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 adhesive composition having antistatic properties, an adhesive film having an antistatic adhesive layer formed on at least one side of a resin film using the adhesive composition, and a surface protective film. Furthermore, 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 used to protect the surface of optical components such as polarizing plates, phase difference plates, and anti-reflective films that constitute liquid crystal displays by being attached to the surface of such optical components, and a surface protection film using the same. [Background technology]

[0002] Conventionally, in the manufacturing process of optical components such as polarizing plates, phase difference plates, and anti-reflective films that make up liquid crystal displays, a surface protection film is applied to temporarily protect the surface of the optical components. Such surface protection films are used only in the manufacturing process of the optical components and are peeled off and removed when the optical components are assembled into the liquid crystal display. Because such surface protection films for protecting the surface of optical components are used only in the manufacturing process, they are sometimes commonly referred to as process films.

[0003] Thus, the surface protection film used in the manufacturing process of optical components has an adhesive layer formed on one side of an optically transparent polyethylene terephthalate (PET) resin film. However, a release film, which has been treated to remove adhesive, is laminated on top of the adhesive layer to protect it until it is bonded to the optical component. Furthermore, optical components such as polarizing plates, phase difference plates, and anti-reflective films undergo product inspections that include optical evaluations of the liquid crystal display's display capability, hue, contrast, and foreign matter contamination while the surface protective film is attached. Therefore, the required performance of the surface protective film is that the adhesive layer is free of air bubbles and foreign matter. Furthermore, in recent years, there have been concerns that the static electricity generated when peeling off the adhesive layer from optical components such as polarizing plates, phase difference plates, and anti-reflective films may affect the electrical control circuits of liquid crystal displays, leading to a demand for adhesive layers with superior antistatic properties. Furthermore, when bonding surface protective films to optical components such as polarizing plates, phase difference plates, and anti-reflective films, it is sometimes necessary to peel off the surface protective film and reapply it for various reasons. In such cases, ease of removal from the optical component (reworkability) is required. Furthermore, it is required that the adhesive does not contaminate the surface to be adhered to, meaning that no adhesive residue is left behind. Furthermore, when the surface protective film is finally peeled off from optical components such as polarizing plates, phase difference plates, and anti-reflective films, it is required that it can be peeled off quickly. In other words, it is required that the adhesive strength does not change much with the peeling speed so that it can be peeled off quickly even at high speeds.

[0004] Thus, in recent years, the required performance of the adhesive layer constituting surface protective films has been to (1) balance the adhesive strength at low and high peeling speeds, (2) prevent the generation of adhesive residue, (3) have excellent antistatic properties, and (4) have rework properties, in order to make surface protective films easy to use. However, while it was possible to satisfy each of the individual performance requirements (1) to (4) for the adhesive layer constituting the surface protective film, simultaneously satisfying all of the performance requirements (1) to (4) for the adhesive layer of the surface protective film was an extremely difficult challenge. In this specification, the "low-speed region" refers to a peeling speed of approximately 0.3 m / min, and the "high-speed region" refers to a peeling speed of approximately 30 m / min.

[0005] For example, the following suggestions are known regarding (1) balancing the adhesive force at low-speed and high-speed peeling speeds, and (2) preventing the generation of adhesive residue.

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

[0007] To solve these problems, an adhesive composition has been proposed in which a copolymer of monomer mixtures is obtained by adding 100 parts by weight of an alkyl (meth)acrylate mainly composed of an alkyl (meth)acrylate having an alkyl group having 8 to 10 carbon atoms, 1 to 15 parts by weight of a copolymerizable compound containing a carboxyl group, and 3 to 100 parts by weight of a vinyl ester of an aliphatic carboxylic acid having 1 to 5 carbon atoms, and a crosslinking agent in an amount equivalent to or greater than the carboxyl group of component b) above is added (Patent Document 2). The adhesive composition described in Patent Document 2 does not exhibit peeling phenomena such as lifting during processing or storage, and moreover, its adhesive strength does not increase significantly over time, and it has excellent re-peelability. Furthermore, it can be re-peeled with little force even after long-term storage, especially in a high-temperature atmosphere, and in that case, no adhesive residue is left on the adherend, and it can also be re-peeled with little force even when peeling at high speed.

