JPH05333342A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To enable the execution of a display with a high contrast and excellent switching characteristics. CONSTITUTION:This liquid crystal element is constituted by holding a chiral smetic liquid crystal 15 having -5.9nc/cm<2> Ps at the upper limit temp. -30 deg.C of SmC* between substrated 11a and 11b which are disposed to face each other in such a manner that the intersection angle of a rubbing treatment is 10 deg.C and the upper substrate 11a exists on the left side of the lower substrate 11b when viewed from the upper substrate. The liquid crystal element is so constituted that the cone angle THETA, pretilt angle alpha, angle delta of inclination of the layer and apparent tilt angle thetaa of the liquid crystal 15 satisfy relations THETA<alpha+delta, ALPHA>delta, THETA>THETAatheta>/2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, a liquid crystal device used in a liquid crystal optical shutter, etc., and more particularly to a ferroelectric liquid crystal device. More specifically, by improving the alignment state of liquid crystal molecules, display characteristics are improved. The present invention relates to an improved liquid crystal element.

[0002]

2. Description of the Related Art A display device of a type in which transmitted light rays are controlled by using a refractive index anisotropy of ferroelectric liquid crystal molecules in combination with a polarizing element has been proposed by Clark and Lagerwall. (U.S. Pat. No. 4,367,924, etc.). This ferroelectric liquid crystal generally has a non-helical chiral smectic C phase (SmC ^* ) or H phase (SmH) in a specific temperature range.
^* ), And in this state, takes one of the first optical stable state and the second optical stable state in response to the applied electric field, and maintains that state when no electric field is applied. It has the property of being stable, that is, bistability, and has a quick response to changes in the electric field, and is expected to be widely used for high-speed and memory type display elements. Is expected to be applied.

In order for the optical modulation element using the liquid crystal having the bistability to exhibit a predetermined driving characteristic, the liquid crystal arranged between the pair of parallel substrates is effectively applied with an electric field. It is necessary to have such a molecular arrangement state.

Further, in the case of a liquid crystal element utilizing the birefringence of liquid crystal, the transmittance under orthogonal Nicols is

[0005]

[Equation 1] (Wherein:. I is the incident light intensity, I is the transmitted light intensity, theta tilt angle of the apparent _a is to be described later, △ n is the refractive index anisotropy, d is the liquid crystal layer thickness, lambda is the wavelength of the incident light It is represented by). The apparent tilt angle θ _a in the non-helical structure appears as the angle in the average molecular axis direction of the twisted liquid crystal molecules in the first and second alignment states. According to the above equation, the maximum transmittance is obtained when the apparent tilt angle θ _a is 22.5 °, and the apparent tilt angle θ _a in the non-helical structure that realizes the bistability is 22.5. .. It is necessary to be as close as possible to.

By the way, as a method of orienting a ferroelectric liquid crystal, a molecular layer composed of a plurality of molecules forming a smectic liquid crystal is oriented uniaxially along its normal line over a large area. It is desirable that the manufacturing process can be realized by a simple rubbing process.

As an alignment method for a ferroelectric liquid crystal, in particular, a chiral smectic liquid crystal having a non-helical structure, for example, the one described in US Pat. No. 4,561,726 is known.

[0008]

However, the alignment method that has been used so far, particularly the alignment method using a rubbing-treated polyimide film, is applied to the strong non-helical structure exhibiting the bistability disclosed by Clark and Raggawall. When it is applied to a dielectric liquid crystal, it has the following problems.

That is, according to the experiments by the present inventors, an apparent tilt angle θ _a (two stable states) in _a ferroelectric liquid crystal having a non-helical structure obtained by aligning with a conventional rubbing-treated polyimide film was obtained. 1/2 of the angle formed by the molecular axis of is smaller than the cone angle (1/2 angle Θ of the apex of the triangular pyramid shown in FIG. 3A described later) in the ferroelectric liquid crystal. It has been found. In particular, the apparent tilt angle θ _{a in a} ferroelectric liquid crystal having a non-helical structure obtained by aligning with a conventional rubbing-treated polyimide film is generally 3 ° to 8 °.
However, the transmittance at that time was at most 3 to 5%.

