JP2000056131A - Phase difference plate, laminated polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liq. crystal display device with excellent visibility as for contrast, monochromatic display or the like in a broad visual angle by providing a thinner phase difference plate which effectively compensates for a double refractivity caused by a liq. crystal cell. SOLUTION: A liq. crystal display device is constituted by a phase difference plate, a laminated polarizing plate, and the phase difference plate and/or the polarizing plate at least on one side of a liq. crystal cell. The phase difference plate satisfies an expression Re: (nx-ny)d<20 nm and an expression Rz: (nz-nx)d<1000 nm, where nx and ny are refractive indexes in an intra-plane, nz is a main refractive index in a direction of the thickness, nx>ny and d is thickness. The laminated polarizing plate consists of a laminated body of the phase difference plate and a polarizing plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate suitable for improving viewing angle characteristics by optical compensation of a liquid crystal cell, a laminated polarizing plate using the retardation plate, and a liquid crystal display device.

[0002]

2. Description of the Related Art A retardation plate is disposed in a liquid crystal cell to compensate for optical characteristics based on birefringence in order to prevent a display color or contrast from being changed by a viewing angle of a display device due to birefringence of liquid crystal. A technique for improving the viewing angle characteristics has been proposed.

Conventionally, as such a compensating phase difference plate,
What laminated | stacked the uniaxially stretched film was known. However, the production efficiency is poor due to the necessity of a laminating step and the necessity of highly controlling the crossing angle of the stretching axis, and the retardation plate is required by laminating two or more uniaxially stretched films, and thus There is a problem that the liquid crystal display device becomes thicker.

[0004]

The object of the present invention is to obtain a thin retardation plate capable of highly compensating for birefringence caused by a liquid crystal cell, and to obtain a liquid crystal display device which is excellent in contrast and visibility such as monochrome display in a wide viewing angle range. As an issue.

[0005]

According to the present invention, an in-plane principal refractive index is set to _nx ,
n _y, the main refractive index in the thickness direction is n _z, and when the thickness is d at n _x> n _y, wherein _{Re: (n x -n y)} d <20nm
When the formula Rz: the (n _z -n _x) d <retardation plate satisfies the 1000 nm, and stacked polarizing plates, characterized in that a laminate it and the polarizer, and a liquid crystal cell An object of the present invention is to provide a liquid crystal display device comprising the retardation plate or the polarizing plate and the retardation plate on at least one side.

[0006]

According to the retardation plate of the present invention, by satisfying the above-mentioned expressions Re and Rz, a change in display characteristics due to a viewing angle based on birefringence of a liquid crystal cell can be highly compensated, and contrast and black and white can be improved. A liquid crystal display device having excellent visibility such as display can be obtained.

[0007]

Retardation plate according to the present invention embodiments of the Invention, the main refractive indices n _x in the plane, n _y, the main refractive index in the thickness direction is n _z, and n _x> n _y in the thickness d And the formula Re: ( _nx −
n _y) d <20nm and the formula _{Rz: (n z -n x)} d <100
It satisfies 0 nm.

A retardation plate exhibiting the above-mentioned characteristics is obtained, for example, by bonding a heat-shrinkable film to one or both sides of a polymer film and treating the polymer film under the application of a shrinkage force by heating to increase the birefringence. It can be obtained by a method of forming a functional film.

In the above, from the viewpoint of achieving the above-mentioned properties efficiently, the heat-shrinkable film has a shrinkage ratio of 5% or more in one direction such as the width direction (MD) and a length direction (T
D) or the like having a shrinkage ratio of 8% or more in a direction orthogonal to the above and a difference in shrinkage in the orthogonal direction of 20% or less can be preferably used.

[0010] On the other hand, the above-mentioned treatment may be carried out by an appropriate method using, for example, a roll stretching machine or a biaxial stretching machine, and the treatment temperature is set to a temperature close to or higher than the glass transition point of the polymer film. It is preferable from the viewpoint of efficient achievement of characteristics. The properties such as the refractive index of the obtained birefringent film can be controlled by the type and thickness of the polymer film, the shrinkage, the processing temperature, the change in the thickness of the polymer film, and the like.

