JPH08199134A - Tacky agent for optical film, optical film having tacky agent layer and liquid crystal display device - Google Patents

Abstract

PURPOSE: To obtain the subject tacky agent consisting essentially of a specific acrylic copolymer, not causing release and not producing foam at the interface between a tacky agent layer and a liquid crystal cell, even under high temperature and humidity and excellent in heat resistance and moisture resistance. CONSTITUTION: This tacky agent consists essentially of an acrylic copolymer obtained by copolymerizing (A) 50-98wt.%, preferably 60-97wt.% acrylic monomer (e.g. n-butyl acrylate) of the formula CH2 =C(R<1> )COOR<2> (R<1> is H or methyl; R<2> is a 2-14C alkyl) with (B) 50-2wt.%, preferably 30-3wt.% imide-containing monomer [preferably a maleimide compound of the formula (R<3> is H or a monofunctional organic group)] copolymerizable with the component A. Furthermore, when the component A is copolymerized with the component B by a bulk polymerization method, a polymerization system by ultraviolet ray irradiation is preferably used. The tacky agent is preferably applied to an optical film provided with an optically transparent protective layer thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic pressure sensitive adhesive which is mainly useful for bonding an optical film to a glass substrate of a liquid crystal cell, and an optical pressure sensitive adhesive layer comprising the acrylic pressure sensitive adhesive layer provided on at least one side of the optical film. The present invention relates to a film and a liquid crystal display device having the optical film arranged on the surface of a liquid crystal cell.

[0002]

2. Description of the Related Art Generally, an optical film is a polarizing plate, such as a stretched polyvinyl alcohol film in which iodine or a dichroic dye is orientated as a polarizer is laminated and adhered on both sides with triacetyl cellulose film. A retardation plate, for example, a retardation plate in which a retardation is generated by stretching a polycarbonate is used.

A liquid crystal display panel is manufactured by adhering these optical films to a glass substrate of a liquid crystal cell. Adhesion of the optical film to the glass substrate is usually performed by previously providing an adhesive layer on one or both surfaces of the optical film and pressing the adhesive layer onto the glass substrate. Adhesive, transparency,
Acrylic adhesives, which are excellent in terms of weather resistance, are often used.

By the way, as liquid crystal display devices have been widely used in various fields such as measuring instruments, electronic timepieces, televisions, and even in-vehicle devices, and the number of occasions in which they are used under harsh conditions has increased, optical films and It is required that the adhesion to the liquid crystal cell via the pressure-sensitive adhesive layer should sufficiently withstand use in a hot and humid atmosphere.

[0005]

However, when an acrylic pressure-sensitive adhesive is used, in an atmosphere of high temperature and high humidity, peeling may occur at the interface between the pressure-sensitive adhesive layer and the liquid crystal cell, or bubbles that hinder visual recognition may occur. There are problems such as occurrence, and they do not always satisfy the above requirements.

In view of the above circumstances, the present invention is an optical having excellent heat resistance and moisture resistance, which does not cause peeling or bubbles at the interface between the pressure-sensitive adhesive layer and the liquid crystal cell even in a hot and humid atmosphere. An object is to provide an acrylic adhesive for films, an optical film with an adhesive layer using this adhesive, and a liquid crystal display device.

[0007]

DISCLOSURE OF THE INVENTION As a result of earnest studies on the above-mentioned objects, the present inventors have found that, in order to solve the problems of peeling and generation of bubbles, the pressure-sensitive adhesive layer can suppress peeling. It was clarified that it is necessary to improve the adhesive strength and the elastic modulus that can prevent the generation of bubbles.

However, it is difficult to make the elastic modulus and the adhesive force compatible with each other, because the improvement of the elastic modulus usually leads to the decrease of the adhesive area and lowers the adhesive force. There is also a method of increasing the adhesive force by subjecting an adherend to a surface treatment with a primer, but the surface treatment causes a new generation of foaming and the problem of bubble generation cannot be overcome.

