Pressure-sensitive adhesive composition

Abstract

To provide an adhesive composition excellent in adhesiveness to a fluoridized glass.SOLUTION: A disclosed adhesive composition includes an isocyanate compound, and an acrylic copolymer obtained by polymerizing an acrylic monomer composition including 55-80 wt.% of (meth)acrylic monomer having 12C or more substituent, 10-35 wt.% of that monomer having 8C or less substituent and 1-10 wt.% of hydroxy group-including (meth)acrylic monomer. The adhesive composition is characterized in that the intensity when applying a film formed by pasting the adhesive composition of 20 μm thickness on a PET film of 50 μm thickness to a fluoridized glass and peeling, is 20 gf / 25 mm or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, and more particularly to a pressure-sensitive adhesive composition that has excellent adhesion to fluorine-treated glass. [Background technology]

[0002] Touch panels are electronic devices that combine display and position input functions, and are widely used in electronic devices such as smartphones, tablets, ATMs, and vending machines. When inputting data onto a touch panel, the user touches it with their fingertips, which makes it prone to staining with fingerprints and other contaminants. The adhesion of such contaminants not only reduces visibility, but also increases the likelihood of malfunctions during input.

[0003] Therefore, fluorine-treated glass, which is less susceptible to adhesion of dirt components and can be easily removed if it does adhere, is now being used for touch panel surfaces.On the other hand, in smartphones and other devices, a protective film is often attached to the touch panel surface, but fluorine-treated glass has low wettability, and conventional adhesives do not provide sufficient adhesive strength. [Prior art documents] [Patent documents]

[0004] Patent Document 1 discloses an anti-slip adhesive film for lenses that has an anti-fouling layer formed from a fluorine silane compound, but does not evaluate the adhesive strength required for a protective film for touch panels. [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-299115 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a pressure-sensitive adhesive composition that has excellent adhesion to fluorine-treated glass. [Means for solving the problem]

[0006] The present invention relates to a pressure-sensitive adhesive composition containing an acrylic copolymer obtained by polymerizing an acrylic monomer composition and an isocyanate compound, characterized in that when a film of the pressure-sensitive adhesive composition formed to a thickness of 20 μm on a 50 μm thick PET film is attached to fluorine-treated glass and then peeled off, the strength of the pressure-sensitive adhesive composition is 20 gf / 25 mm or more. [Effects of the Invention]

[0007] The pressure-sensitive adhesive composition of the present invention has excellent adhesion to fluorine-treated glass, and is therefore particularly useful as a pressure-sensitive adhesive for protective films of touch panels that use fluorine-treated glass as the surface material. DETAILED DESCRIPTION OF THE INVENTION

[0008] The pressure-sensitive adhesive composition of the present invention contains an acrylic copolymer obtained by polymerizing an acrylic monomer composition. The acrylic monomer includes a (meth)acrylic monomer and a monomer copolymerizable therewith. In the present invention, (meth)acrylic includes both acrylic and methacrylic, and a (meth)acrylic monomer refers to a monomer having a (meth)acrylic acid ester structure.

[0009] Examples of the (meth)acrylic monomer having a substituent having 8 or less carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0010] Examples of the (meth)acrylic monomer having a substituent with 9 to 11 carbon atoms include isononyl (meth)acrylate, decyl (meth)acrylate, and undecyl (meth)acrylate.

[0011] Examples of (meth)acrylic monomers having a substituent having 12 or more carbon atoms include lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, isomistyryl (meth)acrylate, isostearyl (meth)acrylate, isododecyl (meth)acrylate, isotridecyl (meth)acrylate, isopentadecyl (meth)acrylate, isohexadecyl (meth)acrylate, and isoheptadecyl (meth)acrylate.

[0012] Examples of the hydroxyl group-containing (meth)acrylic monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxy-3-chloropropyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0013] Other monomers include amide group-containing monomers such as (meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, (meth)acryloylmorpholine, N-vinylpyrrolidone, and diacetone(meth)acrylamide; carboxyl group-containing monomers such as (meth)acrylic acid, itaconic acid, and maleic acid; styrene, acrylonitrile, and vinyl acetate.

[0014] In particular, it is preferable that the monomer composition contains 55 to 80% by weight of a (meth)acrylic monomer having a substituent with 12 or more carbon atoms, 10 to 35% by weight of a (meth)acrylic monomer having a substituent with 8 or less carbon atoms, and 1 to 10% by weight of a hydroxyl group-containing (meth)acrylic monomer. By using these ranges, it is possible to increase adhesion to fluorine-treated glass and reduce the relative dielectric constant.