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

[0009] Furthermore, (4) Regarding rework performance, for example, an adhesive composition has been proposed in which an isocyanate compound curing agent and a specific silicate oligomer are blended in an acrylic resin at a concentration of 0.0001 to 10 parts by weight per 100 parts by weight of the acrylic resin (Patent Document 4). Patent Document 4 discloses that an alkyl acrylate having an alkyl group with about 2 to 12 carbon atoms, an alkyl methacrylate having an alkyl group with about 4 to 12 carbon atoms, or the like is used as a main monomer component, and other functional group-containing monomer components such as, for example, a carboxyl group-containing monomer can be contained. It is generally stated that it is preferable to contain the above main monomer in an amount of 50% by weight or more, 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 Patent Document 4 is said to have reworkability because it has small changes in cohesive force and adhesive force over time even under high temperature or high temperature and high humidity, and exhibits excellent adhesive force to curved surfaces. Generally, when a pressure-sensitive adhesive layer is made soft, adhesive residue is likely to occur, and reworkability tends to decrease. That is, when the film is mistakenly bonded, it is difficult to peel off, and re-bonding tends to be difficult. 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 impart reworkability.

Prior Art Literature

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problem to be Solved by the Invention

[0011] In the prior art, as required performance for the pressure-sensitive adhesive layer constituting a surface protection film, The requirements have been to (1) balance the adhesive strength at low and high peeling speeds, (2) prevent the generation of adhesive residue, (3) have excellent antistatic properties, and (4) have reworkability. However, even if it was possible to satisfy each of these individual performance requirements (1) to (4), it was not possible to satisfy all the performance requirements required for the adhesive layer of a surface protective film.

[0012] The present invention has been made in view of the above circumstances, and aims to provide an adhesive composition, adhesive film, and surface protective film that have excellent antistatic performance, a good balance of adhesive strength at low and high peeling speeds, and also excellent durability and rework performance. [Means for solving the problem]

[0013] To solve the above problems, the present invention provides an adhesive composition containing an antistatic agent, comprising an acrylic polymer mainly composed of an alkyl (meth)acrylate having an alkyl group having 4 to 10 carbon atoms, wherein per 100 parts by weight of the acrylic polymer, the composition contains 85 to 98.5 parts by weight of the alkyl (meth)acrylate, 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, wherein the acid value of the acrylic polymer is 0.01 to 8.0, the antistatic agent is an ionic compound with a melting point of 30 to 50°C, and the composition contains a polyether-modified siloxane compound.

[0014] Furthermore, it is preferable that the alkyl (meth)acrylate, which is the main component, is one or more compounds 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.

[0015] Furthermore, it is preferable that the copolymerizable monomer containing a hydroxyl group 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] Furthermore, it is preferable that the copolymerizable monomer containing the carboxyl group is one or more compounds selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid.

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

[0018] Furthermore, it is preferable that the crosslinking agent is a trifunctional or more isocyanate compound.

[0019] Furthermore, the present invention provides an adhesive film characterized by having an adhesive layer formed by crosslinking the adhesive composition on one or both sides of a resin film.

[0020] Furthermore, the present invention provides a surface protection film characterized by having an adhesive layer formed on one side of a resin film, which is obtained by crosslinking the adhesive composition. [Effects of the Invention]

[0021] According to the present invention, it is possible to satisfy all the performance requirements for the adhesive layer of a surface protective film, which could not be solved by conventional technology, and moreover, to obtain excellent antistatic performance and prevent the occurrence of adhesive residue. [Modes for carrying out the invention]

[0022] The present invention will be described below based on preferred embodiments. The adhesive composition of the present invention is an adhesive composition containing an antistatic agent, comprising an acrylic polymer mainly composed of an alkyl (meth)acrylate having an alkyl group having 4 to 10 carbon atoms, wherein per 100 parts by weight of the acrylic polymer, it contains 85 to 98.5 parts by weight of the alkyl (meth)acrylate, 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, wherein the acid value of the acrylic polymer is 0.01 to 8.0, the antistatic agent is an ionic compound with a melting point of 30 to 50°C, and it contains a polyether-modified siloxane compound.

[0023] The main component alkyl(meth)acrylate is preferably an alkyl(meth)acrylate having an alkyl group with 4 to 10 carbon atoms, and is preferably 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. It is preferable that the acrylic polymer contains 85 to 98.5 parts by weight of the main component alkyl (meth)acrylate per 100 parts by weight.

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

[0025] As the copolymerizable monomer containing a carboxyl group, one or more compounds selected from the group consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid are preferred. It is preferable that the acrylic polymer contains 0.1 to 2 parts by weight of a copolymerizable monomer containing a carboxyl group per 100 parts by weight of the acrylic polymer.

