U.S. patent application number 11/742221 was filed with the patent office on 2007-08-30 for liquid crystal display including compensation film.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Yun Jang, Kyeong-Hyeon KIM, Jang-Kun Song.
Application Number | 20070200988 11/742221 |
Document ID | / |
Family ID | 32822539 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070200988 |
Kind Code |
A1 |
KIM; Kyeong-Hyeon ; et
al. |
August 30, 2007 |
LIQUID CRYSTAL DISPLAY INCLUDING COMPENSATION FILM
Abstract
A liquid crystal display is provided, which includes: a first
panel; a second panel facing the first panel; a liquid crystal
layer interposed between the first panel and the second panel; a
biaxial compensation film disposed on an outer surface of the first
panel; a first polarizing film disposed on an outer surface of the
biaxial compensation film; a C-plate uniaxial compensator disposed
on an outer surface of the second panel and having a horizontal
retardation lower than about 10 nm; and a second polarizing film
disposed on an outer surface of the C-plate uniaxial
compensator.
Inventors: |
KIM; Kyeong-Hyeon;
(Yongin-city, KR) ; Jang; Yun; (Yongin-city,
KR) ; Song; Jang-Kun; (Seoul, KR) |
Correspondence
Address: |
MACPHERSON KWOK CHEN & HEID LLP
2033 GATEWAY PLACE
SUITE 400
SAN JOSE
CA
95110
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
32822539 |
Appl. No.: |
11/742221 |
Filed: |
April 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10745940 |
Dec 23, 2003 |
|
|
|
11742221 |
Apr 30, 2007 |
|
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Current U.S.
Class: |
349/119 |
Current CPC
Class: |
G02F 1/133634
20130101 |
Class at
Publication: |
349/119 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2002 |
KR |
2002-0083710 |
Claims
1. A liquid crystal display comprising: a first panel; a second
panel facing the first panel; a liquid crystal layer interposed
between the first panel and the second panel; a biaxial
compensation film disposed on an outer surface of the first panel;
a first polarizing film disposed on an outer surface of the biaxial
compensation film; a C-plate uniaxial compensator disposed on an
outer surface of the second panel and having a horizontal
retardation lower than about 10 nm; and a second polarizing film
disposed on an outer surface of the C-plate uniaxial compensator,
wherein the C-plate uniaxial compensator comprises a TAC film and
the TAC film has a vertical retardation ranging from about 45 nm to
about 55 nm.
2-31. (canceled)
32. The liquid crystal display of claim 1, wherein the TAC film has
a slow axis parallel to an absorption axis of the second polarizing
film, and the biaxial compensation film has a horizontal
retardation ranging from about 43 nm to about 73 nm and a vertical
retardation ranging from about 95 nm to about 135 nm.
33. The liquid crystal display of claim 1, wherein the TAC film has
a slow axis perpendicular to an absorption axis of the second
polarizing film, and the biaxial compensation film has a horizontal
retardation ranging from about 35 nm to about 65 nm and a vertical
retardation ranging from about 95 nm to about 135 nm.
34. A liquid crystal display comprising: a first panel; a second
panel facing the first panel; a liquid crystal layer interposed
between the first panel and the second panel; a biaxial
compensation film disposed on an outer surface of the first panel;
a first polarizing film disposed on an outer surface of the biaxial
compensation film; a C-plate uniaxial compensator disposed on an
outer surface of the second panel and having a horizontal
retardation lower than about 10 nm; and a second polarizing film
disposed on an outer surface of the C-plate uniaxial compensator,
wherein the C-plate uniaxial compensator comprises a TAC film and
the TAC film has a vertical retardation ranging from about 55 nm to
about 65 nm.
35. The liquid crystal display of claim 34, wherein the TAC film
has a slow axis parallel to an absorption axis of the second
polarizing film, and the biaxial compensation film has a horizontal
retardation ranging from about 50 nm to about 80 nm and a vertical
retardation ranging from about 85 nm to about 125 nm.
36. The liquid crystal display of claim 34, wherein the TAC film
has a slow axis perpendicular to an absorption axis of the second
polarizing film, and the biaxial compensation film has a horizontal
retardation ranging from about 35 nm to about 65 nm and a vertical
retardation ranging from about 85 nm to about 125 nm.
