JP2001316667A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mono-stable ferroelectric liquid-crystal display element having a large cone angle. SOLUTION: A pair of substrates 1 and 2 are located to face each other in an approximately parallel manner. A liquid crystal material containing an SmC* phase is inserted. These substrates are ones subjected to a one-axis orientation treatment in advance and they are placed such that their orientation- treatment orientations be approximately parallel to each other. Into this liquid crystal cell, a liquid crystal material is introduced in an isotropic liquid phase. As the liquid crystal material, a mono-stable ferroelectric liquid-crystal composition having a large cone angle obtained by mixing a bi-stable ferroelectric liquid-crystal composition having a large cone angle with a mono-stable ferroelectric liquid-crystal composition is used. After the introduction, a mono- stable structure in which the normal line of the liquid crystal and the layer are parallel to the orientation-treatment orientation is formed by cooling still the liquid-crystal composition to an SmC* phase of the ordinary temperature. The liquid crystal molecules rotate drawing a cone having a large cone angle by applying an electric field. The apparent tilt angle changes continuously according to the intensity of the applied electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device having a monostable ferroelectric liquid crystal having a large cone angle.

[0002]

2. Description of the Related Art Conventionally, as a liquid crystal display device using a nematic liquid crystal, a twisted nematic (TN) type liquid crystal display device and a super twisted birefringence effect (SB) have been proposed.
There is an E) type liquid crystal display element. However, the TN type liquid crystal display element cannot obtain sufficient contrast because the driving method is complicated and the driving tolerance is narrow. In addition, SBE with a large twist angle is an improved type of TN type liquid crystal display element.
The type liquid crystal display element has a problem that the contrast is reduced and the response speed is reduced with the increase in the screen size of the display.

In order to improve the disadvantages of the above-mentioned liquid crystal display device, a liquid crystal display device using a liquid crystal of a chiral smectic C (hereinafter referred to as SmC *) phase, a so-called surface-stable ferroelectric liquid crystal display device (SSFLC). In 1980. A. It has been proposed by Clark and Lagerwall (JP-A-56-107216, U.S. Pat. No. 4,368,924). This liquid crystal display element has bistability, memory properties and high-speed response. Since the birefringent light in the ferroelectric liquid crystal in the cell changes due to the switching operation, the transmitted light can be controlled by sandwiching the cell with polarizers arranged orthogonally. Further, even when the applied voltage is removed, the alignment of the liquid crystal molecules is maintained in the same state as when the voltage was applied, so that a memory property can be obtained. The switching operation is
Since the spontaneous polarization of the liquid crystal molecules and the electric field directly act on each other, the liquid crystal display device has a high response speed of less than 1/1000 that of the TN type liquid crystal display element, and enables high-speed display. However,
The liquid crystal display device proposed by Clark and Lagerwall also has many problems. The biggest problem is that it is limited to a switch between the two states of light and dark, and therefore, it has a memory property but cannot perform gradation display.

To solve this problem, Japanese Patent Laid-Open Publication No. Hei.
In JP-A-152430, the relationship between the pitch p of the SmC * phase and the cell gap d is d / p> 5, that is, d = 2 μm.
Using SmC * liquid crystal having a pitch of m and p <0.4 μm, the helical axis of the SmC * phase is oriented in the direction of the alignment treatment of the substrate, and the director (molecular axis) of the liquid crystal molecules forms a helix in a stable state. A liquid crystal display cell having such a configuration has been proposed. In this liquid crystal display cell, in a monostable state using the helical distortion effect of the ferroelectric liquid crystal, it is possible to realize a television rate analog gradation with low voltage driving. However, in this case, a liquid crystal system having an extremely short helical pitch is required due to its operation principle in order to obtain high-speed response, and a new problem that uniform alignment is difficult occurs.