The inventors of the present invention have conducted studies to realize a display in which a chiral smectic liquid crystal has a large apparent tilt angle θ _{a in a} non-helical structure and a high-contrast image is displayed. I have found

The chiral smectic liquid crystal generally has a layered structure, but when the transition from the Sa phase to the Sc phase or the Sc ^* phase shrinks the layer spacing, the layer is bent at the center of the upper and lower substrates as shown by 21 in FIG. 2 (chevron). Structure).

As shown in FIG. 2, the bending direction is the orientation state (C) which appears immediately after the transition from the high temperature phase to the Sc ^* phase.
The present inventors have found that there are two possible states, one oriented state 22) and a mixed state of the C1 oriented state (C2 oriented state 23) when the temperature is further lowered. Furthermore, it was newly discovered that when the combination of a specific alignment film and a liquid crystal is used, the above C1 → C2 transition hardly occurs, and depending on the liquid crystal material, the C2 alignment state does not occur at all. Furthermore, it was also found that when a high pretilt alignment film is used, the contrast of the C1 alignment is very high and the contrast of the C2 alignment is close when the relation of Θ <α + δ to be described later is established. Therefore, if a high pretilt alignment film is used to unify the entire display screen to the C1 alignment state, a display with high black and white contrast can be expected.

As shown in FIG. 3, the directors near the substrate in the C1 and C2 orientations are in the cone 31 of FIGS. 3 (a) and 3 (b), respectively. As is well known, the rubbing causes the liquid crystal molecules at the substrate interface to form an angle called a pretilt with respect to the substrate, and the direction is that the liquid crystal molecules lift their heads in the rubbing direction (direction A) (the tip is floating). Will be). From the above, between the cone Θ of the liquid crystal, the pretilt angle α, and the layer tilt angle δ, the relationship of Θ + δ> α in the C1 orientation and Θ−δ> α in the C2 orientation must be established.

Therefore, the condition for producing the C1 orientation without producing the C2 orientation is Θ-δ> α, that is, Θ <α + δ (a).

Further, α <δ (b) is obtained as a condition under which the interface molecules are easily switched from a simple consideration of torque when the interface molecules are transferred (switching) from one position to the other position by the electric field. Be done.

Therefore, in order to form the C1 orientation state more stably, it is effective to satisfy the relationship of (b) in addition to (a).

As a result of further experiments under the conditions (a) and (b), the apparent tilt angle θ _a of the liquid crystal was 3 when the conventional conditions (a) and (b) were not satisfied. 8 to 8 when the conditions (a) and (b) of the present invention are satisfied from about 8 ° to 8 °
It has been empirically obtained that the relational expression of Θ> θ _a > Θ / 2 (c) holds between the cone angle Θ and the cone angle Θ.

As described above, it has become clear that a display in which a high-contrast image is displayed can be realized if the conditions (a), (b), and (c) are satisfied.

However, even in the C1 orientation state satisfying the conditions (a) and (b), the orientation 2 having a high contrast is obtained.
It has also been clarified that a state (hereinafter defined as uniform alignment) and an alignment 2 state having low contrast (hereinafter defined as splay alignment) may exist. The inventors of the present invention studied to destabilize and eliminate the splay alignment and obtain uniform alignment stably, and shift the uniaxial alignment axes of the upper and lower substrates of the liquid crystal cell from each other within a range of 2 to 25 ° (crossing angle). It was found that the alignment method (hereinafter referred to as cross rubbing particularly in the case of rubbing treatment) was effective.

However, the improvement of the alignment only by cross rubbing is still insufficient, and there are still cases in which the splay alignment is stable and the uniform switching characteristics are poor.

Further, in the cross rubbing, since the uniaxial alignment treatment of the upper and lower substrates is shifted, the uniaxial alignment property of the liquid crystal is deteriorated, and in some cases uniform alignment cannot be performed.

An object of the present invention is to provide a liquid crystal device that solves the above problems.

Another object of the present invention is to provide a liquid crystal device using a chiral smectic liquid crystal having a stable uniform orientation and having good switching characteristics.

[0024]

Means and Actions for Solving the Problems The present inventors have
In order to solve the above problems, as a result of extensive studies, the twisting direction of the spiral of the cholesteric phase of the liquid crystal and the cross direction of the cross rubbing are combined to solve the above problems, uniform uniaxial alignment and uniform alignment and It was discovered that the switching characteristic under uniform orientation was good, and the first invention of the present application was achieved. In addition, the inventors of the present invention eliminate the above-mentioned problems by the combination of the polarity of Ps of the chiral smectic liquid crystal used and the cross direction of cross rubbing, and uniform alignment and
It was discovered that the switching characteristic under uniform orientation was good, and the second invention of the present application was achieved.