As the polymer forming the film to be processed, any polymer capable of forming a transparent film can be used, and there is no particular limitation. A polymer which is excellent in transparency and is capable of forming a film having a light transmittance of 80% or more is preferable.

The polymer film can be classified as having a positive or negative birefringence characteristic in relation to the stretching direction and the refractive index. In the present invention, any of them can be used as described above. Therefore, a film made of a polymer exhibiting a positive birefringence property, in which the refractive index in the stretching direction is increased, is more preferable than that in which the properties are efficiently achieved and a material having excellent heat resistance is obtained.

Incidentally, the polymer capable of forming a birefringent film having a positive birefringence characteristic includes, for example, polycarbonate, polyvinyl alcohol, cellulose-based polymers, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene-based Examples thereof include polymers, polysulfones, ponoether sulfones, and polyolefins such as polypropylene. In particular, an amorphous polymer having excellent heat resistance can be preferably used.

The polymer film may be formed by an appropriate method such as a casting method such as a casting method or an extrusion method. A solution casting method such as a casting method is more preferable in that a polymer film having less unevenness in thickness and orientation distortion is obtained. The thickness of the polymer film can be appropriately determined depending on the intended retardation or the like, but is generally from 10 to 500 μm, especially from 20 to 300 μm.

The retardation plate according to the present invention is preferably formed as a single layer of a birefringent film from the viewpoint of thinning and the like, but is formed as a laminate of the same or different birefringent films. It may be protected or reinforced by an isotropic transparent polymer layer or glass layer.

The phase difference plate according to the present invention is, for example, a TN type or a TN type for compensating for a phase difference in a perspective direction in which a decrease in contrast in a front direction is prevented, or compensating for a phase difference in a front direction and a perspective direction. It can be preferably used for compensating viewing angle characteristics due to birefringence in various types of liquid crystal cells such as STN type and π type.

The retardation plate according to the present invention can be preferably used for optical compensation of a liquid crystal cell as described above, but when a display device comprising the liquid crystal cell is accompanied by a polarizing plate, it is used as a laminate with the polarizing plate. You can also. The laminated polarizing plate is illustrated in FIG. 1 is a polarizing plate, 2 is an adhesive layer, and 3 is a retardation plate. In the illustrated example, an adhesive layer 2 made of a pressure-sensitive adhesive is attached to the outside of the retardation plate 3 to adhere to a liquid crystal cell or the like.

Any suitable polarizing plate can be used as the polarizing plate, and there is no particular limitation. In general, iodine and / or a dichroic dye is adsorbed 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 stretched. A polarizing film made of a polyene oriented film, such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, or a product provided with a protective layer thereon is used.

For laminating the retardation plate and the polarizing plate, for example, a transparent adhesive such as acrylic or an adhesive can be used. There is no particular limitation on the type of the adhesive or the like. From the viewpoint of preventing a change in the optical characteristics of the retardation plate or the like, it is preferable that a high-temperature process such as curing or drying is not required at the time of lamination, and that a long-time curing treatment or drying time is not required. When layers having different refractive indices are laminated, an adhesive or the like having an intermediate refractive index is preferably used from the viewpoint of suppressing reflection loss.

The formation of the liquid crystal display device using the retardation plate according to the present invention can be performed according to the conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell and a retardation plate for optical compensation, and a polarizing plate and an illumination system as needed, and incorporating a drive circuit, In the present invention, as described above, there is no particular limitation except that the retardation plate according to the present invention is used for optical compensation and provided on at least one side of the liquid crystal cell, and can be in accordance with the conventional one.

Therefore, it is possible to form a suitable liquid crystal display device such as a liquid crystal display device in which a polarizing plate is disposed on one or both sides of a liquid crystal cell, or a lighting system using a backlight or a reflection plate. In the case of a liquid crystal display device using a polarizing plate, a retardation plate for optical compensation is a liquid crystal cell and a polarizing plate,
In particular, it is more preferable to dispose it between the polarizing plate on the viewing side and the compensation effect. In the arrangement, the above-mentioned laminated polarizing plate may be used.

FIGS. 2 and 3 show examples of the structure of a liquid crystal display device using a polarizing plate. 4 is a liquid crystal cell, 5 is a backlight system, and 6 is a reflective layer. Reference numeral 7 denotes a light diffusion plate.
4 is a backlight type illumination system in which an optical compensation retarder is disposed on both sides, and FIG. 5 has an optical compensation retarder disposed only on one side. The lighting system is of a reflective type.

