JP2531646B2 - Liquid crystal composition and liquid crystal device using the same - Google Patents

Description

The present invention relates to a liquid crystal composition used in a liquid crystal display device, a liquid crystal device used in a liquid crystal-optical shutter, or the like. More specifically, the display and driving characteristics are improved. And a novel liquid crystal composition.

[Prior art]

The use of a liquid crystal element having bistability is described by Clar (Clar
k) and Lagerwall (JP-A-56-107216, U.S. Pat. No. 4,367,924, etc.). As a liquid crystal having bistability, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or H phase (SmH ^* ) is generally used.

This liquid crystal has a first optically stable state and a second
Has a bistable state consisting of an optical stable state of, for example, the liquid crystal is aligned in the first optical stable state with respect to one electric field vector, and is in the second optical stable state with respect to the other electric field vector. The liquid crystal is aligned. In addition, this type of liquid crystal has a property of responding to an applied electric field and maintaining one of the two stable states when no electric field is applied. Also, in addition to the above-mentioned features having bistability,
Ferroelectric liquid crystal has an excellent feature of high-speed response. This is because the spontaneous polarization of the ferroelectric liquid crystal and the applied electric field directly act to induce the transition of the alignment state, which is 3 to 4 orders faster than the response speed due to the action of the dielectric anisotropy and the electric field.

Thus, ferroelectric liquid crystals potentially have very good properties, and the use of such properties provides a fairly useful improvement. In particular, it is expected to be applied to high-speed optical optical shutters and high-density, large-screen displays.

[Problems to be solved by the invention]

For this reason, there has been extensive research on liquid crystal materials with ferroelectric properties, but the ferroelectric liquid crystal materials developed to date are sufficient for use in liquid crystal elements, including their low-temperature operating characteristics and high-speed response. It is hard to say that it has such characteristics.

On the other hand, in order for the ferroelectric liquid crystal having the bistability to exhibit a predetermined driving characteristic, the liquid crystal disposed between the pair of parallel substrates should have the two stable states regardless of the electric field application state. It is necessary that the molecular arrangement state is such that the light between them effectively occurs. For example, for a ferroelectric liquid crystal having an SmC ^* or SmH ^* phase, a region in which the liquid crystal molecular layer having SmC ^* or SmH ^* is perpendicular to the substrate surface, and therefore the liquid crystal molecular axis is aligned substantially parallel to the substrate surface ( Mono domain) needs to be formed. However, in the conventional ferroelectric liquid crystal device having bistability, the alignment state of the liquid crystal having such a domain structure is not always formed satisfactorily.

An object of the present invention is to provide a liquid crystal composition which, by mixing a specific liquid crystal compound, effectively introduces a smectic A phase important for orientation and exhibits a smectic C ^* phase in a low temperature region. It is intended to provide a liquid crystal composition having various display characteristics which cannot be obtained by a single liquid crystal compound, and a liquid crystal device using the composition.

In addition, monodomain formation or a conventional problem,
It is intended to provide a ferroelectric liquid crystal device having improved initial alignment.

[Means and Actions for Solving Problems]

That is, the present invention relates to at least one compound (A) which sequentially undergoes a phase transition from a smectic A phase to a phase having a higher degree of order than the smectic C phase in the temperature decreasing process, and at least one compound (B) showing a chiral smectic phase. And a liquid crystal composition characterized in that the mixing ratio of the compound (A) is less than 50% by weight, and the liquid crystal composition is disposed between a pair of substrates via an alignment control layer. The present invention provides a liquid crystal element.

By using the above liquid crystal composition, smectic A
The temperature range of the phase can be widened, whereby the liquid crystal element in which the liquid crystal composition is arranged can be a liquid crystal element having both the monodomain property of the liquid crystal layer.

Further, the above liquid crystal composition can extend the chiral smectic phase to a low temperature range.

In particular, when the chiral smectic phase is the chiral smectic C phase, excellent high-speed response can be exhibited.

Furthermore, to expand the temperature range of the SmA phase, use two or more types of SmA.
A composition in which a liquid crystal having a phase is mixed is effective, and particularly when a liquid crystal having a chiral molecule and exhibiting an SmA phase is used, a more remarkable effect appears.

 Hereinafter, the present invention will be described in more detail.

