JP6859937B2 - A pressure-sensitive adhesive composition, a pressure-sensitive adhesive for a polarizing plate using the pressure-sensitive adhesive composition, a polarizing plate with a pressure-sensitive adhesive layer, and an image display device. - Google Patents

Description

The present invention relates to an adhesive composition, and more specifically, satisfies various performances required when a polarizing plate used in a liquid crystal display device or the like is used for bonding a liquid crystal cell, and further, the adhesive strength varies. The present invention relates to a pressure-sensitive adhesive composition capable of obtaining a small pressure-sensitive adhesive exhibiting uniform adhesive strength, a pressure-sensitive adhesive for a polarizing plate using the same, a polarizing plate with a pressure-sensitive adhesive layer, and an image display device.

Conventionally, a polarizing plate in which both sides of a polarizing element made of a polyvinyl alcohol (hereinafter, may be abbreviated as PVA) -based film to which polarization property is imparted is protected by a protective film is oriented between two glass plates. A liquid crystal display board is manufactured by laminating on the surface of a liquid crystal cell sandwiching the liquid crystal component. To laminate the polarizing plate on the surface of the liquid crystal cell, a polarizing plate with a pressure-sensitive adhesive layer provided on the surface of the protective film of the polarizing plate is manufactured, and the pressure-sensitive adhesive layer is brought into contact with the surface of the liquid crystal cell and pressed against the surface of the liquid crystal cell. Is usually done by.

The adhesive used for bonding the polarizing plate (protective film) and the liquid crystal cell (glass) has durability that does not cause floating or peeling even in an environment such as high temperature or moist heat, and when exposed to such conditions. However, display resistance unevenness to prevent light leakage from the backlight, reworkability to prevent damage to the liquid crystal cell and generation of adhesive residue on the liquid crystal cell when peeling the polarizing film from the liquid crystal cell, external Various performances such as antistatic property for preventing the failure of the liquid crystal cell due to static electricity are required.

Many studies have been carried out in order to obtain an adhesive that satisfies such various performances. For example, in Patent Document 1, a monomer having a glass transition temperature (Tg) of a homopolymer of 0 ° C. or higher and an aroma An acrylic resin containing a ring-containing monomer and a pressure-sensitive adhesive composed of an ionic compound are described, and it is described that they are excellent in durability, light leakage resistance, and antistatic property in a moist heat environment.

Further, Patent Document 2 describes that a pressure-sensitive adhesive having excellent heat resistance can be obtained by using an acrylic resin obtained by copolymerizing an aromatic ring-containing monomer.

Further, Patent Document 3 proposes to add an oligomer-type silane coupling agent in order to improve the reworkability.

International Publication WO2013 / 099683 Japanese Unexamined Patent Publication No. 59-11114 Japanese Unexamined Patent Publication No. 7-331206

However, even the pressure-sensitive adhesives described in Patent Documents 1 and 2 do not satisfy all the required performances, and in order to satisfy various performances with reference to Patent Documents 1 and 2, homopolymers are used. When a monomer having a high glass transition temperature or a monomer containing an aromatic ring is used in combination, there is a problem that the glass transition temperature of the acrylic resin becomes too high and the reworkability is lowered.

Further, in the disclosure technique of Patent Document 3 for improving the reworkability, even if the oligomer type silane coupling agent is simply used, the average value of the adhesive strength tends to decrease, but the acrylic having a high glass transition temperature. When a based resin is used, the adhesive strength at the time of peeling varies widely, and when it is used for a thinned glass substrate or liquid crystal cell in recent years, it cannot be peeled smoothly during reworking and the liquid crystal cell is damaged. There was a risk that it would end up.

Therefore, in the present invention, under such a background, a monomer having a high glass transition temperature of a homopolymer, particularly an aromatic ring-containing monomer or an alkyl (meth) acrylate having 1 to 2 carbon atoms is used when manufacturing a liquid crystal display device. Durability, reworkability, and antistatic performance when used as an adhesive used for bonding a polarizing plate (protective film) and a liquid crystal cell (glass) even when an acrylic resin with high heat resistance is used. It is an object of the present invention to provide a pressure-sensitive adhesive composition which is excellent in quality, has a small variation in adhesive strength during rework, has uniform adhesive strength, and can obtain a pressure-sensitive adhesive capable of efficiently performing reworking work. Is to be.

However, as a result of intensive studies in view of such circumstances, the present inventor has obtained normal butyl acrylate as an acrylic resin, an aromatic ring-containing monomer, and an alkyl having 1 to 2 carbon atoms (meth) in the pressure-sensitive adhesive composition. ) An acrylic resin having a specific composition containing at least one monomer selected from acrylate and at least one polar group-containing monomer selected from a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and a nitrogen atom-containing monomer. An acrylic resin made of a monomer component having a high glass transition temperature of a homopolymer by containing an ionic compound containing a specific structure and containing a silane coupling agent having a larger weight average molecular weight than normally used is used. Even if there is, it satisfies various required performances such as reworkability, durability, and antistatic property in a well-balanced manner, and further, it has small variation in adhesive strength and uniform adhesive strength, which makes rework work efficient. The present invention has been completed by finding that it is possible to obtain a pressure-sensitive adhesive that can be used as a target.

That is, the gist of the present invention is
Acrylic resin (A)
Ionic compound (B)
Silane coupling agent (C)
A pressure-sensitive adhesive composition containing a cross-linking agent (D).
The acrylic resin (A) is obtained by copolymerizing the following monomers (a1) to (a4) in the following proportions with respect to the total monomer components.
(A1) Normal Butyl Acrylate 5 to 75% by Weight
(A2) At least one monomer selected from an aromatic ring-containing monomer and an alkyl (meth) acrylate having 1 to 2 carbon atoms in an alkyl group 20 to 80% by weight.
(A3) At least one polar group-containing monomer selected from a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and a nitrogen atom-containing monomer 1 to 30% by weight.
(However, it contains at least one of a carboxyl group-containing monomer and a hydroxyl group-containing monomer.)
(A4) Monomers other than (a1) to (a3) 10% by weight or less The ionic compound (B) is an ionic compound having a fluorine-containing anion.
The present invention relates to a pressure-sensitive adhesive composition, wherein the silane coupling agent (C) has a weight average molecular weight of 4,000 or more.

Further, the present invention relates to a pressure-sensitive adhesive for a polarizing plate using the above-mentioned pressure-sensitive adhesive composition, a polarizing plate with a pressure-sensitive adhesive layer, and an image display device.

