Liquid crystal display device having a phase difference plate with one refractive index at an angle to the surface normal

A phase difference plate capable of eliminating contrast changes due to viewing angle changes of display image, coloring phenomenon of display screen, and black and white reversal phenomenon, and a liquid crystal display device capable of displaying images of high quality are presented. A phase difference plate is a drawn and elongated material possessing optical anisotropy such as high polymer compound formed in a flat plate form, and the direction of the minimum principal refractive index na of the three principal refractive indices na, nb, nc of the index ellipsoid is parallel to the y-axis direction, and the direction of the principal refractive index nb is inclined to the normal direction of the surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a phase difference plate and a liquid 
crystal display device, and more particularly to a liquid crystal display 
device for improving the viewing angle characteristics of the display 
screen. 
2. Description of the Related Art 
The liquid crystal display device using nematic liquid crystal display cell 
has been hitherto applied widely in numerical value segment type display 
device such as clock and desktop calculator, and active elements such as 
thin film transistors are formed on the light transmittable substrate of 
liquid crystal display cell as the switching means for selectively driving 
the pixel electrode, and color filter layers of red, green and blue are 
provided as color display means, and depending on the twist angle of 
liquid crystal, (a) the active drive type twisted nematic (TN) liquid 
crystal display system disposing the nematic liquid crystal molecules by 
twisting 90 degrees, and (b) the multiplex drive type super twisted 
nematic (STN) liquid crystal display system making use of sharp steepness 
of transmissivity-liquid crystal applied voltage characteristic by 
defining the twist angle of nematic liquid crystal cell at 90 degrees or 
more are known. 
In the latter (b) multiplex drive type STN liquid crystal display system, 
since peculiar coloring is present, the system of disposing optical 
compensation plates is considered useful for monochromatic display, and 
depending on the optical compensation plates it is classified into (b-1) 
two-layer type double super twisted nematic liquid crystal display system 
using liquid crystal cells twisted and disposed at a twist angle in 
reverse direction to the liquid crystal cell for display, and (b-2) the 
film added type liquid crystal display system disposing a film possessing 
optical anisotropy, and from the viewpoint of lightness of weight and 
cost, the latter (b-2) film added type liquid crystal display system is 
considered advantageous. 
On the other hand, the former (a) active drive type TN liquid crystal 
display system is roughly classified into (a-1) normally black system for 
displaying black color in a state without voltage application to the 
liquid crystal layer (OFF state) by disposing the polarization directions 
of a pair of polarizers parallel to each other, and (a-2) normally white 
system for displaying white color in OFF state by mutually crossing the 
polarization directions orthogonally, and the normally white system is 
considered more useful from the viewpoints of display contrast, color 
reproduction and dependence of display on viewing angle. 
In the conventional TN liquid crystal display device, however, since the 
refractive anisotropy is present in the liquid crystal molecules, and the 
liquid crystal molecules are disposed at inclination to the upper and 
lower electrode substrates, and the contrast of the display image varies 
depending on the viewing angle to observe, and the dependence on the 
viewing angle increases. In particular, as shown in the plan of the liquid 
crystal display cell in FIG. 3 or FIG. 19, when the viewing angle is 
inclined from the screen normal direction to the normal viewing angle 
direction 38, the display image is colored above a certain angle (this is 
called coloring phenomenon), or the black and white are inverted (reversal 
phenomenon). Or as the viewing angle is inclined in the anti-viewing angle 
direction 39, the contrast drops abruptly. 
To improve such dependence on the viewing angle, it may be considered to 
compensate for the phase of light by placing a phase difference plate 
having the direction of one principal refractive index of index ellipsoid 
parallel to the normal direction of the surface, as shown in perspective 
view in FIG. 7, between the liquid crystal layer and polarizer, but even 
by using such phase difference plate, there is a limit for improving the 
reversal phenomenon in the normal viewing angle direction. 
SUMMARY OF THE INVENTION 
It is hence a primary object of the invention to present a phase difference 
plate capable of eliminating contrast changes, coloring phenomenon, and 
reversal phenomenon depending on the viewing angle of the display image in 
order to solve the conventional problems, and a liquid crystal display 
device capable of displaying images of high quality by using such phase 
difference plate. 
The invention presents a phase difference plate forming a material having 
optical anisotropy in a flat plate form, wherein the direction of the 
principal refractive index of the index ellipsoid is inclined to the 
normal direction of the surface. 
In the invention, of the three principal refractive indices of the index 
ellipsoid, the direction of the minimum principal refractive index is 
parallel to the surface, and the directions of the other principal 
refractive indices are inclined to the surface. 
In the invention, of the three principal refractive indices of the index 
ellipsoid, the direction of the minimum principal refractive index is 
parallel to the surface, and the angle .theta. formed by the directions of 
the other principal refractive indices and the surface is in the condition 
of 20.degree..ltoreq..theta..ltoreq.70.degree.. 
The invention also presents a liquid crystal display device comprising: 
a liquid crystal display cell composed of a liquid crystal layer interposed 
between a pair of light transmittable substrates forming a transparent 
electrode layer and orientation film on the surface, 
a pair of polarizers disposed at both sides of the liquid crystal display 
cell, and 
at least one phase difference plate interposed between the liquid crystal 
display cell and polarizers. 
The invention presents a phase difference plate, not having refractive 
index anisotropy within the surface, with the principal refractive index 
nb in the normal direction of the surface smaller than the principal 
refractive indices na, nc within the surface, of which refractive index 
anisotropy is negative, 
wherein the direction of the principal refractive index nb is inclined to 
the normal direction of the surface, and the direction of the principal 
refractive index nb in the normal direction and the direction of the 
principal refractive index nc or na within the surface are inclined 
counterclockwise or clockwise about the direction of the principal 
refractive index na or nc within the surface. 
