JP2000155215A - Wide view angule polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wide view angule polarizing plate enabling to prepare a liquid crystal display, which has good visibility with a broad viewing angle and hardly generates brightness irregularity. SOLUTION: This broad viewing angular polarizing plate is provided with an adhesive layer B (4) on a exposed surface of an optically compensating phase difference plate which is a laminated body obtained by laminating a polarizing plate (1) and the optically compensating phase difference plate (3) with an adhesive layer A (2), wherein 1000% modulus at 90 deg.C of the adhesive layer A is >6 g/mm2 and <=10 g/mm2 and the same of the adhesive layer B is <=6 g/mm2, and the wide view angule polarizing plate is arranged at least on one side of a liquid crystal cell. In such a manner, by the prescribed control for the adhesive layer bonding the polarizing plate with the optically compensating phase difference plate and for the adhesive layer bonding the wide view angule polarizing plate with the liquid crystal cell, a shrinking stress with heat can be mitigated to prevent brightness irregularity due to changing of phase difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-viewing-angle polarizing plate that can form a liquid crystal display device having good visibility in a wide viewing angle range and is less likely to have uneven brightness.

[0002]

BACKGROUND OF THE INVENTION Hitherto, there has been known an optically compensatory retardation plate in which an optically anisotropic layer formed by tilting a discotic liquid crystal polymer is supported by a cellulose triacetate film. It is expected that this can be used to form a liquid crystal display device that shows good visibility over a wide viewing angle by bonding it to a polarizing plate to form a wide viewing angle polarizing plate and bonding it to a liquid crystal cell via an adhesive layer. ing. However, there has been a problem that luminance unevenness occurs in the obtained liquid crystal display device.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wide-viewing-angle polarizing plate capable of forming a liquid crystal display device exhibiting good visibility at a wide viewing angle and hardly causing luminance unevenness.

[0004]

According to the present invention, an adhesive layer (B) is provided on an exposed surface of the optical compensation retardation plate of a laminate in which a polarizing plate and an optical compensation retardation plate are adhered via an adhesive layer (A). 1000% modulus at 90 ° C. of layer A is more than 6 to 10
g / mm ² , and 1000% of the adhesive layer B at 90 ° C.
A wide viewing angle polarizing plate having a modulus of 6 g / mm ² or less, and a liquid crystal display device having the wide viewing angle polarizing plate on at least one side of a liquid crystal cell.

[0005]

According to the present invention, it is possible to obtain a wide-viewing-angle polarizing plate capable of forming a liquid crystal display device which exhibits good visibility at a wide viewing angle and hardly causes luminance unevenness. This is because the pressure-sensitive adhesive layer for bonding the polarizing plate and the optical compensation retardation plate and the pressure-sensitive adhesive layer for bonding the wide viewing angle polarizing plate to the liquid crystal cell were controlled.

That is, while the inventors of the present invention have conducted intensive studies to overcome the above-mentioned problem of luminance unevenness, the occurrence of luminance unevenness is changed to a phase difference caused by a wide viewing angle polarizing plate, particularly an optical compensation phase difference plate. It was clarified that the change in retardation was caused by the thermal shrinkage stress of the cellulose triacetate film supporting the discotic liquid crystal polymer, due to the occurrence of the variation in the light transmittance based on this. This finding is supported by the fact that luminance unevenness is likely to occur in a window frame shape on a liquid crystal display screen.

Therefore, the prevention of the occurrence of the luminance unevenness according to the present invention is considered to be due to the prevention or suppression of the shrinkage stress due to the heat of the cellulose triacetate film. This is considered to be due to the action of relaxing the shrinkage stress due to the heat based on the heat.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A wide viewing angle polarizing plate according to the present invention comprises a laminate in which a polarizing plate and an optical compensation retardation plate are adhered through an adhesive layer A, and an adhesive layer B is provided on the exposed surface of the optical compensation retardation plate. The adhesive layer A has a 1000% modulus at 90 ° C. of more than 6 to 10 g / mm ² , and the adhesive layer B has a 90% modulus.
It has a 1000% modulus at 6 ° C. of 6 g / mm ² or less. An example is shown in FIG. 1 is a polarizing plate,
Reference numeral 2 denotes an adhesive layer A, reference numeral 3 denotes an optical compensation retardation plate, reference numeral 4 denotes an adhesive layer B, reference numeral 5 denotes a wide-viewing-angle polarizing plate composed of the above, and reference numeral 51 denotes a separator as necessary to temporarily protect the adhesive layer B. is there.