The pressure-sensitive adhesive composition of the present invention has various properties such as reworkability, durability, and antistatic property when used as a pressure-sensitive adhesive used for bonding a polarizing plate (protective film) and a liquid crystal cell (glass base material). It is possible to obtain an adhesive that satisfies the required performance in a well-balanced manner, and further, it is possible to obtain an adhesive that has a uniform adhesive strength with little variation in the adhesive strength, so that the liquid crystal cell and the substrate are not damaged during rework. This can be prevented and the liquid crystal display device can be efficiently manufactured.

FIG. 1 is a measurement result of variation in adhesive strength in Example 1 and Comparative Example 2.

Hereinafter, the present invention will be described in detail.
In the present invention, (meth) acrylic means acrylic or methacrylic, (meth) acryloyl means acryloyl or methacryloyl, and (meth) acrylate means acrylate or methacrylate. The acrylic resin is a resin obtained by polymerizing a polymerization component containing at least one (meth) acrylate-based monomer.

The pressure-sensitive adhesive composition of the present invention contains an acrylic resin (A), an ionic compound (B), a silane coupling agent (C) and a cross-linking agent (D) as essential components.

<Acrylic resin (A)>
The acrylic resin (A) used in the present invention is obtained by copolymerizing the following monomer components. That is,
(A1) Normal Buty acrylate (a2) At least one monomer selected from an aromatic ring-containing monomer and an alkyl (meth) acrylate having an alkyl group having 1 to 2 carbon atoms (a3) A carboxyl group-containing monomer, a hydroxyl group-containing monomer and nitrogen. At least one polar group-containing monomer selected from atomic-containing monomers (however, it contains at least one of a carboxyl group-containing monomer and a hydroxyl group-containing monomer).
(A4) Monomers other than (a1) to (a3)

The content ratio of the normal butyl acrylate (a1) is 5 to 75% by weight, preferably 20 to 75% by weight, particularly preferably 20 to 75% by weight, based on the entire monomer components (total of (a1) to (a4)). It is 30 to 70% by weight. If the content ratio is too small, the glass transition temperature of the acrylic resin (A) becomes too high, so that the tackiness when used as an adhesive tends to decrease and the workability tends to decrease. If the content ratio is too large, the heat resistance decreases. There is a tendency.

In the above monomer (a2), examples of the aromatic ring-containing monomer include phenyl (meth) acrylate; benzyl (meth) acrylate; phenoxyalkyl (meth) acrylate such as phenoxyethyl (meth) acrylate and phenoxypropyl (meth) acrylate; Examples thereof include phenoxydialkylene glycol (meth) acrylates such as phenoxydiethylene glycol (meth) acrylate and phenoxydipropylene glycol (meth) acrylate; phenoxypolyethylene glycol (meth) acrylate; phenoxypolyethylene glycol-polypropylene glycol- (meth) acrylate. These may be used alone or in combination of two or more.

Among these, benzyl (meth) acrylate and phenoxyalkyl (meth) acrylate are characterized in that the double refraction of the acrylic resin (A) can be efficiently adjusted and the glass transition temperature of the acrylic resin (A) does not become too high. , Phenoxydialkylene glycol (meth) acrylate is preferable, and benzyl (meth) acrylate is preferable in that the monomer remaining during polymerization does not remain in the pressure-sensitive adhesive layer when the pressure-sensitive adhesive composition is dried and does not cause odor or outgas. Particularly preferable, benzyl acrylate and phenoxyethyl acrylate are particularly preferable in that the glass transition point of the acrylic resin does not rise too much.

Further, in the above-mentioned monomer (a2), examples of the alkyl (meth) acrylate having 1 to 2 carbon atoms of the alkyl group include methyl acrylate (carbon number 1), methyl methacrylate (carbon number 1), ethyl acrylate (carbon number 2), and the like. It is ethyl methacrylate (2 carbon atoms). These may be used alone or in combination of two or more.
Among these, methyl acrylate and ethyl acrylate are preferable because they are excellent in copolymerizability with other monomers and the weight average molecular weight can be easily increased.

The content ratio of the monomer (a2) is 20 to 80% by weight, preferably 25 to 70% by weight, particularly preferably 30 to 30% by weight, based on the entire monomer components (total of (a1) to (a4)). It is 60% by weight. If the content ratio is too small, the heat resistance tends to decrease, and if it is too large, the glass transition temperature of the acrylic resin (A) tends to increase, the tack when used as an adhesive tends to decrease, and the workability tends to decrease. is there.

The polar group-containing monomer (a3) is at least one selected from a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and a nitrogen atom-containing monomer, and further contains at least one of a carboxyl group-containing monomer and a hydroxyl group-containing monomer. is there.

Examples of the carboxyl group-containing monomer include (meth) acrylic acid, dimer acid of acrylic acid such as β-carboxyethyl acrylate, and the like. Among them, acrylic acid in terms of moisture-heat whitening resistance and stability during polymerization. Is preferable.

Examples of the hydroxyl group-containing monomer include primary hydroxyl groups such as hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, and hydroxyoctyl (meth) acrylate. Meta) acrylate; 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, 2- Secondary hydroxyl group-containing (meth) acrylate such as hydroxy-3-phenoxypropyl (meth) acrylate; Tertiary hydroxyl group-containing (meth) acrylate such as 2,2-dimethyl-2-hydroxyethyl (meth) acrylate; N- Examples thereof include hydroxyl group-containing (meth) acrylamide monomers such as (hydroxymethyl) (meth) acrylamide. These may be used alone or in combination of two or more.
In the present invention, the monomer having both a hydroxyl group and a nitrogen atom is included in the hydroxyl group-containing monomer as described above.

Among the above-mentioned hydroxyl group-containing monomers, it has excellent reactivity with a cross-linking agent, improved moisture-heat whitening resistance, excellent reactivity with a cross-linking agent, a solid cross-linked structure, and easy stability of adhesive strength. A primary hydroxyl group-containing monomer is preferable, and further, it is preferable to use 2-hydroxyethyl (meth) acrylate or 4-hydroxybutyl (meth) acrylate because there are few impurities such as di (meth) acrylate and it is easy to produce. ..

As the hydroxyl group-containing monomer, those having a di (meth) acrylate content ratio of 0.5% or less, which is an impurity, are preferably used, particularly preferably 0.2% or less, still more preferably 0.1. % Or less.

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

Examples of the amino group-containing monomer include primary amino group-containing monomers such as aminoalkyl (meth) acrylates such as aminomethyl (meth) acrylate and aminoethyl (meth) acrylate; and t-butylaminoethyl (meth) acrylate and the like. Secondary amino group-containing monomer; Tertiary amino group-containing monomer such as dialkylaminoethyl (meth) acrylate such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate; Examples include structure-containing monomers. These may be used alone or in combination of two or more.

