Surface Protection Film

Abstract

To provide a surface that can satisfy all required performances at the same time: (1) balancing of adhesive strength at a low-speed peeling region and a high-speed peeling region, (2) prevention of occurrence of adhesive residue, (3) excellent anti-static performance, and (4) rework performance.SOLUTION: Adhesive strength of an adhesive layer is 0.05-0.1 N / 25 mm in a low-speed peeling region and 1.0 N / 25 mm or less in a high-speed peeling region, the adhesive layer being obtained by crosslinking an adhesive composition comprising: an acrylic copolymer obtained by copolymerizing (A) a (meth)acrylic acid ester monomer having a C4-C10 alkyl group, (B) a copolymerizable monomer having a hydroxyl group, and (C) a copolymerizable monomer having a carboxyl group; (D) a tri- or more functional isocyanate compound; (E) a crosslinking retarder of a keto-enol tautomeric compound; (F) a crosslinking catalyst; (G) an antistatic agent; and (H) a polyether modified siloxane compound having an HLB value of 7-12.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, more particularly to a pressure-sensitive adhesive composition for a surface protection film used to protect the surfaces of optical members such as a polarizing plate and a retardation plate by adhering to the surfaces of optical members such as a polarizing plate and a retardation plate that constitute a liquid crystal display, and to a surface protection film. [Background technology]

[0002] Conventionally, in the manufacturing process of optical members such as polarizing plates and retardation plates that are components of liquid crystal displays, a surface protection film is attached to temporarily protect the surface of the optical member. Such a surface protection film is used only in the manufacturing process of the optical member, and is peeled off and removed from the optical member when the optical member is assembled into a liquid crystal display. Since such a surface protection film for protecting the surface of the optical member is used only in the manufacturing process, it is also generally called a process film.

[0003] The surface protection film used in the process of manufacturing optical components in this manner 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 laminated on top of the adhesive layer to protect the adhesive layer until it is attached to the optical component. In addition, optical components such as polarizing plates and retardation plates are subjected to product inspection involving optical evaluation of the display performance, hue, contrast, and inclusion of foreign matter of the liquid crystal display panel with a surface protection film attached, so the required performance of the surface protection film is that the adhesive layer must be free of air bubbles and foreign matter. Moreover, in recent years, when peeling off a surface protection film from an optical component such as a polarizing plate or a retardation plate, there has been concern that peeling charge generated by static electricity generated when the adhesive layer is peeled off from the adherend may affect failure of the electrical control circuit of the liquid crystal display, and therefore there is a demand for adhesive layers with excellent antistatic performance. In addition, 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 once 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 which it is attached (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 can be peeled off quickly. In other words, it is required that the adhesive strength does not change much depending on the peeling speed so that the film can be peeled off quickly even when peeled off at high speed.

[0004] Thus, in recent years, the performance requirements for the adhesive layer constituting a surface protection film have been set forth in terms of ease of use when using the surface protection film, including (1) a balance of adhesive strength in the low- and high-peel-speed regions, (2) prevention of adhesive residue, (3) excellent antistatic properties, and (4) reworkability. However, while it was possible to satisfy each of the required performance items (1) to (4) for the adhesive layer constituting the surface protection film individually, it was an extremely difficult task to simultaneously satisfy all of the required performance items (1) to (4) for 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] In an acrylic adhesive layer made by crosslinking 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 with a crosslinking agent as the main component, the 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 known adhesive layer is provided using 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 crosslinking the copolymer with a crosslinking agent (Patent Document 1). Also proposed is a copolymer similar to the above, which is mixed with a small amount of a copolymer of an alkyl (meth)acrylate ester and a copolymerizable compound containing a carboxyl group, and is crosslinked with a crosslinking agent to provide an adhesive layer. However, when used for surface protection of a plastic plate or the like that has a low surface tension and a smooth surface, there are problems such as peeling phenomena such as lifting due to heating during processing or storage, and poor removability when peeled at high speeds, which are 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 mainly composed of 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 group in the above component b) (Patent Document 2). The adhesive composition described in Patent Document 2 does not experience peeling phenomena such as lifting during processing or storage, and furthermore, has a small increase in adhesive strength over time and is excellent in removability; it can be peeled off with little force even after long-term storage, particularly long-term storage under a high-temperature atmosphere, without leaving any adhesive residue on the adherend, and can be peeled off with little force even when peeled off at high speed.