In the phase difference plate of the invention, first and second phase 
difference plates composed of the same phase difference plate are stacked 
up, and the angle of the inclined direction of the principal refractive 
index nb in the normal direction of each phase difference plate is about 
90 degrees. 
According to the invention, the angle formed by the direction of 
inclination of the principal refractive index nb in the normal direction 
of the first phase difference plate and the direction of inclination of 
the principal refractive index nb in the normal direction of the second 
phase plate is about 90 degrees clockwise. 
The invention also presents a liquid crystal display device comprising: 
a liquid crystal display cell composed of a liquid crystal layer interposed 
between a pair of light transmittable substrates forming a transparent 
electrode layer and an orientation film on confronting surfaces, 
a pair of polarizers interposed at both sides of the liquid crystal display 
cell, and 
a phase difference plate interposed between the liquid crystal display cell 
and polarizers. 
In the liquid crystal display cell of the invention, the first phase 
difference plate of the two phase difference plates being stacked up is 
disposed so that the rubbing direction of the remote side substrate of the 
liquid crystal display cell may be nearly equal to the inclination 
direction of the principal refractive index nb in the normal direction of 
the first phase difference plate, and the second phase difference plate is 
disposed so that the rubbing direction of the near side substrate of the 
liquid crystal display cell may be nearly opposite to the inclination 
direction of the principal refractive index nb in the normal direction of 
the second phase difference plate. 
The invention also presents a liquid crystal display device comprising: 
a liquid crystal display cell composed of a liquid crystal layer interposed 
between a pair of light transmittable substrates forming a transparent 
electrode layer and an orientation film on confronting surfaces, 
a pair of polarizers disposed at both sides of the liquid crystal display 
cell, and 
at least one phase difference plate interposed between the liquid crystal 
display cell and polarizers. 
In the invention, one phase difference plate is interposed between the 
liquid crystal display cell and polarizer. 
Moreover, the invention, the inclination direction of the principal 
refractive index nb in the normal direction of the phase difference plate 
is nearly in the opposite direction of the rubbing direction of the near 
side substrate of the liquid crystal display cell. 
According to the invention, light of linear polarization transmits through 
a material having birefringence such as liquid crystal to generate normal 
light and abnormal light, and when converted into elliptical polarization 
according to their phase difference, a phase difference plate having the 
direction of principal refractive index inclined to the normal direction 
of the surface is placed at one side or both sides of the member having 
the birefringence to compensate for the change of phase difference of 
normal light and abnormal light caused by viewing angle, thereby making it 
possible to convert into linear polarization in a wide range of viewing 
angle. 
In such phase difference plate, the direction of the minimum principal 
refractive index of the three principal refractive indices of the index 
ellipsoid is parallel to the surface, and the directions of the other 
refractive indices are inclined to the surface, and it is therefore 
possible to compensate for the phase difference change between normal 
light and abnormal light for the changes of viewing angle in the direction 
in the normal viewing angle direction within a vertical plane to the 
direction of the minimum principal refractive index, including the surface 
normal line. 
Furthermore, when the direction of the principal refractive index is 
parallel to the surface, and the angle .theta. formed by the directions of 
the other principal refractive indices and the surface satisfies the 
condition of 20.degree..ltoreq..theta..ltoreq.70.degree. the phase may be 
compensated favorably for the viewing angle change in a range of 0 to 60 
degrees in the normal viewing angle direction. 
According to the constitution comprising a liquid crystal display cell 
composed of a liquid crystal layer interposed between a pair of light 
transmittable substrates forming a transparent electrode layer and an 
orientation film on confronting surfaces, a pair of polarizers disposed at 
both sides of the liquid crystal display cell, and at least one phase 
difference plate interposed between the liquid crystal display cell and 
polarizers, the coloring phenomenon and reversal phenomenon due to change 
in viewing angle may be eliminated, so that a liquid crystal display 
device being free from dependence on viewing angle may be obtained. 
According to the invention, when light of linear polarization transmits 
through a material having birefringence such as liquid crystal to generate 
normal light and abnormal light, and is converted into elliptical 
polarization according to their phase difference, at one side or both 
sides of the member having the birefringence, by placing at least one 
difference plate, not having refractive index anisotropy within the 
surface, with the principal refractive index nb in the normal direction of 
the surface smaller than the principal refractive indices ha, nc within 
the surface, of which refractive index anisotropy is negative, in which 
the direction of the principal refractive index nb is inclined to the 
normal direction of the surface, and the direction of the principal 
refractive index nb in the normal direction and the direction of the 
principal refractive index nc or na within the surface are inclined 
counterclockwise or clockwise about the direction of the principal 
refractive index na or nc within the surface, the phase difference change 
of normal light and abnormal light occurring due to viewing angle is 
compensated, and it is possible to convert into linear polarization over a 
wide range of viewing angle. 
Besides, by stacking up two of such phase difference plates, and defining 
the angle of the principal refractive index nb of each phase difference 
place formed in the inclination angle at about 90 degrees, it is possible 
to compensate not only the phase difference change in the normal viewing 
angle direction, but also the phase difference change in the anti-viewing 
angle direction and lateral direction. 
The compensation of phase difference change may be executed more securely 
by staking up the two phase difference plates so that the inclination of 
the principal refractive index bn in the normal direction of the first 
phase difference plate and the inclination angle of the principal 
refractive index nb in the normal direction of the second phase difference 
plate may form about 90 degrees clockwise. 
In the constitution comprising a liquid crystal display cell composed of a 
liquid crystal layer interposed between a pair of light transmittable 
substrates forming a transparent electrode layer and orientation film on 
the surface, a pair of polarizers disposed at both sides of the liquid 
crystal display cell, and at least one phase difference plate interposed 
between the liquid crystal display cell and polarizers, the coloring 
phenomenon and reversal phenomenon can be eliminated, and a liquid crystal 
display device free from dependence on viewing angle may be realized. 
