JP7119972B2 - ADHESIVE COMPOSITION AND ADHESIVE USING SAME, ADHESIVE FOR POLARIZING PLATE, AND IMAGE DISPLAY DEVICE - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive using the same, and a pressure-sensitive adhesive for polarizing plates, more specifically, the pressure-sensitive adhesive layer does not whiten even in a wet and heat environment, and furthermore, it has good reworkability. The present invention relates to a pressure-sensitive adhesive composition that forms a pressure-sensitive adhesive that is also excellent.

Conventionally, a polarizing plate, which is a polarizer made of a polyvinyl alcohol-based film or the like with polarizing properties and coated with protective films on both sides, is laminated on the surface of a liquid crystal cell in which an oriented liquid crystal component is sandwiched between two glass plates. and liquid crystal display panels are manufactured. Lamination of the polarizing plate on the surface of the liquid crystal cell is usually carried out by contacting and pressing an adhesive layer provided on the surface of the polarizing plate against the surface of the liquid crystal cell.

Adhesives containing polyvinyl alcohol-based resins are preferably used as adhesives for bonding these protective films and polarizers. A polarizing plate is manufactured by applying a protective film on top and then heating and drying it. In the manufacturing process of the polarizing plate, it is preferable that the moisture contained in the adhesive passes through the protective film, and a highly moisture-permeable triacetyl cellulose film (TAC film) has been suitably used as the protective film. .

However, in recent years, olefinic films, particularly cycloolefinic films (COP films) have come to be used as protective films for polarizers instead of TAC films from the viewpoint of dimensional stability and durability.

In addition, the adhesive used to bond the polarizing plate and the liquid crystal cell (glass substrate) is reworked so that it can be peeled off from the liquid crystal cell without leaving any adhesive residue in the event of misalignment or foreign matter being caught during bonding. sex is required.

On the other hand, when a protective film with low moisture permeability, such as a cycloolefin film, is used as the protective film for the polarizing plate, the pressure-sensitive adhesive layer turns white due to dew condensation when the temperature is returned to room temperature when exposed to a moist and hot environment. There was a problem (wet heat whitening phenomenon).

In response to such problems, Patent Document 1 proposes that a pressure-sensitive adhesive using an acrylic resin obtained by copolymerizing a large amount of a hydroxyl group-containing monomer is excellent in wet heat whitening resistance. Further, Patent Document 2 proposes that a pressure-sensitive adhesive using an oligomeric silane coupling agent is excellent in reworkability. Furthermore, Patent Document 3 proposes a pressure-sensitive adhesive using an alkali metal salt for the purpose of imparting antistatic performance to an acrylic pressure-sensitive adhesive.

JP 2013-213203 A JP 2016-44291 A Japanese Patent Publication No. 2011-51722

However, as in the technique disclosed in Patent Document 1, when many polar groups such as hydroxyl group-containing monomers are used in order to provide wet heat whitening resistance, the adhesive strength becomes too high, and the acrylic resin solution There is a problem that the storage stability is deteriorated. In addition, in the adhesive described in Patent Document 2, both the functional group equivalent and the amount of alkoxy groups are widely defined for the silane coupling agent (silicone alkoxy oligomer) used, and various types of silane coupling agents can be used. Although it is possible to use it, there is still room for improvement in wet heat whitening resistance when using a protective film with low moisture permeability such as a cycloolefin film. Furthermore, the technique disclosed in Patent Document 3 does not take wet heat whitening resistance into consideration at all, and is inferior in reworkability due to the use of a monomer type silane coupling agent.

Therefore, in the present invention, under such a background, a pressure-sensitive adhesive that does not cause whitening even when exposed to high-temperature and high-humidity conditions and is also excellent in reworkability is desired. The object is to provide an agent composition.

However, as a result of extensive research in view of such circumstances, the present inventors have found that, in a pressure-sensitive adhesive composition containing an acrylic resin, an alkali metal salt and an oligomeric silane coupling agent having a specific alkoxy group content are used in combination. By doing so, it was found that a pressure-sensitive adhesive that does not whiten even when exposed to high-temperature and high-humidity conditions, has excellent wet heat whitening resistance, and also has excellent reworkability can be obtained, and completed the present invention.

That is, the gist of the present invention is an acrylic resin (A), an alkali metal salt (B), and one or more reactive functional groups and one or more alkoxy groups in the structure, and the alkoxy group content is 15% by weight. It relates to a pressure-sensitive adhesive composition containing the following oligomeric silane coupling agent (C).

Furthermore, the present invention relates to a pressure-sensitive adhesive, a pressure-sensitive adhesive for polarizing plates, and an image display device using the pressure-sensitive adhesive composition.

The pressure-sensitive adhesive obtained using the pressure-sensitive adhesive composition of the present invention does not undergo whitening even when exposed to high-temperature and high-humidity conditions, has excellent wet heat whitening resistance, and is also excellent in reworkability. And, the pressure-sensitive adhesive composition of the present invention can be used as a pressure-sensitive adhesive suitable for various uses, especially for polarizing plates.

In the present invention, the acrylic resin contains an alkali metal salt and a silane coupling agent, and further, as the silane coupling agent, an oligomeric silane coupling agent having a relatively low alkoxy group content is used to obtain an alkali metal Although there was a concern that reworkability would deteriorate due to the inclusion of salt, the present inventors have found that a pressure-sensitive adhesive composition having excellent wet heat whitening resistance while maintaining reworkability without this problem can be obtained.

The present invention will be described in detail below.
In the present invention, (meth)acryl means acryl or methacryl, (meth)acryloyl means acryloyl or methacryloyl, and (meth)acrylate means acrylate or methacrylate. The acrylic resin is a resin obtained by polymerizing a polymerizable component containing at least one (meth)acrylic acid alkyl ester.

The adhesive composition of the present invention contains an acrylic resin (A), an alkali metal salt (B) and an oligomeric silane coupling agent (C).

<Acrylic resin (A)>
The acrylic resin (A) used in the present invention contains (meth)acrylic acid alkyl ester (a1) as a main component, preferably a polar group-containing monomer (a2), and optionally other copolymerizable monomers. An acrylic resin obtained by copolymerizing a copolymer component containing (a3) can be mentioned.
The term "contained as a main component" means that the content is usually 50% by weight or more, preferably 60% by weight or more, and particularly preferably 70% by weight or more, based on the total copolymer components.

