Liquid crystal display with the pre-tilt angle set within a range that gray scale inversion is prevented

The present invention has an object to eliminate viewing angle dependency in the upward, downward, and right- and left-hand directions, and compensate for optical retardation according to the viewing angle. The liquid crystal display device is provided with at least one optical retardation compensator plate inserted between a liquid crystal display element and polarizer plates. The liquid crystal display element is composed of a pair of electrode substrates and a liquid crystal layer sealed therebetween. The polarizer plates flank the liquid crystal display element. The optical retardation compensator plate has a negative refractive index anisotropy and an inclining refractive index ellipsoid. The liquid crystal layer is divided unequally into divisions having mutually different orientation directions, and the pretilt angle formed by the orientation films and the major axes of liquid crystal molecules in the liquid crystal layer is set within such a range that tone reversion does not occur in the opposite viewing direction when halftone is being displayed by applying to the liquid crystal a voltage that is close to the threshold voltage for the liquid crystal.

FIELD OF THE INVENTION 
The present invention relates to a liquid crystal display device, 
especially, to a liquid crystal display device with the viewing angle 
dependency of the display screen abated by a combination of a liquid 
crystal display element and an optical retardation compensator plate. 
BACKGROUND OF THE INVENTION 
Conventionally, liquid crystal display devices incorporating nematic liquid 
crystal display elements have been in widespread use for 
numeral-segment-type display devices such as watches and calculators, and 
recently the applications are finding more places with word processors, 
notebook-type personal computers, liquid crystal televisions mounted in 
automobiles, etc. 
Generally, a liquid crystal display element has a translucent substrate, 
electrode lines for turning on and off pixels, and other components formed 
on the substrate. For example, in an active-matrix type liquid crystal 
display device, active elements, such as thin-film transistors, are formed 
on the substrate together with the electrode lines as switching means for 
selectively driving pixel electrodes by which voltages are applied across 
the liquid crystal. Moreover, in liquid crystal display devices capable of 
color display, color filter layers having colors such as red, green and 
blue are provided on the substrate. 
Liquid crystal display elements such as the one mentioned above adopt a 
liquid crystal display mode that is suitably selected depending on the 
twist angle of the liquid crystal: some of well-known modes are 
active-driving-type twisted nematic liquid crystal display mode 
(hereinafter, referred to as the TN mode) and the multiplex-driving-type 
super-twisted nematic liquid crystal display mode (hereinafter, referred 
to as the STN mode). 
The TN mode displays images by orientating the nematic liquid crystal 
molecules to a 90.degree. -twisted state so as to direct rays of light 
along the twisted directions. The STN mode utilizes the fact that the 
transmittance is allowed to change abruptly in the vicinity of the 
threshold value of the applied voltage across the liquid crystal by 
expanding the twist angle of the nematic liquid crystal molecules to not 
less than 90.degree.. 
The problem with the STN mode is that the background of the display screen 
sustains a peculiar color due to interference between colors because of 
the use of the birefringence effect of liquid crystal. In order to solve 
this problem and to provide a proper black-and-white display in the STN 
mode, the application of an optical retardation compensator plate is 
considered to be effective. Display modes using the optical retardation 
compensator plate are mainly classified into two modes, that is, the 
double layered super-twisted nematic optical-retardation compensation mode 
(hereinafter, referred to as the DSTN mode) and the film-type 
optical-retardation compensation mode (hereinafter, referred to as the 
film-addition mode) wherein a film having optical anisotropy is provided. 
The DSTN mode uses a two-layered construction that has a display-use liquid 
crystal cell and a liquid crystal cell which are orientated with a twist 
angle in a direction opposite to that of the display-use liquid crystal 
cell. The film-addition mode uses a construction wherein a film having 
optical anisotropy is disposed. Here, the film-addition mode is considered 
to be more prospective from the standpoint of light weight and low costs. 
Since the application of such an optical-retardation compensation mode can 
improve black-and-white display characteristics, color STN liquid crystal 
display devices have been achieved that enable color display by installing 
color-filter layers in STN-mode display devices. 
The TN modes are, on the other hand, classified into the Normally Black 
mode and the Normally White mode. In the Normally Black mode, a pair of 
polarizer plates are placed with their polarization directions parallel to 
each other, and black display is provided in a state where no ON voltage 
is applied across the liquid crystal layer (OFF state). In the Normally 
White mode, a pair of polarizer plates are placed with their polarization 
directions orthogonal to each other, and white display is provided in the 
OFF state. Here, the Normally White mode is considered to be more 
prospective from the standpoints of display contrast, color 
reproducibility, viewing angle dependency, etc. 
However, in the TN-mode liquid crystal display device, liquid crystal 
molecules have a refractive index anisotropy .DELTA.n, and are orientated 
so as to incline to the above and below substrates. For these reasons, the 
viewing angle dependency increases: i.e., the contrast of displayed images 
varies depending upon the direction and angle of the viewer. 
FIG. 12 schematically shows the cross-sectional construction of a TN liquid 
crystal display element 31. This state shows liquid crystal molecules 32 
slanting upward slightly as a result of application of a voltage for 
halftone display. In such a liquid crystal display element 31, a linearly 
polarized ray 35 passing through the surfaces of a pair of substrates 33 
and 34 along the normals thereto, and linearly polarized rays 36 and 37 
passing through those surfaces not along the normals thereto cross the 
liquid crystal molecules 32 at different angles. The liquid crystal 
molecules 32 have a refractive index anisotropy .DELTA.n. Therefore, the 
linearly polarized rays 35, 36 and 37, upon passing through the liquid 
crystal molecules 32 in different directions, produce ordinary and 
extraordinary rays. The linearly polarized rays 35, 36 and 37 are 
converted to elliptically polarized rays according to the phase difference 
between the ordinary and extraordinary rays, which cause the viewing angle 
dependency. 
In addition, in an actual liquid crystal layer, the liquid crystal 
molecules 32 show different tilt angles in the vicinity of the midpoint 
between the substrates 33 and 34 and in the vicinities of the substrates 
33 and 34. The liquid crystal molecules 32 are twisted by 90.degree. 
around the normal. 
For those reasons described so far, the linearly polarized rays 35, 36 and 
37 passing through the liquid crystal layer are affected by the 
birefringence effect in various ways depending upon, for example, the 
directions and the angles thereof, resulting in complex viewing angle 
dependency. 
Such viewing angle dependency can be observed, as examples, in the 
following situations. If the viewing angle increases from the normal to 
the display screen in the standard viewing direction, i.e. downward, and 
exceeds a certain angle, the displayed image has a distinct color 
(hereinafter, referred to as the coloration phenomenon), or is reversed in 
black and white (hereinafter, referred to as the tone reversion 
phenomenon). If the viewing angle increases from the normal in the 
opposite viewing direction, i.e. upward, the contrast decreases abruptly. 
The aforementioned liquid crystal display device has another problem that 
the effectual range of viewing angle narrows with a larger display screen. 
When a large liquid crystal display device is viewed from a short distance 
in the front thereof, the same color may appear different in the uppermost 
and lowermost parts of the large screen due to the effect of the viewing 
angle dependency. This is caused by a wider range of viewing angle 
required to encompass the whole screen surface, which is equivalent to a 
viewing direction which is increasingly far off center. 
To restrain the viewing angle dependency, Japanese Laid-Open Patent 
Applications No. 55-600/1980 (Tokukaisho 55-600) and No. 56-97318/1981 
(Tokukaisho 56-97318) suggest that an optical retardation compensator 
plate (retardation compensator film) be inserted as an optical element 
having optical anisotropy between the liquid crystal display element and 
one of polarizer plates. 
According to the method, the elliptically polarized ray converted from a 
linearly polarized ray by passing through liquid crystal molecules having 
refractive index anisotropy is directed through the optical retardation 
compensator plate(s) disposed on the side(s) of the liquid crystal layer 
having refractive index anisotropy. Hence, the phase difference between 
the ordinary and extraordinary rays which occurs to the viewing angle are 
compensated for, and the elliptically polarized ray is converted back to 
the linearly polarized ray, which enables the restraint of the viewing 
angle dependency. 
Japanese Laid-Open Patent Application No. 5-313159/1993 (Tokukaihei 
5-313159), as an example, discloses an optical retardation compensator 
plate of the above kind having a refractive index ellipsoid with one of 
the principal refractive indices parallel to the normal to the surface of 
the optical retardation compensator plate. Nevertheless, this optical 
retardation compensator plate still cannot satisfactorily restrain the 
tone reversion phenomenon that occurs when the viewing angle increases in 
the standard viewing direction. 
Hence, Japanese Laid-Open Patent Application No. 6-75116/1994 (Tokukaihei 
6-75116) suggests the use of an optical retardation compensator plate 
having a refractive index ellipsoid with the principal refractive indices 
inclining to the normal to the surface of the optical retardation 
compensator plate. This method adopts two kinds of optical retardation 
compensator plates as follows. 
One of the optical retardation compensator plates has such a refractive 
index ellipsoid that the smallest of the three principal refractive 
indices is parallel to the surface, one of the two larger principal 
refractive indices inclines to the surface of the optical retardation 
compensator plate by an angle .theta., the remaining principal refractive 
index inclines to the normal to the optical retardation compensator plate 
by the same angle .theta., and the angle .theta. satisfies 
20.degree..ltoreq..theta..ltoreq.70.degree.. 
The other optical retardation compensator plate has a refractive index 
ellipsoid inclining to the surface, where the three principal refractive 
indices, na, nb, and nc, are mutually related by the inequality na=nc&gt;nb, 
and the direction of the principal refractive index nb parallel to the 
normal to the surface and the direction of either the principal refractive 
index na or nc in the surface recline either clockwise or counterclockwise 
around the direction of the principal refractive index nc or na in the 
surface. 
As for the former optical retardation compensator plate, a uniaxial and 
biaxial optical retardation compensator plate can be used. For the latter 
one, two optical retardation compensator plates, instead of one, can be 
used in such a combination that the two principal refractive indices nb 
form an angle of 90.degree.. 
A liquid crystal display device, incorporating at least one such optical 
retardation compensator plate having an inclining refractive index 
ellipsoid between the liquid crystal display element and the polarizer 
plate, exhibits some restraint in the contrast variations, coloration 
phenomenon, and tone reversion phenomenon caused by the viewing angle 
dependency of the display screen, in comparison with incorporation of an 
optical retardation compensator plate having a refractive index ellipsoid 
with the principal refractive index not inclining to the normal of the 
surface. 
In order to eliminate the tone reversion phenomenon, Japanese Laid-Open 
Patent Application No. 57-186735/1982 (Tokukaisho 57-186835) discloses the 
so-called pixel dividing method, in which a displayed pattern (pixel) is 
divided and orientation is controlled so that each divided segment has its 
own viewing angle characteristics independent from those of the other 
segments. According to the method, since the liquid crystal molecules 
stand upwards in different directions from segment to segment, the viewing 
angle dependency when viewed upward or downward can be eliminated. 
Japanese Laid-Open Patent Applications No. 6-118406/1994 (Tokukaihei 
6-118406) and No. 6-194645/1994 (Tokukaihei 6-194645) disclose 
technologies to combine the pixel dividing method and an optical 
retardation compensator plate. 
The liquid crystal display device disclosed in Japanese Laid-Open Patent 
Application No. 6-118406/1994 includes an optical anisotropic film 
(optical retardation compensator plate) interposed between the liquid 
crystal panel and the polarizer plate to, for example, improve the 
contrast. The retardation compensator plate (optical retardation 
compensator plate) disclosed in Japanese Laid-Open Patent Application No. 
6-194645/1994 is set to have almost no refractive index anisotropy in a 
plane parallel to the surface of the retardation compensator plate and to 
have a smaller refractive index in a plane perpendicular to the surface of 
the retardation compensator plate than the refractive index in a plane 
parallel thereto, in order to have a negative refractive index. Therefore, 
when a voltage is applied, the positive refractive index occurring to the 
liquid crystal display element is compensated for and viewing angle 
dependency can be decreased. 
However, with today's increasingly large demand on a wider effectual range 
of viewing angle and superb display quality, a better restraint in the 
viewing angle dependency is crucial. In this context, the optical 
retardation compensator plate having an inclining refractive index 
ellipsoid as disclosed in Japanese Laid-Open Patent Application No. 
6-75116/1994 (Tokukaihei 6-75116) does not provide satisfactory solutions 
and needs to be improved. 
The pixel dividing method, introduced to eliminate the tone reversion 
phenomenon, does eliminate the tone reversion phenomenon when viewed up or 
down. However, the introduction of the method suffers from disadvantages 
that the contrast is lowered and causes the black color to appear rather 
whitish, resulting in a grey view, and that the viewing angle dependency 
persists when viewed from the right- or left-hand direction. 
