Liquid crystal device and liquid crystal display apparatus

A liquid crystal device is constituted by disposing a chiral smectic liquid crystal between a pair of substrates each provided with an electrode and a uniaxial alignment film. The chiral smectic liquid crystal is placed in such a quasi-smectic A alignment state that the liquid crystal molecules will have a single average molecular axis under no electric field application on a lower temperature side within chiral smectic C phase range, wherein the single average molecular axis can be confirmed as a position providing the darkest state when observed through cross nicol polarizers. Such a quasi-smectic A alignment state is effective in providing a liquid crystal device (or display apparatus) having an improved shock resistance and a good low-temperature storage properties.

FIELD OF THE INVENTION AND RELATED ART 
This invention relates to a liquid crystal device to be used in a liquid 
crystal display device or a liquid crystal-optical shutter, etc., 
particularly a liquid crystal device using of a ferroelectric liquid 
crystal, and a liquid crystal display apparatus using the liquid crystal 
device. 
A display device of the type which controls transmission of light in 
combination with a polarizing device by utilizing the refractive index 
anisotropy of ferroelectric liquid crystal molecules has been proposed by 
Clark and Lagerwall (U.S. Pat. No. 4,367,924, etc.). The ferroelectric 
liquid crystal has generally chiral smectic C phase (SmC*) or H phase 
(SmH*) of a non-helical structure and, in the SmC, or SmH* phase, shows a 
property of assuming either one of a first optically stable state and a 
second optically stable state responding to an electrical field applied 
thereto and maintaining such a state in the absence of an electrical 
field, namely bistability, and also has a quick responsiveness to the 
change in electrical field. Thus, it is expected to be utilized in a high 
speed and memory type display device and particularly to provide a 
large-area, high-resolution display in view of its excellent function. 
Generally, in a liquid crystal device utilizing birefringence of a liquid 
crystal, the transmittance under right angle cross nicols is given by the 
following equation: 
EQU I/I.sub.0 =sin.sup.2 4.theta.a.multidot.sin.sup.2 (.DELTA.nd/.lambda.).pi., 
wherein 
I.sub.0 : incident light intensity, 
I: transmitted light intensity, 
.theta.a: apparent tilt angle, 
.DELTA.n: refractive index anisotropy, 
d: thickness of the liquid crystal layer, 
.lambda.: wavelength of the incident light. 
The apparent tilt angle .theta.a in the above-mentioned non-helical 
structure is recognized as a half of an angle between the average 
molecular axis directions of liquid crystal molecules in a twisted 
alignment in a first orientation state and a second orientation state. 
According to the above equation, it is shown that an apparent tilt angle 
.theta.a of 22.5 degrees provides a maximum transmittance and the apparent 
tilt angle .theta.a in a non-helical structure for realizing bistability 
should desirably be as close as possible to 22.5 degrees in order to 
provide a high transmittance and a high contrast. 
However, when a conventional alignment method, particularly one using a 
polyimide film treated by rubbing, is applied for alignment of a 
ferroelectric liquid crystal in a non-helical structure exhibiting 
bistability reported by Clark and Lagerwall, the following problems are 
encountered. 
That is, it has been found that an apparent tilt angle .theta.a (a half of 
an angle formed between molecular axes at two stable states) in a 
ferroelectric liquid crystal with a non-helical structure obtained by 
alignment with an alignment control film of the prior art has become 
smaller as compared with a a cone angle H (the angle H is a half of the 
apex angle of the cone shown in FIG. 3A as described below) in the 
ferroelectric liquid crystal having a helical structure. Particularly, the 
apparent tilt angle .theta.a in a ferroelectric liquid crystal with a 
non-helical structure obtained by alignment with alignment control films 
of the prior art was found to be generally on the order of 3-8 degrees, 
and the transmittance at that time was at most about 3 to 5%. 
In order to realize a display device comprising a chiral smectic liquid 
crystal disposed to have a large apparent tilt angle .theta.a in a 
non-helical structure and capable of displaying a high contrast image, 
there has been discovered the following. 
That is, it has been clarified that it is possible to realize a display 
providing a high contrast image by using a liquid crystal device, 
comprising: a pair of substrates, and a chiral smectic liquid crystal 
disposed between the substrates, each of the facing surfaces of substrates 
having thereon an electrode for applying a voltage to the liquid crystal 
and a uniaxial alignment film for aligning the liquid crystal; wherein the 
alignment films on the substrates are provided with uniaxial alignment 
axes which cross each other at a prescribed angle and the chiral smectic 
liquid crystal is disposed in such an alignment state that the liquid 
crystal shows a pretilt angle .alpha., a cone angle H, and an inclination 
angle .delta. of the liquid crystal layer (i.e., an angle formed by the 
liquid crystal layer line and a normal to the substrate) satisfying 
relationships of: 
EQU H&lt;.alpha.+.delta. and .delta.&lt;.alpha., 
and such an alignment state includes at least two stable states in which an 
apparent tilt angle .theta.a and the cone angle H satisfies a relationship 
of: 
EQU H&gt;.theta.a&gt;H/2. 
More specifically, a smectic liquid crystal generally has a layer structure 
and, due to a shrinkage of spacing between layers when it causes a 
transition from smectic A phase (SmA) to chiral smectic C phase (SmC*), it 
assumes a chevron structure as shown in FIG. 2 where the layers 21 are 
bent at a mid point between a pair of substrates 24a and 24b. 
There are two alignment states depending on the bending directions as shown 
in FIG. 2, including a C1 alignment state 22 appearing immediately after 
transition from a higher temperature phase to SmC* phase and a C2 
alignment state 23 which appears in mixture with the C2 alignment state on 
further cooling. It have been further discovered (1) that the above C1 C2 
transition does not readily occur when a specific combination of an 
alignment film providing a high pretilt angle a and a liquid crystal is 
used, and the C2 alignment state does not occur at all when a specific 
liquid crystal is used, and (2) that, in C1 alignment state, two stable 
states providing a high contrast (hereinafter inclusively called "uniform 
state") are formed in addition to hitherto-found two stable states 
providing low contrast (hereinafter inclusively called "splay state") 
wherein liquid crystal directors are twisted between the substrates. 
