Surface protective film for polarizing plates

Abstract

To provide a surface protective film for polarizing plates that offers an excellent balance of adhesive strength at both low and high peeling speeds, good adhesion to polarizing plates despite low adhesive strength, and excellent durability, reworkability, and antistatic performance. [Solution] The adhesive layer is formed by crosslinking an adhesive composition containing (A) an acrylic polymer copolymerized from (A) an alkyl group having C4 to C18 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, (D) a polyalkylene glycol mono(meth)acrylic acid monomer, and (E) an alkoxy group-containing alkyl(meth)acrylate monomer, a trifunctional isocyanate compound, (F) a polyether-modified siloxane compound with an HLB value of 7 to 12, and an antistatic agent.

Description

[Technical Field]

[0001] The present invention relates to a surface protective film for polarizing plates. More specifically, the present invention relates to a surface protective film for polarizing plates that has an excellent balance of adhesive strength at low and high peeling speeds, excellent adhesion to polarizing plates despite low adhesive strength, and excellent durability, reworkability, and antistatic performance. [Background technology]

[0002] Conventionally, in the manufacturing process of optical components such as polarizers and phase difference plates, which are components of liquid crystal displays, a surface protection film is applied to temporarily protect the surface 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 when the optical components are assembled into the liquid crystal display. Because such surface protection films for protecting the surface of optical components are used only in the manufacturing process, they are sometimes commonly referred to as process films.

[0003] In the process of manufacturing optical components, the surface protection film used is an optically transparent polyethylene terephthalate (PET) resin film with an adhesive layer formed on one side. However, a release film, which has been treated to protect the adhesive layer, is laminated on top of the adhesive layer until it is bonded to the optical component. Furthermore, optical components such as polarizing plates and phase difference plates undergo product inspections that include optical evaluations of the liquid crystal display's display capability, hue, contrast, and foreign matter contamination while the surface protective film is attached. Therefore, the required performance of the surface protective film is that the adhesive layer is free of air bubbles and foreign matter. Furthermore, in recent years, there have been concerns that the static electricity generated when peeling the adhesive layer off optical components such as polarizing plates and phase difference plates may affect the electrical control circuits of liquid crystal displays, leading to a demand for adhesive layers with superior antistatic properties. Furthermore, when bonding surface protective films to optical components such as polarizers and phase difference plates, it is sometimes necessary to peel off the surface protective film and reapply it for various reasons. In such cases, ease of removal from the optical component (reworkability) is required. Furthermore, when the surface protective film is finally peeled off from optical components such as polarizers and phase difference plates, it is required that it can be peeled off quickly. In other words, even with high-speed peeling, it is required that the adhesive strength does not change much with the peeling speed so that it can be peeled off quickly.

[0004] Thus, in recent years, the required performance of the adhesive layer constituting surface protective films has been to include (i) balancing adhesive strength at both low and high peeling speeds, (ii) excellent antistatic performance, and (iii) reworkability, in order to enhance ease of use when using surface protective films.

[0005] For example, (i) regarding balancing the adhesive force at low and high peeling speeds, the following proposals are known.

[0006] Acrylic adhesive layers, primarily composed of a copolymer of an alkyl (meth)acrylate having an alkyl group with 7 or fewer carbon atoms and a copolymerizable compound containing a carboxyl group, and crosslinked with a crosslinking agent, have problems such as the adhesive transferring to the adherend during long-term adhesion and a significant increase in adhesive strength over time. To avoid this, an adhesive layer is known in which a copolymer of an alkyl (meth)acrylate having an alkyl group with 8 to 10 carbon atoms and a copolymerizable compound having an alcoholic hydroxyl group is used, and this copolymer is crosslinked with a crosslinking agent (Patent Document 1). Furthermore, it has been proposed that a small amount of copolymer of (meth)acrylate alkyl ester and a carboxyl group-containing copolymerizable compound is added to the copolymer similar to the above, and that this copolymer is crosslinked with a crosslinking agent to form an adhesive layer. However, when these are used for surface protection of plastic sheets with low surface tension and smooth surfaces, problems such as peeling due to heating during processing or storage, and poor re-peelability when peeled off at high speeds, which is the domain of manual work, have been reported.

[0007] To solve these problems, an adhesive composition has been proposed in which a copolymer of monomer mixtures is obtained by adding a crosslinking agent in an amount equivalent to or greater than the carboxyl groups of component b) above, to a) 100 parts by weight of an alkyl (meth)acrylate mainly composed of an alkyl (meth)acrylate having an alkyl group having 8 to 10 carbon atoms, b) 1 to 15 parts by weight of a copolymerizable compound containing a carboxyl group, and c) 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms (Patent Document 2). The adhesive composition described in Patent Document 2 does not exhibit peeling phenomena such as lifting during processing or storage, and furthermore, it has a small increase in adhesive strength over time and excellent re-peelability, and can be re-peeled with little force even after long-term storage, especially in a high-temperature atmosphere, without leaving any adhesive residue on the adherend, and can also be re-peeled with little force even when peeled at high speed.

[0008] Furthermore, (ii) regarding excellent antistatic performance, methods for imparting antistatic performance to surface protective films include kneading an antistatic agent into a base film. Examples of antistatic agents 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 sulfonic acid bases, sulfate ester bases, phosphate ester bases, and phosphonic acid bases; (c) amphoteric antistatic agents such as amino acid-based and amino sulfate ester-based agents; (d) nonionic antistatic agents such as amino alcohol-based, glycerin-based, and polyethylene glycol-based agents; and (e) polymer-type antistatic agents with high molecular weights, such as the above-mentioned antistatic agents (Patent Document 3). Furthermore, in recent years, it has been proposed to incorporate such antistatic agents into the base film, or to directly incorporate them into the adhesive layer rather than applying them to the surface of the base film.

[0009] Furthermore, (iii) regarding reworkability, for example, an adhesive composition has been proposed in which an isocyanate compound curing agent and a specific silicate oligomer are blended in an acrylic resin at a concentration of 0.0001 to 10 parts by weight per 100 parts by weight of the acrylic resin (Patent Document 4). Patent Document 4 states that the main monomer component is an alkyl acrylate with an alkyl group having 2 to 12 carbon atoms, or an alkyl methacrylate with an alkyl group having 4 to 12 carbon atoms, and that other functional group-containing monomer components, such as carboxyl group-containing monomers, may also be included. Generally, it is preferable to contain 50% by weight or more of the above main monomer, and it is desirable that the content of the functional group-containing monomer component be 0.001 to 50% by weight, preferably 0.001 to 25% by weight, and more preferably 0.01 to 25% by weight. The adhesive composition described in Patent Document 4 is said to have reworkability because it exhibits little change in cohesive force and adhesive force over time even at high temperatures or high temperature and high humidity, and also shows excellent adhesion to curved surfaces. Generally, making the adhesive layer softer tends to result in adhesive residue and reduced reworkability. In other words, it becomes difficult to peel off and reapply if applied incorrectly. Therefore, it is considered necessary to crosslink monomers with functional groups such as carboxyl groups as the main component to give the adhesive layer a certain hardness in order to maintain 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 [Overview of the project] [Problems that the invention aims to solve]