Among these, a tertiary amino group-containing monomer is preferable in terms of high cross-linking promoting effect and high storage stability of the resin, excellent durability, and excellent adhesion to metals and metal oxides. In that respect, a heterocyclic amine structure-containing monomer such as (meth) acryloylmorpholine is preferable.
Of these, dimethylaminoethyl (meth) acrylate and (meth) acryloyl morpholine are particularly preferable.

Examples of the amide group-containing monomer include (meth) acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide, and N-isopropoxymethyl (meth). N-alkoxyalkyl (meth) acrylamide such as acrylamide, Nn-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide; N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) ) N, N-dialkyl (meth) acrylamide such as acrylamide and the like can be mentioned. These may be used alone or in combination of two or more.

Among these, (meth) acrylamide and N-alkoxyalkyl (meth) acrylamide and N-alkoxyalkyl (meth) acrylamide and N-alkoxyalkyl (meth) acrylamide and N-alkoxyalkyl (meth) acrylamide and N-alkoxyalkyl (meth) acrylamide and N-alkoxyalkyl (meth) acrylamide and N-alkoxyalkyl (meth) Meta) acrylamide and N, N-dialkyl (meth) acrylamide are preferred, especially in terms of copolymerizability with other monomers: acrylamide, methacrylamide, N-ethoxymethylacrylamide, N-butoxymethylacrylamide, N-iso. Butoxymethylacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide, N, N-dipropylacrylamide are preferable, and N, N-dimethylacrylamide, N, N-diethylacrylamide are more preferable.

Among the above nitrogen atom-containing monomers, N, N-dialkyl (meth) acrylamide is most preferable because it is also excellent in storage stability.

The content ratio of the polar group-containing monomer (a3) is 1 to 30% by weight, preferably 2 to 25% by weight, particularly preferably 2 to 25% by weight, based on the entire monomer components (total of (a1) to (a4)). Is 3 to 15% by weight. If the content ratio is too small, the durability and moist heat bleaching resistance (suppressing the whitening phenomenon of the adhesive layer that occurs in a moist heat environment) tend to decrease, and if it is too large, the storage stability and reworkability of the resin are deteriorated. It tends to decrease.

Examples of the monomer (a4) other than the above (a1) to (a3) include various ethylenically unsaturated group-containing monomers. From the viewpoint of the effect of the present invention, the content ratio thereof is 10 with respect to the entire monomer component. By weight% or less, preferably 5% by weight or less.

Examples of the ethylenically unsaturated monomer (a4) include iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-propyl (meth) acrylate, n-hexyl (meth) acrylate, and 2-ethylhexyl ( Meta) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, isotridecyl (meth) acrylate, myristyl (meth) Alkyl groups such as acrylates, isomyristyl (meth) acrylates, cetyl (meth) acrylates, stearyl (meth) acrylates, and isostearyl (meth) acrylates usually have 3 to 24 carbon atoms (preferably 3 to 20, particularly preferably 3). ~ 18, more preferably 3-12) (meth) acrylic acid alkyl ester (excluding n-butyl acrylate (a1)); cyclohexyl (meth) acrylate, isobornyl acrylate, dicyclopentanyl (but not). It has an alicyclic structure such as meta) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentanyloxyethyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and 2-adamantyl (meth) acrylate (meth). Acrylate: 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-butoxydiethylene glycol (meth) acrylate, methoxy Diethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, octoxypolyethylene glycol-polypropylene glycol-mono (meth) ) Acrylate, lauroxypolyethylene glycol mono (meth) acrylate, stearoxypolyethylene recall mono (meth) acrylate and other alkoxy groups and (meth) acrylic acid esters containing an oxyalkylene group can be mentioned. These may be used alone or in combination of two or more.

As a method for producing the acrylic resin (A), conventionally known methods such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization can be used. For example, a monomer component and polymerization initiation in an organic solvent can be used. The agent is mixed or dropped to polymerize under predetermined polymerization conditions. Of these, solution radical polymerization and bulk polymerization are preferable, and solution radical polymerization is particularly preferable in that the acrylic resin (A) can be stably obtained.

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. Examples thereof include aliphatic alcohols such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and ketones such as cyclohexanone.

Among these organic solvents, ethyl acetate, acetone, methyl ethyl ketone, butyl acetate, toluene, and methyl isobutyl ketone are selected from the viewpoints of ease of polymerization reaction, effect of chain transfer, ease of drying when coating with adhesive, and safety. Preferably, particularly preferred are ethyl acetate, acetone and methyl ethyl ketone.

Examples of the polymerization initiator used for such radical polymerization include 2,2'-azobisisobutyronitrile and 2,2'-azobis-2-methylbutyronitrile, which are ordinary radical polymerization initiators. Azo-based initiators such as 4,4'-azobis (4-cyanovaleric acid) and 2,2'-azobis (methylpropionic acid), benzoyl peroxide, laurolyl peroxide, di-t-butyl peroxide, cumene. Examples thereof include organic peroxides such as hydroperoxide, which can be appropriately selected and used according to the monomer to be used. These polymerization initiators can be used alone or in combination of two or more.

The weight average molecular weight of the acrylic resin (A) is preferably 200,000 to 2.5 million, particularly preferably 600,000 to 2 million, and even more preferably 1 million to 1.8 million. If the weight average molecular weight is too small, the durability tends to be lowered, and if it is too large, gelation is likely to occur during polymerization, a large amount of diluting solvent is required during production, the drying property is lowered, and the adhesive layer is contained. The amount of residual solvent increases, and the heat resistance tends to decrease.

The dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, particularly preferably 10 or less, and even more preferably 6 or less. If the degree of dispersion is too high, the cohesive force tends to decrease, and the reworkability tends to decrease or the durability tends to decrease. The lower limit of the degree of dispersion is usually 1.

The weight average molecular weight of the acrylic resin (A) is the weight average molecular weight converted to the standard polystyrene molecular weight, and is high performance liquid chromatography (manufactured by Nippon Waters Co., Ltd., "Waters 2695 (main body)" and "Waters 2414 (detection)". (Vessel) ”), column: Shodex GPC KF-806L (exclusion limit molecular weight: 2 × 10 ⁷ , separation range: 100 to 2 × 10 ⁷ , theoretical number of stages: 10,000 stages / piece, filler material: styrene-divinyl It is measured by using three series of benzene copolymer and filler particle size (10 μm), and the number average molecular weight can also be measured by the same method. The degree of dispersion 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 −45 to 10 ° C., particularly preferably −40 to 0 ° C., and even more preferably −39 to −10 ° C. If the glass transition temperature is too high, the tack tends to decrease and the workability at the time of bonding tends to decrease, and if it is too low, the durability tends to decrease.

