Adhesive composition, adhesive film and surface protective film

Abstract

To provide an adhesive composition, an adhesive film and a surface protective film which have excellent anti-static performance, and are excellent in a balance in adhesive force at a peel rate in a low-speed region and a high-speed region, and in durability performance and rework performance.SOLUTION: An adhesive composition contains 0.1-5 pt(s)wt. of a tri- or more functional isocyanate compound as a cross-linking agent, based on 100 pts.wt. of an acrylic polymer comprising a copolymer which is obtained by copolymerizing 85-98.5 pts.wt. of alkyl (meth)acrylate having 4 to 10 carbon atoms in an alkyl group, 0.5-15 pt(s)wt. of a copolymerizable monomer containing a hydroxyl group, and 0.5-2 pts.wt. of a copolymerizable monomer containing a carboxyl group. An acid value of the acrylic polymer is 0.01-8.0, and an anti-static agent is an ionic compound having a melting point of 30-50°C. Furthermore, a polyether modified siloxane compound having an HLB value of 7-12 is contained.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an antistatic pressure-sensitive adhesive composition, an adhesive film in which an antistatic pressure-sensitive adhesive layer is formed on at least one surface of a resin film using the pressure-sensitive adhesive composition, and a surface protection film. Further, the present invention relates to a surface protection film used in the manufacturing process of a liquid crystal display. More specifically, it is used to protect the surfaces of optical members such as polarizing plates, retardation plates, and antireflection films that make up a liquid crystal display by adhering to the surfaces of these optical members. The present invention relates to a pressure-sensitive adhesive composition for a surface protection film and a surface protection film using the same.

Background Art

[0002] Conventionally, in the manufacturing process of optical members such as polarizing plates, retardation plates, and antireflection films, which are members constituting a liquid crystal display, a surface protection film for temporarily protecting the surface of the optical member is adhered. Such a surface protection film is used only in the process of manufacturing the optical member and is peeled off and removed from the optical member when the optical member is incorporated into the 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 generally sometimes called a process film.

[0003] As described above, the surface protection film used in the process of manufacturing an optical member has an adhesive layer formed on one surface of an optically transparent polyethylene terephthalate (PET) resin film. Until it is bonded to the optical member, a peeled release film for protecting the adhesive layer is bonded on the adhesive layer. In addition, optical members such as polarizing plates, retardation plates, and anti-reflection films are subjected to product inspections involving optical evaluations such as display performance, hue, contrast, and foreign matter inclusion of the liquid crystal display panel in a state where a surface protection film is laminated. Therefore, as a required performance for the surface protection film, it is required that no bubbles or foreign matter adhere to the adhesive layer. In recent years, when peeling the surface protection film from optical members such as polarizing plates, retardation plates, and anti-reflection films, there is a concern that the peeling charge generated along with the static electricity generated when the adhesive layer peels off the adherend may affect the failure of the electric control circuit of the liquid crystal display. Therefore, excellent antistatic performance is required for the adhesive layer. When laminating a surface protection film on optical members such as polarizing plates, retardation plates, and anti-reflection films, for various reasons, the surface protection film may be peeled off once and then re-laminated again. At that time, it is required that it be easily peeled off from the adherend optical member (reworkability). Also at this time, it is required that the adherend is not contaminated and so-called glue residue does not occur. In addition, when finally peeling the surface protection film from optical members such as polarizing plates, retardation plates, and anti-reflection films, it is required that it can be peeled off quickly. That is, it is required that the adhesive strength changes little depending on the peeling speed so that it can be peeled off quickly even by so-called high-speed peeling.

[0004] Thus, in recent years, as required performance for the adhesive layer constituting the surface protection film, (1) to balance the adhesive strength at the peeling speeds in the low-speed region and the high-speed region, (2) to prevent the occurrence of glue residue, (3) to have excellent antistatic performance, and (4) to have rework performance are required from the viewpoint of ease of use when using the surface protection film. However, although each of these (1) to (4) individual required performances for the adhesive layer constituting the surface protection film can be satisfied, it has been a very difficult problem to simultaneously satisfy all of the required performances of (1) to (4) required for the adhesive layer of the surface protection film. In this specification, the "low-speed region" refers to a peeling speed of around 0.3 m / min, and the "high-speed region" refers to a peeling speed of around 30 m / min.

[0005] For example, regarding (1) achieving a balance of adhesive force at the peeling speeds in the low-speed region and the high-speed region, and (2) preventing the occurrence of adhesive residue, the following proposals are known.

