Pressure-sensitive adhesive composition, pressure-sensitive adhesive film, and surface protection film

Abstract

To provide an adhesive composition, an adhesive film and a surface protective film having long pot life and a high cross-linking speed without using an organic tin compound.SOLUTION: There is provided an adhesive composition comprising an acrylic polymer and a crosslinking agent, which comprises (C) 0.1 to 10 pts.wt. of a bifunctional or higher isocyanate compound, (D) 0.001 to 0.5 pt.wt. of a metal chelate compound crosslinking catalyst and (E) 0.1 to 300 pts.wt. of a keto-enol tautomer compound, based on 100 pts.wt. of a copolymer obtained by copolymerizing (A) a (meth)acrylic acid ester monomer having an alkyl group having 4 to 18 carbon atoms and (B) a copolymerizable monomer having a hydroxyl group, wherein the weight part ratio of (E) / (D) is 80 to 600 and the viscosity of the adhesive composition after 8 hrs of storage at 23°C after blending the adhesive composition is less than 1.25 times the viscosity immediately after blending the adhesive composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition and a surface protective film. More specifically, in light of recent environmental concerns that have restricted the use of organotin compounds, the present invention relates to a pressure-sensitive adhesive composition and a surface protective film that have a long pot life and a fast crosslinking rate without using an organotin compound by using a crosslinking catalyst that is a metal chelate compound other than an organotin compound. [Background technology]

[0002] For optical applications, acrylic pressure-sensitive adhesives composed of copolymers of alkyl (meth)acrylate as the main component and copolymerized with acrylic monomers having functional groups such as hydroxyl groups and carboxyl groups are preferred due to their excellent transparency. Furthermore, pressure-sensitive adhesives with various physical properties, such as adhesive strength, that are appropriately adjusted are required. In particular, pressure-sensitive adhesives for surface protection films are required to have an excellent balance of adhesive strength at low and high peel speeds, making them suitable for laminating surface protection films using automatic lamination equipment, so that they can be adapted to the manufacturing process of factory production. Furthermore, pressure-sensitive adhesives that not only have a good balance of adhesive strength but also have excellent physical properties, such as a long pot life, are required.

[0003] Various physical properties of such pressure-sensitive adhesives are adjusted by crosslinking them with an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, or the like, which reacts with functional groups such as hydroxyl groups and carboxyl groups contained in the acrylic pressure-sensitive adhesive made of a copolymer, thereby adjusting adhesive strength, cohesive strength, and the like.

[0004] Conventionally, isocyanate-based crosslinking agents have been widely used as crosslinking agents for acrylic pressure-sensitive adhesives. In addition, in crosslinking reactions using isocyanate-based crosslinking agents, metal chelates are often used as catalysts to promote the crosslinking reaction. In general, organotin compounds such as dibutyltin dilaurate have been used as catalysts for crosslinking reactions because of their excellent reaction speed, but the use of dibutyltin compounds is avoided due to their harmful toxicity. For this reason, there has been a demand for a crosslinking catalyst that is inexpensive and has a superior reaction rate in the crosslinking reaction, as an alternative to the dibutyltin compounds used in combination with isocyanate crosslinking agents, but it has been difficult to find such a catalyst.

[0005] Under these circumstances, Patent Document 1 discloses that, among metal chelates, iron chelates are preferred as crosslinking catalysts to be used in combination with isocyanate-based crosslinking agents, and that tris(acetylacetonato)iron is particularly preferred due to its excellent catalytic activity.

[0006] In the case of an acrylic pressure-sensitive adhesive composition containing a crosslinking catalyst, the crosslinking reaction proceeds gradually even while the composition is left at room temperature. Therefore, in the industrial production of pressure-sensitive adhesives, after the raw materials of the pressure-sensitive adhesive composition are blended, a crosslinking catalyst and a reaction retarder are generally used in combination to stop the crosslinking reaction until the time when the crosslinking reaction is to be initiated. Regarding the combined use of this crosslinking catalyst and reaction retarder, Patent Document 2 discloses a method for producing polyurethane, which uses a reaction urethane mixture containing a catalyst system consisting of a mixture of at least one metal acetylacetonate and acetylacetone, with the weight ratio of the metal acetylacetonate to the acetylacetone being 2:1. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-001440 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-285681 Summary of the Invention [Problem to be solved by the invention]

[0008] In the pressure-sensitive adhesive composition described in Patent Document 1, the amount of metal compound (crosslinking catalyst) added to a copolymer containing (meth)acrylate as a constituent monomer unit and containing a hydroxyl group and a carboxyl group is indicated, but there is no description of the amount of crosslinking retarder added. Furthermore, Patent Document 1 lists methods for suppressing the rate of viscosity increase after blending a crosslinking agent into the pressure-sensitive adhesive composition, such as using a reaction retarder, adding a viscosity increase suppressing solvent, and using a crosslinking agent with blocked functional groups such as blocked isocyanate, but does not provide any specific explanation.

[0009] Furthermore, Patent Document 2 discloses a method for producing polyurethane using a catalyst system containing acetylacetone and a metal acetylacetonate that has excellent stability and good catalytic activity and does not cause premature curing even when a metal acetylacetonate catalyst such as iron or copper, which is highly active at low temperatures, is used. However, the method described in Patent Document 2 uses a weight ratio of metal acetylacetonate to acetylacetone of 2:1, but even when this blending ratio is applied to the manufacturing process of an acrylic adhesive, it is not possible to temporarily suspend the crosslinking reaction.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pressure-sensitive adhesive composition and a surface protection film that have a long pot life and a fast crosslinking rate even without using an organotin compound. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the present invention provides a pressure-sensitive adhesive composition characterized by containing, relative to 100 parts by weight of a copolymer of (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18 and (B) a copolymerizable monomer containing a hydroxyl group as a copolymerizable monomer group, (C) 0.1 to 10 parts by weight of a difunctional or higher isocyanate compound, (D) 0.001 to 0.5 parts by weight of a crosslinking catalyst of a metal chelate compound, and (E) 0.1 to 300 parts by weight of a keto-enol tautomer compound, wherein the weight ratio of (E) / (D) is 70 to 1000.

