CN109563387B

CN109563387B - Acrylic adhesive composition, and adhesive, adhesive for polarizing plate, and image display device each using same

Info

Publication number: CN109563387B
Application number: CN201780044213.6A
Authority: CN
Inventors: 三谷直也; 秋月伸介; 今泉早织; 三谷圣子
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Kasei Corp
Priority date: 2016-08-17
Filing date: 2017-08-10
Publication date: 2021-03-02
Anticipated expiration: 2037-08-10
Also published as: JP6950531B2; JPWO2018034231A1; KR20190040186A; TW201817839A; KR102358556B1; WO2018034231A1; CN109563387A; TWI728167B

Abstract

Providing: when used as an adhesive for attaching a polarizing plate (protective film) to a liquid crystal cell (glass) in the production of a liquid crystal display device, the adhesive exhibits excellent reworkability over a long period of time, is less susceptible to moisture, and does not cause a decrease in durability. An acrylic adhesive composition comprising: an acrylic resin (A); and a silane coupling agent (B) having a structure containing 1 or more reactive functional groups and alkoxy groups, respectively, wherein the silane coupling agent (B) contains a silane coupling agent (B1) having an alkoxy group content of 15 wt% or less and a silane coupling agent (B2) having an alkoxy group content of 20 wt% or more.

Description

Acrylic adhesive composition, and adhesive, adhesive for polarizing plate, and image display device each using same

Technical Field

The present invention relates to an acrylic pressure-sensitive adhesive composition, and a pressure-sensitive adhesive for polarizing plates each using the same, and more particularly to: an acrylic pressure-sensitive adhesive composition which exhibits excellent reworkability over a long period of time and can form a pressure-sensitive adhesive which is less susceptible to moisture and does not cause a decrease in durability.

Conventionally, an image display device has been manufactured by covering both surfaces of a polarizing plate formed of a polarizing film or the like having a polarizing property with a protective film, and laminating the polarizing plate on the surface of a liquid crystal cell having a liquid crystal component aligned between 2 glass plates. In order to laminate a polarizing plate on the surface of the liquid crystal cell, generally, the following is performed: the adhesive layer provided on the surface of the polarizing plate is pressed against the liquid crystal cell surface, and the liquid crystal cell surface is pressed.

As the adhesive for attaching the protective film to the polarizing plate, an adhesive containing a polyvinyl alcohol resin is suitably used, and specifically, an aqueous solution containing a polyvinyl alcohol resin and a crosslinking agent is applied to the polarizing plate, and the protective film is laminated thereon, followed by heating and drying to produce a polarizing plate. In the process of producing the polarizing plate, it is preferable that moisture contained in the adhesive passes through the protective film, and a cellulose triacetate film (TAC film) having high moisture permeability has been suitably used as the protective film, but in recent years, an acrylic film, a polyester film, an olefin film, or the like has been used in place of the TAC film from the viewpoint of dimensional stability and durability. As the olefin-based film, in particular, a cycloolefin-based film (COP film) has been used as a protective film of a polarizing plate.

The adhesive used for attaching the polarizing plate to the liquid crystal cell (glass substrate) is required to have durability such as heat resistance and moist heat resistance. In particular, in a high-temperature and high-humidity environment, the following problems occur: moisture penetrates into the adhesive layer, the adhesion to the glass substrate is reduced, and the polarizing plate partially floats or peels off from the glass substrate. In order to solve such a problem, a silane coupling agent is compounded into the adhesive to improve the moist heat resistance, but in the case of compounding the silane coupling agent, if the polarizing plate with the adhesive layer is stored for a long time, the silane coupling agent is inactivated by moisture in the environment or moisture in the polarizing plate, and a new problem of lowering the durability occurs.

Further, an adhesive used for attaching the polarizing plate to the liquid crystal cell (glass substrate) is required to have reworkability to peel the polarizing plate and reuse the liquid crystal cell when a foreign substance is caught or a positional deviation occurs when the polarizing plate is attached to the liquid crystal cell.

Further, in recent years, since the yield is improved due to the improvement of the precision of the manufacturing process, the reworking process is performed after a certain number of defective products are accumulated, unlike the conventional case where defective products are generated, and the adhesive is required to be capable of maintaining the reworkability for a longer time than the conventional adhesive.

In addition, when a film having a low moisture permeability other than the TAC film, particularly a cycloolefin film is used, if the film is exposed to a moist heat environment, there is a problem that a whitening phenomenon occurs in the pressure-sensitive adhesive layer. This is considered to be because moisture that has slowly entered the pressure-sensitive adhesive layer in a moist heat environment is exposed to normal temperature and condensed, and further because the moisture is covered with a film having low moisture permeability, the moisture cannot be removed and the moisture is accumulated, resulting in whitening.

In response to such a problem, an adhesive having improved resistance to wet heat whitening by using an acrylic resin copolymerized with a plurality of polar group-containing monomers has been proposed.

However, the pressure-sensitive adhesive using the acrylic resin obtained by copolymerizing a large amount of polar group-containing monomers as described above has a problem that the adhesive property to the glass interface is increased due to the influence of the polar group, or the pressure-sensitive adhesive layer is liable to absorb moisture, and hydrolysis of the silane coupling agent is accelerated, whereby the reworkability and the storage stability are further deteriorated.

As such an adhesive excellent in reworkability and initial wet heat resistance, for example, patent document 1 describes an adhesive composition containing: 100 parts by weight of a binder resin (A); and 0.1 to 20 parts by weight of an organoalkoxy oligomer (B) having an epoxy equivalent of 100 to 2000g/mol and an alkoxy group content of 5 to 60% by weight, wherein the binder resin (A) is at least 1 selected from the group consisting of an acrylic binder resin (A1) obtained by polymerizing a monomer having no carboxyl group, a urethane binder resin (A2), and a polyester binder resin (A3).

As an adhesive having excellent resistance to wet-heat whitening, for example, patent document 2 proposes an adhesive using an acrylic resin having an increased amount of hydroxyl groups.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-44291

Patent document 2: japanese patent laid-open publication No. 2013-213203

Disclosure of Invention

Problems to be solved by the invention

However, in the adhesive described in patent document 1, the silane coupling agent (silicone alkoxy oligomer) used is limited in functional group equivalent and alkoxy group content in a wide range, and various types of silane coupling agents can be used, but the adhesive using a silane coupling agent having a large alkoxy group content has a problem that the adhesive strength is low initially and after heating, but the long-term reworkability is poor.

As described in patent document 1, a pressure-sensitive adhesive using a silane coupling agent having a low alkoxy group content for improving reworkability has a problem of poor storage stability while having excellent reworkability.

Further, patent document 2 proposes an adhesive having excellent resistance to wet-heat whitening, but no consideration is given to long-term reworkability and storage stability, and further improvement is required.

Therefore, under such circumstances, the present invention provides an acrylic adhesive composition which, when used as an adhesive for attaching a polarizing plate (protective film) to a liquid crystal cell (glass) in the production of an image display device, can provide an adhesive exhibiting excellent reworkability over a long period of time, which is less susceptible to moisture and which does not cause a decrease in durability, and which, when polar groups are increased in consideration of wet-heat whitening resistance, has excellent reworkability and storage stability.

