Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-03-30
2002-05-07
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S112000, C349S086000, C359S599000
Reexamination Certificate
active
06384884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflecting type liquid crystal display device.
2. Description of the Prior Art
Recently, liquid crystal display devices have been applied to various fields such as notebook type personal computers, monitors, car navigation, scientific electronic calculators, small and medium size TVs, etc. Among these, investigations into reflecting type liquid crystal display devices are being carried out, in order to take advantage of their low energy consumption due to not requiring a backlight, as well as their thinness and light weight for applications in displays for portable devices.
In reflecting type liquid crystal display devices, apart from the TN mode display mode which uses 2 polarizing plates, there are three main types of display modes; GH (Guest Host) mode, high molecular dispersion mode, and single polarizing plate mode.
The GH (Guest Host) mode has the special characteristic of being able to obtain a bright display due to relatively low light absorption. However, there is the disadvantage that, as the two-color ratio of the material cannot be adequately obtained, the contrast is low. The high molecular dispersion mode has the special characteristic of having a wide angle of visibility due to achieving satisfactory light diffusion. However, it has the disadvantage of low reflectance and contrast, and is not yet ready for practical use. Although the single polarizing plate mode has light absorption due to the polarizing plates and is unable to obtain satisfactory brightness, high contrast can be obtained as it uses polarizing plates, and it is becoming the main reflecting type color liquid crystal display device in current use.
An example of the single polarizing plate mode, seen from the observer side, is composed of a polarizing plate, a glass substrate, a drive liquid crystal formed from spirally orientated chiral nematic liquid crystal, a glass substrate, a reflecting plate and reflecting electrode. Both polarizer and analyzer functions are obtained by the incidents light's making two transits of the liquid crystal layer and the polarizing plate when incoming and outgoing via the reflecting layer. For this reason, compared to the reflecting type TN mode which uses 2 polarizing plates and which is used in conventional calculators and watches and the like, by reducing the number of polarizing plates by 1, it has the special characteristics of having brightness and in addition, by using polarizing plates it has the same control effect and satisfactorily high contrast.
In addition, the surface of the reflecting layer of this kind of single polarizing plate mode is formed from a bumpy reflecting plate which has the function of diffusing and reflecting light, or a completely regular reflecting flat metal reflecting surface. With the former bumpy reflecting surface it is possible to obtain a simultaneous light diffusion function and a reflecting function, however, as the polarized state of the entering light is altered at the reflecting surface by the bumps, there is the problem of reduced contrast with the single polarizing plate mode construction which requires maintenance of the polarized state at the reflecting surface.
On the other hand, in the case of a flat metal reflecting surface which obtains regular reflection, although a separate light diffusing light diffusion layer is required, there is no polarizing break down, and it has the special characteristic of achieving high contrast. The characteristics of reflected light with this kind of speculum reflecting surface, comprising a light diffusion layer, depend on the light diffusion layer. In the past for this light diffusion layer there were, for example, mat system anticlear processing of polarizing plates, and a diffraction grating film arrayed so that a refractive index medium having refractive index anisotropy distributes the refractive index two-dimensionally. However, these light diffusion effects have strong wavelength dispersion characteristics, and when the light source is in an environment relatively near to parallel, the reflected light has a yellowish coloring in the regular reflection direction of the light source, and conversely in the direction receding away from the regular reflection direction, there is the problem of bluish coloring. The reason for this is that the light diffusion effect becomes stronger the shorter the wavelength of the wavelength dispersion characteristics of the light diffusion effect of the light diffusion layer.
In this way, in a reflecting type liquid crystal display device formed from a construction of a speculum reflecting layer and a light diffusion layer in a single polarizing plate mode, as wavelength dispersion characteristics of the light diffusion effect of the light diffusion layer are present, there was the problem of coloring of the reflected light. This type of problem is not limited to the single polarizing plate mode, but is an inevitably occurring problem in reflecting type liquid crystal display devices that use a light diffusion layer.
In conventional reflecting type liquid crystal displays, the direction of the surface reflection in the panel display and the largest reflecting strength direction of the reflecting surface correspond, and in practice, the visibility from the brighter looking direction was extremely low.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a simple construction reflecting type liquid crystal desplay device and to realize a low cost device with the characteristic of the largest reflecting strength direction of the reflecting surface coming in a viewing angle direction from which the surface reflection cannot be seen.
According to an aspect of the reflecting type liquid crystal display device of the invention, the device having at least two substrates, a liquid crystal layer sandwiched between these substrates, a reflecting surface which reflects light passing through this liquid crystal layer, and a light diffusion layer which at least diffuses the light reflected by that reflecting surface,
wherein the light diffusion layer is formed of 2 types of refractive index medium with differing refractive indices, and when the refractive index of the first refractive index medium is nA(400) at light wave length 400 nm, and nA(700) at light wave length 700 nm, and the refractive index of the second refractive index medium is nB(400) at light wave length 400 nm, and nB(700) at light wave length 700 nm, then,
(nA(400)
A(700))×0.9≦(nB(400)
B(700))≦(nA(400)
A(700))×1.1 (1)
By the above construction, the wavelength dispersion of the light diffusion effect is reduced.
Further, in the aforementioned, the light diffusion layer is constructed of a fine particle dispersion layer in which fine particles of the second refractive index medium are dispersed in the first refractive index medium, or of a diffraction grating layer in which the first refractive index medium and the second refractive index medium are alternately arranged having regularity in a surface direction.
The light diffusion effect of the light diffusion layer mainly depends on the light diffusion effect and on the light diffraction effect due to the refractive index difference of the 2 types of refractive index medium.
FIG. 2
shows the principle of a case using this kind of light refraction effect. As in
FIG. 2
a
, when medium n
1
of refractive index n
1
and medium n
2
of refractive index n
2
are combined, refraction occurs according to the ratio of the 2 types of refractive index. When the degree of this refraction is represented as an angle of refraction, in accordance with Snell's law, it becomes as in
FIG. 2
b
. Here, &thgr;o is the angle of incidence and &thgr;p is the final outgoing angle. Here, when the wave length dispersion characteristic of the ratio n
1
2
of n
1
and n
2
is large, the aforementioned coloring problems occur because the degree of refraction differs according to the wavelength of the incident light. S
Harada Nozomu
Hisatake Yuzo
Miyake Kazushi
Nakamura Takashi
Chung David
Kabushiki Kaisha Toshiba
Parker Kenneth
Pillsbury & Winthrop
LandOfFree
Reflecting type liquid crystal display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reflecting type liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reflecting type liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2909442