[0012] Furthermore, it is preferable that the pressure-sensitive adhesive composition be stored at 23° C. after formulation and have a viscosity of less than 1.25 times the viscosity immediately after formulation for 8 hours.

[0013] Furthermore, it is preferable that the (B) hydroxyl group-containing copolymerizable monomer is at least one selected from the group consisting of 8-hydroxyoctyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide.

[0014] Among the (C) difunctional or higher isocyanate compounds, the difunctional isocyanate compound is preferably an acyclic aliphatic isocyanate compound produced by reacting a diisocyanate compound with a diol compound. The diisocyanate compound is preferably an aliphatic diisocyanate selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. The diol compound is preferably one selected from the group consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, and polypropylene glycol. Furthermore, among the (C) difunctional or higher isocyanate compounds, the trifunctional isocyanate compound is preferably at least one selected from the group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, a biuret of an isophorone diisocyanate compound, an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound.

[0015] It is also preferable that the pressure-sensitive adhesive composition does not contain an organotin compound as the crosslinking catalyst.

[0016] The copolymer is preferably an acrylic polymer containing at least one of a carboxyl group-containing monomer and a nitrogen-containing vinyl monomer not containing a hydroxyl group as other copolymerizable monomers.

[0017] The pressure-sensitive adhesive composition preferably has a gel fraction of 90 to 100% after crosslinking.

[0018] Furthermore, it is preferable that the adhesive layer obtained by crosslinking the adhesive composition has an adhesive strength of 0.05 to 0.2 N / 25 mm at a low peel speed of 0.3 m / min, and an adhesive strength of 2.0 N / 25 mm or less at a high peel speed of 30 m / min.

[0019] The present invention also provides a pressure-sensitive adhesive film, characterized in that a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition is formed on one or both sides of a resin film.

[0020] The present invention also provides a surface protection film, characterized in that the surface protection film is obtained by forming a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition on one side of a resin film.

[0021] The surface protective film of the present invention can also be used as a surface protective film for a polarizing plate.

[0022] In addition, the surface protection film of the present invention can be used as a surface protection film for any precision electrical and electronic component selected from the group consisting of flexible printed wiring boards, rigid printed wiring boards, and transparent conductive films. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition and a surface protection film that have a long pot life and a fast crosslinking rate without using an organotin compound. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be described below based on preferred embodiments. The pressure-sensitive adhesive composition of the present invention is characterized in that it contains, relative to 100 parts by weight of a copolymer of (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18 and (B) a copolymerizable monomer containing a hydroxyl group as a copolymerizable monomer group, (C) 0.1 to 10 parts by weight of a difunctional or higher isocyanate compound, (D) 0.001 to 0.5 parts by weight of a crosslinking catalyst of a metal chelate compound, and (E) 0.1 to 300 parts by weight of a keto-enol tautomer compound, and the weight ratio of (E) / (D) is 70 to 1000.

[0025] The copolymer may be an acrylic polymer containing at least one of a carboxyl group-containing monomer and a nitrogen-containing vinyl monomer not containing a hydroxyl group as other copolymerizable monomers.

[0026] (A) Examples of (meth)acrylic acid ester monomers having an alkyl group with a carbon number of 4 to 18 include butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, 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)acrylate, and undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, myristyl (meth)acrylate, isomyristyl (meth)acrylate, cetyl (meth)acrylate, isocetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and the like. It is preferable that the copolymer contains 50 to 98 parts by weight of (A) a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, based on 100 parts by weight of the copolymer.

[0027] (B) Examples of copolymerizable monomers containing a hydroxyl group include hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide. It is preferable that the compound is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide. It is preferable that the copolymer contains 0.1 to 10 parts by weight of the (B) copolymerizable monomer containing a hydroxyl group, based on 100 parts by weight of the copolymer.

[0028] The copolymer may contain at least one of a carboxyl group-containing monomer, a nitrogen-containing vinyl monomer not containing a hydroxyl group, and a polyalkylene glycol mono(meth)acrylic acid ester monomer as other copolymerizable monomers.

[0029] The carboxyl group-containing monomer is preferably at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalate. When the copolymer contains a carboxyl group-containing monomer as another copolymerizable monomer, the carboxyl group-containing monomer is preferably contained in an amount of 0.1 to 1.0 part by weight per 100 parts by weight of the copolymer. The copolymer does not necessarily have to contain the carboxyl group-containing monomer.

