JP7510982B2 - Surface protection film for polarizing plates with AG treatment - Google Patents

Description

The present invention relates to a surface protection film for polarizing plates. More specifically, the present invention relates to a surface protection film for polarizing plates that has an excellent balance of adhesive strength at low and high peeling speeds, has excellent adhesion to polarizing plates despite its low adhesive strength, and also has excellent durability, reworkability, and antistatic properties.

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

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 with a release agent to protect the adhesive layer is attached on top of 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.
Furthermore, when a surface protective film is attached to an optical component such as a polarizing plate or a retardation plate, the surface protective film may be peeled off once and then reattached for various reasons, and in such cases, the surface protective 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.

Thus, in recent years, the performance requirements for the adhesive layer that constitutes the surface protection film include (i) a balance of adhesive strength at low and high peel speeds, (ii) excellent antistatic properties, and (iii) reworkability, etc., which are required in terms of ease of use when using the surface protection film.

For example, (i) the following proposals are known regarding balancing adhesive strength at low and high peel speeds:

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 by 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, a copolymer similar to the above is mixed with a small amount of a copolymer of an alkyl (meth)acrylate ester and a copolymerizable compound containing a carboxyl group, and a pressure-sensitive adhesive layer is provided by crosslinking the copolymer with a crosslinking agent. However, when used for surface protection of a plastic plate or the like having a low surface tension and a smooth surface, there are problems such as peeling phenomenon such as lifting due to heating during processing or storage, and poor removability when peeled at high speed, which is the range of manual work.

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 carboxyl group of the above-mentioned b) component (Patent Document 2).
The adhesive composition described in Patent Document 2 does not undergo peeling phenomena such as lifting during processing or storage, and furthermore, the adhesive strength increases little over time, giving it excellent 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.

As for (ii) excellent antistatic performance, a method of kneading an antistatic agent into a substrate film has been disclosed as a method for imparting antistatic performance to a surface protective film. Examples of the antistatic agent disclosed include (a) various cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups, (b) anionic antistatic agents having anionic groups such as sulfonate groups, sulfate groups, phosphate groups, and phosphonate groups, (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.

As for (iii) reworkability, for example, a pressure-sensitive adhesive composition has been proposed in which an isocyanate compound curing agent and a specific silicate oligomer are blended in an acrylic resin in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the acrylic resin (Patent Document 4).
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 the adhesive strength to curved surfaces is also excellent.
In general, when the adhesive layer is made soft, it is easy for adhesive residue to occur and reworkability to decrease. 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.

Japanese Patent Application Laid-Open No. 63-225677 Japanese Patent Application Laid-Open No. 11-256111 Japanese Patent Application Laid-Open No. 11-070629 Japanese Patent Application Laid-Open No. 8-199130

In recent years, the screen size of various displays such as liquid crystal displays has rapidly increased. However, as the screen size of liquid crystal displays has increased, new problems have arisen in the process of manufacturing components for liquid crystal displays. For example, the following problems have arisen with respect to a surface protection film for polarizing plates, which is attached to the surface of a polarizing plate to protect the polarizing plate.
In the prior art, in the manufacturing process of a polarizing plate, which is a component of a liquid crystal display, after a surface protective film is bonded to an adherend, the polarizing plate, there is a demand for the surface protective film to be easily peeled off from the polarizing plate. This demand has been met by reducing the adhesive strength of the adhesive layer formed on the surface protective film.
However, when the adhesive strength of the adhesive layer is reduced to make it easier to peel the surface protection film from the substrate, the adhesion of the surface protection film to the polarizing plate is reduced. As a result, when the size of the polarizing plate becomes larger than before due to the increase in the screen size of liquid crystal displays, a problem arises in that the surface protection film peels off at the ends of the polarizing plate.

The present invention has been made in consideration of the above circumstances, and aims to provide a surface protection film for polarizing plates that has an excellent balance of adhesive strength at both low and high peel speeds, has good adhesion to polarizing plates despite its low adhesive strength, and has excellent durability, reworkability, and antistatic properties.

In order to solve the above-mentioned problems, the present invention provides a surface protection film for polarizing plates, which comprises a resin film and a pressure-sensitive adhesive layer formed on one side thereof by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent, and the acrylic polymer is selected from the group consisting of (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18, (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) a copolymerizable monomer containing a hydroxyl group. The surface protection film for polarizing plates is characterized in that it is made of a copolymer obtained by copolymerizing at least one of a nitrogen-containing vinyl monomer or an alkoxy group-containing alkyl (meth)acrylate monomer that does not contain a crosslinking agent, the crosslinking agent is a trifunctional isocyanate compound, the pressure-sensitive adhesive composition further contains (F) a polyether-modified siloxane compound having an HLB value of 7 to 12, and shows no deviation in a shear retention test for polarizing plates, which is performed by applying a load of 500 g to the surface protection film for polarizing plates that has been cut to a size of 25 mm wide x 35 mm long and leaving it in an atmosphere at a temperature of 23°C for 24 hours after being attached to an AG-treated polarizing plate.

