JP5877099B2 - Composition for transparent adhesive sheet - Google Patents

Description

  The present invention relates to a transparent adhesive sheet for fixing a transparent conductive film, wherein the composition for transparent adhesive sheet, the transparent adhesive sheet comprising the composition for transparent adhesive sheet, and the transparent adhesive sheet are used for laminating a transparent conductive film And the transparent adhesive sheet for transparent conductive film fixation is related with the laminated body characterized by adhere | attaching on the conductive layer surface of a transparent conductive film.

  In recent years, touch panels have begun to be mounted in fields such as mobile phones and game machines. The touch panel is a transparent base material having a transparent conductive film such as silver or ITO (indium tin oxide), glass, a transparent protective sheet for protecting the glass, and an optical member such as a display device such as a liquid crystal display. It is the laminated body bonded together using the transparent adhesive sheet.

  There are two types of touch panels: a resistance film type touch panel that detects mainly by pressure at the time of input and a capacitance type touch panel that detects an input location by static electricity from the human body at the time of input. In the capacitive touch panel, the conductive layer surface of the transparent conductive film is fixed so as to be in contact with the pressure-sensitive adhesive layer surface of the pressure-sensitive adhesive sheet. For this reason, when the pressure-sensitive adhesive layer is in contact with the conductive layer surface of the transparent conductive film, there is a problem that a metal oxidation reaction occurs due to the acid component contained in the pressure-sensitive adhesive, resulting in a decrease in the conductive function. For this reason, the adhesive sheet for fixing a transparent conductive film is required to have high metal corrosion prevention and good adhesion without containing an acid component.

  As a pressure-sensitive adhesive sheet having metal corrosion prevention properties, a pressure-sensitive adhesive sheet containing a metal corrosion inhibitor (for example, Patent Document 1) has been proposed. Moreover, the adhesive sheet (for example, patent document 2) which reduced the corrosivity with respect to a transparent conductive film by containing a specific amount of nitrogen atom containing components with respect to the acid component of an adhesive layer is proposed.

  However, the pressure-sensitive adhesive sheet containing a metal corrosion inhibitor has a problem that the metal corrosion inhibitor is discolored in a durability test and optical properties are deteriorated. In addition, the pressure-sensitive adhesive sheet containing a specific amount of a nitrogen atom-containing component has a problem that an 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, a touch panel or the like includes a member having a step such as a metal wiring or a printing step. For example, in a mobile phone or the like, a touch panel or the like having a member provided with a frame-like printed portion is used. In such an application, the pressure-sensitive adhesive sheet is required to have the ability to fill a step at the same time as the performance of sticking and fixing a member, that is, excellent step following ability. If the transparent adhesive sheet cannot absorb the step, the transparent adhesive sheet floats (bubbles or voids) around the step, causing light reflection loss due to the float (bubbles or voids), and 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 soft and has high adhesive strength, but for the reasons described above, it is required that the adhesive does not contain an acid component and has high adhesiveness. The In response to this requirement, a pressure-sensitive adhesive composition composed of an acrylic polymer having a specific molecular weight not containing an acid component mainly composed of alkoxyalkyl acrylate and a crosslinking agent can achieve both good adhesion and metal corrosion prevention. Giving a transparent adhesive sheet (for example, Patent Document 3) is disclosed.

  However, the pressure-sensitive adhesive composition comprising an acrylic polymer having a specific molecular weight not containing an acid component mainly composed of alkoxyalkyl acrylate and a crosslinking agent does not contain an acid component, so that curing with an isocyanate crosslinking agent is delayed and transparent. There was a problem that it took time to cure the adhesive sheet. In order to solve the problem, addition of an amine compound containing a plurality of hydroxyl groups is also disclosed, but the amine compound may cause yellowing of the transparent adhesive sheet over time.

  In short, the present situation is that an excellent pressure-sensitive adhesive composition that achieves a high level of all properties such as metal corrosion prevention, level difference followability, transparency, and curability has not been obtained.

JP 2006-45315 A JP 2010-144002 A JP 2010-77287 A

  The problem to be solved by the present invention is excellent in curability, and the obtained 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. It is providing the composition for transparent adhesive sheets which is excellent also in level | step difference followability and transparency.

  As a result of intensive studies against the above-mentioned problems of the transparent adhesive sheet for touch panels, the present inventors have (A) a (meth) acrylic copolymer having a specific structural unit, and (B) a crosslinked product. The transparent pressure-sensitive adhesive sheet composition comprising an agent and (C) a tin-based catalyst and having an acid content of less than a predetermined amount is excellent in curability, and the resulting transparent pressure-sensitive adhesive sheet has transparency, pressure-sensitive adhesive properties, and a transparent conductive film. It was found that the metal corrosion prevention property and the step following property were good, and the present invention was completed based on this finding.

  The present invention is shown by the following (1) to (7).