[0015] Furthermore, the (meth)acrylic monomer having a substituent with 12 or more carbon atoms is preferably isostearyl acrylate. The acrylic copolymer can be prepared by polymerizing these monomers by known methods such as solution polymerization, emulsion polymerization, and bulk polymerization, but solution polymerization is preferred.

[0016] Examples of solvents used in solution polymerization include organic solvents such as methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane, isopropyl alcohol, n-butanol, propylene glycol monomethyl ether, propylene glycol dimethyl ether, propylene glycol monomethyl ether acetate, propylene carbonate, etc. However, solvents other than these may also be used without any problems, and two or more solvents may be used in combination.

[0017] It is preferable to use a thermal decomposition type polymerization initiator as the polymerization initiator. Examples of the polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2'-azobis(2-methylpropionate), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis[N-(2-propionate)], 1,1'-azobis(cyclohexane-1-carbonitrile), ... azo compounds such as 1-[(1-cyano-1-methylethyl)azo]formamide, 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), and 1,1'-azobis(1-acetoxy-1-phenylethane); lauroyl peroxide, octanoyl peroxide Organic peroxide compounds such as benzoyl peroxide, ethyl methyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, cumyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, t-butylperoxy-2-ethylhexanoate, dicumyl peroxide, isobutyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di(2-ethylhexyl)peroxydicarbonate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 3,3,5-trimethylcyclohexanoyl peroxide can be used. Moreover, the peroxide compound can be used in combination with a reducing agent such as N,N-dimethyltoluidine or N,N-diethyltoluidine to undergo redox polymerization.

[0018] The polymerization initiator is used in an amount of 0.05 to 3 parts by weight per 100 parts by weight of the monomer. If the amount of the polymerization initiator used is increased, the molecular weight of the resulting copolymer tends to decrease, and if the amount of the polymerization initiator used is decreased, the molecular weight of the resulting copolymer tends to increase.

[0019] It is preferable to add a crosslinking agent to the pressure-sensitive adhesive composition of the present invention. The crosslinking agent reacts with the functional groups in the acrylic copolymer to improve various physical properties. Examples of crosslinking agents include isocyanate compounds and metal chelate compounds. Examples of the isocyanate compound include 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and adducts, isocyanurates, biurets, and allophanates derived from the above isocyanates. The amount of the crosslinking agent to be added is preferably 0.001 to 20 parts by weight based on 100 parts by weight of the acrylic copolymer.

[0020] The pressure-sensitive adhesive composition of the present invention preferably has a relative dielectric constant of 3.5 or less at a frequency of 100 kHz. A relative dielectric constant of 3.5 or less reduces the risk of malfunction when used in a touch panel. In order to achieve a relative dielectric constant of 3.5 or less, it is preferable to use the above-mentioned acrylic monomer composition.

[0021] The adhesive composition of the present invention preferably has a peel strength of 20 gf / 25 mm or more when a film formed by applying the adhesive composition to a 20 μm thick film on a 50 μm thick PET film is attached to fluorine-treated glass, thereby reducing the risk of the protective film peeling off from the touch panel during use when used as an adhesive for the protective film.

[0022] The pressure-sensitive adhesive composition of the present invention may further contain various additives such as an ultraviolet absorber, a near-infrared absorber, an antioxidant, a preservative, an antifungal agent, a tackifying resin, a plasticizer, an antifoaming agent, and a wettability adjuster.

[0023] The present invention will be described in more detail below with reference to examples and comparative examples, but these are given as specific examples and are not intended to limit the scope of the present invention. All parts are by weight. [Example]