In this case, when disposing one phase difference plate, by arranging so 
that the inclination direction of the principal refractive index nb in the 
normal direction of the phase difference plate may be nearly the opposite 
direction of the rubbing direction of the near side substrate of the 
liquid crystal cell, the compensation of the phase difference change may 
be effected more securely. When stacking up two phase difference plates, 
by disposing the first phase difference plate so that the rubbing 
direction of the remote side substrate of the liquid crystal display cell 
may be nearly equal to the inclination direction of the principal 
refractive index nb in the normal direction of the first phase difference 
plate, and the second phase difference plate so that the rubbing direction 
of the near side substrate of the liquid crystal display cell may be 
nearly opposite to the inclination direction of the principal refractive 
index nb in the normal direction of the second phase difference plate, the 
compensation of the phase difference change may be executed more securely. 
As described herein, according to the invention, as the phase difference 
plate inclined in the principal refractive index direction, by using the 
phase difference plate inclined in the directions of the principal 
refractive indices nb, nc about the direction of the minimum principal 
refractive index ha, in particular, it is possible to compensate for 
changes of phase difference corresponding to the viewing angle or exit 
angle occurring in the member possessing birefringence such as liquid 
crystal display cell. Besides, the liquid crystal display device using 
such phase difference plate is capable of preventing lowering of contrast 
ratio due to coloring phenomenon and reversal phenomenon, and therefore 
the contrast ratio in black and white display is not affected by the 
viewing angle direction, and the quality of display image may be improved 
outstandingly. 
In the invention, relating to the phase difference plate negative in the 
refractive index anisotropy, with the principal refractive indices in the 
relation of na=nc&gt;nb, as the phase difference plate inclined in the 
direction of principal refractive index, by staking up at least one phase 
difference plate inclined in the direction of principal refractive index 
nb in the normal direction about the direction of principal refractive 
index na or nc in the surface, in particular, and in the direction of the 
other principal refractive index nc or ha, the phase difference 
corresponding to the viewing angle caused in the liquid crystal display 
cell may be eliminated, and lowering of contrast ratio due to reversal 
phenomenon in the liquid crystal display cell, and viewing angle 
characteristics in the anti-viewing angle direction may be further 
improved. Therefore, the contrasts ratio in black and white display is 
enhanced, and the display quality of the liquid crystal display device is 
improved by far.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now referring to the drawing, preferred embodiments of the invention are 
described below. 
FIG. 1 is a perspective view of a phase difference plate in an embodiment 
of the invention. The phase difference plate 1 is a flat plate in a 
thickness of d being made of a material possessing optical anisotropy, 
such as drawn and elongated high polymer compound, for example, 
polycarbonate and polyester, and defining the surface to be a system of 
rectangular coordinates xyz on the plane x-y, the direction (the fast 
direction) of the minimum principal refractive index na of the three 
principal refrective indices na, nb, nc of the index ellipsoid is parallel 
to the y-axis direction, and the direction of the principal refractive 
index nb is inclined in the direction of arrow 20 at an angle of .theta. 
around the y-axis about the normal direction of the surface (the z-axis in 
FIG. 1). 
FIG. 2 is a sectional exploded view of a liquid crystal display device in 
an embodiment of the invention. The liquid crystal display device 2 is 
composed by stacking up in the sequence shown in FIG. 2, comprising a 
liquid crystal display cell 5 composed by inserting a liquid crystal layer 
12 made of nematic liquid crystal or the like by sealing with a sealing 
member 13, between a pair of glass substrates 6 and 7 forming transparent 
electrode layers 8, 9 made of ITO (indium tin oxide) and orientation films 
10, 11 made of polyimide, polyvinyl alcohol or the like on the surface, a 
pair of polarizers 3, 4 disposed at both sides of the liquid crystal 
display cell 5, and a phase difference plate 1 shown in FIG. 1 interposed 
between the liquid crystal cell 5 and polarizers 3. 
Each surface of orientation films 10, 11 is preliminarily processed by 
rubbing so that the intervening liquid crystal molecules may be twisted by 
about 90 degrees, and as shown in the plan in FIG. 3, the rubbing 
direction of the orientation film 10 on the glass substrate 6 is the 
direction of arrow 21, and the running direction of the orientation film 
11 on the glass substrate 7 is the direction of arrow 22 vertical to arrow 
21. 
FIG. 4 is a perspective exploded view of the liquid crystal display device 
2 shown in FIG. 2. It is configured so that the transmission axis 23 of a 
polarizer 3 and the transmission axis 24 of a polarizer 4 may cross 
orthogonally to each other, and the transmission axis 24 of the polarizer 
4, the rubbing direction 21 of the orientation film 10 of the liquid 
crystal display cell 5, and the fast direction 25 which is the direction 
of the minimum principal refractive index na of the phase difference plate 
1 are set to be parallel to each other, while the transmission axis 23 of 
the polarizer 3 and the rubbing direction 22 of the orientation film 11 of 
the liquid crystal display cell 5 are set to be parallel to each other. 
Therefore, when voltage is not applied to the liquid crystal layer 12 of 
the liquid crystal display cell 5, it is composed in the so-called 
normally white display system, that is, white is displayed as the light is 
allowed to pass through the liquid crystal display device 2. As far as the 
phase difference plate 1 is placed in any of the polarizer 3 and polarizer 
4, the phase can be compensated, or it may be present between the 
polarizer 4 and the liquid crystal display cell 5, or it may be composed 
of two or more plates. 
A practical example of the liquid crystal display device 2, and the result 
of measuring its dependence on viewing angle are explained below. FIG. 5 
is a schematic perspective view showing the measuring system of the 
dependence on viewing angle of the liquid crystal display device 2. The 
contacting surface 26 of the glass substrate 6 of the liquid crystal 
display cell 5 for composing the liquid crystal display device 2 and the 
phase difference plate 1 is set on the reference plane x-y of the system 
or rectangular coordinates xyz, and a photo detector 71 having a specific 
incidental angle is disposed at a position of specific distance from the 
origin of coordinates in the direction of angle .psi. to the normal 
direction 27 of the plane 26, and monochromatic light of wavelength 550 nm 
is emitted from the polarizer 4 side. The output of the photo detector 71 
is amplified to a specific level by an amplifier 72, and recorded by 
recording means 73 such as waveform memory and recorder. 