Means for solving the problems

Accordingly, the present inventors have made extensive studies in view of the above circumstances, and as a result, have found that: an acrylic pressure-sensitive adhesive composition containing an acrylic resin and a silane coupling agent, wherein the combination of a silane coupling agent having a small alkoxy group content and a silane coupling agent having a large alkoxy group content, provides an acrylic pressure-sensitive adhesive composition which exhibits excellent reworkability over a long period of time, is less susceptible to moisture, and does not cause a reduction in durability.

That is, the invention of claim 1 is an acrylic pressure-sensitive adhesive composition comprising: an acrylic resin (A); and a silane coupling agent (B) having a structure containing 1 or more reactive functional groups and alkoxy groups, respectively, wherein the silane coupling agent (B) contains a silane coupling agent (B1) having an alkoxy group content of 15 wt% or less and a silane coupling agent (B2) having an alkoxy group content of 20 wt% or more.

The invention also provides a2 nd aspect of the invention, which is obtained by crosslinking the acrylic adhesive composition of the 1 st aspect with a crosslinking agent (C), a3 rd aspect of the invention, which is obtained by using the adhesive of the 2 nd aspect, and a 4 th aspect of the invention, which is obtained by bonding a polarizing plate and a liquid crystal cell with the adhesive of the 2 nd aspect.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention is an acrylic adhesive composition comprising: the acrylic resin (A) and the silane coupling agent (B) having a structure containing 1 or more reactive functional groups and alkoxy groups, respectively, wherein the silane coupling agent (B) contains a silane coupling agent (B1) having an alkoxy group content of 15 wt% or less and a silane coupling agent (B2) having an alkoxy group content of 20 wt% or more. Therefore, the pressure-sensitive adhesive obtained using the acrylic pressure-sensitive adhesive composition of the present invention is very useful as a pressure-sensitive adhesive for polarizing plates, which exhibits excellent reworkability over a long period of time, is less susceptible to moisture, and does not cause a decrease in durability when used as a pressure-sensitive adhesive for attaching a polarizing plate (protective film) to a liquid crystal cell (glass) in the production of an image display device.

The acrylic resin (A) is an acrylic resin containing 5 to 50 wt% of structural units derived from at least 1 polar group-containing monomer (a1) selected from a hydroxyl group-containing monomer, a carboxyl group-containing monomer and a nitrogen-containing monomer, and has excellent wet-heat whitening resistance and adhesive properties.

When the reactive functional group equivalent of the silane coupling agent (B1) is 1600g/mol or less, the durability is further excellent.

When the weight average molecular weight of the silane coupling agent (B1) is 3000 or more, the reworkability and durability are further excellent.

When the reactive functional group equivalent of the silane coupling agent (B2) is 1000g/mol or less, the durability is further excellent.

When the weight average molecular weight of the silane coupling agent (B2) is 500 or more, the reworkability and durability are further excellent.

Detailed Description

The present invention will be described in detail below.

In the present invention, (meth) acrylic acid means acrylic acid or methacrylic acid, (meth) acryloyl means acryloyl or methacryloyl, and (meth) acrylate means acrylate or methacrylate, respectively. The acrylic resin is a resin obtained by polymerizing a polymerization component containing at least 1 type of (meth) acrylate monomer.

The acrylic pressure-sensitive adhesive composition of the present invention contains an acrylic resin (a) and a silane coupling agent (B) as essential components.

< acrylic resin (A) >

The acrylic resin (a) used in the present invention is preferably an acrylic resin containing a structural unit derived from a polar group-containing monomer (a1), and the content thereof is preferably 5 to 50% by weight, and for example, an acrylic resin obtained by copolymerizing a copolymerization component containing 5 to 50% by weight of a polar group-containing monomer (a1) is preferable.

The acrylic resin (a) may contain, as necessary: alkyl ester (meth) acrylate monomer (a2), and other copolymerizable ethylenically unsaturated monomer (a 3).

The polar group-containing monomer (a1) is at least 1 selected from the group consisting of a hydroxyl group-containing monomer, a carboxyl group-containing monomer and a nitrogen-containing monomer.

Examples of the hydroxyl group-containing monomer include hydroxyalkyl acrylates such as 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and 8-hydroxyoctyl (meth) acrylate, caprolactone-modified monomers such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, alkylene oxide-modified monomers such as diethylene glycol (meth) acrylate and polyethylene glycol (meth) acrylate, and primary hydroxyl group-containing monomers such as 2-acryloyloxyethyl-2-hydroxyethyl phthalate, N-hydroxymethyl (meth) acrylamide, and hydroxyethyl acrylamide; secondary hydroxyl group-containing monomers such as 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 3-chloro-2-hydroxypropyl (meth) acrylate; tertiary hydroxyl group-containing monomers such as 2, 2-dimethyl 2-hydroxyethyl (meth) acrylate.

Among the above hydroxyl group-containing monomers, a primary hydroxyl group-containing monomer is preferable in terms of excellent reactivity with a crosslinking agent and improvement in resistance to wet-heat whitening, and 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferable in terms of less impurities such as di (meth) acrylate and ease of production.

The hydroxyl group-containing monomer is preferably used in a content ratio of di (meth) acrylate as an impurity of 0.5 wt% or less, particularly preferably 0.2 wt% or less, and more preferably 0.1 wt% or less. Specifically, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and 2-hydroxypropyl acrylate are particularly preferable.

Examples of the carboxyl group-containing monomer include acrylic acid dimer acids such as (meth) acrylic acid and β -carboxyethyl acrylate, and among these, (meth) acrylic acid is preferable from the viewpoint of resistance to wet-heat whitening and stability during polymerization.

Examples of the nitrogen-containing monomer include an amino group-containing monomer and an amide group-containing monomer.

Examples of the amino group-containing monomer include a primary amino group-containing monomer such as aminomethyl (meth) acrylate, aminoethyl (meth) acrylate, a secondary amino group-containing monomer such as t-butylaminoethyl (meth) acrylate, ethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and a tertiary amino group-containing monomer such as diethylaminoethyl (meth) acrylate.

Among the above-mentioned amino group-containing monomers, tertiary amino group-containing monomers are preferable, and dimethylaminoethyl (meth) acrylate is particularly preferable, from the viewpoint of storage stability of the resin solution and crosslinking acceleration effect.

Examples of the amide group-containing monomer include (meth) acrylamide; alkoxyalkyl (meth) acrylamide monomers such as methoxymethyl (meth) acrylamide, ethoxymethyl (meth) acrylamide, propoxymethyl (meth) acrylamide, isopropoxymethyl (meth) acrylamide, n-butoxymethyl (meth) acrylamide, and isobutoxymethyl (meth) acrylamide; dialkyl (meth) acrylamide monomers such as dimethyl (meth) acrylamide and diethyl (meth) acrylamide; a hydroxyl-containing amide monomer such as N- (hydroxymethyl) acrylamide; (meth) acryloyl morpholine; and the like.

Among the amide group-containing monomers, alkoxyalkyl (meth) acrylamide monomers and dialkyl (meth) acrylamide monomers are preferable from the viewpoint of stability of the resin solution and the viewpoint of suppressing migration of the antistatic agent.

Among the polar group-containing monomers (a1), a hydroxyl group-containing monomer and a carboxyl group-containing monomer are preferable from the viewpoint of wet-heat whitening resistance and adhesive properties, and a hydroxyl group-containing monomer is more preferable from the viewpoint of excellent wet-heat whitening resistance and excellent long-term reworkability. The polar group-containing monomer (a1) may be used alone or in combination of 2 or more.