As the polarizing plate, any suitable polarizing plate can be used, and the type thereof is not particularly limited. Incidentally, examples thereof include iodine and / or a dichroic dye on a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene / vinyl acetate copolymer-based partially saponified film, and a cellulose-based film. And a polarizing film composed of a polyene oriented film such as a dehydrated polyvinyl alcohol product or a dehydrochlorinated polyvinyl chloride product. The thickness of the polarizing film is usually 5 to 8
0 μm, but not limited to this.

The polarizing plate may be a polarizing film itself or a polarizing film provided with a transparent protective layer on one side or both sides. The transparent protective layer can be formed by an appropriate method such as a film laminating method or a coating method, and an appropriate transparent resin or the like can be used for the formation.

A preferred transparent protective layer is excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy, and the like. Examples thereof include plastics such as polyolefins, polyesters, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, acrylic resins and acetate resins, acrylics and urethanes, acrylic urethanes and epoxies, silicones and the like. Heat-curable or ultraviolet-curable resins.

On the other hand, as an optical compensation retardation plate, for example, a stretched film made of uniaxial or biaxial transparent plastic,
It consists of an alignment film such as a liquid crystal polymer or a substrate with an alignment layer such as a liquid crystal polymer supported on a transparent substrate. Any suitable one for the purpose can be used.

In particular, an optically anisotropic layer composed of a liquid crystal polymer alignment layer, particularly a tilted alignment layer of a discotic liquid crystal polymer, is supported by a cellulose triacetate film in order to achieve a wide viewing angle with good visibility. An optically-compensated phase difference plate can be preferably used. Such optical compensation retardation plates include commercially available products such as WV A02A manufactured by Fuji Photo Film Co., Ltd.

Formation of an adhesive layer A for bonding a polarizing plate and an optical compensation retardation plate to form a wide viewing angle polarizing plate and an adhesive layer B for bonding and fixing the wide viewing angle polarizing plate to a liquid crystal cell or the like. For example, an appropriate adhesive such as acrylic, silicone, polyester, polyurethane, polyamide, polyether, or rubber can be used. Above all,
Acrylic pressure-sensitive adhesives are preferred in terms of optical transparency, pressure-sensitive adhesive properties, and weather resistance.

The attachment of the pressure-sensitive adhesive layer A to the polarizing plate and / or the optically compensating retardation plate may be performed, for example, by applying a solution or a melt of the pressure-sensitive adhesive by a suitable developing method such as a casting method or a coating method. Appropriate methods such as a method of directly attaching to a predetermined surface of an optical compensation retardation plate or a method of forming an adhesive layer on a separator and transferring it to a predetermined surface of a polarizing plate and / or an optical compensation retardation plate according to the method. It can be done in a manner.

In the wide-viewing-angle polarizing plate, the adhesive layer B may be attached to the optically-compensating retardation plate by a method of directly attaching the adhesive layer A to a predetermined surface of the wide-viewing-angle polarizing plate according to the attaching method of the adhesive layer A. Or an appropriate method such as a method in which an adhesive layer B is previously attached to an optical compensation retardation plate and is used for forming a wide viewing angle polarizing plate. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the adhesive force and the like, and is generally 1 to 500 µm, particularly 5 to 200 µm, particularly 10 to 100 µm.

In the present invention, the adhesive layer A has a 1000% modulus at 90 ° C. of more than 6 to 10 g / mm ² , especially 6.1 to 9 for the purpose of preventing luminance unevenness due to stress relaxation. 0.5 g / mm ² , especially 6.5-9.0 g / mm ²
The adhesive layer B has a 1000% modulus at 90 ° C. of 6 g / mm ² or less, particularly 5.5 g.
/ Mm ² or less, particularly 5.0 g / mm ² or less.