These states can be transformed from one to the other by applying a certain 
electric field. More specifically, transition between two splay states is 
caused under application of weak positive and negative pulse electric 
fields, and transition between two uniform states is caused under 
application of strong positive and negative pulse electric fields. By 
using the two uniform states, it is possible to realize a display device 
which is brighter and shows a higher contrast than the conventional 
devices. Accordingly, it is expected that a display with a higher quality 
can be realized by using a display device wherein the entire display area 
is formed in C1 alignment state and the high contrast two states in the C1 
alignment state are used as two states representing white and black 
display states. 
In order to realize C1 alignment state without yielding C2 alignment state 
as described above, the following conditions are required. 
Referring to FIGS. 3A and 3B, directions in the vicinity of the substrates 
in the C1 alignment and C2 alignment are disposed on cones 31 shown in 
FIGS. 3A and 3B, respectively. As is well known, as a result of rubbing, 
liquid crystal molecules contacting a substrate surface form a pretilt 
angle a, the direction of which is such that the liquid crystal molecules 
32 raise a forward end up (i.e., spaced from the substrate surface) in the 
direction of the rubbing indicated by an arrow A (as shown also in FIG. 
2). From the above, it is required that the following relationships are 
satisfied among a cone angle H, the pretilt angle .alpha. and a layer 
inclination angle .delta.; 
H+.delta.&gt;.alpha. in C1 alignment, and 
H-.delta.&gt;.alpha. in C2 alignment. 
Accordingly, the condition for preventing the formation of C2 alignment but 
allowing C1 alignment is 
H-.delta.&lt;.alpha., that is 
EQU H&lt;.alpha.+.delta. (I). 
Further, from simple consideration of a torque acting on a liquid crystal 
molecule at a boundary surface in switching from one position to the other 
position under an electric field, the relationship of .alpha.&gt;.delta.. . . 
(II) is given as a condition for easy switching of such a liquid crystal 
molecule at the boundary. 
Accordingly, in order to form the C1 alignment more stably, it is effective 
to satisfy the condition (II) in addition to the condition (I). 
From further experiments under the conditions of (I) and (II), the apparent 
tilt angle .theta.a is increased from 3-8 degrees obtained when the 
conditions (I) and (II) are not satisfied to 8-16 degrees when the 
conditions (I) and (II) are satisfied according to the present invention, 
and also an empirical relationship of H&gt;.theta.a&gt;H/2 . . . (III) has been 
also found. 
As described above, it has been clarified that the satisfaction of the 
conditions (I), (II) and (III) provides a display device capable of 
displaying a high-contrast image. 
In order to stably form the C1 alignment state and also provide a good 
alignment characteristic, it is also very effective to perform 
cross-rubbing, that is, rubbing a pair of substrates in directions 
intersecting at an angle of 1-25 degrees while the directions A are shown 
generally parallel in FIG. 2. 
Incidentally, a display apparatus using a chiral smectic liquid crystal can 
realize a large screen and a high resolution which by far exceed those 
attained by conventional CRT and TN-type liquid crystal displays. However, 
as the screen size and resolution are increased, the frame frequency 
(frequency constituting one picture) becomes low. This leads to a problem 
that the picture-rewriting speed becomes slow and the motion picture 
display becomes slow, e.g., in cases of smooth scrolling and cursor 
movement on a graphic screen. A solution to this problem has been given 
in, e.g., JP-A 60-31120 and JP-A 1-140198. 
More specifically, there has been disclosed a display apparatus including a 
display panel comprising scanning electrodes and data electrodes arranged 
in a matrix, whole-area writing means for selecting all or a prescribed 
part of the scanning electrodes for writing and partial writing means for 
selecting a part of the above-mentioned all or a prescribed part of the 
scanning electrodes. As a result, a partial motion picture display can be 
performed at a high speed by the partial writing mode, and the partial 
writing and the whole-area writing can be performed compatibly. 
As described above, it has become clear that it is possible to realize a 
large-area and high-resolution display which can display high-contrast 
images at a high speed by incorporating a liquid crystal device satisfying 
the conditions (I), (II) and (III) in the above-described display 
apparatus capable of performing the partial writing. 
Thus, a ferroelectric liquid crystal potentially has very excellent 
characteristics, and by making use of these properties, it is possible to 
provide essential improvements to many of the above-mentioned problems 
with the conventional TN-type devices. Particularly, the application to a 
high-speed optical shutter and a display of a high density and a large 
picture is expected. For this reason, there has been made extensive 
research with respect to liquid crystal materials showing 
ferroelectricity. However, ferroelectric liquid crystal materials 
developed heretofore cannot be said to satisfy sufficient characteristics 
required for a liquid crystal device including an operable temperature 
range, temperature-dependence of response speed, low-temperature storage 
properties, impact or shock resistance, etc. in some cases. 
Generally, a ferroelectric liquid crystal has a clear layer structure at a 
temperature range where the ferroelectric liquid crystal is used, thus 
showing a poor flowability compared with a nematic liquid crystal. 
Accordingly, the ferroelectric liquid crystal has a relatively poor 
brittleness against an external stress such as a force of shock or strain 
and thus causes a zigzag defect comprising C1 alignment and C2 alignment 
for a slight shock. For a great shock, the ferroelectric liquid crystal 
causes a disorder of its layer structure per se, thus resulting in, e.g., 
a sanded texture as disclosed in U.S. Pat. No. 4,674,839 by Tsuboyama et 
al. In general, a shock (or impact) resistance is liable to become worse 
at a low temperature where a viscosity of a liquid crystal is increased to 
provide a poor flowability, resulting in a serious problem in the case of 
transportation by aircraft etc. A lower limit temperature to chiral 
smectic C phase, i.e., a phase transition temperature (Mp) to another 
mesomorphic phase or crystal phase is an essential factor for determining 
low-temperature storage properties. At this stage, it is difficult to 
decrease an Mp of a liquid crystal composition, having overall excellent 
characteristics including a high contrast and a decreased 
temperature-dependence of a response speed providing a high quality image 
in a wide temperature range including room temperature, to a sufficiently 
low temperature region (e.g., below -20.degree. C.). 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a liquid crystal device 
having a good shock resistance particularly at low temperature and a 
liquid crystal display apparatus using the liquid crystal device. 
