Coating processes – Nonuniform coating
Reexamination Certificate
2002-04-30
2003-08-26
Pianalto, Bernard (Department: 1762)
Coating processes
Nonuniform coating
C118S665000, C118S688000, C118S695000, C118S712000, C118S713000, C222S001000, C222S004000, C222S020000, C222S052000, C222S481000, C222S501000, C222S507000, C222S512000, C222S544000, C222S630000, C427S421100
Reexamination Certificate
active
06610364
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for dropping a controlled amount of liquid crystal, and more particularly, to an apparatus and method for dropping a controlled amount of liquid crystal such that an exact and optimal amount of liquid crystal is dispensed onto a substrate for a liquid crystal unit panel.
2. Description of the Related Art
Recently, various portable electric devices such as mobile phones, personal digital assistants (PDA), and notebook computers have been developed, and therefore, the needs for a flat panel display device used in small, light weight, and power-efficient devices for such portable devices have correspondingly increased. To meet such needs, flat panel display device technologies such as liquid crystal display (LCD) technology, plasma display panel (PDP) technology, field emission display (FED) technology, and vacuum fluorescent display (VFD) technology have been actively researched. Of these flat panel display devices, the LCD is highlighted due to current mass production, efficient driving schemes, and superior image quality.
The LCD is a device for displaying information on a screen using refractive anisotropy of liquid crystal. As shown in
FIG. 1
, the LCD
1
comprises a lower substrate
5
, an upper substrate
3
, and a liquid crystal layer
7
formed between the lower substrate
5
and the upper substrate
3
. The lower substrate
5
is a driving device array substrate. A plurality of pixels (not shown) are formed on the lower substrate
5
, and a driving device such as a thin film transistor (TFT) is formed on each pixel. The upper substrate
3
is a color filter substrate, and a color filter layer for reproducing real color is formed thereon. Further, a pixel electrode and a common electrode are formed on the lower substrate
5
and the upper substrate
3
, respectively. An alignment layer is formed on the lower substrate
5
and the upper substrate
3
to align liquid crystal molecules of the liquid crystal layer
7
uniformly.
The lower substrate
5
and the upper substrate
3
are attached by a sealing material
9
, and the liquid crystal layer
7
is formed therebetween. In addition, the liquid crystal molecules are reoriented by the driving device formed on the lower substrate
5
to control the amount of light transmitted through the liquid crystal layer, thereby displaying information.
Fabrication processes for a LCD device can be divided into a driving device array substrate process for forming the driving device on the lower substrate
5
, a color filter substrate process for forming the color filter on the upper substrate
3
, and a cell process. These processes will be described with reference to
FIG. 2
as follows.
At first, a plurality of gate lines and data lines are arranged on the lower substrate to define a pixel area by the driving device array process and the thin film transistor connected to the both gate line and the data line is formed on the each pixel area (S
101
). Also, a pixel electrode, which is connected to the thin film transistor to drive the liquid crystal layer according to a signal applied through the thin film transistor, is formed by the driving device array process.
At the same time, R (Red), G (Green), and B (Blue) color filter layers for reproducing the color and a common electrode are formed on the upper substrate
3
by the color filter process (S
104
).
In addition, the alignment layer is formed on the lower substrate
5
and the upper substrate
3
, respectively. Then, the alignment layer is rubbed to induce a surface anchoring (that is, a pretilt angle and alignment direction) to the liquid crystal molecules of the liquid crystal layer between the lower substrate
5
and the upper substrate
3
(S
102
and S
105
). Thereafter, a spacer for maintaining the cell gap constant and uniform is dispersed on the lower substrate
5
. Then, the sealing material is applied on an outer portion of the upper substrate
3
to attach the lower substrate
5
to the upper substrate
3
by compression (S
103
, S
106
, and S
107
).
The lower substrate
5
and the upper substrate
3
are made from a glass substrate of larger area. That is, the large glass substrate includes a plurality of unit panel areas in which the driving device such as TFT and the color filter layer are formed on. To fabricate the individual liquid crystal unit panel, the assembled glass substrate should be cut into unit panels (S
108
). Thereafter, the liquid crystal is injected into the empty individual liquid crystal unit panel through a liquid crystal injection opening (S
109
). The liquid crystal unit panel filled with the liquid crystal is completed by sealing the liquid crystal injection opening, and each liquid crystal unit panel is inspected (S
110
).
As described above, liquid crystal is injected through the liquid crystal injection opening. At that time, the injection of the liquid crystal is induced by pressure difference.
FIG. 3
shows a device for injecting the liquid crystal into the liquid crystal panel. As shown in
FIG. 3
, a container
12
in which the liquid crystal is contained is placed in a vacuum chamber
10
, and the liquid crystal panel is located on an upper portion of the container
12
. The vacuum chamber
10
is connected to a vacuum pump to maintain a vacuum state. Further, a liquid crystal panel moving device (not shown) is installed in the vacuum chamber
10
to move the liquid crystal panel from the upper part of the container
12
to the surface of the liquid crystal to contact an injection opening
16
of the liquid crystal panel
1
with the liquid crystal
14
(this step is called a liquid crystal dipping injection step).
When the vacuum in the chamber
10
is released by introducing nitrogen gas (N
2
) into the vacuum chamber
10
so that the injection opening of the liquid crystal panel
1
contacts the liquid crystal, liquid crystal
14
is injected into the panel through the injection opening by the pressure difference between the pressure in the liquid crystal panel and the pressure of the vacuum chamber. After the liquid crystal is entirely filled into the panel
1
, the injection opening
16
is sealed by a sealing material to seal the liquid crystal layer (this step is called a liquid crystal vacuum injection step).
However, there are several problems in the liquid crystal dipping injection/vacuum injection method as follows.
First, the time needed to inject the liquid crystal into the panel
1
is increased. Generally, a gap thickness between the driving device array substrate and the color filter substrate in the liquid crystal panel is very narrow as order of magnitude of micrometers, and therefore, a very small amount of liquid crystal is injected into the liquid crystal panel per unit time. For example, it takes about 8 hours to inject the liquid crystal completely in fabrication process of the 15 inches-liquid crystal panel
15
. Thus, the liquid crystal fabrication process time is increased due to the liquid crystal injection of long time, thereby reducing fabricating efficiency.
Second, the liquid crystal consumption is increased in the above liquid crystal injection method. A small amount of liquid crystal of the liquid crystal contained in the container
12
is injected into the liquid crystal panel
1
. However, when the liquid crystal is exposed to atmosphere or to a certain gas, the liquid crystal is contaminated by reaction with the gas. Therefore, the remaining liquid crystal should be discarded after the injection when the liquid crystal
14
contained in the container
12
is injected into a plurality of liquid crystal panels
1
, thereby increasing the liquid crystal panel fabrication cost.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an apparatus for dispensing liquid crystal and a method for controlling a liquid crystal dropping amount that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present in
Kweon Hyug-Jin
Son Hae-Joon
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Pianalto Bernard
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