[0026] In the adhesive composition of the present invention, it is preferable to crosslink the adhesive polymer when forming the adhesive layer. As a method for causing the crosslinking reaction, crosslinking may be performed by photocrosslinking such as ultraviolet light (UV), but it is preferable that the adhesive composition contains a crosslinking agent. Examples of crosslinking agents 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 these, polyisocyanate compounds (bifunctional or trifunctional or higher isocyanate compounds) are preferred, and trifunctional or higher isocyanate compounds are more preferred. It is preferable that the crosslinking agent is contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the acrylic polymer.

[0027] A polyisocyanate compound with three or more functionalities can be any polyisocyanate compound having at least three isocyanate (NCO) groups in one molecule. Polyisocyanate compounds can be classified into aliphatic isocyanates, aromatic isocyanates, acyclic isocyanates, and alicyclic isocyanates, and any of these is acceptable. Specific examples of polyisocyanate compounds include aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and trimethylhexamethylene diisocyanate (TMDI), and aromatic isocyanate compounds such as diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (H6XDI), dimethyl diphenyl diisocyanate (TOID), and tolylene diisocyanate (TDI). Examples of isocyanate compounds with three or more functions include biuret-modified and isocyanurate-modified diisocyanates (compounds having two NCO groups in one molecule), and adduct compounds (polyol-modified compounds) with trivalent or higher polyols (compounds having at least three OH groups in one molecule) such as trimethylolpropane (TMP) and glycerin.

[0028] The adhesive composition of the present invention preferably contains an antistatic agent in order to impart antistatic properties. The antistatic agent is preferably solid at room temperature (e.g., 30°C), and more specifically, the antistatic agent is an ionic compound with a melting point of 30 to 50°C. The antistatic agent may also be a quaternary ammonium salt type ionic compound containing an acryloyl group. These antistatic agents are presumed to have high affinity for acrylic polymers because they have low melting points and long-chain alkyl groups.

[0029] The antistatic agent that is an ionic compound having a melting point of 30 to 50°C is an ionic compound having a cation and an anion, wherein the cation is a nitrogen-containing onium cation such as a pyridinium cation, an imidazolium cation, a pyrimidinium cation, a pyrazolium cation, a pyrrolidinium cation, or an ammonium cation, or a phosphonium cation, a sulfonium cation, or the like, and the anion is hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - ), and other inorganic or organic anionic compounds. A compound having a melting point of 30 to 50°C can be obtained by selecting the chain length of the alkyl group, the position and number of substituents, and the like. The cation is preferably a quaternary nitrogen-containing onium cation, and examples thereof include quaternary pyridinium cations such as 1-alkylpyridinium (the carbon atoms at positions 2 to 6 may be substituted or unsubstituted), quaternary imidazolium cations such as 1,3-dialkylimidazolium (the carbon atoms at positions 2, 4 and 5 may be substituted or unsubstituted), and quaternary ammonium cations such as tetraalkylammonium. The antistatic agent, which is an ionic compound having 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] The acryloyl group-containing quaternary ammonium salt-type ionic compound is an ionic compound having a cation and an anion, wherein the cation is (meth)acryloyloxyalkyltrialkylammonium [R3N + -C n H 2n -OCOCQ=CH2, where Q = H or CH3, R = alkyl] and other (meth)acryloyl group-containing quaternary ammonium, and the anion is hexafluorophosphate (PF6 - ), thiocyanate (SCN - ), organic sulfonate (RSO3 - ), perchlorate (ClO4- ), tetrafluoroborate (BF4 - ), F-containing imide salt (R F 2N - Examples include compounds that are inorganic or organic anions, such as ). F-containing imide salts (R F 2N - ) of R F Examples include perfluoroalkanesulfonyl groups such as trifluoromethanesulfonyl groups and pentafluoroethanesulfonyl groups, as well as fluorosulfonyl groups. Examples of fluorine-containing imide salts include bis(fluorosulfonyl)imide salt [(FSO2)2N - ], bis(trifluoromethanesulfonyl)imide salt [(CF3SO2)2N - ], bis(pentafluoroethanesulfonyl)imide salt [(C2F5SO2)2N - Examples of bissulfonylimide salts include the following: The quaternary ammonium salt type ionic compound containing the acryloyl group is preferably copolymerized in the acrylic polymer at a concentration of 0.1 to 5.0% by weight.

