JPH03103823A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve a visual field angle characteristic by installing a thin phase difference plate between an upper and a lower polarizing plates. CONSTITUTION:In a liquid crystal cell in which a nematic liquid crystal 6 having a positive dielectric constant anisotropy is held between a pair of transparent electrodes 4, 8, and the angle of torsion of a liquid crystal molecule is 90 degrees to 300 degrees, a phase difference plate 2 having a negative refractive index anisotropy, and also, having an in-plane optical biaxial property for generating no phase difference against a light beam which is made incident roughly in parallel on the thickness direction is laminated on its outside, and a pair of polarizing plates 1, 10 are installed on its outside. In this state, when a voltage is applied, when an obliquely incident light passing through one of a pair of polarizing plates 1, 10 passes through a liquid crystal layer of the liquid crystal cell and the phase difference plate 2, a double refraction effect is cancelled by the positive refractive index anisotropy which the liquid crystal 6 has and the negative refractive index anisotropy which the phase difference plate 2 has, the whole phase difference quantity is almost disappeared, and by placing the other polarizing plate, a light shielding state is taken. In such a manner, the visual field angle characteristic is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a technology for improving viewing angle characteristics by laminating retardation plates in twisted nematic type and super twisted nematic type liquid crystal display devices. be.

[Conventional technology]

Conventional twisted nematic type and super twisted nematic type liquid crystal display devices will be described below.

In the former type, a soied nematic type (TN type) liquid crystal display device, the twist angle of the liquid crystal molecules is approximately 90 degrees, and a pair of polarizing plates is installed outside the liquid crystal cell, and these polarization axes (absorption axes) are transparent. It was placed approximately parallel to the long axis direction of the liquid crystal molecules adjacent to the electrode substrate. In this TN type liquid crystal display device, the steepness of the light transmittance-applied voltage characteristic is not sufficient, so when time-division driving is performed, the contrast ratio decreases as the number of scanning lines increases, and the viewing angle also becomes narrow. In addition, the latter super twisted nematic type (STN type) liquid crystal display/device has a twist angle of liquid crystal molecules of 90 degrees or more, and a pair of polarizing plates is installed on the outside of the liquid crystal cell, and these polarization axes (absorption axes) are The angle ranged from 30 degrees to 60 degrees with respect to the long axis direction of the liquid crystal molecules adjacent to the transparent electrode substrate. This S
Due to the twisted structure of liquid crystal molecules and the birefringence effect, TN type liquid crystal display devices have a steeper light transmittance-applied voltage characteristic than TN type liquid crystal display devices, and although the contrast ratio and viewing angle characteristics are improved to some extent, when voltage is applied Poor viewing angle characteristics are unavoidable.

[Problem to be solved by the invention]

In the prior art, especially when used as a display terminal for OA equipment, liquid crystal molecules stand up in the thickness direction of the liquid crystal cell when voltage is applied, resulting in poor viewing angle characteristics in the light tracing state.

An object of the present invention is to provide a liquid crystal display device with improved viewing angle characteristics during multi-division driving with a simple configuration.

[Means to solve the problem]

The liquid crystal display device of the present invention is a liquid crystal cell in which a nematic liquid crystal having positive dielectric constant anisotropy is sandwiched between a pair of transparent electrode substrates, and the twist angle of the liquid crystal molecules is from 90 degrees to 300 degrees. A retardation plate with negative refractive index anisotropy and in-plane biaxiality that does not produce a phase difference for light incident approximately parallel to the thickness direction is laminated, and a pair of polarizing plates is placed on the outside of the retardation plate. It is characterized by having been installed.

[Effect]

In the liquid crystal display device of the present invention, when the obliquely incident light that has passed through one of the pair of polarizing plates when a voltage is applied passes through the liquid crystal layer and the retardation plate of the liquid crystal cell, the positive refractive index anisotropy of the liquid crystal changes. The birefringence effect is canceled by the negative refractive index anisotropy of the retardation plate, the total retardation amount is almost eliminated, and a light shielding state can be achieved by arranging the other polarizing plate. When a voltage is applied to the liquid crystal cell, the liquid crystal molecules are approximately vertically aligned in the thickness direction of the liquid crystal cell. Literature (SID89DIGEST P.378-38
According to 1), it is a liquid crystal cell in which nematic liquid crystals with negative dielectric constant anisotropy are vertically aligned between a pair of transparent electrode substrates,
For a liquid crystal display device in which a retardation plate with negative refractive index anisotropy and an optical axis arranged parallel to the thickness direction is laminated on the outside, and a pair of polarizing plates is installed on the outside, the viewing angle is The effect of improving characteristics is described.

〔Example〕

FIG. 1 is a sectional view of the structure of a liquid crystal display device according to the present invention. In the figure, 1 is an upper polarizing plate, 2 is a retardation plate, 3 is an upper glass substrate, 4 and 8 are transparent electrodes, 5 and 7 are alignment films, 6 is a liquid crystal material, 9 is a lower glass substrate, and 10 is a It shows the lower polarizing plate. 11 is a liquid crystal panel arranged in numbers 3 to 9.

When the twist angle of the liquid crystal of the liquid crystal panel is 225 degrees and the twist direction is to the left, Jn (refractive index anisotropy: ne-no)'
X d (thickness of the liquid crystal layer) was approximately 960 nm, and the angle at which the polarizing plates were arranged was in the range of 45 degrees to 55 degrees. The liquid crystal alignment film was formed by rubbing a polyimide film formed using a spinner or printing. The liquid crystal used was a biphenyl+ester liquid crystal with positive dielectric anisotropy added with a left-handed chiral substance. The material of the retardation plate is acrylic, styrene, or a mixture of acrylic and styrene, which has negative refractive index anisotropy, and is a biaxial material.

lnXd of the retardation plate is the viewing angle. 4 50 at 0 degrees
nm to 20. It is 0 nm. The viewing angle characteristics (equal contrast map) obtained at this time during 1/200 duty driving are shown in FIG. It can be seen that the viewing angle characteristics are considerably improved compared to the viewing angle characteristics of the conventional liquid crystal display device shown in FIG. Further, the response time was 200 msec as an average of the sum of rising and falling times.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a simple structure in which a thin retardation plate is installed between the upper and lower polarizing plates of conventional TN type and STN type liquid crystal display devices can overcome the disadvantages of multi-segment liquid crystal display devices. This makes it possible to improve the poor viewing angle characteristics. Furthermore, the conventional drive circuit can be used as is, and the amplifier is also minimal in terms of weight, thickness, and cost. This is extremely effective when using a liquid crystal display device as a display terminal for equipment for O people.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the structure of a liquid crystal display device according to the present invention;
FIG. 2 is an isocontrast map showing the viewing angle characteristics of the liquid crystal display device of the present invention, and FIG. 3 is an isocontrast map showing the viewing angle characteristics of the conventional liquid crystal display device. ...Upper polarizing plate, ...Retardation plate, 0...Lower polarizing plate, 1...Liquid crystal panel.

Claims (1)

[Claims] A liquid crystal panel consisting of a nematic liquid crystal layer having a twisted structure with a twist angle of 90° to 300° and positive dielectric anisotropy, and a pair of transparent electrode substrates sandwiching this layer, and placed on both sides of this liquid crystal panel. a pair of polarizing plates, disposed between one of the pair of polarizing plates and the liquid crystal panel,
1. A liquid crystal display device comprising a retardation plate having negative refractive index anisotropy and in-plane biaxiality that does not produce a phase difference with respect to light incident substantially parallel to the thickness direction.