U.S. patent application number 09/760889 was filed with the patent office on 2001-06-28 for pretilt angle direction in a liquid crystal cell.
Invention is credited to Choi, Yoo Jin, Kim, Jong Hyung, Kwon, Soon Bum, Nam, Mi Sook, Reznikov, Yuriy, Woo, Joung Won, Yaroshchuk, Oleq, Yoon, Ki Hyuk.
Application Number | 20010005250 09/760889 |
Document ID | / |
Family ID | 19449201 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005250 |
Kind Code |
A1 |
Reznikov, Yuriy ; et
al. |
June 28, 2001 |
Pretilt angle direction in a liquid crystal cell
Abstract
A method is disclosed for controlling a pretilt angle direction
for a liquid crystal cell comprising the steps of first setting the
magnitude of pretilt angle and a plurality of pretilt angle
directions in an alignment layer. This first step is achieved by
irradiating linearly the alignment layer with polarized or
unpolarized UV light. One of the plurality of pretilt angle
directions is then selected by exposing the alignment layer to UV
light a second time.
Inventors: |
Reznikov, Yuriy; (Kyyiv,
UA) ; Yaroshchuk, Oleq; (Kyyiv, UA) ; Woo,
Joung Won; (Seoul, KR) ; Choi, Yoo Jin;
(Anyang-Shi, KR) ; Yoon, Ki Hyuk; (Seoul, KR)
; Nam, Mi Sook; (Anyang-Shi, KR) ; Kim, Jong
Hyung; (Seoul, KR) ; Kwon, Soon Bum; (Seoul,
KR) |
Correspondence
Address: |
LONG ALDRIDGE & NORMAN LLP
Song K. Jung
Suite 600
701 Pennsylvania Avenue N.W.
Washington
DC
20004
US
|
Family ID: |
19449201 |
Appl. No.: |
09/760889 |
Filed: |
January 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09760889 |
Jan 17, 2001 |
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09457388 |
Dec 9, 1999 |
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6226066 |
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09457388 |
Dec 9, 1999 |
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08672183 |
Jun 27, 1996 |
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Current U.S.
Class: |
349/124 ;
349/129 |
Current CPC
Class: |
G02F 1/133788
20130101 |
Class at
Publication: |
349/124 ;
349/129 |
International
Class: |
G02F 001/1337 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 9, 1996 |
KR |
1996-00319 |
Claims
What is claimed is:
1. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell, comprising the steps of:
irradiating said alignment layer on a substrate surface a first
time with non-linearly polarized ultraviolet light to orient
molecules of said alignment layer in a large number pretilt angle
direction, the pretilt angle directions forming pretilt angles,
respectively, relative to a direction parallel to said substrate
surface; and irradiating said alignment layer a second time with
linearly polarized ultraviolet light to select one direction of
said pretilt angle directions.
2. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 1,
wherein a magnitude of said pretilt angles are determined by a
duration of said irradiation step first time.
3. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 1,
wherein said pretilt angles are of equal magnitude
substantially.
4. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 1,
wherein said alignment layer includes a polysiloxane based
material.
5. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 1,
wherein said alignment layer includes
polyvinylfluorocinnamate(PVCN-F).
6. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 1,
wherein said step of irradiating said alignment layer a first time
include a step of irradiating said alignment layer to ultraviolet
light at an angle relative to a normal direction to said substrate
surface, and said step of irradiating said alignment layer a second
time includes a step of irradiating said alignment layer at an
angle substantially equal to ninety degree relative to said
substrate surface.
7. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 6,
wherein said angle is in the range of 0 degree to 60 degree.
8. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 1,
wherein said step of irradiating said alignment layer a first time
include a step of irradiating said alignment layer to ultraviolet
light at a first angle relative to a normal direction to said
substrate surface, and said step of irradiating said alignment
layer a second time includes a step of irradiating said alignment
layer at a second angle relative to normal direction to said
substrate surface.
9. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 8,
wherein a incident direction of said second linearly polarized
ultraviolet light forms an acute angle with said pretilt angle
directions.
10. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 8,
wherein said first and second angle are in the range of 0 degree to
60 degree, respectively.
11. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell, comprising the steps of:
irradiating said alignment layer on a substrate surface a first
time with linearly polarized ultraviolet light to orient molecules
of said alignment layer in first and second pretilt angle
directions, said first and second pretilt angle directions forming
first and second pretilt angles, respectively, relative to a
direction parallel to said substrate surface; and irradiating said
alignment layer a second time with non-linearly polarized
ultraviolet light to select one direction of said first and second
pretilt angle directions.
12. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 11,
wherein a magnitude of said first and second pretilt angles are
determined by a duration of said irradiation step first time.
13. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 11,
wherein said first and second pretilt angles are of equal magnitude
substantially and of opposite sign relative to said parallel
direction to said substrate surface.
14. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 11,
wherein said alignment layer includes a polysiloxane based
material.
15. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 11,
wherein said alignment layer includes
polyvinylfluorocinnamate(PVCN-F).
16. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 11,
wherein said step of irradiating said alignment layer a first time
include a step of irradiating said alignment layer to ultraviolet
light at an angle substantially equal to ninety degree relative to
said substrate surface, and said step of irradiating said alignment
layer a second time includes a step of irradiating said alignment
layer at an angle relative to a normal direction to said substrate
surface.
17. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 16,
wherein a incident direction of said second non-linearly polarized
ultraviolet light forms an acute angle with said one of said first
and second pretilt angle directions.
18. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 16,
wherein said angle is in the range of 0 degree to 60 degree.
19. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 11,
wherein said step of irradiating said alignment layer a first time
include a step of irradiating said alignment layer to ultraviolet
light at a first angle relative to a normal direction to said
substrate surface, and said step of irradiating said alignment
layer a second time includes a step of irradiating said alignment
layer at a second angle relative to a normal direction to said
substrate surface.
20. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 19,
wherein a incident direction of said second non-linearly polarized
ultraviolet light forms an acute angle with said one of said first
and second pretilt angle directions.
21. A method for controlling a pretilt angle direction for an
alignment layer of a liquid crystal cell according to claim 19,
wherein said first and second angles are in the range of 0 degree
to 60 degree, respectively, relative to a normal direction to said
substrate surface.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a liquid crystal cell, and
particularly to a method for controlling a pretilt angle direction
in liquid crystal cell in which photoreaction occur in a
polymerized layer by ultraviolet irradiation.
[0002] Liquid crystals are the liquids consisting of anisotropic
molecules. The average direction of long axes of these molecules is
referred as the director of LC. The director distribution in a LC
bulk is determined by its anchoring on the rigid substrates and
characterized by the direction of the axes of easy orientation,
corresponding to the minimum of the surface energy of an LC,
pretilt angle between the axis of easy orientation and the
substrate plane, and tilt angle between the director of LC and the
substrate plane.
[0003] In order to obtain the uniform brightness and high contrast
ratio of a liquid crystal display, the LC molecules must be
appropriately aligned after being injected between the substrates
of the cell. Not only the value of the director tilt but the
direction of this tilt (i.e. direction of the axis of easy
orientation) is important for normal operation of LC devices
constituting double- and multi-domain structure. Such alignment is
achieved by providing an alignment layer on the surface of the
substrate. A rubbing process can be used for aligning liquid
crystal molecules. In this rubbing process, a polyamide alignment
layer is first coated on the substrate and the rubbing is performed
mechanically, so that microgrooves are formed on the surface of the
alignment layer. The liquid crystal molecules are thus uniformly
aligned due to the intermolecular interaction between the polyamide
molecules and the liquid crystal molecules.