The above-mentioned application of the pixel h dividing method to the use 
of this optical retardation compensator plate results in coloration 
phenomenon when the viewing angle is increased up to 45.degree. in an 
oblique direction. Also, since adopting liquid crystal display elements of 
which the pixels are divided equally (into equal volumes), the application 
has a limited ability in controlling the decrease of the contrast when 
viewed up or down. The reasons are elaborated below. 
The above-mentioned pixel dividing method adopts pixels divided in a ratio 
of equality, averaging the viewing angle characteristics of TN liquid 
crystal display elements in the standard viewing direction (the direction 
in which the display contrast is improved from the normal to the display 
surface) and in the opposite viewing direction (the direction in which the 
display contrast is lowered from the normal to the display surface). 
However, since the real viewing angle characteristics in the standard 
viewing direction and those in the opposite viewing direction are 
reversed, it is difficult to uniformly restrain the decrease in contrast 
in the upward and downward directions by means of the above-mentioned 
application of the pixel dividing method to the use of an optical 
retardation compensator plate. Especially, when the viewing angle 
increases in the standard viewing direction, it is likely that the tone 
reversion phenomenon occurs and that displayed images are too dark to be 
decipherable. 
SUMMARY OF THE INVENTION 
In view of the above problems, the present invention has as objects, on top 
of the improvement by the compensation effects by the optical retardation 
compensator plate having an inclining refractive index ellipsoid, to 
further restrain the viewing angle dependency, and especially, to restrain 
the reversion phenomenon which occurs when the viewing angle increases in 
the standard or opposite viewing direction, to substantially uniformly 
restrain the decrease in contrast and the chances of whitish images 
displayed in such an event, and to effectively restrain the tone reversion 
in the opposite viewing direction when halftone is being displayed by 
applying a voltage that is close to the threshold voltage for the liquid 
crystal. 
In order to accomplish the objects, a liquid crystal display device of a 
first arrangement in accordance with the present invention includes: 
a liquid crystal display element formed by sealing a liquid crystal layer 
between a pair of substrates each of which has an orientation film; 
a pair of polarizers disposed so as to flank the liquid crystal display 
element; and 
at least one optical retardation compensator plate disposed between the 
liquid crystal display element and the polarizers, the optical retardation 
compensator plate having an inclining refractive index ellipsoid, 
wherein the orientation film divides the liquid crystal layer in each pixel 
into a plurality of divisions of mutually different volumes and orientates 
the divisions in mutually different directions, and the pretilt angle 
formed by the orientation films and the major axes of liquid crystal 
molecules in the liquid crystal layer is set within such a range that tone 
reversion does not occur in the opposite viewing direction when halftone 
is being displayed by applying to the liquid crystal a voltage that is 
close to the threshold voltage for the liquid crystal. 
According to the first arrangement above, for a case where a linearly 
polarized ray is converted to an elliptically polarized ray according to 
the phase difference between the ordinary and extraordinary rays developed 
from the linearly polarized ray upon the passing through the liquid 
crystal layer possessing birefringence, the optical retardation 
compensator plate having an inclining refractive index ellipsoid 
compensates for the phase difference. 
However, the compensation function of this kind still falls short of 
satisfying the increasing demand for a better restraint in the viewing 
angle dependency. Bearing that in mind, the inventors of the present 
invention have conducted further research diligently and found out that 
the pretilt angle formed by the orientation films and the major axes of 
liquid crystal molecules in the liquid crystal layer affects the tone 
reversion in the opposite viewing direction, especially, when halftone is 
being displayed by applying to the liquid crystal a voltage that is close 
to the threshold voltage for the liquid crystal, which has led to the 
completion of the present invention. 
With the liquid crystal display device of the first arrangement in 
accordance with the present invention, the pretilt angle of the liquid 
crystal layer sealed in the liquid crystal display element is set within 
such a range that tone reversion does not occur in the opposite viewing 
direction when halftone is being displayed by applying to the liquid 
crystal a voltage that is close to the threshold voltage for the liquid 
crystal. This can eliminate the tone reversion in the opposite viewing 
direction on a screen displaying halftone, and thereby further restrain 
the viewing angle dependency of the screen. The contrast variations and 
coloration are also restrained better than only by the compensation 
function by the optical retardation compensator plate. 
Also with the liquid crystal display device of the first arrangement in 
accordance with the present invention, the liquid crystal layer is 
unequally divided into divisions having orientation of mutually different 
directions. 
This eliminates the difference in the contradictory viewing angle 
characteristics between the standard viewing angle and the opposite 
viewing angle, modifying the two kinds of viewing angle characteristics to 
be similar to each other. It thereby becomes possible to substantially 
uniformly restrain the decrease in contrast and the chances of whitish 
images displayed which occur when the viewing angle increases in the 
standard or opposite viewing direction, and especially to display the 
black color even darker. 
The inventors have found that the larger the pretilt angles are, the less 
likely the tone reversion occurs in the opposite viewing direction when 
halftone is being displayed by applying to the liquid crystal a voltage 
that is close to the threshold voltage for the liquid crystal. However, 
the inventors have also found that too large pretilt angles cause an 
abrupt decrease in luminance in the standard viewing direction when 
halftone is being displayed. Thus, the liquid crystal display device of 
the first arrangement in accordance with the present invention, including 
all the features of the arrangement above, is preferably characterized in 
that the pretilt angle is further set within such a range that luminance 
does not decrease abruptly in the standard viewing direction when halftone 
is being displayed by applying to the liquid crystal a voltage that is 
close to the threshold voltage for the liquid crystal. This can restrain 
the abrupt decrease in luminance in the standard viewing direction when 
halftone is being displayed. 
In order to accomplish the objects, a liquid crystal display device of a 
second arrangement in accordance with the present invention includes: 
a liquid crystal display element formed by sealing a liquid crystal layer 
between a pair of substrates each of which has an orientation film; 
a pair of polarizers disposed so as to flank the liquid crystal display 
element; and 
at least one optical retardation compensator plate disposed between the 
liquid crystal display element and the polarizers, the optical retardation 
compensator plate having an inclining refractive index ellipsoid, 
wherein the orientation film divides the liquid crystal layer in each pixel 
into a plurality of divisions of mutually different volumes and orientates 
the divisions in mutually different directions, and a value of the applied 
voltage for displaying halftone obtained by applying to the liquid crystal 
a voltage that is close to the threshold voltage for the liquid crystal is 
set within such a range that tone reversion does not occur in the opposite 
viewing direction when halftone is being displayed. 
According to the second arrangement above, similarly to the first 
arrangement, for a case where a linearly polarized ray is converted to an 
elliptically polarized ray according to the phase difference between the 
ordinary and extraordinary rays developed from the linearly polarized ray 
upon the passing through the liquid crystal layer possessing 
birefringence, the optical retardation compensator plate having an 
inclining refractive index ellipsoid compensates for the phase difference. 
However, the compensation function of this kind still falls short of 
satisfying the increasing demand for a better restraint in the viewing 
angle dependency. Bearing that in mind, the inventors of the present 
invention have conducted further research diligently and found out that 
the value of applied voltage for displaying halftone obtained by applying 
to the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal affects the tone reversion in the opposite viewing 
direction when halftone is being displayed, which has led to the 
completion of the present invention. 
With the liquid crystal display device of the second arrangement in 
accordance with the present invention, the value of applied voltage for 
displaying halftone obtained by applying to the liquid crystal a voltage 
that is close to the threshold voltage for the liquid crystal is set 
within such a range that tone reversion does not occur in the opposite 
viewing direction when halftone is being displayed. This can eliminate the 
tone reversion in the opposite viewing direction with a screen displaying 
halftone, and thereby further restrain the viewing angle dependency of the 
screen. The contrast variations and coloration are also restrained better 
than only by the compensation function by the optical retardation 
compensator plate. 
Also with the liquid crystal display device of the second arrangement in 
accordance with the present invention, similarly to the first arrangement, 
the liquid crystal layer is unequally divided into divisions having 
orientation of mutually different directions. 
This eliminates the difference in the contradictory viewing angle 
characteristics between the standard viewing angle and the opposite 
viewing angle, modifying the two kinds of viewing angle characteristics to 
be similar to each other. It thereby becomes possible to substantially 
uniformly restrain the decrease in contrast and the chances of whitish 
images displayed which occur when the viewing angle increases in the 
standard or opposite viewing direction, and especially to display the 
black color even darker. 
The voltage for displaying halftone is set in the Normally White mode, as 
an example, by way of the transmittance for the white tone to the 
transmittance for the OFF state. The inventors have found that the lower 
the transmittance is, the less likely the tone reversion occurs in the 
opposite viewing direction when white tone is being displayed. However, 
the inventors have also found that too low transmittances cause an abrupt 
decrease in luminance in the standard viewing direction. Thus, the liquid 
crystal display device of the second arrangement in accordance with the 
present invention, including all the features of the second arrangement 
above, is preferably characterized in that the value of applied voltage 
for displaying halftone obtained by applying to the liquid crystal a 
voltage that is close to the threshold voltage for the liquid crystal is 
further set within such a range that luminance does not decrease abruptly 
in the standard viewing direction when halftone is being displayed. This 
can restrain the abrupt decrease in luminance in the standard viewing 
direction when halftone is being displayed. 
The present invention will become more fully understood from the detailed 
description given hereinbelow and the accompanying drawings which are 
given by way of illustration only, are not in any way intended to limit 
the scope of the claims of the present invention.

DESCRIPTION OF THE EMBODIMENTS 
[First Embodiment] 
Referring to FIGS. 1 through 5, the following description will discuss an 
embodiment in accordance with the present invention. 
As illustrated in FIG. 1, the liquid crystal display device of the present 
embodiment is provided with a liquid crystal display element 1, a pair of 
optical retardation compensator plates 2 and 3, and a pair of polarizer 
plates (polarizers) 4 and 5. 
The liquid crystal display element 1 is constituted by electrode substrates 
6 and 7 that are placed face to face with each other and a liquid crystal 
layer 8 that is sandwiched therebetween. The electrode substrate 6 is 
constructed as follows: a glass substrate (a translucent substrate) 9 is 
provided as a base; a transparent electrode 10, made of ITO (Indium Tin 
Oxide), is formed on the surface, of the glass substrate 9, facing the 
liquid crystal layer 8; and an orientation film 11 is formed on the 
transparent electrode 10. The electrode substrate 7 is constructed as 
follows: a glass substrate (a translucent substrate) 12 is provided as a 
base; a transparent electrode 13, made of ITO, is formed on the surface, 
of the glass substrate 12, facing the liquid crystal layer 8,; and an 
orientation film 14 is formed on the transparent electrode 13. 
Although FIG. 1 shows a construction corresponding to one pixel for 
convenience of explanation, the transparent electrodes 10 and 13, which 
are strip-shaped with a predetermined width, are respectively placed on 
the glass substrates 9 and 12 with predetermined intervals all over the 
liquid crystal display element 1, and are designed so that they are 
orthogonal to each other on the glass substrates 9 and 12, when viewed in 
a direction perpendicular to the substrate surfaces. Portions at which the 
transparent electrodes 10 and 13 intersect each other correspond to pixels 
for carrying out display, and the pixels are placed in a matrix format 
over the entire structure of the present liquid crystal display device. 
The electrode substrates 6 and 7 are bonded by seal resin 15, and a liquid 
crystal layer 8 is sealed inside the space formed by the seal resin 15 and 
the electrode substrates 6 and 7. A voltage is applied via the transparent 
electrodes 10 and 13 by a driving circuit 17 according to display data. 
The orientation films 11 and 14 have areas of two different conditions. By 
means of those areas, the orientation of the liquid crystal molecules in 
the liquid crystal layer 8 is controlled so as to differ between first 
divisions (divided liquid crystal layer, first divided liquid crystal 
layer) 8a and second divisions (divided liquid crystal layer, second 
divided liquid crystal layer) 8b facing the respective two kinds of areas. 
The orientation films 11 and 14 produce the different orientation 
conditions by, for example, providing different pretilt angles to the 
liquid crystal molecules between the two kinds of areas or providing 
opposite pretilt directions to the liquid crystal molecules with respect 
to the normal to the substrate. 
As illustrated in FIG. 2, the pretilt angle is the angle .phi. formed by 
the orientation film 14 (11) and the major axes of liquid crystal 
molecules 20, and determined by the combination of liquid crystal material 
and rubbing treatment of the orientation films 11 and 14. 
In the liquid crystal display device of the present embodiment, in order to 
improve the viewing angle characteristics when the viewing angle increases 
in the upward, downward, right-hand, or left-hand direction, the liquid 
crystal layer 8 is divided unequally, and the pretilt angle of the liquid 
crystal layer 8 is set so as to produce the best properties when combined 
with the compensation function for phase difference by the optical 
retardation compensator plates 2 and 3 (will be described later in 
detail). 
