Adhesive composition and adhesive film

Abstract

To provide an adhesive composition and an adhesive film capable of simultaneously satisfying all of the following required performances: (1) balancing adhesive strength in a low-speed peeling region and a high-speed peeling region, (2) prevention of generating adhesive residue, (3) excellent antistatic performance and (4) reworkability.SOLUTION: There is provided an adhesive composition consisting of a copolymer obtained by copolymerization of (A) a (meth)acrylic acid ester monomer having an alkyl group having 4 to 10 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group and further comprises (D) a tri- or more-functional isocyanate compound, (G) an antistatic agent and (H) a polyether-modified siloxane compound having an HLB value of 7 to 12, wherein the antistatic agent (G) is an ionic compound (provided, not an alkali metal salt) which has a melting point of 30 to 80°C and is solid at 30°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a surface protection film used in the manufacturing process of liquid crystal displays. More specifically, the present invention relates to an adhesive composition for a surface protection film and a surface protection film used for protecting the surfaces of optical members such as polarizing plates and retardation plates that make up a liquid crystal display by adhering to the surfaces of the optical members.

Background Art

[0002] Conventionally, in the manufacturing process of optical members such as polarizing plates and retardation plates, 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] The surface protection film used in the process of manufacturing such an optical member has an adhesive layer formed on one side of an optically transparent polyethylene terephthalate (PET) resin film. However, 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 and retardation plates are subjected to product inspections involving optical evaluations such as the display ability, hue, contrast, and foreign matter inclusion of the liquid crystal display panel in a state where the surface protection film is bonded. Therefore, as a required performance for the surface protection film, it is required that no bubbles or foreign substances adhere to the adhesive layer. In recent years, when peeling the surface protection film from optical members such as polarizing plates and retardation plates, there is 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. In addition, when laminating a surface protection film onto optical members such as polarizing plates and retardation plates, for various reasons, the surface protection film may be peeled off once and then re-laminated. At this time, it is required that the film be easily peeled off from the optical member of the adherend (reworkability). In addition, when finally peeling off the surface protection film from optical members such as polarizing plates and retardation plates, it is required that the film can be peeled off promptly. That is, even in the case of so-called high-speed peeling, it is required that the adhesive strength change little depending on the peeling speed so that the film can be peeled off promptly.

[0004] Thus, in recent years, as the required performance for the adhesive layer constituting the surface protection film, (1) achieving a balance of adhesive strength in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance, etc. are required from the viewpoint of ease of use when using the surface protection film. However, even though each of these (1) to (4) individual required performances, which are the 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.

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

[0006] An acrylic pressure-sensitive adhesive layer mainly composed of a copolymer of an alkyl (meth)acrylate having an alkyl group with 7 or fewer carbon atoms and a carboxyl group-containing copolymerizable compound, which is crosslinked with a crosslinking agent, has a problem that when adhered for a long period of time, the pressure-sensitive adhesive migrates to the adherend side, and the adhesive strength to the adherend increases significantly over time. To avoid this, a pressure-sensitive adhesive layer using 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, which is crosslinked with a crosslinking agent, is known (Patent Document 1). In addition, a small amount of a copolymer of an alkyl (meth)acrylate and a carboxyl group-containing copolymerizable compound is blended with the same copolymer as described above, and a pressure-sensitive adhesive layer crosslinked with a crosslinking agent has been proposed. 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 during high-speed peeling in a manual work area.

[0007] To solve these problems, a pressure-sensitive adhesive composition has been proposed in which an equivalent or more of a crosslinking agent is blended with a copolymer of a monomer mixture obtained by adding a) 100 parts by weight of an alkyl (meth)acrylate having an alkyl group with 8 to 10 carbon atoms as a 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, with respect to the carboxyl group of component b) above (Patent Document 2). In the pressure-sensitive adhesive composition described in Patent Document 2, no peeling phenomenon such as floating occurs during processing or storage, and moreover, the adhesive strength hardly increases over time and the re-peelability is excellent. It can be re-peeled with a small force even after long-term storage, especially under a high-temperature atmosphere, and no adhesive residue remains on the adherend at that time. It can also be re-peeled with a small force even when high-speed peeling is performed.

