Method of manufacturing LCD by dropping liquid crystals on a substrate and then pressing the substrates

Liquid crystal displays are manufactured by dropping liquid crystals on at least one of a pair of liquid crystal display substrates and then placing the pair of liquid crystal display substrates adjacent one another, with the liquid crystals therebetween. The pair of liquid crystal display substrates is pressed toward one another, to thereby discharge excess liquid crystals from between the liquid crystal display substrates. The pair of liquid crystal substrates is then sealed to retain the liquid crystals therebetween. Accordingly, by not requiring the use of injection of liquid crystals, high vacuum processing is not required. Moreover, the number of processing steps can be reduced compared to conventional liquid crystal display manufacturing methods.

FIELD OF THE INVENTION 
This invention relates to liquid crystal displays, and more particularly to 
methods of manufacturing liquid crystal displays. 
BACKGROUND OF THE INVENTION 
Liquid crystal displays (LCDs) are widely used in electronic calculators, 
games, notebook computers and televisions. Liquid crystal displays are 
generally flat and light, can be driven by low voltages and can consume 
low power. 
Referring now to FIG. 1, a cross-sectional view of a liquid crystal display 
is shown. As shown, the liquid crystal display includes a pair of liquid 
crystal display substrates, also referred to herein as upper and lower 
substrates 2 and 2' respectively. A common electrode 3 is included on the 
inner surface of the upper substrate 2 and a scanning electrode 3' is 
included in the inner surface of the lower substrate 2'. Polarizing plates 
1 and 1' are included on the outer surfaces of the upper and lower 
substrates 2 and 2' respectively. Alignment layers 4 and 4' are also 
included on the common electrode 3 and the scanning electrode 3' 
respectively. 
Continuing with the description of FIG. 1, spacers 6 are included between 
the alignment layers 4 and 4' so as to maintain the upper and lower 
substrates 2 and 2' in parallel with each other and spaced apart by a 
predetermined spacing. Liquid crystals 7 are contained between the 
substrates. A seal 5 maintains the liquid crystals between the substrates 
2 and 2'. 
FIG. 2 is a flow chart illustrating conventional methods for manufacturing 
liquid crystal displays. As shown in FIG. 1, at Step 10, the upper and 
lower substrates 2 and 2', including the electrodes 3 and 3', are cleaned. 
The cleaning can prevent the surfaces of the substrate from being 
contaminated. The cleaning Step 10 may include ultrasonic wave washing, 
high temperature drying and cooling. Alignment layers 4 and 4' are then 
formed at Step 12. In particular, a polyimide (PI) resin composition is 
coated on the surfaces of the substrates 2 and 2' to a thickness of about 
600 .ANG.. Then, the solvent in the polyimide resin composition is 
evaporated by heating the substrates 2 and 2', to thereby harden the 
alignment layers 4 and 4'. 
Then, at Step 14, a rubbing process is performed on the surfaces of the 
alignment layers 4 and 4'. The rubbing process allows liquid crystal 
molecules to be aligned in a uniform direction upon injection as described 
below. 
At Step 16, a cleaning process is performed to remove particles that are 
generated during the rubbing Step 14. Spacers 6, having a diameter of 
about 5 .mu.m, are scattered on one of the substrates at Step 18. The 
spacers act to maintain a uniform distance when the upper and lower 
substrates are joined as described below. At Step 20, a sealing agent 5 is 
printed or otherwise formed on at least one of the substrates. The sealing 
agent may be formed by printing using a seal mask or a seal spacer. 
Then, referring to Step 22, the upper and lower substrates 2 and 2' are 
joined and then uniformly pressed together at Step 24 to main a uniform 
cell gap. The seal 5 is then hardened by heating at Step 26. 
