Pressure-sensitive adhesive composition, pressure-sensitive adhesive film and surface protective film of polarizing plate

Abstract

To provide a pressure-sensitive adhesive composition having anti-static performance and an excellent balance of adhesive strength between low and high speed peeling regions, and further being excellent in durability, reworkability, and anti-static property, a pressure-sensitive adhesive film, and a surface protective film of a polarizing plate.SOLUTION: A pressure-sensitive adhesive composition is formed of a copolymer containing a (meth)acrylate ester monomer having a 4-10C alkyl group (A), a hydroxy group-containing copolymerizable monomer (B), a carboxy group-containing copolymerizable monomer (C), and a polyalkylene glycol mono(meth)acrylate monomer (D), and further contains a 3 or more functional isocyanate compound (E), an anti-static agent (H), and a polyether-modified siloxane compound (I), and weight ratios of them based on (A) 100 are (B) 0.1-5.0, (C) 0.35-1.0, and (D) 1-20, and those based on copolymer 100 are (E) 0.5-5.0 and (I) 0.01-0.5.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface protection film used in the manufacturing process of a liquid crystal display, and more particularly to a surface protection film used to protect the surfaces of optical components such as polarizing plates and retardation plates that constitute a liquid crystal display by being attached to the surfaces of the optical components such as polarizing plates and retardation plates. [Background technology]

[0002] Conventionally, in the manufacturing process of optical components such as polarizing plates and retardation plates that constitute liquid crystal displays, surface protection films are applied to temporarily protect the surfaces of the optical components. Such surface protection films are used only in the manufacturing process of the optical components and are peeled off and removed from the optical components when the optical components are incorporated into liquid crystal displays. Since such surface protection films for protecting the surfaces of optical components are used only in the manufacturing process, they are also generally referred to as process films.

[0003] The surface protection film used in the process of manufacturing optical components in this way has an adhesive layer formed on one side of an optically transparent polyethylene terephthalate (PET) resin film, and a release film that has been treated to release the adhesive layer is attached to the adhesive layer to protect it until it is attached to the optical component. Furthermore, optical components such as polarizing plates and retardation plates undergo product inspection with a surface protection film attached, which involves optical evaluation of the display performance, hue, contrast, and presence of foreign matter of the liquid crystal display panel. Therefore, the required performance of the surface protection film is that the adhesive layer must be free of air bubbles and foreign matter. Furthermore, in recent years, when peeling a surface protection film from an optical component such as a polarizing plate or a retardation plate, there has been concern that peeling charge, which occurs as a result of static electricity generated when peeling the pressure-sensitive adhesive layer from the adherend, may affect the electrical control circuits of liquid crystal displays, and therefore there is a demand for pressure-sensitive adhesive layers with excellent antistatic properties. Furthermore, when a surface protection film is attached to an optical component such as a polarizing plate or a retardation plate, the surface protection film may be peeled off and then reattached for various reasons, and in such cases, the surface protection film is required to be easy to peel off from the optical component to be adhered (reworkability). Furthermore, when the surface protection film is finally peeled off from an optical component such as a polarizing plate or a retardation plate, it is required that the film be peeled off quickly, i.e., that the adhesive strength does not change much depending on the peeling speed so that the film can be peeled off quickly even at high speeds.

[0004] Thus, in recent years, the performance requirements for the adhesive layer constituting the surface protection film have been increased in order to ensure ease of use when using the surface protection film, including (1) a balance of adhesive strength in the low-speed peeling region and the high-speed peeling region, (2) prevention of adhesive residue, (3) excellent antistatic properties, and (4) reworkability. However, while it was possible to satisfy each of the required performances (1) to (4) of the adhesive layer constituting the surface protection film individually, it was an extremely difficult task to simultaneously satisfy all of the required performances (1) to (4) required of the adhesive layer of the surface protection film.

[0005] For example, the following proposals are known regarding (1) balancing the adhesive strength in the low-speed peeling region and the high-speed peeling region, and (2) preventing the occurrence of adhesive residue.