As another type of liquid crystal display cell, US Pat. No. 5,172,257 (1992) discloses a twisted ferroelectric liquid crystal optical element in which a twisted ferroelectric liquid crystal is oriented in a direction perpendicular to a surface facing the liquid crystal cell. Has been proposed. This means that when no voltage is applied to the cell,
Light is transmitted by the twisted liquid crystal, and when voltage is applied, the liquid crystal is untwisted, and most of the liquid crystal except for the vicinity of the substrate surface is aligned in the alignment direction. Light is blocked under the polarizer. Here, when the applied voltage is reduced, the twist of the liquid crystal that can be melted becomes partial, and the light is transmitted partly to make the elliptically polarized light linearly.
It is said that gradation control can be performed. However, in this case, when the applied voltage is zero, the light transmittance of the cell cannot be reduced to 0 (dark state), and it is difficult to uniformly align the twist, so that a large and uniform twisted ferroelectric liquid crystal device is manufactured. There is a new problem that is difficult to do. As described above, in the conventional ferroelectric liquid crystal element, it is difficult to realize continuous gray scale display (so-called analog gray scale display), and its practical use is greatly restricted in practical use.

[0006] To solve this drawback, Japanese Patent No. 2982330 and US Patent No. 52145 are disclosed.
No. 23 proposes a monostable ferroelectric liquid crystal display device which has a fast response and can perform analog gradation. This monostable ferroelectric liquid crystal display device has a pair of anti-parallel substrates with Sm.
It is formed by sandwiching a phenylpyrimidine liquid crystal composition having a C * phase. In this liquid crystal display device, the projected component of the smectic cone onto the substrate in the axial direction and the projected component of the liquid crystal molecules on the substrate in the axial direction are respectively the same as the uniaxial alignment processing direction of the substrate. Monostable. When an electric field is applied, the liquid crystal molecules rotate along the cone, and the apparent tilt angle seen on the substrate surface changes continuously according to the intensity of the applied electric field. Since the intensity of the transmitted light under the polarizer continuously increases with an increase in the tilt angle, continuous gradation, that is, analog gradation is possible. Light transmittance T at a certain electric field strength
r can be expressed as a function of the apparent tilt angle θ _app as in Equation 1 below.

[0007]

## EQU1 ## Tr = sin ² (2θ _app ) (1)

In the monostable ferroelectric liquid crystal cell using the phenylpyrimidine liquid crystal composition, the liquid crystal exhibits a highly regular striped structure along the rubbing direction of the alignment film, and the striped structure has a high contrast. Reduce the ratio to 50 or less. For this reason, in order to obtain a high contrast ratio, as a process for removing the striped tissue having a very high regularity,
During the transition from the chiral nematic (N *) phase to the SmC * phase, an electric field of 20 to 50 V is applied at 700 Hz, thereby producing a highly regular striped structure of the monostable ferroelectric liquid crystal cell. Has an inclined bookshelf-shaped monodomain structure, and can provide a linear gradation and a high contrast ratio of 80 or more at a low voltage.

[0009]

However, even in such a monostable ferroelectric liquid crystal cell, since the cone angle of the monostable liquid crystal composition used is small, the brightness of the screen, that is, the light transmittance of 75% or more is required. It is difficult to obtain Tr. What is important for realizing a monostable ferroelectric liquid crystal device with a bright screen is to obtain a monostable liquid crystal composition having a maximum cone angle of 60 ° or more. When the cone angle is 60 °, the maximum light transmittance is 75%. Note that, for a monostable ferroelectric liquid crystal element, the ideal cone angle at which the maximum light transmittance becomes 100% is 90 °.

The present invention has been made in view of such a point, and uses a monostable liquid crystal composition having a large cone angle of 60 ° or more, and has an analog gradation, a high-speed response, and a high contrast ratio. It is an object of the present invention to provide a liquid crystal display device capable of performing bright display with a light transmittance of 75% or more.

[0011]

That is, according to the present invention, a pair of substrates, each of which is subjected to uniaxial orientation treatment and arranged to face each other so that the orientation treatment directions thereof are substantially parallel to each other, are provided. Chiral smectic C
A liquid crystal display device comprising: a liquid crystal layer having a phase; and means for applying an electric field to the liquid crystal layer.

Embedded image (Where R ¹ and R ² each have 1 to 2 carbon atoms)
An alkyl group of 0, and n represents an integer of 1 or 2. A liquid crystal composition having a chiral smectic C phase containing a component represented by the following formula:

Embedded image(However, in the formula, R^Three Is an alkyl group having 1 to 18 carbon atoms
Or an alkoxy group, R ^Four Is an alkyl having 2 to 10 carbon atoms
And k is an integer of 1 or 2, m is an integer of 1 to 10.
Show. Chiral smectic C containing a component represented by
Liquid crystal material mixed with a liquid crystal composition having a phase.
The liquid crystal molecules are formed on the substrate with no electric field applied.
Along the orientation direction and the normal direction of the smectic layer
It is characterized by showing an oriented monostable state.