[0024] Example 1 A monomer mixture was prepared by adding 10 parts of lauryl methacrylate (LMA), 60 parts of isostearyl acrylate (ISTA), 23.9 parts of 2-ethylhexyl acrylate (2EHA), 6 parts of 4-hydroxybutyl (meth)acrylate (4HBA), 0.1 parts of acrylic acid (AA), 0.1 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 20 parts of ethyl acetate as a solvent. 50 parts of ethyl acetate as a solvent was added to a separable flask equipped with a stirrer and reflux condenser, and the mixture was heated to 65°C. Nitrogen gas was introduced for 30 minutes or more to remove oxygen from the polymerization system. The monomer mixture was then added dropwise over 3 hours while maintaining the temperature at 75±1°C, and the mixture was allowed to react for another hour while maintaining the temperature at 75±1°C. The reaction temperature was then raised to 80°C and maintained at 80±1°C for 2 hours to complete the polymerization reaction. After the reaction was complete, the mixture was diluted with 30 parts of ethyl acetate to obtain a pale yellow, transparent, viscous acrylic copolymer solution. The viscosity was 800 mPa·s, the solids content was 50%, and the weight-average molecular weight was 200,000. Furthermore, 0.3 parts by weight of the trifunctional isocyanate compound Coronate HX (manufactured by Tosoh Corporation, trade name) and 0.3 parts by weight of the aluminum chelate compound Nursem Aluminum (manufactured by Nippon Chemical Industry Co., Ltd., trade name) were added as crosslinking agents per 100 parts by weight of the acrylic copolymer to prepare the pressure-sensitive adhesive composition of Example 1.

[0025] Examples 2 to 4, Comparative Examples 1 to 4 Each pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that in addition to the monomers used in Example 1, lauryl acrylate (LA), behenyl methacrylate (VMA), n-butyl (meth)acrylate (BA), and 2-hydroxyethyl (meth)acrylate (2HEA) were used, and the monomer compositions and crosslinking agents were blended in the amounts shown in Table 1.

[0026] [Table 1]

[0027] Preparation of adhesive sheets Each adhesive composition was applied to a release film (a silicone-treated PET film) so that the thickness after drying was 20 μm, and after heating and drying at 100°C for 2 minutes, a 50 μm-thick PET film was laminated onto the film. This sheet was then left in an atmosphere of 40°C and a relative humidity of 50%RH for 3 days to obtain an adhesive sheet. Measurement of weight average molecular weight The weight-average molecular weight of the acrylic copolymer is measured by GPC (gel permeation chromatography) and calculated in terms of polystyrene. The sample was dissolved in tetrahydrofuran to make a 0.1 wt% solution, and then left in an ultrasonic cleaner with water added for 10 minutes. The filtrate was then filtered through a 0.20 μm membrane filter. Analytical equipment: SHIMADZU LC20AD Column: SHIMADZU GPC-80M x 2 Eluent: tetrahydrofuran Flow rate: 1.0ml / min Inlet pressure: 10kgf Detector: Differential refractometer (RI) Column temperature: 40℃ Injection volume: 50μl Eluent: tetrahydrofuran Detector: differential refractometer Standard sample: polystyrene

[0028] Adhesive strength The adhesive sheet was cut into 25 mm wide strips, the release film was removed, and the strips were attached to fluorine-treated glass by rolling them twice with a hand roller to prepare test pieces. The strips were then left to stand in an atmosphere of 23°C and 50% relative humidity for 24 hours, and then pulled in a 180° direction at a pulling rate of 300 mm / min, and the median value was recorded as the adhesive strength.

[0029] relative permittivity The pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets were laminated to form a laminated pressure-sensitive adhesive layer of approximately 200 μm, and the dielectric constant of the laminated pressure-sensitive adhesive layer was measured using the following device. The dielectric constant was determined by averaging the measured values ​​of three samples.

[0030] Measurement method: LCR meter (Device: Wayne Kerr 6440B Impedance Analyzer) Frequency: 1MHz Bias voltage: 2V Measurement environment: 23±1℃, 50±1%RH

[0031] Each of the pressure-sensitive adhesive compositions of the Examples had high adhesive strength to the fluorine-treated glass, while each of the pressure-sensitive adhesive compositions of the Comparative Examples had poor adhesive strength to the fluorine-treated glass.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic copolymer obtained by polymerizing an acrylic monomer composition and an isocyanate compound, wherein a film of the pressure-sensitive adhesive composition formed to a thickness of 20 μm on a 50 μm thick PET film is attached to fluorine-treated glass, and the peel strength when peeled is 20 gf / 25 mm or more; the acrylic monomer composition contains 55 to 80% by weight of a (meth)acrylic monomer having a substituent with 12 or more carbon atoms, 10 to 35% by weight of a (meth)acrylic monomer having a substituent with 8 or less carbon atoms, and 1 to 10% by weight of a hydroxyl group-containing (meth)acrylic monomer; A pressure-sensitive adhesive composition comprising isostearyl acrylate as the (meth)acrylic monomer having a substituent with 12 or more carbon atoms.

2. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the acrylic copolymer has a molecular weight of 100,000 to 400,000.

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