhesive layer comprises: a (meth)acrylic polymer as a base polymer; an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent, as a crosslinking agent; an amino compound having a tertiary-amino group and capable of multidentate coordination and / or an organic tin(IV) compound capable of multidentate coordination, as a low-molecular-weight compound; and fine heat-expandable spheres. The (meth)acrylic polymer includes a constituent unit having an active-hydrogen group.

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet, and more particularly to a pressure-sensitive adhesive sheet that can exhibit easy peelability in response to a thermal stimulus. [Background technology]

[0002] Conventionally, adhesive sheets have been used to fix or temporarily fix workpieces when processing electronic components, etc. For example, adhesive sheets are used as temporary fixing materials for cutting semiconductor wafers or ceramic sheets, or as temporary fixing materials in processes for encapsulating semiconductor chips with resin (chip size package: CSP or wafer level package: WLP). One such adhesive sheet under study is one that has an adhesive layer containing heat-expandable microspheres, and whose adhesive strength decreases as the heat-expandable microspheres expand when heated.

[0003] Typically, the pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer formed by coating (applying and drying) a pressure-sensitive adhesive containing a base polymer and a solvent. Conventionally, aromatic hydrocarbon solvents such as toluene and dichlorobenzene have been widely used as the solvent. Aromatic hydrocarbon solvents are advantageous in that they have excellent solubility and a high boiling point, and therefore, their use allows the production of a pressure-sensitive adhesive with excellent storage stability.

[0004] On the other hand, in recent years, efforts have been made to reduce the use of aromatic hydrocarbon solvents, which have high boiling points, due to the fact that a large amount of energy is required to volatilize the solvent during the formation of the adhesive layer and from the viewpoint of toxicity. For example, the above problems can be solved by using solvents containing non-aromatic hydrocarbons with boiling points below 100°C (non-aromatic hydrocarbon solvents), such as acetone, methyl ethyl ketone, and ethyl acetate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-201452 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a PSA layer is formed using a PSA containing a non-aromatic hydrocarbon solvent with a boiling point of less than 100° C., the PSA layer may not exhibit sufficient adhesive strength. Even if the PSA layer contains a base polymer that can achieve sufficient adhesive strength when combined with an aromatic hydrocarbon solvent, if the non-aromatic hydrocarbon solvent is used instead of the aromatic hydrocarbon solvent, a PSA sheet may not have sufficient adhesive strength.

[0007] The present invention has been made to solve the above-mentioned conventional problems, and its object is to provide an adhesive sheet having an adhesive layer that consumes less thermal energy when forming the adhesive layer and can exhibit excellent adhesive strength. [Means for solving the problem]

[0008] The pressure-sensitive adhesive sheet of the present invention comprises a substrate and a pressure-sensitive adhesive layer disposed on at least one side of the substrate, the pressure-sensitive adhesive layer comprising a (meth)acrylic polymer as a base polymer, an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent as a crosslinking agent, an amino compound having a tertiary amino group capable of polydentate coordination and / or an organotin(IV) compound capable of polydentate coordination as a low molecular weight compound, and heat-expandable microspheres, and the (meth)acrylic polymer comprises a structural unit having an active hydrogen group. In one embodiment, the content of the amino compound having a tertiary amino group capable of polydentate coordination and the content of the organotin (IV) compound capable of polydentate coordination is 0.001 to 10 parts by weight relative to 100 parts by weight of the base polymer. In one embodiment, the amino compound having a tertiary amino group capable of polydentate coordination is an amino compound containing at least two tertiary amino groups in the molecule. In one embodiment, the amino compound having a tertiary amino group capable of polydentate coordination is at least one selected from the group consisting of 1,4-diazabicyclo[2.2.2]octane, 1,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene. In one embodiment, the organotin(IV) compound capable of polydentate coordination is a dialkyltin(IV) fatty acid ester. In one embodiment, the organotin(IV) compound capable of polydentate coordination is at least one selected from the group consisting of dibutyltin(IV) dilaurate, dibutyltin(IV) dioctate, dioctyltin(IV) dilaurate, and dibutyltin(IV) diacetate. In one embodiment, the active hydrogen group is a hydroxyl group and / or a carboxyl group. In one embodiment, the expansion temperature of the heat-expandable microspheres is 80°C to 250°C. In one embodiment, the substrate further comprises another pressure-sensitive adhesive layer on the opposite side to the pressure-sensitive adhesive layer. According to another aspect of the present invention, there is provided a method for producing the above-mentioned PSA sheet, which includes applying a PSA to a substrate to form a PSA coating layer, and drying the PSA coating layer to form a PSA layer. In one embodiment, the product of the drying temperature and drying time when drying the pressure-sensitive adhesive coating layer is 100°C·min to 500°C·min. In one embodiment, the pressure-sensitive adhesive contains a solvent, and the boiling point of the solvent is less than 100°C. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that consumes less heat energy when forming the pressure-sensitive adhesive layer and that is capable of exhibiting excellent adhesive strength. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] A. Overview of adhesive sheets 1 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. The pressure-sensitive adhesive sheet 100 comprises a substrate 10 and a pressure-sensitive adhesive layer 20 disposed on at least one side of the substrate 10.

[0012] The pressure-sensitive adhesive layer contains a (meth)acrylic polymer as a base polymer, an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent as a crosslinking agent, an amino compound having a tertiary amino group capable of polydentate coordination (hereinafter also referred to as a polydentate amino compound) and / or an organotin(IV) compound capable of polydentate coordination (hereinafter also referred to as a polydentate tin(IV) compound) as a low molecular weight compound, and heat-expandable microspheres. In this specification, (meth)acrylic means acrylic and / or methacrylic.