[0030] The polyalkylene glycol mono(meth)acrylate monomer may be a compound in which one of the hydroxyl groups of a polyalkylene glycol is esterified as a (meth)acrylate. The (meth)acrylate group serves as a polymerizable group, allowing it to be copolymerized into the base copolymer. The other hydroxyl group may remain as OH or may be an alkyl ether such as methyl ether or ethyl ether, or a saturated carboxylic acid ester such as acetate. Examples of alkylene groups in polyalkylene glycol include, but are not limited to, ethylene, propylene, and butylene groups. The polyalkylene glycol may be a copolymer of two or more polyalkylene glycols, such as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Examples of polyalkylene glycol copolymers include polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, and polyethylene glycol-polypropylene glycol-polybutylene glycol, and the copolymers may be block copolymers or random copolymers. The polyalkylene glycol mono(meth)acrylate monomer preferably has an average repeat number of alkylene oxides constituting the polyalkylene glycol chain of 3 to 14. The "average repeat number of alkylene oxides" refers to the average number of repeating alkylene oxide units in the "polyalkylene glycol chain" portion contained in the molecular structure of the polyalkylene glycol mono(meth)acrylate monomer.

[0031] The polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from the group consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate. More specifically, polyethylene glycol-mono(meth)acrylate, polypropylene glycol-mono(meth)acrylate, polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-mono(meth)acrylate, polyethylene glycol-polybutylene glycol-mono(meth)acrylate, polypropylene glycol-polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-polybutylene glycol-mono(meth)acrylate; methoxypolyethylene glycol-(meth)acrylate, methoxypolypropylene glycol-(meth)acrylate, methoxypolybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, methoxy-polyethylene glycol ethoxypolyethylene glycol-(meth)acrylate, ethoxypolypropylene glycol-(meth)acrylate, ethoxypolybutylene glycol-(meth)acrylate, ethoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, ethoxypolybutylene glycol-(meth)acrylate, ethoxypolyethylene glycol-polypropylene glycol-(meth)acrylate, ethoxypolyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxypolyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxypolypropylene glycol-polybutylene glycol-(meth)acrylate, ethoxypolyethylene glycol-polypropylene glycol-polybutylene glycol-(meth)acrylate, and the like. The polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably contained in an amount of 0 to 50 parts by weight based on 100 parts by weight of the copolymer. The copolymer may not contain the polyalkylene glycol mono(meth)acrylic acid ester monomer.

[0032] Examples of the nitrogen-containing vinyl monomer that does not contain a hydroxyl group include a vinyl monomer containing an amide bond, a vinyl monomer containing an amino group, and a vinyl monomer having a nitrogen-containing heterocyclic structure. More specifically, examples thereof include N-vinyl-substituted heterocyclic structures such as N-vinyl-2-pyrrolidone, N-vinylpyrrolidone, methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-vinyllaurolactam. Cyclic nitrogen-containing vinyl compounds having a heterocyclic structure; N-(meth)acryloyl-substituted heterocyclic structures such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperazine, N-(meth)acryloylaziridine, N-(meth)acryloylazetidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylpiperidine, N-(meth)acryloylazepane, and N-(meth)acryloylazocane. Cyclic nitrogen-containing vinyl compounds; cyclic nitrogen-containing vinyl compounds having a heterocyclic structure containing a nitrogen atom and an ethylenically unsaturated bond in the ring, such as N-cyclohexylmaleimide and N-phenylmaleimide; unsubstituted or monoalkyl-substituted (meth)acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and Nt-butyl(meth)acrylamide; dialkyl-substituted (meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropylacrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N-ethyl-N-methyl(meth)acrylamide, N-methyl-N-propyl(meth)acrylamide, and N-methyl-N-isopropyl(meth)acrylamide;Dialkylamino(meth)acrylates such as N,N-dimethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminoisopropyl (meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate, N,N-diethylaminomethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N-ethyl-N-methylaminoethyl (meth)acrylate, N-methyl-N-propylaminoethyl (meth)acrylate, N-methyl-N-isopropylaminoethyl (meth)acrylate, N,N-dibutylaminoethyl (meth)acrylate, and t-butylaminoethyl (meth)acrylate; N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide, N N,N-dialkyl-substituted aminopropyl(meth)acrylamides such as N-dipropylaminopropyl(meth)acrylamide, N,N-diisopropylaminopropyl(meth)acrylamide, N-ethyl-N-methylaminopropyl(meth)acrylamide, N-methyl-N-propylaminopropyl(meth)acrylamide, and N-methyl-N-isopropylaminopropyl(meth)acrylamide; N-vinylcarboxylic acid amides such as N-vinylformamide, N-vinylacetamide, and N-vinyl-N-methylacetamide; (meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-ethoxyethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone acrylamide, and N,N-methylenebis(meth)acrylamide; and unsaturated carboxylic acid nitriles such as (meth)acrylonitrile.

[0033] The copolymer preferably contains 0 to 20 parts by weight of the nitrogen-containing vinyl monomer not containing a hydroxyl group relative to 100 parts by weight of the copolymer. The copolymer does not necessarily need to contain the nitrogen-containing vinyl monomer not containing a hydroxyl group.

[0034] The (C) bifunctional or higher isocyanate compound may be at least one or more selected from polyisocyanate compounds having at least two isocyanate (NCO) groups per molecule. Polyisocyanate compounds are classified into aliphatic isocyanates, aromatic isocyanates, acyclic isocyanates, alicyclic isocyanates, etc., and any of these may be used. Specific examples of polyisocyanate compounds include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and trimethylhexamethylene diisocyanate (TMDI), and aromatic isocyanate compounds such as diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (H6XDI), dimethyldiphenylene diisocyanate (TODI), and tolylene diisocyanate (TDI). Examples of tri- or higher functional isocyanate compounds include biuret-modified and isocyanurate-modified difunctional isocyanate compounds (compounds having two NCO groups in one molecule), and adducts (polyol-modified compounds) with tri- or higher polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane (TMP) and glycerin. As the difunctional or higher functional isocyanate compound (C), it is possible to use only the trifunctional isocyanate compound (C-1) or only the difunctional isocyanate compound (C-2).It is also possible to use a combination of the trifunctional isocyanate compound (C-1) and the difunctional isocyanate compound (C-2).