[0031] While there are no particular limitations on specific examples of antistatic agents, examples of ionic compounds with a melting point of 30-50°C include 1-octylpyridinium dodecylbenzenesulfonate, 1-dodecylpyridinium thiocyanate, 3-methyl-1-dodecylpyridinium hexafluoride phosphate, 1-dodecylpyridinium dodecylbenzenesulfonate, and 4-methyl-1-octylpyridinium hexafluoride phosphate. Furthermore, a specific example of the quaternary ammonium salt type ionic compound containing the acryloyl group is dimethylaminomethyl (meth)acrylate methyl hexafluoride phosphate [(CH3)3N + CH2OCOCQ=CH2·PF6 - However, Q=H or CH3], Dimethylaminoethyl (meth)acrylate bis(trifluoromethanesulfonyl)imide methyl salt [(CH3)3N + (CH2)2OCOCQ=CH2·(CF3SO2)2N -However, Q=H or CH3], Dimethylaminomethyl (meth)acrylate bis(fluorosulfonyl)imide methyl salt [(CH3)3N + CH2OCOCQ=CH2·(FSO2)2N - However, examples include Q = H or CH3.

[0032] The 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, and has a normal siloxane unit [-SiR 1 In addition to 2-O-, there are siloxane units having a polyether group [-SiR 1 (R 2 O(R 3 O) n R 4 It has )-O-]. Here, R 1 R is one or more alkyl or aryl groups, 2 and R 3 R is one or more alkylene groups, 4 This represents one or more alkyl groups or acyl groups (terminal groups). Examples of polyether groups include polyoxyethylene groups [(C2H4O)] n ] and polyoxypropylene group [(C3H6O) n Examples of polyoxyalkylene groups include the following: The polyether-modified siloxane compound is preferably a polyether-modified siloxane compound having an HLB value of 7 to 12. Furthermore, it is preferable that the polyether-modified siloxane compound is present in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the acrylic polymer. More preferably, it is 0.1 to 0.5 parts by weight. HLB refers to the hydrophilic-lipophilic balance (hydrophilic-lipophilic ratio) as defined in standards such as JIS K3211 (Terminology for Surfactants). Polyether-modified siloxane compounds can be obtained, for example, by grafting an organic compound having unsaturated bonds and polyoxyalkylene groups onto a polyorganosiloxane main chain having silicon hydride groups via a hydrosilylation reaction. Specifically, examples include dimethylsiloxane-methyl(polyoxyethylene)siloxane copolymers, dimethylsiloxane-methyl(polyoxyethylene)siloxane-methyl(polyoxypropylene)siloxane copolymers, and dimethylsiloxane-methyl(polyoxypropylene)siloxane polymers. By incorporating the aforementioned 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 crosslinking retarders 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 ketoenol tautomer compounds, and in adhesive compositions using a polyisocyanate compound as a crosslinking agent, they block the isocyanate group of the crosslinking agent, thereby suppressing excessive viscosity increase and gelation of the adhesive composition after the addition of the crosslinking agent, and extending the pot life of the adhesive composition. The crosslinking retarder is preferably a ketoenol tautomer compound, and more preferably at least one selected from the group of compounds consisting of acetylacetone and acetateethyl. When the crosslinking retarder is added, it is preferable that it is included in an amount of 1.0 to 5.0 parts by weight per 100 parts by weight of the acrylic polymer.

[0034] The adhesive composition of the present invention may contain a crosslinking catalyst. The crosslinking catalyst can 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 include amine compounds such as tertiary amines, organotin compounds, organolead compounds, organozinc compounds, and other organometallic compounds. Examples of tertiary amines include trialkylamines, N,N,N',N'-tetraalkyldiamines, N,N-dialkylamino alcohols, triethylenediamines, morpholine derivatives, and piperazine derivatives. Examples of organotin compounds include dialkyltin oxides, fatty acid salts of dialkyltin, and fatty acid salts of stannous tin. The crosslinking catalyst is preferably an organotin compound, and more preferably at least one selected from the group of compounds consisting of dioctyl tin oxide and dioctyl tin dilaurate. When the crosslinking catalyst is added, it is preferable that it is included in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the acrylic polymer.

