Pressure sensitive adhesive composition and surface protective film

Abstract

To provide an adhesive composition and a surface protective film having excellent antistatic performance, excellent balance of adhesive strength at a low peeling speed and a high peeling speed and excellent durability and reworkability.SOLUTION: There is provided an acrylic polymer which is obtained by copolymerization of (A) a (meth)acrylic acid ester having an alkyl group having 4 to 18 carbon atoms, (B) a monomer containing a hydroxyl group, (C) a monomer containing a carboxyl group (including the case where it is not contained), (D) a polyalkylene glycol mono(meth)acrylic acid ester or an alkoxy polyalkylene glycol mono(meth)acrylic acid ester and / or (E) a nitrogen-containing vinyl monomer or an alkoxy group-containing alkyl (meth)acrylate monomer and (H-2) an ionic compound containing an acryloyl group and the crosslinking agent comprises (F) a trifunctional or more isocyanate compound and (G) a bifunctional acyclic aliphatic isocyanate compound.SELECTED DRAWING: None

Description

[Technical field]

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

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

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

[0004] Thus, in recent years, the performance requirements for the adhesive layer that constitutes the surface protection film have been set forth in terms of ease of use when using the surface protection film, including (1) a balance of adhesive strength at low and high peel speeds, (2) prevention of adhesive residue, (3) excellent antistatic performance, and (4) rework performance. However, while it was possible to satisfy each of the required performance items (1) to (4) for the adhesive layer constituting the surface protection film individually, it was an extremely difficult task to simultaneously satisfy all of the required performance items (1) to (4) for the adhesive layer of the surface protection film.

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

[0006] In an acrylic adhesive layer, the main component of which is a copolymer of a (meth)acrylic acid alkyl ester having an alkyl group with 7 or less carbon atoms and a carboxyl group-containing copolymerizable compound, and which is crosslinked with a crosslinking agent, there is a problem that the adhesive transfers to the adherend when it is 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 in which 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 is used and crosslinked with a crosslinking agent (Patent Document 1). Also, a proposal has been made in which a small amount of a copolymer of an alkyl (meth)acrylate ester and a copolymerizable compound containing a carboxyl group is blended with the above-mentioned copolymer, and an adhesive layer is provided in which the copolymer is crosslinked 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 phenomena such as lifting due to heating during processing or storage, and poor removability when peeled at high speeds, which is the range of manual work.

[0007] In order to solve these problems, a pressure-sensitive adhesive composition has been proposed in which a) 100 parts by weight of an alkyl (meth)acrylate having an alkyl group having 8 to 10 carbon atoms as the main component, 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 are added to a copolymer of the monomer mixture, and a crosslinking agent is blended in an amount equivalent to or greater than the amount of the carboxyl group in the component b) (Patent Document 2). The adhesive composition described in Patent Document 2 does not suffer from peeling phenomena such as lifting during processing or storage, and furthermore, has a small increase in adhesive strength over time and is excellent in removability; it can be peeled off with little force even after long-term storage, particularly long-term storage under a high-temperature atmosphere, without leaving any adhesive residue on the adherend, and can be peeled off with little force even when peeled off at high speed.

[0008] As for (3) excellent antistatic performance, a method of kneading an antistatic agent into a base film has been disclosed as a method for imparting antistatic properties to a surface protective film. Examples of the antistatic agent disclosed include (a) various cationic antistatic agents having 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.

[0009] Regarding (4) rework performance, for example, a pressure-sensitive adhesive composition has been proposed in which an isocyanate compound curing agent and a specific silicate oligomer are blended in an acrylic resin in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the acrylic resin (Patent Document 4). In Patent Document 4, it is described that the main monomer component is an acrylic acid alkyl ester having an alkyl group with about 2 to 12 carbon atoms or a methacrylic acid alkyl ester having an alkyl group with about 4 to 12 carbon atoms, and that it may contain other functional group-containing monomer components such as a carboxyl group-containing monomer. In general, it is preferable to contain 50% by weight or more of the main monomer, and it is desirable that the content of the functional group-containing monomer component is 0.001 to 50% by weight, preferably 0.001 to 25% by weight, and more preferably 0.01 to 25% by weight. The pressure-sensitive adhesive composition described in Patent Document 4 is described as having reworkability because the change in cohesive strength and adhesive strength over time is small even at high temperature or high temperature and high humidity, and 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, it is difficult to peel off the adhesive layer again when it is applied incorrectly, and it is difficult to reapply the adhesive layer. For this reason, it is considered necessary to crosslink a monomer having a functional group such as a carboxyl group to the base resin to give the adhesive layer a certain hardness in order to provide reworkability. [Prior art documents] [Patent documents]

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

[0011] In conventional technology, the performance requirements for the pressure-sensitive adhesive layer constituting the surface protection film have been to balance the adhesive strength at low and high peeling speeds, to have excellent antistatic properties, rework properties, etc. However, while it has been possible to satisfy each of the individual required performances, it has not been possible to satisfy all the required performances for the pressure-sensitive adhesive layer of the surface protection film.