The content of the polar group-containing monomer (a1) (the total content thereof in the case of using 2 or more kinds in combination) is preferably 5 to 50% by weight, particularly preferably 6 to 30% by weight, further preferably 7 to 25% by weight, and particularly preferably 8 to 20% by weight based on the whole copolymerization components, and if the content is too small, the resistance to wet heat whitening during formation of the adhesive tends to decrease, and if it is too large, gelation tends to occur during polymerization.

Examples of the alkyl ester (meth) acrylate monomer (a2) include those having an alkyl group with a carbon number of usually 1 to 20 (preferably 1 to 18, particularly preferably 1 to 12, and further preferably 1 to 8), and specifically include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (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, cetyl (meth) acrylate, and stearyl (meth) acrylate. These may be used alone or in combination of 2 or more.

Among them, methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate are preferable from the viewpoint of excellent versatility and adhesive properties.

The content of the alkyl ester of (meth) acrylic acid monomer (a2) is preferably 20 to 95 wt%, particularly preferably 40 to 94 wt%, further preferably 45 to 93 wt%, particularly preferably 50 to 92 wt% based on the whole copolymerization component.

If the content is too small, it tends to be difficult to achieve a uniform adhesive property, and if it is too large, the wet heat whitening property tends to be lowered.

Examples of the other copolymerizable ethylenically unsaturated monomer (a3) include aromatic ring-containing monomers such as benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, and o-phenylphenoxyethyl (meth) acrylate; alicyclic-containing monomers such as cyclohexyl (meth) acrylate, cyclohexyloxyalkyl (meth) acrylate, t-butylcyclohexyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, and dicyclopentanyl (meth) acrylate; ether chain-containing monomers such as 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, octyloxypolyethylene glycol-polypropylene glycol-mono (meth) acrylate, lauroyloxypolyethylene glycol mono (meth) acrylate, and stearoyloxypolyethylene glycol mono (meth) acrylate. These may be used alone or in combination of 2 or more.

Among them, from the viewpoint of easy adjustment of refractive index and birefringence and excellent light leakage resistance, aromatic ring-containing monomers (particularly, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, and phenoxydiethylene glycol (meth) acrylate) are preferable, and from the viewpoint of easy adjustment of refractive index and birefringence and excellent adhesion to low-polarity adherends (for example, cycloolefins and the like), alicyclic ring-containing monomers are preferable.

When the acrylic pressure-sensitive adhesive composition of the present invention is used as a polarizing plate, it is preferable to adjust the birefringence of the pressure-sensitive adhesive so that the birefringence of the entire member after the durability test becomes small by adjusting the contents of the aromatic ring-containing monomer and the alicyclic monomer in terms of light leakage resistance.

The content of the other copolymerizable ethylenically unsaturated monomer (a3) is preferably 35% by weight or less, more preferably 25% by weight or less. When the amount of the other copolymerizable ethylenically unsaturated monomer (a3) is too large, the light leakage resistance tends to be low.

The acrylic resin (a) used in the present invention can be produced by suitably selecting the polar group-containing monomer (a1), preferably further suitably selecting the alkyl ester (meth) acrylate monomer (a2) and the other copolymerizable ethylenically unsaturated monomer (a3), and using these polymerization components, for example, in an organic solvent, mixing or dropping the above polymerization components and a polymerization initiator to polymerize the acrylic resin (a).

The polymerization reaction can be carried out by a conventionally known polymerization method such as solution radical polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc., among which solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred.

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, aliphatic alcohols such as n-propanol and isopropanol, 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, and methyl isobutyl ketone are preferably used, and ethyl acetate, acetone, and methyl ethyl ketone are more preferably used, from the viewpoints of easiness of polymerization reaction, chain transfer effect, easiness of drying at the time of adhesive application, and high safety.

These organic solvents may be used alone or in combination of 2 or more.

Examples of the polymerization initiator used in the solution radical polymerization include common radical polymerization initiators, that is, azo initiators such as 2,2 '-azobisisobutyronitrile, 2' -azobis-2-methylbutyronitrile, 4 '-azobis (4-cyanovaleric acid) and 2, 2' -azobis (methylpropionic acid), and organic peroxides such as benzoyl peroxide, lauroyl peroxide, di-t-butyl peroxide and cumene hydroperoxide, and these initiators can be appropriately selected and used depending on the monomers to be used. These polymerization initiators may be used alone or in combination of 2 or more.

The acrylic resin (a) used in the present invention preferably contains 5 to 50% by weight of a structural unit derived from the polar group-containing monomer (a1), particularly preferably 6 to 30% by weight, further preferably 7 to 25% by weight, particularly preferably 8 to 20% by weight, most preferably 8 to 15% by weight. If the amount of the structural unit derived from the polar group-containing monomer is too small, the wet-heat whitening resistance tends to be low, and if it is too large, the reworkability and durability tend to be low.

The weight average molecular weight of the acrylic resin (a) is preferably 60 to 250 ten thousand, particularly preferably 80 to 200 ten thousand, further preferably 100 to 180 ten thousand, and particularly preferably 110 to 160 ten thousand.

If the weight average molecular weight is too small, the durability tends to be low, and if it is too large, a large amount of a diluting solvent is required during production, and the drying property tends to be low, so that the residual solvent becomes large in the adhesive layer, and the heat resistance tends to be low.

The dispersion degree (weight average molecular weight/number average molecular weight) of the acrylic resin (a) is preferably 10 or less, particularly preferably 7 or less, and further preferably 5 or less.

If the dispersion is too high, the reworkability tends to be low or the durability tends to be low. The lower limit of the dispersion degree is usually 1.

The weight average molecular weight is a weight average molecular weight calculated based on a standard polystyrene molecular weight, and a high performance liquid chromatograph ("Waters 2695 (main body)" and "Waters 2414 (detector)") manufactured by japan Waters corporation is used in the column: shodex GPC KF-806L (exclusion limit molecular weight: 2X 10)⁷And separation range: 100 to 2 x 10⁷Theoretical plate number: 10000 grades/root, filler material: styrene-divinylbenzene copolymer, filler particle diameter: 10 μm) was connected in series, and the number average molecular weight was measured by the same method. The degree of dispersion is determined from the weight average molecular weight and the number average molecular weight.

The glass transition temperature (Tg) of the acrylic resin (A) is preferably-80 to 0 ℃, particularly preferably-60 to-10 ℃, and further preferably-50 to-20 ℃.

When the glass transition temperature is too high, the adhesion tends to be easily lowered, and when it is too low, the heat resistance tends to be lowered.

The glass transition temperature is calculated by the following formula Fox.

Tg: glass transition temperature (K) of acrylic resin (A)

Tga: glass transition temperature (K) Wa of homopolymer of monomer a: weight fraction of monomer A

Tgb: glass transition temperature (K) Wb of homopolymer of monomer B: weight fraction of monomer B

Tgn: glass transition temperature (K) Wn of homopolymer of monomer N: weight fraction of monomer N (Wa + Wb +. cndot. + Wn ═ 1)

That is, the glass transition temperature (Tg) of the acrylic resin (a) is a value calculated by substituting the glass transition temperature and the weight fraction of each monomer constituting the acrylic resin (a) into the above-described Fox formula when forming a homopolymer.