According to a second aspect of the present invention, in the liquid crystal display device of the first aspect, the liquid crystal layer has a cone angle of 60 ° or more, and apparent liquid crystal molecules appear on the substrate surface by rotating along the cone. Is characterized in that the tilt angle changes continuously according to the intensity of the applied electric field.

According to a third aspect of the present invention, in the liquid crystal display device of the first aspect, the liquid crystal composition containing the component of the chemical formula 1 is:
It shows a phase transition of liquid phase (Iso) -chiral nematic phase (N *)-smectic A phase (SmA) -chiral smectic C phase (SmC *), and shows chiral smectic C
It is characterized by being monostable in phase.

According to a fourth aspect of the present invention, in the liquid crystal display device of the first aspect, the liquid crystal composition containing the component of the chemical formula 2 is:
It shows a phase transition of liquid phase (Iso) -chiral nematic phase (N *)-chiral smectic C phase (SmC *), and is characterized by being bistable in chiral smectic C phase.

According to a fifth aspect of the present invention, in the liquid crystal display device of the first aspect, the mixed liquid crystal material has a phase transition of a liquid phase (Iso) -chiral nematic phase (N *)-chiral smectic C phase (SmC *). It is characterized by showing.

According to a sixth aspect of the present invention, in the liquid crystal display device of the fourth aspect, the liquid crystal composition containing the component of the chemical formula 2 is:
It has a cone angle of 60 ° or more.

In the present invention, a ferroelectric liquid crystal composition which is monostable in a chiral smectic C phase but has a small cone angle and a ferroelectric liquid crystal composition which is not monostable in a chiral smectic C phase but has a large cone angle And the mixed liquid crystal material is filled in a liquid state between a pair of substrates disposed so as to face each other so that the alignment processing directions are substantially parallel to each other, and then cooled to room temperature. And a monostable ferroelectric liquid crystal layer having a chiral smectic C phase with a large cone angle of 60 ° or more between the substrates is formed. Therefore, in the absence of an applied electric field, the normal of the smectic layer and the liquid crystal molecule axis become parallel to the uniaxial alignment direction, and when an electric field is applied, the liquid crystal molecules rotate along the smectic cone with a large cone angle, and the substrate surface The apparent tilt angle changes continuously according to the strength of the applied electric field. Since the light transmittance under the orthogonal polarizer increases continuously as the apparent tilt angle increases, continuous gradation, that is, analog gradation is obtained, and the maximum light transmittance corresponding to a large cone angle of 60 ° or more is obtained. Highly bright displays of at least 75% are achieved. When the applied electric field disappears, the liquid crystal molecules immediately return to the initial state due to the effect of stabilizing the interface.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a liquid crystal display device according to an embodiment of the present invention. FIG.
FIG. 2 shows a schematic plan view. Two glass substrates are opposed to each other as an upper substrate 1 and a lower substrate 2 of the cell. Transparent electrodes 3 and 4 of, for example, ITO (oxide of indium-tin) are formed on one surface of these substrates.
Uniform alignment layers 5 and 6 are formed on the transparent electrodes 3 and 4. The alignment layers 5 and 6 have, when viewed as a final cell,
The orientation process is performed in the direction shown by the broken line 9 by the mechanical rubbing process (the rubbing directions are indicated by arrows 7 and 8). Thereby, the liquid crystal molecules of the SmC * phase are aligned in the alignment processing direction 9 of the cell. On the other surfaces of the substrates 1 and 2, polarizers 10 and 11 for linearly polarizing are arranged. The polarization direction of the polarizer 10 is parallel to the alignment processing direction 9,
The polarization direction of the polarizer 11 is arranged so as to be perpendicular to the alignment processing direction 9, and the arrangement of these polarization directions can be changed by an optical effect.

