JPH06108054A - Nematic liquid crystal composition and liquid crystal display device using the same - Google Patents

Abstract

(57) [Summary] [Structure] General Formula (I) (R ¹ : C ₂ -C ₇ alkyl, alkenyl, 1, m,
n: 0, 1, X ¹ : H, F) and a compound represented by the general formula (II) (R ^2: alkyl C ₂ -C _7, alkenyl, C _j H _{2j + 1} -
_{O-C k H 2k -,} j: 1~3, k: 2~5 nematic liquid crystal composition containing the compound represented by) and a liquid crystal display device using the same. The nematic liquid crystal composition of the present invention has a low threshold voltage, a high response speed, and a high chemical stability. Therefore, a liquid crystal display device using this is
It has a small change in driving voltage over a wide temperature range and high-speed response, and the flicker and crosstalk phenomenon of the display screen are improved by reducing the dielectric anisotropy. Display characteristics are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nematic liquid crystal composition useful as an electro-optical display material and a liquid crystal display device using the nematic liquid crystal composition.

[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, in recent years, with the increase in processing information of OA equipment,
The amount of information displayed on one screen is increasing, and the conventional TN-L
In terms of display quality such as contrast and viewing angle for CD,
In particular, it has become impossible to meet the demand for high time division driving of word processors, personal computers, and the like.

In such a situation, Scheffer (Sche
FER) et al. [SID '85 Digest, p. 120 (1985)] or Kinugawa et al. [SID '86 Digest, p. 122 (1986)], STN (Super Twisted Nematic) -L
CD has been developed and has begun to spread widely in displays for high information processing such as word processors and personal computers. In order to deal with such a display device, new liquid crystal compounds or liquid crystal compositions have been proposed at present.

[0004]

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

For example, an STN-LCD having a large amount of information such as a word processor and a personal computer is required to have good driving characteristics with a high number of time divisions. Have a big impact.
One way to reduce this is

[0006]

[Equation 1]

(Wherein V _th is a threshold voltage, k is a proportional constant, K is an elastic constant, and Δε is a dielectric anisotropy). A method of reducing a driving voltage by using a material is known. However, since most of such liquid crystal materials increase the viscosity of the liquid crystal material, it is difficult to obtain a good response characteristic, or the capacitance component of each pixel is increased, so that display is possible. However, there is a problem in that the driving frequency range is narrowed and a crosstalk phenomenon is caused thereby.

On the other hand, in the case of a conventional liquid crystal material which can be driven at a low voltage, it is generally known that the prepared resistance value after the initial or accelerated test is low. Such a low resistance value of the liquid crystal material is not preferable because it causes a flicker of the display screen and a decrease in contrast due to an increase in the number of time divisions.

Further, in order to compensate for the dark image quality due to the increase in the amount of information, it is common to use a backlight as an auxiliary light source in STN-LCD. For this reason, liquid crystal materials used for backlight STN-LCDs are required to have new chemical stability such as heat resistance and light resistance.

The problem to be solved by the present invention is TN-LCD.
A liquid crystal composition having a small absolute value of both dielectric anisotropy and elastic constant, a low threshold voltage, a high response speed, and a high chemical stability as a liquid crystal material for STN-LCD In particular, another object of the present invention is to provide a liquid crystal display device using this liquid crystal composition.

[0011]

In order to solve the above problems, the present invention provides, as a first liquid crystal composition, (1) general formula (I)

[0012]

[Chemical 4]

(In the formula, R ¹ represents a linear alkyl group or alkenyl group having 2 to 7 carbon atoms, l, m and n each independently represent 0 or 1, and X ¹ represents H or F. Provided that when m is 0, n is 0.) and (2) the general formula (II)

[0014]

[Chemical 5]

(In the formula, R ² is a linear alkyl group having 2 to 7 carbon atoms, an alkenyl group or C _j H _{2j + 1} -O-C _k H _2k-.
, J represents an integer of 1 to 3, and k represents an integer of 2 to 5. And a nematic liquid crystal composition containing a compound represented by the formula (1).