[0006] In an acrylic adhesive layer mainly composed of a copolymer of an alkyl (meth)acrylate having an alkyl group with 7 or fewer carbon atoms and a copolymerizable compound containing a carboxyl group, and cross-linked with a cross-linking agent, when adhered for a long time, there was a problem that the adhesive migrated to the adherend side and the adhesive force to the adherend increased significantly over time. To avoid this, an adhesive layer provided with a copolymer of an alkyl (meth)acrylate having an alkyl group with 8 to 10 carbon atoms and a copolymerizable compound having an alcoholic hydroxyl group, and cross-linked with a cross-linking agent is known (Patent Document 1). Also, proposals have been made such as providing an adhesive layer in which a small amount of a copolymer of an alkyl (meth)acrylate and a copolymerizable compound containing a carboxyl group is blended with the same copolymer as above and cross-linked with a cross-linking agent. However, when these are used for surface protection of a plastic plate with low surface tension and a smooth surface, there are problems such as peeling phenomena such as floating due to heating during processing or storage, and poor re-peelability when peeling at a high speed in the manual operation area.

[0007] To solve these problems, an adhesive composition has been proposed in which a cross-linking agent in an amount equivalent to or more than the carboxyl group of component b) above is blended with a copolymer of a monomer mixture obtained by adding a) 100 parts by weight of an alkyl (meth)acrylate mainly composed of an alkyl (meth)acrylate having an alkyl group with 8 to 10 carbon atoms, b) 1 to 15 parts by weight of a copolymerizable compound containing a carboxyl group, and c) 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms (Patent Document 2). In the pressure-sensitive adhesive composition described in Patent Document 2, during processing or storage, no peeling phenomenon such as floating occurs. Moreover, it is stated that the adhesive strength does not increase significantly over time, and it has excellent re-peelability. Also, even after long-term storage, especially under high-temperature atmosphere, it can be re-peeled with a small force. At that time, no adhesive residue remains on the adherend, and it can be re-peeled with a small force even when peeled at a high speed.

[0008] Also, regarding (3) excellent antistatic performance, as a method for imparting antistatic properties to the surface protection film, methods such as kneading an antistatic agent into the base film are shown. Examples of antistatic agents include (a) various cationic antistatic agents having cationic groups such as quaternary ammonium salts, pyridinium salts, and primary to tertiary amino groups, (b) anionic antistatic agents having anionic groups such as sulfonate groups, sulfate ester groups, phosphate ester groups, and phosphonate groups, (c) amphoteric antistatic agents such as amino acid-based and amino sulfate ester-based, (d) nonionic antistatic agents such as amino alcohol-based, glycerin-based, and polyethylene glycol-based, (e) polymer-type antistatic agents obtained by polymerizing the above-mentioned antistatic agents, etc. are disclosed (Patent Document 3). In recent years, it has been proposed to directly incorporate such an antistatic agent into the pressure-sensitive adhesive layer, rather than incorporating it into the base film or applying it to the surface of the base film.

[0009] Also, regarding (4) reworkability, for example, a pressure-sensitive adhesive composition has been proposed in which a curing agent for an isocyanate-based compound and a specific silicate oligomer are blended in an amount of 0.0001 to 10 parts by weight with respect to 100 parts by weight of an acrylic resin (Patent Document 4). In Patent Document 4, it is stated that acrylic acid alkyl esters with an alkyl group having about 2 to 12 carbon atoms, methacrylic acid alkyl esters with an alkyl group having about 4 to 12 carbon atoms, etc. can be used as the main monomer component, and other functional group-containing monomer components such as carboxyl group-containing monomers can be included. Generally, it is preferable to contain 50% by weight or more of the above main monomer, and 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 such Patent Document 4 exhibits a small change over time in cohesive force and adhesive force even under high temperature or high temperature and high humidity conditions, and also has an excellent effect on the adhesive force to a curved surface, and thus is said to have reworkability. Generally, if the pressure-sensitive adhesive layer has a soft property, it is likely to cause adhesive residue and the reworkability is likely to decrease. That is, when it is misbonded, it is difficult to peel off and it is likely to be difficult to reattach. For this reason, it is considered necessary to crosslink a monomer having a functional group such as a carboxyl group to the main agent to make the pressure-sensitive adhesive layer have a certain hardness in order to provide reworkability.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0011] In the prior art, as the required performance for the pressure-sensitive adhesive layer constituting the surface protection film, (1) At the peeling speeds in the low-speed region and the high-speed region, to balance the adhesive forces, (2) to prevent the occurrence of adhesive residue, (3) to have excellent antistatic performance, and (4) to have rework performance have been required. However, even though each of these requirements (1) to (4) could be satisfied individually, it was not possible to satisfy all the required performances demanded of the adhesive layer of the surface protection film.

[0012] The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive composition, an adhesive film, and a surface protection film that have excellent antistatic performance, an excellent balance of adhesive forces at the peeling speeds in the low-speed region and the high-speed region, and further excellent durability performance and rework performance.

Means for Solving the Problems

[0013] To solve the above problems, the present invention provides an adhesive composition containing an antistatic agent, which is composed of an acrylic polymer having an alkyl (meth)acrylate having an alkyl group with 4 to 10 carbon atoms as a main component. With respect to 100 parts by weight of the acrylic polymer, 85 to 98.5 parts by weight of the alkyl (meth)acrylate as the main component, 0.1 to 15 parts by weight of a hydroxyl group-containing copolymerizable monomer, 0.1 to 2 parts by weight of a carboxyl group-containing copolymerizable monomer, and 0.1 to 5 parts by weight of a crosslinking agent are contained. The acid value of the acrylic polymer is 0.01 to 8.0, the antistatic agent is an ionic compound having a melting point of 30 to 50°C, and the adhesive composition is characterized by containing a polyether-modified siloxane compound.