[0008] In addition, regarding (3) excellent antistatic performance, as a method for imparting antistatic properties to the surface protection film, a method of kneading an antistatic agent into the base film is shown. Examples of antistatic agents include (a) various cationic antistatic agents having a cationic group such as a quaternary ammonium salt, pyridinium salt, and primary to tertiary amino groups; (b) anionic antistatic agents having an anionic group such as a sulfonate group, sulfate ester group, phosphate ester group, and phosphonate group; (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 adhesive layer, rather than incorporating it into the base film or applying it to the surface of the base film.

[0009] Regarding (4) rework performance, for example, an 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 based on 100 parts by weight of an acrylic resin (Patent Document 4). In Patent Document 4, an alkyl acrylate having about 2 to 12 carbon atoms in the alkyl group or an alkyl methacrylate having about 4 to 12 carbon atoms in the alkyl group, etc. are used as the main monomer components, and it is stated that other monomer components containing functional groups 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 desired to be 0.001 to 50% by weight, preferably 0.001 to 25% by weight, and more preferably 0.01 to 25% by weight. The adhesive composition described in such Patent Document 4 shows little change over time in cohesive force and adhesive force even under high temperature or high temperature and high humidity conditions, and also has excellent curved surface adhesive force, and thus is said to have reworkability. Generally, if the adhesive layer has a soft property, it is likely to cause adhesive residue and the reworkability is likely to decrease. That is, when misbonded, it is difficult to peel off and it is likely to be difficult to reattach. From this, it is considered necessary to crosslink a monomer having a functional group such as a carboxyl group as a main agent to make the 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 adhesive layer constituting the surface protection film, (1) balancing the adhesive force in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance, etc. have been required. However, although each of these (1) to (4) can meet the individual required performance, it has been difficult and impossible to simultaneously meet all the required performance of (1) to (4) required for 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 and a surface protection film capable of simultaneously satisfying all the required performance of (1) balancing the adhesive force in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

Means for Solving the Problem

[0013] To solve the above problems, the present invention is composed of a copolymer containing (A) a (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group. Further, it contains (D) a polyfunctional isocyanate compound having three or more functional groups, (E) a crosslinking retarder, (F) a crosslinking catalyst, (G) an antistatic agent, and (H) a polyether-modified siloxane compound having an HLB value of 7 to 12. With respect to 100 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms, the (B) copolymerizable monomer containing a hydroxyl group is 0.1 to 5.0 parts by weight, and the (C) copolymerizable monomer containing a carboxyl group is 0.35 to 1.0 parts by weight. And the (D) polyfunctional isocyanate compound having three or more functional groups contains at least one selected from hexamethylene diisocyanate compounds and isophorone diisocyanate compounds, thereby providing an adhesive composition. Further, the present invention provides a surface protection film using the above adhesive composition.

Effects of the Invention

[0014] According to the present invention, it is possible to provide an adhesive composition and a surface protection film that can simultaneously satisfy all the required performances, namely, (1) balancing the adhesive force in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

Modes for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described based on preferred embodiments. The pressure-sensitive adhesive composition of the present invention is characterized in that its main component is a copolymer containing (A) a (meth)acrylate monomer having an alkyl group with 4 to 10 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group, and further contains (D) a polyfunctional isocyanate compound having three or more functional groups, (E) a crosslinking retarder, (F) a crosslinking catalyst, (G) an antistatic agent, and (H) a polyether-modified siloxane compound.

[0016] (A) Examples of the (meth)acrylate monomer having an alkyl group with 4 to 10 carbon atoms 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, and the like.

[0017] (B) Examples of the copolymerizable monomer containing a hydroxyl group include hydroxyalkyl (meth)acrylates such as 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and hydroxyl group-containing (meth)acrylamides such as N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide. It is preferably at least one or more selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, and N-hydroxyethyl(meth)acrylamide. (A) It is preferable that 0.1 to 5.0 parts by weight of the copolymerizable monomer containing a hydroxyl group is contained with respect to 100 parts by weight of the (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms. In addition, among the copolymerizable monomers containing a hydroxyl group (B), the total amount of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate is preferably less than 1 part by weight (it is also acceptable if not contained), and is preferably 0 to 0.9 parts by weight.

