U.S. patent application number 08/999801 was filed with the patent office on 2001-11-15 for method for manufacturing a liquid crystal display by using non-rubbing method of polyimide orientation film.
Invention is credited to PARK, HO-YOUNG.
Application Number | 20010040666 08/999801 |
Document ID | / |
Family ID | 19492376 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040666 |
Kind Code |
A1 |
PARK, HO-YOUNG |
November 15, 2001 |
METHOD FOR MANUFACTURING A LIQUID CRYSTAL DISPLAY BY USING
NON-RUBBING METHOD OF POLYIMIDE ORIENTATION FILM
Abstract
A liquid crystal display and a method for manufacturing the same
are provided. An orientation film orientation-processed by a
non-rubbing method using a polymer is formed on the respective
opposing surfaces of first and second substrates. The first and
second substrates on which the orientation films are formed are
sealed to form a space, and then liquid crystal is injected into
the space. A liquid crystal cell into which the liquid crystal has
been injected is heated, and an ultraviolet ray of a predetermined
wavelength is irradiated on the liquid crystal cell for a
predetermined period of time, thereby forming the liquid crystal
display. Thus, the pretilt angle can be increased.
Inventors: |
PARK, HO-YOUNG; (PUSAN-CITY,
KR) |
Correspondence
Address: |
LEYDIG VOIT AND MAYER
700 THIRTEENTH STREET NW
SUITE 300
WASHINGTON
DC
20005
|
Family ID: |
19492376 |
Appl. No.: |
08/999801 |
Filed: |
December 24, 1997 |
Current U.S.
Class: |
349/187 |
Current CPC
Class: |
G02F 1/133788 20130101;
C09K 2323/027 20200801 |
Class at
Publication: |
349/187 |
International
Class: |
G02F 001/13 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 1996 |
KR |
96-76953 |
Claims
What is claimed is:
1. A method for manufacturing a liquid crystal display, said method
comprising the steps of: (a) coating an orientation film on the
respective opposing surfaces of first and second transparent
substrates; (b) orientation-processing said orientation films using
a non-rubbing method; (c) injecting and sealing liquid crystal
between said orientation films to thereby produce a liquid crystal
cell; (d) heating said liquid crystal cell to a predetermined
temperature; and (e) irradiating an ultraviolet ray on said liquid
crystal cell.
2. The method for manufacturing a liquid crystal display as claimed
in claim 1, wherein the temperature for heating said liquid crystal
cell is between 90.degree. C. and 180.degree. C.
3. The method for manufacturing a liquid crystal display as claimed
in claim 1, wherein the wavelength of the ultraviolet ray is
between 200 nm and 250 nm.
4. The method for manufacturing a liquid crystal display as claimed
in claim 1, wherein the thickness of said orientation film is
between 350 .ANG. and 700 .ANG..
5. The method for manufacturing a liquid crystal display as claimed
in claim 1, wherein said steps (d) and (e) are performed
simultaneously.
6. A liquid crystal display manufactured by the method of claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to method for manufacturing a
liquid crystal display which includes a process of forming an
orientation film for aligning liquid crystal and a process of
treating the liquid crystal, and a liquid crystal display
manufactured by the method.
[0003] 2. Description of Related Art
[0004] A general liquid crystal display can be produced in various
sizes ranging from a subminiature size to a large size and diverse
display patterns can be achieved, so that it has been widely
applied to display devices. FIG. 1 shows an example of a liquid
crystal display having liquid crystal having a twist angle between
180.degree. and 270.degree.. As shown in FIG. 1, first and second
transparent electrodes 13 and 14 are isolated from each other in
parallel stripes and intersect each other. The first and second
electrodes 13 and 14 are formed on the opposing surfaces of first
and second transparent substrates 11 and 12, respectively.
Orientation films 16 and 17 are formed on the transparent
electrodes 13 and 14, respectively. Liquid crystal 19 is injected
between the orientation films 16 and 17, and the resultant
structure is sealed by a sealant 18. Polarizing plates 21 and 22
are attached on the outer surfaces of the first and second
transparent substrates 11 and 12, respectively, and the
polarization directions of the polarizing plates 21 and 22
correspond to the twist angle of the liquid crystal 19.
