JPH08216317A - Polarizing plate for liquid crystal display device - Google Patents

Abstract

PURPOSE: To enhance adhesive properties and a durability, such as a resistance to moist heat, by bonding a polarizing film to protective films with a thermosetting adhesive composed mainly of a copolymer of ethylene, vinyl acetate, and acrylate and/or methacrylate monomer. CONSTITUTION: A polarizing plate 4 is formed by adhesively covering a polarizing film 1 with protective films 2. As an adhesive 3 for bonding the polarizing film 1 to the protective films 2, a thermosetting adhesive mainly composed of a copolymer of ethylene, vinyl acetate, and acrylate and/or methacrylate monomer is used. The thermosetting adhesive prepared by mixing 0.1-10 pts.wt. organic peroxide and 0.01-5 pts.wt. silane coupling agent per 100 pts.wt. of the copolymer and kneading the mixture is formed into a predetermined shape for use by a film forming method, such as calendering, T-die extrusion, or inflation. A laminate is formed by overlapping the protective films 2 on the polarizing film 1 through adhesive films of the adhesive 3. The polarizing plate 4 is obtained by heating and pressurizing the laminate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate for a liquid crystal display device used in a liquid crystal display device for the purpose of displaying in the field of optoelectronics by utilizing the response of liquid crystal molecules by an electric field.

[0002]

2. Description of the Related Art Conventionally, the alignment layers of two substrates having a transparent electrode and an alignment layer formed on one surface thereof are opposed to each other, and a liquid crystal layer is interposed therebetween, and A liquid crystal display (LCD) having a polarizing plate bonded to the other surface of the substrate is widely used. In this case, as the polarizing plate, as shown in FIG. 1, a polarizing plate having a structure in which protective films 2 and 2 are adhered to both surfaces of the polarizing film 1 with adhesives 3 is often used. A technique of using a pressure-sensitive adhesive as an adhesive for bonding a film and its protective film (JP-A-57-195208, JP-A-3-12471) and a liquid containing a vinyl monomer or an oligomer as a main component Techniques used (Japanese Patent Laid-Open No. 58-171007, Nitto Denko Corporation) are known.

However, when a pressure sensitive adhesive (adhesive) is used, the durability of the polarizing plate such as heat resistance and moisture heat resistance is extremely low,
Moreover, there is a problem that the adhesive strength is low.

On the other hand, when a liquid material containing a vinyl monomer or an oligomer as a main component is used, the vinyl monomer or the oligomer swells the polarizing film layer or its protective film, which is a constituent element of the polarizing plate, and optically distorts. Since the vinyl monomer is acrylic, the cured film (adhesive layer) is hard, brittle, and easily cracked. Liquid crystal display devices used for mobile terminals are required to have impact resistance (when dropped), which is not suitable for this application, and its application is extremely limited. Adhesion with polarizing film or protective film is extremely limited. Low, since the adhesive is a liquid, there is a problem that it has no function of improving the polarization degree of the polarizing film.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object of the present invention is to provide a polarizing plate for a liquid crystal display device, which is excellent in adhesion and various durability and has high reliability.

[0006]

Means and Action for Solving the Problems The present inventors have
As a result of earnest studies to achieve the above object, a thermosetting adhesive containing ethylene, vinyl acetate and a copolymer of acrylate and / or methacrylate monomers as a main component for adhesion between the polarizing film and the protective film. When used, it firmly adheres the polarizing film and the protective layer, is excellent in various durability such as heat resistance, moisture heat resistance, cold heat resistance cycle, and adheres without affecting the optical function of the polarizing film and the protective layer. It has the function of improving the polarization degree of the polarizing film, and because the cured film is flexible and rich in elasticity, it has the excellent effect of being resistant to external impact and deformation, and is highly reliable. It was found that a polarizing plate having a property is obtained,
The present invention has been completed.

Therefore, according to the present invention, in a polarizing plate which is obtained by adhering and covering a protective film on a polarizing film and laminated on a liquid crystal cell surface substrate of a liquid crystal display device, the polarizing film and the protective film are made of ethylene or vinyl acetate. Also provided is a polarizing plate for a liquid crystal display device, characterized by being bonded with a thermosetting adhesive containing a copolymer of an acrylate-based and / or a methacrylate-based monomer as a main component.

