Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-12-18
2003-06-03
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06573968
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-58106, filed on Dec. 16, 1999, which is hereby incorporated by reference.
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 seal pattern for a liquid crystal display and a method of manufacturing the same.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices with light, thin, low power consumption characteristics have been used, for example, in office automation (OA) equipments and video units. A typical liquid crystal display (LCD) panel has upper and lower substrates and an interposed liquid crystal layer. The upper substrate usually includes common electrodes, while the lower substrate includes switching elements, such as thin film transistors (TFTs), and pixel electrodes.
As the present invention relates to manufacturing liquid crystal display panels, a brief explanation of conventional liquid crystal display manufacturing processes will be discussed. 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 the seal such that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate face each other, forming liquid crystal cells. Liquid crystal material is then injected into those cells through injection holes. The injection holes are then sealed. Finally, polarizing films are attached to the outer surfaces of the upper and lower substrates.
The pixel and common electrodes generate electric fields that control the light passing through the liquid crystal cells. By controlling the electric fields desired characters or images are displayed.
While fabricating the various components of a liquid crystal display, such as the thin film transistors or the color filters, typically requires numerous manufacturing steps, the overall fabrication process is relatively straightforward.
FIG. 1
illustrates a typical liquid crystal panel manufacturing process in some detail. Step st
1
forms an array matrix of thin film transistors and pixel electrodes over an array (lower) substrate.
Step st
2
forms an orientation film over the lower substrate. This involves uniformly depositing a polymer thin film over the lower substrate and then uniformly rubbing the polymer thin film with a fabric. The rubbing process involves rubbing the surface of the polymer thin film to orientate or align the film. A typical orientation film is an organic thin film such as a polyimide thin film.
Step st
3
produces a seal pattern on the lower substrate. When the upper and lower substrates are attached, the seal pattern forms cell spaces that will receive the liquid crystal material. The seal pattern will also prevent the interposed liquid crystal material from leaking out of the completed liquid crystal cell. A thermosetting plastic and a screen-print technology are conventionally used to fabricate the seal pattern.
Step st
4
is to spray spacers over the lower substrate. The spacers have a definite size and act to maintain a precise and uniform space between the upper and lower substrates. Accordingly, the spacers are placed with a uniform density on the lower substrate using either a wet spray method, in which case the spacers are mixed in an alcohol and then sprayed, or a dry spray method in which only the spacers are sprayed. The dry spray method is divided into a static electric spray method that uses static electricity and a non-electric spray method that uses gas pressure. Since static electricity can be harmful to the liquid crystal, the non-electric spray method is widely used.
The next step, st
5
, is to aligned and attached the upper and lower substrates together, and to attach color filters to the upper substrate and the lower substrate. The aligning margin, which is less than a few micrometers, is important. If the upper and lower substrates are aligned and attached beyond the aligning margin, light leaks away such that the liquid crystal cell cannot adequately performed its function.
Step st
6
cuts the liquid crystal element fabricated through the above five steps into individual liquid crystal cells. Conventionally, a liquid crystal material was injected into the space between the upper and the lower substrates before cutting the liquid crystal element into individual liquid crystal cells. However, as displays have become larger, the liquid crystal cells are usually cut first and then the liquid crystal material is injected. The cutting process typically includes scribing using a diamond pen to form cutting lines on a substrate, and a breaking step that separates the substrate along the scribed lines.
Step st
7
actually injects liquid crystal material into the individual liquid crystal cells. Since each individual liquid crystal cell is a few square centimeters in area, but has only a few micrometer gap between plates, a vacuum injection method is effectively and widely used. Generally, the step of injecting the liquid crystal material into the cells takes the longest manufacturing time. Thus, for manufacturing efficiency, it is important to have optimum conditions for vacuum injection.
Now, referring to
FIG. 2
, the screen-print method used for the seal pattern process of the third step (st
3
) is explained.
The screen-print technology is facilitated with a patterned screen
6
and a squeegee
8
. In order to interpose the liquid crystal without leakage, the seal pattern
2
is formed along edges of a substrate
1
. At one side of the edge, an injection hole
4
for injecting the liquid crystal is formed. To form the seal pattern
2
, a thermosetting resin or an ultraviolet-setting epoxy resin and the like is deposited on the substrate
1
, and thereafter a solvent included in the sealant is evaporated for leveling.
At this point, although the epoxy resin itself is not harmful to the liquid crystal, an amine in a thermohardening solvent for forming the thermosetting resin decomposes the liquid crystal. Thus, when using the epoxy resin for the seal pattern
2
, the sealant formed through the screen-print technology should be pre-baked sufficiently with a gradual variance of the baking temperature. Further, in forming the seal pattern, the uniformity in thickness and width of the sealant are very important to maintain the uniform spacing (or gap) between the two substrates.
FIG. 3
shows a different seal-patterning technology, a dispenser-print technology. As shown, the dispenser-print technology uses a dispenser
30
filled with the sealant and a table
100
where the substrate
1
is placed. The dispenser
30
moves over the table
100
and forms the sealant according to the direction of the arrow so as to form the sealant pattern
2
.
FIG. 4
shows a conventional seal pattern formed on a substrate via the above-mentioned seal-patterning technology. Referring to
FIG. 4
, on a substrate
1
, a seal pattern
2
is formed. The seal pattern
2
includes main seal lines
2
a
and an auxiliary seal line
2
b
. As previously explained, the main seal lines
2
a
prevent the leakage of the liquid crystal, while the auxiliary seal line
2
b
surrounds the main seal lines
2
a
to protect the main seal lines
2
a
from a cleaning detergent or an etching solution during a cleaning and etching process.
The cleaning and etching process decreases the thickness of the assembled substrates. A 10% decrease in the substrate thickness result in a 20% decrease in the weight of the liquid crystal display device.
FIG. 5
illustrates the cleaning and etching process in a block diagram.
Before the seventh step, st
7
, of injecting the liquid crystal shown in
FIG. 1
, the assembled substrates produced from the first to sixth steps, st
1
to st
6
, shown in
FIG. 1
, are cleaned manually using a cleaning detergent such as isopropyl alcohol (IPA) or deionized water (DI water). Through the first cleaning step, ST
100
, contaminants such
Dudek James
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
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