Then, liquid crystals 7 are injected into the gap between the adjacent 
substrates 2 and 2' at Step 28. The liquid crystals may be injected by 
wetting one end of the substrates with the liquid crystals in a vacuum 
chamber and then releasing the vacuum to inject the liquid crystals into 
the gap between the upper and lower substrates through a liquid injection 
hole. Thus, the liquid crystal injection process utilizes the pressure 
difference between the inside and the outside of the LCD panel to inject 
the liquid crystals. 
During injection of the liquid crystals in Step 28, the substrates may 
become separated from one another so that the separation distance between 
the panels is larger than the diameter of the spacers 7. Accordingly, the 
space between the two substrate may become nonuniform. In order to obtain 
a uniform spacing, the substrates are pressed together under a pressure of 
about 0.5 kg/cm.sup.2 at Step 30. Then, the injection hole through which 
the liquid crystal was injected is closed. Finally, the panel is cleaned 
at Step 32 and polarizing plates 1 and 1' are formed on the outer surfaces 
of the two substrates at Step 34. 
As described above, conventional manufacturing of liquid crystal displays 
may be complicated because of the large number of processing steps that 
may be involved. Moreover, since pressure differences are used to inject 
liquid crystals, it is desirable for the chamber to be under high vacuum. 
The need to provide high vacuum may involve long pump-down times and may 
therefore slow the manufacturing process. Accordingly, due to the large 
number of steps and the high vacuum processing, the entire process may be 
lengthy. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide improved 
methods of manufacturing liquid crystal displays. 
It is another object of the present invention to provide liquid crystal 
display manufacturing methods that can be relatively uncomplicated and 
that can be performed rapidly. 
It is still another object of the present invention to provide liquid 
crystal display manufacturing methods that do not require high vacuum 
processing. 
These and other objects are provided according to the present invention by 
liquid crystal display manufacturing methods that include the steps of 
dropping liquid crystals on at least one of a pair of liquid crystal 
display substrates and then placing the pair of liquid crystal display 
substrates adjacent one another, with the liquid crystals therebetween. 
The pair of liquid crystal display substrates is pressed toward one 
another, to thereby discharge excess liquid crystals from between the 
liquid crystal display substrates. The pair of liquid crystal substrates 
is then sealed to retain the liquid crystals therebetween. Accordingly, by 
not requiring the use of injection of liquid crystals, high vacuum 
processing is not required. Moreover, the number of processing steps can 
be reduced compared to conventional liquid crystal display manufacturing 
methods. 
Prior to dropping the liquid crystals on the liquid crystal display 
substrates, the liquid crystal substrates are prepared. They may be 
prepared by forming an alignment layer on each of the liquid crystal 
display substrates and rubbing the alignment layers. Spacers are then 
scattered on at least one of the alignment layers, and a sealing layer is 
formed on at least one of the liquid crystal substrates. 
The pressing and sealing steps are preferably performed at subatmospheric 
pressure, but not at high vacuum. The liquid crystal display substrates 
preferably are pressed toward one another until stopped by the spacers. 
The sealing step is preferably performed by heating the pair of liquid 
crystal displays to form the seal. After the sealing step, polarizing 
plates may be formed on each of the liquid crystal display substrates, 
opposite the liquid crystals, and the liquid crystal display can be 
completed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention now will be described more fully hereinafter with 
reference to the accompanying drawings, in which preferred embodiments of 
the invention are shown. This invention may, however, be embodied in many 
different forms and should not be construed as limited to the embodiments 
set forth herein; rather, these embodiments are provided so that this 
disclosure will be thorough and complete, and will fully convey the scope 
of the invention to those skilled in the art. In the drawings, the 
thickness of layers and regions are exaggerated for clarity. Like numbers 
refer to like elements throughout. It will also be understood that when a 
layer is referred to as being "on" another layer, region or substrate, it 
can be directly on the other layer, region or substrate, or intervening 
layers or regions may also be present. 
