Antistatic agent and adhesive composition

Abstract

Provided is an antistatic agent or the like having excellent resin compatibility and antistatic characteristics, which is achieved by an antistatic agent comprising an onium salt represented by formula (1), an adhesive composition containing same, and an antistatic resin (in the formula, R1 represents a hydrocarbon group having 1-4 carbon atoms, the hydrocarbon group represents either a straight chain or a branched chain; and R2 represents a hydrocarbon group having 6-12 carbon atoms, and the hydrocarbon group represents either a straight chain or a branched chain).

Description

Antistatic agent and adhesive composition

[0001] The present invention relates to an antistatic agent using an onium salt consisting of an imidazolium cation and a bis(oxalato)borate anion, and to a pressure-sensitive adhesive composition and an antistatic resin containing the same.

[0002] As a method for imparting antistatic properties to insulating resins, a method of coating the surface of a resin substrate with a conductive coating film containing an antistatic agent is known. Examples of the antistatic agent include electron conductive materials such as carbon black and ITO, but when used in adhesives using resins, they have problems with the hardness and transparency of the adhesive layer. Ion conductive materials using onium salts are known as antistatic agents that impart conductivity while maintaining the transparency of the adhesive layer.

[0003] Other antistatic agents used in resins include solid conductive materials such as metal salts (Patent Document 1).

[0004] Onium salts have attracted attention because they have excellent properties such as nonvolatility, flame retardancy, and high ionic conductivity, and their physical properties and functions can be designed in a variety of ways. Due to these properties, onium salts are used as antistatic agents for various resins.

[0005] It is known that onium salts can be used to impart antistatic properties to adhesives and other materials by using quaternary ammonium salts with chain alkyl groups, such as tetraethylammonium (TEA) and tributylmethylammonium (TBMA). However, TEA and TBMA have poor resin compatibility, and when used in adhesives, they have the disadvantage of impaired permeability and high haze when forming an adhesive layer. Furthermore, to improve the antistatic properties of adhesives using quaternary ammonium salts with chain alkyl groups, a high onium salt content is required. However, adhesives containing high amounts of onium salts have problems such as reduced adhesive strength and contamination of the adherend due to bleed-out. (Patent Documents 2 and 3) Furthermore, environmental concerns about compounds containing perfluoroalkyl groups have arisen due to PFAS regulations, but few ionic conductive materials that do not contain halogens in their molecular structure have been found to meet the antistatic performance requirements of the market. There have been reports of halogen-free antistatic agents with bis(oxalato)borate as the anion, but some have issues with resin compatibility, such as transmittance and haze, and some do not achieve the surface resistance of 10% required for antistatic films for electronic components with a small addition of 3% or less of the resin solid content. 9 No combination of an antistatic agent and an acrylic adhesive that satisfies antistatic performance in the Ω range has been found (Patent Documents 4 and 5).

[0006] JP 6-128539 A JP 2005-290357 A JP 2013-064146 A JP 2019-108414 A JP 2020-007471 A

[0007] The present invention aims to provide an antistatic agent that does not contain halogen in its molecular structure, has excellent resin compatibility, and exhibits sufficient antistatic properties even when added in small amounts. It also aims to provide a pressure-sensitive adhesive composition and an antistatic resin that are excellent in transparency and have low haze by using such an antistatic agent.

[0008] As a result of extensive research, the present inventors have discovered that by using an onium salt composed of an N-alkylimidazolium cation and a bisoxalatoborate anion, which has higher ionic conductivity than alkylammonium and pyridinium, and an N-alkylimidazolium cation having a combination of alkyl chains within a specific range, it is possible to obtain an antistatic agent having excellent resin compatibility and antistatic performance, as well as a pressure-sensitive adhesive composition and antistatic resin having excellent transparency and low haze, and have completed the present invention.

