Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-12-28
2003-06-10
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S045000, C349S005000
Reexamination Certificate
active
06577375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device having a liquid crystal panel and, particularly, to a liquid crystal projector which projects an image of the liquid crystal panel. More specifically, the present invention relates to an improvement in a cooling structure for improving a heat resistant reliability.
2. Description of Related Art
A liquid crystal projector has been mainly used as a so-called home theater system for enjoying various movies at a home. In these days, a projection image quality has been improved by a high definition of liquid crystal panel and a high luminance brightness of lamp. Accordingly, the liquid crystal projector has been also used as a presentation system for projecting a display image of a personal computer on a projection screen.
A construction of the liquid crystal projector is shown in FIG.
1
. Light generated from a light source
1
of a high luminance lamp such as a metal-halide lamp, a xenon lamp or a UHP or the like, is reflected by a spherical reflecting mirror
2
. Then, light reflected by the spherical reflecting mirror
2
transmits through a filter
3
so that unnecessary infrared ray and ultraviolet ray are removed. Further, light transmitting through the filter
3
transmits through an integrator lens
4
and a condenser lens
5
so as to be condensed, and thereafter, passes through an incidence side polarizing plate
6
, and thus, is incident upon a liquid crystal panel
8
. Light emitted from the liquid crystal panel
8
transmits through an emission side polarizing plate
7
, and thereafter, is enlarged and projected by means of a projection lens
9
, and thus, an image is projected onto a screen or the like located ahead of the projector.
The aforesaid structure is of a single-panel type using a sheet of liquid crystal panel including color filters. In addition to the above single-panel type structure, a three-panel type structure is also known such that light from a light source is decomposed into decomposition lights of three primary colors of RGB, and these decomposition lights are incident upon three liquid crystal panels.
A construction of the liquid crystal projector having the above three-panel type structure is shown in FIG.
2
. In
FIG. 2
, like reference numerals used in the case of
FIG. 1
are used to designate components having the same function as components shown in FIG.
1
. In the construction shown in
FIG. 2
, the following components are used; more specifically, dichroic mirrors
10
for transmitting or reflecting an incident light in accordance with a wavelength, a complex prism
11
for synthesizing light, and total reflection mirrors
12
. Light, which is generated from the light source
1
and reflected by the spherical reflecting mirror
2
, transmits through the filter
3
and the integrator lens
4
, and thereafter, is guided to the dichroic mirrors
10
after its optical path is bent by one of the total reflection mirrors
12
. Then, light from the light source
1
is decomposed into three primary color lights of red (R), green (G) and blue (B) by means of two dichroic mirrors
10
for reflecting or transmitting light having different wavelength band. Then, these decomposition lights are transmitted through the liquid crystal panel
8
corresponding to each of three primary colors, and thereafter, are synthesized by the complex prism
11
, and thus, are projected.
In these liquid crystal projectors, there is a tendency for a projected image to be short of a brightness. The first factor is light absorption by polarizers
6
and
7
located front and rear the liquid crystal panel
8
. The second factor is that the liquid crystal panel
8
has an area made small up to a size of about 1 inch in order to miniaturize the liquid crystal projector. More specifically, in the case where an image of the liquid crystal panel
8
having a small area is enlarged and projected to several tens of inches to several hundreds of inches, there is the case where the projected image is short of a brightness.
In order to solve these problems as described above, high output lamps such as high-luminance metal-halide lamp, Ultra High Pressure Mercury lamp and xenon lamp are used as the light source
1
. However, in particular, in the presentation system, demands for further miniaturization, high definition and high luminance are made in the market and a higher output lamp is selected.
For this reason, in the liquid crystal projector system, a disadvantage by a heat is a significant problem.
For example, in general, an iodine-based polarizer is used as the polarizer constituting a liquid crystal display section. However, the iodine-based polarizer is not sufficient in light resistance, heat resistance and damp and heat resistance. For this reason, in particular, in the liquid crystal projector, a dye-based polarizer is used because of being excellent in light resistance, a heat resistance and a damp and heat resistance (see Unexamined Patent Publications (Kokai) No. 9-22008 and 9-22009)
However, in particular, the incidence side polarizer
6
has light transmittance of about 40%, and absorbs most of lights. Further, the polarizer
6
can not maintain its characteristic when becoming a temperature of 70° C. or higher.
Moreover, the liquid crystal panel
8
itself is weak in a heat, and its characteristic is remarkably deteriorated when becoming a temperature of 60° C. or higher.
In order to solve the above problem, in the liquid crystal projector, the following various cooling systems have been proposed.
(1) Air cooling system
Heat generating sections such as the incidence side polarizer
6
, the liquid crystal panel
8
and the emission side polarizer
7
, the light source
1
and a power source section, are cooled by means of a cooling fan, and then, an air having a heat is exhausted.
However, according to this air cooling system, there are a noise problem and a problem that a dust adheres to the liquid crystal panel
8
. More specifically, in the case where an air supply is increased in order to obtain sufficient cooling effect, a fan is rotated at a high speed, and is made into a large size, and thereby, a large noise is generated. For this reason, it is not preferable to apply the above air cooling system to a liquid crystal projector which is used for conducting a presentation in a silent room or for enjoying a movie or the like.
(2) As shown in
FIG. 1
, the incidence side polarizer
6
is arranged in a state of separating from the liquid crystal panel
8
with a distance of about 1 to 5 mm. By doing so, it is possible to prevent a heat of the polarizer
6
from conducting directly to the liquid crystal panel
8
. Further, a cooling air flows between the polarizer
6
and the liquid crystal panel
8
, and thereby, a cooling efficiency can be enhanced.
In this system, the incidence side polarizer
6
, which is a principal heat generating source, is arranged separately and independently, and thereby, an influence to the liquid crystal panel
8
is reduced, and a heat radiating effect can be improved. However, there is a limit in the cooling effect. Moreover, a blue sheet glass or white sheet glass is used as a retaining plate of a polarizing substance in the polarizer
6
. In the blue or white sheet glass, the heat conductivity is worse and a heat radiating effect is insufficient. Therefore, like the case of the above air cooling system, finally, an output of the cooling fan must increased. As a result, it is impossible to solve the above problems relating a noise and dust adhesion.
(3) A heat radiating glass plate having a heat conductivity of 1 W/m.K or more is located on an outer surface of the liquid crystal panel
8
with a sealed space interposed therebetween, so as to enhance a heat radiating effect with respect to a heat generation of the liquid crystal panel
8
. Further, a cooling air is supplied to the heat radiating glass plate so as to prevent a dust from adhering to the liquid crystal panel
8
.
According to the above system, no dust
Banjo Hideki
Ueda Yoshio
Umehara Motohiro
Watanabe Ken'ichi
Hogan & Hartson LLP
Kyocera Corporation
Qi Mike
Ton Toan
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