As the second liquid crystal composition of the present invention,
(1) The compound represented by the general formula (II) and (2) the general formulas (III) to (XII).

[0017]

[Chemical 6]

(In the formula, R ³ is a linear alkyl group having 2 to 7 carbon atoms, an alkenyl group or C _p H _{2p + 1} -O-C _q H _2q-.
, P represents an integer of 1 to 3, q represents an integer of 2 to 5, R ⁴ represents a linear alkyl group having 2 to 7 carbon atoms or C _s H _{2s + 1} -O-C _t. H _2t −, s represents an integer of 1 to 3, and t represents an integer of 2 to 5. And a nematic liquid crystal composition comprising a compound selected from the group consisting of compounds represented by

Further, as the third liquid crystal composition of the present invention,
(1) a compound represented by the general formula (I), (2) a compound represented by the general formula (II), and (3) a compound represented by the general formula (III) to (XII). There is provided a nematic liquid crystal composition containing a compound described below.

The present invention also provides a twisted nematic or super nematic liquid crystal using the above nematic liquid crystal composition.
Provided is a twisted nematic liquid crystal display device.

Representative examples (Nos. 1 to 6) of the compounds represented by the general formula (I) according to the present invention and their phase transition temperatures are shown in Table 1 below, and the compounds represented by the general formula (II) are shown in Table 1. Examples (Nos. 7 and 8) and the phase transition temperatures thereof are shown in Table 2 below, and also in general formulas (III) to (XI).
Examples of typical compounds represented by I) (No. 9)
~ 25) and their phase transition temperatures are shown in Table 3 below.

In the table below, mp is the temperature at which the crystal phase changes to the liquid crystal phase or the isotropic liquid phase, and cp is the temperature at which the liquid crystal phase changes to the isotropic liquid phase. Respectively.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

The compound itself represented by the general formula (II) is disclosed in JP-A-60-120858, and a liquid crystal material using the same is disclosed in JP-A-61-289. It has been known. However, the driving voltage of the composition cannot be sufficiently lowered only by the compound of the general formula (II), and since Δn is large, there is a limitation in application to a liquid crystal display device. When the compound of general formula (II) and the compound of formula (a) are used in combination,
As shown in Comparative Examples described later, there are problems that the specific resistance value of the liquid crystal material is significantly reduced, the liquid crystal material itself turns yellow, and a chemical reaction occurs.

The inventors of the present invention have made extensive studies in order to solve such problems, and as a result, the compound represented by the general formula (II), the general formula (I) and / or the general formula (III) to
It has been found that an excellent nematic liquid crystal composition capable of solving the above problems can be obtained by using in combination with a compound selected from the group consisting of compounds represented by (XII).

The liquid crystal composition of the present invention preferably contains the compound of the general formula (II) in the range of 5 to 35% by weight, particularly preferably 5 to 30% by weight.

One of the characteristics of the first and third liquid crystal compositions of the present invention is that the liquid crystal composition contains the compound represented by the general formula (I), and has the effect of reducing the driving voltage without deteriorating the response speed. Is obtained. In addition, the general formula (I)
The compound is also useful for adjusting the elastic constant of a liquid crystal material that plays an important role in the display characteristics of STN-LCD, and a nematic liquid crystal composition exhibiting an elastic constant ratio K ₃₃ / K ₁₁ depending on the application can be obtained. It can be prepared.

It is considered that such an effect is due to one terminal group of the compound represented by the general formula (I) being an alkyl group or an alkenyl group and the other being a polar group of -OCN. More specifically, the dielectric anisotropy of the compound of the general formula (I) is very small, and the elastic constant ratio K ₃₃ / K ₁₁
It is considered that the absolute value of the elastic constant is very small regardless of the magnitude of.

The first and third liquid crystal compositions of the present invention preferably contain the compound of formula (I) in the range of 5 to 75% by weight, particularly preferably 10 to 50% by weight.

The following experiments were conducted in order to clarify the effects of the compounds of the general formula (I) in the first and third liquid crystal compositions of the present invention. First, a mixed liquid crystal (A) shown below was prepared as a host liquid crystal composed of a currently widely used compound.