EXAMPLE 1 
In the liquid crystal display device 2 in FIG. 2, Using a nematic liquid 
crystal material of which refractive index anisotropy .DELTA.n is 0.08 as 
the liquid crystal layer 12, the thickness of the liquid crystal layer 12 
is set at 4.5 .mu.m, and the high polymer compound such as polycarbonate 
and polyester is drawn and elongated as the phase difference plate 1, and 
as shown in FIG. 1, a uniaxial material is used in which the value of the 
first retardation meaning the product (nc-na)xd of the difference between 
the principal refractive index nc and principal refractive index na and 
thickness d of phase difference plate 1 is 0 nm, and the value of the 
second retardation meaning the product (nc-nb)xd of the difference between 
the principal refractive index nc and principal refractive index nb and 
thickness d of phase difference plate 1 is -100 nm, and the direction of 
the principal refractive index nb is inclined 40 degrees counterclockwise 
indicated by arrow 20 to the normal line of the surface of the phase 
difference plate 1, and similarly the direction of the principal 
refractive index nc forms an angle of 40 degrees to the surface. 
Such liquid crystal display device 2 is installed in the measuring system 
shown in FIG. 5, and when the photo detector 71 is fixed at a specific 
angle .psi., the output level of the photo detector 71 to the applied 
voltage to the liquid crystal display cell 5 is measured, and the result 
is expressed as a graph of transmissivity-liquid crystal applied voltage 
characteristics in FIG. 6. In FIG. 6, line L1 refers to the angle of angle 
.psi.=0 degree, line L2, 30 degrees, and line L3, 45 degrees. It is 
understood from the findings that the transmissivity is lowered to 0% 
until around 4.5 V when the liquid crystal applied voltage is raised 
gradually from zero volt, and is not raised so much if the liquid crystal 
applied voltage is further elevated. At the liquid crystal applied voltage 
of around 1 V, the transmissivity is not so different in lines L1, L2, L3, 
and therefore the improvement of the dependence on viewing angle is 
understood. 
Comparison 1 
A liquid crystal display device 32 in FIG. 8 is similar in structure to the 
liquid crystal display device 2 in FIG. 2 except for the phase difference 
plate 1, and a nematic liquid crystal with the refractive index anisotropy 
.DELTA.n of 0.08 is used as the liquid crystal layer 12, and the thickness 
of the liquid crystal layer 12 is set at 4.5 .mu.m, while a phase 
difference plate 31 shown in FIG. 7 is used instead of the phase 
difference plate 1 shown in FIG. 1. The phase difference plate 31 is 
manufactured by drawing elongation of a high polymer compound such as 
polycarbonate, being of uniaxial material of which value of first 
retardation (nc-na)xd is 0 nm, and value of second retardation (nc-nb)xd 
is -100 nm, and the direction of the principal refractive index nb is 
formed parallel to the normal direction of the surface. 
Such liquid crystal display device 32 was installed in the measuring system 
shown in FIG. 5, same as in Example 1, and the photo detector 71 was fixed 
at a specific angle .psi., and the output level of the photo detector 71 
to the liquid crystal applied voltage was measured, of which result is 
graphically shown in FIG. 9 as the transmissivity-liquid crystal applied 
voltage characteristics. In FIG. 9, line L4 refers to angle .psi.=0 
degree, line L5, 30 degrees, and line L6, 45 degrees. As known from the 
results, as the liquid crystal applied voltage is gradually raised from 
zero vol, the transmissivity is lowered nearly to 0% around 3.2 V in line 
L5, and tends to rise slightly when the liquid crystal applied voltage is 
further raised, while the transmissivity climbs up again without 
completely reaching 0% in line L6. At the liquid crystal applied voltage 
of about 1 V, the transmissivity is lowered as the angle .psi. increases 
from 0 degree. Therefore, it is understood that the dependence on viewing 
angle is improved considerably in Example 1 as compared with Comparison 1. 
EXAMPLE 2 
In the liquid crystal display device 2 in FIG. 2, using a nematic liquid 
crystal material having the refractive index anisotropy .DELTA.n of 0.08 
as the liquid crystal layer 12, the thickness of the liquid crystal layer 
12 was set at 4.5 .mu.m, and the high polymer compound such as 
polycarbonate and polyester is drawn and elongated as the phase difference 
plate 1, being of biaxial material with the first retardation (nc-na)xd of 
220 nm and second retardation (nc-nb)xd of 35 nm, in which the direction 
of the principal refractive index nb is inclined 40 degrees clockwise in 
the opposite direction of the arrow 20 in FIG. 1 to the normal direction 
of the surface of the phase difference plate 1, and the direction of the 
principal refractive index nc is at an angle of 40 degrees clockwise to 
the surface. 
Such liquid crystal display device 2 was installed in the measuring system 
shown in FIG. 5, and the photo detector 71 was fixed at a specific angle 
.psi., and the output level of the photo detector 71 to the liquid crystal 
applied voltage to the liquid crystal display cell 5 was measured, of 
which result is graphically shown in FIG. 10 as the transmissivity-liquid 
crystal applied voltage characteristics. In FIG. 10, line L7 refers to the 
angle .psi. of 0 degree, line L8, 30 degrees, and line L9, 45 degrees. As 
the liquid crystal applied voltage was gradually raised from zero volt, 
the transmissivity dropped to 0% up to around 4.5 V, and if the liquid 
crystal applied voltage was further raised, the transmissivity was not 
elevated again. At the liquid crystal applied voltage of about 1 V, there 
transmissivity was not so different among lines L7, L8, and L9, and it is 
understood that the dependence on viewing angle was improved. 