[0013] The heat-expandable microspheres can be expanded at a predetermined temperature. When a pressure-sensitive adhesive layer containing such heat-expandable microspheres is heated, the heat-expandable microspheres expand, causing unevenness on the adhesive surface (i.e., the surface of the pressure-sensitive adhesive layer), resulting in a decrease or loss of adhesive strength. For example, when the pressure-sensitive adhesive sheet of the present invention is used as a sheet for temporarily fixing workpieces during the processing of electronic components (e.g., printed circuit boards), the adhesive strength required for temporary fixing is exhibited when the workpieces are subjected to the predetermined processing (e.g., dicing, sealing, etc.), and when the workpieces are to be peeled from the pressure-sensitive adhesive sheet after processing, the adhesive strength is reduced or lost by heating, resulting in good peelability.

[0014] In the present invention, by including the above-mentioned low molecular weight compound, a pressure-sensitive adhesive layer with excellent adhesive strength can be formed. The pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet of the present invention can be formed using a solvent with a low boiling point (for example, less than 100°C, preferably 80°C or less, more preferably 60°C or less), and even when formed using such a solvent, it has excellent adhesive strength. According to the present invention, by using the above-mentioned low molecular weight compound, crosslinking of the base polymer proceeds favorably even with small amounts of thermal energy applied during pressure-sensitive adhesive layer formation (typically, thermal energy used to volatilize the solvent from the pressure-sensitive adhesive), and it is thought that as a result, a pressure-sensitive adhesive layer with high cohesive strength and excellent adhesive strength can be obtained.

[0015] According to the present invention, a pressure-sensitive adhesive layer can be formed using a low-boiling-point solvent with minimal thermal energy consumption, thereby providing a pressure-sensitive adhesive sheet that can be produced safely and with minimal environmental and process burden. It also enables the use of heat-expandable microspheres with a low expansion initiation temperature. Furthermore, a pressure-sensitive adhesive sheet can be provided in which deterioration of the heat-expandable microspheres due to heat is suppressed, resulting in excellent releasability.

[0016] The adhesive strength at 23°C when the adhesive layer of the pressure-sensitive adhesive sheet is applied to polyethylene terephthalate is preferably 0.5 N / 20 mm or more, more preferably 1 N / 20 mm to 20 N / 20 mm, even more preferably 2 N / 20 mm to 20 N / 20 mm, and even more preferably 4 N / 20 mm to 20 N / mm. Within these ranges, a pressure-sensitive adhesive sheet useful as a temporary fixing sheet for use in the manufacture of electronic components can be obtained. In this specification, the adhesive strength refers to the adhesive strength in a state where there is no decrease in adhesive strength due to the expansion of the heat-expandable microspheres, and refers to the adhesive strength in a state where the adhesive has not been subjected to a thermal history of 40°C or higher. The adhesive strength refers to the adhesive strength measured according to JIS Z 0237:2009 (lamination conditions: one reciprocal movement of a 2 kg roller, peel speed (pulling speed): 300 mm / min, peel angle: 180°).

[0017] The adhesive strength of the adhesive layer of the pressure-sensitive adhesive sheet when attached to polyethylene terephthalate is preferably reduced to 0.3 N / 20 mm or less (preferably 0.2 N / 20 mm or less, more preferably 0.1 N / 20 mm) by heating. The heating temperature is preferably 70°C to 300°C, more preferably 100°C to 280°C.

[0018] The PSA sheet may further comprise any other appropriate layers. In one embodiment, the PSA sheet further comprises a primer layer disposed between the PSA layer and the substrate. The primer layer allows for a PSA sheet with excellent conformability to adherends. When heated, the PSA layer containing heat-expandable microspheres tends to expand in the thickness direction as the heat-expandable microspheres expand, causing deformation. However, the primer layer suppresses deformation toward the substrate, improving releasability. Another PSA layer may also be provided on the opposite side of the substrate from the PSA layer. That is, the PSA sheet may comprise, in this order, the PSA layer, an optional primer layer, the substrate, and another PSA layer.

[0019] The thickness of the pressure-sensitive adhesive sheet is preferably 3 μm to 300 μm, more preferably 5 μm to 150 μm, and even more preferably 10 μm to 100 μm.

[0020] B.Adhesive layer B-1. (Meth)acrylic polymer The pressure-sensitive adhesive layer is a pressure-sensitive adhesive layer formed from an acrylic pressure-sensitive adhesive, i.e., as described above, contains a (meth)acrylic polymer as a base polymer. The (meth)acrylic polymer may be a polymer (homopolymer or copolymer) using one or more (meth)acrylic acid alkyl esters as a monomer component. The content of the (meth)acrylic polymer is preferably 70 parts by weight or more, more preferably 90 parts by weight or more, even more preferably 95 parts by weight or more, and particularly preferably 100 parts by weight, per 100 parts by weight of the polymer in the pressure-sensitive adhesive layer.

[0021] Specific examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, C1-20 alkyl (meth)acrylate esters such as nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among these, preferred are (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 4 to 20 carbon atoms (more preferably 6 to 20, and particularly preferably 8 to 18), and more preferably 2-ethylhexyl (meth)acrylate.

[0022] The (meth)acrylic polymer contains a structural unit having an active hydrogen group. A (meth)acrylic polymer containing a structural unit having an active hydrogen group can be preferably crosslinked during formation, and by using such a polymer, a pressure-sensitive adhesive layer with excellent adhesiveness can be formed at a relatively low temperature. Examples of the active hydrogen group include a hydroxyl group (alcoholic hydroxyl group, phenolic hydroxyl group), a carboxyl group, and an amino group. Of these, a hydroxyl group and / or a carboxyl group is preferred. The active hydrogen group contained in the (meth)acrylic polymer may be of one type or two or more types. Examples of structural units having an active hydrogen group include structural units derived from carboxyl group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; and structural units derived from hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxydecyl (meth)acrylate, hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl methacrylate.

[0023] The content of the constituent units derived from the monomer having the active hydrogen group is preferably 0.1 to 40% by weight, more preferably 0.5 to 30% by weight, and particularly preferably 1 to 20% by weight, based on all constituent units constituting the acrylic polymer.