[0014] Further, it is preferable that the alkyl (meth)acrylate of the main component is one or more selected from the group of compounds consisting of butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and decyl (meth)acrylate.

[0015] Further, it is preferable that the hydroxyl group-containing copolymerizable monomer is at least one selected from the group of compounds consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide.

[0016] Further, it is preferable that the carboxyl group-containing copolymerizable monomer is one or more selected from the group of compounds 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.

[0017] Further, it is preferable that the polyether-modified siloxane compound is a polyether-modified siloxane compound having an HLB value of 7 to 12.

[0018] Further, it is preferable that the crosslinking agent is a polyfunctional isocyanate compound having three or more functional groups.

[0019] The present invention also provides a pressure-sensitive adhesive film characterized in that a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is formed on one or both sides of a resin film.

[0020] The present invention also provides a surface protection film characterized in that a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is formed on one side of a resin film.

Advantages of the Invention

[0021] According to the present invention, all the performances required for the pressure-sensitive adhesive layer of the surface protection film, which could not be solved by the prior art, can be satisfied, and excellent antistatic performance can be obtained, and the occurrence of adhesive residue can be prevented.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, the present invention will be described based on preferred embodiments. The pressure-sensitive adhesive composition of the present invention is a pressure-sensitive adhesive composition containing an antistatic agent, and is composed of an acrylic polymer mainly composed of an alkyl (meth) acrylate having an alkyl group with 4 to 10 carbon atoms. With respect to 100 parts by weight of the acrylic polymer, 85 to 98.5 parts by weight of the alkyl (meth) acrylate as the main component, 0.1 to 15 parts by weight of a copolymerizable monomer containing a hydroxyl group, 0.1 to 2 parts by weight of a copolymerizable monomer containing a carboxyl group, and 0.1 to 5 parts by weight of a crosslinking agent are contained. The acid value of the acrylic polymer is 0.01 to 8.0, and the antistatic agent is an ionic compound having a melting point of 30 to 50 ° C, and is characterized by containing a polyether-modified siloxane compound.

[0023] As the main component alkyl (meth)acrylate, an alkyl (meth)acrylate having an alkyl group with 4 to 10 carbon atoms is preferred, and it is preferably at least one selected from the group of compounds consisting of butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and decyl (meth)acrylate. Preferably, 85 to 98.5 parts by weight of the main component alkyl (meth)acrylate is contained per 100 parts by weight of the acrylic polymer.

[0024] Examples of the hydroxyl group-containing copolymerizable monomer include hydroxyalkyl (meth)acrylates and hydroxyl group-containing (meth)acrylamides. It is preferably at least one selected from the group of compounds consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide. Preferably, 0.1 to 15 parts by weight of the hydroxyl group-containing copolymerizable monomer is contained per 100 parts by weight of the acrylic polymer.

[0025] Examples of the carboxyl group-containing copolymerizable monomer include one or more 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. Preferably, 0.1 to 2 parts by weight of the carboxyl group-containing copolymerizable monomer is contained with respect to 100 parts by weight of the acrylic polymer.

[0026] It is preferable to crosslink the pressure-sensitive adhesive polymer when forming the pressure-sensitive adhesive layer. As a method for causing the crosslinking reaction, crosslinking may be performed by photo-crosslinking such as ultraviolet rays (UV), but it is preferable that the pressure-sensitive adhesive composition contains a crosslinking agent. Examples of the crosslinking agent include bifunctional or trifunctional or higher isocyanate compounds, bifunctional or trifunctional or higher epoxy compounds, bifunctional or trifunctional or higher acrylate compounds, and metal chelate compounds. Among them, polyisocyanate compounds (bifunctional or trifunctional or higher isocyanate compounds) are preferable, and trifunctional or higher isocyanate compounds are more preferable. Preferably, 0.1 to 5 parts by weight of the crosslinking agent is contained with respect to 100 parts by weight of the acrylic polymer.

[0027] As the polyisocyanate compound having three or more functional groups, a polyisocyanate compound having at least three or more isocyanate (NCO) groups in one molecule may be used. The polyisocyanate compound may be classified into aliphatic isocyanates, aromatic isocyanates, acyclic isocyanates, alicyclic isocyanates, etc., and any of them may be used. Specific examples of the polyisocyanate compound include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (TMDI), and aromatic isocyanate compounds such as diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (H6XDI), dimethyldiphenylene diisocyanate (TOID), tolylene diisocyanate (TDI). Examples of the polyisocyanate compound having three or more functional groups include burette-modified products and isocyanurate-modified products of diisocyanates (compounds having two NCO groups in one molecule), and adduct products (polyol-modified products) with polyols having a trivalent or higher valence such as trimethylolpropane (TMP) and glycerin (compounds having at least three or more OH groups in one molecule).