The glass transition temperature is calculated by the following Fox formula.
Tg: Copolymer glass transition temperature (K)
Tga: Monomer A homopolymer glass transition temperature (K) Wa: Monomer A weight fraction Tgb: Monomer B homopolymer glass transition temperature (K) Wb: Monomer B weight fraction Tgn: Monomer N homo Polymer glass transition temperature (K) Wn: Weight fraction of monomer N (Wa + Wb + ... + Wn = 1)

That is, it is a value calculated by applying the glass transition temperature and the weight fraction when homopolymers of the respective monomers constituting the acrylic resin are applied to the Fox formula.

The glass transition temperature when a homopolymer of a monomer constituting an acrylic resin is used is usually measured by a differential scanning calorimeter (DSC) and conforms to JIS K7121-1987 and JIS K 6240. It can be measured by the method.

The glass transition temperature (Tg) of homopolymers of major monomers is shown below. The Tg of the acrylic resin (A) in the present invention is calculated by the following values.
(A1):
Normal Butyl Acrylate -56 ° C
(A2):
Methyl acrylate 8 ℃
Methyl methacrylate 105 ° C
Ethyl methacrylate 65 ° C
Benzyl acrylate 6 ° C
Phenoxyethyl acrylate-22 ° C
(A3):
Acrylic acid 106 ℃
2-Hydroxyethyl acrylate -15 ° C
2-Hydroxyethyl methacrylate 55 ° C
Dimethylacrylamide 119 ° C
Acryloyl morpholine 145 ° C

In the present invention, 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. As for the refractive index, it is preferable to reduce the difference in the refractive index of each of the members to be laminated because the light loss at the member interface is reduced.
The refractive index is a value measured by a NaD line using a refractive index measuring device (“Abbe refractometer 1T” manufactured by Atago Co., Ltd.) for a thin acrylic resin (A) having a refractive index of about 10 μm to 100 μm.

The haze when the acrylic resin (A) is layered 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 the display tends to deteriorate.

For such haze, the diffusion transmittance and the total light transmittance were measured using HAZE MATER NDH2000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.), and the obtained diffusion transmittance and total light transmittance values were substituted into the following equations. It was calculated. This machine complies with JIS K7361-1.
Haze (%) = (diffusion transmittance / total light transmittance) x 100

<Ionic compound (B)>
The ionic compound (B) of the present invention is required to be an ionic compound composed of a cation and an anion and having a fluorine-containing anion as an anion.

Examples of the fluorine-containing anion include fluorine-containing inorganic anions such as tetrafluoroborate anion, hexafluorophosphate anion, and N, N-bis (fluorosulfonyl) imide; N, N-bis (trifluoromethanesulfonyl) imide, N, N. Fluorine-containing organic anions such as −bis (pentafluoroethanesulfonyl) imide, N, N-bis (heptafluoropropanesulfonyl) imide, and N, N-bis (nonafluorobutanesulfonyl) imide can be mentioned.

Among the above, N, N-bis (fluorosulfonyl) imide, N, N-bis (trifluoromethanesulfonyl) imide, N, N-bis (pentafluoro) are small in that the variation in antistatic performance and adhesive strength is small. Fluorine-containing imide anions such as ethanesulfonyl) imide are preferred.

The cation may be a cation selected from an inorganic cation and an organic cation.
Examples of the inorganic cation include non-metal inorganic cations such as phosphonium cation and sulfonium cation, and metal inorganic cations such as lithium cation, sodium cation, calcium cation and potassium cation.
Examples of the organic cation include a cation having a nitrogen atom such as a quaternary ammonium cation, an imidazolium cation, a pyridinium cation, a piperidinium cation, and a pyrrolidinium cation.

Among these, non-metal cations such as organic cations are preferable in terms of excellent corrosion prevention, excellent reworkability, and small variation in adhesive strength, and among them, quaternary ammonium cations (particularly acyclic quaternary ammonium cations). ), Imidazolium cation, pyridinium cation, piperidinium cation, pyrrolidinium cation and other nitrogen atom-containing cations, particularly quaternary ammonium cation nitrogen atom-containing cation is preferable.

The melting point of the ionic compound (B) of the present invention is preferably 10 to 80 ° C, particularly preferably 25 to 50 ° C. If the melting point is too high, it tends to precipitate at a low temperature, and if it is too low, the color loss of the polarizing plate tends to occur in a moist heat environment.

In the present invention, the content of the ionic compound (B) is preferably 1 to 20 parts by weight, particularly preferably 2 to 15 parts by weight, still more preferably 2- to 100 parts by weight of the acrylic resin (A). 10 parts by weight. If it is too large, the durability tends to decrease, hydrolysis of the substrate or adherend tends to be promoted, and when it is used for a polarizing plate, the degree of polarization tends to decrease. If it is too small, the adhesive strength tends to decrease. The variation tends to be large.

<Silane coupling agent (C)>
The silane coupling agent (C) used in the present invention needs to have a weight average molecular weight of 4,000 or more, more preferably 4,500 or more, particularly preferably 5,000 or more, still more preferably 7. , 500 or more, particularly preferably 10,000 or more. The upper limit of the weight average molecular weight is preferably 100,000, more preferably 80,000, particularly preferably 50,000, and even more preferably 30,000. If the weight average molecular weight is too small, the reworkability tends to decrease, and if it is too large, the compatibility with the acrylic resin (A) tends to decrease and bleed-out tends to decrease the durability.

The above weight average molecular weight is a weight average molecular weight converted to standard polystyrene molecular weight, and is measured by the following method.
Equipment: Gel permeation chromatography detector: Differential refractive index detector RI (RI-8020 type manufactured by Tosoh Corporation, sensitivity 32)
Column: Tosoh TSKguardcolum H _HR- H (1) (φ6 mm x 4 cm), (TSKgelGMH _HR- N (2) (φ7.8 mm x 30 cm),
Solvent: tetrahydrofuran (THF)
Column temperature: 23 ° C. Flow velocity: 1.0 mL / min

The silane coupling agent (C) is an organosilicon compound containing at least one reactive functional group other than the alkoxy group and one or more alkoxy groups bonded to a silicon atom in the structure.

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. From the viewpoint of balance, a mercapto group and an epoxy group are preferable.

The alkoxy group bonded to the silicon atom preferably contains an alkoxy group having 1 to 8 carbon atoms from the viewpoint of durability and storage stability, and is particularly preferably an alkoxy group having 1 to 2 carbon atoms. Specifically, it is a methoxy group or an ethoxy group.

The alkoxy group content of the silane coupling agent (C) is preferably 1 to 30% by weight, particularly preferably 3 to 20% by weight, and even more preferably 5 to 15% by weight. If the content of the alkoxy group bonded to the silicon atom is too small, the adhesion to the liquid crystal cell tends to decrease and the durability tends to decrease, and if it is too large, the reworkability tends to decrease.