The present invention also relates to a surface protection film for polarizing plates, comprising a resin film and a pressure-sensitive adhesive layer formed on one side thereof by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent, the acrylic polymer comprising: (A) 100 parts by weight of at least one or more (meth)acrylic acid ester monomers having an alkyl group with a carbon number of C4 to C18; (B) 2 to 10 parts by weight of at least one or more copolymerizable monomers containing a hydroxyl group; (C) 0.05 to 0.3 parts by weight of at least one or more copolymerizable monomers containing a carboxyl group; (D) 3 to 40 parts by weight of at least one or more polyalkylene glycol mono(meth)acrylic acid ester monomers; (E) 3 to 40 parts by weight of at least one or more nitrogen-containing vinyl monomers not containing a hydroxyl group or an alkoxy-containing alkyl(meth)acrylate monomer; The adhesive composition further contains 0.001 to 0.5 parts by weight of at least one polyether-modified siloxane compound (F) having an HLB value of 7 to 12 per 100 parts by weight of at least one (meth)acrylic acid ester monomer (A) having an alkyl group carbon number of C4 to C18. The surface protection film for polarizing plates is characterized in that it shows no deviation in a shear retention test for polarizing plates, which is performed by applying a load of 500 g to the surface protection film for polarizing plates and leaving it in an atmosphere at a temperature of 23°C for 24 hours after being laminated to an AG-treated polarizing plate and cut to a size of 25 mm wide x 35 mm long.

The polyalkylene glycol mono(meth)acrylic acid ester monomer (D) is 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, and preferably has an average repeat number of alkylene oxides constituting the polyalkylene glycol chain of 3 to 14, a diester content in the monomer of 0.2% or less, a moisture content of 0.1% or less, and solubility in water of a haze value of 2% or less in a 20% aqueous solution.

It is preferable that the (B) copolymerizable monomer containing a hydroxyl group 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.

The (C) carboxyl group-containing copolymerizable monomer is preferably at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic 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.

It is preferable that the trifunctional isocyanate compound is at least one selected from the group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, a biuret of an isophorone diisocyanate compound, an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound.

The (J) antistatic agent is preferably an ionic compound that has a melting point of 25 to 50°C and is solid at 25°C, and is contained in the pressure-sensitive 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 an alkyl group carbon number of C4 to C18 (A).

It is preferable that the adhesive layer has an adhesive strength of 0.04 to 0.2 N/25 mm at a low peel speed of 0.3 m/min against the polarizing plate, and an adhesive strength of 2.0 N/25 mm or less at a high peel speed of 30 m/min.

The pressure-sensitive adhesive layer preferably has a surface resistivity of 9.0×10 ⁺¹¹ Ω/□ or less and a peeling electrification voltage of ±0 to 0.5 kV.

It is preferable that one side of the resin film, opposite the side on which the adhesive layer is formed, is subjected to an antistatic treatment and an antifouling treatment.

According to the present invention, it is possible to provide a surface protection film for polarizing plates that has an excellent balance of adhesive strength at both low and high peel speeds, has good adhesion to polarizing plates despite its low adhesive strength, and has excellent durability, reworkability, and antistatic properties.

The present invention will be described below based on preferred embodiments.
The surface protective film for polarizing plates of the present invention is a surface protective film for polarizing plates, which comprises a resin film and a pressure-sensitive adhesive layer formed on one side thereof by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent, and the acrylic polymer is selected from the group consisting of (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, (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 copolymerizable monomer containing a hydroxyl group. and at least one of a nitrogen-containing vinyl monomer not containing a carboxylic acid and an alkoxy group-containing alkyl (meth)acrylate monomer, the crosslinking agent being a trifunctional isocyanate compound, and the pressure-sensitive adhesive composition further containing (F) a polyether-modified siloxane compound having an HLB value of 7 to 12. The surface protection film for polarizing plates is characterized in that it does not slip in a shear retention strength test for polarizing plates, which is performed by applying a load of 500 g to the surface protection film for polarizing plates and leaving it in an atmosphere at a temperature of 23° C. for 24 hours after being attached to a polarizing plate that has been subjected to an AG treatment and cut to a size of 25 mm in width and 35 mm in length.

The surface protection film for polarizing plates 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, and the acrylic polymer is a polymer having a total of 100 parts by weight of at least one or more (meth)acrylic acid ester monomers having an alkyl group with a carbon number of C4 to C18, a total of 2 to 10 parts by weight of at least one or more copolymerizable monomers containing a hydroxyl group, a total of 0.05 to 0.3 parts by weight of at least one or more copolymerizable monomers containing a carboxyl group, a total of 3 to 40 parts by weight of at least one or more polyalkylene glycol mono(meth)acrylic acid ester monomers, and a total of 3 to 40 parts by weight of at least one or more nitrogen-containing vinyl monomers not containing a hydroxyl group or an alkoxy group-containing ... The surface protection film for polarizing plates is characterized in that it is a copolymer obtained by copolymerizing at least one or more (meth)acrylate monomers in total of 0.1 to 20 parts by weight, the crosslinking agent being a trifunctional isocyanate compound, and the pressure-sensitive adhesive composition further contains at least one or more (F) polyether-modified siloxane compounds having 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 or more (meth)acrylic acid ester monomers having an alkyl group carbon number of C4 to C18, and that the surface protection film for polarizing plates is cut to a size of 25 mm wide x 35 mm long and laminated to a polarizing plate that has been subjected to AG treatment, and is left for 24 hours in an atmosphere at a temperature of 23°C, and shows no deviation in a shear retention test for the polarizing plate.