[0006] Acrylic pressure-sensitive adhesive layers, which are mainly composed of a copolymer of a (meth)acrylic acid alkyl ester having an alkyl group with 7 or less carbon atoms and a carboxyl group-containing copolymerizable compound and which are crosslinked with a crosslinking agent, have the problem that the pressure-sensitive adhesive transfers to the adherend when adhered for a long period of time and the adhesive strength to the adherend increases significantly over time. To avoid this, a pressure-sensitive adhesive layer is known which uses a copolymer of a (meth)acrylic acid alkyl ester having an alkyl group with 8 to 10 carbon atoms and a copolymerizable compound having an alcoholic hydroxyl group and crosslinks this with a crosslinking agent (Patent Document 1). Also proposed are adhesive layers prepared by blending a small amount of a copolymer of a (meth)acrylic acid alkyl ester and a carboxyl group-containing copolymerizable compound with the same copolymer as above and crosslinking the resulting mixture with a crosslinking agent. However, when these are used to protect the surface of a plastic plate or the like that has a low surface tension and a smooth surface, they have problems such as peeling phenomena such as lifting due to heating during processing or storage, and poor removability when peeled at high speeds, which is the range of manual work.

[0007] In order to solve these problems, a pressure-sensitive adhesive composition has been proposed in which a copolymer of a monomer mixture obtained by adding a) 100 parts by weight of a (meth)acrylic acid alkyl ester, the main component of which is a (meth)acrylic acid alkyl ester having an alkyl group having 8 to 10 carbon atoms, b) 1 to 15 parts by weight of a carboxyl group-containing copolymerizable compound, and c) 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms, is blended with a crosslinking agent in an amount equivalent to or greater than the amount of the carboxyl groups in the above-mentioned b) component (Patent Document 2). The pressure-sensitive adhesive composition described in Patent Document 2 does not experience peeling phenomena such as lifting during processing or storage, and furthermore, the adhesive strength increases little over time, making it highly releasable; it can be releasable with little force even after long-term storage, particularly long-term storage under high-temperature conditions, without leaving any adhesive residue on the adherend, and can be releasable with little force even when peeled at high speed.

[0008] Furthermore, with regard to (3) excellent antistatic performance, methods for imparting antistatic properties to a surface protective film include kneading an antistatic agent into a substrate film. Examples of the antistatic agent disclosed include: (a) various cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups; (b) anionic antistatic agents having anionic groups such as sulfonate groups, sulfate ester groups, phosphate ester groups, and phosphonate groups; (c) amphoteric antistatic agents such as amino acid-based and amino sulfate-based; (d) nonionic antistatic agents such as amino alcohol-based, glycerin-based, and polyethylene glycol-based; and (e) polymeric antistatic agents obtained by increasing the molecular weight of the above-mentioned antistatic agents (Patent Document 3). In recent years, it has also been proposed to incorporate such antistatic agents into the base film, or to incorporate them directly into the pressure-sensitive adhesive layer rather than coating the surface of the base film.

[0009] Regarding (4) reworkability, for example, a pressure-sensitive adhesive composition has been proposed in which an isocyanate compound curing agent and a specific silicate oligomer are blended in an acrylic resin in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the acrylic resin (Patent Document 4). Patent Document 4 describes a pressure-sensitive adhesive composition that uses an alkyl acrylate ester having an alkyl group containing about 2 to 12 carbon atoms or an alkyl methacrylate ester having an alkyl group containing about 4 to 12 carbon atoms as the main monomer component, and that may contain other functional group-containing monomer components, such as a carboxyl group-containing monomer. It generally contains 50% by weight or more of the main monomer, and the content of the functional group-containing monomer component is desired to be 0.001 to 50% by weight, preferably 0.001 to 25% by weight, and more preferably 0.01 to 25% by weight. The pressure-sensitive adhesive composition described in Patent Document 4 is described as having reworkability, since it exhibits little change over time in cohesive strength and adhesive strength even at high temperatures or high temperature and humidity, and also exhibits excellent curved surface adhesion. Generally, when the adhesive layer is made soft, adhesive residue tends to occur and reworkability tends to be reduced. That is, when it is applied incorrectly, it becomes difficult to peel off and re-apply. For this reason, it is considered necessary to crosslink a monomer having a functional group such as a carboxyl group with the base resin to give the adhesive layer a certain hardness in order to provide reworkability. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 63-225677 [Patent Document 2] Japanese Patent Application Publication No. 11-256111 [Patent Document 3] Japanese Patent Application Publication No. 11-070629 [Patent Document 4] Japanese Patent Application Publication No. 8-199130 Summary of the Invention [Problem to be solved by the invention]

[0011] In conventional technology, the required performance of the adhesive layer constituting the surface protection film has been to achieve a balance of adhesive strength between the low-speed peel region and the high-speed peel region, excellent antistatic performance, and rework performance, but while it has been possible to satisfy each of these individual required performances, it has not been possible to satisfy all of the required performances required of the adhesive layer of a surface protection film.