[0035] The adhesive composition of the present invention may contain a polyether compound. The polyether compound is a compound having a polyalkylene oxide group, and examples include polyether polyols such as polyalkylene glycol and their derivatives. Examples of the alkylene group of the polyalkylene glycol and the polyalkylene oxide group include, but are not limited to, ethylene groups, propylene groups, and butylene groups. The polyalkylene glycol may be a copolymer of two or more polyalkylene glycols, such as polyethylene glycol, polypropylene glycol, and polybutylene glycol. Examples of polyalkylene glycol copolymers include polyethylene glycol-polypropylene glycol, polyethylene glycol-polybutylene glycol, polypropylene glycol-polybutylene glycol, and polyethylene glycol-polypropylene glycol-polybutylene glycol, and the copolymer may be a block copolymer or a random copolymer. Examples of polyalkylene glycol derivatives include polyoxyalkylene alkyl ethers such as polyoxyalkylene monoalkyl ethers and polyoxyalkylenedialkyl ethers, polyoxyalkylene alkenyl ethers such as polyoxyalkylene monoalkenyl ethers and polyoxyalkylenedialkenyl ethers, polyoxyalkylene aryl ethers such as polyoxyalkylene monoaryl ethers and polyoxyalkylenediaryl ethers, polyoxyalkylene alkylphenyl ethers, polyoxyalkylene glycol fatty acid esters such as polyoxyalkylene glycol monofatty acid esters and polyoxyalkylene glycol difatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene alkylamines, and polyoxyalkylenediamines. Here, examples of alkyl ethers in polyalkylene glycol derivatives include lower alkyl ethers such as methyl ether and ethyl ether, and higher alkyl ethers such as lauryl ether and stearyl ether. Examples of alkenyl ethers in polyalkylene glycol derivatives include vinyl ether, allyl ether, and oleyl ether. Furthermore, examples of fatty acid esters in polyalkylene glycol derivatives include saturated fatty acid esters such as acetate and stearic acid, and unsaturated fatty acid esters such as (meth)acrylic acid and oleic acid. The polyether compound is preferably a compound containing an ethylene oxide group, and more preferably a compound containing a polyethylene oxide group.

[0036] If the polyether compound has polymerizable functional groups, it can also be copolymerized with (meth)acrylic polymers. Preferred polymerizable functional groups are vinyl functional groups such as (meth)acrylic groups, vinyl groups, and allyl groups. Examples of polyether compounds having polymerizable functional groups include polyalkylene glycol mono(meth)acrylic acid esters, polyalkylene glycol di(meth)acrylic acid esters, alkoxy polyalkylene glycol (meth)acrylic acid esters, polyalkylene glycol monoallyl ethers, polyalkylene glycol diallyl ethers, alkoxy polyalkylene glycol allyl ethers, polyalkylene glycol monovinyl ethers, polyalkylene glycol divinyl ethers, and alkoxy polyalkylene glycol vinyl ethers.

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

[0038] The acrylic polymer used as the main component 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 copolymerizable monomer containing a hydroxyl group, and a copolymerizable monomer containing a carboxyl group. The polymerization method of the acrylic polymer is not particularly limited, and any suitable polymerization method such as solution polymerization or emulsion polymerization can be used. Acrylic polymers may also be copolymerized with other monomers such as polyalkylene glycol mono(meth)acrylic acid ester monomers, nitrogen-containing vinyl monomers that do not contain hydroxyl groups, alkyl(meth)acrylate monomers containing alkoxy groups, and quaternary ammonium salt type ionic compounds containing acryloyl groups. The adhesive composition of the present invention can be prepared by blending the above-mentioned acrylic polymer with a crosslinking agent, an antistatic agent, and any other additive as appropriate.

[0039] Furthermore, it is preferable that the acid value of the acrylic polymer is between 0.01 and 8.0. This improves stain resistance and enhances the ability to prevent adhesive residue. Here, "acid value" is one of the indicators that represents the acid content, and is expressed as the number of milligrams of potassium hydroxide required to neutralize 1 gram of polymer containing carboxyl groups.

[0040] Preferably, the adhesive layer formed by crosslinking the aforementioned adhesive composition has an adhesive strength of 0.05 to 0.1 N / 25 mm at a peeling speed of 0.3 m / min in the low-speed range, and an adhesive strength of 1.0 N / 25 mm or less at a peeling speed of 30 m / min in the high-speed range. This results in a performance in which the adhesive strength does not change much with the peeling speed, and enables rapid peeling even at high peeling speeds. Furthermore, when peeling off the surface protective film for reapplication, it does not require excessive force and is easy to peel off from the adherend.