[0009] The present invention is as follows: [1] to [5]

[0010] [1] An antistatic agent comprising an onium salt represented by formula (1). (wherein R1 represents a hydrocarbon group having 1 to 4 carbon atoms, which is either linear or branched; R2 represents a hydrocarbon group having 6 to 12 carbon atoms, which is either linear or branched.) [2] The antistatic agent according to [1], wherein the onium salt represented by formula (1) is 1-methyl-3-hexylimidazolium bisoxalatoborate or 1-methyl-3-octylimidazolium bisoxalatoborate. [3] An antistatic resin comprising the antistatic agent according to any one of [1] to [2] and a resin. [4] A pressure-sensitive adhesive composition comprising the antistatic agent according to any one of [1] to [2] and an acrylic pressure-sensitive adhesive. [5] The pressure-sensitive adhesive composition according to [4], wherein the antistatic agent is contained in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the resin component of the acrylic pressure-sensitive adhesive.

[0011] The antistatic agent of the present invention has high compatibility with resins and can exhibit sufficient antistatic properties even when added in a small amount. Therefore, when the antistatic agent of the present invention is used in a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer having excellent transparency and small haze can be formed, and the antistatic agent can be used in a surface protection film for protecting the surfaces of optical components and electronic materials.

[0012] The present invention will be described below, but the present invention is not limited to the following embodiments.

[0013] [Onium Salt] The antistatic agent of the present invention comprises an onium salt represented by formula (1): This onium salt comprises an N-alkylimidazolium cation and a bisoxalatoborate anion.

[0014] In formula (1), R1 is a hydrocarbon group having 1 to 4 carbon atoms, and this hydrocarbon group may be either linear or branched. Specifically, methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, s-butyl, or tert-butyl is preferred, and from the viewpoint of antistatic performance and resin compatibility, methyl is most preferred. R2 is a hydrocarbon group having 6 to 12 carbon atoms, and this hydrocarbon group may be either linear or branched. Specific examples include an n-hexyl group, a cyclohexyl group, an n-heptyl group, an n-octyl group, an isohexyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, and an n-dodecyl group. From the viewpoint of resin compatibility, a butyl group, an s-butyl group, a tert-butyl group, a cyclobutyl group, an n-pentyl group, a cyclopentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an n-octyl group, an isohexyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, and an n-dodecyl group are preferred. From the viewpoint of the balance between antistatic performance and resin compatibility, an n-hexyl group or an n-octyl group is more preferred.

[0015] In formula (1), the anion represents bisoxalatoborate.

[0016] Of the onium salts represented by formula (1), it is preferable to use 1-methyl-3-hexylimidazolium bisoxalatoborate or 1-methyl-3-octylimidazolium bisoxalatoborate for the antistatic agent of the present invention.

[0017] The onium salt represented by the above formula (1) can be produced by a known method so as to have the above structure. Examples of such a method include the following method. The compound used in this reaction may be a commercially available product or one synthesized by a known method. [Production method of onium salt] By subjecting imidazoles represented by formula (2) to a quaternization reaction with alkyl halides represented by formula (3), onium halides represented by formula (4) can be obtained. In formulas (3) and (4), X is a halide. In formula (5), M ＋ represents a metal ion. The ion exchange reaction of formula (4) and formula (5) produces a (quaternary) onium salt represented by formula (1).

[0018] Examples of the imidazoles of the formula (2) include 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-isopropylimidazole, and 1-butylimidazole.

[0019] Examples of alkyl halides of formula (3) include butyl chloride, s-butyl chloride, tert-butyl chloride, cyclobutyl chloride, n-pentyl chloride, cyclopentyl chloride, isopentyl chloride, neopentyl chloride, tert-pentyl chloride, n-octyl chloride, isohexyl chloride, 2-ethylhexyl chloride, ethyl bromide, propyl bromide, isopropyl bromide, cyclopropyl bromide, butyl bromide, s-butyl bromide, tert-butyl bromide, cyclobutyl bromide, n-pentyl bromide, cyclopentyl bromide, isopentyl bromide, neopentyl bromide, tert-pentyl bromide, n-octyl bromide, isohexyl bromide, 2-ethylhexyl chloride, ethyl bromide, propyl bromide, isopropyl bromide, cyclopropyl bromide, butyl bromide, s-butyl bromide, tert-butyl bromide, cyclobutyl bromide, n-pentyl bromide, cyclopentyl bromide, isopentyl bromide, neopentyl bromide, tert-pentyl bromide, n-octyl bromide, isohexyl bromide, 2-ethylhexyl bromide ...butyl bromide, butyl bromide, butyl bromide, butyl bromide ethylhexyl bromide, ethyl iodide, propyl iodide, isopropyl iodide, cyclopropyl iodide, butyl iodide, s-butyl iodide, tert-butyl iodide, cyclobutyl iodide, n-pentyl iodide, cyclopentyl iodide, isopentyl iodide, neopentyl iodide, tert-pentyl iodide, n-octyl iodide, isohexyl iodide, 2-ethylhexyl iodide, n-nonyl chloride, n-nonyl bromide, n-nonyl iodide, n-decyl chloride, n-decyl bromide, n-decyl iodide, n-undecyl chloride, n-undecyl bromide, n-undecyl iodide, n-dodecyl chloride, n-dodecyl bromide, and n-dodecyl iodide.

