Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-11-27
2002-09-24
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S154000, C349S189000
Reexamination Certificate
active
06456355
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-71352, filed on Nov. 28, 2000 in Korea, which is hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a liquid crystal panel having ribs therein to reduce an injection time of liquid crystal.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) panel has an upper substrate and a lower substrate and a liquid crystal layer interposed therebetween. More specifically, the upper substrate includes common electrodes, while the lower substrate includes switching elements, such as thin film transistors (TFTs), and pixel electrodes.
A manufacturing process and an operation of the liquid crystal cell will be described. Common electrodes and pixel electrodes are formed on upper and lower substrates, respectively. A seal is then formed on the lower substrate. The upper and lower substrates are then bonded together using a sealing material so that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate face each other. Thereafter, liquid crystal panels are completed. A liquid crystal material is injected into a gap between the upper and lower substrates through injection holes. The injection holes are then sealed. Finally, polarizing films are attached to outer surfaces of the upper and lower substrates.
In operation of the liquid crystal panel, light passing through the liquid crystal panel is controlled by electric fields. The electric fields are applied through the pixel and common electrodes. By controlling the electric fields, desired characters or images are displayed on the panel.
Fabrication processes of various components of the liquid crystal display device, such as the thin film transistors or color filters, typically require numerous manufacturing steps. However, the overall fabrication process for the liquid crystal display device is relatively straightforward.
FIG. 1
is a flow chart illustrating a fabricating sequence of the liquid crystal cell for the conventional liquid crystal display device. In the first step (ST
1
), the upper and lower substrates, i.e., a color filter substrate and an array substrate, are initially cleaned. The object of this process is to remove impurities that may exist on the substrate. At this time one or more cells have been already formed on the upper and lower substrates respectively.
In the second step (ST
2
), alignment layers are formed on the upper and lower substrates. The alignment layers are formed on the common and pixel electrodes. This step includes processes for coating an alignment layer, hardening and rubbing. A polyimide-based resin is usually selected for an alignment layer material because it exhibits good alignment characteristics with various liquid crystal materials. A surface of the hardened alignment layer is rubbed by a fabric in order to make scratches in a uniform direction. This rubbing process is needed in order to provide uniform alignment of the liquid crystal molecules and thus provide a display with uniform characteristics. Accordingly, it is very important to form the alignment layer uniformly on a large surface of electrodes.
In the third step (ST
3
), a seal pattern is printed and spacers are dispensed on the substrate. When the upper and lower substrates are attached, the seal patterns form cell gaps that will receive the liquid crystal material. The seal pattern also prevents the interposed liquid crystal material from leaking out of the completed liquid crystal cell. The seal is conventionally fabricated using thermosetting resin including glass fiber and screen-print technology. The seal pattern includes an injection hole and is formed along edges of a display area of each cell. After the seal pattern is printed, spacers are dispensed in order to keep an accurate and uniform cell gap between the upper and lower substrates. Accordingly, spacers have to be dispensed on substrates with a uniform density. There are two ways for dispensing spacers. One is a wet dispensing method which includes spraying a mixture of alcohol and spacers, for example; and the other is a dry dispensing method which includes spraying only spacers.
In the fourth step (ST
4
), the upper and lower substrates are aligned and attached to each other. An aligning error margin in this case is less than a few micrometers. If the upper and lower substrates are aligned and attached with an aligning margin larger than the error margin discussed above, display quality of the liquid crystal display is deteriorated due to a leakage of light during operation of the liquid crystal cell.
In the fifth step (ST
5
), the liquid crystal cell fabricated in the above steps is cut into individual liquid crystal cells. The cutting process includes a step of scribing by which cutting lines are formed on the substrate and a step of breaking, in which the substrate is severed along the scribed lines.
In the sixth step (ST
6
), liquid crystal material is injected into individual liquid crystal cells. Since each individual liquid crystal cell has a gap of only a few micrometers between the substrates per hundreds of square centimeters in area, a vacuum injection method using a pressure difference is widely used for injecting liquid crystal material into this liquid crystal cell. In general, because the injection process of the liquid crystal material into the cells takes the longest time among many fabrication processes for the liquid crystal display device, it is important to optimize the vacuum injection in order to increase the fabrication yield. After the liquid crystal material is injected to the liquid crystal cell, the injection hole needs to be sealed. The injection hole is usually sealed by forming an ultraviolet light curable resin on the injection hole and irradiating an ultraviolet light to the sealed hole. Because inferior goods may be produced by contaminations if the liquid crystal cell is exposed to the air, the liquid crystal cell must be protected from the air and must not be left in the air for a long time when it is not sealed.
After the injection and sealing process, the liquid crystal cell undergoes inspection and grinding processes. In the inspection process, the existence of contaminations in the liquid crystal cell, of point defects caused by an inferiority of the thin film transistor, of line defects caused by severance of the gate and data line, and of defective optical properties caused by a difference of a cell thickness, for example, are inspected.
A conventional injection process for the liquid crystal cell and the degree of the injection in the liquid crystal panel will be explained hereinafter with reference to FIG.
2
and
FIGS. 3A
to
3
C.
FIG. 2
is a schematic diagram illustrating a conventional injection process of the liquid crystal and more particularly illustrating the vacuum injection method whereby the liquid crystal material is injected in a vacuum chamber using a pressure difference between the interior and exterior of the liquid crystal cell. Though this injection process is usually executed using a cell cassette that loads a number of liquid crystal panels at one time, the injection process will be described on the basis of one liquid crystal panel for the sake of convenience. As shown in the
FIG. 2
, a vacuum chamber
2
has an inlet
4
, an outlet
6
for nitrogen gas, and a container
10
having the liquid crystal
8
therein. The liquid crystal panel
14
having the injection hole
12
is disposed over the container
10
in the vacuum chamber
2
. The seal pattern
13
is formed along internal edges of the liquid crystal panel
14
except the injection hole
12
. The seal pattern is needed to form the cell gap for the injection of the liquid crystal and to prevent the leakage of the liquid crystal. Before the injection process is commenced, the interior of the liquid crystal panel
14
should be vacuumed and an autoclave pro
Choi Su-Seok
Choi Suk-Won
Dudek James
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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