The reactive functional group equivalent of the silane coupling agent (C) is preferably 1000 g / mol or less, particularly preferably 100 to 650 g / mol, and even more preferably 300 to 600 g / mol. If the reactive functional group equivalent is too small, the reworkability tends to decrease, and if it is too large, the durability under moist heat conditions tends to decrease.

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

The silane coupling agent (C) used in the present invention may have a weight average molecular weight of 40,000 or more, for example.
3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4 epoxycyclohexyl) A part of the silane compound such as ethyltrimethoxysilane is hydrolyzed and polymerized, or the above silane compound and an alkyl group-containing silane compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane are used. An oligomer-type epoxy group-containing silane coupling agent that is a co-condensed silane compound;
Some of the silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, γ-mercaptopropyldimethoxymethylsilane, and 3-mercaptopropylmethyldimethoxysilane are hydrolyzed and depolymerized, or with the above silane compounds. An oligomer-type mercapto group-containing silane coupling agent which is a silane compound in which alkyl group-containing silane compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane are co-condensed;
Can be mentioned.
Examples of the silane coupling agent other than the above include those substituted with an alkyl group or a polyether group.
These may be used alone or in combination of two or more.

As the silane coupling agent (C) used in the present invention, specifically, "X-24-9590" (weight average molecular weight; 13,700, contained alkoxy group; methoxy) manufactured by Shin-Etsu Chemical Industry Co., Ltd., which is a commercially available product. Group, alkoxy content; 9.5% by weight, reactive functional group; epoxy group, epoxy equivalent 592 g / mol), "X-24-9589" (weight average molecular weight 4,700-containing alkoxy group ethoxy group, alkoxy group contained Amount 14.5% by weight, reactive functional group epoxy group, epoxy equivalent 1509 g / mol).

Further, in the present invention, the content of the silane coupling agent (C) is preferably 0.001 to 5 parts by weight, particularly 0.005 to 1 part by weight, based on 100 parts by weight of the acrylic resin (A). It is preferable, and 0.01 to 0.3 parts by weight is more preferable. If the content is too large, it tends to bleed out and the heat resistance tends to decrease, and if it is too small, the adhesive strength tends to increase and the heat resistance to moisture tends to decrease.

In the acrylic pressure-sensitive adhesive composition of the present invention, a silane coupling agent other than the above-mentioned silane coupling agent (C) can be used as long as the effect of the present invention is not impaired. If the total amount of the acrylic resin (A) is too large, the durability tends to decrease due to bleeding. Therefore, specifically, it is preferably 1 part by weight or less with respect to 100 parts by weight of the acrylic resin (A), and more preferably 0. It is less than 5.5 parts by weight.

<Crosslinking agent (D)>
The cross-linking agent (D) reacts with the functional groups in the acrylic resin (A) to form a cross-linked structure. For example, an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, an aziridine-based cross-linking agent, and a melamine-based cross-linking agent. Examples thereof include agents, aldehyde-based cross-linking agents, amine-based cross-linking agents, metal chelate-based cross-linking agents, and carbodiimide-based cross-linking agents. Among these, it is preferable to use an isocyanate-based cross-linking agent because it improves the adhesion to the base material and is excellent in the reactivity with the base polymer.

Examples of the isocyanate-based cross-linking agent include tolylene diisocyanate-based cross-linking agents such as 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, and xylylene diisocyanate-based cross-linking agents such as 1,3-xylylene diisocyanate. Diphenylmethane-based cross-linking agents such as diphenylmethane-4,4-diisocyanate, aromatic isocyanate-based cross-linking agents such as naphthalene diisocyanate such as 1,5-naphthalenediocyanate; isophorone diisocyanate, 1,4-cyclohexanediisocyanate, 4,4 Alicyclic isocyanate-based cross-linking agents such as'-dicyclohexylmethane diisocyanate, methylcyclohexanediisocyanate, isopropyridendicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane, norbornandiisocyanate; hexamethylenediisocyanate, trimethylhexa Examples thereof include aliphatic isocyanate-based cross-linking agents such as methylene diisocyanate; and adducts, bullets, and isocyanurates of the above isocyanate compounds. These may be used alone or in combination of two or more.

Among these, a tolylene diisocyanate-based cross-linking agent is preferable in terms of pot life and durability, and a non-aromatic isocyanate-based cross-linking agent is preferable in terms of yellowing resistance. Of these, specifically, tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate and trimethylolpropane adducts, and nucleohydrates are preferable because they have an excellent balance of durability, pot life, and cross-linking rate. ..

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

The content of the cross-linking agent (D) is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, particularly preferably 0.05 parts by weight, based on 100 parts by weight of the acrylic resin (A). Is 0.1 to 1.5 parts by weight. If the content is too small, the durability tends to decrease and adhesive residue tends to occur during rework, and if it is too large, the stress relaxation property decreases and the liquid crystal cell tends to warp, resulting in uneven display on the liquid crystal display. It tends to be more likely to occur.

Further, the pressure-sensitive adhesive composition of the present invention contains resin components other than the acrylic resin (A), acrylic monomers, polymerization inhibitors, and antioxidants as other components as long as the effects of the present invention are not impaired. , Corrosion inhibitors, cross-linking accelerators, radical generators, peroxides, various additives such as radical supplements, metal and resin particles and the like can be blended. In addition to the above, a small amount of impurities and the like contained in the raw materials for producing the constituent components of the pressure-sensitive adhesive composition may be contained.

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 with respect to the acrylic resin (A). If the content is too large, the compatibility with the acrylic resin (A) tends to decrease, and the durability tends to decrease.

Thus, the pressure-sensitive adhesive composition of the present invention can be obtained.
The pressure-sensitive adhesive composition of the present invention can be made into a pressure-sensitive adhesive by cross-linking with a cross-linking agent (D), and further, a pressure-sensitive adhesive layer made of such a pressure-sensitive adhesive is laminated on a polarizing plate (optical laminate). Thereby, a polarizing plate with an adhesive layer can be obtained.
It is preferable that the polarizing plate with the pressure-sensitive adhesive layer is further provided with a release sheet on the surface opposite to the polarizing plate of the pressure-sensitive adhesive layer.

As a method for producing the above-mentioned polarizing plate with an adhesive layer, [1] the pressure-sensitive adhesive composition is applied onto the polarizing plate, dried, and then a release sheet is attached, and at least aging at room temperature or in a heated state is performed. Method of performing treatment by one of the methods, [2] A method of applying the pressure-sensitive adhesive composition on a release sheet, drying it, attaching a polarizing plate, and performing the treatment by at least one of aging at room temperature or in a heated state. And so on.
Among these, the method of aging at room temperature by the method of [2] is preferable in that it does not damage the polarizing plate and has excellent substrate adhesion.