[0012] The present invention has been made in consideration of the above circumstances, and aims to provide a surface protection film that has antistatic properties, an excellent balance of adhesive strength between the low-speed peel area and the high-speed peel area, and also has excellent durability, reworkability, and antistatic properties. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the present invention provides a surface protection film comprising a resin film and, on one side thereof, a pressure-sensitive adhesive layer formed by crosslinking a pressure-sensitive adhesive composition containing an acrylic copolymer, an antistatic agent, and a crosslinking agent, wherein the acrylic copolymer is an acrylic copolymer obtained by copolymerizing 100 parts by weight in total of one or more (meth)acrylic acid ester monomers having an alkyl group with a carbon number of C4 to C10, (B) 0.1 to 5.0 parts by weight in total of one or more copolymerizable monomers containing a hydroxyl group, (C) 0.35 to 1.0 part by weight in total of one or more copolymerizable monomers containing a carboxyl group, and (D) 1 to 20 parts by weight of one or more polyalkylene glycol mono(meth)acrylic acid ester monomers. The surface protection film is characterized in that the pressure-sensitive adhesive composition comprises a copolymer, the pressure-sensitive adhesive composition comprising (E) a tri- or higher functional isocyanate compound as the crosslinking agent, (F) a crosslinking retarder, (G) a crosslinking catalyst, (H) an antistatic agent, and (I) a polyether-modified siloxane compound having an HLB value of 7 to 12, the pressure-sensitive adhesive composition comprising 0.5 to 5.0 parts by weight of the (E) tri- or higher functional isocyanate compound per 100 parts by weight of the acrylic copolymer, and the pressure-sensitive adhesive layer has an adhesive strength of 0.05 to 0.1 N / 25 mm in a low-speed peel region of 0.3 m / min and an adhesive strength of 1.0 N / 25 mm or less in a high-speed peel region of 30 m / min.

[0014] 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, and that the total amount of 8-hydroxyoctyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate among the (B) hydroxyl group-containing copolymerizable monomers is 0 to 0.9 parts by weight per 100 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C10 (it is also acceptable if 8-hydroxyoctyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, and 4-hydroxybutyl(meth)acrylate are not contained).

[0015] The (C) carboxyl group-containing copolymerizable monomer is preferably at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate.

[0016] It is preferable that the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is at least one selected from the group consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate.

[0017] The (E) trifunctional or higher 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, and a biuret of an isophorone diisocyanate compound.

[0018] The (H) antistatic agent is preferably an ionic compound having a melting point of 30 to 80°C and contained in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the copolymer, or a quaternary ammonium salt-type acrylic monomer having a melting point of 30 to 80°C and copolymerized in the copolymer in an amount of 0.1 to 5.0% by weight.

[0019] It is preferable that the (I) polyether-modified siloxane compound is a polyether-modified siloxane compound having an HLB value of 7 to 12, and that the (I) polyether-modified siloxane compound is contained in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the copolymer.

[0020] It is preferable that the (F) crosslinking retarder is a keto-enol tautomeric compound, and that the (F) crosslinking retarder is contained in an amount of 1.0 to 5.0 parts by weight per 100 parts by weight of the copolymer.

[0021] It is preferable that the (G) crosslinking catalyst is an organotin compound, and that the (G) crosslinking catalyst is contained in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the copolymer.

[0022] The adhesive layer obtained by crosslinking the adhesive composition preferably has an adhesive strength of 0.05 to 0.1 N / 25 mm in a low-speed peel region of 0.3 m / min, and an adhesive strength of 1.0 N / 25 mm or less in a high-speed peel region of 30 m / min.

[0023] The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has a surface resistance of 5.0 × 10+10 It is preferable that the resistance is Ω / □ or less and the peeling electrification voltage is ±0 to 1 kV.