[0005] The surfaces of the orientation films 16 and 17 are treated
to orient the liquid crystal 19 in a predetermined direction. Here,
treatment of the orientation films is an important factor in
determining the pretilt angle of the orientation films. Preferably,
the pretilt angle is large for effective picture display.
[0006] As a typical orientation film treatment method, there are a
rubbing method for rubbing the orientation films 16 and 17 in a
predetermined direction using a cloth, and a non-rubbing method
including an SiO incline deposition method, a figure transcription
method and a light irradiation method using high-polymerization of
light due to an ultraviolet ray. The rubbing method causes phase
distortion and light dispersion since it is difficult to form fine
and accurate orientation grooves on the orientation film. In
particular, since the pretilt angle of the orientation film depends
on the rubbing pressure, the rubbing pressure must be increased to
obtain a large pretilt angle, and it is also difficult to obtain a
uniform pretilt angle over the entire orientation film.
[0007] The light irradiation method, as an orientation treatment
method performed by exposure to light and development of a
photosensitive film coated on the upper surface of the orientation
film, can arbitrarily control the direction of orientation.
However, by this type of non-rubbing method, there is a limit in
improving the resolution of the picture since the orienting force
is weak and the pretilt angle is not relatively large.
[0008] For example, a pretilt angle of 4 to 6.degree. is obtained
by orienting polyimide (a high polymer compound) using the
non-rubbing method. This pretilt angle is not within the normally
acceptable between 8.degree. and 10.degree.. Therefore, a reversely
twisted domain where liquid crystal molecules are reversely twisted
may be generated.
[0009] In order to solve the above problem, as disclosed in U.S.
Pat. No. 5,464,669 issued to Kang et al. on Nov. 7, 1995, a method
for forming a polyvinyl-4-fluorocinnamate (PVCN-F) film
respectively on two opposing substrates and irradiating
linearly-polarized UV rays having different energies on the
respective PVCN-F films has been developed.
[0010] However, the PVCN-F polymer is relatively expensive, and
since the pretilt angle depends on the difference in energies of
linearly-polarized light, it is difficult to control the amount of
irradiation of light.
SUMMARY OF THE INVENTION
[0011] To solve the above-described problem, it is an object of the
present invention to provide a method for manufacturing a liquid
crystal display by which the pretilt angle of an orientation film
can be increased, and a liquid crystal display manufactured by the
above manufacturing method.
[0012] To accomplish the above object, there is provided a method
for manufacturing a liquid crystal display, the method comprising
the steps of: (a) coating an orientation film on the respective
opposing surfaces of first and second transparent substrates; (b)
orientation-processing the orientation films using a non-rubbing
method; (c) injecting and sealing liquid crystal between the
orientation films to thereby produce a liquid crystal cell; (d)
heating the liquid crystal cell to a predetermined temperature; and
(e) irradiating an ultraviolet ray on the liquid crystal cell.
[0013] Here, it is preferable that the temperature for heating the
liquid crystal cell is between 90.degree. C. and 180.degree. C.
[0014] Also, preferably, the wavelength of the ultraviolet ray is
between 200 nm and 250 nm and the thickness of the orientation film
is between 350 .ANG. and 700 .ANG..
[0015] According to another aspect of the present invention, a
liquid crystal display manufactured by the above method is
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above object and advantage of the present invention will
become more apparent by describing in detail a preferred embodiment
thereof with reference to the attached drawings in which:
[0017] FIG. 1 is a sectional view of a general liquid crystal
display in which a portion thereof has been magnified;
[0018] FIG. 2 is a graph showing variations in the pretilt angle
according to the heating temperature of a liquid crystal cell
according to the present invention;
[0019] FIG. 3 is a graph showing variations in the pretilt angle
according to the wavelength of an ultraviolet ray irradiated on an
orientation film according to the present invention; and
[0020] FIG. 4 is a graph showing variations in the pretilt angle
according to the irradiation time of an ultraviolet ray irradiated
on an orientation film according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] A liquid crystal display manufacturing method according to
the present invention will be described referring to FIG. 1 showing
the configuration of a typical liquid crystal display.
