TWI677547B - Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet - Google Patents

Abstract

The adhesive composition of the present invention includes a (meth) acrylic copolymer having an acid value of 2.5 mgKOH / g or less, and contains a monomer derived from a hydroxyl group in a range of 0.01% by mass to 1% by mass relative to all the structural units. A structural unit of the body; a toluene diisocyanate compound in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer; and an imidazole compound.

Description

Adhesive composition and adhesive sheet

The invention relates to an adhesive composition and an adhesive sheet.

Liquid crystal display devices are often incorporated in image display units such as mobile phones and mobile terminals. A general liquid crystal display device is equipped with a liquid crystal cell, and optical films such as a polarizing plate, a retardation plate, and a brightness enhancement film. In recent years, liquid crystal display devices further equipped with a touch panel are increasing. The liquid crystal cell and the optical film, the optical film, or the optical film and the touch panel are adhered through an adhesive layer formed of an adhesive composition.

Optical films such as polarizing plates are generally formed by laminating members having different shrinkage ratios. Therefore, the optical film is warped due to changes in temperature and humidity, and sometimes the interface between the adhesive layer and the optical film may be warped, peeled, or foamed. In addition, due to changes in temperature and humidity, the stress caused by the optical film tending to shrink and expand cannot be alleviated in the adhesive layer, and the residual stress applied to the adhesive layer may become uneven and cause light leakage. This is the case where so-called white spots occur. Therefore, there is a need for an adhesive composition capable of forming an adhesive layer capable of achieving both durability capable of suppressing warping and peeling and suppression of white spots.

In order to balance durability of the adhesive layer and suppression of white spots, a method has been proposed in which the cohesive force of the adhesive layer is increased and the size change of the optical film is suppressed. For example, in International Publication No. 2011/062127, even after being exposed to high temperature and high humidity for a long time after being adhered to an adherend, it will not be warped or peeled off at the adhesive interface of the adherend and the adhesive layer As an adhesive, an adhesive composition for a polarizing plate is proposed, which includes 100 parts by mass of an acrylic polymer obtained by copolymerizing 1 to 10% by mass of a carboxyl group-containing monomer, and toluene having an isocyanurate structure. 4 to 20 parts by mass of the diisocyanate-based compound.

[Problems to be Solved by the Invention] In recent years, regarding the input method of the touch panel, the electrostatic capacitance method has become the mainstream. In the electrostatic capacitance method, an indium tin oxide (ITO) film constituting a touch panel is in contact with an adhesive layer. Therefore, it is required that the adhesive composition used in the liquid crystal display device does not easily corrode ITO.

However, in the adhesive composition for polarizing plates described in the above-mentioned International Publication No. 2011/062127, the acrylic polymer has an acidic group derived from a monomer containing a carboxyl group, and thus a problem of ITO corrosion occurs.

Generally, if the adhesive composition contains a small amount of acidic groups, ITO corrosion can be suppressed. However, conventional adhesive compositions for polarizing plates use acrylic copolymers having many acidic groups, as described in the aforementioned International Publication No. 2011/062127, in order to be sufficiently flexible and not to cause peeling when forming an adhesive layer. Thing. Here, when an acrylic copolymer having few acidic groups is used in the adhesive composition, the adhesive layer becomes too hard when it is formed, and peeling is likely to occur due to changes in temperature and humidity, which causes a problem of durability. Therefore, an adhesive composition using an acrylic copolymer with few acidic groups and having both durability when forming an adhesive layer and suppression of white spots is unknown. Furthermore, when an acrylic copolymer having few acidic groups is used as the adhesive composition, when the adhesive composition is crosslinked to form an adhesive layer, there are problems such as a slow reaction rate and a long curing period. .

Here, in order to increase the reaction speed and shorten the aging time, a method using a tin compound as a crosslinking catalyst is considered. However, when a tin compound is used as a cross-linking catalyst, durability may be deteriorated. Therefore, a method that does not use a tin compound and can shorten the aging period is required.

The present invention has been made in view of the problems described above, and an object thereof is to provide an adhesive composition and an adhesive sheet that can reduce durability and white point while using an acrylic copolymer with few acidic groups, and can shorten the curing time. [Means for solving problems]

Means for solving the above problems include the following implementation aspects. [1] An adhesive composition comprising a (meth) acrylic copolymer having an acid value of 2.5 mgKOH / g or less, and containing 0.01% by mass to 1% by mass of all structural units derived from a compound having a hydroxyl group. A structural unit of a monomer; a toluene diisocyanate compound in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer; and an imidazole compound. [2] The adhesive composition according to [1], wherein the content of the imidazole compound is in the range of 0.01 to 1.5 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer. [3] The adhesive composition according to [1] or [2], further comprising a silane coupling agent in a range of 0.05 to 1 part by mass based on 100 parts by mass of the (meth) acrylic copolymer. [4] The adhesive composition according to any one of [1] to [3], wherein the acid value of the (meth) acrylic copolymer is 0 mgKOH / g. [5] The adhesive composition according to any one of [1] to [4], wherein the toluene diisocyanate compound is an adduct of a toluene diisocyanate and a polyol. [6] The adhesive composition according to any one of [1] to [5], the value of the storage elastic modulus (G ') at 30 ° C after crosslinking is 2.0 × 10 ⁵ Pa to 1.0 × 10 ⁷ Pa range.

[7] An adhesive sheet having an adhesive layer formed of the adhesive composition according to any one of [1] to [6]. [Effect of the invention]

According to the present invention, it is possible to provide an adhesive composition and an adhesive sheet capable of shortening the curing time while using an acrylic copolymer having few acidic groups, while achieving both durability and suppression of white spots.

Hereinafter, an embodiment which is an example of the present invention will be described. In addition, the numerical range indicated by "~" in this specification means the range which includes the numerical value described before and after "~" as a minimum value and a maximum value, respectively. In addition, regarding the amount of each component in the composition in this specification, when a plurality of substances corresponding to each component in the adhesive composition are used, unless otherwise specified, it means the total amount of the plurality of substances corresponding to the component. Further, the (meth) acrylic group means at least one of an acrylic group and a methacrylic group, and the (meth) acrylate means at least one of an acrylate and a methacrylate. Further, the composition before the crosslinking reaction of the adhesive composition-based (meth) acrylic copolymer and the toluene diisocyanate-based compound ends, for example, means a liquid, paste, or powdery composition. Further, the layer after the crosslinking reaction of the adhesive layer-based (meth) acrylic copolymer and the toluene diisocyanate-based compound is completed, for example, means a solid or gel-like layer.

[Adhesive composition] The adhesive composition of the present invention includes a (meth) acrylic copolymer having an acid value of 2.5 mgKOH / g or less, and a range of 0.01% by mass to 1% by mass with respect to all structural units. Contains a structural unit derived from a monomer having a hydroxyl group; a toluene diisocyanate compound is in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer; and an imidazole compound.