[0028] In order to impart antistatic performance, the pressure-sensitive adhesive composition of the present invention preferably contains an antistatic agent. The antistatic agent is preferably solid at room temperature (for example, 30°C), and more specifically, the antistatic agent is an ionic compound having a melting point of 30 to 50°C. The antistatic agent may be an acryloyl group-containing quaternary ammonium salt type ionic compound. Since these antistatic agents have a low melting point and have a long-chain alkyl group, it is presumed that they have a high affinity with acrylic polymers.

[0029] As an antistatic agent that is an ionic compound with a melting point of 30 to 50 °C, there is an ionic compound having a cation and an anion, and 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, an ammonium cation, etc., or a phosphonium cation, a sulfonium cation, etc., and the anion is an inorganic or organic anion such as hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), alkylbenzenesulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - ), etc. By selecting the chain length of the alkyl group, the position and number of substituents, etc., those with a melting point of 30 to 50 °C can be obtained. The cation is preferably a quaternary nitrogen-containing onium cation, such as a quaternary pyridinium cation such as 1-alkylpyridinium (the carbon atoms at the 2-6 positions may or may not have substituents), or a quaternary imidazolium cation such as 1,3-dialkylimidazolium (the carbon atoms at the 2, 4, and 5 positions may or may not have substituents), and quaternary ammonium cations such as tetraalkylammonium, etc. The antistatic agent that is an ionic compound with a melting point of 30 to 50 °C is preferably contained in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the acrylic polymer.

[0030] As the (meth)acryloyl group-containing quaternary ammonium salt type ionic compound, there is an ionic compound having a cation and an anion, and the cation is a (meth)acryloyl group-containing quaternary ammonium such as (meth)acryloyloxyalkyltrialkylammonium [R3N + -C n H 2n -OCOCQ=CH2, provided that Q = H or CH3, R = alkyl], etc., and the anion is hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), organic sulfonate (RSO3 - ), perchlorate (ClO4- ) Borate (BF4 - ) and compounds which are inorganic or organic anions such as F-containing imide salts (R F 2N - ) etc. are mentioned. Examples of R in the F-containing imide salt (R F 2N - ) include perfluoroalkanesulfonyl groups such as trifluoromethanesulfonyl group and pentafluoroethanesulfonyl group, and fluorosulfonyl group. Examples of the F-containing imide salt include bissulfonylimide salts such as bis(fluorosulfonyl)imide salt [(FSO2)2N F , bis(trifluoromethanesulfonyl)imide salt [(CF3SO2)2N - , and bis(pentafluoroethanesulfonyl)imide salt [(C2F5SO2)2N - . - The acryloyl group-containing quaternary ammonium salt type ionic compound is preferably copolymerized in the acrylic polymer in an amount of 0.1 to 5.0% by weight.

[0031] Specific examples of the antistatic agent are not particularly limited, but specific examples of the ionic compound having a melting point of 30 to 50 °C include 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 3-methyl-1-dodecylpyridinium hexafluorophosphate, 1-dodecylpyridinium dodecylbenzenesulfonate, 4-methyl-1-octylpyridinium hexafluorophosphate, and the like. In addition, specific examples of the acryloyl group-containing quaternary ammonium salt type ionic compound include methyl dimethylaminomethyl (meth)acrylate hexafluorophosphate [(CH3)3N + CH2OCOCQ=CH2·PF6 - , where Q = H or CH3], and methyl dimethylaminoethyl (meth)acrylate bis(trifluoromethanesulfonyl)imide [(CH3)3N + (CH2)2OCOCQ=CH2·(CF3SO2)2N -, provided that Q = H or CH3), dimethylaminomethyl (meth) acrylate bis (fluorosulfonyl) imide methyl salt [(CH3)3N + CH2OCOCQ=CH2·(FSO2)2N - , provided that Q = H or CH3), etc.

[0032] The pressure-sensitive adhesive composition of the present invention contains a polyether-modified siloxane compound. The polyether-modified siloxane compound is a siloxane compound having a polyether group. In addition to the normal siloxane unit [-SiR 1 2-O-], it has a siloxane unit having a polyether group [-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 polyoxyethylene groups [(C2H4O) n and polyoxypropylene groups [(C3H6O) n , etc. polyoxyalkylene groups. The polyether-modified siloxane compound is preferably a polyether-modified siloxane compound having an HLB value of 7 to 12. Further, it is preferable that 0.01 to 0.5 parts by weight of the polyether-modified siloxane compound is contained per 100 parts by weight of the acrylic polymer. More preferably, it is 0.1 to 0.5 parts by weight. HLB is, for example, the hydrophilic-lipophilic balance (hydrophilicity-lipophilicity ratio) defined in JIS K3211 (Terms for Surfactants), etc. The polyether-modified siloxane compound 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 hydrosilyl group by a hydrosilylation reaction. Specifically, dimethylsiloxane·methyl(polyoxyethylene)siloxane copolymer, dimethylsiloxane·methyl(polyoxyethylene)siloxane·methyl(polyoxypropylene)siloxane copolymer, dimethylsiloxane·methyl(polyoxypropylene)siloxane polymer, etc. can be mentioned. By blending the polyether-modified siloxane compound into the adhesive composition, the adhesive strength and rework performance of the adhesive can be improved.

