KR102234826B1 - Composition for transparent adhesive sheet - Google Patents

Abstract

Provides a composition for a transparent adhesive sheet that is excellent in curability and does not corrode the conductive layer even when the resulting transparent adhesive sheet is directly bonded to the conductive layer surface of a transparent conductive film, and is also excellent in step followability and transparency to metal wiring or printing frames. .
In the solid content ratio, (A) 65 to 85 mass% of (meth)acrylic resin, (B) 10 to 30 mass% of polyoxyalkylene polyol, (C) 1.0 to 5.0 mass% of polyisocyanate, and (D ) A tin catalyst containing 0.005 to 0.1 mass%, an acid value of 0 to 5 mgKOH/g, (A) the weight average molecular weight of the (meth)acrylic resin is 100,000 to 600,000, and (B) polyoxy It relates to a composition for a transparent pressure-sensitive adhesive sheet having an alkylene polyol having a number average molecular weight of 500 to 1500.

Description

Composition for transparent adhesive sheet {COMPOSITION FOR TRANSPARENT ADHESIVE SHEET}

The present invention is a transparent adhesive sheet for fixing a transparent conductive film and a transparent adhesive sheet for fixing a transparent conductive film, characterized in that the composition for a transparent adhesive sheet, a transparent adhesive sheet containing the composition for a transparent adhesive sheet, and a transparent adhesive sheet are used for bonding of a transparent conductive film. It relates to a laminate, characterized in that the transparent pressure-sensitive adhesive sheet is adhered to the surface of the conductive layer of the transparent conductive film.

Recently, touch panels are beginning to be mounted on mobile phones and game devices. The touch panel includes a transparent substrate or glass having a transparent conductive film such as silver and ITO (indium tin oxide) on its surface, a transparent protective sheet to protect them, and an optical member such as a display device such as a liquid crystal display, and an optical transparent adhesive sheet. It is a laminated body that is used and bonded.

BACKGROUND ART Touch panels include a resistive type touch panel that detects mainly by pressure during input, and a capacitive type touch panel that detects an input location by static electricity from a human body during input. In a capacitive touch panel, the conductive layer surface of the transparent conductive film is fixed so as to contact the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive sheet. Therefore, there is a problem that an oxidation reaction of the metal component occurs in the transparent conductive film due to the acid component contained in the pressure-sensitive adhesive, and the conductive function is deteriorated. For this reason, there is a demand for an adhesive sheet for fixing a transparent conductive film that contains almost no acid component and has high metal corrosion protection and good adhesion.

As a pressure-sensitive adhesive sheet having metal corrosion protection, a pressure-sensitive adhesive sheet (for example, Patent Document 1) containing a metal corrosion inhibitor has been proposed. Further, a pressure-sensitive adhesive sheet (for example, Patent Document 2) in which corrosiveness to a transparent conductive film is reduced by containing a nitrogen atom-containing component in a specific amount with respect to the acid component of the pressure-sensitive adhesive layer has been proposed.

However, the pressure-sensitive adhesive sheet containing the metal corrosion inhibitor has a problem such as discoloration by the metal corrosion inhibitor when the durability test is performed, thereby lowering the optical properties. In addition, the pressure-sensitive adhesive sheet containing a nitrogen atom-containing component in a specific amount has a problem in that the increase in the electrical resistance value of ITO cannot be sufficiently suppressed due to the acid component contained in the pressure-sensitive adhesive layer.

On the other hand, in a touch panel, etc., a member having a step such as a metal wiring or a printing step may be included. For example, in a mobile phone or the like, a touch panel or the like having a member on which a frame-shaped print portion is applied is used. In such applications, the pressure-sensitive adhesive sheet is required to attach and fix a member and at the same time to fill in a step, that is, excellent step followability. When the transparent pressure-sensitive adhesive sheet cannot absorb the step difference, the transparent pressure-sensitive adhesive sheet is lifted (bubbles or voids) from the adherend in the vicinity of the step, and reflection loss of light occurs due to this lift (bubbles or voids). There is a fear that the visibility of the liquid crystal display may decrease.

In order to obtain excellent level difference followability, it is advantageous that the transparent pressure-sensitive adhesive sheet is flexible and has high adhesive strength, but for the reasons described above, it is required to have high adhesiveness even if it does not contain an acid component. According to this requirement, a transparent pressure-sensitive adhesive composition comprising an acrylic polymer of a specific molecular weight and a crosslinking agent that does not contain an acid component containing an alkoxyalkyl acrylate as a main monomer and a crosslinking agent is compatible with good adhesion and metal corrosion protection. To give (for example, Patent Document 3) is disclosed.

However, since the pressure-sensitive adhesive composition containing an acrylic polymer of a specific molecular weight and a crosslinking agent that does not contain an acid component containing an alkoxyalkyl acrylate as a main monomer does not contain an acid component, curing by an isocyanate crosslinking agent is slow, and the transparent adhesive sheet There was a problem that it takes time to cure. In order to solve this problem, it is also disclosed to add an amine compound containing a plurality of hydroxyl groups, but the amine compound may cause yellowing of the transparent adhesive sheet over time.