(A) (Meth)acrylic acid ester monomers having an alkyl group with a carbon number of 4 to 18 include butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, myristyl (meth)acrylate, isomyristyl (meth)acrylate, cetyl (meth)acrylate, isocetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, etc.

Examples of the (B) copolymerizable monomer 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 the at least one or more copolymerizable monomers containing a hydroxyl group (B) are contained 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, per 100 parts by weight of the at least one or more (meth)acrylic acid ester monomers (A) having an alkyl group with a carbon number of C4 to C18.

It is preferable that the (C) carboxyl group-containing copolymerizable monomer is at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic 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.
The at least one or more copolymerizable monomers containing a carboxyl group (C) are preferably contained 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 the at least one or more (meth)acrylic acid ester monomers (A) having an alkyl group with a carbon number of 4 to 18.

The polyalkylene glycol mono(meth)acrylic acid ester monomer (D) may be a compound in which one of the hydroxyl groups of a polyalkylene glycol is esterified as a (meth)acrylic acid ester. The (meth)acrylic acid ester group is a polymerizable group, so that it can be copolymerized with the base polymer. The other hydroxyl groups may remain as OH, or may be alkyl ethers such as methyl ether or ethyl ether, or saturated carboxylates such as acetate, etc.
Examples of the alkylene group of the polyalkylene glycol include, but are not limited to, an ethylene group, a propylene group, and a butylene group. The polyalkylene glycol may be a copolymer of two or more polyalkylene glycols, such as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Examples of the copolymer of polyalkylene glycol 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.

The (D) polyalkylene glycol mono(meth)acrylic acid ester monomer preferably has an average repeat number of alkylene oxides constituting the polyalkylene glycol chain of 3 to 14. The "average repeat number of alkylene oxides" refers to the average number of repeats of alkylene oxide units in the "polyalkylene glycol chain" portion contained in the molecular structure of the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer.

As the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, it is preferred that the diester content in the monomer is 0.2% or less, the moisture content is 0.1% or less, and the solubility in water is such that the haze value in a 20% aqueous solution state is 2% or less.
The "diester content in the monomer" refers to the content (wt %) of polyalkylene glycol di(meth)acrylate contained in the polyalkylene glycol mono(meth)acrylate monomer (D).
The "moisture content" refers to the content (wt %) of moisture contained in the polyalkylene glycol mono(meth)acrylic acid ester monomer (D).
The "haze value in a 20% aqueous solution" refers to the haze value (%) of a 20% by weight aqueous solution of the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer. In other words, it is necessary that the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer not only has sufficient water solubility (solubility in water) to form a 20% aqueous solution, but also has a low haze value (%) in the 20% aqueous solution (low cloudiness).
In this specification, the haze value of a 20% aqueous solution is a value measured by placing the aqueous solution in a quartz cell with an optical path length of 10 mm and using a haze meter. This index is introduced to select a highly hydrophilic monomer (D) that can provide a solution that is not cloudy even at a high concentration, as a measure of the hydrophilicity of the polyalkylene glycol mono(meth)acrylic acid ester monomer.

The (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from the group consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate.
More specifically, polyethylene glycol-mono(meth)acrylate, polypropylene glycol-mono(meth)acrylate, polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-mono(meth)acrylate, polyethylene glycol-polybutylene glycol-mono(meth)acrylate, polypropylene glycol-polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-polybutylene glycol-mono(meth)acrylate; methoxypolyethylene glycol-(meth)acrylate, methoxypolypropylene glycol-(meth)acrylate, methoxypolybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, methoxy-polyethylene glycol methoxy-polybutylene glycol-polybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-polybutylene glycol-(meth)acrylate; ethoxy polyethylene glycol-(meth)acrylate, ethoxy polypropylene glycol-(meth)acrylate, ethoxy polybutylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polypropylene glycol-polybutylene glycol-(meth)acrylate, ethoxy-polyethylene glycol-polypropylene glycol-polybutylene glycol-(meth)acrylate, and the like.

For every 100 parts by weight of (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18, it is preferable to contain 3 to 40 parts by weight of (D) at least one polyalkylene glycol mono(meth)acrylic acid ester monomer, more preferably 3 to 30 parts by weight, and particularly preferably 5 to 30 parts by weight.