The adhesive composition of the present invention has a low acid value of the (meth) acrylic copolymer of 2.5 mgKOH / g or less. For example, it is not easy to corrode ITO when bonding a touch panel of an electrostatic capacitance method.

Furthermore, when the adhesive composition of the present invention is used as an adhesive layer, when an optical film such as a polarizing plate or a touch panel is attached to an adherend such as a liquid crystal cell, the durability and white point suppression are excellent. The reason is speculated as follows.

The adhesive composition of the present invention includes a crosslinked body obtained by chemically crosslinking a (meth) acrylic copolymer with a toluene diisocyanate compound, and a toluene diisocyanate formed by reacting the toluene diisocyanate compound with each other. Condensate. We believe that the condensate of toluene diisocyanate is relatively hard and can suppress the occurrence of stress, while the crosslinked body is relatively soft and has good adhesion to the adherend. Therefore, it is considered that since the hardness due to the condensed product and the partial softness due to the crosslinked product are in a suitable range, it is considered to be excellent in both durability and suppression of white spots. More specifically, it is estimated as follows.

The adhesive composition of the present invention includes a (meth) acrylic copolymer containing a structural unit derived from a monomer having a hydroxyl group in a range of 0.01% by mass to 1% by mass with respect to all the structural units, that is, a relatively small number of hydroxyl groups (Meth) acrylic copolymer, so that when the adhesive layer is formed, the part becomes soft, has excellent adhesion to the adherend such as a touch panel, an optical film, and a liquid crystal cell, and is not easy to peel off. Specifically, the (meth) acrylic copolymer has a hydroxyl group content of 0.01% by mass or more, the adhesive layer does not become excessively soft, and generation of gas (foaming) from the optical film can be suppressed. The amount is 1.0% by mass or less, the adhesive layer does not become hard and brittle, and peeling from the adherend can be suppressed.

The adhesive composition of the present invention is hardened when the adhesive layer is formed by containing a toluene diisocyanate compound in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer. And can suppress the occurrence of stress. In detail, by containing 5 parts by mass or more of a toluene diisocyanate compound as a crosslinking agent, it has excellent durability (especially heat resistance), and can suppress foaming and peeling. By containing a toluene diisocyanate compound, 30 parts by mass or less can suppress whitening at the time of forming an adhesive layer, and is suitable for bonding of articles requiring transparency such as a touch panel and an optical film.

Furthermore, since the adhesive composition of the present invention contains a toluene diisocyanate compound as a cross-linking agent, it is suitable for bonding of a touch panel and an optical film, and can balance durability and suppression of white spots. On the other hand, if the cross-linking agent is a xylene diisocyanate-based compound, the compatibility between the (meth) acrylic copolymer and the xylene diisocyanate-based compound is poor, the adhesive layer is whitened, and it cannot be used for touch panels, Lamination of articles requiring transparency, such as optical films. When the cross-linking agent is a hexamethylene diisocyanate-based compound, it is not possible to obtain a degree of hardness that suppresses the occurrence of stress when forming the adhesive layer, and white spots are generated. Therefore, it is not possible to achieve both durability and suppression of white spots.

In general, a (meth) acrylic copolymer having no acidic group and having a hydroxyl group as a crosslinkable functional group has poor reactivity with a crosslinking agent and tends to have a long curing time. Therefore, when only a hydroxyl group is used as the crosslinkable functional group, the aging time becomes long, and the crosslinking reaction may not be completed.

On the other hand, by using a toluene diisocyanate compound as a cross-linking agent and an imidazole compound as a cross-linking catalyst, the adhesive composition of the present invention can achieve both durability and suppression of white spots, and can shorten curing time. time.

[(Meth) acrylic copolymer] The adhesive composition of the present invention includes a (meth) acrylic copolymer, having an acid value of 2.5 mgKOH / g or less, and 0.01 mass% to 1 mass with respect to all structural units. The range of% contains a structural unit derived from a monomer having a hydroxyl group. The (meth) acrylic copolymer is preferably a copolymer having an alkyl (meth) acrylate as a main component, and if necessary, a monomer having a carboxyl group, other monomers, or the like may be used as a copolymerization component. Here, a copolymer containing alkyl (meth) acrylate as a main component means a copolymer having 50% by mass or more of the structural unit derived from the alkyl (meth) acrylate with respect to 100% by mass of the structural unit in the copolymer. Thing.

The (meth) acrylic copolymer has an acid value of 2.5 mgKOH / g or less. For example, it is not easy to corrode ITO when bonding a touch panel of an electrostatic capacitance method. From the viewpoint of more appropriately suppressing the corrosion of ITO, the acid value of the (meth) acrylic copolymer is preferably 2.0 mgKOH / g or less, more preferably 1.0 mgKOH / g or less, more preferably 0.5 mgKOH / g or less, and 0 mgKOH / g 特 佳. The acid value is a value calculated from the following calculation formula.

Acid value (mgKOH / g) = (A / B) × 56.1 × 10 × CA = content rate (mass%) of a monomer having a carboxyl group among all monomers used in the (meth) acrylic copolymer B = The molecular weight of the monomer having a carboxyl group used in the (meth) acrylic copolymer is 56.1 based on the molecular weight of KOH. C = Number of carboxyl groups in a molecule of a monomer having a carboxyl group used in a (meth) acrylic copolymer

When the number of monomers having a carboxyl group used in the (meth) acrylic copolymer is two or more, the acid value is obtained from the above calculation formula for each monomer, and the obtained values are totaled to obtain the acid value.

The (meth) acrylic copolymer contains a structural unit derived from a monomer having a hydroxyl group, and the hydroxyl group undergoes a crosslinking reaction with a toluene diisocyanate compound. Therefore, the cohesive force of the adhesive composition is improved, the adhesive force is excellent, and foaming can be suppressed in the durability test.

The alkyl (meth) acrylate which is a main component of the (meth) acrylic copolymer used in the present invention includes, for example, methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) N-butyl acrylate, isobutyl (meth) acrylate, secondary butyl (meth) acrylate, tertiary butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate Ester, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate Octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate. The alkyl group of the alkyl (meth) acrylate may be any of linear, branched, or cyclic. The carbon number of the alkyl group is preferably from 1 to 18, more preferably from 1 to 8, and even more preferably from 1 to 4.

Among them, as the alkyl (meth) acrylate, methyl (meth) acrylate and n-butyl (meth) acrylate are preferable, and methyl acrylate and n-butyl acrylate are more preferable.

In the (meth) acrylic copolymer, the content rate of the structural unit derived from the alkyl (meth) acrylate is preferably 80% by mass or more with respect to the entire structural unit in order to easily adjust the adhesion characteristics and viscoelastic properties, 90 More than mass% is more preferred, and more than 95 mass% is more preferred.