[0034]

[Chemical 7]

(In the above, "%" means "% by weight".) Next, 70% by weight of the mixed liquid crystal (A) and No. 1 shown in Table 1 above. A liquid crystal composition N comprising 30% by weight of the compound 1
o.26 was prepared. In addition, for comparison, No. Formula (a) having a similar structure of the compound of 1 and having a polar group of -CN instead of -OCN.

[0036]

[Chemical 8]

A liquid crystal composition (b) was prepared in the same manner using the compound (1). These composition Nos. 26, (b)
And the mixed liquid crystal (A), nematic phase-isotropic liquid phase transition temperature (T _NI ), dielectric anisotropy (Δε), birefringence (Δn), elastic constants (K ₁₁ , K ₃₃ ), Cell thickness of 8 μm
The threshold voltage (V _th ) when the TN-LCD was constructed, and the viscosity (η) which has an important influence on the response speed were measured. The results are shown in Table 4 below.

[0038]

[Table 5]

From these results, the nematic liquid crystal material No. containing the compound represented by the general formula (I) was obtained. 26 is △
It was found that the drive voltage was low, despite the small value of ε corresponding to 60% of the comparative composition (b). It is considered that this is because the elastic constants K ₁₁ and K ₃₃ have small values due to slight differences in polar groups. Further, according to the present invention No. 26 compositions at 20 ° C.,
It exhibits a low-viscosity characteristic at all temperatures of 0 ° C. and −20 ° C., and particularly at −20 ° C., it has a small value corresponding to 65% of the comparative composition (b). This characteristic is particularly useful for in-vehicle use where high-speed response at low temperatures is important. In this way, the characteristic that both the driving voltage and the response speed can be sufficiently reduced is unprecedented.

The first liquid crystal composition of the present invention comprises (1) a compound represented by the general formula (I) and (2) a general formula (II).
By using the compound represented by the formula (1) together, the effect of maintaining and improving the above-mentioned properties can be obtained.

Further, the second liquid crystal composition of the present invention comprises
By using a compound selected from the group consisting of (1) the compound represented by the general formula (II) and (2) the compound represented by the general formulas (III) to (XII), particularly excellent chemical stability, The effect of reducing the temperature dependence of the threshold value and excellent response characteristics at low temperatures can be obtained.

Further, the third liquid crystal composition of the present invention comprises
(1) a compound represented by the general formula (I), (2) a compound represented by the general formula (II), and (3) a general formula (II)
By using a compound selected from the group consisting of the compounds represented by I) to (XII) in combination, the effect of maintaining and improving the above-mentioned properties can be obtained. Further, it is possible to optimize the elastic constant which plays an important role in display characteristics, and to prepare a nematic liquid crystal composition having an elastic constant ratio K ₃₃ / K ₁₁ according to the application.

The compounds represented by the general formulas (III) to (XII) used in the second and third liquid crystal compositions of the present invention are compounds having a dielectric anisotropy of a medium value of 4 to 12. In general, it is difficult to reduce the threshold voltage of the liquid crystal composition to 1.6 V or less using these compounds, but in the present invention, the compound represented by the general formula (I) is used. And / or a nematic liquid crystal composition that can operate at a sufficiently low driving voltage can be obtained by using it in combination with the compound represented by the general formula (II).

Of these, general formulas (III) to (VII
The compound represented by I) can easily reduce Δn of the liquid crystal composition, and optimize Δn required for the nematic liquid crystal composition to reduce color unevenness of the liquid crystal display device.
It is possible to improve the viewing angle characteristics and increase the contrast ratio. It is useful for obtaining a large elastic constant ratio K ₃₃ / K ₁₁ necessary for the display characteristics of STN-LCD, and can display a lot of information. Further, it has a tendency to expand the nematic phase to the high temperature side and the low temperature side,
The operable temperature range of the liquid crystal display device can be expanded. Further, the viscosity of the nematic liquid crystal composition is improved, and a liquid crystal display device having a high-speed response can be obtained.