[0020] The quaternization reaction of formula (2) using formula (3) may or may not require the use of a solvent. The solvent is not particularly limited as long as it does not affect the reaction. Specific examples of the solvent include acetonitrile, methanol, ethyl acetate, benzene, toluene, xylene, diethyl ether, tetrahydrofuran, and 1,4-dioxane, and acetonitrile is preferred.

[0021] The amount of the compound of formula (3) used may be 0.7 moles or more, preferably 0.9 to 1.5 moles, per mole of the compound of formula (2).

[0022] The reaction temperature in the quaternization reaction is usually 25°C or higher, preferably 30 to 150°C, and particularly preferably 60 to 120°C.

[0023] Examples of the metal salt of formula (5) include lithium bis(oxalato)borate, sodium bis(oxalato)borate, potassium bis(oxalato)borate, etc. Examples of alkali metals and transition metals that form counter cations of the above anions include lithium, sodium, potassium, silver, etc.

[0024] The amount of the compound of formula (5) used in the ion exchange reaction is usually 0.8 moles or more, preferably 0.9 to 1.8 moles, more preferably 1.0 to 1.2 moles, per mole of the compound of formula (4).

[0025] The ion exchange reaction is usually carried out in a solvent. There are no particular limitations on the solvent as long as it does not affect the reaction. Specific examples of the solvent include pure water, acetonitrile, ethyl acetate, benzene, toluene, xylene, diethyl ether, tetrahydrofuran, and 1,4-dioxane, with pure water and acetonitrile being preferred.

[0026] The order of mixing the formula (4), the formula (5), and the solvent is not particularly limited, and the formula (5) may be added after mixing the formula (4) and the solvent, or the formula (5) may be added after mixing the formula (4) and the solvent.

[0027] The reaction temperature in the ion exchange reaction is usually 10°C or higher, preferably 10 to 60°C, and particularly preferably 15 to 50°C.

[0028] To isolate Formula (1) from the reaction solution after the reaction is complete, the solvent and the inorganic salt produced are removed from the reaction solution. If an inorganic salt precipitates in the resulting reaction solution, the reaction solution is filtered to remove the precipitated inorganic salt, and then Formula (1) is isolated by an appropriate combination of unit operations such as concentration, filtration, and extraction. The isolated Formula (1) can be used as an antistatic agent.

[0029] The antistatic agent of the present invention thus obtained is halogen-free. Furthermore, the antistatic agent of the present invention combined with an n-alkylimidazolium-based cationic skeleton has higher ionic conductivity and is superior in compatibility with resins and hydrophobicity compared to an antistatic agent in which an n-alkyl-substituted ammonium-based cationic skeleton or an n-alkyl-substituted pyridinium-based cationic skeleton is selected, and therefore exhibits extremely good antistatic performance.

[0030] [Adhesive Composition] By combining the antistatic agent of the present invention with an acrylic adhesive, an adhesive composition having antistatic properties can be obtained. This adhesive composition having antistatic properties has excellent antistatic properties, excellent transparency, and can form an adhesive layer with low haze. Specifically, the surface resistance of the adhesive layer formed from the adhesive composition is 5.0 × 10 10 Ω or less, more preferably 1.0 × 10 10 The surface resistance is measured with a resistivity meter, and the transmittance and haze are measured with a haze meter. Therefore, the pressure-sensitive adhesive composition of the present invention contains at least the onium salt and an acrylic pressure-sensitive adhesive. The pressure-sensitive adhesive composition of the present invention also includes a pressure-sensitive adhesive ink prepared by dissolving the pressure-sensitive adhesive composition in a soluble organic solvent and a pressure-sensitive adhesive layer formed by applying the pressure-sensitive adhesive ink to a substrate.