The optical retardation compensator plates 2 and 3 are provided between the 
liquid crystal display element 1 and the respective polarizer plates 4 and 
5 disposed to flank the liquid crystal display element 1. The optical 
retardation compensator plates 2 and 3 are constituted by a support base 
made of a transparent organic polymer and discotic liquid crystal. The 
discotic liquid crystal is treated with an oblique orientation technique 
or hybrid orientation, and crosslinked. As a result, the optical 
retardation compensator plates 2 and 3 are formed so as to have a 
refractive index ellipsoid (will be described later in detail) that 
inclines to the optical retardation compensator plates 2 and 3. 
As for the support base of the optical retardation compensator plates 2 and 
3, triacetylcellulose (TAC), which is generally used for polarizer plates, 
is suitably applied with high reliability. Besides this, colorless, 
transparent organic polymeric films made of polycarbonate (PC), 
polyethyleneterephthalate (PET), etc., which are superior in environment 
resistance and chemical resistance, are also suitably applied. 
As illustrated in FIG. 3, each of the optical retardation compensator 
plates 2 and 3 has principal refractive indices na, nb and nc pointing in 
three different directions. The direction of the principal refractive 
index na coincides with the direction of the y-coordinate axis among the 
mutually orthogonal x-, y-, and z-coordinate axes. The direction of the 
principal refractive index nb inclines by .theta. in the direction of 
arrow A with respect to the z-coordinate axis (parallel to a normal to the 
surface) that is perpendicular to the surface of the optical retardation 
compensator plates 2 and 3, which surface corresponds to the screen. The 
direction of the principal refractive index nc inclines by .theta. in the 
direction of arrow B with respect to the x-coordinate axis (the surface). 
The principal refractive indices na, nb, and nc of the optical retardation 
compensator plates 2 and 3 are related to each other by the inequality: 
na=nc&gt;nb. Therefore, there exists only one optic axis, and the optical 
retardation compensator plates 2 and 3 have uniaxiality and a negative 
refractive index anisotropy. The first retardation value, (nc-na).times.d, 
of the optical retardation compensator plates 2 and 3 equals almost 0 nm, 
since na=nc, while the second retardation value, (nc -nb).times.d, is set 
to an arbitral value in a range from 80 nm to 250 nm. By setting the 
second retardation value in such a range, the compensation function for 
phase difference by the optical retardation compensator plates 2 and 3 is 
surely achieved. Note that (nc-na) and (nc-nb) each represent a refractive 
index anisotropy .DELTA.n, and that d represents the thickness of the 
optical retardation compensator plates 2 and 3. 
In general, in optical anisotropic materials such as liquid crystal and 
optical retardation compensator plates (phase difference films), the 
above-mentioned anisotropy of the three-dimensional principal refractive 
indices na, nc and nb is represented by a refractive index ellipsoid. The 
refractive-index anisotropy .DELTA.n assumes different values depending on 
the direction from which the refractive index ellipsoid is observed. 
The angle .theta. by which the direction of the principal refractive 
indices n.sub.b of the optical retardation compensator plates 2 and 3 
incline, i.e. the inclination angle .theta. of the refractive index 
ellipsoids, is set to an arbitrary value in the range 
15.degree..ltoreq..theta..ltoreq.75.degree.. By setting the inclination 
angle .theta. to such a value, regardless of whether the refractive index 
ellipsoids incline clockwise or counterclockwise, the compensation 
function for phase difference by the optical retardation compensator 
plates 2 and 3 is surely achieved. 
Instead of using the two optical retardation compensator plates 2 and 3, 
only one of them may be used and disposed on one side. Alternatively, both 
the optical retardation compensator plates 2 and 3 can be disposed on one 
side, one of them overlapping the other. As a further alternative, three 
or more optical retardation compensator plates may be used. 
As illustrated in FIG. 4, in the present liquid crystal display device, the 
polarizer plates 4 and 5 in the liquid crystal display element 1 are 
arranged so that their absorption axes AX.sub.1 and AX.sub.2 are 
orthogonal to the major axes L.sub.1 and L.sub.2 of liquid crystal 
molecules in contact with the orientation films 11 and 14 respectively 
(see FIG. 1). In the present liquid crystal display device, since the 
major axes L.sub.1 and L.sub.2 are orthogonal to each other, the 
absorption axes AX.sub.1 and AX.sub.2 are also orthogonal to each other. 
Here, as illustrated in FIG. 3, the direction D is defined as a direction 
formed by projecting the direction of the principal refractive index nb, 
which inclines in such a direction to impart anisotropy to the optical 
retardation compensator plates 2 and 3, onto the surface of the optical 
retardation compensator plates 2 and 3. As illustrated in FIG. 4, the 
optical retardation compensator plate 2 is placed so that the direction D 
(direction D.sub.1) is parallel to the major axis L.sub.1, and the optical 
retardation compensator plate 3 is placed so that the direction D 
(direction D.sub.2) is parallel to the major axis L.sub.2. 
With the above-mentioned arrangement of the optical retardation compensator 
plates 2 and 3 and the polarizer plates 4 and 5, the present liquid 
crystal display device can carry out so-called Normally White display 
wherein rays of light are allowed to pass during OFF time so that white 
display is provided. 
The following description will explain in detail the divisions of the 
liquid crystal layer 8 and the aforementioned setting of the pretilt angle 
for the liquid crystal layer 8 that produces the best properties in 
combination with the compensation function for phase difference by the 
optical retardation compensator plates 2 and 3 when the divided liquid 
crystal layer 8 is divided into divisions. 
As mentioned above, each pixel of the liquid crystal layer 8 is divided 
unequally into a first division 8a and a second division 8b to improve the 
viewing angle characteristics when the viewing angle increases in the 
upward, downward, right-hand, or left-hand direction. Specifically, the 
first division 8a and the second division 8b are set to have a ratio 
ranging from 6:4 to 19:1. 
Moreover, the orientation films 11 and 14 orientates the liquid crystal 
molecules to have perpendicular pretilt directions to the first division 
8a and the second division 8b. The pretilt directions P.sub.1 and P.sub.2 
of the orientation film 11 are set in reverse directions between the first 
division 8a and the second division 8b. Similarly, the pretilt directions 
P.sub.3 and P.sub.4 of the orientation film 14 are set in reverse 
directions between the first division 8a and the second division 8b. Note 
that the liquid crystal layer 8 may be divided along either the 
longitudinal direction of the transparent electrode 10 or that of the 
transparent electrode 13. 
The combination of a liquid crystal display element 1 having such a liquid 
crystal layer 8 with the optical retardation compensator plates 2 and 3 
can produce a proper orientation state to the viewing angle 
characteristics in the standard viewing direction and those in the 
opposite viewing direction. This can restrain the decrease in contrast and 
chances of whitish images displayed when the viewing angle increases in 
the upward or downward direction. As a result, especially, it becomes 
possible to display the black color which is highly susceptible to the 
decrease in contrast even darker. 
Moreover, in the liquid crystal display element 1, the first division 8a, 
which is the largest division in a pixel of the liquid crystal layer 8, is 
preferably set so that the inclination direction of the refractive index 
ellipsoid with respect to the optical retardation compensator plates 2 and 
3 is opposite to the pretilt direction of the liquid crystal molecules 
placed in the neighborhood of the orientation films 11 and 14. 
This allows the optical retardation compensator plates 2 and 3 to 
compensate for the imbalance of the optical properties caused by the 
liquid crystal molecules that still incline due to effect of the 
orientation when voltage is applied to the liquid crystal display element 
1. 
Consequently, it becomes possible to restrain the reversion phenomenon 
which occurs when the viewing angle increases in the standard viewing 
direction, and hence to display good images free from indecipherable 
darkness. Also, it becomes possible to restrain the decrease in contrast 
when the viewing angle increases in the opposite viewing direction, and 
hence to display good images free from whiteness. It also becomes possible 
to restrain the reversion phenomenon in the right- and left-hand 
directions. 
Moreover, as mentioned earlier, the pretilt angle of the liquid crystal 
layer 8 is set to produce the best properties when combined with the 
compensation function for phase difference by the optical retardation 
compensator plates 2 and 3. 
Specifically, the pretilt angle is set in a range that does not cause tone 
reversion in the opposite viewing direction in a halftone display state 
where a voltage that is close to the threshold voltage for the liquid 
crystal is applied to the liquid crystal. Here, since the Normally White 
display mode is selected, the halftone display state is close to white 
color. Hereinafter, the halftone display state close to white color will 
be referred to as white tone. 
It has been confirmed through experiments that the larger the pretilt 
angles are, the less likely the tone reversion occurs in the opposite 
viewing direction when white tone is being displayed, whereas too large 
pretilt angles cause an abrupt decrease in luminance in the standard 
viewing direction when white tone is being displayed. Thus, the pretilt 
angle also needs to be set within such a range that luminance does not 
decrease abruptly in the standard viewing direction when white tone is 
being displayed. 
More specifically, used as materials for the liquid crystal and at least 
either the orientation film 11 or the orientation film 14 is a combination 
of orientation film materials and liquid crystal materials that results in 
a pretilt angle larger than 4.degree. and smaller than 15.degree.. More 
preferable is a combination of orientation film materials and liquid 
crystal materials that results in a pretilt angle not smaller than 
6.degree. and not larger than 14.degree.. The ranges are common to all the 
division ratios of the liquid crystal layer 8 mentioned above. 
The setting of the pretilt angle on at least either of the opposite sides 
in a range larger than 4.degree. and smaller than 15.degree. enables the 
liquid crystal display device to be free from problematic tone reversion 
in the opposite viewing direction when white tone is being displayed and 
to be viewed in every direction at the viewing angle of 50.degree. which 
is typically required for liquid crystal display devices. 
Especially, the setting of the pretilt angle in a range not smaller than 
6.degree. and not larger than 14.degree. enables the liquid crystal 
display device to be viewed without tone reversion at all in the opposite 
viewing direction at the viewing angle of 70.degree. when white tone is 
being displayed. 
Selected as the liquid crystal material for the liquid crystal layer 8 of 
the liquid crystal display device in accordance with the present invention 
is a liquid crystal material of which the refractive index anisotropy, 
.DELTA.n(550), to light having a wavelength of 550 nm is designed to be 
within a range larger than 0.060 and smaller than 0.120. More preferably, 
a liquid crystal material of which the refractive index anisotropy, 
.DELTA.n(550), is designed to be within a range not smaller than 0.070 and 
not larger than 0.095 is used. 
As a result, the decrease in contrast ratio in the opposite viewing 
direction and the tone reversion phenomenon in the right- and left-hand 
directions can be further restrained by the compensation function for 
phase difference by the setting of the pretilt angle in the range above, 
as well as by the compensation function by the optical retardation 
compensator plates 2 and 3. 
As explained so far, the liquid crystal display device of the present 
embodiment includes, between the liquid crystal display element 1 and the 
polarizer plates 4 and 5, the optical retardation compensator plates 2 and 
3 each having a refractive index ellipsoid having three principal 
refractive indices, na, nb, and nc, mutually related by the inequality 
na=nc&gt;nb, the refractive index ellipsoid inclining as the direction of the 
principal refractive index nb parallel to the normal to the surface and 
the direction of either the principal refractive index na or nc in the 
surface recline either clockwise or counterclockwise around the direction 
of the principal refractive index nc or na in the surface, 
wherein the liquid crystal layer 8 in each pixel is divided unequally into 
divisions having different orientation directions, and the pretilt angle 
of the liquid crystal layer 8 is set within such a range that tone 
reversion does not occur in the opposite viewing direction when halftone 
is being displayed by applying to the liquid crystal a voltage that is 
close to the threshold voltage for the liquid crystal. 
Consequently from the compensation function for phase difference that 
occurs to the liquid crystal display element 1 according to the viewing 
angle by the optical retardation compensator plates 2 and 3, by the 
setting of the pretilt angle in such a range to produce the best 
combination for the compensation function by the optical retardation 
compensator plates 2 and 3, and also by the divisions of the liquid 
crystal layer 8, the tone reversion phenomenon that occurs when the 
viewing angle increases in the upward or downward direction is restrained, 
and the decrease in contrast and the chances of whitish images displayed 
in such an event are also restrained. Besides, the tone reversion 
phenomenon that occurs in the opposite viewing direction according to the 
viewing angle when white tone (because Normally White display is being 
adopted) is being displayed can be, above all, effectively restrained, 
which produces high quality images. 
Besides, since the liquid crystal display device of the present embodiment 
employs as the liquid crystal material for the liquid crystal layer 8 a 
liquid crystal material of which the refractive index anisotropy, 
.DELTA.n(550), to light having a wavelength of 550, is designed to be 
within a range larger than 0.060 and smaller than 0.120, the decrease in 
contrast ratio in the opposite viewing direction and the tone reversion 
phenomenon in the right- and left-hand directions can be further 
restrained by the compensation function for phase difference by the 
setting of the pretilt angle in the range above, as well as by the 
compensation function by the optical retardation compensator plates 2 and 
3. 