Therefore, as a result of further studies by the present inventors, an acrylic copolymer composed of an acrylic monomer and a specific monomer has an excellent balance between adhesive strength and elastic modulus. When it is used as a pressure-sensitive adhesive for adhering the optical film and the glass substrate, it can withstand use in a high temperature and high humidity atmosphere, that is, peeling occurs at the interface between the pressure-sensitive adhesive layer and the liquid crystal cell even in the above atmosphere. The present invention has been completed by finding that a highly reliable liquid crystal display device having excellent heat resistance and humidity resistance, which does not generate or generate bubbles, can be obtained.

That is, the present invention has the general formula (A); CH
₂ = C (R ¹ ) COOR ² (wherein R ¹ is hydrogen or a methyl group, R ² is an alkyl group having 2 to 14 carbon atoms), and 50 to 98% by weight of an acrylic monomer. , An imide group-containing monomer 50 copolymerizable with this acrylic monomer
The present invention relates to a pressure-sensitive adhesive for an optical film, characterized in that the main component is an acrylic copolymer of 2 wt%.

Further, the present invention has a pressure-sensitive adhesive layer as a form of use of the pressure-sensitive adhesive for optical film, wherein at least one kind of the pressure-sensitive adhesive for optical film is provided on at least one surface of the optical film. The present invention relates to an optical film, and further to a liquid crystal display device characterized in that at least one optical film having the above-mentioned adhesive layer is arranged on the surface of a liquid crystal cell.

[0012]

In the acrylic monomer represented by the general formula (A) in the present invention, R ^{2 in} the formula is, for example, ethyl group, propyl group, butyl group, isobutyl group,
It is an ester of acrylic acid or methacrylic acid consisting of an alkyl group such as an isoamyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an isooctyl group, an isononyl group and an isodecyl group. When the carbon number of R ² is less than 2, it becomes a material having a high glass transition temperature, so-called Tg, and the wettability as a pressure-sensitive adhesive decreases, and the initial adhesiveness (tack) deteriorates. There is an inferior problem.

The acrylic monomer represented by the general formula (A) is used in an amount of 50 to 98% by weight, preferably 60 to 97% by weight, based on the total amount of the monomers, and one or two of them.
More than one seed is used. When the amount is less than 50% by weight, T is similar to the case where the alkyl group has less than 2 carbon atoms.
The component having a low g is too small to exhibit the performance as an adhesive. On the other hand, when it exceeds 98% by weight, the absolute amount of the imide group-containing monomer, which will be described later, is insufficient, and it becomes difficult to improve the adhesive performance.

As the imide group-containing monomer in the present invention, the following general formula (B); (However, R ³ is hydrogen or a monovalent organic group), maleimide compounds, itacone imide compounds, succinimide compounds, and the like are preferably used, and other citracone imide compounds can also be used.

As the maleimide compound, R in the general formula is used.
³ is hydrogen (maleimide itself), or an alkyl group, a cycloalkyl group, an allyl group, an aralkyl group or a monovalent organic group having a functional group further introduced into these groups, for example, a methyl group or an ethyl group. , Propyl group,
Isopropyl group, butyl group, hexyl group, octyl group,
Examples thereof include 2-ethylhexyl group, lauryl group, cyclohexyl group, phenyl group, methylphenyl group, methoxyphenyl group, chlorophenyl group, nitrophenyl group, carboxyphenyl group, and hydroxyphenyl group.

The itacone imide compounds include N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N.
-2 ethylhexyl itaconimide, N-cyclohexyl itaconimide, N-lauryl itaconimide, N-
Examples include octyl itaconimide.

Examples of the succinimide compound include N- (meth) acryloyloxymethylene succinimide and N- (meth) acryloyloxymethylene succinimide.
(Meth) acryloyl-2-oxydimethylene succinimide, N- (meth) acryloyl-6-oxyhexamethylene succinimide, N- (meth) acryloyl-
8-oxyoctamethylenesuccinimide, N- (meth) acryloyl-10-oxydecamethylenesuccinimide, N- (meth) acryloyl-12-oxide decamethylenesuccinimide, N- (meth) acryloyl-2-methyl-3-oxytri Examples thereof include methylene succinimide and N- (meth) acryloyl-4-ethyl-6-oxyhexamethylene succinimide. In addition, N- (meth) acryloyl-10-oxydecamethylenephthalimide, N- (meth) acryloyl-12-
Oxide decamethylene phthalimide, N- (meth) acryloyl-14-oxytetradecamethylene phthalimide, N- (meth) acryloyl-16-oxyhexadecamethylene phthalimide, N- (meth) acryloyl-
18-oxyoctadecamethylenephthalimide, N-
(Meth) acryloyl-2-methyl-3-oxytrimethylenephthalimide, N- (meth) acryloyl-4-
Ethyl-6-oxyhexamethylene phthalimide, N-
(Meth) acryloyl-16-oxyhexadecamethylene-4-methylphthalimide and the like can be mentioned.