The acrylic polymer may further contain at least one of (E) nitrogen-containing vinyl monomers not containing a hydroxyl group or alkoxy group-containing alkyl (meth)acrylate monomers. Among (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, vinyl monomers having an N-vinyl-substituted heterocyclic structure such as N-vinyl-2-pyrrolidone, N-vinylpyrrolidone, methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-vinyllaurylolactam may be used. Cyclic nitrogen-containing vinyl compounds: cyclic nitrogen-containing vinyl compounds having an N-(meth)acryloyl-substituted heterocyclic 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)acryloylazocane. cyclic nitrogen-containing vinyl compounds having a heterocyclic structure having a nitrogen atom and an ethylenically unsaturated bond in the ring, such as N-cyclohexylmaleimide and N-phenylmaleimide; unsubstituted or monoalkyl-substituted (meth)acrylamides, such as (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide and N-t-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; N,N-dimethylaminomethyl(meth)acrylamide, 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 and other dialkylamino (meth)acrylates; N,N-dimethylaminopropyl (meth)acrylamide, N,N-diethylaminopropyl (meth)acrylamide, N,N-dipropyl ... N,N-dialkyl-substituted aminopropyl(meth)acrylamide, N,N-diisopropylaminopropyl(meth)acrylamide, N-ethyl-N-methylaminopropyl(meth)acrylamide, N-methyl-N-propylaminopropyl(meth)acrylamide, N-methyl-N-isopropylaminopropyl(meth)acrylamide, etc.; N-vinyl carboxylic acid amides, such as N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide; (meth)acrylamides, such as N-methoxymethyl(meth)acrylamide, N-ethoxyethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-methylenebis(meth)acrylamide; unsaturated carboxylic acid nitriles, such as (meth)acrylonitrile; etc.

(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 or carboxyl groups. Examples of such monomers include the monomers exemplified above, such as acrylic monomers containing N,N-dialkyl-substituted amino groups or N,N-dialkyl-substituted amide groups; N-vinyl-2-pyrrolidone, N-vinylcaprolactam, N-vinyl-2-piperidone, and other N-vinyl-substituted lactams; and N-(meth)acryloylmorpholine, N-(meth)acryloylpyrrolidine, and other N-(meth)acryloyl-substituted cyclic amines.

Among (E), (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, 2-butoxypropyl ... Examples of suitable acrylates include 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 group-containing alkyl (meth)acrylate monomers have a structure in which an atom of an alkyl group in an alkyl (meth)acrylate is substituted with an alkoxy group.

(E) At least one or more nitrogen-containing vinyl monomers not containing a hydroxyl group or at least one or more alkoxy-containing alkyl (meth)acrylate monomers are preferably contained in a ratio 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, per 100 parts by weight of at least one (meth)acrylic acid ester monomer (A) having an alkyl group with carbon number of C4 to C18. (E-1) Nitrogen-containing vinyl monomers not containing a hydroxyl group and (E-2) Alkoxy-containing alkyl (meth)acrylate monomers may each be used alone or in combination of two or more kinds.

The pressure-sensitive adhesive composition according to the present invention may 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 has a siloxane unit having a polyether group [-SiR ¹ ₂ -O-] in addition to a normal siloxane unit [-SiR ¹ (R ² O(R ³ O) _n R ⁴ )-O-]. Here, R ¹ represents one or more alkyl groups or aryl groups, R ² and R ³ represent 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 polyoxyalkylene groups such as polyoxyethylene group [(C ₂ H ₄ O) _n ] and polyoxypropylene group [(C ₃ H ₆ O) _n ].

It is preferable that the total of (F) at least one polyether-modified siloxane compound having an HLB value of 7 to 12 is contained in a ratio of 0.001 to 0.5 parts by weight per 100 parts by weight of (A) at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18. More preferably, it is 0.01 to 0.5 parts by weight. The HLB value is the hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) specified, for example, in JIS K3211 (terminology for surfactants).

The polyether-modified siloxane compound can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group to 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. The HLB value of the polyether-modified siloxane compound can be adjusted by selecting the ratio of the polyether group to the siloxane group. (F) By blending a polyether-modified siloxane compound having an HLB value of 7 to 12 into the adhesive composition, the adhesive strength and rework performance of the adhesive can be improved.

The trifunctional isocyanate compound may be at least one or more selected from polyisocyanate compounds having three isocyanate (NCO) groups in one molecule. Polyisocyanate compounds are classified into aliphatic isocyanates, aromatic isocyanates, acyclic isocyanates, alicyclic isocyanates, etc., and any of them may be used.

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

The trifunctional isocyanate compound is preferably at least one selected from the group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, a biuret of an isophorone diisocyanate compound, an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound.
(A) The at least one or more trifunctional isocyanate compounds are preferably contained in a total amount of 0.1 to 10 parts by weight, and more preferably 0.1 to 6 parts by weight, per 100 parts by weight of the at least one or more (meth)acrylic acid ester monomers having an alkyl group with a carbon number of C4 to C18.