The glass transition temperature of the monomer constituting the acrylic resin (a) when it forms a homopolymer is usually measured by a Differential Scanning Calorimeter (DSC), and can be measured by a method in accordance with JIS K7121-1987 and JIS K6240.

The refractive index of the acrylic resin (A) is usually 1.440 to 1.600, preferably 1.460 to 1.550, and particularly preferably 1.470 to 1.500. The refractive index is preferably such that the difference in refractive index between the stacked members is small, and the optical loss at the member interface is small.

The above refractive index is as follows: the value of the acrylic resin (A) forming the film was measured by NaD ray at 23 ℃ using a refractive index measuring apparatus ("Abbe refractometer 1T" manufactured by Atago).

The haze of the single layer of the acrylic resin (a) is preferably 1.0 or less, particularly preferably 0.8 or less, and further preferably 0.5 or less. If the haze is too high, the image quality of a display using the haze as a binder tends to be low.

Haze was calculated as follows: the diffusion transmittance and the total light transmittance were measured using a HAZE matrix NDH2000 (manufactured by japan electrochrome industries, ltd.), and the values of the obtained diffusion transmittance and total light transmittance were calculated by substituting the following equations. The machine is based on JIS K7361-1.

Haze (%) - (diffusion transmittance/total transmittance) × 100

The acrylic resin (a) used in the present invention can be obtained in this manner.

< silane coupling agent (B) >

Generally, a silane coupling agent refers to an organosilicon compound containing 1 or more reactive functional groups and alkoxy groups in its structure, respectively.

In the present invention, the silane coupling agent (B) having a structure containing 1 or more reactive functional groups and alkoxy groups respectively contains a silane coupling agent (B1) having an alkoxy group content of 15 wt% or less and a silane coupling agent (B2) having an alkoxy group content of 20 wt% or more.

The alkoxy group defined in the present invention means an alkoxy group derived from an alkoxysilane, and does not include alkoxy groups contained in other molecules.

For example, the end of the polyether portion of the polyether-modified silane and the polyether structure are not included as an alkoxy group.

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

Examples of the alkoxy group include a methoxy group, an ethoxy group, and a propoxy group. Among them, preferred are alkyl groups having 1 to 8 carbon atoms, particularly preferred are alkyl groups having 1 to 2 carbon atoms, specifically methoxy groups and ethoxy groups.

The silane coupling agent (B) may have an organic substituent other than the reactive functional group and the alkoxy group, for example, an alkyl group, a phenyl group, or the like.

The most important feature of the present invention is that the combination of a silane coupling agent (B1) having a small alkoxy group content and a silane coupling agent (B2) having a large alkoxy group content enables the present invention to achieve excellent durability and storage stability while maintaining long-term reworkability.

The content of the alkoxy group in the silane coupling agent (B1) is required to be 15 wt% or less, preferably 1 to 15 wt%, particularly preferably 3 to 15 wt%, and further preferably 5 to 14.5 wt%.

If the content of the alkoxy group is too large, long-term reworkability is lowered.

The weight average molecular weight of the silane coupling agent (B1) is preferably 3000 or more, particularly preferably 4000 to 30000, further preferably 4500 to 20000, and particularly preferably 7000 to 18000.

If the weight average molecular weight is too small, long-term reworkability tends to be low, and if it is too large, bleeding tends to occur, and durability tends to be low.

The reactive functional group equivalent of the silane coupling agent (B1) is preferably 1600g/mol or less, particularly preferably 100 to 1000g/mol, further preferably 200 to 900g/mol, and particularly preferably 300 to 650 g/mol.

When the reactive functional group equivalent is in the above range, the durability tends to be more excellent.

The content of the alkoxy group in the silane coupling agent (B2) is not less than 20% by weight, preferably 20 to 80% by weight, particularly preferably 25 to 70% by weight, and further preferably 30 to 60% by weight.

If the content of the alkoxy group is too small, the storage stability is lowered.

The weight average molecular weight of the silane coupling agent (B2) is preferably 500 or more, preferably 500 to 5000, particularly preferably 500 to 4500, and further preferably 600 to 4000.

If the weight average molecular weight is too small, the long-term reworkability tends to be lowered.

The reactive functional group equivalent of the silane coupling agent (B2) is preferably 1000g/mol or less, particularly preferably 100 to 900g/mol, and further preferably 300 to 800 g/mol.

When the reactive functional group equivalent is in the above range, the durability tends to be improved.

The weight average molecular weights of the silane coupling agents (B1) and (B2) are weight average molecular weights calculated based on the molecular weight of standard polystyrene, and can be measured by the following method. The number average molecular weight can also be measured by the same method, and the degree of dispersion (weight average molecular weight/number average molecular weight) can be determined from the weight average molecular weight and the number average molecular weight.

The device comprises the following steps: gel permeation chromatograph

A detector: differential refractive index detector RI (RI-8020 model manufactured by Tosoh corporation, sensitivity 32)

Column: TSKgel guardcolumn H_HR-H (1) (phi 6 mm. times.4 cm, manufactured by Tosoh corporation), TSKgel GMH_HRN (2) (phi 7.8 mm. times.30 cm, manufactured by Tosoh corporation)

Solvent: tetrahydrofuran (THF)

Column temperature: 23 deg.C

Flow rate: 1.0 mL/min

Here, the weight average molecular weights of the silane coupling agents (B1) and (B2) are preferably such that the weight average molecular weight of the silane coupling agent (B1) is larger than the weight average molecular weight of the silane coupling agent (B2), because long-term reworkability and storage stability tend to be well balanced.

The silane coupling agent (B) may be a monomeric organic silicon compound or an oligomeric organic silicon compound (organosiloxane compound) such as a dimer or trimer obtained by hydrolyzing and polycondensing a part of the organic silicon compound, but is preferably an oligomeric organic silicon compound having a plurality of reactive functional groups and alkoxy groups and having excellent durability and reworkability.

Examples of the silane coupling agent (B) include epoxy group-containing silane coupling agents such as organosilicon compounds such as γ -glycidoxypropyltriethoxysilane and γ -glycidoxypropylmethyldiethoxysilane, oligomeric organosilicon compounds (epoxy group-containing organosiloxy oligomers) obtained by hydrolyzing and polycondensing a part of organosilicon compounds, and organosilicon compounds obtained by modifying a part of these organosilicon compounds with ether; a mercapto group-containing silane coupling agent such as an organosilicon compound such as γ -mercaptopropyltriethoxysilane, an oligomer-type organosilicon compound (e.g., a mercapto group-containing organoxy oligomer) obtained by hydrolyzing and polycondensing a part of an organosilicon compound, etc.; and the like.

Among them, those which are appropriately selected and used so as to satisfy the respective conditions of the silane coupling agents (B1) and (B2) can be used. The silane coupling agents (B1) and (B2) may be used alone in 1 kind, or in combination with 2 or more kinds.

Specific examples of the silane coupling agent (B1) include X-24-9590 (weight-average molecular weight: 13700, methoxy group-containing alkoxy group, alkoxy group content: 9.5% by weight, epoxy group-containing reactive functional group, epoxy equivalent: 592g/mol) which is a commercially available product of shin-Etsu chemical Co., Ltd.