（式中、Ｒ^１は水素原子またはメチル基を表し、Ｒ^２は炭素数１〜６のアルキレン基を表し、Ｒ^３は、ポリオレフィンポリオール又は水添ポリオレフィンポリオールのウレタン結合残基である）で示される構造単位を有する（メタ）アクリル共重合体、（Ｂ）架橋剤、及び（Ｃ）スズ系触媒とを含む透明粘着シート用組成物であり、酸価が５ｍｇＫＯＨ／ｇ以下であることを特徴とする透明粘着シート用組成物。 (1) (A) Formula (I):

(Wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 1 to 6 carbon atoms, and R ³ represents a urethane bond residue of a polyolefin polyol or hydrogenated polyolefin polyol). A composition for transparent adhesive sheet comprising a (meth) acrylic copolymer having a structural unit, (B) a crosslinking agent, and (C) a tin-based catalyst, wherein the acid value is 5 mgKOH / g or less. A composition for a transparent adhesive sheet.

  (2) (A) A (meth) acrylic copolymer having a structural unit represented by chemical formula (I) is (meth) acryloyl in the presence of a polyolefin polyol and / or a hydrogenated polyolefin polyol and a tin-based catalyst. The composition for transparent adhesive sheets according to (1), which is obtained by copolymerizing a group-containing monomer (excluding those having an isocyanate group) and (meth) acryloyloxyalkyl isocyanate.

  (3) (A) A (meth) acrylic copolymer having a structural unit represented by the chemical formula (I) is a carbon of an alkyl group in the presence of a polyolefin polyol and / or a hydrogenated polyolefin polyol, and a tin-based catalyst. (Meth) acrylic acid alkyl ester having 1 to 18 and / or alkoxyalkyl group having 2 to 20 carbon atoms of (meth) acrylic acid alkoxyalkyl ester 90 to 99.5 mol%, containing (meth) acryloyl group The composition for transparent adhesive sheets as described in said (2) obtained by copolymerizing 0-9.5 mol% of polar monomers and 0.5-10 mol% of 2- (meth) acryloyloxyethyl isocyanate.

  (4) The transparent adhesive sheet obtained by hardening the composition for transparent adhesive sheets in any one of said (1)-(3).

  (5) The transparent adhesive sheet according to (4), wherein the gel fraction is 40 to 80%.

  (6) A transparent adhesive sheet for fixing a transparent conductive film, wherein the transparent adhesive sheet according to (4) or (5) is used for bonding a transparent conductive film.

  (7) A laminate, wherein the transparent conductive sheet fixing transparent adhesive sheet according to (6) is adhered to the conductive layer surface of the transparent conductive film.

  The composition for transparent pressure-sensitive adhesive sheets of the present invention includes a step followability of a transparent pressure-sensitive adhesive sheet obtained by including a (meth) acrylic copolymer having a specific structural unit, that is, a polyolefin skeleton, and a group. Good adhesion to the material. Furthermore, by including a tin-based catalyst, the curability of the crosslinking agent is improved, and the curing time of the transparent adhesive sheet can be shortened. Moreover, since it is a composition for transparent adhesive sheets which does not contain an acid substantially, the corrosion of the conductive layer surface of the transparent conductive film by an acid component can be suppressed.

  Hereinafter, the present invention will be described in detail.

In the present specification, the (meth) acryloyl group means CH ₂ ═CH—CO— or CH ₂ ═C (CH ₃ ) —CO—.

（式中、Ｒ^１は水素原子またはメチル基を表し、Ｒ^２は炭素数１〜６のアルキレン基を表し、Ｒ^３は、ポリオレフィンポリオール及び／又は水添ポリオレフィンポリオール（以下、「ポリオレフィンポリオール等」ともいう）のウレタン結合残基）で示される構造単位を有する（メタ）アクリル共重合体、（Ｂ）架橋剤、及び（Ｃ）スズ系触媒とを含む透明粘着シート用組成物であり、酸価が５ｍｇＫＯＨ／ｇ以下であることを特徴とする透明粘着シート用組成物である。 (Composition for transparent adhesive sheet)
The composition for transparent adhesive sheets of the present invention comprises (A) chemical formula (I):

(In the formula, R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 1 to 6 carbon atoms, R ³ represents a polyolefin polyol and / or a hydrogenated polyolefin polyol (hereinafter referred to as “polyolefin polyol etc.”). A composition for transparent adhesive sheet comprising a (meth) acrylic copolymer having a structural unit represented by (urethane bond residue)), (B) a crosslinking agent, and (C) a tin-based catalyst. It is a composition for transparent adhesive sheets characterized by having a value of 5 mgKOH / g or less.

((Meth) acrylic copolymer having structural unit represented by chemical formula (I))
(A) The method for synthesizing the (meth) acrylic copolymer having the structural unit represented by the chemical formula (I) is not particularly limited, but in the presence of a polyolefin polyol and a tin-based catalyst, one or more ( A method of copolymerizing a (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) and a (meth) acryloyl group-containing monomer having an isocyanate group as a functional group, and simultaneously adding a polyolefin polyol or the like to the isocyanate group Is preferred. In this method, the polymerization of the (meth) acryloyl group-containing monomer and the addition reaction of isocyanate and polyolefin polyol, etc., proceed simultaneously, while preventing the phase separation of (meth) acrylic polymer and polyolefin polyol, which are dissimilar polymers. It is possible to synthesize a (meth) acrylic copolymer having a side chain. In addition, in the presence of a tin-based catalyst, one or more (meth) acryloyl group-containing monomers (excluding those having an isocyanate group) and a (meth) acryloyl group-containing monomer having an isocyanate group as a functional group are previously co-polymerized. After the polymerization, a polyolefin polyol or the like can be added to the isocyanate group of the obtained copolymer.