The crosslinking catalyst may be any substance that functions as a catalyst for the reaction (crosslinking reaction) between the acrylic polymer 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, 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-dialkylaminoalcohols, triethylenediamine, morpholine derivatives, and piperazine derivatives.

The metal chelate compound is a compound in which one or more polydentate ligands L are bonded to a central metal atom M. The metal chelate compound may or may not have one or more monodentate ligands X bonded to the metal atom M. For example, when the general formula of a metal chelate compound having one metal atom M is represented by M(L) _m (X) _n , m ≧ 1 and n ≧ 0. When m is 2 or more, m Ls may be the same ligand or different ligands. When n is 2 or more, n Xs may be the same ligand or different ligands.

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

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

Examples of the organotin compound include dialkyltin oxide, 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. As the metal chelate compound, an aluminum chelate compound, a titanium chelate compound, an iron chelate compound, a tin chelate compound, etc. are preferable. As the organotin compound, at least one selected from the group consisting of dioctyltin oxide and dioctyltin dilaurate is preferable.
(A) It is preferable to contain 0.001 to 0.5 parts by weight of at least one crosslinking catalyst per 100 parts by weight of at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18.

Examples of the keto-enol tautomer compound include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, stearyl acetoacetate, etc., and β-diketones such as acetylacetone, 2,4-hexanedione, benzoylacetone, etc. In a pressure-sensitive adhesive composition using a polyisocyanate compound as a crosslinking agent, the keto-enol tautomer compound blocks the isocyanate group of the crosslinking agent, thereby suppressing an excessive increase in viscosity and gelation of the pressure-sensitive adhesive composition after blending with the crosslinking agent, and thereby extending the pot life of the pressure-sensitive adhesive composition.
The keto-enol tautomer compound is preferably at least one selected from the group consisting of acetylacetone and ethyl acetoacetate.
(A) The at least one keto-enol tautomer compound is preferably contained in a total amount of 0.1 to 300 parts by weight, more preferably 1.0 to 30.0 parts by weight, per 100 parts by weight of the at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18.

In contrast to the crosslinking catalyst, the keto-enol tautomer compound has the effect of suppressing crosslinking, so it is preferable to appropriately set the ratio of the keto-enol tautomer compound to the crosslinking catalyst. In order to extend the pot life of the pressure-sensitive adhesive composition and improve its storage stability, it is preferable that the weight ratio of the crosslinking catalyst to the keto-enol tautomer compound (keto-enol tautomer compound/crosslinking catalyst) is 70 to 1000.

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

(J) Examples of antistatic agents include ionic compounds contained in the adhesive composition that have a melting point of 25 to 50°C and are solid at 25°C.

Examples of ionic compounds having a melting point of 25 to 50° C. and that are solid at 25° C. include ionic compounds having a cation and an anion, in which the cation is a nitrogen-containing onium cation such as a pyridinium cation, imidazolium cation, pyrimidinium cation, pyrazolium cation, pyrrolidinium cation, or ammonium cation, or a phosphonium cation, or a sulfonium cation, and the anion is an inorganic or organic anion such as a hexafluorophosphate (PF ₆ ⁻ ), a thiocyanate (SCN ⁻ ), an alkylbenzenesulfonate (RC ₆ H ₄ SO ₃ ⁻ ), a perchlorate (ClO ₄ ⁻ ), a tetrafluoroborate (BF ₄ ⁻ ), a bis(fluorosulfonyl)imide salt (FSI), a bis(trifluoromethanesulfonyl)imide salt (TFSI), or a trifluoromethanesulfonate (TF). It is preferably a solid at room temperature (e.g., 25° C.), and by selecting the chain length of the alkyl group, the position and number of the substituent, etc., it is possible to obtain one having a melting point of 25 to 50° 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.
(A) It is preferable to contain 0.01 to 5.0 parts by weight of at least one or more ionic compounds that have a melting point of 25 to 50° C. and are solid at 25° C., per 100 parts by weight of at least one or more (meth)acrylic acid ester monomers having an alkyl group with a carbon number of C4 to C18.

(J) Specific examples of antistatic agents are not particularly limited, but examples of ionic compounds having a melting point of 25 to 50°C and being solid at 25°C include 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, etc.

In addition, other components may be appropriately blended with known additives such as copolymerizable (meth)acrylic monomers containing alkylene oxides, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, hardening accelerators, plasticizers, fillers, hardening retarders, processing aids, antioxidants, and antioxidants. These may be used alone or in combination of two or more.

The acrylic polymer used in the pressure-sensitive adhesive composition of the present invention is a copolymer obtained by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 18 carbon atoms, (B) at least one copolymerizable monomer containing a hydroxyl group, and (C) at least one copolymerizable monomer containing a carboxyl group. The acrylic polymer may also be a copolymer obtained by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 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)acrylic acid ester monomer, and (E) at least one nitrogen-containing vinyl monomer or alkoxy-containing alkyl(meth)acrylate monomer not containing a hydroxyl group. The polymerization method of the acrylic polymer is not particularly limited, and any appropriate polymerization method such as solution polymerization or emulsion polymerization can be used.
The pressure-sensitive adhesive composition of the present invention can be prepared by further blending the above-mentioned acrylic polymer with (F) a polyether-modified siloxane compound having an HLB value of 7 to 12, a trifunctional isocyanate compound as a crosslinking agent, an ionic compound that has a melting point of 25 to 50° C. and is solid at 25° C. as an antistatic agent, and further with any appropriate additives.