[0024] The present invention also provides a pressure-sensitive adhesive film, characterized in that a pressure-sensitive adhesive layer obtained by crosslinking the above-mentioned pressure-sensitive adhesive composition is formed on one or both sides of a resin film.

[0025] The present invention also provides a surface protection film comprising a pressure-sensitive adhesive layer formed by crosslinking the above-mentioned pressure-sensitive adhesive composition on one side of a resin film, wherein the surface protection film is characterized in that no contamination is transferred to the substrate after tracing the surface protection film with a ballpoint pen through the pressure-sensitive adhesive layer.

[0026] The surface protection film can be used as a surface protection film for a polarizing plate.

[0027] The surface of the resin film opposite to the surface on which the pressure-sensitive adhesive layer is formed is preferably subjected to antistatic and antifouling treatment. [Effects of the Invention]

[0028] According to the present invention, it is possible to satisfy all the performance requirements for the pressure-sensitive adhesive layer of a surface protection film, which could not be achieved with conventional techniques, and to obtain excellent antistatic performance and performance in preventing adhesive transfer. Specifically, it is possible to reduce the amount of antistatic agent added while maintaining antistatic performance, and further improve performance in preventing adhesive transfer. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described below based on preferred embodiments. The pressure-sensitive adhesive composition of the present invention is characterized in that its main ingredient comprises a copolymer containing (A) a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 10, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, and (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and further contains (E) a tri- or higher functional isocyanate compound, (F) a crosslinking retarder, (G) a crosslinking catalyst, (H) an antistatic agent, and (I) a polyether-modified siloxane compound.

[0030] (A) Examples of the (meth)acrylic acid ester monomers having an alkyl group with a carbon number of 4 to 10 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, and decyl (meth)acrylate.

[0031] (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 (B) copolymerizable monomer containing a hydroxyl group is contained in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C10. Furthermore, among the (B) hydroxyl group-containing copolymerizable monomers, the total amount of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate is preferably less than 1 part by weight (it is acceptable if they are not contained), and is preferably 0 to 0.9 parts by weight.

[0032] (C) The copolymerizable monomer containing a carboxyl group is preferably at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate. It is preferable that 0.35 to 1.0 parts by weight of (C) a copolymerizable monomer containing a carboxyl group is contained per 100 parts by weight of (A) a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C10.

[0033] The (D) 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 with the base polymer. The other hydroxyl group may remain as OH or may be converted into an alkyl ether such as methyl ether or ethyl ether, or a saturated carboxylic acid ester such as acetate ester. 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.

[0034] The (D) 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. It is preferable that 1 to 20 parts by weight of (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is contained per 100 parts by weight of (A) (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C10.

[0035] (E) The tri- or higher functional isocyanate compound may be a polyisocyanate compound having at least three isocyanate (NCO) groups in one molecule, and examples thereof include biuret-modified and isocyanurate-modified diisocyanates (compounds having two NCO groups in one molecule) such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate, and adducts (polyol-modified products) with tri- or higher functional polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane and glycerin. The (E) tri- or higher functional isocyanate compound is a polyisocyanate compound having at least three isocyanate (NCO) groups per molecule, and 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, and a biuret of an isophorone diisocyanate compound. The (E) tri- or higher functional isocyanate compound is preferably contained in an amount of 0.5 to 5.0 parts by weight per 100 parts by weight of the copolymer.

[0036] Examples of the (F) crosslinking retarder 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. These are keto-enol tautomeric compounds, and in pressure-sensitive adhesive compositions using a polyisocyanate compound as a crosslinking agent, they 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 thereby extending the pot life of the pressure-sensitive adhesive composition. (F) The crosslinking retarder is preferably a keto-enol tautomeric compound, and particularly preferably at least one selected from the group consisting of acetylacetone and ethyl acetoacetate. The crosslinking retarder (F) is preferably contained in an amount of 1.0 to 5.0 parts by weight per 100 parts by weight of the copolymer.

[0037] The (G) crosslinking catalyst 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, organotin compounds, organolead compounds, organozinc compounds, and other organometallic compounds. Examples of tertiary amines include trialkylamines, N,N,N',N'-tetraalkyldiamines, N,N-dialkylaminoalcohols, triethylenediamine, morpholine derivatives, and piperazine derivatives. Examples of the organic tin compound include dialkyltin oxide, fatty acid salts of dialkyltin, and fatty acid salts of stannous. The crosslinking catalyst (G) is preferably an organotin compound, and particularly preferably at least one selected from the group consisting of dioctyltin oxide and dioctyltin dilaurate. The crosslinking catalyst (G) is preferably contained in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the copolymer.

