JP2000282038A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality liquid crystal displaying device capable of not showing a displaying unevenness caused by a heat generated from a light source and circuits and showing a high contrast simultaneously in a normally black type liquid crystal displaying device. SOLUTION: This liquid crystal displaying device has a pair of base plates, a spacer nipped between them, and a liquid crystal layer formed by filling a liquid crystal material between the pair of the base plates. The liquid crystal material has characteristics that its driving electric voltage threshold value ΔVth changes by <=25 mV in the case of changing temperature by 10-C, and also the changing amount Δ (Δε) of dielectric constant anisotropy in the case of changing temperature by 10-C satisfies Δ (Δε)>=1.45-(Tni/100) (provided that Tni is a temperature that the liquid crystal material changes from the liquid crystal phase to an isotropic phase), and also the liquid crystal material contains a liquid crystal compound having cyano group, by <=35 wt.% content.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black display at low voltage,
The present invention relates to a so-called normally black liquid crystal display device that performs white display at a high voltage.

[0002]

2. Description of the Related Art A liquid crystal display device performs a desired display by changing an alignment direction by applying an electric field to liquid crystal molecules of a liquid crystal layer sandwiched between substrates to change an amount of light transmitted through the liquid crystal layer. It is. The applied electric field is controlled by the drive circuit. The light source of the liquid crystal display device is called a backlight in the case of a transmissive liquid crystal display device, and is installed on the back or side of the liquid crystal display element. In addition, in the case of a reflection type liquid crystal display device, there are a type using external light such as sunlight or indoor lighting, and a type using a light source called a front light installed on the front of the liquid crystal display device. The thickness of the liquid crystal layer of the liquid crystal display device, that is, the distance between the substrates is kept constant by the spacer. For this spacer, a spherical resin or silica is usually used.

When a light source such as a backlight or a front light is used, heat is generated from these light sources. Also, heat is generated from the drive circuit. Due to such heat, a temperature distribution is generated in the plane of the display unit of the liquid crystal display device, and thereby uneven display occurs. The uneven display is caused by a change in the threshold voltage of the liquid crystal due to a change in the temperature of the liquid crystal due to heat.

[0004] The mechanism will be briefly described. The threshold voltage Vth of the liquid crystal depends on the elastic constant (K) of the liquid crystal material and the dielectric anisotropy (Δε) as in the following equation 1.

[0005]

(Equation 1) Here, the temperature change of the elastic constant K is generally larger than the temperature change of the dielectric anisotropy Δε. Therefore, as a result, K / Δε changes due to a temperature change, and the threshold voltage Vth changes.

As a method for solving this problem, (1) a method of reducing the temperature dependence of K and Δε by using a liquid crystal material having a high transition temperature (Tni) from a nematic phase to an isotropic phase. (2) By using a liquid crystal material having a large dielectric anisotropy Δε at room temperature, the temperature dependence of the dielectric anisotropy Δε near room temperature is increased, and the change in K / Δε due to a temperature change is reduced. Method (Takeuchi et al., 4 people, Proceedings of the 23rd LCD Symposium, 230-231 pages, 1997, Takeshita et al., 5)
Name, Proceedings of the 23rd Liquid Crystal Symposium, 368-369
P. 1997). Etc. have been proposed.

However, in the method (1), display unevenness due to heat can be reduced, but the viscosity of the liquid crystal material near room temperature increases due to an increase in the phase transition temperature (Tni).
There is a problem that the response of the liquid crystal becomes extremely slow. In the method of the known example (2), it is necessary to determine the temperature dependence of the dielectric anisotropy Δε in order to reduce display unevenness due to heat, and how to do so. , Not specifically shown.

On the other hand, as another problem other than display unevenness due to heat, there is a problem that it is desired to improve the contrast of a normally black liquid crystal display device.

[0009] The contrast of a liquid crystal display device is represented by the ratio of the luminance during black display to the luminance during white display. In a super twisted nematic (STN) type liquid crystal display device in which the twist angle of the liquid crystal is 240 degrees or more, so-called normally black (or normally closed), which performs black display at low voltage and white display at high voltage. A display method is used. A so-called lateral electric field type liquid crystal display device (for example, Japanese Patent Publication No. 63-21907) in which an electric field is applied to the substrate surface to drive the liquid crystal generally uses a normally black method. In such a normally black liquid crystal display device, a white spot, that is, light leakage occurs around the spacer during black display. Therefore, there is a problem that the black luminance is not sufficiently reduced, and the contrast is reduced.

One of the causes of light leakage is that light is transmitted through the spacer itself during black display, which results in light leakage. In order to reduce this, a method has been proposed in which the spacer body is colored to reduce the transmittance (for example, JP-A-9-25309, JP-A-9-208607, JP-A-9-221507, Kaihei 9-325
342, JP-A-10-104634).

Another cause of the light leakage is that the orientation of the liquid crystal around the spacer is different from the orientation of the portion without the spacer, so that light is transmitted around the spacer even during black display. . In order to reduce the light leakage around the spacer, a method has been proposed in which a liquid crystal molecule is vertically aligned with respect to the surface of the spacer by using a spacer having a long-chain alkyl group or the like added to the surface (see, for example, Japanese Patent Application Laid-Open No. H08-208,878). -262453, JP-A-8-328018, JP-A-9-194842, JP-A-9-244
034, JP-A-10-90691).

There are various types of liquid crystal materials used in liquid crystal display devices. Representative compounds include compounds having a cyano group, fluorine compounds, tolan compounds, and dielectric constants called neutral. There are compounds having almost zero anisotropy. In particular, in an STN mode liquid crystal display device, a compound having a cyano group is mainly used to reduce the driving voltage.

[0013]

SUMMARY OF THE INVENTION In order to improve the contrast of a liquid crystal display device and to reduce display unevenness due to temperature, the inventors have actually added a spacer having a long-chain alkyl group or the like to the surface. An experiment was conducted in which a liquid crystal display device was fabricated using a liquid crystal material having a large dielectric anisotropy Δε. However, although the display unevenness due to heat can be reduced, there is a problem that the contrast is reduced in spite of using the above-mentioned spacer. As a result of detailed examination, the dielectric anisotropy Δε
It was found that the amount of light leakage around the spacer during black display increased with an increase in the contrast, and the contrast decreased. In other words, a liquid crystal material having a large dielectric anisotropy Δε can provide an effect of reducing heat unevenness in display, but with such a material, even if a surface-treated spacer is used, the alignment around the spacer cannot be controlled, resulting in light leakage. The amount cannot be reduced.