[0024] The acrylic polymer may contain, as necessary, units corresponding to other monomer components copolymerizable with the alkyl (meth)acrylate, for the purpose of modifying properties such as cohesive strength, heat resistance, and crosslinkability. Examples of such monomer components include acid anhydride monomers such as maleic anhydride and itaconic anhydride; sulfonic acid group-containing monomers such as styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl(meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; (N-substituted) amide monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, and N-methylolpropane(meth)acrylamide; aminoalkyl(meth)acrylate monomers such as aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate; alkoxyalkyl(meth)acrylate monomers such as methoxyethyl(meth)acrylate and ethoxyethyl(meth)acrylate; N-cyclohexylmaleimide, N-isopropyl Maleimide monomers such as N-butylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; itaconimide monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide; N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide succinimide-based monomers such as N-(meth)acryloyl-8-oxyoctamethylene succinimide; vinyl-based monomers such as vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinylcarboxylic acid amides, styrene, α-methylstyrene, and N-vinylcaprolactam;Cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; acrylic ester monomers having a heterocycle, a halogen atom, a silicon atom, or the like, such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate; hexanediol di(meth)acrylate Examples of suitable monomers include polyfunctional monomers such as acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy acrylate, polyester acrylate, and urethane acrylate; olefin-based monomers such as isoprene, butadiene, and isobutylene; and vinyl ether-based monomers such as vinyl ether. These monomer components may be used alone or in combination of two or more.

[0025] The acrylic pressure-sensitive adhesive may contain any suitable additives as needed, such as tackifiers, plasticizers (e.g., trimellitate ester plasticizers, pyromellitate ester plasticizers, etc.), pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release modifiers, softeners, surfactants, flame retardants, and antioxidants.

[0026] The tackifier contained in the acrylic pressure-sensitive adhesive may be any appropriate tackifier, such as a tackifying resin. Specific examples of the tackifying resin include rosin-based tackifying resins (e.g., unmodified rosin, modified rosin, rosin phenol-based resins, rosin ester-based resins, etc.), terpene-based tackifying resins (e.g., terpene-based resins, terpene phenol-based resins, styrene-modified terpene-based resins, aromatic-modified terpene-based resins, hydrogenated terpene-based resins), hydrocarbon-based tackifying resins (e.g., aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aromatic hydrocarbon resins (e.g., styrene-based resins, xylene-based resins, etc.), aliphatic / aromatic petroleum resins, aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone-based resins, coumarone-indene resins, etc.), phenol-based tackifying resins (e.g., alkylphenol-based resins, xylene-formaldehyde-based resins, resols, novolacs, etc.), ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins. Among these, rosin-based tackifying resins, terpene-based tackifying resins, and hydrocarbon-based tackifying resins (such as styrene-based resins) are preferred. The tackifiers may be used alone or in combination of two or more. The amount of the tackifier added is preferably 5 to 100 parts by weight, more preferably 10 to 50 parts by weight, per 100 parts by weight of the base polymer.

[0027] B-2. Crosslinking agent As described above, the pressure-sensitive adhesive layer contains a crosslinking agent. The crosslinking agent may be an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent. By using such a crosslinking agent, a pressure-sensitive adhesive layer with excellent adhesiveness can be formed at a relatively low temperature.

[0028] The isocyanate crosslinking agent is a compound having an isocyanate group, and specific examples thereof include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; and isocyanate adducts such as a trimethylolpropane / tolylene diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L"), a trimethylolpropane / hexamethylene diisocyanate trimer adduct (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HL"), and an isocyanurate of hexamethylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate HX"). When the adhesive layer contains an isocyanate-based crosslinking agent, the content of the isocyanate-based crosslinking agent can be set to any appropriate amount depending on the desired adhesive strength, and is typically 0.1 to 20 parts by weight, and more preferably 0.5 to 10 parts by weight, per 100 parts by weight of the base polymer.

[0029] The epoxy crosslinking agent is a compound having an epoxy group, and specific examples thereof include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, Inc., trade name "Tetrad C"), 1,6-hexanediol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 1600"), neopentyl glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 1500N"), and 1,6-hexanediol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 1500N"). P"), ethylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 40E"), propylene glycol diglycidyl ether (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Epolite 70P"), polyethylene glycol diglycidyl ether (manufactured by Nippon Oil & Fats Corporation, trade name "Epiol E-400"), polypropylene glycol diglycidyl ether (manufactured by Nippon Oil & Fats Corporation, trade name "Epiol P-200"), sorbitol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol") EX-611), glycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-314"), pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name "Denacol EX-512"), sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, and epoxy resins having two or more epoxy groups in the molecule. When the adhesive layer contains an epoxy-based crosslinking agent, the content of the epoxy-based crosslinking agent can be set to any appropriate amount depending on the desired adhesive strength, and is typically 0.01 to 10 parts by weight, and more preferably 0.03 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0030] B-3.Low molecular compounds As described above, the pressure-sensitive adhesive layer contains a low-molecular-weight compound, an amino compound having a tertiary amino group capable of polydentate coordination (also referred to as a polydentate amino compound) and / or an organotin(IV) compound capable of polydentate coordination (also referred to as a polydentate tin(IV) compound). The low-molecular-weight compound is a compound that can function as a catalyst in the crosslinking reaction of the base polymer when the pressure-sensitive adhesive layer is formed. By using the low-molecular-weight compound capable of polydentate coordination, the active hydrogen groups in the base polymer and the functional groups of the crosslinking agent (isocyanate groups or epoxy groups) can be simultaneously coordinated to one molecule, accelerating the crosslinking reaction. As a result, a pressure-sensitive adhesive layer with excellent adhesive properties can be formed at a relatively low temperature.

[0031] In one embodiment, an amino compound containing at least two tertiary amino groups in the molecule is used as the polydentate amino compound.