[0035] Furthermore, the (C-1) trifunctional isocyanate compound used in the present invention is selected from the (C-1-1) first aliphatic isocyanate compound group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, and a biuret of an isophorone diisocyanate compound. In addition, it is preferable to include at least one or more selected from (C-1-2) a second group of aromatic isocyanate compounds consisting of an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound. It is preferable to use the (C-1-1) first group of aliphatic isocyanate compounds and the (C-1-2) second group of aromatic isocyanate compounds in combination. In the present invention, the balance of adhesive strength between the slow peeling speed region and the fast peeling speed region can be further improved by using, as the (C-1) trifunctional isocyanate compound, at least one selected from the (C-1-1) first group of aliphatic isocyanate compounds and at least one selected from the (C-1-2) second group of aromatic isocyanate compounds in combination. The trifunctional isocyanate compound (C-1) preferably contains at least one selected from the first group of aliphatic isocyanate compounds (C-1-1) and at least one selected from the second group of aromatic isocyanate compounds (C-1-2), with a total content of 0.5 to 5.0 parts by weight per 100 parts by weight of the copolymer. The mixing ratio of the at least one selected from the first group of aliphatic isocyanate compounds (C-1-1) and the at least one selected from the second group of aromatic isocyanate compounds (C-1-2) is preferably within the range of 10%:90% to 90%:10% by weight.

[0036] Furthermore, the (C-2) bifunctional isocyanate compound used in the present invention is preferably an acyclic aliphatic isocyanate compound, which is a compound produced by reacting a diisocyanate compound with a diol compound. For example, when a diisocyanate compound is represented by the general formula "O=C=NXN=C=O" (where X is a divalent group) and a diol compound is represented by the general formula "HO-Y-OH" (where Y is a divalent group), examples of compounds produced by reacting a diisocyanate compound with a diol compound include compounds represented by the following general formula Z.

[0037] [General formula Z] O=C=NX-(NH-CO-OYO-CO-NH-X) n -N=C=O

[0038] Here, n is an integer of 0 or more. When n is 0, the general formula Z represents "O=C=NXN=C=O". The bifunctional acyclic aliphatic isocyanate compound may contain a compound in which n is 0 in the general formula Z (a diisocyanate compound that has not reacted with the diol compound), but it is preferable to contain a compound in which n is an integer of 1 or more as an essential component. The bifunctional acyclic aliphatic isocyanate compound may be a mixture of multiple compounds in which n in the general formula Z is different.

[0039] The diisocyanate compound represented by the general formula "O=C=NXN=C=O" is an aliphatic diisocyanate. X is preferably an acyclic aliphatic divalent group. The aliphatic diisocyanate is preferably one or more compounds selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0040] The diol compound represented by the general formula "HO-Y-OH" is an aliphatic diol. Y is preferably an acyclic aliphatic divalent group. The diol compound is preferably one or more selected from the group consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, and polypropylene glycol.

[0041] The weight ratio (C-1 / C-2) of the (C-1) trifunctional isocyanate compound to the (C-2) difunctional isocyanate compound is preferably 1 to 90. The (C) di- or higher functional isocyanate compound is preferably 0.1 to 10 parts by weight per 100 parts by weight of the copolymer.

[0042] The crosslinking catalyst for (D) the metal chelate compound may be any substance that functions as a catalyst for the reaction (crosslinking reaction) between the copolymer and the crosslinking agent when a polyisocyanate compound is used as the crosslinking agent, and examples thereof include amine compounds such as tertiary amines, metal chelate compounds, organotin compounds, organolead compounds, organozinc compounds, and other organometallic compounds. In the present invention, a metal chelate compound is used as the crosslinking catalyst.

[0043] A metal chelate compound is a compound in which one or more polydentate ligands L are bonded to a central metal atom M. The metal chelate compound may or may not have one or more monodentate ligands X bonded to the metal atom M. For example, the general formula of a metal chelate compound having one metal atom M is M(L) m (X) n When m is 2 or more, m L's may be the same or different ligands. When n is 2 or more, n X's may be the same or different ligands.

[0044] Examples of the metal atom M include Fe, Ni, Mn, Cr, V, Ti, Ru, Zn, Al, Zr, and Sn. Examples of the polydentate ligand L include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone (also known as 2,4-pentanedione), 2,4-hexanedione, and benzoylacetone. These are keto-enol tautomer compounds, and in the polydentate ligand L, the enol may be deprotonated to form an enolate (e.g., acetylacetonate). Examples of the monodentate ligand X include halogen atoms such as chlorine and bromine atoms, acyloxy groups such as pentanoyl, hexanoyl, 2-ethylhexanoyl, octanoyl, nonanoyl, decanoyl, dodecanoyl, and octadecanoyl groups, and alkoxy groups such as methoxy, ethoxy, n-propoxy, isopropoxy, and butoxy groups.

[0045] Specific examples of metal chelate compounds include iron tris(2,4-pentanedionato)(III), iron trisacetylacetonate, titanium trisacetylacetonate, ruthenium trisacetylacetonate, zinc bisacetylacetonate, aluminum trisacetylacetonate, zirconium tetrakisacetylacetonate, iron tris(2,4-hexanedionato)(III), zinc bis(2,4-hexanedionato), titanium tris(2,4-hexanedionato), aluminum tris(2,4-hexanedionato), and zirconium tetrakis(2,4-hexanedionato).

