TWI609937B - Transparent adhesive sheet composition - Google Patents

Abstract

The invention provides a composition for a transparent adhesive sheet. The composition for a transparent adhesive sheet has excellent curability. Even if the obtained transparent adhesive sheet is directly adhered to the surface of the conductive layer of the transparent conductive film, the conductive layer will not be corroded and the metal wiring will be damaged. The print frame has excellent follow-up and transparency. The present invention relates to a composition for a transparent adhesive sheet, which comprises (A) (meth) acrylic resin 65 to 85% by mass and (B) polyoxyalkylene polyol 10 to 30% by mass in terms of solid content ratio. , (C) polyisocyanate 1.0 to 5.0% by mass, and (D) tin-based catalyst 0.005 to 0.1% by mass, and the acid value of the composition for a transparent adhesive sheet is 0 to 5 mgKOH / g, wherein The weight average molecular weight of the (base) acrylic resin is 100,000 to 600,000, and the number average molecular weight of (B) the polyoxyalkylene polyol is 500 to 1500.

Description

Composition for transparent adhesive sheet Field of invention

The present invention relates to a composition for a transparent adhesive sheet, a transparent adhesive sheet formed from the composition for a transparent adhesive sheet, a transparent adhesive sheet for fixing a transparent conductive film characterized by using the transparent adhesive sheet for bonding of a transparent conductive film, and A laminated body characterized in that a transparent adhesive sheet for fixing a transparent conductive film is adhered to the surface of a conductive layer of the transparent conductive film.

Background of the invention

In recent years, touch panels have been mounted on portable phones, game consoles, and the like. Touch panels are optical substrates such as transparent substrates with transparent conductive films such as silver and ITO (indium tin oxide) on the surface, glass, transparent protective sheets to protect them, and display devices such as liquid crystal displays using transparent adhesive sheets for optics. A laminated body in which members are bonded together.

The touch panel mainly includes a resistive film type touch panel that detects using pressure during input, and a capacitive type touch panel that uses an electrostatic detection input portion derived from a human body during input. In the capacitive touch panel, the surface of the conductive layer of the transparent conductive film is fixed so as to be in contact with the surface of the adhesive layer of the adhesive sheet. Therefore, there is an oxidation reaction of a metal component in the transparent conductive film due to an acid component contained in the adhesive, leading to a conductive Problems with reduced electrical function. Therefore, there is a need for a transparent conductive film fixing adhesive sheet that has almost no acid component and has high metal corrosion resistance and good adhesion.

As an adhesive sheet having metal corrosion resistance, an adhesive sheet containing a metal corrosion inhibitor has been proposed (for example, Patent Document 1). In addition, a pressure-sensitive adhesive sheet that reduces the corrosiveness to a transparent conductive film by containing a specific amount of a nitrogen atom-containing component with respect to the acid component of the adhesive layer has been proposed (for example, Patent Document 2).

However, the pressure-sensitive adhesive sheet containing a metal corrosion inhibitor has problems such as discoloration due to the metal corrosion inhibitor during a durability test, and the optical characteristics are reduced. In addition, a pressure-sensitive adhesive sheet containing a specific amount of a nitrogen atom-containing component has a problem that an increase in the resistance value of ITO cannot be sufficiently suppressed due to an acid component contained in the adhesive layer.

On the other hand, touch panels and the like may include metal wiring and members having a height difference such as a printing height difference. For example, a touch panel or the like having a member to which a frame-shaped printed portion is applied is used in a mobile phone or the like. In such an application, the adhesive sheet is required to have the performance of the landfill height difference, in addition to the performance of the adhesive member, that is, the excellent height difference followability. When the transparent adhesive sheet cannot absorb the height difference, the transparent adhesive sheet floats (bubbles, voids) from the adherend around the height difference, and the liquid crystal display may be lost due to the reflection loss of light caused by the floating (bubbles, voids). Visibility is reduced.

In order to obtain excellent height difference followability, it is advantageous that the transparent adhesive sheet is soft and has high adhesive force. However, from the reasons described earlier, high adhesiveness is required even without an acid component. In response to this request, it is disclosed that special features containing alkoxyalkyl acrylate as the main monomer and containing no acid component are disclosed. The adhesive composition of a fixed molecular weight acrylic polymer and a cross-linking agent provides a technical solution of a transparent adhesive sheet capable of achieving both good adhesion and metal corrosion resistance (for example, Patent Document 3).

However, an adhesive composition containing an acrylic polymer having a specific molecular weight containing an alkoxyalkyl acrylate as a main monomer and containing no acid component and a crosslinking agent has the following problems because it does not contain an acid component: the use of isocyanate The curing by the crosslinking agent is slowed, and the curing of the transparent adhesive sheet takes time. In order to solve this problem, a technical solution for adding an amine compound containing a plurality of hydroxyl groups is also disclosed. However, the amine compound may cause the transparent adhesive sheet to yellow over time.

In short, the present situation is that no excellent composition for a transparent adhesive sheet has been obtained which combines all the characteristics such as anti-corrosiveness to metal, level difference followability, transparency, and curability at a high level.

Prior art literature Patent literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2006-45315

Patent Document 2: Japanese Patent Application Laid-Open No. 2010-144002

Patent Document 3: Japanese Patent Application Laid-Open No. 2010-77287

The problem to be solved by the present invention is to provide excellent curability. Even if the obtained transparent adhesive sheet is directly adhered to the surface of the conductive layer of the transparent conductive film, the conductive layer will not be corroded, and the followability of the height difference of the metal wiring and the printed frame and The composition for transparent adhesive sheets which is also excellent in transparency.

The present inventors repeatedly conducted in-depth studies with the aforementioned problems in the transparent adhesive sheet for touch panels as a background, and found that a (meth) acrylic resin containing a specific weight average molecular weight at a specific weight ratio, a specific number average The composition for transparent adhesive sheets of polyoxyalkylene polyol, polyisocyanate, and tin-based catalyst having a molecular weight is excellent in curability, and the transparency, adhesiveness, and metal corrosion resistance of the transparent conductive film of the obtained transparent adhesive sheet, and The height difference has good followability, and the present invention has been completed based on this knowledge.

The present invention is shown in the following (1) to (9).

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

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

(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 the source Structural unit from methyl (meth) acrylate.

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

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

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

(8) A transparent adhesive sheet for fixing a transparent conductive film, characterized in that the transparent adhesive sheet described in (6) or (7) above is used for bonding the transparent conductive film.

(9) A laminated body characterized in that it is attached to the surface of a conductive layer of a transparent conductive film, and the transparent adhesive sheet for fixing a transparent conductive film according to (8) above is adhered.

When the composition for a transparent adhesive sheet of the present invention has a specific structural unit, that is, a polyoxyalkylene skeleton, in the composition, the obtained transparent adhesive sheet has a high level of followability and an excellent adhesion to a substrate. Furthermore, by containing a (D) tin-based catalyst, the curability of the (C) polyisocyanate becomes good, and the curing time of the transparent adhesive sheet can be shortened. Moreover, since the composition for transparent adhesive sheets of this invention does not contain an acid substantially, it can suppress the corrosion of the surface of the conductive layer of a transparent conductive film by an acid component.

detailed description

The present invention is described in detail below.

Note that the present specification, (meth) Bingxi Xi refers to a group 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 is a composition for a transparent adhesive sheet, which comprises (A) (meth) acrylic resin 65 to 85% by mass and (B) polyoxyalkylene as a solid content ratio. Based polyol 10 to 30% by mass, (C) polyisocyanate 1.0 to 5.0% by mass, and (D) tin-based catalyst 0.005 to 0.1% by mass, and the acid value of the composition for a transparent adhesive sheet is 0 to 5 mgKOH / g Among them, the weight average molecular weight of (A) (meth) acrylic resin is 100,000 to 600,000, and the number average molecular weight of (B) polyoxyalkylene polyol is 500 to 1500.

((A) (meth) acrylic resin)

In the present invention, (A) (meth) acrylic resin means that 50 mol% or more of the total structural units derived from the monomers constituting the (meth) acrylic resin are derived from having (meth) acrylic The resin of the structural unit of a fluorenyl monomer is preferably 70 mol% or more, and more preferably 90 mol% or more. The (meth) acrylic monomer (monomer having a (meth) acrylfluorenyl group) used in the polymerization of the (A) (meth) acrylic resin in the present invention is not particularly limited, but it is preferably not Contains carboxyl group (chemical formula: -COOH). When a carboxyl group-containing (meth) acrylic monomer is used, in the (A) (meth) acrylic resin, the structural unit derived from the carboxyl group-containing (meth) acrylic monomer is preferably 0.5 mol% or less, more preferably It is preferably 0.1 mol% or less. Examples of the (meth) acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, ( N-butyl methacrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) Isooctyl acrylate, lauryl (meth) acrylate, isodecyl (meth) acrylate, stearyl (meth) acrylate, tridecyl (meth) acrylate, isostearyl (meth) acrylate (Meth) acrylic acid alkyl esters; cyclohexyl (meth) acrylate, norbornyl (meth) acrylate, isobornyl (meth) acrylate, norbornyl (meth) acrylate, ( Dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, dicyclopentyl (meth) acrylate, dicyclopentyloxyethyl (meth) acrylate, tricyclodecane dihydroxymethyl (Meth) acrylic cyclic alkyl esters such as methyl di (meth) acrylate; methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxy (meth) acrylate Ethyl ester Alkoxyalkyl (meth) acrylates such as 2-methoxyethoxyethyl (meth) acrylate, 2-ethoxyethoxyethyl (meth) acrylate; methoxydiethylene glycol Alkoxy (poly) alkylene glycol (meth) acrylic acid such as alcohol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate Esters; fluoroalkyl (meth) acrylates such as octafluoropentyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethyl (meth) acrylate Dialkylaminoalkyl (meth) acrylates such as methylaminoethyl; fluorenylamino-containing (meth) acrylates such as (meth) acrylamide and diacetone (meth) acrylamide; (meth) ) Epoxy-containing (meth) acrylates such as glycidyl acrylate; silicone modified (meth) acrylates, polyethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylic acid Ester, neopentyl glycol di (methyl) Multifunctional (meth) acrylates such as acrylate, triethylene glycol di (meth) acrylate, and tripropylene glycol di (meth) acrylate. These can be used alone or in combination of two or more.

When considering the compatibility between (A) (meth) acrylic resin and (B) polyoxyalkylene polyol, that is, the transparency of the adhesive layer obtained by curing the composition for a transparent adhesive sheet, relative to the source The content of all the structural units from the monomers constituting the (A) (meth) acrylic resin, the structural units derived from methyl acrylate and / or methyl methacrylate is preferably 5 to 50 mol%, and more preferably 10 to 45 mol%, more preferably 15 to 40 mol%. 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. When it is more than 50 mol%, the Adhesion tends to become smaller. In addition, content of the structural unit derived from methyl acrylate and / or methyl methacrylate means the total amount of the structural unit derived from methyl acrylate and methyl methacrylate.

In addition, from the viewpoint of integration through the reaction of a polyisocyanate and a polyoxyalkylene polyol, the (A) (meth) acrylic resin in the present invention preferably contains a hydroxyl-containing (meth) acrylic monomer As a copolymer component. Examples of the hydroxyl-containing (meth) acrylic monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate 1,3-butanediol (meth) acrylate, 1,4-butanediol (meth) acrylate, 1,6-hexanediol (meth) acrylate, 3- (meth) acrylate 3- Hydroxy-containing (meth) acrylates such as methylpentanediol esters and the like. Among them, 2-hydroxyethyl (meth) acrylate is preferred in terms of copolymerizability and reactivity with other monomers. ester. The structural unit derived from the hydroxyl group-containing (meth) acrylic monomer is preferably contained in an amount of 0.5 to 10 mol%, and more preferably 0.6 in all the structural units derived from the monomers constituting the (A) (meth) acrylic resin. ~ 8 mol%, more preferably 0.7 to 5 mol%. When the content of the structural unit derived from the hydroxyl group-containing (meth) acrylic monomer is less than 0.5 mol%, the reaction with the polyoxyalkylene polyol is reduced, and the cohesive force of the obtained transparent adhesive sheet tends to be smaller than At 10 mol%, since the crosslinking density becomes too high, the resulting transparent adhesive sheet tends to become hard.

In addition, as long as the polymerizability is not impaired, the (A) (meth) acrylic resin in the present invention may use other polymerizable monomers as a copolymerization component. Examples of such a polymerizable monomer include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, and vinylidene chloride. Dichloroethylene, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, dialkyl itaconic acid, dialkyl fumarate, allyl alcohol, propylene chloride, methyl Vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, and the like.

The weight average molecular weight of the (A) (meth) acrylic resin in the present invention must be 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 obtained transparent adhesive sheet becomes small, which is not preferable. On the other hand, when the weight average molecular weight is more than 600,000, the compatibility between (A) (meth) acrylic resin and (B) polyoxyalkylene polyol is deteriorated, and the transparency of the obtained transparent adhesive sheet is deteriorated.

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

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

Column temperature: 40 ° C

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

Flow: 1ml / min

Eluent: tetrahydrofuran

Detector: RI detector

The glass transition temperature (Tg) of the (A) (meth) acrylic resin in the present invention is preferably -80 to 0 ° C, more preferably -70 to -5 ° C, and even more preferably -60 to -10. ℃. When the Tg is higher than 0 ° C, the transparent adhesive sheet becomes hard, and therefore the followability of the height difference tends to deteriorate. On the other hand, when Tg is lower than -80 ° C, cohesion tends to decrease and the strength of the transparent adhesive sheet tends to be insufficient. The Tg of the (A) (meth) acrylic resin can be appropriately adjusted by changing the type and composition ratio of the monomer components used in the polymerization.

Here, Tg refers to a value obtained by the following method. A 10 mg sample was collected from (A) (meth) acrylic resin, and a differential scanning calorimeter (DSC) was used to change the temperature from -80 ° C to 200 ° C at a temperature increase rate of 10 ° C / min to perform differential display. Scanning calorimetry used Tg as the endothermic onset temperature due to glass transition. When two or more Tgs are observed, the arithmetic mean of these Tgs at the absolute temperature is taken as the Tg.

The method for polymerizing (A) (meth) acrylic resin in the present invention is not particularly limited, and solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization can be used. Known methods such as float polymerization and alternating copolymerization. Among these, solution polymerization is particularly preferred from the viewpoints of transparency, water resistance, and the like. The obtained copolymer may be a random copolymer, a block copolymer, or the like.

The polymerization initiator used when polymerizing the (A) (meth) acrylic resin is not particularly limited, and can be appropriately selected from known polymerization initiators 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) Azo polymerization, such as 2,2'-azobis (2,4,4-trimethylpentane), dimethyl-2,2'-azobis (2-methylpropionate), etc. Agents: benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, tert-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis (tert-butyl peroxide) Oil-soluble polymerization initiators such as peroxide-based polymerization initiators such as 3,3,5-trimethylcyclohexane and 1,1-bis (t-butyl peroxide) cyclododecane. These polymerization initiators can be used individually or in combination of 2 or more types. The amount of the polymerization initiator may be a normal amount. For example, it can be selected from a range of about 0.01 to 5 parts by mass relative to 100 parts by mass of the monomer, preferably in a range of 0.015 to 4 parts by mass, and more preferably 0.02 to 3 parts by mass.

In addition, various general solvents can be used for solution polymerization. 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, Alicyclic hydrocarbons such as methylcyclohexane; organic solvents such as ketones such as methyl ethyl ketone and methyl isobutyl ketone. These solvents can be used alone or in combination of two or more.

In addition, the compounding amount of the (A) (meth) acrylic resin in the composition for a transparent adhesive sheet of the present invention must be 65 to 85% by mass based on the total solid content of the composition for a transparent adhesive sheet. It is preferably 70 to 85% by mass, and more preferably 75 to 85% by mass. When the compounding amount of the (A) (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 compounding amount of the (A) (meth) acrylic resin exceeds 85% by mass, sufficient height difference followability cannot be obtained.

((B) Polyoxyalkylene polyol)

The polyoxyalkylene polyol (B) 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. Examples of the (B) polyoxyalkylene polyol include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, and derivatives or copolymers thereof. Among these, polypropylene glycol is preferred because it is easy to adjust the compatibility with the acrylic resin. These can be used alone or in combination of two or more.

The number average molecular weight of the (B) polyoxyalkylene polyol used in the present invention must be 500 to 1500, preferably 700 to 1300, and more preferably 800 to 1200. When the number average molecular weight is less than 500, the followability of the height difference of the transparent 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 is inferior. In addition, the number average molecular weight can be measured by GPC (gel permeation chromatography) using the same method as the weight average molecular weight of (A) (meth) acrylic resin.

(B) Polyoxygen in the composition for a transparent adhesive sheet of the present invention The compounding amount of the alkylene polyol must be 10 to 30% by mass, preferably 13 to 25% by mass, and more preferably 15 to 20% by mass based on the total solid content of the composition for a transparent adhesive sheet. (B) When the compounding quantity of a polyoxyalkylene polyol is less than 10 mass%, the sufficient height difference followability of a transparent adhesive sheet cannot be obtained. On the other hand, when the compounding 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 (C) polyisocyanate in the present invention include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Examples of the (C) polyisocyanate include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), and 2-methyl-1,5-pentane diisocyanate. , 3-methyl-1,5-pentane diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, toluene diisocyanate (TDI), hydrogenated toluene diisocyanate, two Phenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, polyphenylmethane polyisocyanate, xylene diisocyanate, hydrogenated xylene diisocyanate, tetramethylphenylene diisocyanate, norbornene diisocyanate, naphthalene di Isocyanate, trimethylolpropane / toluene diisocyanate trimer adduct, trimethylolpropane / hexamethylene diisocyanate trimer adduct, isocyanurate of hexamethylene diisocyanate And other isocyanate adducts, polyether polyisocyanates, polyester polyisocyanates and the like. These can be used alone or in combination of two or more.

The compounding amount of the (C) polyisocyanate in the composition for a transparent adhesive sheet of the present invention is relative to the total solids of the composition for a transparent adhesive sheet. It must be 1.0 to 5.0% by mass, preferably 1.5 to 4.5% by mass, and more preferably 2.0 to 4.0% by mass. (C) When the compounding quantity of a polyisocyanate is less than 1.0 mass%, sufficient cohesion cannot be obtained, and the intensity | strength of a transparent adhesive sheet will become inadequate. On the other hand, when the compounding quantity of (C) polyisocyanate exceeds 5.0 mass%, the softness | flexibility of the transparent adhesive sheet obtained will become inadequate, and sufficient height difference followability will not be acquired.

((D) Tin-based catalyst)

Examples of the (D) tin-based catalyst used in the present invention include dibutyltin dilaurate, dibutyltin diethylhexanoate, dioctyltin dilaurate, and the like. Among them, dioctyltin dilaurate is preferred from the viewpoints of good curability and safety of the (C) polyisocyanate.

In addition, the compounding amount of the (D) tin-based catalyst in the composition for a transparent adhesive sheet of the present invention must be 0.005 to 0.1% by mass, preferably 0.01 to 0.1% by mass based on the total solid content of the composition for a transparent adhesive sheet. 0.09% by mass, and more preferably 0.02 to 0.080% by mass. (D) When the compounding amount of the tin-based catalyst is less than 0.005 mass%, the curability of the composition for a transparent adhesive sheet is insufficient, and the cohesive force becomes small. When it exceeds 0.1 mass%, the pot life of the transparent adhesive sheet is shortened.

(Composition for transparent adhesive sheet)

The acid value of the composition for a transparent adhesive sheet of the present invention must be 0 to 5 mgKOH / g, preferably 0 to 1 mgKOH / g, more preferably 0 to 0.3 mgKOH / g, and particularly preferably 0 to 0.1 mgKOH / g. When the acid value of the composition for a transparent adhesive sheet is higher than 5 mgKOH / g, it becomes difficult to suppress the corrosion of the surface of the conductive layer of a transparent conductive film. In addition, the group for transparent adhesive sheets The acid value of the compound is a value measured in accordance with JIS K0070. The measurement is performed as follows, for example.

About 2 g of the sample was accurately weighed in a 100 ml conical flask with a precision balance, and 10 ml of a mixed solvent of ethanol / ether = 1/1 (mass ratio) was added thereto and dissolved. Further, 1 to 3 drops of a phenolphthalein ethanol solution as an indicator was added to the container, and the mixture was sufficiently stirred until the sample became uniform. This was titrated with a 0.1 N potassium hydroxide-ethanol solution, and the end point of neutralization was when the light red color of the indicator continued for 30 seconds. From this result, the value obtained using the following formula (1) was used as the acid value of the composition for transparent adhesive sheets.

[Mathematical formula 1] Acid value (mgKOH / g) = [B × f × 5.611] / S (1)

B: dosage of 0.1N potassium hydroxide-ethanol solution (ml)

f: factor of 0.1N potassium hydroxide-ethanol solution

S: sample collection amount (g)

In the composition for a transparent adhesive sheet of the present invention, in order to improve the adhesive force of the obtained transparent adhesive sheet, a tackifier resin may be added as needed within a range that does not reduce the transparency of the transparent adhesive sheet. Examples of the tackifying resin include rosin-based resins such as rosin and rosin esters; terpene-based resins such as diterpene polymers and α-pinene-phenol copolymers; aliphatic (C5) and aromatic systems (C9-based) and other petroleum resins; and styrene-based resins, phenol-based resins, xylene resins, etc. From the viewpoint of light resistance, it is preferable to add an esterified product of hydrogenated rosin having a small amount of unsaturated double bonds, an esterified product of disproportionated rosin, an aliphatic petroleum resin, an aromatic petroleum resin, an acrylic resin having a high Tg, and the like. Adhesive sheet. As the amount of tackifying resin added, excellent 1 to 10 parts by mass is added to 100 parts by mass of the composition for a transparent adhesive sheet.

In addition, the composition for a transparent adhesive sheet of the present invention may further contain various known additives as long as the transparency is not impaired, if necessary. Examples of the additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, antioxidants, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazoles, phosphate esters, and others Flame retardants, antistatic agents such as surfactants, etc.

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

(Transparent adhesive sheet)

The transparent adhesive sheet of this invention is obtained by hardening | curing the said composition for transparent adhesive sheets. More specifically, the optical member can be used for applications in which optical members are bonded (for bonding of optical members), manufacturing applications of optical products, and the like. In addition, the transparent adhesive sheet of the present invention may be an adhesive sheet having a substrate, or a double-sided adhesive sheet formed of only an adhesive layer without a substrate. The optical member is not particularly limited as long as the member has optical characteristics, and examples thereof include members constituting an image display device, a touch panel, and members used in these devices. More specifically, for example, a polarizing plate, a retardation plate, an optical compensation film, a brightness enhancement film, a light guide plate, a reflective film, an anti-reflection film, a transparent conductive film, a pattern design film, a decorative film, a surface protection film, Prisms, lenses, color filters, transparent substrates, and laminated members.

The transparent adhesive sheet of the present invention can be obtained by applying a solution obtained by dissolving a composition for a transparent adhesive sheet in a solvent to a release film, and heating and drying the applied solution to crosslink it, thereby obtaining a transparent adhesive sheet. The film thickness of the transparent adhesive sheet is preferably 5 to 200 μm, more preferably 10 to 150 μm, and still more preferably 15 to 100 μm. If the thickness of the transparent adhesive sheet is less than 5 μm, there is a tendency that it is difficult to adhere the transparent adhesive sheet. When the film thickness of the transparent adhesive sheet is more than 200 μm, there is a tendency that a solvent remains on the sheet and an odor problem occurs. In addition, as a coating (coating) method at the time of forming the transparent adhesive sheet of this invention, a well-known coating method can be used, A common coater can be used, for example, a gravure roll coater, a reverse roll coater, and roll coater Machine, dip roll coater, bar coater, blade coater, sprayer, comma coater, direct coater, etc.

The gel fraction of the transparent adhesive sheet of the present invention is preferably 40% to 80%, more preferably 45% to 75%, and still more preferably 50% to 70%. When the gel fraction is less than 40%, although it can be used, the cohesive force of the transparent adhesive sheet tends to be too small. In addition, when the gel fraction is more than 80%, there is a tendency that the followability of the height difference of the transparent adhesive sheet is deteriorated.

It should be noted that the gel fraction of the transparent adhesive sheet can be determined by the following formula (2) based on the mass of the sample before being immersed in toluene and immersed in toluene at room temperature for 24 hours and dried at 80 ° C for 5 hours. ) Find it.

[Mathematical formula 2] Gel fraction (%) = [(Dry mass of transparent adhesive sheet after toluene dipping (Excluding mass of toluene)) / (mass before toluene immersion of transparent adhesive sheet)] × 100 (2)

(Transparent film for fixing 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, which is obtained by curing the composition for a transparent adhesive sheet, and can be properly adhered to the surface of a conductive layer of a transparent conductive film and is not easily conductive. Corrosion of layers. Therefore, a laminated body in which the sheet for fixing a transparent conductive film is adhered to the surface of the conductive layer 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 be an adhesive sheet with a base material or a double-sided adhesive sheet without a base material and formed of only an adhesive layer. The adhesive layer may be formed of a single layer or a plurality of layers. Among them, from the viewpoint of ensuring transparency and height difference followability, a double-sided adhesive sheet formed of only an adhesive layer without a base material is preferred.

As the transparent conductive film used as the transparent adhesive sheet for fixing the transparent conductive film of the present invention, it is only necessary to have a conductive layer on the surface layer of at least one side, and examples thereof include those in which a conductive material is provided on the surface layer of a transparent substrate by evaporation and coating. Transparent conductive film. There is no particular limitation on the conductive substance that is deposited and applied to the conductive layer of the transparent conductive film. Specific examples include silver, indium tin oxide, indium oxide, tin oxide, zinc oxide, cadmium oxide, gallium oxide, and titanium oxide. Wait. Among them, silver and indium tin oxide, which are excellent in transparency and conductivity, are preferably used. The transparent conductive film is not particularly limited as a base material on which a conductive material is vapor-deposited or coated, and examples thereof include glass and resin films.

It should be noted that the transparent conductive film of the present invention is used for transparent adhesive bonding. The sheet can be obtained by the same method as the aforementioned transparent adhesive sheet.

Examples

Hereinafter, the present invention will be described in more detail through examples and comparative examples, but the present invention is not limited to these examples.

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

The addition ratio (mol%) of each (meth) acrylic monomer is calculated from the total amount (mol) of (meth) acrylic monomers used in the production of (meth) acrylic resin. 500 parts by mass of n-propyl acetate, 320 parts by mass of 2-ethylhexyl acrylate (53 mol%), and 125 parts by mass of methyl methacrylate were added to a reaction vessel provided with a cooling pipe, a nitrogen introduction pipe, a thermometer, and a stirring device ( 38 mol%), 50 parts by mass of isobornyl acrylate (8 mol%), 5 parts by mass (1 mol%) of 2-hydroxyethyl methacrylate, 0.1 parts by mass of 2,2'-azobis (isobutyronitrile), in Polymerization treatment was performed at 95 ° C for 8 hours in a nitrogen stream, and then 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 a (meth) acrylic-type copolymer are measured by the method mentioned previously. In addition, except that the composition ratio of the (meth) acrylfluorene-containing monomer described in Table 1 was changed, the same operation as in the (meth) acrylic copolymer (A-1) was performed to obtain (meth) acrylic Copolymers (A-2) to (A-3). In addition, similar to the (meth) acrylic copolymer (A-1), the (meth) acrylic copolymers (A-2) to (A-3) were also subjected to glass transition temperature and weight average molecular weight. Determination. The results are shown in Table 1.

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

The addition ratio (mol%) of each (meth) acrylic monomer is calculated from the total amount (mol) of (meth) acrylic monomers used in the production of (meth) acrylic resin. In a reaction vessel provided 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 of 2-ethylhexyl acrylate (53 mol%), and 118 parts by mass of methyl methacrylate ( 36 mol%), 50 parts by mass of isobornyl acrylate (7 mol%), 5 parts by mass (1 mol%) of 2-hydroxyethyl methacrylate, 6 parts by mass (3 mol%) of acrylic acid, 2,2'-azobis ( Isobutyronitrile) (0.1 parts by mass) was subjected to polymerization treatment 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 a (meth) acrylic-type copolymer are measured by the method mentioned previously. In addition, similar to the (meth) acrylic copolymers (A-1) to (A-3), the (meth) acrylic copolymer (A-4) was also subjected to glass transition temperature and weight average molecular weight. Determination. The results are shown in Table 1.

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

The (meth) acrylic resin, polyoxyalkylene polyol, polyisocyanate, and tin-based catalyst were compounded with the composition shown in Table 2, and the solid content concentration was adjusted to 50% by mass with n-propyl acetate. The obtained solution was mixed using a disperser at a temperature to obtain a composition solution for a transparent adhesive sheet. In addition, the numerical value regarding (meth) acrylic resin, polyoxyalkylene polyol, polyisocyanate, and tin-type catalyst in Table 2 is shown as the mass with respect to the total solid content of the composition for transparent adhesive sheets %. This composition solution for a transparent adhesive sheet was cast-coated (with a coating layer thickness of 200 μm) to a thickness of 100 μm after drying to peel off one side of a polyethylene terephthalate (PET) film having a thickness of 50 μm. The release-treated surface of the treated release film was heat-dried at 50 ° C for 10 minutes, heat-dried at 80 ° C for 10 minutes, and heat-dried at 110 ° C for 20 minutes. Further, one side of the PET film having a thickness of 38 μm was subjected to release treatment for isolation. The release-treated surface side of the film covers the adhesive side. Then, it aged at 40 degreeC for 72 hours, and produced the double-sided adhesive sheet (baseless type).

(Acid value)

The acid value of the composition for each transparent adhesive sheet was measured using the method described above. The results are shown in Table 2.

(Measurement of resistance value of indium tin oxide film)

The double-sided adhesive sheet obtained above was cut into a size of 50 mm × 50 mm, and a 38 μm-thick PET film on one side was peeled off, so that one side of the double-sided adhesive sheet and one side of the 100 mm × 100 mm indium tin oxide-evaporated PET film The parallel and double-sided adhesive sheet is attached to the surface of the indium tin oxide film in such a manner that the position of the double-sided adhesive sheet is approximately at the center of the indium tin oxide vapor-deposited PET film in the vertical and horizontal directions. For an indium tin oxide vapor-deposited PET film with a double-sided adhesive sheet bonded thereto, a resistance value measuring device ("Loresta-GP" manufactured by Mitsubishi Chemical Corporation) was used to measure one corner of the indium tin oxide film surface. The initial resistance value (R ₁ ) from both ends of the corner lying on its diagonal. In addition, the indium tin oxide vapor-deposited PET film on which the double-sided adhesive sheet was bonded was left at 60 ° C and 90% RH for 500 hours, and then left at 23 ° C and 50% RH for 1 hour. The resistance value (R ₂ ) was measured at the same position as the resistance value. The resistance value increase rate of the indium tin oxide film is calculated by the following formula (3).