Therefore, a uniform display with less heat unevenness,
There is a trade-off between high contrast and a problem that both cannot be achieved.

In order to reduce display unevenness due to heat, the values of the dielectric anisotropy .DELTA..epsilon. And the phase transition temperature Tni may be specifically set in the prior arts (1) and (2). It was not clear.

In order to improve the contrast, it is necessary to consider not only the surface treatment of the spacer but also the interaction between the spacer and the liquid crystal material, but it is unclear how the spacer interacts.

A first object of the present invention is to provide a so-called normally black type liquid crystal display device which performs black display at a low voltage and white display at a high voltage, and has less display unevenness due to heat generated from a light source or a circuit. Another object of the present invention is to provide a high-quality liquid crystal display device that can achieve both high contrast.

A second object of the present invention is to provide a method for designing a liquid crystal material capable of suppressing display unevenness due to heat generated from a light source or a circuit.

A third object of the present invention is to provide a so-called normally black type liquid crystal display device having a high contrast with little light leakage from around the spacer.

[0020]

A liquid crystal display device according to a first embodiment of the present invention is characterized in that a change in the drive voltage threshold ΔVth when the temperature changes by 10 ° C. is smaller than 25 mV. In addition, the liquid crystal material contains a liquid crystal compound having a cyano group at a content of 35% by weight or less.

Furthermore, when the temperature of the liquid crystal material of the liquid crystal display device of the present invention changes by 10 ° C., the change Δ (Δε) in dielectric anisotropy is Δ (Δε) ≧ 1.45- (Tni / 10
0) Satisfy.

Further, the liquid crystal compound having a cyano group of the liquid crystal material is

[0023]

Embedded image (Where X1 and X2 are H or F).

A liquid crystal display device according to a second embodiment of the present invention is a method for designing a liquid crystal material of a normally black super twisted nematic type liquid crystal display device. When the variation Δ (Δε) of the dielectric anisotropy is Δ (Δε) ≧ 1.45- (Tni /
100) (where Tni is a temperature at which the liquid crystal material changes from a liquid crystal phase to an isotropic phase), and a liquid crystal compound constituting the liquid crystal material and its composition are selected.

A liquid crystal display device according to a third embodiment of the present invention is a normally black super twisted nematic liquid crystal display device, which is sandwiched between a pair of substrates. It has a spacer and a liquid crystal layer formed by filling a liquid crystal material between a pair of substrates. The liquid crystal material contains a liquid crystal compound having a cyano group at a content of 35% by weight or less. .

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display according to one embodiment of the present invention will be described.

The liquid crystal display device of the present embodiment uses a liquid crystal material satisfying the following first and second conditions as a liquid crystal material to reduce display unevenness due to heat and achieve high contrast. Make them compatible.

The first condition is a condition for suppressing display unevenness due to heat to such an extent that it cannot be visually recognized.
Dielectric anisotropy Δ when the temperature of the liquid crystal material changes by 10 ° C.
A liquid crystal material whose variation in ε satisfies the following equation is used. (Change of Δε) ≧ 1.45- (Tni / 100) Here, Tni in the above formula indicates a temperature (° C.) at which the liquid crystal changes from a liquid crystal phase to an isotropic phase.

The second condition is that the content of the compound having a cyano group contained in the liquid crystal material is 35% by weight or less of the whole liquid crystal material. This is for the following reasons. In order to design a composition of a liquid crystal material satisfying the first condition, it is effective to use a liquid crystal material having a large dielectric anisotropy Δ 異 方 性 as the liquid crystal material. Dielectric anisotropy Δε
Is zero in an isotropic phase whose temperature is equal to or higher than the phase transition temperature Tni.
This is because the larger the value of ε, the larger the amount of decrease of Δε with the temperature rise. However, when the inventors unconditionally use a material having a large dielectric anisotropy Δε, the liquid crystal molecules may be oriented in parallel (tangential direction) to the surface of the spacer as described in detail later. I noticed that it could cause light leakage around the spacer. This is because liquid crystal molecules having a large dielectric anisotropy Δε tend to have a large dipole moment and strongly interact with the surface of the spacer. Therefore, the second condition is determined to prevent this. First and second
By using a liquid crystal material satisfying the above condition, it is possible to simultaneously reduce display unevenness due to heat and improve contrast. The configuration of the liquid crystal display device of the present embodiment is the same as that of a normal super twisted nematic (STN) liquid crystal display device except that a liquid crystal material is selected so as to satisfy the first and second conditions. Therefore, a brief description will be given here.

The liquid crystal element of the liquid crystal display device according to the present embodiment has a structure in which a liquid crystal layer 6 is interposed between a glass substrate 4a and a glass substrate 4b as shown in FIG. On the surface of the glass substrate 4a on the side of the liquid crystal layer 6, an ITO (Indium Tin Oxide) electrode 5a patterned in a stripe shape and a polyimide alignment film (not shown) are provided.

On the other hand, the surface of the glass substrate 4b on the liquid crystal layer 6 side is provided with a color filter (not shown), an ITO electrode 5b patterned in stripes, and a polyimide alignment film (not shown). The directions of the electrodes 5a and 5b are
They are formed so as to be orthogonal. The distance between the glass substrate 4a and the glass substrate 4b is kept constant by the spacer 7 interposed therebetween. Each polyimide alignment film is rubbed so that the angle formed by the rubbing direction is 60 degrees (the twist angle of the liquid crystal is 240 degrees). In the present embodiment, a spacer 7 whose surface is subjected to a process for vertically aligning liquid crystal molecules is used as the spacer 7. The spacer 7 body is colored and does not transmit light.

On the back side of the liquid crystal element, a light guide 8, a polarizing plate 2a, and a retardation plate 3a are arranged. A backlight 9 is arranged on a side surface of the light guide 8. Further, a retardation plate 3b and a polarizing plate 2b are arranged on the entire surface of the liquid crystal element. The upper and lower electrodes 5a, 5a are provided around the liquid crystal element.
and a drive circuit (not shown) for supplying an electric signal to the liquid crystal, which is connected to b. When the polarizing plates 2a and 2b and the phase difference plates 3a and 3b are mounted, they are arranged so as to display black at low voltage and white at high voltage, similarly to a general STN type liquid crystal display device.