Comparison 2 
The liquid crystal display device 32 shown in FIG. 8 is similar in 
structure to the liquid crystal display device 2 in FIG. 2 except for the 
phase difference plate 1, and the liquid crystal layer 12 is a nematic 
liquid crystal layer with the refractive index anisotropy .DELTA.n of 
0.08, the thickness of the liquid crystal layer 12 is set at 4.5 .mu.m, 
and a phase difference plate 31 shown in FIG. 7 is used instead of the 
phase difference plate 1 shown in FIG. 1. The phase difference plate 31 is 
a drawn and elongated high polymer compound such as polycarbonate, being 
of biaxial material with the first retardation (nc-na)xd of 220 nm and 
second retardation (nc-nb)xd of 35 nm, and the direction of the principal 
refractive index nb is formed parallel to the normal direction of the 
surface. 
Such liquid crystal display device 32 was installed in the measuring system 
shown in FIG. 5 same as in Example 2, and the photo detector 71 was fixed 
at a specific angle .psi., and the output level of the photo detector 71 
to the liquid crystal applied voltage was measured, of which result is 
graphically shown in FIG. 11 as transmissivity-liquid crystal applied 
voltage characteristics. In FIG. 11, line L10 refers to the angle .psi. of 
0 degree, line 11, 30 degrees, and line 12, 45 degrees. As the liquid 
crystal applied voltage was raised gradually from zero volt, the 
transmissivity was lowered nearly to 0% around 2.9 V in line L11, and as 
the liquid crystal applied voltage was further raised, it tended to 
elevate slightly, and in line L12, the transmissivity was nearly 0% around 
2.8 V, and climbed up again by further raising. At the liquid crystal 
applied voltage of around 1 V, the transmissivity was lowered as the angle 
.psi. became larger than 0 degree. In Example 2, therefore, it is 
understood that the dependence on viewing angle was considerably improved 
as compared with this Comparison 2. 
EXAMPLE 3 
In the liquid crystal display device 2 in FIG. 12, using a nematic liquid 
crystal material having the refractive index anisotropy .DELTA.n of 0.08 
as the liquid crystal layer 12, the thickness of the liquid crystal layer 
12 was set at 4.5 .mu.m, and the high polymer compound such as 
polycarbonate and polyester was drawn and elongated as two phase 
difference plates 1a and 1b interposed between the liquid crystal display 
cell 5 and polarizers 3, the phase difference plate 1a being of biaxial 
material with the first retardation (nc-na)xd of 350 nm and second 
retardation (nc-nb)xd of 210 nm, in which the direction of the principal 
refractive index nb is inclined 20 degrees clockwise in the opposite 
direction of the arrow 20 in FIG. 1 to the normal direction of the surface 
of the phase difference plate 1, and the direction of the principal 
refractive index nc is at an angle of 20 degrees clockwise to the surface. 
Moreover, the direction (fast direction) 25a of the minimum principal 
refractive index na is arranged to be parallel to the rubbing direction 21 
of the orientation film 10 on the glass substrate 6. 
On the other hand, the phase difference plate 1b is, similar to the phase 
difference plate 1a, a drawn and elongated high polymer compound such as 
polycarbonate and polyester, being of biaxial material with the first 
retardation (nc-na)xd of 350 nm and second retardation (nc-nb)xd of 210 
nm, in which the direction of the principal refractive index nb is 
inclined 20 degrees counterclockwise indicated by the arrow 20 in FIG. 1 
to the normal direction of the surface of the phase difference plate 1, 
and the direction of the principal refractive index nc is at an angle of 
20 degrees to the surface. Moreover, the direction (fast direction) 25b of 
the minimum principal refractive index na is arranged to be vertical to 
the rubbing direction 21 of the orientation film 10 on the glass substrate 
6. 
Such liquid crystal display device 2 was installed in the measuring system 
shown in FIG. 5, and the photo detector 71 was fixed at a specific angle 
.psi., and the output level of the photo detector 71 to the liquid crystal 
applied voltage to the liquid crystal display cell 5 was measured, of 
which result is graphically shown in FIG. 13 as the transmissivity-liquid 
crystal applied voltage characteristics. In FIG. 13, line L13 refers to 
the angle .psi. of 0 degree, line L14, 30 degrees, and line L15, 45 
degrees. As the liquid crystal applied voltage was gradually raised from 
zero volt, the transmissivity dropped to 0% up to around 4.5 V, and if the 
liquid crystal applied voltage was further raised, the transmissivity was 
not elevated again. At the liquid crystal applied voltage of about 1 V, 
there transmissivity was not so different among lines L13, L14, and L15, 
and it is understood that the dependence on viewing angle was improved. 
Comparison 3 
In this comparison, the liquid crystal display device 34 shown in FIG. 14 
is similar in structure to the liquid crystal display device 2 in FIG. 12 
except for the phase difference plates 1a and 1b, and the liquid crystal 
layer 12 is a nematic liquid crystal layer with the refractive index 
anisotropy .DELTA.n of 0.08, the thickness of the liquid crystal layer 12 
is set at 4.5 .mu.m, and a phase difference plate 31 shown in FIG. 7 is 
used as the phase difference plates 1a and 1b instead of the phase 
difference plate 1 shown in FIG. 1. The phase difference plate 31a is a 
drawn and elongated high polymer compound such as polycarbonate, being of 
biaxial material with the first retardation (nc-na)xd of 350 nm and second 
retardation (nc-nb)xd of 210 nm, and the direction of the principal 
refractive index nb is formed parallel to the normal direction of the 
surface. Moreover, the direction (fast direction) 33a of the minimum 
principal refractive index na is arranged to be parallel to the rubbing 
direction 21 of the orientation film 10 on the glass substrate 6. 
On the other hand, the phase difference plate 31b is, similar to the phase 
difference plate 31a, a drawn and elongated high polymer compound such as 
polycarbonate, being of biaxial material with the first retardation 
(nc-na)xd of 350 nm and second retardation (nc-nb)xd of 210 nm, and the 
direction of the principal refractive index nb is formed parallel to the 
normal direction of the surface. Moreover, the direction (fast direction) 
33b of the minimum principal refractive index na is arranged to be 
vertical to the rubbing direction 21 of the orientation film 10 on the 
glass substrate 6. 
Such liquid crystal display device 34 was installed in the measuring system 
shown in FIG. 5 same as in Example 2, and the photo detector 71 was fixed 
at a specific angle .psi., and the output level of the photo detector 71 
to the liquid crystal applied voltage was measured, of which result is 
graphically shown in FIG. 15 as transmissivity-liquid crystal applied 
voltage characteristics. In FIG. 15, line L16 refers to the angle .psi. of 
0 degree, line 17, 30 degrees, and line 18, 45 degrees. As the liquid 
crystal applied voltage was raised gradually from zero volt, the 
transmissivity was lowered nearly to 0% around 4.5 V, and as the liquid 
crystal applied voltage was further raised, the transmissivity was 
elevated again, and the margin of elevation was larger than in Example 3. 
Furthermore, at the liquid crystal applied voltage of around 1 V, the 
transmissivity dropped as the angle .psi. increased from 0 degree. As 
compared with this comparison, therefore, it is understood that the 
dependence on viewing angle was slightly improved in Example 3. 
Incidentally, instead of the drawn and elongated high polymer compound 
explained in the foregoing embodiments, oblique orientation of liquid 
crystal high polymer such as polycarbonate and polyester may be also 
employed. 
FIG. 16 is a perspective view of a phase difference plate in other 
embodiment of the invention. The phase difference plate 41 is a material 
having optical anisotropy, such as drawn and elongated high polymer 
compound including polystyrene, formed in a flat plate with the thickness 
of d, and defining the surface to be a system of rectangular coordinates 
xyz on plane x-y, the direction of the principal refractive index na, out 
of three principal refractive indices na, rib, nc of the index ellipsoid 
is parallel to the y-axis, and the direction of the principal refractive 
index nb is inclined in the direction of arrow 60 at an angle of .theta. 
about the y-axis to the normal direction (z-axis in FIG. 16) of the 
surface. The direction of the principal refractive index nc is inclined in 
the direction of arrow 59 at an angle of .theta. about the y-axis along 
the surface. Among the principal refractive indices na, nb, no, the 
relation of na=nc&gt;nb is established. 
FIG. 17 is a perspective view of a phase difference plate 42 in a different 
embodiment of the invention. The phase difference plate 42 is composed by 
stacking up two of the phase difference plate 41 shown in FIG. 16. That 
is, the phase difference plate 42 forms an angle of about 90 degrees 
between the inclination direction 61a of the principal refractive index nb 
of the first phase difference plate 41a and the inclination direction 61b 
of the principal refractive index nb of the second phase difference plate 
41b. 
FIG. 18 is a sectional exploded view of a liquid crystal display device 54 
in a further different embodiment of the invention. The liquid crystal 
display device 54 comprises a liquid crystal display cell 45 composed by 
placing a liquid crystal layer 52 made of nematic liquid crystal between a 
pair of glass substrates 46, 47 forming transparent electrode layers 48, 
49 made of ITO or the like and orientation films 50, 51 made of polyimide, 
polyvinyl alcohol or the like on the surface, by sealing with a sealing 
member 53, a pair of polarizers 43, 44 disposed at both sides of the 
liquid crystal display cell 45, and a phase difference plate 42 shown in 
FIG. 17 interposed between the liquid crystal display cell 45 and 
polarizers 43, which are stacked up in the sequence shown in FIG. 18. 
Each surface of the orientation films 50, 51 is pretreated by rubbing so as 
to twist the intervening liquid crystal molecules by about 90 degrees, and 
as shown in the plan in FIG. 19, the rubbing direction of the orientation 
film 50 on the glass substrate 46 is the direction of arrow 62, and the 
rubbing direction of the orientation film 51 on the glass substrate 47 is 
the direction of arrow 63 vertical to arrow 62. 
FIG. 20 is a perspective exploded view of the liquid crystal display device 
shown in FIG. 18. It is configured so that the transmission axis 64 of a 
polarizer 43 and the transmission axis 65 of a polarizer 44 may cross 
orthogonally to each other, and it is set so that the transmission axis 65 
of the polarizer 44, the rubbing direction 62 of the orientation film 50 
of the liquid crystal display cell 45, and the inclination direction 61b 
of the principal refractive index nb of the phase difference plate 41b may 
be parallel to each other, and that the rubbing direction 62 of the 
orientation film 50 of the liquid crystal display cell 45 and the 
inclination direction 61b of the principal refractive index nb of the 
phase difference plate 41b may be opposite to each other. 
On the other hand, it is set so that the transmission axis 64 of the 
polarizer 43, rubbing direction 63 of the orientation film 51 of the 
liquid crystal display cell 45, and the inclination direction 61a of the 
principal refractive index nb of the phase difference plate 41a may be 
parallel to each other, and that the rubbing direction 63 of the 
orientation film 51 of the liquid crystal display cell 45 and the 
inclination direction 61a of the principal refractive index nb of the 
phase difference plate 41a may be in the same direction. Therefore, when 
voltage is not applied to the liquid crystal layer 52 of the liquid 
crystal display cell 45, the light transmits through the liquid crystal 
display device 54 to display white, thereby composing the so-called 
normally white display system. Phase compensation is possible as far as 
the phase difference plate 42 is placed either in the polarizer 43 or in 
the polarizer 44, and it may be interposed between the polarizer 44 and 
the liquid crystal display cell 45. 