The monomer having a hydroxyl group which is a component of the (meth) acrylic copolymer used in the present invention includes a (meth) acrylic monomer having a hydroxyl group, an unsaturated alcohol, and the like.

Examples of the (meth) acrylic monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, ( 4-hydroxybutyl (meth) acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-hydroxybutyl (meth) acrylate, (meth) acrylic acid 1,3-dimethyl-3-hydroxybutyl ester, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate Representative hydroxyalkyl (meth) acrylate; glyceryl mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, poly (meth) acrylate (Ethylene glycol-propylene glycol) ester, N-methylol acrylamide.

Among them, the (meth) acrylic monomer having a hydroxyl group has a carbon number of 1 to 5 in consideration of a good compatibility and copolymerizability with other monomers and a good cross-linking reaction with a crosslinking agent. A hydroxyalkyl (meth) acrylate of a hydroxyalkyl group is preferable, and a hydroxyalkyl (meth) acrylate having a hydroxyalkyl group of 2 to 4 carbon atoms is more preferable. Specifically, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferable, and 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are more preferable.

Examples of the unsaturated alcohol include allyl alcohol and methallyl alcohol.

The (meth) acrylic copolymer contains the structural unit derived from the monomer which has a hydroxyl group in the range of 0.01 mass%-1 mass% with respect to all the structural units. The (meth) acrylic copolymer has a content ratio of a structural unit derived from a monomer having a hydroxyl group of 0.01% by mass or more, the adhesive layer does not become excessively soft, and generation of gas from the optical film can be suppressed (from Foam), since the content is 1.0% by mass or less, the adhesive layer does not become hard and brittle, and peeling from the adherend can be suppressed. The (meth) acrylic copolymer preferably contains a structural unit derived from a monomer having a hydroxyl group in a range of 0.02% by mass to 0.7% by mass, more preferably in a range of 0.03% by mass to 0.5% by mass, and 0.05% by mass. The content in the range of 0.3% by mass is particularly preferred.

When the (meth) acrylic copolymer has an acid value of 2.5 mgKOH / g or less, the (meth) acrylic copolymer may include a monomer having a carboxyl group as a copolymerization component. Examples of the monomer having a carboxyl group include a (meth) acrylic monomer having a carboxyl group. Examples of the (meth) acrylic monomer having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, citraconic acid, cinnamic acid, and succinic acid. Monohydroxyethyl (meth) acrylate, maleic acid monohydroxyethyl (meth) acrylate, fumaric acid monohydroxyethyl (meth) acrylate, phthalic acid monohydroxyethyl (methyl) ) Acrylate, 1,2-dicarboxycyclohexane monohydroxyethyl (meth) acrylate, (meth) acrylic acid dimer, ω-carboxy-polycaprolactone mono (meth) acrylate.

In the (meth) acrylic copolymer, the content of the structural unit derived from the monomer having a carboxyl group is preferably 0.2% by mass or less based on the viewpoint of reducing the acid value and suppressing the corrosion of ITO. 0.05% by mass or less is more preferred, and 0% by mass, that is, not included, is particularly preferred.

The (meth) acrylic copolymer used in the present invention may use other monomers as copolymerization components in addition to the (meth) acrylic acid alkyl ester, the monomer having a hydroxyl group, and the monomer having a carboxyl group. Other monomers include, for example, a (meth) acrylic monomer having an aromatic ring, a (meth) acrylic monomer having a nitrogen atom, and other copolymerizable monomers.

The (meth) acrylic copolymer used in the present invention may contain a (meth) acrylic monomer having an aromatic ring as a copolymerization component. Thereby, the adhesive composition of this invention becomes easy to suppress the white point at the time of using for a polarizing plate.

Examples of the (meth) acrylic monomer having an aromatic ring include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, Ethylene oxide (EO) modified cresol (meth) acrylate, ethylene oxide (EO) modified nonylphenol (meth) acrylate, hydroxyethylated β-naphthol acrylate, (cresol Group) biphenyl acrylate.

The (meth) acrylic copolymer used in the present invention may contain a (meth) acrylic monomer having a nitrogen atom as a copolymerization component. Thereby, the adhesive composition of the present invention can further shorten the curing time.

(Meth) acrylic monomers having a nitrogen atom, for example, aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate , N, N-dimethyl (meth) acrylamide, N, N-diethylacrylamide, N-ethyl (meth) acrylamide, N-methyl (meth) acrylamide , N-isopropyl (meth) acrylamide.

The (meth) acrylic copolymer used in the present invention may contain other copolymerizable monomers as a copolymerization component. Examples of such monomers include aromatic monomers typified by styrene, α-methylstyrene, tertiary butylstyrene, p-chlorostyrene, chloromethylstyrene, vinyltoluene, and vinylpyridine. Vinyl monomers; acrylonitrile and methacrylonitrile as representative vinyl cyanide monomers; vinyl formate, vinyl acetate, vinyl propionate, "vinylversatate" (trade name, new decyl Vinyl acid carboxylate) represented by carboxylic acid vinyl ester monomers; various derivatives of these.

The weight average molecular weight (Mw) of the (meth) acrylic copolymer used in the present invention is not particularly limited, but is preferably in the range of 700,000 to 2 million, and more preferably in the range of 1 to 1.5 million. The weight average molecular weight can be adjusted according to the polymerization reaction temperature, time, amount of organic solvent, and the like. If the weight average molecular weight is in the range of 700,000 to 2 million, the viscosity of the adhesive composition of the present invention is low, and the coatability is good.

The weight average molecular weight (Mw) of the (meth) acrylic copolymer is a value measured by the following method. (Measuring method of weight average molecular weight (Mw)) It measured based on the following (1)-(3). (1) A (meth) acrylic copolymer solution was applied to a release paper and dried at 100 ° C. for 2 minutes to obtain a film-like (meth) acrylic copolymer. (2) The film-like (meth) acrylic copolymer obtained in the above (1) is dissolved in tetrahydrofuran so that the solid content becomes 0.2%. (3) The weight-average molecular weight (Mw) of the (meth) acrylic copolymer was measured using standard gel permeation chromatography (GPC) under the following conditions. (Conditions) GPC: HLC-8220 GPC [manufactured by Tosoh Corporation]. Column: TSK-GEL GMHXL 4 mobile phase solvent: tetrahydrofuran. Flow rate: 0.6ml / min. Column temperature: 40 ° C.