R ^{1 in the} chemical formula (I) is a hydrogen atom or a methyl group. R ^{2 in the} chemical formula (I) is an alkylene group having 1 to 6 carbon atoms, and may be not only a linear alkylene group but also a branched alkylene group. R ² preferably has 2 to 4 carbon atoms. The urethane bond residue such as polyolefin polyol in the description of R ³ refers to a group in the polyolefin polyol excluding a hydroxyl group-derived atom that reacts with an isocyanate group to form a urethane bond.

  In the synthesis of the (meth) acrylic copolymer, it is preferable to charge 1.5 to 3 mol of a polyolefin polyol or the like with respect to 1 mol of the (meth) acryloyl group-containing monomer having an isocyanate group as a functional group, more preferably a polyolefin polyol. Equivalent 1.8 to 2.8 mol amount, more preferably 2.0 to 2.5 mol amount. When the charged amount of polyolefin polyol or the like is less than 1.5 mol with respect to 1 mol of the (meth) acryloyl group-containing monomer having an isocyanate group as a functional group, the polyolefin polyol or the like crosslinks the (meth) acrylic polymer at the time of synthesis. And is not preferable because it gels. In addition, when the amount of polyolefin polyol or the like charged is more than 3 mol, a large amount of polyolefin polyol or the like contained in the transparent adhesive sheet composition is present, and the cohesive strength of the sheet obtained from the transparent adhesive sheet composition is increased. Since it gets worse, it is not preferable. The polyolefin polyol remaining without being incorporated into the acrylic copolymer can be reacted by adding a cross-linking agent. Therefore, there is no problem even if it exists in the composition for transparent adhesive sheet.

  As a method of copolymerizing a (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) and (meth) acryloyloxyalkyl isocyanate, it can be prepared by a known polymerization method. , Solution polymerization method, emulsion polymerization method, bulk polymerization method, polymerization method by ultraviolet irradiation, and the like. In view of transparency, water resistance, cost, etc., a solution polymerization method and a UV polymerization method are preferable, and a solution polymerization method can be particularly preferably used.

  The polymerization initiator used in the copolymerization of the (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) and (meth) acryloyloxyalkyl isocyanate is not particularly limited, and can be appropriately selected from known ones. Can be used. For example, 2,2′-azobisisobutyronitrile, 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), dimethyl-2 , 2'-azobis (2-methylpropionate) and other azo polymerization initiators; benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumylper Oxide, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclo Oil-soluble polymerization initiator such as peroxide polymerization initiators decane are preferably exemplified. A polymerization initiator can be used individually or in combination of 2 or more types. The amount of the polymerization initiator used may be a normal amount, for example, a total of 100 parts by mass of a (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) and a (meth) acryloyloxyalkyl isocyanate component. Can be selected from a range of about 0.01 to 5 parts by mass, preferably 0.02 to 4 parts by mass, and more preferably 0.03 to 3 parts by mass.

  In solution polymerization, various common 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, Examples thereof include organic solvents such as cycloaliphatic hydrocarbons such as cyclohexane and methylcyclohexane, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. A solvent can be used individually or in combination of 2 or more types.

  As the polyolefin polyol used for the production of the (A) (meth) acrylic copolymer of the present invention, for example, commercially available various polyols of saturated and unsaturated alkyl compounds can be used. Examples include polyethylene polyol, polypropylene polyol, polybutadiene polyol, polyisoprene polyol, hydrogenated polybutadiene polyol, hydrogenated polyisoprene polyol, and the like. Among them, hydrogenated 1,2-polybutadiene polyol or hydrogenated polyisoprene polyol is preferable in terms of workability of the liquid transparent adhesive sheet composition, light resistance of the obtained transparent adhesive sheet, and transparency (non-crystallinity). . The hydrogenated 1,2-polybutadiene refers to a compound in which hydrogen is reacted with a double bond portion of 1,2-polybutadiene to change it to a single bond. The same applies to hydrogenated polyisoprene.

  The number average molecular weight of the polyolefin polyol or the like used in the present invention is preferably 500 to 5000, more preferably 1000 to 4000, and further preferably 1500 to 3500. When the number average molecular weight is smaller than 500, the step following property of the resulting transparent pressure-sensitive adhesive sheet is unfavorably deteriorated, and when the number average molecular weight is larger than 5000, the viscosity of the pressure-sensitive adhesive becomes too high. Specific examples of commercially available products such as polyolefin polyols that can be suitably used in the present invention include hydrogenated 1,2-polybutadiene polyols manufactured by Nippon Soda Co., Ltd., product names: GI-1000, GI-2000, GI-3000. (Number average molecular weights are about 1500, about 2100, and about 3000, respectively), hydrogenated polyisoprene polyol manufactured by Idemitsu Kosan Co., Ltd., and product name Epol (number average molecular weight is about 2500).