In short, it is the present situation that an excellent composition for a transparent pressure-sensitive adhesive sheet in which all properties such as metal corrosion protection, step followability, transparency, and curability are compatible at a high level has not been obtained.

Japanese Patent Application Publication No. 2006-45315 Japanese Patent Publication No. 2010-144002 Japanese Patent Laid-Open No. 2010-77287

The problem to be solved by the present invention is excellent in curability, and the resulting transparent adhesive sheet does not corrode the conductive layer even if it is directly bonded to the conductive layer surface of the transparent conductive film, and has excellent step followability and transparency for metal wiring or printing frames. , It is to provide a composition for a transparent adhesive sheet.

The present inventors have repeatedly studied the above problems of the transparent pressure-sensitive adhesive sheet for a touch panel, and as a result, as a result of thorough examination, a specific weight-average molecular weight (meth)acrylic resin, a specific number-average molecular weight polyoxyalkylene polyol, and poly(polyol) It was found that the composition for a transparent adhesive sheet containing an isocyanate and a tin catalyst in a specific weight ratio was excellent in curability, and the transparency and tackiness of the obtained transparent adhesive sheet, and the metal corrosion prevention property of the transparent conductive film and the step difference followability were good. The present invention has been completed based on knowledge.

The present invention is represented by the following (1) to (9).

(1) In solid content ratio, (A) 65 to 85 mass% of (meth)acrylic resin, (B) 10 to 30 mass% of polyoxyalkylene polyol, (C) 1.0 to 5.0 mass% of polyisocyanate, and (D ) A tin catalyst containing 0.005 to 0.1 mass%, an acid value of 0 to 5 mgKOH/g, (A) the weight average molecular weight of the (meth)acrylic resin is 100,000 to 600,000, and (B) polyoxy A composition for a transparent adhesive sheet having a number average molecular weight of 500 to 1500 of an alkylene polyol.

(2) (A) The composition for a transparent adhesive sheet according to the above (1), wherein the (meth)acrylic resin contains 0.5 to 10 mol% of structural units derived from a hydroxyl group-containing (meth)acrylic monomer.

(3) The composition for a transparent adhesive sheet according to the above (2), wherein the hydroxyl group-containing (meth)acrylic monomer is 2-hydroxyethyl (meth)acrylate.

(4) The composition for a transparent adhesive sheet according to any one of (1) to (3), wherein the (A) (meth)acrylic resin contains 5 to 50 mol% of structural units derived from methyl (meth)acrylate.

(5) The composition for transparent adhesive sheets according to any one of (1) to (4), wherein the (A) (meth)acrylic resin has a glass transition point of -80 to 0°C.

(6) A transparent adhesive sheet obtained by curing the composition for transparent adhesive sheets according to any one of (1) to (5) above.

(7) The transparent adhesive sheet according to (6), wherein the gel fraction is 40 to 80%.

(8) The transparent adhesive sheet for fixing a transparent conductive film, wherein the transparent adhesive sheet according to (6) or (7) is used for bonding a transparent conductive film.

(9) A laminate, wherein the transparent adhesive sheet for fixing a transparent conductive film according to the above (8) is adhered to the conductive layer surface of the transparent conductive film.

The composition for a transparent adhesive sheet of the present invention has a specific structural unit, that is, a polyoxyalkylene skeleton in the composition, so that the level difference followability of the obtained transparent adhesive sheet and the adhesive force to the base material are improved. Further, by including (D) a tin catalyst, the curability of the (C) polyisocyanate becomes good, and the curing time of the transparent adhesive sheet can be shortened. In addition, since the composition for a transparent adhesive sheet of the present invention does not contain an acid substantially, corrosion of the surface of the conductive layer of the transparent conductive film due to the acid component can be suppressed.

Hereinafter, the present invention will be described in detail.

In addition, in the present specification, the (meth)acryloyl group means CH ₂ =CH-CO- or CH ₂ =C(CH ₃ )-CO-.

(Composition for transparent adhesive sheet)

The composition for a transparent adhesive sheet of the present invention has a solid content ratio of (A) 65 to 85 mass% of (meth)acrylic resin, (B) 10 to 30 mass% of polyoxyalkylene polyol, and (C) 1.0 to polyisocyanate. 5.0% by mass, (D) 0.005 to 0.1% by mass of a tin catalyst, an acid value of 0 to 5 mgKOH/g, and (A) a weight average molecular weight of the (meth)acrylic resin is 100,000 to 600,000, And (B) the number average molecular weight of the polyoxyalkylene polyol is a composition for a transparent pressure-sensitive adhesive sheet of 500 to 1500.

