Pressure-sensitive adhesive composition, cured product, and pressure-sensitive adhesive sheet

Abstract

To provide an adhesive composition having excellent curability and pot life while maintaining good adhesiveness after heating and curing.SOLUTION: There is provided an adhesive composition which comprises an acrylic polymer (a) having a crosslinkable functional group and a glass transition temperature Tg of -70 to 0°C and a crosslinking agent component (b2) containing an aliphatic or alicyclic polyisocyanate and a block polyisocyanate derived from a blocking agent, wherein the content of a monomer unit having a crosslinkable functional group is 0.1 to 20 mass% based on the total mass of (a) and the content of (b2) is 0.1 to 20 pts.mass based on 100 pts.mass of (a).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, a cured product, and a pressure-sensitive adhesive sheet. [Background technology]

[0002] Polyisocyanates can crosslink polymers containing hydroxyl or carboxyl groups at industrially accessible temperatures ranging from relatively low temperatures above room temperature to approximately 150°C. They exhibit excellent adhesion to substrates and have a moderate pot life at room temperature. Therefore, they are used in a variety of applications, including pressure-sensitive adhesives, adhesives, paints, and plastics. Among these, aromatic, alicyclic, and aliphatic polyisocyanates are used in pressure-sensitive adhesive applications. However, when alicyclic or aliphatic polyisocyanates are used as crosslinking agents in pressure-sensitive adhesives containing carboxyl groups, they experience rapid viscosity increase and gelation within a short period of time (e.g., within one hour), making them unsuitable for mass production. Another issue is that they are prone to viscosity increase when the crosslinking functional group content is high.

[0003] Patent Document 1 discloses a pressure-sensitive adhesive composition obtained by blending a carboxyl group-containing acrylic resin with a polyfunctional isocyanate compound, a β-dicarbonyl compound, and an alcohol having two or more carbon atoms. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-259922 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the pressure-sensitive adhesive composition described in Patent Document 1 is complicated in that it requires the addition of two additional compounds in addition to the crosslinker component consisting of a polyfunctional isocyanate compound. Furthermore, when acetylacetone is blended as the β-dicarbonyl compound, the acetylacetone is acutely toxic and has a high boiling point of 140°C, so there is a possibility that it will remain in the cured product even after heating the pressure-sensitive adhesive composition. Therefore, there is a demand for a pressure-sensitive adhesive composition that can suppress gelation and thickening, that uses fewer components, and that has a safer composition.

[0006] The present invention has been made in view of the above circumstances, and provides a pressure-sensitive adhesive composition that has excellent curability and pot life while maintaining good adhesiveness after heat curing, as well as a cured product and a pressure-sensitive adhesive sheet that use the pressure-sensitive adhesive composition. [Means for solving the problem]

[0007] That is, the present invention includes the following aspects. (1) an acrylic polymer (a) having a crosslinkable functional group and a glass transition temperature Tg of −70° C. or higher and 0° C. or lower; a crosslinker component (b1) containing an aliphatic or alicyclic polyisocyanate; and (c) a secondary or tertiary alcohol, or The acrylic polymer (a), a crosslinker component (b2) containing a blocked polyisocyanate derived from an aliphatic or alicyclic polyisocyanate and a blocking agent; the content of the monomer unit having a crosslinkable functional group relative to the total mass of the acrylic polymer (a) is 0.1% by mass or more and 20% by mass or less, the content of the crosslinking agent component (b1) is 0.05 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the acrylic polymer (a); the content of the secondary or tertiary alcohol (c) is 5 parts by mass or more and 300 parts by mass or less relative to 100 parts by mass of the acrylic polymer (a); The pressure-sensitive adhesive composition, wherein the content of the crosslinking agent component (b2) is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the acrylic polymer (a). (2) The pressure-sensitive adhesive composition according to (1), wherein the aliphatic or alicyclic polyisocyanate has an average number of isocyanate functional groups of 2 or more. (3) The pressure-sensitive adhesive composition according to (1) or (2), wherein the secondary or tertiary alcohol (c) includes a tertiary alcohol. (4) The pressure-sensitive adhesive composition according to any one of (1) to (3), wherein the blocking agent is at least one compound selected from the group consisting of active methylene compounds, oxime compounds, amine compounds, pyrazole compounds, and triazole compounds. (5) The blocking agent is an active methylene compound, The pressure-sensitive adhesive composition according to any one of (1) to (4), wherein the active methylene compound comprises a malonic acid ester having a secondary alkyl group or a malonic acid ester having a tertiary alkyl group. (6) The blocking agent is an active methylene compound, The pressure-sensitive adhesive composition according to any one of (1) to (5), wherein the active methylene compound comprises a malonic acid ester having a secondary alkyl group and a malonic acid ester having a tertiary alkyl group. (7) The weight average molecular weight Mw of the crosslinking agent component (b1) and the crosslinking agent component (b2) is 1.0 × 10 3 Over 1.0 x 10 5 The pressure-sensitive adhesive composition according to any one of (1) to (6), which is: (8) The pressure-sensitive adhesive composition according to any one of (1) to (7), wherein the aliphatic or alicyclic polyisocyanate has at least one structure selected from the group consisting of a urethane structure, an allophanate structure, a biuret structure, a urea structure, and an isocyanurate structure. (9) The pressure-sensitive adhesive composition according to any one of (1) to (8), wherein the acrylic polymer (a) contains one or more acrylic ester units having an alkyl group having 1 to 20 carbon atoms at the terminal of the ester group. (10) The pressure-sensitive adhesive composition according to any one of (1) to (9), wherein the crosslinkable functional group is one or more functional groups selected from the group consisting of a hydroxyl group, a carboxyl group, and an epoxy group. (11) The weight-average molecular weight Mw of the acrylic polymer (a) is 3.0 × 10 5 Over 2.5 x 10 6 The pressure-sensitive adhesive composition according to any one of (1) to (10), which is: (12) A cured product obtained by curing the pressure-sensitive adhesive composition according to any one of (1) to (11) with heat or light. (13) a substrate; a pressure-sensitive adhesive layer on the substrate, A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer is made of a cured product of the pressure-sensitive adhesive composition according to any one of (1) to (11). (14) The pressure-sensitive adhesive sheet according to (13), wherein the thickness of the pressure-sensitive adhesive layer is 0.1 μm or more and 1000 μm or less. (15) The adhesive sheet according to (13) or (14), wherein the adhesive composition is applied to a 38 μm-thick release-treated polyethylene terephthalate film, dried at 130°C for 3 minutes, and cured to form an adhesive layer having a thickness of 45 μm, and the adhesive sheet is then stored in an environment of 23°C and 50% RH for 7 days, immersed in ethyl acetate at 23°C for 1 week, and dried at 120°C for 2 hours, and has a gel fraction of 20% by mass or more and 98% by mass or less. (16) The pressure-sensitive adhesive sheet according to any one of (13) to (15), wherein the pressure-sensitive adhesive sheet has a width of 20 mm and a length of 100 mm, and is provided with a pressure-sensitive adhesive layer of 45 μm in thickness, obtained by applying the pressure-sensitive adhesive composition to a polyethylene terephthalate film of 25 μm in thickness, drying and curing the composition at 130°C for 3 minutes, and after storing the pressure-sensitive adhesive sheet for 7 days in an environment of 23°C and 50% RH, the pressure-sensitive adhesive sheet is pressed back and forth once with a 2 kg roller using a SUS304BA steel plate as an adherend, and after curing at 23°C for 30 minutes, the 180-degree peel adhesive strength measured at 23°C and a speed of 300 mm / min is 0.05 N / 20 mm or more and 40 N / 20 mm or less. [Effects of the Invention]

[0008] According to the pressure-sensitive adhesive composition of the above embodiment, it is possible to provide a pressure-sensitive adhesive composition that is excellent in curability and pot life while maintaining good adhesiveness after heat curing. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following embodiment. The present invention can be practiced with appropriate modifications within the scope of its gist.

[0010] In this specification, the term "polyol" refers to a compound having two or more hydroxy groups (-OH). As used herein, the term "polyisocyanate" refers to a reaction product in which a plurality of monomer compounds having one or more isocyanate groups (-NCO) are bonded together.

[0011] In this specification, the term "structural unit" refers to a structure resulting from one molecule of a monomer in the structure constituting a polyisocyanate, a block polyisocyanate, or an acrylic polymer. For example, a monomer unit having a crosslinkable functional group refers to a structure resulting from one molecule of a monomer having a crosslinkable functional group in an acrylic polymer. The structural unit may be a unit formed directly by a (co)polymerization reaction of a monomer, or may be a unit in which a portion of the unit is converted into a different structure by treating the (co)polymer.

[0012] <Adhesive composition> The pressure-sensitive adhesive composition of the present embodiment comprises: an acrylic polymer (a) having a crosslinkable functional group and a glass transition temperature Tg of −70° C. or higher and 0° C. or lower; a crosslinker component (b1) containing an aliphatic or alicyclic polyisocyanate; and (c) a secondary or tertiary alcohol, or The acrylic polymer (a), and a crosslinker component (b2) containing a blocked polyisocyanate derived from an aliphatic or alicyclic polyisocyanate and a blocking agent.

[0013] That is, the pressure-sensitive adhesive composition of the present embodiment comprises an acrylic polymer (a) having a crosslinkable functional group and a glass transition temperature Tg of −70° C. or higher and 0° C. or lower; a crosslinker component (b1) containing an aliphatic or alicyclic polyisocyanate; and (c) a secondary or tertiary alcohol. Alternatively, the pressure-sensitive adhesive composition of the present embodiment comprises: an acrylic polymer (a) having a crosslinkable functional group and having a glass transition temperature Tg of −70° C. or more and 0° C. or less; and a crosslinker component (b2) containing a blocked polyisocyanate derived from an aliphatic or alicyclic polyisocyanate and a blocking agent.

[0014] The content of the monomer unit having a crosslinkable functional group relative to the total mass of the acrylic polymer (a) is 0.1% by mass to 20% by mass, preferably 0.1% by mass to 18% by mass, more preferably 0.1% by mass to 15% by mass, even more preferably 0.1% by mass to 12% by mass, and particularly preferably 0.1% by mass to 10% by mass. Having the content of the monomer unit having a crosslinkable functional group within the above range ensures good adhesiveness after heat curing. The content of the monomer unit having a crosslinkable functional group can be obtained, for example, by calculating the ratio (percentage) of the mass of the monomer having a crosslinkable functional group relative to the total mass of all monomers used in the synthesis. Alternatively, the content can be calculated, for example, by combining measurement of the acid value and hydroxyl value of the acrylic polymer (a) with measurements by infrared spectroscopy (IR) analysis, nuclear magnetic resonance (NMR) analysis, or mass spectrometry.

[0015] When the pressure-sensitive adhesive composition of this embodiment contains a crosslinker component (b1), the content of the crosslinker component (b1) is 0.05 to 20 parts by mass, preferably 0.1 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.1 to 8 parts by mass, and particularly preferably 0.2 to 7 parts by mass, relative to 100 parts by mass of the acrylic polymer (a). By ensuring that the content of the crosslinker component (b1) is within the above range, the cohesive strength and adhesive strength of the pressure-sensitive adhesive after heat curing can be improved. The content of the crosslinker component (b1) can be calculated, for example, from the blend amounts of the acrylic polymer (a) and the crosslinker component (b1) during the production of the pressure-sensitive adhesive composition. Alternatively, the content of the crosslinker component (b1) can be measured, for example, by IR analysis, NMR analysis, or mass spectrometry. Furthermore, the content of the secondary or tertiary alcohol (c) is 5 parts by mass or more and 300 parts by mass or less, preferably 10 parts by mass or more and 250 parts by mass or less, more preferably 15 parts by mass or more and 250 parts by mass or less, even more preferably 20 parts by mass or more and 250 parts by mass or less, even more preferably 26 parts by mass or more and 250 parts by mass or less, even more preferably 28 parts by mass or more and 250 parts by mass or less, particularly preferably 40 parts by mass or more and 200 parts by mass or less, more particularly preferably 45 parts by mass or more and 200 parts by mass or less, and most preferably 50 parts by mass or more and 200 parts by mass or less. When the content of the secondary or tertiary alcohol (c) is equal to or greater than the above lower limit, the adhesive composition can have excellent adhesion after heat curing and an excellent pot life. On the other hand, when the content of the secondary or tertiary alcohol (c) is equal to or less than the above upper limit, the adhesive composition can have maintained adhesive strength. The content of the secondary or tertiary alcohol (c) can be calculated, for example, from the blending amounts of the acrylic polymer (a) and the secondary or tertiary alcohol (c) during the production of the adhesive composition. Alternatively, the content of the secondary or tertiary alcohol (c) can be measured, for example, by IR analysis, NMR analysis, or mass spectrometry.

[0016] When the pressure-sensitive adhesive composition of this embodiment contains a crosslinker component (b2), the content of the crosslinker component (b2) is 0.1 to 20 parts by mass, preferably 0.1 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.1 to 8 parts by mass, particularly preferably 0.1 to 5 parts by mass, and most preferably 0.5 to 4 parts by mass, per 100 parts by mass of the acrylic polymer (a). When the content of the crosslinker component (b2) is equal to or greater than the lower limit, excellent cohesive strength and adhesive strength can be achieved. On the other hand, when the content is equal to or less than the upper limit, good adhesive strength and pot life can be maintained after heat curing. The content of the crosslinker component (b2) can be calculated, for example, from the amounts of the acrylic polymer (a) and the crosslinker component (b2) blended during the production of the pressure-sensitive adhesive composition. Alternatively, the content of the crosslinker component (b2) can be measured, for example, by IR analysis, NMR analysis, or mass spectrometry.