In the cell thus constructed, the chemical formula 1
A monostable ferroelectric liquid crystal composition A containing the following component:
The mixed liquid crystal material C obtained by mixing the bistable ferroelectric liquid crystal composition B containing the above component is filled in an isotropic phase (liquid phase) or a nematic phase, and cooled to an ambient temperature. This mixed liquid crystal material C also shows a chiral smectic C phase similarly to the liquid crystal compositions A and B. Further, in the mixed liquid crystal material C, the bistability of the liquid crystal composition B is easily suppressed by the interaction between the liquid crystal composition A, which is a monostable component, and the alignment-treated surface. Can be more dominant. On the other hand, the cone angle of the mixed liquid crystal material C is intermediate between the cone angles of the liquid crystal compositions A and B. Therefore, the mixed liquid crystal material C can form a monostable state having a large cone angle of 60 ° or more by setting the optimum mixing ratio of the liquid crystal compositions A and B.

In such a liquid crystal display device, the uniaxial alignment treatment performed on the substrates 1 and 2 is performed by the smectic layer 12.
Is formed so that the normal of the layer is parallel to the orientation direction 9. Thereby, the normal of the layer becomes parallel to the alignment processing direction 9, and the ferroelectric liquid crystal 13 shows a certain monostable state in the absence of an electric field. At this time, the projection component of the smectic cone 14 drawn by the liquid crystal molecules 13 onto the substrate in the axial direction is represented by:
The projection component of the liquid crystal molecules themselves on the substrate in the axial direction is the same as the alignment processing direction 9 of the alignment layers 5 and 6, and this state is monostable as an initial state.

A signal power supply 15 is connected to the electrodes 3 and 4 of the cell.
6, the liquid crystal molecules are rotated along the smectic cone 14 when a voltage is applied, and the alignment direction 9
Apparent tilt angle θ _{ap p} indicating the tilt of the liquid crystal molecule with respect to
Changes continuously according to the intensity of the applied electric field. The intensity of the light transmitted through the liquid crystal display element increases continuously with an increase in the apparent tilt angle, so that a continuous tone, that is, an analog tone is obtained. In addition, since the maximum apparent tilt angle is one half of the cone angle, the maximum light transmittance increases as the cone angle increases, and high brightness with a maximum light transmittance of 75% or more is achieved at a cone angle of 60 ° or more. Is done.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on specific experimental results. First, a liquid crystal cell was prepared as follows.
A polyimide film was applied to a glass substrate on which a transparent electrode was formed, and rubbed for uniaxial orientation. The applied polyimide film exhibited a pretilt angle of 1 ° to 2 °. Another substrate prepared in the same manner as this substrate was arranged so that the rubbing directions were parallel to each other, and the cell gap was 1.4 μm.
m. At that time, two types of parallel cells were prepared, the parallel cells having the same rubbing direction and the anti-parallel cells having the rubbing directions opposite to each other.

As the liquid crystal composition A containing the component represented by the chemical formula 1, a monostable ferroelectric liquid crystal material represented by the chemical formula 3 was used. The cone angle and spontaneous polarization P of this liquid crystal composition A
s is 40 ° and 8.9 nC / cm at room temperature of 25 ° C., respectively.
^{Was 2} .

[0024]

Embedded image

The liquid crystal composition B containing the component represented by the chemical formula 2 is a bistable ferroelectric liquid crystal and has a large cone angle of 86 ° at 25 ° C. and a high spontaneous polarization Ps of 72.7 nC / cm ^2. Indicated. In this example, the liquid crystal compositions A and B were used as a mixture. Table 1 shows the respective phase transition behaviors. At that time, four kinds of liquid crystal compositions C1, C2, C3 and C4 as shown in Table 2 were prepared by changing the mixing ratio of the liquid crystal compositions A and B. Table 3 shows these phase transition behaviors.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

The above mixed liquid crystal material is converted into an isotropic liquid phase (Is
In the state of o), the mixture was poured into an empty cell, and gradually cooled to room temperature at a rate of -0.5 ° C / min. The prepared liquid crystal cell was observed with a polarizing microscope, and the liquid crystal structure of both the parallel cell and the anti-parallel cell was examined. Under a crossed polarizer, the change in light transmittance due to the intensity of the applied electric field of the sample cell was observed at 25 ° C. using 544 nm green light.

Also, the apparent cone angle 2θ of the sample cell
_app was measured according to the following method. First, a single pulse of one polarity is applied to a ferroelectric liquid crystal cell sandwiched between orthogonally arranged polarizers, and the liquid crystal cell is rotated in the horizontal direction with respect to the polarizer, and a first extinction point where light disappears. Ask for. Next, a single pulse of the opposite polarity is applied to the liquid crystal cell, and the liquid crystal cell is rotated with respect to the polarizer to obtain a second extinction point at which light disappears. The rotation angle between the first and second extinction points is measured as an apparent cone angle 2θ _app .

Next, the effect of the liquid crystal cell structure and the physical properties of the liquid crystal material on monostability was examined. The results of the study are described below.

Reference Example 1 Before mixing the liquid crystal compositions A and B, the monostability of the liquid crystal composition A was examined. The liquid crystal composition A is filled in a parallel cell in which the rubbing directions of a pair of substrates are parallel to each other and the directions are the same,
It was gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C / min. This liquid crystal cell is referred to as a sample cell A. When the liquid crystal structure of the sample cell A was observed with a polarizing microscope, the liquid crystal composition A exhibited a uniform monostable structure when the liquid crystal molecules were aligned at 25 ° C. in the absence of an electric field, parallel to the rubbing direction and the normal to the layer. It was confirmed that.

The sample cell A was sandwiched between polarizers arranged orthogonally, and the light transmittance was measured. FIG. 3 shows a driving waveform for evaluating the monostability of the sample cell. The driving waveform alternately changes the polarity of the applied voltage in consideration of the neutral condition for the liquid crystal material. In the sample cell A, a response waveform of the light transmittance Tr as shown in FIG. 4 was obtained with respect to the driving waveform shown in FIG. Here, for convenience, the maximum light transmittance is set to 10
0%. As is apparent from the response waveform of the Tr, the light transmittance increases as the applied voltage increases.
A gradation display was achieved. Analog gray scale can also be achieved by continuously modulating the applied voltage with amplitude.

The cone angle of this sample cell A was 40 ° and the contrast ratio was 110. Further, the response time of the sample cell A was 285 microseconds in the rise time and 385 microseconds in the fall time. As described above, the liquid crystal composition A clearly shows a monostable ferroelectric liquid crystal state having analog gradation in a parallel cell.

Reference Example 2 Next, the bistability of the liquid crystal composition B was examined. A liquid crystal composition B was filled in a parallel cell, and -0.5 from the isotropic phase.
It was gradually cooled to room temperature at a rate of ° C / min. This liquid crystal cell is referred to as a sample cell B. As a result of observing the liquid crystal structure of the sample cell B,
In the SmC * phase, many multi-domain defects having a bistable structure due to disorder of the layer structure were observed. Such structural defects are:
It is considered that a smectic layer and a smectic cone were rapidly formed during the phase transition to the SmC * phase. The sample cell B showed the Tr response waveform of FIG. 5 with respect to the drive waveform of FIG. For convenience, the maximum light transmittance is set to 100%. As is apparent from the Tr response waveform, the light transmittance fluctuates asymmetrically, indicating bistable ferroelectric switching. Thus, the liquid crystal composition B clearly shows a bistable ferroelectric liquid crystal state at room temperature.

Example 1 A liquid crystal composition C1 was filled in a parallel cell and gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C / min. This liquid crystal cell is referred to as a sample cell C. Observation of the liquid crystal structure of the sample cell C revealed that the liquid crystal molecules were 25 ° C. when no electric field was applied.
And oriented parallel to the rubbing direction and the layer normal, and showed a uniform monostable structure. FIG. 6 shows a Tr response waveform of the sample cell C with respect to the drive waveform of FIG. From FIG. 6, it was confirmed that gradation can be achieved by voltage modulation in the sample cell C. This Tr response waveform indicates that the light transmittance increases with an increase in the applied electric field, and that gradation display is achieved. The contrast ratio of this sample cell C was 70.

Example 2 Next, in order to clarify the effect of structural factors at the polyimide interface on monostabilization, a liquid crystal in an antiparallel cell in which the rubbing directions of a pair of substrates are parallel to each other but opposite to each other. Composition C1 was studied. The configuration of the liquid crystal cell and the liquid crystal material are the same as those of the sample cell C prepared earlier, and only the combination of the rubbing directions of the alignment films is different. The anti-parallel cell created in the same manner as the sample cell C is referred to as a sample cell D. Observation of the liquid crystal structure of the sample cell D revealed that this liquid crystal also had a uniform monostable structure similarly to the sample cell C. Further, in the sample cell D, a Tr response waveform as shown in FIG. 7 was obtained with respect to the drive waveform of FIG. From this response waveform, it was confirmed that the light transmittance increased as the applied electric field increased as in the case of the sample cell C. Analog gray scale can also be achieved by continuously amplitude modulating the applied voltage. In the sample cell D, a contrast ratio of 60 was obtained.

Example 3 A liquid crystal composition C2 was charged into a parallel cell and gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C / min. This liquid crystal cell is referred to as a sample cell E. When the liquid crystal structure of the sample cell E was observed, the liquid crystal molecules were 25 ° C. when no electric field was applied.
And oriented parallel to the rubbing direction and the layer normal, and showed a uniform monostable structure. FIG. 8 shows a Tr response waveform of the sample cell E with respect to the drive waveform of FIG. From FIG. 8, it was confirmed that gradation can be achieved by voltage modulation in the sample cell E. This Tr response waveform indicates that the light transmittance increases with an increase in the applied electric field, and that gradation display is achieved. The contrast ratio of the sample cell E is 50
Met.

Example 4 A liquid crystal composition C2 was charged into an anti-parallel cell, and was gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C / min. This liquid crystal cell is referred to as a sample cell F. The sample cell F has the same liquid crystal cell configuration and liquid crystal material as the sample cell E, and differs only in the combination of the rubbing directions of the alignment films. When the liquid crystal structure of the sample cell F was observed, this liquid crystal also showed a uniform monostable structure similarly to the sample cell E. FIG. 9 shows a Tr response waveform of the sample cell F with respect to the drive waveform of FIG.
As is apparent from the Tr response waveform, the light transmittance of the sample cell F increases as the applied electric field increases, similarly to the sample cell E. Analog gray scale can also be achieved by continuously amplitude modulating the applied voltage. The contrast ratio of the sample cell F was 150.

Example 5 A parallel cell was filled with the liquid crystal composition C3, and was gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C./min. This liquid crystal cell is referred to as a sample cell G. Observation of the liquid crystal structure of the sample cell G revealed that the liquid crystal molecules were 25 ° C. when no electric field was applied.
And oriented parallel to the rubbing direction and the layer normal, and showed a uniform monostable structure. FIG. 10 shows a Tr response waveform of the sample cell G with respect to the drive waveform of FIG. FIG.
As a result, it was confirmed that gradation can be achieved by voltage modulation in the sample cell G. This Tr response waveform indicates that the light transmittance increases with an increase in the applied electric field, and that gradation display is achieved. The contrast ratio of the sample cell G is 8
It was 0.

Example 6 A liquid crystal composition C3 was charged into an anti-parallel cell, and was gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C / min. This liquid crystal cell is referred to as a sample cell H. The sample cell H has the same liquid crystal cell configuration and liquid crystal material as the sample cell G, and differs only in the combination of the rubbing directions of the alignment films. When the liquid crystal structure of the sample cell H was observed, this liquid crystal also showed a uniform monostable structure, similarly to the sample cell G. FIG. 11 shows a Tr response waveform of the sample cell H with respect to the drive waveform of FIG. As is clear from the Tr response waveform, the sample cell H
Also, as in the sample cell G, the light transmittance increases as the applied electric field increases. Analog gray scale can also be achieved by continuously amplitude modulating the applied voltage.
The contrast ratio of the sample cell H was 150.

Example 7 A liquid crystal composition C4 was filled in a parallel cell and gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C / min. This liquid crystal cell is referred to as a sample cell I. Observation of the liquid crystal structure of sample cell I showed that the liquid crystal molecules were 25 ° C. when no electric field was applied.
And oriented parallel to the rubbing direction and the layer normal, and showed a uniform monostable structure. FIG. 12 shows a Tr response waveform of the sample cell I with respect to the drive waveform of FIG. FIG.
As a result, it was confirmed that gradation can be achieved by voltage modulation in the sample cell I. This Tr response waveform indicates that the light transmittance increases with an increase in the applied electric field, and that gradation display is achieved. The contrast ratio of the sample cell I is 4
It was 5.