Another object of the present invention is to provide a liquid crystal 
device having an excellent low temperature storage properties and a liquid 
crystal display apparatus using the liquid crystal device. 
As a result of our research, we have found that it is possible to improve a 
shock resistance and low temperature storage properties by a chiral 
smectic liquid crystal capable of providing a specific alignment state at 
a lower temperature side of chiral smectic C phase range. 
That is, according to the present invention, there is provided a liquid 
crystal device, comprising: a pair of substrates and a chiral smectic 
liquid crystal disposed between the pair of substrates, each of the pair 
of substrates having thereon an electrode for applying a voltage to the 
liquid crystal, the pair of substrates being provided with respective 
uniaxial alignment axes extending in directions which are parallel to each 
other or intersect each other at a prescribed angle, wherein 
the chiral smectic liquid crystal is placed in such an alignment state that 
the liquid crystal molecules will have a single average molecular axis 
under no electric field application on a lower temperature side within 
chiral smectic C phase range, wherein the single average molecular axis 
can be confirmed as a position providing the darkest state when observed 
through cross nicol polarizers. 
According to the present invention, there is further provided a liquid 
crystal display apparatus comprising the above liquid crystal device, a 
drive circuit for driving the liquid crystal device and a light source. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
The liquid crystal device according to the present invention is 
characterized by a chiral smectic liquid crystal capable of providing the 
above-mentioned specific alignment state on a lower temperature side 
within chiral smectic C phase. 
Hereinbelow, such a specific alignment state described above is referred to 
as "quasi-smectic A alignment state or quasi-S.sub.A state". A 
quasi-smectic A alignment state is identified by an alignment state 
providing a single average molecular axis which can be confirmed as a 
position providing the darkest state when observed through cross nicol 
polarizers under no electric field application. The single average 
molecular axis extends in substantially the same direction as a central 
axis direction with respect to the uniaxial alignment axes in the above 
observation. Herein, a temperature providing such a single average 
molecular axis on temperature decrease is referred to as "quasi-S.sub.A 
state appearing temperature". 
In another respect, the liquid crystal device according to the present 
invention comprises a chiral smectic liquid crystal capable of providing a 
quasi-smectic A alignment state which appears at a temperature range lower 
than a temperature range where the chiral smectic liquid crystal assumes 
different two alignment states under no electric field application. 
In order to realize a high contrast, the liquid crystal device according to 
the present invention may preferably include a chiral smectic liquid 
crystal being placed in such an alignment state that the liquid crystal 
assumes at least two stable states and provides a pretilt angle .alpha., a 
cone angle H, an inclination angle .delta. of the liquid crystal layer, 
and an apparent tilt angle .theta.a each in the neighborhood of room 
temperature satisfying the following relationships (1) and (2): 
EQU H&lt;.alpha.+.delta. and .delta.&lt;.alpha. (1), 
EQU H&gt;.theta.a&gt;H/2 (2). 
In a preferred embodiment for stably forming C1 alignment state and a good 
alignment characteristic, the liquid crystal device of the present 
invention may preferably have respective uniaxial alignment axes extending 
in directions which intersect each other at an angle of 1-25 degrees. 
In order to improve a uniform alignment characteristic, the liquid crystal 
device of the present invention may preferably comprise the chiral smectic 
liquid crystal being further placed in such an alignment state that the 
liquid crystal molecules will have a single average molecular axis under 
no electric field application in the neighborhood of the upper limit 
temperature within chiral smectic C phase range, wherein the single 
average molecular axis can be confirmed as a position providing the 
darkest state when observed through cross nicol polarizers (Hereinbelow, 
such an alignment state is referred to as "another quasi-smectic A 
phase"). 
The chiral smectic liquid crystal used in the present invention may 
preferably provide a pretilt angle .alpha. of at least 5 degrees. 
For a usable property effective in improving a uniform alignment 
characteristic, the chiral smectic liquid crystal may preferably have a 
temperature characteristic of an inclination angle .delta. such that the 
inclination angle .delta. increases on temperature decrease down to a 
mediate temperature as a temperature giving a maximum of inclination angle 
.delta. and decreases on further temperature decrease below the mediate 
temperature. In the present invention, the mediate temperature may 
preferably appear at a temperature of at least 10.degree. C., more 
preferably at least 25.degree. C., in order to effectively improve a 
temperature-dependence of driving characteristics of the liquid crystal 
device at around room temperature. 
In order to advantageously place chiral smectic liquid crystal in a 
quasi-smectic A alignment state, we have empirically found the following 
tendencies. 
The chiral smectic liquid crystal may preferably have a relatively small 
inclination angle .delta. providing a layer structure closer to a 
bookshelf state. At this time, the liquid crystal shows a cone angle H 
smaller than one at room temperature in many cases. However, the 
quasi-smectic A alignment state appears at various temperature ranges 
depending upon a difference in, e.g., alignment treatment even when the 
same chiral smectic liquid crystal is used. Generally speaking, when a 
pretilt angle a is large, the quasi-smectic A alignment state is liable to 
appear at a relatively higher temperature on a low temperature side within 
Sc* (chiral smectic C phase) range. When the quasi-S.sub.A state starts to 
appear, a value of the inclination angle .delta. is changed depending upon 
values of pretilt angle .alpha., cone angle H, viscosity, etc. The value 
of the inclination angle .delta. cannot not be referred to as an accurate 
numerical value but is about 6 degrees or below as an empirical value. 
