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United States Patent |
5,793,458
|
VanderPloeg
,   et al.
|
August 11, 1998
|
Normally white twisted nematic LCD with positive uniaxial and negative
biaxial retarders
Abstract
A normally white twisted nematic liquid crystal display is provided for
outputting improved viewing characteristics which are defined by high
contrast ratios and reduced inversion. The display includes both positive
and negative retardation films, the negative films being biaxial and
defined by n.sub.x >n.sub.y >n.sub.z in certain embodiments where the "z"
direction is substantially perpendicular to the film plane and the "x" and
"y" directions are substantially parallel to the film plane. By providing
the positive and biaxial negative retarders with specific retardation
values and/or ratios, improved viewing characteristics are provided.
According to other embodiments, a positive and a negative (uniaxial or
biaxial) retarder may be provided on only one side of the liquid crystal
layer.
Inventors:
|
VanderPloeg; John A. (Highland, MI);
Xu; Gang (Northville, MI);
Abileah; Adiel (Farmington Hill, MI)
|
Assignee:
|
OIS Optical Imaging Systems, Inc. (Northville, MI)
|
Appl. No.:
|
768502 |
Filed:
|
December 18, 1996 |
Intern'l Class: |
G02F 001/133.5 |
Field of Search: |
349/118,119,120
|
References Cited
U.S. Patent Documents
4889412 | Dec., 1989 | Clerc et al. | 359/73.
|
5071997 | Dec., 1991 | Harris | 528/353.
|
5138474 | Aug., 1992 | Arakawa | 359/73.
|
5184236 | Feb., 1993 | Miyashita et al. | 349/119.
|
5189538 | Feb., 1993 | Arakawa | 359/73.
|
5213852 | May., 1993 | Arakawa et al. | 428/1.
|
5291323 | Mar., 1994 | Ohnishi et al. | 359/73.
|
5344916 | Sep., 1994 | Harris et al. | 359/73.
|
5406396 | Apr., 1995 | Akatsuka et al. | 359/73.
|
5430565 | Jul., 1995 | Yamanouchi et al. | 359/73.
|
5430566 | Jul., 1995 | Sakaya et al. | 359/73.
|
5504603 | Apr., 1996 | Winker et al. | 359/73.
|
5570214 | Oct., 1996 | Abileah et al.
| |
5576861 | Nov., 1996 | Abileah et al.
| |
5594568 | Jan., 1997 | Abileah et al. | 349/120.
|
Foreign Patent Documents |
4-56802 | Feb., 1992 | JP.
| |
4-97322 | Mar., 1992 | JP.
| |
4311903 | Nov., 1992 | JP.
| |
5257014 | Oct., 1993 | JP.
| |
6-130227 | May., 1994 | JP.
| |
Primary Examiner: Gross; Anita Pellman
Attorney, Agent or Firm: Myers Liniak & Berenato
Parent Case Text
This application is a continuation-in-part (CIP) of Ser. No. 08/559,275,
filed Nov. 15, 1995 (now U.S. Pat. No. 5,657,140), which is a CIP of Ser.
No. 08/167,652, filed Dec. 15, 1993 (now U.S. Pat. No. 5,570,214), and
this application is also a CIP of 08/711,797, filed Sep. 10, 1996, which
is a continuation of 08/167,652, filed Dec. 15, 1993, (now U.S. Pat. No.
5,570,214), the disclosures of which are all hereby incorporated herein by
reference.
Claims
We claim:
1. A normally white twisted nematic liquid crystal display comprising:
a liquid crystal layer for twisting at least one normally incident visible
wavelength of light from about 80.degree. to 100.degree. as it passes
therethrough when said liquid crystal layer is in substantially the
"off-state" thereby defining a twisted nematic display;
a pair of negative biaxial retarders sandwiching said liquid crystal layer
therebetween, wherein n.sub.x >n.sub.y >n.sub.z for each of said negative
biaxial retarders;
a pair of positive retarders sandwiching both said liquid crystal layer and
said negative biaxial retarders therebetween; and
wherein retardation value d.multidot.(n.sub.x -n.sub.z) of each of said
negative biaxial retarders is from about 70 to 130 nm, retardation value
d.multidot.(n.sub.x-n.sub.y) of each of the negative biaxial retarders is
from about 3 to 20 nm, and the retardation value of each of said positive
retarders is from about 70 to 200 nm.
2. The display of claim 1, wherein each of said positive retarders is
uniaxial and the retardation value of each of said positive retarders is
from about 120 to 160 nm.
3. The display of claim 1, wherein the thickness of said liquid crystal
layer is from about 4.8 to 6.0 .mu.m and the .delta.n of said liquid
crystal is from about 0.075 to 0.095 at room temperature, and wherein the
display outputs contrast ratios to the viewer of at least about 30:1 or 30
at horizontal angles along the 0.degree. vertical axis of about
.+-.60.degree. when a driving voltage of from about 5.0 to 6.0 volts is
applied to said liquid crystal layer.
4. The display of claim 3, wherein said display outputs contrast ratios of
at least about 30:1 or 30 at vertical viewing angles along the 0.degree.
horizontal viewing axis between and including about -7.degree. and
+40.degree., when about 5.0 to 6.0 driving volts are applied.
5. The display of claim 1, wherein the n.sub.x index direction of one of
said negative biaxial retarders is oriented from about
80.degree.-100.degree. relative to the n.sub.x index direction of the
other of said negative biaxial retarders.
6. A normally white twisted nematic liquid crystal display comprising:
a liquid crystal layer for twisting at least one normally incident visible
wavelength of light from about 80.degree. to 100.degree. as it passes
therethrough when said liquid crystal layer is in substantially the
"off-state" thereby defining a twisted nematic display;
a pair of negative biaxial retarders sandwiching said liquid crystal layer
therebetween, wherein n.sub.x >n.sub.y >n.sub.z for each of said negative
biaxial retarders;
a pair of positive retarders sandwiching said liquid crystal layer
therebetween; and
wherein the ratio of the positive retardation value d.multidot..delta.n of
the positive retarder to the retardation value d.multidot.(n.sub.x
-n.sub.z) of the negative biaxial retarder on at least one side of said
liquid crystal layer is from about 1:1 to 2:1.
7. The display of claim 6, wherein the retardation value
d.multidot.(n.sub.x -n.sub.z) of each of said negative biaxial retarders
is from about 100 to 200 nm and the retardation value d.multidot..delta.n
of each of said positive retarders is from about 80 to 200 nm.
8. A method of making a twisted nematic liquid crystal display comprising
the steps of:
providing a pair of biaxial negative retarders defined by n.sub.x >n.sub.y
>n.sub.z ;
providing a pair of positive uniaxial retarders;
disposing a twisted nematic liquid crystal layer between said pair of
negative biaxial retarders, and between said pair of positive retarders;
and
disposing said pair of negative biaxial retarders between said pair of
positive retarders so that the resulting display outputs contrast ratios
of at least about 30:1 or 30 at horizontal viewing angles along the
0.degree. vertical viewing axis of about .+-.50.degree..
9. The method of claim 8, further comprising the step of providing
retardation values for said retarders so that the display outputs contrast
ratios of at least about 80:1 or 80 along the 0.degree. vertical viewing
axis at horizontal viewing angles of about .+-.30.degree..
10. The display of claim 9, further comprising the steps of providing each
of said negative biaxial retarders with retardation values
d.multidot.(n.sub.x -n.sub.y) of from about 3 to 20 nm and each of said
positive retarders with retardation values d.multidot..delta.n of from
about 80 to 200 nm.
11. A twisted nematic liquid crystal display comprising:
a twisted nematic liquid crystal layer for twisting at least one visible
wavelength of normally incident light emitted from a backlight from about
80.degree. to 100.degree. when in the off-state;
a positive retarder having a retardation value of from about 80 to 200 nm;
and
a negative biaxial retarder defined by n.sub.x >n.sub.y >n.sub.z having a
retardation value d.multidot.(n.sub.x -n.sub.z) of from about 50 to 150
nm, said negative biaxial retarder being disposed between said liquid
crystal layer and said positive retarder.
12. A twisted nematic liquid crystal display comprising:
a twisted nematic liquid crystal layer for twisting at least one visible
wavelength of normally incident light emitted from a backlight from about
80.degree. to 100.degree. when the liquid crystal layer is in the
off-state;
a positive retarder; and
a negative biaxial retarder defined by n.sub.x >n.sub.y >n.sub.z, said
negative biaxial retarder having a retardation value d.multidot.(n.sub.x
-n.sub.z) of from about 100 to 200 nm.
13. The twisted nematic liquid crystal display of claim 12, wherein said
positive retarder has a retardation value of from about 80 to 200 nm; and
the display exhibits a maximum contrast ratio of at least about 300 when
about 5.5 driving volts are applied in the on-state.
14. The twisted nematic liquid crystal display of claim 13, wherein the
display is of the normally white type, and wherein the negative biaxial
retarder is disposed between said liquid crystal layer and said positive
retarder.
15. A normally white twisted nematic liquid crystal display comprising:
a liquid crystal layer for twisting at least one normally incident visible
wavelength of light as it passes therethrough when said liquid crystal
layer is in substantially the off-state so as to define a twisted nematic
normally white display;
a negative biaxial retarder means located on one side of said liquid
crystal layer and having a retardation value d.multidot.(n.sub.x -n.sub.z)
of from about 70-300 nm and a retardation value d.multidot.(n.sub.x
-n.sub.y) of from about 1-40 nm;
a positive retarder means on the same side of said liquid crystal layer as
said negative biaxial retarder means, said positive retarder means having
a retardation value of from about 80-200 nm; and
wherein said negative biaxial retarder means is defined by n.sub.x >n.sub.y
>n.sub.z.
16. The display of claim 15, wherein positive retarder means is uniaxial
and said liquid crystal layer twists at least one normally incident
visible wavelength of light from about 80.degree.-100.degree. as it passes
therethrough when said liquid crystal layer is in substantially the
off-state;
wherein said biaxial retarder means is made up of at least two separate
retarder sheets laminated together;
wherein said biaxial retarder means has a retardation value
d.multidot.(n.sub.x -n.sub.z) of from about 70 to 260 nm; and
wherein said negative biaxial retarder means and said positive retarder
means are on the rear side of said liquid crystal layer so as to reduce
reflections off of the front of the display.
17. The display of claim 16, wherein said negative biaxial retarder means
has a retardation value d.multidot.(n.sub.x -n.sub.z) of from about 70-130
nm and a retardation value d.multidot.(n.sub.x -n.sub.y) of from about
3-20 nm.
18. A normally white LCD comprising:
a liquid crystal layer;
a positive uniaxial retarder on a first side of said liquid crystal layer;
a biaxial retarder on said first side of said liquid crystal layer; and
an air gap defining an isotropic layer, said air gap located on said first
side of said liquid crystal layer, so as to improve viewing
characteristics of the display.
19. A normally white twisted nematic LCD comprising:
a twisted nematic liquid crystal layer for twisting at least one normally
incident wavelength of light from about 80.degree.-100.degree. as it
passes therethrough when said liquid crystal layer is in substantially the
off-state thereby defining a twisted nematic display; and
first and second retardation members oriented relative to one another so
that the LCD outputs a contrast ratio of at least about 300:1 at a
predetermined viewing angle when approximately 5.5 volts are applied
across said liquid crystal layer in the on-state.
Description
NORMALLY WHITE TWISTED NEMATIC LCD WITH POSITIVE UNIAXIAL AND NEGATIVE
BIAXIAL RETARDERS
This invention relates to a normally white (NW) liquid crystal display
(LCD) including positive uniaxial and negative biaxial (or uniaxial)
retardation films. More particularly, this invention relates to a NW
twisted nematic (TN) LCD including positive and negative retardation films
(birefringent films) of specific values, arranged in a manner so as to
provide improved contrast, wherein the negative retardation films are of a
biaxial nature in certain embodiments.
RELATED APPLICATIONS
This application is related to commonly owned U.S. Pat. No. 5,576,861,
filed Jun. 8, 1994; U.S. Ser. No. 08/235,691, filed Apr. 29, 1994; U.S.
Ser. No. 08/559,275, filed Nov. 15, 1995; U.S. Ser. No. 08/711,797, filed
Sep. 10, 1996, and U.S. Pat. No. 5,570,214, filed Dec. 15, 1993, the
entire disclosures of which are hereby incorporated herein by reference.
Each of these commonly owned applications and/or patents relates to a
liquid crystal display with specific retarder values, contrast ratios,
and/or retarder positions or orientations.
BACKGROUND OF THE INVENTION
Informational data in liquid crystal displays (LCDS) is presented in the
form of a matrix array of rows and columns of numerals or characters (i.e.
pixels) which are generated by a number of segmented electrodes arranged
in a matrix pattern. The segments are connected by individual leads to
driving electronics which apply a voltage to the appropriate combination
of segments and adjacent liquid crystal (LC) material in order to display
the desired data and/or information by controlling the light transmitted
through the liquid crystal (LC) material.