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

[0009] Regarding (4) rework performance, 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). In Patent Document 4, it is described that the main monomer component is an acrylic acid alkyl ester having an alkyl group with about 2 to 12 carbon atoms or a methacrylic acid alkyl ester having an alkyl group with about 4 to 12 carbon atoms, and that it may contain other functional group-containing monomer components such as a carboxyl group-containing monomer. In general, it is preferable to contain 50% by weight or more of the main monomer, and it is desirable that the content of the functional group-containing monomer component is 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 because the change in cohesive strength and adhesive strength over time is small even at high temperature or high temperature and high humidity, and it also shows excellent effect in curved surface adhesive strength. In general, when the adhesive layer is made soft, it is easy for adhesive residue to occur and reworkability is easily reduced. In other words, when it is applied incorrectly, it is difficult to peel off and difficult to reapply. For this reason, it is considered necessary to crosslink a monomer having a functional group such as a carboxyl group to 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 (1) a balance of adhesive strength in the low-speed peel region and the high-speed peel region, (2) prevention of adhesive residue, (3) excellent antistatic performance, and (4) rework performance. Although it has been possible to satisfy each of the required performances (1) to (4) individually, it has been difficult and unrealizable to simultaneously satisfy all of the required performances (1) to (4) required of the adhesive layer of the surface protection film.

[0012] The present invention has been made in consideration 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 can simultaneously satisfy all of the required performances: (1) balancing the adhesive strength in low-speed peeling areas and high-speed peeling areas, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a copolymer comprising (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, and (C) a copolymerizable monomer containing a carboxyl group, and further comprising (D) a tri- or higher functional isocyanate compound, (E) a crosslinking retarder, (F) a crosslinking catalyst, (G) an antistatic agent, and (H) a polyether-modified siloxane compound having an HLB value of 7 to 12, The adhesive composition includes 0.1 to 5.0 parts by weight of the (B) copolymerizable monomer containing a hydroxyl group and 0.35 to 1.0 parts by weight of the (C) copolymerizable monomer containing a carboxyl group, relative to 100 parts by weight of a (meth)acrylic acid ester monomer having a carbon number of C4 to C10 in the group, and the (D) tri- or higher functional isocyanate compound includes at least one selected from a hexamethylene diisocyanate compound and an isophorone diisocyanate compound. The present invention also provides a surface protection film using the pressure-sensitive adhesive composition. Effect of the Invention

[0014] According to the present invention, it is possible to provide a pressure-sensitive adhesive composition and a surface protection film that can simultaneously satisfy all the required performance requirements: (1) balancing the adhesive strength in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] 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 component is a copolymer containing (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, and (C) a copolymerizable monomer containing a carboxyl group, and further contains (D) a tri- or higher functional isocyanate compound, (E) a crosslinking retarder, (F) a crosslinking catalyst, (G) an antistatic agent, and (H) a polyether-modified siloxane compound.

[0016] (A) Examples of the (meth)acrylic acid ester monomer 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.

[0017] (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, as well as 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 0.1 to 5.0 parts by weight of the (B) copolymerizable monomer containing a hydroxyl group is contained 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 (absence of these is acceptable), and is preferably 0 to 0.9 parts by weight.

[0018] The (C) 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 (C) 0.35 to 1.0 part by weight of 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.

[0019] (D) 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 products and isocyanurate modified products of 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 trivalent or higher polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane and glycerin. (D) The trifunctional or higher isocyanate compound is a polyisocyanate compound having at least three isocyanate (NCO) groups in one 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. (D) The trifunctional or higher 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.