[0038] The (H) antistatic agent is preferably solid at room temperature (e.g., 30°C). More specifically, it is preferably an ionic compound having a melting point of 30 to 80°C, contained in an amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the copolymer, or a quaternary ammonium salt-type acrylic monomer having a melting point of 30 to 80°C, copolymerized in the copolymer at 0.1 to 5.0% by weight. In the present invention, as the (H) antistatic agent, (H1) an ionic compound having a melting point of 30 to 80°C is added to the copolymer, or (H2) a quaternary ammonium salt-type acrylic monomer having a melting point of 30 to 80°C is copolymerized into the copolymer. These (H) antistatic agents are presumed to have high affinity with the acrylic copolymer due to their low melting points and long-chain alkyl groups.

[0039] (H1) The ionic compound having a melting point of 30 to 80°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 compounds that are inorganic or organic anions such as 1-alkylpyridinium (the carbon atoms at positions 2 to 6 may be substituted or unsubstituted), 1,3-dialkylimidazolium (the carbon atoms at positions 2, 4, and 5 may be substituted or unsubstituted), and tetraalkylammonium cations.

[0040] (H2) The quaternary ammonium salt type acrylic monomer having a melting point of 30 to 80°C is an ionic compound having a cation and an anion, wherein the cation is (meth)acryloyloxyalkyltrialkylammonium [R3N + -C n H 2n -OCOCQ=CH2, where Q=H or CH3, R=alkyl], and the anion is hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), organic sulfonates (RSO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - ) and other inorganic or organic anions. Specific examples of (H) antistatic agents include, but are not limited to, 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, dimethylaminomethyl acrylate methyl hexafluorophosphate [(CH3)3N + CH2OCOCH=CH2·PF6 - ] etc.

[0041] (I) The polyether-modified siloxane compound is a siloxane compound having a polyether group, and has a normal 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 (I) is a polyether-modified siloxane compound having an HLB value of 7 to 12, and the content of the polyether-modified siloxane compound (I) is preferably 0.01 to 0.5 parts by weight, more preferably 0.1 to 0.5 parts 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). Polyether-modified siloxane compounds can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group onto a polyorganosiloxane main chain having silicon hydride groups via a hydrosilylation reaction. Specific examples include dimethylsiloxane-methyl(polyoxyethylene)siloxane copolymers, dimethylsiloxane-methyl(polyoxyethylene)siloxane-methyl(polyoxypropylene)siloxane copolymers, and dimethylsiloxane-methyl(polyoxypropylene)siloxane polymers. (I) By blending a polyether-modified siloxane compound in a pressure-sensitive adhesive composition, the adhesive strength and reworkability of the pressure-sensitive adhesive can be improved.

[0042] Furthermore, other components that can be appropriately blended include known additives such as copolymerizable alkylene oxide-containing (meth)acrylic monomers, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing accelerators, plasticizers, fillers, curing retarders, processing aids, antioxidants, and antioxidants. These may be used alone or in combination of two or more.

[0043] The copolymer used as the base component in the pressure-sensitive adhesive composition of the present invention can be synthesized by polymerizing (A) a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 10, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, and (D) a polyalkylene glycol mono(meth)acrylic acid ester 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. When the quaternary ammonium salt type acrylic monomer (H2) is used as the antistatic agent (H), the copolymer of the main component used in the pressure-sensitive adhesive composition of the present invention can be synthesized by polymerizing (A) a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C10, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and (H2) a quaternary ammonium salt type acrylic monomer. The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above copolymer with (E) a trifunctional or higher isocyanate compound, (F) a crosslinking retarder, (G) a crosslinking catalyst, (H) an antistatic agent, (I) a polyether-modified siloxane compound, and any other additives as appropriate. Note that when (H2) a quaternary ammonium salt-type acrylic monomer having a melting point of 30 to 80°C is polymerized into the main copolymer, it does not matter whether or not an antistatic agent (H) is further added to the copolymer.