[0031] The acrylic pressure-sensitive adhesive of the present invention preferably contains an acrylic polymer whose main component is an acrylate or methacrylate having an alkyl group having 1 to 14 carbon atoms. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and n-octyl acrylate.

[0032] The mass-average molecular weight of the acrylic polymer is 100,000 to 5,000,000, preferably 200,000 to 4,000,000, and more preferably 300,000 to 3,000,000. If the mass-average molecular weight is less than 100,000, the cohesive strength of the pressure-sensitive adhesive composition may be reduced. On the other hand, if it exceeds 5,000,000, the fluidity of the polymer decreases, resulting in insufficient wettability to the adherend and causing peeling. The mass-average molecular weight can be measured by gel permeation chromatography (GPC).

[0033] The acrylic polymer can be obtained by a general acrylic polymer polymerization method such as solution polymerization, emulsion polymerization, bulk polymerization, or suspension polymerization, and may be any of a random copolymer, a block copolymer, a graft copolymer, or the like.

[0034] Furthermore, by appropriately crosslinking the acrylic polymer, a pressure-sensitive adhesive composition having an adhesive layer with excellent heat resistance can be obtained. Crosslinking methods include adding a crosslinking agent to the acrylic pressure-sensitive adhesive. Examples of crosslinking agents include isocyanate compounds, epoxy compounds, aziridine compounds, and metal chelate compounds.

[0035] The isocyanate compound is a compound having at least two isocyanate groups (—NCO) in the molecule. Specific examples include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate, alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate, aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate and xylylene diisocyanate, and isocyanate adducts such as a trimethylolpropane / tolylene diisocyanate trimer adduct, a trimethylolpropane / hexamethylene diisocyanate trimer adduct and an isocyanurate of hexamethylene diisocyanate.

[0036] Epoxy compounds are compounds having at least two epoxy groups in the molecule. Specific examples include bisphenol A epoxy resins, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, and N,N-diglycidylaniline.

[0037] Aziridine compounds are compounds that have at least two three-membered ring skeletons, each consisting of one nitrogen atom and two carbon atoms, also known as ethyleneimines. Specific examples include diphenylmethane-4,4'-bis(1-aziridinecarboxamide), toluene-2,4-bis(1-aziridinecarboxamide), triethylenemelamine, isophthaloylbis-1-(2-methylaziridine), tris-1-aziridinylphosphine oxide, hexamethylene-1,6-bis(1-aziridinecarboxamide), trimethylolpropane-tri-β-aziridinylpropionate, and tetramethylolmethane-tri-β-aziridinylpropionate.

[0038] Examples of metal chelate compounds include compounds in which acetylacetone or ethyl acetoacetate is coordinated with a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, or zirconium.

[0039] The content of the crosslinking agent is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5.0 parts by mass, relative to 100 parts by mass of the acrylic pressure-sensitive adhesive. If the content is less than 0.01 part by mass, crosslinking is insufficient, resulting in a decrease in the cohesive strength of the pressure-sensitive adhesive composition and insufficient heat resistance. On the other hand, if the content exceeds 10 parts by mass, the cohesive strength of the polymer is high, reducing fluidity and resulting in insufficient wettability to the adherend, which can cause peeling.

[0040] The alkylene oxide group-containing compound is a compound having an alkylene oxide group, and specific examples thereof include alkylene oxide group-containing surfactants, alkylene oxide group-containing polyether polymers, alkylene glycol group-containing (meth)acrylic polymers, etc. Among these, alkylene oxide group-containing surfactants are preferably used because of their good compatibility with acrylic polymers.

[0041] Examples of alkylene oxide group-containing surfactants include nonionic surfactants such as polyoxyalkylene fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyoxyalkylene sorbitol fatty acid esters, polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl allyl ethers, polyoxyalkylene alkylphenyl ethers, polyoxyalkylene derivatives, polyoxyalkylene alkylamines, and polyoxyalkylene alkylamine fatty acid esters; anionic surfactants such as polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkyl ether phosphates, polyoxyalkylene alkylphenyl ether sulfates, and polyoxyalkylene alkylphenyl ether phosphates; and cationic surfactants and zwitterionic surfactants having alkylene oxide groups. Furthermore, the surfactants may have reactive substituents such as (meth)acryloyl groups and allyl groups in the molecule.

