JPH0721143B2 - Ferroelectric chiral smectic liquid crystal composition - Google Patents

Description

The present invention relates to a chiral smectic liquid crystal composition. More specifically, smectic C phase (hereinafter abbreviated as S _C phase)
Addition of a ferroelectric chiral smectic liquid crystal to a liquid crystal compound or liquid crystal composition having a long length makes the helical pitch extremely long, has a large spontaneous polarization, and has excellent responsiveness. Liquid crystal material.

(Prior Art) Liquid crystal compounds are widely used as display materials, but most of such liquid crystal display elements are of the TN type display system, and liquid crystal materials belonging to the nematic phase are used. . Since the TN type display system is a light receiving type, it has the advantages that it does not tire the eyes and that it consumes extremely little power, but it has the drawback that the response is slow and the display cannot be seen depending on the viewing angle. Recently, particularly high-speed response is required for the device, and improvement of the liquid crystal material has been attempted to meet such demand. However, compared to other light-emitting displays (such as EL (electroluminescence) displays and plasma displays), the TN display system has not been able to solve a large delay in response time.
In order to take advantage of the characteristics of liquid crystal display devices such as light receiving type and low power consumption, and to secure the responsiveness comparable to the light emitting type display, it is essential to develop a new liquid crystal display method that replaces the TN type display method. One of such attempts is to use a display device that utilizes the optical switching phenomenon of ferroelectric liquid crystals.
Proposed by NA Clark and ST Lager Wall (Applied Physics Letters (Appl.Phys.Le
tt.) 36 899 (1980)). The existence of the ferroelectric liquid crystal was first announced by RB Meyer in 1975 (J. Physique 36).
Volume L-69 (1975)), from the viewpoint of liquid crystal structure, chiral smectic C phase, chiral smectic I phase, chiral smectic F phase, chiral smectic G phase and chiral smectic H phase ( Below, S _C ^* phase and S _I ^*
Phase, S _F ^* phase, S _G ^* phase, and S _H ^* phase).

When applying the optical switching effect of the S _C ^* phase as a display element, it has three excellent characteristics compared to the TN display method. The first feature is that it responds very fast and its response time is
It is 1/100 or less when compared to the TN display type element. Second
The feature of (1) is that it has a memory effect, and time sharing drive is easy in combination with the above-mentioned high-speed response. The third characteristic is that gray scales can be easily obtained. To take shades of gray with TN display mode, for performing by adjusting the applied voltage, as compared to have challenges such as a voltage dependent temperature-dependent and the response speed of the threshold voltage, S _C ^* When the phase optical switching effect is applied, gradation can be easily obtained by adjusting the polarity reversal time, which is very suitable for graphic display.

There are two possible display methods. One method is a birefringence type using two polarizers, and the other method is a guest-host type using a dichroic dye. Since the S _C ^* phase has spontaneous polarization, reversing the polarity of the applied voltage causes the molecule to invert with the helical axis as the axis of rotation. S _C ^*
Two pieces of liquid crystal composition having a phase are injected into a liquid crystal display cell that has been subjected to an alignment treatment so that the liquid crystal molecules are aligned parallel to the electrode surface, and the director of the liquid crystal molecules and one polarization plane are arranged in parallel. By sandwiching the liquid crystal cell between the polarizers and applying a voltage to reverse the polarity, a bright field and a dark field (determined by the facing angle of the polarizer) can be obtained. On the other hand, when operating as a guest-host type, the non-colored visual field and the colored visual field (determined by the arrangement of the polarizing plate) can be obtained by reversing the polarity of the applied voltage.

The S _C ^* phase has spontaneous polarization, and it is necessary to be able to assume two stable states (bistable (bistable) state) on the electrode surface by reversing the polarity of the applied voltage. In order to obtain this bistable state and high-speed response liquid crystal display element, the cell gear d is made smaller than the spiral pitch P as proposed by NA Clarke et al. It is necessary to unwind the helix. (NAClark et al .; Applied Physics Letters (Appl.Phys.Let
t.) Vol. 36, p. 899 (1980)) The current ferroelectric liquid crystal compounds have helical pitches of 1 to 3 μm.
There are many short compounds such as m, and it is necessary to set the cell gap to about 1 to 2 μm to unwind the helix of these compounds, but this is difficult in terms of cost and yield considering the current cell manufacturing technology. Problem remains. Therefore, in order to avoid the problems in cell manufacturing technology and put the ferroelectric liquid crystal display device into practical use, the spiral pitch is about 5 to 10 μm which is currently used in the TN type display system. It is necessary to make the helical pitch of the ferroelectric liquid crystal material 5 μm or more so that it can be unwound.