((A) (meth)acrylic resin)

In the present invention, (A) (meth)acrylic resin refers to a resin having 50 mol% or more of structural units derived from a monomer having a (meth)acryloyl group with respect to all structural units derived from a monomer constituting the (meth)acrylic resin. And 70 mol% or more of a structural unit is preferable, and 90 mol% or more is more preferable. In addition, there is no particular limitation as a (meth)acrylic monomer (monomer having a (meth)acryloyl group) used in the polymerization of (A) (meth)acrylic resin in the present invention, but a carboxyl group (chemical formula: -COOH) It is preferable not to contain. In the case of using a (meth)acrylic monomer containing a carboxyl group, (A) in the (meth)acrylic resin, the structural unit derived from the (meth)acrylic monomer containing a carboxyl group is preferably 0.5 mol% or less, and 0.1 mol It is more preferable that it is% or less. Examples of (meth)acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and tert- Butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, Alkyl (meth)acrylates such as isodecyl (meth)acrylate, stearyl (meth)acrylate, tridecyl (meth)acrylate, and isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, nor Bornyl (meth)acrylate, isobornyl (meth)acrylate, norbornanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclo Cyclic alkyl (meth)acrylates such as fentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, and tricyclodecanedimethyloldi (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl Alkoxyalkyl (meth)acrylates such as (meth)acrylate, butoxyethyl (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, and 2-ethoxyethoxyethyl (meth)acrylate, Alkoxy (poly) alkylene glycol (meth) acrylate, such as methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, and methoxydipropylene glycol (meth)acrylate, octafluoropentyl (meth) ) Dialkylaminoalkyl (meth)acrylates such as fluorinated alkyl (meth)acrylates such as acrylates, N,N-dimethylaminoethyl (meth)acrylates, and N,N-diethylaminoethyl (meth)acrylates , (Meth)acrylate containing amide groups such as (meth)acrylamide and diacetone (meth)acrylamide, (meth)acrylate containing epoxy groups such as glycidyl (meth)acrylate, and silicone-modified (meth)acrylate , Polyethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) arc Polyfunctional (meth)acrylates, such as a relay, etc. are mentioned. These may be used alone or in combination of two or more.

Considering the compatibility of (A) (meth)acrylic resin and (B) polyoxyalkylene polyol, that is, the transparency of the pressure-sensitive adhesive layer formed by curing the composition for a transparent pressure-sensitive adhesive sheet, (A) constituting the (meth)acrylic resin The content of the structural units derived from methyl acrylate and/or methyl methacrylate with respect to all the monomer-derived structural units is preferably 5 to 50 mol%, more preferably 10 to 45 mol%, and 15 to 40 mol%. It is more preferable. When the content of the structural unit derived from methyl acrylate and/or methyl methacrylate is less than 5 mol%, the compatibility with polyoxyalkylene polyol tends to deteriorate, and when it is more than 50 mol%, the adhesive strength of the transparent adhesive sheet This tends to become smaller. In addition, the content of the structural units derived from methyl acrylate and/or methyl methacrylate refers to the total amount of the structural units derived from methyl acrylate and methyl methacrylate.

In addition, the (A) (meth)acrylic resin in the present invention preferably contains a hydroxyl group-containing (meth)acrylic monomer as a copolymerization component from the viewpoint of being integrated by reacting with a polyoxyalkylene polyol via a polyisocyanate. Do. Examples of the hydroxyl group-containing (meth)acrylic monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 1,3-butanediol (meth)acrylate. ) Hydroxyl group-containing (meth)acrylates such as acrylate, 1,4-butanediol (meth)acrylate, 1,6-hexanediol (meth)acrylate, and 3-methylpentanediol (meth)acrylate. have. Among them, 2-hydroxyethyl (meth)acrylate is preferred from the viewpoint of copolymerization and reactivity with other monomers. The structural unit derived from a hydroxyl-containing (meth)acrylic monomer is preferably 0.5 to 10 mol%, and 0.6 to 8 mol% with respect to the total structural units derived from the monomer constituting the (A) (meth)acrylic resin. It is more preferable, and it is still more preferable to contain 0.7 to 5 mol%. When the content of the constituent unit derived from a hydroxyl-containing (meth)acrylic monomer is less than 0.5 mol%, the reaction with the polyoxyalkylene polyol tends to decrease and the resulting transparent pressure-sensitive adhesive sheet tends to have a small cohesive strength, and when it exceeds 10 mol%, crosslinking Because the density becomes too high, the obtained transparent adhesive sheet tends to become hard.

In addition, in the (A) (meth)acrylic resin in the present invention, other polymerizable monomers can be used as the copolymerization component within a range that does not impair the polymerizability. Examples of such polymerizable monomers include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinylpyridine, Vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamide methyl trimethyl ammonium chloride, allyl trimethyl ammonium chloride, dimethyl allyl vinyl ketone, and the like.

The (A) (meth)acrylic resin in the present invention needs to have a weight average molecular weight of 100,000 to 600,000, preferably 150,000 to 500,000, and more preferably 200,000 to 400,000. (A) When the weight average molecular weight of the (meth)acrylic resin is less than 100,000, the cohesive force of the resulting transparent adhesive sheet becomes small, which is not preferable. On the other hand, when the weight average molecular weight is larger than 600,000, compatibility between (A) (meth)acrylic resin and (B) polyoxyalkylene polyol deteriorates, and transparency of the obtained transparent adhesive sheet deteriorates.