[0046] Examples of organotin compounds include dialkyltin oxides, fatty acid salts of dialkyltins, and fatty acid salts of stannous tin. Traditionally, dibutyltin compounds have been widely used, but in recent years, the toxicity of organotin compounds has been highlighted, and tributyltin (TBT), contained in dibutyltin compounds, in particular, is of concern as an endocrine disruptor. From a safety perspective, long-chain alkyltin compounds such as dioctyltin compounds are preferred. Specific examples of organotin compounds include dioctyltin oxide and dioctyltin dilaurate. While Sn compounds can be used provisionally, in light of the trend toward the use of safer substances, it is preferable to use metal chelate compounds of Al, Ti, Fe, etc., which are safer than Sn. The metal chelate compound in the pressure-sensitive adhesive composition according to the present invention preferably contains at least one selected from the group consisting of aluminum chelate compounds, titanium chelate compounds, and iron chelate compounds. The crosslinking catalyst (D) of a metal chelate compound is preferably contained in an amount of 0.001 to 0.5 parts by weight per 100 parts by weight of the copolymer.

[0047] Examples of the (E) keto-enol tautomer compound include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. In a pressure-sensitive adhesive composition using a polyisocyanate compound as a crosslinking agent, these compounds block the isocyanate groups of the crosslinking agent, thereby suppressing excessive viscosity increase and gelation of the pressure-sensitive adhesive composition after blending the crosslinking agent and extending the pot life of the pressure-sensitive adhesive composition. The (E) keto-enol tautomer compound is preferably contained in an amount of 0.1 to 300 parts by weight per 100 parts by weight of the copolymer.

[0048] Unlike the crosslinking catalyst (D) of the metal chelate compound, the (E) keto-enol tautomer compound has the effect of inhibiting crosslinking, so it is preferable to appropriately set the ratio of the (E) keto-enol tautomer compound to the (D) metal chelate compound crosslinking catalyst. To extend the pot life and improve storage stability of the PSA composition, a higher weight ratio (E) / (D) of the (E) keto-enol tautomer compound to the (D) metal chelate compound crosslinking catalyst is preferred. The value of (E) / (D) is preferably in the range of 70 to 1,000, more preferably 70 to 800, and most preferably 80 to 600.

[0049] More specifically, the PSA composition having an extended pot life according to the present invention is preferably one in which the viscosity of the PSA composition after 8 hours from blending and storage at 23° C. is less than 1.25 times the viscosity immediately after blending, thereby making it possible to obtain a PSA composition in which the increase in viscosity after blending is suppressed.

[0050] The pressure-sensitive adhesive composition of the present invention may contain additives such as an antistatic agent, a polyether siloxane compound, and other conventional additives such as an antioxidant.

[0051] The antistatic agent may be an antistatic agent contained in the pressure-sensitive adhesive composition or an antistatic agent copolymerized in the copolymer. The antistatic agent is preferably contained in an amount of 0.05 to 5.0 parts by weight per 100 parts by weight of the copolymer. The antistatic agent is preferably an ionic compound and / or an acryloyl group-containing ionic compound having a melting point of 25 to 50° C. These antistatic agents are presumed to have high affinity with the acrylic copolymer due to their low melting points and long-chain alkyl groups.

[0052] The ionic compound having a melting point of 25 to 50°C is an ionic compound having a cation and an anion, in which the cation is a nitrogen-containing onium cation such as a pyridinium cation, an imidazolium cation, a pyrimidinium cation, a pyrazolium cation, a pyrrolidinium cation, or an ammonium cation, or a phosphonium cation, a sulfonium cation, or the like, and the anion is a hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - Examples of suitable cations include inorganic or organic anion compounds such as bis(fluorosulfonyl)imide salts (FSI), bis(trifluoromethanesulfonyl)imide salts (TFSI), and trifluoromethanesulfonate salts (TF). These compounds are preferably solid at room temperature (e.g., 25°C), and can have a melting point of 25 to 50°C by selecting the alkyl group chain length, the position and number of substituents, and the like. The cation is preferably a quaternary nitrogen-containing onium cation, and examples thereof include quaternary pyridinium cations such as 1-alkylpyridinium (where the carbon atoms at positions 2 to 6 may be substituted or unsubstituted), quaternary imidazolium cations such as 1,3-dialkylimidazolium (where the carbon atoms at positions 2, 4, and 5 may be substituted or unsubstituted), and quaternary ammonium cations such as tetraalkylammonium. The ionic compound having a melting point of 25 to 50° C. is preferably contained in an amount of 0.05 to 5 parts by weight per 100 parts by weight of the copolymer.

[0053] The acryloyl group-containing ionic compound is an ionic compound having a cation and an anion, and the cation is (meth)acryloyloxyalkyltrialkylammonium [R + -C n H 2n -OCOCQ=CH2, where Q=H or CH3, R=alkyl] and the anion is a (meth)acryloyl group-containing cation such as hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), organic sulfonates (RSO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - ), F-containing imide salt (R F 2N - ) and other inorganic or organic anions. F 2N - )R F Examples of the fluorine-containing imide salt include perfluoroalkanesulfonyl groups such as trifluoromethanesulfonyl and pentafluoroethanesulfonyl groups, and fluorosulfonyl groups. Examples of the fluorine-containing imide salt include bis(fluorosulfonyl)imide salts [(FSO2)2N - ], bis(trifluoromethanesulfonyl)imide salt [(CF3SO2)2N - ], bis(pentafluoroethanesulfonyl)imide salt [(C2F5SO2)2N - and the like. The acryloyl group-containing ionic compound is preferably copolymerized in the copolymer in an amount of 0.1 to 5.0% by weight.

