JPH08120273A - Nematic liquid crystal composition - Google Patents

Abstract

PURPOSE: To obtain a nematic liq. crystal compsn. which exhibits liq. crystallizability in a wide temp. range and has high response speed and voltage retention by incorporating two specific compds. into the same. CONSTITUTION: The compsn. having the properties of inducing and extending a wide nematic phase and an excellent compatibility with other liq. crystal compsns. is prepd. by combining a compd. of formula I [X<11> to X<17> are each H or D provided at least one of them is D] with a compd. of formula II (X<21> to X<27> are each H or D provided at least one of them is D) under such conditions that all of X<11> to X<14> or all of X<15> to X<17> are H in the former compd., that all of X<21> to X<24> or all of X<25> to X<27> are H in the latter compd., and that the sum of the former and latter compds. accounts for 20-100wt.% of the compsn.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a nematic liquid crystal composition useful as an electro-optical display material.

[0002]

2. Description of the Related Art TN-LCD is a typical liquid crystal display device.
(Twisted nematic liquid crystal display element)
Used in clocks, calculators, electronic organizers, pocket computers, word processors, personal computers, etc. On the other hand, the amount of information displayed on one screen is increasing with the increase in processing information of OA devices.
ffer) et al. [SID '85 Digest, p. 120 (1985)] or Kinugawa et al. [SID '86 Digest, p. 122 (1986)]
STN-LCD (Super Twisted Nematic Liquid Crystal Display Device) has been developed and is beginning to be widely used in displays for high information processing such as word processors and personal computers.

Further, because of its excellent display quality, an active matrix type liquid crystal display device has been put on the market as an effective one for application fields of displays such as liquid crystal televisions, projector displays and computers. The active matrix display method uses a TFT for each pixel
A switching element such as (thin film transistor) or MIM (metal insulator metal) is used, and it is important in this method that leakage current is small, that is, high voltage holding ratio. (Hereinafter, these active matrix display type liquid crystal display elements are collectively referred to as TFT-LCD.) Therefore, in order to support such a display element, a new liquid crystal compound or liquid crystal composition, for example, a special publication Publication No. 5-501735, Special Publication 5
The proposals such as -500681 publication and Japanese Patent Publication No. 5-500682 publication have been made. However, these references do not describe the properties of the compounds according to the invention.

[0004]

The TN-LCD and STN-LCD have problems such as chemical stability of liquid crystal materials, operating temperature and response characteristics of liquid crystal display devices.

For example, a high time division number STN-LCD is used as a portable display, and has a wide operating temperature and is required to have high-speed response. However, a liquid crystal material having a wide operating temperature makes it difficult to obtain good response characteristics due to an increase in viscosity. In addition, when used in an STN-LCD that uses a backlight for the purpose of compensating for dark image quality, chemical stability such as heat resistance and light resistance is newly required.

In addition to these required characteristics, particularly in the active matrix system, it is important that the leakage current is small and the voltage holding ratio is high in order to obtain uniform and high contrast. In order to obtain such characteristics,
For example, the compound of the following general formula (2-a) has been used.

[0007]

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(In the formula, R represents an alkyl group,

[0009]

[Chemical 4]

Is a deuterium atom (D) -free 1,4-
Represents a cyclohexylene group. The same applies below. However, even if this compound is used, it is problematic to maintain both nematic liquid crystallinity in a wide temperature range, especially at low temperature, and to sufficiently reduce the high-speed response required for the active matrix system. was there.

The problem to be solved by the present invention is to solve the above problems, and to provide a liquid crystal composition which exhibits liquid crystallinity in a wider temperature range, has a fast response and has a sufficiently high voltage holding ratio. To do.

[0012]

In order to solve the above-mentioned problems, the present invention has the general formula (I)

[0013]

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(In the formula, X ^{11 to} X ¹⁷ each independently represent a hydrogen atom (H) or a deuterium atom (D), but at least one represents a deuterium atom (D)). Compounds and general formula (II)

[0015]

[Chemical 6]

(In the formula, X ^{21 to} X ²⁷ each independently represent a hydrogen atom (H) or a deuterium atom (D), but at least one represents a deuterium atom (D)). Provided is a nematic liquid crystal composition containing a compound.

In the general formula (I), X¹¹~ X¹⁴
At least one of the compounds represents a deuterium atom (D).
It is preferable to contain X in the general formula (II).^{twenty one}
~ X ^{twenty four}At least one of the formulas represents a deuterium atom (D)
It is preferable to contain a compound.

More specifically, in the general formula (I), X
It is preferable that all of ^{11 to} X ¹⁴ or X ^{15 to} X ¹⁷ represent a hydrogen atom (H), and in the general formula (II), X ²¹ to
It is preferred that X ²⁴ or X ^{25 to} X ²⁷ all represent a hydrogen atom (H).