As a method of manufacturing the liquid crystal display device, a well-known general method is used. First, a glass substrate 4a on which an ITO electrode 5a patterned in a stripe pattern is formed is prepared, and a polyimide precursor varnish is applied and baked to form a polyimide alignment film. Further, a glass substrate 4b on which a color filter and ITO electrodes patterned in a stripe pattern are formed is prepared, and a polyimide alignment film is formed in the same manner. Rubbing treatment is performed on these alignment films, and the ITO electrodes 5
The substrates 4a and 4b face each other such that the directions of a and 5b are orthogonal to each other and the rubbing angle of the upper and lower substrates 4a and 4b is 60 degrees (twist angle of the liquid crystal is 240 degrees).
The gap between the substrates is kept constant, and the periphery of the substrates 4a and 4b is bonded with a thermosetting sealant. A liquid crystal material having a preselected composition is sealed in the gap between the bonded substrates 4a and 4b to form a liquid crystal layer 6. A drive circuit is mounted around the liquid crystal element, and a backlight 9, a light guide 8, a polarizing plate 2a, and the like are provided on the back surface, and the polarizing plate 2 is provided on the front surface.
b, etc. are installed to complete the liquid crystal display device.

Next, a description will be given of how the present inventors have derived the first condition for suppressing the above-described display unevenness due to heat in the present liquid crystal display device to such an extent that it cannot be visually recognized.

First, the inventors actually manufactured a liquid crystal display device shown in FIG. 8 in which a liquid crystal layer 6 was formed from a conventional liquid crystal material, and displayed an image. As a result, display unevenness due to heat occurred as time passed. Then, when the surface temperature of the display section was measured, it was 30 ° C. at a low position and 40 ° C. at a high position. Therefore, it was considered that the display unevenness was due to a change in the threshold voltage (Vth) of the liquid crystal depending on the temperature. The display unevenness is caused by the threshold voltage Vth (30 ° C.) at 30 ° C. and the threshold voltage Vth at 40 ° C.
It is considered that the display unevenness can be reduced by reducing the difference of (40 ° C.) and ΔVth = Vth (30 ° C.) − Vth (40 ° C.). In addition. Here, the threshold voltage Vth of the liquid crystal
Is defined as a voltage (V40) at which a relative transmittance of 40% (that is, relative luminance B40) is obtained.

Considering human visibility, the Weber ratio is a well-known value of how much luminance difference a human can recognize. According to it, 10%
It is said that a human can recognize the above difference in luminance. That is, even if a temperature distribution is generated in the display surface, which causes a change in the relative luminance B40 of the liquid crystal, if the change is within 10%, the display unevenness cannot be recognized by a human.
Here, as shown in FIG.
Is obtained, the relative luminance of the portion where the temperature has risen to 40 ° C. becomes larger than B40 by ΔB. Therefore, if ΔB is within 10% of the original B40, that is, if ΔB / B40 ≦ 0.1, humans cannot recognize.

Then, the liquid crystal display device is placed in a thermostat, the temperature of the liquid crystal display device is changed to various temperatures, the relative luminance is measured each time, and the difference from the relative luminance at a temperature of 30 ° C. is obtained. The change ΔB of the relative luminance for each change was measured. Further, a drive voltage V40 at which the relative luminance B40 is obtained at that temperature.
Was measured, and a difference ΔV40 from the drive voltage V40 (= Vth) at a temperature of 30 ° C. was obtained. FIG. 2 shows the relationship between ΔB and ΔV40. As can be seen from FIG. 2, when the change ΔV40 of the drive voltage V40 due to the temperature change is 25 mV or less, the change ΔB of the relative luminance falls within 10% of the relative luminance B40 at the temperature of 30 ° C. Therefore, in order to reduce display unevenness due to heat, ΔV40 ≦
It was found that the voltage had to be 25 mV.

Therefore, in order to satisfy ΔV40 ≦ 25 mV, the above-mentioned equation (1) is used.

[0039]

(Equation 2) , The temperature dependence of the dielectric anisotropy Δε of the liquid crystal is increased, the temperature dependence of the elastic constant K is compensated, and the apparent ΔV
An attempt was made to reduce 40. For this purpose, liquid crystal materials having the same phase transition temperature Tni and different temperature dependences of the dielectric anisotropy Δε were prepared, and ΔV40 of these liquid crystal materials was measured. Also, the dielectric anisotropy Δε of each liquid crystal material
Δ 求 め る at 30 ° C. and 40
The difference Δ (Δε) of Δε at ° C. was determined. FIG. 3 shows the result. In FIG. 3, Δ (Δε) is plotted on the horizontal axis, and ΔV is plotted on the vertical axis.
I got 40. As can be seen from FIG. 3, ΔV40 ≦ 25 m
It can be seen that it is necessary to satisfy Δ (Δε) ≧ 0.7 in order to obtain V. Therefore, by using a liquid crystal material having a difference Δ (Δε) between Δε at 30 ° C. and Δε at 40 ° C. of 0.7 or more, a human can recognize a temperature change of the driving voltage as a luminance difference. It has been found that it is possible to reduce the temperature to a degree or less.

However, here, a liquid crystal material having a phase transition temperature Tni of about 75 ° C. is used. How much Δ (Δε) is required to reduce thermal unevenness depends on the phase transition temperature Tni of the liquid crystal material. This is because, as described above, when the phase transition temperature Tni increases, the temperature dependence of the elastic constant K decreases, and Δ (Δε) for compensating the temperature dependence may be small. Accordingly, liquid crystal materials having different phase transition temperatures Tni were prepared, and Δ (Δε) for measuring ΔV40 ≦ 25 mV was measured in the same manner as described above. Then, the relationship between the determined Δ (Δε) and the phase transition temperature Tni was determined. FIG. 7 shows the result. From FIG. 7, ΔV
In order to satisfy 40 ≦ 25 mV, it was possible to guide that the relationship between Δ (Δε) and Tni needs to satisfy Δ (Δε) ≧ 1.45- (Tni / 100). Therefore, it was found that by using a material in which the relationship between Δ (Δε) and Tni satisfies the above relationship as the liquid crystal material, the temperature change of the driving voltage can be reduced to a level that can be recognized by a human as a luminance difference.