[0012] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a surface protection film that has excellent antistatic performance, an excellent balance of adhesive strength at low and high peel speeds, and further has excellent durability performance and rework performance. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a surface protection film comprising a pressure-sensitive adhesive layer formed on one side of a resin film, the pressure-sensitive adhesive layer being obtained by crosslinking a pressure-sensitive adhesive composition containing an acrylic polymer, (H) an antistatic agent, and a crosslinking agent, the acrylic polymer comprising, when the total amount of the acrylic polymer is 100 parts by weight, 50 to 91 parts by weight of (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, 0.1 to 10 parts by weight of (B) at least one copolymerizable monomer containing a hydroxyl group, 0 to 1.0 parts by weight of (C) a copolymerizable monomer containing a carboxyl group (including the case where the (C) copolymerizable monomer containing a carboxyl group is not contained), and more than 0 to 49.9 parts by weight of (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer or an alkoxy polyalkylene glycol mono(meth)acrylic acid ester monomer as a copolymerizable monomer group. and / or (E) an acrylic polymer of a copolymer obtained by copolymerizing at least one of a nitrogen-containing vinyl monomer not containing a hydroxyl group and an isocyanate group or an alkoxy-containing alkyl (meth)acrylate monomer not containing a hydroxyl group in a total amount of more than 0 parts by weight and not more than 20 parts by weight, wherein the (B) hydroxyl group-containing copolymerizable monomer is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide, and the (H) antistatic agent is contained in an amount of 0.01 to 5.0 parts by weight relative to 100 parts by weight of the copolymer, and the (H) antistatic agent is an ionic compound that is solid at a temperature of 30°C or more and 50°C or less, or is contained in the copolymer in an amount of 0.1 to 5.0 parts by weight relative to 100 parts by weight of the copolymer.and the crosslinking agent is an acryloyl group-containing ionic compound copolymerized at a ratio of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the acrylic polymer, the crosslinking agent is composed of (F) a trifunctional or more isocyanate compound and (G) a difunctional acyclic aliphatic isocyanate compound, the pressure-sensitive adhesive composition contains the (F) trifunctional or more isocyanate compound and the (G) difunctional acyclic aliphatic isocyanate compound in a total ratio of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the acrylic polymer, the weight ratio (F / G) of the (F) trifunctional or more isocyanate compound to the (G) difunctional acyclic aliphatic isocyanate compound is 1 to 90, and the (G) difunctional acyclic aliphatic isocyanate compound is a difunctional acyclic aliphatic isocyanate compound produced by reacting an aliphatic diisocyanate compound with a diol compound.

[0014] In addition, when the total amount of the acrylic polymers in the copolymer is 100 parts by weight, (A) 50 to 91 parts by weight of a (meth)acrylic acid ester monomer having an alkyl group carbon number of C4 to C18, (B) 0.1 to 10 parts by weight of a copolymerizable monomer containing a hydroxyl group, (C) 0 to 1.0 parts by weight of a copolymerizable monomer containing a carboxyl group, (D) 0 to 49.9 parts by weight of a polyalkylene glycol mono(meth)acrylate monomer or an alkoxy polyalkylene glycol mono(meth)acrylate monomer, It is preferable that the composition contains 0 to 20 parts by weight of (E) a nitrogen-containing vinyl monomer that does not contain a hydroxyl group or an isocyanate group, or an alkoxy-containing alkyl (meth)acrylate monomer that does not contain a hydroxyl group.

[0015] It is also preferred that the weight ratio (F / G) of the (F) tri- or higher functional isocyanate compound to the (G) difunctional acyclic aliphatic isocyanate compound is 1 to 90, and the total of the (F) tri- or higher functional isocyanate compound and the (G) difunctional acyclic aliphatic isocyanate compound is 0.1 to 5.0 parts by weight per 100 parts by weight of the acrylic polymer.

[0016] The (G) bifunctional acyclic aliphatic isocyanate compound is a compound produced by reacting a diisocyanate compound with a diol compound. The diisocyanate compound is an aliphatic diisocyanate, and is preferably one selected from the group of compounds consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. The diol compound is preferably one selected from the group of compounds consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, and polypropylene glycol.

[0017] In addition, it is preferable that the (B) hydroxyl group-containing copolymerizable monomer is at least one selected from the group consisting of 8-hydroxyoctyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate, 2-hydroxyethyl(meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide.

[0018] In addition, 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.

[0019] It is also preferred that the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is at least one selected from the group consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate.

[0020] The (F) trifunctional or higher isocyanate compound is preferably at least one selected from the group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, 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.

[0021] The acrylic polymer preferably contains, as the copolymerizable monomer group, at least one of the (E) nitrogen-containing vinyl monomer not containing a hydroxyl group or an alkoxy-containing alkyl (meth)acrylate monomer.

[0022] In addition, the (H) antistatic agent is preferably an ionic compound having a melting point of 30 to 50°C and contained in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of the copolymer, or an acryloyl group-containing ionic compound copolymerized in the copolymer in an amount of 0.1 to 5.0% by weight.

[0023] It is also preferred that the adhesive layer obtained by crosslinking the adhesive composition has an adhesive strength of 0.05 to 0.1 N / 25 mm at a low peel speed of 0.3 m / min, and an adhesive strength of 1.0 N / 25 mm or less at a high peel speed of 30 m / min.

[0024] The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has a surface resistivity of 5.0×10 +10 It is preferable that the resistance is Ω / □ or less and the peeling electrification voltage is ±0 to 1 kV.

[0025] The present invention also provides a surface protection film comprising a resin film and a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition on one or both sides of the resin film.

[0026] The surface protective film of the present invention can also be used as a surface protective film for a polarizing plate.

[0027] In the surface protection film of the present invention, it is preferable that the surface of the resin film opposite to the surface on which the pressure-sensitive adhesive layer is formed is subjected to an antistatic and antifouling treatment. Effect of the Invention