[0018] (C) The copolymerizable monomer containing a carboxyl group is preferably at least one selected from the group of compounds consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate. (A) It is preferable that 0.35 to 1.0 parts by weight of the copolymerizable monomer containing a carboxyl group is contained with respect to 100 parts by weight of the (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms.

[0019] As the (D) polyfunctional isocyanate 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, such as biuret-modified products or isocyanurate-modified products of diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate (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 and glycerin (compounds having at least three or more OH groups in one molecule). (D) The polyisocyanate compound having three or more functional groups is a polyisocyanate compound having at least three or more isocyanate (NCO) groups in one molecule, particularly the isocyanurate form of hexamethylene diisocyanate compound, the isocyanurate form of isophorone diisocyanate compound, the adduct form of hexamethylene diisocyanate compound, the adduct form of isophorone diisocyanate compound, the biuret form of hexamethylene diisocyanate compound, and the biuret form of isophorone diisocyanate compound. It is preferably at least one selected from the group of compounds. (D) The polyisocyanate compound having three or more functional groups is preferably contained in an amount of 0.5 to 5.0 parts by weight based on 100 parts by weight of the copolymer.

[0020] (E) Examples of the crosslinking retarder include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate, and β-diketones such as acetylacetone, 2,4-hexanedione, and benzoylacetone. These are keto-enol tautomeric compounds, and in the pressure-sensitive 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 pressure-sensitive adhesive composition after the addition of the crosslinking agent can be suppressed, and the pot life of the pressure-sensitive adhesive composition can be extended. (E) The crosslinking retarder is preferably a keto-enol tautomeric compound, and is preferably at least one selected from the group of compounds consisting of acetylacetone and ethyl acetoacetate. (E) The crosslinking retarder is preferably contained in an amount of 1.0 to 5.0 parts by weight based on 100 parts by weight of the copolymer.

[0021] (F) The crosslinking catalyst may be any substance that functions as a catalyst for the reaction (crosslinking reaction) between the copolymer and the crosslinking agent when a polyisocyanate compound is used as the crosslinking agent, and examples include amine compounds such as tertiary amines, and organometallic compounds such as 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 derivative, piperazine derivative, and the like. Examples of the organotin compound include dialkyltin oxide, fatty acid salt of dialkyltin, fatty acid salt of stannous, and the like. (F) 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. (F) The crosslinking catalyst is preferably contained in an amount of 0.01 to 0.5 parts by weight based on 100 parts by weight of the copolymer.

[0022] (G) The antistatic agent is preferably solid at room temperature (e.g., 30 °C). More specifically, it is preferably an ionic compound having a melting point of 30 to 80 °C and contained in an amount of 0.5 to 5.0 parts by weight based on 100 parts by weight of the copolymer, or a quaternary ammonium salt type acrylic monomer having a melting point of 30 to 80 °C and copolymerized in the copolymer in an amount of 1.0 to 5.0% by weight. In the present invention, as the (G) antistatic agent, (G1) an ionic compound having a melting point of 30 to 80 °C is added to the copolymer, or (G2) a quaternary ammonium salt type acrylic monomer having a melting point of 30 to 80 °C is copolymerized in the copolymer. These (G) antistatic agents are presumed to have high affinity with the acrylic copolymer because of their low melting points and long-chain alkyl groups.

[0023] (G1) Examples of the ionic compound having a melting point of 30 to 80 °C include ionic compounds having a cation and an anion, where the cation is a nitrogen-containing onium cation such as pyridinium cation, imidazolium cation, pyrimidinium cation, pyrazolium cation, pyrrolidinium cation, ammonium cation, etc., phosphonium cation, sulfonium cation, etc., and the anion is hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), alkylbenzenesulfonate (RC6H4SO3 - ), perchlorate (ClO4- )), compounds that are inorganic or organic anions such as borate (BF4 - ) etc. can be mentioned. By selecting the chain length of the alkyl group, the position and number of substituents, etc., those with a melting point of 30 to 80 °C can be obtained. The cation is preferably a quaternary nitrogen-containing onium cation, such as a quaternary pyridinium cation like 1-alkylpyridinium (the carbon atoms at the 2nd to 6th positions may or may not have substituents), or a quaternary imidazolium cation like 1,3-dialkylimidazolium (the carbon atoms at the 2nd, 4th, and 5th positions may or may not have substituents), and quaternary ammonium cations such as tetraalkylammonium etc. can be mentioned.

