JP2002122740A - Polarizing plate and liquid crystal display using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing plate less liable to cause intrasurface unevenness and capable of attaining uniform display and a liquid crystal display, using the polarizing plate by adjusting the product of the photoelastic coefficient of protective layers themselves and the elastic modulus of an adhesive constituting a polarizing plate to be in a prescribed range. SOLUTION: In a polarizing plate with protective layers on both faces of a polyvinyl alcohol(PVA) polarizer, using iodine or a dichroic dye and an adhesive layer on one face of at least one of the protective layers, the product of the photoelastic coefficient of the protective layers themselves and the elastic modulus of the adhesive constituting the polarizing plate is adjusted to <=8.0×10-12 [m2/N.MPa].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate used in a liquid crystal display device (hereinafter, may be abbreviated as LCD) and a liquid crystal display device having the same. More specifically, the present invention relates to a polarizing plate and a liquid crystal display device useful for a large-sized liquid crystal display device or a liquid crystal display device for high-contrast display.

[0002]

2. Description of the Related Art LCDs are used in personal computers and the like, and have been rapidly increasing in recent years. The use of LCDs is expanding, and in recent years, LCDs are also being used for monitors.

[0003] A polarizing plate is prepared by dyeing a PVA film with dichroic iodine or a dye and then crosslinking the film with boric acid or borax. In addition, uniaxial stretching is performed in the dyeing step and the crosslinking step. This stretching may be performed during the step, or may be performed before or after the step. After the dyeing step and the cross-linking step, it is usually dried using a drier or the like, and bonded to a protective layer such as a triacetyl cellulose (TAC) film using an adhesive.

In recent years, LCDs have become larger and have higher contrasts, and there is a demand for higher quality polarizing plates. Further, when the polarizing plate is mounted on the panel, a slight stress is applied to the polarizing plate when the LCD panel is bonded to the polarizing plate. Due to the stress applied at this time, a change in the refractive index of the protective layer film constituting the polarizing plate tends to cause partial unevenness in the black display of the LCD.

[0005]

According to the present invention, the unevenness which impairs the display quality is focused on the photoelasticity of the material of the protective layer film constituting the polarizing plate, and the unevenness occurs in the plane by selecting the protective layer. It is an object of the present invention to provide a polarizing plate which makes it difficult to perform uniform display and a liquid crystal display device using the same.

[0006]

In order to achieve the above object, a polarizing plate of the present invention comprises a polyvinyl alcohol (PVA) polarizer using iodine or a dichroic dye, provided with protective layers on both surfaces thereof, Wherein the product of the photoelastic coefficient of the protective layer itself and the elastic modulus of the pressure-sensitive adhesive layer is 8.0 × 10 ⁻¹² [m ² / N.
[MPa] or less.

In the polarizing plate, the product of the photoelastic coefficient of the protective layer itself and the elastic modulus of the pressure-sensitive adhesive layer constituting the polarizing plate is:
It is preferably at most 6.5 × 10 ⁻¹² [m ² / N · MPa].

In the above, the product of the photoelastic coefficient of the protective layer itself and the elastic modulus of the pressure-sensitive adhesive layer constituting the polarizing plate is 1.0 ×
It is preferably at least 10 ^-13 [m ² / N · MPa].

[0009] The polarizing plate may have a hard coat layer on the surface of a polyvinyl alcohol (PVA) film. This is because the wear resistance can be improved. The hard coat layer is preferably an acrylic resin.

A reflective plate or a semi-transmissive reflective plate may be bonded to any of the above-described polarizers to form a reflective polarizer or a transflective polarizer. Further, an elliptic or circular polarizing plate may be formed by laminating a retardation plate or a λ plate to the polarizing plate described in any of the above. Further, a polarizing plate may be formed by bonding a viewing angle compensation film to the polarizing plate described in any of the above. Further, a polarizing plate may be formed by bonding a brightness enhancement film to the polarizing plate described in any of the above using an adhesive or a pressure-sensitive adhesive.