[0032] Specific examples of polydentate amino compounds include 1,4-diazabicyclo[2.2.2]octane, 1,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene. These compounds may be used singly or in combination. Among these, 1,4-diazabicyclo[2.2.2]octane is preferred as the polydentate amino compound. 1,4-diazabicyclo[2.2.2]octane is liquid at room temperature and has a high boiling point, making it easily dispersible in adhesives and advantageously less likely to volatilize during heating processes (e.g., drying processes for adhesive coating layers). Another advantage is its extremely poor reactivity with heat-expandable microspheres.

[0033] In one embodiment, a (meth)acrylic polymer having an alcoholic hydroxyl group (i.e., a (meth)acrylic polymer including a structural unit derived from a monomer having an alcoholic hydroxyl group) is used in combination with a multidentate amino compound, because the alcoholic hydroxyl group has a low active hydrogen dissociation ability.

[0034] Examples of polydentate tin(IV) compounds include dialkyltin(IV) fatty acid esters such as dibutyltin(IV) dilaurate, dibutyltin(IV) dioctate, dioctyltin(IV) dilaurate, and dibutyltin(IV) diacetate, and distannoxanes such as tetra-n-butyl-1,3-diacetoxy-distannoxane and tetra-n-butyl-1,3-dichloro-distannoxane. These compounds may be used alone or in combination. Among them, dioctyltin(IV) diacetate is preferably used as the polydentate tin(IV) compound. Dioctyltin(IV) diacetate is advantageous in that it is liquid at room temperature and has a high boiling point, making it easily dispersible in adhesives and less likely to volatilize during heating processes (e.g., drying processes for adhesive coating layers). Another advantage is its extremely poor reactivity with heat-expandable microspheres.

[0035] In one embodiment, a (meth)acrylic polymer having a carboxyl group and / or a phenolic hydroxyl group (i.e., a (meth)acrylic polymer containing a structural unit derived from a monomer having a carboxyl group and / or a structural unit derived from a monomer having a phenolic hydroxyl group) is used in combination with a polydentate tin(IV) compound. This is because carboxyl groups and phenolic hydroxyl groups have high hydrogen dissociation ability and may bond strongly to the polydentate amino compound, thereby terminating the crosslinking reaction.

[0036] The content of the amino compound having a tertiary amino group capable of polydentate coordination and the organotin(IV) compound capable of polydentate coordination is preferably 0.001 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, and even more preferably 0.05 to 3 parts by weight, per 100 parts by weight of the base polymer. Within these ranges, a pressure-sensitive adhesive layer with excellent adhesive properties can be formed at a relatively low temperature. If the content of the polydentate amino compound and the polydentate tin(IV) compound is too high, complex formation (pseudo-crosslinking) between these low-molecular-weight compounds and the crosslinking agent may occur, resulting in an inability to achieve the desired adhesive strength. In this specification, the "content of the amino compound having a tertiary amino group capable of polydentate coordination and the organotin(IV) compound capable of polydentate coordination" refers to the total amount of the polydentate amino compound and the polydentate tin(IV) compound. Therefore, when the pressure-sensitive adhesive layer does not contain a polydentate tin(IV) compound, the "content of amino compounds having a tertiary amino group capable of polydentate coordination and organotin(IV) compounds capable of polydentate coordination" refers to the content of the polydentate amino compound. Also, when the pressure-sensitive adhesive layer does not contain a polydentate amino compound, the "content of amino compounds having a tertiary amino group capable of polydentate coordination and organotin(IV) compounds capable of polydentate coordination" refers to the content of the polydentate tin(IV) compound.

[0037] The boiling point of the low molecular weight compound is preferably 100° C. or higher, more preferably 120° C. or higher, and even more preferably 150° C. or higher. A low molecular weight compound having a boiling point within this range is advantageous in that it is liquid at room temperature and has a high boiling point, so it is easily dispersed in a pressure-sensitive adhesive and is less likely to volatilize during a heating step (for example, a step of drying a pressure-sensitive adhesive coating layer).

[0038] B-4.Thermally expandable microspheres The heat-expandable microspheres can be any suitable type as long as they are capable of expanding or foaming upon heating. For example, microspheres having an elastic shell encapsulating a substance that expands easily upon heating can be used. Such heat-expandable microspheres can be produced by any suitable method, such as coacervation or interfacial polymerization.

[0039] Examples of substances that expand easily when heated include low-boiling liquids such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, normal hexane, isohexane, heptane, octane, petroleum ether, methane halides, and tetraalkylsilanes; and azodicarbonamide, which gasifies by thermal decomposition.

[0040] Examples of materials constituting the shell include polymers composed of nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, and fumaronitrile; carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, and β-carboxyethyl acrylate; styrene monomers such as styrene, α-methylstyrene, and chlorostyrene; and amide monomers such as acrylamide, substituted acrylamide, methacrylamide, and substituted methacrylamide. Polymers composed of these monomers may be homopolymers or copolymers. Examples of such copolymers include vinylidene chloride-methyl methacrylate-acrylonitrile copolymer, methyl methacrylate-acrylonitrile-methacrylonitrile copolymer, methyl methacrylate-acrylonitrile copolymer, and acrylonitrile-methacrylonitrile-itaconic acid copolymer.

[0041] The heat-expandable microspheres may be formed using inorganic or organic blowing agents, such as ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium boron hydroxide, and various azides. Examples of organic blowing agents include fluorinated alkane compounds such as trichloromonofluoromethane and dichloromonofluoromethane; azo compounds such as azobisisobutyronitrile, azodicarbonamide, and barium azodicarboxylate; hydrazine compounds such as paratoluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis(benzenesulfonylhydrazide), and allylbis(sulfonylhydrazide); semicarbazide compounds such as p-toluylenesulfonylsemicarbazide and 4,4'-oxybis(benzenesulfonylsemicarbazide); triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso compounds such as N,N'-dinitrosopentamethylenetetramine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide.