[0004] In the above described rubbing process, however, defects are
formed in the microgrooves which cause light scattering and random
phase distortion. Also during the rubbing process, dust and
electrostatic charges are produced in the alignment layer, so that
the substrate is damaged and yield is decreased.
[0005] To solve the aforementioned problem, photo-alignment process
has been recently introduced. As an example of the photo-alignment
method, a method has proposed by KOBAYASHI, etc. (SID 95 DIGEST,
p.877) in which the pretilt angle direction is determined by
irradiating the UV light twice into an alignment layer consisting
of polyvinylcinnamate (PVCN) based polymer, as shown in FIGS. 1A
and 1B.
[0006] In particular, as shown in FIG. 1A, when the linearly
polarized UV light irradiates to alignment layer 15 in the
direction perpendicular to the surface of the substrate 16, the
alignment layer 15 becomes a photo-polymerized due to cross linking
between polymer molecules. The bonding direction of the
photo-polymer molecules depends on the polarization direction of
the linearly polarized UV light. The liquid crystal is thus aligned
according to the bonding direction of the photo-polymer
molecules.
[0007] Then, the linearly polarized UV light whose polarization
direction is perpendicular to the polarization direction of the
first UV light is irradiated at an angle .phi. to the alignment
layer 15. The pretilt angle of the alignment layer 15 is formed in
this step and the magnitude of the pretilt angle varies according
to the irradiation angle of the UV light. For example, the pretilt
angles are approximately 0.15.degree., 0.26.degree., or
0.30.degree., when the irradiation angles are 30.degree.,
40.degree., or 60.degree., respectively.
[0008] In KOBAYASHI, however, the method has some drawbacks the
thermostability of the tilt angle on the PVCN based materials is
poor, the scope of the pretilt angle is small and does not cover
the range needed for an applications, only polarized exciting light
could be used. Moreover, the method requires rather complicated
geometry of the irradiation and suitable for the only materials
revealing the light-induced easy axis direction perpendicular to
the polarization of the exciting light.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a method
for controlling pretilt angle direction for liquid crystal cell in
which control of the pretilt angle direction is easy and large
pretilt angle can be obtained.
[0010] In order to achieve the object, the method for controlling
pretilt angle for liquid crystal cell comprises the first step of
irradiating UV light to an alignment layer to form pretilt angle
and orient the alignment axis and second step of irradiating UV
light to the alignment layer in the direction of oblique to the
surface. The order of these step is reversible.
[0011] The first and second exposures to UV light can be performed
at an angle, preferably 0-60.degree., or perpendicular to the
substrate surface. Moreover, both polarized and unpolarized UV
light can be used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1A and 1B are views illustrating the conventional
method for controlling pretilt angle for liquid crystal cell;
[0013] FIG. 2 is a view illustrating an UV light irradiation and
birefringence measurement apparatus;
[0014] FIGS. 3A and 3B are views illustrating method for
controlling pretilt angle direction for liquid crystal cell
according to first embodiment of the present invention;
[0015] FIG. 4 is a graph showing pretilt angle dependent on a
absorption energy of the UV light;
[0016] FIGS. 5A and 5B are views illustrating the method for
controlling pretilt angle direction for liquid crystal cell
according to second embodiment of the present invention;
[0017] FIGS. 6A and 6B are views showing the method for controlling
pretilt angle direction according to third embodiment of the
present invention;
[0018] FIGS. 7A and 7B are views showing the method for controlling
pretilt angle direction according to fourth embodiment of the
present invention;
DETAILED DESCRIPTION OF THE INVENTION
[0019] FIG. 2 is a view illustrating ultraviolet (UV) irradiating
and birefringence measuring apparatus for photo-alignment process.
In this device, UV light generated from Hg lamp 11 is linearly
polarized through a lens 12a and a polarizer 17c, and is directed
to the alignment layer 15 coated on substrate 16. A laser beam
generated from a laser 18 is pulsed by beam by a chopped 23, and
then it is polarized by a polarized 17a. The pulsed beam is then
transmitted to the alignment layer 15 through a compensator 25,
through a polarizer 17b and a lens 12b, and finally inputted to a
digital oscilloscope 20 so that the birefringence caused by
anisotropy of the alignment layer 15 can be measured.
