JPH0753867B2 - Liquid crystal composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid crystal composition used for a liquid crystal display device, a liquid crystal device used for a liquid crystal-optical shutter, or the like, and more specifically, a novel liquid crystal composition having improved response characteristics to an electric field. It is about things.

BACKGROUND ART Liquid crystals have been conventionally applied as electro-optical elements in various fields. Most of the liquid crystal devices currently in practical use are, for example, “Applied Physics” by M. Schadt and W. Helfrich.
Letters "Vo.18, No.4 (1971.2.15), P.127-128" Vo "
ltage-Dpendent Optical Activity of a Twiste
d Nematic Liquid Crystal “TN (twisted
nematic) type liquid crystal is used.

These are based on the dielectric alignment effect of liquid crystals, and utilize the effect that the average molecular axis direction is directed in a specific direction by an applied electric field due to the dielectric anisotropy of liquid crystal molecules. The optical response speed limit of these devices is said to be milliseconds, which is too slow for many applications. On the other hand, in the application to a large flat panel display, the drive by the simple matrix method is the most effective in consideration of price and productivity. In the simple matrix system, an electrode configuration in which the scanning electrode group and the signal electrode group are configured in a matrix is adopted,
As a driving scheme, a time-division drive method is adopted in which an address signal is sequentially and selectively applied to the scanning electrode group and a predetermined information signal is selectively applied to the signal electrode group in parallel in synchronization with the address signal. To be done.

However, when the above-mentioned TN type liquid crystal is adopted for the element of such a driving system, the scan electrode is selected and the signal electrode is not selected, or the scan electrode is not selected and the signal electrode is selected (so-called “half-area”). A finite electric field is also applied to the selection point "). If the difference between the voltage applied to the selection point and the voltage applied to the semi-selection point is sufficiently large and the voltage threshold value required to align the liquid crystal molecules perpendicularly to the electric field is set to the intermediate voltage value, the display element is Although it operates normally, when the number of scanning lines (N) is increased, the time (duty ratio) that an effective electric field is applied to one selection point while scanning the entire screen (1 frame) Will decrease at a rate of 1 / N. For this reason, the voltage difference as the effective value applied to the selected point and the non-selected point in the case of performing repeated scanning becomes smaller as the number of scanning lines increases, and as a result, lowering of image contrast and crosstalk occur. It is an unavoidable drawback. Such a phenomenon is caused by a liquid crystal having no bistability (a stable state in which liquid crystal molecules are horizontally aligned with respect to an electrode surface, and vertically aligned only when an electric field is effectively applied. Is an inherently unavoidable problem that occurs when (1) is driven by utilizing the temporal accumulation effect (that is, repeated scanning). In order to improve this point, a voltage averaging method, a two-frequency driving method, a multiple matrix method, etc. have already been proposed, but none of them is sufficient, and the display element has a large screen and high density. The current situation is that the number of scanning lines has reached a ceiling because the number of scanning lines cannot be increased sufficiently.

As a solution to these drawbacks of conventional liquid crystal devices, the use of bistable liquid crystal devices is explained by Clark and Lag.
proposed by Erwall (Japanese Patent Laid-Open No. 56-107216, US Pat. No. 4,367,924, etc.). As a bistable liquid crystal, a chiral smectic C phase (Sm
Ferroelectric liquid crystal having C ^* ) or H phase (SmH ^* ) is used. This ferroelectric liquid crystal has a bistable state consisting of a first optical stable state and a second optical stable state with respect to an electric field. Therefore, it is different from the optical modulation element used in the above-mentioned TN type liquid crystal. Differently, for example, the liquid crystal is aligned in the first optically stable state with respect to one electric field vector, and is aligned with the second optically stable state in the other electric field vector. This type of liquid crystal also responds to the applied electric field by
It has the property (bistability) of taking one of the two stable states and maintaining that state when no electric field is applied.

In addition to the above-mentioned characteristic of having bistability, the ferroelectric liquid crystal has an excellent characteristic 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.

As described above, the ferroelectric liquid crystal potentially has extremely excellent characteristics, and by utilizing such characteristics, it is considerably essential to many of the problems of the conventional TN type element described above. You get an improvement. In particular, it is expected to be applied to high-speed optical optical shutters and high-density, large-screen displays. For this reason, although extensive research has been conducted on liquid crystal materials having ferroelectricity, the ferroelectric liquid crystal materials developed to date are sufficient for use in liquid crystal elements, including low-temperature operating characteristics and high-speed response. It is hard to say that it has characteristics.

Object of the Invention An object of the present invention is to provide a liquid crystal composition exhibiting a smectic C ^* phase in a low temperature region by mixing a specific liquid crystal compound, and at the same time, to obtain various display characteristics which cannot be obtained by a single liquid crystal compound. A liquid crystal composition having the same and a liquid crystal device using the composition.