That is, the first invention of the present application is a liquid crystal element in which a chiral smectic liquid crystal is sandwiched between a pair of substrates each having an electrode for applying a voltage to the liquid crystal and a uniaxial alignment film for aligning the liquid crystal. The processing axes of the alignment films of the upper substrate and the lower substrate intersect, and the crossing direction of the processing axes of the upper substrate with respect to the lower substrate is the same as the twist direction of the spiral of the cholesteric phase of the chiral smectic liquid crystal, and the chiral smectic When the liquid crystal has an alignment state represented by Θ <α + δ, where α is the pretilt angle, Θ is the cone angle, and δ is the tilt angle of the Sm ^* C layer, and the apparent tilt angle is θ _a , Θ> The liquid crystal element is characterized in that θ _a > θ / 2.

The present inventors further match the polarity of Ps of the chiral smectic liquid crystal with the cross direction (polarity) of cross rubbing, and the twist direction of the cholesteric of the chiral smectic liquid crystal used and the cross direction of cross rubbing. It has been found that by selecting a specific combination of Ps size and cross angle, the above problems are improved and uniform orientation and switching characteristics under uniform orientation are improved.

That is, in the third invention of the present application, the chiral smectic liquid crystal is opposed to the liquid crystal while sandwiching the liquid crystal, and electrodes for applying a voltage to the liquid crystal are respectively formed on the opposing surfaces to further align the liquid crystal. A liquid crystal device comprising a pair of substrates that have been subjected to a uniaxial alignment treatment, wherein the uniaxial alignment treatment axes intersect with each other at an angle (hereinafter referred to as “cross angle”), and the intersecting direction is the upper substrate side. When the polarity when the direction of the upper substrate is on the left side with respect to the direction of the lower substrate is negative and the polarity when the direction of the upper substrate is on the right side is positive, the spontaneous polarization of the liquid crystal sandwiched with the polarity (hereinafter referred to as “Ps”). The relation between the magnitude of Ps and the cross angle at a temperature of 30 ° C. from the upper limit temperature of the chiral smectic phase is | Ps | <2nc / cm ² | Cross angle │ <4 ° ｜ Ps ｜ 2NC / cm when ² | cross angle | is ≧ 4 °, and, in the chiral smectic combined liquid of cholesteric the cross direction of the twisting direction and the cross rubbing, the liquid crystal cone angle theta, the pretilt angle alpha, smectic phase used If the tilt angle of the liquid crystal layer is δ,
The liquid crystal has at least 2 represented by Θ <α + δ, α> δ
Two stable states, the at least the two
The liquid crystal element is characterized in that θ _a, which is ½ of the angle formed by the optical axes in the two stable states, satisfies the relationship of Θ> θ _a > Θ / 2.

[0028]

EXAMPLES In the present invention, the cone angle Θ, the layer inclination angle δ, the pretilt angle α, the apparent tilt angle θ _a , and the cholesteric helical pitch were measured as follows.

Measurement of cone angle Θ ± 30 V to ± 50 V, AC of 100 Hz is applied between the upper and lower substrates of the FLC element under orthogonal crossed Nicols, and the FLC element arranged between them is rotated horizontally with the polarizing plate. The first extinction position (position where the transmittance is the lowest) while detecting the optical reaction with (Hamamatsu Photonics Co., Ltd.),
Search for the second extinction position. At this time, 1/2 of the angle from the first extinction position to the second extinction position was defined as the cone angle Θ.

Measurement of Apparent Tilt Angle θ _a After applying a single pulse of the threshold value of the liquid crystal, the FLC element placed between them under no electric field and under orthogonal crossed Nicols is rotated horizontally with the polarizing plate. After searching for the extinction position, and then applying a pulse having a polarity opposite to that of the above-mentioned single-shot pulse, the second extinction position is searched for under no electric field. ½ of the angle from the first extinction position to the second extinction position at this time was defined as θ _a .

Measurement of Layer Inclination Angle δ was measured by X-ray analysis using an X-ray analyzer RAD-IIB (45 KV, 30 mA).