Here, the weight average molecular weight is calculated in terms of polystyrene by measuring at room temperature under the following conditions using gel permeation chromatography (made by Showa Denko Corporation, Shodex (registered trademark) GPC-101).

Column: Showa Denko Corporation, Shodex (registered trademark) LF-804

Column temperature: 40°C

Sample: 0.2% by mass tetrahydrofuran solution of (meth)acrylic resin

Flow rate: 1ml/min

Eluent: Tetrahydrofuran

Detector: RI detector

In addition, the glass transition point (Tg) of the (A) (meth)acrylic resin in the present invention is preferably -80 to 0°C, more preferably -70 to -5°C, and -60 to -10 It is more preferable that it is °C. When the Tg is higher than 0°C, the transparent pressure-sensitive adhesive sheet hardens, and thus the level difference followability tends to deteriorate. On the other hand, when Tg is lower than -80 degreeC, the cohesive force becomes small, and there exists a tendency for the strength of a transparent adhesive sheet to become insufficient. In addition, Tg of (A) (meth)acrylic resin can be suitably adjusted by changing the kind and composition ratio of the monomer component used for polymerization.

Here, Tg refers to what was calculated|required from the following method. (A) 10 mg of sample was collected from (meth)acrylic resin, and differential scanning calorimetry was measured by changing the temperature from -80°C to 200°C at a heating rate of 10°C/min using a differential scanning calorimeter (DSC). Is performed, and the endothermic start temperature by glass transition is taken as Tg. In addition, when two or more Tg are observed, the simple average value at the absolute temperature of these Tg is taken.

The polymerization method of the (A) (meth)acrylic resin in the present invention is not particularly limited, and known methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and alternating copolymerization can be used. Among them, solution polymerization is particularly suitable in terms of transparency and water resistance. In addition, the obtained copolymer may be any of a random copolymer and a block copolymer.

(A) The polymerization initiator used in polymerization of the (meth)acrylic resin is not particularly limited, and can be appropriately selected from known ones and used. For example, 2,2'-azobis (isobutyronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis (2 ,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis( 2,4,4-trimethylpentane), azo polymerization initiators such as dimethyl-2,2'-azobis (2-methylpropionate), benzoyl peroxide, t-butyl hydroperoxide, di-t- Butyl peroxide, t-butylperoxybenzoate, dicumylperoxide, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy) ) Oil-soluble polymerization initiators such as peroxide-based polymerization initiators such as cyclododecane are preferably exemplified. These polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used may be an ordinary amount, for example, it can be selected from the range of about 0.01 to 5 parts by mass per 100 parts by mass of the monomer, preferably 0.015 to 4 parts by mass, and 0.02 to 3 parts by mass. It is more preferable.

In addition, in solution polymerization, various general solvents can be used. Examples of such solvents include esters such as ethyl acetate, n-propyl acetate, and n-butyl acetate, aromatic hydrocarbons such as toluene and benzene, aliphatic hydrocarbons such as n-hexane and n-heptane, cyclohexane, methylcyclohexane, and the like. And organic solvents such as ketones such as alicyclic hydrocarbons, methyl ethyl ketone, and methyl isobutyl ketone. These solvents may be used alone or in combination of two or more.

In addition, as the compounding amount of (A) (meth)acrylic resin in the composition for transparent adhesive sheet of the present invention, it is necessary to be 65 to 85% by mass, and 70 to 85% by mass with respect to the total solid content of the composition for transparent adhesive sheet. It is preferable and it is more preferable that it is 75-85 mass %. (A) When the blending amount of the (meth)acrylic resin is less than 65% by mass, the cohesive force becomes small and the strength of the transparent adhesive sheet becomes insufficient. On the other hand, when the blending amount of (A) (meth)acrylic resin exceeds 85% by mass, sufficient level difference followability cannot be obtained.

((B) polyoxyalkylene polyol)

The (B) polyoxyalkylene polyol used in the present invention is not particularly limited as long as it is a polymer polyol having an ether bond, and a known polymer polyol can be appropriately used. (B) Examples of the polyoxyalkylene polyol include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, and derivatives or copolymers thereof. Among them, polypropylene glycol is preferable because it is easy to adjust the compatibility with an acrylic resin. These may be used individually, or two or more types may be mixed and used for them.

The (B) polyoxyalkylene polyol used in the present invention needs to have a number average molecular weight of 500 to 1500, preferably 700 to 1300, and more preferably 800 to 1200. When the number average molecular weight is less than 500, the level difference followability of the transparent pressure-sensitive adhesive sheet is deteriorated, which is not preferable. On the other hand, when the number average molecular weight exceeds 1500, the transparency of the obtained transparent adhesive sheet deteriorates. In addition, the number average molecular weight can be measured by the method similar to the weight average molecular weight of (A) (meth)acrylic resin by GPC (gel permeation chromatography).