[0033] The adhesive composition of the present invention may contain a crosslinking retarder. Examples of the crosslinking retarder include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, stearyl acetoacetate, and β-diketones such as acetylacetone, 2,4-hexanedione, benzoylacetone. These are keto-enol tautomeric compounds, and in an adhesive composition using a polyisocyanate compound as a crosslinking agent, by blocking the isocyanate groups of the crosslinking agent, excessive viscosity increase and gelation of the adhesive composition after blending of the crosslinking agent can be suppressed, and the pot life of the adhesive composition can be extended. The crosslinking retarder is preferably a keto-enol tautomeric compound, and particularly preferably at least one selected from the group consisting of acetylacetone and ethyl acetoacetate. When the crosslinking retarder is added, it is preferably contained in an amount of 1.0 to 5.0 parts by weight based on 100 parts by weight of the acrylic polymer.

[0034] The pressure-sensitive adhesive composition of the present invention may contain a crosslinking catalyst. 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 thereof include amine compounds such as tertiary amines, organotin compounds, organolead compounds, and organozinc compounds. Examples of the tertiary amine include trialkylamine, N,N,N',N'-tetraalkyldiamine, N,N-dialkylamino alcohol, triethylenediamine, morpholine derivatives, piperazine derivatives, and the like. Examples of the organotin compound include dialkyltin oxide, fatty acid salts of dialkyltin, and fatty acid salts of stannous. The crosslinking catalyst is preferably an organotin compound, and more preferably at least one selected from the group consisting of dioctyltin oxide and dioctyltin dilaurate. When the crosslinking catalyst is added, it is preferably contained in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the acrylic polymer.

[0035] The pressure-sensitive adhesive composition of the present invention may contain a polyether compound. The polyether compound is a compound having a polyalkylene oxide group, and examples thereof include polyether polyols such as polyalkylene glycols and their derivatives. Examples of the alkylene group of the polyalkylene glycol and the polyalkylene oxide group 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. Examples of derivatives of polyalkylene glycols include polyoxyalkylene alkyl ethers such as polyoxyalkylene monoalkyl ethers and polyoxyalkylene dialkyl ethers, polyoxyalkylene alkenyl ethers such as polyoxyalkylene monoalkenyl ethers and polyoxyalkylene dialkenyl ethers, polyoxyalkylene aryl ethers such as polyoxyalkylene monoaryl ethers and polyoxyalkylene diaryl ethers, polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene glycol fatty acid esters such as polyoxyalkylene glycol mono-fatty acid esters and polyoxyalkylene glycol di-fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene alkyl amines, polyoxyalkylene diamines, and the like. Here, examples of the alkyl ether in the polyalkylene glycol derivative include lower alkyl ethers such as methyl ether and ethyl ether, and higher alkyl ethers such as lauryl ether and stearyl ether. Examples of the alkenyl ether in the polyalkylene glycol derivative include vinyl ether, allyl ether, oleyl ether, and the like. Further, examples of the fatty acid ester in the polyalkylene glycol derivative include saturated fatty acid esters such as acetic acid ester and stearic acid ester, and unsaturated fatty acid esters such as (meth)acrylic acid ester and oleic acid ester. The polyether compound is preferably a compound containing an ethylene oxide group, and more preferably a compound containing a polyethylene oxide group.

[0036] When the polyether compound has a polymerizable functional group, it can also be copolymerized with a (meth)acrylic polymer. Preferred polymerizable functional groups are vinylic functional groups such as (meth)acrylic groups, vinyl groups, and allyl groups. Examples of polyether compounds having a polymerizable functional group include polyalkylene glycol mono(meth)acrylate esters, polyalkylene glycol di(meth)acrylate esters, alkoxypolyalkylene glycol (meth)acrylate esters, polyalkylene glycol monoallyl ethers, polyalkylene glycol diallyl ethers, alkoxypolyalkylene glycol allyl ethers, polyalkylene glycol monovinyl ethers, polyalkylene glycol divinyl ethers, alkoxypolyalkylene glycol vinyl ethers, and the like.

[0037] Furthermore, as other components, known additives such as copolymerizable (meth)acrylic monomers containing alkylene oxide, (meth)acrylamide monomers, dialkyl-substituted acrylamide monomers, surfactants, curing accelerators, plasticizers, fillers, curing retardants, processing aids, anti-aging agents, and antioxidants can be appropriately blended. These can be used alone or in combination of two or more.