[0024] (G2) As the quaternary ammonium salt type acrylic monomer having a melting point of 30 to 80 °C, it is an ionic compound having a cation and an anion, and the cation is (meth)acryloyloxyalkyltrialkylammonium [R3N + -C n H 2n -OCOCQ=CH2, provided that Q = H or CH3, R = alkyl] etc. (meth)acrylic group-containing quaternary ammonium, and the anion is hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), organic sulfonate (RSO3 - ), perchlorate (ClO4 - ), borate (BF4 - ) etc. can be mentioned. (G) Specific examples of the antistatic agent are not particularly limited, but 1-octylpyridinium hexafluorophosphate, 1-nonylpyridinium hexafluorophosphate, 2-methyl-1-dodecylpyridinium hexafluorophosphate, 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 1-dodecylpyridinium dodecylbenzenesulfonate, 4-methyl-1-octylpyridinium hexafluorophosphate, dimethylaminomethyl acrylate methyl hexafluorophosphate [(CH3)3N + CH2OCOCH=CH2·PF6 -Examples include "〕".

[0025] (H) 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 polyoxyalkylene groups such as polyoxyethylene group [(C2H4O) n and polyoxypropylene group [(C3H6O) n . (H) The polyether-modified siloxane compound is a polyether-modified siloxane compound having an HLB value of 7 to 12, and it is preferable that 0.01 to 0.5 parts by weight of the (H) polyether-modified siloxane compound is contained per 100 parts by weight of the copolymer. More preferably, it is 0.1 to 0.5 parts by weight. HLB is, for example, the hydrophilic-lipophilic balance (hydrophilic-lipophilic 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 hydrogenated silicon group by a hydrosilylation reaction. Specifically, examples include dimethylsiloxane·methyl(polyoxyethylene)siloxane copolymer, dimethylsiloxane·methyl(polyoxyethylene)siloxane·methyl(polyoxypropylene)siloxane copolymer, dimethylsiloxane·methyl(polyoxypropylene)siloxane polymer, etc. (H) By blending a polyether-modified siloxane compound into the pressure-sensitive adhesive composition, the adhesive strength and rework performance of the pressure-sensitive adhesive can be improved.

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

[0027] The copolymer of the main agent used in the pressure-sensitive adhesive composition of the present invention can be synthesized by polymerizing (A) a (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group. The polymerization method of the copolymer is not particularly limited, and an appropriate polymerization method such as solution polymerization or emulsion polymerization can be used. (G) When using the quaternary ammonium salt type acrylic monomer of (G2) as an antistatic agent, the copolymer of the main agent used in the pressure-sensitive adhesive composition of the present invention can be synthesized by polymerizing (A) a (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, (C) a copolymerizable monomer containing a carboxyl group, and the quaternary ammonium salt type acrylic monomer of (G2). The pressure-sensitive adhesive composition of the present invention can be prepared by blending the above copolymer with (D) a polyfunctional isocyanate compound having three or more functional groups, (E) a crosslinking retardant, (F) a crosslinking catalyst, (G) an antistatic agent, (H) a polyether-modified siloxane compound, and further appropriately any additives. Incidentally, when the quaternary ammonium salt type acrylic monomer having a melting point of 30 to 80 °C of (G2) is polymerized in the copolymer of the main agent, the (G) antistatic agent may or may not be further added to the copolymer.

[0028] It is preferable that the adhesive layer formed by crosslinking the adhesive composition has an adhesive strength of 0.05 to 0.1 N / 25 mm at a low-speed peeling region of 0.3 m / min and an adhesive strength of 1.0 N / 25 mm or less at a high-speed peeling region of 30 m / min. Thereby, a performance in which the adhesive strength hardly changes depending on the peeling speed can be obtained, and it becomes possible to peel off promptly even at high-speed peeling. Also, for reattachment, when peeling off the surface protection film once, an excessive force is not required and it is easy to peel off from the adherend.