SUMMARY OF THE INVENTION That is, the present invention provides the following general formula (I) (In the above general formula, R represents an alkyl group having 1 to 16 carbon atoms. M = 1 or 2, and * represents an asymmetric carbon atom. (Wherein R ¹ represents an alkyl group having 4 to 16 carbon atoms, n = 1 or 2, and a = 0 or 1)), and at least one kind of optically active liquid crystalline lactic acid derivative The following general formula (II) (In the above general formula, p is 4 to 16, q is 1 or 2, r is 1 or 2, and z is 0 or S.
R ^* represents an optically active alkyl group having 5 to 12 carbon atoms. And at least one kind of an optically active liquid crystal compound represented by the formula (1), and a liquid crystal element comprising the liquid crystal composition arranged between a pair of electrode substrates. is there.

According to the research conducted by the present inventors, by mixing the liquid crystal compounds of the above formulas (I) and (II), the temperature range giving a smectic C ^* phase can be improved as compared with the case where each liquid crystal compound is used alone. It has been found that, particularly on the low temperature side, the spread and the response speed are improved, and the display characteristics are improved.

Hereinafter, the present invention will be described in more detail. In the following description, “%” and “part” representing the quantitative ratio are based on weight.

DETAILED DESCRIPTION OF THE INVENTION The liquid crystal compound represented by the formula (I) has the following general formula (A). (In the above general formula, R represents a linear, branched or cyclic saturated or unsaturated hydrocarbon group having 1 to 16 carbon atoms. C
^{* Indicates} an asymmetric carbon atom. X represents a removable substituent selected from an OH group, a halogen, a benzyloxy group, a phenoxy group, a toluenesulfonic acid group, an acetyloxy group, and a trifluoroacetyloxy group) via an optically active substance represented by It is preferably formed. For example, it can be synthesized by the following reaction via an optically active substance in which X is an OH group in the above formula (A).

(Here, R ¹ , R, m, and n are as defined above.) The liquid crystal compound represented by the general formula (II) has the following general formula (B). (In the above general formula, R ^* represents an optically active alkyl group having 5 to 12 carbon atoms. Y represents an OH group, halogen (Br, Cl, I), benzyloxy group, phenoxy group, toluenesulfonic acid group, acetyl group. It represents a detachable substituent selected from an oxy group and a trifluoroacetyloxy group) and is preferably formed via an optically active substance represented by For example, in the above formula (B), it can be synthesized by the following reaction via an optically active substance in which Y is an OH group.

(Here, p, q, and r have the same meanings as above.) The structural formulas of the specific liquid crystal compound examples represented by the general formulas (I) and (II) and the phase transition temperatures of the liquid crystals are shown in Table 1 below. And Table 2
Shown in.

The liquid crystal compound is represented by the general formulas (I) and (II), and the present invention is not limited to the compounds listed here.

In the table, the symbols in the column of phase transition temperature indicate the following phases, respectively.

Cryst .: crystalline phase, SmA: smectic A phase, SmC ^* : chiral smectic C phase, N: nematic phase, Ch: cholesteric phase, Iso: isotropic phase, Sm1, Sm2: SmA, smectic phase other than SmC ^* (end) Identification).

The liquid crystal composition of the present invention is preferably formed by mixing at least one 1 to 99% of the liquid crystal compound of the above formula (I) and at least 99 to 1% of the above liquid crystal compound of the formula (II). .

In addition to the liquid crystal compounds of the above formulas (I) and (II), the liquid crystal device of the present invention is combined with a ferroelectric liquid crystal represented by the following formulas (1) to (13) to obtain SmC ^*. It is possible to lower the temperature and expand the temperature range.

In such a case, the total amount of the liquid crystal compound of the above formula (I) and the liquid crystal compound of the above formula (II) is used in a proportion of 1 to 99%, particularly 5 to 99% of the obtained liquid crystal composition. Preferably.

Further, a composition that can be used as a ferroelectric liquid crystal can be obtained by blending with a smectic liquid crystal which is not itself chiral as represented by the following formulas 1) to 5).

In this case, 1 to 99% by weight of the liquid crystal composition that can obtain the liquid crystal compound of the present invention represented by the general formulas (I) and (II),
It is particularly preferable to use 5 to 95% by weight.

Here, the symbols indicate the following phases, respectively.

Cryst .: crystalline phase, SmA: smectic A phase, SmB: smectic B phase, SmC: smectic C phase, N: nematic phase, Iso .: isotropic phase.

Further, 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. For example, in order to form a liquid crystal element of simple matrix drive, a scan electrode group may be formed on one substrate and a signal electrode group may be formed on the other substrate.

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

Example 1 As a representative example of the liquid crystal compounds, the liquid crystal compounds 5 and 9 among the compounds shown in Table 1 were mixed. A phase diagram showing changes in the phase transition temperature (temperature rising process) of the obtained liquid crystal composition is shown in FIG.