[0028] According to the present invention, it is possible to satisfy all the performance requirements for the adhesive layer of a surface protection film, which could not be achieved by the conventional technology, and also to obtain excellent antistatic performance and prevent the occurrence of adhesive residue. Specifically, it is possible to reduce the amount of antistatic agent added while maintaining excellent antistatic performance, and it is also possible to further improve the performance of preventing the occurrence of adhesive residue. In addition, by using a difunctional acyclic aliphatic isocyanate compound (G) in combination with a trifunctional or higher isocyanate compound (F), excellent crosslinkability and stain resistance are achieved, and furthermore, an excellent balance of adhesive strength is achieved at both low and high peel speeds. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention will be described below based on preferred embodiments. The pressure-sensitive adhesive composition of the present invention is characterized in that its main ingredient is an acrylic polymer of a copolymer containing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, and as a copolymerizable monomer group, at least one selected from the copolymerizable monomer group consisting of (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and (E) a nitrogen-containing vinyl monomer or an alkoxy group-containing alkyl (meth)acrylate monomer that does not contain a hydroxyl group, and further contains (F) a tri- or higher functional isocyanate compound, (G) a difunctional acyclic aliphatic isocyanate compound, and (H) an antistatic agent. In addition, when the total amount of the acrylic polymers in the copolymer is 100 parts by weight, it is preferable that the copolymer contains 50 to 91 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, 0.1 to 10 parts by weight of the (B) copolymerizable monomer containing a hydroxyl group, 0 to 1.0 part by weight of the (C) copolymerizable monomer containing a carboxyl group, 0 to 50 parts by weight of the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer, and 0 to 20 parts by weight of the (E) nitrogen-containing vinyl monomer not containing a hydroxyl group or alkoxy group-containing alkyl (meth)acrylate monomer.

[0030] (A) Examples of (meth)acrylic acid ester monomers having an alkyl group with a carbon number of 4 to 18 include butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, myristyl (meth)acrylate, isomyristyl (meth)acrylate, cetyl (meth)acrylate, isocetyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and the like. When the total amount of the acrylic polymers in the copolymer is 100 parts by weight, it is preferable that (A) the (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18 is contained in a proportion of 50 to 91 parts by weight.

[0031] (B) Examples of copolymerizable monomers containing a hydroxyl group include hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, 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. When the total amount of the acrylic polymers in the copolymer is taken as 100 parts by weight, the copolymer preferably contains 0.1 to 10 parts by weight of the (B) copolymerizable monomer containing a hydroxyl group.

[0032] It is preferable that the (C) copolymerizable monomer containing a carboxyl group is at least one selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, 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. When the total amount of the acrylic polymers in the copolymer is 100 parts by weight, the copolymer preferably contains the copolymerizable monomer having a carboxyl group (C) in an amount of 0 to 1.0 part by weight. In the pressure-sensitive adhesive layer according to the present invention, the pressure-sensitive adhesive composition does not necessarily need to contain the copolymerizable monomer having a carboxyl group (C).

[0033] The (D) polyalkylene glycol mono(meth)acrylic acid ester monomer may be a compound in which one of the multiple 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 it can be copolymerized with the base polymer. The other hydroxyl group may remain as OH, or may be an alkyl ether such as methyl ether or ethyl ether, or a saturated carboxylate ester such as acetate ester. The alkylene group of the polyalkylene glycol includes, but is not limited to, an ethylene group, a propylene group, a butylene group, etc. The polyalkylene glycol may be a copolymer of two or more polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polybutylene glycol, etc. The copolymer of polyalkylene glycol includes polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, etc., and the copolymer may be a block copolymer or a random copolymer. It is preferable that the average repeat number of alkylene oxide constituting the polyalkylene glycol chain of the (D) polyalkylene glycol mono(meth)acrylate monomer is 3 to 14. The "average repeat number of alkylene oxide" refers to the average number of repeating alkylene oxide units in the "polyalkylene glycol chain" portion contained in the molecular structure of the (D) polyalkylene glycol mono(meth)acrylate monomer.

[0034] The (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably at least one selected from the group consisting of polyalkylene glycol mono(meth)acrylate, methoxypolyalkylene glycol (meth)acrylate, and ethoxypolyalkylene glycol (meth)acrylate. More specifically, polyethylene glycol-mono(meth)acrylate, polypropylene glycol-mono(meth)acrylate, polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-mono(meth)acrylate, polyethylene glycol-polybutylene glycol-mono(meth)acrylate, polypropylene glycol-polybutylene glycol-mono(meth)acrylate, polyethylene glycol-polypropylene glycol-polybutylene glycol-mono(meth)acrylate; methoxypolyethylene glycol-(meth)acrylate, methoxypolypropylene glycol-(meth)acrylate, methoxypolybutylene glycol-(meth)acrylate, methoxy-polyethylene glycol-polypropylene glycol-(meth)acrylate, methoxy-polyethylene glycol methoxy-polybutylene 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-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. When the total amount of the acrylic polymers in the copolymer is 100 parts by weight, the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer is preferably contained in an amount of 0 to 50 parts by weight. In the pressure-sensitive adhesive layer according to the present invention, the pressure-sensitive adhesive composition does not necessarily need to contain the (D) polyalkylene glycol mono(meth)acrylic acid ester monomer.

[0035] Among (E), the nitrogen-containing vinyl monomer (E-1) may be a vinyl monomer containing an amide bond, a vinyl monomer containing an amino group, a vinyl monomer having a nitrogen-containing heterocyclic structure, etc. More specifically, N-vinyl-substituted heterocyclic structures such as N-vinyl-2-pyrrolidone, N-vinylpyrrolidone, methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylmorpholine, N-vinylcaprolactam, and N-vinyllaurylolactam may be mentioned. Cyclic nitrogen-containing vinyl compounds having a heterocyclic structure substituted with N-(meth)acryloyl, such as N-(meth)acryloylmorpholine, N-(meth)acryloylpiperazine, N-(meth)acryloylaziridine, N-(meth)acryloylazetidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylpiperidine, N-(meth)acryloylazepane, and N-(meth)acryloylazocane. Cyclic nitrogen-containing vinyl compounds; cyclic nitrogen-containing vinyl compounds having a heterocyclic structure 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 Nt-butyl(meth)acrylamide; dialkyl-substituted (meth)acrylamides, such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropylacrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N-ethyl-N-methyl(meth)acrylamide, N-methyl-N-propyl(meth)acrylamide, and N-methyl-N-isopropyl(meth)acrylamide;Dialkylamino(meth)acrylates such as N,N-dimethylaminomethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, N,N-dimethylaminoisopropyl(meth)acrylate, N,N-dimethylaminobutyl(meth)acrylate, N,N-diethylaminomethyl(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N-ethyl-N-methylaminoethyl(meth)acrylate, N-methyl-N-propylaminoethyl(meth)acrylate, N-methyl-N-isopropylaminoethyl(meth)acrylate, N,N-dibutylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate; N,N-dimethylaminopropyl(meth)acrylamide, N,N-diethylaminopropyl(meth)acrylamide, N N,N-dialkyl-substituted aminopropyl(meth)acrylamide 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.