Specific examples of structural formulas and phase transition temperatures of the liquid crystal compounds (A) and (B) used in the present invention are shown in Tables 1 and 2.

As can be seen from Table 1, the liquid crystal compound (A) of the present invention
The phase having a higher degree of order than the smectic C phase refers to, for example, a Cryst. Phase other than the smectic C phase.

 The symbols in the table indicate the following phases, respectively.

Cryst: crystalline phase SmA: smectic A phase Iso: isotropic phase SmC ^* chiral smectic C phase ch: cholesteric phase Sm3: SmA, SmC ^* smectic phase other than ^* (unidentified) Table 1 smectic from isotropic phase during cooling process Specific examples of the liquid crystal compound (A) exhibiting a phase transition to a phase having a higher degree of order than the A phase and the smectic C phase P'-heptylbiphenylcarboxylic acid-P "-(2-octyloxypropyloxy) carbonylphenyl ester P-n-dodecyloxybenzoic acid-P '-(2-pentyloxypropyloxycarbonyl) phenyl ester Table 2 Specific examples of the liquid crystal compound (B) exhibiting a chiral smectic phase from an isotropic phase in the temperature decreasing process The compound of A and the compound of B of the liquid crystal composition used in the present invention
The ratio of the liquid crystal varies depending on the type of liquid crystal used, but in general, 1 to
It is preferred to use 99% by weight, especially 2-80% by weight.

The temperature range of SmA in the compound A is 1 ° C or higher, preferably 3 ° C or higher.

The liquid crystal element of the present invention is obtained by disposing the liquid crystal composition of the present invention obtained as described above between a pair of electrode substrates. The cell thickness of the liquid crystal element is preferably as thin as possible, generally 0.5 μ to 20 μ, particularly 1 μ to 5 μm.
μ is suitable.

The substrate is made of a glass plate or a plastic plate, and a transparent electrode is formed on the substrate.

And a substrate provided with such a transparent electrode, for example,
Inorganic insulating materials such as silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, polyvinyl alcohol, polyimide, polyamideimide, polyesterimide It is possible to provide an orientation control film formed by using an organic insulating substance such as polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine resin, urea resin or acrylic resin. it can.

The uniaxial alignment treatment axis imparted to this alignment control film is obtained by forming a film of the above-mentioned inorganic insulating material or organic insulating material and then rubbing the surface in one direction with velvet, cloth or paper. To be In particular, in the present invention, it is preferable to use a polyimide film, a polyamide film, or a polyvinyl alcohol film having a uniaxial alignment treatment axis provided by a rubbing treatment as the alignment control film. The orientation control film 105 may be provided on only one substrate.

In another preferred embodiment of the present invention, an inorganic insulating substance such as SiO or SiO ₂ is formed on the substrate by oblique vapor deposition to obtain an alignment control film having a uniaxial alignment treatment axis. it can.

Further, after forming a film of the above-mentioned inorganic insulating material or organic insulating material, the surface of the film is etched by the oblique etching method, whereby the orientation control effect can be imparted to the surface.

It is preferable that the above-mentioned orientation control film also functions as an insulating film at the same time. For this reason, the thickness of the orientation control film can be set generally in the range of 100Å to 1 µ, and preferably in the range of 500Å to 5000Å. This insulating film also has an advantage of being able to prevent the generation of a current generated due to impurities contained in the liquid crystal layer in a trace amount, and therefore does not deteriorate the liquid crystal compound even if the operation is repeated.

In the liquid crystal element of the present invention, the same substrate as the above-mentioned alignment control film can be provided on the other substrate a.

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 The liquid crystal compound of A described in Table 1 and the liquid crystal compound of B described in Table 2 (16) were mixed. The change in phase transition temperature (temperature rising process) of the obtained liquid crystal composition is shown in FIG. 1 as a phase diagram.

As is clear from FIG. 1, the liquid crystal compound and (16) were mixed at 24: 7.
When mixed at a ratio of 6, the temperature range of the smectic A phase necessary for improving the orientation was widened. In addition, the temperature range of SmC ^* expanded widely to around room temperature and kept SmC ^* relatively stable even at the supercooling temperature.