Contrast ratio (CR) is one of the most important attributes considered in
determining the quality of both normally white (NW) and normally black
(NB) LCDs. The contrast ratio (CR) in a normally white display is
determined in low ambient conditions by dividing the "off-state" light
transmission (high intensity white light) by the "on-state" or darkened
transmitted intensity. For example, if the "off-state" transmission is 200
fL at a particular viewing angle and the "on-state" transmission is 5 fL
at the same viewing angle, then the display's contrast ratio at that
particular viewing angle is 40 (or 40:1) for the particular "on-state"
driving voltage utilized.
Accordingly, in normally white LCDs, a significant factor adversely
limiting contrast ratio is the amount of light which leaks through the
display in the darkened or "on-state." In a similar manner, in normally
black displays, a significant factor limiting the contrast ratio
achievable is the amount of light which leaks through the display in the
darkened or "off-state." The higher and more uniform the contrast ratio of
a particular display over a wide range of viewing angles, the better the
LCD in most applications.
Normally black (NB) twisted nematic displays typically have better contrast
ratio contour curves or characteristics then do their counterpart NW
displays (i.e. the NB image can often be seen better at large or wide
viewing angles). However, NB displays are optically different than NW
displays and are much more difficult to manufacture due to their high
dependence on the cell gap or thickness "d" of the liquid crystal layer as
well as on the temperature of the liquid crystal (LC) material itself.
Accordingly, a long-felt need in the art has been the ability to construct
a normally white display with high contrast ratios over a large range of
viewing angles, rather than having to resort to the more difficult and
expensive to manufacture NB displays in order to achieve these
characteristics.
What is often needed in NW LCDs is an optical compensating or retarding
element(s), i.e. retardation film(s), which introduces a phase delay that
restores the original polarization state of the light, thus allowing the
light to be substantially blocked by the output polarizer (analyzer) in
the "on-state." Optical compensating elements or retarders are known in
the art and are disclosed, for example, in U.S. Pat. Nos. 5,184,236;
5,189,538; 5,406,396; 4,889,412; 5,344,916; 5,196,953; 5,138,474; and
5,071,997.
The disclosures of 08/559,275; and U.S. Pat. Nos. 5,570,214 and 5,576,861
(all incorporated herein by reference) in their respective "Background"
sections illustrate and discuss contrast ratio, and driving voltage versus
intensity (fL), graphs of prior art NW displays which are less than
desirable. Prior art NW LCD viewing characteristics are problematic in
that, for example, their contrast ratios are limited both horizontally and
vertically (and are often non-symmetric), and their gray level performance
lacks consistency.
Gray level performance, and the corresponding amount of inversion, are also
important in determining the quality of an LCD. Conventional active matrix
liquid crystal displays (AMLCDs) typically utilize anywhere from about 8
to 64 different driving voltages. These different driving voltages are
generally referred to as "gray level" voltages. The intensity of light
transmitted through the pixel(s) or display depends upon the driving
voltage utilized. Accordingly, conventional gray level voltages are used
to generate dissimilar shades of color so as to create different colors
and images when, for example, the shades are mixed with one another.
Preferably, the higher the driving voltage in a normally white display, the
lower the intensity (fL) of light transmitted therethrough. The opposite
is true in NB displays. Thus, by utilizing multiple gray level driving
voltages, one can manipulate either a NW or NB LCD to emit desired
intensities and shades of light/color. A gray level voltage V.sub.ON is
generally known as any driving voltage greater than V.sub.th (threshold
voltage) up to about 4.0 to 6.5 volts.
Gray level intensity in an LCD is dependent upon the display's driving
voltage. It is desirable in NW displays to have an intensity versus
driving voltage curve at a given viewing angle wherein the intensity of
light emitted from the display or pixel continually and monotonically
decreases as the driving voltage increases. In other words, it is
desirable to have gray level performance in a NW pixel such that the
transmission intensity (fL) at 6.0 volts is less than that at 5.0 volts,
which is in turn less than that at 4.0 volts, which is less than that at
3.0 volts, which is in turn less than that at 2.0 volts, etc. Such desired
gray level curves across a wide range of view allows the intensity of
light reaching viewers at different viewing angles to be easily and
consistently controlled.
U.S. Pat. Nos. 5,576,861 and 5,570,214 discuss, in their respective
"Background" sections, prior art NW LCDs with inversion problems (e.g.
inversion humps, specifically their transmission versus driving voltage
graphs). As discussed therein, inversion humps are generally undesirable.
A theoretically perfect driving voltage versus intensity (fL) curve for an
NW display would have a decreased intensity (fL) for each increase in gray
level driving voltage at all viewing angles. In contrast to this,
inversion humps represent increase(s) in intensity of radiation emitted
from the LCD or light valve (LV) for a corresponding increase in gray
level driving voltage. Accordingly, it would satisfy a long-felt need in
the art if a normally white TN liquid crystal display could be provided
with no or little inversion and improved contrast ratios over a wide range
of viewing angles.
U.S. Pat. No. 5,344,916 discloses a liquid crystal display including
positive and negative retardation films. The negative uniaxial retarders
(or birefringent films) of the '916 patent have as a characteristic that
n.sub.x =n.sub.y >n.sub.z. The "z" direction or axis is perpendicular to
the plane of the film, while the "x" and "y" axes (of n.sub.x and n.sub.y)
are parallel to the retardation film plane. Thus, the optical axes of the
negative retardation films in the '916 patent are perpendicular to the
film plane. It is noted that n.sub.x, n.sub.y, and n.sub.z are the
respective indices of refraction.
Unfortunately, while use of the negative retardation films of the '916
patent improves contrast over some prior art LCDs, twisted nematic (TN)
displays including same may suffer from less than desirable contrast
ratios at large viewing angles. Pointedly, the disclosure of the '916
patent does not appreciate, suggest, or disclose the use of negative
biaxial and positive retarders together at specified values, ratios,
and/or locations to even further improve viewing characteristics of an LCD
as discussed below by the instant inventors.
U.S. Pat. No. 5,189,538 (see also 5,138,747) discloses a super twisted
nematic (STN) LCD including films having different birefringent values.
Unfortunately, STN LCDs have no real optical correspondence or correlation
to .apprxeq.90.degree. TN LCDs with regard to the behavior of the image
due to retarders. In other words, teachings regarding retarders in STN
devices (e.g. 270.degree. twist) often have little or no relevance with
regard to TN (.apprxeq.90.degree. twist) LCDs due to the substantially
different optical characteristics of STNs.
U.S. Pat. No. 4,889,412 discloses an LCD with electrically controlled
birefringence (ECB) and negative anisotropy. Unfortunately, ECB displays
do not use twisted nematic LC material as does the instant invention.
Again, ECB display teachings are generally unrelated to TN
(.apprxeq.90.degree. twist) displays with regard to retardation teachings
and principles.
U.S. Pat. No. 5,291,323 discloses a liquid crystal display with "positive
and negative compensating films each with its optical axis parallel to the
surface." Unfortunately, the disclosure and teaching of the '323 patent
are unrelated to TN displays such as those of the instant invention, in
that the '323 patent relates to supertwisted (e.g. 240.degree. twist)
LCDs.
The term "rear" when used herein but only as it is used to describe
substrates, polarizers, electrodes, buffing films or zones, and
orientation films means that the described element is on the backlight
side of the liquid crystal material, or in other words, on the side of the
LC material opposite the viewer.
The term "front" when used herein but only as it is used to describe
substrates, polarizers, electrodes, buffing films or zones and orientation
films means that the described element is located on the viewer side of
the liquid crystal material.
The actual LCDs and light valves made and/or tested herein included a
liquid crystal material with a birefringent value (.delta.n) of 0.084 at
room temperature, Model No. ZLI-4718 obtained from Merck, unless specified
otherwise.
The term "retardation value" as used herein for uniaxial retarders means
"d.multidot..delta.n" of the retardation film or plate, where "d" is the
film or plate thickness and ".delta.n" is the film birefringence (i.e.
difference in indices of refraction).
The term "interior" when used herein to describe a surface or side of an
element (or an element itself), means that closest to the liquid crystal
material.
The term "light valve" as used herein means a liquid crystal display
including a rear linear polarizer, a rear transparent substrate, a rear
continuous pixel electrode, a rear orientation film, an LC layer, a front
orientation film, a front continuous pixel electrode, a front substrate,
and a front polarizer (i.e. without the presence of color filters and
active matrix driving circuitry such as TFTs). Such a light valve may also
include retardation film(s) disposed on either side of the LC layer as
described with respect to each example and embodiment herein. In other
words, a "light valve" (LV) may be referred to as one giant pixel without
segmented electrodes.
For all circular contrast ratio graphs herein, e.g. FIGS. 11(d), 12, 15(b),
16, 17, 18, 21(b), 22(b), 23, 24(b), 25, 26(b), 27(b), 28, 29, 30(b), 31,
32(b), 33(b), and 34(b); "EZContrast" equipment available from Eldim of
Caen, France (ID #204F) was used to develop these graphs. This equipment
includes a system for measuring Luminance and Contrast versus viewing
angle (incident and azimuth angle), utilizing 14 bits A/D conversion to
give luminance measurements from 1/10 to 8,000 cd/m.sup.2, with an
accuracy of 3% and a fidelity of 1%. A temperature regulated CCD sensor
and photopic response (specially designed lenses) are part of this
commerically available Eldim system and corresponding software. The
measurement device of this Eldim system includes a specially designed
large viewing angle optical device having a numerical aperture of 0.86.
The Eldim software is Windows.TM. 3.1 based, running on any 486 and above
PC, supporting DDE interface with other programs.
It is apparent from the above that there exists a need in the art for a
normally white liquid crystal display wherein the viewing zone of the
display has both high contrast ratios and little or no inversion over a
wide range of viewing angles.
This invention will now be described with respect to certain embodiments
thereof, accompanied by certain illustrations wherein:
SUMMARY OF THE INVENTION
Generally speaking this invention fulfills the above-described needs in the
art by providing a normally white twisted nematic liquid crystal display
comprising:
a liquid crystal layer for twisting at least one normally incident visible
wavelength of light from about 80.degree. to 100.degree. as it passes
therethrough when the liquid crystal layer is in substantially the
"off-state" thereby defining a normally white twisted nematic display;
a pair of negative biaxial retarders sandwiching the liquid crystal layer
therebetween, wherein n.sub.x >n.sub.y >n.sub.z for each of the negative
biaxial retarders;
a pair of positive retarders; and
wherein the retardation value d.multidot.(n.sub.x -n.sub.z) of each of the
negative biaxial retarders is from about 70 to 130 nm, and the retardation
value d.multidot.(n.sub.x -n.sub.y) of each of the negative biaxial
retarders is from about 1 to 20 nm, and the retardation value
d.multidot..delta.n of each of the two positive retarders is from about 70
to 200 nm.
This invention further fulfills the above-described needs in the art by
providing a method of making a twisted nematic LCD comprising the steps
of:
providing a pair of negative biaxial retarders each defined by n.sub.x
>n.sub.y >n.sub.z ;
providing a pair of positive uniaxial retarders;
disposing a twisted nematic liquid crystal layer between the pair of
negative biaxial retarders, and also between the pair of positive uniaxial
retarders; and
disposing the pair of negative biaxial retarders between the pair of
positive retarders so that the resulting display outputs contrast ratios
of at least about 30 at horizontal viewing angles along the 0.degree.
vertical axis between about .+-.40.degree..
According to certain embodiments, an isotropic air gap may be provided to
improve viewing characteristics.
According to still further embodiments, positive and negative (uniaxial or
biaxial) retarders may be provided on only one side (e.g. the rear) of the
LC layer.
This invention will now be described with respect to certain embodiments
thereof, along with reference to the accompanying illustrations, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the optical components of a NW twisted
nematic LCD including a pair of positive retarders and a pair of biaxial
negative retarders according to an embodiment of this invention.
FIG. 2 illustrates the angular relationship between the respective axes
shown in FIG. 1 according to one embodiment of this invention, as viewed
from the point of view of the viewer.
FIG. 3 illustrates the angular relationship between the axes shown in FIG.
1 according to another embodiment of this invention, again, from the point
of view of the viewer.
FIG. 4(a) is a side cross-sectional view of the FIG. 1 LCD according to
certain embodiments of this invention.
FIG. 4(b) is a side cross-sectional view of the FIG. 1 LCD according to
another embodiment of this invention.
FIG. 5(a) illustrates the arrangement of the respective axes of the Example
1 TFT RGB AMLCD as viewed from the point of view of the viewer (i.e. from
the front).
FIG. 5(b) is a white light contrast ratio graph of the normally white RGB
TFT AMLCD made and tested in Example 1, when 5.5 driving volts were
applied across the LC material in the on-state.
FIG. 6 is a transmission (fL) versus driving voltage (volts) curve of
vertical angles along the 0.degree. horizontal axis, for the TFT AMLCD
tested in Example 1.