[0020] Examples of the (E) 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 ketoenol tautomer compounds, and in a pressure-sensitive adhesive composition using a polyisocyanate compound as a crosslinking agent, they can block the isocyanate group 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 crosslinking retarder (E) is preferably a keto-enol tautomeric compound, and more preferably at least one selected from the group consisting of acetylacetone and ethyl acetoacetate. The crosslinking retarder (E) is preferably contained in an amount of 1.0 to 5.0 parts by weight based on 100 parts by weight of the copolymer.

[0021] The (F) 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 of the crosslinking catalyst 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 organotin compound include dialkyltin oxide, fatty acid salts of dialkyltin, and fatty acid salts of stannous tin. The crosslinking catalyst (F) is preferably an organotin compound, and more preferably at least one selected from the group consisting of dioctyltin oxide and dioctyltin dilaurate. The crosslinking catalyst (F) is preferably contained in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the copolymer.

[0022] The (G) antistatic agent is preferably solid at room temperature (e.g., 30°C), and more specifically, is preferably an ionic compound having a melting point of 30 to 80°C, contained in an amount of 0.5 to 5.0 parts by weight relative to 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 1.0 to 5.0% by weight. In the present invention, as the (G) antistatic agent, (G1) an ionic compound having a melting point of 30 to 80°C is added to the copolymer, or (G2) a quaternary ammonium salt-type acrylic monomer having a melting point of 30 to 80°C is copolymerized in the copolymer. These (G) antistatic agents are presumed to have high affinity with the acrylic copolymer because they have low melting points and long-chain alkyl groups.

[0023] (G1) Ionic compounds having a melting point of 30 to 80°C include ionic compounds having a cation and an anion, the cation being 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, a phosphonium cation, or a sulfonium cation, and the anion being a hexafluorophosphate (PF 6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC 6 H4 SO 3 - ), perchlorate (ClO 4 - ), tetrafluoroborate (BF 4 - ) and other inorganic or organic anion compounds. By selecting the chain length of the alkyl group, the position and number of the substituent, and other factors, it is possible to obtain compounds having a melting point of 30 to 80°C. The cation is preferably a quaternary nitrogen-containing onium cation, and examples thereof include quaternary pyridinium cations such as 1-alkylpyridinium (wherein the carbon atoms at positions 2 to 6 may be substituted or unsubstituted), quaternary imidazolium cations such as 1,3-dialkylimidazolium (wherein the carbon atoms at positions 2, 4, and 5 may be substituted or unsubstituted), and quaternary ammonium cations such as tetraalkylammonium.

[0024] (G2) 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, the cation being (meth)acryloyloxyalkyltrialkylammonium [R 3 N + -C n H 2n -OCOCQ=CH 2 , where Q=H or CH 3 , R = alkyl], and the anion is hexafluorophosphate (PF 6 - ), thiocyanate (SCN - ), organic sulfonates (RSO 3 - ), perchlorate (ClO 4 - ), tetrafluoroborate (BF 4 - ) and other inorganic or organic anions. Specific examples of the (G) antistatic agent 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, dimethylaminomethylacrylate methyl hexafluorophosphate [(CH 3 ) 3 N + CH 2 OCOCH=CH 2 ·PF 6 - ] etc.

[0025] (H) Polyether-modified siloxane compounds are siloxane compounds having polyether groups, and do not contain the usual siloxane unit [-SiR 1 2 In addition to the siloxane unit [-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 4 indicates one or more alkyl groups, acyl groups, etc. (terminal groups). The polyether group is a polyoxyethylene group [(C 2 H 4 O) n ] and polyoxypropylene group [(C 3 H 6 O) n ] and the like polyoxyalkylene groups. The polyether-modified siloxane compound (H) is a polyether-modified siloxane compound having an HLB value of 7 to 12, and the content of the polyether-modified siloxane compound (H) 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 (terminology for surfactants). 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 a silicon hydride group by 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 (H) polyether-modified siloxane compound in the pressure-sensitive adhesive composition, the adhesive strength and rework performance of the pressure-sensitive adhesive can be improved.