A practical embodiment of thus obtained liquid crystal display device 54 
and the result of measurement of its dependence on viewing angle are 
explained. FIG. 21 is a schematic perspective view showing the measuring 
system of the dependence on viewing angle of the liquid crystal display 
device 54. The contact surface 66 of the glass substrate 46 of the liquid 
crystal display cell 45 for composing the liquid crystal display device 54 
and the phase difference plate 41b is set on the reference plane x-y of 
the system of rectangular coordinates xyz, and the photo detector 71 
having a specific incidental angle is placed same as in FIG. 5 at a 
position of a specific distance from the origin of the coordinates, in a 
direction of angle .psi. to the normal direction 67 of the surface 66, and 
monochromatic color of wavelength 550 nm is entered from the polarizer 44 
side. The output of the photo detector 71 is amplified to a specific level 
in an amplifier 72, and recorded by recording means 73 such as waveform 
memory and recorder. It is measured in four directions, normal viewing 
angle direction, right direction, anti-viewing angle direction, and left 
direction. 
EXAMPLE 4 
In the liquid crystal display device 54 in FIG. 18, using a nematic liquid 
crystal material of which refractive index anisotropy .DELTA.n is 0.08 as 
the liquid crystal layer 52, the thickness of the liquid crystal layer 52 
is set at 4.5 .mu.m, and a high polymer compound such as polystyrene is 
drawn and elongated as phase difference plates 41a, 41b for composing the 
phase difference plate 42, being, as shown in FIG. 16, a uniaxial material 
in which the value of the first retardation meaning the product (nc-na)xd 
of the difference between the principal refractive index nc and principal 
refractive index na and thickness d of phase difference plates 41a and 41b 
is 0 nm, and the value of the second retardation meaning the product 
(nc-nb)xd of the difference between the principal refractive index nc and 
principal refractive index nb and thickness d of phase difference plates 
41a and 41b is 100 nm, and the direction of the principal refractive index 
nb is inclined 20 degrees clockwise indicated by arrow 60 to the normal 
line of the surface of the phase difference plates 41a and 41b, and 
similarly the direction of the principal refractive index nc forms an 
angle of 20 degrees to the surface. 
Such liquid crystal display device 54 is installed in the measuring system 
shown in FIG. 21, and when the photo detector 71 is fixed at a specific 
angle .psi., the output level of the photo detector 71 to the applied 
voltage to the liquid crystal display cell 45 is measured, and the result 
is expressed as a graph of transmissivity-liquid crystal applied voltage 
characteristics in FIG. 22. In FIG. 22, line L21 refers to the 
characteristic curve at angle .psi.=0 degree. The lines L22, L23, L24, and 
L25 represent the characteristic curves as seen at a position inclined by 
angle .psi. of 30 degrees in the normal viewing angle direction, right 
direction, anti-viewing angle direction and left direction. It is 
understood from he findings hat he transmissivity is almost flat at the 
applied voltage of 3.5 V to 5.5 V. It is also known that the 
transmissivity when voltage is applied is not so different whether seen 
from above or inclined in the viewing angle. 
Besides, in lines L23 and L25, it is almost same as the applied 
voltage-transmissivity characteristic as seen from above, and it is 
confirmed that the lateral asymmetricity is almost unchanged. Moreover, in 
line L24, the transmissivity when voltage is applied is considerably 
lowered, and black display is realized, which suggests ha the anti-viewing 
angle direction is improved. 
The contrast ratio of the normal viewing angle direction and anti-viewing 
angle direction of the liquid crystal display device 54 is shown in Table 
1 below. 
TABLE 1 
______________________________________ 
Contrast ratio 
Normal viewing 
Anti-viewing 
angle direction 
angle direction 
______________________________________ 
Liquid crystal display 
76 18 
device 54 
Liquid crystal display 
10 8 
device 80 
Without phase difference 
42 4 
plate TN 
______________________________________ 
Comparison 4 
A liquid crystal display device 80 in FIG. 23 is similar in construction to 
the liquid crystal display device 54 in FIG. 18 except for the phase 
difference plate 82, and a nematic liquid crystal material with the 
refractive index anisotropy .DELTA.n of 0.08 is used as the liquid crystal 
layer 52, the thickness of the liquid crystal layer 52 is set at 4.5 
.mu.m, and a phase difference plate 81 shown in FIG. 24 is used instead of 
the phase difference plate 41 shown in FIG. 16. Phase difference plates 
81a and 81b for composing the phase difference plate 82 are a drawn and 
elongated high polymer compound such as polystyrene, being of a uniaxial 
material with the first retardation (nc-na)xd of 0 nm and second 
retardation (nc-nb)xd of 100 nm, and the direction of the principal 
refractive index nb is formed parallel to the normal line of the surface. 
It is configured so that the direction 83a of the principal refractive 
index nc of the first phase difference plate 81a may be parallel to the 
rubbing direction of the orientation film 51 on the glass substrate 47, 
and that the direction 83c of the principal refractive index nc of the 
second phase difference plate 81b may be parallel to the rubbing direction 
62 of the orientation film 50 on the glass substrate 46. 
FIG. 25 is a graph showing the applied voltage-transmissivity 
characteristics of the liquid-crystal display device 80. In FIG. 25, the 
characteristic curve as observing the liquid crystal display device 80 
from above is represented by line L26, and the characteristic curves as 
seen from the position inclined by angle .psi. of 30 degrees in the normal 
viewing angle direction, right direction, anti-viewing angle direction, 
and left direction are indicated by lines L27, L28, L29, and L30, 
respectively. In line L27 in FIG. 25, the transmissivity once lowered at 
applied voltage of 2.7 was raised again from 3.0 V, and reversal 
phenomenon was observed. In addition, it was known that the transmissivity 
when voltage was applied was lowered when the viewing angle was inclined. 
Besides, lines L28 and L30 were found to be slightly asymmetrical laterally 
as compared with lines L23, L25 in FIG. 22. Furthermore, in line L29, the 
transmissivity with voltage applied was not fully lowered. 