[0036] As the (E-1) nitrogen-containing vinyl monomer, it is preferable that it does not contain a hydroxyl group, and more preferable that it does not contain a hydroxyl group or a carboxyl group.As such a monomer, the above-mentioned monomers are preferable, for example, 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; N-(meth)acryloylmorpholine, N-(meth)acryloylpyrrolidine and other N-(meth)acryloyl-substituted cyclic amines.

[0037] 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.

[0038] When the total amount of the acrylic polymers in the copolymer is 100 parts by weight, it is preferable that (E-1) nitrogen-containing vinyl monomer not containing a hydroxyl group or (E-2) alkoxy-containing alkyl (meth)acrylate monomer is contained in a ratio of 0 to 20 parts by weight. (E-1) nitrogen-containing vinyl monomer not containing a hydroxyl group and (E-2) alkoxy-containing alkyl (meth)acrylate monomer may be used alone or in combination of two or more kinds. In the pressure-sensitive adhesive layer according to the present invention, the pressure-sensitive adhesive composition may not contain (E) nitrogen-containing vinyl monomer not containing a hydroxyl group or alkoxy-containing alkyl (meth)acrylate monomer.

[0039] (F) The trifunctional or higher isocyanate compound may be at least one or two or more selected from polyisocyanate compounds having at least three or more 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. Specific examples of polyisocyanate compounds include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and trimethylhexamethylene diisocyanate (TMDI), and aromatic isocyanate compounds such as diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (H6XDI), dimethyldiphenylene diisocyanate (TOID), and tolylene diisocyanate (TDI). Examples of the trifunctional or higher isocyanate compound include biuret modified diisocyanates (compounds having two NCO groups in one molecule), isocyanurate modified diisocyanates, and adducts (polyol modified diisocyanates) with trivalent or higher polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane (TMP) and glycerin. The trifunctional or higher isocyanate compound (F) is preferably contained in an amount of 0.5 to 5.0 parts by weight per 100 parts by weight of the copolymer.

[0040] Furthermore, the (F) trifunctional or higher isocyanate compound used in the present invention preferably includes at least one selected from (F-1) a first aliphatic isocyanate compound group consisting of an isocyanurate of a hexamethylene diisocyanate compound, an isocyanurate of an isophorone diisocyanate compound, an adduct of a hexamethylene diisocyanate compound, an adduct of an isophorone diisocyanate compound, a biuret of a hexamethylene diisocyanate compound, and a biuret of an isophorone diisocyanate compound, and at least one selected from (F-2) a second aromatic isocyanate compound group consisting of an isocyanurate of a tolylene diisocyanate compound, an isocyanurate of a xylylene diisocyanate compound, an isocyanurate of a hydrogenated xylylene diisocyanate compound, an adduct of a tolylene diisocyanate compound, an adduct of a xylylene diisocyanate compound, and an adduct of a hydrogenated xylylene diisocyanate compound. It is preferable to use the first aliphatic isocyanate compound group (F-1) and the second aromatic isocyanate compound group (F-2) in combination. In the present invention, the balance of adhesive strength between the low-speed peeling region and the high-speed peeling region can be further improved by using at least one selected from the first aliphatic isocyanate compound group (F-1) and at least one selected from the second aromatic isocyanate compound group (F-2) in combination as the trifunctional or higher isocyanate compound (F). In addition, the (F) trifunctional or higher isocyanate compound contains at least one selected from the (F-1) first aliphatic isocyanate compound group and at least one selected from the (F-2) second aromatic isocyanate compound group, and is preferably contained in a total amount of 0.5 to 5.0 parts by weight per 100 parts by weight of the copolymer. In addition, the mixing ratio of the at least one selected from the (F-1) first aliphatic isocyanate compound group and the at least one selected from the (F-2) second aromatic isocyanate compound group is preferably within the range of 10%:90% to 90%:10% by weight (F-1):(F-2).

[0041] Furthermore, the (G) bifunctional acyclic aliphatic isocyanate compound used in the present invention is a bifunctional isocyanate compound that is acyclic and aliphatic. The (G) bifunctional acyclic aliphatic isocyanate compound is preferably a compound produced by reacting a diisocyanate compound with a diol compound. For example, when a diisocyanate compound is represented by the general formula "O=C=NXN=C=O" (where X is a divalent group) and a diol compound is represented by the general formula "HO-Y-OH" (where Y is a divalent group), an example of a compound produced by reacting a diisocyanate compound with a diol compound is a compound represented by the following general formula Z.

[0042] [General formula Z] O=C=NX-(NH-CO-OYO-CO-NH-X) n -N=C=O

[0043] Here, n is an integer of 0 or more. When n is 0, the general formula Z represents "O=C=NXN=C=O". The (G) bifunctional acyclic aliphatic isocyanate compound may contain a compound in which n is 0 in the general formula Z (a diisocyanate compound unreacted with the diol compound), but it is preferable to contain a compound in which n is an integer of 1 or more as an essential component. The (G) bifunctional acyclic aliphatic isocyanate compound may be a mixture of multiple compounds in which n in the general formula Z is different.

[0044] The diisocyanate compound represented by the general formula "O=C=NXN=C=O" is an aliphatic diisocyanate. X is preferably an acyclic aliphatic divalent group. The aliphatic diisocyanate is preferably one or more selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0045] The diol compound represented by the general formula "HO-Y-OH" is an aliphatic diol. Y is preferably an acyclic aliphatic divalent group. The diol compound is preferably one or more selected from the group consisting of 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol monohydroxypivalate, polyethylene glycol, and polypropylene glycol.