[0044] The adhesive layer obtained by crosslinking the adhesive composition preferably has an adhesive strength of 0.05 to 0.1 N / 25 mm in a low-speed peel region of 0.3 m / min and an adhesive strength of 1.0 N / 25 mm or less in a high-speed peel region of 30 m / min. This results in performance in which the adhesive strength changes little depending on the peel speed, enabling rapid peeling even at high speeds. Furthermore, even when the surface protection film is peeled off once for re-adhesion, excessive force is not required, and it can be easily peeled off from the adherend.

[0045] The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has a surface resistance of 5.0 × 10 +10 Preferably, the surface resistivity is Ω / □ or less, and the peeling electrification voltage is ±0 to 1 kV. In the present invention, "±0 to 1 kV" means 0 to -1 kV and 0 to +1 kV, i.e., -1 to +1 kV. A high surface resistivity results in poor performance in dissipating static electricity generated by charging during peeling. Therefore, by sufficiently reducing the surface resistivity, the peeling electrification voltage that occurs in conjunction with static electricity generated when the pressure-sensitive adhesive layer is peeled off from the adherend can be reduced, and the peeling electrification voltage that occurs in conjunction with static electricity generated when the pressure-sensitive adhesive layer is peeled off from the adherend can be prevented from affecting the electrical control circuits, etc. of the adherend.

[0046] 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 95 to 100%. Such a high gel fraction prevents excessive adhesive strength in the low-speed peel region, 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.

[0047] 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 (I) in a well-balanced blend, and therefore has antistatic properties, an excellent balance of adhesive strength between the low-speed peel region and the high-speed peel region, and also excellent durability, reworkability (no transfer of contamination to the adherend after tracing the surface protection film with a ballpoint pen through the pressure-sensitive adhesive layer), and antistatic properties. Therefore, the pressure-sensitive adhesive composition of the present invention can be suitably used as a surface protection film for polarizing plates.

[0048] As the base film of the pressure-sensitive adhesive layer and the release film (separator) that protects the adhesive surface, a resin film such as a polyester film can be used. The substrate 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 coating or kneading in an antistatic agent, on the side opposite to the side on which the pressure-sensitive adhesive layer of the resin film 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]

[0049] The present invention will be specifically described below with reference to examples.

[0050] <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 in the reactor was replaced with nitrogen gas. Then, 100 parts by weight of 2-ethylhexyl acrylate, 0.9 parts by weight of 8-hydroxyoctyl acrylate, 0.5 parts by weight of acrylic acid, 3 parts by weight of polyethylene glycol monoacrylate, and 60 parts by weight of a solvent (ethyl acetate) 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. [Examples 2 to 9 and Comparative Examples 1 to 9] The acrylic copolymer solutions used in Examples 2 to 9 and Comparative Examples 1 to 9 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 Table 1 (A) to (D).

[0051] <Production of Pressure-Sensitive Adhesive Composition and Surface Protective Film> [Example 1] To the acrylic copolymer solution 1 (100 parts by weight of the acrylic copolymer) prepared as described above, 1.5 parts by weight of 1-octylpyridinium hexafluorophosphate, 0.1 parts by weight of KF-351A (a polyether-modified siloxane compound with an HLB of 12), and 2.5 parts by weight of acetylacetone were added and stirred, followed by the addition of 1.5 parts by weight of Coronate HX (an isocyanurate of a hexamethylene diisocyanate compound) and 0.02 parts by weight of dioctyltin dilaurate, and the mixture was stirred 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 the solvent was removed by drying at 90°C, 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 9 and Comparative Examples 1 to 9] Surface protection films of Examples 2 to 9 and Comparative Examples 1 to 9 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 (E) to (I), respectively.

[0052] In Table 1, the compounding ratio of each component is shown in parentheses, with the total of Group (A) being 100 parts by weight. The compound names of the abbreviations for each component used in Table 1 are shown in Table 2. Coronate (registered trademark) HX and Coronate HL are trade names of Nippon Polyurethane Industry Co., Ltd., Takenate (registered trademark) D-140N is a trade name of Mitsui Chemicals, Inc., Duranate (registered trademark) 24A-100 is a trade name of Asahi Kasei Chemicals Corporation, and KF-351A, KF-352A, KF-353, KF-640, and X-22-6191 are trade names of Shin-Etsu Chemical Co., Ltd.

