Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-04-06
2002-06-18
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06407783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device. In particular, it relates to a transmissive type liquid crystal display device provided with a back light at its rear side.
2. Discussion of Background
In the transmissive type liquid crystal display device provided with a back light at its rear side, a light shielding layer is provided at an inner side of the cell to improve visibility.
FIG. 2
is a diagrammatical cross-sectional view of a typical conventional device.
In
FIG. 2
, a liquid crystal display device
10
comprises a pair of transparent substrates
11
,
12
made glass or the like wherein a terminal portion
11
a
is formed on the transparent substrate
11
. Transparent electrodes
111
,
121
of ITO (Indium Tin Oxide) each having a predetermined display pattern are formed on the transparent substrates
11
,
12
although the figure does not shown in detail. A light shielding layer
112
is provided on the transparent substrate
11
at a position excluding a portion corresponding to the display pattern. On a terminal portion
11
a
, there are formed a first lead-out electrode group
131
drawn directly from the transparent electrode
111
of the transparent substrate
11
and a second lead-out electrode group
132
connected to the transparent electrode
121
from the other transparent substrate
12
.
The transparent substrates
11
,
12
are bonded by interposing a periphery sealing member
14
made of an epoxy resin or the like so that the transparent electrodes
111
,
121
oppose to each other. Liquid crystal
15
is sealingly put in a cell gap thus produced. The periphery sealing member
14
includes a transfer material of, for instance, conductive beads, and the transparent electrode
121
on the other transparent substrate
12
is connected electrically to the second lead-out electrode group
132
on the terminal portion
11
a
by means of the transfer material.
Polarizers
161
,
162
are disposed at outer surface sides of the transparent substrates
11
,
12
. In this liquid crystal display device
10
, the transparent substrate
11
having the light shielding layer
112
is determined as a rear side, and a back light
17
is provided in rear of the transparent substrate
11
. Accordingly, the transparent substrate
12
is to be a top surface side.
In forming the above-mentioned light shielding layer, a printing method was mainly employed to the conventional device. However, in order to obtain a sufficient shielding property of 2 or more in terms of an optical density (OD value) by the printing method, the film thickness of the light shielding layer reached 3—4 &mgr;m. Accordingly, there was such drawback that smoothness in the top surface was poor and fine processing could not be performed due to a restriction in accuracy of printing. Accordingly, in an attempt of forming the cell gap to be small, it was only possible to reduce the dimension of the gap to about 6 &mgr;m at most due to the restriction on the film thickness by the printing. Further, even in this case, a short-circuit between the opposing transparent substrates and unevenness of the gap often occurred due to protections formed in the light shielding layer by which there were problems of bad yield or a poor quality of products.
Further, as methods for realizing a partial color display by using the cell provided with the light shielding layer at its rear side, there were a method for conducting color-printing to an outer portion of the cell by screen printing, a method for partially coloring by disposing a color filter in an outside portion of the cell and a method for printing a color layer on an inner surface of the cell by screen printing or off-set printing. However, there were problems as follows.
In the method for printing or attaching a color filter to an outer surface of the cell, it was impossible to avoid color shifting due to parallax, and the application of different colors in a fine pattern was difficult, whereby it was only possible to form a rough pattern having the intervals of line of about 1 mm or more. Further, in the method for disposing a color filter in the cell by printing, the printing should be conducted on the ITO; transparent electrode, and accordingly, a voltage was applied to the liquid crystal layer through the color filter, which deteriorated the threshold property. Further, there was a method for changing colors to be displayed by forming sections having different colors in a color polarizer. However, this method was too expensive to use.
On the other hand, there has been well known a technique to prepare a color filter with use of a black resist and a color resin, which has become practical for a full dot display such as a large sized display using STN (Super Twisted Nematic), TFT (Thin Film Transistor) or the like.
The light shielding layer used for the color filter for TFTs does not require electrical insulation properties, and it is rather preferred to have a certain degree of conductive properties. It is because when an ITO film is formed on the color filter, the conductive properties of the light shielding layer compensate the ITO film having insufficient conductive properties and exhibit excellent operating characteristics even though the ITO film has a relatively high resistance value.
On the other hand, in a case of using a color filter for STN in which an ITO film having a stripe-like patterning on the color filter, it is not preferable to have conductive properties from the viewpoints of assuring electrical insulation properties between lines and reduction in the electrostatic capacity. However, the smoothness of the top surface is an important factor for the color filter used for STN, and therefore, it is necessary to form a insulating smoothing layer of resin on the color filter.
Since the resin having a insulating smoothing layer has electrical insulation properties, use of the light shielding layer having low electrical insulation properties on the color filter does not create a big problem. Namely, although a certain material having high insulation properties and high light absorbance was known, persons have not found any usage to the material having such excellent characteristics.
Further, the bonding strength between the transparent substrate and the light shielding layer formed by printing was insufficient, and it was impossible to print the periphery sealing member on the light shielding layer. Accordingly, when a display portion of a liquid crystal panel mounted on an automobile is observed from an oblique direction and if the angle of visibility is too deep to be out of the light shielding layer, the light of the back light may leak.
In order to prevent such disadvantage, a black ink was printed on a region of a top surface of the cell including a portion corresponding to the periphery sealing member into a flame like shape so as to prevent the leakage of light. However, this technique inevitably increased the number of processes. Besides the abovementioned problem, there was proposed a color display system to display different colors by driving the cell at a low duty ratio. However, this technique had the problem as follows. Namely, in using the method for printing the color filter or bonding the color filter on an outer portion of the cell, it is necessary to broaden the distance between patterned portions in order to prevent colors from mixing due to parallax, and accordingly, it is impossible to provide precisely divided colors.
On the other hand, in the method for printing the color filter in an inner surface of the cell, the color purity was poor although there was no problem in precision, and reliability was low. Even in the method for printing the color filter in an inner surface of the cell, it was necessary for the light shielding layer formed by printing to have a film thickness of 2-4 &mgr;m to obtain a sufficient absorbance, and therefore, the production of an uneven film thickness was unavoidable. Accordingly, an unevenness of cell gap was resulted whereby
Hattori Kizo
Iguchi Shinsuke
Kohno Masanori
Ohgawara Masao
Teramoto Takero
Nguyen Hoan C.
Optrex Corporation
Parker Kenneth
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