[0011] In recent years, there has been a rapid increase in the size of various displays, such as liquid crystal displays (LCDs). However, with the increase in screen size of LCDs, new problems are arising in the manufacturing process of LCD components. For example, the following problems are occurring with surface protection films for polarizing plates, which are laminated to the surface of polarizing plates to protect them. In conventional technology, in the manufacturing process of polarizing plates, which are components of liquid crystal displays, when peeling off the surface protective film from the polarizing plate after it has been bonded to the polarizing plate, the desire to make it easier to peel off has been met by reducing the adhesive strength of the adhesive layer formed on the surface protective film. However, if the adhesive strength of the adhesive layer is reduced to make it easier to peel the surface protection film from the adherend, the adhesion of the surface protection film to the polarizing plate decreases. Therefore, with the increase in the size of the liquid crystal display, when the size of the polarizing plate becomes larger than before, there is a problem that the surface protection film peels off at the edge of the polarizing plate.

[0012] The present invention has been made in view of the above circumstances, and an object thereof is to provide a surface protection film for a polarizing plate which has an excellent balance of adhesive strength at a low peeling speed and a high peeling speed, has good adhesion to the polarizing plate despite having a small adhesive strength, and is excellent in durability, reworkability, and antistatic performance.

Means for Solving the Problems

[0013] In order to solve the above problems, the present invention provides a surface protection film for a polarizing plate, on one side of a resin film, an adhesive layer is formed by crosslinking an adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent, wherein the acrylic polymer is a copolymer obtained by copolymerizing: (A) at least one (meth)acrylic acid ester monomer having an alkyl group with 4 to 18 carbon atoms; (B) at least one copolymerizable monomer containing a hydroxyl group; (C) at least one copolymerizable monomer containing a carboxyl group; (D) at least one polyalkylene glycol mono(meth)acrylate monomer; and (E) at least one nitrogen-containing vinyl monomer not containing a hydroxyl group or an alkoxy group-containing alkyl (meth)acrylate monomer; the crosslinking agent is a trifunctional isocyanate compound; the adhesive composition further contains (F) a polyether-modified siloxane compound having an HLB value of 7 to 12; and the surface protection film for a polarizing plate, cut to a size of 25 mm in width × 35 mm in length, is bonded to a polarizing plate subjected to an AG treatment, and no displacement occurs in a shear retention force test for the polarizing plate, which is carried out by applying a load of 500 g and leaving it standing in an atmosphere at 23°C for 24 hours.

[0014] Further, the present invention provides a surface protective film for a polarizing plate, on one side of which an adhesive layer is formed by crosslinking an adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent. The acrylic polymer is a copolymer obtained by copolymerizing: (A) at least one or more (meth)acrylic acid ester monomers having an alkyl group with 4 to 18 carbon atoms in a total amount of 100 parts by weight; (B) at least one or more copolymerizable monomers containing a hydroxyl group in a total amount of 2 to 10 parts by weight; (C) at least one or more copolymerizable monomers containing a carboxyl group in a total amount of 0.05 to 0.3 parts by weight; (D) at least one or more polyalkylene glycol mono(meth)acrylate monomers in a total amount of 3 to 40 parts by weight; and (E) at least one or more nitrogen-containing vinyl monomers or alkoxy group-containing alkyl (meth)acrylate monomers not containing a hydroxyl group in a total amount of 0.1 to 20 parts by weight. The crosslinking agent is a trifunctional isocyanate compound. The adhesive composition further contains, with respect to 100 parts by weight in total of at least one or more (meth)acrylic acid ester monomers having an alkyl group with 4 to 18 carbon atoms in the above (A), at least one or more polyether-modified siloxane compounds having an HLB value of 7 to 12 in a proportion of 0.001 to 0.5 parts by weight. The surface protective film for a polarizing plate, which is cut into a size of 25 mm in width × 35 mm in length and laminated on a polarizing plate subjected to AG treatment, is characterized in that there is no deviation in the shear holding force test for the polarizing plate, which is carried out by applying a load of 500 g and leaving it standing in an atmosphere at 23°C for 24 hours.

[0015] The (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from the group of compounds consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate, wherein the average number of repeating alkylene oxides constituting the polyalkylene glycol chain is 3 to 14, the diester content in the monomer is 0.2% or less, the water content is 0.1% or less, and the solubility in water is preferably such that the haze value in a 20% aqueous solution is 2% or less.

[0016] Preferably, the copolymerizable monomer containing the hydroxyl group (B) is at least one selected from the group of compounds 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.

[0017] Preferably, the copolymerizable monomer containing the (C) carboxyl group is at least one selected from the group of compounds consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid.

[0018] Preferably, the trifunctional isocyanate compound is at least one compound selected from the group consisting of isocyanurate of a hexamethylene diisocyanate compound, isocyanurate of an isophorone diisocyanate compound, adduct of a hexamethylene diisocyanate compound, adduct of an isophorone diisocyanate compound, burette of a hexamethylene diisocyanate compound, burette of an isophorone diisocyanate compound, isocyanurate of a tolylene diisocyanate compound, isocyanurate of a xylylene diisocyanate compound, isocyanurate of a hydrogenated xylylene diisocyanate compound, adduct of a tolylene diisocyanate compound, adduct of a xylylene diisocyanate compound, and adduct of a hydrogenated xylylene diisocyanate compound.

[0019] Preferably, the (J) antistatic agent is an ionic compound that is solid at 25°C with a melting point of 25 to 50°C, and is contained in the adhesive composition in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of at least one (meth)acrylic acid ester monomer having C4 to C18 carbon atoms in the (A) alkyl group, with a total of 100 parts by weight.

[0020] Preferably, the adhesive strength of the adhesive layer to the polarizing plate at a low peeling speed of 0.3 m / min is 0.04 to 0.2 N / 25 mm, and the adhesive strength at a high peeling speed of 30 m / min is 2.0 N / 25 mm or less.

[0021] The surface resistivity of the adhesive layer is 9.0 × 10 +11 It is preferable that the impedance is Ω / □ or less and the stripping band voltage is ±0 to 0.5kV.

[0022] It is preferable that the side of the resin film opposite to the side on which the adhesive layer is formed is treated with an antistatic and antifouling treatment. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a surface protective film for polarizing plates that has an excellent balance of adhesive strength at low and high peeling speeds, good adhesion to polarizing plates despite low adhesive strength, and excellent durability, reworkability, and antistatic performance. [Modes for carrying out the invention]

[0024] The present invention will be described below based on preferred embodiments. The polarizing plate surface protection film of the present invention is a surface protection film for polarizing plates in which an adhesive layer is formed on one side of a resin film by crosslinking an adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent, wherein the acrylic polymer comprises (A) at least one (meth)acrylic acid ester monomer having C4 to C18 alkyl groups, (B) at least one copolymerizable monomer containing a hydroxyl group, (C) at least one copolymerizable monomer containing a carboxyl group, (D) at least one polyalkylene glycol mono(meth)acrylic acid ester monomer, and (E) containing a hydroxyl group. The surface protective film for polarizing plates is characterized by no displacement in a shear strength test against a polarizing plate, which is performed by applying a load of 500g to a polarizing plate and leaving it for 24 hours in an atmosphere at 23°C with an AG treatment, and is cut to dimensions of 25 mm wide x 35 mm long, and laminated onto an AG-treated polarizing plate.