The glass transition temperature (Tg) of the (meth) acrylic copolymer used in the present invention is preferably -80 ° C or higher in order to provide sufficient cohesion of the adhesive composition and make it exhibit sufficient durability. Above -60 ° C is more preferred. The glass transition temperature (Tg) of the (meth) acrylic copolymer is -20 in order for the adhesive composition to exhibit sufficient adhesion to the support substrate and to exhibit durability such as no peeling. It is preferably below ℃, and more preferably below -40 ° C.

The glass transition temperature (Tg) of the (meth) acrylic copolymer is a value obtained by converting an absolute temperature (K) obtained by calculation according to the following formula into a Celsius temperature (° C).

[Number 1] In the formula, Tg ₁ , Tg ₂ ,... And Tg _n are the absolute temperatures when the monomers of monomer 1, monomer 2, ..., and monomer n are homopolymers ( K) The glass transition temperature. m ₁ , m ₂ , ... and m _n are Mohr fractions of each monomer.

In addition, "the glass transition temperature represented by the absolute temperature (K) when the homopolymer is formed" means the glass transition represented by the absolute temperature (K) of the homopolymer obtained by polymerizing the monomer alone temperature. The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) (manufactured by Seiko Instruments Inc., EXSTAR6000) in a nitrogen gas stream with a sample temperature of 10 mg and a temperature increase rate of 10 The measurement was performed under the condition of ℃ / minute, and the inflection point of the obtained DSC curve was taken as the glass transition temperature of the homopolymer.

Regarding representative monomers, "the glass transition temperature of a homopolymer in degrees Celsius (° C)", methyl acrylate is 5 ° C, ethyl acrylate is -27 ° C, and n-butyl acrylate is -57 ° C. , 2-ethylhexyl acrylate is -76 ° C, 2-hydroxyethyl acrylate is -15 ° C, 4-hydroxybutyl acrylate is -39 ° C, tertiary butyl acrylate is 41 ° C, and acrylic acid is 163 ° C. For example, by using these representative monomers, the glass transition temperature (Tg) of the (meth) acrylic copolymer can be appropriately adjusted. In addition, by subtracting 273 from the absolute temperature (K), the absolute temperature (K) can be converted into the Celsius temperature (° C), and adding the 273 to the Celsius temperature (° C) can convert the Celsius temperature (° C) into the absolute temperature ( K).

The manufacturing method of the (meth) acrylic-type copolymer used by this invention is not specifically limited, It can manufacture by polymerizing a monomer by methods, such as solution polymerization, emulsion polymerization, and suspension polymerization. In addition, when the adhesive composition of the present invention is prepared after manufacture, solution polymerization is preferred in that the processing steps are relatively simple and can be performed in a short time.

Solution polymerization can generally be used to add the specified organic solvent, monomer, polymerization initiator, and chain transfer agent used in the polymerization tank, and heat it under stirring in a nitrogen stream or at the reflux temperature of the organic solvent. Reaction for several hours. The weight-average molecular weight of the (meth) acrylic copolymer can be adjusted to the desired value by adjusting the reaction temperature, time, amount of solvent, and type or amount of catalyst.

Examples of the organic solvent for polymerization used in the production of the (meth) acrylic copolymer include aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, alcohol compounds, and the like. . These organic solvents may be used alone or in combination of two or more. Examples of the polymerization initiator include organic peroxides and azo compounds that can be used in a usual polymerization method.

[Toluene diisocyanate compound] The adhesive composition of the present invention contains a toluene diisocyanate compound in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer. The function of the toluene diisocyanate compound as a crosslinking agent.

Toluene diisocyanate compounds include toluene diisocyanate, dimers of toluene diisocyanate, adducts of toluene diisocyanate and polyols, trimers of toluene diisocyanate, or isocyanurates of pentamers. Various toluene diisocyanate-based compounds such as toluene diisocyanate and bisureton of toluene diisocyanate. The above-mentioned considerations are that the reactivity is excellent and the cross-linking density can be increased, and the compatibility with the (meth) acrylic copolymer is excellent, the adduct of toluene diisocyanate and a polyhydric alcohol is preferable, and the toluene diisocyanate and the three are The adduct of methylolpropane is particularly preferred.

The content of the toluene diisocyanate compound in the adhesive composition is in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer. By containing 5 parts by mass or more of the toluene diisocyanate-based compound, foaming and peeling can be suppressed, and durability (especially heat resistance) is excellent. By containing 30 parts by mass or less of the toluene diisocyanate-based compound, whitening at the time of forming an adhesive layer can be suppressed, and it is suitable for bonding of articles requiring transparency such as a touch panel and an optical film.

The content of the toluene diisocyanate compound in the adhesive composition is preferably in a range of 10 to 30 parts by mass relative to 100 parts by mass of the (meth) acrylic copolymer, and in a range of 12 to 30 parts by mass. Better. Thereby, the durability at the time of formation of an adhesive bond layer, and suppression of white spots are more excellent.

Toluene diisocyanate-based compounds may be used commercially available products. As a commercially available product, "CORONATEL" (trade name) manufactured by Japan Polyurethanes Industrial Co., Ltd. can be suitably used as an adduct of toluene diisocyanate and trimethylolpropane, and manufactured by Japan Polyurethanes Industrial Co., Ltd. "CORONATE2030" is an isocyanurate of toluene diisocyanate.

[Other crosslinkers] The adhesive composition of the present invention may contain other crosslinkers other than toluene diisocyanate compounds within a range that does not impair the object of the present invention. Other crosslinking agents are not particularly limited, and examples thereof include polyisocyanate compounds, polyepoxide compounds, polyaziridine compounds, and metal chelate compounds other than toluene diisocyanate-based compounds. These other crosslinking agents can be used individually or in combination of 2 or more types with a toluene diisocyanate compound.

[Imidazole compound] The adhesive composition of the present invention contains an imidazole compound. The imidazole compound has, for example, a function as a crosslinking catalyst in the adhesive composition. By containing the imidazole compound in the adhesive composition, it is possible to maintain excellent durability and further shorten the curing time.

The imidazole compound is not particularly limited as long as it is a compound having at least one imidazole ring in the molecule. From the standpoint of shortening the aging time and extending the pot life, an N-substituted imidazole compound is preferred. The N-substituted imidazole compound is not particularly limited as long as it is a compound having at least one imidazole ring in the molecule and having no hydrogen atom on the nitrogen atom of the imidazole ring.

Specific examples of the N-substituted imidazole compound include compounds represented by the following general formula (I).

[Chemical 1]

In the general formula (I), R ₁ , R ₂ and R ₄ each independently represent a hydrogen atom or a substituent, and R ₃ represents a substituent. In the general formula (I), preferably, R ₁ , R ₂ , and R ₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, and R ₃ represents an alkyl group, an aryl group, or an aralkyl group. R ₁ and R ₂ or R ₃ and R ₄ may be connected to each other to form a cyclic structure.