One or more of these imide group-containing monomers are used in the range of 50 to 2% by weight, preferably 30 to 3% by weight, based on the total amount of the monomers. If it exceeds 50% by weight, the initial adhesiveness is impaired, and if it is less than 2% by weight, the effect of improving the adhesive properties in a hot and humid atmosphere cannot be obtained.

In the present invention, in addition to the acrylic monomer represented by the general formula (A) and the imide group-containing monomer, other monomers copolymerizable therewith may be used. it can. Such other monomer is used in one kind or two or more kinds in the range of 30% by weight or less, preferably 25% by weight or less of the total amount of the monomers. 30% by weight
When it exceeds, it becomes difficult to develop the performance as an acrylic type and it becomes difficult to balance the properties as an adhesive.

Examples of such other monomer include (meth)
Acrylic acid, carboxyethyl acrylate, itaconic acid, maleic acid, crotonic acid and other carboxyl group-containing monomers, maleic anhydride, itaconic anhydride and other acid anhydride monomers, (meth) acrylic acid 2- Hydroxyethyl,
A hydroxyl group-containing monomer such as 2-hydroxypropyl (meth) acrylate and an epoxy group-containing monomer such as glycidyl (meth) acrylate are preferable. These produce an intermolecular reaction of the acrylic copolymer by the reaction with the intermolecular crosslinking agent, and bring good results in improving adhesive properties such as cohesive force.

In addition to the above monomers, sulfonic acid group-containing monomers such as 2-acrylamido-2-methylpropanesulfonic acid, phosphoric acid group-containing monomers such as 2-hydroxyethylacryloyl phosphate, ( Amide-based monomers such as (meth) acrylamide and N-substituted (meth) acrylamide, vinyl acetate, N-vinylpyrrolidone, N-vinylcarboxylic acid amides, vinyl-based monomers such as styrene, and divinyl-based such as divinylbenzene. Monomer, 1,4
Di (meth) acrylate monomers such as -butyldi (meth) acrylate and 1,6-hexyldi (meth) acrylate, methyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate , Polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, fluorine (meth) acrylate, silicon (meth) acrylate, etc. represented by the general formula (A) -(Meth) acrylic acid ester-based monomers other than the -to-based monomers may also be used.

Further, a polyfunctional acrylate or the like is also used if necessary. For example, when it is desired to carry out post-crosslinking under a non-crosslinking agent using an electron beam or the like, hexanedioldi (meth) acrylate, (poly) ethyleneglycoldi (meth) acrylate, (poly) propyleneglycol Luzi (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol lute (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth)
Acrylate, dipentaerythritol hexa (meta)
Acrylate, other epoxy (meth) acrylate,
Polyester (meth) acrylate, urethane (meth)
Acrylate is used.

In the present invention, the acrylic monomer represented by the above general formula (A) and the imide group-containing monomer, or these and the above other monomers are subjected to a solution polymerization method and an emulsion polymerization method. An acrylic copolymer is produced by copolymerization by a conventional method using a conventionally known polymerization method such as a compounding method, a bulk polymerization method or a suspension polymerization method. In the case of the bulk polymerization method, a polymerization method using ultraviolet irradiation is preferably adopted.

In the above copolymerization, a polymerization initiator,
If necessary, it can be used in the range of 0.001 to 5% by weight based on the whole polymerization raw material (solid content). As such a polymerization initiator, the following various thermal polymerization initiators and photopolymerization initiators are used. In addition, in the emulsion polymerization method, potassium persulfate, ammonium persulfate, hydrogen peroxide, and the like, and redox initiators in which these are used in combination with a reducing agent are also preferably used.

As the thermal polymerization initiator, benzoyl peroxide, tert-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbone can be used.
Di-n-propylperoxydicarbonate, di (2-ethoxyethyl) peroxydicarbonate, t
ert-butyl peroxynedecanoate, tert
-Butyl peroxypivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl per
Examples thereof include organic peroxides such as oxide and diacetylperoxide. Further, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl-2,
2'-azobis (2-methylpropionate), 4,4
′ -Azobis (4-cyanovaleric acid), 2,2′-
Azobis (2-hydroxymethylpropionitrile),
Also included are azo compounds such as 2,2'-azobis [2- (2-imidazolin-2-yl) propane].

As the photopolymerization initiator, 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone, α-hydroxy-α, α'-dimethylacetophenone, methoxyacetophenone, 2 , 2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1- [4-
(Methylthio) -phenyl] -2-morpholinopropane-1 and other acetophenone-based initiators; benzoin ethyl ether, benzoin isopropyl ether and other benzoin ether-based initiators; benzyl dimethyl ketal and other ketals Type initiators; benzophenone, benzoylbenzoic acid, benzophenone type initiators such as 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone,
2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,
Thioxanthone-based initiators such as 4-diethylthioxanthone and 2,4-diisopropylthioxanthone; and camphorquinone, halogenated ketones, acylphosphinoxides, acylphosphonates and the like.

The pressure-sensitive adhesive for optical films of the present invention contains the acrylic copolymer thus obtained as a main component, and if necessary, natural or synthetic resins, glass fibers,
Fillers such as glass beads, metal powder, and inorganic powder, additives such as pigments and colorants, and antioxidants can be included as optional components.

In this pressure-sensitive adhesive for optical film, a polyfunctional isocyanate is used after an acrylic copolymer is obtained.
Compounds (for example, tolylene diisocyanate, trimethylolpropane tolylene diisocyanate, diphenylmethane triisocyanate, etc.), epoxy compounds (for example, polyethylene glycol diglycidyl ether)
(For example, ter, trimethylolpropane triglycidyl ether), a melamine resin, a metal salt, a metal chelate compound and the like known intermolecular crosslinking agents may be added to carry out the crosslinking treatment. The type and blending amount of the intermolecular crosslinking agent can be appropriately selected depending on the type and content of the functional group in the acrylic copolymer involved in the reaction with the intermolecular crosslinking agent. In addition, a cross-linking treatment using active rays such as electron beam irradiation may be performed.

As the optical film applied to the present invention, a polarizing film and a retardation film are commonly used. The polarizing film is not particularly limited, and examples thereof include a polyvinyl alcohol type film or a partially formalized polyvinyl alcohol type film, an ethylene-vinyl acetate copolymer type saponified film,
It can be obtained by a method of adsorbing and orienting iodine and / or a dichroic dye on a hydrophilic film such as a cellulose type film, or a method of dehydrating a polyvinyl alcohol type film to form a polyene. Also, the retardation film is not particularly limited, but for example, a stretched plastic film such as a polycarbonate film or a polyvinyl alcohol film can be used.

In the present invention, an optical film such as a polarizing film or a retardation film having an optically transparent protective layer on one side or both sides is preferably used. The protective layer is formed by a method of adhering a plastic film by means of an adhesive, melting, welding, or the like, a method of treating a coating layer of a curable resin with a curing means such as heating, ultraviolet rays or electron beams. be able to. Examples of the plastic film include cellulose acetate film such as cellulose acetate diacetate, cellulose acetate triacetate, acrylic resin film, polycarbonate resin film, and the like.
A polyester-based resin film, a polyethersulfone-based resin film, a polysulfone-based resin film, a polyimide-based resin film and the like are preferably used.

In the present invention, the optical film having the pressure-sensitive adhesive layer is provided by providing the pressure-sensitive adhesive for the optical film of the present invention on at least one surface of such an optical film, preferably on the surface of the protective layer formed as described above. Obtainable. At that time, using two or more kinds of pressure-sensitive adhesives for optical films having different acrylic copolymer monomer compositions, these are separately provided on both sides of the optical film, or laminated on both sides or one side. You may do it.