The present invention will be described in more detail below. The polarizing plate of the present invention is, for example, a polarizing plate having a structure as shown in FIG. 1 described above, which is used as an adhesive for bonding the polarizing film 1 and the protective film 2 to each other. It is characterized by using a thermosetting adhesive containing a copolymer of ethylene, vinyl acetate and acrylate and / or methacrylate monomers as a main component. Here, the content of vinyl acetate units in this copolymer is preferably 5 to 50% by weight, and more preferably 14 to 45% by weight. When the content of the vinyl acetate unit is lower than 5% by weight, the transparency and optical uniformity of the heat-cured adhesive layer are insufficient, while when it exceeds 50% by weight, the transparency and optical uniformity are good. However, the strength and durability of the adhesive layer tend to be significantly reduced.

Examples of the acrylate-based monomer and the methacrylate-based monomer include acrylic acid, methacrylic acid and their esters. Specifically, (meth) acrylate, ethyl (meth) acrylate and the like ( In addition to (meth) acrylic acid lower alkyl ester, glycidyl (meth) acrylic acid and the like are exemplified. These may be used alone or in combination of two or more, but the content of the acrylate-based and methacrylate-based units in the copolymer is 0.01 to 10% by weight, particularly It is preferably 0.05 to 5% by weight. If this content exceeds 10% by weight, workability may decrease.

An organic peroxide is added to the adhesive according to the present invention for curing. As the organic peroxide to be added, any one can be used as long as it decomposes at a temperature of 70 ° C. or higher to generate a radical, but has a half-life of 10
It is more preferable that the decomposition temperature in time is 50 ° C. or higher, and it can be selectively used in consideration of film forming processing temperature, crosslinking temperature, storage stability and the like.

Examples of usable peroxides are 2,
5-Dimethylhexane-2,5-dihydroxyperoxide; 2,5-Dimethyl-2,5-di (t-butylperoxy) hexyne-3; di-t-butylperoxide; t-butylcumylperoxide 2,5-dimethyl-2,5-di (t-butylperoxy) hexane;
Dicumyl peroxide; α, α'-bis (t-butylperoxyisopropyl) benzene; n-butyl-4,
4-bis- (t-butylperoxy) valerate; 2,
2-bis (t-butylperoxy) butane; 1,1-bis (t-butylperoxy) cyclohexane; 1,1-
Bis (t-butylperoxy) -3,3,5-trimethylcyclohexane; t-butylperoxybenzoate; benzoyl peroxide; t-butylperoxyacetate; 1,1-bis (t-butylperoxy)-
3,3,5-Trimethylcyclohexane; 1,1-bis (t-butylperoxy) cyclohexane; Methylethylketone peroxide; t-Butyl hydroperoxide; p-Mentane hydroperoxide; Hydroxyheptyl peroxide; Chlorhexanone peroxide Octanoyl peroxide; Decanoyl peroxide; Lauroyl peroxide; Cumyl peroxide octoate; Succinic agit peroxide; Acetyl peroxide; t-Butylperoxy (2-ethylhexanoate); Oxide; benzoyl peroxide; t-butyl peroxyisobutyrate; 2,4-dichlorobenzoyl peroxide and the like.

As the organic peroxide, one of these is used.
The seeds may be used alone or in combination of two or more,
The amount added is 0.1 with respect to 100 parts by weight of the above copolymer.
-10 parts by weight is sufficient.

A silane coupling agent can be added to the adhesive of the present invention as an adhesion promoter. As this silane coupling agent, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane,
γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl)
There are ethyltrimethoxysilane, γ-chloropropylmethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, etc. , These 1 type can be used individually or in mixture of 2 or more types. The addition amount of these silane coupling agents is the same as that of the copolymer 1 above.
Usually 0.01 to 5 parts by weight is sufficient with respect to 00 parts by weight.

