Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-10-23
2001-11-06
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S116000, C349S110000, C349S139000
Reexamination Certificate
active
06313895
ABSTRACT:
TITLE OF THE INVENTION
Reflecting Plate, Reflection type Liquid Crystal Display Device and Processes for Manufacturing Same
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflecting plate to be used in a matrix display apparatus for reflecting an incident light, and a method for manufacturing the reflecting plate. More particularly, the invention relates to a reflection type liquid crystal display apparatus for effecting a display by reflecting an incident light on pixel electrode surfaces but without using any backlight, and a method for manufacturing the liquid crystal display apparatus.
2. Description of the Related Art
Of liquid crystal display apparatuss, the reflection type for effecting a display by reflecting an incident light coming from the outside has been noted for its low power consumption because of no necessity for a backlight as a light source and for its thin and light construction. In order to acquire a brighter display in the reflection type liquid crystal display apparatus, it is necessary to prepare a reflecting plate which has optimum reflecting characteristics for increasing the intensity of light to be scattered to the observer. For this necessity, the formation of a reflecting plate which has an uneven surface capable of realizing the “paper white” has been accepted as an important technique.
Japanese Unexamined Patent Publication JP-A
5
-323371 (1993) has disclosed a technique for forming uneven spots on a surface of the reflecting plate with a photosensitive resin by the photo process.
FIGS. 9A and 9B
are top plan views showing a mask
1
b
of the prior art to be used for forming the uneven spots on the surface of the reflecting plate.
FIG. 9A
is a top plan view showing one pixel
61
of the mask
1
b
.
FIG. 9B
is a diagram showing an arrangement relation of unit patterns of the mask
1
b.
The shape of the pixel
61
of the mask
1
b
is so designed that about two hundreds of circular regions
62
, for example, are arranged at random so as to form the uneven spots for suppressing the interference of the reflected lights. The pixel
61
is a square having sides
63
of 100 &mgr;m to 1,000 &mgr;m, for example, and has a unit pattern, as designated by a symbol
64
. The mask
1
b
is designed to determine the entire arrangement of uneven spots by repeating the mirror reflections of the unit pattern
64
.
The method of manufacturing the reflecting plate having the uneven spots will be described by using the masks
1
b
.
FIG. 4
is a perspective view for explaining an exposure step in the general reflecting plate manufacturing method. A photosensitive resin film
17
is formed over a predetermined substrate
10
. A spherical exposure lamp
18
of a stepper device is arranged above the photosensitive resin film
17
of the substrate
10
to expose the photosensitive film
17
through a mask
1
. The area to be irradiated by one exposure is dependent upon the size of the exposure lamp
18
and is no more at present than a size of a diagonal length of about 12.7 cm at the most. When a reflecting plate having a diagonal length of about 12.7 cm or more is to be manufacture, a predetermined number of exposure steps are repeated by moving the location of the mask
1
or the substrate
10
. By one exposure, for example, only an exposure face A is exposed in the substrate
10
. After this, different exposure faces B to H are sequentially exposed by moving the mask
1
or the substrate
10
. By causing the circular regions
62
, as owned by the conventional mask
1
b
used as the mask, to act as light shielding portions, for example, the regions of the photosensitive resin film
17
other than the circular regions
62
are exposed to the light.
When the exposed photosensitive resin film
17
is developed with a developer, circular columns are formed on regions corresponding to the circular regions
62
. These circular columns are rounded to convexes having rounded surfaces by a heat treatment at 120 to 250° C. All over the surface of the substrate
10
is formed a light reflecting film made of a metallic thin film, so as to cover the convexes. This light reflecting film is formed by the convexes into a continuously curved surface having gently conical uneven spots. The reflecting plate thus formed to have the uneven surface increases the intensity of light directed toward the observer so that it provides a bright paper white display when used in the reflection type liquid crystal display apparatus.
The mask
1
b
of the prior art is designed by repeating the mirror reflections of the unit pattern of the pixel
61
having the circular regions
62
, as described above. The reflecting plate is made convex by the mask
1
b
so that the reflection type liquid crystal display apparatus utilizing the reflection plate can provide the bright paper white display. In case the reflection plate is large-sized, however, the exposure step is repeated plural times, and accordingly the reflecting characteristics are lowered with the result that the display quality is lowered in the display apparatus. That will be detailed in the following.
“
FIG. 10
is a diagram illustrating an exposure intensity distribution by the exposure lamp
18
of the stepper device. By joining the points each having an equal exposure intensity in a region
23
to be exposed with curves, the portions of the high and low exposure intensities are expressed with contour lines
24
expressing gentle uneven spots. The exposure intensities become higher as arrows
25
come closer to a region
26
and the weaker as the arrows
25
come the closer to a region
27
. This difference in the exposure intensity causes a dispersion of about 3% in the exposed region
23
and accordingly a nonuniformity in the exposure.”
FIG. 11
is a diagram illustrating an optical intensity distribution of the case in which the exposure step is repeated plural times in different positions. For example, the exposures are executed in the order of exposure faces A, B, C and D. The exposure intensity gently changes for the exposure of only the face A but abruptly changes at each seam
28
between the faces for the exposures of two or more times in different positions. This abrupt change in the exposure intensity is observed as the exposure nonuniformity.
FIGS. 12A and 12B
are perspective views illustrating a difference in shape between convexes
21
due to the exposure intensity.
FIG. 12A
shows the case in which the exposure intensity is high, and
FIG. 12B
shows the case in which the exposure intensity is low. Each circular column
20
to be formed on the surface of the substrate
10
is the thinner for the higher exposure intensity. By the heat treatment of the circular columns
20
, the convexes
21
are rounded to have smooth surfaces. If the convexes
21
have a height d, they are the steeper for the higher exposure intensity and the gentler for the lower exposure intensity. The convexes
21
are given the different shapes as a result of the exposure nonuniformity.
FIGS. 13A and 13B
are graphs illustrating the difference in the reflecting characteristics between the convexes
21
due to the exposure intensity.
FIG. 13A
illustrates the case in which the exposure intensity is high, and
FIG. 13B
illustrates the case in which the exposure intensity is low. The abscissa indicates an azimuth angle, and the ordinate indicates a reflection intensity. The reflection intensity is different at the portions of high and low exposure intensities because of the different shapes of the convexes
21
. Specifically, the change in the reflection intensity is small over a wide range of visual angle at the portions of high exposure intensity and large over a range of visual angle at the portions of low exposure intensity.
FIGS. 14A and 14B
are diagrams illustrating the change in the reflecting characteristics of a reflecting plate
71
in the case of using the conventional mask
1
b
in different positions.
FIG. 14A
illustrates a pattern of the reflecting characteristics, and
FIG. 14B
illustr
Ban Mariko
Kimura Naofumi
Mitsui Seiichi
Tsuda Kazuhiko
Conlin David G.
Dike Bronstein Roberts & Cushman IP Group
Ngo Julie
Sharp Kabushiki Kaisha
Sikes William L.
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