On the other hand, in a case where a pretilt angle is relatively large and 
a chiral smectic liquid crystal assumes C1 uniform alignment state 
satisfying the above-mentioned relationships (1) and (2), the chiral 
smectic liquid crystal is placed in another quasi-smectic A alignment 
state at the neighborhood of the upper limit temperature of Sc* in many 
cases. At visual observation, "quasi-smectic A alignment state" and 
"another quasi-smectic A alignment state" cannot be distinguished from 
each other. However, the two alignment states can be distinguished by, 
e.g., measurement of cone angle H at switching of the chiral smectic 
liquid crystal under electric field application. More specifically, 
"another quasi-smectic A alignment state" cannot be said to a state 
showing a memory characteristic because the liquid crystal molecules in 
one stable state are moved to align along a center axis direction of the 
uniaxial alignment axes at a velocity on the order of several 
milli-seconds. On the other hand, "quasi-smectic A alignment state" can be 
said to a state showing a memory characteristic during a certain time 
because the movement of the liquid crystal molecules as described above is 
caused to occur at a velocity on the order of 0.1 second to several tens 
of seconds. Such a movement that liquid crystal molecules switched (or 
oriented) to one stable state (i.e., a state where a cone angle H is 
formed by the optical axis direction in one stable state and the center 
axis direction of the uniaxial alignment axes) by electric field 
application is successively caused to occur in the smectic layer formation 
direction (i.e., a direction perpendicular to the center axis direction of 
the alignment control axes). 
The "quasi-smectic A alignment state" provides a liquid crystal device with 
an improved shock resistance and a stable alignment state causing no 
disorder of alignment caused by crystallization. This reason may be 
attributable to results obtained from X-ray diffraction experiment as 
follows. 
FIG. 8 shows a graph of X-ray diffraction patterns of a liquid crystal 
composition (Composition D used in Example 2-5 appearing hereinafter) 
constituting a liquid crystal cell (cell gap: 1.2 .mu.m, alignment film: 
"LQ-1802") for illustrating a change of layer structure at various 
temperatures (-10.degree. C., 10.degree. C., 30.degree. C., 50.degree. C. 
and 70.degree. C.). Each X-ray diffraction pattern is obtained by scanning 
with respect to .theta.axis on condition that an angle of 2.theta. is 
fixed at 3 degrees (corresponding to a layer spacing of 300 nm in Bragg 
condition). Referring to FIG. 8, the sharp peaks (at 10.degree. C. to 
50.degree. C.) on the diffraction patterns, shows a longer correlation 
length (i.e., a longer orderly (or constant) layer distance) of the layer 
structure and the broad peaks (at -10.degree. C.) shows a shorter 
correlation length (i.e., a shorter orderly layer distance) of the layer 
structure. That is, the peak shape in Sc*.fwdarw.quasi-S.sub.A phase 
transition at -10.degree. C. is broader than that in Sc* at 10.degree. to 
50.degree. C. This reason is not clarified as yet but may be mainly 
attributable to an improvement in a flexibility of the layer structure in 
Sc*.fwdarw.quasi-S.sub.A phase transition. Such a layer structure in 
quasi-S.sub.A phase is presumably effective for absorbing an external 
shock. 
According to a study of our research group, a value and a temperature 
dependence of a layer inclination angle .delta. of a liquid crystal layer 
can be changed by controlling factors of liquid crystal compounds 
contained therein, such as a skeleton structure, side chain lengths and an 
affinity of combination. In many cases, a type of a liquid crystal tending 
to provide a broader smectic A temperature range changes considerably the 
temperature dependence of .delta.. 
A preferred embodiment of the liquid crystal device will now be described 
with reference to FIG. 1 which is a schematic sectional view of the 
device. Referring to FIG. 1, the device includes a pair of substrates 
(glass plates) 11a and 11b coated with transparent electrodes 12a and 12b, 
respectively, of In.sub.2 O.sub.3, ITO (indium tin oxide), etc., then with 
200 to 3000 .ANG.-thick insulating films 13a and 13b, respectively, of 
SiO.sub.2, TiO.sub.2, Ta.sub.2 O.sub.5, etc., and further with 50 to 1000 
.ANG.-thick polyimide alignment films 14a and 14b formed, e.g., by 
applying and baking a polyamide acid represented by the following formula: 
##STR1## 
The alignment films 14a and 14b are respectively provided with uniaxial 
alignment axes by rubbing in directions (denoted by arrows A in FIG. 1) 
which are generally parallel and in the same direction but intersect each 
other at a clockwise or counter-clockwise angle of 0-25 degrees. The 
direction of clockwise (or counter-clockwise) intersection angle is 
determined herein by the direction of rotation of the alignment axis 
provided to the upper alignment film 14a from the alignment axis provided 
to the lower alignment film 14b as viewed from the upper substrate 11a. 
Between the substrates 11a and 11b is disposed a chiral smectic C liquid 
crystal 15, and the spacing between the substrates 11a and 11b is set to a 
value (e.g., 0.1-3 .mu.m) which is sufficiently small to suppress the 
formation of a helical structure of the chiral smectic C liquid crystal 
15, thus resulting in bistable alignment states of the liquid crystal 15. 
The small spacing is held by spacer beads 16 of, e.g., silica or alumina, 
dispersed between the substrates. The thus-formed cell structure is 
sandwiched between a pair of polarizers 17a and 17b to provide a liquid 
crystal device. 
A simple matrix-type display apparatus using a liquid crystal device 
comprising a ferroelectric liquid crystal disposed between a pair of 
substrates as described above may be driven by driving methods as 
disclosed by, e.g., JP-A 59-193426, JP-A 59-193427, JP-A 60-156046 and 
JP-A 60-156047. 
FIG. 4 is a waveform diagram showing an example set of driving waveforms 
used in such a driving method. FIG. 5 is a plan view showing an electrode 
matrix used in a ferroelectric liquid crystal panel 51 of a simple 
matrix-type. The liquid crystal panel 51 shown in FIG. 5 includes scanning 
electrodes 52 and data electrodes 53 intersecting each other so as to 
constitute a pixel at each intersection together with a ferroelectric 
liquid crystal disposed between the scanning electrodes 52 and data 
electrodes 53. 