FIG. 3 is a flow diagram illustrating methods of manufacturing liquid 
crystal displays according to the present invention. As shown in FIG. 1, a 
common electrode 3 and a scanning electrode 3' are formed on a pair of 
liquid crystal display substrates 2 and 2' respectively. The common 
electrode 3 and the scanning electrode 3' may be stripe-type electrodes, 
for example having a width of about 330 .mu.m. The pitch from one 
electrode to another may also be about 330 .mu.m. The electrodes may be 
formed of a transparent conductive material, such as an indium tin oxide 
(ITO) thin film. Then, referring to FIG. 3, the substrates are cleaned at 
Step 40, an alignment layer is printed and heated at Step 42, the 
alignment layers are rubbed at Step 44 and cleaned at Step 46, spacers are 
scattered on at least one of the alignment layers at Step 48, and a 
sealing agent (also referred to as a sealing layer) is printed on at least 
one of the substrates at Step 50. Since Steps 40, 42, 44, 46, 48 and 50 
correspond to Steps 10, 12, 14, 16, 18 and 20 respectively of FIG. 2, they 
will not be described in detail again. 
Then, at Step 52, both substrates are installed in a vacuum chamber. The 
vacuum chamber can include a first portion through which liquid crystal is 
dropped, a second portion in which the substrates are placed adjacent one 
another, and a third portion in which the substrates are pressed and 
heated. The operations that are performed in Step 52 will now be described 
in detail. 
First, the substrates are put in the chamber and the chamber is closed and 
decompressed. Although the chamber is decompressed, a high vacuum need not 
be produced in the chamber. For example, a pressure of 20 Torr may be 
maintained, which is higher than the vacuum state that is generally used 
to inject liquid crystals into a gap between liquid crystal display 
substrates. 
Then, the liquid crystals are dropped onto at least one of the pair of 
liquid crystal display substrates, while under vacuum. The substrates are 
then placed adjacent one another, with the liquid crystals and the spacers 
therebetween. Then, surplus liquid crystals are discharged by pressing the 
pair of liquid crystal display substrates toward one another. The liquid 
crystal substrates are then sealed by hardening the sealing agent using a 
thermal treatment. 
The chamber is then restored to atmospheric pressure. The substrates are 
then cleaned at Step 54, and the polarizing plates are fixed on the outer 
surfaces of the substrates at Step 56. Steps 54 and 56 correspond to 
conventional Steps 32 and 34 of FIG. 2 and need not be described again. 
It will also be understood that although the steps of dropping liquid 
crystals, placing the pair of liquid crystal display substrates adjacent 
one another and pressing the pair of liquid crystal display substrates one 
another may be performed in a single processing chamber, they also may be 
performed in separate processing chambers. Moreover, the sealing agent may 
also be coated in the processing chamber and may be sealed in the 
processing chamber, depending upon the sealing agent that is used. For 
example, for sealing agents that can be hardened by ultraviolet rays, the 
sealing agent can be formed in the same chamber and hardening time may be 
reduced because a heater is not needed to heat the substrates. 
Accordingly, compared to the prior art, the number of processing steps may 
be reduced. In particular, the step of injecting liquid crystal under high 
vacuum, pressing the substrates, closing an injection hole and hardening 
the sealing agent may be replaced by the steps of dropping liquid crystal, 
placing the substrates adjacent one another, pressing the substrates and 
hardening the seal. In conventional manufacturing, long times may be 
needed to obtain the high vacuum state that is used to inject the liquid 
crystal. In contrast, in the present invention, since the pressure need 
not be a high vacuum, but rather can be in the range of about 20 Torr, the 
processing time may be shortened to one-tenth that of conventional 
manufacturing. Accordingly, manufacturing costs may be reduced due to the 
simplified processing and less strenuous vacuum processing requirements. 
In the drawings and specification, there have been disclosed typical 
preferred embodiments of the invention and, although specific terms are 
employed, they are used in a generic and descriptive sense only and not 
for purposes of limitation, the scope of the invention being set forth in 
the following claims.