The alkyl group (R ₁ to R ₄ ) in the general formula (I) may be linear or branched. The carbon number of the alkyl group is preferably 1 to 2. The aryl group (R ₁ to R ₄ ) in the general formula (I) is preferably 6 to 10 carbon atoms, and more preferably a phenyl group or a naphthyl group. The aralkyl group (R ₁ to R ₄ ) in the general formula (I) is preferably composed of an alkylene group having 1 to 2 carbon atoms and an aryl group having 6 to 10 carbon atoms, and more preferably a benzyl group or a phenethyl group.

The N-substituted imidazole compound represented by the general formula (I), from the viewpoint of shortening the aging time and extending the pot life, R ₃ is an alkyl group or an aralkyl group, and R ₁ , R _2, and R ₄ are each independently hydrogen Atoms, alkyls or aryls are preferred. The N-substituted imidazole compound represented by the general formula (I) is selected from the group consisting of 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole. At least one of the groups is more preferred. R ₃ and R ₄ are connected to each other to form a 5- to 6-membered saturated aliphatic ring, and R ₁ and R ₂ are connected to each other to form a 6-membered aromatic ring. It is also preferable from the viewpoint of shortening the curing time. , Preferably 2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole.

The content of the imidazole compound in the adhesive composition is from 0.01 to 1.5 parts by mass relative to 100 parts by mass of the (meth) acrylic copolymer in terms of shortening the curing time and extending the pot life. The range of 0.05 to 1.2 parts by mass is more preferred, the range of 0.1 to 1.0 parts by mass is particularly preferred, and the range of 0.3 to 0.7 parts by mass is particularly preferred.

Examples of the N-substituted imidazole compound used in the present invention include commercially available products such as "Curezol 1,2DMZ", "Curezol 1B2MZ", "Curezol 1B2PZ", "Curezol TBZ", manufactured by Shikoku Chemical Industries, Ltd. .

[Silane coupling agent] The adhesive composition of the present invention preferably further contains a silane coupling agent. When the adhesive composition contains a silane coupling agent, the adhesive layer exhibits better adhesion to glass, and a liquid crystal display device with a polarizing plate assembled is exposed to a high temperature or high temperature and humidity environment. The adhesive layer and the polarizing plate or the liquid crystal cell are still less prone to peel.

Examples of the silane coupling agent include a coupling agent having a mercapto group, a coupling agent having an epoxy group, a coupling agent having a carboxyl group, a coupling agent having an amine group, a coupling agent having a hydroxyl group, and a sulfonamide Coupling agent having a base, coupling agent having an isocyanate group, coupling agent having an isocyanurate skeleton. These silane coupling agents may be used alone or in combination of two or more.

As the silane coupling agent, a commercially available product may be used as a commercially available product. For example, "KBM-403", "KBM-303", and "KBM-402" manufactured by Shin-Etsu Chemical Industry Co., Ltd. , "KBE-402" and "KBE-403" (trade names) are typical silane coupling agents with epoxy groups.

When the adhesive composition of the present invention contains a silane coupling agent, the content of the silane coupling agent in the adhesive composition is 0.01 to 1.0 part by mass based on 100 parts by mass of the (meth) acrylic copolymer. The range is preferably 0.02 to 0.7 parts by mass, and more preferably 0.1 to 0.5 parts by mass.

[Solvent] In the adhesive composition of the present invention, a solvent may be added in order to improve coating properties with respect to an optical film such as a polarizing plate, a touch panel, and a liquid crystal cell.

As the solvent, for example, hydrocarbons such as hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane can be listed; methylene chloride, trichloroethane , Trichloroethylene, tetrachloroethylene, dichloropropane, represented by halogenated hydrocarbons; methanol, ethanol, propanol, isopropanol, butanol, isobutanol, diacetone alcohol represented by alcohols; diethyl ether, two Isopropyl ether, di Ethers represented by alkane and tetrahydrofuran; ketones represented by acetone, methyl ethyl ketone, methyl isobutanone, isophorone, cyclohexanone; methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate, acetic acid Amyl esters are typical esters; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate are typical polyols; organic solvents of these derivatives.

[Other components] The adhesive composition of the present invention may suitably contain the above-mentioned silane coupling agent, solvent, and other crosslinking agents in addition to the (meth) acrylic copolymer, toluene diisocyanate compound, and imidazole compound, if necessary. , Weathering stabilizers, tackifiers, plasticizers, softeners, peeling aids, dyes, pigments, inorganic fillers, surfactants, antioxidants, metal corrosion inhibitors, ultraviolet absorbers, hindered amine compounds, etc. Light stabilizers, etc.

In order to further improve the durability and suppress the white point of the adhesive composition of the present invention, the storage elastic modulus (G ') at 30 ° C after crosslinking is in the range of 2.0 × 10 ⁵ Pa to 1.0 × 10 ⁷ Pa Preferably, a range of 2.0 × 10 ⁵ Pa to 1.0 × 10 ⁷ Pa is more preferred, and a range of 3.0 × 10 ⁵ Pa to 5.0 × 10 ⁶ Pa is particularly preferred. The storage elastic modulus of the adhesive composition is a value measured according to the method described in Examples.

[Adhesive sheet] The adhesive sheet of the present invention has an adhesive layer formed of the above-mentioned adhesive composition. The adhesive sheet of the present invention may be a substrate-free type adhesive sheet without a substrate, or may be a substrate-type adhesive sheet having an adhesive layer on at least one side of a substrate such as an optical film. Even if the adhesive layer is exposed to a high-temperature environment or a high-temperature and high-humidity environment, the interface with the adherend is not prone to warp or peel, so the durability of the adhesive sheet of the present invention is excellent.

In the adhesive sheet of the present invention, the thickness of the adhesive layer is not particularly limited, and can be appropriately selected according to the application and required performance. The thickness of the adhesive layer includes, for example, a range of 1 μm to 100 μm.

When the adhesive sheet of the present invention is used for optical applications, it is preferable that the adhesive layer has high transparency. Specifically, the total light transmittance of the adhesive layer in the visible wavelength range measured according to JIS K 7361 (1997) is preferably 85% or more, and more preferably 90% or more. The haze of the adhesive layer measured according to JIS K 7136 (2000) is preferably 2.5% or less, more preferably 2.0% or less, and even more preferably 1.5% or less.

The exposed adhesive layer of the adhesive sheet of the present invention can be protected by a release film. The peeling film is not particularly limited as long as it can be easily peeled from the adhesive layer, and examples thereof include a resin film that is easily peeled off on at least one side using a peeling treatment agent. Examples of the resin film include a polyester film typified by a polyethylene terephthalate film. Examples of the peeling treatment agent include a fluorine-based resin, paraffin, silicone, and a long-chain alkyl compound. The peeling film protects the surface of the adhesive layer until the adhesive sheet is actually used, and is not peeled off during use.