Note that although the liquid crystal display device of Normally White 
display has been taken as an example in the description above, the same 
effects can be obtained with a liquid crystal display device of Normally 
Black display by achieving compensation function for phase difference by 
the setting of the pretilt angle within such a range that tone reversion 
does not occur in the opposite viewing direction when halftone (black 
tone) is being displayed by applying to the liquid crystal a voltage that 
is close to the threshold voltage for the liquid crystal, as well as by 
the compensation function by the optical retardation compensator plates 2 
and 3. 
Note also that although the liquid crystal display device of a simple 
matrix method has been taken as an example in the description of the 
embodiment above, the present invention can be alternatively applied to a 
liquid crystal display device of an active matrix method using active 
switching elements such as TFTs. 
[Second Embodiment] 
Referring to FIG. 1, the following description will discuss another 
embodiment in accordance with the present invention. Here, for 
convenience, members of the present embodiment that have the same function 
as members of the first embodiment, and that are mentioned in the first 
embodiment are indicated by the same reference numerals and description 
thereof is omitted. 
The liquid crystal display device of the present embodiment is configured 
almost in the same manner as is the liquid crystal display device of the 
first embodiment shown in FIG. 1, except the following points: 
The liquid crystal display device of the first embodiment includes the 
liquid crystal layer 8 of which the pretilt angle is set in a range that 
does not cause tone reversion in the opposite viewing direction in a 
halftone display state where a voltage that is close to the threshold 
voltage for the liquid crystal is applied to the liquid crystal layer 8, 
so as to produce the best properties when combined with the compensation 
function for phase difference by the optical retardation compensator 
plates 2 and 3. 
The liquid crystal display device of the present embodiment, by contrast, 
includes a liquid crystal layer 8 such that the value of the applied 
voltage for displaying halftone obtained by applying to the liquid crystal 
layer 8 a voltage that is close to the threshold voltage for the liquid 
crystal is set within such a range that tone reversion does not occur in 
the opposite viewing direction when halftone is being displayed, so as to 
produce the best properties when combined with the compensation function 
for phase difference by the optical retardation compensator plates 2 and 
3. 
Next, the above differences will be explained in detail. 
Since the liquid crystal display device of the present embodiment is of 
Normally White display, the value of the applied voltage for realizing 
halftone display state where a voltage that is close to the threshold 
voltage for the liquid crystal is applied to the liquid crystal, i.e. 
white tone, is set within such a range that tone reversion does not occur 
in the opposite viewing direction when that voltage is being applied. 
It has been confirmed through experiments that the lower the transmittance 
when white tone is being displayed is, the less likely the tone reversion 
occurs in the opposite viewing direction when white tone is being 
displayed. On the other hand, too low transmittances cause an abrupt 
decrease in luminance in the standard viewing direction and in the right- 
and left-hand directions. Thus, the voltage applied to the liquid crystal 
that determines the transmittance when white tone is being displayed needs 
to be set also within such a range that luminance does not decrease 
abruptly in the standard viewing direction and in the right- and left-hand 
directions when white tone is being displayed. 
Specifically, the voltage applied to the liquid crystal when white tone is 
being displayed is set to derive a transmittance higher than 85% that in 
the OFF state where the voltage applied to the liquid crystal is zero. In 
such a case, the voltage applied to the liquid crystal when white tone is 
being displayed is more preferably set to derive a transmittance in a 
range not less than 90% and not more than 97% that in the OFF state. The 
ranges are common to all the division ratios above of the liquid crystal 
layer 8. 
The setting of the voltage applied to the liquid crystal when white tone is 
being displayed so as to derive a transmittance higher than 85% that in 
the OFF state enables the liquid crystal display device to be free from 
problematic tone reversion in the opposite viewing direction when white 
tone is being displayed and to be viewed in every direction at the viewing 
angle of 50.degree. which is typically required for liquid crystal display 
devices. 
Especially, the setting of the voltage applied to the liquid crystal when 
white tone is being displayed so as to derive a transmittance in a range 
not less than 90% and not more than 97% that in the OFF state enables the 
liquid crystal display device to be viewed without tone reversion at all 
in the opposite viewing direction at the viewing angle of 70.degree. when 
white tone is being displayed. 
As explained above, the liquid crystal display device of the present 
embodiment includes, between the liquid crystal display element 1 and the 
polarizer plates 4 and 5, the optical retardation compensator plates 2 and 
3 each having a refractive index ellipsoid having three principal 
refractive indices, na, nb, and nc, mutually related by the inequality 
na=nc&gt;nb, the refractive index ellipsoid inclining as the direction of the 
principal refractive index nb parallel to the normal to the surface and 
the direction of either the principal refractive index na or nc in the 
surface recline either clockwise or counterclockwise around the direction 
of the principal refractive index nc or na in the surface, wherein the 
liquid crystal layer 8 in each pixel is divided unequally into divisions 
having different orientation directions, and the value of the applied 
voltage for realizing halftone display where a voltage that is close to 
the threshold voltage for the liquid crystal is applied to the liquid 
crystal is set within such a range that tone reversion does not occur in 
the opposite viewing direction in the state where that voltage is applied. 
Consequently from the compensation function for phase difference that 
occurs to the liquid crystal display element 1 according to the viewing 
angle by the optical retardation compensator plates 2 and 3, by the 
setting of the pretilt angle in such a range to produce the best 
combination for the compensation function by the optical retardation 
compensator plates 2 and 3, and also by the divisions of the liquid 
crystal layer 8, the tone reversion phenomenon that occurs when the 
viewing angle increases in the upward or downward direction is restrained, 
and the decrease in contrast and the chances of whitish images displayed 
in such an event are also restrained. Besides, the tone reversion 
phenomenon that occurs in the opposite viewing direction according to the 
viewing angle when white tone (because Normally White display is being 
adopted) is being displayed can be, above all, effectively restrained, 
which produces high quality images. 
Besides, similarly to the liquid crystal display device of the previous 
embodiment, by employing as the liquid crystal material for the liquid 
crystal layer 8 a liquid crystal material of which the refractive index 
anisotropy, .DELTA.n(550), to light having a wavelength of 550 nm is 
designed to be within a range larger than 0.060 and smaller than 0.120, 
and more preferably, within a range not smaller than 0.070 and not larger 
than 0.095, the decrease in contrast ratio in the opposite viewing m 
direction and the tone reversion phenomenon in the right-and left-hand 
directions can be further restrained by the compensation function for 
phase difference by the setting of the voltage applied to the liquid 
crystal when white tone is being displayed in the range above, as well as 
by the compensation function by the optical retardation compensator plates 
2 and 3. 
Note that although the liquid crystal display device of Normally White 
display has been taken as an example in the description above, the same 
effects can be obtained with a liquid crystal display device of Normally 
Black display by achieving compensation function for phase difference by 
the setting of the voltage to be applied to the liquid crystal for 
halftone (black tone) display obtained by applying to the liquid crystal a 
voltage that is close to the threshold voltage for the liquid crystal 
within such a range that tone reversion does not occur in the opposite 
viewing direction when halftone is being displayed, as well as by the 
compensation function by the optical retardation compensator plates 2 and 
3. 
Note also that similarly to the first embodiment, apart from the liquid 
crystal display device of a simple matrix method, the present invention 
can be applied to a liquid crystal display device of an active matrix 
method using active switching elements such as TFTs. 
EXAMPLES 
Referring to FIGS. 1, 6, and 11(a) to 11(c), the following description will 
explain examples of the liquid crystal display devices of the first and 
second embodiments in comparison with comparative examples. 
First Example 
In the present embodiment, viewing angle dependency of the liquid crystal 
display device was measured by using a measuring system including a light 
receiving element 21, an amplifier 22, and a recording device 23 as shown 
in FIG. 6. The liquid crystal cell 16 of the liquid crystal display device 
is placed so that the surface 16a facing the glass substrate 9 lies on the 
reference plane X-Y of the rectangular coordinates XYZ. The light 
receiving element 21 is an element capable of receiving light at a certain 
solid light receiving angle, and is located a predetermined distance away 
from the original point of the coordinates at an angle (viewing angle) of 
.phi. with respect to the Z-direction orthogonal to the surface 16a. 
Upon measurement, monochromatic light having a wavelength of 550 nm is 
emitted from the surface opposite the surface 16a to irradiate the liquid 
crystal cell 16 in the measuring system. Part of the monochromatic light 
having passed through the liquid crystal cell 16 enters the light 
receiving element 21. Output by the light receiving element 21 is 
amplified to a predetermined level by the amplifier 22, and recorded in 
the recording device 23, such as a waveform memory or a recorder. 
Here, three samples #1 to #3 were prepared by using Optomer AL (product 
name), available from Japan Synthetic Rubber Co., Ltd., as the orientation 
films 11 and 14 of the liquid crystal cell 16 of the liquid crystal 
display device shown in FIG. 1, using liquid crystal materials having 
respective division ratios of the first and second divisions 8a and 8b set 
to 6:4, 17:3, and 19:1 as the liquid crystal layer 8, and setting the 
thickness of the cells (of the liquid crystal layers 8) to 5 .mu.m. 
Used as the optical retardation compensator plates 2 and 3 of the samples 
#1 to #3 are those constituted by a transparent support base (e.g., 
triacetylcellulose (TAC)) on which discotic liquid crystal is applied. The 
discotic liquid crystal is treated with an oblique orientation technique, 
and crosslinked. The optical retardation compensator plates 2 and 3 each 
have resulting first and second retardation values of 0 and 100 nm 
respectively, a principal refractive index nb inclining by 20.degree. in 
the direction of arrow A with respect to the z-coordinate axis of the x-, 
y-, and z-coordinates system, and a principal refractive index nc 
inclining by 20.degree. in the direction of arrow B with respect to the 
x-coordinate axis (that is, the inclination angle of the refractive index 
ellipsoid .theta.=20.degree.) as shown in FIG. 3. 
Here, the samples #1 to #3 were placed in the measuring system shown in 
FIG. 6, and the output levels by the light receiving element 21 in 
response to the applying of voltage to the samples #1 to #3 were measured 
with the light receiving element 21 being fixed at a certain angle .phi.. 
The measurement was done, assuming that the Y-direction points the top side 
of the screen and the X-direction points the left-hand direction (standard 
viewing direction) of the screen, while disposing the light receiving 
element 21 in the upward direction, the downward direction, and the right- 
and left-hand directions with the angle .phi. being maintained at 
30.degree.. The measurement was also done with the light receiving element 
21 placed in the Z-direction. 
FIGS. 7(a), 7(b), and 7(c) show the results. FIGS. 7(a), 7(b), and 7(c) are 
graphs showing transmittance of light with respect to the voltage applied 
to the samples #1 to #3 (the transmittance versus liquid crystal applied 
voltage characteristics of the samples #1 to #3), FIG. 7(a) showing the 
results of measurement of the sample #1 having a division ratio of 6:4, 
FIG. 7(b) showing the results of measurement of the sample #2 having a 
division ratio of 17:3, FIG. 7(c) showing the results of measurement of 
the sample #3 having a division ratio of 19:1. 
Referring to FIGS. 7(a) to 7(c), the solid curved lines L1 represent the 
characteristics in the Z-direction, the broken curved lines L2 represent 
the characteristics in the downward direction, the dotted curved lines L3 
represent the characteristics in the right-hand direction, the alternate 
long and short dashes curved lines L4 represent the characteristics in the 
upward direction, and the alternate long and two short dashes curved lines 
L5 represent the characteristics in the left-hand direction. 
It was confirmed from FIG. 7(b), illustrating the transmittance versus 
liquid crystal applied voltage characteristics of the sample #2 having a 
division ratio of 17:3, that the curved lines L2, L3, L4, and L5 moved 
closer to the curved line L1 in the halftone display area. Therefore, it 
was possible to obtain substantially the same viewing angle 
characteristics in the halftone display area even when the viewing angle 
increased in the upward, downward, right-hand, or left-hand direction of 
the screen. 
With the measurement in the downward direction, the transmittance stayed as 
low as about 7% in the ON state, and no tone reversion phenomenon was 
confirmed. With the measurement in the upward direction, it was confirmed 
that the transmittance was lower than that measured in the downward 
direction, and was substantially reduced in the ON state. 
The substantially same improvements on the viewing angle characteristics 
were confirmed with the samples #1 and #3 shown in FIGS. (a) and 7(c). 
In particular, as shown in FIG. 7(a), a tendency started to appear at the 
division ratio of 6:4 that the curved line L2 (downward direction) and the 
curved line L4 (upward) moved closer toward each other in the halftone 
display area and in the ON state, and the tendency became more evident 
with larger division ratios. Meanwhile, as shown in FIG. 7(c), a tendency 
started to appear at the division ratio of 19:1 that the curved line L2 
(downward direction) and the curved line L1 (Z-direction) moved closer 
toward each other, and the tendency became more evident with smaller 
division ratios. This restrained the phenomenon for displayed images to be 
too dark to be decipherable in the downward direction (the standard 
viewing direction). 
Further examination by means of division ratios having smaller increments 
confirmed that when the division ratio was set in the range from 7:3 to 
9:1, e.g. 17:3 as in the aforementioned case, the viewing angle 
characteristics were improved and became well-balanced between the upward 
direction and the downward direction. 
The liquid crystal display device has the two optical retardation 
compensator plates 2 and 3 on the sides of the liquid crystal display 
element 1. However, the viewing angle characteristics above can be 
obtained by either of the two optical retardation compensator plates 2 and 
3. When only one optical retardation compensator plate is used, the 
viewing angle characteristics in the upward and downward directions are 
improved and become well-balanced, but those in the right- and left-hand 
directions are asymmetric. By contrast, when two optical retardation 
compensator plates ares used, the viewing angle characteristics in the 
upward and downward directions are improved as in the above case, and in 
addition those in the right- and left-hand directions are improved and 
become symmetric as in the upward and downward directions. 
For comparison, a comparative sample #101 was prepared with the division 
ratio between the first divisions 8a and 8b set to 1:1, and placed in the 
measuring system shown in FIG. 6 to measure for the viewing angle 
dependency. The results are shown in FIG. 8 as a graph showing the 
transmittance versus liquid crystal applied voltage characteristics. 
Referring to that graph, the solid curved line L11 represents the 
characteristics in the Z-direction, the broken curved line L12 represents 
the characteristics in the downward direction, the dotted curved line L13 
represents the characteristics in the right-hand direction, the alternate 
long and short dashes curved line L14 represents the characteristics in 
the upward direction, and the alternate long and two short dashes curved 
line L15 represents the characteristics in the left-hand direction. 
It was confirmed from those results that the transmittance was lowered 
substantially in an ON state in the right- and left-hand directions and 
that there is no problem with the viewing angle characteristics. It was 
confirmed that by contrast the transmittance was not lowered substantially 
in an ON state in the upward and downward directions. The liquid crystal 
display device of the present comparative example has viewing angle 
dependency in the upward and downward directions. 
Second Example 
In the present example, seven sample cells #11 to #17 were prepared by 
using Optomer AL (product name), available from Japan Synthetic Rubber 
Co., Ltd., as the orientation films 11 and 14 of the liquid crystal cell 
16 of the liquid crystal display device shown in FIG. 1, selecting 
suitable liquid crystal materials to set the pretilt angles to 
2.0.degree., 4.0.degree., 6.0.degree., 8.0.degree., 14.0.degree., 
15.0.degree., and 16.0.degree. with respect to the orientation films 11 
and 14, and setting the thickness of the cells (of the liquid crystal 
layers 8) to 5 .mu.m. The first and second divisions 8a and 8b of the 
liquid crystal layer 8 were set to be 17:3. 
Homogeneous cells were prepared by injecting thereinto the materials for 
the samples #11 to #17, and measured with a pretilt angle measuring 
device, NSMAP-300LCD (Sigma Optical Machinery Co., Ltd.), for the pretilt 
angles of the samples #11 to #17. 
Used as the optical retardation compensator plates 2 and 3 of the samples 
#11 to #17 are the optical retardation compensator plates 2 and 3 of the 
same kind as those in the first example above including discotic liquid 
crystal treated with an oblique orientation technique. 
Tables 1 to 7 show results of visual observations of the sample cells #11 
to #17 under white light with various voltages applied for white tone. 
TABLE 1 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
100% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
60.degree. 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
70.degree. 
x.sub.1 
.DELTA..sub.2 
.DELTA..sub.1 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
______________________________________ 
(In Table 1, ".smallcircle." represents that no tone reversion was 
observed in the opposite viewing direction, ".DELTA..sub.1 " represents 
that no tone reversion was observed in the opposite viewing direction, bu 
that tone is distorted within the extent that did not pose any problem fo 
real use, ".DELTA..sub.2 " represents that tone reversion was observed in 
the opposite viewing direction within the extent that did not pose any 
problem for real use, "x.sub.1 " represents that # tone reversion was 
observed in the opposite viewing direction, and "x.sub.2 " represents tha 
a decrease in luminance was evident in the standard viewing direction to 
the extent unbearable for real use.) 
Supposing that the transmittance along the normal to the surface of the 
liquid crystal cell 16 is 100% in an OFF state where the voltage applied 
to the liquid crystal layer is zero, Table 1 shows results of display 
conditions when white tone is being displayed by setting a value that 
derives 100% of the transmittance along the normal for each sample. 
Table 1 shows that in a case where the voltage when white tone was being 
displayed was set to cause the transmittance to be 100%, the samples #14 
and #15, having respective pretilt angles of 8.0.degree. and 14.0.degree., 
displayed high quality images with no tone reversion being observed in the 
opposite viewing direction at a viewing angle of 70.degree.. 
Up to a viewing angle of 60.degree., the sample #13, having a pretilt angle 
of 6.0.degree., had no problems at all and displayed high quality images. 
At a viewing angle of 70.degree., tone was distorted, although not 
reversed, with the sample #13 in the opposite viewing direction only 
within the extent that did not pose any problem for real use. 
Up to a viewing angle of 60.degree., the sample #12, having a pretilt angle 
of 4.0.degree., had no problems at all and displayed high quality images. 
At a viewing angle of 70.degree., tone reversion was observed with the 
sample #12 only within the extent that did not pose any problem for real 
use. 
Up to a viewing angle of 60.degree., the sample #16 with the pretilt angle 
of 15.0.degree. displayed high quality images. However, at a viewing angle 
of 70.degree., a decrease in luminance was evident in the standard viewing 
direction to the extent unbearable for real use. 
With the sample #11, having a pretilt angle of 2.0.degree., tone reversion 
was observed in the opposite viewing direction at a viewing angle as low 
as 50.degree.. With the sample #17, having a pretilt angle of 
16.0.degree., a decrease in luminance was evident in the standard viewing 
direction at a viewing angle as low as 50.degree. to the extent unbearable 
for real use. 
TABLE 2 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
97% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
60.degree. 
x.sub.1 
.DELTA..sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
70.degree. 
x.sub.1 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
______________________________________ 
(In Table 2, ".smallcircle." represents that no tone reversion was 
observed in the opposite viewing direction, ".DELTA..sub.1 " represents 
that no tone reversion was observed in the opposite viewing direction, bu 
that tone is distorted within the extent that did not pose any problem fo 
real use, "x.sub.1 " represents that tone reversion was observed in the 
opposite viewing direction, and "x.sub.2 " represents that a decrease in 
luminance was evident in the standard viewing # direction to the extent 
unbearable for real use.) 
Table 2 shows results observed by setting a voltage for white tone for each 
sample to cause the transmittance to be 97% that in an OFF state. 
Table 2 shows that in a case where the voltage when white tone was being 
displayed was set to cause the transmittance to be 97%, the samples #13, 
#14, and #15, having respective pretilt angles of 6.0.degree., 
8.0.degree., and 14.0.degree., displayed high quality images with no tone 
reversion being observed in the opposite viewing direction at a viewing 
angle of 70.degree.. 
Up to a viewing angle of 50.degree., the sample #12, having a pretilt angle 
of 4.0.degree., displayed high quality images with no tone reversion being 
observed in the opposite viewing direction. At a viewing angle of 
60.degree., tone was distorted with the sample #12. However, the sample 
#12 did not pose any problem for real use, because tone was not reversed. 
The sample #16 with the pretilt angle of 15.0.degree. displayed high 
quality images up to a viewing angle of 50.degree.. However, at a viewing 
angle of 60.degree., a decrease in luminance was evident in the standard 
viewing direction to the extent unbearable for real use. 
With the sample #11, having a pretilt angle of 2.0.degree., tone reversion 
was observed in the opposite viewing direction at a viewing angle as low 
as 50.degree.. With the sample #17, having a pretilt angle of 
16.0.degree., a decrease in luminance was evident in the standard viewing 
direction at a viewing angle as low as 50.degree. to the extent unbearable 
for real use. 
TABLE 3 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
95% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
60.degree. 
x.sub.1 
.DELTA..sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
70.degree. 
x.sub.1 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
______________________________________ 
(In Table 3, ".smallcircle." represents that no tone reversion was 
observed in the opposite viewing direction, ".DELTA..sub.1 " represents 
that no tone reversion was observed in the opposite viewing direction, bu 
that tone is distorted within the extent that did not pose any problem fo 
real use, "x.sub.1 " represents that tone reversion was observed in the 
opposite viewing direction, and "x.sub.2 " represents that a decrease in 
luminance was evident in the standard viewing # direction to the extent 
unbearable for real use.) 
Table 3 shows results observed by setting a voltage for white tone for each 
sample to cause the transmittance to be 95% that in an OFF state. Those 
results were the same as in Table 2 in which the voltage was set to cause 
the transmittance to be 97%. 
TABLE 4 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
92% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
.DELTA..sub.2 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
60.degree. 
x.sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
70.degree. 
x.sub.1 
.DELTA..sub.2 
.smallcircle. 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
______________________________________ 
(In Table 4, ".smallcircle." represents that no tone reversion was 
observed in the opposite viewing direction, ".DELTA..sub.2 " represents 
that tone reversion was observed in the opposite viewing direction within 
the extent that did not pose any problem for real use, "x.sub.1 " 
represents that tone reversion was observed in the opposite viewing 
direction, and "x.sub.2 " represents that a decrease in luminance was 
evident in the standard viewing direction to the extent # unbearable for 
real use.) 
Table 4 shows results observed by setting a voltage for white tone for each 
sample to cause the transmittance to be 92% that in an OFF state. 
Table 4 shows that in a case where the voltage when white tone was being 
displayed was to cause the transmittance to be 92%, the samples #13, #14, 
and #15, having respective pretilt angles of 6.0.degree., 8.0.degree., and 
14.0.degree., displayed high quality images with no tone reversion being 
observed in the opposite viewing direction at a viewing angle of 
70.degree.. 
Up to a viewing angle of 60.degree., the sample #12, having a pretilt angle 
of 4.0.degree., displayed high quality images with no tone reversion being 
observed in the opposite viewing direction. At a viewing angle of 
70.degree., tone was reversed with the sample #12. However, the tone 
reversion was within the extent that did not pose any problem for real 
use. The sample #16 with the pretilt angle of 15.0.degree. displayed high 
quality images up to a viewing angle of 50.degree.. However, at a viewing 
angle of 60.degree., a decrease in luminance was evident in the standard 
viewing direction to the extent unbearable for real use. Tone reversion 
was observed at a viewing angle of 50.degree. with the sample #11, having 
a pretilt angle of 2.0.degree., within the extent that did not pose any 
problem for real use. 
With the sample #17, having a pretilt angle of 16.0.degree., a decrease in 
luminance was evident in the standard viewing direction at a viewing angle 
as low as 50.degree. to the extent unbearable for real use. 
TABLE 5 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
90% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
.DELTA..sub.1 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.DELTA..sub.3 
x.sub.2 
60.degree. 
.DELTA..sub.2 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.DELTA..sub.3 
x.sub.2 
x.sub.2 
70.degree. 
x.sub.1 
.DELTA..sub.1 
.smallcircle. 
.smallcircle. 
x.sub.2 
x.sub.2 
x.sub.2 
______________________________________ 
(In Table 5, ".smallcircle." represents that no tone reversion was 
observed in the opposite viewing direction, ".DELTA..sub.1 " represents 
that no tone reversion was observed in the opposite viewing direction, bu 
that tone is distorted within the extent that did not pose any problem fo 
real use, ".DELTA..sub.2 " represents that tone reversion was observed in 
the opposite viewing direction within the extent that did not pose any 
problem for real use, ".DELTA..sub.3 " represents that # a decrease in 
luminance was observed in the standard viewing direction within the exten 
that did not pose any problem for real use, "x.sub.1 " represents that 
tone reversion was observed in the opposite viewing direction, and 
"x.sub.2 " represents that a decrease in luminance was evident in the 
standard viewing direction to the extent unbearable for real use.) 
Table 5 shows results observed by setting a voltage for white tone for each 
sample to cause the transmittance to be 90% that in an OFF state. 
Table 5 shows that in a case where the voltage when white tone was being 
displayed was set to cause the transmittance to be 90%, the samples #13 
and #14, having respective pretilt angles of 6.0.degree. and 8.0.degree., 
displayed high quality images with no tone reversion being observed in the 
opposite viewing direction at a viewing angle of 70.degree.. 
Up to a viewing angle of 50.degree., the sample #15, having a pretilt angle 
of 14.0.degree., displayed high quality images. At a viewing angle of 
60.degree., a decrease in luminance was observed in the standard viewing 
direction within the extent that did not pose any problem for real use. Up 
to a viewing angle of 60.degree., the sample #12, having a pretilt angle 
of 4.0.degree., displayed high quality images with no tone reversion being 
observed even in the opposite viewing direction. At a viewing angle of 
70.degree., tone was distorted within the extent that did not pose any 
problem for real use, but no tone reversion was observed. With the sample 
#16 with the pretilt angle of 15.0.degree., a decrease in luminance was 
observed in the standard viewing direction at a viewing angle of 
50.degree. within the extent that did not pose any problem for real use. 
With the sample #11, having a pretilt angle of 2.0.degree., tone was 
distorted at a viewing angle of 50.degree. and reversed at a viewing angle 
of 60.degree. within the extent that did not pose any problem for real 
use. 
With the sample #17, having a pretilt angle of 16.0.degree., a decrease in 
luminance was evident in the standard viewing direction at a viewing angle 
as low as 50.degree. to the extent unbearable for real use. 
TABLE 6 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
87% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.smallcircle. 
.DELTA..sub.3 
x.sub.2 
x.sub.2 
60.degree. 
.DELTA..sub.3 
.DELTA..sub.3 
.DELTA..sub.3 
.DELTA..sub.3 
.DELTA..sub.3 
x.sub.2 
x.sub.2 
70.degree. 
x.sub.2 
x.sub.2 
x.sub.2 
x.sub.2 
x.sub.2 
x.sub.2 
x.sub.2 
______________________________________ 
(In Table 6, ".smallcircle." represents that no tone reversion was 
observed in the opposite viewing direction, ".DELTA..sub.3 " represents 
that a decrease in luminance was observed in the standard viewing 
direction within the extent that did not pose any problem for real use, 
and "x.sub.2 " represents that a decrease in luminance was evident in the 
standard viewing direction to the extent unbearable for real use.) 
Table 6 shows results observed by setting a voltage for white tone for each 
sample to cause the transmittance to be 87% that in an OFF state. 
Table 6 shows that in a case where the voltage when white tone was being 
displayed was set to cause the transmittance to be 87%, the samples #12, 
#13, and #14, having respective pretilt angles of 4.0.degree., 6.0.degree. 
and 8.0.degree., displayed high quality images up to a viewing angle of 
50.degree.. However, at a viewing angle of 60.degree., a decrease in 
luminance was observed in the standard viewing direction within the extent 
that did not pose any problem for real use. At a viewing angle of 
70.degree., a decrease in luminance was evident in the standard viewing 
direction to the extent unbearable for real use. 
At viewing angles of 50.degree. and 60.degree., a decrease in luminance was 
observed with the sample #15, having a pretilt angle of 14.0.degree., in 
the standard viewing direction within the extent that did not pose any 
problem for real use. At a viewing angle of 70.degree., a decrease in 
luminance was evident in the standard viewing direction to the extent 
unbearable for real use. 
With the samples #16 and #17, having respective pretilt angles of 
15.0.degree. and 16.0.degree., a decrease in luminance was evident in the 
standard viewing direction at a viewing angle as low as 50.degree. to the 
extent unbearable for real use. 
Up to a viewing angle of 50.degree., the sample #11, having a pretilt angle 
of 2.0.degree., displayed high quality images with no tone reversion being 
observed in the opposite viewing direction. However, at a viewing angle of 
60.degree., a decrease in luminance was observed in the standard viewing 
direction within the extent that did not pose any problem for real use. At 
a viewing angle of 70.degree., a decrease in luminance was evident in the 
standard viewing direction to the extent unbearable for real use. 
TABLE 7 
______________________________________ 
Applied voltage for white tone set to derive a transmittance 
85% that in the OFF state 
Pretilt angle (.degree.) 
Viewing Angle 
2.0 4.0 6.0 8.0 14.0 15.0 16.0 
(.theta.) 
#11 #12 #13 #14 #15 #16 #17 
______________________________________ 
50.degree. 
.DELTA..sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
60.degree. 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
70.degree. 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
x.sub.3 
______________________________________ 
(In Table 7, ".DELTA..sub.3 " represents that a decrease in luminance was 
observed in the standard viewing direction within the extent that did not 
pose any problem for real use, and "x.sub.3 " represents that a decrease 
in luminance was evident in the standard viewing direction and in the 
right and lefthand directions to the extent unbearable for real use.) 
Table 7 shows results observed by setting a voltage for white tone for each 
sample to cause the transmittance to be 85% that in an OFF state. 
Table 7 shows that in a case where the voltage when white tone was being 
displayed was set to cause the transmittance to be 85%, a decrease in 
luminance was evident with the samples #12, #13, #14, #15, #16, and #17, 
having respective pretilt angles of 4.0.degree., 6.0.degree. 8.0.degree., 
14.0.degree., 15.0.degree. and 16.0.degree., in the standard viewing 
direction and in the right- and left-hand directions at a viewing angle as 
low as 50.degree. to the extent unbearable for real use. 
At a viewing angle of 50.degree., a decrease in luminance was observed with 
the sample #11, having a pretilt angle of 2.0.degree., in the standard 
viewing direction within the extent that did not pose any problem for real 
use. At a viewing angle of 60.degree., a decrease in luminance was evident 
in the standard viewing direction to the extent unbearable for real use. 
It can be concluded from Tables 1 to 7 that tone reversion can be 
restrained in the opposite viewing direction by adjusting the pretilt 
angle or the transmittance when white tone is being displayed. It can be 
also concluded that in such an event, at a value ranging from 95% to 97% 
to which the transmittance is normally set as the transmittance for white 
tone, the setting of the pretilt angle in a range larger than 4.degree. 
and smaller than 15.degree. permits high quality images to be displayed at 
a viewing angle of 50.degree. with tone reversion being restrained in the 
opposite viewing direction and no decrease in luminance being observed in 
the standard viewing direction. It can be further concluded that the 
setting of the pretilt angle in a range not less than 6.degree. and not 
more than 14.degree. permits high quality images to be displayed at a wide 
viewing angle of 70.degree. with tone reversion being restrained in the 
opposite viewing direction and no decrease in luminance being observed in 
the standard viewing direction. 
Moreover, it can be concluded that at a pretilt angle of 4.degree. to 
14.degree., to which the pretilt angle is normally set, such setting that 
a transmittance not higher than 85% is derived as the transmittance when 
white tone is being displayed permits high quality images to be displayed 
at a viewing angle of 50.degree. with tone reversion being restrained in 
the opposite viewing direction and no decrease in luminance being observed 
in the standard viewing direction. It can be also concluded that such 
setting that a transmittance within a range not less than 90% and not more 
than 97% is derived permits high quality images to be displayed at a wide 
viewing angle of 70.degree. with tone reversion being restrained in the 
opposite viewing direction and no decrease in luminance being observed in 
the standard viewing direction. 
Moreover, it can be concluded that a combination of the adjustment of the 
pretilt angle and that of the transmittance when white tone is being 
displayed further enhances the effects of improvement. 
Next, viewing angle dependency of the liquid crystal display device was 
checked with the same samples #11 and #14 as above by using a measuring 
system including a light receiving element 21, an amplifier 22, and a 
recording device 23 as shown in FIG. 6. 
In this measuring system, the liquid crystal cell 16 of the liquid crystal 
display device is placed so that the surface 16a facing the glass 
substrate 9 lies on the reference plane X-Y of the rectangular coordinates 
XYZ. The light receiving element 21 is an element capable of receiving 
light at a certain solid light receiving angle, and is located a 
predetermined distance away from the original point of the coordinates at 
an angle (viewing angle) of .phi. with respect to the Z-direction 
orthogonal to the surface 16a. 
Upon measurement, monochromatic light having a wavelength of 550 nm is 
emitted from the surface opposite the surface 16a to irradiate the liquid 
crystal cell 16 in the measuring system. Part of the monochromatic light 
having passed through the liquid crystal cell 16 enters the light 
receiving element 21. Output by the light receiving element 21 is 
amplified to a predetermined level by the amplifier 22, and recorded in 
the recording device 23, such as a waveform memory or a recorder. 
Here, the output level by the light receiving element 21 in response to the 
applying of voltage to the samples #11 and #14 was measured with the light 
receiving element 21 being fixed at a certain angle .phi.. 
The measurement was done, assuming that the Y-direction is the left-hand 
side of the screen and the X-direction is the downward direction (standard 
viewing direction) of the screen, while disposing the light receiving 
element 21 in the upward direction (opposite viewing direction), the 
downward direction (standard viewing direction), and the right- and 
left-hand directions with the angle .phi. being maintained at 50.degree.. 
Graphs in FIGS. 9(a) to 9(c) show results, illustrating the behavior of the 
light transmittances of the samples #14 and #11, having respective pretilt 
angles of 8.0.degree. and 2.0.degree., in response to voltage applied 
thereto, that is, the transmittance versus liquid crystal applied voltage 
characteristics. 
FIG. 9(a) shows results of the measurement from the upward direction in 
FIG. 5. FIG. 9(b) shows results of the measurement from the downward 
direction in FIG. 5. FIG. 9(c) shows results of the measurement from the 
left-hand direction in FIG. 5. The same results as those shown in FIG. 
9(c) were obtained from the measurement from the right-hand direction. 
Hereinafter, the right- and left-hand directions. 
Referring to FIG. 9(a), the curved alternative long and short dash line L21 
represents results of measurement in the front direction, i.e. the 
direction normal to the surface. Both the sample #11 and the sample #14 
exhibit the same transmittance versus liquid crystal applied voltage 
characteristics. 
Referring to FIGS. 9(a) to 9(c), the solid lines L22, L24, and L26 
represent the sample #14, and the broken lines L23, L25, and L27 represent 
the sample #11. 
To compare the sample #14 with the sample #11 in terms of transmittance 
versus liquid crystal applied voltage characteristics in the upward 
direction in FIG. 9(a), the curved line L23 for the sample #11 has a bumpy 
shape, or rise and fall of the transmittance, between about 1 V and 2 V. 
By contrast, the curved line L22 for the sample #14 is flat between about 
1 V and 2 V with the transmittance staying at a value, and has no bumpy 
shape, showing that the sample #14 is free from the tone reversion 
phenomenon. 
To compare those samples in terms of transmittance versus liquid crystal 
applied voltage characteristics in the downward, left-hand, and right-hand 
directions in FIGS. 9(b) and 9(c), the curved lines L24 and L26 for the 
sample #14 and the curved lines L25 and L27 for the sample #11 show that 
the transmittance of the sample #14 drops a little more quickly than that 
of the sample #11. However, the transmittance of the sample #14 starts to 
conform to that of the sample #11 at around 2 V in FIG. 9(b) and at around 
2.7 V in FIG. 9(c). Therefore, it can be confirmed that the larger pretilt 
angle equalling 8.0.degree. has no adverse effects. 
The same results were obtained with samples prepared in the same manner as 
the samples #11 to #17 except that those samples each include optical 
retardation compensator plates 2 and 3 composed of discotic liquid crystal 
treated with hybrid orientation on a transparent support base. 
Second Example 
In the present example, three samples #21 to #23 were prepared by using 
Optomer AL (product name), available from Japan Synthetic Rubber Co., 
Ltd., as the orientation films 11 and 14 of the liquid crystal cell 16 of 
the liquid crystal display device shown in FIG. 1, using as the liquid 
crystal layer 8 (division ratio, 17:3) liquid crystal materials of which 
the pretilt angle is 6.degree. and of which the refractive index 
anisotropies .DELTA.n(550) at a wavelength of 550 nm are 0.070, 0.080, and 
0.095 respectively, and setting the thickness of the cells (of the liquid 
crystal layers 8) to 5 .mu.m. 
In the same manner as in the previous example, homogeneous cells were 
prepared by injecting thereinto the materials for the samples #21 to #23, 
and measured with a pretilt angle measuring device, NSMAP-3000LCD (Sigma 
Optical Machinery Co., Ltd.), for the pretilt angles of the samples #21 to 
#23. 
Used as the optical retardation compensator plates 2 and 3 of the samples 
#21 to #23 are the optical retardation compensator plates 2 and 3 of the 
same kind as those in the first example above including discotic liquid 
crystal treated with an oblique orientation technique. 
The samples #21 to #23 were placed in the measuring system shown in FIG. 6 
to measure the output level by the light receiving element 21 in response 
to the applying of voltage to the samples #21 to #23 with the light 
receiving element 21 being fixed at a certain angle .phi.. 
The measurement was done, assuming that the Y-direction is the left-hand 
side of the screen and the X-direction is the downward direction (standard 
viewing direction) of the screen, while disposing the light receiving 
element 21 in the upward direction (opposite viewing direction) and the 
right- and left-hand directions with the angle .phi. being maintained at 
50.degree.. 
Graphs in FIGS. 10(a) to 10(c) show results, illustrating the behavior of 
light transmittance of the samples #21 to #23 in response to voltage 
applied thereto, that is, the transmittance versus liquid crystal applied 
voltage characteristics. 
Referring to FIGS. 10(a) to 10(c), the curved alternative long and short 
dash lines L31, L34, and L37 represent the sample #21 using a liquid 
crystal material of .DELTA.n(550)=0.070 for the liquid crystal layer 8, 
the solid lines L32, L35, and L38 represent the sample #22 using a liquid 
crystal material of .DELTA.n(550)=0.080 for the liquid crystal layer 8, 
and the broken lines L33, L36, and L39 represent the sample #23 using a 
liquid crystal material of .DELTA.n(550)=0.095 for the liquid crystal 
layer 8. 
Two comparative samples #201 and #202 were also prepared as a comparative 
example for the present example in the same manner as the samples of the 
present example except that those samples #201 and #202 use liquid crystal 
materials of which the refractive index anisotropies .DELTA.n(550) at a 
wavelength of 550 nm are 0.060 and 0.120 as the liquid crystal layer 8 
(division ratio, 17:3) of the liquid crystal cell 16 shown in FIG. 1. The 
measuring system shown in FIG. 6 was used to measure the output level by 
the light receiving element 21 in response to the applying of voltage to 
the samples #201 and #202 with the light receiving element 21 being fixed 
at a certain angle .phi. in the same manner as in the present example. 
The measurement was done, assuming that the Y-direction is the upward 
direction of the screen and the X-direction is the downward direction 
(standard viewing direction) of the screen, while disposing the light 
receiving element 21 in the upward direction and the right- and left-hand 
directions with the angle .phi. being maintained at 50.degree.. 
Graphs in FIGS. 11(a) to 11(c) show results, illustrating the behavior of 
light transmittance of the samples #201 to #202 in response to voltage 
applied thereto, that is, the transmittance versus liquid crystal applied 
voltage characteristics. 
FIG. 11(a) shows results of the measurement from the upward direction in 
FIG. 5. FIG. 11(b) shows results of the measurement from the right-hand 
direction in FIG. 5. FIG. 11(c) shows results of the measurement from the 
left-hand direction in FIG. 5. 
Referring to FIGS. 11(a) to 11(c), the solid curved lines L40, L42, and L44 
represent the sample #201 using a liquid crystal material having 
.DELTA.n(550)=0.060 for the liquid crystal layer 8, and the broken curved 
lines L41, L43, and L45 represent the sample #202 using a liquid crystal 
material having .DELTA.n(550) of 0.120 for the liquid crystal layer 8. 
To compare the samples #21 to #23 and the samples #201 and #202 in terms of 
transmittance versus liquid crystal applied voltage characteristics in the 
upward direction in FIGS. 10(a) and 11(a), the curved lines L31, L32, and 
L33 show that the transmittances drop by sufficient amounts with higher 
voltages. By contrast, in comparison with the curved lines L31, L32, and 
L33 in FIG. 10(a), the curved line L41 shows that the transmittance does 
not drop sufficiently with higher voltages, and the curved line L40 shows 
that the transmittance drops and then rises with higher voltages, 
resulting in tone reversion phenomenon. 
To compare the samples #21 to #23 and the samples #201 and #202 in terms of 
transmittance versus liquid crystal applied voltage characteristics in the 
right-hand direction in FIGS. 10(b) and 11(b), the curved lines L34, L35, 
and L36 show that the transmittances drop almost to zero with higher 
voltages. The curved line L42 shows that the transmittance drops almost to 
zero with higher voltages as in FIG. 10(b), while the curved line L43 
shows that tone reversion phenomenon occurs. 
The same results as in the right-hand direction were obtained in the 
left-hand direction with the samples #21 to #23 and the samples #201 and 
#202: namely, the curved lines L37, L38, and L39 in FIG. 10(c) and the 
curved line in FIG. 11(c) show that the transmittances drop almost to zero 
with higher voltages, whilst the curved line L45 in FIG. 11(c) alone shows 
that tone reversion phenomenon occurs. 
Visual observations were conducted of the samples #21 to #23 and the 
samples #201 and #202 under white light. 
The samples #21 to #23 and the sample #201 showed coloration in no 
direction at a viewing angle of 50.degree., displaying good images. By 
contrast, the sample #202 showed coloration ranging from yellow to orange 
in the right- and left-hand directions at a viewing angle of 50.degree.. 
It can be concluded from those results shown in FIGS. 10(a) to 10(c) that 
if the liquid crystal layer 8 is made of a liquid crystal material of 
which the refractive index anisotropy .DELTA.n(550) at a wavelength of 550 
nm is 0.070, 0.080, or 0.095, the transmittance drops by a sufficient 
amount with higher voltages, thereby shows no tone reversion phenomenon, 
expanding the effective viewing angle, and shows no coloration phenomenon, 
greatly improving the display quality of the liquid crystal display 
device. 
It can be concluded, on the other hand, from those results in FIGS. 11(a) 
to 11(c) that if the liquid crystal layer 8 is made of a liquid crystal 
material of which the refractive index anisotropy .DELTA.n(550) at a 
wavelength of 550 nm is 0.060 or 0.120, the viewing angle dependency is 
not restrained satisfactorily. 
The same results were obtained with samples prepared in the same manner as 
the samples #21 to #23 and the samples #201 and #202 except that those 
samples include optical retardation compensator plates 2 and 3 composed of 
discotic liquid crystal treated with hybrid orientation on a transparent 
support base. 
The transmittance versus liquid crystal applied voltage characteristics 
were examined for the dependency thereof upon the inclination angle 
.theta. of the refractive index ellipsoid of the optical retardation 
compensator plates 2 and 3, by varying the inclination angle .theta.. The 
results were such that the transmittance versus liquid crystal applied 
voltage characteristics remained virtually unchanged irrelevant to the 
orientation state of the discotic liquid crystal of the optical 
retardation compensator plates 2 and 3, as long as the inclination angle 
.theta. stayed in the range of 
15.degree..ltoreq..theta..ltoreq.75.degree.. It was also observed that 
when the inclination angle .theta. was varied out of that range, the 
effective viewing angle did not become wider in the opposite viewing 
direction. 
The transmittance versus liquid crystal applied voltage characteristics 
were examined for the dependency thereof upon the second retardation value 
of the optical retardation compensator plates 2 and 3, by varying the 
second retardation value. The results were such that the transmittance 
versus liquid crystal applied voltage characteristics remained virtually 
unchanged irrelevant to the orientation state of the discotic liquid 
crystal of the optical retardation compensator plates 2 and 3, as long as 
the second retardation value stayed in the range of 80 nm to 250 nm. It 
was also observed that when the second retardation value was varied out of 
that range, the effective viewing angle did not become wider in the 
horizontal directions. 
In light of the results of the visual observations of the comparative 
samples #201 and #202, three samples #24 to #26 were prepared in the same 
manner as in the present example except that the samples #24 to #26 used 
liquid crystal materials of which the refractive index anisotropies 
.DELTA.n(550) at a wavelength of 550 nm are 0.065, 0.100, and 0.115 as the 
liquid crystal layer 8 of the liquid crystal cell 16 shown in FIG. 1. The 
measuring system shown in FIG. 6 was used to measure the output level by 
the light receiving element 21 in response to the applying of voltage to 
the samples #24 to #26 with the light receiving element 21 being fixed at 
a certain angle .phi. in the same manner as in the present example. Visual 
observations were also conducted of the samples #24 to #26 under white 
light. 
The results show that the transmittance of the sample #25 with the 
refractive index anisotropy .DELTA.n(550) of 0.100 and that of the sample 
#26 with the refractive index anisotropy .DELTA.n(550) of 0.115 rose 
slightly with higher voltages in the right- and left-hand directions with 
the angle .phi. of 50.degree.. However, no tone reversion phenomenon was 
visually confirmed, and those rises in the transmittances were within the 
extent that did not pose any problem for real use. The results show no 
problem at all in the upward direction. 
Meanwhile, similarly to the transmittance of the aforementioned comparative 
sample #201 shown in FIG. 11(a), the transmittance of the sample #24 with 
the refractive index anisotropy .DELTA.n(550) of 0.065 dropped slightly 
and then rose with higher voltages in the upward direction. However, the 
rise in the transmittance was relatively small as compared with that of 
the sample #201, being within the extent that did not pose any problem for 
real use. The results show no problem at all in the right- and left-hand 
directions. 
Visual observation discovered slight coloration ranging from yellow to 
orange with the samples #25 and #26, however, within the extent that did 
not pose any problem for real use. Visual observation also discovered 
slight bluish coloration with the sample #24, however, also within the 
extent that did not pose any problem for real use. 
As a supplement, the sample #24 and the comparative sample #201 were 
measured for transmittances when white tone was being displayed in the 
direction normal to the surface of the liquid crystal cell 16, by applying 
a voltage of about 1 V. The results show that the transmittance of the 
comparative sample #201 dropped to the extent unbearable for real use, 
while the transmittance of the sample #24 dropped slightly, however, 
within the extent that did not pose any problem for real use. 
The same results were obtained in a case where Optomer AL (product name), 
available from Japan Synthetic Rubber Co., Ltd., was used as the 
orientation films 11 and 14 of the liquid crystal cell 16 of the liquid 
crystal display device shown in FIG. 1, and liquid crystal materials that 
formed pretilt angles of 4.degree., 8.degree., and 14.degree. to the 
orientation films 11 and 14 were used as the liquid crystal layer 8. 
As detailed above, the liquid crystal display device in accordance with the 
present invention is arranged to include: 
a liquid crystal display element formed by sealing a 
90.degree.-twist-orientated liquid crystal layer between a pair of 
translucent substrates, each substrate having a transparent electrode 
layer and an orientation film on a surface thereof facing the other; 
a pair of polarizers disposed so as to flank the liquid crystal display 
element; and 
at least one optical retardation compensator plate disposed between the 
liquid crystal display element and the polarizers, the optical retardation 
compensator plate having a refractive index ellipsoid having three 
principal refractive indices, na, nb, and nc, mutually related by the 
inequality na=nc&gt;nb, the refractive index ellipsoid inclining as the 
direction of the principal refractive index nb parallel to the normal to 
the surface and the direction of either the principal refractive index na 
or nc in the surface recline either clockwise or counterclockwise around 
the direction of the principal refractive index nc or na in the surface, 
and 
the liquid crystal display device is further arranged so that the 
orientation film divides the liquid crystal layer in each pixel into a 
plurality of divisions of mutually different volumes and orientates the 
divisions in mutually different directions and that the pretilt angle 
formed by the orientation films and the major axes of liquid crystal 
molecules in the liquid crystal layer is set within such a range that tone 
reversion does not occur in the opposite viewing direction when halftone 
is being displayed by applying to the liquid crystal a voltage that is 
close to the threshold voltage for the liquid crystal. 
The liquid crystal display device in accordance with the present invention, 
including all the features of the arrangement above, is preferably further 
arranged so that 
the pretilt angle is further within such a range that luminance does not 
decrease abruptly in the standard viewing direction when halftone is being 
displayed by applying to the liquid crystal a voltage that is close to the 
threshold voltage for the liquid crystal. 
Consequently, with the liquid crystal display devices in accordance with 
the present invention, it becomes possible to restrain change in phase 
difference of the liquid crystal display element better than only by the 
compensation function by the optical retardation compensator plate, 
especially, to eliminate the tone reversion in the opposite viewing 
direction on a screen displaying halftone by applying to the liquid 
crystal a voltage that is close to the threshold voltage for the liquid 
crystal, and thereby to further restrain the viewing angle dependency of 
the screen. Therefore, the liquid crystal display device including such an 
optical retardation compensator plate and a liquid crystal display element 
can prevent tone reversion phenomenon from occurring and the contrast 
ratio in the opposite viewing direction from decreasing. 
In addition, the compensation effect by the unequally divided liquid 
crystal layer eliminates the difference in the contradictory viewing angle 
characteristics between the standard viewing angle and the opposite 
viewing angle, modifying the two kinds of viewing angle characteristics to 
be similar to each other. It thereby becomes possible to substantially 
uniformly restrain the decrease in contrast and the chances of whitish 
images displayed which occur when the viewing angle increases in the 
standard or opposite viewing direction. 
Specifically, the range that does not cause tone reversion in the opposite 
viewing direction when halftone is being displayed by applying to the 
liquid crystal a voltage that is close to the threshold voltage for the 
liquid crystal, and that does not cause an abrupt decrease in luminance in 
the standard viewing direction when halftone is being displayed refers to 
the setting of the pretilt angle in each orientation segment of the 
divided liquid crystal layer on at least one of the substrates within a 
range larger than 4.degree. and smaller than 15.degree.. 
Therefore the liquid crystal display device in accordance with the present 
invention, including all the features of the arrangement above, is 
preferably further arranged so that 
the pretilt angle is set within a range larger than 4.degree. and smaller 
than 15.degree. in each orientation segment of the divided liquid crystal 
layer on at least one of the substrates. 
With this arrangement, although in some instances still incapable of 
completely eliminating tone reversion in the opposite viewing direction, 
the setting can restrain the tone reversion phenomenon on the liquid 
crystal screen to the extent that the liquid crystal screen can be viewed 
from any direction without serious problems for real use at the viewing 
angle of 50.degree., which is the viewing angle typically required for 
liquid crystal display devices. 
For a case of liquid crystal display devices with wider viewing angles such 
as 70.degree., the range that does not cause tone reversion in the 
opposite viewing direction when halftone is being displayed by applying to 
the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal, and that does not cause an abrupt decrease in 
luminance in the standard viewing direction when halftone is being 
displayed refers to the setting of the pretilt angle within a range not 
smaller than 6.degree. and not larger than 14.degree.. 
Therefore the liquid crystal display device in accordance with the present 
invention, including all the features of the arrangement above, is 
preferably further arranged so that 
the pretilt angle is set within a range not smaller than 6.degree. and not 
larger than 14.degree.. 
According to this arrangement, it becomes possible with liquid crystal 
display devices with wider viewing angles such as 70.degree. to completely 
eliminate the tone reversion in the opposite viewing direction on a screen 
displaying halftone by applying to the liquid crystal a voltage that is 
close to the threshold voltage for the liquid crystal. 
For these reasons, with the arrangement, the quality of images displayed by 
the liquid crystal display device is greatly improved in comparison with 
conventional liquid crystal display devices. 
Another liquid crystal display device in accordance with the present 
invention is arranged to include: 
a liquid crystal display element formed by sealing a 
90.degree.-twist-orientated liquid crystal layer between a pair of 
translucent substrates, each substrate having a transparent electrode 
layer and an orientation film on a surface thereof facing the other; 
a pair of polarizers disposed so as to flank the liquid crystal display 
element; and 
at least one optical retardation compensator plate disposed between the 
liquid crystal display element and the polarizers, the optical retardation 
compensator plate having a refractive index ellipsoid having three 
principal refractive indices, na, nb, and nc, mutually related by the 
inequality na=nc&gt;nb, the refractive index ellipsoid inclining as the 
direction of the principal refractive index nb parallel to the normal to 
the surface and the direction of either the principal refractive index na 
or nc in the surface recline either clockwise or counterclockwise around 
the direction of the principal refractive index nc or na in the surface, 
and 
the liquid crystal display device is further arranged so that the 
orientation film divides the liquid crystal layer in each pixel into a 
plurality of divisions of mutually different volumes and orientates the 
divisions in mutually different directions and that the value of applied 
voltage for displaying halftone obtained by applying to the liquid crystal 
a voltage that is close to the threshold voltage for the liquid crystal is 
set within such a range that tone reversion does not occur in the opposite 
viewing direction when halftone is being displayed. 
Moreover, the liquid crystal display device in accordance with the present 
invention, including all the features of the arrangement above, is 
preferably further arranged so that 
the value of applied voltage for displaying halftone obtained by applying 
to the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal is set within such a range that luminance does not 
decrease abruptly in the standard viewing direction when halftone is being 
displayed. 
Consequently, with the liquid crystal display devices of the above 
arrangement in accordance with the present invention, it is possible to 
restrain change in phase difference of the liquid crystal display element 
better than only by the compensation function by the optical retardation 
compensator plate, especially, to eliminate the tone reversion in the 
opposite viewing direction on a screen displaying halftone by applying to 
the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal, and thereby to further restrain the viewing angle 
dependency of the screen. Therefore, the liquid crystal display device 
including such an optical retardation compensator plate and a liquid 
crystal display element can prevent tone reversion phenomenon from 
occurring and the contrast ratio in the opposite viewing direction from 
decreasing. 
In addition, the compensation effect by the unequally divided liquid 
crystal layer eliminates the difference in the contradictory viewing angle 
characteristics between the standard viewing angle and the opposite 
viewing angle, modifying the two kinds of viewing angle characteristics to 
be similar to each other. It thereby becomes possible to substantially 
uniformly restrain the decrease in contrast and the chances of whitish 
images displayed which occur when the viewing angle increases in the 
standard or opposite viewing direction. 
Specifically, the range that does not cause tone reversion in the opposite 
viewing direction when halftone is being displayed by applying to the 
liquid crystal a voltage that is close to the threshold voltage for the 
liquid crystal, and that does not cause an abrupt decrease in luminance in 
the standard viewing direction when halftone is being displayed refers to 
the setting of the value of applied voltage for displaying halftone 
obtained by applying to the liquid crystal a voltage that is close to the 
threshold voltage for the liquid crystal so as to obtain a transmittance 
higher than 85% that in a bright state (OFF state) where no voltage is 
applied to the liquid crystal. 
Therefore, the liquid crystal display device in accordance with the present 
invention, including all the features of the arrangement above, is 
preferably arranged so that 
the value of applied voltage for displaying halftone obtained by applying 
to the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal is set to obtain a transmittance higher than 85% that 
in a bright state where no voltage is applied to the liquid crystal. 
With this arrangement, although in some instances still incapable of 
completely eliminating tone reversion in the opposite viewing direction, 
the setting can restrain the tone reversion phenomenon on the liquid 
crystal screen to the extent that the liquid crystal screen can be viewed 
from any direction without serious problems for real use at the viewing 
angle of 50.degree., which is the viewing angle typically required for 
liquid crystal display devices. 
For a case of liquid crystal display devices with wider viewing angles such 
as 70.degree., the range that does not cause tone reversion in the 
opposite viewing direction when halftone is being displayed by applying to 
the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal, and that does not cause an abrupt decrease in 
luminance in the standard viewing direction when halftone is being 
displayed refers to the setting of the value of applied voltage for 
displaying halftone obtained by applying to the liquid crystal a voltage 
that is close to the threshold voltage for the liquid crystal so as to 
obtain a transmittance within a range not less than 90% and not more than 
97% that in a bright state (OFF state) where no voltage is applied to the 
liquid crystal. 
Therefore, the liquid crystal display device in accordance with the present 
invention, including all the features of the arrangement above, is 
preferably arranged so that 
the value of applied voltage for displaying halftone obtained by applying 
to the liquid crystal a voltage that is close to the threshold voltage for 
the liquid crystal is set to obtain a transmittance within a range not 
less than 90% and not more than 97% that in a bright state where no 
voltage is applied to the liquid crystal. 
According to the arrangement it becomes possible with liquid crystal 
display devices with wider viewing angles such as 70.degree. to completely 
eliminate the tone reversion in the opposite viewing direction on a screen 
displaying halftone by applying to the liquid crystal a voltage that is 
close to the threshold voltage for the liquid crystal. 
For these reasons, with the arrangement, the quality of images displayed by 
the liquid crystal display device is greatly improved in comparison with 
conventional liquid crystal display devices. 
The liquid crystal display device in accordance with the present invention, 
including all the features of the arrangement above, is preferably further 
arranged so that 
the refractive index anisotropy, .DELTA.n(550), of the liquid crystal 
material for the liquid crystal layer to light having a wavelength of 550 
nm is set within a range larger than 0.060 and smaller than 0.120. 
This is because of a confirmation that if the refractive index anisotropy, 
.DELTA.n(550), of the liquid crystal material to light having a wavelength 
of 550 nm, which is approximately the mid-range of the visible region of 
the spectrum, is either not larger than 0.060 or not smaller than 0.120, 
tone reversion phenomenon and/or a decrease in contrast ratio occur(s) 
depending upon the viewing direction. Therefore, the phase difference that 
occurs to the liquid crystal display element in accordance with the 
viewing angle can be eliminated by setting the refractive index 
anisotropy, .DELTA.n(550), of the liquid crystal material to light having 
a wavelength of 550 nm so as to be within a range larger than 0.060 and 
smaller than 0.120. This can further restrain the contrast variations and 
tone reversion phenomenon in the right- and left-hand directions, as well 
as the coloration phenomenon that occurs depending upon the viewing angle. 
For these reasons, by employing the arrangement to set the refractive index 
anisotropy .DELTA.n(550) within a range larger than 0.060 and smaller than 
0.120, the quality of images displayed by the liquid crystal display 
device above in accordance with the present invention is further improved. 
In such an event the phase difference that occurs to the liquid crystal 
display element in accordance with the viewing angle can be more 
effectively eliminated by setting the refractive index anisotropy, 
.DELTA.n(550), of the liquid crystal material for the liquid crystal layer 
to light having a wavelength of 550 nm so as to be within a range not 
smaller than 0.070 and not larger than 0.095. This can surely restrain the 
contrast variations, coloration phenomenon, and tone reversion phenomenon 
in the right- and left-hand directions of the images displayed by the 
liquid crystal display device according to the viewing angle. 
Moreover, the liquid crystal display device of the above arrangement in 
accordance with the invention, is preferably arranged so that 
the or each optical retardation compensator plate has a refractive index 
ellipsoid inclining by an inclination angle set within a range of 
15.degree. to 75.degree.. 
By setting the inclination angle of the refractive index ellipsoid to be 
within a range of 15.degree. to 75.degree. with respect to the or each 
optical retardation compensator plate incorporated in the liquid crystal 
display device, it is assured that the present invention provides the 
aforementioned compensation function for the phase difference by the 
optical retardation compensator plate. Therefore, the visibility of the 
liquid crystal display device of the above arrangement in accordance with 
the present invention can be surely improved. 
Moreover, the liquid crystal display device of the above arrangement in 
accordance with the invention, is preferably arranged so that the or each 
optical retardation compensator plate has a product, (n.sub.a 
-n.sub.b).times.d, of the difference between the principal refractive 
indices, na and nb, and the thickness, d, of the optical retardation 
compensator plate, the product being set to be from 80 nm to 250 nm. 
By setting the product, (n.sub.a -n.sub.b).times.d, of the difference 
between the principal refractive indices, na and nb, and the thickness, d, 
of the optical retardation compensator plate, so as to be from 80 nm to 
250 nm with respect to the or each optical retardation compensator plate 
incorporated in the liquid crystal display device, it is assured that the 
present invention provides the aforementioned compensation function for 
the phase difference by the optical retardation compensator plate. 
Therefore, the visibility of the liquid crystal display device of the 
above arrangement in accordance with the present invention can be surely 
improved. 
Moreover, as described earlier, the liquid crystal display device in 
accordance with the present invention is preferably further arranged so 
that 
the optical retardation compensator plate is placed so that in the largest 
divided liquid crystal layer in each pixel, the direction of the 
inclination of the refractive index ellipsoid is opposite to the direction 
of the inclination of the liquid crystal molecules in a vicinity of the 
inner side of the orientation film when a voltage is applied to the liquid 
crystal molecules by the transparent electrodes. 
With the arrangement, if the direction of the inclination of the refractive 
index ellipsoid to the surface of the optical retardation compensator 
plate is opposite in the largest divided liquid crystal layer to the 
direction of the inclination of the liquid crystal molecules when a 
voltage is applied to the liquid crystal molecules, the optical properties 
by the liquid crystal molecules and those of the refractive index 
ellipsoid, i.e. the optical retardation compensator plate are set to be 
opposite to each other. Therefore, although the liquid crystal molecules 
in the vicinity of the inner surface of the orientation film do not stand 
up on the application of voltage due to the effect of the orientation, the 
optical retardation compensator plate can compensate for the imbalance of 
the optical properties caused by the liquid crystal molecules. 
Consequently, it becomes possible to restrain the reversion phenomenon when 
the viewing angle increases in the standard viewing direction, and hence 
to display good images free from indecipherable darkness. Also, it becomes 
possible to restrain the decrease in contrast when the viewing angle 
increases in the opposite viewing direction, and hence to display good 
images free from whiteness. It also becomes possible to restrain the 
reversion phenomenon in the right- and left-hand directions. 
For these reasons, with the arrangement, the viewing angle characteristics 
of the liquid crystal display device in accordance with the present 
invention is greatly improved. 
Moreover, as described earlier, the liquid crystal display device in 
accordance with the present invention is preferably further arranged so 
that 
a first divided liquid crystal layer and a second divided liquid crystal 
layer are provided as the divided liquid crystal layer, and the ratio of 
the volumes of the first and second divided liquid crystal layers is set 
in a range from 6:4 to 19:1. 
Hence, the viewing angle characteristics are more surely improved by the 
arrangement of specifying the inclination direction of the refractive 
index ellipsoid. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art intended to be included within 
the scope of the following claims.