JP2001166133A - Optically compensated polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop an optically compensated polarizing plate which is thin and excellent in the production efficiency and with which a liquid crystal display device having excellent display quality can be formed. SOLUTION: The optically compensated polarizing plate consists of a laminated body 1 of a phase difference plate 12 or 13 and a polarizing plate 11 or 14. When these two standard laminated bodies having the same structure are disposed with the phase difference plates are placed on the inside, and the polarizing plates are arranged in the cross-Nicol position, the leakage rate of light in the normal direction is <=0.2% on the entire surface. The liquid crystal display device has this optically compensated polarizing plate on at least one side of a liquid crystal cell 3. Thus, the extremely thin optically compensated polarizing plate is obtained by using one phase difference plate, and the thin liquid crystal display device which is excellent in display quality such as contrast and homogeneity while compensating the phase difference of a TFT liquid crystal cell, is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin, optically compensating polarizing plate which can be used to form a liquid crystal display device having excellent display quality and has excellent manufacturing efficiency.

[0002]

2. Description of the Related Art Conventionally, as an optically compensating polarizing plate capable of forming a liquid crystal display device having excellent display quality in a wide viewing angle range by compensating for a phase difference due to birefringence of a TFT type liquid crystal cell or the like with a wide angle in the front and in the oblique directions. It has been known that a retardation plate obtained by laminating uniaxially stretched films with their stretching directions orthogonal to each other is bonded to a polarizing plate. However, the use of a plurality of retardation plates is bulky and the thickness of the liquid crystal display device is increased, and a lamination process in which the optical axis of the retardation plate is regulated is required, resulting in poor production efficiency.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to develop an optically compensating polarizing plate which is thin and has excellent manufacturing efficiency for forming a liquid crystal display device having excellent display quality.

[0004]

According to the present invention, there is provided a laminated body of a retardation plate and a polarizing plate, which is provided with a standard laminated body of the same structure, with the retardation plate side inside, and a polarizing plate formed of a crossed Nicol. An optically compensating polarizer characterized by having a leakage light rate in the normal direction of 0.2% or less on the entire surface when the optical compensating polarizer is arranged so as to have the optical compensating polarizer on at least one side of a liquid crystal cell. A feature of the present invention is to provide a liquid crystal display device.

[0005]

According to the present invention, an optically compensating polarizing plate having excellent thickness can be obtained with high production efficiency by using a single retardation plate, and a TN type, a π type or a VA type can be obtained by using it. Etc. TF
By compensating for the phase difference of a T-type liquid crystal cell or the like, a thin liquid crystal display device having excellent display quality such as contrast and display uniformity can be formed. In particular, the retardation plate has a phase difference of R1 in the normal direction, and a phase difference of 40 with respect to the normal direction with the slow axis as the rotation axis.
When the phase difference in the vertical direction in the state inclined at an angle is R2 and R2 / R1 by them is β, R1 ≦ 1000
nm, β ≧ 1.12 and the variation in the angle of the slow axis in the plane is within ± 3 degrees,
A liquid crystal display device having excellent display quality such as contrast can be formed by compensating for a phase difference due to a liquid crystal cell in a wide viewing angle range of front and perspective.

That is, the phase difference is defined by the product (Δnd) of the refractive index difference (Δn) of the birefringent light and the optical path length (d). In this case, the above β is the angle dependence of the phase difference. In terms of characteristics, R1 ≦ 1000 nm and a small deviation with controlled variation in optical axis makes it possible to highly compensate for a phase difference particularly in a front direction of a TFT type liquid crystal display device or the like, thereby achieving high contrast and high display quality. By achieving the homogeneity and satisfying β ≧ 1.12, the phase difference in the oblique direction can be highly compensated and the display quality can be improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optically compensating polarizing plate according to the present invention comprises a laminate of a retardation plate and a polarizing plate. The light leakage rate in the normal direction when the plates are arranged so as to be crossed Nicols is 0.2% or less over the entire surface. An example is shown in FIG. 1 is an optical compensation polarizing plate, 11 and 14 are polarizing plates, and 12 and 13 are retardation plates. The figure illustrates a liquid crystal display device in which 3 is a liquid crystal cell and 2 is an adhesive layer.

[0008] As the retardation plate, a stretched film made of a suitable polymer having light transmittance is used. Above all, a film having a light transmittance of 75% or more, particularly 85% or more, which is excellent in light transmittance, is preferable. From the viewpoint of obtaining a retardation plate having excellent heat resistance, a polymer made of a polymer having a positive birefringence and having a high refractive index in the stretching direction is preferable.

Incidentally, examples of the polymer having a positive birefringence described above include polycarbonate, polyvinyl alcohol, cellulose resin, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene resin, polysulfone, and polyether. And polyolefins such as sulfone and polypropylene.