[0029] The surface resistance value of the adhesive layer formed by crosslinking the adhesive composition is preferably 5.0×10 +10 Ω / □ or less and the peeling charging voltage is preferably ±0 to 1 kV. In the present invention, “±0 to 1 kV” means 0 to -1 kV and 0 to +1 kV, that is, -1 to +1 kV. If the surface resistance value is large, the performance of discharging the static electricity generated by charging during peeling is poor. Therefore, by making the surface resistance value 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 etc. of the adherend.

[0030] The gel fraction of the adhesive layer (adhesive after crosslinking) formed by crosslinking the adhesive composition of the present invention is preferably 95 to 100%. Since the gel fraction is high in this way, the adhesive strength in the low-speed peeling region does not become excessive, elution of unpolymerized monomers or oligomers from the copolymer is reduced, reworkability and durability in high temperature and high humidity are improved, and contamination of the adherend can be suppressed.

[0031] The pressure-sensitive adhesive film of the present invention is formed by forming a pressure-sensitive adhesive layer obtained 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 obtained by crosslinking the pressure-sensitive adhesive composition of the present invention on one side of a resin film. Since the components (A) to (H) described above are well-balanced in the pressure-sensitive adhesive composition of the present invention, (1) it is possible to balance the adhesive forces in the low-speed peeling region and the high-speed peeling region, (2) prevent the occurrence of adhesive residue, (3) have excellent antistatic performance, and (4) 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). It is possible to simultaneously satisfy all the required performances. Therefore, it can be suitably used as a surface protection film for polarizing plates.

[0032] 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, 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 brought into contact with the adhesive surface of the pressure-sensitive adhesive layer, a release treatment is performed with a silicone-based, fluorine-based release agent, etc.

Examples

[0033] Hereinafter, the present invention will be specifically described with reference to examples.

[0034] <Production of acrylic copolymer> [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, 60 parts of a solvent (ethyl acetate) was added to the reaction apparatus together with 100 parts by weight of 2-ethylhexyl acrylate, 0.9 parts by weight of 8-hydroxyoctyl acrylate, and 0.5 parts by weight of acrylic acid. Thereafter, 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours, and the reaction was carried out at 65 °C for 6 hours to obtain an acrylic copolymer solution 1 used in Example 1 having a weight average molecular weight of 5,000,000. [Examples 2 to 9 and Comparative Examples 1 to 9] Acrylic copolymer solutions used in Examples 2 to 9 and Comparative Examples 1 to 9 were obtained in the same manner as the acrylic copolymer solution 1 used in Example 1 above, except that the monomer composition was as described in (A) to (C) of Table 1.

[0035] [Production of Adhesive Composition and Surface Protection Film] [Example 1] To 100 parts by weight of the acrylic copolymer solution 1 (in which the acrylic copolymer was 100 parts by weight) produced as described above, 1.5 parts by weight of 1-octylpyridinium hexafluorophosphate, 0.1 part by weight of KF-351A (a polyether-modified siloxane compound with an HLB of 12), and 2.5 parts by weight of acetylacetone were added and stirred. Then, 1.5 parts by weight of Coronate HX (an isocyanurate form of a hexamethylene diisocyanate compound) and 0.02 part by weight of dioctyltin dilaurate were 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 polyethylene terephthalate (PET) film coated with a silicone resin, and then dried at 90 °C to remove the solvent, thereby obtaining an adhesive sheet having an adhesive layer thickness of 25 μm. Thereafter, the adhesive sheet was transferred onto the surface of a polyethylene terephthalate (PET) film that had been subjected to antistatic and antifouling treatment on one 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 (PET film coated with a silicone resin)". [Examples 2 to 9 and Comparative Examples 1 to 9] Except that the compositions of the additives were made as described in (D) to (H) of Table 1, surface protective films of Examples 2 to 9 and Comparative Examples 1 to 9 were obtained in the same manner as the surface protective film of Example 1 above.

[0036] In Table 1, the mixing ratios of the respective components are shown with the numerical values of the parts by weight obtained by setting the total of group (A) to 100 parts by weight enclosed in parentheses. Also, 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 and HL are product names of Nippon Polyurethane Industry Co., Ltd., Takenate (registered trademark) D-140N is a product name of Mitsui Chemicals, Inc., Duranate (registered trademark) 24A-100 is a product name of Asahi Kasei Chemicals Corporation, and KF-351A, KF-352A, KF-353, KF-640, and X-22-6191 are product names of Shin-Etsu Chemical Co., Ltd.