Measurement of pretilt angle α Jpn. J. Appl. Phys. vol9 (198
0) NO. 10, according to the method (crystal rotation method) described in Short Notes 2013.

That is, substrates rubbed in parallel and in opposite directions were bonded to each other to form a cell having a cell thickness of 20 μm, and
The liquid crystal (A) having the SmA phase was sealed in the range of 60 ° C to 60 ° C and the measurement was performed. The liquid crystal (A) is a mixed liquid crystal containing phenylpyrimidine as a main component, which is generally contained in a ferroelectric liquid crystal composition.

While rotating the liquid crystal cell in a plane perpendicular to the upper and lower substrates and containing the alignment treatment axis, helium / neon laser light having a polarization plane making an angle of 45 ° with the rotation axis is irradiated from a direction perpendicular to the rotation axis. The transmitted light intensity was measured with a photodiode through a polarizing plate having a transmission axis parallel to the incident polarization plane on the opposite side.

The angle formed by the center of the hyperbolic group of transmitted light intensity formed by interference and the line perpendicular to the liquid crystal cell is φ _x
Then, the pretilt angle α ₀ was obtained by substituting in the following equation.

[0036]

[Equation 2]

Measurement of Cholesteric Helical Pitch The cholesteric helical pitch is determined by the method of Matsumura et al. [Applied Physics, 43 (1974) 12] using the wedge method of cano.
5] was measured.

The direction of the helical pitch is the contact method (Gray et al., Mol, Crys) for the liquid crystal and the ch phase whose helical pitch direction is known in advance.
t. , Lig. Cryst. , 34 (Lett.),
(1977) 211. ), Or mix with a liquid crystal whose pitch direction is known in advance while changing the ratio, measure the pitch at each ratio, and if there is a divergence tendency at a certain ratio from the ratio and pitch length, reverse direction, continuous If so, it was determined as the same direction.

Examples in which the liquid crystal element according to the present invention is prepared will be described below.

FIG. 1 shows a schematic sectional view of an example of the liquid crystal element of the present invention.

In FIG. 1, reference numeral 15 is a ferroelectric liquid crystal layer, 11a and 11b are glass substrates 12a and 12b, transparent electrodes, 13a and 13b are insulating films, 14a and 14b are alignment control films, 16 is a spacer, 17a and Reference numeral 17b indicates a polarizing plate.

On the two glass substrates 11a and 11b, In ₂ O ₃ , SnO _{2 and} ITO (Indium-Tin Oxide; Indium-Tin Oxi) are respectively provided.
The transparent electrodes 12a and 12b made of a thin film such as de) are covered. On top of that, for example, silicon nitride, silicon carbide containing hydrogen, silicon oxide, boron nitride,
Insulating films 13a and 13b made of hydrogen-containing boron nitride, cerium oxide, aluminum oxide, zirconium oxide, titanium oxide, magnesium fluoride, etc. are formed, and polyvinyl alcohol, polyimide, polyamideimide are further formed thereon. Rubbing a liquid crystal by rubbing a thin film of a polymer such as polyester imide, polyparaxylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate, polyamide, polystyrene, or cellulose resin with gauze or acetate flocking cloth. Orientation control films 14a and 14b arranged in the direction
Are formed. Further, these insulating film and orientation control film are not necessarily two layers, and may be a single layer as long as they have both properties.

The two glass substrates 11a and 11b are held by the spacer 16 at arbitrary intervals. For example, there is a method in which silica beads and alumina beads having a predetermined diameter are used as spacers and sandwiched between two glass substrates, and the periphery is sealed with a sealing material, for example, an epoxy adhesive material. Alternatively, a polymer film or glass fiber may be used as the spacer. A liquid crystal exhibiting ferroelectricity is enclosed between the two glass substrates to form a ferroelectric liquid crystal layer 15.

The ferroelectric liquid crystal layer 15 in which the ferroelectric liquid crystal is enclosed generally has a thickness of 0.5 to 20 μm, preferably 1 to 20 μm.
It is 5 μm.