[0046] The weight ratio (F / G) of the (F) tri- or higher functional isocyanate compound to the (G) difunctional acyclic aliphatic isocyanate compound is preferably 1-90. The total amount of the (F) tri- or higher functional isocyanate compound and the (G) difunctional acyclic aliphatic isocyanate compound is preferably 0.1 to 5.0 parts by weight based on 100 parts by weight of the acrylic polymer.

[0047] The (H) antistatic agent is preferably (H-1) an ionic compound having a melting point of 30 to 50° C., or (H-2) an acryloyl group-containing ionic compound. In the present invention, as the (H) antistatic agent, (H-1) an ionic compound having a melting point of 30 to 50° C. is added to the copolymer, or (H-2) an ionic compound containing an acryloyl group is copolymerized into the copolymer. These (H) antistatic agents are presumed to have high affinity with the acrylic copolymer because they have low melting points and long-chain alkyl groups.

[0048] (H-1) The ionic compound having a melting point of 30 to 50°C is an ionic compound having a cation and an anion, in which the cation is a nitrogen-containing onium cation such as a pyridinium cation, an imidazolium cation, a pyrimidinium cation, a pyrazolium cation, a pyrrolidinium cation, or an ammonium cation, or a phosphonium cation, a sulfonium cation, or the like, and the anion is a hexafluorophosphate (PF 6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC 6 H 4 SO 3 - ), perchlorate (ClO 4 - ), tetrafluoroborate (BF 4 -Examples of the cation include compounds which are inorganic or organic anions such as tetraalkylammonium cations. The cation is preferably a solid at room temperature (e.g., 30°C), and a melting point of 30 to 50°C can be obtained by selecting the chain length of the alkyl group, the position and number of the substituents, etc. 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. The (H-1) ionic compound having a melting point of 30 to 50° C. is preferably contained in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of the copolymer.

[0049] (H-2) The acryloyl group-containing ionic compound is an ionic compound having a cation and an anion, and the cation is (meth)acryloyloxyalkyltrialkylammonium [R 3 N + -C n H 2n -OCOCQ=CH 2 , where Q=H or CH 3 , R = alkyl], and the anion is hexafluorophosphate (PF 6 - ), thiocyanate (SCN - ), organic sulfonates (RSO 3 - ), perchlorate (ClO 4 - ), tetrafluoroborate (BF 4 - ), F-containing imide salt (R F 2 N - ) and other inorganic or organic anions. F 2 N - )R FExamples of the F-containing imide salt include perfluoroalkanesulfonyl groups such as trifluoromethanesulfonyl and pentafluoroethanesulfonyl groups, and fluorosulfonyl groups. Examples of the F-containing imide salt include bis(fluorosulfonyl)imide salts [(FSO 2 ) 2 N - 〕, bis(trifluoromethanesulfonyl)imide salt [(CF 3 SO 2 ) 2 N - 〕, bis(pentafluoroethanesulfonyl)imide salt〔(C 2 F 5 SO 2 ) 2 N - and the like. The acryloyl group-containing ionic compound (H-2) is preferably copolymerized in the copolymer in an amount of 0.1 to 5.0% by weight.

[0050] Specific examples of the (H) antistatic agent are not particularly limited, but specific examples of (H-1) ionic compounds having a melting point of 30 to 50°C include 1-octylpyridinium hexafluorophosphate, 1-nonylpyridinium hexafluorophosphate, 2-methyl-1-dodecylpyridinium hexafluorophosphate, 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 1-dodecylpyridinium dodecylbenzenesulfonate, and 4-methyl-1-octylpyridinium hexafluorophosphate. Specific examples of (H-2) acryloyl group-containing ionic compounds include dimethylaminomethyl(meth)acrylate methyl hexafluorophosphate [(CH 3 ) 3 N + CH 2 OCOCQ=CH 2 ·PF 6 - , where Q=H or CH 3 〕, dimethylaminoethyl (meth)acrylate bis(trifluoromethanesulfonyl)imide methyl salt〔(CH 3 ) 3 N + (CH2 ) 2 OCOCQ=CH 2 ·(CF 3 SO 2 ) 2 N - , where Q=H or CH 3 〕, dimethylaminomethyl methacrylate bis(fluorosulfonyl)imide methyl salt〔(CH 3 ) 3 N + CH 2 OCOCQ=CH 2 ·(FSO 2 ) 2 N - , where Q=H or CH 3 ] etc.

[0051] The pressure-sensitive adhesive composition may optionally contain a polyether-modified siloxane compound. The polyether-modified siloxane compound is a siloxane compound having a polyether group, and has a general siloxane unit [-SiR 1 2 In addition to the siloxane unit [-SiR 1 (R 2 O(R 3 O) n R 4 )-O-], where R 1 is one or more alkyl or aryl groups, R 2 and R 3 is one or more alkylene groups, R 4 indicates one or more alkyl groups, acyl groups, etc. (terminal groups). The polyether group is a polyoxyethylene group [(C 2 H 4 O) n ] and polyoxypropylene group [(C 3 H 6 O) n ] and the like polyoxyalkylene groups. The polyether-modified siloxane compound is preferably a polyether-modified siloxane compound having an HLB value of 7 to 12. The content of the polyether-modified siloxane compound is preferably 0.01 to 0.5 parts by weight, more preferably 0.1 to 0.5 parts by weight, per 100 parts by weight of the copolymer. HLB is the hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) defined in, for example, JIS K3211 (terminology for surfactants). Polyether-modified siloxane compounds can be obtained, for example, by grafting an organic compound having an unsaturated bond and a polyoxyalkylene group onto a polyorganosiloxane main chain having a silicon hydride group by a hydrosilylation reaction.Specific examples include dimethylsiloxane-methyl(polyoxyethylene)siloxane copolymer, dimethylsiloxane-methyl(polyoxyethylene)siloxane-methyl(polyoxypropylene)siloxane copolymer, and dimethylsiloxane-methyl(polyoxypropylene)siloxane polymer. By blending the polyether-modified siloxane compound in the pressure-sensitive adhesive composition, the adhesive strength and rework performance of the pressure-sensitive adhesive can be improved. If the pressure-sensitive adhesive composition does not contain the polyether-modified siloxane compound, the cost becomes lower.

