Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-06-29
2001-05-29
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000, C349S096000, C349S117000
Reexamination Certificate
active
06239852
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a liquid crystal display device and, more particularly, to a reflection-type liquid crystal display device used in portable information terminals, for example.
A reflection-type liquid crystal display device using external light as its light source can be greatly reduced in consumption power as compared with transmission-type liquid crystal display devices. Therefore, there is a demand for development thereof toward the use in various portable devices such as portable information terminals, for example.
Reflection-type liquid crystal display devices are required to have a view angle not smaller than 60° under a predetermined condition. To deal with this requirement, the Inventors tried to employ an anti-glare film. That is, in a reflection-type liquid crystal display device, an anti-glare film for multiplex refraction of light from a liquid crystal layer is laid on the outer surface of a front substrate. The view angle can be increased by the film. This film simultaneously makes it possible to alleviate entry of external light caused by reflection from the surface the observer-side substrate (front substrate) on which displayed images are observed.
However, in the reflection-type liquid crystal display device using an anti-glare film, if the diffusion power is increased to ensure an ample view angle, letters on the display blur due to multiplex refraction. That is, deterioration of the display quality has been recognized as a problem.
Aside from it, the Inventors also tried to diffuse emitted light and expand the view angle by placing a single refraction layer for single refraction of light from the liquid crystal layer between the front substrate and the polarizing plate in a reflection-type liquid crystal display device.
However, in the case where the single refraction layer is interposed between the front substrate and the polarizing plate, when the refraction power is increased to obtain an ample view angle, the diffusion property gets weaker as the wavelength of light becomes longer, and wavelength dispersion occurs. It results in causing “coloring” which is the phonomenon where emitted light is recognized as different colors when observed from different angles. The Inventors has been aware of this problem through this trial.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a reflection-type liquid crystal display device having a sufficiently wide view angle and a high display quality.
To attain the object, the invention is characterized in sequentially stacking a single refraction layer, a polarizing plate and a diffusing layer on a front substrate. The term “single refraction layer” used in the invention pertains to a layer capable of refracting incident light while maintaining its vibrating direction. The diffusing layer pertains to a layer for refracting incident light by randomly changing its vibrating direction.
More specifically, according to the invention, there is provided a liquid crystal display device comprising:
a front substrate and a rear substrate disposed in a mutually facing relation;
a liquid crystal layer sandwiched between the front substrate and the rear substrate;
a mirror-reflection layer laid on the rear substrate;
a single refraction layer provided on an outer surface of the front substrate;
a polarizing plate provided on an outer surface of the single refraction layer; and
a diffusing layer provided on an outer surface of the polarizing plate to diffuse light from the single refraction layer.
According to the invention, there is further provided a liquid crystal display device of a reflection type including a transparent substrate, a liquid crystal layer provided behind the transparent substrate, and reflecting means provided behind the liquid crystal layer to introduce external light through the transparent substrate, reflect it by the reflecting means and externally release it through the transparent substrate to thereby display a predetermined image, comprising:
a single refraction layer provided on a front surface side of the transparent substrate;
a polarizing plate provided on the single refraction layer; and
a diffusing layer provided on the polarizing plate to diffuse light from the single refraction layer.
In these liquid crystal display devices, the diffusing layer may be a multiplex refraction layer for refracting light from said single refraction layer toward a plurality of directions.
These liquid crystal display devices may further comprise a &lgr;/4 phase plate interposed between said single refraction layer and said polarizing plate.
The crystal layer may be switched in response to an applied voltage between a mode for releasing incident light to the single refraction layer while maintaining the phase thereof and a mode for releasing incident light after shifting the phase there of by &pgr;/2.
The liquid crystal layer may be a twisted nematic liquid crystal.
The mirror-reflection layer may commonly function as a driving electrode on the part of said rear substrate for applying a voltage to said liquid crystal layer.
The single refraction layer may be made by spreading transparent grains with a second refractive index in a transparent medium with a first refractive index different from the second refractive index.
The single refraction layer may have a haze degree Hd (%) equal to or lower than 46.
The diffusing layer may be a multiplex refraction layer for refracting light from the single refraction layer toward a plurality of directions, has a haze degree Hz (%) not larger than 40/t (where t is the distance from said multiplex refraction layer to said mirror-reflecting layer).
The multiplex refraction layer and said single refraction layer may have in combination a total haze Ht (%) not less than 50 and not larger than 70.
By using any of the above-summarized constructions, refraction powers of the single refraction layer and the diffusing layer can be chosen within a range preventing “coloring” or blurs of letters, and after the single refraction layer refracts incident light in a certain direction while maintaining its vibrating direction, the diffusing layer refracts the light from the single refraction layer in random directions. Therefore, sufficient diffusion of light is realized without disordering polarized components of light from liquid crystal cells. As a result, the invention realizes both a view angle equivalent or wider than that of a conventional device and a high display quality without “coloring” and letter blurs.
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Higuchi Yoshinori
Hisatake Yuzo
Oono Atsuko
Chowdhury Tarifur R.
Dudek James A.
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
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