A liquid crystal display apparatus may be constituted by using the liquid 
crystal device for a display panel and by adopting an arrangement and data 
format comprising image data accompanied with scanning line address data 
and also a communication synchronization scheme using a SYNC signal as 
shown in FIGS. 6 and 7. 
Referring to FIG. 6, the liquid crystal display apparatus 101 includes a 
graphic controller 102, a display panel 103, a scanning line drive circuit 
104, a data line drive circuit 105, a decoder 106, a scanning signal 
generator 107, a shift resistor 108, a line memory 109, a data signal 
generator 110, a drive control circuit 111, a graphic central processing 
unit (GCPU) 112, a host central processing unit (host CPU) 113, and an 
image data storage memory (VRAM) 114. 
Image data are generated in the graphic controller 102 in an apparatus body 
and transferred to the display panel 103 (illuminated with a backlight 
(not shown)) by signal transfer means shown in FIGS. 6 and 7. The graphic 
controller 102 principally comprises a CPU (or GCPU, central processing 
unit) 112 and a VRAM (video-RAM, image data storage memory) 114 and is in 
charge of management and communication of image data between a host CPU 
113 and the liquid crystal display apparatus (FLCD) 101. The control of 
image display according to the present invention is principally 
accomplished by the graphic controller 102. Incidentally, a light source 
is disposed at the back of the display panel 103. 
The values of cone angle H, apparent tilt angle .theta.a, liquid crystal 
layer inclination angle .delta. and pretilt angle .alpha. referred to 
herein are based on values measured according to the following methods. 
Measurement of Cone Angle H 
An liquid crystal device was sandwiched between right angle-cross nicol 
polarizers and rotated horizontally relative to the polarizers under 
application of an AC voltage of .+-.30 V to .+-.50 V and 100 Hz between 
the upper and lower substrates of the device while measuring a 
transmittance through the device by a photomultiplier (available from 
Hamamatsu Photonics K.K.) to find a first extinct position (a position 
providing the lowest transmittance) and a second extinct position. A cone 
angle H was measured as a half of the angle between the first and second 
extinct positions. 
Measurement of Apparent Tilt Angle .theta.a 
An liquid crystal device sandwiched between right angle cross nicol 
polarizes was supplied with a single pulse of one polarity exceeding the 
threshold voltage of the ferroelectric liquid crystal and was then rotated 
under no electric field horizontally relative to the polarizers to find a 
first extinction position. Then, the liquid crystal device was supplied 
with a single pulse of the opposite polarity exceeding the threshold 
voltage of the ferroelectric liquid crystal and was then rotated under no 
electric field relative to the polarizers to find a second extinct 
position. An apparent tilt angle .theta.a was measured as a half of the 
angle between the first and second extinct positions. 
Measurement of Liquid Crystal Layer Inclination Angle .delta. 
The method used was basically similar to the method used by Clark and 
Largerwal (Japanese Display '86, Sep. 30-Oct. 2, 1986, p.p. 456-458) or 
the method of Ohuchi et al (J.J.A.P., 27 (5) (1988), p.p. 725-728). The 
measurement was performed by using a rotary cathode-type X-ray diffraction 
apparatus (available from MAC Science), and 80 .mu.m-thick microsheets 
(available from Corning Glass Works) were used as the substrates so as to 
minimize the X-ray absorption with the glass substrates of the liquid 
crystal cells. 
Measurement of pretilt angle .alpha. 
The measurement was performed according to the crystal rotation method as 
described at Jpn. J. Appl. Phys. vol. 19 (1980), No. 10, Short Notes 2013. 
More specifically, a pair of substrates rubbed in mutually parallel and 
opposite directions were applied to each other to form a cell having a 
cell gap of 20 .mu.m, which was then filled with a liquid crystal mixture 
assuming SmA phase in the temperature range of 10.degree.-55.degree. C. 
obtained by mixing 80 wt. % of a ferroelectric liquid crystal ("CS-1014", 
mfd. by Chisso K.K.) with 20 wt. % of a compound represented by the 
following formula: 
##STR2## 
For measurement, the liquid crystal cell was rotated in a plane 
perpendicular to the pair of substrates and including the aligning 
treatment axis and, during the rotation, the cell was illuminated with a 
helium-neon laser beam having a polarization plane forming an angle of 45 
degrees with respect to the rotation plane in a direction normal to the 
rotation plane, whereby the intensity of the transmitted light was 
measured by a photodiode from the opposite side through a polarizer having 
a transmission axis parallel to the polarization plane. 
An angle .phi..sub.x between a normal to the cell and the incident beam 
direction for providing the central point of a family of hyperbolic curves 
in the interference figure thus obtained was substituted in the following 
equation to find a pretilt angle .alpha..sub.o, 
##EQU1## 
wherein n.sub.o denotes the refractive index of ordinary ray, and n.sub.e 
denotes the refractive index of extraordinary ray. 
The chiral smectic liquid crystal used in the present invention comprises 
at least one mesomorphic compounds, preferably a liquid crystal 
composition comprising at least two mesomorphic compounds. 
Examples of the mesomorphic compound may include those represented by the 
following structural formulae. 
##STR3## 
wherein R.sub.1 denotes a linear or branched alkyl group having 1-18 
carbon atoms; X.sub.1 denotes a single bond, --O--, --COO-- or --OCO--; 
X.sub.2 denotes a single bond, --OCH.sub.2 --, --COO-- or --OCO--; n is an 
integer of 3-16; and A.sub.1 denotes 
##STR4## 
wherein R.sub.2 and R.sub.3 independently denote a linear or branched 
alkyl group having 1-18 carbon atoms; X.sub.3 denotes a single bond, 
--O--, --OCO--, or --COO--; and A.sub.2 denotes 
##STR5## 
wherein R.sub.4 to R.sub.17 independently denote a linear or branched 
alkyl group capable of having a substituent such as fluorine (optically 
active or inactive). 