[0017] The pressure-sensitive adhesive composition of the present embodiment has the above-described configuration, and therefore has excellent curability and pot life while maintaining good adhesiveness and cohesive strength after heat curing. Next, each component contained in the pressure-sensitive adhesive composition of the present embodiment will be described in detail below.

[0018] <Acrylic polymer (a)> The acrylic polymer (a) has a crosslinkable functional group and a glass transition temperature Tg of -70°C or higher and 0°C or lower. The acrylic polymer (a) contains one or more polymerizable acrylic monomer units having a crosslinkable functional group and one or more polymerizable acrylic monomer units not having a crosslinkable functional group, and is obtained by copolymerizing these monomers.

[0019] Examples of the crosslinkable functional group capable of crosslinking with the crosslinking agent component (b) include a hydroxyl group, a carboxyl group, and an epoxy group, with a hydroxyl group being preferred. The acrylic polymer (a) may contain one type of crosslinkable functional group alone, or may contain two or more different types of crosslinkable functional groups in combination. That is, the acrylic polymer (a) may be obtained by polymerizing one type of polymerizable monomer having one or more crosslinkable functional groups in one molecule alone, or may be obtained by copolymerizing two or more types of polymerizable monomers having different types of crosslinkable functional groups in combination.

[0020] Examples of the polymerizable monomer having one or more crosslinkable functional groups in one molecule include the following (i) to (v), which may be used singly or in combination of two or more. (i) Acrylic esters having a hydroxyl group, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, and 6-hydroxyhexyl acrylate. (ii) Methacrylates having a hydroxyl group, such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 4-hydroxybutyl methacrylate, and 6-hydroxyhexyl methacrylate. (iii) (meth)acrylic acid esters having a polyvalent hydroxy group, such as acrylic acid monoester or methacrylic acid monoester of glycerin, and acrylic acid monoester or methacrylic acid monoester of trimethylolpropane. (iv) Unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, etc. (v) Polymerizable monomers having an epoxy group such as glycidyl methacrylate, 1,2-epoxy-4-vinylcyclohexane, allyl glycidyl ether, 4-hydroxybutyl acrylate glycidyl ether, etc.

[0021] Examples of other monomers copolymerizable with the polymerizable monomer include the following (i) to (iii), which may be used singly or in combination of two or more. (i) Methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate (meth)acrylate esters such as decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, benzyl (meth)acrylate, and cyclohexyl (meth)acrylate. (ii) Unsaturated amides such as (meth)acrylamide, N-methylolacrylamide, diacetoneacrylamide, and dimethylaminopropylacrylamide. (iii) Styrene, vinyltoluene, vinyl acetate, (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate.

[0022] Furthermore, as other monomers copolymerizable with the polymerizable monomer, polymerizable ultraviolet-stable monomers disclosed in Reference 1 (JP-A-1-261409) and Reference 2 (JP-A-3-006273) may be used. Specific examples of the polymerizable ultraviolet-stable monomer include 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, and 2-hydroxy-4-(3-methacryloxy-2-hydroxypropoxy)benzophenone.

[0023] Among these, the acrylic polymer (a) preferably contains one or more acrylate units having an alkyl group having 1 to 20 carbon atoms at the ester group terminal. The acrylic ester unit having an alkyl group having 1 to 20 carbon atoms at the ester group terminal may or may not contain a crosslinkable functional group. The number of carbon atoms in the alkyl group of the acrylate unit containing a crosslinkable functional group is from 1 to 20, preferably from 1 to 18, and more preferably from 2 to 18. On the other hand, the number of carbon atoms in the alkyl group of the acrylate unit not containing a crosslinkable functional group is from 1 to 20, preferably from 1 to 18, more preferably from 2 to 18, and even more preferably from 4 to 18.

[0024] For example, the acrylic polymer (a) can be obtained by solution polymerizing the above-mentioned monomer components in the presence of a known radical polymerization initiator such as a peroxide or an azo compound, and diluting the resultant with an organic solvent, etc., as necessary.

[0025] The aqueous-based acrylic polymer (a) can be produced by a known method such as solution polymerization of an olefinically unsaturated compound followed by conversion into an aqueous phase, or emulsion polymerization. In this case, water solubility or water dispersibility can be imparted by neutralizing the acidic moiety of a carboxylic acid-containing monomer such as acrylic acid or methacrylic acid, or a sulfonic acid-containing monomer, with an amine or ammonia.

[0026] [Glass transition temperature of acrylic polymer (a)] The glass transition temperature Tg of the acrylic polymer (a) is -70°C or higher and 0°C or lower, preferably -70°C or higher and -5°C or lower, more preferably -70°C or higher and -10°C or lower, and even more preferably -70°C or higher and -15°C or lower. When the glass transition temperature Tg of the acrylic polymer (a) is within the above range, the adhesive strength and cohesive strength of the cured product of the pressure-sensitive adhesive composition tend to be superior. The glass transition temperature of the acrylic polymer (a) can be, for example, the value measured using a differential scanning calorimetry (DSC) measurement device at a heating rate of 5°C / min after vacuum drying after removing the organic solvent and water from the acrylic polymer (a) solution under reduced pressure.

[0027] [Weight average molecular weight of acrylic polymer (a)] The weight average molecular weight Mw of the acrylic polymer (a) is 3.0 × 10 5 Over 2.5 x 10 6 Preferably, it is 4.0 x 10 or less. 5 Over 2.0 x 10 6 More preferably, it is 4.5×10 or less. 5 Over 1.8 x 10 6 More preferably, it is 4.5×10 5 Over 1.7 x 10 6 It is particularly preferable that the weight-average molecular weight Mw of the acrylic polymer (a) is within the above range. When the weight-average molecular weight Mw of the acrylic polymer (a) is within the above range, the adhesive strength, cohesive strength, and durability of the cured product of the pressure-sensitive adhesive composition tend to be superior. The weight-average molecular weight Mw of the acrylic polymer (a) can be measured, for example, using the method described in the Examples below.

[0028] <Crosslinking agent component (b)> The pressure-sensitive adhesive composition of the present embodiment contains, as the crosslinker component (b), a crosslinker component (b1) containing a polyisocyanate or a crosslinker component (b2) containing a blocked polyisocyanate.

[0029] [Crosslinking agent component (b1)] The polyisocyanate contained in the crosslinker component (b1) is a reaction product obtained by reacting a plurality of monomer compounds having one or more isocyanate groups (-NCO) (hereinafter, sometimes referred to as "isocyanate monomers"). The isocyanate monomers used in the production of polyisocyanates are one or more diisocyanates selected from the group consisting of aliphatic diisocyanates and alicyclic diisocyanates. The diisocyanate preferably has a carbon number of 4 or more and 30 or less. Specific examples of diisocyanates include the following: These diisocyanates may be used alone or in combination of two or more. (1) Aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (hereinafter sometimes referred to as "HDI"), 2,2,4-trimethyl-1,6-diisocyanatohexane, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 2-methylpentane-1,5-diisocyanate (MPDI), and lysine diisocyanate (hereinafter sometimes referred to as "LDI"). (2) Alicyclic diisocyanates such as isophorone diisocyanate (hereinafter sometimes referred to as "IPDI"), 1,3-bis(diisocyanatemethyl)cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, diisocyanate norbornane, and di(isocyanatemethyl)norbornane.

[0030] The isocyanate monomer is preferably HDI or IPDI because of its industrial availability, and more preferably HDI because it reduces the viscosity of the crosslinking agent component.

[0031] As the isocyanate monomer used in producing the polyisocyanate, either an aliphatic diisocyanate or an alicyclic diisocyanate may be used alone or in combination, but it is preferable to use a combination of an aliphatic diisocyanate and an alicyclic diisocyanate, and it is particularly preferable to use HDI and IPDI. By using an aliphatic diisocyanate and an alicyclic diisocyanate, the elastic modulus and cohesive strength of the PSA can be improved.

[0032] In the polyisocyanate, from the viewpoint of improving the elastic modulus and cohesive strength of the pressure-sensitive adhesive, the mass ratio of the constituent units derived from aliphatic diisocyanates to the constituent units derived from alicyclic diisocyanates (constituent units derived from aliphatic diisocyanates / constituent units derived from alicyclic diisocyanates) is preferably 50 / 50 or more and 95 / 5 or less, more preferably 55 / 45 or more and 93 / 7 or less, even more preferably 60 / 40 or more and 91 / 9 or less, and even more preferably 65 / 35 or more and 90 / 10 or less. When the mass ratio of the structural units derived from aliphatic diisocyanates to the structural units derived from alicyclic diisocyanates is equal to or greater than the above lower limit, it is possible to more effectively prevent the elongation and flexibility of the PSA from decreasing, while when the mass ratio is equal to or less than the above upper limit, it is possible to further improve the elastic modulus and cohesive strength of the PSA. The mass ratio of the constituent units derived from aliphatic diisocyanates to the constituent units derived from alicyclic diisocyanates can be calculated, for example, using the following method. First, the mass of the unreacted aliphatic diisocyanate and the mass of the unreacted alicyclic diisocyanate are calculated from the mass of the unreacted diisocyanate after the reaction and the aliphatic diisocyanate concentrations and alicyclic diisocyanate concentrations in this unreacted diisocyanate obtained by gas chromatographic measurement. Next, the calculated mass of the unreacted aliphatic diisocyanate and the unreacted alicyclic diisocyanate are subtracted from the mass of the charged aliphatic diisocyanate and the mass of the alicyclic diisocyanate, respectively, and the obtained differences are taken as the masses of the constituent units derived from aliphatic diisocyanates and the masses of the constituent units derived from alicyclic diisocyanates, respectively. Next, the mass ratio of the aliphatic diisocyanate-derived structural units to the alicyclic diisocyanate-derived structural units is obtained by dividing the mass of the aliphatic diisocyanate-derived structural units by the mass of the alicyclic diisocyanate-derived structural units.

[0033] As the isocyanate monomer used in the production of polyisocyanate, the isocyanate monomers shown below may further be used. (1) Aromatic diisocyanates such as diphenylmethane-4,4'-diisocyanate (MDI), 1,5-naphthalene diisocyanate, tolylene diisocyanate (TDI), xylylene diisocyanate, and m-tetramethylxylylene diisocyanate (TMXDI). (2) Triisocyanates such as 4-isocyanatomethyl-1,8-octamethylene diisocyanate (hereinafter sometimes referred to as "NTI"), 1,3,6-hexamethylene triisocyanate (hereinafter sometimes referred to as "HTI"), bis(2-isocyanatoethyl) 2-isocyanatoglutarate (hereinafter sometimes referred to as "GTI"), and lysine triisocyanate (hereinafter sometimes referred to as "LTI").

[0034] (Polyol) The polyisocyanate is preferably derived from the above-mentioned diisocyanate and a polyol having an average hydroxyl functionality of 2.0 to 8.0. This allows the average number of isocyanate groups in the resulting polyisocyanate to be increased. In the polyisocyanate, urethane groups are formed by the reaction between the hydroxyl groups of the polyol and the isocyanate groups of the diisocyanate.

[0035] The average number of hydroxyl functional groups in the polyol is preferably from 2.0 to 8.0, more preferably from 2 to 6, and even more preferably from 2 to 5. The average number of hydroxyl functional groups in the polyol referred to here is the number of hydroxyl groups present in one molecule of the polyol.

[0036] The number average molecular weight of the polyol is preferably 50 or more and 5,000 or less, more preferably 100 or more and 4,500 or less, more preferably 130 or more and 4,300 or less, and even more preferably 200 or more and 4,200 or less, from the viewpoint of flexibility of the adhesive. When the number-average molecular weight of the polyol is within the above range, the adhesive composition containing the crosslinker component (b1) has excellent adhesive strength, cohesive strength, and flexibility. The number-average molecular weight Mn of the polyol is, for example, the number-average molecular weight measured by gel permeation chromatography (GPC) using polystyrene as the standard.

[0037] Examples of such polyols include trimethylolpropane, glycerol, and polycaprolactone polyols derived from trihydric or higher polyhydric alcohols and ε-caprolactone. Commercially available polycaprolactone polyols include, for example, Daicel Corporation's "Placcel 303" (number average molecular weight 300), "Placcel 305" (number average molecular weight 550), "Placcel 308" (number average molecular weight 850), "Placcel 309" (number average molecular weight 900), "Placcel 312" (number average molecular weight 1250), "Placcel 320" (number average molecular weight 2000), "Placcel 205" (number average molecular weight 530), "Placcel 210" (number average molecular weight 1000), "Placcel 220" (number average molecular weight 2000), "Placcel 230" (number average molecular weight 3000), and "Placcel 240" (number average molecular weight 4000).

[0038] The polyisocyanate may have at least one structure selected from the group consisting of an allophanate structure, a uretdione structure, an iminooxadiazinedione structure, an isocyanurate structure, a urea structure, a urethane structure, and a biuret structure. Among these, it is preferable that the polyisocyanate has at least one structure selected from the group consisting of a urethane structure, an allophanate structure, a biuret structure, a urea structure, and an isocyanurate group.

[0039] (Production method of polyisocyanate) The method for producing polyisocyanate will be described in detail below. Polyisocyanates can be obtained by simultaneously producing polyisocyanates in the presence of excess isocyanate monomers through an allophanate reaction to form an allophanate structure, a uretdione reaction to form a uretdione structure, an iminooxadiazinedione reaction to form an iminooxadiazinedione structure, an isocyanurate reaction to form an isocyanurate structure, a urea reaction to form a urea structure, a urethane reaction to form a urethane structure, and a biuret reaction to form a biuret structure, and then removing the unreacted isocyanate monomers after the reactions are completed. That is, the polyisocyanates obtained by the above reactions are reaction products in which multiple isocyanate monomers are bonded together and have one or more structures selected from the group consisting of allophanate structures, uretdione structures, iminooxadiazinedione structures, isocyanurate structures, urea structures, urethane structures, and biuret structures. Alternatively, the above reactions may be carried out separately and the resulting polyisocyanates may be mixed in a specific ratio. From the viewpoint of ease of production, it is preferable to carry out the above reaction at one time to obtain a polyisocyanate, but from the viewpoint of freely adjusting the molar ratio of each functional group, it is preferable to produce them separately and then mix them.

[0040] (1) Method for producing allophanate structure-containing polyisocyanate The allophanate structure-containing polyisocyanate can be obtained by adding an alcohol to an isocyanate monomer and using an allophanate reaction catalyst. The alcohol used to form the allophanate structure is preferably an alcohol formed only from carbon, hydrogen and oxygen. Specific examples of the alcohol include, but are not limited to, monoalcohols, dialcohols, etc. These alcohols may be used alone or in combination of two or more. Examples of the monoalcohol include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, and nonanol. Examples of the dialcohol include ethylene glycol, 1,3-butanediol, neopentyl glycol, and 2-ethylhexanediol. Among these, the alcohol is preferably a monoalcohol, and more preferably a monoalcohol having a molecular weight of 200 or less.

[0041] The allophanatization reaction catalyst includes, but is not limited to, alkyl carboxylates of tin, lead, zinc, bismuth, zirconium, zirconyl, and the like. Examples of tin alkylcarboxylates (organotin compounds) include tin 2-ethylhexanoate and dibutyltin dilaurate. Examples of lead alkylcarboxylates (organic lead compounds) include lead 2-ethylhexanoate. Examples of zinc alkylcarboxylates (organic zinc compounds) include zinc 2-ethylhexanoate. Examples of bismuth alkylcarboxylates include bismuth 2-ethylhexanoate. Examples of zirconium alkylcarboxylates include zirconium 2-ethylhexanoate. Examples of zirconyl alkylcarboxylates include zirconyl 2-ethylhexanoate. These catalysts can be used alone or in combination of two or more. The isocyanuration reaction catalyst described below can also serve as an allophanation reaction catalyst. When the allophanation reaction is carried out using the isocyanuration reaction catalyst described below, an isocyanurate group-containing polyisocyanate (hereinafter, sometimes referred to as an "isocyanurate-type polyisocyanate") is naturally also produced. Among these, it is preferable from the viewpoint of economical production to carry out the allophanate formation reaction and the isocyanurate formation reaction using an isocyanurate formation reaction catalyst described below as the allophanate formation reaction catalyst.

[0042] The lower limit of the amount of the allophanate reaction catalyst used is preferably 10 ppm by mass, more preferably 20 ppm by mass, even more preferably 40 ppm by mass, and particularly preferably 80 ppm by mass, relative to the mass of the charged isocyanate monomer. The upper limit of the amount of the allophanate reaction catalyst used is preferably 1000 ppm by mass, more preferably 800 ppm by mass, even more preferably 600 ppm by mass, and particularly preferably 500 ppm by mass, relative to the mass of the charged isocyanate monomer. That is, the amount of the allophanate reaction catalyst used is preferably 10 ppm by mass or more and 1000 ppm by mass or less, more preferably 20 ppm by mass or more and 800 ppm by mass or less, even more preferably 40 ppm by mass or more and 600 ppm by mass or less, and particularly preferably 80 ppm by mass or more and 500 ppm by mass or less, relative to the mass of the charged isocyanate monomer.

[0043] The lower limit of the allophanatization reaction temperature is preferably 40°C, more preferably 60°C, further preferably 80°C, and particularly preferably 100°C. The upper limit of the allophanate reaction temperature is preferably 180°C, more preferably 160°C, and even more preferably 140°C. That is, the allophanation reaction temperature is preferably 40°C or higher and 180°C or lower, more preferably 60°C or higher and 160°C or lower, even more preferably 80°C or higher and 140°C or lower, and particularly preferably 100°C or higher and 140°C or lower. When the allophanation reaction temperature is equal to or higher than the above lower limit, the reaction rate can be further improved. When the allophanation reaction temperature is equal to or lower than the above upper limit, coloration of the polyisocyanate tends to be more effectively suppressed.

[0044] (2) Method for producing uretdione structure-containing polyisocyanate When a polyisocyanate having a uretdione structure is derived from an isocyanate monomer, it can be produced, for example, by polymerizing the isocyanate monomer using a uretdione reaction catalyst or by heat. The uretdione-forming reaction catalyst is not particularly limited, but examples thereof include tertiary phosphines such as trialkylphosphine, tris(dialkylamino)phosphine and cycloalkylphosphine, Lewis acids, and the like. Examples of trialkylphosphines include tri-n-butylphosphine and tri-n-octylphosphine. Examples of tris(dialkylamino)phosphines include tris-(dimethylamino)phosphine. Examples of cycloalkylphosphines include cyclohexyl-di-n-hexylphosphine. Examples of Lewis acids include boron trifluoride and zinc oxychloride.

[0045] Many of the catalysts for the uretdione formation reaction can also promote the isocyanurate formation reaction at the same time. When a uretdione-forming reaction catalyst is used, it is preferable to add a deactivator for the uretdione-forming reaction catalyst such as phosphoric acid or methyl paratoluenesulfonate to terminate the uretdione-forming reaction when the desired yield is achieved. When one or more diisocyanates selected from the group consisting of the aliphatic diisocyanates and the alicyclic diisocyanates are heated without using a uretdione reaction catalyst to obtain a polyisocyanate having uretdione groups, the heating temperature is preferably 120° C. or higher, more preferably 150° C. or higher and 170° C. or lower, and the heating time is preferably 1 hour or longer and 4 hours or shorter.

[0046] (3) Method for producing iminooxadiazinedione structure-containing polyisocyanate When an iminooxadiazinedione structure-containing polyisocyanate is derived from an isocyanate monomer, an iminooxadiazinedione-forming reaction catalyst is usually used. Examples of the iminooxadiazinedione catalyst include those shown in 1) or 2) below. 1) General formula M[F n ], or the general formula M[F n (HF) m (Poly)hydrogen fluoride represented by the formula (wherein m and n are integers satisfying the relationship m / n>0. M is an n-charged cation (mixture) or one or more radicals with a total valence of n.) 2) General formula R 1 -CR'2-C(O)O-, or general formula R 2 A compound comprising a compound represented by =CR'-C(O)O- and a quaternary ammonium cation or a quaternary phosphonium cation. (In the formula, R 1 and R 2 are each independently a linear, branched, or cyclic, saturated or unsaturated perfluoroalkyl group having from 1 to 30 carbon atoms. A plurality of R's are each independently a hydrogen atom, or an alkyl or aryl group having from 1 to 20 carbon atoms which may contain a heteroatom.

[0047] Specific examples of the compound 1) ((poly)hydrogen fluoride) include tetramethylammonium fluoride hydrate, tetraethylammonium fluoride, and the like. Specific examples of the compound 2) include 3,3,3-trifluorocarboxylic acid, 4,4,4,3,3-pentafluorobutanoic acid, 5,5,5,4,4,3,3-heptafluoropentanoic acid, and 3,3-difluoroprop-2-enoic acid. Among them, as the iminooxadiazinedione-forming reaction catalyst, 1) is preferred from the viewpoint of availability, and 2) is preferred from the viewpoint of safety.

[0048] The lower limit of the amount of the iminooxadiazinedione catalyst used is not particularly limited, but from the viewpoint of reactivity, it is preferably 5 ppm, more preferably 10 ppm, and even more preferably 20 ppm by mass relative to the raw material isocyanate monomer such as HDI. The upper limit of the amount of the iminooxadiazinedione catalyst used is preferably 5000 ppm, more preferably 2000 ppm, and even more preferably 500 ppm by mass relative to the raw material isocyanate monomer such as HDI, from the viewpoint of suppressing coloration and discoloration of the product and controlling the reaction. That is, the amount of the iminooxadiazinedione catalyst used is preferably 5 ppm or more and 5000 ppm or less, more preferably 10 ppm or more and 2000 ppm or less, and even more preferably 20 ppm or more and 500 ppm or less, by mass ratio relative to the raw material isocyanate monomer such as HDI.

[0049] The lower limit of the reaction temperature for the iminooxadiazinedione formation is not particularly limited, but from the viewpoint of the reaction rate, it is preferably 40°C, more preferably 50°C, and even more preferably 60°C. From the viewpoint of suppressing coloration and discoloration of the product, the upper limit of the reaction temperature for iminooxadiazinedione formation is preferably 150° C., more preferably 120° C., and even more preferably 110° C. That is, the reaction temperature for iminooxadiazinedione formation is preferably 40° C. or higher and 150° C. or lower, more preferably 50° C. or higher and 120° C. or lower, and even more preferably 60° C. or higher and 110° C. or lower.

[0050] The iminooxadiazinedione formation reaction can be terminated when the desired iminooxadiazinedione group content is reached. The iminooxadiazinedione formation reaction can be terminated, for example, by adding an acidic compound to the reaction solution. Examples of acidic compounds include phosphoric acid, acidic phosphate esters, sulfuric acid, hydrochloric acid, and sulfonic acid compounds. This neutralizes the iminooxadiazinedione formation reaction catalyst or inactivates it by thermal decomposition or chemical decomposition. After the reaction is terminated, filtration is performed, if necessary.

[0051] (4) Method for producing isocyanurate structure-containing polyisocyanate Examples of catalysts for deriving a polyisocyanate containing an isocyanurate structure from an isocyanate monomer include commonly used isocyanuration reaction catalysts.

[0052] The isocyanuration reaction catalyst is not particularly limited, but is preferably a basic catalyst in general. Specific examples of the isocyanuration reaction catalyst include the following: 1) Hydroxides of tetraalkylammonium such as tetramethylammonium, tetraethylammonium, and tetrabutylammonium, and organic weak acid salts of the above tetraalkylammonium such as acetate, propionate, octylate, caprate, myristate, and benzoate. 2) Hydroxides of aryltrialkylammonium such as benzyltrimethylammonium and trimethylphenylammonium, and organic weak acid salts of the above aryltrialkylammonium such as acetate, propionate, octylate, caprate, myristate, and benzoate. 3) Hydroxyalkylammonium hydroxides such as trimethylhydroxyethylammonium, trimethylhydroxypropylammonium, triethylhydroxyethylammonium, and triethylhydroxypropylammonium, and organic weak acid salts such as acetates, propionates, octylates, caprates, myristates, and benzoates of the above hydroxyalkylammoniums. 4) Metal salts of tin, zinc, lead, etc. of alkylcarboxylic acids such as acetic acid, propionic acid, caproic acid, octylic acid, capric acid, and myristic acid. 5) Metal alcoholates such as sodium and potassium. 6) Aminosilyl group-containing compounds such as hexamethylenedisilazane. 7) Mannich bases. 8) Mixtures of tertiary amines and epoxy compounds. 9) Phosphorus compounds such as tributylphosphine.

[0053] Among these, from the viewpoint of preventing the generation of unnecessary by-products, the isocyanuration reaction catalyst is preferably a quaternary ammonium hydroxide or a weak organic acid salt of a quaternary ammonium, and more preferably a tetraalkylammonium hydroxide, a weak organic acid salt of a tetraalkylammonium, an aryltrialkylammonium hydroxide, or a weak organic acid salt of an aryltrialkylammonium.

[0054] The upper limit of the amount of the isocyanurate reaction catalyst used is preferably 1000 ppm by mass, more preferably 500 ppm by mass, and even more preferably 100 ppm by mass, relative to the mass of the charged isocyanate monomer. On the other hand, the lower limit of the amount of the isocyanurate reaction catalyst used is not particularly limited, but may be, for example, 10 ppm by mass.

[0055] The isocyanurate reaction temperature is preferably 50° C. or higher and 120° C. or lower, and more preferably 60° C. or higher and 90° C. or lower. When the isocyanurate reaction temperature is equal to or lower than the upper limit, coloration of the polyisocyanate tends to be more effectively suppressed.

[0056] When a desired conversion rate (the ratio by mass of polyisocyanate produced in the isocyanuration reaction to the mass of the charged isocyanate monomer) is reached, the isocyanuration reaction is stopped by adding an acidic compound (e.g., phosphoric acid, acidic phosphate ester, etc.). In order to obtain polyisocyanate, it is necessary to stop the reaction in an early stage. However, since the reaction rate of the isocyanuration reaction is very fast in the early stage, it is difficult to stop the reaction in an early stage, and therefore the reaction conditions, particularly the amount and method of adding the catalyst, must be carefully selected. For example, a method of adding the catalyst in portions at regular intervals is recommended as a suitable method. Therefore, the conversion rate of the isocyanurate reaction to obtain polyisocyanate is preferably 10% or more and 60% or less, more preferably 15% or more and 55% or less, and even more preferably 20% or more and 50% or less. By keeping the conversion rate of the isocyanurate reaction at or below the upper limit, the viscosity of the blocked polyisocyanate component can be further reduced. Furthermore, by keeping the conversion rate of the isocyanurate reaction at or above the lower limit, the reaction termination operation can be more easily carried out.

[0057] When deriving a polyisocyanate containing an isocyanurate group, a monohydric to hexahydric alcohol can be used in addition to the above isocyanate monomer. Examples of alcohols that can be used include non-polymerizable alcohols and polymerizable alcohols. The term "non-polymerizable alcohol" used herein refers to an alcohol that does not have a polymerizable group. Meanwhile, the term "polymerizable alcohol" refers to an alcohol obtained by polymerizing a monomer that has a polymerizable group and a hydroxyl group. Examples of non-polymerizable alcohols include polyhydric alcohols such as monoalcohols, diols, triols, and tetraols. Examples of monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, n-octanol, n-nonanol, 2-ethylbutanol, 2,2-dimethylhexanol, 2-ethylhexanol, cyclohexanol, methylcyclohexanol, and ethylcyclohexanol. Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,2-propanediol, 1,5-pentanediol, and 2-methyl-2,3-butanediol. Examples of the hexanediol include hexanediol, 1,6-hexanediol, 1,2-hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol, 2,3-dimethyl-2,3-butanediol, 2-ethyl-hexanediol, 1,2-octanediol, 1,2-decanediol, 2,2,4-trimethylpentanediol, 2-butyl-2-ethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol. Examples of triols include glycerin and trimethylolpropane. An example of the tetraols is pentaerythritol.