37. A liquid crystal display comprising: a first panel; a second
panel facing the first panel; a liquid crystal layer interposed
between the first panel and the second panel; a biaxial
compensation film disposed on an outer surface of the first panel;
a first polarizing film disposed on an outer surface of the biaxial
compensation film; a C-plate uniaxial compensator disposed on an
outer surface of the second panel and having a horizontal
retardation lower than about 10 nm; and a second polarizing film
disposed on an outer surface of the C-plate uniaxial compensator,
wherein the C-plate uniaxial compensator comprises two TAC films
and each of the TAC films has a vertical retardation ranging from
about 45 nm to about 55 nm.
38. The liquid crystal display of claim 37, wherein each of the TAC
films has a slow axis parallel to an absorption axis of the second
polarizing film, and the biaxial compensation film has a horizontal
retardation ranging from about 65 nm to about 95 nm and a vertical
retardation ranging from about 42 nm to about 82 nm.
39. The liquid crystal display of claim 37, wherein the TAC films
have slow axes parallel to each other and perpendicular to an
absorption axis of the second polarizing film, and the biaxial
compensation film has a horizontal retardation ranging from about
45 nm to about 75 nm and a vertical retardation ranging from about
42 nm to about 82 nm.
40. The liquid crystal display of claim 37, wherein one of the TAC
films has a slow axis parallel to an absorption axis of the second
polarizing film, the other of the TAC films has a slow axis
perpendicular to the absorption axis of the second polarizing film,
and the biaxial compensation film has a horizontal retardation
ranging from about 55 nm to about 85 nm and a vertical retardation
ranging from about 42 nm to about 82 nm.
41. A liquid crystal display comprising: a first panel; a second
panel facing the first panel; a liquid crystal layer interposed
between the first panel and the second panel; a biaxial
compensation film disposed on an outer surface of the first panel;
a first polarizing film disposed on an outer surface of the biaxial
compensation film; a C-plate uniaxial compensator disposed on an
outer surface of the second panel and having a horizontal
retardation lower than about 10 nm; and a second polarizing film
disposed on an outer surface of the C-plate uniaxial compensator,
wherein the C-plate uniaxial compensator comprises two TAC films
and each of the TAC films has a vertical retardation ranging from
about 55 nm to about 65 nm.
42. The liquid crystal display of claim 41, wherein each of the TAC
films has a slow axis parallel to an absorption axis of the second
polarizing film, and the biaxial compensation film has a horizontal
retardation ranging from about 80 nm to about 110 nm and a vertical
retardation ranging from about 20 nm to about 60 nm.
43. The liquid crystal display of claim 41, wherein the TAC films
have slow axes parallel to each other and perpendicular to an
absorption axis of the second polarizing film, and the biaxial
compensation film has a horizontal retardation ranging from about
55 nm to about 85 nm and a vertical retardation ranging from about
20 nm to about 60 nm.
44. The liquid crystal display of claim 41, wherein one of the TAC
films has a slow axis parallel to an absorption axis of the second
polarizing film, the other of the TAC films has a slow axis
perpendicular to the absorption axis of the second polarizing film,
and the biaxial compensation film has a horizontal retardation
ranging from about 65 nm to about 95 nm and a vertical retardation
ranging from about 20 nm to about 60 nm.
Description
BACKGROUND OF THE INVENTION
[0001] (a) Field of the Invention
[0002] The present invention relates to a liquid crystal display,
and in particular, to a liquid crystal display including a
compensation film.
[0003] (b) Description of the Related Art
[0004] A liquid crystal display ("LCD") includes upper and lower
panels having field-generating electrodes, a liquid crystal (LC)
layer interposed therebetween, and a pair of polarizing films
attached on outer surfaces of the panels. An electric field is
generated in the LC layer by applying electric voltages to the
field-generating electrodes. The intensity of the electric field is
adjusted to control orientations of LC molecules, which determine a
polarization of light passing through the LC layer, and the
polarizing films convert the polarization of the light into the
transmittance of the light, thereby displaying desired images.
[0005] A typical LCD includes a common electrode provided on a
panel and a plurality of pixel electrodes provided on another
panel. The common electrode and the pixel electrode generate
electric field for re-arranging LC molecules to control the
transmittance of light passing through the panels. The LCD further
includes a plurality of thin film transistors (TFTs) for switching
voltages applied to the pixel electrodes.
