JPH08216316A - Polarizing plate for liquid crystal display device - Google Patents

Abstract

PURPOSE: To enhance adhesive properties and a durability, such as a resistance to heat and a resistance to moist heat, by bonding a polarizing film to protective films with a photosetting adhesive composed mainly of an ethylene-vinyl acetate copolymer. CONSTITUTION: A polarizing plate 4 is formed by adhesively covering a polarizing film 1 with protective films 2 to be laminated on a liquid crystal cell surface substrate of a liquid crystal display device. As an adhesive 3 for bonding the polarizing film 1 to the protective films 2, a photosetting adhesive is used. The photosetting adhesive prepared by mixing 0.1-10 pts.wt. photosensitizer and 0.01-5 pts.wt. silane coupling agent per 100 pts.wt. of ethylene-vinyl acetate copolymer and kneading the mixture is formed into a predetermined shape for use by a film forming method, such as calendering, rolling, 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, pressurizing, and photosetting 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 earnestly studying to achieve the above object, when a photocurable adhesive containing ethylene-vinyl acetate copolymer as a main component was used for adhesion between the polarizing film and the protective film, the polarizing film and the protective layer Firmly adheres to each other, has excellent durability such as heat resistance, moisture heat resistance, cold heat resistance cycle, etc., can be attached without affecting the optical function of the polarizing film or protective layer, and the polarization degree of the polarizing film Since the cured film is flexible and rich in elasticity, it has the excellent effect of being resistant to external impact and deformation, and it is possible to obtain a highly reliable polarizing plate. Find out,
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 is laminated on a liquid crystal cell surface substrate of a liquid crystal display device, the polarizing film and the protective film are ethylene-vinyl acetate. Provided is a polarizing plate for a liquid crystal display device, which is bonded by a photo-curable adhesive containing a copolymer as a main component.

The present invention will be described in more detail below. The polarizing plate of the present invention is, for example, as an adhesive for bonding the polarizing film 1 and the protective film 2 in the polarizing plate having the structure shown in FIG. It is characterized by using a photocurable adhesive containing an ethylene-vinyl acetate copolymer as a main component. Here, the vinyl acetate content of the ethylene-vinyl acetate copolymer is preferably 10 to 50% by weight, more preferably 14 to 45% by weight. If the vinyl acetate content is less than 10% by weight, the transparency and optical uniformity of the photocured adhesive layer will not be sufficient, while if it exceeds 50% by weight, the transparency and optical uniformity will be good, The strength and durability of the adhesive layer tend to be significantly reduced.

A photosensitizer is added to cure the photocurable adhesive according to the present invention. Examples of usable photosensitizers include benzoin, benzophenone, benzoin methyl ether, benzoin ethyl ether, Benzoin isopropyl ether, benzoin isobutyl ether, dibenzyl, 5-nitroacenaphthene, hexachlorocyclopentadiene, paranitrodiphenyl, paranitroaniline, 2,4,6-trinitroaniline, 1,
Examples thereof include 2-benzanthraquinone, 3-methyl-1,3-diaza-1,9-benzanthrone, and these may be used alone or in combination of two or more.

The addition amount of the photosensitizer in the present invention is 0.1 to 100 parts by weight of the ethylene-vinyl acetate copolymer.
It is preferably 10 parts by weight.

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 usually 0.01 to 5 parts by weight per 100 parts by weight of the ethylene-vinyl acetate copolymer.

Further, in order to improve or adjust the physical properties (mechanical strength, optical properties, adhesiveness, heat resistance, wet heat resistance, weather resistance, crosslinking rate) of the photocurable adhesive of the present invention, the present invention 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. One or a mixture of two or more of these is ethylene-acetic acid. The vinyl copolymer is used in an amount of 0.1 to 50 parts by weight, preferably 0.5 to 30 parts by weight, based on 100 parts by weight. If it is less than 0.1 parts by weight, the improving effect of improving the mechanical strength may be deteriorated.
If the amount exceeds 0 parts by weight, workability during preparation of the adhesive and film formability may be deteriorated.

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 added is appropriately selected, but it is preferably 1 to 200 parts by weight, more preferably 5 to 200 parts by weight, relative to 100 parts by weight of the ethylene-vinyl acetate copolymer.
It is 150 parts by weight.

In addition to the above additives, the photocurable 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.

The photocurable adhesive of the present invention is obtained by uniformly mixing the ethylene-vinyl acetate copolymer with the above-mentioned additives and kneading them with an extruder, a roll or the like, and then calendering, rolling, T
The film can be formed into a predetermined shape by a film forming method such as die extrusion or inflation. 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 ethylene-vinyl acetate copolymer and the above-mentioned 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 even on the surface of the film. It can be applied and cured, and then adhesively cured.

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 photo-curable adhesive may be cured by irradiating the laminated body with ultraviolet rays using an ordinary mercury lamp or the like. Further, in order to accelerate the curing, the laminate may be heated in advance to about 40 to 120 ° C. and then irradiated with ultraviolet rays.

In this case, first, the adhesive of the present invention is interposed between the polarizing film and the protective film, and 50 to 120
0.01 to 20 kg / c at 70 ° C, especially 70 to 100 ° C
m ^2, especially 2 at a pressure of 0.1 to 10 / cm ²
It is recommended to carry out photo-curing after heating and pressing for -20 minutes, especially 5-10 minutes.