[0038] The acrylic polymer as the main component used in the adhesive composition of the present invention can be synthesized by copolymerizing an alkyl (meth)acrylate having an alkyl group with 4 to 10 carbon atoms, a hydroxyl group-containing copolymerizable monomer, and a carboxyl group-containing copolymerizable monomer. The polymerization method of the acrylic polymer is not particularly limited, and an appropriate polymerization method such as solution polymerization or emulsion polymerization can be used. Other monomers such as polyalkylene glycol mono(meth)acrylate ester monomers, nitrogen-containing vinyl monomers not containing a hydroxyl group, alkoxy group-containing alkyl (meth)acrylate monomers, and acryloyl group-containing quaternary ammonium salt-type ionic compounds may be copolymerized with the acrylic polymer. The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above acrylic polymer with a crosslinking agent, an antistatic agent, and further optionally any additives.

[0039] Also, the acid value of the acrylic polymer is preferably 0.01 to 8.0. Thereby, the contamination can be improved and the performance of preventing the occurrence of adhesive residue can be enhanced. Here, the "acid value" is one of the indexes representing the acid content, and is expressed by the number of mg of potassium hydroxide required to neutralize 1 g of the polymer containing a carboxyl group.

[0040] The adhesive layer formed by crosslinking the pressure-sensitive adhesive composition preferably has an adhesive force of 0.05 to 0.1 N / 25 mm at a peeling speed of 0.3 m / min in the low-speed region and an adhesive force of 1.0 N / 25 mm or less at a peeling speed of 30 m / min in the high-speed region. Thereby, a performance in which the adhesive force hardly changes depending on the peeling speed can be obtained, and it becomes possible to peel off quickly even by peeling at a high speed. Also, for reattachment, when the surface protection film is peeled off once, an excessive force is not required and it is easy to peel off from the adherend.

[0041] The surface resistivity of the adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is 5.0×10 +11 Ω / □ or less, and the peeling charging voltage is preferably ±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, that is, -0.5 to +0.5 kV. If the surface resistivity is large, the performance of discharging the static electricity generated by charging during peeling is poor. Therefore, by making the surface resistivity sufficiently small, the peeling charging voltage generated along with the static electricity generated when the adherend peels off the adhesive layer can be reduced, and it is possible to suppress the influence on the electric control circuit of the adherend.

[0042] The gel fraction of the pressure-sensitive adhesive layer (pressure-sensitive adhesive after crosslinking) formed by crosslinking the pressure-sensitive adhesive composition of the present invention is preferably 95 to 100%. Since the gel fraction is high in this way, the adhesive force does not become excessive at the peeling speed in the low-speed region, the elution of unpolymerized monomers or oligomers from the acrylic polymer is reduced, the reworkability and durability at high temperature and high humidity are improved, and contamination of the adherend can be suppressed.

[0043] The pressure-sensitive adhesive film of the present invention is formed by forming a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition of the present invention on one or both sides of a resin film. Further, the surface protection film of the present invention is a surface protection film formed by forming a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition of the present invention on one side of a resin film. Since each component of the pressure-sensitive adhesive composition of the present invention is blended in a well-balanced manner, it has excellent antistatic performance, excellent balance of adhesive force at the peeling speeds in the low-speed region and the high-speed region, and further excellent durability performance and rework performance (no contamination transfer to the adherend after tracing on the surface protection film with a ballpoint pen through the pressure-sensitive adhesive layer). Therefore, it can be suitably used as a surface protection film for polarizing plates, retardation plates, and antireflection films.

[0044] As the base film of the pressure-sensitive adhesive layer and the release film (separator) for protecting the adhesive surface, a resin film such as a polyester film can be used. On the surface of the base film opposite to the side where the pressure-sensitive adhesive layer of the resin film is formed, an antifouling treatment with a silicone-based or fluorine-based release agent, coating agent, silica fine particles, etc., and an antistatic treatment by applying or kneading an antistatic agent can be performed. On the surface of the release film that is in contact with the adhesive surface of the pressure-sensitive adhesive layer, a release treatment is performed with a silicone-based or fluorine-based release agent.

Examples

[0045] Hereinafter, the present invention will be specifically described with reference to examples.

[0046] <Production of acrylic polymer> [Example 1] Nitrogen gas was introduced into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube to replace the air in the reaction apparatus with nitrogen gas. Then, 90 parts by weight of 2-ethylhexyl acrylate, 9 parts by weight of 8-hydroxyoctyl acrylate, 1.0 part by weight of acrylic acid, and 60 parts by weight of a solvent (ethyl acetate) were added to the reaction apparatus. Then, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours and reacted at 65°C for 6 hours to obtain an acrylic polymer solution 1 used in Example 1 with 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 6 and Comparative Examples 1 to 3] Except that the composition of the monomers was made as described in (A) to (C) of Table 1, respectively, acrylic polymer solutions used in Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as the acrylic polymer solution 1 used in Example 1 above. In Tables 1 and 2, (A) is an alkyl (meth) acrylate as the main component, (B) is a copolymerizable monomer containing a hydroxyl group, and (C) is a copolymerizable monomer containing a carboxyl group.