[0006] Among the LCDs, a vertically aligned mode LCD aligning the
LC molecules vertical to the panels and including crossed
polarizers are increasingly preferred because of its high contrast
ratio and wide viewing angle.
[0007] The LCD has a problem of light leakage from a side view,
which deteriorates lateral visibility and narrows lateral viewing
angle. The lateral light leakage may be caused by two reasons.
[0008] First, although there is no retardation from a front view
since light path from the front view coincides with optic axis of
the vertically aligned LC layer, the light path from the side view
is offset from the optic axis and this results in the retardation
and the change of the light polarization to yield light leakage.
Second, although the light from the front view experiences crossed
polarization axes, the light from the side view experiences
obliquely intersecting polarization axes to yield light
leakage.
[0009] Although the light leakage may be reduced by using
compensation films (or retardation films), the compensation films
are very expensive to increase the manufacturing cost of the
LCD.
SUMMARY OF THE INVENTION
[0010] A liquid crystal display is provided, which includes: a
first panel; a second panel facing the first panel; a liquid
crystal layer interposed between the first panel and the second
panel; a biaxial compensation film disposed on an outer surface of
the first panel; a first polarizing film disposed on an outer
surface of the biaxial compensation film; a C-plate uniaxial
compensator disposed on an outer surface of the second panel and
having a horizontal retardation lower than about 10 nm; and a
second polarizing film disposed on an outer surface of the C-plate
uniaxial compensator.
[0011] Each of the first and the second polarizing films may
include a polarizing layer and a pair of protective layers,
preferably including TAC having a vertical retardation ranging from
about 45 nm to about 65 nm, attached on both surfaces of the
polarizing layer.
[0012] The biaxial compensation film has a vertical retardation
(R.sub.th(c-plate)) and the C-plate uniaxial compensator has a
horizontal retardation R.sub.0(biaxial) and a vertical retardation
R.sub.th(biaxial), which preferably satisfy:
R.sub.0(biaxial)=[0.0028.times.(R.sub.th(c-plate)).sup.2-0.00833.times.R.-
sub.th(c-plate)+50].+-.15 nm; and
R.sub.th(biaxial)=[-0.0007.times.(R.sub.th(c-plate)).sup.2-0.9583.times.R-
.sub.th(c-plate)+1659 .+-.20 nm.
[0013] The C-plate uniaxial compensator includes one or two TAC
films.
[0014] The TAC film has a vertical retardation ranging from about
45 nm to about 55 nm or from about 55 nm to about 65 nm.
[0015] For the liquid crystal display including one TAC film having
a vertical retardation ranging from about 45 nm to about 55 run,
the biaxial compensation film preferably has a horizontal
retardation ranging from about 43 nm to about 73 nm and a vertical
retardation ranging from about 95 nm to about 135 nm when the TAC
film has a slow axis parallel to an absorption axis of the second
polarizing film, while the biaxial compensation film preferably has
a horizontal retardation ranging from about 35 nm to about 65 nm
and a vertical retardation ranging from about 95 nm to about 135 nm
when the TAC film has a slow axis perpendicular to an absorption
axis of the second polarizing film.
[0016] For the liquid crystal display including one TAC film having
a vertical retardation ranging from about 55 nm to about 65 nm, the
biaxial compensation film preferably has a horizontal retardation
ranging from about 50 nm to about 80 nm and a vertical retardation
ranging from about 85 nm to about 125 nm when the TAC film has a
slow axis parallel to an absorption axis of the second polarizing
film, the biaxial compensation film has a horizontal retardation
ranging from about 35 nm to about 65 nm and a vertical retardation
ranging from about 85 nm to about 125 nm when the TAC film has a
slow axis perpendicular to an absorption axis of the second
polarizing film.
[0017] For the liquid crystal display including two TAC films
having a vertical retardation ranging from about 45 nm to about 55
nm, the biaxial compensation film preferably has a horizontal
retardation ranging from about 65 nm to about 95 nm and a vertical
retardation ranging from about 42 nm to about 82 nm, the biaxial
compensation film preferably has a horizontal retardation ranging
from about 45 nm to about 75 nm and a vertical retardation ranging
from about 42 nm to about 82 nm when each of the TAC films has a
slow axis parallel to an absorption axis of the second polarizing
film, when the TAC films have slow axes parallel to each other and
perpendicular to an absorption axis of the second polarizing film,
and the biaxial compensation film preferably has a-horizontal
retardation ranging from about 55 nm to about 85 nm and a vertical
retardation ranging from about 42 nm to about 82 nm when one of the
TAC films has a slow axis parallel to an absorption axis of the
second polarizing film and the other of the TAC films has a slow
axis perpendicular to the absorption axis of the second polarizing
film.