Here, since the temperature distribution of the liquid crystal display device was 30 ° C. where the temperature distribution was low and 40 ° C. where the temperature distribution was high, Δ (Δε) was defined as the difference between Δε at 30 ° C. and Δε at 40 ° C. However, this temperature distribution does not always reach 30 ° C. to 40 ° C. due to a change in room temperature. However, it is considered that the difference between the highest temperature and the lowest temperature in the temperature distribution does not significantly change even if the room temperature slightly changes, and in the case of the liquid crystal display device of the present embodiment, the temperature difference is considered to be about 10 ° C. Can be Further, since the change of Δε around room temperature is almost linear, it is considered that the above relationship holds even when Δ (Δε) is the amount of change in dielectric anisotropy Δε when the temperature of the liquid crystal material changes by 10 ° C. Can be Accordingly, the first condition that the liquid crystal material of the liquid crystal display device of the present embodiment should satisfy is that the amount of change in dielectric anisotropy Δε when the temperature of the liquid crystal material changes by 10 ° C. satisfies the following expression. Liquid crystal material, (change in Δε) ≧ 1.45- (Tni / 100) (where Tni in the above formula indicates a temperature (° C.) at which the liquid crystal undergoes a phase transition from a liquid crystal phase to an isotropic phase). The condition of using could be derived. Under the first condition, display unevenness due to heat can be suppressed to such an extent that it cannot be visually recognized.

Considering, for example, that the amount of change in the dielectric anisotropy Δε when the temperature of the liquid crystal material changes by 10 ° C. is distributed depending on the composition of the liquid crystal material, display unevenness due to heat cannot be visually recognized with a margin. In order to suppress this, it is desirable to select a liquid crystal material so as to satisfy (change amount of Δε) ≧ 1.5− (Tni / 100).

Next, how the inventors have derived the second condition to be satisfied by the liquid crystal material of the liquid crystal display device of the present embodiment will be described. This second condition is
This is a condition for realizing a high contrast.
% By weight or less. This suppresses the dipole moment of the entire liquid crystal material composition from becoming too high, and prevents light leakage around the spacer 7.

First, the inventors prepared liquid crystal cells for measurement using various liquid crystal materials in order to confirm the cause of light leakage in a conventional liquid crystal display device. This liquid crystal cell for measurement is
The liquid crystal layer 6 is interposed between the glass substrates 4a and 4b with the spacer 7 interposed therebetween. Glass substrates 4a, 4
On b, electrodes 5a and 5b are not formed, but polyimide alignment films are formed. Glass substrate 4a
The rubbing direction of the polyimide alignment film is the glass substrate 4b.
Was made antiparallel to the rubbing direction of the polyimide film. This cell is generally called an anti-parallel alignment cell.

In this cell, (1) PCH 302 (1-
(4-ethoxyphenyl) -4-propylcyclohexane) and PCH304 (1- (4-butoxyphenyl)-
Equivalent mixture of 4-propylcyclohexane), (2) ZLI-1083 (3-component mixture of cyanoPCH (PCH means phenylcyclohexane)) manufactured by Merck,
(3) Liquid crystals of the mixture of the above (1) and (2) are respectively injected, and under the crossed Nicols of the polarizing plate, the rubbing direction of the cell and the polarizing axis of one of the polarizing plates are made to coincide with each other. The orientation of the liquid crystal in was observed.

The use of a compound having a cyano group as in the above (2) and (3) is necessary in order to design a composition of a liquid crystal material satisfying the first condition. This is because it is effective to use a compound having a group. However, the inventors have considered that the compound having a cyano group may influence light leakage around the spacer 7.

As a result, when a mixture of equal amounts of PCH302 and PCH304 was injected, as shown in FIG. 4, a bright portion 41 was observed annularly around the spacer 7, and a dark portion was formed outside the bright portion 41. . In the bright part 41, dark part lines 42 and 43 were observed crosswise in a direction coinciding with the polarization axis of the polarizing plate. From observation using a polarizing microscope, it is estimated that the liquid crystal molecules 13 are oriented perpendicular to the surface of the spacer 7 (radially around the spacer 7) around the spacer 7 as shown in FIG. (FIG. 4). FIG. 9 (a)
Shows only one molecule around the spacer 7, but actually, a plurality of molecules corresponding to the length in the radial direction of the light portion 41 are vertically oriented. In the dark portion outside the bright portion 41, the liquid crystal molecules are aligned in parallel with the rubbing direction. For this reason, outside the bright portion 41, the light cannot pass through the orthogonal polarizing plates, and thus becomes a dark portion. Further, the spacer 7 itself is also observed as a dark part because of the light-shielding treatment. In the part where the liquid crystal molecules 13 around the spacer 7 are radially aligned, only the part where the alignment direction of the liquid crystal molecules 13 and the polarization axis of the polarizing plate coincide with each other is observed as dark part lines 42 and 43. A portion where the alignment direction of the liquid crystal molecules 13 is inclined with respect to the polarization axis of the polarizing plate is observed as a bright portion 41 because a polarized component that transmits through the polarizing plate is generated.

Next, to a mixture of equal amounts of PCH302 and PCH304, a liquid crystal material in which ZLI-1083, which is a mixture of cyanoPCH, was added at a weight ratio of 20%, 30%, 35%, and 40%, and 100% of ZLI-1083. It was made and injected into the parallel alignment cell described above. A 100% liquid crystal material of ZLI-1083 was similarly injected into the parallel alignment cell. Then, the orientation of the liquid crystal around the spacer was observed. The results are shown in FIGS. In FIGS. 5A to 5E, an equal mixture of PCH302 and PCH304 is added to PCH302.
30R.

As shown in FIGS. 5A and 5B, when the content of ZLI-1083 is 30% by weight or less, the orientation around the spacer 7 is almost the same as in FIG. Was not done. However, when the content of ZLI-1083 was 35% by weight or more, the orientation around the spacer was significantly changed as shown in FIGS. 5 (c) to 5 (e). From the observation using a polarizing microscope, when the content of ZLI-1083 in FIG. 5C is 35% by weight, the orientation of the liquid crystal molecules is perpendicular to the surface of the spacer 7 as shown in FIG. It is considered that the aligned liquid crystal molecules 13 and the liquid crystal molecules 13 aligned in parallel are mixed. Further, when ZLI-1083 is 100% by weight, the liquid crystal molecules 13 have the spacer 7 except for the rubbing direction.
It is presumed that they are oriented almost parallel to the surface of FIG.
(C)).

The difference in the orientation of the liquid crystal molecules 13 around the spacer depending on the content of ZLI-1083 can be explained by the difference in the magnitude of the dipole moment of each liquid crystal molecule 13. The dipole moment of the compound having a cyano group and the neutral compound was calculated by molecular orbital calculation MOPAC93 (AM1). 4-methyl- (4-cyanophenyl) cyclohexane, 4-methyl- (4-cyano-), which are compounds having large dielectric anisotropy.
The dipole moment of 3,5-difluorophenyl) cyclohexane is 3.93 Debye and 5.43 Debye, respectively, whereas bis (4-methylcyclohexane) and bis (4-methylbenzene) satisfying Δε ≦ 1 ) Were very small, 0.035 debye and 0.027 debye, respectively.