Such an aging treatment is carried out in order to balance the adhesive physical characteristics as the reaction time of the chemical cross-linking of the pressure-sensitive adhesive, and the aging conditions are such that the temperature is usually room temperature to 70 ° C. and the time is usually 1 day to 30 days. Specifically, it may be carried out under the conditions of, for example, 23 ° C. for 1 to 20 days, 23 ° C. for 3 to 10 days, 40 ° C. for 1 to 7 days, and the like.

When applying the pressure-sensitive adhesive composition, it is preferable to dilute the pressure-sensitive adhesive composition with a solvent and apply it, and the dilution concentration is preferably 5 to 60% by weight, particularly preferably 10 as the heating residue concentration. ~ 30% by weight.

The solvent is not particularly limited as long as it dissolves the pressure-sensitive adhesive composition, and is, for example, an ester solvent such as methyl acetate, ethyl acetate, methyl acetoacetate, ethyl acetoacetate, acetone, methyl ethyl ketone, and the like. A ketone solvent such as methylisobutylketone, an aromatic solvent such as toluene and xylene, and an alcohol solvent such as methanol, ethanol and propyl alcohol can be used. Among these, ethyl acetate and methyl ethyl ketone are preferably used from the viewpoints of solubility, dryness, price and the like.

The pressure-sensitive adhesive composition is applied by a conventional method such as roll coating, die coating, gravure coating, comma coating, or screen printing.

The thickness of the pressure-sensitive adhesive layer in the obtained polarizing plate with a pressure-sensitive adhesive layer is preferably 5 to 100 μm, particularly preferably 10 to 50 μm, and further preferably 10 to 30 μm.
If the thickness of the pressure-sensitive adhesive layer is too thin, the pressure-sensitive adhesive for polarizing plates does not have sufficient stress relaxation properties, and the durability tends to decrease. Tends to decline.

The gel fraction of the pressure-sensitive adhesive layer produced by the above method is preferably 30 to 100%, particularly preferably 40 to 95%, and further preferably 50 from the viewpoint of durability performance and suppression of decrease in polarization degree. ~ 90%. If the gel fraction is too low, durability tends to be insufficient or reworkability tends to decrease, and if it is too high, floating or peeling tends to occur.

The gel fraction is a measure of the degree of cross-linking (degree of curing), and is calculated by, for example, the following method. That is, the pressure-sensitive adhesive is collected by picking from the pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer formed on the base material, the pressure-sensitive adhesive is wrapped in a 200-mesh SUS wire mesh, and immersed in ethyl acetate at 23 ° C. for 24 hours. The weight percentage of the remaining insoluble adhesive component is defined as the gel fraction.

It is preferable that the pressure-sensitive adhesive layer produced by the above method has a good tack feeling when touched with a finger because it has good wettability when actually applied to an adherend, and thus tends to improve workability. ..

As for the electrical characteristics of the pressure-sensitive adhesive layer obtained by using the pressure-sensitive adhesive composition of the present invention, a low surface resistance value is preferable as a countermeasure against static electricity, and particularly preferably 1 × 10 ¹² Ω / □ or less, more preferably 5 ×. It is 10 ¹¹ Ω / □ or less, particularly preferably 1 × 10 ¹¹ Ω / □ or less. If the surface resistance value is too high, it is difficult to obtain antistatic performance, and it tends to be difficult to recover from display defects of the liquid crystal display due to static electricity.

In the polarizing plate with an adhesive layer of the present invention, if the polarizing plate has a release sheet directly or has a release sheet, the release sheet is peeled off, and then the adhesive layer surface is attached to the glass base material of the liquid crystal cell and used for, for example, a liquid crystal display board. And the image display device is manufactured.

When the pressure-sensitive adhesive composition of the present invention is formed into a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed by cross-linking, the average adhesive strength thereof is appropriately determined depending on the material of the adherend and the like, but glass such as a liquid crystal cell When attached to a substrate, it preferably has an adhesive force of 0.1 to 20 N / 25 mm, and particularly preferably 0.1 to 10 N / 25 mm.

Further, in terms of reducing damage to the adherend, it is preferable that there is little variation in the adhesive strength of the pressure-sensitive adhesive layer, and the coefficient of variation of the adhesive strength calculated from the following formula (1) is preferably less than 4%. , More preferably less than 3%.
Coefficient of variation of adhesive strength = standard deviation of adhesive strength / average value of adhesive strength x 100 ... (1)

Average value of adhesive strength: When the peeling start point is the peeling distance of 0 mm and the peeling end point is the peeling distance of 120 mm, the peeling distance of 30 mm to 110 mm is used as the measuring part, and the average of the adhesive strength for 1600 points measured every 0.05 mm. The value was used. The measured values near the peeling start point and peeling end point were excluded from the measurement as noise.

Standard deviation of adhesive strength: When the peeling start point is the peeling distance of 0 mm and the peeling end point is the peeling distance of 120 mm, the peeling distance of 30 mm to 110 mm is used as the measuring part, and the standard deviation value for the measured value of 1600 points every 0.05 mm is used. Using.
The measured values near the peeling start point and peeling end point were excluded from the measurement as noise.

The average value of the adhesive strength (average adhesive strength) is measured as follows.
That is, the polarizing plate with the pressure-sensitive adhesive layer was cut to a width of 25 mm, the release sheet was peeled off, the surface of the pressure-sensitive adhesive layer was washed with methanol and then dried at 50 ° C. for 20 minutes under 23 ° C. and 50% RH conditions. After allowing to stand for 3 hours, the polarizing plate and the glass plate are bonded to each other by pressing against a non-alkali glass plate (“Eagle XG” manufactured by Corning Inc.). Then, after performing an autoclave treatment (50 ° C., 0.5 MPa, 20 minutes), the mixture was allowed to stand at 23 ° C. and 50% RH for 24 hours, and then a 180 ° peeling test was performed. calculate.

The pressure-sensitive adhesive obtained by using the pressure-sensitive adhesive composition of the present invention has an excellent balance of various performances such as rework resistance, durability, and antistatic property, and further, the variation in adhesive strength during rework is small and uniform. Since a pressure-sensitive adhesive having a high adhesive strength can be obtained, it is useful as a pressure-sensitive adhesive for a polarizing plate for bonding a polarizing plate and a glass substrate or the like.

Examples of the protective film constituting the polarizing plate include a triacetyl cellulose-based film, an acrylic film, a polyethylene-based film, a polypropylene-based film, and a cycloolefin-based film. However, it is also preferably used.

Hereinafter, 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 gist of the present invention is not exceeded. In the example, "part" and "%" mean the weight standard.