[0041] The adhesive layer formed by crosslinking the aforementioned adhesive composition has a surface resistivity of 5.0 × 10 +11 The resistivity is preferably Ω / □ or less, and the peel band voltage is preferably ±0 to 0.5kV. In this invention, "±0 to 0.5kV" means 0 to -0.5kV and 0 to +0.5kV, i.e., -0.5 to +0.5kV. If the surface resistivity is high, the ability to dissipate static electricity generated by charging during peeling is poor. By making the surface resistivity sufficiently low, the peel band voltage generated by static electricity when the adhesive layer is peeled off by the adherend can be reduced, thereby suppressing its impact on the electrical control circuit of the adherend.

[0042] The gel fraction of the adhesive layer (adhesive after crosslinking) obtained by crosslinking the adhesive composition of the present invention is preferably 95 to 100%. This high gel fraction prevents excessive adhesion at low peeling speeds, reduces the elution of unpolymerized monomers or oligomers from the acrylic polymer, improves reworkability and durability at high temperatures and humidity, and suppresses contamination of the adherend.

[0043] The adhesive film of the present invention is formed by creating an adhesive layer on one or both sides of a resin film, which is formed by crosslinking the adhesive composition of the present invention. The surface protection film of the present invention is a surface protection film formed by creating an adhesive layer on one side of a resin film, which is formed by crosslinking the adhesive composition of the present invention. Because the adhesive composition of the present invention has a well-balanced blend of each component, it has excellent antistatic performance, excellent balance of adhesive strength at low and high peeling speeds, and also excellent durability and rework performance (no contamination transfer to the adherend after tracing the surface protection film with a ballpoint pen via the adhesive layer). For this reason, it can be suitably used as a surface protection film for polarizing plates, phase difference plates, and anti-reflective films.

[0044] For the base film of the adhesive layer and the release film (separator) that protects the adhesive surface, resin films such as polyester film can be used. The base film can be treated with antifouling treatments such as silicone-based or fluorine-based release agents or coatings, silica microparticles, etc., on the side opposite to the side where the adhesive layer of the resin film is formed, or with antistatic treatments such as application or mixing of antistatic agents. The release film is treated with a release agent, such as a silicone-based or fluorine-based release agent, on the side that comes into contact with the adhesive surface of the adhesive layer. [Examples]

[0045] The present invention will be specifically described below with reference to examples.

[0046] <Manufacturing of acrylic polymers> [Example 1] Nitrogen gas was introduced into a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube to replace the air in the reactor with nitrogen gas. Then, 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 solvent (ethyl acetate) were added to the reactor. Subsequently, 0.1 parts by weight of azobisisobutyronitrile was added dropwise over 2 hours as a polymerization initiator, and the reaction was carried out at 65°C for 6 hours to obtain acrylic polymer solution 1, which was used in Example 1, with a weight-average molecular weight of 500,000. A portion of the acrylic polymer was taken and used as a sample for measuring the acid value, as described later. [Examples 2-6 and Comparative Examples 1-3] Except for the monomer compositions being as described in (A) to (C) of Table 1, the acrylic polymer solutions used in Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as acrylic polymer solution 1 used in Example 1 above. In Tables 1 and 2, (A) is the main component alkyl (meth)acrylate, (B) is a copolymerizable monomer containing a hydroxyl group, and (C) is a copolymerizable monomer containing a carboxyl group.

[0047] [Table 1]

[0048] <Manufacturing of adhesive compositions and surface protective films> [Example 1] To the acrylic polymer solution 1 of Example 1 prepared as described above, 2.0 parts by weight of 1-octylpyridinium dodecylbenzenesulfonate and 0.1 parts by weight of KF-351A (a polyether-modified siloxane compound with HLB=12) were added and stirred. Then, 1.0 part by weight of Coronate HX (an isocyanurate of a hexamethylene diisocyanate compound) was added and stirred to obtain the adhesive composition of Example 1. This adhesive composition was applied to a release film made of a silicone resin-coated polyethylene terephthalate (PET) film, and the solvent was removed by drying at 90°C to obtain an adhesive sheet with an adhesive layer thickness of 25 μm. Subsequently, an adhesive sheet was transferred to the side of a polyethylene terephthalate (PET) film that had been treated with antistatic and antifouling properties on one side, opposite to the side that had been treated with antistatic and antifouling properties, thereby obtaining the surface protection film of Example 1 having a laminated structure of "antistatic and antifouling treated PET film / adhesive layer / release film (silicone resin coated PET film)". [Examples 2-6 and Comparative Examples 1-3] Except for using additive compositions as described in (D) to (F) of Table 2, surface protective films for Examples 2 to 6 and Comparative Examples 1 to 3 were obtained in the same manner as the surface protective film for Example 1 described above. 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 values ​​in parts by weight, calculated with the total of groups (A) to (C) as 100 parts by weight, enclosed in parentheses. Table 2 shows the compound names of the abbreviated symbols used in Table 1. Note that Coronate® HX, HL, and L are trade names of Nippon Polyurethane Industry Co., Ltd.; Takenate® D-140N, D-127N, D-110N, and D-120N are trade names of Mitsui Chemicals, Inc.; and KF-351A, KF-352A, KF-353, KF-640, and X-22-6191 are trade names of Shin-Etsu Chemical Co., Ltd.