Examples of the (meth)acrylic acid alkyl ester (a1) include those in which the number of carbon atoms in the alkyl group is usually 1 to 20 (preferably 1 to 18, particularly preferably 1 to 12, more preferably 1 to 8), Preferred are aliphatic (meth)acrylic acid alkyl esters, specifically methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-propyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate Acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, and the like. These may be used alone or in combination of two or more.

Among these (meth)acrylic acid alkyl esters (a1), methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate are preferred from the viewpoint of excellent adhesive properties and excellent stability during polymerization.

The content of the (meth)acrylic acid alkyl ester (a1) in the acrylic resin (A) is preferably 10% by weight or more, more preferably 30% by weight or more, and particularly preferably 50 to 99.9% by weight. . If the content is too small, adhesive physical properties and durability tend to decrease.

Further, from the viewpoint of excellent compatibility with the alkali metal salt (B), it is more preferable to contain methyl acrylate, ethyl acrylate, and n-butyl acrylate. % by weight or more is preferable, and 40 to 99.9% by weight is preferable.

Next, the polar group-containing monomer (a2) will be explained.
The polar group-containing monomer (a2) in the present invention refers to a copolymerizable ethylenically unsaturated monomer having a hydroxyl group-containing monomer, a carboxyl group-containing monomer, or a nitrogen atom-containing monomer. It preferably contains at least one selected from monomers, carboxyl group-containing monomers, and nitrogen atom-containing monomers.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl ( Acrylic acid hydroxyalkyl esters such as meth) acrylate, caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, oxyalkylene-modified monomers such as diethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, etc., 2- Primary hydroxyl group-containing monomers such as acryloyloxyethyl-2-hydroxyethyl phthalate, N-methylol (meth) acrylamide, hydroxyethyl acrylamide; 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3 - secondary hydroxyl group-containing monomers such as chloro 2-hydroxypropyl (meth)acrylate; and hydroxyl group monomers such as 2,2-dimethyl 2-hydroxyethyl (meth)acrylate.

Among the hydroxyl group-containing monomers, primary hydroxyl group-containing monomers are preferable in terms of excellent reactivity with the cross-linking agent and improved wet heat whitening resistance, and 2-hydroxyethyl (meth) acrylate in terms of stability during polymerization. is preferred, and 4-hydroxybutyl (meth)acrylate is preferred in terms of rapid reactivity with the cross-linking agent and short aging. Furthermore, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferable because they contain few impurities such as di(meth)acrylate and are easy to produce.

As the hydroxyl group-containing monomer, it is also preferable to use one having a content of di(meth)acrylate, which is an impurity, of 0.5% or less, particularly preferably 0.2% or less, and further preferably 0.1%. % or less, and specifically, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and 2-hydroxypropyl acrylate with such impurity amounts are particularly preferred.

Examples of the carboxyl group-containing monomer include dimer acids of acrylic acid such as (meth)acrylic acid and β-carboxyethyl acrylate. Meth)acrylic acid is preferred.

Examples of the nitrogen atom-containing monomer include amino group-containing monomers, amide group-containing monomers, and other nitrogen atom-containing monomers.

Examples of the amino group-containing monomer include primary amino group-containing monomers such as aminomethyl (meth)acrylate and aminoethyl (meth)acrylate; secondary amino group-containing monomers such as t-butylaminoethyl (meth)acrylate; Examples include tertiary amino group-containing monomers such as ethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate.
Among the above amino group-containing monomers, tertiary amino group-containing monomers are preferable in that they have a high cross-linking promoting effect and high resin storage stability.

Amide group-containing monomers include, for example, (meth)acrylamide; methoxymethyl (meth)acrylamide, ethoxymethyl (meth)acrylamide, propoxymethyl (meth)acrylamide, iso-propoxymethyl (meth)acrylamide, n-butoxymethyl (meth)acrylamide, ) acrylamide, alkoxyalkyl (meth)acrylamide monomers such as iso-butoxymethyl (meth)acrylamide; dialkyl (meth)acrylamide monomers such as dimethyl (meth)acrylamide and diethyl (meth)acrylamide; N-(hydroxymethyl)acrylamide hydroxyl group-containing amide monomers such as (meth)acryloylmorpholine and other heterocyclic amide monomers; and the like.

Among the above amide group-containing monomers, (meth)acryloylmorpholine, alkoxyalkyl (meth)acrylamide-based monomers, and dialkyl (meth)acrylamide-based monomers are preferred from the standpoint of resin solution stability and suppression of migration of antistatic agents. preferable.

Among such polar group-containing monomers (a2), it is preferable to have a hydroxyl group-containing monomer and a carboxyl group-containing monomer from the viewpoint of excellent reactivity with the cross-linking agent.

The content of the polar group-containing monomer (a2) is preferably 0.1 to 20% by weight, more preferably 0.2 to 15% by weight, and particularly preferably 0% by weight, based on the total copolymerization components. .5 to 10% by weight. If the content is too high, the reworkability tends to be lowered, and if it is too low, the durability tends to be lowered.

In applications where corrosion is a problem, when a carboxyl group-containing monomer is included as the polar group-containing monomer (a2), the content is preferably 1% by weight or less with respect to the entire copolymerization component. .

Other copolymerizable ethylenically unsaturated monomers (a3) include, for example, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) ) acrylates, aromatic ring-containing monomers such as orthophenylphenoxyethyl (meth)acrylate; cyclohexyl (meth)acrylate, cyclohexyloxyalkyl (meth)acrylate, tert-butylcyclohexyloxyethyl (meth)acrylate, isobornyl (meth)acrylate , Dicyclopentanyl (meth) acrylate and other alicyclic-containing monomers; 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) Acrylate, 2-butoxydiethylene glycol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate , octoxypolyethyleneglycol-polypropyleneglycol-mono(meth)acrylate, lauroxypolyethyleneglycol mono(meth)acrylate, stearoxypolyethyleneglycol mono(meth)acrylate, and other ether chain-containing monomers. These may be used alone or in combination of two or more.

Among these, it is easy to adjust the refractive index and birefringence, light leak resistance It is the ability to prevent light leakage), aromatic ring-containing monomers are preferable, and benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, and phenoxydiethylene glycol (meth) acrylate are particularly preferable, An alicyclic-containing monomer is preferred because it facilitates adjustment of the refractive index and birefringence and provides excellent adhesion to low-polar adherends (eg, cycloolefins, etc.).

The acrylic resin (A) used in the present invention contains a (meth)acrylic acid alkyl ester (a1), preferably a polar group-containing monomer (a2), and other copolymerizable ethylenically unsaturated monomers (a3). It can be produced, for example, by mixing or adding dropwise such polymerization components and a polymerization initiator into an organic solvent and polymerizing by using appropriately selected and contained polymerization components.

The above polymerization reaction can be carried out by conventionally known polymerization methods such as solution radical polymerization, suspension polymerization, bulk polymerization and emulsion polymerization. Among these, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred. polymerization.

Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, n-propyl alcohol, and isopropyl alcohol. and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone.

Among these organic solvents, ethyl acetate, acetone, methyl ethyl ketone, butyl acetate, toluene, methyl Isobutyl ketone is preferably used, more preferably ethyl acetate, acetone and methyl ethyl ketone.
These organic solvents may be used alone or in combination of two or more.

Further, the polymerization initiator used for such solution radical polymerization includes, for example, 2,2'-azobisisobutyronitrile and 2,2'-azobis-2-methylbutyronitrile, which are ordinary radical polymerization initiators. , 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis (methylpropionic acid) and other azo initiators, benzoyl peroxide, lauroyl peroxide, di-tert-butyl peroxide, Examples include organic peroxides such as cumene hydroperoxide and the like, which can be appropriately selected and used according to the monomer to be used. These polymerization initiators may be used alone or in combination of two or more.

The weight average molecular weight of the acrylic resin (A) thus obtained is preferably 400,000 to 2,500,000, particularly preferably 600,000 to 2,000,000, and still more preferably 800,000 to 1,800,000. If the weight-average molecular weight is too small, the durability tends to decrease. tend to

The degree of dispersion (weight average molecular weight/number average molecular weight) of the acrylic resin (A) is preferably 10 or less, particularly preferably 7 or less, and still more preferably 5 or less.
If the degree of dispersion is too high, the reworkability tends to deteriorate and the durability tends to deteriorate. The lower limit of such dispersity is usually 1.

The above weight average molecular weight is the weight average molecular weight in terms of standard polystyrene molecular weight. : Shodex GPC KF-806L (exclusion limit molecular weight: 2×10 ⁷ , separation range: 100 to 2×10 ⁷ , number of theoretical plates: 10,000 plates/line, filler material: styrene-divinylbenzene copolymer, filler Particle size: 10 μm), and the number average molecular weight can be measured by the same method. Further, the dispersity is obtained from the weight average molecular weight and the number average molecular weight.

The glass transition temperature (Tg) of the acrylic resin (A) is preferably -100 to -10°C, particularly preferably -70 to -10°C, and more preferably -65 to -15°C. If the glass transition temperature is too high, the tack tends to decrease, and if it is too low, the heat resistance tends to decrease.

Ｔｇ ：アクリル系樹脂（Ａ）のガラス転移温度（Ｋ）
Ｔｇａ：モノマーＡのホモポリマーのガラス転移温度（Ｋ）
Ｗａ：モノマーＡの重量分率
Ｔｇｂ：モノマーＢのホモポリマーのガラス転移温度（Ｋ）
Ｗｂ：モノマーＢの重量分率
Ｔｇｎ：モノマーＮのホモポリマーのガラス転移温度（Ｋ）
Ｗｎ：モノマーＮの重量分率
（Ｗａ＋Ｗｂ＋・・・＋Ｗｎ＝１） The glass transition temperature is calculated from the following Fox formula.

Tg: Glass transition temperature (K) of acrylic resin (A)
Tga: glass transition temperature of homopolymer of monomer A (K)
Wa: weight fraction of monomer A Tgb: glass transition temperature (K) of homopolymer of monomer B
Wb: weight fraction of monomer B Tgn: glass transition temperature (K) of homopolymer of monomer N
Wn: Weight fraction of monomer N (Wa + Wb + ... + Wn = 1)

That is, the glass transition temperature (Tg) of the acrylic resin (A) is obtained by applying the glass transition temperature and the weight fraction when each monomer constituting the acrylic resin (A) is a homopolymer to Fox's formula. This is the value calculated by
The glass transition temperature of a homopolymer of the monomers constituting the acrylic resin (A) is usually measured by a differential scanning calorimeter (DSC), and is JIS K7121-1987 or JIS K 6240. It can be measured by a method conforming to

The acrylic resin (A) generally has a refractive index of 1.440 to 1.600, preferably 1.460 to 1.550, and particularly preferably 1.470 to 1.500. It is preferable to reduce the difference in the refractive indices of the members to be laminated so as to reduce the optical loss at the interfaces of the members.

The above refractive index is a value obtained by measuring the acrylic resin (A) formed into a thin film at 23° C. with a NaD line using a refractive index measuring device (“Abbe refractometer 1T” manufactured by Atago Co., Ltd.).

The haze of the acrylic resin (A) single layer is preferably 1.0 or less, particularly preferably 0.8 or less, and still more preferably 0.5 or less. If the haze is too high, the image quality of the display tends to deteriorate.

Haze is determined by measuring diffuse transmittance and total light transmittance using HAZE MATER NDH2000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and substituting the obtained values of diffuse transmittance and total light transmittance into the following formula. , is calculated. This machine complies with JIS K7361-1.
Haze (%) = (diffuse transmittance/total light transmittance) x 100

Thus, the acrylic resin (A) used in the present invention is obtained.

<Alkali metal salt (B)>
The alkali metal salt (B) used in the present invention is a salt of an alkali metal cation and anion. Alkali metal cations include lithium cations, sodium cations and potassium cations . Among such alkali metal cations, lithium cations are preferred because they are particularly excellent in resistance to wet heat whitening.

Examples of the anion of the alkali metal salt (B) include organic anions and inorganic anions. Among such anions, sulfonium anions, imide anions, and fluorine-containing anions are preferable from the viewpoint of excellent wet heat whitening resistance.

Combinations of the above alkali metal cations and anions include, for example, N,N-bis(fluorosulfonyl)imidelithium, N,N-bis(trifluoromethanesulfonyl)imidelithium, N,N-bis(nonafluorosulfonylethane)imide Lithium and the like are preferable because they are particularly excellent in resistance to moist heat whitening.

The content of the alkali metal salt (B) is preferably 0.1 to 20 parts by weight, more preferably 1 to 15 parts by weight, based on 100 parts by weight of the acrylic resin (A). It is preferably 2 to 5 parts by weight. If the content is too small, the wet heat whitening resistance tends to be lowered, and if it is too large, the reworkability and durability tend to be lowered.

<Oligomer type silane coupling agent (C)>
A silane coupling agent is generally an organosilicon compound containing one or more reactive functional groups and one or more alkoxy groups in its structure.
In the present invention, the oligomeric silane coupling agent (C) contains one or more reactive functional groups and one or more alkoxy groups in its structure and the alkoxy group content is 15% by weight or less.

Examples of the reactive functional group include epoxy group, (meth)acryloyl group, mercapto group, hydroxyl group, carboxyl group, amino group, amide group, isocyanate group and the like. Among these, an epoxy group and a mercapto group are preferable from the viewpoint of excellent durability and reworkability.

The alkoxy group in the present invention refers to an alkoxy group derived from alkoxysilane, and does not include other alkoxy groups contained in the molecule.
For example, the ends of the polyether portion of the polyether-modified silane and the polyether structure are not included as alkoxy groups.
Examples of the alkoxy group include a methoxy group, an ethoxy group, a propidoxy group, and the like. Among these, an alkoxy group having 1 to 8 carbon atoms is preferable, an alkoxy group having 1 to 2 carbon atoms is particularly preferable, and specifically a methoxy group and an ethoxy group.

In addition, the oligomeric silane coupling agent (C) may have an organic substituent other than the reactive functional group and the alkoxy group, such as an alkyl group or a phenyl group.

The alkoxy group content of the oligomeric silane coupling agent (C) must be 15% by weight or less, preferably 1 to 15% by weight, particularly preferably 3 to 14.5% by weight, and more preferably 6 to 12% by weight. If the alkoxy group content is too high, the reworkability tends to deteriorate. If the amount is too small, the durability tends to decrease.

The weight-average molecular weight of the oligomeric silane coupling agent (C) is preferably 2,000 or more, particularly preferably 2,300 to 30,000, more preferably 3,000 to 20,000, still more preferably 4,000 to 18,000. When the weight average molecular weight is within the above range, the reworkability and durability tend to be well balanced.

The above weight average molecular weight is the weight average molecular weight in terms of standard polystyrene molecular weight, and can be measured by the following method.
Apparatus: Gel permeation chromatograph Detector: Differential refractive index detector RI (RI-8020 type manufactured by Tosoh Corporation, sensitivity 32)
Column: TSKgel guard column HHR-H (1 piece) (manufactured by Tosoh Corporation φ6 mm × 4 cm), TSKgel GMHHR-N (2 pieces) (manufactured by Tosoh Corporation φ7.8 mm × 30 cm)
Solvent: Tetrahydrofuran (THF)
Column temperature: 23°C
Flow rate: 1.0 mL/min

In addition, the reactive functional group equivalent weight of the oligomeric silane coupling agent (C) is preferably 1600 g/mol or less, particularly preferably 1500 g/mol or less, still more preferably 100 g/mol to 1000 g/mol, and particularly preferably. is between 150 and 900 g/mol, most preferably between 300 and 700 g/mol. If the functional group equivalent is within the above range, the durability tends to be excellent. If it is too much, the reworkability tends to deteriorate.

The oligomeric silane coupling agent (C) is an oligomeric silane coupling agent. It is an organosilicon compound (organosiloxane compound).

Examples of the oligomeric silane coupling agent (C) include oligomers obtained by partially hydrolyzing and polycondensing organosilicon compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropylmethyldiethoxysilane. Oligomeric epoxy group-containing silane coupling agents, such as type organosilicon compounds (epoxy group-containing silicone alkoxy oligomers, etc.), or oligomeric type organosilicon compounds obtained by ether-modifying a part of these oligomeric type organosilicon compounds; γ-mercaptopropyl and oligomeric mercapto group-containing silane coupling agents such as oligomeric organosilicon compounds (mercapto group-containing silicone alkoxy oligomers, etc.) obtained by partially hydrolyzing and polycondensing organosilicon compounds such as triethoxysilane.
From these, an oligomer type silane coupling agent may be appropriately selected and used so as to satisfy each condition. Moreover, the said oligomer-type silane coupling agent (C1) may use only 1 type, and may use 2 or more types together.

As the oligomer type silane coupling agent (C), specifically, "X-24-9590" (weight average molecular weight: 13,700, containing alkoxy group: methoxy group, Alkoxy group content: 9.5% by weight, reactive functional group: epoxy group, epoxy equivalent: 592 g/mol), "X-24-9589" (weight average molecular weight: 4,700, contained alkoxy group: ethoxy group, Alkoxy group content: 14.5%, reactive functional group: epoxy group, epoxy equivalent: 1509 g/mol), "X-24-9579A" and the like.
Among these, "X-24-9590" is particularly preferred.

The content of the oligomeric silane coupling agent (C) is preferably 0.001 to 2 parts by weight, particularly preferably 0.005 to 1 part by weight, relative to 100 parts by weight of the acrylic resin (A). , more preferably 0.01 to 0.5 parts by weight, more preferably 0.015 to 0.3. If the content is too high, bleed-out tends to occur and the durability tends to decrease, and if it is too low, the reworkability tends to decrease.

In addition, in the adhesive composition of the present invention, a silane coupling agent other than the oligomeric silane coupling agent (C) can be used within a range that does not impair the effects of the invention. If the content is too high, the durability tends to be lowered due to bleeding. Therefore, the content of the silane coupling agent other than the oligomeric silane coupling agent (C) is specifically 0.5 parts by weight or less with respect to 100 parts by weight of the acrylic resin (A). is preferred, more preferably 0.3 parts by weight or less, and particularly preferably 0.1 parts by weight or less.

The adhesive composition of the present invention preferably contains a cross-linking agent (D) in addition to the acrylic resin (A), alkali metal salt (B) and silane coupling agent (C).

<Crosslinking agent (D)>
Examples of the cross-linking agent (D) include isocyanate cross-linking agents, epoxy cross-linking agents, aziridine cross-linking agents, melamine cross-linking agents, aldehyde cross-linking agents, amine cross-linking agents, and metal chelate cross-linking agents. Among these, it is preferable to use an isocyanate-based cross-linking agent from the viewpoint of improving the adhesiveness to the substrate and having excellent reactivity with the acrylic resin (A).

Examples of the isocyanate-based cross-linking agents include tolylene diisocyanate-based cross-linking agents such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, xylylene diisocyanate-based cross-linking agents such as 1,3-xylylene diisocyanate, Aromatic isocyanate cross-linking agents such as diphenylmethane-based cross-linking agents such as diphenylmethane-4,4-diisocyanate and naphthalene diisocyanate-based cross-linking agents such as 1,5-naphthalenediisocyanate; isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 4,4 Alicyclic isocyanate cross-linking agents such as '-dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, norbornane diisocyanate; hexamethylene diisocyanate, trimethylhexa Aliphatic isocyanate cross-linking agents such as methylene diisocyanate; and adducts, burettes, and isocyanurates of the above isocyanate compounds.

Among these isocyanate-based cross-linking agents, tolylene diisocyanate-based cross-linking agents are preferable in terms of pot life and durability, and xylylene diisocyanate-based cross-linking agents or isocyanurate skeleton-containing isocyanate-based cross-linking agents are preferable in terms of shortening the aging time. A non-aromatic-free isocyanate-based cross-linking agent is preferred from the standpoint of yellowing resistance. Specifically, among these, tolylene diisocyanate, xylylene diisocyanate, adducts of hexamethylene diisocyanate and trimethylolpropane, and nurates are preferable in that they have an excellent balance of durability, pot life, and crosslinking speed. .

Examples of the epoxy-based cross-linking agent include bisphenol A/epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether. , trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidylerythritol, diglycerol polyglycidyl ether and the like.

Examples of the aziridine-based cross-linking agent include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4 '-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide) and the like.

Examples of the melamine-based cross-linking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexaptoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins. .

Examples of the aldehyde cross-linking agent include glyoxal, malondialdehyde, succindialdehyde, maleinedialdehyde, glutaredialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

Examples of the amine-based cross-linking agent include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetramine, diethylenetriamine, triethyltetramine, isophoronediamine, amino resins, and polyamides.

Examples of the metal chelate-based cross-linking agents include acetylacetone and acetoacetyl ester coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, panadium, chromium, and zirconium. mentioned.

The cross-linking agent (D) may be used alone or in combination of two or more.

The content of the crosslinking agent (D) is preferably 0.01 to 10 parts by weight, particularly preferably 0.05 to 5 parts by weight, more preferably 0.05 to 5 parts by weight, with respect to 100 parts by weight of the acrylic resin (A). is 0.08 to 3 parts by weight, particularly preferably 0.1 to 1.5 parts by weight. If the content is too low, the durability tends to decrease, and if it is too high, the stress relaxation property tends to decrease, the substrate tends to warp, and long-term aging tends to be required.

Furthermore, the pressure-sensitive adhesive composition of the present invention may contain, as other components, a resin component, an acrylic monomer, a polymerization inhibitor, an antioxidant, a corrosion inhibitor, a cross-linking accelerator, as long as the effects of the present invention are not impaired. Various additives such as radical generators, peroxides, radical scavengers, antistatic agents (excluding alkali metal salts), metals, resin particles and the like can be blended. In addition to the above, it may contain a small amount of impurities contained in raw materials for manufacturing constituent components of the pressure-sensitive adhesive composition.

The content of the other components is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, and further preferably 0.5 parts by weight or less, relative to 100 parts by weight of the acrylic resin (A). . If the content is too large, the compatibility with the acrylic resin (A) tends to decrease, and the wet heat whitening resistance tends to decrease.

Thus, by mixing the acrylic resin (A), the alkali metal salt (B) and the oligomeric silane coupling agent (C), preferably further the cross-linking agent (D), and optionally other components, A pressure-sensitive adhesive composition of the present invention can be obtained.

In addition, the mixing method is not particularly limited, and various methods such as a method of mixing each component at once, a method of mixing an arbitrary component and then mixing the remaining components all at once or sequentially, etc. are adopted. can do.

The pressure-sensitive adhesive composition of the present invention can be made into a pressure-sensitive adhesive by cross-linking (curing). An optical member with an adhesive layer can be obtained.
It is preferable to further provide a release sheet on the surface of the pressure-sensitive adhesive layer opposite to the surface of the optical member of the pressure-sensitive adhesive layer-attached optical member.

As a method for producing the optical member with the pressure-sensitive adhesive layer, [1] the pressure-sensitive adhesive composition is applied onto the optical member, dried, then a release sheet is attached, and the pressure-sensitive adhesive layer is dried at normal temperature (23° C.) or in a heated state. [2] A pressure-sensitive adhesive composition is coated on a release sheet, dried, and then laminated with an optical member, at least either at room temperature (23°C) or in a heated state. and the like. Among these methods, the method [2], in which aging is performed at room temperature, is preferable because it does not damage the optical member and is excellent in adhesiveness to the optical member.
In the above, it is particularly effective when the optical member is a polarizing plate.

Such aging treatment is carried out in order to balance the adhesive physical properties as the reaction time for chemical crosslinking of the adhesive, and the aging conditions are usually room temperature to 70° C. and the time is usually 1 to 30 days. Specifically, the conditions may be, for example, 23° C. for 1 to 20 days, 23° C. for 3 to 10 days, and 40° C. for 1 to 7 days.

When applying the pressure-sensitive adhesive composition, it is preferable to apply the pressure-sensitive adhesive composition after diluting it with a solvent. 30% by weight.

The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition. Ketone solvents such as methyl isobutyl ketone, aromatic solvents such as toluene and xylene, and alcohol solvents such as methanol, ethanol and propyl alcohol can be used. Among these, ethyl acetate and methyl ethyl ketone are preferably used in terms of solubility, drying property, price, and the like.

In addition, application of the pressure-sensitive adhesive composition is carried out by conventional methods such as roll coating, die coating, gravure coating, comma coating and screen printing.

The gel fraction of the pressure-sensitive adhesive layer produced by the above method is preferably 30 to 95% by weight, particularly preferably 35 to 90% by weight, more preferably 35 to 90% by weight, from the viewpoint of durability performance and suppression of decrease in degree of polarization. is 50 to 85% by weight. If the gel fraction is too low, the reworkability tends to deteriorate, and if it is too high, lifting and peeling tend to occur.

The gel fraction is a measure of the degree of cross-linking (degree of curing), and is calculated, for example, by the following method. That is, the adhesive is collected by picking from an adhesive sheet in which an adhesive layer is formed on a base material such as an optical member, especially a polarizing plate, wrapped in a 200-mesh SUS wire mesh, and acetic acid adjusted to 23 ° C. After immersion in ethyl for 24 hours, the weight percentage of the undissolved adhesive component remaining in the wire mesh is defined as the gel fraction.

The pressure-sensitive adhesive layer produced by the above method preferably has a moderate tackiness when touched with a finger, because it has good wettability when actually applied to an adherend, and workability tends to increase, which is preferable. .

As for the electrical properties of the pressure-sensitive adhesive layer obtained using the resin composition of the present invention, it is preferable that the surface resistance value is low as a countermeasure against static electricity, particularly preferably 5×10 ¹² Ω or less, further preferably 5×10 ¹¹ Ω. Below, it is particularly preferably 1×10 ¹¹ Ω or less. If the surface resistance value is too high, the pressure-sensitive adhesive tends to be electrified, which tends to cause display unevenness due to static electricity when used for liquid crystal displays.

In the present invention, the pressure-sensitive adhesive layer-bearing optical member, particularly the pressure-sensitive adhesive layer-bearing polarizing plate, is applied directly or, if a release sheet is provided, after peeling off the release sheet, the pressure-sensitive adhesive layer surface is laminated to a glass substrate, for example. It is provided for a liquid crystal display panel.

The reworkability of the pressure-sensitive adhesive of the present invention is preferably such that the pressure-sensitive adhesive layer does not adhere to the adherend when peeled off. Also, the adhesive strength at the time of peeling is preferably 30 N/25 mm or less, more preferably 0.1 to 25 N/mm, particularly preferably 0.1 to 20 N/mm. If the adhesive strength is too high, the adherend tends to be easily damaged during rework.

The adhesive strength is calculated as follows.
The polarizing plate with an adhesive layer was cut into a width of 25 mm, the release film was peeled off, and the adhesive layer side was pressed against an alkali-free glass plate (manufactured by Corning, "Eagle XG") to form a polarizing plate. A glass plate is laminated. After that, autoclave treatment (50° C., 0.5 MPa, 20 minutes) is performed, and after leaving for 24 hours at 23° C. and 50% RH, a peeling test is performed at a peeling angle of 180° and a peeling rate of 300 mm/min. As for long-term reworkability, a peeling test is performed at a peeling angle of 180° and a peeling rate of 300 mm/min after leaving the film at 23° C. and 50% RH for a predetermined period after autoclave treatment.

The pressure-sensitive adhesive composition of the present invention can provide a pressure-sensitive adhesive that is excellent in durability and wet heat whitening resistance, as well as storage stability and reworkability in a well-balanced manner. It is useful as a pressure-sensitive adhesive for polarizing plates that bonds polarizing plates and glass substrates together.

Examples of the protective film that constitutes the polarizing plate include triacetyl cellulose film, acrylic film, polyethylene film, polypropylene film, cycloolefin film, etc. The present invention is applicable to the polarizing plate using any of the protective films. A polarizing plate laminated with a cycloolefin film is particularly preferable because the effect of the present invention can be easily obtained.

Further, by using the adhesive, the polarizing plate and the liquid crystal cell can be bonded together to produce an image display device, and the resulting image display device can be produced with high accuracy and has excellent durability.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, "parts" and "%" mean weight standards.

First, various acrylic resins were prepared as follows. The weight average molecular weight, dispersity, and glass transition temperature of the acrylic resin (A) and the silane coupling agent (B) were measured according to the methods described above.
The viscosity was measured in accordance with JIS K5400 (1990) 4.5.3 rotational viscometer method.

<Acrylic resin (A)>
The following were prepared as the acrylic resin (A) (see Table 1).

[Production of acrylic resin (A-1)]
71.3 parts of n-butyl acrylate (a1), 8 parts of 2-hydroxyethyl acrylate (a2), acrylic 0.7 parts of acid (a2), 20 parts of benzyl acrylate (a3), 53 parts of ethyl acetate, 42 parts of acetone, and 0.013 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator were charged, and the internal temperature was adjusted to the boiling point. to start the reaction. Then, 30 parts of an ethyl acetate solution containing 0.04% of AIBN was added dropwise, and after reacting at reflux temperature for 3.25 hours, it was diluted with ethyl acetate to give an acrylic resin (A-1) solution (solid content: 21.3%). , viscosity 5,440 Pa·s/25°C, acrylic resin (A-1); weight average molecular weight 1,270,000, glass transition temperature -42°C, dispersion degree 4.3).

[Production of acrylic resin (A-2)]
69.3 parts of n-butyl acrylate (a1), 10 parts of 2-hydroxyethyl acrylate (a2), acrylic 0.7 parts of acid (a2), 20 parts of benzyl acrylate (a3), 53 parts of ethyl acetate, 42 parts of acetone, and 0.013 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator were charged, and the internal temperature was adjusted to the boiling point. to start the reaction. Then, 30 parts of an ethyl acetate solution containing 0.04% of AIBN was added dropwise, and after reacting at reflux temperature for 3.25 hours, it was diluted with ethyl acetate to obtain an acrylic resin (A-2) solution (solid content: 21.5%). , viscosity 6,840 Pa·s/25°C, acrylic resin (A-2); glass transition temperature -41°C, weight average molecular weight 1,270,000, dispersion degree 4.3).

[Production of acrylic resin (A-3)]
91.3 parts of n-butyl acrylate (a1), 8 parts of 2-hydroxyethyl acrylate (a2), acrylic 0.7 parts of acid (a2), 53 parts of ethyl acetate, 42 parts of acetone, and 0.013 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator were charged, and the internal temperature was raised to the boiling point to initiate the reaction. rice field. Then, 30 parts of an ethyl acetate solution containing 0.04% of 2,2-azobis-2,4-dimethylvaleronitrile (ADVN) was added dropwise, reacted at reflux temperature for 3.25 hours, and diluted with ethyl acetate to give an acrylic solution. System resin (A-3) solution (solid content 21.7%, viscosity 6,000 Pa s / 25 ° C., acrylic resin (A-3); glass transition temperature -53 ° C., weight average molecular weight 1,390,000, degree of dispersion 3.5) was obtained.

The monomers used above were from the following manufacturers.
・ n-butyl acrylate (Tg-56 ° C. manufactured by Mitsubishi Chemical Corporation)
・ 2-hydroxyethyl acrylate (Tg-15 ° C. manufactured by Osaka Organic Chemical Co., Ltd.)
・Acrylic acid (Tg106°C, manufactured by Mitsubishi Chemical Corporation)
・ Benzyl acrylate (Viscoat #160 Tg 6 ° C. manufactured by Osaka Organic Chemical Co., Ltd.)
Moreover, the above Tg is the Tg of a homopolymer of each monomer.

<Alkali metal salt (B)>
The following alkali metal salts were prepared.
(B-1) N,N-bis(trifluoromethanesulfonyl)imidelithium (manufactured by Morita Chemical Co., Ltd.)

<Ionic compound (B') other than alkali metal salt>
The following ionic compounds other than alkali metal salts were prepared.
(B'-1) tributylmethylammonium-N,N-bis(trifluoromethanesulfonyl)imide

<Silane coupling agent>
The following were prepared as an oligomer type silane coupling agent and a monomer type coupling agent. The weight average molecular weight of the oligomeric silane coupling agent was measured according to the method described above. As for the content of alkoxy groups, reactive functional groups, epoxy equivalents or mercapto equivalents, and alkoxy groups contained, catalog values were used unless otherwise specified.

(C-1): Shin-Etsu Chemical Co., Ltd., "X-24-9590" (weight average molecular weight: 13,700, alkoxy group content: 9.5%, reactive functional group: epoxy group, epoxy equivalent: 592 g / mol, containing alkoxy group: methoxy group)

(C-2): "X-24-9589" manufactured by Shin-Etsu Chemical Co., Ltd. (weight average molecular weight: 4,700, alkoxy group content: 14.5%, reactive functional group; epoxy group, epoxy equivalent: 1509 g / mol, containing alkoxy group: ethoxy group)

As for the amount of alkoxy group at C-2 and the epoxy equivalent, values measured by the following method were used.

[X-24-9589]
About 50 mg of the sample was weighed into a vial and dissolved in 1 mL of d-chloroform to prepare a 5% (w/v) chloroform solution. This was placed in a sample tube for NMR measurement, and 1H NMR measurement was performed under the following conditions.

≪Measurement conditions≫
Measuring device: Ascend TM 400 manufactured by Bruker
Probe: cryo probe Pulse program: single pulse Measurement temperature: 23°C (296K)
Accumulation times: 16 times Pulse delay time: 10 sec

(C'-1): Shin-Etsu Chemical Co., Ltd., "X-41-1059A" (weight average molecular weight: 2,270, alkoxy group content: 42%, reactive functional group: epoxy group, epoxy equivalent: 350 g / mol, containing alkoxy group: methoxy group, ethoxy group)

(C'-2): Shin-Etsu Chemical Co., Ltd., "KBM-403" (monomeric silane coupling agent alkoxy group content: 39% (value calculated from structural formula), reactive functional group: epoxy group, Epoxy equivalent 236.3 g / mol, containing alkoxy group: methoxy group)

<Crosslinking agent (D)>
The following were prepared as a cross-linking agent (D).
(D-1): Adduct of tolylene diisocyanate and trimethylolpropane (manufactured by Tosoh Corporation, "Coronate L55E")

<Examples 1-2, Comparative Examples 1-5>
The above components were blended as shown in Table 2 below, and the solid content concentration was adjusted to 12.5% with ethyl acetate to obtain an adhesive composition.

Using the pressure-sensitive adhesive composition obtained above, evaluation samples were prepared as described below, and the following performances were evaluated. Evaluation results are shown in Tables 3 and 4.

[Production of pressure-sensitive adhesive layer-attached polarizing plates [I] and [II]]
The obtained pressure-sensitive adhesive composition was applied to a release sheet having a thickness of 38 μm ("Lumirror SP-0138BU" manufactured by Mitsui Chemicals Tohcello Co., Ltd.) so that the thickness after drying was 25 μm, dried at 100 ° C. for 3 minutes, A polarizing plate having triacetyl cellulose (TAC) films laminated on both sides was laminated with the pressure-sensitive adhesive layer on the opposite side of the release sheet on one TAC film surface, and aged in an environment of 23°C x 50% RH for 7 days. , to obtain a polarizing plate [I] with an adhesive layer (layer structure: release sheet/adhesive layer/TAC film 1/polarizer/TAC film 2). (TAC film 1: thickness 40 μm, TAC film 2: 60 μm)
A pressure-sensitive adhesive layer-attached polarizing plate [II] was obtained in the same manner, except that the COP surface of the corona-treated cycloolefin film/polarizer/TAC film was bonded to the pressure-sensitive adhesive layer surface.
The TAC film is a triacetyl cellulose film (thickness 60 μm), and the COP film is a cycloolefin film (thickness 50 μm).
The following evaluations were performed using the pressure-sensitive adhesive layer-attached polarizing plate [I] and the pressure-sensitive adhesive layer-attached polarizing plate [II].

[Reworkability]
The polarizing plate [I] with the adhesive layer obtained above was cut to a width of 25 mm, the release sheet was peeled off, and the adhesive layer surface was made of non-alkali glass ("Eagle XG" manufactured by Corning: thickness 1.1 mm). After pressing, laminating with a 2 kg roller, autoclave treatment (0.5 MPa × 50 ° C. × 20 minutes), left at rest in an environment of 23 ° C. × 50% RH for 1 day and 20 days, then peeled off. The adhesive strength was measured when peeled off at an angle of 180° and a peel speed of 300 mm/min, and evaluated according to the following criteria.

(Evaluation criteria) 1 day later ◎: Less than 10 N/25 mm and no adhesive residue ○: 10 N/25 mm or more and less than 30 N/25 mm and no adhesive residue △: 30 N/25 mm or more with no adhesive residue ×: Adhesive residue (evaluation criteria) 20 days later ◎: Less than 25 N/25 mm and no adhesive residue ○: 25 N/25 mm or more and less than 30 N/25 mm and no adhesive residue △: 30 N/25 mm or more with no adhesive residue ×・・・Adhesive residue

〔durability〕
The obtained polarizing plates [I] and [II] with an adhesive layer were cut into pieces of 20 cm × 15 cm, the release sheet was peeled off, and the adhesive layer surface was covered with non-alkali glass ("Eagle XG" manufactured by Corning Inc.: thickness 1.5 cm). 1 mm) and pasted together by reciprocating twice with a 2 kg roller, followed by autoclave treatment (0.5 MPa×50° C.×20 minutes) to prepare a sample for initial durability test.
The obtained samples were subjected to the following evaluations with respect to the polarizing plate after exposure under the conditions of (1) heat resistance (80° C.×500 hours).
(Evaluation criteria)
◯: foaming on the entire surface of the polarizing plate or no floating at the edges ×: foaming on the entire surface of the polarizing plate or floating at the edges

[Wet heat whitening resistance]
The obtained polarizing plate [II] with an adhesive layer was cut into a size of 3.5 cm×3.5 cm, the release sheet was peeled off, and the adhesive layer surface was covered with non-alkali glass ("Eagle XG" manufactured by Corning Inc.: thickness 1.5 cm). 1 mm) and pasted together by two reciprocating motions with a 2 kg roller, followed by autoclave treatment (0.5 MPa x 50°C x 20 minutes) to prepare a sample for wet heat whitening resistance test.
Initial haze was measured for the resulting sample. Then, after exposure to an environment of 60° C.×90% RH for 250 hours, it was taken out and allowed to stand at room temperature. Then, the haze immediately after removal was measured to evaluate the wet heat whitening resistance. The haze value is a value obtained by subtracting the value of 1.1 mm alkali-free glass as a blank.
(Evaluation criteria) · Haze immediately after removal ○ ... less than 1% × ... 1% or more

[Gel fraction]
The release sheet of the obtained polarizing plate with adhesive layer [I] was peeled off, the adhesive was picked from the adhesive layer surface, wrapped in a SUS 200-mesh wire mesh, and then placed in ethyl acetate adjusted to 23° C. for 24 hours. After immersion, the weight percentage of the undissolved adhesive component remaining in the wire mesh was defined as the gel fraction (%).

[Antistatic property]
<Surface resistance value>
After the adhesive layer-attached polarizing plate [I] was allowed to stand in an atmosphere of 23° C.×50% RH for 24 hours, the release sheet of the adhesive layer was removed and a surface resistivity measuring device (manufactured by Mitsubishi Chemical Analytech, Inc.) was measured. The surface resistivity (Ω/cm ² ) of the pressure-sensitive adhesive layer was measured using an apparatus named "Hiresta-UP MCP-HT450").

From the above results, an acrylic resin (A) containing a polar group-containing monomer more than usual, an alkali metal salt (B), and an acrylic resin using an oligomer-type silane coupling agent (C) having an alkoxy group content of 15% by weight or less It can be seen that Examples 1 and 2 using the adhesive obtained from the adhesive composition are excellent in reworkability and wet heat whitening resistance.
On the other hand, it can be seen that Comparative Examples 1 to 3, in which no alkali metal salt is used, are excellent in reworkability but inferior in wet heat whitening resistance. Comparative Examples 4 and 5, in which an alkali metal salt was used but did not use a silane coupling agent having an alkoxy group content of 15% by weight or less, were excellent in wet heat whitening resistance but inferior in reworkability. .

The whitening phenomenon of the pressure-sensitive adhesive layer is considered to be caused by condensation of water that has entered the pressure-sensitive adhesive layer under high-temperature and high-humidity conditions when the temperature returns to room temperature, and further agglomeration and whitening. It is presumed that when a highly hygroscopic alkali metal salt is used, the alkali metal salt dispersed in the adhesive effectively disperses water and suppresses whitening.
In addition, since alkali metal salts have high hygroscopicity, if a silane coupling agent with a large amount of alkoxy groups is used, the reworkability will deteriorate due to the hydrolysis reaction of the silane coupling agent. It is presumed that by using the agent, even if an alkali metal salt is used, excessive reaction does not occur and reworkability can be maintained.

The pressure-sensitive adhesive composition of the present invention exhibits excellent reworkability over a long period of time when used as a pressure-sensitive adhesive for bonding a polarizing plate (protective film) and a liquid crystal cell (glass) during the manufacture of a liquid crystal display device. And, even when using a polarizing plate with a low-polarity film such as a cycloolefin film as a protective film, it is possible to obtain a pressure-sensitive adhesive excellent in resistance to moist and heat whitening. It is useful as a pressure-sensitive adhesive for optical members for bonding optical components, particularly as a pressure-sensitive adhesive for polarizing plates for bonding a polarizing plate and a glass substrate of a liquid crystal cell.

Claims (9)

An acrylic resin (A), an alkali metal salt (B), and an oligomer-type silane coupling containing one or more reactive functional groups and one or more alkoxy groups in the structure and an alkoxy group content of 15% by weight or less. containing an agent (C) ,
the alkali metal salt (B) is a salt of an alkali metal cation and anion;
the alkali metal cation is a lithium cation, a sodium cation, or a potassium cation;
A pressure-sensitive adhesive composition, wherein the oligomeric silane coupling agent (C) has a reactive functional group equivalent weight of 100 g/mol to 1000 g/mol . 2. The pressure-sensitive adhesive composition according to claim 1, wherein the oligomeric silane coupling agent (C) has a weight average molecular weight of 2,000 or more. A copolymer component in which the acrylic resin (A) contains 0.1 to 20% by weight of at least one polar group-containing monomer (a2) selected from hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen atom-containing monomers. 3. The pressure-sensitive adhesive composition according to claim 1, which is a copolymerized acrylic resin. The adhesive composition according to any one of claims 1 to 3, wherein the content of the alkali metal salt (B) is 0.1 to 20 parts by weight per 100 parts by weight of the acrylic resin (A). . The adhesive according to any one of claims 1 to 4, wherein the content of the oligomeric silane coupling agent (C) is 0.001 to 2 parts by weight with respect to 100 parts by weight of the acrylic resin (A). agent composition. 6. The pressure-sensitive adhesive composition according to any one of claims 1 to 5, further comprising a cross-linking agent (D). 7. A pressure-sensitive adhesive obtained by cross-linking the pressure-sensitive adhesive composition according to any one of claims 1 to 6. A pressure-sensitive adhesive for a polarizing plate, which is obtained by using the pressure-sensitive adhesive according to claim 7. 8. An image display device comprising a polarizing plate and a liquid crystal cell bonded together with the pressure-sensitive adhesive according to claim 7.