[0018] For the liquid crystal display including two TAC films
having a vertical retardation ranging from about 55 nm to about 65
nm, the biaxial compensation film preferably has a horizontal
retardation ranging from about 80 nm to about 110 nm and a vertical
retardation ranging from about 20 nm to about 60 nm when each of
the TAC films has a slow axis parallel to an absorption axis of the
second polarizing film, the biaxial compensation film preferably
has a horizontal retardation ranging from about 55 nm to about 85
nm and a vertical retardation ranging from about 20 nm to about 60
nm when the TAC films have slow axes parallel to each other and
perpendicular to an absorption axis of the second polarizing film,
and the biaxial compensation film preferably has a horizontal
retardation ranging from about 65 nm to about 95 nm and a vertical
retardation ranging from about 20 nm to about 60 nm when one of the
TAC films has a slow axis parallel to an absorption axis of the
second polarizing film and the other of the TAC films has a slow
axis perpendicular to the absorption axis of the second polarizing
film.
[0019] The first polarizing film may include a polarizing layer and
a light recycling layer combined with the polarizing layer.
[0020] The first polarizing film serves as a polarizer and the
second polarizing film serves as an analyzer, or vice versa.
[0021] One of the first and the second panels includes a plurality
of pixel electrodes and a plurality of thin film transistors
connected to the pixel electrodes.
[0022] The liquid crystal layer may have a homeotropic alignment,
and the first and the second panels may include first and second
electrodes, respectively, for generating an electric field
rearranging molecules in the liquid crystal layer. At least one of
the first and the second electrodes may have a cutout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will become more apparent by
describing embodiments thereof in detail with reference to the
accompanying drawings in which:
[0024] FIG. 1 is a sectional view of an LCD according to an
embodiment of the present invention;
[0025] FIG. 2 is a graph illustrating phase retardations of a
biaxial compensation film as function of a vertical phase
retardation of a C-plate uniaxial compensation film;
[0026] FIG. 3 is a graph showing a contrast ratio (C/R) along a
diagonal direction as function of a viewing angle for various
cases; and
[0027] FIG. 4 is a graph showing an x color coordinate of a black
state LCD as function of viewing angle for various cases.
DETAILED DESCRIPTION OF EMBODIMENTS
[0028] 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. The present
invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth
herein.
[0029] In the drawings, the thickness of layers, films and regions
are exaggerated for clarity. Like numerals refer to like elements
throughout. It will be understood that when an element such as a
layer, film, region or substrate is referred to as being "on"
another element, it can be directly on the other element or
intervening elements may also be present In contrast, when an
element is referred to as being "directly on" another element,
there are no intervening elements present.
[0030] Now, liquid crystal displays according to embodiments of the
present invention will be described with reference to the
accompanying drawings.
[0031] FIG. 1 is a sectional view of an LCD according to an
embodiment of the present invention.
[0032] Referring to FIG. 1, an LCD according an embodiment of the
present invention includes a pair of panels 1 and 2 facing each
other and separated from each other with a predetermined gap, a
liquid crystal (LC) layer 3 filled in the gap between the two
panels 1 and 2, a pair of polarizing films including a polarizer 10
and an analyzer 20 disposed on outer surfaces on the panels 1 and
2, and a pair of phase compensation films (or retardation films) 14
and 24 disposed between the panels 1 and 2 and the polarizing films
10 and 20.
[0033] The panel 1 includes a substrate preferably made of
transparent glass, a plurality of gate lines (not shown), a
plurality of data lines (not shown), an array of thin film
transistors (TFTs) (not shown) connected to the gate lines and the
data lines, and an array of pixel electrodes (not shown) connected
to the TFTs. The TFTs transmit data voltages from the data lines in
response to gate signals from the gate lines.
[0034] The panel 2 includes a substrate (not shown) preferably made
of transparent glass, a black matrix (not shown) having a plurality
of openings facing the pixel electrodes, an array of color filters
(not shown) facing the pixel electrodes, and a common electrode
(not shown) preferably made of transparent conductive material such
as indium tin oxide (ITO) and indium zinc oxide (IZO). However, the
black matrix, the color filters, and/or the common electrode may be
provided on the panel 1.
[0035] LC molecules in the LC layer 3 are aligned vertical (or
homeotropical) to the surface of the panels 1 and 2.
[0036] The pixel electrodes and/or the common electrode may have at
least one cutout (not shown) for determining the tilt directions of
the LC molecules.
[0037] The exemplary configurations of the panels 1 and 2 and the
LC layer 3 are illustrated in US Patent Application Publication No.
2002/0145695 A1, which is incorporated in this specification by
reference.
[0038] Each polarizing film 10 or 20 includes a polarizing layer 12
or 22 preferably made of polyvinyl alcohol (PVA) and a pair of
protective layers 13 and 15 or 13 and 25 preferably made of
triacetyl-cellulose (TAC) and attached on both surfaces of the
polarizing layer 12 or 22. The polarizing film 10 or 20 may further
include an anti-glare or anti-reflective layer attached on one of
the protective layers 13 and 15 or 13 and 25.
[0039] The polarizer film 10 may further include a light recycling
layer (not shown) combined with the polarizing layer 12. The light
recycling layer preferably includes a commercially available Dual
Brightness Enhancement Film-Diffuse (DBEF-D), Bepol, or Nipocs.
[0040] The polarizing films 10 and 20 preferably have crossed
polarization axes.
[0041] The compensation film 14 preferably includes a C-plate
uniaxial compensation film or a quasi C-plate uniaxial compensation
film, while the compensation film 24 preferably includes a biaxial
compensation film.
[0042] The compensation film 14 is preferably made of cheap and
reliable TAC and it may have a double-layered structure including
two layers adhering to each other with an adhesive or including two
laminated layers. However, the compensation film 14 may be made of
another material instead of TAC.
[0043] A horizontal phase retardation R.sub.0 and a vertical phase
retardation R.sub.th of a retardation film are defined as
R.sub.0=(n.sub.x-n.sub.y).times.d and
R.sub.th=(n.sub.z-(n.sub.x+n.sub.y)/2).times.d, where d is the
thickness of a retardation film. Since a C plate has refractive
dielectric anisotropy satisfying n.sub.x=n.sub.y>n.sub.z when
the z axis is defined to be normal to the surface of the film and
n.sub.x, n.sub.y and n.sub.z are refractive indices in x, y and z
directions, respectively, the horizontal phase retardation R.sub.0
of the C plate is zero. In the meantime, a quasi C plate satisfies
a relation R.sub.0<10<<R.sub.th. A TAC film, which has a
horizontal and vertical phase retardations R.sub.0 and R.sub.th
satisfying the relations R.sub.0<10 and 5R.sub.0<R.sub.th, is
a quasi C plate.
[0044] The biaxial compensation film 24 satisfies
n.sub.x.noteq.n.sub.y.noteq.n.sub.z. The vertical and the
horizontal phase retardations R.sub.th and R.sub.0 of the biaxial
compensation film 24 are determined depending on the vertical phase
retardation R.sub.th of the compensation film 14 such that:
R.sub.0(biaxial)=[0.0028.times.(R.sub.th(c-plate)).sup.2-0.00833.times.R.-
sub.th(c-plate)+50].+-.15 nm (1)
R.sub.th(biaxial)=[-0.0007.times.(R.sub.th(c-plate)).sup.2-0.9583.times.R-
.sub.th(c-plate)+165].+-.20 nm (2)
[0045] Relations 1 and 2, which are obtained from experiments, give
a viewing angle equal to or larger than about 85 degrees in a
direction making an angle of about 45 degrees with the polarization
axes of the polarizing films 10 and 20.
[0046] FIG. 2 is a graph illustrating the phase retardations of the
biaxial compensation film as function of the vertical phase
retardation of the C-plate uniaxial compensation film as shown in
Relations 1 and 2.
[0047] The positions of the C-plate uniaxial compensation film 14
and the biaxial compensation film 24 can be exchanged.
[0048] TABLE 1 illustrates some cases of combinations of the
retardations of the biaxial film and the C-plate, which are easily
obtained. TABLE-US-00001 TABLE 1 Case 1 Case 2 Case 3 Case 4
R.sub.th(c-plate) 50 60 100 120 R.sub.0(biaxial) 50 60 70 80
R.sub.th(biaxial) 115 105 62 40
[0049] The values 50, 60, 100 and 120 of the vertical phase
retardation R.sub.th of the C-plate are chosen because they are
easily realized by using commercially available TAC films. There
are two kinds of the commercially available TAC films, one having a
thickness of 80 microns and a vertical phase retardation R.sub.th
of 50 nm and the other having a thickness of 100 microns and a
vertical phase retardation R.sub.th of 60 nm. The retardations of
100 nm and 120 nm are obtained by using a pair of the TAC films.
Here, the TAC film with the retardation of about 50 nm practically
gives the retardation in the range from about 45 nm to about 55 nm,
and similarly, the TAC film the retardation of about 60 nm
practically gives the retardation in the range from about 55 nm to
about 65 nm.
[0050] As described above, the TAC film is not an ideal C-plate
uniaxial film, and it gives a horizontal retardation R.sub.0 of
about 0-10 nm. Considering the non-zero horizontal retardation of
the TAC films, the horizontal phase retardation R.sub.0 shown in
TABLE 1 is varied. It is considered when slow axes of the TAC films
are parallel to and perpendicular to an absorption axis of the
polarizer adjacent thereto.
[0051] TABLE 2 illustrates the case that the slow axes of the TAC
films are parallel to the absorption axis of the polarizer. Since
the non-vanishing horizontal retardations R.sub.0 of the TAC films
deteriorate the viewing angle, it is preferable that the horizontal
retardation R.sub.0 of the biaxial film is increased.
TABLE-US-00002 TABLE 2 Easy Axes of TAC//Absorption Axis of
Polarizer One 50 nm One 60 nm Two 50 nm Two 60 nm TAC TAC TAC TAC
R.sub.th(c-plate) 50 60 100 120 R.sub.0(biaxial) 58 65 80 95
R.sub.th(biaxial) 115 105 62 40
[0052] The parallelism between the slow axes of the TAC films and
the absorption axis of the polarizer facilitates the manufacturing
of the polarizer. In detail, since the TAC film is rolled along its
slow axis and the polarizing film is rolled along its absorption
axis, the two rolls are aligned in parallel and unrolled to be
laminated or attached such that the slow axis of the TAC film and
the absorption axis of the polarizer are aligned parallel.
[0053] Next, the case that at least one of the slow axes of the TAC
films and the absorption axis of the polarizer are perpendicular to
each other is described.
[0054] TABLE 3 illustrates the case with one sheet of TAC film.
Since the non-vanishing horizontal retardation R.sub.0 of the TAC
film improves the viewing angle, it is preferable that the
horizontal retardation R.sub.0 of the biaxial film is decreased.
TABLE-US-00003 TABLE 3 Slow Axis of TAC .perp. Absorption Axis of
Polarizer One 50 nm TAC One 60 nm TAC R.sub.th(c-plate) 50 60
R.sub.0(biaxial) 50 50 R.sub.th(biaxial) 115 105
[0055] TABLE 3 shows that a sheet of 60 nm TAC film matches with a
biaxial compensation film of commercially available Arton with
R.sub.0=50 and R.sub.th=105 or S-cina R.sub.0=50 and
R.sub.th=90.
[0056] TABLE 4 illustrates the case with two sheets of TAC films.
TABLE-US-00004 TABLE 4 Two Two 50 nm TAC 60 nm TAC Two Two
Absorption Axis// Absorption Axis// 50 nm TAC 60 nm TAC TAC1 .perp.
TAC1 .perp. Absorption Axis .perp. Absorption Axis .perp. TAC2 TAC2
TAC1//TAC2 TAC1//TAC2 R.sub.th(c-plate) 100 120 100 120
R.sub.0(biaxial) 70 80 60 70 R.sub.th(biaxial) 62 40 62 40
[0057] In TABLE 4, "Absorption Axis//TAC1.perp.TAC2" means that the
slow axis of 10 one of the TAC films is parallel to the absorption
axis of the polarizer, while the slow axis of the other of the TAC
films is perpendicular to the absorption axis of the polarizer, and
"Absorption Axis.perp.TAC1//TAC2" means that the slow axes of the
TAC films are perpendicular to the absorption axis of the
polarizer.