Further, the compounds represented by the general formulas (IX) to (XII) can increase the Δn of the liquid crystal composition, and the Δn required for the nematic liquid crystal composition is optimized to obtain a liquid crystal display device. It is possible to reduce the color unevenness and increase the contrast ratio. Further, a large elastic constant ratio K ₃₃ / K ₁₁ can be easily obtained, which is useful for improving the display characteristics of a viewfinder or the like. In particular, it is possible to obtain a high-speed response liquid crystal display device that has a tendency to expand the nematic phase to a high temperature side, can extend the drivable temperature range of the liquid crystal display device, and does not deteriorate the viscosity of the nematic liquid crystal composition. It is possible. Furthermore, the compounds of the general formulas (IX) to (XII) are
Many of them have a tendency to lower the driving voltage than the compounds of II) to (VIII).

The second and third liquid crystal compositions of the present invention each contain a compound selected from the group consisting of compounds represented by the general formulas (III) to (VIII) in the range of 0 to 30% by weight. Is preferable, and the total amount is 10 to 80% by weight.
It is preferable to contain in the range of. Alternatively, each of the compounds selected from the group consisting of the compounds represented by the general formulas (IX) to (XII) is preferably contained in the range of 0 to 25% by weight, and the total amount thereof is contained in the range of 5 to 80% by weight. It is preferable. Of course, when properties suitable for a higher level liquid crystal display device are required, the liquid crystal composition of the present invention is a compound selected from the group consisting of compounds represented by the general formulas (III) to (VIII) and a general compound. Formula (IX)
It is more preferable to use a compound selected from the group consisting of compounds represented by to (XII) in combination.

Further, as shown in Examples below, by using the liquid crystal composition of the present invention, it is possible to provide a liquid crystal display device in which the temperature dependence of the threshold voltage is improved.

As a conventional technique for improving the temperature dependence of the threshold voltage, it is known to use a chiral compound whose induced pitch has a negative temperature dependence.
The present invention is excellent in that it can solve the problems caused by the addition of such a compound, that is, the problems such as deterioration of viscosity, increase of threshold voltage, troublesome adjustment, and cost increase.

Further, the liquid crystal composition of the present invention has the general formula (I
By containing a compound selected from the group consisting of compounds represented by II) to (XII), it is also recognized that a larger pretilt angle can be formed. In particular,
Although only the compound represented by the general formula (I) or the general formula (II) has no particular effect on the pretilt angle formed, the terminal group in the compound represented by the general formula (III) to (XII) is A compound having an alkoxyalkyl group or a liquid crystal composition containing a large amount of the same forms a large pretilt angle, and this compound or the liquid crystal composition is mixed with a compound represented by the general formula (I) and / or the general formula (II). Also in the case, the effect of improving and maintaining the pretilt angle can be obtained. Due to such an effect of improving and maintaining the pretilt angle, stripe domains are less likely to occur, and the yield in manufacturing STN-LCD can be improved.

Further, the liquid crystal composition of the present invention is chemically stable and has a high resistance value, as shown in Examples described later, and thus can be displayed at a wide driving frequency.

The liquid crystal composition of the present invention has the above general formula (I).
In addition to the compounds (XII) to (XII), 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. Typical examples of such liquid crystal compounds are given below.

[0052]

[Chemical 9]

(In the above general formula, R represents an alkyl group, an alkenyl group or an alkoxyalkyl group, and X represents H or F.)

[0054]

The present invention will be described in detail below with reference to examples.
The invention is not limited to these examples. Further, in the following examples and comparative examples, "%" represents "% by weight".

The specific resistance of the composition was determined by placing 2 g of the liquid crystal composition in an ampoule tube, degassing in a vacuum, enclosing it by a process of nitrogen substitution, enclosing it at 150 ° C. for 1 hour in a heat acceleration test, and for 10 hours in an ultraviolet ray. The specific resistance of the liquid crystal composition after the irradiation acceleration test "SUNTEST" (manufactured by Original Hanau) was measured.