The retardation plate used in the present invention is obtained by, for example, stretching a film made of a polymer or controlling the retardation characteristics by an appropriate method such as a method of controlling the refractive index in the thickness direction. Can be. As the film, a film formed by an appropriate method such as a casting method such as a casting method or an extrusion method can be used. In particular, a film with less thickness unevenness and orientation distortion unevenness by a solution casting method such as a casting method can be preferably used.

The thickness of the film can be appropriately determined depending on the intended retardation characteristics of the retardation plate. Generally, 5-500 μm, especially 10-400 μm, especially 20-
The thickness is 300 μm. The film to be processed may be a non-oriented film or an oriented film that has been subjected to an appropriate orientation treatment such as uniaxial stretching in advance.

Compensation of the phase difference in the oblique direction which suppresses the decrease of the contrast in the front (normal line) direction in the TN type liquid crystal cell, and the front and the side by compensating the phase difference between the front and the oblique direction in the π type or VA type liquid crystal cell. From the point of obtaining a liquid crystal display device with excellent display quality such as contrast and display uniformity at a wide viewing angle with a squint, the phase difference in the normal direction is R1, and the slow axis is the rotation axis. The phase difference in the vertical direction in a state of being tilted by 40 degrees is defined as R2, and R2 / R1 by them is used.
When β is represented by β, a retardation plate satisfying R1 ≦ 1000 nm and β ≧ 1.12 and having a variation in the angle of the slow axis in the plane within ± 3 degrees can be preferably used.

The above-mentioned retardation plate exhibiting the retardation characteristics and the optical axis variation characteristics is, for example, a biaxial stretching system such as a simultaneous system or a sequential system, or a uniaxial stretching system such as a uniaxial transverse system (in the width direction of a long film). The film can be efficiently obtained by a method of stretching at a temperature near the glass transition temperature of the polymer forming the film, particularly at a temperature higher than the glass transition temperature. In the case of the biaxial stretching method, the stretching ratio in the short axis direction, that is, the width (horizontal) direction of the long film is set to 50% or less from the viewpoint of efficiently satisfying the deviation between R1 and β and the optical axis. Is preferred.

The above-mentioned control of the refractive index in the thickness direction of the film is performed, for example, by bonding one or more heat-shrinkable films to one or both surfaces of the film via an adhesive layer or the like, and applying heat shrinkage by heating. The method can be carried out by applying a shrinking force of the conductive film to the film and stretching or shrinking the film in one or both directions in the longitudinal or horizontal direction under the action of the shrinking force.

[0015] The retardation plate which can be preferably used has as small a variation in the retardation as possible due to birefringence and the orientation axis such as the slow axis, and especially the retardation in the transmitted light in the normal direction perpendicular to the film surface. Are formed in a thickness of 10 nm or less, particularly 5 nm or less. The characteristics of R1 and β described above are
It can be controlled by a method in which conditions such as the type and thickness of the film, the stretching ratio and the stretching temperature are changed.

The optical compensation polarizing plate is a retardation plate 1 as shown in FIG.
It can be formed by laminating the polarizing plates 11 and 14 with the polarizing plates 2 and 13. Such lamination can be performed by a method of sequentially and separately laminating during the manufacturing process of the liquid crystal display device. However, by preliminarily laminating, it is possible to improve the production efficiency of the liquid crystal display device with excellent quality stability and laminating workability. There are advantages. When laminating, the arrangement angle of the optical axis such as the slow axis or transmission axis of the retardation plate and the polarizing plate is not particularly limited, but it is generally preferable to arrange them in a parallel relationship or an orthogonal relationship from the viewpoint of the compensation effect and the like.

An appropriate adhesive may be used for laminating the retardation plate and the polarizing plate, but an adhesive layer is preferably used from the viewpoint of maintaining optical characteristics by suppressing thermal stress. The adhesive layer may be made of any suitable material such as acrylic, silicone, polyester, polyurethane, polyether, and rubber, and is not particularly limited. Above all, acrylic ones are preferably used in terms of heat resistance and optical characteristics.

The adhesive layer may contain, if necessary, fillers, pigments, coloring agents, antioxidants, etc. made of natural or synthetic resins, glass fibers, glass beads, metal powders and other inorganic powders. Can be added.
In addition, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles.

An appropriate polarizing plate can be used as the polarizing plate. By the way, as an example, 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, and an ethylene / vinyl acetate copolymer-based partially saponified film. A stretched film, a polarizing film made of a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, and the like can be given.

The polarizing plate may have a transparent protective layer on one or both sides of the polarizing film.
Further, the polarizing plate may be a reflection type or a semi-transmission type having a reflection layer, a half mirror, and the like. The reflective polarizing plate is used to form a liquid crystal display device or the like that reflects and reflects incident light from the viewing side (display side). There are advantages such as easy reduction in thickness of the display device.