As described above, a liquid crystal molecule having a cyano group is:
Since the dipole moment is large, the interaction with the surface of the spacer 7 is increased, and the liquid crystal molecules 13 are aligned parallel to the surface of the spacer 7. Estimating the relationship between the change in alignment around the spacer 7 and the dipole moment of the entire liquid crystal composition, it is found that when the dipole moment of the entire liquid crystal composition becomes 1.2 to 1.4 Debye or more, the vicinity of the spacer 7 is reduced. Vertical orientation is lost. When the vertical alignment is lost in this way, the amount of light leakage around the spacer 7 increases.

When such a liquid crystal material is used in the above-described STN mode liquid crystal display device of the present embodiment, when the content of ZLI-1083 is 30% by weight or less, peripheral light leakage of the spacer 7 is small, and Although a high contrast of about 50: 1 or more was obtained, the content of ZLI-1083 whose peripheral orientation was changed was 40%.
When the liquid crystal material was used in an amount of not less than weight%, light leakage around the spacer was large, and the contrast was as low as about 30: 1.

Therefore, the amount of light leakage around the spacer 7 in the above-described STN type liquid crystal display device of the present embodiment was quantitatively measured by the following method. First, the voltage-transmittance characteristics of the minute display area not including the spacer are measured, and the minimum transmittance and the voltage (Voff) for providing the minimum transmittance are measured. Next, one spacer is placed in a region having the same area as the measurement region.
The voltage-transmittance characteristics in the case where there are
f Measure the transmittance when applying. Find the difference between the two transmittances,
This difference is divided by the number of spacers (beads) existing per 1 mm ² to obtain the amount of light leakage per spacer.
This value is calculated when there is one spacer per 1 mm ²
This is a value indicating how much the minimum transmittance is increased. FIG. 6 shows the relationship between the measurement results and the content of ZLI-1083.
As is apparent from FIG. 6, when the content of the compound having a cyano group (in this case, cyano PCH) exceeds 35% by weight, the amount of light leakage increases rapidly with the change in the orientation around the spacer. I understand. Accordingly, in order to obtain high contrast, the second condition of the present embodiment is that the content of the compound having a cyano group must be 35% by weight or less and the liquid crystal must be vertically aligned on the spacer surface. Was derived.

As described above, according to the present embodiment, ST
In the N-mode liquid crystal display device, as a first condition, the amount of change in the dielectric anisotropy Δε when the temperature of the liquid crystal material changes by 10 ° C. is (change in Δε) ≧ 1.45. -(Tni / 100) is satisfied, and as a second condition, the amount of the compound having a cyano group contained in the liquid crystal material is 35% by weight or less of the entire liquid crystal material, thereby reducing display unevenness due to heat.
High contrast can be achieved.

In order to design the composition of the liquid crystal material satisfying the first condition, it is effective to use a liquid crystal material having a large dielectric anisotropy Δε as the liquid crystal material as described above. As condition 2, the compound having a cyano group needs to be 35% by weight or less of the whole liquid crystal material. Therefore, this cannot be achieved only with cyano PCH, which has a Δε of about 12 alone. 4-cyano-3,5
A liquid crystal compound having a -difluorophenyl structure or a 4-cyano-3-fluorophenyl structure has a ΔΔ of 2
0 or more, and Δ 大 き い is about 75 at the largest value.
Therefore, all or part of a compound having a cyano group in a liquid crystal composition is replaced with a liquid crystal compound having a 4-cyano-3,5-difluorophenyl structure or a 4-cyano-3-fluorophenyl structure. so,
(The change of Δε) ≧ 1.45- (Tni / 100), preferably the change of Δε) ≧ 1.5− (Tni / 100) and the content of the liquid crystal compound having a cyano group is 35
A liquid crystal material of not more than 30% by weight, preferably not more than 30% by weight can be obtained. As a result, display unevenness due to heat can be reduced and high contrast can be realized. This 4-cyano-3,5
Examples of the liquid crystal compound having a -difluorophenyl structure or a 4-cyano-3-fluorophenyl structure include compounds having various chemical structures shown in Chemical formula 1 (Chemical formula 1)
Wherein R represents an alkyl group, an alkoxyl group, or an alkenyl group).

[0056]

Embedded image In the above-described embodiment, the liquid crystal display device that satisfies the first condition and the second condition at the same time has been described in order to simultaneously suppress display unevenness due to heat generation and achieve high contrast. A liquid crystal display device that satisfies only one of these conditions may be used. For example, when only the first condition is satisfied, the effect of suppressing display unevenness due to heat generation can be reliably obtained. In this case, the first condition is (change amount of Δε) ≧ 1.45- (Tni / 100)
From the equation, it is clear how much the amount of change of Δε should be designed, so that the liquid crystal material can be easily designed according to the phase transition temperature Tni. On the other hand, when only the second condition is satisfied, the effect of suppressing light leakage around the spacer can be reliably obtained. Also in this case, the second condition is a specific numerical value condition in which the content of the compound having a cyano group contained in the liquid crystal material is 35% by weight or less of the entire liquid crystal material, so that the liquid crystal composition is easily designed. be able to. (Example 1) As Example 1, FIG.
The STN type liquid crystal display device was manufactured. Spacer 7
The spacer described in JP-A-8-328018 was used in which the surface of the spacer was modified with a long-chain alkyl group. The liquid crystal layer 6 comprises 10% by weight of a transethylene derivative having a 4-cyano-3,5-difluorophenyl structure in a molecule described in JP-A-4-300861, 15% by weight of cyanoPCH, and 35% of a tolane compound. %, And a liquid crystal composition comprising 40% by weight of a neutral compound. The content of the liquid crystal compound having a cyano group in this liquid crystal composition was 25% by weight, and the above-described second condition, that is, the content of the liquid crystal compound having a cyano group was 35% by weight or less was satisfied. .

Further, ΔΔ of this liquid crystal composition at 25 ° C. was measured by the above-mentioned method, and was found to be 9. Next, when a difference between Δε at 30 ° C. and 40 ° C. of the liquid crystal composition was measured, Δ (Δε) was 0.72. Further, the liquid crystal composition had a phase transition temperature Tni of 80 ° C. Therefore, 1.45- (Tni / 100) = 1.45- (80/1
00) = 0.65, and Δ (Δ
ε) ≧ 1.45- (Tni / 100).