In the liquid crystal composition of the present invention, the total content of the compounds represented by the general formulas (I) and (II) is preferably in the range of 20 to 100% by weight. The phase transition temperatures of the compounds represented by the general formulas (I) and (II) according to the present invention are shown in Table 1 below. In Table 1 below, m.
p. represents the temperature at which the crystal phase transitions to the liquid crystal phase or the isotropic liquid phase, and cp. represents the temperature at which the liquid crystal phase transitions to the isotropic liquid phase. In addition, each liquid crystal compound,
Impurities were removed by a method such as distillation, column purification, and recrystallization, and a sufficiently purified product was used.

[0020]

[Table 1]

The liquid crystal composition of the present invention is characterized in that the compound represented by the general formula (I) and the compound represented by the general formula (II) are used in combination as an essential component.
The liquid crystal composition thus obtained has a property of inducing and expanding a wider nematic phase, and has excellent compatibility with other liquid crystal compounds, for example, a liquid crystal composition used in combination with a liquid crystal compound having a smectic phase. Thus, the nematic liquid crystallinity can be maintained for a long period of time even when stored at low temperature. In particular, regarding the compatibility, as compared with the compound of the general formula (2-a), whether the hydrogen atom (H) of the 1,4-cyclohexylene group is replaced with a deuterium atom (D),
Alternatively, it was revealed from the examples described later that a particular effect is exhibited by a slight difference in whether the side chain group is an alkenyl group or an alkyl group.

The compounds represented by the general formulas (I) and (II) are elastic constant ratios (K ₃₃ /
K ₁₁ ) can be increased by the side chain group, and thus a nematic liquid crystal composition having an elastic constant ratio depending on the application can be prepared. Further, this nematic liquid crystal composition has a composition of about 20 c. p. A liquid crystal material having a low viscosity and having a high-speed response in a wide temperature range can be easily obtained by combining it with another compound. Therefore, the nematic liquid crystal composition of the present invention exhibits useful properties for preparing a nematic liquid crystal composition that can be used in a wide temperature range without impairing the excellent properties of other liquid crystal compounds or liquid crystal compositions. .

The nematic liquid crystal composition of the present invention was subjected to a heating acceleration test and an ultraviolet irradiation acceleration test shown in Examples described later, and it was found that the nematic liquid crystal composition had a high voltage holding ratio of 98% or more even after each acceleration test and a chemical reaction. It was also confirmed that it was very stable and had a high resistance value.

The second characteristic of the liquid crystal composition of the present invention is that one or more hydrogen atoms (H) of two 1,4-cyclohexylene groups in the compounds represented by the general formulas (I) and (II). ) Is substituted with a deuterium atom (D).
Such a liquid crystal composition has a property of stabilizing a nematic phase at a low temperature, and in particular, can retain the nematic liquid crystallinity for a longer period even when stored at a low temperature. The present inventors have clarified the effect of a compound having a cyclohexane ring substituted with a deuterium atom in Japanese Patent Application Nos. 5-104144 and 5-182734. Further, the compounds represented by the general formulas (I) and (II) having the above-mentioned deuterium atoms have elastic constants and ratios thereof which are significant depending on the position of the substituted deuterium atom, or an advantageous threshold value. The voltage is shown, and the electro-optical characteristics according to the application can be easily made.

The liquid crystal composition of the present invention has the general formulas (I) and (I
In addition to the compound I), in order to improve other properties of the liquid crystal composition, a normal nematic liquid crystal, a smectic liquid crystal, a cholesteric liquid crystal or the like recognized as a liquid crystal compound may be contained.

As described above, the nematic liquid crystal composition of the present invention is a liquid crystal composition which exhibits liquid crystallinity in a wider temperature range, has a fast response, and has a sufficiently high voltage holding ratio, and has no flicker. ST that does not occur and has excellent contrast
It was confirmed to be useful for liquid crystal display devices such as N-LCD and TFT-LCD.

[0027]

The present invention will be described in detail below with reference to examples.
The present invention is not limited to these examples. In the examples, the meanings of the symbols of the measured characteristics are as follows.

T _NI : Nematic phase-isotropic liquid phase transition temperature (° C.) T → _N : Crystal phase or smectic phase-nematic phase transition temperature (° C.) V _th : TN-LCD having a liquid crystal layer thickness d of 6 μm Threshold voltage (V) Δε: Dielectric anisotropy Δn: Birefringence η: Viscosity at 20 ° C. (cp) τr = τd: Light is transmitted when voltage is applied from the state where no voltage is applied. The response time (msec) in which the rise time τr until reaching the state becomes equal to the fall time τd until the light stops transmitting after the voltage is applied (msec). Put in ampoule tube, vacuum deaeration, nitrogen substitution treatment and sealing,
The test was conducted at 180 ° C. for 1 hour for heating promotion test and for 10 hours for ultraviolet irradiation promotion test “SUNTEST” (manufactured by Original Hanau). The specific resistance and voltage holding ratio of the liquid crystal composition were measured before and after the accelerated test.

