JPH07110405A - Optical compensation film and liquid crystal display device using same - Google Patents

Abstract

PURPOSE:To improve coloring property, angle of view characteristics, and contrast of a fast-response ST-LCD by forming a positive uniaxial optical anisotropic layer having the optical axis in the normal direction of the layer on a polysulfone polymer film. CONSTITUTION:Any material having intrinsic birefringence can be used for the compd. used for the positive uniaxial optical anisotropic layer having the optical axis in the normal direction of the film. If the material has small absolute value of intrinsic birefringence, it can be used by increasing the thickness or molecular orientation. The value of intrinsic birefringence is preferably >=0.02, and more preferably >=0.04. A thermoplastic film used as the material consists of a polymer having positive or negative intrinsic birefringence. To obtain the optical axis in the normal direction of the film, a polymer having negative intrinsic birefringence by biaxial stretching is preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation film used for color correction of a high-speed response liquid crystal display device and improving viewing angle characteristics, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Liquid crystal display devices have many features such as low voltage and low power consumption, which can be directly connected to an IC circuit, various display functions, and weight reduction. It is widely used as a display device for word processors and personal computers. Among them, a twisted nematic liquid crystal display device (hereinafter STN-LCD) having a twist angle of liquid crystal molecules of 160 ° or more has a larger capacity than a conventional twisted nematic liquid crystal display device (TN-LCD) having a twist angle of 90 °. Is possible and is currently the mainstream of liquid crystal display devices.

However, the STN-LCD has a problem that the displayed image is colored in blue or yellow (blue mode or yellow mode). For this reason, the contrast and visibility are low in black and white display, and colorization is extremely difficult. there were. So to compensate for this coloring,
A two-layer liquid crystal black-and-white or color display using a reverse twisted STN liquid crystal cell has been proposed. However, since a plurality of liquid crystal cells are used, the weight and volume of the display device increase, or the cost increases. There is another problem that the viewing angle characteristic is deteriorated such that the contrast sharply decreases with a slight change in the viewing angle or the background color changes.

In order to solve this problem, Japanese Patent Laid-Open No. 63-
No. 167303, No. 63-167304, No. 63-1
89804, 63-261302, 63-14.
9624, JP-A-1-201607 and 1-201.
608, 1-105217, JP-A-2-2853.
No. 03, No. 2-59702, No. 2-24406, No. 2-146002, No. 2-257103, JP-A-3.
-23404, 3-126012, 3-181.
As described in Japanese Patent Publication No. 905, No. 3-194503, etc., a method of using a retardation plate instead of the reverse twist STN liquid crystal has been proposed.

According to these methods, the coloring of the STN-LCD is significantly improved, the weight and volume of the display device itself is significantly reduced, and the cost is reduced, but the STN-LCD is reduced.
The viewing angle characteristics of were hardly improved.

Therefore, in order to improve this viewing angle characteristic,
JP-A-2-285303, JP-A-2-160204, EP-0482620A2, JP-A5-1579
In JP-A-11-1999, a method was proposed in which a birefringent film having a refractive index in the thickness direction larger than that in the direction perpendicular to the optical axis of the birefringence was prepared and used as a retardation plate. According to this method, the change in contrast depending on the viewing angle is reduced,
Although the viewing angle characteristics are improved, the effect is still small and the manufacturing process is complicated, so that it is difficult to increase the productivity and reduce the cost.

Further, JP-A-2-256023, JP-A-3-141303, JP-A-3-14122, and JP-A-3-24.
In Japanese Patent No. 502, there has been proposed a method in which one film each having positive and negative intrinsic birefringence values or a laminated film is used as a retardation plate. According to this method, the birefringence of the two films can be adjusted according to the characteristics of the liquid crystal cell, so that the viewing angle characteristics can be improved more precisely, but the use of two or more separately prepared birefringent films. Is necessary, and the cost is increased accordingly. In addition, JP-A-4-5
Japanese Patent Laid-Open No. 1101 discloses a method for improving the viewing angle problem by using only a film having a negative intrinsic birefringence value as a retardation plate.

Although these methods can greatly improve the viewing angle characteristics of conventional LCDs, they have a fast response LCD.
On the other hand, it was not possible to improve the hue and contrast of the front face, and further, the viewing angle characteristics were hardly improved. As a method of compensating for the tint when this high-speed LCD is viewed from the front and increasing the contrast, there are methods disclosed in Japanese Patent Application Laid-Open No. 4-365002 and Japanese Patent Application No. 2881871.
It is known to use a polymer film of high wavelength dispersion type, specifically a polysulfone-based polymer, as described in the specification. However, JP-A-5-
As described in JP-A-150116, since the polysulfone-based polymer film has a high Tg, the above-mentioned JP-A-2-285303, JP-A-2-160204,
It is difficult to apply the manufacturing method of performing heat deformation such as EP-0482620A2 and JP-A-5-157911. Further, Japanese Patent Laid-Open No. 5-241019 discloses that
The polymer liquid crystal is homeotropically aligned on the thermoplastic polymer film. However, the alignment of the polymer liquid crystal by an electric field requires a long time, and since it is a polymer, the degree of alignment does not increase.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a large amount of an optical compensation film which can significantly improve the coloring, viewing angle characteristics, and contrast of STN-LCD having a high response speed at a low cost. . Another object of the present invention is to provide a liquid crystal display device using the optical compensation film, which has improved background coloring, viewing angle characteristics, and contrast.

[0010]

Means for Solving the Problems The above-mentioned problems are (1) disposing a positive uniaxial optically anisotropic layer having an optical axis in the normal direction of the film on a film made of a polysulfone polymer. An optical compensation film characterized by: (2) The optical compensation film as described in (1) above, wherein the film made of a polysulfone polymer has an in-plane optical axis and positive uniaxiality. (3) The optical compensation film according to (1) or (2) is provided on at least one of a pair of polarizing plates disposed on both sides of the liquid crystal cell and the liquid crystal cell. Was achieved by the liquid crystal display device.

The birefringent film made of the polysulfone-based polymer of the present invention has, for example, a basic skeleton shown below, and not only a homopolymer having only this basic skeleton,
It may be a copolymer, a derivative thereof, a blended product or the like. The method for synthesizing these polysulfone-based polymers is not particularly limited, and ordinary methods can be applied.

[0012]

[Chemical 1]

In the present invention, the compound used for the positive uniaxial optically anisotropic layer having an optical axis in the normal direction of the film is not particularly limited as long as it is a substance having an intrinsic birefringence value. Although it can be sufficiently utilized by increasing the thickness or increasing the molecular orientation even if the absolute value of is small, the intrinsic birefringence value is preferably 0 in order not to be restricted by them. 0.02 or more, more preferably 0.04 or more. As a material satisfying the above, a thermoplastic film, Japanese Patent Application No. 5-58
Examples thereof include the compounds capable of photoisomerization described in No. 23 specification, polymers containing the compounds, liquid crystal compounds, and the like.

The thermoplastic plastic film is made of a polymer having a positive or negative intrinsic birefringence value, and specifically, a compound having a high wavelength dispersion value described in Japanese Patent Application No. 4-320480. Is preferred. From the viewpoint of having an optical axis in the normal direction of the film, a polymer having a negative intrinsic birefringence value that can obtain the performance by biaxial stretching is preferable.

The above-mentioned photoisomerizable compound or a polymer containing the compound is coated on a polysulfone-based polymer film and then irradiated with light from a direction perpendicular to the film surface to give a normal line. It is more preferable because the optical axis of the direction can be easily obtained.

The liquid crystal compound may be either a low molecular weight liquid crystal or a high molecular weight liquid crystal, but a low molecular weight liquid crystal is preferable from the viewpoint of viscosity when applied on a polysulfone polymer film. Specific examples of the low-molecular liquid crystals include Schiff liquid crystals, azoxy liquid crystals, cyanobiphenyl liquid crystals, cyanophenylcyclohexane liquid crystals, cyanophenyl ester liquid crystals, benzoic acid phenyl ester liquid crystals, cyclohexanecarboxylic acid phenyl ester liquid crystals, and phenyl. Examples include pyrimidine-based liquid crystals and phenyldioxane-based liquid crystals. In order to make the optical axis of these low-molecular liquid crystals the normal direction, ordinary methods such as an electric field and a magnetic field can be applied, but in order to avoid complication in the device, the vertical alignment film is made of polysulfone-based polymer. It is preferably placed on the united film. Here, the vertical alignment film is a thin film that aligns liquid crystal molecules in the vertical direction. Specific examples of the vertical alignment film include, but are not limited to, a polyimide film, a SiO vapor deposition film, and a silane coupling agent.

The present invention will be described in detail below with reference to examples.

[0018]

Example Preparation of polysulfone film (FN-1 ) 51.0 g of polysulfone (trade name: Udel P-3500, manufactured by Amoco Japan) was added to methylene chloride 249.
After dissolving in 0 g, it was cast on a stainless steel band, dried until the residual volatile content became 8%, peeled off, and further dried to give a residual volatile content of 3% and a film thickness of 75μ.
m polysulfone film (PS-F1) was prepared.
Polysulfone film (PS-F1) was longitudinally uniaxially stretched by 33% under a temperature condition of 173 ° C to obtain a birefringent film (F
N-1) was prepared.

Of polycarbonate film (FN-2)
Dissolved 51.0 g of prepared polycarbonate (trade name: Lexan) in 249.0 g of methylene chloride, cast on a stainless steel band, dried to a residual volatile content of 8%, and then peeled off. By further drying, the residual volatile matter content is 3% and the film thickness is 75 μm.
S-F2) was prepared. Polycarbonate film (P
The birefringent film (FN-2) was prepared by subjecting S-F2) to longitudinal uniaxial stretching of 20% under a temperature condition of 150 ° C.

Preparation of Optical Compensation Film (KH-1) Polysulfone film (FN-1) was vapor-deposited with SiO, and a low-molecular liquid crystal (MBBA) was applied thereon.
Then, the optical compensation film (KH-1) was adjusted by heating to 50 ° C. and cooling.

Preparation of Optical Compensation Film (KH-2) The polymer compound (K-1) is coated on the polysulfone film (FN-1), and the film is irradiated with light from the direction normal to the film surface. Therefore, the optical compensation film (K
H-2) was adjusted.

Preparation of Optical Compensation Film (KH-3) The polymer compound (K-2) was coated on the polysulfone film (FN-1), and the film was heated at 110 ° C. for 20K.
A current electric field of V was applied in the thickness direction for homeotropic alignment, and the optical compensation film (KH-3) was adjusted by rapidly cooling to 25 ° C. while applying the electric field.

Preparation of optical compensation film (KH-4) Optical compensation film (KH-4) in the same manner as optical compensation film (KH-3) except that polycarbonate film ( FN-2) is used. Was adjusted.

[0024]

[Chemical 2]

Evaluation of viewing angle dependence of retardation value The retardation value (Re (0)) of the birefringent film and the optical compensation film obtained in the above examples when viewed from the front. The ratio of the retardation value (Re (40)) and the chromatic dispersion value when viewed from the direction inclined by 40 ° from the optical axis were measured. However, the retardation value was measured using an ellipsometer AEP-100 (Shimadzu Corporation), and the chromatic dispersion value was a retardation value for light of 450 nm and a retardation value for light of 590 nm. It is the ratio of the values. The results are shown in Table 1.

[0026]

[Table 1]

Evaluation of Viewing Angle Dependence by Liquid Crystal Panel A high-speed response liquid crystal display was disassembled, and the optical compensation film produced in the above example was viewed from the front instead of the optical compensation film on the viewing side of the STN liquid crystal cell. The optical axis was constructed so as to maximize the contrast in the case of the above, and a liquid crystal panel for a monochrome display was manufactured. The obtained liquid crystal panel had high front contrast and exhibited a very wide viewing angle.

As can be seen from these results, according to the present invention, coloring of STN-LCD having high-speed response, viewing angle characteristics,
Also, it can be seen that the optical compensation film with significantly improved contrast can be supplied at low cost.

Claims (3)

[Claims] 1. An optical compensation film comprising a film made of a polysulfone polymer and a positive uniaxial optically anisotropic layer having an optical axis in the normal direction of the film. 2. The optical compensation film according to claim 1, wherein the film made of a polysulfone polymer has an in-plane optical axis and positive uniaxiality. 3. The optical compensation film according to claim 1 is provided on at least one of a pair of polarizing plates arranged on both sides of a liquid crystal cell and the liquid crystal cell. Liquid crystal display device.