Specific examples of the silane coupling agent (B2) include commercially available products of shin-Etsu chemical Co., Ltd, "X-41-1059A" (weight average molecular weight: 2300, methoxy group-containing, ethoxy group-containing, alkoxy group-containing, 42 wt% reactive functional group: epoxy group-containing, epoxy equivalent: 350g/mol), "X-41-1810" (weight average molecular weight: 640, methoxy group-containing, alkoxy group-containing, 30 wt% reactive functional group: mercapto group-containing, mercapto group-equivalent: 450g/mol), "X-41-1805" (weight average molecular weight: 3450 wt%, methoxy group-containing, ethoxy group-containing, alkoxy group-containing, mercapto group-equivalent: 800g/mol), and the like.

Among them, "X-41-1059A" is particularly preferable from the viewpoint of storage stability and durability.

The content of the silane coupling agent (B1) is preferably 0.001 to 1 part by weight, particularly preferably 0.015 to 0.5 part by weight, further preferably 0.020 to 0.2 part by weight, and further preferably 0.025 to 0.15 part by weight, based on 100 parts by weight of the acrylic resin (a).

If the content is too large, the durability tends to be lowered, and if it is too small, the long-term reworkability tends to be lowered.

The content of the silane coupling agent (B2) is preferably 0.001 to 1 part by weight, particularly preferably 0.015 to 0.5 part by weight, further preferably 0.02 to 0.2 part by weight, and particularly preferably 0.025 to 0.15 part by weight, based on 100 parts by weight of the acrylic resin (a).

The content ratio (weight ratio) of the silane coupling agent (B1) to the silane coupling agent (B2) is preferably (B1): 50:1 to 1:5 (B2), particularly preferably (B1): 30:1 to 1:2 (B2), and further preferably (B1): 10:1 to 1:1 (B2).

When the content ratio is within the above range, the balance between durability and reworkability tends to be excellent.

In the acrylic pressure-sensitive adhesive composition of the present invention, silane coupling agents other than the silane coupling agents (B1) and (B2) may be used within a range not interfering with the effects of the invention, and if the content of the silane coupling agent is too large, the durability tends to be lowered by bleeding. Therefore, the content of the silane coupling agent other than the silane coupling agents (B1) and (B2) is, specifically, preferably 0.5 parts by weight or less, more preferably 0.3 parts by weight or less, and particularly preferably 0.1 parts by weight or less, based on 100 parts by weight of the acrylic resin (a).

The acrylic pressure-sensitive adhesive composition of the present invention preferably contains a crosslinking agent (C) and an antistatic agent (D) in addition to the acrylic resin (a) and the silane coupling agent (B).

< crosslinking agent (C) >)

Examples of the crosslinking agent (C) include isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, melamine crosslinking agents, aldehyde crosslinking agents, amine crosslinking agents, and metal chelate crosslinking agents, and among them, isocyanate crosslinking agents are preferably used in terms of improving adhesiveness to a base material and excellent reactivity with a base polymer.

Examples of the isocyanate crosslinking agent include aromatic isocyanate crosslinking agents such as toluene diisocyanate crosslinking agents such as 2, 4-toluene diisocyanate and 2, 6-toluene diisocyanate, xylylene diisocyanate crosslinking agents such as 1, 3-xylylene diisocyanate, diphenylmethane crosslinking agents such as diphenylmethane-4, 4-diisocyanate, and naphthalene diisocyanate crosslinking agents such as 1, 5-naphthalene diisocyanate; alicyclic isocyanate-based crosslinking agents such as isophorone diisocyanate, 1, 4-cyclohexane diisocyanate, 4 '-dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4, 4' -diisocyanate, 1, 3-diisocyanatomethylcyclohexane, norbornane diisocyanate and the like; aliphatic isocyanate crosslinking agents such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate; and adducts, biurets, isocyanurates and the like of the above isocyanate-based compounds.

Among these isocyanate crosslinking agents, toluene diisocyanate crosslinking agents are preferable from the viewpoint of pot life and durability, xylylene diisocyanate crosslinking agents or isocyanate crosslinking agents having an isocyanurate skeleton are preferable from the viewpoint of shortening the aging time, and non-aromatic and non-isocyanate crosslinking agents are preferable from the viewpoint of yellowing resistance. Among them, specifically, toluene diisocyanate, xylylene diisocyanate, an adduct of hexamethylene diisocyanate and trimethylolpropane, and an isocyanurate are preferable from the viewpoint of excellent balance among durability, pot life, and crosslinking speed.

Examples of the epoxy crosslinking agent include bisphenol a epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol triglycidyl ether, 1, 6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, and diglycerol polyglycidyl ether.

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

Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexabutoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resins.

Examples of the aldehyde-based crosslinking agent include glyoxal, malonaldehyde, succinaldehyde, malealdehyde, glutaraldehyde, formaldehyde, acetaldehyde, and benzaldehyde.

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

Examples of the metal chelate-based crosslinking agent include acetylacetone and acetoacetyl ester complexes of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

The crosslinking agent (C) may be used alone, or 2 or more kinds may be used in combination.

The content of the crosslinking agent (C) is preferably 0.01 to 5 parts by weight, particularly preferably 0.05 to 1.5 parts by weight, and further preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the acrylic resin (A).

If the content is too small, the durability tends to be low, and if it is too large, the stress relaxation property tends to be low, the substrate tends to be easily warped, or aging tends to take a long time.

< antistatic agent (D) >

The acrylic pressure-sensitive adhesive composition of the present invention preferably further contains an antistatic agent (D), and as the antistatic agent (D), an ionic compound (D1) is particularly suitable.

The ionic compound (D1) is preferably one containing an ionic compound formed from at least one of a metal salt and an organic salt, from the viewpoint of measures against charging.

Examples of the metal salt include alkali metal salts such as lithium salt, sodium salt, calcium salt, and potassium salt, alkaline earth metal salts, and phosphonium salts.

Examples of the organic salt include onium salts such as ammonium salts, imidazolium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, and sulfonium salts.

Among them, from the viewpoint of excellent corrosion resistance, excellent long-term reworkability, and excellent storage stability, organic salts are preferable, onium salts formed from nitrogen-containing cations such as ammonium cation, imidazolium cation, pyridinium cation, piperidinium cation, and pyrrolidinium cation are more preferable, and ammonium salts, particularly ammonium salts formed from acyclic ammonium cation and N, N-bis (trifluoromethanesulfonyl) imide anion, and ammonium salts formed from acyclic ammonium cation and N, N-bis (fluorosulfonyl) imide anion are more preferable.

The melting point of the ionic compound (D1) is preferably from 10 to 100 ℃, particularly preferably from 20 to 80 ℃, and particularly preferably from 25 to 50 ℃. If the melting point is too high, the film tends to be easily precipitated at low temperature, and if it is too low, the film tends to be easily discolored in a hot and humid environment.

The content of the antistatic agent (D) is preferably 0.5 to 10 parts by weight, more preferably 2 to 8 parts by weight, still more preferably 2 to 5 parts by weight, and particularly preferably 2.5 to 4.5 parts by weight, based on 100 parts by weight of the acrylic resin (a). If the content is too small, antistatic performance cannot be obtained, and display unevenness due to static electricity tends to occur, while if it is too large, the polarization degree of the polarizing plate tends to decrease, or the durability tends to decrease due to bleeding.

Further, the acrylic pressure-sensitive adhesive composition of the present invention may contain, as other components, various additives such as a resin component, an acrylic monomer, a polymerization inhibitor, an antioxidant, an anticorrosive agent, a crosslinking accelerator, a radical generator, a peroxide, a radical scavenger, and metal and resin particles, within a range not to impair the effects of the present invention. In addition to the above, a small amount of impurities and the like contained in a raw material for producing a constituent component of the acrylic pressure-sensitive adhesive composition may be contained.

The content of the other component is preferably 5 parts by weight or less, particularly preferably 1 part by weight or less, and further preferably 0.5 part by weight or less, based on 100 parts by weight of the acrylic resin (a). When the content is too large, compatibility with the acrylic resin (A) tends to be lowered and resistance to wet-heat whitening tends to be lowered.

The acrylic pressure-sensitive adhesive composition of the present invention can be obtained by mixing the acrylic resin (a), the silane coupling agent (B), if necessary, the crosslinking agent (C), the antistatic agent (D), and other components in this manner. The mixing method is not particularly limited, and it is possible to use: a method of mixing the components at the same time; various methods such as a method of mixing arbitrary components and then mixing the remaining components simultaneously or sequentially.

The acrylic pressure-sensitive adhesive composition of the present invention can be cured (crosslinked) to form a pressure-sensitive adhesive, and further, an optical member with a pressure-sensitive adhesive layer can be obtained by laminating and forming a pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive on an optical member (optical laminate).

In the optical member with an adhesive layer, a release sheet is preferably further provided on a surface of the adhesive layer opposite to the optical member surface.

Examples of the method for producing the optical member with an adhesive layer include:

a method [ 1] in which an acrylic pressure-sensitive adhesive composition is applied to an optical member, dried, and then a release sheet is attached thereto, and curing treatment is performed at least at room temperature (23 ℃) or in a heated state;

[ method 2] an acrylic pressure-sensitive adhesive composition is applied to a release sheet, dried, and then bonded to an optical member, and the optical member is subjected to curing treatment at least at room temperature or in a heated state;

and the like. Among them, the method [ 2] is preferably a method in which the curing is performed at room temperature, from the viewpoint of not damaging the optical member and of being excellent in adhesion to the optical member.

In the above, the optical member is particularly effective when it is a polarizing plate.

The curing treatment is performed to achieve a balance of adhesive properties represented by a reaction time of chemical crosslinking of the adhesive, and the curing conditions are usually room temperature to 70 ℃ and 1 to 30 days, specifically, for example, 1 to 20 days at 23 ℃,3 to 10 days at 23 ℃, 1 to 7 days at 40 ℃.

In the application of the acrylic pressure-sensitive adhesive composition, the acrylic pressure-sensitive adhesive composition is preferably diluted in a solvent and applied, and the diluted concentration is preferably 5 to 60% by weight, and particularly preferably 10 to 30% by weight, in terms of the solid content concentration.

The solvent is not particularly limited as long as the acrylic pressure-sensitive adhesive composition is dissolved, and examples thereof include ester solvents such as methyl acetate, ethyl acetate, methyl acetoacetate, and ethyl acetoacetate, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, aromatic solvents such as toluene and xylene, and alcohol solvents such as methanol, ethanol, and propanol. Among them, ethyl acetate and methyl ethyl ketone are preferably used in view of solubility, drying property, price, and the like.

The application of the adhesive composition can be performed by a common method such as roll coating, die coating, gravure coating, comma coating, screen printing, or the like.

The gel fraction of the pressure-sensitive adhesive layer produced by the above method is preferably 30 to 95 wt%, particularly preferably 40 to 90 wt%, and further preferably 60 to 85 wt%, from the viewpoints of durability and suppression of a decrease in polarization degree. If the gel fraction is too low, the reworkability tends to be low, and if it is too high, the floating and peeling tend to occur easily.

The gel fraction is an index of the degree of crosslinking (degree of curing), and is calculated, for example, by the following method. That is, an adhesive was collected from an optical member, particularly from an adhesive sheet having an adhesive layer formed on a substrate such as a polarizing plate, by a picker, the adhesive was coated on a 200-mesh SUS metal mesh, and the metal mesh was immersed in ethyl acetate adjusted to 23 ℃ for 24 hours, and the weight percentage of the insoluble adhesive component remaining in the metal mesh was defined as the gel fraction.

When the gel fraction of the binder is adjusted to the above range, the gel fraction can be achieved by adjusting the type and amount of the crosslinking agent.

The pressure-sensitive adhesive layer produced by the above method is preferable because the wettability when the pressure-sensitive adhesive layer is actually attached to an adherend is good when the pressure-sensitive adhesive layer has a relatively good sense of tackiness when touched with a finger, and therefore, the workability tends to be improved.

As the electrical characteristics of the pressure-sensitive adhesive layer obtained using the acrylic resin composition of the present invention, the surface resistance value is preferably 1X 10¹²Omega or less, particularly preferably 1X 10¹¹Omega is less, more preferably 5X 10¹⁰Omega is less than or equal to. If the surface resistance value is too high, the polarizing plate and the adhesive layer tend to be easily charged, and display unevenness tends to be easily caused.

The thickness of the dried pressure-sensitive adhesive layer in the optical member with a pressure-sensitive adhesive layer obtained is preferably 5 to 200. mu.m, particularly preferably 10 to 100. mu.m, and further preferably 10 to 30 μm. If the thickness of the pressure-sensitive adhesive layer is too small, the pressure-sensitive adhesive properties tend to be less stable, and if it is too large, the amount of moisture that enters from the end portions tends to increase, and the storage stability tends to decrease.

In the present invention, an optical member with an adhesive layer, particularly a polarizing plate with an adhesive layer, is supplied to, for example, an image display device by directly bonding an adhesive layer surface to a glass substrate or by bonding an adhesive layer surface to a glass substrate after peeling a release sheet when the release sheet is present.

The initial adhesive force of the adhesive of the present invention is suitably determined depending on the material of the adherend and the like. For example, when the adhesive is bonded to a glass substrate such as a liquid crystal cell, the adhesive has an adhesive strength of preferably 15N/25mm or less, particularly preferably 0.1 to 12N/25mm, and more preferably 0.5 to 8N/25 mm.

The long-term adhesive strength (reworkability) of the pressure-sensitive adhesive of the present invention is suitably determined depending on the material of the adherend, etc.

For example, when the adhesive is bonded to a glass substrate such as a liquid crystal cell, the adhesive strength after 40 days of bonding is preferably 0.1 to 20N/25mm, particularly preferably 1 to 15N/25mm, and further preferably 1 to 10N/25 mm.

The above initial adhesive force was calculated as follows.

The polarizing plate with the pressure-sensitive adhesive layer was cut to a width of 25mm, the release film was peeled off, and the pressure-sensitive adhesive layer side was pressed against an alkali-free glass plate (manufactured by corning corporation, "EAGLE XG") to bond the polarizing plate to the glass plate. After that, after autoclave treatment (50 ℃ C.. times.0.5 MPa.times.20 minutes) was performed, the steel sheet was left at 23 ℃ C.. times.50% RH for 24 hours, and then a peel test was performed at a peel angle of 180 ℃ and a peel speed of 300 mm/minute. Further, regarding long-term reworkability, after autoclave treatment, the steel sheet was left at 23 ℃ X50% RH for a predetermined time, and then a peel test was performed at a peel angle of 180 ° and a peel speed of 300 mm/min.

The acrylic adhesive composition of the present invention can provide an adhesive having excellent durability and resistance to wet heat whitening, and having a good balance between storage stability and reworkability, and is useful as an adhesive for optical members, particularly an adhesive for polarizing plates for bonding a polarizing plate to a glass substrate or the like.