The liquid crystal composition of this example was injected into the parallel alignment cell used in the embodiment, and the liquid crystal state around the spacer 7 was observed. As a result, it was confirmed that the liquid crystal composition was vertically aligned on the spacer surface. .

A liquid crystal display device having the structure shown in FIG. 8 was manufactured using the liquid crystal composition of this embodiment and the spacer 7, and the surface temperature of the display portion was measured.
It was 31 ° C at a low place. However, in spite of such a temperature difference, in the visual image quality inspection, display unevenness due to the temperature distribution was not observed at all, and a display with high uniformity was obtained. The difference between V40 of the lowest temperature portion and V40 of the highest temperature portion was 18 mV. When the contrast of this liquid crystal display device was measured, it was 59: 1, and both display uniformity and high contrast were achieved. (Example 2) As Example 2, FIG.
The STN type liquid crystal display device was manufactured. Note that the liquid crystal composition constituting the liquid crystal layer 6 was the same as the liquid crystal composition described in Example 1.
5% by weight of a transethylene derivative having a cyano-3,5-difluorophenyl structure in the molecule,
Was used, and a liquid crystal composition composed of 25% by weight, 35% by weight of a tolan compound, and 35% by weight of a neutral compound was used.

The content of the liquid crystal compound having a cyano group in this liquid crystal composition was 30% by weight, and the content of the liquid crystal compound having a cyano group was 35% by weight or less under the above second condition. Meets

When the difference between Δε of the liquid crystal composition at 30 ° C. and 40 ° C. was measured, Δ (Δε) = 0.7.
It was 6. The phase transition temperature Tni was 90 ° C. Therefore, 1.45- (Tni / 100) = 1.45- (90/1
00) = 0.55, and the first condition Δ (Δ
ε) ≧ 1.45- (Tni / 100).

When the liquid crystal display device shown in FIG. 8 was manufactured using this liquid crystal composition, no display unevenness due to temperature distribution was observed, and a display with high uniformity was obtained. The difference between V40 of the lowest temperature portion and V40 of the highest temperature portion was 23 mV. When the contrast of this liquid crystal display device was measured, it was 50: 1. Further, when the amount of light leakage in black display was measured, it was 0.7.
It was 0 × 10 ⁻⁴ % · mm ² / piece. Therefore, the liquid crystal display device of the present embodiment achieved both display uniformity and high contrast. (Example 3) As Example 3, FIG.
The STN type liquid crystal display device was manufactured. Note that the liquid crystal composition constituting the liquid crystal layer 6 was the same as the liquid crystal composition described in Example 1.
5% by weight of a transethylene derivative having a cyano-3,5-difluorophenyl structure in the molecule,
, 20% by weight of a liquid crystal compound having a 4-cyano-3-fluorophenyl structure in the molecule, 30% by weight of a tolan compound, and 35% by weight of a neutral compound.

The content of the liquid crystal compound having a cyano group in this liquid crystal composition was 35% by weight, and the content of the liquid crystal compound having a cyano group under the second condition was 35% by weight.
The following conditions are satisfied.

When the difference between Δε of the liquid crystal composition at 30 ° C. and 40 ° C. was measured, Δ (Δε) = 0.7.
It was 2. The phase transition temperature Tni was 96 ° C. Therefore, 1.45- (Tni / 100) = 1.45- (96/1
00) = 0.49 and Δ (Δ
ε) ≧ 1.45- (Tni / 100).

When the liquid crystal display device shown in FIG. 8 was manufactured using this liquid crystal composition, no display unevenness due to temperature distribution was observed at all, and a display with high uniformity was obtained. The difference between V40 of the lowest temperature portion and V40 of the highest temperature portion was 11 mV. When the contrast of this liquid crystal display device was measured, it was 42: 1. Further, when the amount of light leakage in black display was measured, it was 1.1.
It was 5 × 10 ⁻⁴ % · mm ² / piece. Therefore, the liquid crystal display device of the present embodiment achieved both display uniformity and high contrast. (Example 4) As Example 4, an alignment state around a spacer 7 of a liquid crystal composition to which a compound having a 4-cyano-3,5-difluorophenyl structure or a compound having a 4-cyano-3-fluorophenyl structure was added. Was observed. The observation method is
In the above embodiment, ZLI-1083 was added to the mixture of PCH302 and PCH304, and the same method as that for observing the peripheral orientation of the spacer was used.

First, PCH302, PCH304 and 4-propyl-4 'described in JP-B-3-77175.
-(3-Pentenyl) bicyclohexane was mixed to obtain a parent liquid crystal mixture. When only the base liquid crystal was placed in the parallel alignment cell, a state of vertical alignment on the surface of the spacer 7 was observed as in the case of the mixture of PCH302 and PCH304 (FIG. 4).

Next, 4-cyano-3,5 used in Example 1 was used.
-A compound having a difluorophenyl structure was added at different concentrations and injected into a parallel alignment cell. Observation of the orientation around the spacer revealed that the orientation state changed significantly between the addition amounts of 30% by weight and 40% by weight, as in the case of ZLI-1083. Furthermore, when the amount of light leakage was measured,
0.68 × 10 ⁻⁴ % · mm ^{2 when the} amount of addition is 30% by weight
/ Piece, but 1.58 × 10 ^-4 when 40% by weight was added.
% · Mm ² / piece.

Accordingly, even in the case of a compound having a 4-cyano-3,5-difluorophenyl structure or a 4-cyano-3-fluorophenyl structure, similar to cyanoPCH,
If the addition amount exceeds 30 to 35% by weight, the peripheral orientation of the spacer is remarkably changed, and the contrast is lowered. Therefore, in order to realize a high contrast, the upper limit of the addition amount of a compound having a 4-cyano-3,5-difluorophenyl structure or a 4-cyano-3-fluorophenyl structure is 35% by weight, preferably 30% by weight.

Next, the aforementioned PCH 302 and PCH 30
The base liquid crystal composed of 4, and 4-propyl-4 '-(3-pentenyl) bicyclohexane was prepared by using 4
A compound having a -cyano-3,5-difluorophenyl structure and cyanoPCH were added such that the total amount of both added was 30% by weight, and Δε of the mixed liquid crystal was measured. As a result, when the addition amount of the compound having a 4-cyano-3,5-difluorophenyl structure is 5% by weight or less,
The difference Δ (Δ) between Δε of the liquid crystal composition at 30 ° C. and 40 ° C.
ε) was found to be Δ (Δε) <1.45- (Tni / 100).

From the above results, the addition amount of the compound having a 4-cyano-3,5-difluorophenyl structure or 4-cyano-3-fluorophenyl structure is at least 5% by weight and at most 35% by weight. %, Preferably not more than 30% by weight. Example 5 Next, as Example 5, a reflective liquid crystal display device shown in FIG.

The reflection plate 10 was formed on the glass substrate 4a by aluminum evaporation. An insulating layer 11 is provided thereon and ITO
An electrode 5a was provided. Also, the side where the user looks at the liquid crystal display,
That is, the light guide 108 was arranged on the front of the device, and the front light 12 was arranged on the side. The liquid crystal material used and other configurations are the same as those of the transmission type liquid crystal display device described in the first embodiment.

The image of the reflection type liquid crystal display device shown in FIG. 10 was displayed, and the front light was turned on for a long time. When the temperature of the display surface was measured, the portion near the light was about 35
° C and the center of the display section was 28 ° C. In spite of such a temperature difference, no thermal unevenness was observed by visual inspection, and a display with high uniformity was obtained. (Example 6) As Example 6, an apparatus having the same structure as the liquid crystal display of Example 1 was composed of a compound having 50% by weight of a cyano group, 45% by weight of a neutral compound, and 5% by weight of a tolane compound. A liquid crystal composition was injected.

The difference Δ (Δε) between the dielectric anisotropy Δε at 30 ° C. and 40 ° C. of this liquid crystal was 0.81. The phase transition temperature Tni of the liquid crystal was 80 ° C. Therefore, the liquid crystal composition of the present example was 1.45− (Tni / 100) = 1.4.
5− (80/100) = 0.65, which satisfies the above-described first condition Δ (Δε) ≧ 1.45- (Tni / 100).

However, since the content of the compound having a cyano group in this liquid crystal composition is 50% by weight, the content of the liquid crystal compound having a cyano group, which is the above second condition, is 35% by weight or less. Does not meet.

Further, with respect to this liquid crystal, the liquid crystal alignment around the spacer was observed using the above-mentioned parallel alignment cell.
As a result, it was found that the orientation was in the middle of FIGS. 5 (d) and 5 (e). The amount of light leakage around the spacer when black display was performed on the liquid crystal display device was measured.
It was 7 × 10 ⁻³ % mm ² / piece.

When an image was displayed on this liquid crystal display device, the temperature distribution on the display surface was almost the same as in Example 1. Further, display unevenness due to this temperature distribution was not observed, and a display with high uniformity was obtained. The difference between V40 at the highest and lowest temperatures was significantly smaller by 6 mV. Therefore, an effect of suppressing display unevenness due to the temperature distribution could be obtained.

However, when the contrast was measured, it was 35: 1, which was lower than that of the liquid crystal display of Example 1. The reason for this is that the liquid crystal display device does not satisfy the second condition, so that a large amount of light leaks around the spacer during black display, and the brightness of black display increases.

The arrangement of the polarizing plate and the phase difference plate of the liquid crystal display device manufactured in Example 6 was changed so that a so-called normally white (normally open) liquid crystal displaying white at low voltage and displaying black at high voltage. A display device was manufactured. When a high voltage was applied and the amount of light leaking around the spacer was measured in a state where black display was performed, almost no light leak was detected. This is because, when a high voltage is applied, the liquid crystal molecules around the spacer also respond to the electric field and rise.
Therefore, there is almost no light leakage around the spacer. However, in the normally white method, other side effects such as poor color purity of display colors were large. (Embodiment 7) As Embodiment 7, a device having the same structure as the liquid crystal display device of Embodiment 1 is composed of a compound having 20% by weight of a cyano group, 65% by weight of a neutral compound, and 15% by weight of a tolane compound. A liquid crystal composition was injected.

Therefore, the content of the compound having a cyano group in this liquid crystal composition was 20% by weight, and the content of the liquid crystal compound having a cyano group, which was the second condition in the above embodiment, was 35% by weight. The following conditions are satisfied.

The difference Δ (Δε) between the dielectric anisotropy Δε at 30 ° C. and 40 ° C. of the liquid crystal was 0.57. The phase transition temperature Tni of this liquid crystal was 82 ° C. Therefore, this liquid crystal composition has 1.5- (Tni / 100) = 1.5- (82 /
100) = 0.68,1.45- (Tni / 100) = 1.
45− (82/100) = 0.63, and the first condition Δ (Δε) ≧ 1.5− (Tni / 100), Δ
None of (Δε) ≧ 1.45- (Tni / 100) is satisfied.

With respect to this liquid crystal, the liquid crystal alignment around the spacer was observed using the above-described parallel alignment cell. As a result, it was found that the liquid crystal molecules were vertically aligned on the spacer surface. When the amount of light leakage around the spacer when black display was performed on the liquid crystal display device was measured, 0.65 × 1
It was 0 ^-3 % · mm ² / piece. When an image was displayed on this liquid crystal display device, the contrast was as good as 62: 1. This is because the liquid crystal composition of this example satisfies the second condition.

However, the liquid crystal composition of this example is
Since the first condition is not satisfied, display unevenness due to the temperature distribution is observed as a result of the visual inspection, and the display uniformity is low, although the temperature distribution on the display surface is almost the same as that in the first embodiment. Was. When the difference between V40 at the highest temperature and V40 at the lowest temperature was measured, it was remarkably large at 58 mV, and it was found that the change in drive voltage due to this temperature difference was visually observed as uneven display.

When the liquid crystal display device according to the present invention is applied to a display unit of a computer system, a communication system, a mobile navigation system, etc., the visibility of display in the system is improved.

[0084]

According to the present invention, in a so-called normally black type liquid crystal display device which performs black display at a low voltage and white display at a high voltage, display unevenness due to heat generation from a light source or a circuit is reduced, and A high-quality liquid crystal display device that can achieve both high contrast can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a change ΔB in relative luminance B40 and a change ΔV40 in drive voltage V40 when a temperature of a liquid crystal material changes in the liquid crystal display device according to one embodiment of the present invention.

FIG. 2 is a graph showing a relationship between ΔV40 and ΔB when the temperature of a liquid crystal material changes, and a range where ΔB is within 10% of B40 in the liquid crystal display device according to one embodiment of the present invention.