As is clear from FIG. 1, when the liquid crystal compounds 5 and 9 are mixed at a ratio of 1: 1, the temperature range of SmC ^* is greatly expanded and SmC ^* is increased.
You can see that ^* is kept stable. The spontaneous polarization at this mixing ratio was 3.2 nC / cm ² 125 ° C.

The spontaneous polarization is described by K. Miyasato et al. “Direct measurement method of spontaneous polarization of ferroelectric liquid crystal by triangular wave” (Journal of Japan Society of Applied Physics).
22 , No. 10, L (661) 1983, (“Direct Method with Tr
iangular Waves for Measuring Spontaneous Polarizat
ion in Ferroelectric Liquid Crystal ", as describ
ed by K. Miyasato et al. (Jap.J.Appl.Phys.22, No.10,
L661 (1983))).

The response speed of the above liquid crystal composition (1: 1 mixture) was measured. That is, the liquid crystal composition is sandwiched between a pair of electrode substrates that have been subjected to a rubbing treatment on a polyimide coating covering the electrodes,
With a liquid crystal layer thickness of 2 μm, a voltage of 10 V was applied as a peak-to-peak voltage, and an optical response under a crossed Nicols was detected to measure the response speed.

The results are shown in Table 3 below.

As can be seen from the above, the mixed liquid crystal composition (5 + 9 (1: 1)) according to the present invention has a faster response and a better response speed than a single liquid crystal compound even at a low temperature.

Example 2 Liquid crystal compound 3 and liquid crystal compound 9 were mixed at a ratio of 75:25 to obtain a liquid crystal composition. This liquid crystal composition has a temperature drop of 5
It showed a SmC ^* phase at ~ 45 ° C. Using this composition, an element was prepared in the same manner as in Example 1, and the response speed was changed under exactly the same conditions.
When measured at a temperature of 30 ° C., the characteristic was improved to 350 μsec as compared with the case where a single liquid crystal compound was used. (Note that the response speed of liquid crystal compound 3 alone at 70 ° C is 40
It is 0 μsec. Example 3 The liquid crystal compound 5 and the liquid crystal compound 10 shown in Table 1 were
A liquid crystal composition was obtained by mixing at a ratio of 70:30. The liquid crystal composition had a SmC ^* phase at −2 ° C. to 78 ° C. in the temperature decreasing process.

A device was prepared using this liquid crystal composition in the same manner as in Example 1, and the measurement was carried out under the same conditions at a response speed of 30 ° C., and it was 300 μsec, and the response speed was improved. (Note that the response speed of the liquid crystal compound 10 alone at 45 ° C. was 1800 μsec.) Effects of the Invention As can be seen from the above examples, according to the present invention, the general formula (I) and the general formula (II) were obtained. By mixing the liquid crystal compounds represented by, as compared with each single liquid crystal compound,
It is possible to obtain a liquid crystal composition having excellent properties such as a smectic C phase spreading to the low temperature side and an improved response speed which are not found in a single liquid crystal compound.

[Brief description of drawings]

The drawing is a phase diagram showing changes in composition of the phase transition temperature due to mixing of the liquid crystal compound 5 and the liquid crystal compound 9 according to Example 1.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Kenji Shinjo Kenji Shinjo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-62-123141 (JP, A) JP-A-62 -281854 (JP, A) JP 62-205056 (JP, A)

Claims (2)

[Claims] 1. A general formula (I) (In the above general formula, R represents an alkyl group having 1 to 16 carbon atoms. M = 1 or 2, and * represents an asymmetric carbon atom. (Wherein R ¹ represents an alkyl group having 4 to 16 carbon atoms, n = 1 or 2, and a = 0 or 1)), and at least one kind of optically active liquid crystalline lactic acid derivative The following general formula (II) (In the above general formula, p is 4 to 16, q is 1 or 2, r is 1 or 2, and z is 0 or S.
R ^* represents an optically active alkyl group having 5 to 12 carbon atoms. ) A liquid crystal composition containing at least one kind of an optically active liquid crystal compound represented by 2. General formula (I) (In the above general formula, R represents an alkyl group having 1 to 16 carbon atoms. M = 1 or 2, and * represents an asymmetric carbon atom. (Wherein R ¹ represents an alkyl group having 4 to 16 carbon atoms, n = 1 or 2, a = 0 or 1) and an optically active liquid crystalline lactic acid derivative represented by the following general formula (II ) (In the above general formula, p is 4 to 16, q is 1 or 2, r is 1 or 2, and z is 0 or S.
R ^* represents an optically active alkyl group having 5 to 12 carbon atoms. ) A liquid crystal device comprising a liquid crystal composition containing at least one kind of an optically active liquid crystal compound represented by the formula (1), disposed between a pair of electrode substrates.