Examples of the protective film constituting the polarizing plate include cellulose triacetate films, acrylic films, polyethylene films, polypropylene films, cycloolefin films, and the like, and the polarizing plate of the present invention using any protective film can be suitably used.

Further, by using the adhesive, it is possible to produce an image display device by attaching a polarizing plate to a liquid crystal cell, and the obtained image display device can be produced with high accuracy and has excellent durability.

Examples

The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the invention does not exceed the gist thereof. In the examples, "part" and "%" are based on weight.

First, various acrylic resins were prepared as follows. The acrylic resin (a) and the weight average molecular weight, the degree of dispersion, and the glass transition temperature were measured by the methods described above.

The viscosity was measured by the 4.5.3 rotational viscometer method according to JIS K5400 (1990).

< acrylic resin (A) >

[ production of acrylic resin (A-1) ]

8 parts of 2-hydroxyethyl acrylate (a1), 0.7 part of acrylic acid (a1), 71.3 parts of n-butyl acrylate (a2), 20 parts of benzyl acrylate (a3), 53 parts of ethyl acetate, 42 parts of acetone, and 0.013 part of Azobisisobutyronitrile (AIBN) as a polymerization initiator were put into a four-necked round-bottomed flask equipped with a reflux condenser, a stirrer, a nitrogen-blowing port, and a thermometer, and the internal temperature was raised to the boiling point to start the reaction. Then, 30 parts of an ethyl acetate solution containing 0.04% AIBN was added dropwise thereto, and the mixture was reacted at a reflux temperature for 3.25 hours, and then diluted with ethyl acetate to obtain an acrylic resin (A-1) solution (solid content: 21.3%, viscosity: 5440 mPas/25 ℃, acrylic resin (A-1): glass transition temperature-42 ℃, weight average molecular weight: 127 ten thousand, and degree of dispersion: 4.3).

The monomers used in the above were those from the following manufacturers.

2-hydroxyethyl acrylate (Tg-15 ℃ C. manufactured by Osaka organic chemical Co., Ltd.)

Acrylic acid (Tg 106 ℃ C. manufactured by Mitsubishi chemical corporation)

Butyl acrylate (Tg-56 ℃ C. manufactured by Mitsubishi chemical corporation)

Benzyl acrylate (Viscoat #160 Tg 6 ℃ manufactured by Osaka organic Chemicals Co., Ltd.)

The Tg is the Tg of a homopolymer of each monomer.

[ production of acrylic resins (A-2) and (A-3) ]

The acrylic resin (A-1) was produced by the above-mentioned method for producing the acrylic resin (A-1) using the copolymerization components shown in Table 1, to obtain acrylic resin (A-2) and (A-3) solutions. The acrylic resin (A-2) and acrylic resin (A-3) solutions obtained were as shown in Table 1.

[ Table 1]

< silane coupling agent (B) >

As the silane coupling agent (B), the following were prepared. The weight average molecular weight and the degree of dispersion of the silane coupling agent (B) were measured by the methods described above. Further, the values in the table for the alkoxy group content, the reactive functional group, the epoxy equivalent or mercapto equivalent, and the alkoxy group-containing are used.

·(B1-1)：

(X-24-9590, manufactured by shin-Etsu chemical Co., Ltd., "X-24-9590", weight-average molecular weight: 13700, dispersibility: 3.44, alkoxy group content: 9.5%, reactive functional group: epoxy group, epoxy equivalent: 592g/mol, alkoxy group-containing: methoxy group)

·(B2-1)：

(X-41-1059A, manufactured by shin-Etsu chemical Co., Ltd., "X-41-1059A", weight-average molecular weight: 2270, dispersibility: 1.86, alkoxy group content: 42%, reactive functional group: epoxy group, epoxy equivalent: 350g/mol, alkoxy group-containing: methoxy group, ethoxy group)

·(B2-2)：

(X-41-1805, weight average molecular weight 3450, dispersity 1.85, alkoxy content 50%, reactive functional group mercapto, mercapto equivalent 800g/mol, alkoxy-containing methoxy, ethoxy)

< crosslinking agent (C) >)

As the crosslinking agent (C), the following were prepared.

(C-1): adduct of tolylene diisocyanate and trimethylolpropane (available from Tosoh corporation, "CORONATE L55E": 55% as an active ingredient)

< antistatic agent (D) >

As the antistatic agent (D), the following were prepared.

(D1-1): n, N-bis (trifluoromethanesulfonyl) imide tri-N-butylammonium (product of 3M Co., Ltd., "FC-4400")

< examples 1 to 4, comparative examples 1 to 5 >

The above components (a) to (D) were mixed as shown in table 2 below, and the solid content concentration was adjusted to 12.5% with ethyl acetate to obtain an acrylic pressure-sensitive adhesive composition.

[ Table 2]

Note) () is the compounding weight parts based on solid content.

Using the acrylic pressure-sensitive adhesive composition obtained above, samples for evaluation were prepared as follows, and the following properties were evaluated. The evaluation results are shown in table 3.

[ production of polarizing plates with adhesive layer [ I ] and [ II ]

The obtained acrylic pressure-sensitive adhesive composition was applied to a release sheet (Lumiror SP-0138BU, manufactured by TOHCELLO Co., Ltd.) having a thickness of 38 μm so that the thickness after drying became 25 μm, and after drying at 100 ℃ for 3 minutes, the pressure-sensitive adhesive layer on the opposite side to the release sheet was adhered to one TAC film surface of the polarizing plate having cellulose Triacetate (TAC) films laminated on both surfaces thereof, and the sheet was cured at 23 ℃ X50% RH for 7 days to obtain a polarizing plate [ I ] (layer constitution; release sheet/pressure-sensitive adhesive layer/TAC film 1/polarizer/TAC film 2, TAC film 1: thickness 40 μm, TAC film 2: 60 μm) having a pressure-sensitive adhesive layer.

In addition, a polarizing plate [ II ] with an adhesive layer was obtained in the same manner except that the COP side of the cycloolefin film/polarizer/TAC film subjected to the corona treatment was bonded to the adhesive layer side.

The TAC film was a cellulose triacetate film (thickness: 60 μm), and the COP film was a cycloolefin film (thickness: 50 μm).

The following evaluations were carried out using the polarizing plate with an adhesive layer [ I ] and the polarizing plate with an adhesive layer [ II ].

[ reworkability ]

The polarizing plate [ I ] with an adhesive layer obtained in the above was cut into a width of 25mm, the release sheet was peeled, the adhesive layer surface was pressed to an alkali-free glass (EAGLE XG manufactured by corning corporation: thickness 1.1mm), and the plate was adhered with a 2kg roller, autoclave treatment (0.5MPa × 50 ℃ × 20 minutes) was performed, and then the plate was allowed to stand in an environment of 23 ℃ × 50% RH for 1 day, 40 days, and 50 days, and then the adhesive force at the time of peeling at a peeling angle of 180 ° and a peeling speed of 300 mm/minute was measured, and evaluated in the following criteria.