[0042] The particle size of the heat-expandable microspheres before heating is preferably 0.5 μm to 80 μm, more preferably 5 μm to 45 μm, even more preferably 10 μm to 20 μm, and particularly preferably 10 μm to 15 μm. Therefore, the average particle size of the heat-expandable microspheres before heating is preferably 6 μm to 45 μm, more preferably 15 μm to 35 μm. The particle size and average particle size are values ​​determined by particle size distribution measurement using a laser scattering method.

[0043] The heat-expandable microspheres preferably have an appropriate strength so that they do not burst until their volumetric expansion rate reaches at least 5 times, more preferably at least 7 times, and even more preferably at least 10 times. When such heat-expandable microspheres are used, their adhesive strength can be efficiently reduced by heat treatment.

[0044] The expansion initiation temperature of the heat-expandable microspheres is preferably 80°C to 250°C, more preferably 80°C to 230°C, even more preferably 80°C to 200°C, even more preferably 80°C to 150°C, particularly preferably 80°C to 120°C, and most preferably 80°C to 100°C. In this specification, the expansion initiation temperature of heat-expandable microspheres refers to the lowest temperature at which the thickness of the pressure-sensitive adhesive layer (when a primer layer is used, the total thickness of the primer layer and the pressure-sensitive adhesive layer) increases by 5% or more from room temperature. For example, the expansion initiation temperature may correspond to the temperature at which the adhesive strength of a pressure-sensitive adhesive tape decreases to 1.0 N / 20 mm or less and 50% or less of the initial adhesive strength.

[0045] The content of the heat-expandable microspheres in the pressure-sensitive adhesive layer can be appropriately set depending on the desired adhesive strength reduction, etc. The content of the heat-expandable microspheres is, for example, 1 to 150 parts by weight, preferably 10 to 130 parts by weight, and more preferably 25 to 100 parts by weight, per 100 parts by weight of the base polymer that forms the pressure-sensitive adhesive layer.

[0046] The arithmetic surface roughness Ra of the pressure-sensitive adhesive layer before the heat-expandable microspheres expand (ie, before heating) is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less.

[0047] The thickness of the pressure-sensitive adhesive layer is preferably 5 μm to 70 μm, more preferably 10 μm to 60 μm, even more preferably 15 μm to 55 μm, and most preferably 20 μm to 50 μm.

[0048] C. Base material The substrate may be made of any suitable material. The substrate may be, for example, a plastic film, a plastic sheet, or various sheet-like materials such as paper, cloth, nonwoven fabric, metal foil, or plastic laminates thereof, or laminates of plastics. Among these, plastic films and plastic sheets (hereinafter referred to as plastic films) are most preferred from the standpoints of ease of handling and cost. The material of the plastic film may be selected as needed from the standpoints of strength, heat resistance, and the like. Examples of suitable plastic materials include olefin-based resins containing α-olefins as monomer components, such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer (EVA); polyesters, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); polyvinyl chloride (PVC); polyphenylene sulfide (PPS); amide-based resins, such as polyamide (nylon) and wholly aromatic polyamide (aramid); polyether ether ketone (PEEK), polyimide, polyetherimide, polystyrene, and acrylic resin. These materials can be used alone or in combination of two or more. The plastic film may be an unstretched film, a uniaxially oriented film, or a biaxially oriented film. These films may be laminated films consisting of two or more film layers, or, from the viewpoint of ease of handling, films containing a lubricant such as inert particles may be used.

[0049] The thickness of the substrate is preferably 200 μm or less, more preferably 1 μm to 200 μm, even more preferably 5 μm to 200 μm, particularly preferably 10 μm to 200 μm, particularly preferably 20 μm to 200 μm, and most preferably 30 μm to 200 μm.

[0050] The substrate may be subjected to a surface treatment, such as corona treatment, chromic acid treatment, ozone exposure, flame exposure, high-voltage shock exposure, ionizing radiation treatment, or coating with a primer.

[0051] D. Primer layer The undercoat layer contains any suitable adhesive. Examples of adhesives that can be used for the undercoat layer include acrylic adhesives, rubber adhesives, and silicone adhesives. Of these, acrylic adhesives are preferred. Active energy ray-curable acrylic adhesives (hereinafter referred to as active energy ray-curable adhesives) may also be used. Preferably, the adhesive that makes up the undercoat layer is the same as the adhesive that makes up the adhesive layer. In addition to the above, the undercoat layer may be an organic material exhibiting rubber-like elasticity. For this reason, it is sometimes referred to as a rubber-like organic elastomer.

[0052] The thickness of the undercoat layer is preferably 1 μm to 100 μm, more preferably 1 μm to 80 μm, even more preferably 1 μm to 60 μm, still more preferably 1 μm to 40 μm, particularly preferably 5 μm to 35 μm, and most preferably 10 μm to 30 μm. Within these ranges, a PSA sheet can be obtained that exhibits excellent liner peeling operability and minimizes the influence of the heat-expandable microspheres on the substrate when heated.

[0053] The elastic modulus of the undercoat layer is preferably 0.001 MPa to 10 MPa, more preferably 0.01 MPa to 8 MPa, and more preferably 0.5 MPa to 5 MPa. In this specification, the elastic modulus refers to the elastic modulus measured by nanoindentation in an environment of 23°C. The elastic modulus measured by nanoindentation refers to the elastic modulus determined from the applied load-indentation depth curve obtained by continuously measuring the load and indentation depth on an indenter (triangular pyramidal shape) when the indenter is pressed into a sample (indentation speed: 1000 nm / sec, indentation depth: 800 nm) during loading and unloading.

[0054] E. Another adhesive layer The separate adhesive layer may contain any suitable adhesive. Examples of adhesives constituting the separate adhesive layer include acrylic adhesives, rubber adhesives, and silicone adhesives. Furthermore, an active energy ray-curable acrylic adhesive (hereinafter referred to as an active energy ray-curable adhesive) may also be used as the adhesive. Details of the adhesive are described, for example, in JP 2015-168711 A. The disclosure of this publication is incorporated herein by reference.

[0055] F. Manufacturing method of adhesive sheet The pressure-sensitive adhesive sheet can be produced by any suitable method. Examples of methods for producing a pressure-sensitive adhesive sheet include a method in which a pressure-sensitive adhesive is directly applied (applied and dried) onto a substrate, and a method in which a pressure-sensitive adhesive is applied (applied and dried) onto any suitable substrate, and the resulting coating layer is transferred to the substrate. When the pressure-sensitive adhesive sheet has the undercoat layer, the undercoat layer can be formed, for example, by applying a composition (adhesive) for forming the undercoat layer onto the substrate or the pressure-sensitive adhesive layer.

[0056] In one embodiment, a method for producing a pressure-sensitive adhesive sheet includes applying a pressure-sensitive adhesive to a substrate to form a pressure-sensitive adhesive coating layer, and drying the pressure-sensitive adhesive coating layer to form a pressure-sensitive adhesive layer.

[0057] The adhesive forming the adhesive layer contains the (meth)acrylic polymer as a base polymer, the crosslinking agent, the polydentate amino compound and / or the polydentate tin(IV) compound as a low molecular weight compound, and the heat-expandable microspheres. Typically, the adhesive further contains any suitable solvent.

[0058] Preferably, the solvent has a boiling point of less than 100°C. The pressure-sensitive adhesive sheet of the present invention can exhibit sufficient adhesive strength even when a solvent with a relatively low boiling point is used and the pressure-sensitive adhesive coating layer is dried at a low temperature. Such a pressure-sensitive adhesive sheet can reduce energy consumption during production. Furthermore, the pressure-sensitive adhesive sheet can prevent deterioration of the heat-expandable microspheres and exhibit excellent releasability. A non-aromatic hydrocarbon solvent is preferably used as the solvent. The non-aromatic hydrocarbon solvent may be a solvent consisting of one non-aromatic hydrocarbon solvent or two or more non-aromatic hydrocarbon solvents. The non-aromatic hydrocarbon solvent may also contain a solvent other than the non-aromatic hydrocarbon solvent. Examples of non-aromatic hydrocarbon solvents include aliphatic hydrocarbons such as cyclohexane and heptane; halogenated hydrocarbons such as methylene chloride and chloroform; ketones such as acetone, ethyl acetate, and 2-butanone; and cyclic ethers such as tetrahydrofuran. Among these, ethyl acetate or 2-butanone is preferred.

[0059] Examples of the method for applying the pressure-sensitive adhesive include coating methods using a die coater, a comma coater, a gravure coater, etc. As a drying method, heat drying is preferably adopted. For example, drying can be carried out by placing the pressure-sensitive adhesive coating layer for a desired period of time in a dryer equipped with a blower that can forcibly convect air at a predetermined temperature.

[0060] The drying temperature is preferably 55°C or higher but lower than 100°C, more preferably 60°C to 90°C, and even more preferably 65°C to 90°C. Within this range, a pressure-sensitive adhesive layer can be formed efficiently, and unwanted expansion of the heat-expandable microspheres and deterioration of the heat-expandable microspheres can be prevented. Furthermore, a pressure-sensitive adhesive layer with a desirable surface shape can be formed. The drying temperature may be changed stepwise; for example, the pressure-sensitive adhesive layer may be formed by increasing the drying temperature over time.

[0061] The drying time can be any appropriate time depending on the pressure-sensitive adhesive layer composition, drying temperature, etc. The drying time is, for example, 1 to 10 minutes. If it is within this range, the pressure-sensitive adhesive layer can be formed efficiently.

[0062] The drying step may be controlled by the product of the drying temperature and drying time when drying the pressure-sensitive adhesive coating layer. The product of the drying temperature and drying time is preferably 100°C·min to 500°C·min, and more preferably 100°C·min to 350°C·min. Within this range, a pressure-sensitive adhesive layer with excellent adhesiveness can be formed efficiently.

[0063] G.Applications The pressure-sensitive adhesive sheet can be preferably used as a temporary fixing sheet when processing any appropriate member (for example, an electronic component such as a semiconductor chip). In one embodiment, the pressure-sensitive adhesive sheet can be used as a sheet for temporarily fixing a semiconductor chip when manufacturing a CSP (Chip Size / Scale Package) or a WLP (Wafer Level Package).

[0064] In one embodiment, the pressure-sensitive adhesive sheet is in a roll form. [Example]

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" are by weight unless otherwise specified. In this specification, the expansion initiation temperature of heat-expandable microspheres is determined by the following method. The adhesive sheet was sandwiched between 10 mm-thick heat-resistant glass plates (140 mm x 140 mm) heated to the specified temperature (described below) on a hot plate (Shamal Hot Plate "HHP-411") for one minute, then cooled to room temperature. The lowest temperature at which the adhesive layer thickness measured with a dial gauge increased by 5% or more from the pre-heating thickness was determined as the foaming initiation temperature of the heat-expandable microspheres. Here, the specified temperature was set in 5°C increments starting from 50°C (i.e., 50°C, 55°C, 60°C, etc.), and a new adhesive sheet was used each time the specified temperature was changed. The adhesive layer whose thickness was measured was the adhesive layer (containing heat-expandable microspheres). If a primer layer (a rubbery organic elastic layer) was present, the measurement also included the primer layer (a rubbery organic elastic layer). The foaming initiation temperature measured by this method for heat-expandable microspheres F-36D is 85°C, and that for F-50D is 105°C.

[0066] [Production Example 1] Production of base polymer 1 100 parts of 2-ethylhexyl acrylate (EHA), 1 part of methyl methacrylate (MMA), 4 parts of 2-hydroxyethylhexyl acrylate (HEA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to ethyl acetate, and the mixture was heated to obtain an ethyl acetate solution of an acrylic copolymer (polymer 1).

[0067] [Production Example 2] Production of Base Polymer 2 65 parts of ethyl acrylate (EA), 5 parts of butyl acrylate (BA), 30 parts of 2-ethylhexyl acrylate (EHA), 5 parts of methyl methacrylate (MMA), 3 parts of 2-hydroxyethylhexyl acrylate (HEA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to ethyl acetate, and the mixture was heated to obtain an ethyl acetate solution of an acrylic copolymer (polymer 2).