[0022] First and second transparent electrodes 13 and 14 each
having a predetermined pattern are formed on the opposing surfaces
of first and second transparent substrates 11 and 12 which have
been thoroughly cleaned. Orientation films 16 and 17 are coated on
opposing surfaces of the first and second transparent substrates 11
and 12 on which the transparent electrodes 13 and 14 are formed,
using polyimide having a long-chain alkyl group. A typical
well-known material can be used as the polyimide. The thickness of
the orientation film is between 300 .ANG. and 1000 .ANG.,
preferably, between 350 .ANG. and 700 .ANG.. Also, preferably, the
plastic temperature of the orientation film is between 150.degree.
C. and 200.degree. C. Furthermore, the orientation films 16 and 17
are orientation-treated by a non-rubbing method including the
aforementioned light irradiation method and the shape transcription
method.
[0023] After the orientation films 16 and 17 are completely formed,
liquid crystal is injected between the orientation films 16 and 17,
and the resultant structure is sealed at the edges by a sealant
18.
[0024] Then, a process for increasing the pretilt angle is
performed as follows. That is, the liquid crystal cell into which
liquid crystal has been injected is heated at a predetermined
temperature. Here, it is preferable that the heating temperature is
between 90.degree. C. and 180.degree. C., with the optimal
temperature being between 100.degree. C. and 120.degree. C. When
the heating temperature is lower than 90.degree. C., irradiation of
an ultraviolet ray (to be described later) does not have a
significant effect on increasing the pretilt angle. When the
heating temperature is greater than 180.degree. C., the liquid
crystal may be damaged.
[0025] Thereafter, the heated cell is irradiated with an
ultraviolet ray. Here, it is preferable that the wavelength of the
ultraviolet ray is between 200 nm and 500 nm, and that time for
irradiation is between approximately 6 minutes and 15 minutes. In
particular, the optimal wavelength of the ultraviolet ray is
between 300 nm and 440 nm to increase the pretilt angle. If the
wavelength of the ultraviolet ray is not between 200 nm and 500 nm,
any increase in the pretilt angle will be minimal.
[0026] According to the present invention, the heating of the
liquid crystal cell can be simultaneously performed with the
irradiation of the ultraviolet ray.
[0027] The effects of the present invention can be more clearly
shown through the following experimental example.
EXPERIMENTAL EXAMPLE
[0028] In this experiment, PVC1 from Aldrich Chemical CO. was used
as the material for the orientation film, the plastic temperature
and the thickness of the orientation film were about 200.degree. C.
and 400 .ANG., respectively, and the twist angle of liquid crystal
used was 260.degree..
[0029] FIG. 2 shows variations in the pretilt angle according to
the heating temperature of the liquid crystal cell. The wavelength
of the irradiated ultraviolet ray was about 350 nm, and the
irradiation time was about 12 minutes. As shown in FIG. 2, when the
heating temperature of the liquid crystal cell was lower than
90.degree. C., the increase in pretilt angle was minimal.
[0030] FIG. 3 shows the pretilt angle depending on the wavelength
of the ultraviolet ray used to irradiate the liquid crystal cell.
The time for irradiating the ultraviolet ray was 12 minutes, and
the temperature for heating the liquid crystal cell was 120.degree.
C. As shown in FIG. 3, the pretilt angle increased significantly
when an ultraviolet ray having a wavelength between 200 nm and 500
nm was used.
[0031] FIG. 4 shows variations in the pretilt angle according to
the irradiation time of the ultraviolet ray irradiated on the
liquid crystal cell. The temperature for heating the liquid crystal
cell was 120.degree. C., and the wavelength of the ultraviolet ray
was 350 nm. As shown in FIG. 4, it was evident that the preferred
time for irradiating the ultraviolet ray was between 6 minutes and
15 minutes.
* * * * *