FIG. 7 is a transmission versus driving voltage graph for horizontal angles
along the 0.degree. vertical viewing axis, for the TFT AMLCD tested in
Example 1.
FIG. 8(a) illustrates the arrangement of the respective axes in the TFT RGB
AMLCD of Example 2, as viewed from the front of the display (i.e. as by
the viewer).
FIG. 8(b) is a white light contrast ratio graph of the NW TFT RGB AMLCD
that was made and tested in Example 2, when 5.5 driving volts were applied
across the liquid crystal material in the on-state.
FIG. 9 is a transmission versus driving voltage graph for vertical angles
along the 0.degree. horizontal viewing axis of the TFT AMLCD tested in
Example 2.
FIG. 10 is a transmission versus driving voltage graph for horizontal
angles along the 0.degree. vertical viewing axis for the TFT AMLCD tested
in Example 2.
FIG. 11(a) is a side cross-sectional view of a normally white AMLCD in
accordance with FIG. 1, according to another embodiment of this invention,
wherein air gaps are provided between the respective transparent
substrates and their adjacent retarder laminates.
FIG. 11(b) is a side cross-sectional view of an AMLCD in accordance with
FIG. 1, according to yet another embodiment of this invention where the
display is provided with air gaps between the retarders and the liquid
crystal material on each side of the LC.
FIG. 11(c) illustrates the angular relation between the axes of the TFT RGB
AMLCD made and tested in Example 3.
FIG. 11(d) is a white light contrast ratio graph of the Example 3 normally
white TFT RGB AMLCD as shown in FIGS. 1, 11(a), and 11(c), where
d.multidot.(n.sub.x -n.sub.z)=100 nm for each of the two negative biaxial
retarders, and d.multidot..delta.n=140 nm for each of the positive
uniaxial retarders.
FIG. 12 is a white light contrast ratio graph of the light valve (LV) made
and tested in Example 4 in accordance with FIGS. 1, 2, and 11(a) when the
cell gap of LC layer 9 was 5.2 .mu.m, 5.5 driving volts were applied
across the LC in the on-state, and d.multidot.(n.sub.x -n.sub.z) was 75 nm
for each of the negative biaxial retarders.
FIG. 13 is a schematic diagram of the optical components of a NW twisted
nematic LCD according to another embodiment of this invention, wherein a
positive uniaxial retarder and a negative biaxial retarder are provided on
only one side of the LC material.
FIG. 14 illustrates the angular relationship between the respective optical
axes of the FIG. 13 embodiments.
FIG. 15(a) illustrates the orientation of the axes of the NW RGB TFT AMLCD
made and tested in Example 5 in accordance with FIG. 13.
FIG. 15(b) is white light contrast ratio graph of the Example 5 RGB TFT
AMLCD, in accordance with FIGS. 13 and 15(a), when the cell gap was 5.7
.mu.m, 5.5 driving volts were applied in the on-state, d.multidot..delta.n
was 140 nm for the sole positive uniaxial retarder, and
d.multidot.(n.sub.x -n.sub.z) was 100 nm for the sole biaxial negative
retarder.
FIG. 16 is a white light contrast ratio graph of the NW LV made and tested
in Example 6, in accordance with FIG. 1, where the cell gap was 5.20
.mu.m, 5.5 driving volts were applied, d.multidot..delta.n for each
positive uniaxial retarder was 140 nm, d.multidot.(n.sub.x -n.sub.z) was
100 nm for each of the negative biaxial retarders, and both biaxial
negative retarders were rotated symmetrically 180.degree. with respect to
the FIG. 2 embodiment.
FIG. 17 is a white light contrast ratio graph of the NW LV made and tested
in Example 7, where the cell gap was 5.20 .mu.m, 5.5 driving volts were
applied, d.multidot.(n.sub.x -n.sub.z) was 100 nm for each of the biaxial
negative retarders, d.multidot..delta.n was 140 nm for each of the
positive uniaxial retarders, and the n.sub.x axis of each of the biaxial
retarders was aligned parallel to the adjacent polarizer transmission
axis.
FIG. 18 is a white light contrast ratio graph of the Example 8 NW LV which
was similar to that of FIGS. 16-17, except that the same negative biaxial
retarders were rotated such that their respective n.sub.x optical axes
were aligned substantially perpendicular to their adjacent polarizer
transmission axes in this Example.
FIG. 19 is a schematic diagram of the optical components of a NW twisted
nematic LCD according to another embodiment of this invention, wherein a
pair of negative uniaxial retarders were provided on a single side of the
LC material.
FIG. 20 is a schematic diagram illustrating the optical components of a
normally white TN LCD according to another embodiment of this invention
wherein a negative uniaxial retarder and a positive uniaxial retarder were
provided on each side of the LC layer.
FIG. 21(a) illustrates, from the front of the display, the arrangement of
the axes of the NW light valve of Example 9.
FIG. 21(b) is a white light contrast ratio graph of the NW LV made and
tested in Example 9, in accordance with FIG. 20, where each of the two
negative uniaxial retarders had a retardation value of d.multidot..delta.n
100 nm, the cell gap was 5.20 .mu.m, and 5.5 driving volts were applied to
the LC in the on-state.
FIG. 22(a) illustrates the angular relationship, from the front of the
display, between the axes of the NW light valves of Examples 10 and 11.
FIG. 22(b) is a white light contrast ratio graph of the NW LV made and
tested in Example 10 in accordance with FIGS. 19 and 22(a), wherein the
two uniaxial negative retarders each had a retardation value of about 100
nm and the cell gap "d" was 5.20 .mu.m.
FIG. 23 is a white light contrast ratio graph of the NW light valve made
and tested in Example 11, in accordance with FIGS. 19 and 22(a) and
similar to the FIG. 22 light valve, except that each negative uniaxial
retarder had a retardation value of about 120 nm.
FIG. 24(a) illustrates the angular relationship of the axes in the NW LVs
of Examples 12-13, made in accordance with FIG. 1.
FIG. 24(b) is a white light contrast ratio graph of the normally white LV
made and tested in Example 12, in accordance with FIGS. 1 and 24(a), where
the cell gap was 5.75 .mu.m, 6.0 driving volts were applied in the
on-state, and d.multidot.(n.sub.x -n.sub.z)=100 nm for each of the
negative biaxial retarders.
FIG. 25 is a white light contrast ratio graph of the NW LV made and tested
in Example 13, in accordance with FIGS. 1 and 24(a), where the cell gap
was 4.75 .mu.m, 6.0 driving volts were applied, and d.multidot.(n.sub.x
-n.sub.z)=100 nm for each of the negative biaxial retarders.
FIG. 26(a) illustrates the relationship between the axes of the Example 14
NW light valve.
FIG. 26(b) is white light contrast ratio graph of the NW LV made and tested
in Example 14, in accordance with FIGS. 1 and 26(a), where the cell gap
was 5.20 .mu.m, 5.5 driving volts were applied in the on-state, and
d.multidot.(n.sub.x -n.sub.z)=100 nm for the rear negative biaxial
retarder and 75 nm for the front negative biaxial retarder.
FIG. 27(a) illustrates the angular relationship of the axes of the NW light
valves of Examples 15 and 16.
FIG. 27(b) is a white light contrast ratio graph for the normally white
light valve made and tested in Example 15, in accordance with FIG. 27(a),
where the cell gap was 5.20 .mu.m, 5.5 driving volts were applied in the
on-state, and d.multidot.(n.sub.x -n.sub.z)=117 nm for each of the two
negative biaxial retarders.
FIG. 28 is a white light contrast ratio graph in accordance with FIGS. 1
and 27(a), for the normally white LV of Example 16, where the cell gap was
5.20 .mu.m, 5.5 driving volts were applied in the on-state, and
d.multidot.(n.sub.x -n.sub.z)=100 nm for each of the two negative biaxial
retarders.
FIG. 29 is a white light contrast ratio graph of the NW light valve made
and tested in Example 17, in accordance with FIG. 1, where the cell gap
was 5.20 .mu.m, 5.5 driving volts were applied in the on-state, and
d.multidot.(n.sub.x -n.sub.z)=100 nm for each of the two negative biaxial
retarders.
FIG. 30(a) illustrates the angular relationship from the point of view of
the viewer, of the axes of the NW light valves of Examples 18 and 19.
FIG. 30(b) is a white light contrast ratio graph of the NW light valve made
and tested in Example 18, in accordance with FIGS. 1 and 30(a), where the
cell gap was 5.20 .mu.m, 5.5 driving volts were applied in the on-state,
and d.multidot.(n.sub.x -n.sub.z)=100 nm for the rear negative biaxial
retarder and 83 nm for the front biaxial negative retarder.
FIG. 31 is a white light contrast ratio graph of the normally white LV made
and tested in Example 19, in accordance with FIGS. 1 and 30(a), where the
cell gap was 5.20 .mu.m, 5.5 driving volts were applied in the on-state,
and d.multidot.(n.sub.x -n.sub.z)=83 nm for each of the two negative
biaxial retarders.
FIG. 32(a) illustrates the relationship between the axes for the NW light
valve made and tested in Example 20.
FIG. 32(b) is a white light contrast ratio graph of the NW light valve of
Example 20, in accordance with FIGS. 1 and 32(a) where the cell gap was
5.20 .mu.m, 5.5 driving volts were applied, and d.multidot.(n.sub.x
-n.sub.z)=83 nm for the rear negative biaxial retarder and 100 nm for the
front biaxial negative retarder.
FIG. 33(a) illustrates the angular relationship between the axes of the
Example 21 NW light valve.
FIG. 33(b) is a white light contrast ratio graph of the NW light valve of
Example 21, in accordance with FIGS. 1 and 33(a), where the cell gap was
5.20 .mu.m, 5.5 driving volts were applied in the on-state, and
d.multidot.(n.sub.x -n.sub.z)=83 nm for the rear biaxial negative retarder
and 100 nm for the front biaxial negative retarder.
FIG. 34(a) illustrates the angular relationship between the axes of the
Example 22 NW light valve.
FIG. 34(b) is a white light contrast ratio graph of the NW light valve of
Example 22, in accordance with FIG. 13, where the cell gap was 5.20 .mu.m,
5.5 driving volts were applied in the on-state, and d.multidot.(n.sub.x
-n.sub.z)=a total of about 285 nm for a stack of laminated negative
biaxial retarders on the rear side of the LC layer. No front retarders
were provided in Example 22.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THIS INVENTION
Referring now more particularly to the accompanying drawings in which like
reference numerals indicate like parts throughout the several views.
FIG. 1 is an exploded schematic view of the optical components and their
respective orientations of a twisted nematic NW LCD according to a first
embodiment of this invention, this LCD being a light valve (LV) or an
AMLCD having a matrix array of pixels and colored (e.g. RGB or RGBW)
subpixels according to certain embodiments. As shown, this display
includes from the rear forward toward viewer 1, conventional backlight 3,
rear or light-entrance linear polarizer 5, rear positive uniaxial retarder
2, rear negative biaxial retarder 4 (including indices of refraction
n.sub.x, n.sub.y, and n.sub.z), rear buffing or orientation film 7,
twisted nematic (TN) liquid crystal layer 9, front buffing or orientation
film 11, front negative biaxial retarder 13 (including indices of
refraction n.sub.x, n.sub.y, and n.sub.z), front positive uniaxial
retarder 14, and finally front or light-exit linear polarizer 15.
Glass substrates are located on both sides of liquid crystal layer 9 so as
to be disposed between the respective orientation films and their adjacent
negative biaxial retarders. Driving electrodes are disposed between the
substantially transparent substrates and their adjacent orientation
layers. A key to our invention is the surprise finding that when the
positive and negative retarders referenced above are within a particular
retardation value(s) range and/or ratio, or are arranged in predetermined
positions in the LCD, improved viewing characteristics of the display
result. For example, the viewing angle of the LCD is wider/larger, while
inversion is lessened.
Retarders 4 and 13 are said to be "negative" as n.sub.z is less than both
n.sub.x and n.sub.y. Indices of refraction n.sub.x and n.sub.y, while
being co-planar, are oriented at a 90.degree. angle relative to one
another. Index of refraction n.sub.z is perpendicular to the plane defined
by the n.sub.x and n.sub.y directions. Retarders 4 and 13 each have a
retardation value d.multidot.(n.sub.x -n.sub.z)=85 nm, and a value
d.multidot.(n.sub.x -n.sub.y)=8 nm, in certain embodiments.
Backlight 3 is conventional in nature and emits substantially collimated,
or alternatively diffused, light toward the display panel. Backlight 3 may
be, for example, the backlighting assembly disclosed in commonly owned
U.S. Pat. No. 5,161,041, the disclosure of which is hereby incorporated
herein by reference. Other conventional high intensity substantially
collimated or diffuse backlight assemblies may also be used.