Example 2 A polyimide-forming solution ("PIQ" manufactured by Hitachi Chemical Co., Ltd .; nonvolatile concentration: 14, 5) on a glass substrate provided with an ITO film in a stripe shape having a width of 62.5 μm and a width of 62.5 μm as an electrode.
wt%) with a spinner coater, and 200 at 120 ℃ for 30 minutes.
The coating was formed by heating at 60 ° C for 60 minutes and then at 350 ° C for 30 minutes.

Next, rub the pair of glass substrates with the coating film under a pressure of 100 g / cm ² , and stack the pair of rubbed glass substrates so that the upper and lower rubbing directions are parallel to each other. The removed area was sealed. The distance between the pair of glass substrates at this time was 2 μm.

Next, the liquid crystal composition of Example 1 was heated to form an isotropic phase, and the liquid crystal composition was injected into the cell prepared above under reduced pressure from the injection port and the injection port was sealed. This cell was gradually cooled to lower the temperature, and a pair of polarizers were placed in a crossed Nicols state while maintaining the temperature at about 35 ° C, and microscopic observation revealed that SmC ^* with a monodomain non-helical structure was formed. I was able to confirm that

Further, the response speed was measured by detecting an optical response under a crossed Nicols by applying a voltage of 10 V as a peak-to-peak voltage for the above liquid crystal element.

 The results are shown in Table 3 below.

As can be seen from the above, a liquid crystal device composed of the mixed liquid crystal composition according to the present invention has a faster response than a single liquid crystal compound, and a liquid crystal device having an improved response speed can be obtained particularly at a low temperature.

Example 3 The liquid crystal of A described in Table 1 and the liquid crystal of B described in Table 2 (22) were mixed at a ratio of 40:60 to obtain a liquid crystal composition. It had an SmA phase at 54-66 ° C.

In addition, it has SmC ^* phase in a wide temperature range from 21 to 54 ℃ and room temperature, and maintains SmC ^* relatively stable even at supercooling temperature.

Example 4 A polyvinyl alcohol-forming aqueous solution (“R-2105” manufactured by Kuraray Co., Ltd .; nonvolatile content concentration 2 wt%) was applied onto a glass substrate having a pitch of 100 μm and a width of 62.5 μm and provided with a striped ITO film as an electrode. It was applied by a machine and heated at 180 ° C. for 60 minutes to form a coating film.

 Hereinafter, an element was prepared in the same manner as in Example 2.

Next, a liquid crystal device was prepared by using the liquid crystal composition of Example 3 in the same manner as in Example 2 and then observed under a microscope. As a result, it was found that SmC ^* having a monodomain non-helical structure was formed. It could be confirmed.

Furthermore, when the response speed of the above liquid crystal element was measured at 26 ° C. by the same method as in Example 2, the response speed was improved to 350 μs. (Of liquid crystal compound (22) by itself
The response speed at 30 ° C. was 470 μs. Example 5 The liquid crystal of A described in Table 1 and the liquid crystal of B described in Table 2 (19) were mixed at a ratio of 25:75 to obtain a liquid crystal composition. It had SmA at 40-47 ° C. In addition, it has a SmC ^* phase in the temperature range from 29 to 40 ° C, which is close to room temperature, and maintains SmC ^* relatively stable even at supercooling temperatures.

Example 6 A polyvinyl alcohol-forming aqueous solution (“EG-25” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was formed on a glass substrate having a 100 μm pitch, a 62.5 μm width and a striped ITO film as an electrode.
Nonvolatile content (2 wt%) is applied with a spinner coater and 180 ℃
Was heated for 60 minutes to form a coating film.

 Hereinafter, an element was formed by the same method as in Example 2.

Next, a liquid crystal element was prepared by using the liquid crystal composition of Example 5 in the same manner as in Example 5 and then observed under a microscope. As a result, it was found that SmC ^* having a monodomain non-helical structure was formed. It could be confirmed.

Furthermore, when the response speed of the above liquid crystal element was measured at 35 ° C. in the same manner as in Example 2, the response speed was improved to 170 μsec. (Of the liquid crystal compound (19) alone
The response speed at 35 ° C. was 250 μs. Example 7 The liquid crystal of A in Table 1, the liquid crystal of B in Table 2 (22) and the liquid crystal of B
And a liquid crystal (23) represented by the following formula, which belongs to, were mixed in a ratio of 4: 3: 3 to obtain a liquid crystal composition. It had a SmC ^* phase in a wide temperature range of -35 ° C to 54 ° C.