[0025] Furthermore, the polarizing plate surface protection film of the present invention is a surface protection film for polarizing plates in which an adhesive layer is formed on one side of a resin film by crosslinking an adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent, wherein the acrylic polymer is (A) 100 parts by weight of at least one (meth)acrylic acid ester monomer having C4 to C18 alkyl groups, (B) 2 to 10 parts by weight of at least one copolymerizable monomer containing a hydroxyl group, (C) 0.05 to 0.3 parts by weight of at least one copolymerizable monomer containing a carboxyl group, (D) 3 to 40 parts by weight of at least one polyalkylene glycol mono(meth)acrylic acid ester monomer, and (E) nitrogen-containing vinyl monomer or alkoxy-containing monomer that does not contain a hydroxyl group. The adhesive composition comprises a copolymer obtained by copolymerizing 0.1 to 20 parts by weight of at least one type of acrylic (meth)acrylate monomer, the crosslinking agent being a trifunctional isocyanate compound, and the adhesive composition further contains (A) 0.001 to 0.5 parts by weight of at least one type of polyether-modified siloxane compound having an HLB value of 7 to 12, per 100 parts by weight of at least one type of (meth)acrylic acid ester monomer having C4 to C18 in the alkyl group, and the adhesive composition comprises (F) 0.001 to 0.5 parts by weight of at least one type of polyether-modified siloxane compound having an HLB value of 7 to 12, and is bonded to an AG-treated polarizing plate, cut to dimensions of 25 mm wide x 35 mm long, and subjected to a shear holding force test on the polarizing plate, in which a load of 500 g is applied and left for 24 hours in an atmosphere of 23°C.

[0026] (A) Examples of (meth)acrylic acid ester monomers with C4 to C18 in the alkyl group include butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and undecyl Examples include methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, myristyl methacrylate, isomiristyl methacrylate, cetyl methacrylate, isocetyl methacrylate, stearyl methacrylate, and isostearyl methacrylate.

[0027] (B) Examples of copolymerizable monomers containing hydroxyl groups 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. (A) It is preferable to contain at least one (meth)acrylic acid ester monomer having C4 to C18 alkyl groups in a total of 100 parts by weight of (B) at least one copolymerizable monomer containing a hydroxyl group in a ratio of 2 to 10 parts by weight, more preferably 3.5 to 10 parts by weight, and particularly preferably 4.2 to 10 parts by weight.

[0028] (C) Preferably, the copolymerizable monomer containing a carboxyl group is at least one selected from the group of compounds consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid. (A) It is preferable that the mixture contains at least one copolymerizable monomer containing a carboxyl group in a proportion of 0.05 to 0.3 parts by weight, more preferably 0.05 to 0.25 parts by weight, and particularly preferably 0.05 to 0.2 parts by weight, per 100 parts by weight of at least one (meth)acrylic acid ester monomer having C4 to C18 in the alkyl group.

[0029] (D) The polyalkylene glycol mono(meth)acrylic acid ester monomer can be any compound in which one of the multiple hydroxyl groups of the polyalkylene glycol is esterified as a (meth)acrylic acid ester. Since the (meth)acrylic acid ester group is a polymerizable group, it can be copolymerized with the main polymer. The other hydroxyl groups may remain as OH groups, or they may be alkyl ethers such as methyl ether or ethyl ether, or saturated carboxylic acid esters such as acetate esters, etc. The alkylene groups in polyalkylene glycol include, but are not limited to, ethylene groups, propylene groups, 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 copolymer may be a block copolymer or a random copolymer.

[0030] (D) The polyalkylene glycol mono(meth)acrylic acid monomer preferably has an average repeating number of alkylene oxides constituting the polyalkylene glycol chain of 3 to 14. The "average repeating number of alkylene oxides" is the average number of repeating alkylene oxide units in the "polyalkylene glycol chain" portion included in the molecular structure of (D) polyalkylene glycol mono(meth)acrylic acid monomer.

[0031] (D) The polyalkylene glycol mono(meth)acrylic acid ester monomer preferably has a diester content of 0.2% or less, a water content of 0.1% or less, and a haze value of 2% or less in a 20% aqueous solution. "Diester content in monomer" refers to the content (by weight) of polyalkylene glycol di(meth)acrylic acid ester contained in the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer. "Moisture content" refers to the percentage (by weight) of water contained in (D) polyalkylene glycol mono(meth)acrylic acid ester monomer. "Haze value in 20% aqueous solution" refers to the haze value (%) of an aqueous solution containing (D) polyalkylene glycol mono(meth)acrylic acid monomer in a 20% by weight aqueous solution. In other words, (D) polyalkylene glycol mono(meth)acrylic acid monomer must not only have sufficient water solubility to form a 20% aqueous solution, but also have a low haze value (%) in the 20% aqueous solution (less turbidity). In this specification, the haze value of a 20% aqueous solution is the value measured by placing the aqueous solution in a quartz cell with a path length of 10 mm and using a haze meter. This index was introduced to select highly hydrophilic monomers that yield a solution without turbidity even at high concentrations, as it represents the degree of hydrophilicity of (D) polyalkylene glycol mono(meth)acrylic acid ester monomers.

[0032] (D) The polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from the group of compounds 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, methoxypolyethylene glycol Examples include polybutylene glycol-(meth)acrylate, methoxy-polypropylene glycol-polybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-polybutylene glycol-(meth)acrylate; ethoxypolyethylene glycol-(meth)acrylate, ethoxypolypropylene glycol-(meth)acrylate, ethoxypolybutylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polypropylene glycol-polybutylene glycol-(meth)acrylate, and ethoxypolyethylene glycol-polypropylene glycol-polybutylene glycol-(meth)acrylate.