(evaluation criteria)

1 day after application

Not more than 5N/25mm

O.over 5N/25mm and below 10N/25mm

X 10N/25mm or more

After 40 days

10N/25mm or less

O. over 10N/25mm and below 15N/25mm

Delta. 15N/25mm or more and less than 20N/25mm

X 20N/25mm or more, or generation of residual glue

After 50 days

10N/25mm or less

O. over 10N/25mm and below 18N/25mm

Delta. 18N/25mm or more and less than 20N/25mm

X 20N/25mm or more, or generation of residual glue

[ durability ]

< evaluation of initial durability >

The polarizing plate [ I ] with the adhesive layer was cut into 20 cm. times.15 cm, the release sheet was peeled off, the adhesive layer was pressed against an alkali-free glass (EAGLE XG manufactured by Corning corporation: thickness 1.1mm), and the laminate was adhered by reciprocating 2 times with a 2kg roller, and then, autoclave treatment (0.5 MPa. times.50 ℃ C. times.20 minutes) was performed to prepare a sample for initial durability test.

The polarizing plate exposed to the conditions of (1) heat resistance (80 ℃ C. × 250 hours) and (2) moist heat resistance (60 ℃ C. × 90% RH × 250 hours) was evaluated for the obtained sample as follows.

(evaluation criteria)

O. No foaming was observed on the entire surface of the polarizing plate or no floating was observed at the end

Foaming was visible on the entire surface of the polarizing plate or floating was visible at the end

< evaluation after deterioration acceleration test >

The polarizing plate [ I ] with the pressure-sensitive adhesive layer was exposed to an atmosphere of 45 ℃ and 90% RH for 3 days, and then subjected to temperature/humidity control at 23 ℃ and 50% RH for 7 days. Then, the sheet was cut into 20cm × 15cm, the release sheet was peeled off, the adhesive layer was pressed to an alkali-free glass (EAGLE XG manufactured by corning corporation: thickness 1.1mm), the sheet was pasted by reciprocating 2 times with a 2kg roller, and then autoclave treatment (0.5MPa × 50 ℃ × 20 minutes) was performed to prepare a sample for the deterioration acceleration test.

(evaluation criteria)

[ resistance to Damp-Heat whitening ]

The polarizing plate [ II ] with the adhesive layer obtained was cut into 3.5 cm. times.3.5 cm, the release sheet was peeled off, the adhesive layer was pressed against an alkali-free glass (EAGLE XG, manufactured by Corning corporation, thickness 1.1mm), and the sheet was stuck by reciprocating 2 times with a 2kg roller, and then, a sample for a wet-heat whitening resistance test was prepared by autoclave treatment (0.5 MPa. times.50 ℃ C. times.20 minutes).

The sample thus obtained was exposed to an atmosphere of 60 ℃ x 90% RH for 250 hours, and then taken out and left to stand at room temperature. Then, the haze 3 hours after the removal was measured, and the wet-heat whitening resistance was evaluated according to the following criteria. The haze value is obtained by subtracting the value of 1.1mm alkali-free glass as a blank.

(evaluation criteria)

Haze after 3 hours of removal

Very good. less than 1%

O.1% or more but less than 2%

Delta. 2% or more but less than 4%

X.4% or more

[ gel fraction ]

The release sheet of the polarizing plate [ I ] with the adhesive layer obtained was peeled off, the adhesive was picked up from the adhesive layer side, coated with a 200-mesh SUS metal mesh, and then immersed in ethyl acetate adjusted to 23 ℃ for 24 hours, and the gel fraction was determined as the weight percentage of the insoluble adhesive component remaining in the metal mesh.

[ antistatic Property ]

< surface resistance value >

The polarizing plate [ I ] with an adhesive layer was allowed to stand in an atmosphere of 23 ℃ X50% RH for 24 hours, and then the release sheet of the adhesive layer was removed, and the surface resistivity of the adhesive layer was measured with a surface resistivity measuring apparatus (manufactured by Mitsubishi chemical ANALYTECH, under the apparatus name "Hiresta-UP MCP-HT 450").

[ Table 3]

From the above results, it is clear that examples 1 to 4 using a pressure-sensitive adhesive obtained from an acrylic pressure-sensitive adhesive composition using a combination of a silane coupling agent (B1) having an alkoxy group content of 15 wt% or less and a silane coupling agent (B2) having an alkoxy group content of 20 wt% or more have good long-term reworkability, storage stability, and durability in a well-balanced manner.

On the other hand, comparative examples 1 and 2, in which the silane coupling agent (B2) having an alkoxy group content of 20 wt% or more was not used, but only the silane coupling agent (B1) having an alkoxy group content of 15 wt% or less was used, were found to have excellent long-term reworkability, but poor storage stability.

It is also found that comparative examples 3 to 5, in which the silane coupling agent (B1) having an alkoxy group content of 15 wt% or less was not used, but only the silane coupling agent (B2) having an alkoxy group content of 20 wt% or more, had poor long-term reworkability.

Further, an image display device was produced by bonding a polarizing plate and a liquid crystal cell using the adhesive obtained by crosslinking the acrylic adhesive composition of examples 1 to 4, and as a result, the obtained image display device was produced with high accuracy and excellent durability.

The above embodiments are merely examples and are not to be construed as limiting the present invention. Various modifications obvious to those skilled in the art are intended to be within the scope of the present invention.

Industrial applicability

The acrylic adhesive composition of the present invention is useful as an adhesive for optical members for bonding a display and an optical member constituting the display, particularly an adhesive for polarizing plates for bonding glass substrates of polarizing plates and liquid crystal cells, and the like, since the acrylic adhesive composition can provide an adhesive which exhibits excellent reworkability over a long period of time, is less susceptible to moisture, and does not cause a decrease in durability when used as an adhesive for bonding a polarizing plate (protective film) and a liquid crystal cell (glass) in the production of a liquid crystal display device.

Claims

1. An acrylic adhesive composition characterized by comprising:

an acrylic resin (A); and a silane coupling agent (B) having a structure containing 1 or more reactive functional groups and alkoxy groups,

the silane coupling agent (B) contains a silane coupling agent (B1) having an alkoxy group content of 15 wt% or less and a silane coupling agent (B2) having an alkoxy group content of 20 wt% or more,

the weight average molecular weight of the silane coupling agent (B2) is 500 or more.

2. The acrylic adhesive composition according to claim 1, wherein the acrylic resin (A) is an acrylic resin containing 5 to 50% by weight of a structural unit derived from at least 1 polar group-containing monomer (a1) selected from the group consisting of a hydroxyl group-containing monomer, a carboxyl group-containing monomer and a nitrogen-containing monomer.

3. The acrylic adhesive composition according to claim 1 or 2, wherein the silane coupling agent (B1) has a reactive functional group equivalent weight of 1600g/mol or less.

4. The acrylic adhesive composition according to claim 1 or 2, wherein the silane coupling agent (B1) has a weight average molecular weight of 3000 or more.

5. The acrylic adhesive composition according to claim 1 or 2, wherein the silane coupling agent (B2) has a reactive functional group equivalent weight of 1000g/mol or less.

6. The acrylic adhesive composition according to claim 1 or 2, further comprising a crosslinking agent (C).

7. The acrylic adhesive composition according to claim 1 or 2, characterized by further comprising an antistatic agent (D).

8. An adhesive obtained by crosslinking the acrylic adhesive composition according to any one of claims 1 to 7 with a crosslinking agent (C).

9. An adhesive for a polarizing plate, which is produced by using the adhesive according to claim 8.

10. An image display device, which is obtained by bonding a polarizing plate and a liquid crystal cell with the adhesive according to claim 8.