Example 1 Ti-Si (1: 1) was formed on a glass substrate having a transparent electrode.
Was formed by spin coating, and a 1% NMP solution of polyamic acid LQ1802 manufactured by Hitachi Chemical Co., Ltd. was applied thereon by a spinner and baked at 270 ° C. for 1 hour. This substrate was rubbed, and the rubbing direction was parallel to another substrate that had been subjected to the same treatment, the intersecting direction was left, and the intersecting angle was 6 °.
With a gap of 1.5 μm
A liquid crystal device was prepared by injecting a ferroelectric liquid crystal into the gap. The pretilt angle of the cell was 16 ° as measured by the crystal rotation method. The liquid crystal used was a mixed liquid crystal containing phenylpyrimidine as a main component, and the cone angle was 15.4 ° at room temperature, the layer tilt angle was 10.3 °, and the Ps was 6.8 nc / cm ² . The ch pitch was left-handed and the pitch length was 16 μm at the center temperature of the ch phase.

The liquid crystal element was kept at 100 ° C. for 5 hours, then gradually cooled at a rate of 1 ° C. for 1 minute, and observed under a microscope at room temperature. As a result, C1 orientation was uniformly maintained in the initial orientation state. Almost the entire surface was in a uniform state.

The apparent tilt angle was 11.0 ° between the two uniform states.

When a rectangular pulse having a peak value of 24 V is applied,
Switching between uniforms occurred with a pulse width of 16 μs.

Comparative Example 1 A liquid crystal element was prepared by using the above-mentioned ferroelectric liquid crystal in a liquid crystal cell prepared exactly as in Example 1. The liquid crystal used was a mixed liquid crystal containing phenylpyrimidine as the main component, the cone angle was 14.3 ° at room temperature, the layer tilt angle was 9.6 °, Ps was 4.3 nc / cm ² , and the ch pitch was right twist. The pitch length was 30 μm at the central temperature of the ch phase.

The liquid crystal element was kept at 100 ° C. for 5 hours, then gradually cooled at a rate of 1 ° C. for 1 minute and observed under a microscope at room temperature. The uniform alignment state was lost, and there was a part where only the dark field was obtained with the vertical alignment state. Since the uniform orientation state was lost, even when a pulse having a peak value of 24 V was applied while changing the pulse width (1 μs to 20 ms), clear full-surface switching was not obtained.

Example 2 A liquid crystal cell was prepared in the same manner as in Example 1 except that the intersecting direction was right and the intersecting angle was 6 ° in Example 1, and the same strength as in Comparative Example 1 was provided in the gap. A liquid crystal element was prepared by injecting a dielectric liquid crystal.

The liquid crystal device was manufactured in the same manner as in Example 1, except that
When kept at 0 ° C., gradually cooled, and observed under a microscope at room temperature, the C1 orientation was uniformly maintained in the initial orientation state.
About 90% was in a spray state and the remaining about 10% was in a uniform state. The apparent tilt angle was 10.6 ° between the two uniform states.

When a rectangular pulse having a peak value of 24 V is applied,
Switching between uniforms occurred with a pulse width of 35 μs.

Comparative Example 2 A liquid crystal element was prepared by injecting the same ferroelectric liquid crystal as in Example 1 into the cell prepared exactly as in Example 2.

The liquid crystal element was set to 100 ° C. exactly as in Example 1.
After observing under a microscope at room temperature, the uniaxial orientation was deteriorated in the initial orientation state, uniform orientation was lost, and about 80% of the portion was in the vertical orientation state where only dark field was obtained. Met. Since the uniform alignment state was lost, a pulse with a peak value of 24 V was changed (1 μs to 2
Even if the voltage was applied for 0 ms, clear switching was not obtained on the entire surface.

As described above, from Examples 1 and 2 and Comparative Examples 1 and 2,
It has been found that when the cross direction of the uniaxial alignment treatment and the twist direction of the cholesteric helix of the chiral smectic liquid crystal match, the uniform alignment property and the switching property are improved.

Example 3 On a glass substrate having a transparent electrode, Ti--Si (1:
The thin film of 1) was formed by spin coating, and a 1% NMP solution of polyamic acid LQ1802 manufactured by Hitachi Chemical Co., Ltd. was applied thereon by a spinner and baked at 270 ° C. for 1 hour. This substrate is rubbed, and the rubbing direction is parallel to another substrate that has been subjected to the same treatment, and the crossing direction is negative (left),
A liquid crystal element was prepared by laminating a gap of 1.5 μm so that the intersecting angle was 6 °, and injecting a ferroelectric liquid crystal into the gap. The pretilt angle of the cell was 14.2 ° as measured by the crystal rotation method.
The liquid crystal used was a mixed liquid crystal containing phenylpyrimidine as a main component, the cone angle was 14 ° at room temperature, and the tilt angle of the layer was 9.
The polarity of 2 ° and Ps was negative, and the size was 6 nc / cm ² .

The liquid crystal element was held at 100 ° C. for 5 hours, then gradually cooled at a rate of 1 ° C. for 1 minute, and observed under a microscope at room temperature. As a result, C1 orientation was maintained in the initial orientation, and about 99. 5% was in a uniform state and the remaining 0.5% was in a splayed state.

The apparent tilt angle was 11.2 ° between the two uniform states.

When a rectangular pulse having a peak value of 24 V is applied,
Switching between uniforms occurred with a pulse width of 20 μs.

Comparative Example 3  The cross direction is positive (right) and the cross angle is 6 °
A liquid crystal cell was prepared in the same manner as in Example 3. This liquid
The ferroelectric liquid crystal used in Example 3 was injected into the crystal cell to give a liquid crystal.
The device was created.

This liquid crystal element was manufactured by the same method as that of the embodiment.
When kept at ℃, slowly cooled, and observed under a microscope at room temperature, the C1 orientation was maintained in the initial orientation state, but about 95
% Was in the spray state and the remaining 5% was in the uniform state.

The apparent tilt angle was 11.1 ° between the two uniform states. This liquid crystal element has a peak value of 24V
When the pulse was applied, the spray state was stable and switching between the uniform 2 states was hard to occur, and the obtained threshold value was 75 μs, which was much slower than that in Example 3.

As can be seen from Example 3 and Comparative Example 3, Ps
It was found that when the polarity of No. 1 was negative, the negative crossing angle between the upper and lower substrates had better uniform orientation and switching characteristics under uniform orientation.

Example 4 A cell prepared in the same manner as in Comparative Example 3 was mixed with a liquid crystal containing phenylpyrimidine as a main component and had a cone angle of 13.5 at room temperature.
°, the inclination angle of the layer was 10 ° at room temperature, the polarity of Ps was positive, and the size was 1.0 nc / cm ² .

The liquid crystal element was held at 100 ° C., gradually cooled and observed under a microscope at room temperature in the same manner as in Example 3. As a result, C1 orientation was maintained in the initial orientation state, and about 95% was in a uniform state, and the remaining 5% was in the spray state.

The apparent tilt angle was 10.7 ° between the two uniform states.

When a rectangular pulse having a peak value of 24 V was applied to this liquid crystal element, switching between uniform states occurred with a pulse width of 95 μs.

Comparative Example 4  The cell prepared in the same manner as in Example 3 was used in Example 4.
Liquid crystal was injected to prepare a liquid crystal element.

The liquid crystal element was held in the same manner as in Example 3, gradually cooled, and observed under a microscope at room temperature. As a result, the C1 orientation was maintained in the initial orientation state, and about 90% was in the splay state, and the remaining 10 % Was in a uniform state.

The apparent tilt angle was 10.7 ° between the two uniform states.

When a rectangular pulse having a crest value of 24 V was applied to this liquid crystal element, the splay state was stable and switching between the two uniform states was less likely to occur, and the obtained threshold value was 200 μs, which is considerably slower than that in Example 4. became.

As can be seen from Example 4 and Comparative Example 4, Ps
It was found that the positive orientation of the upper and lower substrates had a better uniform orientation and the switching characteristics under the uniform orientation when the polarity of was positive.

As described above, from Examples 3.4 and Comparative Examples 3.4,
The product of the polarity of the crossing direction of the uniaxial alignment treatment of the upper and lower substrates and the polarity of the spontaneous polarization of the chiral smectic liquid crystal is positive, and the chiral smectic liquid crystal liquid has Θ <α.
It has been found that the liquid crystal element having an apparent tilt angle of + δ of Θ>θa> Θ / 2 has very good uniform orientation and switching characteristics under uniform orientation. Example 5 Ti-Si (1: 1) on a glass substrate provided with a transparent electrode.
Was formed by spin coating, and a 1% NMP solution of polyamic acid LQ1802 manufactured by Hitachi Chemical Co., Ltd. was applied thereon by a spinner and baked at 270 ° C. for 1 hour. This substrate is rubbed, and the rubbing direction is parallel to another substrate that has been subjected to the same treatment, the crossing direction is negative, and the cross angle is 10 °, that is, the cross angle is -10 ° (hereinafter, the polarity is " +) Or “−”), a gap of 1.5 μm was kept, and a chiral smectic liquid crystal was injected into the gap to prepare a liquid crystal element. The pretilt angle of the cell was 17.1 ° as measured by the above-mentioned crystal rotation method.