In producing the acrylic polymer, 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 inclusion of moisture in the pressure-sensitive adhesive composition. In particular, it is preferable to use the polyalkylene glycol mono(meth)acrylic acid ester monomer (D) having a low moisture content, since it has high hydrophilicity.
In order to avoid an increase in the viscosity of the adhesive composition, it is preferable to minimize the amount of polyfunctional (bifunctional or higher) monomers that can function as crosslinking agents used in the production of the acrylic polymer base. In particular, it is preferable to use polyalkylene glycol mono(meth)acrylic acid ester monomer (D) with a small diester content, since the corresponding diester content is a di(meth)acrylic acid ester of a bifunctional monomer.

The acrylic polymer preferably contains 50 to 100 parts by weight of an acrylic monomer, such as a (meth)acrylic acid ester monomer, (meth)acrylic acid, or a (meth)acrylamide, based on 100 parts by weight of the acrylic polymer.
The acid value of the acrylic polymer is preferably 0.01 to 8.0, which can improve staining properties and improve the ability to prevent adhesive residue.
Here, the "acid value" is an index representing the acid content, and is expressed as the number of milligrams of potassium hydroxide required to neutralize 1 g of a polymer containing a carboxyl group.

The adhesive layer obtained by crosslinking the adhesive composition has an adhesive strength to a polarizing plate of 0.04 to 0.2 N/25 mm at a low peel speed of 0.3 m/min, and preferably has an adhesive strength of 2.0 N/25 mm or less at a high peel speed of 30 m/min. This provides performance in which the adhesive strength changes little depending on the peel speed, and enables rapid peeling even at high speeds. In addition, when the surface protection film is peeled off once for re-application, excessive force is not required, and it is easy to peel off from the adherend.

The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition preferably has a surface resistivity of 9.0×10 ⁺¹¹ Ω/□ or less and a peeling electrification voltage of ±0 to 0.5 kV. In the present invention, "±0 to 0.5 kV" means 0 to -0.5 kV and 0 to +0.5 kV, i.e., -0.5 to +0.5 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 the influence on the electric control circuit of the adherend can be suppressed.

The gel fraction of the adhesive layer obtained by crosslinking the adhesive composition is preferably 95 to 100%. With such a high gel fraction, the adhesive strength is not excessively high at low peel speeds, and the elution of unpolymerized monomers or oligomers from the acrylic polymer is reduced, improving reworkability and durability at high temperatures and high humidity, and suppressing contamination of the adherend.

An adhesive film is obtained by forming an adhesive layer formed by crosslinking the adhesive composition on one or both sides of a resin film. The surface protection film for polarizing plates of the present invention is a surface protection film formed by forming an adhesive layer formed by crosslinking the adhesive composition on one side of a resin film. The surface protection film for polarizing plates of the present invention has no slippage in a shear retention test when attached to a polarizing plate, has good adhesion to the polarizing plate despite its small adhesive strength, and is excellent in 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 polarizing plates include TAC-based films (triacetyl cellulose-based compounds), acrylic films, and the like.

The test conditions for shear retention force include, for example, a load (mass of weight) of 500 g, an environmental temperature of 23°C, and a standing time of 24 hours. These test conditions are suitable as guidelines for determining whether the adhesion of the surface protection film to the polarizing plate is good. The contact area (dimensions) of the polarizing plate surface protection film to the polarizing plate, which is the adherend in the shear retention force test, is, for example, 25 mm x 35 mm. The details of the test method (apparatus, etc.) may be in accordance with, for example, the retention force test of JIS Z 0237 (Test method for adhesive tapes and adhesive sheets).

As the resin film serving as the substrate of the pressure-sensitive adhesive layer and the release film (separator) protecting the pressure-sensitive adhesive surface, a resin film such as a polyester film can be used.
The resin film serving as the substrate may be subjected to an antifouling treatment using a silicone-based or fluorine-based release agent or coating agent, silica microparticles, or the like, or an antistatic treatment by coating or kneading an antistatic agent, on the side opposite the side on which the pressure-sensitive adhesive layer is formed.
The release film is subjected to a release treatment with a silicone-based or fluorine-based release agent on the surface thereof that is to be mated with the adhesive surface of the adhesive layer.