In addition, as the compounding amount of the (B) polyoxyalkylene polyol in the composition for transparent adhesive sheet of the present invention, it is necessary to be 10 to 30% by mass and 13 to 25% by mass with respect to the total solid content of the composition for transparent adhesive sheet. It is preferable and it is more preferable that it is 15-20 mass %. (B) When the blending amount of the polyoxyalkylene polyol is less than 10% by mass, the transparent pressure-sensitive adhesive sheet cannot obtain sufficient level difference followability. On the other hand, when the blending amount of the (B) polyoxyalkylene polyol exceeds 30% by mass, the cohesive force becomes small and the strength of the transparent adhesive sheet becomes insufficient.

((C) polyisocyanate)

Examples of the polyisocyanate (C) in the present invention include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. (C) Examples of polyisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2-methyl-1,5-pentane diisocyanate, and 3-methyl-1,5-pentane Diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, tolylene diisocyanate (TDI), hydrogenated tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, polyphenylmethane poly Isocyanate, xylene diisocyanate, hydrogenated xylene diisocyanate, tetramethylxylylene diisocyanate, norbornene diisocyanate, naphthalene diisocyanate, trimethylolpropane/tolylenediisocyanate trimer adduct, trimethylolpropane/hexamethylenediisocyanate trimer An isocyanate adduct, such as a sieve adduct and an isocyanurate body of hexamethylene diisocyanate, a polyether polyisocyanate, a polyester polyisocyanate, etc. are mentioned. These may be used individually or may be used in combination of 2 or more types.

In addition, as the compounding amount of the polyisocyanate (C) in the composition for transparent adhesive sheets of the present invention, it is necessary to be 1.0 to 5.0% by mass, preferably 1.5 to 4.5% by mass, based on the total solid content of the composition for transparent adhesive sheets, It is more preferable that it is 2.0 to 4.0 mass %. (C) When the blending amount of the polyisocyanate is less than 1.0% by mass, sufficient cohesive force cannot be obtained, and the strength of the transparent adhesive sheet becomes insufficient. On the other hand, when the blending amount of (C) polyisocyanate exceeds 5.0% by mass, the flexibility of the resulting transparent pressure-sensitive adhesive sheet is insufficient, and sufficient level difference followability cannot be obtained.

((D) tin catalyst)

Examples of the tin catalyst used in the present invention include dibutyltin dilaurate, dibutyltin diethylhexoate, dioctyltin dilaurate, and the like. Among them, (C) the curability of the polyisocyanate is good, and from the viewpoint of safety, dioctyl tin dilaurate is preferable.

In addition, as the compounding amount of the (D) tin catalyst in the composition for transparent adhesive sheets of the present invention, it is necessary to be 0.005 to 0.1% by mass, preferably 0.01 to 0.09% by mass, based on the total solid content of the composition for transparent adhesive sheets. It is more preferable that it is 0.02 to 0.080 mass %. (D) When the blending amount of the tin catalyst is less than 0.005% by mass, the curability of the composition for a transparent adhesive sheet is insufficient, and the cohesive force decreases, and when it is more than 0.1% by mass, the potable time at the time of producing the transparent adhesive sheet is short. Lose.

(Composition for transparent adhesive sheet)

The composition for a transparent adhesive sheet of the present invention needs to have an acid value of 0 to 5 mgKOH/g, preferably 0 to 1 mgKOH/g, more preferably 0 to 0.3 mgKOH/g, and 0 to It is particularly preferred that it is 0.1 mgKOH/g. When the acid value of the composition for transparent adhesive sheets is higher than 5 mgKOH/g, it becomes difficult to suppress corrosion on the surface of the conductive layer of the transparent conductive film. In addition, the acid value of the composition for transparent adhesive sheets is a value measured in conformity with JIS K0070. For example, it measures as follows.

About 2 g of a sample is precisely weighed in a 100 ml Erlenmeyer flask with a precision balance, and 10 ml of a mixed solvent of ethanol/diethyl ether=1/1 (mass ratio) is added and dissolved therein. In addition, 1 to 3 drops of a phenolphthalein ethanol solution is added to this container as an indicator, and the sample is sufficiently stirred until it becomes uniform. This is titrated with a 0.1N potassium hydroxide-ethanol solution, and when the pale red color of the indicator continues for 30 seconds, it is taken as the end point of neutralization. As a result, the value obtained using the following equation (1) is taken as the acid value of the composition for transparent pressure-sensitive adhesive sheets.

To the composition for a transparent adhesive sheet of the present invention, if necessary, in order to improve the adhesive strength of the obtained transparent adhesive sheet, a tackifying resin may be added within a range not lowering the transparency of the transparent adhesive sheet. Examples of the tackifying resin include rosin-based resins such as rosin and esterified products of rosin; Terpene resins such as diterpene polymers and α-pinene-phenol copolymers; Petroleum resins such as aliphatic (C5) and aromatic (C9); In addition, a styrenic resin, a phenolic resin, a xylene resin, etc. are mentioned. From the viewpoint of light resistance, it is preferable to add a hydrogenated rosin with few unsaturated double bonds or an esterified product of a disproportionated rosin, an aliphatic or aromatic petroleum resin, an acrylic resin having a high Tg, or the like to the transparent adhesive sheet. As the addition amount of the tackifying resin, it is preferable to add 1 to 10 parts by mass with respect to 100 parts by mass of the composition for transparent adhesive sheets.