[0042] The alkylene oxide group-containing compound may be used alone or in combination of two or more. The blending amount is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the acrylic polymer. If the blending amount is less than 0.01 part by mass, bleeding may occur.

[0043] The pressure-sensitive adhesive composition of the present invention may contain a silane compound, which can improve adhesion to substrates such as films and glass.

[0044] Examples of silane compounds include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyldimethoxymethylsilane, and 3-glycidoxypropylethoxydimethylsilane. Two or more of these may be used in combination.

[0045] The amount of the onium salt represented by formula (1) in the pressure-sensitive adhesive composition of the present invention is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and particularly preferably 0.5 to 5.0 parts by mass, per 100 parts by mass of the acrylic pressure-sensitive adhesive. By setting the amount in this range, a pressure-sensitive adhesive composition with even more excellent electrical properties can be obtained.

[0046] The pressure-sensitive adhesive composition of the present invention can be used in combination with other binder resins, antioxidants, ultraviolet absorbers, lubricants, etc., within the scope of not impairing the effects of the present invention.

[0047] When preparing a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed on a substrate, the pressure-sensitive adhesive composition of the present invention may be applied directly to the substrate, or a pressure-sensitive adhesive ink prepared by dissolving the pressure-sensitive adhesive composition in a soluble organic solvent may be applied to the substrate. These pressure-sensitive adhesive compositions or pressure-sensitive adhesive inks can be applied to substrates such as resin films or glass, and then dried as necessary to prepare pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer formed on the surface of these substrates. The thickness of the pressure-sensitive adhesive layer is preferably 3 to 100 μm, more preferably 5 to 50 μm.

[0048] [Adhesive Ink] Examples of organic solvents used in the adhesive ink include alcohol-based solvents such as methanol, ethanol, propanol, isopropyl alcohol (IPA), and butanol; glycol-based solvents such as ethylene glycol, propylene glycol, butylene glycol, polyethylene glycol, polypropylene glycol, and polyoxyethylene-polyoxypropylene copolymers; ether alcohol-based solvents such as monomethyl ether, monoethyl ether, monopropyl ether, monoisopropyl ether, and monobutyl ether of the glycol-based solvents; polyether-based solvents such as dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, ethyl propyl ether, ethyl isopropyl ether, and ethyl butyl ether of the glycol-based solvents; ketone-based solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate, ethyl acetate, and butyl acetate; and hydrocarbon-based solvents such as hexane, heptane, octane, cyclopentane, cyclohexane, toluene, and xylene. Among these, toluene, MEK, ethyl acetate, butyl acetate, and IPA are particularly preferred.

[0049] [Substrate] Examples of the substrate include a polyethylene terephthalate (PET) film, a polycarbonate film, a polystyrene film, an acrylic film, a cellulose triacetate film, a polyethylene film, and a polypropylene film.

[0050] [Method for producing pressure-sensitive adhesive sheet] Examples of a method for applying a pressure-sensitive adhesive composition or the like to a substrate include roll coating, gravure coating, reverse coating, die coating, comma coating, etc. When drying is performed to remove the solvent from the liquid film coated on the substrate or the like, the temperature is preferably 50° C. or higher and 150° C. or lower, from the viewpoint of promoting curing of the liquid film.

[0051] For the purpose of protecting the adhesive surface, a separator may be attached to the surface of the adhesive layer as needed. The separator may be paper or a plastic film, with plastic film being preferred due to its excellent surface smoothness.

[0052] Examples of plastic films include polyethylene films, polypropylene films, polybutene films, polybutadiene films, polymethylpentene films, polyvinyl chloride films, polyethylene terephthalate films, polybutylene terephthalate films, and polyurethane films.

[0053] The pressure-sensitive adhesive composition of the present invention and a pressure-sensitive adhesive sheet produced using the same can be used for plastic products, etc. In particular, they can be used as a surface protection film for protecting the surfaces of optical components such as polarizing plates, wavelength plates, optical compensation films, light diffusion sheets, and reflective sheets used in liquid crystal displays, etc., and as a protective film for electronic materials and semiconductor components.