[0058] TABLE 5 summarizes TABLEs 1 to 4. TABLE-US-00005 TABLE 5
C-plate TAC Biaxial Type Relation R.sub.0 R.sub.th Material Case 1
One Abs. Axis//TAC 58 .+-. 15 115 .+-. 20 Arton, Case 2 50 nm Abs.
Axis.perp.TAC 50 .+-. 15 115 .+-. 20 S-cina, TAC RAC, Case 3 One
Abs. Axis//TAC 65 .+-. 15 105 .+-. 20 etc. Case 4 60 nm Abs.
Axis.perp.TAC 50 .+-. 15 105 .+-. 20 TAC Case 5 Two Abs. Axis// 80
.+-. 15 62 .+-. 20 50 nm TAC1// TAC TAC2 Case 6 Abs. Axis .perp. 60
.+-. 15 62 .+-. 20 TAC1//TAC2 Case 7 Abs. Axis// 70 .+-. 15 62 .+-.
20 TAC1// .perp.TAC2 Case 8 Two Abs. Axis// 95 .+-. 15 40 .+-. 20
60 nm TAC1// TAC TAC2 Case 9 Abs. Axis .perp. 70 .+-. 15 40 .+-. 20
TAC1//TAC2 Case 10 Abs. Axis// 80 .+-. 15 40 .+-. 20 TAC1
.perp.TAC2
[0059] In TABLE 5, "Abs. Axis//TAC1//TAC2" means that the slow axes
of the TAC films are parallel to the absorption axis of the
polarizer, "Abs. Axis.perp.TAC1//TAC2" means that the slow axes of
one of the TAC films are perpendicular to the absorption axis of
the polarizer, and "Abs. Axis//TAC1.perp.TAC2" means that the slow
axis of one of the TAC films is parallel to the absorption axis of
the polarizer, while the slow axis of the other of the TAC films is
perpendicular to the absorption axis of the polarizer.
[0060] It is noted that TAC shown in TABLE 5 does not include TAC
used as the protection layers 13, 15, 23 and 25. Each of the TAC
layers 13, 15, 23 and 25 may have a vertical retardation R.sub.th
ranging from about 45 nm to about 65 nm and a horizontal
retardation R.sub.0 ranging from about zero to about 10 nm. The TAC
layers 13, 15, 23 and 25 have slow axes parallel to the absorption
axes of the respective polarizing films 10 and 20.
[0061] Among the above-arranged ten cases, Cases 1-4 with one TAC
film are advantageous in the manufacturing cost, and Cases 3 and 4
exhibit a viewing angle and color characteristics better than or at
least as good as cases using two biaxial films. In particular, Case
4 shows a viewing angle and color characteristics better than the
cases using two biaxial films.
[0062] FIG. 3 is a graph showing a contrast ratio (C/R) along a
diagonal direction as function of a viewing angle for Cases 3 and 4
and a conventional case using two biaxial films.
[0063] Referring to FIG. 3, Case 4 shows the contrast ratio (C/R)
higher than the conventional case for all angles from zero degrees
to about 80 degrees. Although the contrast ratio of Case 3 is
higher than the conventional one in some angular ranges and it is
lower than the conventional one in other angular ranges, the
contrast ratio of Case 3 is equal to or higher than about 10 for
all angular ranges, which is comparable with the conventional
case.
[0064] FIG. 4 is a graph showing an x color coordinate of a black
state LCD as function of viewing angle for Cases 3 and 4 and a
conventional case using two biaxial films.
[0065] As shown in FIG. 4, Cases 3 and 4 exhibit higher x color
coordinates in a black state than the conventional case for all
angular ranges. This means that Cases 3 and 4 reduce bluish
phenomenon such that the black states in Cases 3 and 4 is closer to
a perfect black than that in the conventional art.
[0066] The manufacturing cost of the compensation films for the
cases using one C-plate uniaxial film and one biaxial film is
cheaper than that for the cases using two biaxial films by about
1/4 to about 2/3.
[0067] While the present invention has been described in detail
with reference to the preferred embodiments, those skilled in the
art will appreciate that various modifications and substitutions
can be made thereto without departing from the spirit and scope of
the present invention as set forth in the appended claims.
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