Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-06-01
2002-01-08
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S184000, C349S189000
Reexamination Certificate
active
06337730
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on Japanese Patent Application Nos. Hei. 10-153233 filed on Jun. 2, 1998, Hei. 10-247537 filed on Sep. 1, 1998, and Hei. 10-317983 filed on Nov. 9, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to a liquid crystal cell to be suitably adopted in a liquid crystal display device or the like, and a process for manufacturing the liquid crystal cell.
2. Description of the Related Art
In recent years, the liquid crystal cell is utilized as a display element for a TV set, a personal computer or a work station, or a display element for a watch, a calculator or a measurement device because it is suited for a light weight and for a thin shape.
This display element is caused to transmit, reflect or shade a light mainly by utilizing the shuttering action of the liquid crystal.
The liquid crystal to be used in the display element is represented by a nematic liquid crystal or a smectic liquid crystal.
A conventional liquid crystal cell has a cell structure, as shown in FIG.
22
. This liquid crystal cell is constructed by interposing a seal
903
in a band shape between the outer peripheral portions of two parallel electrode substrates
901
and
902
, by providing a number of spherical spacers
904
between the two electrode substrates
901
and
902
on the inner peripheral sides of the seal
903
, and by filling a liquid crystal through a liquid crystal filling port of the seal
903
.
Here, the electrode substrate
901
is constructed by laminating a plurality of transparent electrodes
901
b
, a (not-shown) insulating film and an orientation film
901
c
on the inner surface of a glass substrate
901
a
. On the other hand, the electrode substrate
902
is constructed by laminating a plurality of transparent electrodes
902
b
, a (not-shown) insulating film and an orientation film
902
c
on the inner surface of a glass substrate
902
a
. Here, the plurality of transparent electrodes
902
b
are arranged to intersect the plurality of transparent electrodes
901
b
. Reference numeral
905
designates a polarizing sheet in FIG.
22
.
When the liquid crystal cell is made of a nematic liquid crystal, if caused to establish a flow in the nematic liquid crystal by a local pressure or impact from the outside, its orientation state is restored after releasing the pressure or impact.
When the liquid crystal cell is made of a smectic liquid crystal, however, if an orientation defect in the smectic liquid crystal or a disturbance in the liquid crystal layer structure is caused by a local pressure or impact from the outside, its orientation state is not restored even after releasing the local pressure or impact.
On the other hand, when the liquid crystal cell is made of a smectic liquid crystal, an orientation disturbance or a defect is likely to occur in the smectic liquid crystal at the periphery of the spherical spacer, and the display characteristics of the liquid crystal cell are deteriorated.
For this, it is conceivable (as disclosed in Japanese Patent Application Laid-Open No. 7-318912 or U.S. Pat. No. 5,559,621) that the liquid crystal cell using the smectic liquid crystal is given a cell structure, as shown in FIG.
23
.
This liquid crystal cell is constructed by interposing a seal
908
in a band shape between two electrode substrates
906
and
907
parallel to each other, providing a plurality of barrier walls
909
between the two electrode substrates
906
and
907
on the inner peripheral side of the seal
908
and filling a smectic liquid crystal through a liquid crystal filling port of the seal
908
.
Here, the electrode substrate
906
is constructed by laminating a plurality of transparent electrodes
906
b
, an insulating film
906
c
and an orientation film
906
d
on the inner surface of a glass substrate
906
a
. On the other hand, the electrode substrate
907
is constructed by laminating a plurality of transparent electrodes
907
b
, a (not-shown) insulating film and an orientation film
907
c
on the inner surface of a glass substrate
907
a.
Each barrier wall
909
is clamped between the orientation film
906
d
of the electrode substrate
906
and the glass substrate
907
a
of the electrode substrate
907
so that it is positioned to lie between the adjoining two of the plurality of orientation films
907
c.
According to this liquid crystal cell, each barrier wall
909
exhibits a rigidity enough to prevent a defect in the liquid crystal layer of the smectic liquid crystal even a local pressure or impact is applied to the liquid crystal cell from the outside. In the presence of a linear space between the individual barrier walls
909
, it is possible to suppress the disturbance in the orientation of the smectic liquid crystal.
However, in the liquid crystal cell of
FIG. 23
, at a cooling step of cooling the liquid crystal cell after the two electrode substrates
906
and
907
are filled with the smectic liquid crystal, a zigzag orientation defect A, as shown in
FIGS. 24
,
25
, appears in the liquid crystal layer of the smectic liquid crystal.
This point will be described in detail. When the smectic liquid crystal is used as the liquid crystal, it is necessary to fill the smectic liquid crystal under the circumstance of a temperature (at 80 to 120° C.) corresponding to an isotropic phase. After this filling operation, the liquid crystal filling port of the liquid crystal cell is plugged, and the liquid crystal cell is cooled.
In
FIG. 26
, a “graph a” plots changes in a volume change rate against a temperature of the cell structure of a liquid crystal cell when the change at 80° C. is “1”, and a “graph b” plots changes in the volume change rate against a temperature of the smectic liquid crystal.
It is found from these two “graph a” and “graph b” that the coefficient of thermal expansion of the smectic liquid crystal is considerably larger than that of the cell structure. Therefore, after the cooling operation, the smectic liquid crystal shrinks more than the cell structure. This means that the volume shrinkage rate of the smectic liquid crystal is considerably larger than that of the cell structure.
Accordingly, the smectic liquid crystal is pulled by the inner surface of the electrode substrate under its surface tension so that this tension generates a stress in the smectic liquid crystal. As a result, an orientation defect A, as shown in
FIGS. 24 and 25
, is generated in the liquid crystal layer of the smectic liquid crystal.
If the space between the adjoining two barrier walls
909
is enlarged in the liquid crystal cell of
FIG. 23
, it is possible to prevent the occurrence of the orientation defect A of the liquid crystal layer, which might otherwise be caused by the difference between the volume shrinkage of the smectic liquid crystal and the volume shrinkage of the cell structure.
However, if the space of the individual barrier walls
909
is taken widely by every two or three of the plurality of transparent electrodes
907
b
, the dielectric constants between the two electrode substrates
906
and
907
are different from each other at the portions with and without the barrier walls
909
of the two electrode substrates
906
and
907
.
As a result, a phenomenon to invite deterioration in the display characteristics such as the crosstalk occurs at the time of driving the liquid crystal cell. That is, in order to prevent this phenomenon, the space of the individual barrier walls
909
has to be so narrowed that the barrier walls
909
are provided for every transparent electrode
907
b.
Other problems on the liquid crystal cell, as shown in
FIG. 23
, will be described with reference to
FIGS. 27
to
29
. Here,
FIG. 27
is a top plan view of
FIG. 23
, and
FIG. 28
is a section taken along line XXVIII—XXVIII of FIG.
27
. In
FIG. 28
, there are omitted the transparent electrodes
906
b
and
907
b
, the insulating film
906
c
and the orientation films
906
d
and
907
c
Inoguchi Kazuhiro
Kaneko Takahisa
Maekawa Kenji
Matsumoto Naoki
Miyashita Koichi
Denso Corporation
Pillsbury Winthrop L.L.P.
Schechter Andrew
Ton Toan
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