[0068] [Production Example 3] Production of Base Polymer 3 90 parts of 2-ethylhexyl acrylate (EHA), 5 parts of acrylic acid (AA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to ethyl acetate, and the mixture was heated to obtain an ethyl acetate solution of an acrylic copolymer (polymer 3).

[0069] [Production Example 4] Production of Base Polymer 4 65 parts of ethyl acrylate (EA), 5 parts of butyl acrylate (BA), 30 parts of 2-ethylhexyl acrylate (EHA), 5 parts of methyl methacrylate (MMA), 10 parts of 2-hydroxyethylhexyl acrylate (HEA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to 2-butanone, and the mixture was heated to obtain an ethyl acetate solution of an acrylic copolymer (polymer 4).

[0070] [Production Example 5] Production of Base Polymer 5 100 parts of 2-ethylhexyl acrylate (EHA), 1 part of methyl methacrylate (MMA), 4 parts of 2-hydroxyethylhexyl acrylate (HEA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated to obtain a toluene solution of an acrylic copolymer (polymer 5).

[0071] [Production Example 6] Production of Base Polymer 6 65 parts of ethyl acrylate (EA), 5 parts of butyl acrylate (BA), 30 parts of ethylhexyl acrylate (EHA), 3.5 parts of 2-hydroxyethylhexyl acrylate (HEA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated to obtain a toluene solution of an acrylic copolymer (polymer 6).

[0072] [Production Example 7] Production of Base Polymer 7 70 parts of ethyl acrylate (EA), 3 parts of butyl acrylate (BA), 30 parts of ethylhexyl acrylate (EHA), 5 parts of methyl methacrylate (MMA), 3.5 parts of 2-hydroxyethylhexyl acrylate (HEA), and 0.2 parts of benzoyl peroxide as a polymerization initiator were added to toluene, and the mixture was heated to obtain a toluene solution of an acrylic copolymer (polymer 7).

[0073] [Example 1] (Preparation of primer layer / substrate laminate) Mixed solution A was prepared by mixing a toluene solution of polymer 6 (polymer 6: 100 parts), 1.5 parts of an isocyanate crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., trade name "Coronate L"), and 0.05 parts of dioctyltin dilaurate. The mixed solution A was applied to one surface of a substrate (manufactured by Toray Industries, Inc., product name "Lumirror S10", thickness: 25 μm) using an applicator so that the thickness after solvent evaporation (drying) would be 13 μm. Thereafter, the solvent was evaporated (dried) at 150°C for 1 minute using a forced convection hot air drying oven, yielding an undercoat layer / substrate laminate. (Preparation of MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) laminate) An adhesive (mixed solution B) was prepared by mixing an ethyl acetate solution of polymer 1 (100 parts polymer), 1.5 parts of an isocyanate crosslinker (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L"), 0.01 parts of a polydentate amino compound (1,4-diazabicyclo[2.2.2]octane, manufactured by Sigma-Aldrich), 10 parts of a tackifying resin (manufactured by Sumitomo Bakelite Co., Ltd., product name "Sumilite PR12603"), and 30 parts of thermally expandable microspheres (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., product name "F36-D", foaming initiation temperature: 85°C, average particle size: 13 μm). The pressure-sensitive adhesive (mixed solution B) was applied to the release-treated surface of a liner (PET film, manufactured by Mitsubishi Plastics, Inc., product name "MRF-38") coated with a silicone-based release agent so that the thickness after solvent evaporation (drying) would be 35 μm. The solvent was then evaporated (dried) at 65°C for 5 minutes using a forced convection hot air drying oven to obtain an MRF38 (liner) / pressure-sensitive adhesive layer (containing heat-expandable microspheres) laminate. (Preparation of MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) / undercoat layer / substrate laminate) The MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) and the primer layer / substrate laminate were bonded together so that the adhesive layer (containing heat-expandable microspheres) and the primer layer faced each other, to obtain an MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) / primer layer / substrate laminate. (Preparation of MRF50 (liner) / another adhesive layer laminate) Mixed solution C was prepared by mixing a toluene solution of polymer 7 (100 parts of polymer 7), 1.5 parts of an isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L"), 10 parts of a plasticizer (manufactured by DIC Corporation, product name "Monocizer W700"), and 0.05 parts of dioctyltin dilaurate. The mixed solution C was applied to the release agent-coated surface of a liner (PET film, manufactured by Mitsubishi Plastics, Inc., product name "MRF-38") coated with a silicone-based release agent so that the thickness after solvent evaporation (drying) would be 7 μm. Thereafter, the solvent was evaporated (dried) at 150°C for 1 minute using a forced convection hot air drying oven to obtain an MRF50 (liner) / another pressure-sensitive adhesive layer laminate. (Preparation of adhesive sheet with liner) An MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) / primer layer / substrate laminate and an MRF50 (liner) / another adhesive layer laminate were bonded together so that the substrate and the other adhesive layer faced each other, to obtain a liner-attached adhesive sheet (MRF38 (liner) / adhesive layer (containing heat-expandable microspheres) / primer layer / substrate / other adhesive layer / MRF50 (liner)).

[0074] [Examples 2 to 5, Comparative Examples 1 to 4] A liner-attached PSA sheet was obtained in the same manner as in Example 1, except that the PSA layer was formed using the base polymer shown in Table 1 (a 2-butanone solution of polymer 4 was used in Example 5, and a toluene solution of polymer 5 was used in Comparative Examples 2 and 3), the low molecular weight compound shown in Table 1 was used in the amount shown in Table 1, the crosslinking agent shown in Table 1 was used in the amount shown in Table 1, and the heat-expandable microspheres shown in Table 1 were used in the amount shown in Table 1, and the PSA coating layer was dried at the temperature and for the time shown in Table 1. The heat-expandable microspheres "F-50D" are manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. under the trade name "F-50D" (foaming initiation temperature: 105°C, average particle size: 14 μm). The crosslinking agent "TC" is an epoxy-based crosslinking agent (manufactured by Mitsubishi Gas Chemical Company, Inc. under the trade name "Tetrad C").