(Example 1)

[0030]

[Chemical 7]

A nematic liquid crystal composition (3-1) consisting of
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 83.9 ° C. T → _N : +23. ° C V _th : 1.63 V Δε: 8.7 Δn: 0.085 η: 21.0 c. p τr = τd: 33.5 msec Specific resistance before test: 7.2 × 10 ¹³ Ω c
m Specific resistance after accelerated heating test: 4.3 × 10 ¹³ Ω c
m Specific resistance after UV irradiation acceleration test: 4.4 × 10 ¹³ Ω c
m Voltage holding ratio before test: 98.8% (Measuring temperature 80 ℃) Voltage holding ratio after heating acceleration test: 98.0% (Measuring temperature 80 ℃) Voltage holding ratio after UV irradiation acceleration test: 98.2% ( A measurement temperature of 80 ° C.) When an active matrix liquid crystal display device using the nematic liquid crystal composition (3-1) as a constituent material was produced, it was confirmed that the leakage current was small and flicker did not occur.

The nematic liquid crystal composition (3-1)
A liquid crystal composition was prepared by adding a chiral substance "S-811" (manufactured by Merck & Co., Inc.) to. On the other hand, an organic film of "SAN EVER 150" (manufactured by Nissan Kagaku Co., Ltd.) is rubbed on the opposing flat transparent electrodes to form an alignment film, and STN-LCD with a twist angle of 220 degrees is formed.
A display cell was produced. The liquid crystal composition was injected into this cell to form a liquid crystal display device, and the display characteristics were measured.
As a result, the threshold voltage is low, high time division characteristics are excellent,
ST with improved display screen flickering and crosstalk
A liquid crystal display device having N-LCD display characteristics was obtained.

(Comparative Example 1)

[0034]

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A nematic liquid crystal composition (3-2) consisting of
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 86.0 ° C. T → _N : +35. C. V _th : 1.67 V Δε: 8.7 Δn: 0.085 η: 21.0 c. p τr = τd: 34.6 msec From the above, the liquid crystal composition (3-1) of the present invention has a nematic phase at a wider temperature than the liquid crystal composition (3-2), It is clear that the expansion of the nematic phase is large especially on the low temperature side.

(Comparative Example 2)

[0037]

[Chemical 9]

A nematic liquid crystal composition (3-3) consisting of
Was prepared and various properties of this composition were measured. The result is T
_NI was 89.9 ℃, but T → _N is 59 ℃.
The nematic phase transition temperature was reached, and the device could not be operated at room temperature, and _Vth , Δε, Δn, η, and τr = τd could not be measured.

From the above, the liquid crystal composition (3-
It is clear that 1) has a nematic phase at a wider temperature than the liquid crystal composition (3-3), and that the nematic phase expands particularly at low temperatures. It is clear that this shows a particular effect due to the slight difference in the alkenyl group.

(Comparative Example 3)

[0041]

[Chemical 10]

A nematic liquid crystal composition consisting of (3-4)
Was prepared and various properties of this composition were measured. The result is T
_{Although NI} was 65.4 ° C., T → _N became a crystal phase-nematic phase transition temperature of 58.5 ° C., so that it could not be operated at room temperature, and V _th , Δε, Δn, η, τr = Τd was not measured.

From the above, the liquid crystal composition (3-
It is clear that 1) has a nematic phase at a wider temperature than that of the liquid crystal composition (3-4), and the expansion of the nematic phase is particularly large on the low temperature side. This is an effect obtained by combining the compound of the general formula (I) and the compound of the general formula (II), and shows that it is possible to prepare a nematic liquid crystal composition that can be driven at a wide temperature.
Thus, whether the hydrogen atom (H) of the 1,4-cyclohexylene group is replaced by a deuterium atom (D),
Alternatively, it is clear that a particular effect is exhibited by a slight difference in whether the side chain group is an alkenyl group or an alkyl group.

[0044]

The nematic liquid crystal composition of the present invention exhibits a nematic phase in a wider temperature range and has a high response speed,
It has a high voltage holding ratio and high chemical stability. Therefore, the liquid crystal display device using this can improve the flicker of the display screen and the crosstalk phenomenon, and has good drive characteristics and display characteristics in the TN-LCD, STN-LCD or the active matrix method with a large amount of information. Is obtained.

Claims (4)

[Claims] 1. A compound represented by the general formula (I): (In the formula, X ^{11 to} X ¹⁷ are each independently a hydrogen atom (H).
Or represents a deuterium atom (D), but at least one represents a deuterium atom (D). ) And a compound represented by the general formula (II): (In the formula, X ^{21 to} X ²⁷ are each independently a hydrogen atom (H).
Or represents a deuterium atom (D), but at least one represents a deuterium atom (D). ) A nematic liquid crystal composition comprising a compound represented by the formula: 2. The nematic liquid crystal composition according to claim 1, wherein X ^{11 to} X ¹⁴ or X ^{15 to} X ¹⁷ in the general formula (I) each represent a hydrogen atom (H). 3. The nematic liquid crystal composition according to claim 1, wherein X ^{21 to} X ²⁴ or X ^{25 to} X ²⁷ in the general formula (II) each represent a hydrogen atom (H). 4. The nematic liquid crystal according to claim 1, 2 or 3, wherein the total content of the compounds represented by the general formulas (I) and (II) is in the range of 20 to 100% by weight. Composition.