  In order to obtain a (meth) acrylic copolymer having a structural unit represented by the chemical formula (I) of the present invention, an addition reaction such as a polyolefin polyol is performed on an isocyanate group, that is, a urethanization reaction. A known urethanization catalyst can be used for the urethanization reaction, and a tin-based catalyst is particularly preferable. Examples of tin-based catalysts include dibutyltin dilaurate, dibutyltin diethylhexoate, dioctyltin dilaurate, and the like. The amount of urethanization catalyst used is based on the total mass of raw materials used for the reaction (that is, (meth) acryloyl group-containing monomers (excluding those having an isocyanate group), (meth) acryloyloxyalkyl isocyanate, polyolefin polyol, etc. ) Based on the total mass of, usually 10 to 300 ppm, preferably 30 to 250 ppm, more preferably 50 to 200 ppm. This urethanization catalyst can also be used as a curing agent for a crosslinking agent added when producing a transparent adhesive sheet. In addition, the reaction conditions for the addition reaction are preferably 30 to 100 ° C., and preferably continued for about 1 to 5 hours.

  The (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) used for the polymerization of the (meth) acrylic copolymer of the present invention is not particularly limited, and may be used alone or in combination of two or more. Those which can be used and do not contain a carboxyl group (chemical formula: —COOH) are preferred. For example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, isobutyl (meth) acrylate, n -Hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, isodecyl (meth) acrylate, stearyl (meth) acrylate, tridecyl (meth) acrylate, isostearyl (meth) Alkyl (meth) acrylates such as acrylate, cyclohexyl (meth) acrylate, norbornyl (meth) acrylate, isobornyl (meth) acrylate, norbornanyl (meth) acrylic , Dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, tricyclodecane dimethylol di (meth) Cyclic alkyl (meth) acrylate such as acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, 2-methoxyethoxyethyl (meth) acrylate, 2-ethoxyethoxyethyl (meth) acrylate Alkoxyalkyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) a Alkoxy (poly) alkylene glycol (meth) acrylate such as relate, fluorinated alkyl (meth) acrylate such as octafluoropentyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl ( Dialkylaminoalkyl (meth) acrylates such as (meth) acrylate, amide group-containing (meth) acrylates such as (meth) acrylamide, diacetone (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Acrylate, 4-hydroxybutyl (meth) acrylate, 1,3-butanediol (meth) acrylate, 1,4-butanediol (meth) acrylate, 1,6-hexanediol (meth) acrylate, 3- Hydroxyl group-containing (meth) acrylate such as methylpentanediol (meth) acrylate, epoxy group-containing (meth) acrylate such as glycidyl (meth) acrylate, silicon-modified (meth) acrylate, polyethylene glycol di (meth) acrylate, diethylene glycol di (meth) Examples thereof include polyfunctional (meth) acrylates such as acrylate, neopentyl glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tripropylene glycol di (meth) acrylate.

  Examples of the (meth) acryloyl group-containing monomer having an isocyanate group as a functional group suitably used for the polymerization of the (meth) acrylic copolymer of the present invention include 2- (meth) acryloyloxyethyl isocyanate, 3- (Meth) acryloyloxypropyl isocyanate, 4- (meth) acryloyloxybutyl isocyanate, 6- (meth) acryloyloxyhexyl isocyanate and the like. Among these, 2- (meth) acryloyloxyethyl isocyanate is preferable from the viewpoint of reactivity with a hydroxyl group.

  One or more (meth) acryloyl group-containing monomers (excluding those having an isocyanate group) and (meth) acryloyloxyalkyl isocyanate that are preferably used for the polymerization of the (meth) acrylic copolymer of the present invention are alkyl groups. (Meth) acrylic acid alkyl ester having 1 to 18 carbon atoms and / or (meth) acrylic acid alkoxyalkyl ester having 2 to 20 carbon atoms of 2 to 20 carbon atoms, (meth) acryloyl Copolymerization is preferably performed with a composition of 0 to 9.5 mol% of the group-containing polar monomer and 0.5 to 10 mol% of 2- (meth) acryloyloxyethyl isocyanate. More preferably, the (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms of the alkyl group and / or the (meth) acrylic acid alkoxyalkyl ester having 2 to 20 carbon atoms of 92 to 99.5 mol. %, (Meth) acryloyl group-containing polar monomer 0 to 7.5 mol%, 2- (meth) acryloyloxyethyl isocyanate 0.5 to 5 mol%. More preferably, the (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl group and / or the (meth) acrylic acid alkoxyalkyl ester having 2 to 20 carbon atoms in the alkoxyalkyl group is 94.5 to 99. 0.5 mol%, (meth) acryloyl group-containing polar monomer 0-5.0 mol%, 2- (meth) acryloyloxyethyl isocyanate 0.5-4.0 mol%. Here, the (meth) acryloyl group-containing polar monomer includes a (meth) acryloyl group-containing monomer having a polar group such as an amino group, an amide group or a hydroxyl group in the molecule. More specifically, monomers such as dialkylaminoalkyl (meth) acrylate, amide group-containing (meth) acrylate, and hydroxyl group-containing (meth) acrylate are exemplified. Of these, diacetone acrylamide is preferable in terms of heat-resistant yellowing and cohesive strength.

  The copolymerization ratio of the (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms in the alkyl group and / or the (meth) acrylic acid alkoxyalkyl ester having 2 to 20 carbon atoms in the alkoxyalkyl group is less than 90 mol%. In such a case, the adhesiveness is deteriorated, which is not preferable. When the amount is more than 99.5 mol%, the copolymerization ratio of 2- (meth) acryloyloxyethyl isocyanate is too small. This is not preferable because the desired adhesive strength cannot be obtained. When the copolymerization ratio of the polar monomer is more than 9.5 mol%, the water resistance of the transparent adhesive sheet is deteriorated, which is not preferable. When the copolymerization ratio of 2- (meth) acryloyloxyethyl isocyanate is less than 0.5 mol%, the addition with polyolefin polyol or the like is reduced, and the desired adhesive strength cannot be obtained. In this case, the amount of the polyolefin polyol to be added is increased, and the cohesive force of the transparent pressure-sensitive adhesive sheet is lowered, which is not preferable.