The transparent protective layer can be appropriately formed as a coating layer of a polymer or an adhesive layer of a protective film. The formation of the transparent protective layer includes a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like. Is preferably used. Examples include polyester resins and acetate resins, polyethersulfone resins and polycarbonate resins, polyamide resins and polyimide resins, polyolefin resins and acrylic resins, or acrylic, urethane and acrylic urethane resins. Examples of such resins include thermosetting resins such as epoxy resins and silicone resins, and ultraviolet curing resins. The surface of the transparent protective layer may be formed into a fine uneven structure by containing fine particles.

The reflection type polarizing plate can be formed by an appropriate method such as a method in which a reflection layer made of metal or the like is provided on one side of the polarizing plate via a transparent resin layer or the like as necessary. Specific examples thereof include a transparent resin layer such as a protective film that has been subjected to a mat treatment as required, and a foil or a vapor-deposited film made of a reflective metal such as aluminum provided on one surface, or a surface fineness due to the inclusion of fine particles in the transparent resin layer. An example in which a metal reflective layer is provided on the concavo-convex structure by an appropriate method such as a vapor deposition method or a plating method is given. The transflective polarizing plate can be obtained by making the above-mentioned reflective layer a transflective type such as a half mirror.

The above-mentioned layers such as the retardation plate and the polarizing plate, the transparent protective layer and the adhesive layer are made of, for example, an ultraviolet ray such as a salicylate compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound or a nickel complex compound. Ultraviolet absorbing ability can be provided by a method of treating with an absorbent.

The optically compensating polarizing plate according to the present invention comprises a standard laminated body having the same structure and the retardation plate side on the inside.
In addition, when the polarizing plate is arranged so as to be crossed Nicols, the light leakage rate in the normal direction is 0.2% or less over the entire surface. It is possible to prevent non-uniformity of luminance due to variation in degree, and to achieve excellent display uniformity. The leak light rate more preferable than the improvement of display uniformity or the like is 0.15% or less, particularly 0.10% or less, and particularly 0.08% or less.

As a standard laminate having the same structure as the optical compensation polarizing plate for determining the leakage light rate, the leakage light rate examined in the same manner as described above is as small as 0.2% or less. Although it is possible to use those, from the viewpoint of the inspection efficiency and the like based on the manufacturing process of the optical compensation polarizing plate, it was obtained by cutting the laminate into a predetermined size while sequentially laminating a long retardation plate and a polarizing plate. Based on the optically compensating polarizing plate, it is preferable to inspect the previously formed one between the adjacent optically compensating polarizing plates before and after the formation, and sequentially inspect the next formed one as a standard laminate.

The optically compensating polarizing plate according to the present invention can be used, for example, to compensate for a phase difference in the oblique direction in which a decrease in contrast in the front (normal line) direction is prevented or to compensate for a phase difference in the front and oblique directions. It can be preferably used for compensating viewing angle characteristics due to birefringence in various types of liquid crystal cells such as a liquid crystal cell of a type, STN type, and π type. In practical use, for example, it can be applied as an optical member of an appropriate form such as one provided with an adhesive layer on one or both surfaces thereof for the purpose of bonding to another member such as a liquid crystal cell.

The formation of the liquid crystal display device using the optically compensating polarizing plate 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, an optical compensation polarizing plate, and an illumination system as necessary, and incorporating a drive circuit. There is no particular limitation except that the optical compensating polarizing plate according to the present invention is provided on at least one side of the liquid crystal cell 3 as described above, and can be in accordance with the conventional one.

Therefore, a liquid crystal display device in which a polarizing plate is disposed on one or both sides of a liquid crystal cell, a transmission type or a reflection type using a backlight or a reflection plate or a transflective reflection plate in an illumination system, or a combination of a reflection type and a transmission type. An appropriate liquid crystal display device such as a mold can be formed. In this case, the optical compensation polarizing plate is provided with the retardation plates 12 and 13 on the viewing side and / or the viewing back side, particularly at least the viewing side of the liquid crystal cell 3 as shown in the figure.
Is preferably disposed between the liquid crystal cell 3 and the polarizing plates 11 and 14 from the viewpoint of compensation effect and the like.

In the above description, 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 the liquid crystal display device, for example, appropriate optical elements such as a diffusion plate, an anti-glare layer, an antireflection film, a protective layer and a protective plate can be appropriately arranged. Such an element can be used for forming a liquid crystal display device in the form of the above-mentioned optical member laminated with an optical compensation polarizing plate.