Example 8 A liquid crystal composition C4 was charged into an anti-parallel cell, and was gradually cooled from the isotropic phase to room temperature at a rate of -0.5 ° C./min. This liquid crystal cell is referred to as a sample cell J. The sample cell J has the same liquid crystal cell configuration and liquid crystal material as the sample cell I, and differs only in the combination of the rubbing directions of the alignment films. When the liquid crystal structure of the sample cell J was observed, this liquid crystal also showed a uniform monostable structure similarly to the sample cell I. FIG. 11 shows a Tr response waveform of the sample cell J with respect to the drive waveform of FIG. As is clear from the Tr response waveform, the sample cell J
Also in the sample cell I, the light transmittance increases as the applied electric field increases. Analog gray scale can also be achieved by continuously amplitude modulating the applied voltage.
The contrast ratio of the sample cell J was 25.

Examination of Cone Angle Next, with respect to the sample cell, the change in the cone angle depending on the mixing ratio of the liquid crystal composition B was observed. The result is shown in FIG. As shown in this figure, the apparent cone angle measured was 6 as the mixing ratio of the liquid crystal composition B was increased.
It continuously increases from 0 ° to 86 °. Here, according to Equation 1 showing the relationship with the light transmittance described above, 100%
The ideal cone angle for obtaining a light transmittance brightness of 90 is
It should be noted that a cone angle of 86 °, which is close to this ideal cone angle, was obtained. in this way,
By changing the mixing ratio, the cone angle of the monostable ferroelectric liquid crystal cell and the resulting brightness can be adjusted. When the content of the liquid crystal composition B exceeds 60%, the monostability starts to deteriorate and the contrast ratio starts to decrease. From the relationship between the mixing ratio of the liquid crystal composition B and the cone angle, the change in the maximum light transmittance depending on the mixing ratio of the liquid crystal composition B was determined. The result is shown in FIG. As shown in this figure, the maximum light transmittance increases from 90% to 99%. Thus, it is clear that Mixed Composition C provides a high degree of brightness along with analog gradation. Table 4 shows the measurement results of the cone angle of each sample cell and the corresponding maximum light transmittance.

Examination of Responsivity The response time of the sample cell at an applied voltage of 5 V was observed. FIG. 1 shows the results as a function of the mixing ratio of the liquid crystal composition B.
6 and 17. FIG. 16 shows a rise response time from the electric field zero state due to the application of the electric field, and FIG. 17 shows a fall response time from the electric field application state to the electric field zero state. In these figures, the rise response time is almost constant, but the fall response time increases with the mixing ratio of the liquid crystal composition B. Table 4 summarizes the measurement results of the response speed of each sample cell. In particular, it is estimated that the fast response from the zero electric field state is due to the extremely high stability of the monostable state.

[0046]

[Table 4]

When the measurement results of the parallel cell and the anti-parallel cell were compared with each other, it was confirmed that the apparent cone angle dependence on the electric field, the response speed, and the pulse driving characteristics hardly changed. Therefore,
In both the parallel cell and the anti-parallel cell, a monostable ferroelectric liquid crystal state capable of analog gradation and high-speed operation can be realized by using the liquid crystal composition of the above embodiment.

[0048]

As described above, according to the present invention, by mixing a monostable ferroelectric liquid crystal composition and a bistable ferroelectric liquid crystal composition having a large cone angle of 60 ° or more, a 60 ° A monostable ferroelectric composition having a large cone angle as described above can be obtained, and by using this liquid crystal composition, a monostable ferroelectric composition having high brightness display performance as well as analog gradation and high-speed response can be obtained. A liquid crystal display device can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a cell configuration of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a plan view illustrating a liquid crystal structure of a liquid crystal display device according to one embodiment of the present invention.

FIG. 3 is a diagram showing driving waveforms applied to sample cells A to J.

FIG. 4 is a diagram showing a Tr response waveform of a sample cell A.

FIG. 5 is a diagram showing a Tr response waveform of a sample cell B.

FIG. 6 is a diagram showing a Tr response waveform of a sample cell C.

FIG. 7 is a diagram showing a Tr response waveform of a sample cell D.

FIG. 8 is a diagram showing a Tr response waveform of a sample cell E.

FIG. 9 is a diagram showing a Tr response waveform of a sample cell F.

FIG. 10 is a diagram showing a Tr response waveform of a sample cell G.

FIG. 11 is a diagram showing a Tr response waveform of a sample cell H.

FIG. 12 is a diagram showing a Tr response waveform of a sample cell I.

FIG. 13 is a diagram showing a Tr response waveform of a sample cell J.

FIG. 14 is a diagram showing a relationship between a mixing ratio of a liquid crystal composition B and a cone angle.

FIG. 15 is a diagram showing the relationship between the mixing ratio of the liquid crystal composition B and the maximum light transmittance.

FIG. 16 is a graph showing a relationship between a mixing ratio of a liquid crystal composition B and a rise response time.

FIG. 17 is a graph showing a relationship between a mixture ratio of a liquid crystal composition B and a fall response time.

[Explanation of symbols]

1, 2,... Substrate, 3, 4,... Transparent electrode, 5, 6,... Alignment layer, 7, 8,.
0, 11 ... polarizer, 12 ... smectic layer, 13 ...
... liquid crystal molecules, 14 ... smectic cone

Continued on the front page F term (reference) 2H088 EA03 JA18 KA14 KA16 KA20 LA06 LA07 MA13 MA18 4H027 BA06 BD08 BD17 BD18 BD24 DD07 DE01 DE07 DF01 DF07

Claims (6)

[Claims] 1. A uniaxial orientation treatment is applied to each of
Facing each other so that the processing directions are substantially parallel to each other
A pair of substrates and a chiral smect inserted between the substrates.
A liquid crystal layer having a tic C phase and an electric field applied to the liquid crystal layer
Wherein the liquid crystal layer has a chemical formula 1(However, in the formula, R¹ , R^Two Are each 1 to 2 carbon atoms
An alkyl group of 0, and n represents an integer of 1 or 2. )
Having chiral smectic C phase containing component to be prepared
Crystal composition and a compound of formula 2(However, in the formula, R^Three Is an alkyl group having 1 to 18 carbon atoms
Or an alkoxy group, R ^Four Is an alkyl having 2 to 10 carbon atoms
And k is an integer of 1 or 2, m is an integer of 1 to 10.
Show. Chiral smectic C containing a component represented by
Liquid crystal material mixed with a liquid crystal composition having a phase.
The liquid crystal molecules are formed on the substrate with no electric field applied.
Along the orientation direction and the normal direction of the smectic layer
Liquid crystal display element characterized by exhibiting an oriented monostable state
Child. 2. The liquid crystal display device according to claim 1, wherein
The liquid crystal layer has a cone angle of 60 ° or more, and the apparent tilt angle appearing on the substrate surface changes continuously according to the intensity of the applied electric field when the liquid crystal molecules rotate along the cone. Liquid crystal display element. 3. The liquid crystal display device according to claim 1, wherein
The liquid crystal composition containing the component of the chemical formula 1 has a liquid phase (Is
o) -Chiral nematic phase (N *)-Smectic A
Phase (SmA) -Chiral smectic C phase (SmC *)
A liquid crystal display device having the following phase transition and being monostable in a chiral smectic C phase. 4. The liquid crystal display device according to claim 1, wherein
The liquid crystal composition containing the component of the chemical formula 2 has a liquid phase (Is
o) A liquid crystal display device exhibiting a phase transition of -chiral nematic phase (N *)-chiral smectic C phase (SmC *) and being bistable in the chiral smectic C phase. 5. The liquid crystal display device according to claim 1, wherein
The mixed liquid crystal material is a liquid phase (Iso) -chiral nematic phase (N *)-chiral smectic C phase (SmC *)
A liquid crystal display device characterized by exhibiting a phase transition of 6. The liquid crystal display device according to claim 4, wherein
A liquid crystal display device, wherein the liquid crystal composition containing the component of Chemical Formula 2 has a cone angle of 60 ° or more.