In the above, the control of the modulus of the pressure-sensitive adhesive layer can be controlled by a conventional method such as adjusting the degree of cross-linking or the molecular weight by controlling the molecular weight of the base polymer in the pressure-sensitive adhesive, the content of the cross-linkable functional group, and the blending ratio of the cross-linking agent. Can be performed in a simple manner.

The above 1000% modulus is obtained by laminating an adhesive layer so as to have a thickness of 1 mm.
× 10mm size through a tensile tester at 90 ° C
A stress-strain curve is obtained by performing a tensile test at a speed of 300 mm / min and a chuck interval of 10 mm under the atmosphere described above, and the stress at 1000% strain (elongation) can be obtained from the curve (the same applies hereinafter).

As shown in FIG. 1, for the pressure-sensitive adhesive layer B provided on the optically compensating retardation plate of the wide-viewing-angle polarizing plate, it is necessary to prevent the adhesive strength from being reduced due to contamination or the like until it is used for bonding. For this purpose, the separator 51 or the like is temporarily attached as necessary, and the cover is provided. As the separator, for example, an appropriate thin body such as a plastic film or a rubber sheet, paper or cloth, a nonwoven fabric or a net, a foamed sheet or a metal foil, or a laminate thereof may be used. An appropriate one according to the related art, such as one coated with an appropriate release agent such as a system, may be used.

The polarizing plate, the transparent protective layer, the optically compensating retardation plate, the adhesive layer, and the like forming the wide viewing angle polarizing plate may be formed of, for example, a salicylate compound, a benzophenol compound, a benzotriazole compound, or the like, if necessary. It may have ultraviolet absorbing ability by a method of treating with an ultraviolet absorbing agent such as a cyanoacrylate compound or a nickel complex compound.

The wide viewing angle polarizing plate according to the present invention is obtained by bonding a polarizing plate and an optical compensation retardation plate in advance for the purpose of preventing quality variation and improving the assembling efficiency of a liquid crystal display device. In addition, an adhesive layer is provided in advance on the adhesive layer so that the adhesive layer can be adhered to a liquid crystal cell or the like via the adhesive layer. Therefore, it can be preferably used for forming a liquid crystal display. When the polarizing plate and the optical compensation phase difference plate are bonded to each other, their optic axes can be set at an appropriate angle according to the intended phase difference characteristic or the like.

The formation of the liquid crystal display device can be performed according to a conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate, an optical compensation retardation plate, and an illumination system as required, and incorporating a driving circuit. In is not particularly limited except that the wide viewing angle polarizing plate according to the present invention is used,
It can be according to the conventional.

Therefore, an appropriate liquid crystal display device such as a liquid crystal display device having a polarizing plate disposed on one or both sides of a liquid crystal cell or a device using a backlight or a reflector for an illumination system can be formed. In that case, the wide viewing angle polarizer according to the present invention can be installed on one side or both sides of the liquid crystal cell. According to such a wide-viewing-angle polarizing plate, an optically compensating retardation plate can be arranged between the polarizing plate and the liquid crystal cell, so that the polarizing plate has an excellent compensating effect. It is particularly preferable to arrange a viewing angle polarizing plate.

FIGS. 2 and 3 show examples of the structure of the liquid crystal display device described above. Reference numeral 5 denotes a wide viewing angle polarizing plate, 6 denotes a liquid crystal cell, 7 denotes a backlight system, 9 denotes a reflection layer, and 8 denotes a light diffusion plate. FIG. 2 shows a backlight-type illumination type in which a wide viewing angle polarizing plate 5 is arranged on both sides of a liquid crystal cell 6, and FIG. 3 shows a wide viewing angle polarizing plate arranged only on one side of the liquid crystal cell. This is a reflection type illumination type.

The liquid crystal cell may be of any type such as TN type, STN type and π type.
In forming a liquid crystal display device, one or two or more appropriate optical layers such as a diffusion plate, an antiglare layer, an antireflection film and a protective plate can be arranged at appropriate positions.