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

<Production of Acrylic Polymer>
[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. Thereafter, 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 repeat number n of alkylene oxide constituting polyalkylene glycol chain = 12, diester content in monomer is 0.1%, solubility in water is haze value in 20% aqueous solution state is 0.8%, moisture content is 0.05%), and 1 part by weight of N-vinylpyrrolidone were added together with 60 parts by weight of a solvent (ethyl acetate). Thereafter, 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 polymer solution used in Example 1 having a weight average molecular weight of 500,000. A part of the acrylic polymer was collected and used as a sample for measuring the acid value described later.
[Examples 2 to 8 and Comparative Examples 1 to 4]
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, except that the monomer compositions were as shown in Table 1 (A) to (E), respectively.

<Production of Pressure-Sensitive Adhesive Composition and Surface Protective Film>
[Example 1]
To the acrylic polymer solution of Example 1 produced as described above, 0.05 parts by weight of a polyether-modified siloxane compound (HLB value of 7), 1.0 parts by weight of 1-octylpyridinium hexafluorophosphate, and 8.5 parts by weight of acetylacetone were added and stirred, and then 4.0 parts by weight of Coronate HX (an isocyanurate of a hexamethylene diisocyanate compound) and 0.1 parts by weight of titanium trisacetylacetonate were added and mixed with stirring to obtain a pressure-sensitive adhesive composition of Example 1. This pressure-sensitive 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 a pressure-sensitive adhesive sheet having a pressure-sensitive 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 8 and Comparative Examples 1 to 4]
The surface protection films of Examples 2 to 8 and Comparative Examples 1 to 4 were obtained in the same manner as the surface protection film of Example 1 above, except that the compositions of the additives were changed as shown in Table 2 (F) to (J), respectively.

In Tables 1 and 2, the blending ratio of each component is shown in parentheses in parts by weight, calculated assuming the total of group (A) to be 100 parts by weight.
The compound names of the abbreviations of each component used in Tables 1 and 2 are shown in Tables 3 and 4. Note that Coronate (registered trademark) HX, Coronate (registered trademark) HL, and Coronate (registered trademark) L are trade names of Nippon Polyurethane Industry Co., Ltd., and Takenate (registered trademark) D-140N, D-127N, D-110N, and D-120N are trade names of Mitsui Chemicals, Inc. In the (D) group in Table 3, the value of "n" is the average repeat number of alkylene oxides 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 state.

<Test method and evaluation>
The surface protection films in Examples 1 to 8 and Comparative Examples 1 to 4 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 pressure-sensitive adhesive layer, which was used as a measurement sample for gel fraction and surface resistivity.
The surface protection film with the pressure-sensitive adhesive layer exposed was then attached to the surface of a polarizing plate attached to a liquid crystal cell via the pressure-sensitive adhesive layer, and left for one day, after which it was autoclaved at 50° C. and 5 atm for 20 minutes, and then left for another 12 hours at room temperature to prepare a sample for measuring adhesive strength, peeling electrification voltage, shear retention strength (displacement), reworkability, and durability. The polarizing plate to be adhered was a polarizing plate with an AG treatment on its surface.

<Gel Fraction>
After aging, the mass of the pressure-sensitive adhesive layer separated from the measurement sample before being attached to the polarizing plate was accurately measured, and the sample was immersed in toluene for 24 hours and then filtered through a 200-mesh wire net. The filtered product 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 pressure-sensitive adhesive layer (the pressure-sensitive adhesive layer after crosslinking) from the following formula:
Gel fraction (%)=insoluble portion mass (g)/pressure-sensitive adhesive layer mass (g)×100

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

<Surface resistivity>
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 resistivity (Ω/□) of the adhesive layer was measured using a resistivity meter Hiresta UP-HT450 (manufactured by Mitsubishi Chemical Analytech).

<Peeling Charging Voltage>
When the measurement sample obtained above was peeled off at 180° at a tensile speed of 30 m/min, the voltage (charged voltage) generated by charging the polarizing plate having the AG treatment 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 taken as the peeling charged voltage (kV).
<Shear holding force for polarizing plate>
A surface protection film (adhesive layer thickness: 20 μm) cut to dimensions of 25 mm width x 35 mm length was bonded to a polarizing plate whose surface had been subjected to AG treatment, and a load of 500 g was applied to the surface protection film bonded to the polarizing plate in an atmosphere at a temperature of 23° C., and the displacement (mm) of the surface protection film after leaving it for 24 hours was measured.

<Reworkability>
The surface protective film of the measurement sample obtained above was traced with a ballpoint pen (load 500 g, 3 round trips), and then the surface protective film was peeled off from the polarizing plate to observe the surface of the polarizing plate to confirm that there was no contamination transfer to the polarizing plate. The evaluation target criteria were as follows: "○" if there was no contamination transfer to the polarizing plate, "△" if contamination transfer was confirmed in at least a part along the track traced with the ballpoint pen, and "×" if contamination transfer was confirmed along the track traced with the ballpoint pen and the adhesive was also confirmed to have peeled off from the adhesive surface.

<Durability>
The measurement sample obtained above was left in an atmosphere of 60°C and 90% RH for 250 hours, then taken out 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 "×".