Next, a liquid crystal display device according to the present invention is characterized in that the polarizing plate described above is provided on at least one side of a liquid crystal cell.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, attention was paid to the photoelastic system number of a protective layer film of a polarizing plate and the elastic modulus of an adhesive, and a specific range was selected. That is, the product of the photoelastic coefficient of the protective layer itself and the elastic modulus of the adhesive constituting the polarizing plate is 8.0 × 1.
0 ^-12 [m ² / N · MPa] or less, preferably 6.5 × 1
By setting the value to 0 ^-12 [m ² / N · MPa] or less, it was possible to realize a polarizing plate and a liquid crystal display device using the polarizing plate, which hardly generate in-plane unevenness and enable uniform display.

In the polarizing plate of the present invention, a polarizer having a polarizing function is obtained by subjecting a PVA film, which is a raw material of the polarizing plate, to swelling, dyeing, stretching, cross-linking, drying and the like.
Using an adhesive or an adhesive for the polarizer, TAC,
A polarizing plate is obtained by laminating a film such as polyethylene terephthalate (PET) as a protective layer.

In the manufacturing process of the polarizer, swelling, dyeing,
The order of the four steps of stretching and crosslinking is not particularly limited, and the four steps may be performed separately or in combination. That is, the “stretching step”
Usually, it is often performed simultaneously with the “dyeing step” and “crosslinking step”, but may be performed in another step. Further, the dyeing step and the crosslinking step may be performed simultaneously. The polarizing film is made of the above 3
After the step, the film is dried, and is manufactured by laminating with a film such as a TAC (triacetylcellulose) film or a PET film to be a protective layer.

An appropriate transparent film can be used as a protective film material serving as a transparent protective layer provided on one side or both sides of a polarizer (polarizing film). As an example of the polymer, an acetate resin such as triacetylcellulose is generally used, but is not limited thereto.

A transparent protective film that can be particularly preferably used in view of polarization characteristics and durability is a triacetyl cellulose film whose surface is saponified with an alkali or the like. When transparent protective films are provided on both sides of the polarizing film, transparent protective films made of different polymers or the like may be used on both sides.

The transparent protective film used for the protective layer includes:
As long as the object of the present invention is not impaired, a hard coat treatment, an anti-reflection treatment, a treatment for preventing sticking, diffusion or anti-glare, or the like may be performed. The hard coat treatment is performed for the purpose of preventing the surface of the polarizing plate from being scratched. For example, a hardened film excellent in hardness and slipperiness by an appropriate ultraviolet curable resin such as a silicone resin is coated on the surface of the transparent protective film. Can be formed.

On the other hand, the antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the related art. In addition, sticking prevention is for the purpose of preventing adhesion with the adjacent layer,
The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sandblasting method or an embossing method. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing transparent fine particles.

Examples of the transparent fine particles include silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide having an average particle size of 0.5 to 20 μm. Fine particles may be used, or organic fine particles composed of crosslinked or uncrosslinked polymer particles or the like may be used. The use amount of the transparent fine particles is generally 2 to 70 parts by weight, particularly 5 to 50 parts by weight, per 100 parts by weight of the transparent resin.

The anti-glare layer containing the transparent fine particles can be provided as the transparent protective layer itself or as a coating layer on the surface of the transparent protective layer. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle compensation function) for diffusing light transmitted through the polarizing plate to increase the viewing angle.
The above-described anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer, and the like can be provided as an optical layer made of a sheet or the like provided with such a layer, separately from the transparent protective layer.

In the present invention, the bonding treatment between the polarizer (polarizing film) and the transparent protective film as the protective layer is not particularly limited. For example, an adhesive comprising a vinyl alcohol-based polymer or boric acid Or borax,
It can be carried out via an adhesive comprising at least a water-soluble cross-linking agent of a vinyl alcohol-based polymer such as glutaraldehyde, melamine, and oxalic acid. Such an adhesive layer can be formed as a coating and drying layer of an aqueous solution, but when preparing the aqueous solution, if necessary, other additives,
A catalyst such as an acid can also be blended.

[0022]

The present invention will be described more specifically with reference to the following examples and comparative examples.