  The molecular weight of the (A) (meth) acrylic copolymer in the present invention is preferably 50,000 to 1,000,000, more preferably 80,000 to 800,000, and 100,000 to 500,000. More preferably it is. When the weight average molecular weight is less than 50,000, the cohesive force of the polymer becomes small and the adhesiveness becomes low. When the weight average molecular weight is larger than 1,000,000, the viscosity of the transparent adhesive sheet composition becomes too high, which is not preferable.

In addition, the value of the weight average molecular weight in this invention is measured at normal temperature on the following conditions using gel permeation chromatography (The Showa Denko KK make, Shodex GPC-101), and is calculated by polystyrene conversion. Is.
Column: Showa Denko LF-804
Column temperature: 40 ° C
Sample: 0.2 mass% tetrahydrofuran solution of copolymer Flow rate: 1 ml / min Eluent: Tetrahydrofuran

  The glass transition temperature of the (A) (meth) acrylic copolymer of the present invention is preferably −5 to −70 ° C. from the viewpoint of the strength and adhesive strength of the transparent pressure-sensitive adhesive sheet. More preferably, it is −10 to −60 ° C. When it is lower than −70 ° C., the resulting transparent pressure-sensitive adhesive sheet becomes too soft, which is not preferable because the adhesive strength of the transparent pressure-sensitive adhesive sheet is lowered. Moreover, when higher than -5 degreeC, since a transparent adhesive sheet becomes hard too much by low temperature, it is unpreferable. Here, the glass transition temperature (Tg) refers to that obtained from the following method. A 10 mg sample was taken from the (meth) acrylic copolymer, and the differential scanning calorimeter (DSC) was used to perform differential scanning by changing the temperature from −80 ° C. to 200 ° C. at a heating rate of 10 ° C./min. Calorimetry is performed, and the endothermic start temperature due to glass transition is defined as Tg. When two Tg's are observed, the average value of the two Tg's is taken.

(Crosslinking agent)
The crosslinking agent (B) used in the composition for transparent adhesive sheet of the present invention is not particularly limited as long as it is a polyfunctional compound having at least two groups bonded to hydroxyl groups such as polyolefin polyol. it can. (B) A crosslinking agent can be used individually or in mixture of 2 or more types. In the present invention, by using the crosslinking agent (B), when the acrylic pressure-sensitive adhesive layer is formed, the acrylic polymer is crosslinked to improve the durability of the transparent pressure-sensitive adhesive sheet. Examples of the crosslinking agent (B) that can be used in the present invention include a polyfunctional melamine compound, a polyfunctional epoxy compound, and a polyfunctional isocyanate compound.

  Examples of the polyfunctional melamine compound include methylated trimethylol melamine and butylated hexamethylol melamine. Moreover, as a polyfunctional epoxy compound, diglycidyl aniline, glycerol diglycidyl ether, etc. are mentioned, for example. Furthermore, examples of the polyfunctional isocyanate compound include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2-methyl-1,5-pentane diisocyanate, and 3-methyl-1,5. -Pentane diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, tolylene diisocyanate (TDI), hydrogenated tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, reaction product of trimethylolpropane and tolylene diisocyanate, trimethylolpropane and hexamethylene Reaction products with diisocyanate, polyether polyisocyanate, polyester polyisocyanate, hydrogenated xylene diiso Aneto include hydrogenated tetramethyl xylene diisocyanate. Among them, it is preferable to use a polyfunctional isocyanate compound (isocyanate crosslinking agent) as a crosslinking agent because of its reactivity with a hydroxyl group such as polyolefin polyol, and 1,6-hexamethylene diisocyanate of an aliphatic isocyanate in terms of yellowing resistance ( HDI), isophorone diisocyanate (IPDI), and hydrogenated diphenylmethane diisocyanate are preferably used.

  (B) Although there is no restriction | limiting in particular as the usage-amount of a crosslinking agent, For example, 0.1-10 mass parts is preferable normally with respect to 100 mass parts of (meth) acryl copolymers, More preferably, it is 0.8. It is 2-9 mass parts, More preferably, it is 0.5-8 mass parts. (B) When the amount of the crosslinking agent used is less than 0.1 parts by mass, the cohesive force of the transparent adhesive sheet is unsatisfactory, and (B) when the amount of the crosslinking agent used is more than 10 parts by mass. Since the transparent adhesive sheet becomes too hard, it is not preferable.