[0026] Furthermore, as other components, known additives such as copolymerizable (meth)acrylic monomers containing alkylene oxides, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing accelerators, plasticizers, fillers, curing retarders, processing aids, antioxidants, antioxidants, etc. can be appropriately blended. These can be used alone or in combination of two or more kinds.

[0027] 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, and (C) a copolymerizable monomer containing a carboxyl group. 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 a quaternary ammonium salt type acrylic monomer (G2) is used as the antistatic agent (G), 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, and (G2) a quaternary ammonium salt type acrylic monomer. The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above-mentioned copolymer with (D) a trifunctional or higher isocyanate compound, (E) a crosslinking retarder, (F) a crosslinking catalyst, (G) an antistatic agent, (H) a polyether-modified siloxane compound, and further any additives as appropriate. Note that when (G2) a quaternary ammonium salt-type acrylic monomer having a melting point of 30 to 80°C is polymerized in the copolymer as the main component, (G) an antistatic agent may or may not be further added to the copolymer.

[0028] 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 peeling region of 0.3 m / min, and an adhesive strength of 1.0 N / 25 mm or less in a high-speed peeling region of 30 m / min. This provides performance in which the adhesive strength changes little depending on the peeling speed, and allows for rapid peeling even at high-speed peeling. In addition, even when the surface protection film is peeled off once for re-adhesion, excessive force is not required, and it is easy to peel off from the adherend.

[0029] 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 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. If the surface resistivity is high, the performance of dissipating static electricity generated by charging during peeling is poor. Therefore, by making the surface resistivity sufficiently small, the peeling electrification voltage generated by static electricity generated when the pressure-sensitive adhesive layer is peeled off from the adherend is reduced, and it is possible to suppress the influence on the electric control circuit of the adherend.

[0030] The gel fraction of the pressure-sensitive adhesive layer (crosslinked pressure-sensitive adhesive) obtained by crosslinking the pressure-sensitive adhesive composition of the present invention is preferably 95 to 100%. With such a high gel fraction, the adhesive strength in the low-speed peeling region is not excessively high, the elution of unpolymerized monomers or oligomers from the copolymer is reduced, reworkability and durability at high temperatures and high humidity are improved, and contamination of the adherend can be suppressed.

[0031] The adhesive film of the present invention is formed by forming an adhesive layer formed by crosslinking the adhesive composition of the present invention on one side or both sides of a resin film. The surface protection film of the present invention is formed by forming an adhesive layer formed by crosslinking the adhesive composition of the present invention on one side of a resin film. The adhesive composition of the present invention contains the above-mentioned components (A) to (H) in a well-balanced manner, and therefore can simultaneously satisfy all the required performances of (1) balancing the adhesive strength in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance (no contamination transfer to the adherend after tracing the surface protection film with a ballpoint pen through the adhesive layer). Therefore, it can be suitably used as a surface protection film for a polarizing plate.

[0032] As the base film of the pressure-sensitive adhesive layer and the release film (separator) that protects the pressure-sensitive 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, or silica microparticles or the like, or an antistatic treatment by coating or kneading 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 is to be joined to the adhesive surface of the adhesive layer. EXAMPLES

[0033] The present invention will now be described in detail with reference to examples.

[0034] <Production of Acrylic Copolymer> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a 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, and 60 parts of a solvent (ethyl acetate) were added to the reactor. Then, 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator was dropped over 2 hours, and the mixture was reacted at 65°C for 6 hours to obtain 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 (C), respectively.

[0035] <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) produced as described above, 1.5 parts by weight of 1-octylpyridinium hexafluorophosphate, 0.1 parts by weight of KF-351A (polyether-modified siloxane compound with HLB=12), and 2.5 parts by weight of acetylacetone were added and stirred, and then 1.5 parts by weight of Coronate HX (isocyanurate of hexamethylene diisocyanate compound) and 0.02 parts by weight of dioctyltin dilaurate were added and stirred to obtain an adhesive composition of Example 1. This adhesive composition was applied onto a release film made of a silicone resin-coated polyethylene terephthalate (PET) film, and the solvent was removed by drying at 90° C. to obtain an adhesive sheet with an adhesive layer thickness of 25 μm. Thereafter, an adhesive sheet was transferred to the side opposite the antistatic and antifouling treated side of a polyethylene terephthalate (PET) film having one side treated with antistatic and antifouling treatment, thereby obtaining a surface protection film of Example 1 having a laminate 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 as shown in Table 1 (D) to (H), respectively.

[0036] In Table 1, the compounding ratio of each component is shown in parentheses in parts by weight, calculated with the total of group (A) being 100 parts by weight. The compound names of the abbreviations of each component used in Table 1 are shown in Table 2. Note that Coronate (registered trademark) HX and Coronate HL are product names of Nippon Polyurethane Industry Co., Ltd., Takenate (registered trademark) D-140N is a product name of Mitsui Chemicals, Inc., Duranate (registered trademark) 24A-100 is a product name of Asahi Kasei Chemicals Corporation, and KF-351A, KF-352A, KF-353, KF-640, and X-22-6191 are product names of Shin-Etsu Chemical Co., Ltd.

[0037] [Table 1]

[0038] [Table 2]

[0039] <Test methods and evaluation> The surface protection films in Examples 1 to 9 and Comparative Examples 1 to 9 were aged for 7 days under 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 the 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 prepare a sample for measuring adhesive strength, peeling electrification voltage and durability.

[0040] <Gel fraction> After aging, the mass of the measurement sample before bonding to the polarizing plate was accurately measured, and it was immersed in toluene for 24 hours and then filtered through a 200-mesh wire screen. The filtered material was then dried at 100°C for 1 hour, and the mass of the residue was accurately measured to calculate the gel fraction of the adhesive layer (adhesive after crosslinking) using the following formula. Gel fraction (%) = insoluble portion mass (g) / adhesive mass (g) × 100

[0041] <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 at a low speed (0.3 m / min) and a high speed (30 m / min) using a tensile tester, and the peel strength measured was taken as the adhesive strength.

[0042] <Surface resistance> After aging and before bonding to a 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).

[0043] <Peeling charge 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 by the charging of the polarizing plate 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.

[0044] <Reworkability> After tracing the surface protection film of the measurement sample obtained above with a ballpoint pen, the surface protection film was peeled off from the polarizing plate and the surface of the polarizing plate was observed to confirm that there was no contamination transfer to the polarizing plate. The evaluation target criteria were as follows: "○" indicates that there was no contamination transfer to the polarizing plate, and "×" indicates that contamination transfer was confirmed in at least a part of the path traced with the ballpoint pen.

[0045] <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 another 12 hours, after which the adhesive strength was measured and it was confirmed that there was no clear 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 "○", and if it exceeded 1.5 times, it was evaluated as "×".

[0046] The evaluation results are shown in Table 3. The surface resistance is expressed as "m×10 +n " is expressed as "mE+n" (where m is any real value and n is a positive integer).

[0047] [Table 3]

[0048] 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 peeling charge voltage was less than Ω / □, the peeling charge 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 low-speed peeling areas and high-speed peeling areas, (2) preventing adhesive residue, (3) excellent antistatic properties, and (4) reworkability.

[0049] The surface protection film of Comparative Example 1 had low adhesive strength in the low-speed peel region of 0.3 m / min, possibly due to the excessive amount of (B) hydroxyl group-containing monomer. 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 adhesive strength in the high-speed peel region of 30 m / min were too high, the peel resistance voltage was high, the reworkability and durability were poor, and the gel fraction was low, possibly because the amount of (B) hydroxyl group-containing monomer was too small, the amount of (D) isocyanate compound was too large, and the HLB value of (H) polyether-modified siloxane compound was too small. In the surface protection film of Comparative Example 3, the adhesive strength in the low peel speed region of 0.3 m / min was low, the surface resistance value was high, the peel resistance voltage was high, and the reworkability and durability were poor, possibly due to the presence of an excess of (B) hydroxyl group-containing monomer, an excess of (C) acid-containing monomer, and an excessively large HLB value of (H) polyether-modified siloxane compound.

[0050] In the surface protection film of Comparative Example 4, the adhesive strength in the low-speed peel region of 0.3 m / min was low and the durability was poor, possibly because the amount of (C) acid-containing monomer was insufficient. 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 adhesive strength in the high-speed peel region of 30 m / min were too high, the peel resistance voltage was high, the reworkability and durability were poor, and the gel fraction was low, possibly due to an excess of (B) hydroxyl group-containing monomer and an insufficient amount of (D) isocyanate compound. The surface protection film of Comparative Example 6 did not contain the (E) crosslinking retarder and contained an excessive amount of the (F) crosslinking catalyst, which resulted in a too short pot life and crosslinking having progressed before coating, making it impossible to coat the film.

[0051] The surface protection film of Comparative Example 7 contained (A) an MA having an alkyl group at C1 in a (meth)acrylic acid ester monomer having an alkyl group, and did not contain (F) a crosslinking catalyst. Perhaps because of this, 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 was high, the peel resistance voltage was high, and the reworkability and durability were poor. In the surface protection film of Comparative Example 8, the amount of (G) antistatic agent was insufficient and (H) polyether-modified siloxane compound was not blended. Perhaps because of this, 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 peel resistance voltage was high, and the reworkability was poor. In the surface protection film of Comparative Example 9, the melting point of the (G) antistatic agent was less than 30°C (liquid at room temperature) and the (H) polyether-modified siloxane compound was in excess, which may be because the adhesive strength in the low-speed peel region of 0.3 m / min was low, the peel resistance voltage was high, and the durability was poor. Thus, the surface protection films of Comparative Examples 1 to 9 were unable to simultaneously satisfy all of the required performance requirements: (1) balancing the adhesive strength in the low-speed peel area and the high-speed peel area, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

Claims

1. A surface protection film comprising a resin film and a pressure-sensitive adhesive layer formed on one side of the resin film, the pressure-sensitive adhesive layer being formed by crosslinking a pressure-sensitive adhesive composition containing an acrylic copolymer, the acrylic copolymer is a copolymer obtained by copolymerizing (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, and (C) a copolymerizable monomer containing a carboxyl group; the pressure-sensitive adhesive composition further comprises: (D) a tri- or higher functional isocyanate compound; (E) a crosslinking retarder of a keto-enol tautomer compound; (F) a crosslinking catalyst; (G) an antistatic agent; and (H) a polyether-modified siloxane compound having an HLB value of 7 to 12; the (B) copolymerizable monomer containing a hydroxyl group is contained in an amount of 0.1 to 5.0 parts by weight, and the (C) copolymerizable monomer containing a carboxyl group is contained in an amount of 0.35 to 1.0 parts by weight, relative to 100 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 10; A surface protection film characterized in that the adhesive layer has a thickness of 25 μm, and has an adhesive strength of 0.05 to 0.1 N / 25 mm in a low-speed peeling region at 0.3 m / min, and an adhesive strength of 1.0 N / 25 mm or less in a high-speed peeling region at 30 m / min.

2. 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 0 to 0.9 parts by weight (it is also permissible if 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are not contained), The surface protective film according to claim 1, characterized in that the (C) copolymerizable monomer containing a carboxyl group is at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate.

3. The surface protective film according to claim 1 or 2, characterized in that, relative to 100 parts by weight of the copolymer, an ionic compound is contained in an amount of 0.5 to 5.0 parts by weight, the (H) polyether-modified siloxane compound having an HLB value of 7 to 12 is contained in an amount of 0.01 to 0.5 parts by weight, the (E) keto-enol tautomer compound crosslinking retarder is contained in an amount of 1.0 to 5.0 parts by weight, and the (F) crosslinking catalyst is an organotin compound, and the (F) crosslinking catalyst is contained in an amount of 0.01 to 0.5 parts by weight relative to 100 parts by weight of the copolymer.

4. 4. The surface protective film according to claim 1, which is used to protect a surface of an optical member.

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