Rear and front polarizers, 5 and 15 respectively, are linear in nature
according to certain embodiments of this invention, and their respective
linear transmission axes P.sub.R and P.sub.F are oriented substantially
perpendicular to one another (.+-.about 10.degree.) so that LCDs of
different embodiments of this invention are of the normally white (NW)
type. Therefore, when a driving voltage (e.g. 0.0 or 0.1 V) below the
threshold voltage V.sub.th is applied by the electrodes across liquid
crystal (LC) layer 9, transmission axes P.sub.R and P.sub.F of polarizers
5 and 15, respectively, are oriented such that the light emitted from
backlight 3 proceeds through and is linearly polarized in direction
P.sub.R by rear polarizer 5, is then twisted (e.g. from about 80.degree.
to 100.degree. ) by twisted nematic LC layer 9, and finally exits front
polarizer or analyzer 15 via transmission axis P.sub.F thus reaching
viewer 1. The light reaches viewer 1 because its polarization direction
upon reaching front polarizer 15 is similar to the direction defined by
transmission axis P.sub.F. Thus, a NW display or pixel to which a voltage
less than V.sub.th is applied is said to be in the "off-state" and appears
white (or colored if color filters are present) to the viewer. These
conventional polarizers 5 and 15 are commercially available from, for
example, Nitto Denko America, as #G1220DUN or 102555-7.
However, when a substantial driving voltage (i.e. greater than the
threshold voltage V.sub.th) is applied across selected NW pixels of the
matrix array, the light transmitted through rear polarizer 5 is not
twisted as much by LC layer 9 and thus is at least partially blocked by
front polarizer 15 due to the fact that the polarization direction of
light reaching the interior surface of front polarizer 15 is substantially
perpendicular (or otherwise non-aligned) to transmission axis P.sub.F,
thereby resulting in substantially no, or a lessor amount of, light
reaching viewer 1 by way of the selected pixel(s) to which the substantial
driving voltage (e.g. 4-6.5 volts) is applied. Thus, driven pixels in the
LCD appear darkened to viewer 1, these pixels said to be in the "on-state.
"
In certain embodiments of this invention, transmission axis P.sub.R of rear
polarizer 5 and transmission axis P.sub.F of front polarizer 15 are
oriented in a manner substantially perpendicular (.+-.about 10.degree.) to
one another as shown in FIGS. 1-3 so as to define a NW twisted nematic
(TN) cell. However, polarizers 5 and 15 may alternatively be oriented in
other manners which also render the display of the NW type.
Rear and front orientation or buffing films 7 and 11, respectively, are
each from about 250-500 .ANG. thick, and may be made of a substantially
transparent polyimide as is known in the art. Rear orientation film 7 is
conventionally buffed or oriented in direction B.sub.R as shown in FIGS.
1-3. Likewise, front orientation film 11 is conventionally buffed in
direction B.sub.F. Buffing directions B.sub.R and B.sub.F are oriented
substantially perpendicular (.+-.about 10.degree.) to one another so as to
allow the molecules of liquid crystal layer 9, when in the off or
non-driven state, to be twisted from about 80.degree. to 100.degree.,
preferably about 90.degree.. The term "off-state" means that a voltage
below the threshold voltage (V.sub.th) is applied across LC layer 9.
Liquid crystal layer 9 has a thickness "d" of from about 4.0 to 6.5 .mu.m
according to certain embodiments, preferably from about 5.0 to 6.0 .mu.m.
Layer 9 has a birefringent value .delta.n of from about 0.08 to 0.10
according to certain embodiments, preferably from about 0.084 to 0.086.
The voltage applied across LC layer 9 determines the degree of twisting of
the liquid crystal molecules and thus dictates the polarization direction
of light emitted from the front or viewer side of layer 9. In turn, the
polarization direction of light reaching front polarizer 15 dictates the
amount of light permitted to pass therethrough via axis P.sub.F and reach
viewer 1, in that the closer aligned transmission axis P.sub.F and the
polarization direction of light reaching polarizer 15, the more light that
is allowed to pass and reach viewer 1. While the application of a voltage
>V.sub.th to layer 9 causes the LC molecules to substantially align
vertically (to a degree that is a function of the voltage applied), the LC
molecules do not completely stand on end or become perfectly aligned in
the vertical direction as is known in the art. This gives rise to the need
for retardation (or birefringent) films.
Positively birefringent uniaxial retardation plates or films 2 and 14 (e.g.
A-plates) with optical axes R.sub.R and R.sub.F respectively (i.e. slow
axes) in this embodiment (FIGS. 1-2) are disposed on opposing sides of
layer 9 thereby sandwiching LC layer 9 therebetween. According to certain
alternative embodiments, positive retarders 2 and 14 may be positive
uniaxial tilted retarders of the type disclosed in co-assigned Ser. No.
08/383,200 or U.S. Pat. No. 5,504,603, the disclosures of which are hereby
incorporated herein by reference. Slightly biaxial positive retarders will
also suffice for films 2 and 14 in certain alternative embodiments.
Retardation films 2 and 14, in said certain embodiments of this invention,
when positively birefringent and uniaxial in nature, may be obtained from,
for example, Nitto Corporation, Japan, or Nitto Denko America,
Incorporated, New Brunswick, N.J. as Model No. NRF-140 (i.e. 140 nm
positive uniaxial retarders).
It is noted that U.S. Pat. No. 5,570,214 (parent hereto) discloses positive
uniaxial retarders, each having a retardation value d.multidot..delta.n of
from about 80 to 200 nm, more preferably from about 100-160 nm, and most
preferably from about 120 to 140 nm.
Negative biaxial retarders 4 and 13 are defined by the characteristic
n.sub.x >n.sub.y >n.sub.z where n.sub.x, n.sub.y, and n.sub.z are
respective indices of refraction, and the "z" direction is substantially
perpendicular to the film plane while the "x" and "y" directions are
substantially parallel to the film plane as shown in FIG. 1. According to
certain embodiments of this invention, the n.sub.x index direction of
retarder 4 differs from the n.sub.x index direction of retarder 13 by from
about 80.degree.-100.degree., preferably about 90.degree., while their
respective planes are parallel. Negative biaxial retarders 4 and 13 may
also be obtained from Nitto Denko America or Nitto Corporation (Japan).
According to certain embodiments, the positive and negative retarders, and
the polarizers, may all be separate sheets, although they alternatively
may be all integrally formed or laminated together with a known laminating
material according to other embodiments. Thus, films 2, 4, and 5, (and/or
films 13-15) , for example, may be laminated together to form a single
laminated sheet having a positive retarder, a negative biaxial retarder,
and a polarizer.
FIGS. 2 and 3 illustrate the relationship between the FIG. 1 axes according
to different embodiments of this invention, from the point of view of
viewer 1. With reference to FIG. 2, rear transmission axis P.sub.R, rear
optical or slow retarder axis R.sub.R, and front buffing direction B.sub.F
are substantially parallel (.+-.about 10.degree.) to one another, while
rear buffing direction B.sub.R, front polarizer transmission axis P.sub.F,
and front positive retarder axis R.sub.F are also substantially parallel
(.+-.about 10.degree.) to one another thereby causing the display to
output substantially symmetrical viewing characteristics relative to the
"normal" (0.degree. horizintal, 0.degree. vertical) viewing angle. In such
embodiments, axis P.sub.R and direction B.sub.R are substantially
perpendicular to one another as are axis P.sub.F and direction B.sub.F. A
display having such an optical arrangement is said to be "X-buffed." The
term "X-buffed" means that rear polarizer transmission axis P.sub.R is
substantially perpendicular to rear buffing direction B.sub.R, while the
front polarizer transmission axis P.sub.F is substantially perpendicular
to the front buffing direction B.sub.F.
While the FIG. 2 optical configuration of the FIG. 1 NW display illustrates
front retarder axis R.sub.F being substantially parallel to front
transmission axis P.sub.F, and rear retarder axis R.sub.R being
substantially parallel to rear polarizer transmission axis P.sub.R, the
positive retarder optical axes (i.e. the slow axes) of retarders 2 and 14
may be angled from these positions as, for example, shown in the FIG. 3
embodiment.
FIG. 3 illustrates a configuration according to another embodiment of this
invention corresponding to the FIG. 1 display. As shown in FIG. 3, .phi.
may equal from about 1.degree.-10.degree. in either direction. This means,
for example, that front positive retarder optical axis R.sub.F may be
rotated .phi..degree. from axis P.sub.F in the counterclockwise direction
(as viewed from the viewpoint of viewer 1), while rear positive retarder
optical axis R.sub.R of retarder 2 is rotated .phi..degree. in the
clockwise direction relative to rear polarizer transmission axis P.sub.R.
By angling the slow axes of positive retarders 2 and 14 symmetrically in
such a manner that .phi. equals from about 1.degree.-10.degree. (e.g.
3.degree.), the viewing zone of best contrast output by the display is
shiftable in the vertical direction. This is of particular interest, for
example, in avionic cockpit applications when the display's best viewing
zone is needed, not at normal, but at a predetermined vertical viewing
angle with respect thereto (e.g. at an angle +20.degree. vertical of
normal).
The slow axes R.sub.R and R.sub.F of positive retarders 2 and 14 may be
angled .phi. either symmetrically or non-symmetrically with respect to one
another according to certain embodiments of this invention, depending on
the desired viewing characteristics of the display. Angle .phi. for each
positive retarder axis may be adjusted from about 0.degree. to 10.degree.
in either the positive or negative direction (i.e. clockwise or
counterclockwise). More preferably, .phi. may be from about 3.degree. to
8.degree., and most preferably from about 3.degree. to 5.degree. in either
direction. By adjusting .phi. for both (or alternatively only one) of the
positive retarders, the position of the highest contrast viewing zone may
be shifted vertically and the highest contrast areas (i.e. the "eyes" of
the contrast plots) in the viewing zone may be spaced closer or further
apart. This is particularly useful when not only the pilot, but also the
co-pilot view a display within a cockpit.
It has been found that by providing the positive uniaxial and negative
biaxial retarders of this invention with particular retardation or
birefringent values, predetermined positions, and/or retardation value
ratios, improved viewing characteristics (e.g. higher contrast ratios,
wider viewing zones, and/or reduced inversion) of a normally white TN LCD
may be achieved.
According to certain embodiments of this invention, the retardation value
of each of the two positive uniaxial retarders 2 and 14 is from about 70
to 200 nm, more preferably from about 80 nm to 200 nm, even more
preferably from about 120 to 160 nm, and most preferably about 140 nm. In
combination with these positive retarder values, it has been found that
excellent results are achieved when the d.multidot.(n.sub.x -n.sub.z)
birefringent value (retardation value) of each of negative biaxial
retardation films 4 and 13 is from about 50 to 150 nm, more preferably
from about 70 to 130 nm, and most preferably from about 75-110 nm. In
combination with these values, biaxial negative retarders 4 and 13 each
have a retardation value d.multidot.(n.sub.x -n.sub.y) of from about 1 to
40 nm, more preferably from about 3 to 20 nm, and most preferably from
about 6 to 12 nm.
U.S. Pat. No. 5,570,214 (parent hereto) discloses negative biaxial
retarders (n.sub.x >n.sub.y >n.sub.z), each having a retardation value
d.multidot.(n.sub.x -n.sub.z) of from about 100 to 200 nm.
According to a preferred embodiment of this invention, each of rear
positive uniaxial retarder 2 and front positive uniaxial retarder 14 has a
retardation value of about 140 nm while each of rear negative biaxial
retarder 4 and front negative biaxial retarder 13 has a retardation value
d.multidot.(n.sub.x -n.sub.z) of about 100 nm, and a retardation value
d.multidot.(n.sub.x -n.sub.y) of about 12 nm.
According to certain other embodiments, it has been found that improved
viewing characteristics result when the retardation values of the positive
uniaxial and negative biaxial retarders are maintained within a particular
ratio range. The ratio of the positive retardation value of each of
positive retarders 2 and 14 to the negative biaxial retardation value
d.multidot.(n.sub.x -n.sub.z) of each of retarders 4 and 13 is from about
0.8:1 to 3:1 (more preferably from about 1:1 to 2:1) according to certain
embodiments. Even more preferably, the retardation value ratio for the
positive retardation value d.multidot..delta.n to the biaxial retardation
value d.multidot.(n.sub.x -n.sub.z) is from about 1.2:1 to 1.5:1.
The retardation values of each of the like (e.g. positive) retarders need
not be identical, but the ratio range is typically met by both sets of
positive:negative retardation values. The improved viewing characteristics
resulting from maintaining the positive and negative retarder values
within these ratios will be illustrated below with respect to the numerous
examples set forth below.