Furthermore, in order to improve or adjust the physical properties (mechanical strength, optical properties, adhesiveness, heat resistance, moist heat resistance, weather resistance, crosslinking rate) and the like of the thermosetting adhesive of the present invention, the present invention is used. In, a compound containing an acryloxy group, a methacryloxy group or an allyl group can be added.

Most commonly used compounds for this purpose are acrylic acid or methacrylic acid derivatives such as their esters and amides. In this case, as the ester residue, in addition to alkyl groups such as methyl, ethyl, dodecyl, stearyl and lauryl, cyclohexyl group, tetrahydrofurfuryl group, aminoethyl group, 2
-Hydroethyl group, 3-hydroxypropyl group, 3-chloro-2-hydroxypropyl group and the like. Further, esters of acrylic acid or methacrylic acid with a polyfunctional alcohol such as ethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, pentaerythritol and the like are also used. Acrylamide is a typical amide. Examples of the allyl group-containing compound include triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl isophthalate, diallyl maleate and the like. It is used by adding 0.1 to 50 parts by weight, preferably 0.5 to 30 parts by weight to 100 parts by weight of the combined product. If it is less than 0.1 part by weight, the improving effect of improving the mechanical strength may be deteriorated, and if it exceeds 50 parts by weight, workability and film-forming property during preparation of the adhesive may be deteriorated.

Further, a hydrocarbon resin may be added to the adhesive of the present invention for the purpose of improving workability and workability such as bonding. In this case, the added hydrocarbon resin may be a natural resin type or a synthetic resin type. As the natural resin type, rosin, rosin derivative and terpene type resin are preferably used. For rosin, gum resins, tall oil resins and wood resins can be used. As the rosin derivative, rosin is hydrogenated, heterogenized, polymerized,
Esterified or metal chloride can be used.
As the terpene-based resin, terpene-based resins such as α-pinene and β-pinene, and terpene-phenolic resins can be used. Also, as other natural resins, dammar,
It does not matter if you use corbal or shellac. On the other hand, petroleum-based resins, phenol-based resins, and xylene-based resins are preferably used in the synthetic resin system. Among petroleum-based resins, aliphatic petroleum resin, aromatic petroleum resin, alicyclic petroleum resin, copolymer petroleum resin, hydrogenated petroleum resin, pure monomer petroleum resin,
A coumarone indene resin can be used. As the phenol resin, an alkylphenol resin or a modified phenol resin can be used. As the xylene-based resin, a xylene resin or a modified xylene resin can be used.

The amount of the above-mentioned hydrocarbon resin to be added is appropriately selected, but is preferably 1 to 200 parts by weight, more preferably 5 to 150 parts by weight, based on 100 parts by weight of the above copolymer.

In addition to the above additives, the thermosetting adhesive of the present invention may contain a small amount of an ultraviolet absorber, an antiaging agent, a dye, a processing aid and the like. In addition, in some cases, a small amount of additives such as silica gel, calcium carbonate, and fine particles of silicon copolymer may be included.

In the thermosetting adhesive of the present invention, the above copolymer and the above additives are uniformly mixed and kneaded by an extruder, a roll or the like, and then calender, roll, T-die extrusion, inflation or the like. It can be used by forming a film into a predetermined shape by a film forming method. In film formation, embossing may be performed in order to prevent blocking and facilitate deaeration during pressure bonding with a polarizing film or a protective film. Further, the above copolymer and the above additives are uniformly dissolved in a solvent that does not affect the protective film or the polarizing film, and can be used as a solution-type adhesive, which is evenly applied to the surface of the film. After the temporary pressure bonding, the adhesive can be cured by heating.

The polarizing film used in the polarizing plate of the present invention is not limited at all, and iodine and / or dichroic dyes are adsorbed and aligned on a hydrophilic polymer containing a hydroxy group such as polyvinyl alcohol and saponified EVA. A stretched general polarizing film is used. The protective film is not limited at all, and commercially available cellulose-based, polyester-based, polycarbonate-based films and the like are preferably used.

The curing conditions for the thermosetting adhesive of the present invention depend on the type of organic peroxide used, but 70 to 1
70 ° C, especially 70-150 ° C for 2-60 minutes, especially 5-3
It is preferably 0 minutes. In this case, the curing is preferably 0.01 to 50 kgf / mm ² , especially 0.1 to 20 k.
It is recommended to work under a pressure of gf / mm ² .

[0022]

EFFECT OF THE INVENTION In the polarizing plate according to the present invention, the thermosetting adhesive layer has excellent flexibility, elasticity, impact resistance and high adhesive strength, so that the strength and reliability of the polarizing plate as a whole are significantly improved. It is a thing. Further, since the processing can be carried out at a low temperature, the bonding processing can be carried out without adversely affecting the polarizing film layer having a low heat resistance limit. Moreover, unlike a conventional liquid adhesive containing a large amount of an acrylic monomer, it does not swell the surface of a polarizing film or a protective film and does not damage it, so that the function as a polarizing plate is reduced at all. It is possible to perform the bonding without the need. Furthermore, in terms of durability such as heat resistance, moisture heat resistance, and cold heat resistance cycle, the above-mentioned copolymer crosslinked by thermosetting is rich in heat resistance and cold heat cycle resistance, and in particular, it can prevent intrusion of moisture and humidity. , The deterioration of the polarizing film, which is sensitive to moisture, can be sufficiently prevented. This is not observed in the conventional liquid adhesive containing an acrylic monomer or oligomer as a main component and is a particularly preferable point. Further, when the thermosetting adhesive of the present invention is formed into a film by using a T-die, a calender roll or the like, the molecular axes of the copolymer tend to be uniformly arranged in the film forming direction, and this property is In addition to the polarization degree of the polarizing film, it also has the effect of improving the polarization degree of the entire polarizing plate.

[0023]

EXAMPLES Hereinafter, the present invention will be specifically described by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Ethylene-vinyl acetate-glycidyl methacrylate copolymer (Bond First 2
A, manufactured by Sumitomo Chemical Co., Ltd .: vinyl acetate content 8%, glycidyl methacrylate content 3%) 100 parts by weight, 1 part by weight lauroyl peroxide, 0.5 parts by weight γ-glycidoxypropyltrimethoxysilane, 5 parts by weight of triallyl isocyanurate was mixed, and an adhesive film A having a thickness of 50 μm was produced with a 40 mm extruder. Then,
As shown in FIG. 1, a polarizing film and a protective film made of a triacetate film having a thickness of 50 μm were superposed on each other via the adhesive film A. This laminate is set between hot presses, and 90 kg for 15 minutes, 0.5 kg / cm
^It was heated and pressed at a pressure of ² to obtain a polarizing plate A.

Example 2 Ethylene-vinyl acetate-glycidyl methacrylate copolymer (Bond First 2
B, manufactured by Sumitomo Chemical Co., Ltd .: vinyl acetate content 5%, glycidyl methacrylate content 12%) 100 parts by weight, 2 parts by weight of benzoyl peroxide, 2 parts by weight of γ-methacryloxypropylmethoxysilane, and ethylene glycol dimethacrylate. 20 parts by weight were uniformly dissolved in a toluene solvent at 60 ° C. to prepare an adhesive solution B having a solute concentration of 15% by weight.

This solution B was applied onto two uniaxially stretched polyester films, which were protective films, and a coating film having a uniform thickness was obtained by the bar coating method. Toluene component is volatilized for 1 hour in an oven at 50 ° C, and dry thickness is 25 μm.
A dry adhesive layer of A polarizing film is interposed between these two uniaxially stretched polyester films, and in a rubber bag,
Heating was performed at 90 ° C. for 30 minutes in a vacuum state. afterwards,
The laminate was taken out of the rubber bag to obtain a polarizing plate B.