The chiral smectic liquid crystal used in the present invention may 
preferably be a liquid crystal composition comprising at least one 
mesomorphic compound of the formula (3) and at least one mesomorphic 
compound of the formula (4). In this instance, the liquid crystal 
composition may preferably contain 1-30 wt. % in total of the mesomorphic 
compound of the formula (3) and 1-30 wt. % in total of the mesomorphic 
compound of the formula (4). 
Specific examples of the mesomorphic compound of the formula (3) may 
include those shown in Table 1 below. In Table 1, the respective 
abbreviations denotes the following alkyl groups or aromatic groups. 
##STR6## 
TABLE 1 
______________________________________ 
(3) 
R.sub.1 
X.sub.1 A.sub.1 X.sub.2 n 
______________________________________ 
met -- prylphe -- 3 
but -- prylphe -- 3 
hex -- prylphe -- 4 
oct -- prylphe -- 4 
dec -- prylphe -- 4 
und -- prylphe -- 4 
dod -- prylphe -- 4 
tet -- prylphe -- 4 
ocd -- prylphe -- 4 
oct O prylphe -- 4 
dec O prylphe -- 4 
tet O prylphe -- 4 
oct -- phepry2 OCH.sub.2 
3 
dec -- phepry2 OCH.sub.2 
4 
dod -- phepry2 OCH.sub.2 
6 
dec COO phepry2 -- 5 
dec OOC phepry2 OCH.sub.2 
4 
dec -- prylphe COO 5 
dec -- prylphe OOC 4 
dec -- prylphe -- 10 
hex -- prylphe -- 14 
oct -- prylphe -- 16 
oct -- prylphephe -- 4 
hex -- pheprylphe -- 5 
oct -- phepry2phe -- 3 
dec -- phephepry2 -- 4 
dec -- prylphephe OCH.sub.2 
5 
hep OOC phephepry2 -- 5 
2mb -- prylphe -- 5 
______________________________________ 
Specific examples of the mesomorphic compound of the formula (4) may 
include those shown in Table 1 below. In Table 1, the respective 
abbreviations denotes the following alkyl groups or aromatic groups. 
##STR7## 
TABLE 2 
______________________________________ 
(4) 
R.sub.2 A.sub.2 X.sub.3 R.sub.3 
______________________________________ 
met phe -- but 
pro phe -- hex 
hex phe -- oct 
oct phe -- oct 
dec phe -- oct 
und phe -- dec 
dod phe -- dec 
tet phe -- dec 
ocd phe -- dec 
dec phe -- dec 
oct phe -- dec 
hex phe O dec 
oct phe O dec 
dec phe O dec 
hex phe -- dec 
oct phe -- dod 
oct phe -- ocd 
hex phe COO oct 
oct phe COO oct 
dec phe COO oct 
hex phe OOC oct 
oct phe OOC oct 
dec phe OOC oct 
hex cyc -- und 
oct cyc -- und 
dec cyc -- dod 
dod cyc -- dod 
2mb phe -- oct 
oct phe O 2mb 
______________________________________ 
Hereinbelow, the present invention will be described more specifically 
based on Examples to which the present invention is not intended to be 
limited, however. In the Examples, "part(s)" used for describing 
compositions are all by weight. 
Examples 1-1 to 3-5, Comparative Examples 1-1 to 3-2 
Two 1.1 mm-thick glass plates (diagonal distance: 14 in.) were provided as 
a pair of substrates and were respectively coated with transparent ITO 
stripe electrodes each having a side metal wire of molybdenum, followed by 
coating with a 1500 .ANG.-thick tantalum oxide as a transparent dielectric 
film by sputtering. 
A solution in NMP of a polyimide precursor ("LQ 1802" mfd. by Hitachi Kasei 
K.K. or "LP-64" mfd. by Toray K.K.) was applied onto the tantalum oxide 
film and baked at 200.degree.-270.degree. C. (200.degree. C. for LP-64, 
270.degree. C. for LQ-1802) to form a 100-300 .ANG.-thick (100.ANG. for 
LP-64, 300.ANG. for LQ-1802) polyimide alignment film. The baked film was 
then rubbed with acetate fiber planted cloth. A pretilt angle is 
controlled by, e.g., changing rubbing conditions including a degree of 
pressing, rotation speed of a rubbing roller and a substrate feed 
velocity. Then, on one of the substrates, epoxy resin adhesive particles 
having an average particle size of 5.5 .mu.m ("Torepearl" (trade name), 
available from Toray K.K.) were dispersed at a density of 50 
particles/mm.sup.2 by the Nord Son electrostatic dispersion method and, on 
the other substrate, silica micro-beads having an average particle size of 
1.2 .mu.m were dispersed at a density of 300 particles/mm.sup.2 by the 
Knudsen electrostatic dispersion method. Then, a liquid adhesive ("Struct 
Bond" (trade name), mfd. by Mitsui Toatsu Kagaku K.K.) as a sealing member 
was applied by printing in a thickness of 6 .mu.m. Then, the two glass 
plates were applied to each other so that their rubbed directions extended 
generally in the same direction but intersected each other at a 
counterclockwise angle of 0-10 degrees, and bonded to each other by 
applying a pressure of 2.8 kg/cm.sup.2 at 70.degree. C. for 5 min, 
followed by further curing of the two types of adhesives under a pressure 
of 0.63 kg/cm.sup.3 at 150.degree. C. for 4 hours to form a blank cell. 
Then, blank cells prepared in the above described manner were respectively 
evacuated to a reduced pressure of 10.sup.-4 torr and then filled with 
liquid crystal compositions A-H, a ferroelectric liquid crystal 
(ZLI-3233", mfd. by Merk Co.), a ferroelectric liquid crystal ("CS-1014", 
mfd. by Chisso K.K.), respectively, to prepare liquid crystal devices. The 
liquid crystal compositions A-H were prepared by mixing mesomorphic 
compounds in prescribed proportions, respectively. For instance, the 
liquid crystal compositions G and H were prepared by mixing the following 
mesomorphic compounds in the indicated proportions below. 