[0020] FIGS. 3A and 3B illustrate first embodiment of the present
invention. In this embodiment, the alignment layer includes
polysiloxane based material or polyvinylfluorocinnamate (PVCN-F).
In this alignment layer, pretilt angle and the direction of the
easy axis are determined by one time irradiation of the UV light.
The structural formulas of the polysiloxanecinnamate and PVCN-F are
indicated below. Further, these materials can be used in other
embodiments of the present invention. 1
[0021] examples of polysiloxanecinnamate include: 2
[0022] Z=OH, CH.sub.3 or a mixture of OH and CH.sub.3
[0023] m=10-100
[0024] l=1,3,4,5,6,7,8,9 or 10
[0025] K=0,1 or 2
[0026] X,x.sub.1,Y=H,F,Cl,CN,CF.sub.3,OCF.sub.3,C.sub.nH.sub.2n+1
or OC.sub.nH.sub.2n+1 (n=1-10)
[0027] The polymer solution, the polysiloxanecinnamate or PVCN-F
solution, is prepared using 1:1 mixture of 1,2-dichloroetane and
chlorobenzene. A concentration of the solution is 20 g/l. A droplet
of this solution is dropped in the center of the substrate and then
coated on the whole area of the substrate by a spin-coating for 20
second at 2,000 rpm. As a result, a polymer film is deposited on
the substrate. The thickness of the film, measured by Linnik
interferometer, is 1,000 .ANG., and can be controlled by changing
the concentration of the polymer solution and/or revolution speed
of a spin-coating machine used for spin-coating.
[0028] As shown in FIG. 3A, when the linearly polarized UV light
190 is irradiated to the alignment layer 15 in the perpendicular
direction of the surface of the substrate, the direction of
alignment-axis is determined to be perpendicular to the
polarization direction of the UV light. Further, two symmetric and
bidirectional pretilt angles .phi..sub.1 are created on both sides
of the alignment-axis. The size of the pretilt angle .phi..sub.1 is
variable and depends on the duration of UV exposure, i.e., the
amount of UV energy absorbed by alignment layer 15.
[0029] FIG. 4 is a graph showing the relation between the pretilt
angle and the irradiation time of the UV light, i.e., the amount of
absorption energy of the UV light. As shown in the figure, the
larger the absorption energy is, the smaller the pretilt angle
becomes. Accordingly, the direction of the alignment axis is
determined by the polarization direction of the UV light
irradiation, and the size of pretilt angle is dependent upon the
amount of UV absorption energy.
[0030] After irradiating linearly polarized UV light, another light
is irradiated to the layer to the direction oblique to the surface
of the alignment layer, that is, one direction of two symmetric
pretilt angles is then selected by irradiating alignment layer 15
at an angle .theta..sub.1, 0.degree.<.theta..sub.1
.ltoreq.60.degree. with non-linearly polarized UV light, specially
unpolarized UV light 200, such that all the molecules of alignment
layer 15 are oriented at one of the symmetric pretilt angle
directions, as in FIG. 3B. The alignment layer 15 preferably
includes polysiloxane based material or PVCN-F. In this case, the
irradiation direction of the second UV light forms acute angle with
one of two symmetric pretilt angle directions.
[0031] FIGS. 5A and 5B illustrate a second embodiment of the
present invention. In the figure, unpolarized UV light(wavelength
.lambda.=365 nm) 210 irradiates alignment layer 15 coated on the
substrate 16 at an angle .theta..sub.2 to the normal direction of
the surface of the substrate 16. Although unpolarized UV light is
used in this embodiment, the non-linearly polarized UV light, which
means that the light is circularly or elliptically polarized, or
the light does not polarized can be used either. .theta..sub.2 is
preferably in the range of
0.degree.<.theta..sub.2.ltoreq.60.degree.. After the initial
irradiation shown in FIG. 5A, the molecules of alignment layer 15
are set or oriented with a large number of one sided pretilt angle
directions, while the magnitude of the pretilt angles formed by
each of these directions with the surface is substantially the
same. After the second irradiation shown in FIG. 5B, however, only
one of the pretilt angle directions will be selected.
[0032] Thereafter, when linearly polarized UV light 220 irradiates
the alignment layer 15 at a perpendicular angle, as shown in FIG.
5B, only the pretilt angle direction perpendicular to the
polarization direction of this UV light is selected, so that the
desired pretilt angle direction can be obtained. Furthermore, the
size or magnitude of the pretilt angle produced in the alignment
layer 15 varies depending upon the amount of UV energy absorbed, as
noted above with respect to FIG. 4.
[0033] FIGS. 6A and 6B illustrate a third embodiment of the present
invention. As shown in FIG. 6A, unpolarized UV light 230 irradiates
alignment layer 15 at an angle .theta..sub.3 to the normal
direction of the surface of the substrate, where the .theta..sub.3
is in the range of 0.degree.<.theta..sub.3.ltoreq.60.degree..
Thereafter, linearly polarized UV light 240 irradiates alignment
layer 15 again at an angle .theta..sub.4, as shown in FIG. 6B,
where the .theta..sub.4 is in the range of
0.degree.<.theta..sub.4.ltoreq.60.degree..
[0034] The resulting orientations of the molecules of alignment
layer 15 after the steps shown in FIGS. 6A and 6B is similar to
that of FIGS. 5A and 5B, respectively. Namely, after the
irradiation shown in FIG. 6A, the molecules of the alignment layer
15 are oriented at a large number of one sided pretilt angle
directions, as in FIG. 5A. Moreover, as in FIG. 5B, only one of
these directions is selected after the second irradiation shown in
FIG. 5B. The irradiation direction of the second UV light forms
acute angle with the pretilt angle directions by first irradiation.
In this embodiment, non-linearly polarized UV light, including
circularly polarized, elliptically polarized, and unpolarized UV
light, can be used instead of unpolarized UV light. By using
non-linearly polarized UV light, the method becomes simplified
compared with the conventional method using linearly polarized UV
light.
[0035] A fourth embodiment of the present invention is shown in
FIGS. 7A and 7B. As shown in FIG. 7A, linearly polarized light 250
irradiates alignment layer 15 at an angle .theta..sub.5,
0.degree.<.theta..sub.5.- ltoreq.60.degree., relative to the
normal of the surfaces of alignment layer 15 to orient the
molecules of alignment layer 15 at first and second pretilt angle
directions, similar to that shown in FIG. 3A. One of these
directions is then selected by irradiating alignment layer 15 at an
angle .theta..sub.6, 0.degree.<.theta..sub.5.ltoreq.60.degree.,
with non-linearly polarized UV light, specially unpolarized UV
light 260, such that all the molecules of alignment layer 15 are
oriented at one of the first and second pretilt angle directions,
as in FIG. 7B. In this embodiment, the irradiation direction of the
second UV light forms acute angle with one of the first and second
pretilt angle directions.
[0036] In aforementioned methods according to the present
invention, the size of the pretilt angle and the two symmetric
pretilt angle directions are determined by an initial exposing an
alignment layer including a polysiloxane based material or PVCN-F
to UV light. One of these pretilt angles is then selected by a
second exposure to UV light. Accordingly, the pretilt angle can be
controlled easily.
[0037] While the invention has been described in its preferred
embodiments, this should not be construed as limitation on the
scope of the present invention. Accordingly, the scope of the
present invention should be determined not by the embodiment
illustrated, but by the appended claims and their legal
equivalents.
* * * * *