[0030]

EXAMPLE 1 A 20 wt% methylene dichloride solution of polycarbonate having a molecular weight of about 80,000 and comprising a polycondensate of phosgene and bisfinol A was cast on a steel drum, which was continuously peeled off and dried. The obtained long film having a thickness of 60 μm and a retardation of almost 0 is subjected to a biaxial stretching process of 35% in the vertical direction and 35% in the horizontal direction at 162 ° C. through a simultaneous biaxial stretching machine to obtain a retardation plate. The optically compensatory polarizing plate was obtained by laminating the polarizing plates having a leakage light rate of 0.02% in crossed Nicols via an acrylic adhesive layer so that their slow axis and transmission axis were in a parallel relationship. .

Example 2 A sequential biaxial stretching method in which a uniaxial stretching process of 15% in the machine direction at 157 ° C. using a roll stretching machine and a 40% uniaxial stretching process in a transverse direction at 176 ° C. using a tenter was adopted. Otherwise, a retardation plate was obtained in the same manner as in Example 1, and this was laminated with a polarizing plate to obtain an optical compensation polarizing plate.

Example 3 A retardation plate was obtained in the same manner as in Example 1 except that only a uniaxial stretching process of 90% in the horizontal direction was performed at 170 ° C. with a tenter, and the retardation plate was laminated with a polarizing plate to provide optical compensation. A polarizing plate was obtained.

Comparative Example In addition to a sequential biaxial stretching method in which a uniaxial stretching process of 82% in the longitudinal direction was performed at 160 ° C. with a roll stretching machine, and a uniaxial stretching process of 55% in the horizontal direction was performed at 160 ° C. with a tenter. Obtained a retardation plate according to Example 1, and laminated it with a polarizing plate to obtain an optical compensation polarizing plate.

Evaluation Test The retardation plates obtained in the Examples and Comparative Examples were subjected to a phase difference meter based on the parallel Nicol rotation method (KOB, manufactured by Oji Scientific Instruments).
(RA21-ADH) to measure the variation (shift) of the phase difference and the slow axis angle, and the above-mentioned β was calculated from the measured values.

The optical compensating polarizing plates obtained in Examples and Comparative Examples were cut out from adjacent positions, and two of them were arranged so that their retardation plates were on the inner side and the polarizing plates were in a crossed Nicols state. The leakage light rate in the normal direction was examined (CMS-500, manufactured by Murakami Color Research Laboratory).

The above results are shown in the following table. R1 β shift (degree) Leakage light rate (%) Example 1 14 6.79 ± 3.0 0.03 Example 2 48 1.65 ± 1.5 0.06 Example 3 270 1.19 ± 0. 5 0.06 Comparative Example 117 1.99 ± 6.0 3.3

The optically compensating polarizing plates obtained in Examples 1 to 3 were replaced with TN
A liquid crystal display device was formed by bonding a polarizing plate to both sides of a liquid crystal cell on the outside, and the display characteristics were examined.
Excellent display quality with excellent contrast and display uniformity over a wide viewing angle range of front and perspective. From the above results and table, it can be seen that a liquid crystal display device having excellent display quality can be formed by compensating for the phase difference due to the liquid crystal cell in a wide viewing angle range of front and perspective.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a liquid crystal display device (an example of an optical compensation polarizing plate).

[Explanation of symbols]

 1: optical compensation polarizing plate 11, 14: polarizing plate 12, 13: retardation plate 3: liquid crystal cell

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Seiji Kondo 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA06 BA25 BB03 BB13 BB23 BB24 BB26 BB28 BB43 BB44 BB51 BC22 2H091 FA08X FA08Z FA11X FA11Z FA14Z FB02 FC09 FC18 FD06 FD09 FD10 FD14 HA07 HA08 KA10 LA17 LA19 5G435 AA18 BB12 FF01 FF02 FF05 KK07

Claims (4)

[Claims] 1. A laminate comprising a retardation plate and a polarizing plate,
A standard laminated body having the same structure and the retardation plate side thereof are arranged inside, and when the polarizing plate is arranged in a crossed Nicols state, the leakage light rate in the normal direction is 0.
An optically compensating polarizing plate, which is 2% or less. 2. The method according to claim 1, wherein the retardation plate is made of a polymer having a positive birefringence, and the retardation in the normal direction is R1, and the slow axis is a rotation axis, and 40 degrees with respect to the normal direction. When the vertical phase difference in the inclined state is R2 and R2 / R1 thereby is β, R1 ≦ 1000 nm,
An optically compensating polarizing plate that satisfies β ≧ 1.12 and has a variation in the angle of the slow axis in the plane within ± 3 degrees. 3. The optically compensating polarizing plate according to claim 1, wherein the polarizing plate has an adhesive layer on one or both sides. 4. A liquid crystal display device comprising the optical compensation polarizing plate according to claim 1 on at least one side of a liquid crystal cell.