[0047] [Table 1]

[0048] [Production of Adhesive Composition and Surface Protection Film] [Example 1] To 1 part by weight of the acrylic polymer solution 1 of Example 1 produced as described above, 2.0 parts by weight of 1-octylpyridinium dodecylbenzenesulfonate and 0.1 part by weight of KF-351A (a polyether-modified siloxane compound with an HLB of 12) were added and stirred. After that, 1.0 part by weight of Coronate HX (an isocyanurate form of a hexamethylene diisocyanate compound) was added and stirred and mixed to obtain the 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, the adhesive sheet was transferred onto the surface of a polyethylene terephthalate (PET) film that was subjected to antistatic and antifouling treatment on one side, on the side opposite to the antistatic and antifouling-treated surface, to obtain the surface protection film of Example 1 having a laminated structure of "antistatic and antifouling-treated PET film / adhesive layer / release film (silicone resin-coated PET film)". [Examples 2 to 6 and Comparative Examples 1 to 3] Surface protection films of Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as the surface protection film of Example 1 described above, except that the composition of the additives was made as described in (D) to (F) in Table 2. In Tables 1 and 2, (D) is a crosslinking agent, (E) is an antistatic agent, and (F) is a polyether-modified siloxane compound.

[0049]

Table 2

[0050] Table 1 shows the numerical values of parts by weight obtained by setting the total of groups (A) to (C) to 100 parts by weight, surrounded by parentheses. In addition, the compound names of the abbreviations of the respective components used in Table 1 are shown in Table 2. Note that Coronate (registered trademark) HX, HL, and L are product names of Nippon Polyurethane Industry Co., Ltd., Takenate (registered trademark) D-140N, D-127N, D-110N, and D-120N are product names of Mitsui Chemicals, Inc., and KF-351A, KF-352A, KF-353, KF-640, and X-22-6191 are product names of Shin-Etsu Chemical Co., Ltd.

[0051] <Test Methods and Evaluation> After aging the surface protection films in Examples 1 to 6 and Comparative Examples 1 to 3 for 7 days in an atmosphere of 23°C and 50% RH, the release film (PET film coated with silicone resin) was peeled off to expose the adhesive layer, which was used as a measurement sample for surface resistivity. Furthermore, the surface protection film with the adhesive layer exposed was laminated on the surface of a polarizing plate attached to a liquid crystal cell through the adhesive layer, left for 1 day, then autoclave-treated at 50°C, 5 atmospheres for 20 minutes, and left at room temperature for an additional 12 hours, which was used as a measurement sample for adhesive strength, peel charging voltage, reworkability, and durability.

[0052] <Acid Value> The acid value of the acrylic polymer was determined by dissolving the sample in a solvent (a mixture of diethyl ether and ethanol in a volume ratio of 2:1), using a potentiometric automatic titrator (manufactured by Kyoto Electronic Industry Co., Ltd., AT-610), performing potentiometric titration with a potassium hydroxide ethanol solution having a concentration of about 0.1 mol / l using the above potentiometric titrator, and measuring the amount of the potassium hydroxide ethanol solution required to neutralize the sample. Then, the acid value was determined from the following formula. Acid value = (B × f × 5.611) / S B = Amount (ml) of 0.1 mol / l potassium hydroxide ethanol solution used for titration f = Factor of 0.1 mol / l potassium hydroxide ethanol solution S = Mass (g) of solid content of sample

[0053] <Adhesive Strength> The obtained measurement sample (a 25-mm-wide surface protection film laminated on the surface of a polarizing plate) was peeled off at a peeling speed in the low-speed range (0.3 m / min) and a peeling speed in the high-speed range (30 m / min) using a tensile testing machine in the 180° direction, and the measured peeling strength was taken as the adhesive strength.

[0054] <Surface resistivity> After aging and before laminating on the polarizing plate, the peeling film (PET film coated with silicone resin) was peeled off to expose the adhesive layer, and the surface resistivity of the adhesive layer was measured using a resistivity meter High Resista UP-HT450 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0055] <Peeling charging voltage> When the obtained measurement sample was peeled off at a peeling speed of 30 m / min in the 180° direction, the voltage (charging voltage) generated by the charging of the polarizing plate was measured using high-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Corporation), and the maximum value of the measured values was taken as the peeling charging voltage.

[0056] <Reworkability> After tracing on the surface protection film of the obtained measurement sample with a ballpoint pen (load: 500 g, 3 round trips), the surface protection film was peeled off from the polarizing plate, and the surface of the polarizing plate was observed to confirm that there was no contamination transfer. The evaluation criteria were as follows: "○" when there was no contamination transfer to the polarizing plate, "△" when contamination transfer was confirmed at least partially along the trace traced with the ballpoint pen, and "×" when contamination transfer was confirmed along the trace traced with the ballpoint pen and detachment of the adhesive was also confirmed from the adhesive surface.

[0057] <Durability> The obtained measurement sample was left in an atmosphere of 60°C and 90% RH for 250 hours, taken out at room temperature, and further left for 12 hours. Then, the adhesive strength was measured and compared with the initial adhesive strength to confirm that there was no obvious increase. The evaluation criteria were as follows: "○" when the adhesive strength after the test was 1.5 times or less of the initial adhesive strength, and "×" when it exceeded 1.5 times.