[0037]

Table 1

[0038]

Table 2

[0039] <Test Methods and Evaluations> After aging the surface protective films in Examples 1 to 9 and Comparative Examples 1 to 9 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 gel fraction and surface resistance value. Furthermore, the surface protective film with the adhesive layer exposed was bonded to the surface of a polarizing plate adhered to a liquid crystal cell through the adhesive layer, left for 1 day, then subjected to autoclave treatment 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, and durability.

[0040] <Gel Fraction> After aging, accurately measure the mass of the measurement sample before laminating it to the polarizing plate. Immerse it in toluene for 24 hours and then filter it through a 200-mesh wire mesh. Then, dry the filtrate at 100 °C for 1 hour, accurately measure the mass of the residue, and calculate the gel fraction of the adhesive layer (crosslinked adhesive) from the following formula. Gel fraction (%) = Mass of insoluble part (g) / Mass of adhesive (g) × 100

[0041] <Adhesive strength> The peeling strength measured by peeling the measurement sample obtained above (the surface protection film with a width of 25 mm laminated on the surface of the polarizing plate) at low speed (0.3 m / min) and high speed (30 m / min) using a tensile testing machine in the 180° direction was taken as the adhesive strength.

[0042] <Surface resistance> After aging and before laminating it to the polarizing plate, peel off the release film (PET film coated with silicone resin) to expose the adhesive layer, and measure the surface resistance of the adhesive layer using a resistivity meter High Resista UP-HT450 (manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0043] <Peeling charging voltage> The voltage (charging voltage) generated when the polarizing plate is charged during 180° peeling of the measurement sample obtained above at a peeling speed of 30 m / min was measured using high-precision electrostatic sensors SK-035 and SK-200 (manufactured by Keyence Corporation), and the maximum value of the measured value was taken as the peeling charging voltage.

[0044] <Reworkability> After tracing over the surface protection film of the measurement sample obtained above with a ballpoint pen, peel off the surface protection film from the polarizing plate and observe the surface of the polarizing plate to confirm that there is no contamination transfer to the polarizing plate. The evaluation criteria were evaluated as "○" when there was no contamination transfer to the polarizing plate and "×" when contamination transfer was confirmed at least partially along the traced trajectory of the ballpoint pen.

[0045] <Durability> The measured sample obtained above was left standing in an atmosphere of 60 °C and 90% RH for 250 hours, then taken out at room temperature and left standing for an additional 12 hours. After that, the adhesive strength was measured and it was confirmed that there was no obvious increase compared to the initial adhesive strength. The evaluation criteria were as follows: when the adhesive strength after the test was 1.5 times or less of the initial adhesive strength, it was evaluated as "○"; when it exceeded 1.5 times, it was evaluated as "×".

[0046] Table 3 shows the evaluation results. The surface resistance value was expressed in the format of "m×10 +n " being expressed as "mE+n" (where m is an arbitrary real value and n is a positive integer).

[0047]

Table 3

[0048] For the surface protection films of Examples 1 to 9, the adhesive strength in the low-speed peeling region of 0.3 m / min was 0.05 to 0.1 N / 25 mm, the adhesive strength in the high-speed peeling region of 30 m / min was 1.0 N / 25 mm or less, the surface resistance value was 5.0×10 +10 Ω / □ or less, the peeling charging voltage was ±0 to 1 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 standing in an atmosphere of 60 °C and 90% RH for 250 hours. That is, it simultaneously satisfied all the required performances of (1) achieving a balance of adhesive strength in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

[0049] For the surface protection film of Comparative Example 1, perhaps because the (B) hydroxyl group-containing monomer was excessive, the adhesive strength in the low-speed peeling region of 0.3 m / min was low as a result. In the surface protection film of Comparative Example 2, perhaps because the amount of (B) hydroxyl group-containing monomer was too small, the amount of (D) isocyanate compound was too large, and the HLB value of (H) polyether-modified siloxane compound was too small, the adhesive force at the low-speed peeling region of 0.3 m / min and the adhesive force at the high-speed peeling region of 30 m / min were too large, the peel-off withstand voltage was high, the reworkability and durability were poor, and the gel fraction was low. In the surface protection film of Comparative Example 3, perhaps because the amount of (B) hydroxyl group-containing monomer was too large, the amount of (C) acid-containing monomer was too large, and the HLB value of (H) polyether-modified siloxane compound was too large, the adhesive force at the low-speed peeling region of 0.3 m / min was low, the surface resistance value was high, the peel-off withstand voltage was high, and the reworkability and durability were poor.