Therefore, the viewing angle characteristic of the liquid crystal display 
device 54 shown in FIG. 18 is found to be considerably improved as 
compared with the viewing angle characteristics of the conventional liquid 
crystal display device 80 shown in FIG. 23. As the phase difference plate 
41, meanwhile, oblique orientation of liquid crystal high polymer or 
rolling of high polymer film may be employed. Rolling means to pass a film 
between upper and lower rollers. 
EXAMPLE 5 
A liquid crystal display device 85 in FIG. 26 is similar in construction to 
the liquid crystal display device 54 in FIG. 18 except for the phase 
difference plate 86, and a nematic liquid crystal material with the 
refractive index anisotropy .DELTA.n of 0.08 is used as the liquid crystal 
layer 52, the thickness of the liquid crystal layer 52 is set at 4.5 
.mu.m, and a phase difference plate 86 shown in FIG. 27 is used instead of 
the phase difference plate 41 shown in FIG. 16. The phase difference plate 
86 is a drawn and elongated high polymer compound such as polystyrene, 
being of a uniaxial material with the first retardation (nc-na)xd of 0 nm 
and second retardation (nc-nb)xd of 200 nm, and the direction of the 
principal refractive index nb is inclined 25 degrees clockwise indicated 
by arrow 60 to the normal direction of the surface of the phase difference 
plate 86, and similarly the direction of the principal refractive index 
forms an angle of 25 degrees to the surface. 
FIG. 28 is a perspective view showing the constitution of the liquid 
crystal display device 85. As shown in FIG. 28, the transmission axes 64, 
65 of polarizers 43, 44 of the liquid crystal display device 85 are 
configured so as to be vertical to the rubbing directions 62, 63 of the 
orientation films 50, 51 on the glass substrates 46, 47, respectively, and 
the inclination direction 87 of the principal refractive index nb in the 
anisotropic direction of the phase difference plate 86 is set opposite to 
the rubbing direction 62 of the orientation film 50 of the glass substrate 
46. Therefore, when the voltage is applied, the liquid crystal display 
device 85 allows the light to pass to display white, which is called 
normally white display. 
FIG. 29 is a graph showing the applied voltage-transmissivity 
characteristics of the liquid crystal display device 85. In FIG. 31, the 
characteristic curve as seen from above the liquid crystal display device 
85, that is, from an angle .psi. of 0 degree is indicated by solid line 
L31. The characteristic curves as seen from a position inclined by an 
angle .psi. of 30 degrees in the normal viewing angle direction and 
anti-viewing angle direction of the liquid crystal display device 85 are 
represented by lines L32 and L33, respectively. In line L32 in FIG. 29, it 
is confirmed that the transmissivity is almost flat from the applied 
voltage of 3.5 V to 5.5 V. It is also known that the transmissivity with 
voltage applied is hardly changed whether seen from above or when inclined 
in the viewing angle. In line L33, the transmissivity with voltage applied 
is lowered considerably, and black is displayed, and it is confirmed that 
the anti-viewing angle direction is improved. 
The contrast ratio of the normal viewing angle direction and anti-viewing 
angle direction of the liquid crystal display device 85 is shown in Table 
2 below. 
TABLE 2 
______________________________________ 
Contrast ratio 
Normal viewing 
Anti-viewing 
angle direction 
angle direction 
______________________________________ 
Liquid crystal display 
147 19 
device 85 
Liquid crystal display 
11 7 
device 88 
Without phase difference 
42 4 
plate TN 
______________________________________ 
Comparison 5 
A liquid crystal display device 88 in FIG. 30 is similar in construction to 
the liquid crystal display device 85 in FIG. 26 except for the phase 
difference plate 89, and a nematic liquid crystal material with the 
refractive index anisotropy .DELTA.n of 0.08 is used as the liquid crystal 
layer 52, the thickness of the liquid crystal layer 52 is set at 4.5 
.mu.m, and a phase difference plate 89 shown in FIG. 31 is used instead of 
the phase difference plate 86 shown in FIG. 27. The phase difference plate 
89 is a drawn and elongated high polymer compound such as polystyrene, 
being of a uniaxial material with the first retardation (nc-na)xd of 0 nm 
and second retardation (nc-nb)xd of 200 nm, and the direction of the 
principal refractive index nb is formed parallel to the normal line of the 
surface. In FIG. 30, moreover, the direction of the principal refractive 
index nc of the phase difference plate 89 is formed parallel to the 
surface. The direction 90 of the principal refractive index nc of the 
phase difference plate 89 is, disposed parallel to the rubbing direction 
62 of the orientation film 50 of the glass substrate 46. 
FIG. 32 is a graph showing the applied voltage-transmissivity 
characteristics of the liquid crystal display device 88. In FIG. 32, the 
characteristic curve as observing the liquid crystal display device 88 
from above is represented by line L34, and the characteristic curves as 
seen from the position inclined by angle .psi. of 30 degrees in the normal 
viewing angle direction and anti-viewing angle direction are indicated by 
lines L35 and L36, respectively. In line L34 in FIG. 32, the 
transmissivity once lowered at applied voltage of 2.7 V was raised again 
from 3.0 V, and reversal phenomenon was observed. In addition, it was 
Known that the transmissivity when voltage was applied was lowered when 
the viewing angle was inclined. Similarly, in line L36 in FIG. 32, it was 
confirmed that the transmissivity with voltage applied was not lowered 
completely. 
Therefore, the viewing angle characteristics of the liquid crystal display 
device 85 shown in FIG. 26 were known to be considerably improved as 
compared with the viewing angle characteristics of the conventional liquid 
crystal display device 88 shown in FIG. 30. As the phase difference plate 
86, meanwhile, oblique orientation of liquid crystal high polymer or 
rolling of high polymer film may be also employed. 
The invention may be embodied in other specific forms without departing 
from the spirit of essential characteristics thereof. The present 
embodiments are therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description and all changes 
which come within the meaning and the range of equivalency of the claims 
are therefore intended to be embraced therein.