In the examples, the symbols of the measured characteristics have the following meanings. T _NI : Nematic phase-isotropic liquid phase transition temperature (° C) Δε: Dielectric anisotropy Δn: Birefringence V _th : Threshold voltage (V) τ when a TN-LCD having a cell thickness of 8 μm is constructed _r = τ _d : rise time (τ _r ) from the state where no voltage is applied to the state where light is transmitted when voltage is applied, and the fall time (time when light is no longer transmitted from the state where voltage is applied except voltage) ( Response time (msec) where τ _d ) becomes equal η _T : Viscosity (cp) at T ° C. K ₁₁ , K ₂₂ , K ₃₃ : Elastic constant (Newton) K ₃₃ / K ₁₁ , K ₃₃ / K ₂₂ : Elastic constant ratio

Reference Example 1 No. 2 in Table 2 7 and No.
The following purification was performed on the compound of 8 in the final step of the synthesis.

First, 3% neutral alumina purification agent, 3% silica gel purification agent and 5% activated carbon were added to No. No. 7 compound or No. 7 It was mixed with the compound of Example 8 and stirred at a temperature of a liquid crystal phase state for 2 hours. Then, each compound was purified by filtration using a 0.1 μm membrane filter. Thus obtained No. 7 and No. The compounds of 8 were mixed in equal amounts, and 2 g of this mixed liquid crystal was put into an ampoule tube, degassed in vacuum, and then subjected to nitrogen substitution treatment and sealed, and the specific resistance after a heating acceleration test at 150 ° C. for 1 hour was measured. did.

As a result, the specific resistance of the unpurified mixed liquid crystal was 1.
The specific resistance of the mixed liquid crystal after purification was 2.0 × 10 ¹⁰ Ω · cm, while it was 0 × 10 ⁹ Ω · cm. In the following examples and comparative examples of the present invention, it is clear that all such purified compounds are used and that they have high chemical reliability.

(Example 1)

[0061]

[Chemical 10]

A nematic liquid crystal composition No. 27
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 93.6 ° C. Δε: 11.3 Δn: 0.120 V _th : 1.55 V η ₂₀ : 19.5 cp

This nematic liquid crystal composition No. A chiral substance “S-811” (manufactured by Merck) was added to 27 to prepare a mixed liquid crystal. On the other hand, an organic film of "SAN EVER 150" (manufactured by Nissan Kagaku Co., Ltd.) was rubbed on the opposing flat transparent electrodes to form an alignment film, and a STN-LCD display cell with a twist angle of 220 degrees was produced. The above-mentioned mixed liquid crystal was injected into this cell to construct a liquid crystal display device, and display characteristics were measured. As a result, the STN-LCD has a low threshold voltage, excellent high time division characteristics, and improved display screen flicker and crosstalk.
A liquid crystal display device having display characteristics was obtained.

With respect to the chiral substance, the peculiar spiral pitch P of the mixed liquid crystal and the cell thickness d of the display cell due to the addition of the chiral substance are Δn · d = 0.85 and d / P = 0.53. Was added.

(Example 2)

[0066]

[Chemical 11]

A nematic liquid crystal composition No. 28
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 75.9 ° C. Δε: 9.5 Δn: 0.113 V _th : 1.52 V η ₂₀ : 16.5 cp η ₀ : 48.4 cp η _-20 : 219 cp

(Example 3)

[0069]

[Chemical 12]

A nematic liquid crystal composition No. 29
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 73.6 ° C. Δε: 8.0 Δn: 0.104 V _th : 1.55 V K ₁₁ : 6.7 × 10 ⁻¹² newton K ₃₃ : 17.1 × 10 ⁻¹² newton K ₃₃ / K ₁₁ : 2.54

(Example 4)

[0072]

[Chemical 13]

A nematic liquid crystal composition No. Thirty
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 87.3 ° C. Δε: 7.9 Δn: 0.091 V _th : 1.58 V K ₁₁ : 8.3 × 10 ⁻¹² newton K ₃₃ : 16.5 × 10 ⁻¹² newton K ₃₃ / K ₁₁ : 1.98 Specific resistance before test: 2.1 × 10 ¹² Ω · c
m Specific resistance after accelerated heating test: 4.6 × 10 ¹¹ Ω ・ c
m Specific resistance after UV irradiation acceleration test: 4.8 × 10 ¹¹ Ω ・ c
m