The liquid crystal used in this example is a mixed liquid crystal containing phenylpyrimidine as a main component, and at a temperature 30 ° C. below the maximum temperature of the chiral smectic phase (hereinafter referred to as “Tc-30 ° C.”), the cone angle Θ is 15 °, layer inclination angle 10.3 °, Ps polarity is negative and size is 5.9 nc
Was / cm ² . Ch pitch is. With a left-handed twist, the pitch length was 19 μm at the center temperature of the Ch phase.

The liquid crystal element was held at 100 ° C. for 5 hours, then gradually cooled at a rate of 1 ° C. for 1 minute and observed under a microscope at room temperature. As a result, C1 orientation was maintained in the initial orientation state.
Almost the entire surface was in a uniform state. The apparent tilt angle α was 10.8 ° between the two uniform states.

When a rectangular pulse having a peak value of 15 V was applied, switching between uniforms occurred with a pulse width of 15 μs.

Comparative Example 5 A liquid crystal cell was prepared in the same manner as in Example 5 except that the cross angle was -2 °. The liquid crystal element was prepared by injecting the chiral smectic liquid crystal used in Example 5 into this liquid crystal cell.

This liquid crystal device was manufactured in the same manner as in Example 5
Microscopic observation at room temperature after aging at 0 ° C. and slow cooling revealed that the C1 orientation was maintained in the initial orientation, but about 70% was in the splay state and the remaining 30% was in the uniform state. When a rectangular pulse with a peak value of 15 V was applied to this liquid crystal element, the spray state was stable,
Switching between the two states of uniform became less likely to occur, and the obtained threshold value was 31 μs.

Comparative Examples 6-10 Cross angles of -6 °, -4 °, -2 °, 0 °, +, respectively.
A liquid crystal cell was prepared in the same manner as in Example 5 except that the angle was set to 6 °, and the chiral smectic liquid crystal used in Example 5 was injected into each liquid crystal cell to prepare a liquid crystal element.
An exactly the same experiment was performed. The results are shown below.

[0081]

[Table 1] From Example 5 and Comparative Examples 5 to 10 at Tc-30 ° C |
When Ps | is 5.9 nc / cm ² , | Cross angle |
It was found that when ≧ 4 °, good uniform orientation and switching characteristics in uniform were exhibited.

Example 6 A liquid crystal cell was prepared in the same manner as in Comparative Example 5 (cross angle −2 °). A liquid crystal containing phenylpyrimidine as a main component having the following characteristics was injected into the cell, aged at 100 ° C. and slowly cooled in the same manner as in Example 5, and observed under a microscope at room temperature.

Cone angle: 14.5 °, Ps (at Tc-30 ° C.): -0.9 nc / cm ² δ: 9.8 ° Ch Pitch: Left twist 37 μm (Ch center temperature) C1 on the entire surface in the initial orientation state The orientation was maintained and almost the entire surface was in a uniform state. The apparent tilt angle was 10.3 ° between the two uniform states. When a rectangular pulse having a peak value of 25 V was applied to this liquid crystal element, switching between uniforms occurred with a pulse width of 45 μs.

Comparative Examples 11 to 16 Cross angles were -10 °, -6 °, -4 °, 0 °,
A liquid crystal cell was prepared in the same manner as in Example 5 except that + 4 ° and + 6 ° were used, and the liquid crystal used in Example 6 was injected to prepare a liquid crystal element. The same experiment as in Example 5 was performed.
The results are shown below.

[0085]

[Table 2] From Example 6 and Comparative Examples 11 to 16, when | Ps | at Tc−30 ° C. was 0.9 nc / cm ² , | cross angle | <4 ° showed good uniform orientation and uniform switching characteristics. Turned out to show.

Examples 7 to 11 Liquid crystals having different Ps were injected into the cells prepared by substantially the same method as in Example 5 to examine the uniform orientation. The results are shown below.