[Mathematical formula 3] Resistance increase rate of indium tin oxide film (%) = ((R ₂ -R ₁ ) / R ₁ ) × 100 (3)

The evaluation of the resistance value increase rate was performed based on the following criteria. The results are shown in Table 2.

￮: The resistance value increase rate is less than 5%

△: The resistance value increase rate is more than 5% and less than 10%

×: Resistance increase rate is 10% or more

(Total transmittance measurement)

The double-sided pressure-sensitive adhesive sheet obtained above was cut into a size of 30 mm × 30 mm, and a single-sided 38 μm-thick peeling PET film existing in the release PET film on both sides of the double-sided pressure-sensitive adhesive sheet was peeled off, laminated on a glass plate, and the obtained laminate was laminated. The body was used as a measurement sample. For the measurement sample, "HR-100" manufactured by Murakami Color Technology Research Co., Ltd. was used to measure the total light transmittance (%). The results are shown in Table 2.

(Adhesion measurement of double-sided adhesive sheet)

After cutting the size of 25 mm × 100 mm from the double-sided adhesive sheet obtained above, peeling off a 38 μm thick PET film on one side of the double-sided adhesive sheet, and re-sticking a 50 μm-thick PET film that was corona-treated on one side, The adhesive surface (measurement surface) was stuck to a 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 measurement sample was left to stand in an environment of 23 ° C. and 50% humidity for 24 hours, and a 180 ° direction tensile test was performed at a peeling speed of 300 mm / min in accordance with JIS Z0237 to measure the adhesion of the double-sided adhesive sheet to the glass plate Force (N / 25mm). The obtained measured value was made into the adhesive force. The results are shown in Table 2.

(Elevation follow-up evaluation)

The 38 μm-thick peeling PET film on one side of the double-sided adhesive sheet obtained above was peeled, and the double-sided adhesive sheet was bonded to a glass plate having a thickness of 0.5 mm, a length of 50 mm and a width of 40 mm with a thickness of 15 μm and a width of 5 mm. A printed glass plate with a window frame shape printed thereon, and after peeling the peeled PET film on the other side, it was bonded to a glass plate having a thickness of 0.5 mm, a length of 50 mm, and a width of 40 mm. Minutes After heat and pressure treatment and fixing, the floating of the adhesive layer in the height difference portion was visually observed.

Evaluation of the height difference followability was performed based on the following criteria. The results are shown in Table 2.

￮: The state where the adhesive layer floats is not recognized in the part with the height difference

△: A slightly floating state of the adhesive layer was confirmed in a portion having a height difference

×: The part with a height difference confirmed that the adhesive layer was significantly floating

(Gel fraction measurement)

Using the obtained transparent adhesive sheet, the gel fraction was measured by the method described above. The results are shown in Table 2.

Claims (9)

A composition for a transparent adhesive sheet, comprising: (A) (meth) acrylic resin 65 to 85% by mass; (B) polyoxyalkylene polyol 10 to 30% by mass; (C) ) Polyisocyanate 1.0 to 5.0% by mass; and (D) tin-based catalyst 0.005 to 0.1% by mass, and the acid value of the composition for a transparent adhesive sheet is 0 to 5 mgKOH / g, of which (A) (meth) acrylic acid The weight average molecular weight of the resin-like resin is 100,000 to 600,000, and the number average molecular weight of (B) the polyoxyalkylene polyol is 500 to 1500. The composition for a transparent adhesive sheet according to claim 1, wherein the (A) (meth) acrylic resin contains 0.5 to 10 mol% of a structural unit derived from a hydroxyl-containing (meth) acrylic monomer. The composition for a transparent adhesive sheet according to claim 2, wherein the hydroxyl-containing (meth) acrylic monomer is 2-hydroxyethyl (meth) acrylate. The composition for a transparent adhesive sheet according to any one of claims 1 to 3, wherein the (A) (meth) acrylic resin contains 5 to 50 mol% of a structural unit derived from methyl (meth) acrylate. The composition for a transparent adhesive sheet according to any one of claims 1 to 3, wherein (A) the (meth) acrylic resin has a glass transition temperature of -80 to 0 ° C. A transparent adhesive sheet obtained by curing the composition for a transparent adhesive sheet according to any one of claims 1 to 5. For example, the transparent adhesive sheet of claim 6 has a gel fraction of 40% to 80%. A transparent adhesive sheet for fixing a transparent conductive film, which is characterized in that a transparent adhesive sheet as claimed in claim 6 or 7 is used for bonding the transparent conductive film. A laminated body is characterized in that it is attached to the surface of a conductive layer of a transparent conductive film and is adhered with a transparent adhesive sheet for fixing a transparent conductive film as in claim 8.