Comparative Experiment A liquid crystal device was prepared in the same manner as in Example 2 except that the following composition was used, and the response speed was measured.

Composition A (invention) Liquid crystal compound of Table 1 (compound corresponding to A) 30 parts by weight Liquid crystal compound (16) of Table 2 (compound corresponding to B) 70 parts by weight Composition B (comparative example) 30 parts by weight Liquid crystal compound (16) in Table 2 (compound corresponding to B) 70 parts by weight Composition A Composition B Response speed (40 ° C) 313 μs 335 μs (30 ° C.) 75 μs 442 μs From the above results, composition A Is lower than composition B (30
Response speed at ℃) is faster, and temperature change (30
The fluctuation of the response speed with ℃ and 40 ℃) is smaller.

〔The invention's effect〕

As can be seen from the above examples, a compound having an optically active group and causing a phase transition from an isotropic phase to a phase having a higher degree of order than the smectic A phase and the smectic C phase and a compound exhibiting a chiral smectic phase By mixing and, the temperature range of the smectic A phase necessary for improving the orientation can be expanded, and further, the chiral smectic phase can be expanded to a low temperature range. As a result, an improvement in response speed was also found, and a liquid crystal composition having excellent characteristics not found in a single liquid crystal compound was obtained.

Further, according to the liquid crystal device of the present invention using the above liquid crystal composition, it is possible to achieve both the operation of the device based on the bistability of the ferroelectric liquid crystal and the monodomain property of the liquid crystal layer.

[Brief description of drawings]

FIG. 1 shows the liquid crystal compound and the liquid crystal compound (1
FIG. 6 is a phase diagram showing changes in composition of phase transition temperature due to mixing in 6).

 ─────────────────────────────────────────────────── (72) Inventor Shunji Utsumi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Akira Tsuboyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Incorporated (72) Inventor Sachiko Futami 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-60-32748 (JP, A) JP-A-59-128357 (JP , A) JP 61-203984 (JP, A)

Claims (11)

(57) [Claims] 1. At least one compound (A) and a compound (B) exhibiting a chiral smectic phase, which sequentially undergo phase transitions from a smectic A phase to a phase having a higher degree of order than the smectic C phase in the course of cooling. And a mixture ratio of the compound (A) is less than 50% by weight. 2. The liquid crystal composition according to claim 1, which contains two or more kinds of the compound (B). 3. The liquid crystal composition according to claim 1, wherein the liquid crystal composition is a liquid crystal composition which sequentially undergoes a phase transition from a smectic A phase to a chiral smectic phase during a temperature lowering process. 4. The chiral smectic phase is C phase and H
The liquid crystal composition according to claim 1, which is a phase, an F phase, a J phase, a K phase, an I phase, or a G phase. 5. The liquid crystal composition according to claim 1, wherein the temperature range of the smectic A phase in the temperature lowering process of the compound (A) is 1 ° C. or higher. 6. A chiral compound and at least one compound (A) which sequentially undergo phase transition from a smectic A phase to a phase having a higher degree of order than the smectic C phase in a temperature lowering process between a pair of substrates via an orientation control layer. The compound (A) containing at least one compound (B) exhibiting a smectic phase,
And a liquid crystal composition having a blending ratio of less than 50% by weight. 7. The liquid crystal composition comprises the compound (B) 2
The liquid crystal device according to claim 6, which contains at least one species. 8. The liquid crystal device according to claim 6, wherein the liquid crystal composition is a liquid crystal composition which sequentially undergoes a phase transition from a smectic A phase to a chiral smectic phase during a temperature lowering process. 9. The chiral smectic phase in the liquid crystal composition is C phase, H phase, F phase, J phase, K phase, I phase, or G phase.
The liquid crystal element according to claim 6, which is in a phase. 10. The liquid crystal device according to claim 6, wherein the temperature range of the smectic A phase in the temperature lowering process of the compound (A) is 1 ° C. or higher. 11. The liquid crystal device according to claim 6, wherein the alignment control film is a polyimide film, a polyamide film or a polyvinyl alcohol film which has been uniaxially rubbed.