The weight average molecular weight of the acrylic resin (A), the degree of dispersion, the glass transition temperature, the weight average molecular weight of the silane coupling agent, and the gel fraction of the pressure-sensitive adhesive were measured according to the above-mentioned method.
The glass transition temperature of the acrylic resin (A) is calculated using the Fox formula described above, and the glass transition temperature when a homopolymer of the monomers constituting the acrylic resin (A) is used is usually measured by DSC. The values described in the literature and the values described in the catalog were used.
The viscosity was measured according to the 4.5.3 rotational viscometer method of JIS K5400 (1990).

[Manufacturing of acrylic resin (A-1)]
Normal butyl acrylate (a1) 64.5 parts, methyl acrylate (a2) 30 parts, 2-hydroxyethyl acrylate in a 4-neck round bottom flask equipped with a reflux cooler, a stirrer, a nitrogen gas inlet and a thermometer. (A3) 5 parts, acrylic acid (a3) 0.5 parts, ethyl acetate 83 parts, acetone 42 parts, and 0.0126 parts of azobisisobutyronitrile (AIBN) as a polymerization initiator were charged, and 2,2'-. Azobis-2,4-dimethylvaleronitrile (ADVN) acetic acid solution (ADVN: 0.0126 parts, ethyl acetate 30 parts) is added dropwise and reacted at reflux temperature for 3.25 hours, then diluted with ethyl acetate to make an acrylic system. Resin (A-1) solution (solid content 17.4%, viscosity 4,120 mPa · s / 25 ° C; acrylic resin (A-1): glass transition temperature-37.5 ° C, weight average molecular weight 1.41 million, degree of dispersion 4.0) was obtained (see Table 1).

[Manufacturing of acrylic resin (A-2)]
Normal butyl acrylate (a1) 59.5 parts, methyl acrylate (a2) 25 parts, benzyl acrylate (a2) in a 4-neck round bottom flask equipped with a reflux cooler, a stirrer, a nitrogen gas inlet and a thermometer. 10 parts, 2-hydroxyethyl acrylate (a3) 5 parts, acrylic acid (a3) 0.5 parts, ethyl acetate 83 parts, acetone 42 parts, azobisisobutyronitrile (AIBN) 0.0126 parts as a polymerization initiator , 2'-azobis-2,4-dimethylvaleronitrile (ADVN) acetic acid solution (ADVN: 0.0126 parts, ethyl acetate 30 parts) was dropped and reacted at reflux temperature for 3.25 hours, and then acrylic. Acrylate resin (A-1) solution diluted with ethyl (solid content 16.4%, viscosity 2,620 mPa · s / 25 ° C; acrylic resin (A-1): glass transition temperature −34.7 ° C. , Weight average molecular weight 1.4 million, dispersity 3.5) (see Table 1).

[Manufacturing of acrylic resin (A-3)]
In a 4-neck round bottom flask equipped with a reflux cooler, a stirrer, a nitrogen gas inlet and a thermometer, 52.3 parts of normal butyl acrylate (a1), 20 parts of methyl acrylate (a2), and benzyl acrylate (a2). 19 parts, 2-hydroxyethyl acrylate (a3) 8 parts, acrylic acid (a3) 0.7 parts, ethyl acetate 54.9 parts, acetone 42 parts, azobisisobutyronitrile (AIBN) as a polymerization initiator 0. Add 013 parts, react with azobisisobutyronitrile acetic acid solution at reflux temperature for 3.25 hours, dilute with ethyl acetate, and dilute with acrylic resin (A-1) solution (solid content 22.9%). Acrylic resin (A-1): glass transition temperature -31.0 ° C., weight average molecular weight 1.4 million, dispersibility 4.3) was obtained (see Table 1).

<Ionic compound>
The following were prepared as ionic compounds.
Ionic compound having fluorine as an anion (B-1): Ionic compound composed of ammonium cation and N, N-bis (fluorosulfonyl) imidebi (“MP-402” manufactured by Daiichi Kogyo Seiyaku Co., Ltd., melting point 47 ° C.)
(B-2): Trin-butylmethylammonium N, N- (trifluoromethanesulfonyl) imide (“FC-4400” manufactured by 3M Ltd., melting point 27.5 ° C.)

<Silane coupling agent>
The following silane coupling agents were prepared.
(C-1): "X-24-9590" manufactured by Shin-Etsu Chemical Industry Co., Ltd. (weight average molecular weight; 13,700, alkoxy group content: 9.5% by weight, reactive functional group; epoxy group, epoxy equivalent 592 g / Mol, containing alkoxy group; methoxy group)
(C'-1): "X-41-1059A" manufactured by Shin-Etsu Chemical Industry Co., Ltd. (weight average molecular weight; 2,300, alkoxy group content: 42% by weight, reactive functional group; epoxy group, epoxy equivalent 350 g / mol, containing alkoxy group; methoxy group, ethoxy group)
(C'-2): "X-41-1805" manufactured by Shin-Etsu Chemical Industry Co., Ltd. (weight average molecular weight 3,450;, alkoxy group content; 50% by weight, reactive functional group; mercapto group, mercapto equivalent 800 g / mol, containing alkoxy group; methoxy group, ethoxy group)

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

<Examples 1 to 3 and Comparative Examples 1 to 3>
Each component (A) to (D) prepared and prepared as described above is blended as shown in Table 2 below, and the solid content concentration is adjusted to 12.5% with ethyl acetate to prepare an adhesive composition. I got something.

[Preparation of polarizing plate with adhesive layer]
The obtained pressure-sensitive adhesive composition was applied to a 38 μm polyester-based release sheet (“Therapeutic WZ” manufactured by Toray Co., Ltd.) so that the thickness after drying was 20 μm, dried at 100 ° C. for 3 minutes, and then triacetyl cellulose ("Therapeutic WZ"). TAC) An adhesive layer surface on the opposite side of the release sheet is attached to the surface of one TAC film of a polarizing plate in which films are laminated on both sides, and cured in a 23 ° C. × 50% RH environment for 7 days with an adhesive layer. A polarizing plate was obtained (layer structure; release sheet / adhesive layer / TAC film / polarizer / TAC film).
Using the obtained polarizing plate with an adhesive layer, the gel fraction, antistatic performance, reworkability (average adhesive strength, variation in adhesive strength), and durability were evaluated as follows. The results are shown in Table 2.
Further, with respect to Example 1 and Comparative Example 2, the measurement results of the variation in adhesive strength are shown in FIG.

<Antistatic property>
[Surface resistance value]
After allowing the above polarizing plate with an adhesive layer to stand in an atmosphere of 23 ° C. × 50% RH for 24 hours, the release sheet of the adhesive layer is removed and a surface resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd., device name “ The surface resistivity value of the pressure-sensitive adhesive layer was measured using "Hiresta-UP MCP-HT450") and evaluated according to the following criteria.
◎ ・ ・ ・ 1 × 10 ¹¹ Ω / less than □,
〇 ・ ・ ・ 1 × 10 ¹¹ Ω / □ or more, 5 × 10 ¹¹ Ω / □ or less △ ・ ・ ・ 5 × 10 ¹¹ Ω / □ or more, 1 × 10 ¹² Ω / □ or less × ・ ・ ・ 1 × 10 ¹² Ω / □ or more.

<Durability>
The obtained polarizing plate with an adhesive layer is cut into a size of 15 cm × 20 cm cm × 160 cm, the release sheet is peeled off, and the adhesive layer surface is pressed against alkaline glass (“Eagle XG” manufactured by Corning Inc .: thickness 0.7 mm) to 2 kg. After two reciprocating movements with a roller, they were subjected to an autoclave treatment (0.5 Mpa × 50 ° C. × 20 minutes) to prepare a sample for durability test.
Using the obtained durability test sample, the following durability test was performed and evaluated.

[Heat resistance test]
250 hours in an atmosphere of 85 ° C [moisture resistance test]
Durability test for 250 hours in an atmosphere of 60 x 90 ° C (evaluation standard)
○ ・ ・ ・ No floating was seen between the polarizing plate and the glass × ・ ・ ・ Floating was seen between the polarizing plate and the glass

<Reworkability>
[Average adhesive strength]
The polarizing plate with the adhesive layer obtained above is cut to a width of 25 mm, the release sheet is peeled off, and the adhesive layer surface is pressed against alkali-free glass ("Eagle XG" manufactured by Corning Inc .: thickness 1.1 mm) with a 2 kg roller. After bonding and autoclaving (0.5 Mpa x 50 ° C x 20 minutes), letting it stand in a 23 ° C x 50% RH environment for 1 day and 15 days, then peeling it off to 180 ° and peeling distance. The average value of 1600 points of adhesive strength for every 0.05 mm at a peeling distance of 30 mm to 110 mm out of 120 mm was obtained. The same measurement was performed twice, the average value was calculated, and the evaluation was made according to the following criteria.
(Evaluation criteria)
◎ ・ ・ ・ 5N / 25mm or less 〇 ・ ・ ・ 5N / 25mm or more and less than 10N / 25mm Δ ・ ・ ・ 10N / 25mm or more and less than 20N / mm × ・ ・ ・ 20N / 25mm or more or adhesive residue occurs

[Variation of adhesive strength]
In the above rework test, the coefficient of variation of the adhesive force at 1600 points of the adhesive force at every 0.05 mm at a peeling distance of 30 mm to 110 mm was calculated from the following formula. The same measurement was performed twice, the average value was calculated, and the evaluation was made according to the following criteria.
Coefficient of variation = (standard deviation of 1600 points of adhesive strength with peeling distance of 30 mm to 110 mm) / average adhesive strength (evaluation standard)
◎ ・ ・ ・ Less than 2.5 〇 ・ ・ ・ 2.5 or more and less than 4 △ ・ ・ ・ 4 or more and less than 5 × ・ ・ ・ 5 or more

From the results in Table 2, in the example using the pressure-sensitive adhesive composition containing the ionic compound (B) having a fluorine-containing anion and the high-molecular-weight silane coupling agent (C), the glass transition temperature with high durability was obtained. It can be seen that even when an acrylic resin obtained by copolymerizing a polymerization component having a high polymer content is used, in addition to the reworkability, the variation in adhesive strength is small and stable peeling strength can be exhibited.
This is because the ionic compound having a fluorine-containing anion and the high-molecular-weight silane coupling agent are both contained in the pressure-sensitive adhesive layer, so that the ionic compound and the silane coupling agent are segregated on the surface of the pressure-sensitive adhesive, and as a result, Since the wetting of the adherend is improved, it is considered that the adhesive strength varies little and uniform adhesive strength can be exhibited.

On the other hand, in Comparative Examples 1 and 2 using the pressure-sensitive adhesive composition containing no silane coupling agent having a weight average molecular weight of 4,000 or more, the coefficient of variation of the pressure-sensitive adhesive strength is large and the pressure-sensitive adhesive strength varies. I understand.
Further, it can be seen that in Comparative Example 3 in which the ionic compound having a fluorine-containing anion is not used, not only the antistatic performance but also the coefficient of variation of the adhesive strength is large, and the adhesive strength varies.
It can be seen that the difference in the adhesive strength is clear from FIG. 1, which shows the measurement results of Example 1 and Comparative Example 2.

The pressure-sensitive adhesive composition of the present invention has various properties such as reworkability, durability, and antistatic property when used as a pressure-sensitive adhesive used for bonding a polarizing plate (protective film) and a liquid crystal cell (glass base material). It is possible to obtain an adhesive that satisfies the required performance in a well-balanced manner, and further, it is possible to obtain an adhesive layer that not only has a low average adhesive strength but also has a small variation in the adhesive strength and exhibits a uniform adhesive strength. .. Therefore, it is possible to prevent damage to the liquid crystal cell and the substrate during rework, and it is possible to efficiently manufacture a liquid crystal display device, which is very useful as an adhesive for a polarizing plate.

Claims (4)

Acrylic resin (A)
Ionic compound (B)
Silane coupling agent (C)
A pressure-sensitive adhesive composition containing a cross-linking agent (D).
The acrylic resin (A) is obtained by copolymerizing the following monomers (a1) to (a4) in the following proportions with respect to the total monomer components.
(A1) Normal Butyl Acrylate 5 to 75% by Weight
(A2) At least one monomer selected from an aromatic ring-containing monomer and an alkyl (meth) acrylate having 1 to 2 carbon atoms in an alkyl group 20 to 80% by weight.
(A3) At least one polar group-containing monomer selected from a carboxyl group-containing monomer, a hydroxyl group-containing monomer, and a nitrogen atom-containing monomer 1 to 30% by weight.
(However, it contains at least one of a carboxyl group-containing monomer and a hydroxyl group-containing monomer.)
(A4) Monomers other than (a1) to (a3) 10% by weight or less The ionic compound (B) is an ionic compound having a fluorine-containing anion.
A pressure-sensitive adhesive composition, wherein the silane coupling agent (C) has a weight average molecular weight of 4,000 or more. A pressure-sensitive adhesive for polarizing plates, wherein the pressure-sensitive adhesive composition according to claim 1 is crosslinked by a cross-linking agent (D). A polarizing plate with a pressure-sensitive adhesive layer, which comprises a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive for a polarizing plate according to claim 2. An image display device according to claim 3, wherein the polarizing plate with an adhesive layer is used.

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