[0054] Specific examples of antistatic agents include, but are not limited to, ionic compounds having a melting point of 25 to 50°C, such as 1-octylpyridinium hexafluorophosphate, 1-nonylpyridinium hexafluorophosphate, 2-methyl-1-dodecylpyridinium hexafluorophosphate, 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 1-dodecylpyridinium dodecylbenzenesulfonate, 4-methyl-1-octylpyridinium hexafluorophosphate, and quaternary ammonium salts of trifluoromethanesulfonic acid. Specific examples of acryloyl group-containing ionic compounds include dimethylaminomethyl (meth)acrylate methyl hexafluorophosphate [(CH3)3N + CH2OCOCQ=CH2·PF6 - , where Q=H or CH3], dimethylaminoethyl (meth)acrylate bis(trifluoromethanesulfonyl)imidomethyl salt [(CH3)3N + (CH2)2OCOCQ=CH2·(CF3SO2)2N - , where Q=H or CH3], dimethylaminomethyl methacrylate bis(fluorosulfonyl)imidomethyl salt [(CH3)3N + CH2OCOCQ=CH2·(FSO2)2N - , where Q=H or CH3).

[0055] The polyether-modified siloxane compound is a siloxane compound having a polyether group, and has a general siloxane unit [—SiR 1 2-O-)], as well as siloxane units with polyether groups [—SiR 1 (R 2 O(R 3 O) n R 4 )-O-], where R 1 is one or more alkyl or aryl groups, R 2 and R 3 is one or more alkylene groups, R 4indicates one or more alkyl groups, acyl groups, etc. (terminal groups). The polyether group is a polyoxyethylene group [(C2H4O) n ] and polyoxypropylene group [(C3H6O) n and the like. The polyether-modified siloxane compound preferably has an HLB value of 7 to 15. The content of the polyether-modified siloxane compound is preferably 0.01 to 1.0 part by weight, more preferably 0.1 to 0.5 part by weight, per 100 parts by weight of the copolymer. HLB is the hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) defined in, for example, JIS K3211 (surfactant terminology). The polyether-modified siloxane compound can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group onto a polyorganosiloxane main chain having a silicon hydride group via a hydrosilylation reaction. Specific examples include dimethylsiloxane-methyl(polyoxyethylene)siloxane copolymer, dimethylsiloxane-methyl(polyoxyethylene)siloxane-methyl(polyoxypropylene)siloxane copolymer, and dimethylsiloxane-methyl(polyoxypropylene)siloxane polymer. By blending the polyether-modified siloxane compound in the pressure-sensitive adhesive composition, the adhesive strength and reworkability of the pressure-sensitive adhesive can be improved. If the pressure-sensitive adhesive composition does not contain the polyether-modified siloxane compound, the cost will be lower.

[0056] Examples of the antioxidant include hindered phenol-based antioxidants, polyphenol compounds, and tocopherol-based compounds. Among these, tocopherol-based compounds are preferred. Tocopherol-based compounds are generally vitamin E and are naturally occurring chemical substances. Therefore, they have little adverse effect on the human body, are highly safe to handle, and are environmentally friendly. Furthermore, because they are oil-soluble and liquid at room temperature, they are also excellent in compatibility with the pressure-sensitive adhesive composition and in precipitation resistance. By incorporating a tocopherol-based compound as the antioxidant, the storage stability of the pressure-sensitive adhesive is improved, thereby improving the pot life of the pressure-sensitive adhesive composition incorporating a curing agent. The tocopherol-based compound used in the present invention is preferably a compound in which the ferrule hydroxyl group of tocopherol has not been converted to an ester or the like, and has a ferrule hydroxyl group, since it is incorporated into the adhesive composition (and is not metabolized as in the human body). Examples include tocopherol and tocotrienol. It is known that tocopherol and tocotrienol are classified into natural compounds (d-forms), non-natural compounds (l-forms), and racemic mixtures of these compounds (dl-forms), which are equal mixtures of these compounds. Natural compounds (d-forms) and racemic compounds (dl-forms) are preferred because they are sometimes used as food additives, etc. Specific examples of tocopherol compounds include at least one selected from the group consisting of d-α-tocopherol, dl-α-tocopherol, d-β-tocopherol, dl-β-tocopherol, d-γ-tocopherol, dl-γ-tocopherol, d-δ-tocopherol, dl-δ-tocopherol, d-α-tocotrienol, dl-α-tocotrienol, d-β-tocotrienol, dl-β-tocotrienol, d-γ-tocotrienol, dl-γ-tocotrienol, d-δ-tocotrienol, and dl-δ-tocotrienol. Two or more tocopherol compounds may be used in combination. As a food additive, "mixed tocopherols" is a mixture whose main components are d-α-tocopherol, d-β-tocopherol, d-γ-tocopherol, and d-δ-tocopherol, while "tocotrienol" is a mixture whose main components are d-α-tocotrienol, d-β-tocotrienol, d-γ-tocotrienol, and d-δ-tocotrienol. When the pressure-sensitive adhesive composition of the present invention contains a tocopherol-based compound, it preferably contains 0.01 to 5 parts by weight of the tocopherol-based compound per 100 parts by weight of the copolymer.

[0057] Furthermore, other components that can be appropriately blended include known additives such as copolymerizable (meth)acrylic monomers containing alkylene oxide, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing catalysts, plasticizers, fillers, curing retarders, processing aids, antioxidants, and antioxidants. These may be used alone or in combination of two or more.