In the above, the forming parts of the liquid crystal display device are as follows:
They may be laminated and integrated, or may be in a separated state. In forming a liquid crystal display device, for example, appropriate optical elements such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer and a protective plate can be appropriately arranged.

As the retardation plate for optical compensation, a retardation plate for compensating a phase difference due to birefringence of a liquid crystal cell over a wide viewing angle range is preferably used. Thereby, prevention of coloring or the like is achieved over a wide viewing angle range. The liquid crystal cell to be applied is arbitrary, but can be preferably applied to a TN type or π type liquid crystal cell for forming a TFT type liquid crystal display device or the like.

[0025]

EXAMPLE 1 Polycarbonate having a molecular weight of about 80,000 and comprising polycondensate of phosgene and bisphenol A was treated with methylene dichloride.
The weight% solution was continuously cast on a steel drum, which was sequentially peeled off and dried to obtain a polycarbonate film having a thickness of 60 μm and a phase difference of almost 0.

Next, a polypropylene film having an MD shrinkage of 10% and a TD shrinkage of 6% is adhered to one side of the film via an acrylic pressure-sensitive adhesive layer.
The polypropylene film was shrunk at 0 ° C. by 3% and then peeled to obtain a birefringent film (retardation film) having a thickness of 65 μm.

Example 2 A polycarbonate film having a thickness of 100 μm and a retardation of almost 0 was obtained in the same manner as in Example 1, and a polypropylene film having an MD shrinkage of 30% and a TD shrinkage of 35% was acrylic-based on both surfaces. The polypropylene film was adhered via a pressure-sensitive adhesive layer and subjected to 19% shrinkage at 160 ° C. by a roll stretching machine and then peeled off to obtain a 142 μm thick birefringent film (retardation plate).

Comparative Example A polypropylene film having an MD shrinkage of 40% and a TD shrinkage of 15% was adhered to both sides, and 158 with a roll stretching machine.
A birefringent film (retardation plate) having a thickness of 77 μm was obtained in the same manner as in Example 1 except that the polypropylene film was shrunk at 15 ° C. by 15%. This film contains the TD
Wrinkles occurred in the direction, making it impractical.

[0029] Evaluation Test 1 optical properties embodiment, the birefringent film obtained in Comparative Example, the principal refractive indices n _x in the film plane and the thickness direction, n _y, examined n _z (Oji Scientific Ltd. instruments, KOBRA −21ADH; parallel Nicol rotation method principle), and Re and Rz were calculated from the values.

The results are shown in the following table.

Evaluation Test 2 Polarizing plates were arranged on both sides of the TN type liquid crystal cell via the retardation films obtained in Examples 1 and 2, and the display characteristics due to the contrast in the front direction and the change in viewing angle were examined. The liquid crystal display device was high in display quality and excellent in visibility with no change in display characteristics over a wide viewing angle range.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a laminated polarizing plate.

FIG. 2 is a cross-sectional view illustrating a liquid crystal display device.

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

[Explanation of symbols]

 1: polarizing plate 2: adhesive layer 3: retardation plate 4: liquid crystal cell

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoshi Kawahara 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Hiroyuki Yoshimi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka F-term in Nitto Denko Corporation (reference) 2H049 BA02 BA06 BA42 BB03 BB42 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FA31X FA37X FB02 FC01 FC07 FC09 FD06 KA01 LA16 LA17 LA19

Claims (4)

[Claims] The principal refractive indices n _x of 1. A plane, n _y, the main refractive index in the thickness direction is n _z, and when the thickness is d at n _x> n _y, wherein Re: (n and _x -n _y) d <20nm, the formula Rz: (n
_z -n _x) d <retardation plate satisfies the 1000 nm. 2. The retardation plate according to claim 1, wherein the retardation plate is made of a polymer having a positive birefringence characteristic. 3. A laminated polarizing plate comprising a laminate of the retardation plate according to claim 1 and a polarizing plate. 4. The method according to claim 1, wherein at least one side of the liquid crystal cell is provided.
Or a liquid crystal display device comprising the retardation plate according to 2 or a polarizing plate and the retardation plate.