[0058] The polymerizable alcohol is not particularly limited, but examples thereof include polyester polyols, polyether polyols, acrylic polyols, polyolefin polyols, and the like.

[0059] The polyester polyols are not particularly limited, but examples thereof include products obtained by a condensation reaction between a dibasic acid alone or a mixture thereof and a polyhydric alcohol alone or a mixture thereof. The dibasic acid is not particularly limited, but examples thereof include at least one dibasic acid selected from the group consisting of carboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, and terephthalic acid. The polyhydric alcohol is not particularly limited, but examples thereof include at least one polyhydric alcohol selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, and glycerin. Examples of polyester polyols include polycaprolactones obtained by ring-opening polymerization of ε-caprolactone using the above polyhydric alcohols.

[0060] The polyether polyols are not particularly limited, but examples thereof include polyether polyols obtained by adding alkylene oxides, either singly or in mixture, to polyhydric alcohols, either singly or in mixture, using an alkali metal hydroxide or a strongly basic catalyst; polyether polyols obtained by reacting alkylene oxides with polyamine compounds; and so-called polymer polyols obtained by polymerizing acrylamide or the like using the above polyethers as a medium. Examples of alkali metals include lithium, sodium, potassium, etc. Examples of strong basic catalysts include alcoholates, alkylamines, etc. Examples of the polyhydric alcohol include the same ones as those exemplified above for the polyester polyols. Examples of alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, cyclohexene oxide, and styrene oxide. Examples of polyamine compounds include ethylenediamines.

[0061] The acrylic polyols are not particularly limited, but examples thereof include copolymers of a single or a mixture of an ethylenically unsaturated bond-containing monomer having a hydroxyl group and a single or a mixture of other ethylenically unsaturated bond-containing monomers copolymerizable therewith. The ethylenically unsaturated bond-containing monomer having a hydroxyl group is not particularly limited, but examples thereof include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate. The other ethylenically unsaturated bond-containing monomer copolymerizable with the ethylenically unsaturated bond-containing monomer having a hydroxyl group is not particularly limited, and examples thereof include acrylic acid esters, methacrylic acid esters, unsaturated carboxylic acids, unsaturated amides, vinyl-based monomers, and vinyl-based monomers having a hydrolyzable silyl group. Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, benzyl acrylate, and phenyl acrylate. Examples of methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, benzyl methacrylate, and phenyl methacrylate. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and itaconic acid. Examples of unsaturated amides include acrylamide, methacrylamide, N,N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic acid amide, and maleimide. Examples of vinyl monomers include glycidyl methacrylate, styrene, vinyltoluene, vinyl acetate, acrylonitrile, and dibutyl fumarate. Examples of vinyl monomers having a hydrolyzable silyl group include vinyltrimethoxysilane, vinylmethyldimethoxysilane, and γ-(meth)acryloxypropyltrimethoxysilane.

[0062] Examples of polyolefin polyols include hydroxyl-terminated polybutadiene and hydrogenated products thereof.

[0063] (5) Method for producing urea structure-containing polyisocyanate When a polyisocyanate containing a urea structure is derived from an isocyanate monomer, it can be produced, for example, by mixing an excess of the isocyanate monomer with water or a primary or secondary amine, and adding a urea reaction catalyst as necessary. The polyisocyanate containing a urea structure can be obtained, for example, by stirring at a temperature of 23° C. or higher for 30 minutes or longer (preferably 60 minutes or longer).

[0064] (6) Method for producing urethane structure-containing polyisocyanate When a polyisocyanate containing a urethane structure is derived from an isocyanate monomer, it can be produced by, for example, mixing an excess of the isocyanate monomer, the polyol, and, if necessary, an alcohol other than the polyol, and, if necessary, adding a urethane reaction catalyst. Examples of the polyol include the same polyols as those exemplified above in the "polyol" section. Examples of the alcohol other than the polyol include those exemplified in the above "Method for producing isocyanurate group-containing polyisocyanate" except for those exemplified in the above "Polyol". The urethanization reaction catalyst is not particularly limited, but examples thereof include tin-based compounds, zinc-based compounds, and amine-based compounds. The urethane reaction temperature is preferably 50°C or higher and 160°C or lower, and more preferably 60°C or higher and 120°C or lower. When the urethanization reaction temperature is equal to or lower than the upper limit, coloration of the polyisocyanate tends to be more effectively suppressed. The urethane reaction time is preferably 30 minutes to 4 hours, more preferably 1 hour to 3 hours, and even more preferably 1 hour to 2 hours. The molar ratio of the isocyanate groups of the isocyanate monomer to the molar amount of hydroxyl groups of the polyol (and, if necessary, alcohol other than the polyol) is preferably 2 / 1 or more and 50 / 1 or less. When this molar ratio is equal to or more than the above-mentioned lower limit, the viscosity of the polyisocyanate can be made lower. When this molar ratio is equal to or less than the above-mentioned upper limit, the yield of the urethane group-containing polyisocyanate can be made higher.

[0065] (7) Method for producing biuret structure-containing polyisocyanate The biuretizing agent for deriving a polyisocyanate containing a biuret structure from an isocyanate monomer is not particularly limited, but examples thereof include water, monohydric tertiary alcohols, formic acid, organic primary monoamines, and organic primary diamines. The amount of isocyanate groups per mole of biuretizing agent is preferably 6 moles or more, more preferably 10 moles or more, and even more preferably 10 moles or more but 80 moles or less. When the molar amount of isocyanate groups per mole of biuretizing agent is equal to or greater than the above-mentioned lower limit, the viscosity of the polyisocyanate becomes sufficiently low, and when it is equal to or less than the above-mentioned upper limit, the low-temperature curing property of the resin film formed is further improved.

[0066] A solvent may be used during the biuretization reaction. The solvent may be any solvent that dissolves the isocyanate monomer and the biuretization agent such as water and forms a homogeneous phase under the reaction conditions. Specific examples of the solvent include ethylene glycol-based solvents and phosphoric acid-based solvents. Examples of ethylene glycol solvents include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-propyl ether acetate, ethylene glycol monoisopropyl ether acetate, ethylene glycol mono-n-butyl ether acetate, ethylene glycol diacetate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di-n-propyl ether, ethylene glycol diisopropyl ether, ethylene glycol di-n-butyl ether, ethylene glycol methyl ethyl ether, ethylene glycol methyl isopropyl ether, ethylene glycol methyl-n-butyl ether, ethylene glycol ethyl-n-propyl ether, ethylene glycol ethyl isopropyl ether, ethylene glycol ethyl-n-butyl ether, ethylene glycol-n-propyl-n-butyl ether, ethylene glycol isopropyl-n-butyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-propyl ether acetate, diethylene glycol monoisopropyl ether acetate, diethylene glycol mono-n-butyl ether acetate, diethylene glycol diacetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol di-n-propyl ether, diethylene glycol diisopropyl ether, diethylene glycol di-n-butyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl isopropyl ether, diethylene glycol methyl-n-propyl ether, diethylene glycol methyl-n-butyl ether, diethylene glycol ethyl isopropyl ether, diethylene glycol ethyl-n-propyl ether, diethylene glycol ethyl-n-butyl ether, diethylene glycol-n-propyl-n-butyl ether, and diethylene glycol isopropyl-n-butyl ether. Examples of the phosphoric acid solvent include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, and tributyl phosphate. These solvents may be used alone or in combination of two or more. Among these, the ethylene glycol solvent is preferably ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol diacetate, or diethylene glycol dimethyl ether. As the phosphoric acid-based solvent, trimethyl phosphate or triethyl phosphate is preferred.

[0067] The biuretization reaction temperature is preferably 70° C. or higher and 200° C. or lower, and more preferably 90° C. or higher and 180° C. or lower. By keeping the temperature at or below the upper limit, coloration of the polyisocyanate tends to be more effectively prevented.

[0068] The above-mentioned allophanate formation reaction, uretdione formation reaction, iminooxadiazinedione formation reaction, isocyanurate formation reaction, urethanization reaction, and biuret formation reaction may be carried out sequentially, or some of them may be carried out in parallel. After the reaction is completed, unreacted isocyanate monomer can be removed from the reaction mixture by thin film distillation, extraction, or the like to obtain a polyisocyanate.

[0069] Furthermore, an antioxidant or an ultraviolet absorber may be added to the obtained polyisocyanate, for example, for the purpose of suppressing coloration during storage. Examples of antioxidants include hindered phenols such as 2,6-di-tert-butyl-p-cresol. Examples of ultraviolet absorbers include benzotriazole and benzophenone. These antioxidants and ultraviolet absorbers may be used alone or in combination of two or more. The amount of these added is preferably 10 ppm by mass or more and 500 ppm by mass or less relative to the mass of polyisocyanate.

[0070] (Average number of isocyanate functional groups in polyisocyanate) The average number of isocyanate functional groups in the polyisocyanate is preferably 2 or more, more preferably 2 or more and 20 or less, even more preferably 2 or more and 10 or less, particularly preferably 2 or more and 9 or less, and most preferably 2 or more and 8 or less, from the viewpoint of enhancing the curability and cohesive strength of the pressure-sensitive adhesive composition. The average number of isocyanate functional groups of the polyisocyanate can be measured by the method described in the examples below.

[0071] [Crosslinking agent component (b2)] The blocked polyisocyanate contained in the crosslinking agent component (b2) is a reaction product of a polyisocyanate and a blocking agent, i.e., in the blocked polyisocyanate, at least some of the isocyanate groups in the polyisocyanate are blocked with a blocking agent.

[0072] The polyisocyanate used in the production of the blocked polyisocyanate is an aliphatic or alicyclic polyisocyanate, and examples thereof include the same polyisocyanates as exemplified above for the "crosslinking agent component (b1)".

[0073] (blocking agent) Specific examples of blocking agents used in the production of blocked polyisocyanates include 1) alcohol-based compounds, 2) alkylphenol-based compounds, 3) phenol-based compounds, 4) active methylene-based compounds, 5) mercaptan-based compounds, 6) acid amide-based compounds, 7) acid imide-based compounds, 8) imidazole-based compounds, 9) urea-based compounds, 10) oxime-based compounds, 11) amine-based compounds, 12) imide-based compounds, 13) bisulfites, 14) pyrazole-based compounds, 15) triazole-based compounds, etc. More specific examples of blocking agents include the following:

[0074] 1) Alcohol compounds: alcohols such as methanol, ethanol, 2-propanol, n-butanol, sec-butanol, 2-ethyl-1-hexanol, 2-methoxyethanol, 2-ethoxyethanol, and 2-butoxyethanol. 2) Alkylphenol compounds: mono- and di-alkylphenols having an alkyl group having 4 or more carbon atoms as a substituent. Specific examples of the alkylphenol compounds include mono-alkylphenols such as n-propylphenol, iso-propylphenol, n-butylphenol, sec-butylphenol, tert-butylphenol, n-hexylphenol, 2-ethylhexylphenol, n-octylphenol, and n-nonylphenol; and di-n-propylphenol, diisopropylphenol, isopropyl cresol, di-n-butylphenol, di-tert-butylphenol, di-sec-butylphenol, di-n-octylphenol, di-2-ethylhexylphenol, and di-n-nonylphenol. 3) Phenolic compounds: phenol, cresol, ethylphenol, styrenated phenol, hydroxybenzoic acid esters, etc. 4) Active methylene compounds: malonic acid esters having a primary alkyl group, such as dimethyl malonate, diethyl malonate, dipropyl malonate, dibutyl malonate, dicyclohexyl malonate, and diphenyl malonate; malonic acid esters having a secondary alkyl group, such as di-sec-butyl malonate, diisopropyl malonate, and isopropylethyl malonate; malonic acid esters having a tertiary alkyl group, such as di-tert-butyl malonate, di-tert-pentyl malonate, and tert-butylethyl malonate; methyl acetoacetate, ethyl acetoacetate, methyl isobutanoylacetate, ethyl isobutanoylacetate, acetylacetone, and the like. 5) Mercaptan compounds: butyl mercaptan, dodecyl mercaptan, etc. 6) Acid amide compounds: acetanilide, acetic acid amide, ε-caprolactam, δ-valerolactam, γ-butyrolactam, etc. 7) Acid imide compounds: succinimide, maleimide, etc. 8) Imidazole compounds: imidazole, 2-methylimidazole, etc. 9) Urea compounds: urea, thiourea, ethyleneurea, etc. 10) Oxime compounds: formaldoxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, cyclohexanone oxime, etc. 11) Amine compounds: diphenylamine, aniline, carbazole, di-n-propylamine, diisopropylamine, isopropylethylamine, etc. 12) Imine compounds: ethyleneimine, polyethyleneimine, etc. 13) Bisulfite compounds: sodium bisulfite, etc. 14) Pyrazole compounds: pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, etc. 15) Triazole compounds: 3,5-dimethyl-1,2,4-triazole, etc.

[0075] Among the above blocking agents, in terms of availability and the viscosity, curing temperature, and curing time of the resulting blocked polyisocyanate, at least one compound selected from the group consisting of active methylene compounds, oxime compounds, amine compounds, pyrazole compounds, and triazole compounds is preferred, active methylene compounds are more preferred, and malonic acid esters having a secondary alkyl group or malonic acid esters having a tertiary alkyl group are even more preferred. Examples of malonic acid esters having a secondary alkyl group and malonic acid esters having a tertiary alkyl group include compounds represented by the following general formula (I) (hereinafter, sometimes referred to as "compound (I)"). The blocking agent may contain one type of compound (I) alone or two or more types in combination. Among these, it is particularly preferable to use a combination of a malonic acid ester having a secondary alkyl group and a malonic acid ester having a tertiary alkyl group as the blocking agent.