[0058] The copolymer used as the main component in the pressure-sensitive adhesive composition of the present invention can be synthesized by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18 and (B) a copolymerizable monomer containing a hydroxyl group as a copolymerizable monomer. The polymerization method for the copolymer is not particularly limited, and any appropriate polymerization method such as solution polymerization or emulsion polymerization can be used. The copolymer may also contain at least one of a carboxyl group-containing monomer and a nitrogen-containing vinyl monomer that does not contain a hydroxyl group as other copolymerizable monomers. The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above-mentioned copolymer with (C) a difunctional or higher isocyanate compound, (D) a crosslinking catalyst of a metal chelate compound, (E) a keto-enol tautomer compound, and further any additives as appropriate.

[0059] The copolymer is preferably an acrylic polymer, and preferably contains 50 to 100% by weight of an acrylic monomer such as a (meth)acrylic acid ester monomer, (meth)acrylic acid, or a (meth)acrylamide. The acid value of the copolymer is preferably 8.0 or less, more preferably 0.01 to 8.0, which can improve staining resistance and improve the ability to prevent adhesive residue. Here, the "acid value" is an index that indicates the acid content, and is expressed as the number of milligrams of potassium hydroxide required to neutralize 1 g of a polymer containing a carboxyl group.

[0060] The adhesive layer obtained by crosslinking the adhesive composition preferably has an adhesive strength of 0.05 to 0.2 N / 25 mm at a low peel speed of 0.3 m / min and an adhesive strength of 2.0 N / 25 mm or less at a high peel speed of 30 m / min. This allows for little change in adhesive strength despite the peel speed, enabling rapid peeling even at high peel speeds. Furthermore, even when the surface protection film is peeled off for re-adhesion, excessive force is not required, and it can be easily peeled off from the adherend.

[0061] The pressure-sensitive adhesive layer (pressure-sensitive adhesive after crosslinking) obtained by crosslinking the pressure-sensitive adhesive composition of the present invention preferably has a gel fraction of 90 to 100%. Such a high gel fraction prevents excessive adhesive strength at low peel speeds, reduces elution of unpolymerized monomers or oligomers from the copolymer, improves reworkability and durability at high temperatures and high humidity, and suppresses contamination of the adherend.

[0062] The pressure-sensitive adhesive film of the present invention comprises a pressure-sensitive adhesive layer formed on one or both sides of a resin film by crosslinking the pressure-sensitive adhesive composition of the present invention. The surface protection film of the present invention comprises a pressure-sensitive adhesive layer formed on one side of a resin film by crosslinking the pressure-sensitive adhesive composition of the present invention. The pressure-sensitive adhesive composition of the present invention contains the above-mentioned components (A) to (E) in a well-balanced blend, and therefore has a long pot life and a fast crosslinking rate even without the use of an organotin compound. Therefore, the surface protection film of the present invention can be suitably used as a surface protection film for polarizing plates or as a surface protection film for any precision electrical / electronic component selected from the group consisting of flexible printed wiring boards, rigid printed wiring boards, and transparent conductive films.

[0063] In the pressure-sensitive adhesive film and surface protection film according to the present invention, a polyester film or the like can be used as the base material for the resin film or the release film (separator) that protects the pressure-sensitive adhesive layer. In addition, the resin film may be subjected to an antifouling treatment using a silicone-based or fluorine-based release agent or coating agent, silica microparticles, or the like, or an antistatic treatment by applying or kneading in an antistatic agent, on the side opposite to the side on which the pressure-sensitive adhesive layer is formed. The release film is subjected to a release treatment with a silicone-based or fluorine-based release agent on the surface thereof that faces the adhesive surface of the adhesive layer. [Example]

[0064] The present invention will be specifically described below with reference to examples.

[0065] <Production of acrylic copolymer> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, and the air inside the reactor was replaced with nitrogen gas. Then, 100 parts by weight of 2-ethylhexyl acrylate and 3.5 parts by weight of 8-hydroxyoctyl acrylate were added to the reactor. Then, 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours, and the mixture was allowed to react at 65°C for 6 hours, yielding an acrylic copolymer solution 1 used in Example 1 with a weight-average molecular weight of 500,000. A portion of the acrylic copolymer was sampled and used as a sample for measuring the acid value, which will be described later. [Examples 2 to 6 and Comparative Examples 1 to 3] The acrylic copolymer solutions used in Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as in the acrylic copolymer solution 1 used in Example 1 above, except that the monomer compositions were as shown in (A), (B), and (I) in Table 1.

[0066] <Production of Pressure-Sensitive Adhesive Composition and Surface Protective Film> [Example 1] To the acrylic copolymer solution 1 of Example 1 produced as described above, 6.0 parts by weight of acetylacetone was added and stirred, and then 1.5 parts by weight of Coronate HX (an isocyanurate of a hexamethylene diisocyanate compound) and 0.05 parts by weight of tris(2,4-pentanedionato)iron(III) were added and mixed with stirring to obtain a pressure-sensitive adhesive composition of Example 1. This pressure-sensitive adhesive composition was applied to a release film made of a silicone resin-coated polyethylene terephthalate (PET) film, and then dried at 90°C to remove the solvent, yielding a pressure-sensitive adhesive sheet with a pressure-sensitive adhesive layer thickness of 25 μm. Then, an adhesive sheet was transferred to the side opposite the antistatic and antifouling treated side of a polyethylene terephthalate (PET) film that had been treated with antistatic and antifouling treatment on one side, thereby obtaining a surface protection film of Example 1 having a laminated structure of "antistatic and antifouling treated PET film / adhesive layer / release film (silicone resin coated PET film)". [Examples 2 to 6 and Comparative Examples 1 to 3] The surface protection films of Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as the surface protection film of Example 1 above, except that the compositions of the additives were changed as shown in Table 1 (C) to (E), respectively.