Further, when the display element using the ferroelectric liquid crystal is brought into the two stable states described above, the threshold voltage Ec, the helical pitch P and the magnitude Ps of the spontaneous polarization necessary for the inversion of the molecule are set.
Between There is a relationship (RB Meyer; more crystal crystal and liquid crystal (Mol.Cryst.Liq.Cryst.),
Volume 40, page 33 (1977)). In the equation (1), K is an elastic constant when the molecule rotates and deforms. As is clear from the equation (1), in order to reduce the threshold voltage,
The spiral pitch must be long and the spontaneous polarization must be large. However, there is no compound having a long helical pitch and a large spontaneous polarization among the present ferroelectric liquid crystal compounds, and almost all the compounds have a short helical pitch. Therefore, by mixing several kinds of ferroelectric liquid crystal compounds, a ferroelectric liquid crystal composition having a long helical pitch and a large spontaneous polarization must be prepared.

As described above, a ferroelectric liquid crystal composition having a long helical pitch is required due to the relationship between the bistable state and the threshold voltage.

(Problems to be Solved by the Invention) As described above, the first object of the present invention is to provide a high-speed response display by using a cell of a cell gap which is almost the same as a cell currently widely used in the TN type display system. It is an object of the present invention to provide a ferroelectric liquid crystal composition having a long helical pitch and a large spontaneous polarization that can be practically used.

A second object of the present invention is to provide an optical switching element having a high response speed.

(Means for Solving Problems) In the Japanese Patent Application No. 58-186312, the inventors of the present invention have already disclosed that a spiral chiral twist is a right-handed chiral smectic liquid crystal compound and a helix twist is a left-handed chiral. The invention of a ferroelectric chiral smectic liquid crystal composition comprising a smectic liquid crystal compound was shown. In the specification of the application, as a method for lengthening the helical pitch, in addition to the method relating to the invention of the application in which a compound having a right-handed helix and a compound having a left-handed helix are mixed, a ferroelectric chiral smectic It has been described that a method according to the invention in which a liquid crystal compound and a compound having a smectic C phase that does not have a helical structure are mixed is conceivable, the latter being S _C with a very large spontaneous polarization.
^* It is stated that it is only applicable to compounds with phases.

However, after that, many chiral smectic liquid crystal compounds with extremely large spontaneous polarization were realized one after another (see, for example, Japanese Patent Application Nos. 59-119590 and 59-185151), but these helical pitches were small. It has become significant to obtain a practical liquid crystal composition by mixing a ferroelectric liquid crystal compound having a larger spontaneous polarization with a liquid crystal compound having an S _C phase.

That is, the first aspect of the present invention is (1) a ferroelectric chiral smectic liquid crystal compound having a smectic C phase and not having a helical structure, and a ferroelectric chiral smectic liquid crystal compound having a helical structure. In the liquid crystal composition, a liquid crystal compound having a smectic C phase and having no helical structure is represented by the general formula (X) or (XI) (In the formula (X), R ¹⁸ represents an alkyloxy group having 9 to ¹⁸ carbon atoms, R ¹⁹ represents an alkyl group having 7 to 18 carbon atoms, and has the formula (XI)
R ²⁰ represents an alkyl group having 6 to 18 carbon atoms or an alkyloxy group, and R ²¹ represents an alkyl group having 5 to 18 carbon atoms. ) Is at least one compound selected from the group of compounds represented by the formula, and a ferroelectric chiral smectic liquid crystal compound having a helical structure is represented by the general formula (In the formula (I), m and n each represent an integer of 1 or 2, and X represents _{-CH = N -, - CH 2} O-, —N═CH—, —OCH ₂ — or a single bond, R ¹ represents an alkyl group or an alkoxy group having 1 to 18 carbon atoms, and Y is an alkyl group having an asymmetric carbon atom, an alkyloxy group, an alkoxycarbonyl. Group, alkanoyl group or alkanoyloxy group. ) At least one compound selected from the group of compounds represented by

Aspects of the present invention include (2) in the formula (I) in the preceding paragraph, Y is A ferroelectric chiral smectic liquid crystal composition represented by the following formula, which is a group having an asymmetric carbon atom.

An optical switching element using the ferroelectric chiral smectic liquid crystal composition according to the item (1) or (2).