[0076] [ka]

[0077] (In general formula (I), R 11is a hydroxy group, an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group, an amino group which may contain one or more substituents selected from the group consisting of a hydroxy group and an alkyl group, an aryl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group, or an alkoxy group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. However, the amino group may be cyclic. R 12 , R 13 and R 14 are each independently a hydrogen atom; an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group; or an aryl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. The amino group may be cyclic. However, R 12 , R 13 and R 14 There is one or less hydrogen atom.)

[0078] R 11 When is an alkyl group having no substituent, the alkyl group preferably has 1 or more and 30 or less carbon atoms, more preferably 1 or more and 8 or less carbon atoms, even more preferably 1 or more and 6 or less carbon atoms, and particularly preferably 1 or more and 4 or less carbon atoms. Specific examples of the unsubstituted alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a sec-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a 1-methylbutyl group, an n-hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,3-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an n-octyl group, an isooctyl group, a 2-ethylhexyl group, a nonyl group, and a decyl group.

[0079] Also, R 11 When is an alkyl group having a substituent, the substituent is a hydroxy group or an amino group. Examples of the alkyl group containing a hydroxy group as a substituent include a hydroxymethyl group, a hydroxyethyl group, and a hydroxypropyl group. Examples of the alkyl group containing an amino group as a substituent include an aminomethyl group, an aminoethyl group, an aminopropyl group, and an aminobutyl group. Examples of the alkyl group containing a hydroxy group and an amino group as a substituent include a hydroxyaminomethyl group, a hydroxyaminoethyl group, and a hydroxyaminopropyl group.

[0080] R 11 When is an amino group having a substituent, the substituent is a hydroxy group or an alkyl group. An example of an amino group having a hydroxy group as a substituent is a hydroxyamino group (—NH—OH). Examples of the amino group having an alkyl group as a substituent include a methylamino group, an ethylamino group, an n-butylamino group, a dimethylamino group, a diethylamino group, a dipropylamino group, a diisopropylamino group, a di-n-butylamino group, a di-tert-butylamino group, a di-sec-butylamino group, a diisobutylamino group, and a 2,6-dimethylpiperidyl group. Examples of the amino group having a hydroxy group and an alkyl group as a substituent include a hydroxymethyleneamino group, a hydroxyethyleneamino group, a hydroxypropyleneamino group, and a hydroxybutyleneamino group. Examples of the amino group in which two substituents are linked to each other to form a ring include cyclic secondary amino groups such as an ethyleneimino group, an azacyclobutyl group, a pyrrolidyl group, a piperidyl group, a 2,6-dimethylpiperidyl group, and a hexamethyleneimino group.

[0081] R 11When is an aryl group having no substituent, the aryl group preferably has 5 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, and even more preferably 6 to 14 carbon atoms. Specific examples of the aryl group include monocyclic aromatic hydrocarbon groups, bicyclic aromatic hydrocarbon groups, tricyclic aromatic hydrocarbon groups, tetracyclic aromatic hydrocarbon groups, pentacyclic aromatic hydrocarbon groups, hexacyclic aromatic hydrocarbon groups, and heptacyclic aromatic hydrocarbon groups. Examples of the monocyclic aromatic hydrocarbon group include a phenyl group, a benzyl group, a tolyl group, and an o-xylyl group. Examples of the bicyclic aromatic hydrocarbon group include an indanyl group, an indenyl group, a pentalenyl group, an azulenyl group, a naphthyl group, and a tetrahydronaphthyl group. Examples of the tricyclic aromatic hydrocarbon group include an anthracenyl group, a fluorenyl group, a phenalenyl group, and a phenanthrenyl group. Examples of the tetracyclic aromatic hydrocarbon group include a pyrenyl group, a naphthacenyl group, and a chrysenyl group. Examples of the pentacyclic aromatic hydrocarbon group include a perylenyl group, a picenyl group, and a pentacenyl group. Examples of the hexacyclic aromatic hydrocarbon group include a naphthopyrenyl group. An example of the heptacyclic aromatic hydrocarbon group is a coronenyl group.

[0082] R 11 When is an aryl group having a substituent, the substituent is a hydroxy group or an amino group. Examples of aryl groups containing a hydroxy group as a substituent include a phenol group. An example of an aryl group containing an amino group as a substituent is an aniline group. Examples of aryl groups containing a hydroxy group and an amino group as substituents include aminophenol groups (hydroxyaniline groups).

[0083] R 11When the alkoxy group is an alkoxy group having no substituent, the number of carbon atoms in the alkoxy group is preferably from 1 to 30, more preferably from 1 to 8, even more preferably from 1 to 6, and particularly preferably from 1 to 4. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, a tert-butoxy group, a sec-butoxy group, an isobutoxy group, an n-pentoxy group, an isopentoxy group, a neopentoxy group, a tert-pentoxy group, a 1-methylbutoxy group, an n-hexoxy group, a 2-methylpentoxy group, a 3-methylpentoxy group, a 2,2-dimethylbutoxy group, a 2, Examples include a 3-dimethylbutoxy group, an n-heptoxy group, a 2-methylhexoxy group, a 3-methylhexoxy group, a 2,2-dimethylpentoxy group, a 2,3-dimethylpentoxy group, a 2,4-dimethylpentoxy group, a 3,3-dimethylpentoxy group, a 3-ethylpentoxy group, a 2,2,3-trimethylbutoxy group, an n-octoxy group, an isooctoxy group, a 2-ethylhexoxy group, a nonynoxy group, and a decyloxy group.

[0084] R 11 When is an alkoxy group having a substituent, the substituent is a hydroxy group or an amino group. Examples of the alkoxy group containing a hydroxy group as a substituent include a hydroxymethyleneoxy group, a hydroxyethyleneoxy group, a hydroxypropyleneoxy group, and a hydroxybutyleneoxy group. Examples of the alkoxy group containing an amino group as a substituent include an aminomethyleneoxy group, an aminoethyleneoxy group, an aminopropyleneoxy group, and an aminobutyleneoxy group. Examples of the alkoxy group containing a hydroxy group and an amino group as a substituent include a hydroxyaminomethylidyneoxy group, a hydroxyaminoethylidyneoxy group, and a hydroxyaminopropylidyneoxy group.

[0085] Among them, R 11 As the alkoxy group, an alkoxy group having or having no substituent is preferred, and an alkoxy group having no substituent is more preferred.

[0086] In general formula (I), R 12 , R 13 and R 14 are each independently a hydrogen atom; an alkyl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group; or an aryl group which may contain one or more substituents selected from the group consisting of a hydroxy group and an amino group. In the amino group, two of the substituents may be linked to each other to form a ring. However, R 12 , R 13 and R 14 There is one or less hydrogen atom. The alkyl group and the aryl group include the above-mentioned "R 11 " are examples of the same. Examples of the amino group in which two substituents are linked to each other to form a ring include cyclic secondary amino groups such as an ethyleneimino group, an azacyclobutyl group, a pyrrolidyl group, and a piperidyl group. Among them, R 12 is a hydrogen atom or an alkyl group having or without a substituent, and R 13 and R 14 are each independently preferably an alkyl group having or without a substituent, and R 12 is a hydrogen atom or an alkyl group having no substituent, and R 13 and R 14 are each independently an alkyl group having no substituent.

[0087] Specific examples of preferred compounds (I) include malonic acid esters having a secondary alkyl group, such as diisopropyl malonate, isopropylethyl malonate, and di-sec-butyl malonate; and malonic acid esters having a tertiary alkyl group, such as tert-butylethyl malonate, di-tert-butyl malonate, and di-tert-pentyl malonate. Among these, when compound (I) is a malonic acid ester having a secondary alkyl group, diisopropyl malonate is particularly preferred, and when compound (I) is a malonic acid ester having a tertiary alkyl group, di-tert-butyl malonate is particularly preferred.

[0088] (Method for producing blocked polyisocyanate) The blocked polyisocyanate can be obtained, for example, by reacting a polyisocyanate with the above-mentioned blocking agent. The blocking reaction between the polyisocyanate and the blocking agent can be carried out regardless of the presence or absence of a solvent, and a blocked polyisocyanate is obtained.

[0089] From the viewpoint of storage stability of the PSA composition, the mixing ratio of the polyisocyanate to the blocking agent is preferably such that the molar ratio of the active hydrogen groups contained in the blocking agent relative to the isocyanate groups contained in the polyisocyanate is 1 is 0.5 or more and 3.0 or less, more preferably 0.8 or more and 2.0 or less, even more preferably 0.9 or more and 1.5 or less, even more preferably 0.9 or more and 1.3 or less, and particularly preferably 0.9 or more and 1.2 or less.

[0090] In the blocking reaction, organic metal salts of tin, zinc, lead, etc., tertiary amine compounds, alcoholates of alkali metals such as sodium, etc., may be used as catalysts. The amount of catalyst added varies depending on the temperature of the blocking reaction, etc., but is usually from 0.05 to 1.5 parts by mass, preferably from 0.1 to 1.0 part by mass, per 100 parts by mass of polyisocyanate.

[0091] The blocking reaction can generally be carried out at a temperature of −20° C. or higher and 150° C. or lower, preferably 0° C. or higher and 130° C. or lower, and more preferably 10° C. or higher and 120° C. When the temperature of the blocking reaction is equal to or higher than the above lower limit, the reaction rate can be further increased, and when the temperature is equal to or lower than the above upper limit, side reactions can be further suppressed. After the blocking reaction, a neutralization treatment may be carried out by adding an acidic compound or the like. The acidic compound may be an inorganic acid or an organic acid. Examples of inorganic acids include hydrochloric acid, phosphorous acid, and phosphoric acid. Examples of organic acids include methanesulfonic acid, p-toluenesulfonic acid, dioctyl phthalate, and dibutyl phthalate.

[0092] The completion of the reaction can be determined by, for example, confirming the disappearance or reduction of isocyanate groups using infrared spectroscopy or the like.

[0093] When a solvent is used, it is sufficient to use a solvent that is inactive to isocyanate groups. When a solvent is used, the content of solids derived from the polyisocyanate and the blocking agent per 100 parts by mass of the blocked polyisocyanate composition may usually be from 10 to 95 parts by mass, preferably from 15 to 90 parts by mass, and more preferably from 20 to 85 parts by mass.

[0094] [Physical properties of crosslinker component (b)] The weight average molecular weight Mw of the crosslinking agent component (b1) and the crosslinking agent component (b2) is 8.0 × 10 2 Over 1.0 x 10 5 Less than 1.0 x 10 is preferable. 3 Over 8.0 x 10 4 Less than 1.5 x 10 is preferable. 3 Over 7.0 x 10 4 The following is more preferable. When the weight-average molecular weight Mw is within the above range, the viscosity of the crosslinking agent component (b1) and the crosslinking agent component (b2) can be maintained at a better level. The weight-average molecular weight Mw can be measured, for example, by gel permeation chromatography (hereinafter sometimes abbreviated as "GPC").

[0095] <Secondary or tertiary alcohol (c)> The pressure-sensitive adhesive composition of this embodiment, when it contains a crosslinking agent component (b1), also contains a secondary or tertiary alcohol (c). By containing a predetermined amount of the secondary or tertiary alcohol (c), the pressure-sensitive adhesive composition of this embodiment maintains good adhesiveness after heat curing, while exhibiting excellent cohesive strength and pot life.

[0096] Examples of the secondary or tertiary alcohol (c) include secondary alcohols such as isopropyl alcohol and isobutyl alcohol; and tertiary alcohols such as tert-butyl alcohol. These secondary or tertiary alcohols may be used alone or in combination of two or more. Furthermore, only secondary alcohols or only tertiary alcohols may be used, or secondary and tertiary alcohols may be used in combination.

[0097] Among these, the secondary or tertiary alcohol (c) preferably contains a tertiary alcohol, more preferably contains tert-butyl alcohol, and even more preferably is tert-butyl alcohol.

[0098] <Other ingredients> The pressure-sensitive adhesive composition of the present embodiment may further contain other additives. Examples of other additives include curing agents other than the crosslinking agent component (b) that can react with the crosslinkable functional group in the acrylic polymer (a), curing catalysts, solvents, pigments (extender pigments, colored pigments, metallic pigments, etc.), photopolymerization initiators, ultraviolet absorbers, light stabilizers, radical stabilizers, anti-yellowing agents that suppress coloring during the baking process, coating surface conditioners, flow conditioners, pigment dispersants, antifoaming agents, thickeners, film-forming aids, etc.

[0099] Examples of the curing agent include melamine resins, urea resins, epoxy group-containing compounds or resins, carboxyl group-containing compounds or resins, acid anhydrides, alkoxysilane group-containing compounds or resins, and hydrazide compounds.

[0100] The curing catalyst may be a basic compound or a Lewis acid compound. Examples of the basic compound include metal hydroxides, metal alkoxides, metal carboxylates, metal acetylacetinates, hydroxides of onium salts, onium carboxylates, halides of onium salts, metal salts of active methylene compounds, onium salts of active methylene compounds, aminosilanes, amines, and phosphines. The onium salts are preferably ammonium salts, phosphonium salts, or sulfonium salts. Examples of the Lewis acid compound include organotin compounds, organozinc compounds, organotitanium compounds, and organozirconium compounds.

[0101] Examples of the solvent include 1-methylpyrrolidone, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, 3-methoxy-3-methyl-1-butanol, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether (DPDM), propylene glycol dimethyl ether, methyl ethyl ketone, and acetone. Examples of suitable solvents include methyl isobutyl ketone, propylene glycol monomethyl ether acetate, ethanol, methanol, isopropanol, 1-propanol, isobutanol, 1-butanol, tert-butanol, 2-ethylhexanol, cyclohexanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, ethyl acetate, isopropyl acetate, butyl acetate, toluene, xylene, pentane, isopentane, hexane, isohexane, cyclohexane, solvent naphtha, and mineral spirits. These solvents may be used alone or in combination of two or more.