[0054] [Antistatic Resin] As described above, the antistatic agent of the present invention can be combined with an acrylic adhesive to obtain a pressure-sensitive adhesive composition with antistatic properties. However, it is also possible to simply incorporate this agent into various resins to impart conductivity to the resin, thereby forming an antistatic resin. Examples of resins that can incorporate the antistatic agent of the present invention include acrylic adhesives, as well as synthetic resins such as polyethylene terephthalate, polypropylene, and polycarbonate, as well as various adhesives or release agents (silicone-based adhesives, urethane-based adhesives, rubber-based adhesives, silicone-based release agents, fluorine-based release agents, acrylic-based release agents, etc.). The performance of the antistatic resin of the present invention is the same as that of the adhesive layer.

[0055] The antistatic resin of the present invention can be produced in the same manner as antistatic resins using conventional known antistatic agents. For example, if the resin is an acrylic adhesive, or a synthetic resin such as polyethylene terephthalate, polypropylene, or polycarbonate, or various adhesives or release agents (such as silicone adhesives, urethane adhesives, rubber adhesives, silicone release agents, fluorine-based release agents, or acrylic release agents), the antistatic resin can be obtained by mixing the resin with the acrylic adhesive. Furthermore, if an acrylic resin monomer is used as the resin raw material, the antistatic resin of the present invention can be obtained by adding a photopolymerization initiator to a solution containing the acrylic resin monomer and the antistatic agent of the present invention, and then applying the solution to the surface of the resin, and irradiating the resin with ultraviolet light.

[0056] The present invention will be described in detail below by way of examples, but the present invention is not limited to these examples in any way.

[0057] Example 1 [Preparation of Antistatic Agent] 1-methyl-3-hexylimidazolium bisoxalatoborate was prepared as follows.

[0058] 17.33 g of hexyl bromide and 20 g of acetonitrile were added to 8.21 g of 1-methylimidazole, and the mixture was heated and stirred at 85°C for 5 hours. After removing the solvent by concentration, pure water and hexane were added and the mixture was separated. Unreacted hexyl bromide was removed, and the mixture was then concentrated to obtain 24.47 g of 1-methyl-3-hexylimidazolium bromide (yield: 99%). 100 g of acetonitrile was added to 24.47 g of the synthesized 1-methyl-3-hexylimidazolium bromide to dissolve it, and then 21.10 g of lithium bis(oxalato)borate was added and stirred for 2 hours. The solvent was removed by concentration, and the mixture was washed with dichloromethane and pure water. The mixture was then concentrated again to obtain 28.05 g of 1-methyl-3-hexylimidazolium bis(oxalato)borate (yield: 80%). This was used as an antistatic agent.

[0059] [Preparation of adhesive ink] Acrylic adhesive ((meth)acrylic polymer, Mw 500,000, manufactured by Soken Chemical & Engineering Co., Ltd., 1499M, non-volatile content 30%): 10 g Curing agent (isocyanate compound, manufactured by Soken Chemical & Engineering Co., Ltd., D-90, non-volatile content 0.85%): 0.1 g Antistatic agent (1-methyl-3-hexylimidazolium bisoxalatoborate): 0.06 g The above composition was diluted with MEK to a non-volatile content concentration of 25 parts by mass, to prepare an adhesive ink.

[0060] Example 2 An adhesive ink was prepared without making any changes to the process of Example 1 except that the onium salt of 1-methyl-3-octylimidazolium bisoxalatoborate was used instead of the onium salt.

[0061] [Preparation of Antistatic Agent] 1-methyl-3-octylimidazolium bisoxalatoborate was prepared as follows.