[0053] [Table 1]

[0054] [Table 2]

[0055] <Test method and evaluation> The surface protection films of Examples 1 to 9 and Comparative Examples 1 to 9 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, which was used as a sample for measuring gel fraction and surface resistance value. Furthermore, this surface protection film with the adhesive layer exposed was attached to the surface of a polarizing plate attached to a liquid crystal cell via the adhesive layer, and after leaving it for one day, it was autoclaved at 50°C and 5 atmospheres for 20 minutes and then left at room temperature for a further 12 hours to be used as a sample for measuring adhesive strength, peeling electrification voltage and durability.

[0056] <Gel fraction> After aging, the mass of the measurement sample before bonding to the polarizing plate was accurately measured, immersed in toluene for 24 hours, and then filtered through a 200-mesh wire netting. The filtered material was then dried at 100°C for 1 hour, and the mass of the residue was accurately measured, and the gel fraction of the pressure-sensitive adhesive layer (pressure-sensitive adhesive after crosslinking) was calculated using the following formula. Gel fraction (%) = insoluble portion mass (g) / adhesive mass (g) × 100

[0057] <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 speed (0.3 m / min) and a high speed (30 m / min), and the peel strength measured was taken as the adhesive strength.

[0058] <Surface resistance> After aging and before bonding to the polarizing plate, the release film (a silicone resin-coated PET film) was peeled off to expose the adhesive layer, and the surface resistance of the adhesive layer was measured using a resistivity meter, Hiresta UP-HT450 (manufactured by Mitsubishi Chemical Analytech).

[0059] <Peeling electrification voltage> The measurement sample obtained above was peeled off at an angle of 180° at a tensile speed of 30 m / min, and the voltage (charged voltage) generated when the polarizing plate was charged was measured using high-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Corporation). The maximum measured value was taken as the peeling charged voltage.

[0060] <Reworkability> The surface protection film of the measurement sample obtained above was traced with a ballpoint pen (500 g load, 3 strokes back and forth), and then the surface protection film was peeled off from the polarizing plate and the surface of the polarizing plate was observed to confirm that no contamination had been transferred to the polarizing plate. The evaluation criteria were as follows: "○" if there was no contamination transfer to the polarizing plate, "△" if contamination transfer was confirmed in at least a portion along the ballpoint pen trace, and "×" if contamination transfer was confirmed along the ballpoint pen trace and adhesive detachment was confirmed from the adhesive surface.

[0061] <Durability> The measurement samples obtained above were left in an atmosphere of 60°C and 90% RH for 250 hours, then removed to room temperature and left for a further 12 hours, after which the adhesive strength was measured to confirm that there was no significant increase compared to the initial adhesive strength.The evaluation target criteria were as follows: if the adhesive strength after the test was 1.5 times or less of the initial adhesive strength, it was evaluated as "Good", and if it exceeded 1.5 times, it was evaluated as "Poor".

[0062] The evaluation results are shown in Table 3. The surface resistance is expressed in m×10 +n " is expressed as "mE+n" (where m is any real number and n is a positive integer).

[0063] [Table 3]

[0064] The surface protection films of Examples 1 to 9 had an adhesive strength of 0.05 to 0.1 N / 25 mm in a low-speed peeling region of 0.3 m / min, an adhesive strength of 1.0 N / 25 mm or less in a high-speed peeling region of 30 m / min, and a surface resistance of 5.0 × 10 +10 The surface resistance was Ω / □ or less, the peeling electrification voltage was ±0 to 1 kV, and after tracing the surface protection film with a ballpoint pen through the adhesive layer, no contamination was transferred to the adherend, and the film also had excellent durability when left in an atmosphere of 60°C and 90% RH for 250 hours. In other words, it simultaneously satisfies all the requirements: (1) balancing adhesive strength in the low-speed peeling area and the high-speed peeling area, (2) preventing adhesive residue, (3) excellent antistatic properties, and (4) reworkability.

