JP2015000945A - Adhesive composition, adhesive layer, and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition which allows rapid crosslinking without using a tin compound, to solve problems of conventional acrylic adhesives; and to provide an adhesive layer and an adhesive sheet, composed of the same.SOLUTION: The adhesive composition includes: 100 pts.mass of an acrylic polymer (A) having hydroxyl group and carboxyl group; 0.1-15 pts.mass of an isocyanate-based crosslinking agent (B); 0.002-0.5 pt.mass of a catalyst (C) using iron as an active center; and a compound (D) exhibiting keto-enol tautomerism, wherein the weight ratio (D/C) of the compound (D) exhibiting keto-enol tautomerism to the catalyst (C) using iron as an active center is 3-70.

Description

  The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive sheet. Specifically, the present invention relates to a pressure-sensitive adhesive sheet with little performance change over time, and a pressure-sensitive adhesive composition and a pressure-sensitive adhesive layer used therefor.

  Adhesive sheets are used in various aspects such as fixing (joining), conveying, protecting, and decorating articles. A typical example of such a pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive layer formed using a pressure-sensitive adhesive composition (acrylic pressure-sensitive adhesive composition) having an acrylic polymer as a base polymer. As such an acrylic polymer, a copolymer of a monomer mainly composed of (meth) acrylic acid alkyl ester (main component) and further containing an appropriate functional group is used. In particular, by using an acrylic polymer having a carboxyl group as a functional group, the adhesive force to a polar adherend such as a metal plate or a resin plate is improved, and an appropriate cohesive force can be imparted.

  In the pressure-sensitive adhesive sheet, an acrylic polymer having a functional group such as a hydroxyl group and a crosslinking agent that reacts with the functional group are blended to form a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive layer is formed by crosslinking the acrylic polymer. Since cross-linking is a chemical reaction, time is required to progress and stabilize over time. Moreover, the adhesive force changes as the crosslinking proceeds. Therefore, it is necessary to complete the crosslinking reaction at an early stage. Therefore, for example, in the combination of an acrylic copolymer having a hydroxyl group and an isocyanate crosslinking agent, a metal catalyst such as a tin compound has been used (see Patent Document 1). However, in recent years, from the viewpoint of environmental response, the use of specific metals has been subject to laws and regulations and concerns.

  Therefore, the use of a catalyst having iron as an active center has been studied as a metal catalyst instead of a tin compound (see Patent Document 2). However, it was confirmed that when an acrylic polymer having a carboxyl group was used, the catalytic function of iron was lowered and the crosslinking reaction could not be completed quickly. As described above, if the crosslinking reaction is not completed immediately after the production, for example, when an external pressure is applied to the pressure-sensitive adhesive sheet during the production or storage, problems such as deformation of the pressure-sensitive adhesive layer or the incorporation of scratches occur.

JP 2005-314513 A JP 2011-001440 A

  Therefore, the object of the present invention is to solve the problems in the case of using an iron catalyst instead of the conventionally used tin compound. An object of the present invention is to provide a pressure-sensitive adhesive composition with little change, and a pressure-sensitive adhesive layer and a pressure-sensitive adhesive sheet comprising the same.

  As a result of intensive studies to achieve the above object, the present inventors have determined that a specific amount of an acrylic polymer having a hydroxyl group and a carboxyl group is crosslinked with an isocyanate-based crosslinking agent in the presence of an iron catalyst. In combination with a compound that causes keto-enol tautomerism, the deactivation of the catalytic function of the iron catalyst due to the carboxyl group is prevented, and when it is used as an adhesive layer, it is found that the crosslinking reaction proceeds promptly. The invention has been completed.

That is, the present invention provides 100 parts by mass of an acrylic polymer (A) having a hydroxyl group and a carboxyl group,
Isocyanate-based crosslinking agent (B) 0.1 parts by mass to 15 parts by mass,
0.002 parts by mass to 0.5 parts by mass of catalyst (C) having iron as an active center,
A pressure-sensitive adhesive composition comprising a compound (D) that causes keto-enol tautomerism,
Provided is a pressure-sensitive adhesive composition in which the weight ratio (D / C) of the compound (D) causing keto-enol tautomerism to the catalyst (C) having iron as an active center is 3 to 70.

  In particular, in the pressure-sensitive adhesive composition of the present invention, the acrylic polymer (A) having a hydroxyl group and a carboxyl group (65) mass% to 99.89 (meth) acrylic acid alkyl ester having an alkyl group having 4 to 12 carbon atoms. It is preferable to contain, as a constituent component, 1% by mass to 25% by mass of a hydroxyl group-containing monomer and 0.01% to 10% by mass of a carboxyl group-containing monomer.

  In the pressure-sensitive adhesive composition of the present invention, the catalyst (C) having iron as an active center is preferably an iron chelate compound, and the compound (D) causing the keto-enol tautomerism is A β-diketone is preferred.

  Moreover, this invention provides the adhesive layer formed by bridge | crosslinking the said adhesive composition.

  Furthermore, this invention provides the adhesive sheet formed by forming the said adhesive layer on a support body.

  When the pressure-sensitive adhesive composition of the present invention is used as a pressure-sensitive adhesive layer, the crosslinking reaction proceeds promptly. For this reason, after the pressure-sensitive adhesive sheet is formed, the cross-linking proceeds quickly so that the characteristics are stable.For example, it is not necessary to provide a post-crosslinking step such as aging. It is possible to obtain effects such as prevention of occurrence of contamination and scratches.

Hereinafter, embodiments of the present invention will be described in detail. The pressure-sensitive adhesive composition of the present invention comprises 100 parts by mass of an acrylic polymer (A) having a hydroxyl group and a carboxyl group,
Isocyanate-based crosslinking agent (B) 0.1 parts by mass to 15 parts by mass,
0.002 parts by mass to 0.5 parts by mass of catalyst (C) having iron as an active center,
A pressure-sensitive adhesive composition comprising a compound (D) that causes keto-enol tautomerism,
The weight ratio (D / C) of the compound (D) causing keto-enol tautomerism to the catalyst (C) having iron as the active center is 3 to 70.