As a method for providing the pressure-sensitive adhesive, for example, a pressure-sensitive adhesive solution in which the concentration of the acrylic copolymer is about 10 to 40% by weight using a single solvent or a mixed solvent such as toluene and ethyl acetate is used. There is a method in which it is directly cast or coated on the surface and then dried. Alternatively, a method may be used in which the above-mentioned pressure-sensitive adhesive solution is applied to a thin leaf surface-treated with a release agent, dried, and then transferred onto the optical film.

A liquid crystal display device can be manufactured by disposing the optical film having the pressure-sensitive adhesive layer thus obtained on the surface of the liquid crystal cell, mainly on the surface of the glass substrate, with the pressure-sensitive adhesive layer interposed therebetween. . At this time, two or more kinds of optical films having a pressure-sensitive adhesive layer may be laminated, and for example, a polarizing film having a pressure-sensitive adhesive layer may be laminated on the surface of a liquid crystal cell via a retardation film having a pressure-sensitive adhesive. You can buy it. Further, the liquid crystal display device may be formed by a method in which a pressure-sensitive adhesive is directly applied between the optical film and the liquid crystal cell to provide a pressure-sensitive adhesive layer having a single layer or a laminated structure.

[0034]

As described above, in the present invention, the main component is an acrylic copolymer which is composed of an acrylic monomer and an imide group-containing monomer and is excellent in the balance property of the adhesive force and the elastic modulus. By using, excellent in heat resistance and moisture resistance, without causing peeling or bubbles at the interface between the pressure-sensitive adhesive layer and the liquid crystal cell even in a hot and humid atmosphere,
It is possible to provide a highly reliable acrylic pressure-sensitive adhesive, an optical film with a pressure-sensitive adhesive layer using the pressure-sensitive adhesive, and a liquid crystal display device.

[0035]

EXAMPLES Next, examples of the present invention will be described to more specifically describe. In the following, "parts" means "parts by weight".

Example 1 A reaction vessel equipped with a cooling tube, a nitrogen introducing tube, a thermometer, and a stirrer was charged with 94.9 parts of n-butyl acrylate, 0.1 part of 2-hydroxyethyl acrylate, and cyclohexylmaleimide. 5 parts and 0.3 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator were added, and the mixture was copolymerized in ethyl acetate under a stream of nitrogen gas at 60 ° C for 4 hours and then at 70 ° C for 2 hours. An acrylic copolymer solution having a solid content concentration of 30% by weight was obtained.

To this solution, 2 parts of trimethylolpropane tolylene diisocyanate as an intermolecular cross-linking agent was added per 100 parts of the acrylic copolymer to give an adhesive for optical films. Further, this adhesive was applied onto a release paper so that the thickness after drying would be 20 to 25 μm, and after drying, an optical film [NPF-G5 manufactured by Nitto Denko Corporation] was used.
220 DU] to prepare an optical film having an adhesive layer. Further, a liquid crystal display device was produced by disposing the optical film having this pressure-sensitive adhesive layer on the glass substrate surface of the liquid crystal cell via the pressure-sensitive adhesive layer.

Examples 2 to 6 Five kinds of acrylic copolymer solutions were prepared in the same manner as in Example 1 except that the composition of the monomer mixture was changed as shown in Tables 1 and 2. The same amount of intermolecular crosslinking agent as in Example 1 was blended with to prepare 5 types of pressure-sensitive adhesives for optical films. Further, using these pressure-sensitive adhesives, an optical film having a pressure-sensitive adhesive layer and a liquid crystal display device were produced in the same manner as in Example 1. For reference, the composition of the monomer mixture of Example 1 is also shown in Table 1.

Comparative Examples 1 to 3 Three kinds of acrylic copolymer solutions were prepared in the same manner as in Example 1 except that the composition of the monomer mixture was changed as shown in Table 3. The same intermolecular crosslinking agent as in 1 was blended in the same amount to prepare three kinds of pressure-sensitive adhesives for optical films. Also, using these adhesives, in the same manner as in Example 1,
An optical film having an adhesive layer and a liquid crystal display device were produced respectively.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

In the above Examples 1 to 6 and Comparative Examples 1 to 3, in order to examine the adhesive strength of the pressure-sensitive adhesive for optical film,
Separately, a test piece was prepared by forming a pressure-sensitive adhesive layer having a thickness of 50 μm on a polyester film having a thickness of 25 μm by the same method as in each example, and an adhesive strength test was conducted in the following manner. In addition, in order to examine the heat resistance and humidity resistance of the liquid crystal display device in a high temperature and high humidity atmosphere, the optical film having the pressure-sensitive adhesive layer prepared in each example was separately applied to a glass plate at 50 ° C. for 3 days.
A test piece was prepared by adhering under a condition of Kg / cm ² , and a heat resistance test and a humidity resistance test were conducted in the following manner. The results are shown in Table 4 below.

<Adhesion test> After cutting the test piece into a width of 20 mm, a 2 Kg rubber roller was reciprocated once on the glass plate and pressure-bonded. After this pressure bonding, it was left in an atmosphere of 23 ° C. for 30 minutes, and peeled at 180 ° under a peeling speed of 300 mm / min to measure the adhesive force.

<Heat Resistance Test> The test piece was subjected to a standing test at 90 ° C. for 500 hours to examine the generation state of bubbles. The evaluation criteria are as follows. ◎: No bubbles are recognized ○: Bubbles that do not affect the visibility are recognized ×: Bubbles that affect the visibility are recognized

<Moisture resistance test> A test piece was tested at 50 ° C. and 90% R
It was subjected to a standing test under H for 1,000 hours to examine the state of peeling. The evaluation criteria are as follows. ◎: Peeling is not recognized ○: Peeling that does not affect the visibility is recognized ×: Peeling that affects the visibility is recognized

[0047]

[Table 4]

As is clear from the results shown in Table 4 above, the pressure-sensitive adhesives for optical films of Examples 1 to 6 of the present invention have a larger adhesive force than those of Comparative Examples 1 to 3 and have a high temperature. It can be seen that even in a humid atmosphere, it exhibits excellent heat resistance and moisture resistance without causing peeling or generating bubbles at the interface between the pressure-sensitive adhesive layer and the glass substrate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuko Yamamoto, 1-2, Shimohozumi, Ibaraki, Osaka Prefecture Nitto Denko Co., Ltd. (72) Naoshi Yamaoka, 1-2, Shihohozumi, Ibaraki, Osaka Prefecture Nitto Denko Corporation

Claims (7)

[Claims] 1. A compound represented by the general formula (A); CH ₂ ═C (R ¹ ) CO
50% to 98% by weight of an acrylic monomer represented by OR ² (wherein R ¹ is hydrogen or a methyl group, and R ² is an alkyl group having 2 to 14 carbon atoms); A pressure-sensitive adhesive for an optical film, which comprises, as a main component, an acrylic copolymer with 50 to 2% by weight of an imide group-containing monomer copolymerizable with. 2. In the acrylic copolymer, as the monomer constituting the copolymer, an acrylic monomer represented by the general formula (A) and an imide group-containing monomer copolymerizable therewith are used. The pressure-sensitive adhesive for an optical film according to claim 1, which further contains another monomer copolymerizable with them in a proportion of 30% by weight or less. 3. The imide group-containing monomer has the following general formula (B); A maleimide compound represented by the formula (wherein R ³ is hydrogen or a monovalent organic group).
The pressure-sensitive adhesive for an optical film according to. 4. The pressure-sensitive adhesive for an optical film according to claim 1, wherein the imide group-containing monomer is an itacone imide compound. 5. The pressure-sensitive adhesive for an optical film according to claim 1, wherein the imide group-containing monomer is a succinimide compound. 6. The pressure-sensitive adhesive for an optical film according to claim 1, which is provided on at least one surface of the optical film.
An optical film having a pressure-sensitive adhesive layer, wherein at least one kind is provided. 7. A liquid crystal display device, wherein at least one optical film having the pressure-sensitive adhesive layer according to claim 6 is arranged on the surface of a liquid crystal cell.