[0050] In the surface protection film of Comparative Example 4, perhaps because the amount of (C) acid-containing monomer was too small, the adhesive force at the low-speed peeling region of 0.3 m / min was low and the durability was poor. In the surface protection film of Comparative Example 5, perhaps because the amount of (B) hydroxyl group-containing monomer was too large and the amount of (D) isocyanate compound was too small, the adhesive force at the low-speed peeling region of 0.3 m / min and the adhesive force at the high-speed peeling region of 30 m / min were too large, the peel-off withstand voltage was high, the reworkability and durability were poor, and the gel fraction was low. In the surface protection film of Comparative Example 6, since (E) crosslinking retarder was not blended and (F) crosslinking catalyst was excessive, perhaps the pot life became too short and crosslinking proceeded before coating, so coating could not be performed.

[0051] In the surface protection film of Comparative Example 7, since it contained MA having a C1 alkyl group in the (meth)acrylate monomer having an alkyl group (A) and (F) crosslinking catalyst was not blended, perhaps the adhesion at the low-speed peeling region of 0.3 m / min and the adhesion at the high-speed peeling region of 30 m / min were too large, the surface resistance value was high, the peel-off withstand voltage was high, and the reworkability and durability were poor. In the surface protection film of Comparative Example 8, the amount of the (G) antistatic agent was too small, and the (H) polyether-modified siloxane compound was not blended. For this reason, the adhesive force at the low-speed peeling region of 0.3 m / min and the adhesive force at the high-speed peeling region of 30 m / min were too large, the peel-off withstand voltage was high, and the reworkability was poor. In the surface protection film of Comparative Example 9, the melting point of the (G) antistatic agent was less than 30°C (liquid at room temperature), and the amount of the (H) polyether-modified siloxane compound was too large. For this reason, the adhesive force at the low-speed peeling region of 0.3 m / min was low, the peel-off withstand voltage was high, and the durability was poor. As described above, in the surface protection films of Comparative Examples 1 to 9, it was not possible to simultaneously satisfy all the required performances of (1) achieving a balance in the adhesive force in the low-speed peeling region and the high-speed peeling region, (2) preventing the occurrence of adhesive residue, (3) excellent antistatic performance, and (4) rework performance.

Claims

1. It is composed of a copolymer obtained by copolymerizing (A) a (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms, (B) a copolymerizable monomer containing a hydroxyl group, and (C) a copolymerizable monomer containing a carboxyl group. Furthermore, it contains (D) a polyfunctional isocyanate compound having three or more functional groups, (G) an antistatic agent, and (H) a polyether-modified siloxane compound having an HLB value of 7 to 12. Based on 100 parts by weight of the (A) (meth)acrylic acid ester monomer having an alkyl group with 4 to 10 carbon atoms, 50 parts by weight or more of one selected from the group consisting of butyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, 0.1 to 5.0 parts by weight of the (B) copolymerizable monomer containing a hydroxyl group, and 0.35 to 1.0 parts by weight of the (C) copolymerizable monomer containing a carboxyl group are included. The pressure-sensitive adhesive composition is characterized in that the (G) antistatic agent is an ionic compound (excluding alkali metal salts) having a melting point of 30 to 80 °C and being solid at 30 °C.

2. The pressure-sensitive adhesive composition according to Claim 1, wherein the (B) copolymerizable monomer containing a hydroxyl group is at least one selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, N-hydroxy (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, and N-hydroxyethyl (meth)acrylamide.

3. The pressure-sensitive adhesive composition according to Claim 1 or 2, characterized in that 0.5 to 5.0 parts by weight of an ionic compound and 0.01 to 0.5 parts by weight of the (H) polyether-modified siloxane compound having an HLB value of 7 to 12 are included based on 100 parts by weight of the copolymer.

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.

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