[0067] [Table 1]

[0068] In Table 1, the numerical values ​​in parts by weight, calculated with the total of group (A) being 100 parts by weight, are shown in parentheses. The ratios of (E) / (D) are shown in Table 2. The compound names of the abbreviations of each component used in Table 1 are shown in Table 3. Coronate (registered trademark) HX, HL, and L are trade names of Nippon Polyurethane Industry Co., Ltd., Takenate (registered trademark) D-140N is a trade name of Mitsui Chemicals, Inc., and Duranate (registered trademark) D101 is a trade name of Asahi Kasei Chemicals Corporation.

[0069] [Table 2]

[0070] [Table 3]

[0071] <Test method and evaluation> The surface protection films of Examples 1 to 6 and Comparative Examples 1 to 3 were aged for 7 days in an atmosphere of 23°C and 50% RH, and then the release film (a silicone resin-coated PET film) was peeled off to expose the adhesive layer. The surface protection film with the exposed adhesive layer was then attached to the surface of a polarizing plate attached to a liquid crystal cell via the adhesive layer, left for 1 day, autoclaved at 50°C and 5 atmospheres for 20 minutes, and then left at room temperature for a further 12 hours to prepare a sample for measuring adhesive strength.

[0072] <Adhesive strength> The measurement sample obtained above (a 25 mm wide surface protection film attached to the surface of a polarizing plate) was peeled in a 180° direction using a tensile tester at a low peeling speed (0.3 m / min) and a high peeling speed (30 m / min), and the measured peel strength was taken as the adhesive strength.

[0073] <Pot life> The viscosity η0 (initial viscosity) of the PSA composition was measured immediately after blending the additives (C) to (E). The PSA composition was then left sealed at 23°C for 8 hours, after which the viscosity η1 (viscosity after 8 hours) of the PSA composition was measured. The value of η1 when η0 was set to 1.0, i.e., the ratio of η1 / η0, was calculated as an index of pot life. The evaluation criteria were as follows: a viscosity after 8 hours that was less than 1.25 times the initial viscosity was evaluated as "Good," a viscosity that was 1.25 to less than 1.50 times the initial viscosity was evaluated as "Average," and a viscosity that was 1.50 times or more or gelled after 8 hours was evaluated as "Poor."

[0074] Table 4 shows the evaluation results.

[0075] [Table 4]

[0076] The surface protection films of Examples 1 to 6 had an adhesive strength of 0.05 to 0.2 N / 25 mm at a low peel speed of 0.3 m / min and an adhesive strength of 2.0 N / 25 mm or less at a high peel speed of 30 m / min, and had a sufficiently long pot life. That is, the adhesive strength is well balanced at both low and high peel speeds, and furthermore, the pot life is long and the properties as a surface protection film are excellent. Furthermore, the surface protection films of Examples 1 to 6 are highly safe because the pressure-sensitive adhesive composition does not contain an organotin compound.

[0077] The surface protection film of Comparative Example 1 showed excessive adhesive strength at a low peel speed of 0.3 m / min and a high peel speed of 30 m / min, possibly because it did not contain (C) a difunctional or higher isocyanate compound, which serves as a crosslinking agent. The surface protection film of Comparative Example 2 had a short pot life due to a small ratio of the keto-enol tautomer compound (E) to the crosslinking catalyst of the metal chelate compound (D). The surface protection film of Comparative Example 3 could not be coated because the ratio of (E) keto-enol tautomer compound to (D) metal chelate compound crosslinking catalyst was small, resulting in a too short pot life and crosslinking having progressed before coating. As described above, the surface protection films of Comparative Examples 1 to 3 were unable to simultaneously satisfy all the required performance characteristics, namely, an excellent balance of adhesive strength at both low and high peel speeds, and a long pot life.

Claims

1. A pressure-sensitive adhesive composition containing an acrylic polymer and a crosslinking agent, the acrylic polymer is a copolymer obtained by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18 and (B) at least one copolymerizable monomer containing a hydroxyl group as a copolymerizable monomer group, the pressure-sensitive adhesive composition contains, relative to 100 parts by weight of the copolymer, (C) 0.1 to 10 parts by weight of a difunctional or higher isocyanate compound as the crosslinking agent, (D) 0.001 to 0.5 parts by weight of a crosslinking catalyst of a metal chelate compound, and (E) 0.1 to 300 parts by weight of a keto-enol tautomer compound, wherein the weight ratio of (E) / (D) is 80 to 600; A pressure-sensitive adhesive composition, characterized in that the pressure-sensitive adhesive composition is blended and then stored at 23°C, and the viscosity of the pressure-sensitive adhesive composition after 8 hours is less than 1.25 times the viscosity immediately after blending.

2. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the copolymer is an acrylic polymer containing at least one of a carboxyl group-containing monomer and a nitrogen-containing vinyl monomer not containing a hydroxyl group as other copolymerizable monomers.

3. 3. A pressure-sensitive adhesive film comprising a resin film and a pressure-sensitive adhesive layer formed on one or both sides thereof, the pressure-sensitive adhesive layer being formed by crosslinking the pressure-sensitive adhesive composition according to claim 1 or 2.

4. A surface protection film comprising a resin film and a pressure-sensitive adhesive layer formed on one side thereof, the pressure-sensitive adhesive layer being obtained by crosslinking the pressure-sensitive adhesive composition according to claim 1 or 2.

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