JPS63277295A - Ferroelectric liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide the titled composition capable of preventing contrast reduction due to orientation defect and enabling uniform driving when used in matrix display and light shutter for printer, containing specified amount of a specific biphenyl compound. CONSTITUTION:The objective liquid crystal composition made up of (A) 0.1-80wt.% of an optically active compound and (B) 20-99.9wt.% of an optically inactive substance pref. comprising (i) 5-50wt.% of a biphenyl compound of formula I (R1-R6 are each alkyl or alkoxy), (ii) 5-50wt.% of a second compound of formula II and (iii) 5-50wt.% of a third compound of formula III (n is 1 or 2).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a ferroelectric liquid crystal composition exhibiting ferroelectric properties for use in matrix display devices, optical shutters for printers, and the like.

[Prior Art] In recent years, electro-optical devices using ferroelectric liquid crystals have been attracting attention. (For example, N, A, CIark, S, T.

Lagerwall, Appl, Phys, Lett
, 36, 899 (1980)) Ferroelectric liquid crystals have a characteristic of having spontaneous polarization, that is, exhibiting ferroelectricity, in liquid crystal phases such as chiral smectic C phase (abbreviated as SmC'' phase) and chiral smectic H phase. In this respect, it has characteristics that are significantly different from the nematic phase or cholesteric phase that have been conventionally used in display elements and the like.

Several phases are known as the ferroelectric smectic phase, but the phase that is expected to be applied to applications such as optical shutters is the SmC phase, so the following explanation will be based on the SmC phase.
An example of the C'' phase will be explained.

In the SmC' phase, liquid crystal molecules have a layered structure, and the long axis direction of the molecules is oriented obliquely with respect to the direction of layer stacking lines.

In addition, the molecular structure contains an optically active substance with an asymmetric center, and the inclination direction of one molecule has a helical structure that is shifted between layers. Furthermore, the SmC" phase has spontaneous polarization perpendicular to the long axis direction of the molecules and parallel to the circumferential plane, and the orientation direction of the molecules changes in response to an external electric field so that the polarity of the spontaneous polarization matches the electric field. 9 The features of this electro-optical effect include a response time that is 10 to 1000 times faster than the effect using conventional nematic liquid crystals, and a memory property. has been discovered, and is expected to be applied to large-screen dot matrix display devices, high-speed optical shutter devices, etc.

However, it also has many problems.

The biggest problem is that it is difficult to fabricate the device. In other words, SmC" liquid crystal has a phase that is closer to a crystal than the nematic liquid crystal that has been used conventionally, and obtaining a good orientation that is uniformly aligned on a substrate is difficult, similar to single crystal growth. Normally, alignment holes or Zig-zag
It is common practice to eliminate an alignment defect called walL (abbreviated as Z 7°W). For this reason, many attempts have been made to obtain good alignment by selecting the phase series and alignment control method of the liquid crystal and optimizing alignment creation conditions such as temperature. In particular, research is being conducted on the orientation control of Sn+C'' liquid crystals using the rubbing method that has been used in conventional nematic liquid crystal display devices7 (for example, the 1986 Liquid Crystal Symposium Abstracts Collection 1 series Fi+, (Single FI5, etc.) [Problems to be solved by the invention] However, the alignment of ferroelectric liquid crystals has many alignment defects such as ZZW, which causes problems such as a decrease in contrast and difficulty in uniform driving. Therefore, a defect-free and well-oriented ferroelectric liquid crystal element like ZZW has been desired.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problem No. R1s R* represents a linear or branched alkyl group or alkoxy group) from 5 to 50 wt
% of the ferroelectric liquid crystal composition.

The present invention aims at making alignment defects such as ZZW less likely to occur even when using the rubbing method used to create the alignment of conventional nematic liquid crystals by adding a biphenyl compound represented by the above general formula (1). Can be done.

The biphenyl compound represented by the general formula H) has two linear or branched alkyl groups or alkoxy groups of Ri%R3 at both ends of biphenyl, and can be used as a ferroelectric liquid crystal composition. As long as there is no problem in compatibility with other constituent compounds, the compound itself may or may not exhibit optical activity.

Therefore, in general, R1 and R3 may be an alkyl group or an alkoxy group having about I to 12 carbon atoms.

In particular, this ferroelectric liquid crystal composition contains an optically active compound of 0.1
~80wt% and optically inactive compounds 20~99.9wt%
It is preferable that the biphenyl compound represented by the general formula (1) is an optically inactive biphenyl compound, whereby the physical properties of the ferroelectric liquid crystal composition can be easily set, and the desired properties can be obtained. A ferroelectric liquid crystal composition with special characteristics can be obtained.

In this case, the optically inactive compound is 20 to 99.9 wt% and the optically active compound is 0.1 to 80 wt%, even if the optically active compound is less than 1 wt%.
This is because even if it exceeds 0 wt%, it becomes difficult to form a liquid crystal composition that exhibits ferroelectric properties with desired characteristics, making it impractical.

Further, the optically inactive compound of such a ferroelectric liquid crystal composition is a compound of the general formula (+), and a compound of the general formula Rs e n
A compound represented by -COODR-(III) (in the formula, R3, R4, Rs, R- each represents a linear or branched alkyl group or an alkoxy group, and 0 represents 1 or 2), respectively (1 ) 5-50 wt%, (I
N) 5-50wt%, (III) 5-50wt%
By having such a composition, orientation defects such as ZZW are particularly hard to occur.

R of these compounds of general formula (11) and general formula (m)
An alkyl group or an alkoxy group represented by s, Ra, R, or Ro can also be used if there is no problem in compatibility with other compounds constituting the ferroelectric liquid crystal composition;
As with lbRs, it may be an alkyl group or an alkoxy group having about 1 to 12 carbon atoms.

FIG. 1 is a cross-sectional view of a ferroelectric liquid crystal electro-optical element driven by the present invention. Transparent conductive films (2a), (2b) and alignment control films (3a), (3b) are formed on the surfaces of two transparent substrates (1a), (1b), respectively. Conductive film (2a
) and (2b) are electrodes for applying an electric field to the salivary layer (4) held between the substrates, which constitute a scanning electrode group and a signal electrode group, respectively, and are used to generate an electro-optical response. It is made of Inn's, Snug, etc., and is formed in a predetermined pattern.

The alignment control films (3a) and (3b) horizontally align the liquid crystal, and typical examples include an organic polymer film,
In particular, it is preferable to form a polyimide polymer film and rub it in a certain direction with a cloth, but in addition, it is preferable to use a polyamide polymer film, a polyisidamide polymer film, a polyvaraxylylene film, etc., and rub it. An obliquely deposited film such as □ is also effective, and the orientation control film may be formed by directly rubbing the conductive films (2a) and (2b) without forming an overcoat film.

After performing such an alignment process, a spacer, for example,
Organic beads and alumina particles are sandwiched and the surrounding area is fixed with a sealant (5) to form a cell. At this time, the orientation control directions of the two substrates are made parallel to each other.

Thereafter, the ferroelectric liquid crystal composition is heated to the cholesteric phase or isotropic phase, and injected into the cell.1. : After that, seal it. Two polarizing plates (6a) and (6b) are arranged outside the cell so that the polarizing plates are orthogonal to each other and form a constant angle with the orientation control direction of the substrate. This angle varies depending on the liquid crystal material, operating temperature of the device, driving method, etc., and the angle that provides the best contrast characteristics should be selected. In some cases, the polarization axes of the two polarizing plates may be arranged with the polarization axes shifted from orthogonal. be.

A light source (7) is placed on the side of the substrate 1Ibl so that light is transmitted to the opposite side. In addition, when using a reflective type, what is necessary is just to provide a reflective plate on the outer side of a polarizing plate (6b).

FIG. 2 shows an example of the pattern of conductive films (2a) and (2b) 7, which are used in dot matrix display elements and the like. On one substrate, a horizontal striped scanning electrode group C
3 to Cn are patterned, and on the other substrate, vertically striped signal electrode groups S and ~Sm are patterned. Intersection islands of 92 sets of electrode groups, ~Amn, become pixels.

One of the scanning electrode groups Ci is selected by the method described below, and at that time, pixels ^i, ~Airn are written by signals applied to the signal electrode groups S, ~Sm, and then Ci ``l is written. By selecting and repeating this process, all pixels are written.

The ferroelectric liquid crystal composition used in the present invention contains 5 to 50 wt of the biphenyl compound represented by the above-mentioned general formula (1).
, %, and has a liquid crystal phase exhibiting bistability depending on the polarity of the i-field, specifically, a liquid crystal composition having a chiral smectic C phase (SmC' phase) can be used. Compositions can be used.

Compounds exhibiting optical activity other than the biphenyl compound used in the liquid crystal composition of the present invention include the following compounds.

In the following examples, Ro represents an optically active alkyl group or alkoxy group, R represents a linear or branched alkyl group or alkoxy group, and one compound has the same Ro,
Even if R is shown, they are not necessarily the same group.

R″″(Ba moxibustion coo-@)-R R(滲00(ParR1square4oo *R
+) and the compounds of general formula (III) that do not exhibit optical activity include the following compounds.

In the following examples, R represents a linear or branched alkyl group or an alkoxy group, and even if the same R is shown in one compound, they are not necessarily the same group.

Compounds in which part of the hydrogen atoms of these benzene rings, cyclohexane rings, etc. are substituted with halogens, cyano groups, methyl groups, etc. can also be used.

Further, in the ferroelectric liquid crystal composition used in the present invention, a liquid crystal having a smectic phase (SmA phase) in a temperature range higher than that of a liquid crystal phase exhibiting ferroelectricity is preferable from the viewpoint of symmetry of bistability. Isotropic phase (■ phase) or nematic phase (
Ne phase) or cholesteric phase (ch phase), S
When using a liquid crystal that changes directly to a ferroelectric liquid crystal phase such as SmC'' phase without going through the +t+A phase, two types of alignment states are obtained in which the direction of the liquid crystal molecular layer differs with respect to the direction of normal alignment control. If two types of orientation states coexist, it will lead to a decrease in contrast, so if two types of orientation states coexist,
When cooling from phase to ferroelectric liquid crystal phase such as SmC” phase,
It is necessary to take measures such as applying a DC electric field having a polarity in one direction to align the substrate in only one of two types of orientation states. In terms of stability of the device created in this way, between the first stable state and the second stable state, the stable state that matches the polarity of the electric field applied during cooling is more stable. leading to decreased bistability. On the other hand, in a liquid crystal with a 5ffl^ phase, there is only one direction of the liquid crystal molecular layer, and there is no need for means such as applying an electric field. good.

Further, it is more preferable for the liquid crystal used in the present invention to have a ch phase in a higher temperature range than a liquid crystal phase exhibiting ferroelectricity, from the viewpoint of alignment uniformity. Regarding the method for creating the alignment of this liquid crystal, an element with extremely good orientation can be created by using the method disclosed in Japanese Patent Application No. 59-274073. When using a liquid crystal that has a ch phase at a certain temperature, the length of the helical pitch in the ch phase pl is the substrate (1
The distance between a) and (1b) is at least 4 times the distance #(d). In addition, it is desirable to have an SmΔ phase between the ch phase and the SmC'' phase from the viewpoint of alignment uniformity.For such a liquid crystal composition, an optically active substance, a smectic liquid crystal compound, or a nematic liquid crystal compound is preferably used. - Non-liquid crystal additives may be added as necessary, and may be mixed appropriately within the scope of the present invention described above.Especially, in order to lengthen the pitch in the ch phase. It is effective to mix an optically active substance that produces a left helix and an optically active substance that produces a right helix depending on the magnitude of the force that produces the helix.

Typically, the length of the helical pitch in the ch phase changes with temperature. To obtain uniform orientation, use Flesteric-
It is necessary to satisfy the condition p>4d just above the smectic phase transition point.

However, if the temperature range that satisfies this condition is limited to the vicinity of the transition point, the helical structure will not unravel and the material will transition to a smectic phase if the rate of temperature drop is fast. In this case, since uniform orientation cannot be obtained, it is necessary to maintain the temperature at a temperature that satisfies p>4d until the helical structure is unwound, or to slow down the temperature drop rate. For this reason, the temperature range in which the helical pitch p is four times or more the distance between substrates d is 5°C below the cholesteric-smectic phase transition point.
It is preferable to cover the above range, and more preferably to cover the entire temperature range of the Ch phase.

Note that the Ch phase referred to herein also includes a Ne phase formed by a nematic liquid crystal that is made to have a specific pitch by adding an optically active substance to the nematic liquid crystal.

[Function] According to the present invention, the general formula (1) is contained in the ferroelectric liquid crystal composition.
By containing 5 to 50 wt% of the biphenyl compound, a ferroelectric liquid crystal electro-optical element is obtained which is unlikely to cause alignment defects like zZW even when alignment is controlled by rubbing method, although the reason is unknown. be able to.

[Example] Using a substrate on which polyimide was overcoated on the electrodes of a substrate with patterned striped electrodes and rubbed, the periphery was sealed with a sealing material so that the cell gap was 2 μm, and the inside was etc. A ferroelectric liquid crystal composition having a perfect cholesteric phase, a smectic A phase, and a chiral smectic C phase in this order was sealed.

Specific compositions of this example and comparative example are shown in Table 1. The values in Table 1 indicate wt% of each compound.

Examples with these examples! ~Example 8 is a composition containing a biphenyl compound, and Comparative Example 1 and Comparative Example 2 are compositions containing no biphenyl compound.

Table 1 Optically inactive compound (1) @ 10-II -1010510-
-01010910! OIn 5 10 - -@
-5-5-------- ■ -5-5-------- (II) @ 7 7212011 5 5 727
7■ 30 30 +5 17 30
30 30 30 30 30 (III) @
20 20 20 19 20 20 20 -
20 26o 55-25---55 ■ +0 10 16 14 10 14 16 -
10 24 Others ■ −−−−−−10−−− ■ −−−−−−−+5 − − ■ −−−−−−−20−− ■ 4444254444 @ 4444265444 Compounds used in Examples and Comparative Examples The molecular structure is shown below. In the formula, Cn represents a linear alkyl group or a linear alkylene group having n carbon atoms.

Chemical structure Abbreviation Optically inactive compound of general formula (+) 5 Optically inactive compound of general formula (IN) Optical inactive compound of general formula (In) cs-+oo te-C6■ Co(j,, ΣH Comparative Example 1 is a compound in which the biphenyl compound of Example 1 is completely replaced with phenylpyrimidine, and Comparative Example 2 is a compound in which the biphenyl compound of Example 1 is replaced with phenylpyrimidine. In Example 2, the biphenyl compound of Example 1 was replaced with a biphenyl compound having a different alkyl chain structure.In the case of Comparative Example 1.2 It's a big zZW
The alignment state is quite poor, and the contrast is low because light leaks from the ZZW defect in a cross-niffle state.

On the other hand, in the case of Example 1.2, no alignment defects such as zzW were observed, and it was found that an extremely good alignment state could be obtained.

Example 3 is an example in which the type and concentration of the biphenyl compound in Example 1 is kept almost the same, but the concentration of other optically inactive compounds is changed, and Example 4 is an example in which the type and concentration of the biphenyl compound in Example 2 is changed. This is an example in which the concentrations of the optically inactive compounds were kept the same, but the concentrations of the other optically inactive compounds were changed.

Examples 5 and 6 are examples in which the type and concentration of the biphenyl compound were the same as in Example 1, but the concentrations of the other optically inactive compounds and optically active compounds were changed.

Example 7 is an example in which the concentration of the biphenyl compound is reduced and phenylcyclohexane is added instead, and Example 8 is an example in which the ester compound of general formula (III) of Example 1 is replaced with another optically inactive compound. This is an example using .

In the liquid crystal electro-optical elements using any of the compositions of Examples 3 to 7, good alignment without ZzW was obtained as in Example 1.2.

Although the liquid crystal electro-optical element using the composition of Example 8 hardly produced ZZW, ZZW sometimes occurred in some of the devices, although it was very slight.

[Effects of the Invention] The present invention provides a liquid crystal electro-optical element using a composition to which 5 to 50 wt% of the biphenyl compound represented by the general formula (1) is added, thereby making it difficult for alignment defects such as zzW to occur. It has the advantage that orientation can be easily obtained, contrast reduction due to orientation defects can be prevented, and uniform driving can be achieved.

The present invention can be applied in various ways without detracting from the effects of the present invention, and can be applied in various fields including display elements and optical printers in the future.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic configuration of an electro-optical element driven by the present invention. FIG. 2 is a plan view of an example of an electrode pattern for driving the liquid crystal composition of the present invention. Ia, 1b: Transparent substrates 2a, 2b: Conductive films 3a, 3b: Alignment control film 4: Liquid crystal layers 6a, 6b: Polarizing plate Fig. 1 Fig. 2 Signal power supply group i3r Bz 53 ---- 3m.

Claims (3)

[Claims] (1) General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ( I
) (wherein R_1, R_2
represents a linear or branched alkyl group or alkoxy group) in an amount of 5 to 50 wt%. (2) Consists of 0.1 to 80 wt% of an optically active compound and 20 to 99.9 wt% of an optically inactive compound, and has the general formula (I
2. The ferroelectric liquid crystal composition according to claim 1, which contains an optically inactive biphenyl compound represented by: (3) The optically inactive compound is a compound represented by the general formula (I) and the general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ The compound represented by (II) and the general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (III ) (wherein R_3, R_4, R_5, R_6 each represent a linear or branched alkyl group or alkoxy group, and n represents 1 or 2), respectively (I)5
~50wt%, (II) 5-50wt%, (III) 5-5
The ferroelectric liquid crystal composition according to claim 2, containing 0 wt%.