[0075] [Example 6] A pressure-sensitive adhesive sheet with a liner was obtained in the same manner as in Example 1, except that dioctyltin dilaurate was not blended into the undercoat layer.

[0076] <Evaluation> After peeling the liners from the liner-attached PSA sheets obtained in the Examples and Comparative Examples, the PSA sheets were subjected to the following evaluations. The results are shown in Table 1. Note that Comparative Example 1 could not be evaluated due to cohesive failure of the PSA layer, which was thought to be caused by insufficient crosslinking of the base polymer, and Comparative Example 3 could not be evaluated due to foaming of the heat-expandable microspheres during production.

[0077] (1) Adhesive strength The pressure-sensitive adhesive sheets obtained in the examples and comparative examples were cut to a size of 20 mm in width and 140 mm in length. A polyethylene terephthalate film (trade name "Lumirror S-10" manufactured by Toray Industries, Inc.; thickness: 25 μm, width: 30 mm) was attached as an adherend to the adhesive layer side of the adhesive sheet, with 5 mm protruding from both sides in the width direction, by rolling a 2 kg roller back and forth once in accordance with JIS Z 0237:2009. Another pressure-sensitive adhesive layer was attached to a metal plate (SUS304 plate, thickness 3 mm) via double-sided tape (manufactured by Nitto Denko Corporation, product name "No. 500") to prepare a measurement sample. The adherend was then peeled off the adhesive sheet in the lengthwise direction at a peel angle of 180° and a peel speed (tensile speed) of 300 mm / min, and the load was measured. The maximum load (maximum load excluding the peak top at the beginning of the measurement) was calculated, and this maximum load was divided by the tape width to determine the adhesive strength (N / 20 mm width). The above operation was carried out in an atmosphere at a temperature of 23°C. Adhesive strength of 4N / 20mm or more was rated as excellent (◎ in the table), adhesive strength of 2N / 20mm or more but less than 4N / 20mm was rated as good (◯ in the table), adhesive strength of 0.5N / 20mm or more but less than 2N / 20mm was rated as fair (△ in the table), and adhesive strength of less than 0.5N / 20mm was rated as poor (× in the table).

[0078] (2) Thermal peelability evaluation The pressure-sensitive adhesive sheets obtained in the examples and comparative examples were cut to a size of 20 mm in width and 140 mm in length. A metal plate (SUS304 plate, thickness 3 mm, width 30 mm, length 160 mm) was placed on the adhesive layer side of the adhesive sheet as an adherend, and a 2 kg roller was rolled back and forth once to bond the adhesive sheet and the metal plate together to create an evaluation sample. A 10 mm thick heat-resistant glass plate (140 mm x 140 mm) was placed on a hot plate (Shamal hot plate "HHP-411") set to 120°C, and the heat-resistant glass plate was heated to 120°C. The above sample was placed on a hot plate (Shamal hot plate "HHP-411") set to 120°C with the adhesive sheet facing up, and then the above heat-resistant glass plate set to 120°C was placed on top of the adhesive sheet (i.e., a laminated structure of hot plate / metal plate / adhesive sheet / glass plate was created). The time until the adhesive layer peeled (separated) from the SUS plate was measured. If the time required for separation was within 3 minutes, it was rated as excellent (◎ in the table), if it was more than 3 minutes but within 7 minutes, it was rated as good (○ in the table), if it was more than 7 minutes but within 10 minutes, it was rated as fair (△ in the table), and if it exceeded 10 minutes or no separation occurred, it was rated as unacceptable (× in the table).

[0079] [Table 1] [Explanation of symbols]

[0080] 10 Base material 20 adhesive layer 100 adhesive sheets

Claims

1. A substrate and a pressure-sensitive adhesive layer disposed on at least one side of the substrate, The pressure-sensitive adhesive layer is a (meth)acrylic polymer as a base polymer; an isocyanate-based crosslinking agent and / or an epoxy-based crosslinking agent as a crosslinking agent; an amino compound having a tertiary amino group capable of multidentate coordination as a low molecular weight compound; and heat-expandable microspheres, the (meth)acrylic polymer contains a structural unit having an active hydrogen group, the amino compound having a tertiary amino group capable of polydentate coordination is an amino compound containing at least two tertiary amino groups in the molecule, the content of the amino compound having a tertiary amino group capable of polydentate coordination is 0.001 parts by weight to 10 parts by weight based on 100 parts by weight of the base polymer; Adhesive sheet.

2. The pressure-sensitive adhesive sheet according to claim 1, wherein the amino compound having a tertiary amino group capable of polydentate coordination is at least one selected from the group consisting of 1,4-diazabicyclo[2.2.2]octane, 1,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the active hydrogen group is a hydroxyl group and / or a carboxyl group.

4. 4. The pressure-sensitive adhesive sheet according to claim 1, wherein the expansion temperature of the heat-expandable microspheres is 80°C to 250°C.

5. The pressure-sensitive adhesive sheet according to claim 1 , further comprising another pressure-sensitive adhesive layer on the opposite side of the substrate to the pressure-sensitive adhesive layer.

6. Applying an adhesive to a substrate to form an adhesive coating layer; and and drying the pressure-sensitive adhesive coating layer to form a pressure-sensitive adhesive layer. A method for producing the pressure-sensitive adhesive sheet according to any one of claims 1 to 5.

7. The method for producing a pressure-sensitive adhesive sheet according to claim 6, wherein the product of the drying temperature and drying time when drying the pressure-sensitive adhesive coating layer is 100°C·min to 500°C·min.

8. the adhesive contains a solvent, The boiling point of the solvent is less than 100°C. The method for producing the pressure-sensitive adhesive sheet according to claim 6 or 7.

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