(Tin-based catalyst)
Examples of the (C) tin-based catalyst used in the present invention include dibutyltin dilaurate, dibutyltin diethylhexoate, and dioctyltin dilaurate. Among these, (B) the curability of the crosslinking agent is good, and dioctyltin dilaurate is preferable from the viewpoint of safety. (C) The tin-based catalyst is preferably used in the range of 0.001 to 0.100 parts by mass with respect to 100 parts by mass of (A) (meth) acrylic copolymer, and 0.003 to 0.080. It is more preferable that it is a mass part, and it is further more preferable that it is 0.005-0.050 mass part. When the (C) tin-based catalyst is less than 0.001 part by mass with respect to 100 parts by mass of the (A) (meth) acrylic copolymer, the curability of the transparent adhesive sheet composition is not sufficient, and the cohesive force is When it becomes more than 0.100 parts by mass, the pot life at the time of producing the pressure-sensitive adhesive sheet tends to be shortened.

(Composition for transparent adhesive sheet)
The transparent adhesive sheet composition of the present invention preferably has an acid value of 0 to 5 mgKOH / g, more preferably 0 to 1 mgKOH / g, still more preferably 0 to 0.3 mgKOH / g, and particularly preferably 0 to 5 mgKOH / g. 0.1 mg KOH / g is preferred. When the acid value is higher than 5 mgKOH / g, it becomes difficult to suppress corrosion of the conductive layer surface of the transparent conductive film. The acid value of the composition is a value measured according to JIS K0070. For example, measurement is performed as follows.

Ｂ：０．１Ｎ水酸化カリウム−エタノール溶液の使用量（ｍｌ）
ｆ：０．１Ｎ水酸化カリウム−エタノール溶液のファクター
Ｓ：試料の採取量（ｇ） About 2 g of a sample is precisely weighed into 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. Further, 1 to 3 drops of phenolphthalein ethanol solution is added to this container as an indicator, and the mixture is sufficiently stirred until the sample becomes uniform. This is titrated with a 0.1N potassium hydroxide-ethanol solution, and the end point of neutralization is taken when the indicator is light red for 30 seconds. The value obtained from the result using the following general formula (1) is defined as the acid value of the composition.

B: Amount of 0.1N potassium hydroxide-ethanol solution used (ml)
f: Factor of 0.1N potassium hydroxide-ethanol solution S: Amount of sample collected (g)

  In order to improve the adhesive force of the obtained transparent pressure-sensitive adhesive sheet, a tackifier resin may be added to the transparent pressure-sensitive adhesive sheet composition of the present invention as long as the transparency is not lowered. Examples of tackifier resins include rosin resins such as rosin and rosin esterified products; terpene resins such as diterpene polymers and α-pinene-phenol copolymers; aliphatic (C5) and aromatic ( Petroleum resin such as C9); styrene resin, phenol resin, xylene resin and the like. It is possible to add a hydrogenated rosin or a disproportionated rosin ester, an aliphatic or aromatic petroleum resin, an acrylic resin having a high Tg, or the like to the transparent pressure-sensitive adhesive sheet from the viewpoint of light resistance. preferable. As addition amount of tackifying resin, it is preferable to add 1-10 mass parts with respect to 100 mass parts of compositions for transparent adhesive sheets.

  Moreover, the composition for transparent adhesive sheets of this invention may contain the well-known various additives in the range which does not impair transparency as needed. Additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, antioxidants, light stabilizers, UV absorbers, polymerization inhibitors, benzotriazole-based light stabilizers, phosphate esters System and other flame retardants, and antistatic agents such as surfactants.

  Moreover, you may dilute the composition for transparent adhesive sheets of this invention using an organic solvent for the purpose of the viscosity adjustment at the time of coating. 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 may be used alone or in combination of two or more. Among these, n-propyl acetate is preferable from the viewpoint of solubility of polyolefin polyol and the like.

(Transparent adhesive sheet)
The transparent adhesive sheet of the present invention is obtained by curing the composition for transparent adhesive sheet. More specifically, it is used for applications for bonding optical members (for optical member bonding), optical product manufacturing applications, and the like. Moreover, even if the transparent adhesive sheet of this invention has a base material, it may be a double-sided adhesive sheet which does not have a base material but consists only of an adhesive layer. Although it will not specifically limit if it is a member which has an optical characteristic as an optical member, For example, the member used for an image display apparatus, a touchscreen, or these apparatuses is mentioned. More specifically, for example, a polarizing plate, a retardation plate, an optical compensation film, a brightness enhancement film, a light guide plate, a reflection 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 a member in which these are laminated.

  A transparent adhesive sheet can be obtained by apply | coating the solution which melt | dissolved the composition for transparent adhesive sheets in the solvent to a peeling film, heat-drying, and making it bridge | crosslink. 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. When the film thickness of the transparent adhesive sheet is thinner than 5 μm, it tends to be difficult to bond the transparent adhesive sheet. When the film thickness of the transparent adhesive sheet is thicker than 200 μm, the solvent may remain on the sheet and the problem of odor may occur. In addition, for coating (coating) in the method for forming an optical pressure-sensitive adhesive sheet of the present invention, a known coating method can be used. Conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters Coating can be performed using a dip roll coater, bar coater, knife coater, spray coater, comma coater, direct coater or the like.

  The gel fraction of the transparent adhesive sheet of the present invention is preferably 40 to 80%, more preferably 45 to 70%, and still more preferably 50 to 65%. Even if the gel fraction is less than 40%, it can be used, but the cohesive force of the transparent adhesive sheet becomes too small. Moreover, when a gel fraction is larger than 80%, the level | step difference followability of a transparent adhesive sheet worsens and is unpreferable.