Next, a reference example will be described. 1 and 2 are (I)
In the formula, m = 1, n = 2 R ¹ = C ₈ H ₁₇ O- those compounds, namely To the compound A represented by the formula (VI): R ¹⁰ = C ₈ H ₁₇ O-, R ¹¹
= C ₈ H ₁₇ O- compounds which do not take a helical structure is, namely In the binary system in which the compound having the S _C phase is mixed, the measured temperature (T) is 15 ° C. lower than the S _C ^* -S _A phase transition temperature (T _C ) (hereinafter, T-T _C = 15 ° C.). , And the concentration dependence of the magnitude of spontaneous polarization (Ps) of the binary mixture and the reciprocal of the helical pitch (1 / P). As is clear from FIGS. 1 and 2, the magnitude of spontaneous polarization and the reciprocal of the helical pitch show additivity corresponding to composition, and the magnitude of spontaneous polarization is 8 at a compound A concentration of 20% by weight. .
It is as large as 5 nC / cm ^2, and the length of the helical pitch is as long as 33 μm, suggesting that a ferroelectric chiral smectic liquid crystal composition having a long helical pitch can be easily obtained.

3 and 4 are equations (I) in which m = 1, n = 1, R = C ₈ H ₁₇ O- those compounds, namely In the compound C represented by the formula (III), R ₄ ═C ₈ H ₁₇ O—, R ⁵
= C ₁₀ H ₂₁ O-, a compound having no helical structure, that is, Of the binary system to which the compound having the S _C phase shown in is added
-T is a diagram illustrating a P _S and 1 / P in _C = -15 ° C.. As is clear from FIGS. 3 and 4, when the compound C is 30% by weight, the magnitude of spontaneous polarization is 1.2 nC / cm ² , and the length of the helical pitch is 7.1 μm, which is very long. It is suggested that a ferroelectric chiral smectic liquid crystal composition having a long helical pitch can be easily obtained.

(Effects of the Invention) As described above, in Japanese Patent Application No. 58-186312, a chiral smectic liquid crystal compound in which the helical twist is clockwise and a chiral smectic liquid crystal compound in which the helical twist is counterclockwise. The present invention has the following advantages over the invention of a ferroelectric liquid crystal composition consisting of That is, by using as a component the chiral smectic liquid crystal compound having a large spontaneous polarization, which has recently appeared in large numbers, the selection range of the ferroelectric chiral smectic liquid crystal compound as the component (a) is expanded. Yes. In other words, a ferroelectric chiral smectic liquid crystal composition having a long helical pitch may be formed from only one kind of ferroelectric chiral smectic liquid crystal compound without being restricted by the twist direction of the helix. can get.

(A) A ferroelectric chiral smectic liquid crystal material can be obtained relatively inexpensively, and thus an optical switching element having a high-speed response can be obtained inexpensively. Generally, optically active 2-alkanols are expensive, and accordingly, the ferroelectric chiral smectic liquid crystal compound made from them is expensive. Compared with this, since a liquid crystal compound having an S _C phase can be produced at a low cost like a general nematic liquid crystal compound at present, the composition of the present invention can be obtained at a relatively low cost. Y in the formula (I) is Many of these compounds have very large spontaneous polarization of 80 to 100 nC / cm ^2, and these ferroelectric liquid crystal compounds give compositions with sufficiently large spontaneous polarization even when added in small amounts. .

(C) the chiral smelling Chi poke liquid crystal compound and a ferroelectric chiral smelling lipped poke liquid crystal composition comprising a chiral smelling lipped poke crystal compound around twisted way is left spiral twist way is clockwise spiral, S _C phase The helical pitch of the composition can be further extended by adding a liquid crystal compound having Fine tuning of the helical pitch is relatively easy in this composition.

( _D ) The S _C ^* phase lower limit temperature of the composition can be lowered. The liquid crystal compound having a S _C phase many compounds having a nematic phase to the high temperature side, it is possible to anticipate the same effect as when adding Therefore nematic liquid crystal compound.

In addition to the above (a) to (d), the effects of the present invention are shown in the following examples.

(Examples) The present invention will be described in detail below with reference to Examples and Reference Examples, but the present invention is not limited to these Examples.
Note that the magnitude of spontaneous polarization is Sawyer-
Tower) method, and the spiral pitch was measured by using a cell whose spiral axis was parallel to the substrate, and the spacing of the striped pattern corresponding to the full pitch was directly measured by a polarizing microscope.

Example 1 In the formula (I) Two compounds of formula (I) A compound and The compound of the formula (III) and the compound of the formula (X) are mixed with four kinds of chiral smectic liquid crystal compounds in total of one compound each of The following chiral smectic liquid crystal composition was prepared. The S _C ^* phase temperature range of this composition is 8-53 ° C, 38 ° C (ie T
The magnitude of spontaneous polarization at −T _C = −15 ° _C is 10 nC / cm ² ,
The helical pitch was 18 μm.