The adhesive sheet of the present invention can be produced, for example, by applying the adhesive composition of the present invention to a release film and a substrate, and drying and curing for a certain period of time to form an adhesive layer. The aging conditions may be, for example, 1 to 10 days in an environment of 23 ° C. and 50% RH (relative humidity). By curing the adhesive layer, a (meth) acrylic copolymer can be sufficiently crosslinked by a toluene diisocyanate compound.

An adhesive sheet without a substrate type can be produced, for example, by applying the adhesive composition to the release-treated surface of the release film and drying it to form a layer of the adhesive composition. The exposed surface that is not in contact with the release film overlaps another release film to contact the release-treated surface, and is aged to form an adhesive layer.

A substrate-type adhesive sheet can be produced by a method of applying an adhesive composition to a substrate such as an optical film, or can be produced by a method of applying an adhesive composition to a release film. These methods include, for example, applying a pressure-sensitive adhesive composition to the release-treated surface of the release film and drying it to form a layer of the adhesive composition, and the exposed surface of the obtained layer that is not in contact with the release film. A method of bonding a substrate and curing it to form an adhesive layer.

Examples of the substrate having a substrate-type adhesive sheet include an optical film. Specific examples of the optical film include an optical film used in a liquid crystal display device. More specifically, optical films such as a polarizing plate, a retardation plate, an anti-reflection film, a viewing angle widening film, a brightness enhancement film, and an ITO film may be mentioned. Among these, as the base material of the adhesive sheet having a base material type, an optical film is preferable, and a polarizing plate is more preferable.

The polarizing plate may have at least a polarizing plate. For example, a polarizing plate having a protective film on one side of the polarizing plate and a polarizing plate having a protective film on both sides of the polarizing plate can be used. As a polarizing plate of the polarizing plate, for example, a polyvinyl alcohol (PVA) film having iodine adsorbed and oriented can be used, and as a protective film of the polarizing plate, for example, a cellulose triacetate (TAC) film can be used.

When a polarizing plate is used as a substrate, an adhesive layer can be formed on a PVA film or a TAC film.

Methods for applying an adhesive composition to a release film or a substrate include a gravure roll coater, a reverse roll coater, a kiss-roll coater, a dip roll coater, a coating rod, A known method of a knife coater, a spray coater, or the like.

The adhesive sheet of the present invention is suitable for bonding an optical film or the like of a liquid crystal display device. That is, the adhesive sheet of the present invention is suitable for bonding optical films such as a polarizing plate, a retardation film, an anti-reflection film, a viewing angle widening film, a brightness enhancement film, and an ITO film, and the above-mentioned optical film, liquid crystal cell, and glass Substrate and protective film bonding. In addition, the adhesive sheet of the present invention is suitable for bonding a touch panel with a liquid crystal cell, a glass substrate, a protective film, and the like.

As an example of the adhesive sheet of the present invention, a substrate-free type adhesive sheet having a structure (release film / adhesive layer / release film) obtained by laminating a release film on both sides of the adhesive layer may be cited; A substrate-type adhesive sheet having a structure (optical film / adhesive layer / release film) obtained by laminating an optical film on one side of the adhesive layer and a release film on the other side is provided. [Example]

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

[Production of (meth) acrylic copolymer] (Production Example 1) In a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux cooling tube, 99.99 parts by mass of butyl acrylate (BA) was added as (a After mixing 0.01 parts by mass of alkyl acrylate and 2-hydroxyethyl acrylate (2HEA) as a monomer having a hydroxyl group, and 110 parts by mass of ethyl acetate as a solvent, the reactor was replaced with nitrogen. Then, the mixture in the reactor was stirred while the temperature was raised to 70 ° C, and then 0.04 parts by mass of azobisdimethylvaleronitrile (ABVN) was sequentially added as a polymerization initiator and 40 parts by mass of ethyl acetate was used as a solvent. It was allowed to polymerize in hours. After the completion of the polymerization reaction, ethyl acetate was used as a solvent to dilute the solid content to 24.0% by mass. Thus, a solution of a BA / 2HEA copolymer ((meth) acrylic copolymer) was obtained.

(Production Example 2 to Production Example 13) In Production Example 2 to Production Example 13, when a (meth) acrylic copolymer was produced, it was used in the same manner as in Production Example 1 except that the monomer composition shown in the following Table 1 was used. Method to obtain a solution of a (meth) acrylic copolymer. In Table 1, MA indicates methyl acrylate, AA indicates acrylic acid, and 4HBA indicates 4-hydroxybutyl acrylate.

Table 1 shows the monomer composition (parts by mass), acid value, glass transition temperature (Tg), and weight average molecular weight (Mw) of the (meth) acrylic copolymers obtained in Production Examples 1 to 13. The acid value, Tg, and Mw of the (meth) acrylic copolymer are calculated and measured as described above. Specifically, the acid value of the (meth) acrylic copolymer of Production Example 7 was calculated as follows. (1 / 72.1) × 56.1 × 10 × 1 = 7.8 In addition, the molecular weight of AA is 72.1, and the number of carboxyl groups in one molecule of AA is 1. [Table 1]

[Preparation of Adhesive Composition] (Example 1) 416.7 parts by mass (solid content: 100.0 parts by mass) of a solution of the (meth) acrylic copolymer obtained in Production Example 1 was used as a toluene diisocyanate compound. CORONATEL (manufactured by Japan Polyurethanes Industry Co., Ltd., adduct of toluene diisocyanate and trimethylolpropane, 15.0 parts by mass) 20.0 parts by mass, Curezol TBZ (Shikoku Chemical Industry Co., Ltd. ) Manufactured by the company, 2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole) 0.3 parts by mass of KBM-403 (Shin-Etsu Chemical Industry Co., Ltd.) as a silane coupling agent (SC agent) The company produced 3-glycidoxypropyltrimethoxysilane, with an effective ingredient of 0.4 parts by mass) and 0.4 parts by mass was sufficiently stirred and mixed to obtain an adhesive composition.

(Examples 2 to 17) In Examples 2 to 17, the adhesive composition was prepared in the same manner as in Example 1 except that the composition of the adhesive composition shown in Table 2 below was set.

(Comparative Examples 1 to 4) In Comparative Examples 1 to 4, the solution of the (meth) acrylic copolymer obtained in Production Examples 7, 8, 12, and 13 was used instead of the (meth) acrylic acid obtained in Production Example 1. A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the solution was a copolymer solution. In addition, the (meth) acrylic copolymer obtained in Production Examples 7 and 8 had an acid value exceeding 2.5 mgKOH / g, and the (meth) acrylic copolymer obtained in Production Examples 12 and 13 was a 2HEA copolymerization component. They are less than 0.01% by mass and more than 1% by mass.