[0065] The surface protection film of Comparative Example 1, possibly because it did not contain (D) polyalkylene glycol mono(meth)acrylate monomer, had low adhesive strength in the low-speed peel region of 0.3 m / min and slightly poor reworkability. In the surface protection film of Comparative Example 2, the adhesive strength in the low-speed peel region of 0.3 m / min and the high-speed peel region of 30 m / min were too high, the peel withstand voltage was high, the reworkability and durability were poor, and the gel fraction was low, probably because the amount of (B) hydroxyl group-containing monomer was too small, the amount of (D) polyalkylene glycol mono(meth)acrylic acid ester monomer was too small, the amount of (E) isocyanate compound was too large, and the HLB value of (I) polyether-modified siloxane compound was too small. The surface protection film of Comparative Example 3 had low adhesive strength in the low-speed peel region of 0.3 m / min, high surface resistance, high peel voltage resistance, and poor durability, possibly due to the presence of an excess of (B) hydroxyl group-containing monomer, an excess of (C) acid-containing monomer, an excess of (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, and an excessively large HLB value of (I) polyether-modified siloxane compound.

[0066] The surface protection film of Comparative Example 4 had low adhesive strength in the low-speed peel region of 0.3 m / min, and was poor in reworkability and durability, possibly because it contained an insufficient amount of (C) acid-containing monomer and did not contain (D) polyalkylene glycol mono(meth)acrylic acid ester monomer. In the surface protection film of Comparative Example 5, the adhesive strength in the low-speed peel region of 0.3 m / min and the high-speed peel region of 30 m / min were too high, the peel withstand voltage was high, the reworkability and durability were poor, and the gel fraction was low, probably because the amount of (B) hydroxyl group-containing monomer was excessive, the amount of (D) polyalkylene glycol mono(meth)acrylic acid ester monomer was too small, and the amount of (E) isocyanate compound was too small. The surface protection film of Comparative Example 6 did not contain (F) crosslinking retarder and contained an excessive amount of (G) crosslinking catalyst, which resulted in a too short pot life and crosslinking proceeding before coating, making it impossible to coat.

[0067] The surface protection film of Comparative Example 7 contained (A) an MA having a C1 alkyl group in a (meth)acrylic acid ester monomer having an alkyl group, (B) an excessive amount of a hydroxyl group-containing monomer, did not contain (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and did not contain (G) a crosslinking catalyst. Perhaps these reasons are due to the fact that the adhesive strength in the low-speed peel region of 0.3 m / min and the adhesive strength in the high-speed peel region of 30 m / min were too high, the surface resistance value was high, the peel resistance voltage was high, and the reworkability and durability were poor. The surface protection film of Comparative Example 8 contained an excessive amount of (D) polyalkylene glycol mono(meth)acrylic acid ester monomer and did not contain (I) polyether-modified siloxane compound. This may be because the adhesive strength in the low-speed peel region of 0.3 m / min and the high-speed peel region of 30 m / min was too high, the surface resistance was high, the peel voltage resistance was high, and the reworkability was somewhat poor. The surface protection film of Comparative Example 9 did not contain (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, the melting point of (H) antistatic agent was less than 30°C (liquid at room temperature), and the amount of (I) polyether-modified siloxane compound was excessive. These factors probably resulted in low adhesive strength in the low-speed peel region of 0.3 m / min, high peel withstand voltage, slightly poor reworkability, and poor durability. As such, the surface protection films of Comparative Examples 1 to 9 were unable to simultaneously satisfy all of the required performance requirements: (1) balancing adhesive strength in the low-speed peeling region and the high-speed peeling region, (2) preventing adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

Claims

1. A pressure-sensitive adhesive composition comprising a copolymer containing (A) a (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 10, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, and (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and further containing (E) a tri- or higher functional isocyanate compound, (H) an antistatic agent, and (I) a polyether-modified siloxane compound, the copolymer contains 0.1 to 5.0 parts by weight of the (B) hydroxyl group-containing copolymerizable monomer, 0.35 to 1.0 part by weight of the (C) carboxyl group-containing copolymerizable monomer, and 1 to 20 parts by weight of the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, relative to 100 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C10; and the copolymer contains 0.5 to 5.0 parts by weight of the (E) tri- or higher functional isocyanate compound, relative to 100 parts by weight of the copolymer; The pressure-sensitive adhesive composition is characterized in that the polyether-modified siloxane compound (I) is a polyether-modified siloxane compound having an HLB value of 7 to 12, and the polyether-modified siloxane compound (I) is contained in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the copolymer.

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

3. A surface protection film for a polarizing plate, comprising the adhesive film according to claim 2, wherein the adhesive layer is formed on one side of the resin film.

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