[0033] (A) It is preferable to contain at least one (meth)acrylic acid ester monomer having C4 to C18 alkyl groups in a total of 100 parts by weight of at least one (meth)acrylic acid ester monomer in a total of 3 to 40 parts by weight of at least one (D) polyalkylene glycol mono(meth)acrylic acid ester monomer in a total of 3 to 30 parts by weight, and particularly preferable to contain at least 5 to 30 parts by weight of at least one (meth)acrylic acid ester monomer in a total of 10

[0034] Acrylic polymers may further contain (E) at least one nitrogen-containing vinyl monomer or alkoxy-group-containing alkyl (meth)acrylate monomer that does not contain a hydroxyl group. Of (E), (E-1) nitrogen-containing vinyl monomers include vinyl monomers containing an amide bond, vinyl monomers containing an amino group, and vinyl monomers having a nitrogen-containing heterocyclic structure. More specifically, N-vinyl-substituted heterocyclic structures such as N-vinyl-2-pyrrolidone, N-vinylpyrrolidone, methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-vinyllaurillolactam. Cyclic nitrogen vinyl compounds having a structure; such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperazine, N-(meth)acryloylaziridine, N-(meth)acryloylazetidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylpiperidine, N-(meth)acryloylazepane, and N-(meth)acryloylazokane, which have an N-(meth)acryloyl-substituted heterocyclic structure. Cyclic nitrogen vinyl compounds; cyclic nitrogen vinyl compounds having a heterocyclic structure with a nitrogen atom and an ethylene-based unsaturated bond in the ring, such as N-cyclohexylmaleimide and N-phenylmaleimide; unsubstituted or monoalkyl-substituted (meth)acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and Nt-butyl(meth)acrylamide; dialkyl-substituted (meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropylacrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N-ethyl-N-methyl(meth)acrylamide, N-methyl-N-propyl(meth)acrylamide, and N-methyl-N-isopropyl(meth)acrylamide;Dialkylamino(meth)acrylates such as N,N-dimethylaminomethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminoisopropyl(meth)acrylate, N,N-dimethylaminobutyl(meth)acrylate, N,N-diethylaminomethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N-ethyl-N-methylaminoethyl(meth)acrylate, N-methyl-N-propylaminoethyl(meth)acrylate, N-methyl-N-isopropylaminoethyl(meth)acrylate, N,N-dibutylaminoethyl(meth)acrylate, t-butylaminoethyl(meth)acrylate, etc.; N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N Examples include N,N-dialkyl-substituted aminopropyl(meth)acrylamides such as N-dipropylaminopropyl(meth)acrylamide, N,N-diisopropylaminopropyl(meth)acrylamide, N-ethyl-N-methylaminopropyl(meth)acrylamide, N-methyl-N-propylaminopropyl(meth)acrylamide, and N-methyl-N-isopropylaminopropyl(meth)acrylamide; N-vinyl carboxylic acid amides such as N-vinylformamide, N-vinylacetamide, and N-vinyl-N-methylacetamide; (meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-ethoxyethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone acrylamide, and N,N-methylenebis(meth)acrylamide; and unsaturated carboxylic acid nitriles such as (meth)acrylonitrile.

[0035] (E-1) Nitrogen-containing vinyl monomers are preferably those that do not contain hydroxyl groups, and more preferably those that do not contain hydroxyl groups and carboxyl groups. Preferred monomers for this purpose include the monomers exemplified above, for example, acrylic monomers containing N,N-dialkyl-substituted amino groups or N,N-dialkyl-substituted amide groups; N-vinyl-substituted lactams such as N-vinyl-2-pyrrolidone, N-vinylcaprolactam, and N-vinyl-2-piperidone; and N-(meth)acryloyl-substituted cyclic amines such as N-(meth)acryloylmorpholine and N-(meth)acryloylpyrrolidine.

[0036] Of (E), the (E-2) alkoxy group-containing alkyl (meth)acrylate monomers include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-propoxyethyl (meth)acrylate, 2-isopropoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-methoxypropyl (meth)acrylate, 2-ethoxypropyl (meth)acrylate, 2-propoxypropyl (meth)acrylate, 2-isopropoxypropyl (meth)acrylate, and 2- Examples include toxypropyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 3-propoxypropyl (meth)acrylate, 3-isopropoxypropyl (meth)acrylate, 3-butoxypropyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, 4-ethoxybutyl (meth)acrylate, 4-propoxybutyl (meth)acrylate, 4-isopropoxybutyl (meth)acrylate, and 4-butoxybutyl (meth)acrylate. These alkoxy-containing alkyl (meth)acrylate monomers have a structure in which the alkyl group atoms in the alkyl (meth)acrylate are substituted with alkoxy groups.

[0037] (A) At least one (meth)acrylic acid ester monomer having an alkyl group with 4 to 18 carbon atoms, preferably contains a total of 0.1 to 20 parts by weight, more preferably 0.3 to 10 parts by weight, and particularly preferably 0.3 to 8 parts by weight, of at least one of (E) a nitrogen-containing vinyl monomer containing no hydroxyl group or an alkoxy group-containing alkyl (meth)acrylate monomer, based on 100 parts by weight in total. (E-1) A nitrogen-containing vinyl monomer containing no hydroxyl group and (E-2) an alkoxy group-containing alkyl (meth)acrylate monomer can be used alone or in combination of two or more thereof.

[0038] The adhesive composition according to the present invention can contain (F) a polyether-modified siloxane compound having an HLB value of 7 to 12. The polyether-modified siloxane compound is a siloxane compound having a polyether group, and in addition to a normal siloxane unit [-SiR 1 2-O-], it has a siloxane unit [-SiR 1 (R 2 O(R 3 O) n R 4 )-O-] having a polyether group. Here, R 1 is one or more alkyl groups or aryl groups, R 2 and R 3 are one or more alkylene groups, and R 4 represents one or more alkyl groups, acyl groups, etc. (terminal groups). Examples of the polyether group include polyoxyethylene groups [(C2H4O) n and polyoxypropylene groups [(C3H6O) n , etc., that is, polyoxyalkylene groups.

[0039] (A) Preferably, the product contains (F) at least one polyether-modified siloxane compound with an HLB value of 7 to 12 in a ratio of 0.001 to 0.5 parts by weight per 100 parts by weight of at least one (meth)acrylic acid ester monomer having an alkyl group with C4 to C18. More preferably, the ratio is 0.01 to 0.5 parts by weight. The HLB value is the hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) as defined in, for example, JIS K3211 (Surfactant Terminology).

[0040] Polyether-modified siloxane compounds can be obtained, for example, by grafting an organic compound having unsaturated bonds and polyoxyalkylene groups onto a polyorganosiloxane main chain having silicon hydride groups via a hydrosilylation reaction. Specifically, examples include dimethylsiloxane-methyl(polyoxyethylene)siloxane copolymer, dimethylsiloxane-methyl(polyoxyethylene)siloxane-methyl(polyoxypropylene)siloxane copolymer, and dimethylsiloxane-methyl(polyoxypropylene)siloxane polymer. The HLB value of the polyether-modified siloxane compound can be adjusted by selecting the ratio of polyether groups to siloxane groups. (F)By incorporating a polyether-modified siloxane compound with an HLB value of 7 to 12 into an adhesive composition, the adhesive strength and rework performance of the adhesive can be improved.

[0041] The trifunctional isocyanate compound can be at least one or more polyisocyanate compounds selected from those having three isocyanate (NCO) groups in one molecule. Polyisocyanate compounds can be classified into aliphatic isocyanates, aromatic isocyanates, acyclic isocyanates, and alicyclic isocyanates, and any of these is acceptable.

[0042] Examples of trifunctional isocyanate compounds include bifunctional isocyanate compounds (compounds having two NCO groups in one molecule), such as bifunctional isocyanate compounds, isocyanurate compounds, and adduct compounds (polyol-modified compounds) with trivalent or higher polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane (TMP) and glycerin.

[0043] The trifunctional isocyanate compound is preferably at least one selected from the group of compounds consisting of isocyanurate derivatives of hexamethylene diisocyanate compounds, isocyanurate derivatives of isophorone diisocyanate compounds, adduct derivatives of hexamethylene diisocyanate compounds, adduct derivatives of isophorone diisocyanate compounds, burette derivatives of hexamethylene diisocyanate compounds, burette derivatives of isophorone diisocyanate compounds, isocyanurate derivatives of tolylene diisocyanate compounds, isocyanurate derivatives of xylylene diisocyanate compounds, isocyanurate derivatives of hydrogenated xylylene diisocyanate compounds, adduct derivatives of tolylene diisocyanate compounds, adduct derivatives of xylylene diisocyanate compounds, and adduct derivatives of hydrogenated xylylene diisocyanate compounds. (A) It is preferable that the mixture contains at least one trifunctional isocyanate compound in a ratio of 0.1 to 10 parts by weight, and more preferably 0.1 to 6 parts by weight, per 100 parts by weight of at least one (meth)acrylic acid ester monomer having C4 to C18 in the alkyl group.

[0044] A crosslinking catalyst can be any substance that functions as a catalyst for the reaction (crosslinking reaction) between an acrylic polymer and a crosslinking agent when a polyisocyanate compound is used as the crosslinking agent. Examples include amine compounds such as tertiary amines, metal chelate compounds, organotin compounds, organolead compounds, organozinc compounds, and other organometallic compounds. Examples of tertiary amines include trialkylamines, N,N,N',N'-tetraalkyldiamines, N,N-dialkylamino alcohols, triethylenediamines, morpholine derivatives, and piperazine derivatives.

[0045] A metal chelate compound is a compound in which one or more polydentate ligands L are bonded to a central metal atom M. A metal chelate compound may or may not have one or more monodentate ligands X bonded to the metal atom M. For example, the general formula for a metal chelate compound with one metal atom M is M(L) m (X) n When expressed as , m≧1 and n≧0. If m is 2 or greater, the m Ls may be the same ligand or different ligands. If n is 2 or greater, the n Xs may be the same ligand or different ligands.

[0046] Examples of metal atoms M include Fe, Ni, Mn, Cr, V, Ti, Ru, Zn, Al, Zr, and Sn. Examples of polydentate ligand L include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, as well as β-diketones such as acetylacetone (also known as 2,4-pentanedione), 2,4-hexanedione, and benzoylacetone. These are ketoenol tautomer compounds, and in the case of polydentate ligand L, the enol may be deprotonated enolates (e.g., acetylacetonate). Examples of monodentate ligand X include halogen atoms such as chlorine and bromine atoms, acyloxy groups such as pentanoyl, hexanoyl, 2-ethylhexanoyl, octanoyl, nonanoyl, decanoyl, dodecanoyl, and octadecanoyl groups, and alkoxy groups such as methoxy, ethoxy, n-propoxy, isopropoxy, and butoxy groups.

[0047] Specific examples of metal chelating compounds include tris(2,4-pentanedionato)iron(III), iron trisacetylacetonate, titanium trisacetylacetonate, ruthenium trisacetylacetonate, zinc bisacetylacetonate, aluminum trisacetylacetonate, zirconium tetrakisacetylacetonate, tris(2,4-hexanedionato)iron(III), bis(2,4-hexanedionato)zinc, tris(2,4-hexanedionato)titanium, tris(2,4-hexanedionato)aluminum, and tetrakis(2,4-hexanedionato)zirconium.

[0048] Examples of organotin compounds include dialkyltin oxides, fatty acid salts of dialkyltin, and fatty acid salts of stannous tin. The crosslinking catalyst is preferably a metal chelate compound or an organotin compound. Preferred metal chelate compounds include aluminum chelate compounds, titanium chelate compounds, iron chelate compounds, and tin chelate compounds. The organotin compound is preferably at least one compound selected from the group consisting of dioctyl tin oxide and dioctyl tin dilaurate. (A) Preferably, the crosslinking catalyst is contained in a ratio of 0.001 to 0.5 parts by weight per 100 parts by weight of at least one (meth)acrylic acid ester monomer having C4 to C18 in the alkyl group.

[0049] Examples of ketoenol tautomer compounds include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, as well as β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. In adhesive compositions using polyisocyanate compounds as crosslinking agents, ketoenol tautomer compounds can block the isocyanate groups of the crosslinking agent, thereby suppressing excessive viscosity increases and gelation of the adhesive composition after the addition of the crosslinking agent, and extending the pot life of the adhesive composition. Preferably, the ketoenol tautomer compound is at least one compound selected from the group consisting of acetylacetone and ethyl acetoethyl. (A) It is preferable that the mixture contains at least one ketoenol tautomer compound in a ratio of 0.1 to 300 parts by weight, and more preferably 1.0 to 30.0 parts by weight, per 100 parts by weight of at least one (meth)acrylic acid ester monomer having C4 to C18 alkyl groups.

[0050] Since ketoenol tautomer compounds have the opposite effect of crosslinking catalysts, inhibiting crosslinking, it is preferable to appropriately set the ratio of ketoenol tautomer compounds to crosslinking catalysts. To extend the pot life of the adhesive composition and improve storage stability, it is preferable that the weight ratio of crosslinking catalyst to ketoenol tautomer compounds (ketoenol tautomer compound / crosslinking catalyst) be 70 to 1000.

[0051] (J) The antistatic agent is preferably an ionic compound that is solid at 25°C and has a melting point of 25 to 50°C. In this invention, as an antistatic agent (J), an ionic compound that is solid at 25°C and has a melting point of 25 to 50°C is added to the adhesive composition. These antistatic agents (J) are presumed to have high affinity with acrylic polymers because they have a low melting point and contain long-chain alkyl groups.

[0052] (J) Examples of antistatic agents include ionic compounds that are solid at 25°C and have a melting point of 25-50°C, which are included in the adhesive composition.

[0053] Ionic compounds that are solid at 25°C with a melting point of 25-50°C include ionic compounds having a cation and anion, where the cation is a nitrogen-containing onium cation such as pyridinium cation, imidazolium cation, pyrimidinium cation, pyrazolium cation, pyrrolidinium cation, ammonium cation, phosphonium cation, sulfonium cation, etc., and the anion is hexafluoride phosphate (PF6) -), thiocyanate (SCN - ), alkylbenzene sulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - Examples include inorganic or organic anionic compounds such as bis(fluorosulfonyl)imide salts (FSI), bis(trifluoromethanesulfonyl)imide salts (TFSI), and trifluoromethanesulfonates (TF). It is preferable that the compound be solid at room temperature (e.g., 25°C), and by selecting the chain length of the alkyl group, the position and number of substituents, a compound with a melting point of 25 to 50°C can be obtained. The cation is preferably a quaternary nitrogen-containing onium cation, and examples include quaternary pyridinium cations such as 1-alkylpyridinium (the carbon atoms at positions 2 to 6 may have substituents or be unsubstituted), quaternary imidazolium cations such as 1,3-dialkylimidazolium (the carbon atoms at positions 2, 4, and 5 may have substituents or be unsubstituted), and quaternary ammonium cations such as tetraalkylammonium. (A) Preferably, the mixture contains at least one ionic compound that is solid at 25°C and has a melting point of 25 to 50°C in a ratio of 0.01 to 5.0 parts by weight per 100 parts by weight of at least one (meth)acrylic acid ester monomer having an alkyl group with C4 to C18 carbon atoms.

[0054] (J) Specific examples of antistatic agents are not limited to those mentioned above. Examples of ionic compounds that are solid at 25°C and have a melting point of 25-50°C include 1-octylpyridinium hexafluoride phosphate, 1-nonylpyridinium hexafluoride phosphate, 2-methyl-1-dodecylpyridinium hexafluoride phosphate, 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 1-dodecylpyridinium dodecylbenzenesulfonate, and 4-methyl-1-octylpyridinium hexafluoride phosphate.

[0055] Furthermore, other known additives containing alkylene oxides, such as copolymerizable (meth)acrylic monomers, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing accelerators, plasticizers, fillers, curing retarders, processing aids, anti-aging agents, and antioxidants, can be appropriately blended as other components. These can be used individually or in combination of two or more.

[0056] The acrylic polymer used in the adhesive composition of the present invention is a copolymer obtained by copolymerizing (A) at least one (meth)acrylic acid ester monomer having C4 to C18 in its alkyl group, (B) at least one copolymerizable monomer containing a hydroxyl group, and (C) at least one copolymerizable monomer containing a carboxyl group. Alternatively, the acrylic polymer may be a copolymer obtained by copolymerizing (A) at least one (meth)acrylic acid ester monomer having C4 to C18 in its alkyl group, (B) at least one copolymerizable monomer containing a hydroxyl group, (C) at least one copolymerizable monomer containing a carboxyl group, (D) at least one polyalkylene glycol mono(meth)acrylic acid ester monomer, and (E) at least one nitrogen-containing vinyl monomer or alkoxy-group-containing alkyl(meth)acrylate monomer that does not contain a hydroxyl group. The polymerization method of the acrylic polymer is not particularly limited, and appropriate polymerization methods such as solution polymerization and emulsion polymerization can be used. The adhesive composition of the present invention can be further prepared by blending the above-mentioned acrylic polymer with a polyether-modified siloxane compound having a (F)HLB value of 7 to 12, a trifunctional isocyanate compound as a crosslinking agent, an ionic compound that is solid at 25°C with a melting point of 25 to 50°C as an antistatic agent, and any other additive as appropriate.

[0057] When manufacturing acrylic polymers, it is preferable to carry out the polymerization reaction under anhydrous conditions, such as solution polymerization using an anhydrous organic solvent, in order to reduce the incorporation of water into the adhesive composition. In particular, (D) polyalkylene glycol mono(meth)acrylic acid ester monomer has high hydrophilicity, so it is preferable to use one with a low water content. In order to avoid an increase in the viscosity of the adhesive composition, it is preferable to minimize the amount of polyfunctional (bifunctional or more) monomers that can function as crosslinking agents in each monomer used in the production of the main acrylic polymer. In particular, for (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, since the corresponding diester component is a di(meth)acrylic acid ester of a bifunctional monomer, it is preferable to use one with a low diester content.

[0058] The acrylic polymer preferably contains acrylic monomers such as (meth)acrylic acid ester monomers, (meth)acrylic acid, and (meth)acrylamides in a proportion of 50 to 100 parts by weight per 100 parts by weight of the acrylic polymer. Furthermore, the acid value of the acrylic polymer is preferably 0.01 to 8.0. This improves stain resistance and enhances the ability to prevent adhesive residue. Here, "acid value" is one of the indicators that represents the acid content, and is expressed as the number of milligrams of potassium hydroxide required to neutralize 1 gram of polymer containing carboxyl groups.

[0059] Preferably, the adhesive strength of the crosslinked adhesive layer on the polarizing plate is 0.04 to 0.2 N / 25 mm at a low peeling speed of 0.3 m / min, and 2.0 N / 25 mm or less at a high peeling speed of 30 m / min. This provides performance in which the adhesive strength does not change much with the peeling speed, and enables quick peeling even at high peeling speeds. Furthermore, when peeling off the surface protective film for reapplication, it does not require excessive force and is easy to peel off from the adherend.

[0060] The adhesive layer formed by crosslinking the aforementioned adhesive composition has a surface resistivity of 9.0 × 10 +11 The resistivity is preferably Ω / □ or less, and the peel band voltage is preferably ±0 to 0.5kV. In this invention, "±0 to 0.5kV" means 0 to -0.5kV and 0 to +0.5kV, i.e., -0.5 to +0.5kV. If the surface resistivity is high, the ability to dissipate static electricity generated by charging during peeling is poor. Therefore, by making the surface resistivity sufficiently low, the peel band voltage generated by static electricity when the adhesive layer is peeled off by the adherend is reduced, and it is possible to suppress the effect on the electrical control circuit of the adherend, etc.

[0061] The gel fraction of the adhesive layer formed by crosslinking the aforementioned adhesive composition is preferably 95 to 100%. This high gel fraction prevents excessive adhesion at low peeling speeds, reduces the elution of unpolymerized monomers or oligomers from the acrylic polymer, improves reworkability and durability at high temperatures and humidity, and suppresses contamination of the adherend.

[0062] An adhesive film can be obtained by forming an adhesive layer, formed by crosslinking the aforementioned adhesive composition, on one or both sides of a resin film. Furthermore, the polarizing plate surface protection film of the present invention is a surface protection film in which an adhesive layer, formed by crosslinking the aforementioned adhesive composition, is formed on one side of a resin film. The polarizing plate surface protection film of the present invention exhibits no slippage in shear holding force tests when bonded to a polarizing plate, good adhesion to the polarizing plate despite low adhesive strength, and excellent durability, reworkability, and antistatic performance. For this reason, it can be suitably used as a surface protection film for polarizing plates. Examples of polarizing plates include glare, plain (general purpose), and anti-glare (AG). Examples of protective film materials for the surface of the polarizing plate include TAC-based films (triacetylcellulose compounds) and acrylic films.

[0063] For example, the test conditions for shear holding strength include a load (mass of weight) of 500g, an ambient temperature of 23°C, and a standing time of 24 hours. These test conditions are suitable as a guideline for determining whether the adhesion of the surface protective film to the polarizing plate is good. The contact area (dimensions) of the surface protective film for polarizing plates to the polarizing plate, which is the adherend in the shear holding strength test, is 25mm x 35mm. Details of the test method (apparatus, etc.) may be in accordance with, for example, the holding strength test in JIS Z 0237 (Test Method for Adhesive Tapes and Adhesive Sheets).

[0064] For the resin film that serves as the base material for the adhesive layer, and for the release film (separator) that protects the adhesive surface, resin films such as polyester film can be used. The resin film used as the base material can be treated on the side opposite to the side where the adhesive layer is formed with silicone-based or fluorine-based release agents or coating agents, or with antifouling treatments such as silica microparticles, or with antistatic treatments such as application or mixing of antistatic agents. The release film is treated with a release agent, such as a silicone-based or fluorine-based release agent, on the side that comes into contact with the adhesive surface of the adhesive layer. [Examples]

[0065] The present invention will be specifically described below with reference to examples.

[0066] <Manufacturing of acrylic polymers> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube to replace the air in the reactor with nitrogen gas. Then, 100 parts by weight of 2-ethylhexyl acrylate, 8.0 parts by weight of 8-hydroxyoctyl acrylate, 0.1 parts by weight of acrylic acid, 8 parts by weight of polypropylene glycol monoacrylate (average number of repeats of alkylene oxide constituting the polyalkylene glycol chain n=12, diester content in monomer is 0.1%, solubility in water is 0.8% haze value in a 20% aqueous solution, water content is 0.05%), and 1 part by weight of N-vinylpyrrolidone, along with 60 parts by weight of solvent (ethyl acetate). Subsequently, 0.1 parts by weight of azobisisobutyronitrile was added dropwise over 2 hours as a polymerization initiator, and the reaction was carried out at 65°C for 6 hours to obtain an acrylic polymer solution with a weight-average molecular weight of 500,000, which was used in Example 1. A portion of the acrylic polymer was taken and used as a sample for measuring the acid value, as described later. [Examples 2-8 and Comparative Examples 1-4] Except for the monomer compositions being as described in (A) to (E) of Table 1, the acrylic polymer solutions used in Examples 2 to 8 and Comparative Examples 1 to 4 were obtained in the same manner as the acrylic polymer solution used in Example 1 above.

[0067] <Manufacturing of adhesive compositions and surface protective films> [Example 1] To the acrylic polymer solution of Example 1 prepared as described above, 0.05 parts by weight of a polyether-modified siloxane compound (HLB value 7), 1.0 part by weight of 1-octylpyridinium hexafluoride phosphate, and 8.5 parts by weight of acetylacetone were added and stirred. Then, 4.0 parts by weight of Coronate HX (isocyanurate of a hexamethylene diisocyanate compound) and 0.1 parts by weight of titanium trisacetylacetonate were added and stirred to obtain the adhesive composition of Example 1. This 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 to obtain an adhesive sheet with an adhesive layer thickness of 25 μm. Subsequently, an adhesive sheet was transferred to the side of a polyethylene terephthalate (PET) film that had been treated with antistatic and antifouling properties on one side, opposite to the side that had been treated with antistatic and antifouling properties, thereby obtaining the 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 2-8 and Comparative Examples 1-4] Except for using additive compositions as described in (F) to (J) of Table 2, surface protective films for Examples 2 to 8 and Comparative Examples 1 to 4 were obtained in the same manner as the surface protective film for Example 1 described above.

[0068] In Tables 1 and 2, the proportions of each component are shown in parentheses, calculated using a total of 100 parts by weight for group (A). Tables 3 and 4 show the compound names of the abbreviated symbols used for each component in Tables 1 and 2. Note that Coronate® HX, HL, and L are trade names of Nippon Polyurethane Industry Co., Ltd., and Takenate® D-140N, D-127N, D-110N, and D-120N are trade names of Mitsui Chemicals, Inc. For group (D) in Table 3, the value of "n" is the average number of repeats of alkylene oxide constituting the polyalkylene glycol chain. The value of "diester" is the diester content (%) in the monomer. The value of "moisture" is the moisture content (%). The value of "haze" is the haze value (%) in a 20% aqueous solution.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] [Table 4]

[0073] <Test Methods and Evaluation> The surface protective films from Examples 1-8 and Comparative Examples 1-4 were aged for 7 days at 23°C and 50% RH. After aging, the release film (silicone resin-coated PET film) was peeled off to expose the adhesive layer, which was then used as the sample for measuring gel fraction and surface resistivity. Furthermore, this surface protection film with the adhesive layer exposed was bonded to the surface of a polarizing plate attached to a liquid crystal cell via the adhesive layer, left for one day, then autoclaved at 50°C, 5 atmospheres for 20 minutes, and left at room temperature for another 12 hours. This was used as a sample for measuring adhesive strength, peel voltage, shear holding force (slip), reworkability, and durability. The polarizing plate to be bonded was a polarizing plate with an anti-glare (AG) treatment on its surface.

[0074] <Gel fraction> After aging, the mass of the adhesive layer separated from the sample before bonding to the polarizing plate was accurately measured, immersed in toluene for 24 hours, and then filtered through a 200-mesh wire mesh. After drying the filtrate at 100°C for 1 hour, the mass of the residue was accurately measured, and the gel fraction of the adhesive layer (adhesive layer after crosslinking) was calculated using the following formula. Gel fraction (%) = Mass of insoluble portion (g) / Mass of adhesive layer (g) × 100

[0075] <Adhesive strength> The sample obtained above (a 25 mm wide surface protective film bonded to the surface of a polarizing plate with an AG treatment) was peeled off in the 180° direction using a tensile testing machine at a low peeling speed (0.3 m / min) and a high peeling speed (30 m / min), and the measured peel strength was defined as the adhesive strength (N / 25 mm).

[0076] <Surface resistivity> After aging, before bonding to the polarizing plate, the release film (silicone resin-coated PET film) was peeled off to expose the adhesive layer, and the surface resistivity (Ω / □) of the adhesive layer was measured using a resistivity meter, Hi-Resta UP-HT450 (manufactured by Mitsubishi Chemical Analytec).

[0077] <Strip voltage> The sample obtained above was peeled 180° at a tensile speed of 30 m / min. The voltage (band voltage) generated by the charging of the AG-treated polarizing plate on its surface was measured using high-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Corporation), and the maximum measured value was defined as the peeled band voltage (kV). <Shear holding force for polarizing plates> A polarizing plate with an anti-glare (AG) treatment on its surface was bonded to a surface protection film (with an adhesive layer thickness of 20 μm) cut to dimensions of 25 mm wide x 35 mm long. A load of 500 g was applied to the surface protection film bonded to the polarizing plate in a 23°C atmosphere, and the displacement (mm) of the surface protection film was measured after 24 hours.

[0078] <Reworkability> After tracing the surface protective film of the measurement sample obtained above with a ballpoint pen (load 500g, 3 back-and-forth strokes), the surface protective film was peeled off 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 criteria were as follows: "○" if there was no contamination transfer to the polarizing plate, "△" if contamination transfer was confirmed at least partially along the traced path of the ballpoint pen, and "×" if contamination transfer was confirmed along the traced path of the ballpoint pen and the adhesive was also confirmed to have detached from the adhesive surface.

[0079] <Durability> The sample obtained above was left in an atmosphere of 60°C and 90% RH for 250 hours, then removed to room temperature and left for another 12 hours. The adhesive strength was then measured and confirmed to be no significant increase compared to the initial adhesive strength. The evaluation 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 "○"; if it exceeded 1.5 times, it was evaluated as "×".

[0080] Table 5 shows the evaluation results. Note that the surface resistivity is "m × 10 +n This was expressed using the formula "mE+n" (where m is an arbitrary real number and n is a positive integer). Furthermore, the displacements listed in Table 5 represent the measured displacement (mm) of the surface protective film during the shear holding force test on the polarizing plate.

[0081] [Table 5]

[0082] The surface protective films in Examples 1-8 exhibited an adhesive strength of 0.04-0.2 N / 25mm to the polarizing plate at a low peeling speed of 0.3 m / min, an adhesive strength of 2.0 N / 25mm or less at a high peeling speed of 30 m / min, and a surface resistivity of 9.0 × 10⁻⁶. +11 The resistance was less than Ω / □, the delamination voltage was ±0 to 0.5kV, there was no displacement in the shear holding strength test after being left at 23°C for 24 hours with a load of 500g, there was no contamination transfer to the substrate after tracing the surface protective film with a ballpoint pen through the adhesive layer, and it also showed excellent durability when left in a 60°C, 90%RH atmosphere for 250 hours. In other words, (1) despite its low adhesive strength, it has good adhesion to polarizing plates, (2) it is durable, (3) it is reworkable, and (4) it has excellent antistatic properties, thus simultaneously meeting all the required performance characteristics.

[0083] The surface protective film of Comparative Example 1 had (C) an excessive amount of copolymerizable monomers containing carboxyl groups, the acrylic polymer did not contain (D) polyalkylene glycol mono(meth)acrylic acid ester monomers, the adhesive composition did not contain (F) polyether-modified siloxane compounds with an HLB value of 7 to 12, (G) an insufficient amount of trifunctional isocyanate compounds, and (J) no antistatic agent, resulting in excessively high adhesive strength at low peeling speeds of 0.3 m / min and high peeling speeds of 30 m / min, high surface resistivity and peel band voltage, shear retention force tests showed displacement, and poor reworkability and durability.

[0084] The surface protective film of Comparative Example 2 had (C) too few copolymerizable monomers containing carboxyl groups, (D) too many diesters of polyalkylene glycol mono(meth)acrylic acid monomers, a high water content, low solubility in water, and (F) too high an HLB value for the polyether-modified siloxane compound, resulting in excessively high adhesive strength at low peeling speeds of 0.3 m / min and high peeling speeds of 30 m / min, high surface resistivity and peel band voltage, and shear retention force tests showed displacement, resulting in poor durability.

[0085] The surface protective film of Comparative Example 3 had an acrylic polymer that (B) did not contain copolymerizable monomers containing hydroxyl groups, (C) contained an excessive amount of copolymerizable monomers containing carboxyl groups, and (D) had a high diester content of polyalkylene glycol mono(meth)acrylic acid ester monomers, resulting in a high water content and low solubility in water. Consequently, it had a low gel fraction, very high adhesion at low peeling speeds of 0.3 m / min and high peeling speeds of 30 m / min, a high peeling voltage despite low surface resistivity, and poor reworkability.

[0086] The surface protective film in Comparative Example 4 had an excessively high HLB value for the (F) polyether-modified siloxane compound, resulting in shear displacement in the shear strength test.

[0087] Thus, the surface protection films in Comparative Examples 1 to 4 failed to simultaneously satisfy all the required performance characteristics, including (1) good adhesion to the polarizing plate despite low adhesive strength, (2) durability, (3) reworkability, and (4) excellent antistatic performance. [Industrial applicability]

[0088] The surface protective film for polarizing plates according to the present invention solves the problem of the conventional technology, where reducing the adhesive strength of the adhesive layer to make the surface protective film easier to peel off from the adherend reduces the adhesion strength of the surface protective film to the polarizing plate. As the size of liquid crystal displays increases and the size of polarizing plates becomes larger than before, the surface protective film peels off at the edges of the polarizing plate. Therefore, it has great industrial value.

Claims

1. A surface protective film for polarizing plates, An adhesive layer is formed on one side of a resin film by crosslinking an adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent which is an ionic compound that is solid at 25°C with a melting point of 25 to 50°C, and whose cation is a 1-alkylpyridinium cation and an anion is a hexafluoride phosphate anion. The aforementioned acrylic polymer (A) 100 parts by mass of at least one (meth)acrylic acid ester monomer having C4 to C18 in the alkyl group, (B) A total of 2 to 10 parts by mass of at least one copolymerizable monomer containing a hydroxyl group, (C) A total of 0.05 to 0.3 parts by mass of at least one copolymerizable monomer containing a carboxyl group, (D) A total of 3 to 40 parts by mass of at least one polyalkylene glycol mono(meth)acrylic acid ester monomer, (E) A copolymer obtained by copolymerizing 0.1 to 20 parts by mass of at least one alkyl (meth)acrylate monomer containing an alkoxy group with the following: The adhesive composition is characterized in that it contains, as a crosslinking agent, a trifunctional isocyanate compound in a proportion of 0.1 to 6 parts by mass per 100 parts by mass of at least one (meth)acrylic acid ester monomer having C4 to C18 in the alkyl group, and further contains, (F) a total of 0.001 to 0.5 parts by mass of at least one polyether-modified siloxane compound having an HLB value of 7 to 12.

2. The polarizing plate surface protection film according to claim 1, wherein one side of the resin film, opposite to the side on which the adhesive layer is formed, is treated with an antistatic treatment and an antifouling treatment.

3. The surface protective film for polarizing plates according to claim 1 or 2, wherein the antistatic agent is at least one selected from the group consisting of 1-octylpyridinium hexafluoride phosphate, 1-nonylpyridinium hexafluoride phosphate, 2-methyl-1-dodecylpyridinium hexafluoride phosphate, and 4-methyl-1-octylpyridinium hexafluoride phosphate.

4. The surface protective film for polarizing plates according to any one of claims 1 to 3, wherein the adhesive composition further contains a crosslinking catalyst and a ketoenol tautomer compound.

5. The surface protective film for polarizing plates according to any one of claims 1 to 4, wherein the trifunctional isocyanate compound is an isocyanurate derivative of a hexamethylene diisocyanate compound.

6. The surface protective film for polarizing plates according to any one of claims 1 to 5, wherein the gel fraction of the adhesive layer is 95 to 100%, the adhesive strength to the polarizing plate at a low peeling speed of 0.3 m / min is 0.04 to 0.2 N / 25 mm, and the adhesive strength at a high peeling speed of 30 m / min is 2.0 N / 25 mm or less.

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