The evaluation results are shown in Table 5. The surface resistivity was expressed by the formula "m×10 ⁺ⁿ " as "mE+n" (where m is an arbitrary real number, and n is a positive integer).
The deviations shown in Table 5 indicate the measured deviations (mm) of the surface protective film in the test of the shear holding strength against the polarizing plate.

The surface protection films of Examples 1 to 8 had an adhesive strength of 0.04 to 0.2 N/25 mm at a low peel speed of 0.3 m/min against a polarizing plate as an adherend, an adhesive strength of 2.0 N/25 mm or less at a high peel speed of 30 m/min, a surface resistivity of 9.0 x 10 ⁺¹¹ Ω/□ or less, a peel electrification voltage of ±0 to 0.5 kV, no slippage in a shear holding strength test after being left at 23°C for 24 hours under a load of 500 g, no contamination transfer to the adherend after tracing the surface protection film with a ballpoint pen through the adhesive layer, and excellent durability when left in an atmosphere of 60°C and 90% RH for 250 hours.
That is, (1) the adhesive strength is small yet the adhesion to the polarizing plate is good, (2) the durability, (3) the reworkability, and (4) the antistatic performance are excellent, and all the required performances are satisfied at the same time.

The surface protection film of Comparative Example 1 had an excessive amount of (C) copolymerizable monomer containing a carboxyl group, the acrylic polymer did not contain (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, the adhesive composition did not contain (F) polyether-modified siloxane compound with an HLB value of 7 to 12, and contained an insufficient amount of (G) trifunctional isocyanate compound, and did not contain (J) antistatic agent. This may be because the adhesive strength was too high at a low peel speed of 0.3 m/min and at a high peel speed of 30 m/min, the surface resistivity and peel electrification voltage were high, there was a deviation in the shear retention test, and the reworkability and durability were poor.

The surface protection film of Comparative Example 2 had an insufficient amount of (C) copolymerizable monomer containing a carboxyl group, a high amount of diester of (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, a high moisture content, low solubility in water, and an excessively large HLB value of (F) polyether-modified siloxane compound. As a result, the adhesive strength was too high at a low peel speed of 0.3 m/min and a high peel speed of 30 m/min, the surface resistivity and peel electrification voltage were high, there was a deviation in the shear retention test, and the durability was poor.

The surface protection film of Comparative Example 3 had an acrylic polymer that did not contain (B) a copolymerizable monomer containing a hydroxyl group, contained an excessive amount of (C) a copolymerizable monomer containing a carboxyl group, and had a high diester content of (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, a high water content, and low solubility in water, resulting in a low gel fraction, very high adhesive strength at a low peel speed of 0.3 m/min and a high peel speed of 30 m/min, high peel charging voltage despite a low surface resistivity, and poor reworkability.

The surface protection film of Comparative Example 4 had an excessively large HLB value for the polyether-modified siloxane compound (F), and there was a deviation in the shear retention strength test.

As such, the surface protection films of Comparative Examples 1 to 4 were unable to simultaneously satisfy all the required performance characteristics, namely (1) good adhesion to the polarizing plate despite low adhesive strength, (2) durability, (3) reworkability, and (4) excellent antistatic performance.

The surface protection film for polarizing plates according to the present invention solves the problem of the conventional technology that when the adhesive strength of the adhesive layer is reduced to make it easier to peel the surface protection film from the adherend, the adhesion strength of the surface protection film to the polarizing plate is reduced, and therefore when the size of the polarizing plate becomes larger than before due to the increase in the size of the screen of the liquid crystal display, the surface protection film peels off at the edge of the polarizing plate, and therefore has great industrial value.

Claims (2)

A surface protection film for a polarizing plate that has been subjected to AG treatment,
a pressure-sensitive adhesive layer formed on one surface of a resin film, the pressure-sensitive adhesive layer being formed by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer, a crosslinking agent, and an antistatic agent;
The acrylic polymer is
(A) 100 parts by weight of at least one (meth)acrylic acid ester monomer having an alkyl group carbon number of 4 to 18;
(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 in total;
(E) 0.1 to 20 parts by weight of at least one nitrogen-containing vinyl monomer not containing a hydroxyl group selected from the group consisting of acrylic monomers containing an N,N-dialkyl-substituted amino group or an N,N-dialkyl-substituted amide group, N-vinyl-substituted lactams, and N-(meth)acryloyl-substituted cyclic amines ,
A copolymer of
the (B) hydroxyl group-containing copolymerizable monomer is at least one selected from the group consisting of 8-hydroxyoctyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide,
The pressure-sensitive adhesive composition contains, as the crosslinking agent, 0.1 to 6 parts by weight of a trifunctional isocyanate compound relative to 100 parts by weight of the at least one (A) (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18, and further contains, as the crosslinking agent, 0.001 to 0.5 parts by weight of the at least one polyether-modified siloxane compound having an HLB value of 7 to 12. The AG-treated surface protection film for polarizing plates according to claim 1, in which an antistatic treatment and an antifouling treatment are performed on one side of the resin film opposite the side on which the adhesive layer is formed.