Example 3 Ethylene-vinyl acetate-glycidyl methacrylate copolymer (Bond First 2
B, manufactured by Sumitomo Chemical Co., Ltd .: vinyl acetate content 5%, glycidyl methacrylate content 12%) to 100 parts by weight,
1,1-bis (t-butylperoxy) -3,3,5-
5 parts by weight of trimethylcyclohexane, 5 parts by weight of γ-methacryloxypropylmethoxysilane, and 3 parts of alicyclic hydrocarbon resin Alcon M-100 (manufactured by Arakawa Chemical Industry Co., Ltd.)
0 parts by weight and 5 parts by weight of neopentyl glycol diacrylate were kneaded with a roll mill set at 70 ° C., and an adhesive film C having a thickness of 100 μm was applied by an electric heat press at a pressure of 50 kg / cm ² at 80 ° C. for 15 minutes. It was made.
A polarizing film and a triacetyl cellulose protective film were integrated by the same method as in Example 1 to obtain a polarizing plate C.

[Comparative Example 1] On one side of a triacetyl cellulose protective film, a liquid mixture comprising 100 parts by weight of methyl methacrylate, 10 parts by weight of glycidyl methacrylate and 1 part by weight of azobisisobutyrylonitrile was applied to prepare a polarizing film. Then, they were bonded to each other on both sides by pressure bonding and left in an oven maintained at 90 ° C. for 60 minutes to obtain a polarizing plate D.

The above four types of polarizing plates were tested for heat resistance and moist heat resistance, and examined for appearance abnormalities such as peeling, misalignment, and foaming. The results are summarized in Table 1.

If the above-mentioned abnormality was not recognized, it was judged as acceptable, and if not, it was judged as unacceptable.

[0031]

[Table 1]

The polarizing plates of Examples A to C were flat laminates without any distortion or unevenness in the visual inspection after production. On the other hand, in the polarizing plate D of the comparative example, there is a problem that an optical fluctuation is generated in the boundary layer of the bonding surface due to dissolution or swelling on the surface of the constituent member, which is considered to be caused by the acrylic monomer, and thus the transmitted image looks distorted. Was observed.

Further, as is clear from the results of Table 1, the polarizing plates according to the present invention all have high adhesion to the constituent members and a crosslinked structure formed in the ethylene-vinyl acetate- (meth) acrylate copolymer. Due to its high durability,
No abnormalities were found in both heat resistance and moisture heat resistance tests, and it was found that they have high reliability in practical use. However,
In the case of the comparative example, a shift of about 0.5 to 1.0 mm was observed between the polarizing film and the protective layer in both tests, and a peeling of adhesion of about 5 mm from the edge was observed in the moisture and heat resistance test.

From the above, according to the present invention, it is possible to provide a polarizing plate having excellent adhesion and various durability and high reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a polarizing plate.

[Explanation of symbols]

 1 Polarizing film 2 Protective film 3 Adhesive 4 Polarizing plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location // C09J 4/06 JBN C09J 4/06 JBN 123/08 JCH 123/08 JCH JCK JCK 131/04 JCX 131/04 JCX

Claims (5)

[Claims] 1. A polarizing plate comprising a polarizing film and a protective film adhered and coated thereon, which is laminated on a surface substrate of a liquid crystal cell of a liquid crystal display device, wherein the polarizing film and the protective film are made of ethylene, vinyl acetate or acrylate. /
Alternatively, a polarizing plate for a liquid crystal display device, which is adhered by a thermosetting adhesive containing a copolymer of a methacrylate monomer as a main component. 2. A thermosetting adhesive is used as the copolymer 100.
The polarizing plate for a liquid crystal display device according to claim 1, wherein 0.1 to 10 parts by weight of an organic peroxide and 0.01 to 5 parts by weight of a silane coupling agent are added to parts by weight. . 3. A thermosetting adhesive is used as the copolymer 100.
3. The liquid crystal display according to claim 1, wherein 0.1 to 50 parts by weight of at least one of an acryloxy group-containing compound, a methacryloxy group-containing compound and an allyl group-containing compound is added to parts by weight. Polarizer for equipment. 4. A thermosetting adhesive is used as the copolymer 100.
The polarizing plate for liquid crystal display device according to any one of claims 1 to 3, wherein 1 to 200 parts by weight of a hydrocarbon resin is added to parts by weight. 5. The content of vinyl acetate units in the copolymer is 5 to 50% by weight, and the content of acrylate and / or methacrylate units is 0.01 to 10% by weight. Item 5. A polarizing plate for a liquid crystal display device according to any one of items 1 to 4.