(Comparative Example 5) In Comparative Example 5, the same method as in Example 3 was used except that the amount of the toluene diisocyanate compound was less than 5 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer. An adhesive composition is prepared.

(Comparative Examples 6 and 7) In Comparative Example 6, in addition to the use of a xylene diisocyanate-based compound, Takenate D-110N (manufactured by Takeda Pharmaceutical Industries, Ltd.) in place of the toluene diisocyanate-based compound as a cross-linking agent, An adhesive composition was prepared by the same method as in Example 2. In Comparative Example 7, Sumijule N-75 (manufactured by Sumika Bayer Urethane Co., Ltd.), which is a hexamethylene diisocyanate-based compound, was used instead of toluene diisocyanate-based compound as a crosslinking agent. An adhesive composition was prepared in the same manner.

(Comparative Example 8) In Comparative Example 8, except that dibutyltin dilaurate was used instead of the imidazole compound as a crosslinking catalyst, an adhesive composition was prepared by the same method as in Example 3.

(Comparative Example 9) Comparative Example 9 was prepared in the same manner as in Example 2 except that the amount of the toluene diisocyanate compound was more than 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer. Adhesive composition.

[Production of Adhesive Sheet Samples] Using the adhesive composition of each of the examples and comparative examples obtained above, adhesive sheet samples were produced in the following order. First, an adhesive composition was applied on a surface of a release film (made by Fujimori Industry Co., Ltd., 100E-0010NO23) which had been surface-treated with a silicone-based release agent, so that the coating amount after drying became 20 g. / cm ² . Then, the release film after the adhesive composition was applied was dried at 100 ° C. for 90 seconds using a hot air circulation dryer to form a layer of the adhesive composition on the release film. Then, one side of a polarizing plate having a cellulose triacetate (TAC) / polyvinyl alcohol (PVA) / TAC structure was laminated with a layer of an adhesive composition on a release film and bonded, and pressed by a pressure roller Pick up. After compression bonding, autoclave treatment (50 ° C, 5kg / cm ² , 20 minutes), and curing at 35 ° C, 45% RH for 96 hours to produce a laminate with a release film / adhesive layer / polarizing plate Sample of a layered adhesive sheet.

The composition of the adhesive composition obtained in Examples 1 to 17 and Comparative Examples 1 to 9, the measurement results and evaluation results of the adhesive composition and the adhesive sheet samples are shown in Table 2 below.

[Table 2]

The crosslinking agents a to c and the crosslinking catalysts d to g shown in Table 2 are shown below. Crosslinking agent a: CORONATEL (manufactured by Japan Polyurethane Industries, Ltd., adduct of toluene diisocyanate and trimethylolpropane). Crosslinking agent b: Takenate D-110N (manufactured by Takeda Pharmaceutical Co., Ltd., Xylene diisocyanate compound) Crosslinking agent c: Sumijule N-75 (manufactured by Sumika Bayer Urethane Co., Ltd., hexamethylene diisocyanate compound) Crosslinking catalyst d: Curezol TBZ (Shikoku Chemical Industry ( Company), 2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole) Cross-linking catalyst e: Curezol 1B2MZ (manufactured by Shikoku Chemical Industry Co., Ltd., 1-benzyl -2-methylimidazole) Crosslinking catalyst f: Curezol 1B2PZ (manufactured by Shikoku Chemical Industries, Ltd., 1-benzyl-2-phenylphenylimidazole) Crosslinking catalyst g: Dibutyltin dilaurate SC agent : KBM-403 (by Shin-Etsu Chemical Industry Co., Ltd., 3-glycidoxypropyltrimethoxysilane)

In Table 2, "ND1" indicates that evaluation cannot be performed due to haze, and "ND2" indicates that evaluation cannot be performed due to peeling.

[Evaluation of ITO Corrosion Inhibition Properties] On the surface of the ITO film (trade name Tetolight TCF KB300N03-125-U3 / P, manufactured by Oike Industry Co., Ltd.) cut into a length of 30 mm × a width of 95 mm Both ends were thinly coated with a silver paste (trade name DOTITE FA-401CA, manufactured by Fujikura Kasei Co., Ltd.) so that the width became 15 mm, and fired at 140 ° C for 15 minutes. The adhesive sheet samples obtained using the adhesive composition of each example and each comparative example were cut into 30 mm in length × 75 mm in width, and the release film of the adhesive sheet sample was peeled off to expose the adhesive layer. After the exposed adhesive layer filled the gap between the silver paste and the silver paste, the adhesive sheet sample was attached to the conductive surface of the ITO film, and then cut into a length of 20 mm and a width of 95 mm. After cutting, autoclave treatment was performed under the conditions of 0.5 MPa, 40 ° C, and 30 minutes to obtain a corrosion inhibitory test sample. The probes of the tester were placed on the silver paste portions at both ends of the corrosion inhibition test sample, and the resistance value before the test was measured. Then, the corrosion-inhibition test sample was left to stand under conditions of 60 ° C. and 90% RH for 250 hours to perform a corrosion-inhibition test. Take out the corrosion-inhibition test sample after the test, and set the probes of the tester at the silver paste part at both ends of the corrosion-inhibition test sample under the environment of 23 ° C and 50% RH to measure the resistance value after the test. The rate of change of the resistance value is calculated from the resistance value before the test and the resistance value after the test according to the following formula. (Formula) Change rate of resistance value (%) = [(resistance value after test-resistance value before test) ÷ resistance value before test] × 100 According to the change rate (%) of the resistance value calculated by using the above formula, and The following evaluation criteria evaluated ITO corrosion resistance. In addition, if the evaluation result is A or B, the corrosion of ITO is small, and there is no problem in practical use. Evaluation Criteria A: The rate of change in resistance value was less than 10%. B: The change rate of the resistance value is 10% or more and less than 20%. C: The rate of change of the resistance value is 20% or more.

[Evaluation of Durability (80 ° C, 60 ° C × 90% RH)] A test piece having a length of 140 mm × 260 mm (long side) of 45 mm with respect to the absorption axis was prepared by cutting the adhesive sheet sample prepared as described above. And peeling off the release film of the test piece to expose the adhesive layer. Then, the exposed surface of the adhesive layer was brought into contact with one side of a 0.7 mm alkali-free glass plate "# 1737" manufactured by Corning Corporation, and attached using a laminator to prepare a sample for durability evaluation. Then, an autoclave treatment (50 ° C, 5 kg / cm ² , 20 minutes) was applied to the sample, and the sample was left for 24 hours under the conditions of 23 ° C and 50% RH. Then, they were left in a high-temperature environment of 80 ° C. or a high-temperature and high-humidity environment of 60 ° C. × 90% RH for 500 hours, and the state of blistering, peeling, or warping was visually observed, and evaluated according to the following evaluation criteria. In addition, if the evaluation result is A or B, the durability is excellent, and there is no problem in practical use. Evaluation criterion A: No blistering or peeling was observed at all. B: Foaming was hardly seen, and peeling did not occur at a position of 0.5 mm or more from the outer peripheral end of the two sides. C: Foaming was noticeable, and peeling occurred at a position more than 0.5 mm from the outer peripheral end of the two sides.