[0062] 20.28 g of octylbromide and 20 g of acetonitrile were added to 8.21 g of 1-methylimidazole, and the mixture was heated and stirred at 85°C for 5 hours. After concentration to remove the solvent, pure water and hexane were added and the mixture was separated. Unreacted octylbromide was removed, and the mixture was then concentrated to obtain 27.25 g of 1-methyl-3-octylimidazolium bromide (yield: 99%). 100 g of acetonitrile was added to 27.25 g of the synthesized 1-methyl-3-octylimidazolium bromide to dissolve it, and then 21.10 g of lithium bis(oxalato)borate was added and stirred for 2 hours. The solvent was removed by concentration, and the mixture was washed with dichloromethane and pure water. The mixture was then concentrated again to obtain 32.17 g of 1-methyl-3-octylimidazolium bis(oxalato)borate (yield: 85%). This was used as an antistatic agent.

[0063] Comparative Example 1 An adhesive ink was prepared without making any changes to the process of Example 1, except that the onium salt used in Example 1 was replaced with an onium salt of tributylmethylammonium bis(trifluoromethanesulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code 352-27751).

[0064] Comparative Example 2 An adhesive ink was prepared without making any changes to the process of Example 1 except that the onium salt used was replaced with an onium salt of 1-octyl-3-methylpyridinium bisoxalatoborate.

[0065] [Preparation of Antistatic Agent] 1-octyl-3-methylpyridinium bisoxalatoborate was prepared as follows.

[0066] To 9.31 g of 3-methylpyridine, 20.28 g of octylbromide and 20 g of acetonitrile were added, and the mixture was heated and stirred at 85°C for 5 hours. After concentration to remove the solvent, pure water and hexane were added and the mixture was separated. Unreacted octylbromide was removed, and the mixture was then concentrated to obtain 28.33 g of 1-octyl-3-methylpyridinium bromide (yield: 99%). 100 g of acetonitrile was added to 28.33 g of the synthesized 1-octyl-3-methylpyridinium bromide to dissolve it, and then 21.10 g of lithium bis(oxalato)borate was added and stirred for 2 hours. The solvent was removed by concentration, and the mixture was washed with dichloromethane and pure water. After concentration again, 31.14 g of 1-octyl-3-methylpyridinium bis(oxalato)borate (yield: 80%) was obtained. This was used as an antistatic agent.

[0067] Comparative Example 3 An adhesive ink was prepared without making any changes to the process of Example 1 except that the onium salt used in Example 1 was replaced with an onium salt of 1-methyl-3-ethylimidazolium bisoxalatoborate.

[0068] [Preparation of Antistatic Agent] 1-methyl-3-ethylimidazolium bisoxalatoborate was prepared as follows.

[0069] To 8.21 g of 1-methylimidazole, 11.44 g of ethyl bromide and 20 g of acetonitrile were added, and the mixture was heated and stirred at 60°C for 5 hours. After concentration to remove the solvent, pure water and hexane were added and the mixture was separated. Unreacted ethyl bromide was removed, and the mixture was then concentrated to obtain 18.92 g of 1-methyl-3-ethylimidazolium bromide (yield: 99%). 100 g of acetonitrile was added to 18.92 g of the synthesized 1-methyl-3-ethylimidazolium bromide to dissolve it, and then 21.10 g of lithium bis(oxalato)borate was added and stirred for 2 hours. The solvent was removed by concentration, and the mixture was washed with dichloromethane and pure water. The mixture was then concentrated again to obtain 17.71 g of 1-methyl-3-ethylimidazolium bis(oxalato)borate (yield: 60%). This was used as an antistatic agent.

[0070] Comparative Example 4 An adhesive ink was prepared without making any changes to the process of Example 1 except that the onium salt used in Example 1 was replaced with an onium salt of 1-methyl-3-hexadecylimidazolium bisoxalatoborate.

[0071] [Preparation of Antistatic Agent] 1-methyl-3-hexadecylimidazolium bisoxalatoborate was prepared as follows.

[0072] 32.06 g of hexadecyl bromide and 20 g of acetonitrile were added to 8.21 g of 1-methylimidazole, and the mixture was heated and stirred at 85°C for 12 hours. After concentration, the solvent was removed, and then pure water and hexane were added to separate the mixture. Unreacted hexadecyl bromide was removed, and the mixture was then concentrated to obtain 32.93 g of 1-methyl-3-hexadecylimidazolium bromide (yield: 85%). 100 g of acetonitrile was added to 32.93 g of the synthesized 1-methyl-3-hexadecylimidazolium bromide to dissolve it, and then 18.12 g of lithium bis(oxalato)borate was added and stirred for 2 hours. The solvent was removed by concentration, and the mixture was washed with dichloromethane and pure water. The mixture was then concentrated again to obtain 30.68 g of 1-methyl-3-hexadecylimidazolium bis(oxalato)borate (yield: 73%). This was used as an antistatic agent as is.