(Example 5)

[0075]

[Chemical 14]

A nematic liquid crystal composition No. 31
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 72.8 ° C. Δε: 8.4 Δn: 0.101 V _th : 1.46 V K ₁₁ : 7.4 × 10 ⁻¹² newton K ₃₃ : 16.6 × 10 ⁻¹² newton K ₃₃ / K ₁₁ : 2.24

This nematic liquid crystal composition No. A chiral substance “S-811” was added to 31 in the same manner as in Example 1 to prepare a mixed liquid crystal. Using this mixed liquid crystal, a STN-LCD having a twist angle of 220 degrees was produced in the same manner as in Example 1,
The display characteristics were measured. As a result, the threshold voltage is low,
A liquid crystal display device having excellent high time division characteristics, STN-LCD display characteristics with improved flickering of display screen and crosstalk phenomenon was obtained.

With respect to the chiral substance, the peculiar helix pitch P of the mixed liquid crystal by the addition of the chiral substance and the cell thickness d of the display cell are Δnd = 0.85 and d / P = 0.53. Was added.

(Example 6)

[0080]

[Chemical 15]

A nematic liquid crystal composition No. 32
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 81.0 ° C. Δε: 7.3 Δn: 0.118 V _th : 2.11 V τr = τd: 19.0 milliseconds

(Embodiment 7)

[0083]

[Chemical 16]

A nematic liquid crystal composition No. 33
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 92.2 ° C. Δε: 6.7 Δn: 0.112 V _th : 1.96 V

(Embodiment 8)

[0086]

[Chemical 17]

A nematic liquid crystal composition No. 34
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 104.7 ° C. Δε: 7.3 Δn: 0.132 V _th : 1.98 V

(Example 9)

[0089]

[Chemical 18]

A nematic liquid crystal composition No. 35
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 91.0 ° C. Δε: 6.9 Δn: 0.111 V _th : 1.80 V

(Example 10)

[0092]

[Chemical 19]

A nematic liquid crystal composition No. 36
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 91.0 ° C. Δε: 7.3 Δn: 0.118 V _th : 1.91 V

This nematic liquid crystal composition No. In the same manner as in Example 1, 36 was added with a chiral substance “S-811” to prepare a mixed liquid crystal. Using this mixed liquid crystal, an STN-LCD having a twist angle of 220 degrees was produced in the same manner as in Example 1, and the display characteristics were measured. As a result, a liquid crystal display device having a low threshold voltage, excellent high time division characteristics, and STN-LCD display characteristics with improved display screen flicker and crosstalk phenomenon was obtained.

The chiral substance is adjusted so that the inherent helical pitch P of the mixed liquid crystal and the cell thickness d of the display cell due to the addition of the chiral substance are Δn · d = 0.85 and d / P = 0.53. Was added.

(Example 11)

[0097]

[Chemical 20]

A nematic liquid crystal composition No. 37
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 96.0 ° C. Δε: 6.9 Δn: 0.109 V _th : 1.89 V

(Example 12)

[0100]

[Chemical 21]

A nematic liquid crystal composition No. 38
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 95.9 ° C. Δε: 6.5 Δn: 0.120 V _th : 2.14 V

(Example 13)

[0103]

[Chemical formula 22]

A nematic liquid crystal composition No. 39
Was prepared and various properties of this composition were measured. The results were as follows. T _NI : 88.2 ° C. Δε: 9.1 Δn: 0.131 V _th : 1.69 V τr = τd: 30.6 milliseconds η ₂₀ : 21.5 cp η ₀ : 69.4 cp η _-20 : 352 cp K ₁₁ : 9.1 x 10 ^-12 newton K ₂₂ : 3.2 x 10 ^-12 newton K ₃₃ : 19.5 x 10 ^-12 newton K ₃₃ / K ₁₁ : 1.95 K ₃₃ / K ₂₂ : 6.10

(Comparative Example 1)

[0106]

[Chemical formula 23]

A comparative mixed liquid crystal (c) consisting of:
Various properties of this composition were measured. The results were as follows. T _NI : 96.5 ° C. Δε: 12.8 Δn: 0.150 V _th : 1.91 V η ₂₀ : 32.1 cp K ₁₁ : 10.5 × 10 ⁻¹² newton K ₂₂ : 3.0 X 10 ^-12 newton K ₃₃ : 31.8 x 10 ^-12 newton K ₃₃ / K ₁₁ : 3.02 K ₃₃ / K ₂₂ : 10.5

This mixed liquid crystal (c) and the nematic liquid crystal composition No. 1 of Example 1 were used. T _NI of 27 is almost equal, but N
o. The composition No. 27 has a lower threshold voltage, although the dielectric anisotropy is smaller than that of the mixed liquid crystal (c). In addition, No. It is clear that the composition of 27 also has excellent viscosity. It is considered that such an effect is due to the small absolute values of the dielectric anisotropy and elastic constant of the compound of the general formula (I).

(Comparative Example 2)

[0110]

[Chemical formula 24]

A comparative mixed liquid crystal (d) consisting of:
Various properties of this composition were measured. The results were as follows. T _NI : 87.3 ° C. Δε: 12.1 Δn: 0.120 V _th : 1.62 V τr = τd: 54.2 milliseconds η ₂₀ : 27.0 cp η ₀ : 98.0 cp η _-20 : Scale over K ₁₁ : 8.4 × 10 ^-12 newton K ₂₂ : 4.3 × 10 ^-12 newton K ₃₃ : 22.8 × 10 ^-12 newton K ₃₃ / K ₁₁ : 2.71 K ₃₃ / K ₂₂ : 5.30

This mixed liquid crystal (d) and the nematic liquid crystal composition No. 1 of Example 13 were used. T _NI of 39 is almost equal, but N
o. It was found that the composition No. 39 was excellent in response time and viscosity at each temperature, and particularly nematic liquid crystallinity was obtained more stably in a low temperature range. It is considered that such an effect is due to the small absolute values of the dielectric anisotropy and elastic constant of the compound of the general formula (I).

Example 14 The nematic liquid crystal composition of Example 13 No. 39 and the mixed liquid crystal (d) of Comparative Example 2 were used to produce a twisted nematic liquid crystal display device (TN-L
CD) respectively. The threshold voltage of this liquid crystal display device at each temperature was measured, and the results are shown in FIG.

From FIG. 1, it is clear that the liquid crystal composition of the present invention has a smaller change in the threshold voltage with respect to the temperature change as compared with the comparative mixed liquid crystal. It is possible to provide a liquid crystal display device in which the temperature dependence of voltage is improved.

Further, since the temperature dependence of the threshold voltage is reduced, it is possible to solve the problems related to the time division driving of TN-LCD and STN-LCD, and to obtain good driving characteristics with a high number of time divisions. Therefore, it is possible to provide an excellent liquid crystal display device capable of expanding the temperature margin of time-division driving.

Further, unlike the prior art, it is not necessary to use a chiral compound whose induced pitch has a negative temperature dependence in order to improve the temperature dependence of the threshold voltage, and the addition of such a compound is not necessary. Defects caused by, namely, deterioration of viscosity,
It is clear that problems such as increase in threshold voltage, troublesome adjustment, and cost increase can be solved.

(Comparative Example 3)

[0118]

[Chemical 25]

A comparative mixed liquid crystal (e) consisting of:
Various properties of this composition were measured. The results were as follows. T _NI : 89.5 ° C. Δε: 10.0 Δn: 0.120 V _th : 1.69 V Specific resistance before test: 6.4 × 10 ¹¹ Ω · c
m Specific resistance after heating accelerated test: 9.9 × 10 ⁹ Ω ・ cm Specific resistance after ultraviolet irradiation accelerated test: 8.9 × 10 ¹⁰ Ω ・ c
m

This mixed liquid crystal (e) and the nematic liquid crystal composition No. 3 of Example 4 were used. T _NI of 30 is almost equal, but N
o. It was confirmed that the composition of No. 30 has a low threshold voltage and can be displayed at a low voltage, although it has a smaller dielectric anisotropy than the mixed liquid crystal (e).

Furthermore, it is clear that the chemical stability by each accelerated test is also excellent. It is considered that such an effect is due to the small absolute values of the dielectric anisotropy and elastic constant of the compound of the general formula (I).

(Example 15) Examples 1 to 1 of the present invention
2 g of each of the nematic liquid crystal compositions of 13 and the mixed liquid crystal (e) of Comparative Example 3 was placed in an ampoule tube, degassed in vacuum, and subjected to nitrogen substitution, sealed and stored in a cool dark place for 6 months. After storage, various properties were measured and compared with the results immediately after preparation, but no significant change was observed in the nematic liquid crystal composition of the present invention, but the mixed liquid crystal (e) turned yellow and precipitation of solid matter. Was recognized, and the specific resistance was deteriorated.

(Comparative Example 4) No. 2 in Table 2 7 and N
o. Equivalent mixed liquid crystals of the compound of 8 and mixed liquid crystal (A) and a mixed liquid crystal containing the compound of formula (a) for comparison as three components were prepared. 2 g of this mixed liquid crystal was placed in an ampoule tube, degassed in vacuum, subjected to nitrogen substitution treatment and sealed, and the specific resistance after a heat acceleration test at 150 ° C. for 1 hour was measured.
As shown in the figure.

The specific resistance of most of the prepared mixed liquid crystals was 1.0 × 10 ¹⁰ Ω · cm or less, which proved to be chemically unstable. This also occurred in a mixture of other liquid crystal compound having -CN other than the compound of the formula (a) and the compound represented by the general formula (II).

Therefore, it has been revealed that it is practically difficult to use the liquid crystal compound having the polar group —CN and the compound represented by the general formula (II) together.

[0126]

The nematic liquid crystal composition of the present invention has a low threshold voltage, a high response speed, and a high chemical stability.

Therefore, in the liquid crystal display device of the present invention using this, the fluctuation of the driving voltage is small in a wide temperature range,
It has a high-speed response and improves the flicker and crosstalk phenomenon of the display screen by reducing the dielectric anisotropy. Therefore, good drive characteristics and display characteristics can be obtained even in an STN-LCD having a large amount of information.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between temperature and threshold voltage in liquid crystal compositions of the present invention and a comparative example.

FIG. 2 is a chart showing a relationship between a mixing ratio and a specific resistance value in a comparative three-component liquid crystal composition.

Claims (4)

[Claims] 1. A general formula (I): (In the formula, R ¹ represents a linear alkyl group or an alkenyl group having 2 to 7 carbon atoms, l, m and n each independently represent 0 or 1, and X ¹ represents H or F. However, m
When is 0, n is 0. ) And a compound represented by the general formula (II): (In the formula, R ² is a linear alkyl group having 2 to 7 carbon atoms,
Represents an alkenyl group or C _j H _{2j + 1} -O-C _k H _2k- , j
Represents an integer of 1 to 3, and k represents an integer of 2 to 5. ) A nematic liquid crystal composition comprising a compound represented by the formula: 2. A compound represented by the general formula (II) according to claim 1 and (2) general formulas (III) to (XI).
I) [Chemical Formula 3] (In the formula, R ³ is a linear alkyl group having 2 to 7 carbon atoms,
Alkenyl or _{C p H 2p + 1 -O-} C q H 2q - represents, p
Represents an integer of 1 to 3, q represents an integer of 2 to 5,
R ⁴ is a linear alkyl group having 2 to 7 carbon atoms or C _s H
_{2s + 1 -O-C t H} 2t - represents, s represents an integer of 1 to 3, t is an integer of 2-5. ) A nematic liquid crystal composition containing a compound selected from the group consisting of compounds represented by 3. General formulas (III) to (X) according to claim 2.
The nematic liquid crystal composition according to claim 1, containing a compound selected from the group consisting of compounds represented by II). 4. A twisted nematic or super twisted nematic liquid crystal display device using the nematic liquid crystal composition according to claim 1.