[0102] In addition, known pigments (extender pigments, colored pigments, metallic pigments, etc.), ultraviolet absorbers, light stabilizers, radical stabilizers, anti-yellowing agents that suppress coloring during the baking process, coating surface conditioners, flow conditioners, pigment dispersants, antifoaming agents, thickeners, and film-forming aids can be appropriately selected and used.

[0103] <Method of manufacturing pressure-sensitive adhesive composition> The pressure-sensitive adhesive composition can be produced by a conventionally known method, for example, a melt-kneading method using a general mixer such as a Banbury mixer, a single-screw extruder, a twin-screw extruder, a co-kneader, or a multi-screw extruder, or a method in which the components are dissolved or dispersed and mixed, then coated onto a film using a coater or the like, and the solvent is then removed by heating.

[0104] The pressure-sensitive adhesive composition of the present embodiment may be foamed to achieve the effects of weight reduction, flexibility, and improved adhesion. Foaming methods include chemical methods, physical methods, and the use of thermally expandable microballoons. In each method, bubbles can be distributed inside the material by adding a chemical foaming agent such as an inorganic foaming agent or an organic foaming agent, or a physical foaming agent, or by adding thermally expandable microballoons.

[0105] Furthermore, hollow fillers (pre-expanded balloons) may be added to make the material lighter, more flexible, and more adhesive.

[0106] The pressure-sensitive adhesive composition of the present embodiment may contain a tackifying resin to adjust adhesive strength and cohesive strength. Examples of tackifying resins include rosin-based tackifying resins, terpene-based tackifying resins, petroleum-based tackifying resins, and styrene-based tackifying resins. These tackifying resins may be used alone or in combination of two or more. The softening point of the tackifying resin is preferably 90°C or higher and 160°C or lower.

[0107] ≪Cured product≫ The cured product of this embodiment is obtained by curing the pressure-sensitive adhesive composition described above with heat or light. The cured product of this embodiment has good adhesiveness.

[0108] The cured product of the present embodiment can be produced, for example, by dissolving the above-described pressure-sensitive adhesive composition in a solvent in which it can be dissolved, applying the composition to an adherend using a coater or the like, drying the composition as necessary, and then curing the composition by heat or light. Examples of methods for applying the pressure-sensitive adhesive composition to an adherend include methods using an applicator, roll coater, knife coater, gravure coater, etc. When drying is performed after the application, examples include a heat drying method in which the obtained laminate is placed in a dryer or the like and dried at a temperature of 50°C to 150°C for 1 minute to 30 minutes. Other drying methods include natural drying, hot air drying, infrared drying, etc.

[0109] In the case of curing by heat, the heating temperature can be 70°C or higher and 150°C or lower, 75°C or higher and 145°C or lower, or 80°C or higher and 140°C or lower.

[0110] When curing is performed by light, examples of the light include ultraviolet light. Examples of the method of ultraviolet irradiation include methods using known ultraviolet light irradiation devices such as a xenon lamp, a xenon-mercury lamp, a metal halide lamp, a high-pressure mercury lamp, and a low-pressure mercury lamp. The irradiation dose of ultraviolet light is, for example, 0.01 J / cm. 2 More than 5J / cm 2 The range can be as follows:

[0111] <Adhesive sheet> The pressure-sensitive adhesive sheet of the present embodiment includes a substrate and a pressure-sensitive adhesive layer on the substrate. The pressure-sensitive adhesive layer is made of a cured product of the pressure-sensitive adhesive composition described above. In the pressure-sensitive adhesive sheet of this embodiment, the pressure-sensitive adhesive layer has excellent adhesiveness.

[0112] The substrate is not particularly limited, but examples thereof include paper such as fine paper, coated paper, cast-coated paper, thermal paper, and inkjet paper; fabrics such as woven fabric and nonwoven fabric; resin films such as polyvinyl chloride, synthetic paper, polyethylene terephthalate (PET), polypropylene, polyethylene, cellulose triacetate, cellulose diacetate, polystyrene, polycarbonate, nylon, polyvinyl alcohol, ethylene-vinyl acetate copolymer, and polyimide; porous resin films such as porous polypropylene film; vapor-deposited films in which aluminum or the like is vapor-deposited on PET, polyolefin, or the like; and metal foil. The substrate may have a release-treated surface.

[0113] In the pressure-sensitive adhesive sheet of this embodiment, the thickness of the pressure-sensitive adhesive layer can be determined appropriately depending on the application, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.5 μm or more and 900 μm or less, even more preferably 1 μm or more and 800 μm or less, and particularly preferably 3 μm or more and 700 μm or less.

[0114] The pressure-sensitive adhesive sheet of the present embodiment can be produced, for example, by applying the pressure-sensitive adhesive composition to a substrate, drying it if necessary, and then curing it. Examples of the application method and curing method include the same methods as those exemplified above for the "cured product."

[0115] The pressure-sensitive adhesive sheet of this embodiment is prepared by applying the pressure-sensitive adhesive composition to a 38 μm-thick polyethylene terephthalate film that has been subjected to a release treatment, drying at 130° C. for 3 minutes, and curing the composition to form a 45 μm-thick pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet is then stored at 23° C. and 50% RH for 7 days, immersed in ethyl acetate at 23° C. for 1 week, and dried at 120° C. for 2 hours. The gel fraction is preferably 20% to 98% by mass, more preferably 25% to 98% by mass, even more preferably 33% to 98% by mass, particularly preferably 35% to 98% by mass, and most preferably 37% to 98% by mass. Having a gel fraction within the above range provides superior curability.

[0116] The pressure-sensitive adhesive sheet of this embodiment is a 20 mm wide and 100 mm long pressure-sensitive adhesive sheet comprising a 45 μm thick pressure-sensitive adhesive layer formed by coating the pressure-sensitive adhesive composition on a 25 μm thick polyethylene terephthalate film, drying and curing the composition at 130°C for 3 minutes, and then storing the pressure-sensitive adhesive sheet for 7 days in an environment of 23°C and 50% RH. After this, the pressure-sensitive adhesive sheet is pressed back and forth once with a 2 kg roller using a SUS304BA steel plate as the adherend, and then cured at 23°C for 30 minutes. The 180-degree peel adhesive strength measured at 23°C and a speed of 300 mm / min is preferably from 0.05 N / 20 mm to 40 N / 20 mm, more preferably from 0.1 N / 20 mm to 40 N / 20 mm, even more preferably from 0.1 N / 20 mm to 38 N / 20 mm, particularly preferably from 0.1 N / 20 mm to 35 N / 20 mm, and most preferably from 0.1 N / 20 mm to 33 N / 20 mm. [Example]

[0117] The present embodiment will be described in more detail below based on examples and comparative examples, but the present embodiment is not limited to the following examples in any way.

[0118] <Test items> The acrylic polymer, polyisocyanate component, and blocked polyisocyanate component obtained in the synthesis examples were subjected to measurement and evaluation of their physical properties according to the methods described below.

[0119] [Physical Properties 1] (Isocyanate group (NCO) content) In order to measure the NCO content of the polyisocyanate component, for the blocked polyisocyanate component, the polyisocyanate before being blocked with a blocking agent was used as the measurement sample.

[0120] First, 2 g to 3 g of the measurement sample was weighed out into a flask (Wg). Next, 20 mL of toluene was added to dissolve the measurement sample. Next, 20 mL of a 2 N toluene solution of di-n-butylamine was added, mixed, and left at room temperature for 15 minutes. Next, 70 mL of isopropyl alcohol was added and mixed. Next, this liquid was titrated with a 1 N hydrochloric acid solution (factor F) as an indicator. The obtained titration value was V2 mL. Next, the titration value obtained without the polyisocyanate sample was V1 mL. Next, the isocyanate group (NCO) content (mass%) of the polyisocyanate was calculated using the following formula.

[0121] Isocyanate group (NCO) content (mass%) = (V1-V2) x F x 42 / (W x 1000) x 100

[0122] [Physical Properties 2] (Number average molecular weight and weight average molecular weight) The number average molecular weight and weight average molecular weight are measured by gel permeation chromatography (GPC) using the following equipment, and are based on polystyrene standards. To measure the number average molecular weight of the polyisocyanate component, the polyisocyanate before blocking with a blocking agent was used as the measurement sample for the blocked polyisocyanate component. For the weight average molecular weight, the blocked polyisocyanate component was used as is as the measurement sample. The measurement conditions are shown below.

[0123] (Measurement conditions) Equipment: Tosoh Corporation, HLC-802A Column: Tosoh Corporation, G1000HXL x 1 G2000HXL x 1 G3000HXL x 1 Carrier: Tetrahydrofuran Detection method: differential refractometer

[0124] [Physical Properties 3] (average number of isocyanate functional groups) The average number of isocyanate functional groups (average NCO number) of the polyisocyanate component was calculated using the following formula. In the formula, "Mn" refers to the number average molecular weight of the polyisocyanate component before blocking with a blocking agent, and the value measured in "Property 2" above was used for this. For the blocked polyisocyanate component, "NCO content" refers to the isocyanate group content of the polyisocyanate component measured before blocking with a blocking agent, and the value calculated in "Property 1" above was used for this.

[0125] Average number of isocyanate functional groups = (Mn × MCO content × 0.01) / 42

[0126] [Physical Properties 4] (Solid content of polyisocyanate or blocked polyisocyanate) The solid content of the polyisocyanate or blocked polyisocyanate was determined as follows. First, an aluminum dish with a bottom diameter of 38 mm was precisely weighed. Then, approximately 1 g of the polyisocyanate or blocked polyisocyanate produced in the Examples and Comparative Examples was placed on the aluminum dish and precisely weighed (W1). The polyisocyanate or blocked polyisocyanate was then adjusted to a uniform thickness. The polyisocyanate or blocked polyisocyanate placed on the aluminum dish was then kept in an oven at 105°C for 1 hour. After the aluminum dish returned to room temperature, the polyisocyanate or blocked polyisocyanate remaining on the aluminum dish was precisely weighed (W2). The solids content (mass%) of the polyisocyanate or blocked polyisocyanate was then calculated using the following formula:

[0127] Solid content of polyisocyanate or blocked polyisocyanate (mass%) = W2 / W1×100

[0128] [Physical Properties 5] (glass transition temperature Tg) The glass transition temperature of the acrylic polymer was determined by evaporating the organic solvent and water from the acrylic polymer solution under reduced pressure, then vacuum-drying the solution and measuring the temperature using a differential scanning calorimetry (DSC) analyzer at a heating rate of 5°C / min.

[0129] [Preparing adhesive sheet 1] (Preparation of adhesive sheet for measuring 180-degree peel adhesive strength) The pressure-sensitive adhesive compositions obtained in the Examples and Comparative Examples were coated onto a 25 μm polyethylene terephthalate (PET) film using an applicator to a dry thickness of 45 μm, and then dried at 130°C for 3 minutes. The film was then stored in an environment of 23°C and 50% RH for 7 days to obtain a pressure-sensitive adhesive sheet for measuring 180° peel adhesion. For compositions with a short pot life that gelled, coating was performed before gelation. For those that did not gel immediately after preparation, coating was performed 8 hours after the pressure-sensitive adhesive composition was prepared to prepare a pressure-sensitive adhesive sheet for measuring 180° peel adhesion.

[0130] [Preparing adhesive sheet 2] (Preparation of adhesive sheet for gel fraction measurement) The pressure-sensitive adhesive compositions obtained in the Examples and Comparative Examples were applied to a 38 μm-thick release-treated PET film using an applicator so that the thickness after drying would be 45 μm, and then dried for 3 minutes at 130° C. Thereafter, the film was stored in an environment of 23° C. and 50% RH for 7 days to obtain a pressure-sensitive adhesive sheet for gel fraction measurement.

[0131] [Rating 1] (pot life) The viscosity of the pressure-sensitive adhesive compositions obtained in the examples and comparative examples was measured after 8 hours of storage in an environment of 23°C and 50% RH. The viscosity increase (times) was calculated using the following formula. Those that did not gel after 8 hours were evaluated as having a good pot life, those with a viscosity increase of 2 times or less were evaluated as having an even better pot life, those with a viscosity increase of close to 1 time or less than 1 time were evaluated as having an even better pot life, and those with a viscosity increase of 0.9 times or more and 1.1 times or less were evaluated as having an especially good pot life.

[0132] (Thickening rate) = (Viscosity of the pressure-sensitive adhesive composition after 8 hours of storage) / (Viscosity of the pressure-sensitive adhesive composition immediately after blending)

[0133] [Rating 2] (180 degree peel adhesive strength) The pressure-sensitive adhesive sheet obtained by the above method was cut into a width of 20 mm and a length of 100 mm to obtain a test piece. Using a SUS304BA steel plate as the adherend, the test piece was pressed against the steel plate by rolling a 2 kg roller back and forth once, and after curing at 23°C for 30 minutes, the 180° peel adhesive strength was measured at a speed of 300 mm / min. A 180° peel adhesive strength of 0.05 N / 20 mm or more (adhesive) was evaluated as having good adhesiveness.

[0134] For Examples 1 to 17 and 22 and Comparative Example 4, the adhesive strength retention rate (%) was calculated using the following formula: When the adhesive strength retention rate was 90% or more and 130% or less, the adhesive strength retention rate was evaluated as good.