______________________________________ 
Composition G 
wt. 
Structural formula parts 
______________________________________ 
##STR8## 8 
##STR9## 12 
##STR10## 2 
##STR11## 6 
##STR12## 2 
##STR13## 10 
##STR14## 9 
##STR15## 4 
##STR16## 2 
##STR17## 5 
##STR18## 5 
##STR19## 2 
##STR20## 10 
##STR21## 2 
##STR22## 6 
##STR23## 5 
##STR24## 7 
##STR25## 3 
______________________________________ 
______________________________________ 
Composition H 
wt. 
Structural formula parts 
______________________________________ 
##STR26## 8 
##STR27## 9 
##STR28## 6 
##STR29## 6 
##STR30## 2 
##STR31## 6 
##STR32## 6 
##STR33## 8 
##STR34## 2 
##STR35## 2 
##STR36## 4 
##STR37## 5 
##STR38## 7 
##STR39## 2 
##STR40## 1 
##STR41## 9 
##STR42## 1 
##STR43## 3 
##STR44## 10 
##STR45## 3 
______________________________________ 
Each of the liquid crystal compositions A-H and the ferroelectric liquid 
crystals (ZLI-3233 and CS-1014) was cooled to 30.degree. C. providing 
chiral smectic C phase through phases including cholesteric phase and 
smectic A phase or smectic A phase. 
The liquid crystal compositions A-H and the ferroelectric liquid crystals 
showed the following properties including phase transition temperatures 
TpT (.degree. C.), spontaneous polarization Ps (nC/cm.sup.2) at 30.degree. 
C., cone angle H (degrees) at 30.degree. C., and inclination angle .delta. 
(degrees) of a liquid crystal layer at various temperatures. The 
properties of TpT, Ps and H were shown in Table 3 below and the properties 
of .delta. were shown in Table 4 below, respectively. 
TABLE 3 
__________________________________________________________________________ 
Ps .theta. 
T.sub.PT (.degree.C.) (nC/cm.sup.2) 
(degrees) 
Liquid Crystal 
Cry Sc* S.sub.A Ch Iso 
(30.degree. C.) 
(30.degree. 
__________________________________________________________________________ 
C.) 
##STR46## 
##STR47## 
##STR48## 
##STR49## 
5.8 14.5 
B 
##STR50## 
##STR51## 
##STR52## 
##STR53## 
5.8 14.9 
C 
##STR54## 
##STR55## 
##STR56## 
##STR57## 
6.1 16.0 
D 
##STR58## 
##STR59## 
##STR60## 
##STR61## 
6.1 14.9 
E 
##STR62## 
##STR63## 
##STR64## 
##STR65## 
7.5 15.5 
F 
##STR66## 
##STR67## 
##STR68## 
##STR69## 
3.4 14.1 
G 
##STR70## 
##STR71## 
##STR72## 
##STR73## 
5.6 14.3 
H 
##STR74## 
##STR75## 
##STR76## 
##STR77## 
5.8 15.7 
ZLI-3233 
##STR78## 
##STR79## 
##STR80## 
##STR81## 
9.9 29.0 
CS-1014 
##STR82## 
##STR83## 
##STR84## 
##STR85## 
4.7 21.0 
__________________________________________________________________________ 
Cry: Crystal or higherorder smectic phase 
Sc*: Chiral smectic C phase 
S.sub.A : Smectic A phase 
Ch: Cholesteric phase 
Iso: Isotropic phase 
TABLE 4 
______________________________________ 
Layer inclination angle .delta. (deg.) 
L.C. -10.degree. C. 
0.degree. C. 
10.degree. C. 
20.degree. C. 
30.degree. C. 
40.degree. C. 
50.degree. C. 
______________________________________ 
A -- 6.1 8.9 10.3 10.4 8.7 -- 
B -- -- 6.2 8.9 10.0 10.5 9.7 
C 5.4 8.5 11.0 12.2 12.8 12.6 11.4 
D 1.4 5.9 8.1 9.6 10.2 10.3 9.6 
E 4.6 7.3 8.8 10.0 10.7 10.7 10.0 
F -- -- 12.4 12.5 12.3 11.4 9.6 
G -- -- 4.8 7.8 9.3 9.8 9.4 
H -- 4.8 7.6 9.4 10.6 11.0 10.0 
ZLI- 29.1 28.7 28.4 27.8 27.0 25.7 23.9 
3233 
CS- 15.5 17.7 18.8 19.1 18.5 16.6 12.5 
1014 
______________________________________ 
(Examples 1-1 to 1-7, Comparative Examples 1-1 to 1-3) 
The above-prepared liquid crystal devices were subjected to a shock test at 
0.degree. C. by using a drop testing apparatus ("DT-50", mfd. by Toshida 
Seiki K.K.). More specifically, the shock test was performed by observing 
a change in an alignment state of a liquid crystal within a cell on 
condition of increasing an impact from 20 G to 80 G (G: acceleration of 
gravity=9.8 m/sec.sup.2) by an increment of 10 G. 
The results of the shock test were shown in Table 5 below together with 
each cell structure (alignment film, pretilt angle .alpha., intersection 
angle .phi.), apparent tilt angle .theta.a, and quasi-S.sub.A state 
appearing temperature. 
TABLE 5 
__________________________________________________________________________ 
Cell structure Appearing temp. 
Alignment 
.alpha. 
.phi.*.sup.1 
.theta.a at 30.degree. C. 
of quasi-S.sub.A 
Shock test*.sup.2 
L.C. film (deg.) 
(deg.) 
(deg.) (.degree.C.) 
(at 0.degree. C.) 
__________________________________________________________________________ 
Ex. No. 
1-1 B LQ-1802 
16 8 10 1 80G 
1-2 B " 20 10 11 2 " 
1-3 A " 17 6 11 -4 " 
1-4 E " 16 8 12 -10 70G 
80G det. 
1-5 E " 14 4 12 -11 70G 
80G det. 