[0073] Comparative Example 5 An adhesive ink was prepared without changing the process of Example 1 except that the onium salt was replaced with an onium salt of tetraethylammonium bisoxalatoborate.

[0074] [Preparation of Antistatic Agent] Tetraethylammonium bisoxalatoborate was prepared as follows.

[0075] 100 g of acetonitrile was added to 21.01 g of tetraethylammonium bromide to dissolve it, and then 21.31 g of lithium bis(oxalato)borate was added and stirred for 2 hours. The solvent was removed by concentration, and the mixture was washed with dichloromethane and pure water. Concentration again gave 20.61 g (yield 65%) of tetraethylammonium bis(oxalato)borate. This was used as an antistatic agent.

[0076] [Coating Conditions] The adhesive ink was coated onto a PET film using a bar coater to a thickness of approximately 25 μm after drying, and then dried in a hot air dryer at 120° C. for 3 minutes to prepare a test piece (adhesive film).

[0077] [Measurement of Surface Resistivity] Using a Hirester UP (manufactured by Mitsubishi Chemical Analytech Corporation, product name "MCP-HT450"), a probe was pressed against the coated surface of the test piece at a temperature of 23±2°C, a humidity of 50±5% RH, and an applied voltage of 100 V, and the stable surface resistance value was measured after 30 seconds had elapsed.

[0078] [Measurement of Transmittance and Haze Value] The transmittance and haze of the adhesive layer side of the adhesive film from which the separator had been peeled off were measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH5000").

[0079] The results of Examples 1 and 2 and Comparative Examples 1 to 5 are shown in Table 1.

[0080] As described above, the pressure-sensitive adhesive compositions of Examples 1 and 2 of the present invention have a surface resistance value (1×10 10The compositions of Comparative Examples 1, 3, 4, and 5 all had a haze value of 1.5% or less and a transmittance of 92% or more, which are the criteria for resin compatibility. On the other hand, the compositions of Comparative Examples 1, 3, 4, and 5 all did not satisfy the criteria for haze value and transmittance, and Comparative Example 2 had a surface resistance value exceeding the criteria, indicating that the compositions lacked the performance required for an antistatic property-imparting PSA composition.

[0081] In particular, comparing Examples 1 and 2 with Comparative Examples 3 and 4, which are all antistatic agents of the same N-alkylimidazolium salt, Comparative Example 3, which has a short alkyl chain (R1 in formula (1)), is thought to have low hydrophobicity, resulting in poor resin compatibility and both the haze value and transmittance falling outside the range. In Comparative Example 4, which has a long alkyl chain (R1 in formula (1)), the increased molecular weight is thought to have affected a decrease in the electrical conductivity of the antistatic agent, resulting in a high surface resistance value when made into a resin composition. Therefore, it is thought that alkyl chains within a specific range, including those used in embodiments of the present invention, satisfy both the surface resistance value and resin compatibility and are effective.

[0082] The present invention can be used as a surface protection film for protecting the surface of an optical member.

Claims

1. An antistatic agent comprising an onium salt represented by formula (1): (In formula (1), R1 represents a hydrocarbon group having 1 to 4 carbon atoms, which is either linear or branched. R2 represents a hydrocarbon group having 6 to 12 carbon atoms, which is either linear or branched.) 2. The antistatic agent according to claim 1, wherein the onium salt represented by the formula (1) is 1-methyl-3-hexylimidazolium bisoxalatoborate or 1-methyl-3-octylimidazolium bisoxalatoborate.

3. An antistatic resin comprising the antistatic agent according to claim 1 or 2 and a resin.

4. A pressure-sensitive adhesive composition comprising the antistatic agent according to claim 1 or 2 and an acrylic pressure-sensitive adhesive.

5. The adhesive composition according to claim 4, characterized in that it contains 0.1 to 10 parts by mass of an antistatic agent per 100 parts by mass of the resin component of the acrylic adhesive.

Images