[Evaluation of White Spot] A test piece having a length of 140 mm × 260 mm (long side) having a length of 45 mm with respect to the absorption axis was prepared from the adhesive sheet sample prepared as described above, and the peeling film of the test piece was peeled off. The adhesive layer is exposed. Then, the sample of the adhesive sheet exposed by the adhesive layer was made to intersect the polarizing axes of the polarizing plates perpendicularly to each other, and the two sheets of 0.7 mm alkali-free glass plate "# 1737" manufactured by Corning Corporation were laminated using a laminator to Make white evaluation samples. Then, an autoclave treatment (50 ° C, 5 kg / cm ² , 20 minutes) was applied to the sample, and the sample was left for 24 hours under the conditions of 23 ° C and 50% RH. Then, it was left to stand at 70 ° C and 0% RH for 500 hours. After being left to stand, using a uniform light source under the conditions of 23 ° C. and 50% RH, the state of the white point was visually observed, and evaluation was performed according to the following evaluation criteria. In addition, if the evaluation result is A or B, white point suppression is excellent, and there is no problem in practical use. Evaluation criterion A: No white spots were observed at all. B: Almost no white spots were observed. C: Many white spots were observed.

[Evaluation of maturation time] The surface treatment surface of a release film (made by Fujimori Industry Co., Ltd., 100E-0010NO23) having been surface-treated with a silicone-based release agent was applied so that the thickness after drying was 20 μm. Adhesive composition. Then, the release film after the adhesive composition was applied was dried at 100 ° C. for 60 seconds using a hot air circulation dryer to form a layer of the adhesive composition on the release film. The surface-treated surface of a release film (made by Fujimori Industry Co., Ltd., 25E-0010BD) that has been surface-treated with a silicone-based release agent is bonded to a layer of the adhesive composition to produce an adhesive composition. Thin slices. Then, the produced adhesive layer was stored in an environment of 23 ° C. × 50% RH, and the gel fractions were measured after 96 hours and 168 hours from the start of storage, and evaluated according to the following evaluation criteria. In addition, if the evaluation result is A, the work efficiency is improved, and there is no problem in practical use. Evaluation Criteria A: The difference in gel fraction after 96 hours of aging and 168 hours after aging was within 3%. B: The difference in gel fraction between 96 hours after aging and 168 hours after aging was greater than 3%.

[Evaluation of pot life] Regarding the adhesive composition of each example and each comparative example, it has been confirmed that the coating film formed by applying the adhesive composition does not cause streak defects such as white turbidity and uneven application. And the storage time of the thickness can be evenly coated, which is the so-called pot life. Storage conditions were 23 ° C and 50% RH. The coating film was obtained by the following method. The release coating film (100E-0010NO23, manufactured by Fujimori Industry Co., Ltd.) has been surface-treated with a silicone-based release agent so that the coating amount after drying becomes 25 g / cm ² . The adhesive composition was dried at 100 ° C for 90 seconds using a hot air circulation dryer to obtain a coating film. The state of the dried coating film was visually observed at each storage time, and evaluated using the following evaluation criteria. In addition, if the evaluation result is A or B, there is no problem in practical use. Evaluation criterion A: When the storage time was 48 hours, no streak-like defects were observed in the coating film. B: When the storage time was 24 hours, no streak-like defects were observed on the coating film, but when it was 48 hours, streak-like defects were observed on the coating film. C: When the storage time was 24 hours, streak-like defects were observed on the coating film, and gelation occurred.

[Measurement of storage elastic modulus (G ')] The storage elastic modulus (G') of the adhesive composition of each example and each comparative example was measured by the following method. The prepared adhesive composition was coated, dried, and aged under the same conditions as in the production of the above-mentioned adhesive sheet sample to form a 20 μm adhesive layer. The adhesive layers were bonded to each other so that the formed adhesive layer had a thickness of 600 μm, and a dynamic viscoelasticity measuring device (Physica MCR301, manufactured by Anton Paar) was used, and the evaluation temperature was 30 ° C., using a cone: 8 mmφ, Measurement gap: 0.6 mm, while applying shear stress at a frequency of 1 Hz, the storage elastic modulus (G ') (Pa) was also measured. The results are shown in Table 2.

[Results] In Examples 1 to 17, it was found that the ITO corrosion resistance, durability (at 80 ° C. and 60 ° C. × 90% RH, respectively), white point, and aging period were all evaluated as B or higher, and there was no problem in practical use. On the other hand, in Comparative Examples 1 to 9, it was found that any of ITO corrosion inhibition, durability (at 80 ° C. and 60 ° C. × 90% RH, respectively), white point, and ripening period were evaluated as C or could not be measured ( Due to the haze and flaking caused by whitening), there are problems in practical use.

Claims (7)

An adhesive composition comprising: a (meth) acrylic copolymer having an acid value of 2.5 mgKOH / g or less, and containing 0.01% by mass to 1% by mass of all the structural units derived from a monomer having a hydroxyl group A structural unit; a toluene diisocyanate compound in a range of 5 to 30 parts by mass based on 100 parts by mass of the (meth) acrylic copolymer; and an imidazole compound represented by the following formula (I), In formula (I), R ₁ , R ₂ , and R ₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, R ₃ represents an alkyl group, an aryl group, or an aralkyl group, and R ₁ and R ₂ , or R ₃ and R ₄ may be connected to each other to form a cyclic structure. For example, the adhesive composition according to item 1 of the patent application range, wherein the content of the imidazole compound is in the range of 0.01 to 1.5 parts by mass relative to 100 parts by mass of the (meth) acrylic copolymer. For example, the adhesive composition according to item 1 or 2 of the patent application range includes a silane coupling agent in a range of 0.05 to 1 part by mass relative to 100 parts by mass of the (meth) acrylic copolymer. For example, the adhesive composition of claim 1 or 2, wherein the (meth) acrylic copolymer has an acid value of 0 mgKOH / g. For example, the adhesive composition of claim 1 or 2, wherein the toluene diisocyanate compound is an adduct of toluene diisocyanate and a polyol. For example, the adhesive composition in the first or second scope of the patent application, the value of the storage elastic modulus (G ') at 30 ° C after crosslinking is in the range of 2.0 × 10 ⁵ to 1.0 × 10 ⁷ Pa. An adhesive sheet has an adhesive layer formed from the adhesive composition according to any one of claims 1 to 6.