(Acrylic polymer (A))
The pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A) having a hydroxyl group and a carboxyl group. The acrylic polymer (A) is an acrylic polymer having, on the main chain or side chain, a functional group containing active hydrogen such as a hydroxyl group or a carboxyl group that can react with the isocyanate-based crosslinking agent (B) described later. Such an acrylic polymer (A) comprises at least a (meth) acrylic acid alkyl ester as a main component, and a hydroxyl group-containing monomer and a carboxyl group-containing monomer (hereinafter sometimes referred to as “functional group-containing monomer”). As a constituent component, it can be obtained by copolymerization of monomer components composed of these monomers.

  In the present invention, the (meth) acrylic acid alkyl ester which is a main monomer constituting the acrylic polymer (A) is preferably a (meth) acrylic acid alkyl ester having an alkyl group having 4 to 12 carbon atoms. Specific examples thereof include, for example, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, amyl (meth) acrylate, isoamyl (meth) acrylate, and hexyl (meth). Acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) Examples include acrylate, undecyl (meth) acrylate, and dodecyl (meth) acrylate.

  These (meth) acrylic acid alkyl esters having an alkyl group having 4 to 12 carbon atoms may be used alone or in combination, but the total content is 65% by mass in the monomer component. It is preferably ˜99.89% by mass, more preferably 76% by mass to 99.48% by mass, and further preferably 80% by mass to 91.97% by mass. When the content ratio of the (meth) acrylic acid alkyl ester is less than 65% by mass, the content of functional group-containing monomers and other monomers described later increases, the glass transition temperature of the acrylic polymer increases, and the fluidity increases. In some cases, a sufficient adhesion area cannot be obtained and the article cannot be fixed. Further, it may be difficult to adjust the degree of crosslinking (gel content). On the other hand, when the content of the (meth) acrylic acid alkyl ester exceeds 99.89% by mass, the content of the functional group-containing monomer is reduced, resulting in insufficient crosslinking and the cohesive strength of the pressure-sensitive adhesive composition is obtained. There may not be.

In the present invention, the hydroxyl group-containing monomer is a monomer containing a hydroxyl group capable of reacting with a crosslinking agent such as an isocyanate compound. Specific examples thereof include, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meta ) Acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, [4- (hydroxymethyl) cyclohexyl] methyl acrylate And the like, and the like.
N-methylol acrylamide, N-methylol methacrylamide, N- (2-hydroxyethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, N- (2-hydroxypropyl) acrylamide, N- (2-hydroxypropyl) ) Methacrylamide, N- (1-hydroxypropyl) acrylamide, N- (1-hydroxypropyl) methacrylamide, N- (3-hydroxypropyl) acrylamide, N- (3-hydroxypropyl) methacrylamide, N- (2 -Hydroxybutyl) acrylamide, N- (2-hydroxybutyl) methacrylamide, N- (3-hydroxybutyl) acrylamide, N- (3-hydroxybutyl) methacrylamide, N- (4-hydroxybutyl) acrylamide, N- 4-hydroxybutyl) such as methacrylamide N- hydroxyalkyl (meth) acrylamide; and the like.
Among these hydroxyl group-containing monomers, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferable from the viewpoint of their polymerizability and reactivity with the crosslinking agent, and 4-hydroxybutyl acrylate is particularly preferable. preferable.

  These hydroxyl group-containing monomers may be used alone or in combination, but the total content is preferably 1% by mass to 25% by mass in the monomer component, and 5% by mass to 20% by mass. %, More preferably 8% by mass to 15% by mass. When the content ratio of the hydroxyl group-containing monomer is less than 1% by mass, the cross-linking is insufficient, the cohesive force of the pressure-sensitive adhesive composition cannot be obtained, and the pressure-sensitive adhesive sheet is displaced or peeled off when the article is fixed. May cause adhesive residue. On the other hand, when the content ratio of the hydroxyl group-containing monomer exceeds 25% by mass, the cohesive force of the acrylic polymer is increased, so that the fluidity is lowered, and a sufficient adhesion area cannot be obtained and the article cannot be fixed. is there.

  In the present invention, the carboxyl group-containing monomer is a monomer containing a carboxyl group. Specific examples thereof include (meth) acrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Among these carboxyl group-containing monomers, acrylic acid is preferred from the viewpoints of polymerizability, cohesiveness, cost, and versatility.

  These carboxyl group-containing monomers may be used alone or in combination, but the total content is preferably 0.01% by mass to 10% by mass in the monomer component, and 0.02 It is more preferably from 9% by mass to 9% by mass, and further preferably from 0.03% by mass to 8% by mass. When the content ratio of the carboxyl group-containing monomer is less than 0.01% by mass, the adhesive force to the polar adherend may be insufficient. On the other hand, if the content ratio of the carboxyl group-containing monomer exceeds 10% by mass, the cohesive force of the acrylic polymer increases, so that the fluidity is lowered, and a sufficient adhesion area cannot be obtained and the article cannot be fixed. There is.

  In this invention, you may use other monomers other than the (meth) acrylic-acid alkylester which has a C4-C12 alkyl group mentioned above, a hydroxyl-containing monomer, and a carboxyl group-containing monomer as a monomer component. Examples of such other monomers include (meth) acrylic acid alkyl esters having an alkyl group other than those having 4 to 12 carbon atoms. Specific examples of the (meth) acrylic acid alkyl ester having an alkyl group other than 4 to 12 carbon atoms used in the present invention include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (Meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate, eicosyl (meta) ) Acrylate and the like.

Other monomers that can be used in the present invention include cyclic (meth) acrylamides such as N- (meth) acryloylmorpholine and N-acryloylpyrrolidine;
(Meth) acrylamide, N-substituted (meth) acrylamide (for example, N-alkyl (meth) acrylamide such as N-ethyl (meth) acrylamide, Nn-butyl (meth) acrylamide;
N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dipropyl (meth) acrylamide, N, N-diisopropyl (meth) acrylamide, N, N-di (n-butyl) Acyclic (meth) acrylamides such as (meth) acrylamide, N, N-dialkyl (meth) acrylamide such as N, N-di (t-butyl) (meth) acrylamide);
N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl- N-vinyl cyclic amides such as 3,5-morpholinedione;
Monomers having an amino group, such as aminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate;
Monomers having a maleimide skeleton, such as N-cyclohexylmaleimide and N-phenylmaleimide;
Nitrogen atom-containing monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-2-ethylhexylitaconimide, N-laurylitaconimide, N-cyclohexylitaconimide and the like; Etc.

Other examples of monomers that can be employed as other monomers include monomers having an epoxy group, such as glycidyl (meth) acrylate and allyl glycidyl ether;
Monomers having an alkoxy group such as methoxyethyl (meth) acrylate, methoxypropyl (meth) acrylate, methoxyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate;
Monomers having a cyano group, such as acrylonitrile and methacrylonitrile;
Styrene monomers such as styrene and α-methylstyrene;
Α-olefins such as ethylene, propylene, isoprene, butadiene, isobutylene;
A monomer having an isocyanate group, such as 2-methacryloyloxyethyl isocyanate;
Vinyl ester monomers such as vinyl acetate and vinyl propionate;
Vinyl ether monomers such as vinyl ether; (meth) acrylic acid esters having a heterocyclic ring such as tetrahydrofurfuryl (meth) acrylate;
Monomers having halogen atoms, such as fluorine (meth) acrylate;
Monomers having an alkoxysilyl group, such as 3-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane;
Monomers having a siloxane bond, such as silicone (meth) acrylate;
(Meth) acrylates having an alicyclic hydrocarbon group, such as cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate;
And (meth) acrylates having an aromatic hydrocarbon group such as phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, and phenoxydiethylene glycol (meth) acrylate.

  Other monomers include, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene Glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, hexanediol di (meth) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, di Pentaerythritol hexa (meth) acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, divinylben Emissions, butyl di (meth) acrylate, may be used polyfunctional monomers such as hexyl di (meth) acrylate.

  These other monomers may be used alone or in combination, but the total content is preferably 33% by mass or less, and 18% by mass or less in the monomer component. Is more preferable, and it is further more preferable that it is 10 mass% or less. When the content ratio of the other monomer exceeds 33% by mass, the content of (meth) acrylic acid alkyl ester having an alkyl group having 4 to 12 carbon atoms is decreased, and the glass transition temperature of the acrylic polymer is increased to flow. In some cases, the adhesiveness is lowered, and a sufficient adhesion area cannot be obtained and the article cannot be fixed.

  The acrylic polymer used in the present invention preferably has a weight average molecular weight of 100,000 to 3,000,000, more preferably 200,000 to 2,000,000, and further preferably 300,000 to 1,500,000. If the weight average molecular weight is less than 100,000, the cohesive force of the pressure-sensitive adhesive layer tends to decrease, and the pressure-sensitive adhesive sheet may be displaced when the article is fixed, or adhesive residue may be generated when the pressure-sensitive adhesive sheet is peeled off. On the other hand, if the weight average molecular weight exceeds 3 million, the cohesive force tends to increase due to the effect of the entanglement of the polymer and the fluidity tends to decrease, and there is a case where a sufficient adhesion area cannot be obtained and the article cannot be fixed. is there. In the present invention, the weight average molecular weight of the acrylic polymer refers to a value in terms of standard polystyrene obtained by measurement by GPC (gel permeation chromatography).

  The acrylic polymer used in the present invention has a glass transition temperature (Tg) of preferably 0 ° C. or lower (usually −100 ° C. or higher), more preferably −10 ° C. or lower, and −20 ° C. or lower. More preferably. When the glass transition temperature is higher than 0 ° C., the cohesive force is increased, the fluidity is lowered, and there is a case where a sufficient adhesion area cannot be obtained and the article cannot be fixed. In addition, the glass transition temperature of an acrylic polymer can be adjusted in the said range by changing suitably the monomer component and composition ratio to be used. As the glass transition temperature of the acrylic polymer in the present invention, a measurement method using a dynamic viscoelasticity device or a calculated value based on the FOX equation can be used.

  The polymerization method of the acrylic polymer used in the present invention is not particularly limited, and it can be polymerized by a known method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization. Moreover, any of a random copolymer, a block copolymer, etc. may be sufficient as the obtained copolymer.

(Isocyanate-based crosslinking agent (B))
The pressure-sensitive adhesive composition of the present invention contains an isocyanate-based crosslinking agent (B). Examples of the isocyanate-based crosslinking agent (B) include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate, alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate, 2,4 -Tolylene diisocyanate, aromatic isocyanates such as 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, trimethylolpropane / tolylene diisocyanate trimer adduct (trade name Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.), trimethylol Propane / hexamethylene diisocyanate trimer adduct (trade name Coronate HL, manufactured by Nippon Polyurethane Industry Co., Ltd.), Isocyanate of hexamethylene diisocyanate Examples thereof include isocyanate adducts such as nurate (trade name: Coronate HX, manufactured by Nippon Polyurethane Industry Co., Ltd.). These compounds may be used alone or in combination.

  In this invention, content of an isocyanate type crosslinking agent (B) is 0.1 mass part-15 mass parts with respect to 100 mass parts of acrylic polymers (A), and it is 1 mass part-13 mass parts. Preferably, it is 2 mass parts-9 mass parts, More preferably, it is 3 mass parts-6 mass parts. When the content of the isocyanate-based crosslinking agent (B) is less than 0.1 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), crosslinking formation becomes insufficient and the cohesive force of the pressure-sensitive adhesive layer cannot be obtained. When the article is fixed, the pressure-sensitive adhesive sheet may be displaced, or adhesive residue may be generated when the pressure-sensitive adhesive sheet is peeled off. On the other hand, if the content of the isocyanate-based crosslinking agent (B) exceeds 15 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), the crosslinking proceeds so much that the cohesive force increases and the fluidity is lowered. In some cases, it is impossible to obtain a proper bonding area and the article cannot be fixed.

  The pressure-sensitive adhesive composition of the present invention may contain other crosslinking agent as required in addition to the isocyanate-based crosslinking agent. As other crosslinking agents, for example, epoxy crosslinking agents, melamine resins, aziridine derivatives, metal chelate compounds and the like are used. These compounds may be used alone or in combination.

  Examples of the epoxy-based crosslinking agent include N, N, N ′, N′-tetraglycidyl-m-xylenediamine (trade name: TETRAD-X, manufactured by Mitsubishi Gas Chemical Company) and 1,3-bis (N, N— And diglycidylaminomethyl) cyclohexane (trade name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc.). These compounds may be used alone or in combination.

  Examples of the melamine resin include hexamethylol melamine. Examples of the aziridine derivative include a commercially available product name HDU (manufactured by Mutual Pharmaceutical Company), a product name TAZM (manufactured by Mutual Pharmaceutical Company), and a product name TAZO (manufactured by Mutual Pharmaceutical Company). These compounds may be used alone or in combination.

  Examples of the metal chelate compound include aluminum, titanium, nickel, and zirconium as metal components, and acetylene, methyl acetoacetate, ethyl acetoacetate, ethyl lactate, and acetylacetone as chelate components. These compounds may be used alone or in combination.

  When a crosslinking agent other than these isocyanate crosslinking agents (B) is used in combination, the amount used is not particularly limited as long as the effects of the present invention are not impaired, but the total amount with the isocyanate crosslinking agent (B) is an acrylic polymer (A ) 100 parts by weight, preferably 0.1 parts by weight to 15 parts by weight, more preferably 1 part by weight to 13 parts by weight, still more preferably 2 parts by weight to 9 parts by weight, It is particularly preferably 3 to 6 parts by mass.

  In the pressure-sensitive adhesive composition of the present invention, the gel content after crosslinking with a crosslinking agent is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more ( Usually 98% or less). When the gel content is less than 80% by mass, the cohesive force of the pressure-sensitive adhesive layer becomes small, and the pressure-sensitive adhesive sheet may be displaced when the article is fixed, or adhesive residue may be easily generated when the pressure-sensitive adhesive sheet is peeled off. On the other hand, if the gel fraction exceeds 98% by mass, the cohesive force of the acrylic polymer is increased, so that the fluidity is lowered, and there is a case where a sufficient adhesion area cannot be obtained and the article cannot be fixed.

  The gel content in the present invention refers to a pressure-sensitive adhesive layer W1 g (about 0.1 g) immersed in ethyl acetate at about 25 ° C. for 1 week, then taken out of the pressure-sensitive adhesive layer from ethyl acetate and dried at 130 ° C. for 2 hours. It is a value calculated by measuring the subsequent weight W2g and (W2 / W1) × 100 (mass%).

(Catalyst with iron as active center (C))
The pressure-sensitive adhesive composition of the present invention contains a catalyst (C) having iron as an active center (hereinafter sometimes referred to as iron catalyst (C)). As the iron catalyst (C), an iron chelate compound can be suitably used. For example, it can be represented by the general formula Fe (X) (Y) (Z). The iron chelate compound is a combination of (X) (Y) (Z), Fe (X) ₃ , Fe (X) ₂ (Y), Fe (X) (Y) ₂ , Fe (X) (Y) (Z ). In the iron chelate compound Fe (X) (Y) (Z), (X) (Y) (Z) is a ligand for Fe. For example, when X, Y or Z is a β-diketone, β- As diketones, acetylacetone, hexane-2,4-dione, heptane-2,4-dione, heptane-3,5-dione, 5-methyl-hexane-2,4-dione, octane-2,4-dione, 6 -Methylheptane-2,4-dione, 2,6-dimethylheptane-3,5-dione, nonane-2,4-dione, nonane-4,6-dione, 2,2,6,6-tetramethylheptane -3,5-dione, tridecane-6,8-dione, 1-phenyl-butane-1,3-dione, hexafluoroacetylacetone, ascorbic acid and the like.

  When X, Y or Z is a β-ketoester, the β-ketoester is methyl acetoacetate, ethyl acetoacetate, acetoacetate-n-propyl, acetoacetate isopropyl, acetoacetate-n-butyl, acetoacetate-sec-butyl, Acetoacetic acid-tert-butyl, methyl propionyl acetate, ethyl propionyl acetate, propionyl acetate-n-propyl, isopropyl propionyl acetate, propionyl acetate-n-butyl, propionyl acetate-sec-butyl, propionyl acetate-tert-butyl, benzyl acetoacetate Dimethyl malonate, diethyl malonate and the like.

  In the present invention, an iron catalyst other than the iron chelate compound can be used. For example, a compound of iron and an alkoxy group, a halogen atom, or an acyloxy group can be used. In the case of a compound of iron and an alkoxy group, as an alkoxy group, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, hexyloxy Group, heptyloxy group, octyloxy group, 2-ethylhexyl group, phenoxy group, cyclohexyloxy group, benzyloxy group, 1-benzylnaphthyloxy group and the like.

  In the case of a compound of iron and a halogen atom, examples of the halogen atom include fluorine, chlorine, bromine and iodine.

  In the case of a compound of iron and an acyloxy group, as the acyloxy group, 2-ethylhexylic acid, octylic acid, naphthenic acid, resin acid (abietic acid, neoabietic acid, d-pimalic acid, iso-d-pimalic acid, podocarpic acid, Gluconic acid, fumaric acid, citric acid, aspartic acid, α-ketoglutamic acid, malic acid, succinic acid, aliphatic organic acids mainly composed of amino acids such as glycine and histidine, benzoic acid, cinnamic acid, p- Aromatic fatty acids mainly composed of oxycinnamic acid and the like.

  In the present invention, among these catalysts (C) having iron as an active center, an iron chelate compound having a β-diketone as a ligand is preferable from the viewpoint of reactivity and curability, and particularly tris (acetylacetonate) iron. Is preferably used. These iron catalysts (C) may be used alone or in combination of two or more.

  In this invention, content of the catalyst (C) which makes iron an active center is 0.002 mass part-0.5 mass part with respect to 100 mass parts of acrylic polymers (A), and 0.003 mass part- It is preferably 0.3 parts by mass, and more preferably 0.004 parts by mass to 0.2 parts by mass. If the content of the iron catalyst (C) is less than 0.002 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), the adhesive force of the adhesive sheet immediately after production with insufficient curability is increased, When the adhesive sheet is peeled off, adhesive residue may be easily generated, and the change in adhesive force with time may increase. on the other hand. When the content of the iron catalyst (C) exceeds 0.5 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), ketoeenol required for preventing the deactivation of the iron catalyst (C) described later is used. The required content of the compound (D) that causes variability increases, and the compound (D) remains as a residue in the pressure-sensitive adhesive sheet, and the change in the adhesive strength over time may increase.

  In the present invention, it is preferable to adjust the blending amount of the catalyst (C) having iron as an active center according to the content of the isocyanate-based crosslinking agent (B). That is, it is preferable to mix | blend an iron catalyst (C) with the quantity used as 0.05 mass%-12.5 mass% with respect to the compounding quantity (weight) of an isocyanate type crosslinking agent (B), 0.075 mass%- It is more preferable to mix | blend in the quantity used as 7.5 mass%. When the content of the iron catalyst (C) is less than 0.05% by mass with respect to the isocyanate-based crosslinking agent (B), the adhesive strength of the adhesive sheet immediately after production due to insufficient curability is increased. When peeling off, adhesive residue may be easily generated, and the change in adhesive strength with time increases. When the content of the iron catalyst (C) exceeds 12.5% by mass with respect to the isocyanate-based crosslinking agent (B), the ketoeenol tautomerism necessary for preventing the deactivation of the iron catalyst (C) described later is achieved. The necessary content of the compound (D) to be raised increases, the compound (D) remains as a residue in the pressure-sensitive adhesive sheet, and the change in pressure-sensitive adhesive force with time may increase.

（Ｒ１，Ｒ２，Ｒ３は水素、アルキル基、アルケニル基、アリール基等の置換基であって、分子内にヘテロ原子やハロゲン原子を含んでいてもよい） (Compound (D) causing keto-enol tautomerism)
The pressure-sensitive adhesive composition of the present invention contains a compound (D) that causes keto-enol tautomerism (hereinafter sometimes referred to as ketoeenol tautomer (D)). The keto-enol tautomer compound (D) is a compound that causes tautomerism between keto (ketone, aldehyde) and enol (see Chemical Formula 1), and acts as a chelating agent for the iron catalyst. And a compound that prevents deactivation of the catalytic function due to the carboxyl group. That is, in the iron catalyst (C), when a carboxyl group is present, the carboxyl group changes the chemical structure of the iron catalyst (C), thereby reducing the catalytic function, but the compound (D) causing keto-enol tautomerism (D ), The compound (D) that causes keto-enol tautomerism over the carboxyl group coordinates preferentially in the vicinity of the iron catalyst (C), thereby blocking the change in the chemical structure of the iron catalyst (C). This is considered to prevent the deactivation.

(R1, R2, and R3 are substituents such as hydrogen, an alkyl group, an alkenyl group, and an aryl group, and may contain a hetero atom or a halogen atom in the molecule)

Examples of the compound (D) that causes keto-enol tautomerism include methyl acetoacetate, ethyl acetoacetate, acetoacetate-n-propyl, isopropyl acetoacetate, acetoacetate-n-butyl, acetoacetate-sec-butyl, acetoacetate. T-butyl acetate, methyl propionyl acetate, ethyl propionyl acetate, propionyl acetate-n-propyl, isopropyl propionyl acetate, propionyl acetate-n-butyl, propionyl acetate-sec-butyl, propionyl acetate-tert-butyl, benzyl acetoacetate, Β-ketoesters such as dimethyl malonate and diethyl malonate;
Acetylacetone, hexane-2,4-dione, heptane-2,4-dione, heptane-3,5-dione, 5-methyl-hexane-2,4-dione, octane-2,4-dione, 6-methylheptane -2,4-dione, 2,6-dimethylheptane-3,5-dione, nonane-2,4-dione, nonane-4,6-dione, 2,2,6,6-tetramethylheptane-3, Β-diketones such as 5-dione, tridecane-6,8-dione, 1-phenyl-butane-1,3-dione, hexafluoroacetylacetone, ascorbic acid;
Acid anhydrides such as acetic anhydride;
And ketones such as acetone, methyl ethyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, methyl phenyl ketone, cyclohexanone, and the like. Among these compounds, it is preferable to use β-diketones having a high effect of preventing the deactivation of the catalytic function due to the carboxyl group, and among them, acetylacetone is more preferable.

  The content of the compound (D) that causes keto-enol tautomerism is such that the weight ratio (D / C) of the keto-enol tautomer (D) to the catalyst (C) having iron as the active center is 3 to 70. It is preferably contained so as to be 10 to 70, more preferably 20 to 60, and still more preferably 40 to 55. When the content ratio of the keto-enol tautomeric compound (D) and the iron catalyst (C) exceeded 70, the keto-enol tautomeric compound (D) was excessively contained relative to the iron catalyst (C). In this state, the keto-enol tautomer compound (D) causes a side reaction with the isocyanate-based cross-linking agent (C) in the compounded solution, so that the number of isocyanate groups capable of reacting with hydroxyl groups during curing decreases, and sufficient curability is obtained. I can't do that. On the other hand, when the content ratio of the keto-enol tautomeric compound (D) and the iron catalyst (C) is less than 3, the keto-enol tautomeric compound (D) is too small relative to the iron catalyst (C). It becomes in the contained state, and the deactivation of the catalyst function due to the carboxyl group cannot be prevented, and the curing becomes insufficient.

  In the compound (D) causing keto-enol tautomerism, the weight ratio (D / C) of the keto-enol tautomer compound (D) to the catalyst (C) having iron as an active center is 3 to 70. In such a case, it is preferable that 0.15 to 35 parts by mass is added to 100 parts by mass of the acrylic polymer (A), and 0.2 to 20 parts by mass is more preferable. When the content of the keto-enol tautomeric compound (D) exceeds 35 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), the compound (D) remains as a residue in the pressure-sensitive adhesive sheet. There is a case where the change in the adhesive strength is large. On the other hand, when the content of the keto-enol tautomeric compound (D) is less than 0.15 parts by mass with respect to 100 parts by mass of the acrylic polymer (A), deactivation of the catalytic function due to the carboxyl group can be prevented. However, the curing may be insufficient.

  Furthermore, the pressure-sensitive adhesive composition of the present invention may contain other known additives, such as powders such as colorants and pigments, surfactants, plasticizers, tackifiers, low molecular weights, and the like. Polymer, surface lubricant, leveling agent, antioxidant, corrosion inhibitor, light stabilizer, UV absorber, polymerization inhibitor, silane coupling agent, inorganic or organic filler, metal powder, particulate, foil Or the like can be added as appropriate according to the use for which the material is used.

(Adhesive layer)
The pressure-sensitive adhesive layer of the present invention is obtained by crosslinking the above pressure-sensitive adhesive composition. The pressure-sensitive adhesive sheet of the present invention is formed by forming such a pressure-sensitive adhesive layer on a support. At that time, the pressure-sensitive adhesive composition is generally crosslinked after application of the pressure-sensitive adhesive composition, but it is also possible to transfer a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive composition after crosslinking to the support. .

  In the pressure-sensitive adhesive layer of the present invention, the gel content after crosslinking with a crosslinking agent is preferably 80% by mass or more, more preferably 85% by mass or more, and further preferably 90% by mass or more (usually). Weight 98% or less). When the gel content is less than 80% by mass, the cohesive force of the pressure-sensitive adhesive layer becomes small, and the pressure-sensitive adhesive sheet may be displaced when the article is fixed, or adhesive residue may be easily generated when the pressure-sensitive adhesive sheet is peeled off. On the other hand, if the gel content exceeds 98% by mass, the cohesive force of the acrylic polymer is increased, so that the fluidity is lowered, and there is a case where a sufficient adhesion area cannot be obtained and the article cannot be fixed.

  The method for forming the pressure-sensitive adhesive layer is not particularly limited. For example, the pressure-sensitive adhesive layer is prepared by applying the pressure-sensitive adhesive composition to a support, drying and removing the polymerization solvent, and forming the pressure-sensitive adhesive layer on the support. . Thereafter, curing may be performed for the purpose of adjusting the component transfer of the pressure-sensitive adhesive layer or adjusting the crosslinking reaction. In particular, in order to advance the crosslinking reaction, heating can be performed at 100 to 140 ° C. for about 15 seconds to 2 minutes. In addition, when a pressure-sensitive adhesive composition is applied on a support to produce a pressure-sensitive adhesive layer, one or more solvents other than the polymerization solvent are newly added to the pressure-sensitive adhesive composition so that the pressure-sensitive adhesive composition can be uniformly applied on the support. You may add to.

  Moreover, as a formation method of the adhesive layer of this invention, the well-known method used for manufacture of an adhesive sheet is used. Specific examples include roll coating, gravure coating, reverse coating, roll brushing, spray coating, air knife coating, and the like.

  Although the thickness of the adhesive layer of this invention can be suitably determined according to the use, it is 1 micrometer-1000 micrometers normally, Preferably it is about 5 micrometers-500 micrometers.

(Adhesive sheet)
The pressure-sensitive adhesive sheet of the present invention is formed by forming the pressure-sensitive adhesive layer on a support. The pressure-sensitive adhesive sheet of the present invention may be formed in a rolled form or may be formed in a stacked form. That is, the pressure-sensitive adhesive sheet of the present invention can have any form such as a sheet form, a tape form, and a film form. Further, cutting, punching, or the like may be performed in an appropriate form depending on the purpose of use.

  The support is not particularly limited as long as it can be formed into a sheet or film. For example, polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene Polyolefin films such as propylene copolymer, ethylene / 1-butene copolymer, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, ethylene / vinyl alcohol copolymer, polyethylene terephthalate, polyethylene naphthalate, poly Polyester film such as butylene terephthalate, polyacrylate film, polystyrene film, nylon 6, nylon 6,6, polyamide film such as partially aromatic polyamide, polyvinyl chloride film, polyvinylidene chloride film, polycarbonate Tofirumu, polyfluoroethylene film, a polyimide film, such as polyvinyl alcohol film.

  The thickness of the support in the present invention is usually about 5 μm to 200 μm, preferably about 10 μm to 100 μm.

  If necessary, the support may be released with a silicone, fluorine, long chain alkyl or fatty acid amide release agent, silica powder or other mold release and antifouling treatment, acid treatment, alkali treatment, primer treatment. Further, anti-adhesion treatment such as corona treatment, plasma treatment and ultraviolet treatment, coating type, kneading type, vapor deposition type and the like can be carried out.

  If necessary, the pressure-sensitive adhesive sheet of the present invention can be bonded to a release film (separator) for the purpose of protecting the pressure-sensitive adhesive layer surface. The material constituting the release film includes paper and plastic film, but a plastic film is preferably used from the viewpoint of excellent surface smoothness. The film is not particularly limited as long as it can protect the pressure-sensitive adhesive layer. For example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer. Examples thereof include a coalesced film, a polyethylene terephthalate film, a polybutylene terephthalate film, a polyurethane film, and an ethylene-vinyl acetate copolymer film.

  The thickness of the release film is usually about 5 μm to 200 μm, preferably about 10 μm to 100 μm. For the release film, if necessary, mold release and antifouling treatment with a silicone, fluorine, long chain alkyl or fatty acid amide release agent, silica powder, etc., coating type, kneading type, vapor deposition An antistatic treatment such as a mold can also be performed.

  Hereinafter, examples and the like specifically showing the configuration and effects of the present invention will be described, but the present invention is not limited to these. In addition, the evaluation item in an Example etc. measured as follows.

<Measurement of weight average molecular weight of acrylic polymer>
The weight average molecular weight of the produced acrylic polymer was measured by GPC (gel permeation chromatography).

Device: HLC-8220GPC, manufactured by Tosoh Corporation
column:
Sample column: manufactured by Tosoh Corporation, TSK guard column Super HZ-H (1) + TSK gel Super HZM-H (2)
Reference column; manufactured by Tosoh Corporation, TSKgel Super H-RC (1)
Flow rate: 0.6ml / min
Injection volume: 10 μl
Column temperature: 40 ° C
Eluent: THF
Injection sample concentration: 0.2% by mass
Detector: differential refractometer The weight average molecular weight was calculated in terms of polystyrene.

<Preparation of pressure-sensitive adhesive sheet for evaluation>
On the polyethylene terephthalate (PET) film (thickness 38 μm), the pressure-sensitive adhesive composition solutions of Examples and Comparative Examples to be described later were applied and dried at 130 ° C. for 30 seconds to remove the solvent and remove the pressure-sensitive adhesive layer (thickness). 25 μm) was formed. Thereafter, it was covered with a release film surface-treated with a release agent and allowed to stand at room temperature (23 ° C.) for 1 hour to obtain an evaluation pressure-sensitive adhesive sheet immediately after production. The pressure-sensitive adhesive sheet was stored for 4 days at room temperature (23 ° C.) and 50% RH, and used as a pressure-sensitive adhesive sheet for evaluation after aging.

<Measurement of adhesive strength>
Each of the prepared pressure-sensitive adhesive sheets for evaluation was cut into a size of 20 mm in width and 100 mm in length, and rubbed 10 times with a clean cloth impregnated with isopropyl alcohol. The sample was pressure-bonded by the method described above to obtain a sample for adhesion evaluation. This evaluation sample is allowed to stand in a measurement environment of 23 ° C. and 50% RH for 30 minutes, and then a high speed adhesive strength [N / 20 mm] is obtained using a high speed peel tester under conditions of a tensile speed of 30 m / min and a peel angle of 180 °. It was measured. Further, the low-speed adhesive force [N / 20 mm] was measured under the conditions of a tensile speed of 0.3 m / min and a peeling angle of 180 °.

  In the present invention, the progress of crosslinking was evaluated based on the rate of change between the adhesive strength of the pressure-sensitive adhesive sheet immediately after production and the adhesive strength of the pressure-sensitive adhesive sheet after aging. That is, the rate of change in this evaluation is a value obtained by dividing the adhesive strength of the pressure-sensitive adhesive sheet after aging by the pressure-sensitive adhesive strength of the pressure-sensitive adhesive sheet immediately after production (that is, the rate of change = the pressure-sensitive adhesive strength of the pressure-sensitive adhesive sheet after aging) If the rate of change of the pressure-sensitive adhesive sheet) is 0.60 or more, it is determined that the change in the pressure-sensitive adhesive force is small, and it is determined that the crosslinking has proceeded sufficiently immediately after production. The high-speed adhesive strength is a measure of the difficulty of peeling off the adhesive sheet, while the low-speed adhesive strength is a measure of whether or not the article can be fixed. Both the high-speed adhesive strength and the low-speed adhesive strength change. The rate needs to be 0.60 or more.

[Preparation of Acrylic Polymer (1)]
A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, a cooler, and a dropping funnel, 100 parts by mass of 2-ethylhexyl acrylate (2EHA) as a monomer component, 10 parts by mass of 4-hydroxybutyl acrylate (4HBA) Part, acrylic acid (AA) 0.06 part by mass, azobisisobutyronitrile 0.2 part by mass as polymerization initiator, ethyl acetate 356 part by mass, nitrogen gas was introduced while stirring gently, The polymerization temperature was maintained at around 60 ° C. for about 3 hours to carry out a polymerization reaction to prepare an acrylic polymer solution. The weight average molecular weight of the obtained acrylic polymer (1) was 610,000, and the glass transition temperature calculated from the formula of FOX was −67 ° C.

[Preparation of acrylic polymer (2)]
Similar to the preparation of acrylic polymer (1) except that 100 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of 4-hydroxybutyl acrylate (4HBA) and 5 parts by mass of acrylic acid (AA) were used as monomer components. Then, an acrylic polymer solution was prepared. The weight average molecular weight of the obtained acrylic polymer (2) was 630,000, and the glass transition temperature calculated from the formula of FOX was −63 ° C.

[Preparation of acrylic polymer (3)]
Preparation of acrylic polymer (1) except that 100 parts by mass of 2-ethylhexyl acrylate (2EHA), 10 parts by mass of 2-hydroxyethyl acrylate (HEA), and 0.06 parts by mass of acrylic acid (AA) were used as monomer components. In the same manner as above, an acrylic polymer solution was prepared. The weight average molecular weight of the obtained acrylic polymer (3) was 610,000, and the glass transition temperature calculated from the formula of FOX was −66 ° C.

[Preparation of acrylic polymer (4)]
Similar to the preparation of acrylic polymer (1) except that 100 parts by weight of 2-ethylhexyl acrylate (2EHA), 10 parts by weight of 4-hydroxybutyl acrylate (4HBA) and 2 parts by weight of acrylic acid (AA) were used as monomer components. Then, an acrylic polymer solution was prepared. The weight average molecular weight of the obtained acrylic polymer (4) was 620,000, and the glass transition temperature calculated from the formula of FOX was −65 ° C.

[Preparation of acrylic polymer (5)]
An acrylic polymer solution was prepared in the same manner as the acrylic polymer (1) except that 100 parts by mass of 2-ethylhexyl acrylate (2EHA) and 0.06 parts by mass of acrylic acid (AA) were used as monomer components. The weight average molecular weight of the obtained acrylic polymer (5) was 400,000, and the glass transition temperature calculated from the formula of FOX was −70 ° C.

Example 1
[Preparation of pressure-sensitive adhesive sheet using pressure-sensitive adhesive composition]
For 100 parts by mass (solid content) of the above acrylic polymer (1), 4 parts by mass of trimethylolpropane / tolylene diisocyanate trimer adduct (trade name “Coronate L”, manufactured by Nippon Polyurethane Industry Co., Ltd.) as a crosslinking agent, iron Tris (acetylacetonato) iron (made by Nippon Kagaku Sangyo Co., Ltd., trade name “Narsem Ferric Acid”) 0.005 part by mass as a catalyst, acetylacetone (AcAc) 0.25 part by mass as a compound causing keto-enol tautomerism Was further diluted with toluene so that the solid content concentration was 29% by mass, followed by stirring to obtain an adhesive composition. Using this, an adhesive sheet for evaluation was produced according to the production method.

(Examples 2 to 6, Comparative Examples 1 to 4)
A pressure-sensitive adhesive composition was prepared by the same procedure as in Example 1 according to the formulation shown in Table 1, and a pressure-sensitive adhesive sheet for evaluation was prepared.
In the table, “C / HX” in the crosslinking agent is an isocyanurate of hexamethylene diisocyanate (product name “Coronate HX” manufactured by Nippon Polyurethane Industry Co., Ltd.), and “OL-1” in the catalyst is dioctyltin dilaurate ( Shown by Tokyo Fine Chemical Co., Ltd., trade name “Environator OL-1”).

  The pressure-sensitive adhesive compositions of Examples 1 to 6 have a pressure-sensitive adhesive force immediately after production and a change rate of the pressure-sensitive adhesive strength of the pressure-sensitive adhesive sheet after aging is 0.60 or more, and have a stable pressure-sensitive adhesive force immediately after production. It was confirmed that it was obtained. That is, for the acrylic polymer having a carboxyl group, it was confirmed that the isocyanate crosslinking was almost completed immediately after production, and it was confirmed that the catalytic function of the iron catalyst was not deactivated. In Examples, in Example 2, stick-slip was confirmed at the time of peeling for both high-speed adhesive force and low-speed adhesive force. Stick-slip is a vibration phenomenon that occurs on the peeling surface, and it may be preferable in some cases because it may cause damage to the adherend and breakage of the adherend. There is no.

  On the other hand, in the pressure-sensitive adhesive composition of Comparative Example 1 in which the compound (D) causing keto-enol tautomerism was not blended, the catalytic function of the iron catalyst was deactivated by the carboxyl group in the acrylic polymer, and immediately after the production, Since the cross-linking reaction was not completed, it was confirmed that the cross-linking proceeded by aging, and the adhesive strength after aging changed greatly compared to that immediately after the production. In addition, since the pressure-sensitive adhesive compositions of Comparative Examples 2 and 3 did not have a hydroxyl group in the acrylic polymer, the crosslinking did not proceed and the cohesive force was insufficient, and it was confirmed that the cohesive failure occurred in the measurement of the adhesive force. . In Comparative Example 4 using a tin-based catalyst, since the catalytic activity is lower than that of the iron catalyst, the crosslinking reaction is not completed immediately after the production, the crosslinking proceeds by aging, and the adhesive strength after aging is produced. It was confirmed that there was a great change compared to immediately after.

Claims (6)

100 parts by mass of an acrylic polymer (A) having a hydroxyl group and a carboxyl group,
Isocyanate-based crosslinking agent (B) 0.1 parts by mass to 15 parts by mass,
0.002 parts by mass to 0.5 parts by mass of catalyst (C) having iron as an active center,
A pressure-sensitive adhesive composition comprising a compound (D) that causes keto-enol tautomerism,
The adhesive composition whose weight ratio (D / C) of the compound (D) which causes keto-enol tautomerism with respect to the catalyst (C) which has iron as an active center is 3-70. The acrylic polymer (A) having a hydroxyl group and a carboxyl group is (meth) acrylic acid alkyl ester having an alkyl group having 4 to 12 carbon atoms, 65 mass% to 99.89 mass%, hydroxyl group-containing monomer 1 mass% to 25 2. The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition comprises 0.01% by mass to 10% by mass of a carboxyl group-containing monomer as a constituent component. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the catalyst (C) having iron as an active center is an iron chelate compound. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the compound (D) that causes keto-enol tautomerism is a β-diketone. The adhesive layer formed by bridge | crosslinking the adhesive composition as described in any one of Claims 1-4. The adhesive sheet formed by forming the adhesive layer of Claim 5 on a support body.