[0087]

[Table 3] As can be seen from Examples 7 to 11, when | Ps |> ² nc / cm ² at Tc−30 ° C., | cross angle | ≧ 4 °,
When | Ps | < ² nc / cm ² , | Cross angle | <
It was found that the uniform orientation is improved when the twist direction of the Ch pitch is 4 ° and the cross direction of the cross rubbing is the same.

[0088]

The liquid crystal device of the present invention has good switching characteristics under uniform orientation, the uniform orientation is stably obtained, and high-contrast and high-quality display can be performed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a liquid crystal element of the present invention.

FIG. 2 is an explanatory diagram of two kinds of alignment states of C1 and C2.

FIG. 3 is an explanatory diagram showing a relationship among a cone angle, a pretilt angle, and a layer tilt angle in C1 and C2 orientations.

[Explanation of symbols]

 11a, 11b Substrate 12a, 12b Transparent electrode 13a, 13b Insulating film 14a, 14b Alignment control film 15 Ferroelectric liquid crystal 16 Spacer 17a, 17b Polarizing plate 21 Liquid crystal layer 22 C1 Alignment state 23 C2 Alignment state

(72) Inventor Yu Mizuno 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Innovator Masanobu Asaoka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masahiro Terada, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. A liquid crystal element comprising a chiral smectic liquid crystal sandwiched between a pair of substrates each having an electrode for applying a voltage to the liquid crystal and a uniaxial alignment film for aligning the liquid crystal, the upper substrate comprising: The processing axis of the alignment film of the lower substrate intersects, and the intersecting direction of the processing axis of the upper substrate with respect to the lower substrate is the same as the twist direction of the spiral of the cholesteric phase of the chiral smectic liquid crystal, and the chiral smectic liquid crystal has a pretilt angle. α, cone angle Θ, S
When the inclination angle of the m ^* C layer was [delta], has an orientation state represented by Θ <α + δ, when the tilt angle of the apparent and theta _a theta
> Θ _a > θ / 2, a liquid crystal element. 2. A liquid crystal device comprising a pair of substrates each having an electrode for applying a voltage to the liquid crystal and a uniaxial alignment film for orienting the liquid crystal, wherein a chiral smectic liquid crystal is sandwiched between an upper substrate and a lower substrate. When the processing axis of the alignment film intersects and the processing axis of the upper substrate intersects with the processing axis of the lower substrate as viewed from the upper substrate side, the left side is negative and the right side is positive. The chiral smectic liquid crystal has a pretilt angle of α, a cone angle of Θ, and a tilt angle of the Sm ^* C layer of δ, where the product of the polarity of the spontaneous polarization of the smectic liquid crystal and the polarity of the crossing direction is positive. Then, the liquid crystal element has an orientation state represented by Θ <α + δ, and Θ> θ _a > Θ / 2 when an apparent tilt angle is θ _a . 3. A chiral smectic liquid crystal, and an electrode for sandwiching the liquid crystal and facing each other and applying a voltage to the liquid crystal is formed on each of the facing surfaces, and a uniaxial alignment treatment for aligning the liquid crystal is further performed. A liquid crystal element comprising a pair of substrates provided, wherein uniaxial alignment treatment axes intersect with each other at an angle (hereinafter referred to as “cross angle”), and the intersecting direction of the lower substrate when viewed from the upper substrate side. When the polarity of the upper substrate on the left side of the direction is negative and the polarity on the right side is positive, the polarity of the spontaneous polarization (hereinafter referred to as “Ps”) of the sandwiched liquid crystal is defined. Has a positive product relation,
When the relationship between the magnitude of Ps and the cross angle at a temperature 30 ° C. below the chiral smectic phase upper limit is | Ps | < ² nc / cm ² , | cross angle | <6 ° | Ps | ≧ ² nc / cm ² | cross Angle | ≧ 6 °, and the intersecting direction of the processing axis of the upper substrate with respect to the lower substrate is the same as the twist direction of the cholesteric spiral of the chiral smectic liquid crystal, and the cone angle Θ, pretilt angle α, and smectic of the liquid crystal are When the tilt angle of the liquid crystal layer in the phase is δ, the liquid crystal has Θ <α + δ, α> δ
Which has at least two stable states, and θ _a, which is ½ of the angle formed by the optical axes in the at least two stable states, satisfies the relation of θ> θ _a > θ / 2. A liquid crystal element characterized by: