Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
1997-12-24
2001-12-04
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S123000, C349S191000, C428S001260
Reexamination Certificate
active
06327018
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 material and a process of treating the liquid crystal, and a liquid crystal display manufactured by the method.
2. Description of Related Art
A conventional 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. Liquid crystal displays have been widely applied to display devices.
FIG. 1
shows an example of a liquid crystal display having a liquid crystal having a twist angle between 180° and 270°. As shown in
FIG. 1
, first and second transparent electrodes
13
and
14
are isolated from each other in parallel stripes and cross each other. The first and second electrodes
13
and
14
are located on the opposing surfaces of first and second transparent substrates
11
and
12
, respectively. Orientation films
16
and
17
cover the transparent electrodes
13
and
14
, respectively. Liquid crystal material
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 to 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
.
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 an effective picture display.
Examples of orientation film treatment methods include: a rubbing method for rubbing the orientation films
16
and
17
in a predetermined direction using a cloth, a non-rubbing method including an SiO inclined angle deposition method, a figure transcription method and a light irradiation method using high-polymerization of light due to ultraviolet radiation. 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.
The light irradiation method, as an orientation treatment method performed by exposure to light and development of a photosensitive film coating the upper surface of the orientation film, can arbitrarily control the direction of orientation. However, in 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.
For example, a pretilt angle of 4 to 6° is obtained by orienting polyimide (a high polymer compound) using the non-rubbing method. This pretilt angle is not within the normally acceptable range between 8° and 10°. Therefore, a reversely twisted domain where liquid crystal molecules are reversely twisted may be generated.
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.
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 light irradiation.
SUMMARY OF THE INVENTION
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.
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.
Here, it is preferable that the temperature for heating the liquid crystal cell is between 90° C. and 180° C.
Also, preferably, the wavelength of the ultraviolet radiation is between 200 nm and 250 nm and the thickness of the orientation film is between 350 Å and 700 Å.
According to another aspect of the present invention, a liquid crystal display manufactured by the above method is provided.
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patent: 5073294 (1991-12-01), Shannon et al.
patent: 5186985 (1993-02-01), Estes et al.
patent: 5464669 (1995-11-01), Kang et al.
patent: 5498762 (1996-03-01), Eguchi
patent: 5518782 (1996-05-01), Takao et al.
patent: 5607732 (1997-03-01), Miyamoto et al.
patent: 5623354 (1997-04-01), Lien et al.
patent: 5653845 (1997-08-01), Kawata
patent: 5764326 (1998-06-01), Hasegawa et al.
patent: 5817743 (1998-10-01), Gibbons et al.
patent: 5824377 (1998-10-01), Pirwitz et al.
patent: 5991001 (1999-11-01), Park
patent: 4-12322 (1992-01-01), None
patent: 5-53118 (1993-03-01), None
patent: 10-123531 (1998-05-01), None
Toko et al, TN-LCDs Fabricated by Non-Rubbing showing Wide and Homogeneous Viewing Angular Characteristics and Excellent Voltage, SID 93 Digest, pp. 622-625, 1993.
Chowdhury Tarifur R.
Leydig , Voit & Mayer, Ltd.
Samsung Display Device Co., Ltd.
Sikes William L.
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