[0052] Furthermore, as other components, known additives such as copolymerizable (meth)acrylic monomers containing alkylene oxides, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing accelerators, plasticizers, fillers, curing retarders, processing aids, antioxidants, antioxidants, etc. can be appropriately blended. These can be used alone or in combination of two or more kinds.

[0053] The copolymer of the main component used in the pressure-sensitive adhesive composition of the present invention can be synthesized by copolymerizing at least one of (A) (meth)acrylic acid ester monomers having an alkyl group with a carbon number of C4 to C18, and (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and (E) at least one selected from a copolymerizable monomer group consisting of a nitrogen-containing vinyl monomer not containing a hydroxyl group or an alkoxy-containing alkyl(meth)acrylate monomer. The polymerization method of the copolymer is not particularly limited, and any appropriate polymerization method such as solution polymerization or emulsion polymerization can be used. When (H-2) an acryloyl group-containing ionic compound is used as (H) the antistatic agent, the copolymer of the main component used in the pressure-sensitive adhesive composition of the present invention can be synthesized by copolymerizing (A) at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of C4 to C18, as a copolymerizable monomer group, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, (D) a polyalkylene glycol mono(meth)acrylic acid ester monomer, and (E) at least one monomer selected from the copolymerizable monomer group consisting of a nitrogen-containing vinyl monomer not containing a hydroxyl group or an alkoxy group-containing alkyl (meth)acrylate monomer, and (H-2) the acryloyl group-containing ionic compound. The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above-mentioned copolymer with (F) a trifunctional or higher isocyanate compound, (G) a bifunctional acyclic aliphatic isocyanate compound, (H) an antistatic agent, and further with any additives as appropriate. Note that when (H-2) an acryloyl group-containing ionic compound is polymerized in the copolymer of the main component, (H) an antistatic agent may or may not be added to the copolymer.

[0054] The copolymer is preferably an acrylic polymer, and preferably contains 50 to 100% by weight of an acrylic monomer such as a (meth)acrylic acid ester monomer, (meth)acrylic acid, or a (meth)acrylamide. The acid value of the 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.

[0055] The adhesive layer obtained by crosslinking the adhesive composition preferably has an adhesive strength of 0.05 to 0.1 N / 25 mm at a low peeling speed of 0.3 m / min, and an adhesive strength of 1.0 N / 25 mm or less at a high peeling speed of 30 m / min. This provides performance with little change in adhesive strength depending on the peeling speed, and enables rapid peeling even at high-speed peeling. In addition, even when the surface protection film is peeled off once for re-adhesion, excessive force is not required, and it is easy to peel off from the adherend.

[0056] The pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has a surface resistivity of 5.0×10 +10 It is preferable that the surface resistivity is Ω / □ or less, and the peeling electrification voltage is ±0 to 1 kV. In the present invention, "±0 to 1 kV" means 0 to -1 kV and 0 to +1 kV, i.e., -1 to +1 kV. If the surface resistivity is high, the performance of dissipating static electricity generated by charging during peeling is poor. Therefore, by making the surface resistivity sufficiently small, the peeling electrification voltage caused by static electricity generated when the pressure-sensitive adhesive layer is peeled off from the adherend is reduced, and it is possible to suppress the influence on the electric control circuit of the adherend.

[0057] The gel fraction of the pressure-sensitive adhesive layer (crosslinked pressure-sensitive adhesive) obtained by crosslinking the pressure-sensitive adhesive composition of the present invention is preferably 95 to 100%. With such a high gel fraction, the adhesive strength is not excessively high at a low peel speed, the elution of unpolymerized monomers or oligomers from the copolymer is reduced, reworkability and durability at high temperatures and high humidity are improved, and contamination of the adherend can be suppressed.

[0058] The adhesive film of the present invention is formed by forming an adhesive layer formed by crosslinking the adhesive composition of the present invention on one or both sides of a resin film. The surface protective film of the present invention is formed by forming an adhesive layer formed by crosslinking the adhesive composition of the present invention on one or both sides of a resin film. The adhesive composition of the present invention has a well-balanced blend of the above-mentioned components (A) to (H), and therefore has excellent antistatic performance, an excellent balance of adhesive strength at low and high peeling speeds, and also excellent durability and rework performance (no contamination transfer to the adherend after tracing the surface protective film with a ballpoint pen through the adhesive layer). Therefore, it can be suitably used as a surface protective film for a polarizing plate.

[0059] As the base film of the pressure-sensitive adhesive layer and the release film (separator) that protects the pressure-sensitive adhesive surface, a resin film such as a polyester film can be used. The substrate film may be subjected to an antifouling treatment using a silicone-based or fluorine-based release agent or coating agent, or silica microparticles or the like, or an antistatic treatment by coating or kneading an antistatic agent, on the side opposite to the side on which the pressure-sensitive adhesive layer of the resin film is formed. The release film is subjected to a release treatment with a silicone-based or fluorine-based release agent on the surface thereof that is to be joined to the adhesive surface of the adhesive layer. EXAMPLES

[0060] The present invention will now be described in detail with reference to examples.