[0058] Table 3 shows the evaluation results. The surface resistivity is expressed by the method of changing " +n m×10

[0059]

Table 3

[0060] For the surface protection films of Examples 1 to 6, the adhesive force at a peeling speed of 0.3 m / min in the low-speed region was 0.05 to 0.1 N / 25 mm, the adhesive force at a peeling speed of 30 m / min in the high-speed region was 1.0 N / 25 mm or less, the surface resistivity was 5.0×10 +11 Ω / square or less, the peeling charging voltage was ±0 to 0.5 kV, and there was no contamination transfer to the adherend after tracing on the surface protection film with a ballpoint pen through the adhesive layer, and it also had excellent durability when left for 250 hours in an atmosphere of 60°C and 90% RH. That is, it simultaneously satisfies all the required performances of (1) achieving a balance of adhesive force at the peeling speeds in the low-speed region and the high-speed region, (2) preventing the occurrence of adhesive residue, (3) having excellent antistatic performance, and (4) having rework performance.

[0061] For the surface protection film of Comparative Example 1, the amount of alkyl (meth)acrylate as the main component was too small, the amount of copolymerizable monomer containing a hydroxyl group was too large, it did not contain a copolymerizable monomer containing a carboxyl group, and perhaps because the HLB value of the polyether-modified siloxane compound was too small, the adhesive force at a peeling speed of 0.3 m / min in the low-speed region was small, the surface resistivity and the peeling charging voltage were high, and the durability was poor. For the surface protection film of Comparative Example 2, since the amount of copolymerizable monomer containing a carboxyl group was too large with respect to the alkyl (meth)acrylate as the main component, the pot life became too short and crosslinking proceeded before coating, so coating could not be performed. The surface protection film of Comparative Example 3 did not contain a carboxyl group-containing copolymerizable monomer, a crosslinking agent, and an antistatic agent. Perhaps because the HLB value of the polyether-modified siloxane compound was too small, the adhesive force at a peeling speed of 0.3 m / min in the low-speed region and the adhesive force at a peeling speed of 30 m / min in the high-speed region were too large, the surface resistivity and the peeling charging voltage were high, and the reworkability and durability were poor. Thus, in the surface protection films of Comparative Examples 1 to 3, it was not possible to simultaneously satisfy all the required performances of (1) achieving a balance of adhesive force at the peeling speeds in the low-speed region and the high-speed region, (2) preventing the occurrence of adhesive residue, (3) having excellent antistatic performance, and (4) having rework performance.

Claims

1. An adhesive composition containing an acrylic polymer, an antistatic agent, and a crosslinking agent, wherein the acrylic polymer is composed of a copolymer obtained by copolymerizing, based on 100 parts by weight of the acrylic polymer, at least one or more alkyl (meth)acrylates having an alkyl group with 4 to 10 carbon atoms in a total amount of 85 to 98.5 parts by weight, at least one or more copolymerizable monomers containing a hydroxyl group in a total amount of 0.5 to 15 parts by weight (however, excluding the case where the total amount of at least one or more copolymerizable monomers containing a hydroxyl group is 0.1 to 5.0 parts by weight based on 100 parts by weight of the total amount of at least one or more alkyl (meth)acrylates having an alkyl group with 4 to 10 carbon atoms), and at least one or more copolymerizable monomers containing a carboxyl group in a total amount of 0.5 to 2 parts by weight, and the adhesive composition contains, based on 100 parts by weight of the acrylic polymer, the crosslinking agent, a polyfunctional isocyanate compound having three or more functional groups, in a proportion of 0.1 to 5 parts by weight, the acid value of the acrylic polymer is 0.01 to 8.0, the antistatic agent is an ionic compound having a melting point of 30 to 50 °C, and the adhesive composition further contains a polyether-modified siloxane compound having an HLB value of 7 to 12. The ionic compound is an ionic compound having a cation and an anion, the cation is one selected from the group consisting of a pyridinium cation, an imidazolium cation, a pyrimidinium cation, a pyrazolium cation, a pyrrolidinium cation, an ammonium cation, a phosphonium cation, and a sulfonium cation, and the anion is a hexafluorophosphate anion (PF ６ － ), a thiocyanate anion (SCN － ), an alkylbenzenesulfonate anion (RC ６ H ４ SO ３ － ), a perchlorate anion (ClO ４ － ), or a tetrafluoroborate anion (BF ４ － ), and is one selected from the group consisting of:

2. The alkyl (meth)acrylate having an alkyl group with 4 to 10 carbon atoms is one or more selected from the group consisting of butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, and decyl (meth)acrylate. The adhesive composition according to Claim 1, characterized in that it is

3. ​ The 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 pressure-sensitive adhesive composition according to claim 1 or 2, characterized in that it is one or more of them.

4. A pressure-sensitive adhesive film, characterized in that a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 3 is formed on one or both sides of a resin film.

5. A surface protection film, characterized in that a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition according to any one of claims 1 to 3 is formed on one side of a resin film.

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