FIG. 3 shows a relationship between ΔV40 and a change Δ (Δε) in dielectric anisotropy Δε when a temperature of a liquid crystal material changes from 30 ° C. to 40 ° C. in the liquid crystal display device according to one embodiment of the present invention; Also, a graph showing a range of Δ (Δε) for suppressing ΔV40 to 25 mV or less.

FIG. 4 illustrates a PCH 302 in one embodiment of the present invention.
FIG. 4 is an explanatory diagram schematically showing a light transmission state when the vicinity of a spacer 7 of a parallel alignment cell filled with a mixture of PEG and PCH304 is observed under crossed Nicols.

FIG. 5 shows (a) to (c) in one embodiment of the present invention.
(D) A parallel alignment cell filled with a liquid crystal material obtained by adding a mixture of PCH302 and PCH304 with 20-60% of a mixture of cyano-based compounds ZLI-1083, and (e) A parallel alignment cell filled with only ZLI-1083 around the spacer 7 FIG. 4 is an explanatory view schematically showing a light transmission state when the image is observed under crossed Nicols.

FIG. 6 is a graph showing the relationship between the content of a cyano compound in a liquid crystal composition and the amount of light leakage around a spacer 7 in black display in the liquid crystal display device according to one embodiment of the present invention.

FIG. 7 is a graph showing a range in which a change Δ (Δε) in dielectric anisotropy of a liquid crystal material should be satisfied in relation to a phase transition temperature Tni in the liquid crystal display device according to one embodiment of the present invention.

FIG. 8 is an explanatory diagram illustrating a configuration of a normally black liquid crystal display device according to an embodiment of the present invention.

FIGS. 9A, 9B, and 9C are explanatory diagrams showing alignment states of liquid crystal molecules around a spacer 7 in FIGS. 4 and 5C and 5E, respectively.

FIG. 10 is an explanatory diagram illustrating a configuration of a reflective liquid crystal display device according to a fifth embodiment of the present invention.

[Explanation of symbols]

2a, 2b: polarizing plate, 3a, 3b: retardation plate, 4a, 4
b: glass substrate, 5a, 5b: electrode, 6: liquid crystal layer, 7:
Spacer, 8,108 light guide, 9 backlight
10: reflector, 11: insulating layer, 12: front light.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichi Komura 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Katsumi Kondo Inventor 7-1, Omikamachi, Hitachi City, Ibaraki No. 1 Inside Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Toshiki Asakura 3300 Hayano, Mobara City, Chiba Prefecture Inside Display Group, Hitachi, Ltd. Within the Manufacturing Display Group

Claims (17)

[Claims] 1. A liquid crystal device comprising: a pair of substrates; a spacer sandwiched between the pair of substrates; and a liquid crystal layer formed by filling a liquid crystal material between the pair of substrates. The change ΔVth of the drive voltage threshold when the temperature changes by 10 ° C. is smaller than 25 mV,
In addition, the liquid crystal material contains a liquid crystal compound having a cyano group at a content of 35% by weight or less. 2. The liquid crystal display device according to claim 1, wherein the amount of change Δ (Δε) in dielectric anisotropy when the temperature changes by 10 ° C. is Δ (Δε) ≧ 1.45. (Tni / 100) (where Tni is a temperature at which a liquid crystal material changes from a liquid crystal phase to an isotropic phase). 3. The liquid crystal display device according to claim 1,
When the variation Δ (Δε) of the dielectric anisotropy is Δ (Δε) ≧
A liquid crystal display device characterized by satisfying 1.5- (Tni / 100). 4. The liquid crystal display device according to claim 1, wherein the content of the liquid crystal compound having the cyano group in the liquid crystal material is 30% by weight or less. 5. The liquid crystal display device according to claim 1, wherein the liquid crystal compound having a cyano group is: (Wherein X1 and X2 are H or F) A compound having a chemical structure represented by the following formula: 6. The liquid crystal display device according to claim 1, wherein the liquid crystal compound having a cyano group is 4-cyano-
A liquid crystal display device comprising at least one of a liquid crystal compound having a 3,5-difluorophenyl structure in a molecule and a liquid crystal compound having a 4-cyano-3-fluorophenyl structure in a molecule. 7. The liquid crystal display device according to claim 4, wherein
The liquid crystal material comprises a liquid crystal compound having the 4-cyano-3,5-difluorophenyl structure in a molecule and
A liquid crystal display device comprising at least one of a liquid crystal compound having a cyano-3-fluorophenyl structure in a molecule at a content of 5% by weight or more. 8. The liquid crystal display device according to claim 1, wherein said spacer is light-shielding. 9. The liquid crystal display device according to claim 1, wherein said spacer is treated so that liquid crystal is vertically aligned on a surface of said spacer. 10. The liquid crystal display device according to claim 9, wherein the surface of the spacer is modified with a long-chain alkyl group. 11. The liquid crystal display device according to claim 1, wherein said liquid crystal layer is of a so-called super twisted nematic type having a twist angle of 240 degrees or more. 12. A normally black, super twisted nematic liquid crystal display device, comprising: a pair of substrates; a spacer sandwiched between the pair of substrates; and a liquid crystal material interposed between the pair of substrates. A liquid crystal layer formed by filling, wherein the liquid crystal material contains a liquid crystal compound having a cyano group at a content of 35% by weight or less. 13. The liquid crystal display device according to claim 12, wherein the liquid crystal compound having a cyano group is 4-cyano-
A liquid crystal display device comprising at least one of a liquid crystal compound having a 3,5-difluorophenyl structure in a molecule and a liquid crystal compound having a 4-cyano-3-fluorophenyl structure in a molecule. 14. A method of designing a liquid crystal material for a normally black super twisted nematic liquid crystal display device, wherein the amount of change in dielectric anisotropy Δ when the temperature changes by 10 ° C.
The liquid crystal material is configured so that (Δε) satisfies Δ (Δε) ≧ 1.45- (Tni / 100) (where Tni is a temperature at which the liquid crystal material changes from a liquid crystal phase to an isotropic phase). A method for designing a liquid crystal material of a liquid crystal display device, comprising selecting a liquid crystal compound and a composition thereof. 15. A computer system having a display unit,
A computer system, wherein the display unit comprises the liquid crystal display device according to claim 1-3. 16. A communication system having a display unit, wherein the display unit comprises the liquid crystal display device according to claim 1. Description: 17. A mobile navigation system having a display unit, wherein the display unit comprises the liquid crystal display device according to claim 1. Description: