Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing... – Injecting liquid crystal
Reexamination Certificate
2000-10-13
2001-09-04
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
Injecting liquid crystal
C349S086000, C349S153000, C349S190000
Reexamination Certificate
active
06285435
ABSTRACT:
FIELD OF TECHNOLOGY
The present invention relates to a liquid crystal display apparatus, and to a liquid crystal display element used as an optical shutter.
RELATED TECHNOLOGY
Liquid crystal display elements have become practical for use in flat, large-screen display devices in information processing devices, particularly portable personal computers, and televisions and other video products. Of the various LCD elements available, the polymer dispersed type has been of particular interest in recent years.
This polymer dispersed LCD element comprises a pair of glass substrates with a conductive coating, and disposed therebetween a liquid crystal layer in which liquid crystals are dispersed in as droplets or networked crystals in a polymer matrix. Depending upon whether a voltage is applied to the liquid crystal layer, the LCD element switches between a state transmitting or dispersing incident light from a backlight.
A conventional liquid crystal display element is described next below with reference to
FIG. 9A
,
FIG. 9B
, FIG.
9
C.
FIG. 12
,
FIG. 21
, and FIG.
22
. The structure of a polymer dispersed LCD element is shown first in
FIG. 9A
at normal temperature (e.g., 20° C.). LCD element
200
comprises glass plates
51
and
52
, seal
53
, liquid crystal
54
, polymer matrix
55
, and spacer
56
.
The glass plates
51
and
52
each have a transparent electrode made from a conductive film of ITO (indium tin oxide). The polymer matrix
55
is a polymer compound with a three-dimensional networked structure. The liquid crystals
54
are liquid crystals dispersed in the polymer matrix
55
. A liquid crystal layer
57
disposed between glass plates
51
and
52
is formed from the liquid crystals
54
and polymer matrix
55
.
The seal
53
is coated to the circumferential edge of the glass plates
51
and
52
, and seals the liquid crystal layer
57
. A plurality of spacers
56
is distributed in the liquid crystal layer
57
to hold a constant gap width between the glass plates
51
and
52
. A voltage application means, not shown in the figure, is disposed to the glass plates
51
and
52
for applying a desired voltage to the liquid crystal layer
57
.
In a conventional polymer dispersed LCD element, the average particle diameter of spacers
56
is less than the gap width between the glass plates, and the internal pressure of the liquid crystal layer
57
is set lower than atmospheric pressure. Pressure pushing from the outside to the inside therefore acts on the liquid crystal layer
57
, and the gap width between the two glass plates is held to the particle diameter of the spacer
56
. It should be noted that the spacers
56
are the same as those used in a twisted nematic LCD element.
Referring below to
FIGS. 9B and 9C
, phenomena occurring in the conventional polymer dispersed shown in
FIG. 9A
as a result of a rapid change in temperature are described.
FIG. 9B
illustrates the state when the LCD element
200
, which is shown in
FIG. 9A
at a normal temperature, rises from normal temperature to a high temperature (85 degrees C. in this example), and
FIG. 9C
illustrates the state when the LCD element
200
drops rapidly from the high temperature state shown in
FIG. 9B
to normal temperature.
As shown in
FIG. 9A
, when the LCD element
200
is at normal temperature, substantially no pressure is applied by the glass plates
51
and
52
to the spacers
56
because the size of the spacers
56
is the same as the gap width. However, the volume of the matrix
55
and liquid crystals
54
increases when the temperature rises, and the internal pressure of the liquid crystal layer
57
therefore rises. Unlike the perimeter area, the middle portion of the glass plates
51
and
52
is not fixed by a seal
53
and therefore deforms due to the effect of this increased internal pressure, resulting in a gradual increase in the gap width from the perimeter area to the center. The expanded liquid crystals therefore collect in the center area, and the LCD element
200
deforms as shown in FIG.
9
B.
When the LCD element
200
is then rapidly cooled to normal temperature from the state shown in
FIG. 9B
, the liquid crystal layer
57
contracts. The liquid crystals concentrated in the center cannot completely return to the original condition at this time, however, and a large part thereof is left in the middle. The gap between the glass plates
51
and
52
is therefore different in this area as shown in FIG.
9
C.
Irregularity in the thickness of the liquid crystal layer is thus induced in a conventional polymer dispersed LCD element as a result of expansion and contraction of the liquid crystal layer caused by a rapid change in temperature, and a dramatic deterioration in display quality occurs as a result.
A first object of the present invention is therefore to resolve the above-described conventional problem by providing a liquid crystal display element whereby distortion of the gap width resulting from a sudden change in temperature can be prevented, and uniformity of displayed images can be improved.
The configuration of a conventional LCD element is described next referring to the partially exploded perspective view in FIG.
12
. LCD element
140
comprises glass plates
131
a
and
131
b
, transparent electrodes
132
a
and
132
b
, seal
133
, conductive material
134
a
and
134
b
, opening
135
, active element formation area
136
, and liquid crystal layer
137
.
The glass plates
131
a
and
131
b
are transparent panels made of glass, each comprising an ITO (indium tin oxide) conductive film as a transparent electrode
132
a
and
132
b
. A seal
133
is formed near the perimeter of the glass plate
131
a
or
131
b
. The opening
135
is a discontinuity provided in the seal
133
, and is used for filling liquid crystals to the liquid crystal layer
137
. Liquid crystals are injected to the liquid crystal layer
137
through the opening
135
.
The active element formation area
136
is an area on transparent electrode
132
b
in which a TFT element is formed for each pixel of the LCD element. The conductive material
134
a
and
134
b
is a conductive paste coated onto transparent electrode
132
b
, and electrically connecting transparent electrode
132
a
and transparent electrode
132
b.
A vacuum injection method is generally used to inject a liquid crystal material to a conventional LCD element
140
thus comprised. In this method, an empty LCD element (
140
) with a liquid crystal layer
137
that has not been filled with liquid crystal, that is, an empty cell, is placed in a depressurized tank to create a vacuum inside the cell, and the tank is then returned to normal pressure with the opening
135
in contact with a liquid crystal material to inject the liquid crystal material to the cell.
In addition to penetrating the liquid crystal layer
137
, the liquid crystal material also penetrates the gap between the glass plates
131
and
132
to the outside of the seal
133
(hereafter referred to as the “outside gap”) when a liquid crystal material is thus injected to an empty LCD element
140
. This occurs as a result of capillary action due to the height of the seal
133
, that is, the width between the glass plates
131
and
132
, being a gap of only several micrometers. It is therefore necessary to wash and remove any liquid crystal material that has penetrated this outside gap after the opening
135
is sealed.
However, when liquid crystals penetrating said outside gap are removed by washing in the above-described conventional LCD element, the conductive material
134
a
and
134
b
is contaminated or removed in certain cases. When this occurs, the impedance between the transparent electrodes
132
a
and
132
b
is significantly increased and conductivity is impaired, leading to deterioration of the image quality of displayed images.
Therefore, a second object of the present invention is to resolve the above-described conventional problem by providing a LCD element and manufacturing method whereby the conductive material
134
a
and
134
b
is protect
Inoue Kazuo
Nishiyama Seiji
Uemura Tsuyoshi
Chowdhury Tarifur R.
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Sikes William L.
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