S _C ^* phase temperature range of the composition of the ferroelectric chiral smelling lipped poke liquid crystal composition in Reference Example 2 to 11 in Reference Example 2 to 11 Table 1, the composition in each example in Table 2, T-T _C = The magnitude of spontaneous polarization (Ps) and the length of helical pitch (P) at -15 ° C are shown.

From Table 1 and Table 2, by mixing the S _C compound and the ferroelectric chiral smectic liquid crystal, a ferroelectric chiral smectic liquid crystal composition having a long helical pitch and a large spontaneous polarization can be obtained. Was shown.

Reference Example 12 The ferroelectric chiral smectic liquid crystal composition of Reference Example 3 was coated with polyvinyl alcohol (PVA) as an alignment treatment agent, and the surface was rubbed to carry out parallel alignment treatment. The liquid crystal cell is injected between two polarizers arranged in a crossed Nicols state to form a so-called birefringent display element, 0.5Hz, 15V
When a low frequency AC was applied, a clear switching operation with very good contrast was observed, and a liquid crystal display device with a very fast response time of 2 msec at 30 ° C was obtained.

Reference Example 13 The ferroelectric chiral smectic liquid crystal composition of Reference Example 10 was supplemented with 3 wt% of anthraquinone dye D-16 (manufactured by BDH).
A so-called guest-host type composition was added and injected into a cell similar to that of Reference Example 12, and a 1-plate polarizer was placed so that the plane of polarization was parallel to the molecular axis. When a low-frequency alternating current was applied, a clear switching operation with very good contrast was observed, and the response time was 30
A color liquid crystal display device with a very fast response of 1.2 msec at ℃ was obtained.

[Brief description of drawings]

1 and 2 are diagrams showing the magnitude of spontaneous polarization and the reciprocal of the helical pitch of a binary system consisting of compound A and compound B, respectively, and FIGS. 3 and 4 are diagrams showing compound C and compound D, respectively.
FIG. 5 is a similar view for a binary system consisting of

Claims (3)

[Claims] 1. A ferroelectric chiral smectic liquid crystal composition comprising a liquid crystal compound having a smectic C phase and not having a helical structure and a ferroelectric chiral smectic liquid crystal compound having a helical structure, wherein
A liquid crystal compound having a smectic C phase and having no helical structure is represented by the general formula (X) or (XI) (In the formula (X), R ¹⁸ represents an alkyloxy group having 9 to ¹⁸ carbon atoms, R ¹⁹ represents an alkyl group having 7 to 18 carbon atoms, and has the formula (XI)
R ²⁰ represents an alkyl group having 6 to 18 carbon atoms or an alkyloxy group, and R ²¹ represents an alkyl group having 5 to 18 carbon atoms. ) Is at least one compound selected from the group of compounds represented by the formula, and a ferroelectric chiral smectic liquid crystal compound having a helical structure is represented by the general formula (In the formula (I), m and n each represent an integer of 1 or 2, and X represents _{-CH = N -, - CH 2} O-, —N═CH—, —OCH ₂ — or a single bond, R ¹ represents an alkyl group or an alkoxy group having 1 to 18 carbon atoms, and Y is an alkyl group having an asymmetric carbon atom, an alkyloxy group, an alkoxycarbonyl. Group, alkanoyl group or alkanoyloxy group. ) A ferroelectric chiral smectic liquid crystal composition, which is at least one compound selected from the group of compounds represented by 2. Y in the general formula (I) is The ferroelectric chiral smectic liquid crystal composition according to claim 1, which is a group having an asymmetric carbon atom represented by: 3. An optical switching device using a ferroelectric chiral smectic liquid crystal composition, wherein the ferroelectric chiral smectic liquid crystal composition has the general formula (X) or (X
I) (In the formula (X), R ¹⁸ represents an alkyloxy group having 9 to ¹⁸ carbon atoms, R ¹⁹ represents an alkyl group having 7 to 18 carbon atoms, and has the formula (XI)
R ²⁰ represents an alkyl group having 6 to 18 carbon atoms or an alkyloxy group, and R ²¹ represents an alkyl group having 5 to 18 carbon atoms. ) A compound having at least one helical structure selected from the group of compounds represented by (In the formula (I), m and n each represent an integer of 1 or 2, and X represents _{-CH = N -, - CH 2} O-, —N═CH—, —OCH ₂ — or a single bond, R ¹ represents an alkyl group or an alkoxy group having 1 to 18 carbon atoms, and Y is an alkyl group having an asymmetric carbon atom, an alkyloxy group, an alkoxycarbonyl. Group, alkanoyl group or alkanoyloxy group. ) A ferroelectric chiral smectic liquid crystal composition comprising a compound having at least one helical structure selected from the group of compounds represented by
Optical switching element.