[0027]

EXAMPLE 1 A polarizing plate obtained by stretching a polyvinyl alcohol film having a thickness of 80 μm by a factor of 5 in an aqueous iodine solution, drying the film, and adhering a cellulose triacetate film to both sides thereof through a polyvinyl alcohol-based adhesive layer. Is bonded to an optical compensation retardation plate (WV A02A, manufactured by Fuji Photo Film Co., Ltd.) via an acrylic adhesive layer A having a thickness of 25 μm, and the thickness provided on a separator on the exposed surface of the optical compensation retardation plate A 25-μm acrylic pressure-sensitive adhesive layer B was transferred to obtain a wide-viewing-angle polarizing plate.
The adhesive layer A has a modulus (1 at 90 ° C.).
000% modulus, the same applies hereinafter) of 8 g / mm ² , and adhesive layer B having a modulus of 3.8 g / mm ² .

Comparative Example 1 The adhesive layers A and B had a modulus of 30 g / mm ^2.
A wide-viewing-angle polarizing plate was obtained in the same manner as in Example 1 except that the above-mentioned polarizing plate was used.

Comparative Example 2 A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the adhesive layer A used had a modulus of 30 g / mm ² and the adhesive layer B used had a modulus of 8 g / mm ^2. Was.

Comparative Example 3 A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the adhesive layer A having a modulus of 30 g / mm ² was used.

Comparative Example 4 A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the adhesive layer B having a modulus of 30 g / mm ² was used.

Comparative Example 5 A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the adhesive layer B having a modulus of 8 g / mm ² was used.

Comparative Example 6 Adhesive layer A having a modulus of 3.8 g / mm ² was prepared.
A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the adhesive layer B having a modulus of 30 g / mm ² was used.

Comparative Example 7 Adhesive layer A having a modulus of 3.8 g / mm ² was prepared.
A wide viewing angle polarizing plate was obtained in the same manner as in Example 1 except that the adhesive layer B having a modulus of 8 g / mm ² was used.

Evaluation Test 200 mm × 1 from the wide viewing angle polarizing plate obtained in each of Examples and Comparative Examples so that the angle was 45 degrees with respect to the absorption axis of the polarizing plate.
A 50 mm size sample is cut out and adhered to one surface of a glass plate via the adhesive layer B, and a similar sample is applied to the other surface of the glass plate via the adhesive layer B, and the polarizing plate becomes crossed Nicols. After leaving for 24 hours in an atmosphere of 60 ° C., the sample was taken out, and 9 points were taken out of the sample (four points at the intersections of the four corners and the diagonal, and the middle points of the four sides connecting the four corners). Was examined, and the difference between the maximum value and the minimum value was determined.

The above results are shown in the following table.

From the table, it can be seen that in the example, the variation in the in-plane light transmittance is small, and the window frame-shaped luminance unevenness is suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a wide viewing angle polarizing plate.

FIG. 2 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 3 is a cross-sectional view of another example of a liquid crystal display device.

[Explanation of symbols]

 5: wide viewing angle polarizing plate 1: polarizing plate 2: adhesive layer A 3: optical compensation retardation plate 4: adhesive layer B 6: liquid crystal cell

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Masayuki Satake 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA06 BA14 BA25 BA27 BB02 BB44 BB51 2H091 FA08X FA08Z FA11X FA11Z FA37X FB02 FC23 FD06 GA16 GA17 HA07 HA10 LA04 LA19

Claims (3)

[Claims] 1. An adhesive layer B is provided on an exposed surface of the optical compensation phase difference plate of a laminate in which a polarizing plate and an optical compensation phase difference plate are adhered via an adhesive layer A, and the adhesive layer A has a temperature of 90 ° C. Is more than 6 to 10 g / mm ² , and the adhesive layer B has a 1000% modulus at 90 ° C. of 6
g / mm ² or less. 2. The wide viewing angle polarizing plate according to claim 1, wherein the optical compensation retardation plate comprises an optically anisotropic layer made of a liquid crystal polymer supported by a cellulose triacetate film. 3. A liquid crystal display device comprising the wide viewing angle polarizing plate according to claim 1 on at least one side of a liquid crystal cell.