[0135] (Adhesive force retention rate)= {(180-degree peel adhesive strength of adhesive composition containing secondary or tertiary alcohol) / (180-degree peel adhesive strength of adhesive composition not containing secondary or tertiary alcohol)}×100

[0136] That is, for the pressure-sensitive adhesive compositions obtained in Examples 1 to 4, 9 to 16 and Comparative Example 4, the 180-degree peel adhesive strength of the pressure-sensitive adhesive composition obtained in Comparative Example 1 was defined as the "180-degree peel adhesive strength of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol," and the adhesive strength retention rate was calculated using the above formula. Furthermore, for the pressure-sensitive adhesive compositions obtained in Examples 5 and 6, the 180-degree peel adhesive strength of the pressure-sensitive adhesive composition obtained in Comparative Example 2 was defined as the "180-degree peel adhesive strength of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol," and the adhesive strength retention rate was calculated using the above formula. Furthermore, for the pressure-sensitive adhesive compositions obtained in Examples 7 and 8, the 180-degree peel adhesive strength of the pressure-sensitive adhesive composition obtained in Comparative Example 3 was defined as the "180-degree peel adhesive strength of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol," and the adhesive strength retention rate was calculated using the above formula. For the pressure-sensitive adhesive composition obtained in Example 17, the 180-degree peel adhesive strength of the pressure-sensitive adhesive composition obtained in Comparative Example 6 was defined as the "180-degree peel adhesive strength of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol," and the adhesive strength retention rate was calculated using the above formula. For the pressure-sensitive adhesive composition obtained in Example 22, the 180-degree peel adhesive strength of the pressure-sensitive adhesive composition obtained in Comparative Example 5 was defined as the "180-degree peel adhesive strength of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol," and the adhesive strength retention rate was calculated using the above formula.

[0137] [Rating 3] (gel fraction) Approximately 0.1 g to 0.2 g of the pressure-sensitive adhesive sheet obtained by the above method was sampled, wrapped in a mesh sheet, and immersed in ethyl acetate for one week, and then dried at 120°C for two hours. The gel fraction (mass%) was then calculated using the following formula. Those with a gel fraction of 20 mass% or more were evaluated as having good curability.

[0138] (gel fraction) = (Sample mass after drying) / (Sample mass before adding ethyl acetate) × 100

[0139] For Examples 1 to 17 and 22 and Comparative Example 4, the gel fraction retention (%) was calculated using the following formula: A gel fraction retention of 90% or more was evaluated as having good retention of curability.

[0140] (Gel fraction retention rate) = ((Gel fraction of pressure-sensitive adhesive composition containing secondary or tertiary alcohol) / (Gel fraction of pressure-sensitive adhesive composition not containing secondary or tertiary alcohol))×100

[0141] That is, for the pressure-sensitive adhesive compositions obtained in Examples 1 to 4, 9 to 16 and Comparative Example 4, the gel fraction retention was calculated using the above formula, with the gel fraction of the pressure-sensitive adhesive composition obtained in Comparative Example 1 being defined as the "gel fraction of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol." Furthermore, for the pressure-sensitive adhesive compositions obtained in Examples 5 and 6, the gel fraction retention was calculated using the above formula, with the gel fraction of the pressure-sensitive adhesive composition obtained in Comparative Example 2 being defined as the "gel fraction of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol." Furthermore, for the pressure-sensitive adhesive compositions obtained in Examples 7 and 8, the gel fraction retention was calculated using the above formula, with the gel fraction of the pressure-sensitive adhesive composition obtained in Comparative Example 3 being defined as the "gel fraction of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol." Furthermore, for the pressure-sensitive adhesive composition obtained in Example 17, the gel fraction retention was calculated using the above formula, with the gel fraction of the pressure-sensitive adhesive composition obtained in Comparative Example 6 being defined as the "gel fraction of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol." Furthermore, for the pressure-sensitive adhesive composition obtained in Example 22, the gel fraction retention was calculated using the above formula, with the gel fraction of the pressure-sensitive adhesive composition obtained in Comparative Example 5 being defined as the "gel fraction of a pressure-sensitive adhesive composition not containing a secondary or tertiary alcohol."

[0142] <Synthesis of acrylic polymer (a)> [Synthesis Example 1-1] (Synthesis of acrylic polymer a-1) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser was charged with 97 parts by mass of n-butyl acrylate (BA) and 3 parts by mass of acrylic acid (AA), and 150 parts by mass of ethyl acetate as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) was charged as a polymerization initiator, and the reaction was carried out at 65°C for 8 hours. After the reaction, the mixture was cooled to obtain an acrylic polymer a-1 with a solids concentration of 40% by mass. The weight-average molecular weight Mw of the acrylic polymer a-1 measured after removing the solvent was 6.8 x 10 5 The glass transition temperature Tg was −52.2° C.

[0143] [Synthesis Example 1-2] (Synthesis of acrylic polymer a-2) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser was charged with 82 parts by mass of 2-ethylhexyl acrylate (2EHA), 14 parts by mass of methyl acrylate (MA), and 4 parts by mass of acrylic acid (AA), and 150 parts by mass of ethyl acetate was added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 63°C for 8 hours. After the reaction, the mixture was cooled to obtain an acrylic polymer a-2 with a solids concentration of 40% by mass. The weight-average molecular weight Mw of the acrylic polymer a-2 measured after removing the solvent was 6.6 x 10 5 The glass transition temperature Tg was −58.1° C.

[0144] [Synthesis Example 1-3] (Synthesis of acrylic polymer a-3) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser was charged with 96.4 parts by mass of n-butyl acrylate (BA), 0.6 parts by mass of 4-hydroxybutyl acrylate (4-HBA), and 3 parts by mass of acrylic acid (AA), and 150 parts by mass of ethyl acetate was added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 65°C for 8 hours. After the reaction, the mixture was cooled to obtain an acrylic polymer a-3 with a solids concentration of 40% by mass. The weight-average molecular weight Mw of the acrylic polymer a-3 measured after removing the solvent was 6.9 x 10 5 The glass transition temperature Tg was −52.1° C.

[0145] [Synthesis Example 1-4] (Synthesis of acrylic polymer a-4) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser was charged with 81.5 parts by mass of 2-ethylhexyl acrylate (2EHA), 0.5 parts by mass of 4-hydroxybutyl acrylate (4-HBA), 14 parts by mass of methyl acrylate (MA), and 4 parts by mass of acrylic acid (AA), and 150 parts by mass of ethyl acetate was added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 63°C for 8 hours. After the reaction, the mixture was cooled to obtain an acrylic polymer a-4 with a solids concentration of 40% by mass. The weight-average molecular weight Mw of the acrylic polymer a-4 measured after removing the solvent was 6.8 x 10 5 The glass transition temperature Tg was −57.9° C.

[0146] [Synthesis Example 1-5] (Synthesis of acrylic polymer a-5) 96 parts by mass of 2-ethylhexyl acrylate (2EHA) and 4 parts by mass of acrylic acid (AA) were added to a four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser, and 150 parts by mass of ethyl acetate was added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 62°C for 8 hours. After the reaction, the mixture was cooled to obtain acrylic polymer a-5 with a solids concentration of 40% by mass. The weight average molecular weight Mw of acrylic polymer a-5 measured after removing the solvent was 6.9 x 10 5 The glass transition temperature Tg was −66.2° C.

[0147] [Synthesis Example 1-6] (Synthesis of acrylic polymer a-6) Into a four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser, 96 parts by mass of isononyl acrylate (iNA), 4 parts by mass of acrylic acid (AA), and 150 parts by mass of ethyl acetate were added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 61°C for 8 hours. After the reaction, the mixture was cooled to obtain acrylic polymer a-6 with a solids concentration of 40% by mass. The weight average molecular weight Mw of acrylic polymer a-6 measured after removing the solvent was 7.2 x 10 5 The glass transition temperature Tg was −54.2° C.

[0148] [Synthesis Example 1-7] (Synthesis of acrylic polymer a-7) 96 parts by mass of 2-ethylhexyl acrylate (2EHA) and 4 parts by mass of acrylic acid (AA) were added to a four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser, and 150 parts by mass of ethyl acetate was added as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 62°C for 8 hours. After the reaction, the mixture was cooled to obtain acrylic polymer a-7 with a solids concentration of 40% by mass. The weight average molecular weight Mw of acrylic polymer a-7 measured after removing the solvent was 6.9 x 10 5 The glass transition temperature Tg was −66.2° C.

[0149] [Synthesis Example 1-8] (Synthesis of acrylic polymer a-8) A four-neck flask equipped with a stirrer, thermometer, nitrogen gas inlet tube, and condenser was charged with 87 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of N-vinylpyrrolidone, and 3 parts by mass of 4-hydroxybutyl acrylate (4-HBA), and 150 parts by mass of ethyl acetate as a solvent. Next, while stirring under a nitrogen gas atmosphere, 0.15 parts by mass of AIBN was added as a polymerization initiator, and the reaction was carried out at 65°C for 8 hours. After the reaction, the mixture was cooled to obtain an acrylic polymer a-8 with a solids concentration of 40% by mass. The weight-average molecular weight Mw of the acrylic polymer a-8 measured after removing the solvent was 6.6 x 10 5The glass transition temperature Tg was −57.1° C.

[0150] <Synthesis of polyisocyanates and blocked polyisocyanates> [Synthesis Example 2-1] (Synthesis of Polyisocyanate P-1) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 100 parts by mass of hexamethylene diisocyanate (HDI) under a nitrogen stream. 224.9 parts by mass (an amount that would give an NCO / OH ratio of 15.2) of a trifunctional polycaprolactone polyol (Daicel Chemical Industries, Ltd., "Placcel 308" (trade name), average hydroxyl functionality: 3, number-average molecular weight: 850, hydroxyl value: 195 mgKOH / g) was added under stirring. The temperature inside the reactor was maintained at 100°C for 110 minutes. The reaction was terminated when the yield reached 41% by mass. The reaction solution was filtered, and unreacted HDI was removed using a thin-film distillation apparatus to obtain polyisocyanate P-1. The resulting polyisocyanate P-1 had an NCO content of 9.3% by mass, an average isocyanate functionality of 3.9, and a number-average molecular weight Mn of 1.76 x 10 3 , weight average molecular weight Mw is 2.62 × 10 3 In addition, the obtained polyisocyanate P-1 1 H-NMR analysis and IR spectrum analysis confirmed the presence of a urethane structure.

[0151] [Synthesis Example 2-2] (Synthesis of Blocked Polyisocyanate BP-1) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 80 mol% diisopropyl malonate and 20 mol% di-tert-butyl malonate, respectively, based on 100 mol% of the isocyanate groups in the polyisocyanate P-1 obtained in Synthesis Example 2-1, under nitrogen flow. Dipropylene glycol dimethyl ether (DPDM) was then added to adjust the solids content to 65% by mass. Next, 1.0 parts by mass of a methanol solution containing sodium methylate (28% by mass, based on the total mass of the solution) was added dropwise while stirring the solution. An external bath was then adjusted to raise the solution temperature to 52°C, and the reaction was continued at 52°C for at least 7 hours to obtain blocked polyisocyanate BP-1 with a solids content of 65% by mass. The average number of isocyanate functional groups in blocked polyisocyanate BP-1 was 3.9, and the weight-average molecular weight Mw was 6.21 x 10. 3 It was.

[0152] [Synthesis Example 2-3] (Synthesis of Polyisocyanate P-2) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 100 parts by mass of HDI and 5.2 parts by mass of a trifunctional polycaprolactone polyol derived from a trihydric alcohol and ε-caprolactone (Daicel Chemical Industries, Ltd., "PLACCEL 303" (trade name), average hydroxyl group functionality: 3, number-average molecular weight: 300) under a nitrogen stream. The temperature inside the reactor was maintained at 86°C for 1 hour with stirring to carry out a urethane reaction. The temperature inside the reactor was then maintained at 62°C, and an isocyanuration catalyst, tetramethylammonium caprylate, was added. When the yield reached 51% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was filtered, and unreacted HDI was removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter sometimes referred to as "polyisocyanate P-2"). The NCO content of the obtained polyisocyanate P-2 was 18.9% by mass, the average number of isocyanate functional groups was 5.4, the number average molecular weight was 1200, and the weight average molecular weight Mw was 3.18 × 10 3 In addition, the obtained polyisocyanate P-2 1 H-NMR analysis confirmed the presence of isocyanurate groups.

[0153] [Synthesis Example 2-4] (Synthesis of Blocked Polyisocyanate BP-2) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 85 mol% diisopropyl malonate and 15 mol% di-tert-butyl malonate, respectively, based on 100 mol% of the isocyanate groups in the polyisocyanate P-2 obtained in Synthesis Example 2-3, under nitrogen flow. DPDM was then added to adjust the solids content to 65% by mass. Next, 1.0 parts by mass of a methanol solution containing sodium methylate (28% by mass relative to the total mass of the solution) was added dropwise while stirring the solution. An external bath was then adjusted to maintain the solution temperature at 48°C, and the reaction was continued for at least 8 hours at 48°C to obtain blocked polyisocyanate BP-2 with a solids content of 65% by mass. The average number of isocyanate functional groups in blocked polyisocyanate BP-2 was 5.4, and the weight-average molecular weight Mw was 8.22 x 10 3 It was.

[0154] [Synthesis Example 2-5] (Synthesis of Polyisocyanate P-3) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 70 parts by mass of HDI, 30 parts by mass of IPDI, and 3.2 parts by mass of trimethylolpropane (average hydroxyl group functionality: 3, molecular weight: 134), a trihydric alcohol, under a nitrogen stream. The temperature inside the reactor was maintained at 85°C for 1.5 hours with stirring to carry out a urethane reaction. The temperature inside the reactor was then maintained at 78°C, and 0.012 parts by mass of the isocyanuration catalyst tetramethylammonium caprylate was added. When the yield reached 44% by mass, phosphoric acid was added to terminate the reaction. The reaction solution was filtered, and unreacted HDI and IPDI were removed using a thin-film evaporator to obtain an isocyanurate-type polyisocyanate (hereinafter sometimes referred to as "polyisocyanate P-3"). The NCO content of the obtained polyisocyanate P-3 was 19.0% by mass, the average number of isocyanate groups was 5.5, the number average molecular weight was 1210, and the weight average molecular weight Mw was 2.95×10 3 In addition, the obtained polyisocyanate P-31 H-NMR analysis confirmed the presence of isocyanurate groups.