In Examples and Comparative Examples, each triacetylcellulose (TAC) film was used with a single transmittance of 4
A polarizer having a polarization degree of 3.0% and a polarization degree of 99.9% (a polyvinyl alcohol (PVA) film is immersed in water to swell to a certain extent, then immersed in an aqueous iodine solution, iodine is fixed in PVA, and the film is uniaxially stretched. Then, a polarizer is bonded to both surfaces of a polarizer obtained by crosslinking with 3 to 6% boric acid using a polyvinyl alcohol-based adhesive to form a polarizing plate. The pressure-sensitive adhesive was formed so that the thickness after drying was 20 μm. A 15-inch large polarizing plate having an absorption axis angle of 45 degrees as viewed from the pressure-sensitive adhesive layer was prepared, and bonded to both surfaces of the glass plate in crossed Nicols.

The polarizing plate bonded to the glass plate is 50
It was set on a 00 cd / cm ² light table and visually checked in a dark room to check the state of sticking unevenness.

The above results are shown in Tables 3 and 4. In Tables 3 and 4, the polarizer protective layers 1 to 3 have different photoelastic coefficients as shown in Table 1, and the pressure sensitive adhesives A to C have different elastic moduli as shown in Table 2.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

As is clear from Tables 1 to 4, within the scope of the present invention, it is possible to provide a polarizing plate which is less likely to cause in-plane unevenness and enables uniform display, and a liquid crystal display device using the same. did it.

[0031]

As described above, according to the present invention, the product of the photoelastic system number of the protective layer itself and the elastic modulus of the adhesive constituting the polarizing plate is 8.0 × 10 ⁻¹² [m ² / N · MPa],
A polarizing plate that is preferably 6.5 × 10 ⁻¹² [m ² / N · MPa] or less, and in which in-plane unevenness hardly occurs and uniform display is possible, and a liquid crystal display device using the same Can be provided.

Continued on the front page (72) Inventor Eiji Hamamoto 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Yoichiro Sugino 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko stock Within the Company (72) Inventor Senri Yoshikawa 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Naofumi Mihara 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F term (for reference) 2H049 BA02 BA03 BA04 BA07 BA26 BA27 BB33 BB43 BB51 BB62 BC22 2H091 FA07X FA07Z FA37X FA37Z FB02 FB12 FC14 GA16 GA17 KA10 LA16 2K009 AA02 AA12 AA15 BB28 CC03 CC09 CC03 CC02 DD02 JA01 JA11

Claims (9)

[Claims] 1. A polarizing plate comprising: a polyvinyl alcohol-based polarizer using iodine or a dichroic dye; protective layers on both sides; and an adhesive layer on at least one side of the protective layer. A polarizing plate, wherein the product of its own photoelastic system number and the elastic modulus of the pressure-sensitive adhesive layer is 8.0 × 10 ⁻¹² [m ² / N · MPa] or less. 2. The polarizing plate according to claim 1, wherein the product of the photoelastic coefficient of the protective layer itself and the elastic modulus of the pressure-sensitive adhesive layer is 6.5 × 10 ⁻¹² [m ² / N · MPa] or less. . 3. The polarizing plate according to claim 1, further comprising a hard coat layer on the surface of the polarizing plate. 4. The polarizing plate according to claim 3, wherein the hard coat layer is an acrylic resin. 5. A polarizing plate comprising a polarizing plate according to claim 1 and a reflecting plate or a semi-transmissive reflecting plate bonded to the polarizing plate according to claim 1. 6. A polarizing plate obtained by laminating a retardation plate or a λ plate to the polarizing plate according to claim 1 to form an elliptically or circularly polarizing plate. 7. A polarizing plate comprising the polarizing plate according to claim 1 and a polarizing plate formed by laminating a viewing angle compensation film. 8. A polarizing plate, wherein a polarizing plate is formed by laminating a brightness enhancement film on the polarizing plate according to claim 1 using an adhesive or a pressure-sensitive adhesive. 9. A liquid crystal display device comprising the polarizing plate according to claim 1 on at least one side of a liquid crystal cell.