[0061] <Production of Acrylic Copolymer> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube, and the air in the reactor was replaced with nitrogen gas. Then, 100 parts by weight of 2-ethylhexyl acrylate, 3.0 parts by weight of 8-hydroxyoctyl acrylate, 10 parts by weight of polypropylene glycol monoacrylate (average repeat number n of alkylene oxide constituting the polyalkylene glycol chain = 12) and 60 parts by weight of a solvent (ethyl acetate) were added to the reactor. Then, 0.1 parts by weight of azobisisobutyronitrile as a polymerization initiator was dropped over 2 hours, and the mixture was reacted at 65 ° C for 6 hours to obtain an acrylic copolymer solution 1 used in Example 1 with a weight average molecular weight of 500,000. A part of the acrylic copolymer was collected and used as a measurement sample for the acid value described later. [Examples 2 to 9 and Comparative Examples 1 to 4] The acrylic copolymer solutions used in Examples 2 to 9 and Comparative Examples 1 to 4 were obtained in the same manner as in the acrylic copolymer solution 1 used in Example 1 above, except that the monomer compositions were as shown in Table 1 (A) to (E) and (H-2), respectively.

[0062] [Table 1]

[0063] <Production of Pressure-Sensitive Adhesive Composition and Surface Protective Film> [Example 1] To the acrylic copolymer solution 1 of Example 1 produced as described above, 1.5 parts by weight of 1-octylpyridinium hexafluorophosphate was added and stirred, and then 2.0 parts by weight of Coronate HX (isocyanurate of hexamethylene diisocyanate compound) and 0.5 parts by weight of the bifunctional acyclic aliphatic isocyanate compound G-1 of Synthesis Example 1 were added and mixed by stirring to obtain an adhesive composition of Example 1. This adhesive composition was applied onto a release film made of a silicone resin-coated polyethylene terephthalate (PET) film, and then dried at 90° C. to remove the solvent, thereby obtaining an adhesive sheet with an adhesive layer thickness of 25 μm. Thereafter, an adhesive sheet was transferred to the side opposite the antistatic and antifouling treated side of a polyethylene terephthalate (PET) film having one side treated with antistatic and antifouling treatment, thereby obtaining a surface protection film of Example 1 having a laminate structure of "antistatic and antifouling treated PET film / adhesive layer / release film (silicone resin coated PET film)". [Examples 2 to 9 and Comparative Examples 1 to 4] Surface protection films of Examples 2 to 9 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 as shown in Table 2 (F) to (H), respectively.

[0064] [Table 2]

[0065] Tables 1 and 2 are two separate tables showing the compounding ratios of each component, and in each table, the numerical values ​​in parts by weight calculated with the total of group (A) being 100 parts by weight are enclosed in parentheses. The compound names of the abbreviations of each component used in Tables 1 and 2 are shown in Tables 3 and 4. Coronate (registered trademark) HX, HL, and L are product names of Nippon Polyurethane Industry Co., Ltd., and Takenate (registered trademark) D-140N, D-127N, D-110N, and D-120N are product names of Mitsui Chemicals, Inc. In Table 1, among the (H) antistatic agents, the (H-2) acryloyl group-containing quaternary ammonium salt type ionic compound copolymerized in the copolymer is listed in a column separate from the (H) antistatic agent added after polymerization.

[0066] [Table 3]

[0067] [Table 4]

[0068] <Synthesis of bifunctional acyclic aliphatic isocyanate compounds> The bifunctional acyclic aliphatic isocyanate compounds of Synthesis Examples 1 to 3 were synthesized by the following method. As shown in Tables 5 and 6, a diisocyanate and a diol compound were mixed in a molar ratio of NCO / OH=16 and reacted at 120°C for 3 hours, and then the unreacted diisocyanate was removed under reduced pressure using a thin-film evaporator to obtain the desired bifunctional acyclic aliphatic isocyanate compound.

[0069] [Table 5]

[0070] [Table 6]

[0071] <Test methods and evaluation> The surface protection films in Examples 1 to 9 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 adhesive layer, which was used as a sample for measuring surface resistivity. Furthermore, this surface protection film with the adhesive layer exposed was attached to the surface of a polarizing plate attached to a liquid crystal cell via the adhesive layer, and after leaving it for one day, it was autoclaved at 50°C and 5 atmospheres for 20 minutes and then left at room temperature for a further 12 hours to prepare a sample for measuring adhesive strength, peeling charge voltage, reworkability and durability.

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

[0073] <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 of the adhesive layer was measured using a resistivity meter, Hiresta UP-HT450 (manufactured by Mitsubishi Chemical Analytech).

[0074] <Peeling charge voltage> The measurement sample obtained above was peeled off at an angle of 180° at a tensile speed of 30 m / min, and the voltage (charged voltage) generated by the polarizing plate being charged was measured using high-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Corporation). The maximum measured value was taken as the peeling charged voltage.

[0075] <Reworkability> The surface protective film of the measurement sample obtained above was traced with a ballpoint pen (500g load, 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 adhesive detachment was confirmed from the adhesive surface.

[0076] <Durability> The measurement samples obtained above were left in an atmosphere of 60°C and 90% RH for 250 hours, then removed to room temperature and left for another 12 hours, after which the adhesive strength was measured and it was confirmed that there was no clear increase compared to the initial adhesive strength. The evaluation target criteria were as follows: if the adhesive strength after the test was 1.5 times or less of the initial adhesive strength, it was evaluated as "○", and if it exceeded 1.5 times, it was evaluated as "×".

[0077] The evaluation results are shown in Table 7. The surface resistivity is expressed as "m×10 +n " is expressed as "mE+n" (where m is any real value and n is a positive integer).

[0078] [Table 7]

[0079] The surface protection films of Examples 1 to 9 had an adhesive strength of 0.05 to 0.1 N / 25 mm at a low peel speed of 0.3 m / min, an adhesive strength of 1.0 N / 25 mm or less at a high peel speed of 30 m / min, and a surface resistivity of 5.0 × 10 +10 The peeling charge voltage was less than Ω / □, the peeling charge voltage was ±0 to 1 kV, and after tracing the surface protection film with a ballpoint pen through the adhesive layer, no contamination was transferred to the adherend, and the film also had excellent durability when left in an atmosphere of 60°C and 90% RH for 250 hours. In other words, it simultaneously satisfies all the required performance requirements: (1) balancing adhesive strength at both low and high peel speeds, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic properties, and (4) reworkability.