Moreover, the composition for transparent adhesive sheets of this invention may contain various well-known additives, as needed, as long as transparency is not impaired. As additives, plasticizers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazole-based, phosphate ester-based and other flame retardants, antistatic agents such as surfactants, etc. Can be lifted.

In addition, the composition for a transparent adhesive sheet of the present invention may be diluted with an organic solvent for the purpose of adjusting the viscosity at the time of application. Examples of the organic solvent used include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, n-propanol, isopropanol, n-propyl acetate, and the like. I can. These organic solvents may be used alone or in combination of two or more.

(Transparent Adhesive Sheet)

The transparent adhesive sheet of the present invention is obtained by curing the composition for transparent adhesive sheets. More specifically, it is used for bonding optical members (for bonding optical members), for manufacturing optical products, and the like. Moreover, the transparent adhesive sheet of this invention may have a base material, and may be a double-sided adhesive sheet which does not have a base material and contains only an adhesive layer. The optical member is not particularly limited as long as it is a member having optical properties, and examples thereof include a member constituting an image display device, a touch panel, or a member used in these devices. More specifically, for example, a polarizing plate, a retardation plate, an optical compensation film, a brightness enhancing film, a light guide plate, a reflective film, an antireflection film, a transparent conductive film, a design film, a decorative film, a surface protection film, a prism, a lens, a color filter , A transparent substrate, and further, a member in which these are laminated.

The transparent adhesive sheet of the present invention can be obtained by applying a solution in which the composition for a transparent adhesive sheet is dissolved in a solvent to a release film, and heating and drying the applied solution to crosslink. The thickness of the transparent adhesive sheet is preferably 5 to 200 µm, more preferably 10 to 150 µm, and even more preferably 15 to 100 µm. When the film thickness of the transparent adhesive sheet becomes thinner than 5 μm, there is a tendency that bonding of the transparent adhesive sheet becomes difficult. When the film thickness of the transparent pressure-sensitive adhesive sheet becomes thicker than 200 µm, the solvent remains on the sheet and tends to cause a problem of odor. In addition, as a coating (coating) method for forming the transparent adhesive sheet of the present invention, it is possible to use a known coating method, and a common coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater , Dip roll coater, bar coater, knife coater, spray coater, comma coater, direct coater, etc. can be used to coat.

The gel fraction of the transparent adhesive sheet of the present invention is preferably 40 to 80%, more preferably 45 to 75%, and even more preferably 50 to 70%. Even when the gel fraction is less than 40%, it can be used, but the cohesive force of the transparent adhesive sheet tends to decrease. In addition, when the gel fraction is larger than 80%, there is a tendency that the level difference followability of the transparent pressure-sensitive adhesive sheet is deteriorated.

In addition, the gel fraction of the transparent adhesive sheet is determined by the following equation (2) based on the mass of the sample before toluene immersion and after immersion in toluene at room temperature for 24 hours and drying at 80°C for 5 hours.

(Transparent adhesive sheet for fixing a transparent conductive film)

The transparent adhesive sheet for fixing a transparent conductive film of the present invention is a transparent adhesive sheet for fixing a transparent conductive film formed by curing the composition for a transparent adhesive sheet. It is difficult to cause corrosion. Therefore, the laminate obtained by bonding the sheet for fixing the transparent conductive film to the conductive layer surface of the transparent conductive film can be suitably used as a touch panel. In addition, the transparent adhesive sheet for fixing a transparent conductive film of the present invention may have a base material or may be a double-sided adhesive sheet including only an adhesive layer without having a base material. In addition, it does not matter whether the pressure-sensitive adhesive layer is made of a single layer or a plurality of layers are laminated. Especially, it is preferable that it is a double-sided adhesive sheet which does not have a base material and contains only an adhesive layer from the viewpoint of securing transparency and level difference followability.

As the transparent conductive film in which the transparent adhesive sheet for fixing a transparent conductive film of the present invention is used, any one having a conductive layer on at least one surface layer may be used, and a transparent conductive film provided with a conductive material on the surface layer of a transparent substrate by vapor deposition or coating can be exemplified. have. The conductive material to be vapor-deposited or coated in the conductive layer of the transparent conductive film is not particularly limited, but specifically, silver, indium tin oxide, indium oxide, tin oxide, zinc oxide, cadmium oxide, gallium oxide, titanium oxide, etc. I can. Among them, silver and indium tin oxide excellent in transparency and conductivity are suitably used. In the transparent conductive film, the substrate on which the conductive material is vapor-deposited or coated is not particularly limited, and examples thereof include glass and resin films.

Moreover, the transparent adhesive sheet for fixing a transparent conductive film of this invention can be obtained by the method similar to the said transparent adhesive sheet.