As shown in FIGS. 1-3, each negative biaxial retarder has two separate
retardation values defined by d.multidot.(n.sub.x -n.sub.z) and
d.multidot.(n.sub.x -n.sub.y) respectively. As illustrated in the FIG. 1-3
embodiments, the "x", or n.sub.x, direction of the front negative biaxial
retarder 13 (i.e. FBR.sub.x) is oriented in a different direction (by
about 90.degree. ) than the corresponding "x", or n.sub.x, direction
(RBR.sub.x) of rear biaxial retarder 4. As illustrated in FIGS. 2-3, the
n.sub.x direction (FBR.sub.x) of front biaxial retarder 13 is oriented at
about 0.degree. (.+-.about 5.degree.), while the n.sub.x direction
(RBR.sub.x) of rear biaxial retarder 4 is oriented about 90.degree.
clockwise therefrom (.+-.about 5.degree.). Thus, rear polarization axis
P.sub.R and buffing direction B.sub.F each approximately bisect the
90.degree. angle defined between the respective n.sub.x directions
RBR.sub.x and FBR.sub.x, of retarders 4 and 13. Likewise, the n.sub.y
directions (RBR.sub.y and FBR.sub.y) of the two negative biaxial retarders
4 and 13 differ from one another by about 90.degree. in a similar manner.
As will be discussed below, directions RBR.sub.x, RBR.sub.y, FBR.sub.x,
and FBR.sub.y may be adjusted according to ceratin alternative embodiments
with the n.sub.y directions always being about 90.degree. from the
corresponding n.sub.x directions in the film plane.
FIG. 4(a) is a side cross-sectional view of a normally white AMLCD or light
valve (LV) corresponding to FIG. 1, according to certain embodiments of
this invention. As illustrated from backlight 3 forward toward viewer 1,
the display includes rear polarizer 5, rear positive retarder 2 (e.g.
A-plate), rear biaxial negative retarder 4, transparent glass or plastic
protective sheet 21, conventional index matching oil layer 23,
substantially transparent glass or plastic substrate 25, rear electrode(s)
27, rear orientation or buffing film 7, twisted nematic liquid crystal
layer 9, front orientation or buffing film 11, front electrode(s) 29 for
applying a voltage across the LC layer in conjunction with electrode(s)
27, front substantially transparent plastic or glass substrate 31, index
matching oil layer 33, transparent plastic or glass protective sheet 35,
front negative biaxial retarder 13, front positive retarder (e.g. A-plate)
14, and finally front polarizer or analyzer 15. According to this FIG.
4(a) embodiment, the two rear retarders 2, 4, rear polarizer 5, and sheet
21 are laminated together to form a single unit and thereafter secured to
rear substrate 25 with index matching oil 23 layer disposed therebetween
so as to ensure that no air gap is present between layers 21 and 25.
Additionally, layers 13, 14, 15, and 35 are laminated together as a single
unit and thereafter applied to the front surface of substrate 31 with
index matching oil layer 33 disposed therebetween. Again, oil layer 33 is
provided so as to ensure that no air gap or non-index matched layer exists
between layers 31 and 35. It will be understood by those of skill in the
art that, in AMLCD embodiments, one of electrodes 27 and 29 represents a
common and continuous electrode which extends across substantially the
entire display area, while the other electrode is divided up into a
plurality of individual pixel electrodes, one per pixel or subpixel. Color
filters (not shown) may also be provided between one of the electrode
layers 27 and 29 and their adjacent substrates, such color filters being
red (R), green (G), and blue (B) (in a triad arrangement) according to
certain embodiments.
FIG. 4(b) is a side cross-sectional view of a normally white display, as
shown in FIG. 1, according to another embodiment of this invention. As
shown in FIG. 4(b) from the rear forward toward viewer 1, this LCD or LV
includes rear glass or plastic substantially transparent cover sheet 41,
laminating adhesive layer 42, rear polarizer 5, laminating adhesive layer
43, rear positive retarder 2, laminating adhesive layer 45, rear negative
biaxial retarder 4, index matching oil layer 23, rear substantially
transparent plastic or glass substrate 25, rear electrode 27, rear
orientation or buffing film 7, twisted nematic LC layer 9 having a
substantially constant thickness "d" across the viewing area of the
display, front orientation or buffing film 11, front electrode 29, front
substantially transparent plastic or glass substrate 31, index matching
oil layer 33, front biaxial negative retarder 13, laminating adhesive
layer 47, front positive retarder 14, laminating adhesive layer 49, front
polarizer 15, laminating adhesive layer 51, and finally front
substantially transparent glass or plastic cover sheet 53. In accordance
with the FIG. 4(b) embodiment, rear cover sheet 41, rear polarizer 5, and
rear retarders 2 and 4 are laminated together via adhesive layers 42, 43,
and 45 so as to form a single unit which is thereafter secured to the rear
surface of substrate 25 with index matching oil layer 23 disposed
therebetween. Likewise, front cover sheet 53, front polarizer 15, and
front retarders 13-14 are laminated together via adhesive layers 47, 49,
and 51 as a single unit and thereafter secured to the front surface of
substrate 31 with index matching oil layer 33 disposed therebetween.
Relative to the FIG. 4(a) embodiment, the cover sheets are located
differently in FIG. 4(b), and conventional laminating adhesive layers (42,
43, 45, 47, 49, and 51) which do not substantially affect optical
characteristics are provided between the laminated sheets. Such adhesive
layers may, of course, also be provided in the FIG. 4(a) embodiment.
FIG. 11(a) illustrates an additional embodiment of this invention wherein
isotropic air gaps 61 are provided on each side of liquid crystal layer 9.
Surprisingly, as will be discussed below relative to certain examples
herein, the provision of air gaps 61 between their adjacent retarders (4
and 13) and LC layer 9 has been found to result in improved viewing
characteristics of the display. The embodiments in accordance with FIGS.
11(a) and 11(b) are similar to those of FIGS. 4(a) and 4(b), respectively,
except that, instead of index matching oil layers, isotropic air gaps 61
are provided.
As shown in FIG. 11(a), front substantially planar air gap 61 is provided
between glass or plastic protective sheet 35 and front substrate 31 while
rear air gap 61 is disposed between the outer surface of rear substrate 25
and rear protective sheet 21. These air gaps 61, in their illustrated
positions, are formed by simply securing (e.g. via clamps or the like) the
laminated product (e.g. 13, 14, 15, and 35 with corresponding laminating
adhesives) to the front side of substrate 31 without any index matching
oil or adhesive layer therebetween. Without the provision of index
matching oil or adhesive between layers 31 and 35, air gap 61, which
represents an isotropic layer, results. The air gap 61 on the rear of the
LC layer 9 is formed in a similar manner. Air gaps 61 in FIG. 11(a) create
an index mismatch between: (i) layers 21 and 25; and (ii) layers 31 and
35. These isotropic layers 61 alter or reflect light rays from backlight 3
to different degrees. In other words, known "S" and "P" waves are
reflected in different manners as they enter, pass through, and exit air
gaps 61 on both sides of the liquid crystal layer. The provision of the
air gaps improves the display's inversion-relation characteristics, and
creates more rounded shoulders in the viewing zone as will be seen below
in certain examples herein.
FIG. 11(b) illustrates an embodiment similar to FIG. 4(b), except that
isotropic air gaps 61 are provided on either side of LC layer 9.
FIGS. 13 and 14 illustrate the optical components of a normally white AMLCD
or LV according to another embodiment of this invention. Unlike the
previous embodiments discussed above, the FIG. 13-14 embodiment is
provided with a positive uniaxial 2 and a negative biaxial 4 retarder on
only one side (e.g. the rear) of liquid crystal layer 9. The two retarders
2 and 4 may be provided on the rear side of the LC layer 9, as shown in
FIG. 13, in order to reduce reflections off of the front of the display.
As illustrated from the rear forward toward viewer 1 in FIG. 13, the
display according to this embodiment includes rear polarizer 5 having
transmission axis P.sub.R, rear positive uniaxial retarder 2 having slow
axis R.sub.R, rear negative biaxial retarder 4 including indices of
refraction n.sub.x, n.sub.y, and n.sub.z, rear orientation layer 7
including buffing direction B.sub.R twisted nematic liquid crystal (LC)
layer 9 having thickness "d", front orientation layer 11 having buffing
direction B.sub.F, and finally front linear analyzer or polarizer 15
having transmission axis P.sub.F. With regard to negative biaxial retarder
4, the direction corresponding to index of refraction n.sub.z is aligned
substantially perpendicular to the film's surface, while the directions
corresponding to indices n.sub.x and n.sub.y are substantially planar to
the surface of film 4. As will be appreciated by those of skill in the
art, the directions corresponding to n.sub.x (RBR.sub.x) and n.sub.y
(RBR.sub.y ) are substantially perpendicular to one another within the
defined plane. Alternatively, the two illustrated retarders 2 and 4 may
instead be located on the front side of LC layer 9 (instead of the rear).
The retardation values of retarders 2 and 4 may be the same as discussed
throughout this disclosure, although, for retarder 4, retardation value
d.multidot.(n.sub.x -n.sub.z) may be from about 70-300 nm, while
d.multidot.(n.sub.x -n.sub.y) may be from about 1 to 40 nm in this
embodiment. One or more negative biaxial retarders may be laminated
together to form retarder 4.
FIG. 14 illustrates the angular relationship between the axes of the FIG.
13 embodiment as viewed from the point of view of viewer 1. As shown, the
rear and front buffing directions are at right angles to one another
.+-.about 10.degree., the front and rear polarizer axes are at right
angles to one another .+-.about 10.degree., the slow axis R.sub.R of
positive retarder 2 is substantially parallel to transmission axis P.sub.R
of rear polarizer 5 .+-.about 10.degree., and the direction (RBR.sub.x)
corresponding to the n.sub.x index of refraction of biaxial retarder 4 is
oriented at approximately a 45.degree. angle with respect to all polarizer
axes, all buffing directions, and the slow axis R.sub.R of retarder 2. In
other words, direction RBR.sub.x of retarder 4 substantially bisects the
approximate 90.degree. angle defined between the polarizer axis directions
according to this embodiment. It will be recognized, however, that the
directional alignment of direction RBR.sub.x may be adjusted in either
direction according to alternative embodiments of this invention as will
be discussed below.
FIG. 19 is an exploded schematic view of the optical components of a NW
display or light valve according to still another embodiment of this
invention. As shown in FIG. 19, this embodiment includes a pair of
negative uniaxial retarders 71 and 72 provided on one side (e.g. the rear
side as shown) of liquid crystal layer 9. Unlike the biaxial retarders
discussed above, negative uniaxial retarders 71 and 72 of this embodiment
are defined by n.sub.x =n.sub.y >n.sub.z. In other words, each of negative
retarders 71 and 72 is substantially uniaxial and defines an optical
retardation axis in the direction substantially perpendicular to the plane
of each film. Thus, the optical axis of each negative retarder 71 and 72
is substantially in the "z" direction. The retardation value
d.multidot.(n.sub.z -n.sub.x) of each retarder 71 and 72 may be from about
-60 to -200 nm according to certain embodiments of this invention, more
preferably from about -80 to -150 nm, and most preferably from about -100
to -140 nm. With regard to negative uniaxial retarders 71 and 72, because
n.sub.x =n.sub.y, the retardation value is defined by d.multidot.(n.sub.z
-n.sub.x) or alternatively in the same manner by d.multidot.(n.sub.z
-n.sub.y), both of which result in substantially the same retardation
value. Because n.sub.x and n.sub.y are greater than n.sub.z, retarders 71
and 72 are considered "negative." Exemplary such negative uniaxial
retarders are disclosed and discussed in U.S. Pat. Nos. 5,344,916 and
5,071,997, incorporated herein by reference.
As shown in FIG. 19 from the rear forward toward viewer 1, the normally
white TN display or LV according to this embodiment includes rear
polarizer 5, rear positive uniaxial retarder 2 having slow axis R.sub.R,
first negative uniaxial retarder 71, second negative uniaxial retarder 72,
rear buffing layer 7, twisted nematic LC layer 9, front buffing layer 11,
optional front positive uniaxial retarder 14 having slow axis R.sub.F, and
finally front linear polarizer 15 including transmission axis P.sub.F. As
with all positive retarders discussed herein, retardation value
d.multidot..delta.n for each of positive uniaxial retarders 2 and 14 is
from about 70 to 200 nm, more preferably from about 80 to 200 nm, even
more preferably from about 120 to 160 nm, and most preferably about 140
nm.
FIG. 20 is an exploded schematic illustrating the optical components of yet
another embodiment of a NW LCD or LV according to this invention. As shown
in FIG. 20, this embodiment includes negative uniaxial retarder 73 on the
rear side of LC layer 9, and another negative uniaxial retarder 74 on the
front side of LC layer 9. Negative retarders 73 and 74 as shown in FIG. 20
are similar to retarders 71 and 72 of FIG. 19, in that each is defined by
n.sub.x =n.sub.y >n.sub.z. Thus, negative retarders 73 and 74 each include
an optical axis aligned substantially perpendicular to the plane of each
film. As illustrated from the rear forward, the FIG. 20 embodiment
includes rear polarizer 5, rear positive uniaxial retarder 2, negative
uniaxial retarder 73, rear buffing layer 7, LC layer 9, front buffing
layer 11, front negative uniaxial retarder 74, front positive uniaxial
retarder 14, and finally front polarizer 15. The retardation value for
each of negative retarders 73 and 74 is similar to that discussed above
with respect to retarders 71 and 72 in the FIG. 19 embodiment.