[0155] [Synthesis Example 2-6] (Synthesis of Blocked Polyisocyanate BP-3) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 83 mol% diisopropyl malonate and 17 mol% di-tert-butyl malonate, respectively, based on 100 mol% of the isocyanate groups in the polyisocyanate P-3 obtained in Synthesis Example 2-5, under nitrogen flow. DPDM was then added to adjust the solids content to 65% by mass. Next, 1.0 parts by mass of a methanol solution containing sodium methylate (28% by mass, based on the total mass of the solution) was added dropwise while stirring the solution. An external bath was then adjusted to raise the solution temperature to 52°C, and the reaction was continued at 52°C for at least 8 hours to yield blocked polyisocyanate BP-3 with a solids content of 65% by mass. The average number of isocyanate functional groups in blocked polyisocyanate BP-3 was 5.5, and the weight-average molecular weight Mw was 7.22 x 10. 3 It was.

[0156] [Synthesis Example 2-7] (Synthesis of Polyisocyanate P-4) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 100 parts by mass of hexamethylene diisocyanate (HDI) under a nitrogen stream. The temperature inside the reactor was raised to 50°C, and then 8.0 parts by mass of trimethylolpropane was added while stirring. The temperature inside the reactor was maintained at 67°C for 5 hours, after which the reaction was terminated. The reaction solution was filtered, and unreacted HDI was removed using a thin-film distillation apparatus to obtain polyisocyanate P-4. The resulting polyisocyanate P-4 had an NCO content of 17.3% by mass, an average number of isocyanate functional groups of 3.5, and a number-average molecular weight Mn of 8.52 x 10 2 , weight average molecular weight Mw is 1.22 × 10 3 In addition, the obtained polyisocyanate P-4 1 H-NMR analysis and IR spectrum analysis confirmed the presence of a urethane structure.

[0157] [Synthesis Example 2-8] (Synthesis of Blocked Polyisocyanate BP-4) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 80 mol% diisopropyl malonate and 20 mol% di-tert-butyl malonate, respectively, based on 100 mol% of the isocyanate groups in the polyisocyanate P-4 obtained in Synthesis Example 2-7, under nitrogen flow. Dipropylene glycol dimethyl ether (DPDM) was then added to adjust the solids content to 65% by mass. Next, 1.0 parts by mass of a methanol solution containing sodium methylate (28% by mass, based on the total mass of the solution) was added dropwise while stirring the solution. An external bath was then adjusted to raise the solution temperature to 53°C, and the reaction was continued at 53°C for at least 7 hours to obtain blocked polyisocyanate BP-4 with a solids content of 65% by mass. The average number of isocyanate functional groups in blocked polyisocyanate BP-4 was 3.5, and the weight-average molecular weight Mw was 3.25 x 10. 3 It was.

[0158] [Synthesis Example 2-9] (Synthesis of Blocked Polyisocyanate BP-5) A four-neck flask equipped with a thermometer, stirring blade, and reflux condenser was charged with 90 mol% diisopropyl malonate and 10 mol% di-tert-butyl malonate, respectively, based on 100 mol% of the isocyanate groups in the polyisocyanate P-1 obtained in Synthesis Example 2-1, under nitrogen flow. Dipropylene glycol dimethyl ether (DPDM) was then added to adjust the solids content to 65% by mass. Next, 1.0 parts by mass of a methanol solution containing sodium methylate (28% by mass, based on the total mass of the solution) was added dropwise while stirring the solution. An external bath was then adjusted to raise the solution temperature to 52°C, and the reaction was continued at 52°C for at least 7 hours to yield blocked polyisocyanate BP-5 with a solids content of 65% by mass. Blocked polyisocyanate BP-5 had an average isocyanate functionality of 3.9 and a weight-average molecular weight Mw of 6.91 x 10 3 It was.

[0159] <Production of Pressure-Sensitive Adhesive Composition> [Examples 1 to 22 and Comparative Example 4] (Production of Pressure-Sensitive Adhesive Compositions A-a1 to A-a22 and A-b4) The type and amount of polyisocyanate, and the amounts of tert-butyl alcohol (tBu-OH) and ethyl acetate added were the amounts shown in Tables 1 to 3 or 6 relative to 100 parts by mass of the acrylic polymer. tBu-OH and ethyl acetate were added to the polyisocyanate in this order and stirred, followed by the addition of the acrylic polymer and stirring until uniform, to obtain a pressure-sensitive adhesive composition with a solids content of 25% by mass.

[0160] [Examples 23 to 36] (Production of Pressure-Sensitive Adhesive Compositions A-a23 to A-a36) A solution that had been mixed in advance so that the type and amount of blocked polyisocyanate and the amount of ethyl acetate added were as shown in Tables 4 and 5 was added to 100 parts by mass of the acrylic polymer, and the mixture was stirred until homogenous, thereby obtaining a pressure-sensitive adhesive composition with a solid content of 25% by mass.

[0161] [Comparative Examples 1 to 3 and 5 to 6] (Production of Pressure-Sensitive Adhesive Compositions A-b1 to A-b3 and A-b5 to A-b6) A solution that had been premixed so that the type and amount of polyisocyanate added and the amount of ethyl acetate added were in the amounts shown in Table 6 was added to 100 parts by mass of the acrylic polymer, and the mixture was stirred until homogenous, thereby obtaining a pressure-sensitive adhesive composition with a solids content of 25% by mass.

[0162] The pressure-sensitive adhesive compositions obtained in the examples and comparative examples were evaluated using the methods described above, and the results are shown in Tables 1 to 6 below.

[0163] [Table 1]

[0164] [Table 2]

[0165] [Table 3]

[0166] [Table 4]

[0167] [Table 5]

[0168] [Table 6]

[0169] As can be seen from Tables 1 to 3, the pressure-sensitive adhesive compositions A-a1 to A-a22 (Examples 1 to 22), which contained an acrylic polymer (a), a polyisocyanate as the crosslinking agent component (b1), and a secondary or tertiary alcohol (c), maintained good adhesiveness after heat curing while exhibiting excellent curability and pot life. Furthermore, in a comparison of adhesive compositions A-a1 to A-a4 (Examples 1 to 4) with different contents of secondary or tertiary alcohol (c), it was found that the adhesiveness after heat curing tended to be better as the content of secondary or tertiary alcohol (c) decreased, while the gel fraction tended to be higher (better curability) and the gel fraction retention rate tended to be better as the content of secondary or tertiary alcohol (c) increased.

[0170] As can be seen from Tables 4 and 5, the pressure-sensitive adhesive compositions A-a23 to A-a36 (Examples 23 to 36) containing an acrylic polymer (a) and a blocked polyisocyanate as the crosslinking agent component (b2) exhibited excellent curability and pot life while maintaining good adhesiveness. Furthermore, in comparisons of adhesive compositions A-a23 to A-a24, A-a30 to A-a31 (Examples 23 to 24, 30 to 31) which differ in the content of blocked polyisocyanate, comparisons of adhesive compositions A-a25 to A-a26 (Examples 25 to 26), comparisons of adhesive compositions A-a27 to A-a28 (Examples 27 to 28), and comparisons of adhesive compositions A-a32 to A-a33 (Examples 32 to 33), it was found that the curability tended to improve as the content of blocked polyisocyanate increased, whereas the adhesive properties after heat curing tended to improve as the content of blocked polyisocyanate decreased. Furthermore, in a comparison of PSA compositions A-a28 and A-a34 (Examples 28 and 34), which contain different types of blocked polyisocyanates, the composition containing a blocked polyisocyanate with a larger average number of isocyanate functional groups tended to have better curability, while the composition containing a blocked polyisocyanate with a smaller weight-average molecular weight Mw tended to have better adhesiveness after heat curing. Furthermore, in a comparison of PSA compositions A-a23 and -a27 (Examples 23 and 27), PSA compositions A-a24 and A-a28 (Examples 24 and 28), and PSA compositions A-a25 and A-a29 (Examples 25 and 29), which use different types of acrylic polymer (a), the compositions using a higher content of monomer units having a carboxy group as a crosslinkable functional group tended to have better curability. Furthermore, in a comparison of PSA compositions A-a34 and A-a35 (Examples 34 and 35), which use different types of acrylic polymer (a), the composition using acrylic polymer a-4 tended to have better adhesiveness after heat curing, while the composition using acrylic polymer a-8 tended to have better curability.

[0171] On the other hand, as shown in Table 6, the adhesive compositions A-b1 to A-b3 and A-b5 to A-b6 (Comparative Examples 1 to 3 and 5 to 6), which contained an acrylic polymer (a) and a polyisocyanate as the crosslinker component (b1) but did not contain a secondary or tertiary alcohol (c), exhibited good curability and adhesiveness after heat curing, but gelled during storage and had a poor pot life. Furthermore, the adhesive composition A-b4 (Comparative Example 4), which contained an acrylic polymer (a), a polyisocyanate as the crosslinker component (b1), and a secondary or tertiary alcohol (c) in an amount of 1 part by mass of the secondary or tertiary alcohol (c) per 100 parts by mass of the acrylic polymer (a), exhibited good curability and adhesiveness after heat curing, but gelled during storage and had a poor pot life. [Industrial Applicability]

[0172] According to the pressure-sensitive adhesive composition of the present embodiment, it is possible to provide a pressure-sensitive adhesive composition that is excellent in curability and pot life while maintaining good adhesiveness after heat curing.

Claims

1. an acrylic polymer (a) having a crosslinkable functional group and a glass transition temperature Tg of −70° C. or higher and 0° C. or lower; a crosslinking agent component (b2) containing a blocked polyisocyanate derived from an aliphatic or alicyclic polyisocyanate and a blocking agent; the content of the monomer unit having a crosslinkable functional group relative to the total mass of the acrylic polymer (a) is 0.1% by mass or more and 20% by mass or less, the content of the crosslinking agent component (b2) is 0.1 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the acrylic polymer (a), the blocking agent is an active methylene compound, The pressure-sensitive adhesive composition, wherein the active methylene compound comprises a malonic acid ester having a secondary alkyl group or a malonic acid ester having a tertiary alkyl group.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the aliphatic or alicyclic polyisocyanate has an average number of isocyanate functional groups of 2 or more.

3. 3. The pressure-sensitive adhesive composition according to claim 1, wherein the blocking agent is at least one compound selected from the group consisting of active methylene compounds, oxime compounds, amine compounds, pyrazole compounds, and triazole compounds.

4. the blocking agent is an active methylene compound, The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the active methylene compound comprises a malonic acid ester having a secondary alkyl group and a malonic acid ester having a tertiary alkyl group.

5. The weight average molecular weight Mw of the crosslinking agent component (b2) is 1.0 × 10 ３ Above 1.0 x 10 ５ The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein:

6. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the aliphatic or alicyclic polyisocyanate has at least one structure selected from the group consisting of a urethane structure, an allophanate structure, a biuret structure, a urea structure, and an isocyanurate structure.

7. The pressure-sensitive adhesive composition according to any one of claims 1 to 6, wherein the acrylic polymer (a) contains one or more acrylic ester units having an alkyl group having 1 to 20 carbon atoms at a terminal of the ester group.

8. The pressure-sensitive adhesive composition according to any one of claims 1 to 7, wherein the crosslinkable functional group is one or more functional groups selected from the group consisting of a hydroxyl group, a carboxyl group, and an epoxy group.

9. The weight average molecular weight Mw of the acrylic polymer (a) is 3.0 × 10 ５ 2.5 x 10 ６ The pressure-sensitive adhesive composition according to any one of claims 1 to 8, wherein:

10. A cured product obtained by curing the pressure-sensitive adhesive composition according to any one of claims 1 to 9 with heat or light.

11. A substrate; a pressure-sensitive adhesive layer on the substrate, A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer comprises a cured product of the pressure-sensitive adhesive composition according to any one of claims 1 to 9.

12. The pressure-sensitive adhesive sheet according to claim 11, wherein the pressure-sensitive adhesive layer has a thickness of 0.1 μm or more and 1000 μm or less.

13. 13. The pressure-sensitive adhesive sheet according to claim 11 or 12, wherein the pressure-sensitive adhesive composition is applied to a 38 μm-thick release-treated polyethylene terephthalate film, dried at 130°C for 3 minutes, and cured to form a 45 μm-thick pressure-sensitive adhesive layer, and the pressure-sensitive adhesive sheet is then stored in an environment of 23°C and 50% RH for 7 days, immersed in ethyl acetate at 23°C for 1 week, and dried at 120°C for 2 hours, thereby calculating a gel fraction of 20% by mass or more and 98% by mass or less.

14. The pressure-sensitive adhesive sheet according to any one of claims 11 to 13, wherein the pressure-sensitive adhesive sheet has a width of 20 mm and a length of 100 mm, and is provided with a pressure-sensitive adhesive layer of 45 μm in thickness, the pressure-sensitive adhesive composition being coated on a polyethylene terephthalate film of 25 μm in thickness, dried at 130°C for 3 minutes and cured. After storing the pressure-sensitive adhesive sheet for 7 days in an environment of 23°C and 50% RH, the pressure-sensitive adhesive sheet is pressed back and forth once with a 2 kg roller using a SUS304BA steel plate as an adherend, and aged at 23°C for 30 minutes, and then the 180-degree peel adhesive strength measured at 23°C and a speed of 300 mm / min is 0.05 N / 20 mm or more and 40 N / 20 mm or less.

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