[Example]

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited at all by these examples.

<Synthesis of (meth)acrylic resins (A-1) to (A-3)>

The addition ratio (mol%) of each (meth)acrylic monomer was calculated from the total amount (mol) of the (meth)acrylic monomers used in the production of the (meth)acrylic resin. In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, and a stirring device, 500 parts by mass of n-propyl acetate, 320 parts by mass (53 mol%) of 2-ethylhexyl acrylate, and 125 parts by mass (38 mol%) of methyl methacrylate ), 50 parts by mass (8 mol%) of isobornyl acrylate, 5 parts by mass (1 mol%) of 2-hydroxyethyl methacrylate, 0.1 parts by mass of 2,2'-azobis (isobutyronitrile), and nitrogen After polymerization treatment at 95°C for 8 hours in an air stream, it was cooled to 30°C to obtain a (meth)acrylic copolymer (A-1). The obtained (meth)acrylic copolymer (A-1) had a glass transition temperature of -30°C and a weight average molecular weight of 200,000. In addition, the glass transition temperature and weight average molecular weight of the (meth)acrylic copolymer were measured by the method described above. In addition, except changing the composition ratio of the (meth)acryloyl group-containing monomer shown in Table 1, in the same manner as in the (meth)acrylic copolymer (A-1), (meth)acrylic copolymers (A-2) to ( A-3) was obtained. Moreover, similarly to the (meth)acrylic copolymer (A-1), the glass transition temperature and the weight average molecular weight were measured for the (meth)acrylic copolymers (A-2) to (A-3). Table 1 shows the results.

<Synthesis of (meth)acrylic resin (A-4)>

The addition ratio (mol%) of each (meth)acrylic monomer was calculated from the total amount (mol) of the (meth)acrylic monomers used in the production of the (meth)acrylic resin. In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer and a stirring device, 500 parts by mass of n-propyl acetate, 320 parts by mass (53 mol%) of 2-ethylhexyl acrylate, and 118 parts by mass (36 mol%) of methyl methacrylate ), isobornyl acrylate 50 parts by mass (7 mol%), 2-hydroxyethyl methacrylate 5 parts by mass (1 mol%), acrylic acid 6 parts by mass (3 mol%), 2,2'-azobis (isobuty Lonitrile) 0.1 part by mass was added, polymerization was carried out at 95°C for 8 hours in a nitrogen stream, and then cooled to 30°C to obtain a (meth)acrylic copolymer (A-4). The obtained (meth)acrylic copolymer (A-4) had a glass transition temperature of -30°C and a weight average molecular weight of 230,000. In addition, the glass transition temperature and weight average molecular weight of the (meth)acrylic copolymer were measured by the method described above. Moreover, similarly to the (meth)acrylic copolymer (A-1) to (A-3), the glass transition temperature and the weight average molecular weight were also measured about the (meth)acrylic copolymer (A-4). Table 1 shows the results.

(Examples 1 to 3 and Comparative Examples 1 to 5)

In the composition shown in Table 2, (meth)acrylic resin, polyoxyalkylene polyol, polyisocyanate, and tin catalyst were blended, and the solid content concentration was adjusted to 50% by mass with n-propyl acetate, and the resulting solution was used at room temperature. The composition solution for a transparent adhesive sheet was obtained by mixing using a disper. In Table 2, the numerical values relating to the (meth)acrylic resin, polyoxyalkylene polyol, polyisocyanate, and tin catalyst represent mass% with respect to the total solid content of the composition for a transparent adhesive sheet. This transparent adhesive sheet composition solution is cast on one side of a 50 μm-thick polyethylene terephthalate (PET) film on the peeling-treated surface of a separator that has been subjected to a peeling treatment so that the thickness after drying becomes 100 μm (coating layer thickness) 200 µm), heat-dried at 50°C for 10 minutes, 80°C for 10 minutes, and 110°C for 20 minutes, and the peeling-treated side of the separator which has been stripped on one side of a PET film having a thickness of 38 μm, is a pressure-sensitive adhesive. Cover on the side. And aging was performed at 40 degreeC for 72 hours, and the double-sided adhesive sheet (inorganic material type) was produced.

(Acid value)

The acid value of each composition for transparent adhesive sheets was measured by the above method. Table 2 shows the results.

(Measurement of electrical resistance value of indium tin oxide film)

Cut the double-sided adhesive sheet obtained above into a size of 50 mm×50 mm, peel off the 38 μm-thick PET film on one side, and one side of the double-sided adhesive sheet and one side of the 100 mm×100 mm indium tin oxide deposited PET film The double-sided pressure-sensitive adhesive sheet was bonded to the surface of the indium tin oxide film so that it became parallel and the position of the double-sided pressure-sensitive adhesive sheet was approximately the center of the indium tin oxide-evaporated PET film in the vertical and horizontal directions. For the indium tin oxide-deposited PET film to which the double-sided adhesive sheet was bonded, the initial electrical resistance value (R ₁ ) was measured using an electric resistance value measuring instrument ("Loresta GP" manufactured by Mitsubishi Chemical Industries, Ltd.). In addition, the indium tin oxide-deposited PET film to which the double-sided adhesive sheet was bonded was allowed to stand for 500 hours under conditions of 60°C and 90%RH, and left to stand for 1 hour under conditions of 23°C and 50%RH, and then the initial electrical resistance value was measured. The electrical resistance value (R ₂ ) was measured at the same location as in FIG. The rate of increase in the electrical resistance value of the indium tin oxide film was calculated by the following equation (3).