[0051] <Test Methods and Evaluation> The surface protective films in Examples 1-6 and Comparative Examples 1-3 were aged for 7 days at 23°C and 50% RH. After that, the release film (silicone resin-coated PET film) was peeled off to expose the adhesive layer, which was used as the sample for surface resistivity measurement. Furthermore, this surface protection film with the adhesive layer exposed was bonded to the surface of a polarizing plate attached to a liquid crystal cell via the adhesive layer, left for one day, then autoclaved at 50°C and 5 atmospheres for 20 minutes, and left at room temperature for another 12 hours. This was used as a sample for measuring adhesive strength, peel voltage, reworkability, and durability.

[0052] <Acid value> The acid value of acrylic polymers was determined by dissolving the sample in a solvent (a mixture of diethyl ether and ethanol in a volume ratio of 2:1) and performing a potentiometric titration using a potentiometric automatic titrator (Kyoto Electronics Manufacturing Co., Ltd., AT-610) with a potassium hydroxide ethanol solution of approximately 0.1 mol / l. The amount of potassium hydroxide ethanol solution required to neutralize the sample was measured. The acid value was then calculated using the following formula. Acid value = (B × f × 5.611) / S B = Volume (ml) of 0.1 mol / l potassium hydroxide ethanol solution used in the titration. f = 0.1 mol / l potassium hydroxide ethanol solution factor S = Mass of solid content in the sample (g)

[0053] <Adhesive strength> The sample obtained above (a 25 mm wide surface protective film laminated onto the surface of a polarizing plate) was peeled off in the 180° direction using a tensile testing machine at low peel speeds (0.3 m / min) and high peel speeds (30 m / min), and the peel strength was measured and defined as the adhesive strength.

[0054] <Surface resistivity> After aging, before bonding to the polarizing plate, the release film (silicone resin-coated PET film) was peeled off to expose the adhesive layer, and the surface resistivity of the adhesive layer was measured using a resistivity meter, Hi-Resta UP-HT450 (manufactured by Mitsubishi Chemical Analytec).

[0055] <Strip voltage> The voltage (band voltage) generated when the polarizing plate was charged after peeling the sample obtained above at a tensile speed of 30 m / min at 180° 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 defined as the peeled band voltage.

[0056] <Reworkability> After tracing the surface protective film of the measurement sample obtained above with a ballpoint pen (load 500g, 3 back-and-forth strokes), the surface protective film was peeled off the polarizing plate and the surface of the polarizing plate was observed to confirm that there was no contamination transfer to the polarizing plate. The evaluation criteria were as follows: "○" if there was no contamination transfer to the polarizing plate, "△" if contamination transfer was confirmed at least partially along the traced path of the ballpoint pen, and "×" if contamination transfer was confirmed along the traced path of the ballpoint pen and the adhesive was also confirmed to have detached from the adhesive surface.

[0057] <Durability> The sample obtained above was left in an atmosphere of 60°C and 90% RH for 250 hours, then removed to room temperature and left for another 12 hours. The adhesive strength was then measured and confirmed to be no significant increase compared to the initial adhesive strength. The evaluation criteria were as follows: if the adhesive strength after the test was 1.5 times or less of the initial adhesive strength, it was evaluated as "○"; if it exceeded 1.5 times, it was evaluated as "×".

[0058] Table 3 shows the evaluation results. Note that the surface resistivity is "m × 10 +n This was expressed using the formula "mE+n" (where m is an arbitrary real number and n is a positive integer).

[0059] [Table 3]

[0060] The surface protective films in Examples 1-6 had an adhesive strength of 0.05-0.1 N / 25 mm at a peeling speed of 0.3 m / min in the low-speed range, an adhesive strength of 1.0 N / 25 mm or less at a peeling speed of 30 m / min in the high-speed range, and a surface resistivity of 5.0 × 10⁻⁶. +11 The resistance was less than Ω / □, the peeling voltage was ±0 to 0.5kV, there was no contamination transfer to the substrate after tracing over the surface protective film with a ballpoint pen via the adhesive layer, and it exhibited excellent durability when left for 250 hours in an atmosphere of 60°C and 90%RH. In other words, it simultaneously satisfies all the required performance aspects: (1) balancing adhesive strength at low and high peeling speeds, (2) preventing the generation of adhesive residue, (3) having excellent antistatic properties, and (4) having reworkability.

[0061] The surface protective film in Comparative Example 1 had insufficient alkyl (meth)acrylate as the main component, excessive hydroxyl group-containing copolymerizable monomers, and no carboxyl group-containing copolymerizable monomers. It also had an insufficient HLB value for the polyether-modified siloxane compound, resulting in low adhesive strength at a peeling speed of 0.3 m / min in the low-speed range, high surface resistivity and peeling band voltage, and poor durability. In Comparative Example 2, the surface protective film had an excessive amount of copolymerizable monomers containing carboxyl groups relative to the main component alkyl (meth)acrylate. As a result, the pot life was too short, and crosslinking progressed before application, making coating impossible. The surface protective film in Comparative Example 3 did not contain a copolymerizable monomer containing a carboxyl group, a crosslinking agent, or an antistatic agent. Perhaps because the HLB value of the polyether-modified siloxane compound was too low, the adhesive strength at a peeling speed of 0.3 m / min in the low-speed range and at a peeling speed of 30 m / min in the high-speed range was too high, resulting in high surface resistivity and peel voltage, and poor reworkability and durability. Thus, the surface protective films in Comparative Examples 1 to 3 failed to simultaneously satisfy all the required performance characteristics: (1) balancing adhesive strength at low and high peeling speeds, (2) preventing the generation of adhesive residue, (3) having excellent antistatic performance, and (4) having reworkability.

Claims

1. An adhesive composition containing an acrylic polymer, an antistatic agent, and a crosslinking agent, The aforementioned acrylic polymer Amount to 100 parts by weight of the acrylic polymer: A total of 85 to 93 parts by weight of at least one alkyl (meth)acrylate having an alkyl group having 4 to 10 carbon atoms, A total of 6.5 to 9.5 parts by weight of at least one copolymerizable monomer containing a hydroxyl group but not a carboxyl group, A total of 0.5 to 1.5 parts by weight of at least one copolymerizable monomer containing a carboxyl group but not a hydroxyl group, It consists of a copolymer obtained by copolymerizing the following: The adhesive composition contains, in a proportion of 0.1 to 5 parts by weight of a trifunctional or more isocyanate compound, which is the crosslinking agent, per 100 parts by weight of the acrylic polymer. The acid value of the aforementioned acrylic polymer is 0.01 to 8.

0. The antistatic agent is an ionic compound with a melting point of 30 to 50°C. Said ionic compound is an ionic compound having a cation and an anion, wherein said cation is one selected from the group consisting of pyridinium cations, imidazolium cations, pyrimidinium cations, pyrazolium cations, pyrrolidinium cations, ammonium cations, phosphonium cations, and sulfonium cations, and said 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 － ), a tetrafluoroborate anion (BF ４ － ), which is one selected from the group consisting of, The adhesive composition is characterized in that it further contains a polyether-modified siloxane compound having an HLB value of 7 to 12.

2. The adhesive composition according to claim 1, characterized in that the alkyl (meth)acrylate having an alkyl group having 4 to 10 carbon atoms 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.

3. The adhesive composition according to claim 1 or 2, characterized in that the copolymerizable monomer containing a carboxyl group but not a hydroxyl group is one or more selected from the group of compounds consisting of (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxypropylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyltetrahydrophthalic acid.

4. An adhesive film characterized by having an adhesive layer formed on one or both sides of a resin film, which is obtained by crosslinking the adhesive composition according to any one of claims 1 to 3.

5. A surface protection film characterized by having an adhesive layer formed on one side of a resin film, which is obtained by crosslinking the adhesive composition according to any one of claims 1 to 3.

Images