JPH04279695A - Ferroelectric liquid crystal composition - Google Patents

Abstract

PURPOSE:To provide the subject new composition containing a specific matrix liquid crystal exhibiting a smectic C phase and a chiral dopant composed of an optically active compound, having minimized temperature-dependency of response speed and useful as a material for liquid crystal display element. CONSTITUTION:The objective composition contains (A) preferably 5-50wt.% of a matrix liquid crystal exhibiting smectic C phase and containing (i) a compound expressed by formula I (R<1> and R<2> are 4-12C alkyl or alkoxy) and (ii) a compound expressed by formula II (R<3> and R<4> are 4-12C alkyl or alkoxy) and (B) preferably 10-80wt.% of a chiral dopant composed of an optically active compound.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a novel ferroelectric liquid crystal composition useful as an electro-optical display material, and in particular, the temperature dependence of its response speed is extremely small compared to conventional liquid crystal materials. The present invention provides a ferroelectric liquid crystal composition useful as a material for liquid crystal display elements.

0002

[Prior Art] Liquid crystal display devices that are currently widely used are of the twisted nematic (TN) type or super twisted nematic (STN) type, which mainly utilize nematic liquid crystals. However, it has the major drawback that its response speed is much slower than that of light-emitting display systems such as CRTs, and this has severely limited its application. Although other liquid crystal display systems are being studied from various angles, the reality is that little improvement has been made in response characteristics.

However, recently discovered liquid crystal display elements using ferroelectric smectic liquid crystals have become capable of responding more than 100 times faster than conventional TN type display elements. Furthermore, it has been revealed that because it has bistable properties, it can retain its display even when the power is turned off. For this reason, it has great potential for use in large-screen high-resolution displays, flat-screen televisions, optical shutters, printer heads, etc., and active research and development is currently being conducted to put it into practical use.

The liquid crystal phase of ferroelectric liquid crystal belongs to the tilted chiral smectic phase, and among these, the chiral smectic C (hereinafter abbreviated as Sc*) phase, which has the lowest viscosity, is practically desirable. Many liquid crystal compounds exhibiting the Sc* phase (hereinafter referred to as Sc* compounds) have already been synthesized and studied, but none with sufficient properties to be used as optical switching elements for ferroelectric liquid crystal displays is yet known. It has not been done. Therefore, by mixing with other liquid crystal compounds, Sc*
It is used as a liquid crystal composition exhibiting a phase (hereinafter referred to as Sc* liquid crystal composition). Studies on such Sc* liquid crystal compositions are being actively conducted, and currently, a chiral dopant consisting of an optically active compound is added to a base liquid crystal exhibiting a non-chiral smectic C (hereinafter abbreviated as Sc) phase. The most common method is to As a result, it has become possible to obtain Sc* liquid crystal compositions that have characteristics such as high-speed response, good alignment, and a wide operating temperature range.

[0005]

[Problem to be solved by the invention] However, the above S
Most of the c* liquid crystal compositions exhibit a steep change in the temperature dependence of response speed, which has been a major obstacle in the production of actual devices. Therefore, a liquid crystal composition whose response speed is less dependent on temperature has been desired.

For example, Japanese Patent Application Laid-Open No. 2-38485, Japanese Patent Application Publication No. 2-38486, and Japanese Patent Application Publication No. 2-3848
Although the Sc* liquid crystal composition described in Publication No. 7 is known,
The response speeds of these liquid crystal compositions at 25° C. and 40° C. differed by 2.5 to 3 times, and the temperature dependence of the response speeds was extremely large.

[0007] The problem to be solved by the present invention is to provide a ferroelectric liquid crystal composition that has high-speed response, good alignment, a wide operating temperature range, and has a small temperature dependence of its response speed. There is a particular thing.

[0008]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides the following ferroelectric liquid crystal composition. That is, (1) general formula (I)

[0009]

[Chemical formula 3]

(In the formula, R1 and R2 each independently represent a straight-chain or branched alkyl group or alkoxyl group having 4 to 12 carbon atoms, but preferably R1 is a straight-chain or branched alkyl group having 4 to 12 carbon atoms. Represents a chain alkoxyl group, R
2 represents a linear alkyl group having 4 to 12 carbon atoms. ) and general formula (II)

0011
]

[C4]

(In the formula, R3 and R4 each independently represent a linear or branched alkyl group or alkoxyl group having 4 to 12 carbon atoms, but preferably R3, R4
One of these represents a linear alkoxyl group having 4 to 12 carbon atoms, and the other represents a linear alkyl group having 4 to 12 carbon atoms. ) A ferroelectric liquid crystal composition is provided in which a chiral dopant consisting of (2) an optically active compound is added to a base liquid crystal that contains a compound represented by (2) and exhibits an Sc phase, and more preferably has an Sc phase. 5 to 50% by weight of the compound represented by general formula (I) in the parent liquid crystal shown.
, and the compound represented by general formula (II) at 10 to 80
% by weight of a ferroelectric liquid crystal composition.

The compound represented by the general formula (I) is a compound that exhibits an Sc phase over a relatively wide temperature range, especially up to a high temperature range, and has low viscosity as a tricyclic compound, so it does not exhibit an Sc phase. This compound is suitable for preparing the parent liquid crystal shown in FIG.

The Sc* liquid crystal composition according to the present invention contains the compound represented by the general formula (I) as a main component of the parent liquid crystal, but if the content is less than 5% by weight, the effect will be low. If it exceeds 50% by weight, the viscosity of the base liquid crystal increases and the response speed becomes slow, so it is preferably contained in the base liquid crystal in an amount of 5 to 50% by weight. Examples of compounds represented by general formula (I) are shown in Table 1.

[0015]

[Table 1]

(In the table, Cr represents the crystalline phase, I represents the isotropic liquid phase, N represents the nematic phase, SA represents the smectic A phase, Sc represents the smectic C phase, SB represents the smectic B phase, and S3 represents the smectic A phase. , S4 each represent a smectic phase of unknown attribution.) On the other hand, the compound of general formula (II) is a compound that shows or does not show an Sc phase in a very low temperature range, but has a very low viscosity and a high speed This compound is suitable for preparing parent liquid crystals.

The Sc* liquid crystal composition according to the present invention contains the compound represented by the general formula (II) as a main component of the parent liquid crystal, but if the content is less than 10% by weight, the effect will be low. , if it exceeds 80% by weight, the S of the parent liquid crystal
Since the temperature range of the c phase becomes too low, 1
The content is preferably 0 to 80% by weight. General formula (II
Examples of compounds represented by ) are shown in Table 2.

[0018]

[Table 2]

(In the table, Cr represents a crystalline phase, I represents an isotropic liquid phase, N represents a nematic phase, SA represents a smectic A phase, and Sc represents a smectic C phase.) Sc* liquid crystal of the present invention A feature of the composition is that the temperature dependence of its response speed is very small.

[0020] Here, the base liquid crystal (A
) was prepared. This parent liquid crystal (A) is Sc up to 42°C.
The phase shows an SA phase up to 51.5°C and an N phase up to 72°C.

[0021] The parent liquid crystal (A) is

[0022]

[C5]

It consists of the following. (The composition ratio represents weight %. The same applies hereinafter.) 98% of this base liquid crystal (A) and the formula

[0024]

[C6]

The Sc* liquid crystal composition prepared from 2% of the optically active lactone derivative represented by
*Indicates phase. This composition was filled into a cell with a thickness of about 2 μm, and the response speed when an electric field strength of 10 Vp-p/μm was applied was measured. The results are shown in Table 3.

[0026]

[Table 3]

As is clear from this result, when the temperature is 40
Even when the temperature changes from °C to 25 °C, the response speed changes by only about 15%, from 76 μs to 88 μs, which is an extremely small change compared to conventional ferroelectric liquid crystal materials. I can say that. This extremely small temperature dependence of the response speed can be said to be an excellent feature of the liquid crystal composition of the present invention. Therefore, the ferroelectric liquid crystal composition of the present invention is very suitable for producing devices as actual display materials.

[0028]

[Examples] The present invention will be specifically explained below with reference to Examples, but the gist and scope of the present invention are not limited by these Examples.

In this example, the phase transition temperature was measured using a polarizing microscope equipped with a temperature control stage and a differential scanning calorimeter (DSC). Further, all percentages in the composition represent weight percentages. (Example 1) Base liquid crystal (A) 98% and formula

[0030]

[C7]

(2R,4R)-2-[4-(
3-fluoro-4-octyloxybenzoyloxy)
An Sc* liquid crystal composition consisting of 2% phenyl]-4-decanolide was prepared. This Sc* liquid crystal composition exhibited an Sc* phase up to 44.5°C, an SA phase up to 50°C, and an N* phase up to 74°C. Moreover, its melting point was not clear.

Next, using this liquid crystal composition, a liquid crystal cell was prepared according to the following procedure. First, an ITO vapor-deposited glass plate (electrode area: 70 mm2) commercially available from EHC Company was washed and dried. A polyimide forming solution "PIQ" (manufactured by Hitachi Chemical Co., Ltd.) was applied to this using a spinner coater to form a polyimide film (substrate A).

Similarly, a polyimide film containing a spacer was formed using the above polyimide forming solution mixed with a glass fiber spacer (substrate B).
. After rubbing substrates A and B with nylon cloth, apply a thermosetting epoxy adhesive to one substrate, and stack substrates A and B so that the rubbing directions are parallel and opposite to each other. Combine and leave at 80℃ for 3 hours.
It was cured and cells were created.

The above-mentioned liquid crystal composition was heated to form an isotropic liquid phase and then injected into the thus prepared cell.
Slow cooling was performed at a rate of 1° C. per minute to orient the N* phase, SA phase, and then Sc* phase to obtain a liquid crystal display element. The thickness of this cell was measured and found to be 2.0 μm.

A rectangular wave with an electric field strength of 10 Vp-p/μm was applied to this cell, and its electro-optical response speed, spontaneous polarization, and tilt angle were measured.

[0036]

[Table 4]

[0037] Contrast was good. From this result, it was found that the Sc* liquid crystal composition according to the present invention was
The difference in response time at 0.degree. C. was only about 15%, indicating that the temperature dependence of the response speed of the liquid crystal composition of the present invention is very small. (Example 2) Chiral dopant consisting of 80% base liquid crystal (A) and the following composition

[0038]

[Chemical formula 8]

A 20% Sc* liquid crystal composition was prepared. This Sc* liquid crystal composition maintains the Sc* phase up to 44°C.
The SA phase was shown up to 0.5°C, and the N* phase was shown up to 71.5°C. A liquid crystal display element was prepared in exactly the same manner as in Example 1, and its electro-optic response speed was measured.
The response speed is 34 μs at 25°C and 2 μs at 40°C.
The response time was 4 μsec, which confirmed a high-speed response with very little temperature dependence.

[0040]

[Effect of the invention] The ferroelectric liquid crystal composition according to the present invention has
It exhibits the Sc* phase over a wide temperature range, and is capable of a high-speed response of 100 microseconds or less, and the temperature dependence of the response speed is extremely small. Therefore, the ferroelectric liquid crystal composition of the present invention is extremely useful as a material for optical switching elements for display.

Claims (5)

[Claims] Claim 1 (1) General formula (I) [Formula 1] (wherein, R1 and R2 each independently have a carbon atom number of 4
~12 linear or branched alkyl groups or alkoxyl groups. ), and compounds represented by the general formula (
II) [Formula 2] (wherein, R3 and R4 each independently have a carbon atom number of 4
~12 linear or branched alkyl groups or alkoxyl groups. 1. A ferroelectric liquid crystal composition comprising: a host liquid crystal exhibiting a smectic C (Sc) phase containing a compound represented by (2) a chiral dopant consisting of an optically active compound. 2. The ferroelectric liquid crystal composition according to claim 1, wherein R1 is a linear alkoxyl group having 4 to 12 carbon atoms, and R2 is a linear alkyl group having 4 to 12 carbon atoms. thing. [Claim 3] One of R3 or R4 has 4 or more carbon atoms.
3. The ferroelectric liquid crystal composition according to claim 2, wherein one of the 12 linear alkoxyl groups is a linear alkyl group having 4 to 12 carbon atoms. 4. 5 to 50% by weight of a compound represented by general formula (I) and 10 to 80% by weight of a compound represented by general formula (II) in a host liquid crystal exhibiting a smectic C (Sc) phase.
2. The ferroelectric liquid crystal composition according to claim 1, wherein the ferroelectric liquid crystal composition contains % by weight. 5. A liquid crystal display element comprising the ferroelectric liquid crystal composition according to claim 1, 2, 3, or 4 as a constituent element.