The evaluation of the increase rate of the electrical resistance value was performed based on the following criteria. Table 2 shows the results.

○; Less than 5% increase in electrical resistance

△; 5 to less than 10% increase in electrical resistance

×; 10% or more of increase rate of electrical resistance

(Total light transmittance measurement)

The double-sided adhesive sheet obtained above was cut out to a size of 30 mm x 30 mm, and the peeling PET film having a thickness of 38 μm on one side of the peeling PET film on both sides of the double-sided adhesive sheet was peeled off, and a sample for measurement that was bonded to a glass plate. It was made into. About the sample for measurement, the total light transmittance (%) was measured using "HR-100 type" manufactured by Murakami Shikisai Institute of Technology. Table 2 shows the results.

(Measurement of adhesion of double-sided adhesive sheet)

The double-sided adhesive sheet obtained above was cut into a size of 25 mm×100 mm, and the 38 μm-thick peeling PET film was peeled off from one side of the double-sided adhesive sheet, and a 50 μm-thick PET film subjected to corona treatment on one side was reassembled. After attaching, the adhesive surface (measurement surface) was attached to the test plate, and a 2 kg rubber roller (width: about 50 mm) was reciprocated once to prepare a sample for measurement. A glass plate was used as a test plate. The obtained sample for measurement was allowed to stand for 24 hours in an environment of 23°C and 50% humidity, and a tensile test in the 180° direction was performed at a peel rate of 300 mm/min according to JIS ZO237, and the adhesion of the double-sided adhesive sheet to the glass plate (N/25mm) was measured. The obtained measured value was taken as the adhesive force. Table 2 shows the results.

(Step followability evaluation)

The 38 µm-thick peeling PET film on one side of the double-sided adhesive sheet obtained above was peeled off, and the double-sided adhesive sheet was put on a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm, and a window frame shape having a thickness of 15 µm and a width of 5 mm. After bonding to a glass plate with printed printed on it, peeling off the peeling PET film on the other side, bonding with a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm was performed, and a pressure of 5 atm, 70° C., After heat-pressing treatment was performed and fixed under the conditions of 10 minutes, the lifting of the adhesive layer at the stepped portion was visually observed.

The evaluation of the level difference followability was performed based on the following criteria. Table 2 shows the results.

○; A state in which the adhesive layer is not lifted up in the stepped area

△; A state in which the adhesive layer is slightly lifted in the part where there is a step difference

×; A state in which the adhesive layer is clearly lifted up in the stepped area

(Gel fraction measurement)

Using the obtained transparent adhesive sheet, the gel fraction was measured by the method described above. Table 2 shows the results.

Claims (9)

By solid secretion,
(A) 65 to 85% by mass of (meth)acrylic resin,
(B) 10 to 30 mass% of polyoxyalkylene polyol, and
(C) 1.0 to 5.0 mass% of polyisocyanate, and
(D) 0.005 to 0.1% by mass of tin catalyst
And, the acid value is 0 to 5 mgKOH/g,
(A) The weight average molecular weight of the (meth)acrylic resin is 100,000 to 600,000, and the number average molecular weight of the (B) polyoxyalkylene polyol is 500 to 1500, the composition for a transparent adhesive sheet. The method of claim 1,
(A) The composition for transparent adhesive sheets in which (A) (meth)acrylic resin contains 0.5-10 mol% of structural units derived from a hydroxyl-containing (meth)acrylic monomer. The method of claim 2,
A composition for a transparent adhesive sheet, wherein the hydroxyl group-containing (meth)acrylic monomer is 2-hydroxyethyl (meth)acrylate. The method according to any one of claims 1 to 3,
(A) The composition for transparent adhesive sheets in which the (meth)acrylic resin contains 5-50 mol% of structural units derived from methyl (meth)acrylate. The method according to any one of claims 1 to 3,
(A) The composition for transparent adhesive sheets whose glass transition point of (meth)acrylic-type resin is -80 to 0 degreeC. A transparent adhesive sheet obtained by curing the composition for transparent adhesive sheets according to any one of claims 1 to 3. The method of claim 6,
A transparent adhesive sheet having a gel fraction of 40 to 80%. The transparent adhesive sheet for fixing a transparent conductive film, wherein the transparent adhesive sheet according to claim 6 is used for bonding a transparent conductive film. A laminate, wherein the transparent adhesive sheet for fixing a transparent conductive film according to claim 8 is adhered to the conductive layer surface of the transparent conductive film.