[0080] The surface protection film of Comparative Example 1 did not contain any of the crosslinking agents (F) a trifunctional or higher isocyanate compound or (G) a difunctional acyclic aliphatic isocyanate compound. Therefore, the adhesive strength at a low peel speed of 0.3 m / min and a high peel speed of 30 m / min was too high, the surface resistivity and peel electrification voltage were high, and the reworkability and durability were poor. The surface protection film of Comparative Example 2 did not contain the (G) difunctional acyclic aliphatic isocyanate compound, but instead contained a uretdione ring-containing diisocyanate compound, which is a difunctional cyclic isocyanate compound. Therefore, the adhesive strength at a high peel speed of 30 m / min was too high and the durability was poor. The surface protective film of Comparative Example 3 contains an excessive amount of (F) a trifunctional or higher isocyanate compound. (G) Possibly because it did not contain a difunctional acyclic aliphatic isocyanate compound, the pot life was too short and crosslinking had progressed before coating, making it impossible to coat. The surface protection film of Comparative Example 4 had too much adhesive strength at a high peel speed of 30 m / min and poor durability, possibly because it contained a larger amount of (G) difunctional acyclic aliphatic isocyanate compound compared to (F) trifunctional or higher isocyanate compound. Thus, the surface protection films of Comparative Examples 1 to 4 were unable to simultaneously satisfy all of the required performance requirements: (1) balancing adhesive strength at low and high peel speeds, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic polymer and a crosslinking agent, The acrylic polymer comprises, when the total amount of the acrylic polymer is 100 parts by weight, (A) 50 to 91 parts by weight of at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 18, (B) 0.1 to 10 parts by weight of at least one hydroxyl group-containing copolymerizable monomer 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; (C) 0 to 1.0 parts by weight of a total of copolymerizable monomers containing a carboxyl group (however, this also includes the case where the (C) copolymerizable monomers containing a carboxyl group are not contained), as a copolymerizable monomer group, (D) a total amount of at least one of a polyalkylene glycol mono(meth)acrylic acid ester monomer containing a hydroxyl group or an alkoxy polyalkylene glycol mono(meth)acrylic acid ester monomer not containing a hydroxyl group is more than 0 parts by weight and not more than 49.9 parts by weight, and / or (E) a total amount of at least one of a nitrogen-containing vinyl monomer not containing a hydroxyl group, a carboxyl group, and an isocyanate group or an alkoxy group-containing alkyl (meth)acrylate monomer not containing a hydroxyl group is more than 0 parts by weight and not more than 20 parts by weight, (H-2) at least one acryloyl group-containing ionic compound in a total amount of more than 0.01 parts by weight and not more than 5.0 parts by weight, is an acrylic polymer of a copolymer obtained by copolymerizing the crosslinking agent comprises (F) a trifunctional or higher isocyanate compound and (G) a difunctional acyclic aliphatic isocyanate compound, the pressure-sensitive adhesive composition contains the (F) tri- or higher functional isocyanate compound and the (G) difunctional acyclic aliphatic isocyanate compound in a total amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the acrylic polymer, a weight ratio (F / G) of the (F) tri- or higher functional isocyanate compound to the (G) difunctional acyclic aliphatic isocyanate compound is 1 to 90; A pressure-sensitive adhesive composition, characterized in that the (G) bifunctional acyclic aliphatic isocyanate compound is a bifunctional acyclic aliphatic isocyanate compound produced by reacting an aliphatic diisocyanate compound with a diol compound.

2. A pressure-sensitive adhesive composition comprising an acrylic polymer, an antistatic agent (H), and a crosslinking agent, The acrylic polymer comprises, when the total amount of the acrylic polymer is 100 parts by weight, (A) 50 to 91 parts by weight of at least one (meth)acrylic acid ester monomer having an alkyl group with a carbon number of 4 to 18, (B) 0.1 to 10 parts by weight of at least one hydroxyl group-containing copolymerizable monomer 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; (C) 0 to 1.0 parts by weight of a total of copolymerizable monomers containing a carboxyl group (however, this also includes the case where the (C) copolymerizable monomers containing a carboxyl group are not contained), as a copolymerizable monomer group, (D) a total amount of at least one of a polyalkylene glycol mono(meth)acrylic acid ester monomer containing a hydroxyl group or an alkoxy polyalkylene glycol mono(meth)acrylic acid ester monomer not containing a hydroxyl group is more than 0 parts by weight and not more than 49.9 parts by weight, and / or (E) a total amount of at least one of a nitrogen-containing vinyl monomer not containing a hydroxyl group, a carboxyl group, and an isocyanate group or an alkoxy group-containing alkyl (meth)acrylate monomer not containing a hydroxyl group is more than 0 parts by weight and not more than 20 parts by weight, (H-2) at least one acryloyl group-containing ionic compound in a total amount of more than 0.01 parts by weight and not more than 5.0 parts by weight, is an acrylic polymer of a copolymer obtained by copolymerizing the crosslinking agent comprises (F) a trifunctional or higher isocyanate compound and (G) a difunctional acyclic aliphatic isocyanate compound, The (H) antistatic agent is (H-1) an ionic compound having a melting point of 30 to 50° C., the pressure-sensitive adhesive composition contains the (F) tri- or higher functional isocyanate compound and the (G) difunctional acyclic aliphatic isocyanate compound in a total amount of 0.1 to 5.0 parts by weight per 100 parts by weight of the acrylic polymer, a weight ratio (F / G) of the (F) tri- or higher functional isocyanate compound to the (G) difunctional acyclic aliphatic isocyanate compound is 1 to 90; A pressure-sensitive adhesive composition, characterized in that the (G) bifunctional acyclic aliphatic isocyanate compound is a bifunctional acyclic aliphatic isocyanate compound produced by reacting an aliphatic diisocyanate compound with a diol compound.

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

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