1-6 G " 17 10 11 3 80G 
1-7 H " 21 8 12 -11 70G 
80G det. 
Comp. Ex. 
1-1 F " 16 8 13 Not appeared 
50G det. 
1-2 ZLI-3233 
" 14 4 6 " 30G det. 
1-3 CS-1014 
" 20 10 15 " 40G det. 
__________________________________________________________________________ 
*.sup.1 : Cell intersection angle. 
*.sup.2 : For example, "80G" means that an alignment state is not changed 
under an impact of 80G, and "80G det." means that an alignment state is 
changed and disordered (i.e., deteriorated) to cause a sanded texture or 
to cause a sanded texture and zigzag defects. 
As apparent from the above results, the liquid crystal devices (Ex. 1-1 to 
1-7) comprising the liquid crystal composition showing a quasi-smectic A 
alignment state on a lower temperature side (e.g., -11.degree. C. to 
3.degree. C.) within chiral smectic C phase range provided a good shock 
resistance at 0.degree. C. compared with those (Comp. Ex. 1-1 to 1-3) 
comprising the liquid crystal composition not showing a quasi-smectic A 
alignment state. 
Then, each of the liquid crystal devices was cooled to -20.degree. C. and 
kept at -20.degree. C. for 100 hours, and then subjected to observation of 
an alignment state. As a result, the liquid crystal devices according to 
the present invention used in Examples 1-1 to 1-7 caused substantially no 
change in the alignment state. On the other hand, the liquid crystal 
devices used in Comparative Examples 1-1 to 1-3 (i.e., not showing 
quasi-S.sub.A state) showed a considerable disorder of the alignment state 
being attributable to crystallization. Accordingly, the liquid crystal 
devices providing quasi-S.sub.A state improved low-temperature storage 
properties when compared with those failing to provide quasi-S.sub.A 
state. (Examples 2-1 to 2-7, Comparative Examples 2-1 and 2-2) 
Nine liquid crystal devices were prepared in the above-mentioned manner and 
evaluated in the same manner as in the above examples except for changing 
a test temperature to -5.degree. C. 
The results are shown in the following Table 6. 
TABLE 6 
__________________________________________________________________________ 
Cell structure Appearing temp. 
Alignment 
.alpha. 
.phi.*.sup.1 
.theta.a at 30.degree. C. 
of quasi-S.sub.A 
Shock test*.sup.2 
L.C. film (deg.) 
(deg.) 
(deg.) (.degree.C.) 
(at -5.degree. C.) 
__________________________________________________________________________ 
Ex. No. 
2-1 A LQ-1802 
20 10 12 -3 80G 
2-2 B " 20 10 11 2 " 
2-3 C " 16 8 11 -12 70G 
80G det. 
2-4 D " 15 0 12 -10 80G 
2-5 D " 18 4 13 -9 70G 
80G det. 
2-6 G " 19 6 12 3 80G 
2-7 H " 17 6 12 -12 " 
Comp. Ex. 
2-1 F " 17 8 13 Not appeared 
50G det. 
2-2 CS-1014 
" 20 10 15 " 40G det. 
__________________________________________________________________________ 
*.sup. 1 : Cell intersection angle. 
*.sup.2 : For example, "80G" means that an alignment state is not changed 
under an impact of 80G, and "80G det." means that an alignment state is 
changed and disordered (i.e., deteriorated) to cause a sanded texture or 
to cause a sanded texture and zigzag defects. 
As apparent from the above results, the liquid crystal devices providing 
quasi-S.sub.A state according to the present invention stably showed a 
good shock resistance when compared with those failing to provide 
quasi-S.sub.A state. 
(Examples 3-1 to 3-5, Comparative Examples 3-1 and 3-2) 
Seven liquid crystal devices were prepared in the above-mentioned manner 
and evaluated in the same manner as in the above examples 2-1 to 2-7 
except for changing the alignment film "LQ-1802" to an alignment film 
"LP-64". 
The results are shown in the following Table 7. 
TABLE 7 
__________________________________________________________________________ 
Cell structure Appearing temp. 
Alignment 
.alpha. 
.phi.*.sup.1 
.theta.a at 30.degree. C. 
of quasi-S.sub.A 
Shock test*.sup.2 
L.C. film (deg.) 
(deg.) 
(deg.) (.degree.C.) 
(at -5.degree. C.) 
__________________________________________________________________________ 
Ex. No. 
3-1 A LP-64 2 0 6 -6 70G 
80G det. 
3-2 B " " 0 6 -1 80G 
3-3 D " " 1 7 -12 70G 
80G det. 
3-4 G " " 0 8 0 80G 
3-5 H " " 0 8 -13 60G 
70G det. 
Comp. Ex. 
3-1 C " " 0 7 Not appeared 
40G det. 
3-2 ZLI-3233 
" " 2 8 " 30G det. 
__________________________________________________________________________ 
*.sup.1 : Cell intersection angle. 
*.sup.2 : For example, "80G" means that an alignment state is not changed 
under an impact of 80G, and "80G det." means that an alignment state is 
changed and disordered (i.e., deteriorated) to cause a sanded texture or 
to cause a sanded texture and zigzag defects. 
As apparent from the above results, the liquid crystal devices (Ex. 3-1 to 
3-5) comprising the liquid crystal composition showing a quasi-smectic A 
alignment state on a lower temperature side (e.g., -13.degree. C. to 
0.degree. C.) within chiral smectic C phase range provided a good shock 
resistance at -5.degree. C. compared with those (Comp. Ex. 3-1 to 3-2) 
comprising the liquid crystal composition not showing a quasi-smectic A 
alignment state. 
As described hereinabove, according to the present invention, there is 
provided a liquid crystal device comprising a chiral smecticliquid crystal 
characterized by showing a quasi-smectic A alignment state (i.e., having a 
single average molecular axis) on a lower temperature side of chiral 
smectic C phase range when observed through cross nicol polarizers under 
no voltage application. Such a liquid crystal device provided a good shock 
resistance and low-temperature storage properties.