According to other embodiments of this invention, NW TN LVs or AMLCDs may
be made as shown in FIGS. 20-21, except that no retarders are provided on
the front side of LC layer 9. In other words, the retarders 14 and 74 in
FIG. 20 may be eliminated.
This invention will now be described with respect to certain examples as
follows. In each of the Examples set forth below, the LC layer had a
.delta.n of 0.084, the thickness "d" of the LC layer 9 in each AMLCD or LV
was substantially constant across the entire viewing area, the front and
rear polarizers 5 and 15 were linear, and each of the positive uniaxial
retarders had a retardation value (d.multidot..delta.n) of 140 nm. The
negative biaxial retarder(s) were interior the positive retarders.
Additionally, FIGS. 5(a), 8(a), 11(c), 14, 15(a), 21(a), 22(a), 24(a),
26(a), 27(a), 30(a), 32(a), 33(a), and 34(a) all illustrate the axes from
the point of view of LCD viewer 1. The Examples below show that certain NW
LCDs according to this invention have a contrast ratio greater than 30:1
horizontally .+-.60.degree. and vertically from -7.degree. up to
+40.degree..
EXAMPLE 1
In this first Example, a normally white (NW) RGB thin film transistor (TFT)
AMLCD was constructed as shown in FIGS. 1 and 5(a) so as to have first and
second positive uniaxial retarders 2 and 14 on opposite sides of LC layer
9, and also first and second negative biaxial retarders 4 and 13 on
opposite sides of LC layer 9. The negative biaxial retarder on each side
of the liquid crystal layer 9 was sandwiched between the adjacent positive
retarder and layer 9. The retardation value d.multidot..delta.n for each
positive retarder 2 and 14 was about 140 nm. The retardation value
d.multidot.(n.sub.x -n.sub.z) was about 83 nm for each negative biaxial
retarder 4 and 13, while the retardation value d.multidot.(n.sub.x
-n.sub.y) was about 6 nm for each of biaxial retarders 4 and 13.
With reference to FIG. 5(a), the slow axis R.sub.F of front positive
retarder 14 was parallel to the transmission axis P.sub.F of front
polarizer 15, while the slow axis R.sub.R of rear positive retarder 2 was
parallel to the transmission axis P.sub.R of rear polarizer 5. Direction
RBR.sub.x (i.e. n.sub.x direction) of rear biaxial negative retarder 4 was
oriented 45.degree. counterclockwise (from the viewpoint of viewer 1)
relative to rear polarizer transmission axis P.sub.R, while direction
FBR.sub.x (n.sub.x direction) of front biaxial retarder 13 was oriented at
the 2.degree. mark, or in other words, clockwise 41.degree. from rear
polarizer transmission axis P.sub.R. Referring still to FIG. 5(a), the
following axes were at the following angular locations given a 0.degree.
axis located 2.degree. clockwise of FBR.sub.x : FBR.sub.x at 2.degree.,
R.sub.R at 43.degree., P.sub.R at 43.degree., B.sub.F at 45.degree.,
RBR.sub.x at 88.degree., FBR.sub.y at 92.degree., B.sub.R at 135.degree.,
P.sub.F and R.sub.F at 137.degree., and RBR.sub.y at 178.degree.. While
these axes also extend across the 0.degree.-180.degree. axis, their
angular positions in the third and fourth quadrants (i.e. from
180.degree.-360.degree.) are not listed above, but are shown in FIG. 5(a).
Still referring to this Example, the thickness "d" of LC layer 9 was
approximately 5.20 .mu.m, while LC layer 9 had a birefringent value of
about 0.084. Layer 9 twisted normally incident light approximately 9020
when in the off-state.
FIG. 5(b) is a white light contrast ratio graph of the AMLCD of this
Example, when 5.5 driving volts were applied to liquid crystal layer 9 in
the on-state. As shown, at this driving voltage, the AMLCD of this Example
emitted to viewer 1 a contrast ratio of at least about 20:1 over a
horizontal anglular span of at least about 120.degree. (preferably at
least about 140.degree.) along the 0.degree. vertical viewing axis.
Furthermore, the AMLCD emitted a contrast ratio greater than about 30:1
over a horizontal angular span of at least about 105.degree. . Vertically,
the display emitted a contrast ratio of at least about 20:1 over a
vertical span, along the 0.degree. horizontal viewing axis, of at least
about 45.degree.. The viewing characteristics illustrated in FIG. 5(b) as
a result of the negative biaxial retarders utilized in combination with
the positive uniaxial retarders of this embodiment are surprisingly
superior to those of the prior art as a result of the retardation values
provided, as well as the locations of the retarders and their respective
axes in the display stack.
FIG. 6 is a transmission (fL) versus driving voltage (volts) graph of the
AMLCD of this first Example, at a plurality of vertical viewing angles
along the 0.degree. horizontal viewing axis. As shown, there are very few
inversion humps. In this Figure, and in all transmission (intensity)
versus driving voltage graphs herein, the "y" axis represents intensity
(fL) while the "x" axis represents the driving voltage (volts) applied to
the display or light valve via electrodes 27 and 29.
FIG. 7 is a transmission versus driving voltage graph of the AMLCD of this
first Example, showing substantially no inversion at a plurality of
horizontal viewing angles along the 0.degree. vertical viewing axis.
EXAMPLE 2
In this second Example (see FIGS. 1 and 8(a)-10), a normally white RGB TFT
AMLCD in accordance with FIGS. 1 and 8(a) was made and tested. Positive
retarders 2 and 14 each had a retardation value of about 140 nm. The
retardation value d.multidot.(n.sub.x -n.sub.z) for each of the negative
biaxial retarders 4 and 13 was about 77 nm, while the retardation value
d.multidot.(n.sub.x -n.sub.y) for each of retarders 4 and 13 was about 7
nm. The thickness "d" of LC layer 9 was about 5.20 in this AMLCD.
FIG. 8(a) illustrates the angular relationship between the various axes of
the AMLCD of this Example. As shown, given a 0.degree. axis located
45.degree. clockwise from the front buffing direction B.sub.F the
respective axes were located as follows: FBR.sub.x at 0.degree., R.sub.R
at 43.5.degree., B.sub.F at 45.degree., P.sub.R at 45.degree., RBR.sub.y
at 90.degree., FBR.sub.y at 90.degree., P.sub.F at 135.degree., R.sub.F at
135.degree., B.sub.R at 135.degree., and RBR.sub.y at 180.degree..
Corresponding positions in the third and fourth quadrants are not listed
but are shown in FIG. 8(a). As will be appreciated from the disclosure set
forth above, direction RBR.sub.y will always be 90.degree.
counterclockwise from RBR.sub.x, while the same is true for FBR.sub.y
relative to FBR.sub.x .
FIG. 8(b) is a white light contrast ratio graph of the AMLCD of this second
Example when 5.5 driving volts were applied to the LC layer in the
on-state. As shown, the AMLCD exhibited a contrast ratio of at least about
40:1 over a horizontal angular span of at least about 120.degree..
Furthermore, the display exhibited a contrast ratio of at least about 80:1
from horizontal angles of from about -53.degree. to +60.degree..
Vertically, the display exhibited a 10:1 contrast ratio over a vertical
angular span along the 0.degree. horizontal viewing axis of at least about
50.degree.. At the -60.degree. horizontal viewing axis, the AMLCD
exhibited at least a 10:1 contrast ratio over a vertical angular span of
at least about 68.degree..
FIG. 9 is a transmission (fL) versus driving voltage (volts) graph at a
plurality of vertical viewing angles along the 0.degree. horizontal
viewing axis for the AMLCD of this Example. As shown, very little
inversion was present for the positive angles. FIG. 10 is a transmission
versus driving voltage graph for the AMLCD of this Example at a plurality
of horizontal viewing angles along the 0.degree. vertical viewing axis.
Again, the graph illustrates very little inversion at the illustrated
horizontal angles.
EXAMPLE 3
In this third Example, a normally white TFT RGB AMLCD with an air gap 61 on
each side of LC layer 9 was made and tested as follows in accordance with
FIGS. 1, 11(a), 11(c), and 11(d). The display of this Example differed
from those of the previous two Examples in that no index matching oil was
provided in this Example adjacent the exterior sides of the substantially
transparent substrates, thereby permitting the formation of air gaps 61 as
shown in FIG. 11(a). The front and rear positive uniaxial retarders 2 and
14 each had a retardation value of about 140 nm, while the retardation
value d.multidot.(n.sub.x -n.sub.z) as about 100 nm for each of negative
biaxial retarders 4 and 13. The retardation value d.multidot.(n.sub.x
-n.sub.y) for each of retarders 4 and 13 was about 12 nm. LC layer 9 had a
thickness of about 5.20 .mu.m in this Example.
FIG. 11(c) illustrates, from the point of view of viewer 1, the angular
relationship between the various axes of this AMLCD. Given a 0.degree.
axis 1.degree. clockwise of FBR.sub.x, the various axes were located as
follows: FBR.sub.x at 1.degree., P.sub.R at 44.degree., R.sub.R at
44.degree., B.sub.F at 45.degree., RBR.sub.x at 89.degree., FBR.sub.y at
91.degree., B.sub.R at 135.degree., P.sub.F at 136.degree., R.sub.F at
136.degree., and RBR.sub.y at 179.degree.. Again, third and fourth
quadrant angular positions are not listed, but are shown in FIG. 11(c).
FIG. 11(d) is a white light contrast ratio graph of the AMLCD of this
Example. As shown, air gaps 61 provide for more rounded shoulders and a
more rounded viewing zone. The maximum contrast ratio in this plot was
156.19. As illustrated, the AMLCD, when 5.5 driving volts were applied in
the on-state, exhibited a contrast ratio of at least about 10:1 over a
horizontal angular span along the 0.degree. vertical viewing axis of at
least about 120.degree.. Vertically, the display exhibited a contrast
ratio of at least about 10:1 over a vertical span along the 0.degree.
horizontal axis of at least about 55.degree.. The high 80:1 and above
contrast ratio area extended, at about 10.degree. vertical, horizontally
at least about 70.degree..
EXAMPLE 4
A NW TFT RGB AMLCD similar to that of the third Example was made and tested
in this fourth Example, the only difference between this and the third
Example being the retardation values of the negative biaxial retarders.
Each of biaxial retarders 4 and 13 in this fourth Example had a
retardation value d.multidot.(n.sub.x -n.sub.z) of about 75 nm and a
retardation value d.multidot.(n.sub.x -n.sub.y) of about 9 nm. Otherwise,
everything was the same as in Example 3, and as shown in FIGS. 11(a) and
11(c), including the provision of air gaps 61. Examples 3 and 4 are the
only Examples herein, in which air gap(s) were provided. Index matching
oil was utilized in all other Examples.
FIG. 12 is a white light contrast ratio graph of the AMLCD of this fourth
Example, when 5.5 driving volts were applied in the on-state. Note the
rounded shoulders of the high contrast zone. Again, this AMLCD exhibited a
contrast ratio (CR) of at least about 10:1 over a horizontal angular span
of at least about 120.degree., and a contrast ratio of at least about 80:1
over a horizontal angular span of at least about 75.degree.. Vertically,
the high contrast ratio zone of about 80:1 and above extended over an
angular span of at least about 23.degree.. The maximum contrast in FIG. 12
was 293.88 while the minimum was 0.88.
EXAMPLE 5
In this fifth Example, a normally white RGB TFT AMLCD having a cell gap of
5.7 .mu.m was made and tested in accordance with FIGS. 13, 15(a), and
15(b). As shown in FIG. 13, this AMLCD included rear positive uniaxial
retarder 2 and rear negative biaxial retarder 4, but no front retarders.
The retardation value d.multidot..delta.n for positive retarder 2 was 140
nm, while the retardation value d.multidot.(n.sub.x -n.sub.z) was 100 nm
for biaxial retarder 4, and retardation value d.multidot.(n.sub.x
-n.sub.y) was 12 nm for retarder 4. No air gaps were present, nor were any
present in any of the remaining Examples discussed hereinafter.
FIG. 15(a) illustrates, from the point of view of viewer 1, the
relationship between the axes of the AMLCD of this fifth Example. Given a
0.degree. axis 45.degree. clockwise from front buffing direction B.sub.F,
the axes of this AMLCD were arranged as follows: R.sub.R at 41.degree.,
P.sub.R at 45.degree., B.sub.F at 45.degree., RBR.sub.x at 90.degree.,
B.sub.R at 135.degree., P.sub.F at 135.degree., and RBR.sub.y at
180.degree.. Third and fourth quadrant angles are shown in FIG. 15(a).
FIG. 15(b) is a white light contrast ratio graph of the NW AMLCD of this
fifth Example when 5.5 driving volts were applied to the display in the
on-state. As shown, the display exhibited a contrast ratio of at least
about 80:1 over a horizontal anglular span of at least about 65.degree..
Additionally, the display exhibited at least a 10:1 contrast ratio over a
horizontal angular span of at least about 140.degree.. Vertically, the
display exhibited at least a 10:1 contrast ratio along the 0.degree.
horizontal viewing axis of at least about 48.degree.. The maximum CR in
FIG. 15(b) was 132.95 while the minimum was 0.40.