[0021]

EFFECT OF THE INVENTION In the polarizing plate according to the present invention, the photocurable adhesive layer is rich in flexibility, elasticity and impact resistance, and has a high adhesive force, 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 ethylene-vinyl acetate copolymer crosslinked by photocuring has excellent heat resistance and cold heat cycle resistance, and especially prevents the ingress of moisture and humidity. Therefore, 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 photocurable adhesive of the present invention is formed into a film by using a T-die, a calendar roll or the like, ethylene-
The molecular axes of the vinyl acetate copolymer tend to be evenly arranged in the film-forming direction, and this property is added to the polarization degree of the polarizing film, which also exerts the effect of improving the polarization degree of the entire polarizing plate.

[0022]

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. In the following examples, parts indicate parts by weight.

[Example 1] 1 part of benzoin isopropyl ether and 100 parts of γ-glycidoxypropyltrimethoxysilane per 100 parts of ethylene-vinyl acetate copolymer (Ultrasene 627 manufactured by Tosoh Corporation: vinyl acetate content 20%) Was mixed with 5 parts of triallyl isocyanurate to prepare an adhesive film A having a thickness of 50 μm 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 laminated body is set between electrothermal presses and heated at 90 ° C. for 1 hour.
The plate was heated and pressurized at a pressure of 0.5 kg / cm ² for 5 minutes and then irradiated with a 4 kw high-pressure mercury lamp for 30 minutes on one side for a total of 1 minute to obtain a polarizing plate A.

[Example 2] 2 parts of benzophenone and γ- were added to 100 parts of ethylene-vinyl acetate copolymer (Ultracene 760 manufactured by Tosoh Corporation: vinyl acetate content 42%).
2 parts of methacryloxypropyl methoxysilane and 20 parts of ethylene glycol dimethacrylate 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 as a protective film, and a coating film having a uniform thickness was obtained by the bar coating method. The toluene component was volatilized in an oven at 50 ° C. for 1 hour to obtain a dry adhesive layer having a dry thickness of 25 μm. These two polarizing films
It was interposed between a sheet of uniaxially stretched polyester film, and heated in a rubber bag at 90 ° C. for 30 minutes in a vacuum state.
Then, the laminate was taken out from the rubber bag, and a 4 kW high-pressure mercury lamp was irradiated with ultraviolet rays for 30 minutes on each side for a total of 1 minute to obtain a polarizing plate B.

[Example 3] 5 parts of 1,2-benzanthraquinone and 5 parts of γ-methacryloxypropylmethoxy were added to 100 parts of an ethylene-vinyl acetate copolymer (Ultrasene 634 manufactured by Tosoh Corporation: vinyl acetate content 26%). 5 parts of silane, 30 parts of alicyclic hydrocarbon resin Alcon M-100 (manufactured by Arakawa Chemical Industry Co., Ltd.), and 5 parts of neopentyl glycol diacrylate were kneaded with a roll mill set at 70 ° C., and then 80 ° C. by an electric heat press. × 15 minutes, 50kg / c
Adhesive film C with a film thickness of 100 μm applied under a pressure of m ²
Was produced. In the same manner as in Example 1, the polarizing film and the triacetyl cellulose protective film were integrated, and then a 4 kw high-pressure mercury lamp was irradiated with ultraviolet rays for 30 minutes on each side for a total of 1 minute to obtain a polarizing plate C.

[Comparative Example 1] A liquid mixture comprising 100 parts of ethyl methacrylate, 10 parts of glycidyl methacrylate and 1 part of azobisisobutyrylonitrile was applied to one side of a triacetyl cellulose protective film, and both sides of the polarizing film were applied. The pieces were stuck together, pressure-bonded, and allowed to stand in an oven for 60 minutes while being kept at 90 ° C. to obtain a polarizing plate D.

With respect to the polarizing plates of Examples and Comparative Examples, heat resistance and moist heat resistance tests were carried out to examine whether or not there was an abnormal appearance such as peeling, misalignment or foaming. The results are summarized in Table 1. In addition, if the above-mentioned abnormality is not recognized, pass,
If not, it was judged as a failure.

[0028]

[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 have high adhesiveness to the constituent members and high durability due to the cross-linking structure formed in the ethylene-vinyl acetate copolymer. 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, both tests showed 0.5 to 1.0 between the polarizing film and the protective layer.
In the moisture and heat resistance test, a deviation of about 5 mm and an adhesive peeling of about 5 mm from the edge portion were observed.

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 the 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 131/04 131 / 04

Claims (5)

[Claims] 1. A polarizing plate comprising a polarizing film and a protective film adhered and coated thereon, which is laminated on a liquid crystal cell surface substrate of a liquid crystal display device, wherein the polarizing film and the protective film are made of an ethylene-vinyl acetate copolymer. A polarizing plate for a liquid crystal display device, characterized in that it is adhered with a photo-curable adhesive as a main component. 2. The photocurable adhesive contains 0.1 to 1 part of a photosensitizer per 100 parts by weight of an ethylene-vinyl acetate copolymer.
The polarizing plate for a liquid crystal display device according to claim 1, wherein 0 part by weight and 0.01 to 5 parts by weight of a silane coupling agent are added. 3. The photocurable adhesive contains 0.1 to 50 parts of at least one of an acryloxy group-containing compound, a methacryloxy group-containing compound and an allyl group-containing compound, based on 100 parts by weight of an ethylene-vinyl acetate copolymer. The polarizing plate for a liquid crystal display device according to claim 1 or 2, wherein the polarizing plate is added by weight. 4. The photocurable adhesive contains 1 to 2 parts of a hydrocarbon resin based on 100 parts by weight of an ethylene-vinyl acetate copolymer.
The polarizing plate for a liquid crystal display device according to claim 1, wherein the polarizing plate is added in an amount of 00 parts by weight. 5. The polarizing plate for a liquid crystal display device according to claim 1, wherein the vinyl acetate content of the ethylene-vinyl acetate copolymer is 10 to 50% by weight.