The gel fraction of the transparent adhesive sheet was determined by the following general formula (2) based on the mass of the sample before immersion in toluene and after immersion in toluene at room temperature for 24 hours and drying at 80 ° C. for 5 hours. ).

(Transparent adhesive sheet for fixing transparent conductive film)
The transparent pressure-sensitive adhesive sheet for fixing a transparent conductive film of the present invention is a transparent pressure-sensitive adhesive sheet for fixing a transparent conductive film obtained by curing the composition for transparent pressure-sensitive adhesive sheet, and can be suitably bonded to the conductive layer surface of the transparent conductive film, In addition, the conductive layer is hardly corroded. Therefore, a laminate in which the transparent conductive film fixing sheet is bonded to the conductive layer surface of the transparent conductive film can be suitably used as a touch panel. Further, 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 pressure-sensitive adhesive sheet having only a pressure-sensitive adhesive layer without having a base material. Moreover, even if the adhesive layer consists of a single layer, multiple layers may be laminated | stacked. Especially, it is preferable that it is a double-sided adhesive sheet which does not have a base material but consists only of an adhesive layer from a viewpoint of ensuring transparency and level | step difference followable | trackability.

  As the transparent conductive film in which the transparent adhesive sheet for fixing the transparent conductive film of the present invention is used, it is sufficient that it has a conductive layer on at least one surface layer, and the conductive material is provided on the surface layer of the transparent substrate by vapor deposition or coating. The obtained transparent conductive film is mentioned. The conductive material to be deposited or coated on the conductive layer of the transparent conductive film is not particularly limited, and specifically, silver, indium tin oxide, indium oxide, tin oxide, zinc oxide, cadmium oxide, gallium oxide, titanium oxide, etc. Is mentioned. Of these, silver and indium tin oxide, which are excellent in transparency and conductivity, are preferably used. In the transparent conductive film, the substrate on which the conductive material is deposited or coated is not particularly limited, and examples thereof include glass and resin films.

  In addition, the transparent adhesive sheet for transparent conductive film fixation of this invention can be obtained by the method similar to the said transparent adhesive sheet.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

<Synthesis of (meth) acrylic copolymers (A-1) to (A-12)>
In a reaction vessel equipped with a cooling tube, a nitrogen introduction tube, a thermometer, and a stirring device, 500 parts of n-propyl acetate, hydrogenated polyolefin diol (GI-3000, manufactured by Nippon Soda Co., Ltd., hydroxyl value 29.5 mgKOH / g, number (Average molecular weight 3800) 299 parts (0.08 mol), dioctyltin dilaurate 0.03 parts (0.05 mmol), 2-ethylhexyl acrylate 126 parts (0.65 mol), isobornyl acrylate 69 parts (0.32 mol), 2 -4.7 parts (0.03 mol) of methacryloyloxyethyl isocyanate (manufactured by Showa Denko KK, Karenz MOI (registered trademark)) and 0.1 part of 2,2-azuisobutylnitrile were placed in a nitrogen stream at 95 ° C. (Meth) acrylate having a glass transition temperature of −40 ° C. and a weight average molecular weight of 150,000. To obtain a copolymer (A-1). In addition, the measurement of the glass transition temperature of a (meth) acryl copolymer and a weight average molecular weight was performed by the method described above. In addition, the (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) shown in Table 1, (meth) acryloyloxyalkyl isocyanate, polyolefin polyol, etc. ) In the same manner as the acrylic copolymer (A-1), (meth) acrylic copolymers (A-2) to (A-12) were 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-12). . The results are shown in Table 1.

(Examples 1 to 9 and Comparative Examples 1 to 3 )
Each of the compositions shown in Table 2 was blended with a crosslinking agent, polyolefin polyol, etc., and the solid content concentration was adjusted with n-propyl acetate, and the pressure-sensitive adhesive composition solution (solid content concentration: 50 mass%) was dispersed at room temperature. The composition solution for transparent adhesive sheets was prepared by mixing using. This solution is cast-coated (coating layer thickness) so that the thickness after drying is 50 μm on the release-treated surface of a separator on which one side of a 50 μm-thick polyethylene terephthalate (PET) film has been subjected to release treatment. 150 μm), and dried by heating at 50 ° C. for 5 minutes and 110 ° C. for 3 minutes, and then the release side of the separator on which one side of a 50 μm-thick PET film has been peeled is covered on the adhesive side To do. And aging was performed at 40 degreeC for 72 hours, and the double-sided adhesive sheet (base material-less type) was produced.

(Acid value)
The acid value of each composition was measured by the method described above. The results are shown in Table 2.
(Measurement of electrical resistance of indium tin oxide film)
The double-sided pressure-sensitive adhesive sheet obtained above is cut to a size of 50 mm × 50 mm, the peeled PET film with a thickness of 38 μm on one side is peeled off, and bonded to the indium tin oxide film surface of the 100 mm × 100 mm indium tin oxide deposited PET film. . An electrical resistance value measuring machine (“Lorester GP” manufactured by Mitsubishi Chemical Corporation) was used at both ends of the bonded double-sided PSA sheet, and the initial electrical resistance value (R ₁ ) was measured. The indium tin oxide-deposited PET film on which the double-sided adhesive sheet is bonded is allowed to stand for 500 hours under conditions of 60 ° C. and 90% RH and for one hour under conditions of 23 ° C. and 50% RH. The resistance value (R ₂ ) was measured. The increase rate of the electric resistance value of the indium tin oxide film was calculated by the following general formula (3).