EXAMPLE 6
In the sixth Example, a normally white light valve having a cell gap of
5.20 .mu.m was made and tested in accordance with FIGS. 1 and 16. The
front and rear positive uniaxial retardation films 14 and 2 each had a
retardation value of 140 nm, while each of the front and rear negative
biaxial retarders 13 and 4, respectively, had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 100 nm and d.multidot.(n.sub.x -n.sub.y)
of 12 nm. In each of the negative biaxial retarders, n.sub.x was about
1.5855, n.sub.y was about 1.5853, and n.sub.z was about 1.5839. With
regard to the optical axes of this sixth Example, they were arranged as
shown in FIG. 2 except that each of the negative biaxial retarders was
rotated 180.degree. symmetrically.
FIG. 16 is a white light contrast ratio graph of the normally white light
valve of this sixth Example. As shown, the output included two "eyes",
both located below the 0.degree. vertical viewing axis. 5.5 driving volts
were applied to this light valve in the on-state to come up with the FIG.
16 graph. The maximum CR in FIG. 16 was 101.18 while the minimum was 1.01.
EXAMPLE 7
In this seventh Example, a normally white light valve (LV) having a cell
gap of 5.20 .mu.m was made and tested in accordance with FIGS. 1 and 17.
Each of the positive uniaxial retarders 2 and 14, respectively, had a
retardation value d.multidot..delta.n of 140 nm. Each of the negative
biaxial retarders 4 and 13, respectively, had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 100 nm and d.multidot.(n.sub.x -n.sub.y)
of 12 nm. The axes of this NW light valve were as shown in FIGS. 1 and 2
except that the n.sub.x direction (RBR.sub.x and FBR.sub.x) of each of the
biaxial retarders was parallel to the adjacent polarizer transmission
axis. In other words, FBR.sub.x was substantially parallel to P.sub.F,
while RBR.sub.x, was substantially parallel to P.sub.R. FIG. 17 is a white
light contrast ratio graph of this NW LV when 5.5 driving volts were
applied in the on-state. As illustrated, the highest contrast area was
located in the lower vertical viewing area, or below the 0.degree.
vertical viewing axis. The light valve in FIG. 17 exhibited a 10:1
contrast ratio along the 0.degree. vertical viewing axes only over a
horizontal angular span of less than about 85.degree.. The maximum CR in
FIG. 17 was 92.03 while the minimum was 1.26.
EXAMPLE 8
In this eighth Example, a normally white LV having a cell gap of about 5.20
.mu.m was made and tested in accordance with FIGS. 1 and 18. Each of the
positive retarders 2 and 14 had a retardation value of about 140 nm. Each
of the negative biaxial retarders 4 and 13 had retardation values the same
as in Example 7. The NW LV of this eighth Example had its axes arranged as
shown in FIGS. 1 and 2, except that the n.sub.x direction of each negative
biaxial retarder was aligned substantially perpendicular to the
corresponding adjacent polarizer transmission axis. In other words,
FBR.sub.x was substantially perpendicular to P.sub.F, while RBR.sub.x was
substantially perpendicular to P.sub.R.
FIG. 18 is a white light contrast ratio graph of this NW LV when 5.5
driving volts were applied in the on-state. As shown, the display
exhibited two "eyes" in the lower vertical viewing zone. Again, this LV
exhibited a contrast ratio along the 0.degree. vertical viewing axes of
10:1 over a horizontal angular span of less than about 90.degree.. The
maximum CR in FIG. 18 was 95.65 while the minimum was 1.03.
EXAMPLE 9
In this ninth Example, a normally white LV having a cell gap of 5.20 .mu.m
was made and tested in accordance with FIGS. 20, 21(a), and 21(b). As
shown in FIG. 20, this NW LV had rear and front positive uniaxial
retarders 2 and 14, each having a retardation value of 140 nm.
Additionally, this LV included rear and front negative uniaxial retarders
73 and 74, respectively, each having a retardation value
d.multidot..delta.n of 100 nm. These two negative uniaxial retarders were
defined by n.sub.x =n.sub.y .noteq.n.sub.z. The optical axis of each of
retarders 73 and 74 was substantially perpendicular to the plane of each
film (i.e. in the "z" direction). FIG. 21(a) illustrates the relationship
between the axes of this NW LV given a 0.degree. axis 45.degree. clockwise
of B.sub.F. The axes were aligned as follows as shown in FIG. 21(a):
R.sub.R at 43.5.degree., B.sub.F at 45.degree., P.sub.R at 47.5.degree.,
B.sub.R at 135.degree., P.sub.F at 132.5.degree., and R.sub.F at
138.5.degree.. For each of the negative uniaxial retarders 73 and 74 in
this Example, the index of refraction n.sub.x equaled the index of
refraction n.sub.y.
FIG. 21(b) is a white light contrast ratio (CR) graph of the NW LV of this
Example when 5.5 driving volts were applied to the LC layer 9 in the
on-state. As shown, the LV exhibited a contrast ratio along the 0.degree.
vertical viewing axis of at least about 10:1 over a horizontal angular
span of at least about 120.degree.. The display also exhibited a contrast
ratio of at least about 80:1 over a horizontal angular span of at least
about 68.degree.. The maximum CR in FIG. 21(b) was 177.68 while the
minimum was 0.50.
EXAMPLE 10
In this tenth Example, a normally white LV was made and tested in
accordance with FIGS. 19, 22(a), and 22(b). As shown in FIG. 19, this NW
LV included rear positive uniaxial retarder 2, a first rear negative
uniaxial retarder 71, and second rear uniaxial negative retarder 72. In
contrast to FIG. 19, no front retarder was provided in the LV of this
Example. In other words, only front polarizer 15 was located on the front
side of LC layer 9, in addition to the typical orientation film,
substrate, etc. For each of negative uniaxial retarders 71 and 72, n.sub.x
=n.sub.y in this Example. The optical axis of each of retarders 71 and 72
was aligned in the "z" direction. Positive uniaxial retarder 2 had a
retardation value of 140 nm, while each of negative uniaxial retarders 71
and 72 had a retardation value d.multidot..delta.n of 100 nm for a total
negative retardation of 200 nm on the rear side of the LC layer 9.
As shown in FIG. 22(a), given a 0.degree. axes 45.degree.clockwise of
B.sub.F, the axes of this NW LV were oriented as follows from the point of
view of viewer 1: R.sub.R at 41.degree., P.sub.R at 46.degree., B.sub.F at
45.degree., B.sub.R at 135.degree., and P.sub.F at 135.degree..
FIG. 22(b) is a white light contrast ratio graph of the NW LV of this tenth
Example when about 5.5 driving volts were applied to the LC layer in the
on-state. The maximum contrast ratio of FIG. 22(b) was 166.83, while the
minimum contrast ratio was 0.84. As illustrated, this LV exhibited a
contrast ratio of at least about 80:1 over a horizontal anglular span of
at least about 80.degree.. Additionally, at about 20.degree.vertical, the
display exhibited at least a 20:1 contrast ratio over a horizontal
anglular span of at least about 120.degree.. Vertically, along the
0.degree. horizontal viewing axis, the display exhibited at least a 10:1
contrast ratio over a vertical angular span of at least about 57.degree..
EXAMPLE 11
In this eleventh Example, an NW LV was made and tested. The NW LV of this
Example was the same as that of Example 10, except that each of the two
rear negative uniaxial retarders had a retardation value of 120 nm
(instead of 100 nm). The axes of this NW LV were as shown in FIG. 22(a)
and as discussed above in Example 10. FIG. 23 is a normally white contrast
ratio graph of the NW LV of this Example when 5.5 volts were applied to
the LC in the on-state. This LV had, as in Example 10, a cell gap "d" of
about 5.20 .mu.m. The maximum contrast ratio in FIG. 23 was 357.70, while
the minimum contrast ratio was 0.57. As illustrated in FIG. 23, this LV
exhibited a contrast ratio of at least about 80:1 over an angular span of
at least about 105.degree.. Additionally, this display exhibited a
contrast ratio of at least about 50:1 over an angular span of at least
about 120.degree. as measured along the proximate longitudinal axis of the
high contrast ratio region. Vertically, along the 0.degree. horizontal
viewing axis, this LV exhibited a contrast ratio of at least about 10:1
over a vertical angular span of at least about 63.degree..
EXAMPLE 12
In this twelfth Example, an NW LV having a cell gap "d" of 5.75 .mu.m was
made and tested in accordance with FIGS. 1, 24(a), and 24(b). Each of the
front 14 and rear 2 positive uniaxial retarders had a retardation value
d.multidot..delta.n of 140 nm. Meanwhile, each of the rear 4 and front 13
negative biaxial retarders had a retardation value d.multidot.(n.sub.x
-n.sub.z) of 100 nm and a retardation value d.multidot.(n.sub.x -n.sub.y)
of 12 nm. As shown in FIG. 24(a), this NW LV included numerous axes with
the following relation given a 0.degree. axis 45.degree. clockwise of
B.sub.F as viewed from viewer 1: FBR.sub.x at 2.degree., R.sub.R at
40.degree., P.sub.R at 44.degree., B.sub.F at 45.degree., RBR.sub.x at
89.degree., B.sub.R at 135.degree., P.sub.F at 137.degree., and R.sub.F at
141.degree..
FIG. 24(b) is a white light contrast ratio of the NW LV of this twelfth
Example when 6.0 driving volts were applied to the LC in the on-state. The
maximum contrast ratio in FIG. 24(b) was 228.0 while the minimum was 1.09.
As shown, along the 0.degree. vertical viewing axis, this LV exhibited a
contrast ratio of at least about 30:1 over a horizontal angular span of at
least about 120.degree.. Additionally, this LV exhibited, along the
0.degree. horizontal viewing axis, a contrast ratio of at least about 10:1
over a vertical angular span of at least about 70.degree.. The extent of
the high contrast 80:1 ratio range extended horizontally to horizontal
viewing angles of at least about -50 and +50 along the 0.degree. vertical
viewing axis.
EXAMPLE 13
In this thirteenth Example, a NW LV similar to that of Example 12 was made
and tested. The LV of this thirteenth Example was the same as that in
Example 12, except that the cell gap was only 4.75 .mu.m in this Example
(instead of 5.75 .mu.m in Example 12). Otherwise, the retardation values,
axis alignments, etc. were the same. FIG. 25 is a white light contrast
ratio graph of the LV of this thirteenth Example when 6.0 driving volts
were applied to the LC in the on-state. As can be seen, the 80:1 high
contrast viewing zone was divided into two separate areas, one to the left
and one to the right of the 0.degree. horizontal viewing axis.
Additionally, the viewing zone was shifted slightly vertically, and
exhibited excellent viewing characteristics at horizontal angles in the
vertical viewing zone of about .+-.30.degree.. The maximum CR in FIG. 25
was 156.31 while the minimum was 0.53.
EXAMPLE 14
In this fourteenth Example, a NW LV having a cell gap of 5.20 .mu.m was
made and tested in accordance with FIGS. 1, 26(a), and 26(b). Each of the
front and rear positive uniaxial retarders 2 and 14 had a retardation
value of 140 nm. The rear negative biaxial retarder 4 had a retardation
value d.multidot.(n.sub.x -n.sub.z) of 100 nm, and a retardation of
d.multidot.(n.sub.x -n.sub.y) of 12 nm. Meanwhile, the front negative
biaxial retarder 13 had a retardation value d.multidot.(n.sub.x -n.sub.z)
of 75 nm, and a retardation value d.multidot.(n.sub.x -n.sub.y) of 9 nm.
The cell gap of this LV was 5.20 .mu.m.
FIG. 26(a) illustrates the angular relationship between the axes of this LV
given a 0.degree. axis 45.degree. clockwise of B.sub.F. As illustrated,
the axes were oriented as follows: FBR.sub.x at 2.degree., R.sub.R at
40.degree., P.sub.R at 44.degree., B.sub.F at 45.degree., RBR.sub.x at
89.degree., B.sub.R at 135.degree., R.sub.F at 137.degree., and P.sub.F at
137.degree..
FIG. 26(b) is a white light contrast ratio graph of the NW LV of this
fourteenth Example when 5.5 driving volts were applied to the LC in the
on-state. The maximum contrast ratio in FIG. 26(b) was 199.92 while the
minimum was 0.68. As will be appreciated by those of skill in the art, the
maximum contrast ratio is marked by the cross symbol in the high contrast
(white) viewing area. As shown, this LV exhibited a contrast ratio of at
least about 10:1 over a horizontal anglular span of at least about
130.degree.. Vertically, the display exhibited a contrast ratio of at
least about 10:1 over a vertical angular span of at least about
65.degree.. Along the 0.degree. vertical viewing axis, the display
exhibited a contrast ratio of at least about 20:1 over a horizontal
angular span of at least about 110.degree..
EXAMPLE 15
In this fifteenth Example, a NW LV having a cell gap of 5.20 .mu.m was made
and tested in accordance with FIGS. 1, 27(a), and 27(b). Each of the
positive uniaxial retarders 2 and 14 had a retardation value of 140 nm.
Rear negative biaxial retarder 4 had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 117 nm and a retardation value
d.multidot.(n.sub.x -n.sub.y) of 12 nm. The front negative biaxial
retarder 13 had the same retardation values as rear biaxial retarder 4.
FIG. 27(a) illustrates the angular relationship between the axes of this
NW LV given a 0.degree. axis 45.degree. clockwise of B.sub.F. The axes
were aligned as follows: FBR.sub.x, at 2.degree., P.sub.R at 44.degree.,
R.sub.R at 44.degree., B.sub.F at 45.degree., RBR.sub.x at 89.degree.,
B.sub.R at 135.degree., R.sub.F at 137.degree., and P.sub.F at
137.degree..
FIG. 27(b) is a white light contrast ratio graph of the NW LV of this
fifteenth Example when 5.5 driving volts were applied to the LC in the
on-state. The maximum contrast ratio marked by the cross symbol in FIG.
27(b) was 199.48, while the minimum was 0.80. As illustrated, the 80:1
contrast ratio region extended from about -55.degree. horizontal to about
+53.degree. horizontal.
EXAMPLE 16
In this sixteenth Example, a NW LV having a cell gap of 5.20 .mu.m was made
and tested in accordance with FIGS. 1, 27(a), and 28. The relationship
between the respective axes of this LV was the same as in Example 15 (see
FIG. 27(a)). However, in this sixteenth Example, the rear negative biaxial
retarder 4 had retardation values d.multidot.(n.sub.x -n.sub.z) of 100 nm
and d.multidot.(n.sub.x -n.sub.y) of 9 nm. The front biaxial retarder 13
had the same retardation values as the rear retarder 4 in this sixteenth
Example. Both positive retarders 2 and 14 each had a retardation value
d.multidot..delta.n of 140 nm.
FIG. 28 is a white light contrast ratio graph of the NW LV of this
sixteenth Example when 5.5 driving volts were applied to the LC in the
on-state. The maximum contrast ratio of FIG. 28 was 293.76 while the
minimum was 0.71. The high contrast ratio zone of at least about 80:1
extended horizontally from viewing angles of about -54.degree. to
+54.degree.. Meanwhile, along the 0.degree. horizontal viewing axis, the
display exhibited a contrast ratio of at least about 80:1 over a vertical
range of at least about 22.degree., and a ratio of at least about 10:1
over a vertical range of at least about 65.degree..
EXAMPLE 17
In this seventeenth Example, an NW LV having a cell gap of 5.20 .mu.m was
made and tested in accordance with FIGS. 1 and 29. Each of the positive
retarders had a retardation value of 140 nm. Each of the rear and front
negative biaxial retarders 4 and 13, respectively, had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 100 nm and a retardation value
d.multidot.(n.sub.x -n.sub.y) of about 8 nm in this Example. The axes of
this LV were the same as in Example 16 (see FIG. 27(a)), except that rear
positive retarder axis R.sub.R was rotated clockwise 3.degree. from its
position shown in FIG. 27(a). Otherwise, all axis alignments were the same
as in Example 16 and FIG. 27(a).
FIG. 29 is a white light contrast ratio graph of the NW LV of this
seventeenth Example when 5.5 driving volts were applied to the LC in the
on-state. The maximum contrast ratio in FIG. 29 was 314.13, while the
minimum was 0.63. Vertically, along the 0.degree. horizontal axis, the LV
exhibited a contrast ratio of at least about 10:1 over a vertical angular
span of at least about 70.degree.. Horizontally, along the 0.degree.
vertical viewing axis, the LV of this Example exhibited a contrast ratio
of at least about 20:1 over a horizontal angular span of at least about
120.degree.. At a vertical viewing angle of about +5.degree., the LV of
this Example exhibited a contrast ratio of at least about 30:1 over a
horizontal angular span of at least about 120.degree..
EXAMPLE 18
In this eighteenth Example, an NW LV having a cell gap "d" of 5.20 .mu.m
was made and tested in accordance with FIGS. 1, 30(a), and 30(b). Each of
the positive retarders 2 and 14 had a retardation value of 140 nm. The
rear negative biaxial retarder had a retardation value d.multidot.(n.sub.x
-n.sub.z) of 100 nm and a retardation value d.multidot.(n.sub.x -n.sub.y)
of 8 nm. The front negative biaxial retarder 13 had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 83 nm and a retardation value
d.multidot.(n.sub.x -n.sub.y) of 6 nm.
FIG. 30(a), from the point of view of viewer 1, illustrates the
relationship between the different axes of the LV of this Example, given a
0.degree. axis 45.degree. clockwise of B.sub.F. The axes were aligned as
follows: FBR.sub.x, at 2.degree., P.sub.R at 44.degree., R.sub.R at
44.degree., B.sub.F at 45.degree., RBR.sub.x at 89.degree., B.sub.R at
135.degree., P.sub.F at 137.degree., and R.sub.F at 138.5.degree..
FIG. 30(b) is a white light contrast ratio graph of the NW LV of this
Example when 5.5 driving volts were applied to the LC in the on-state. The
maximum contrast ratio in FIG. 30(b) was 237.48, while the minimum was
0.76. As illustrated, at about +5.degree. vertical, the display of this
Example exhibited a contrast ratio of at least about 40:1 over a
horizontal angular span of at least about 120.degree.. Additionally, the
display of this Example, at this viewing angle, exhibited a contrast ratio
of at least about 30:1 over this horizontal angular span of at least about
120.degree..
EXAMPLE 19
In this nineteenth Example, an NW LV in accordance with FIGS. 1, 30(a), and
31 was made and tested. The LV of this nineteenth Example was the same as
that of Example 18, except that the rear negative biaxial retarder 4 also
had a retardation value d.multidot.(n.sub.x -n.sub.z) of 83 nm and a
retardation value d.multidot.(n.sub.x -n.sub.y) of 6 nm. Everything else
was the same as in Example 18 (see FIG. 30(a)).
FIG. 31 is a white light contrast ratio graph of the LV of this nineteenth
Example when 5.5 driving volts were applied to the LC in the on-state. As
shown, at the 0.degree. vertical viewing axis, this LV would display
exhibited a contrast ratio of at least about 20:1 over a horizontal
angular span of at least about 120.degree.. Vertically, along the
0.degree. horizontal axis, this LV exhibited a contrast ratio of at least
about 10:1 over a vertical angular span of at least about 60.degree.. The
high contrast ratio area of at least about 80:1 extended from about
-50.degree. horizontal to about +52.degree. horizontal. The highest
contrast ratio in FIG. 31 was 192.04, located at the cross symbol, while
the minimum was 0.62.
EXAMPLE 20
In this twentieth Example, an NW LV in accordance with FIGS. 1, 32(a), and
32(b) was made and tested. This LV had a cell gap of 5.20 .mu.m. Each of
the positive uniaxial retarders 2 and 14 had a retardation value of 140
nm. Rear negative biaxial retarder 4 had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 83 nm and a retardation value
d.multidot.(n.sub.x -n.sub.y) of 6 nm. Front negative biaxial retardation
film 13 in this twentieth Example had a retardation value
d.multidot.(n.sub.x -n.sub.z) of 100 nm, and a retardation value
d.multidot.(n.sub.x -n.sub.y) of 12 nm. For the rear negative biaxial
retarder, n.sub.x was about 1.5854, n.sub.y was about 1.5853, and n.sub.z
was about 1.5841. For the front negative biaxial retarder in this Example,
n.sub.x was about 1.5855, n.sub.y was about 1.5853, and n.sub.z was about
1.5839.
FIG. 32(a), from the point of view of viewer 1, illustrates the
relationship between the axes of the LV of this Example, given a 0.degree.
axis 45.degree. clockwise of front buffing direction B.sub.F. As
illustated, the axes were aligned as follows: FBR.sub.x at 2.degree.,
R.sub.R at 42.5.degree., P.sub.R at 44.degree., B.sub.F at 45.degree.,
RBR.sub.x at 89.degree., R.sub.F at 133.degree., B.sub.R at 135.degree.,
and P.sub.F at 137.degree..
FIG. 32(b) is a white light contrast ratio of the LV of this twentieth
Example when 5.5 driving volts were applied to the LC in the on-state. The
maximum contrast ratio in FIG. 32(b) was 263.47, while the minimum was
0.79. As illustrated, at about +5.degree. vertical, the high contrast zone
of at least about 80:1 extended over a horizontal angular span of at least
about 110.degree., while the display also exhibited a contrast ratio of at
least about 30:1 over this horizontal angular span of at least about
120.degree.. At about +4.degree. vertical, this display or light valve
exhibited a contrast ratio of at least about 50:1 over a horizontal
angular span of at least about 113.degree.. Vertically, along the
0.degree. horizontal axis, this display exhibited a contrast ratio of at
least about 10:1 over a vertical angular span of at least about
70.degree..
EXAMPLE 21
In this twenty-first Example, an NW LV was made and tested in accordance
with FIGS. 1, 33(a), and 33(b). The cell gap "d" for the LV of this
Example was 5.20 .mu.m. Each of the positive uniaxial retarders had a
retardation value of about 140 nm. The front negative biaxial retarder 13
had a retardation value d.multidot.(n.sub.x -n.sub.z) of 100 nm and a
value d.multidot.(n.sub.x -n.sub.y) of 12 nm, while rear biaxial retarder
4 had values d.multidot.(n.sub.x -n.sub.z)=83 nm and d.multidot.(n.sub.x
-n.sub.y)=6 nm. FIG. 33(a) illustrates the angular relationship between
the axes of this NW LV. FIG. 33(b) is a white light CR graph of this LV
when 5.5 driving volts were applied to LC layer 9 in the on-state. The
maximum CR for FIG. 33(b) was 334.20, while the minimum was 0.87.
In FIG. 33(b), the NW LV of this Example had a contrast ratio of at least
about 20:1 over a horizontal angular span of at least about 120.degree.
along the 0.degree. vertical viewing axis. Additionally, this display had
a contrast ratio of at least about 10:1 over a vertical angular span of at
least about 70.degree. along the 0.degree. horizontal viewing axis. Along
the 0.degree. vertical viewing axis, the NW LV had a contrast ratio at
this driving voltage of at least about 40:1 over a horizontal angular span
of at least about 105.degree..
EXAMPLE 22
In this twenty-second Example, an NW LV was made and tested in accordance
with FIGS. 13, 34(a), and 34(b). The cell gap for the LV of this Example
was 5.20 .mu.m, while 5.5 driving volts was utilized in the on-state with
respect to FIG. 34(b). No front retarders were provided (see FIG. 13).
From the rear forward, the display included rear polarizer 5, rear 140 nm
positive retarder 2, three separate negative biaxial retarders 4 laminated
together as a single unit, rear buffing layers 7, LC layer 9, front
buffing layer 11, and front polarizer 15. Each of the three negative
biaxial retarders 4 laminated together in this Example had a retardation
value d.multidot.(n.sub.x -n.sub.z) of 95 nm and a retardation value
d.multidot.(n.sub.x -n.sub.y) of 11 nm. Thus, the "total" retardation for
the three negative biaxial retarders provided between layers 2 and 7, was
a retardation value d.multidot.(n.sub.x -n.sub.z) of 285 nm, and a
retardation value d.multidot.(n.sub.x -n.sub.y) of 33 nm. FIG. 34(a)
illustrates the angular relationship between the axes of this NW LV. As
shown, given a 0.degree. axis 45.degree. clockwise from B.sub.F, the axes
were aligned as follows: R.sub.R at 41.5.degree., B.sub.F at 45.degree.,
P.sub.R at 46.5.degree., RBR.sub.x, at 91.5.degree., R.sub.F at
135.degree., B.sub.R at 135.degree., and RBR.sub.y at 181.5.degree..
FIG. 34(b) is a white light contrast ratio of the LV of this twenty-second
Example when 5.5 driving volts were applied in the on-state. The maximum
contrast ratio in FIG. 34(a) was 354.55, while the minimum was 0.57. As
shown, the high contrast area is skewed slightly to the right due to the
provision of retarders on only one side of the LC layer.
The pretilt angle of the displays and LVs herein may be about 3.degree. in
certain embodiments, and the value of d/p (thickness/natural pitch of the
LC material) of the LC layers may be about 0.25. Additionally, the Eldin
EZ Contrast System was utilized to come up with the circular contrast
ratio graph disclosed herein (e.g. see FIGS. 11(d), 12, 15(b), 16, 17, 18,
21(b), 22(b), 23, 24(b), 25, 26(b), 27(b), 28, 29, 30(b), 31, 32(b), and
33(b)).
Once given the above disclosure, many other features, modifications, and
improvements will become apparent to the skilled artisan. Such other
features, modifications, and improvements are therefore considered to be a
part of this invention. The scope of which is to be determined by the
following claims.
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