The rate of increase in electrical resistance value was evaluated according to the following criteria. The results are shown in Table 2.
○: Electrical resistance value increase rate of less than 5% Δ; Electrical resistance value increase rate of less than 5 to 10% ×: Electrical resistance value increase rate of 10% or more

(Total light transmittance measurement)
The pressure-sensitive adhesive sheet obtained above was cut into a size of 30 mm × 30 mm, and the peeled PET film on one side of the peeled PET film present on both sides of the pressure-sensitive adhesive sheet was peeled off and bonded to a glass plate as a measurement sample. . About the sample for a measurement, the total light transmittance (%) was measured using "HR-100 type" by Murakami Color Research Laboratory. The results are shown in Table 2.

(Measurement of adhesive strength of adhesive sheet)
The double-sided pressure-sensitive adhesive sheet obtained above was cut to a size of 25 mm × 100 mm, the peeled PET film on one side of the double-sided pressure-sensitive adhesive sheet was peeled off, and a 50 μm thick PET film that had been subjected to corona treatment on one side was reattached. The adhesive surface (measurement surface) was affixed to the test plate, and a 2 kg rubber roller (width: about 50 mm) was reciprocated once to prepare a measurement sample. A glass plate was used as a test plate. The obtained sample for measurement is allowed to stand for 24 hours in an environment of 23 ° C. and 50% humidity, and subjected to a tensile test in the 180 ° direction at a peeling rate of 300 mm / min in accordance with JIS Z0237. The adhesive force (N / 25 mm) to was measured. The obtained measured value was defined as adhesive strength. The results are shown in Table 2.

(Step following ability evaluation)
Remove the peeled PET film on one side of the double-sided pressure-sensitive adhesive sheet obtained above onto a glass plate with a thickness of 0.5 mm, length 50 mm, width 40 mm, window frame thickness 15 μm, width 5 mm, and double-sided adhesive. After the sheets were bonded together and the peeled PET film on one side was peeled off, 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, and heated under conditions of 5 atm, 70 ° C. and 10 minutes. After fixing by performing pressure treatment, the floating of the pressure-sensitive adhesive layer at the step portion was visually observed.

The step following ability was evaluated according to the following criteria. The results are shown in Table 2.
○: The state in which the pressure-sensitive adhesive layer is not lifted at the stepped portion Δ: The state in which the pressure-sensitive adhesive layer is slightly lifted at the stepped portion ×: The pressure-sensitive adhesive layer is clearly lifted at the stepped portion Confirmed state

(Gel fraction measurement)
The gel fraction was measured by the method described above using the obtained transparent adhesive sheet. The results are shown in Table 2.

Claims (7)

(A) Chemical formula (I):

(Wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group having 1 to 6 carbon atoms, and R ³ represents a urethane bond residue of a polyolefin polyol or hydrogenated polyolefin polyol). A composition for transparent adhesive sheet comprising a (meth) acrylic copolymer having a structural unit, (B) a crosslinking agent, and (C) a tin-based catalyst, wherein the acid value is 5 mgKOH / g or less. A composition for a transparent adhesive sheet. The transparent adhesive sheet obtained by hardening the composition for transparent adhesive sheets of Claim 1 . The transparent adhesive sheet according to claim 2 , wherein the gel fraction is 40 to 80%. The transparent adhesive sheet of Claim 2 or 3 is used for bonding of a transparent conductive film, The transparent adhesive sheet for transparent conductive film fixation characterized by the above-mentioned. The transparent adhesive sheet for transparent conductive film fixation of Claim 4 is adhere | attached on the conductive layer surface of the transparent conductive film, The laminated body characterized by the above-mentioned. In the presence of a polyolefin polyol and / or hydrogenated polyolefin polyol, and a tin-based urethanization catalyst, a (meth) acryloyl group-containing monomer (excluding those having an isocyanate group) and a (meth) acryloyloxyalkyl isocyanate are added. Copolymerized with a polymerization initiator,
(A) Chemical formula (I):

(In the formula, R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkylene group having 1 to 6 carbon atoms.
R ³ is a urethane bond of polyolefin polyol or hydrogenated polyolefin polyol.
A (meth) acrylic copolymer having a structural unit represented by (combined residues) is prepared, and then (B) a crosslinking agent is blended to produce a composition for a transparent adhesive sheet having an acid value of 5 mgKOH / g or less. A method for producing a composition for a transparent pressure-sensitive adhesive sheet. (A) The (meth) acrylic copolymer having the structural unit represented by the chemical formula (I) is an alkyl group in the presence of a polyolefin polyol and / or a hydrogenated polyolefin polyol, and a tin-based urethanization catalyst. (Meth) acrylic acid alkyl ester having 1 to 18 carbon atoms and / or (meth) acrylic acid alkoxyalkyl ester having 2 to 20 carbon atoms and 2 to 20 carbon atoms, (meth) acryloyl group The composition for transparent adhesive sheets of Claim 6 obtained by copolymerizing the containing polar monomer 0-9.5 mol% and 2- (meth) acryloyloxyethyl isocyanate 0.5-10 mol% with a polymerization initiator. Manufacturing method.