JPH0359954B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a time-division drive liquid crystal display device, and particularly to a time-division drive liquid crystal display device provided with a liquid crystal composition suitable for a time-division drive system. [Prior Art] FIG. 1 shows an example of a twisted nematic (TN type) liquid crystal display device, which is one type of field effect liquid crystal display device. In the liquid crystal display device shown in the figure, a first substrate 1 and a second substrate 2 each made of transparent glass or the like are spaced apart from each other by a predetermined distance, for example, 5 to 15 μm.
The peripheries thereof are sealed with a sealing member 3 made of, for example, fritted glass or organic adhesive, and a nematic phase liquid crystal 4 is sealed in the internal space formed by these members. The predetermined spacing is obtained by a spacer 5, for example of fiber glass, glass powder or the like. Note that the sealing member 3 may also be used as a spacer without using the spacer 5 in particular. The first and second substrates 1 and 2 each have a predetermined pattern of electrodes 6 formed on their opposing inner surfaces, and furthermore, on the surfaces in contact with the liquid crystal, liquid crystal molecules near the surfaces are aligned in a desired fixed direction. The liquid crystal alignment control surfaces 7 and 8 are used to control liquid crystal alignment. Such an orientation control surface can be formed by, for example, an oblique evaporation film in which SiO is deposited obliquely to the substrate surface on a substrate surface having electrodes, or an organic polymer thin film or an inorganic thin film is coated on the substrate surface. It is made by applying a so-called rubbing process in which the surface is rubbed in a certain direction with cotton or the like. Regarding the liquid crystal alignment direction, the liquid crystal alignment control surface 7 of the first substrate 1 has a first fixed direction, and the second substrate 2 has a first constant direction.
By selecting the second fixed direction and making each direction different for the liquid crystal alignment control surface 8,
The molecules of the nematic phase liquid crystal 4 sandwiched between the substrates 1 and 2 are twisted and oriented from the first direction to the second direction. The angle between the first direction and the second direction, that is, the twist angle of the liquid crystal molecules can be arbitrarily selected, but generally approximately 90 degrees is selected as shown in FIG. A first polarizing plate 9 and a second polarizing plate 10 are arranged on the outside of the substrates 1 and 2, respectively. In this case, the angle between the polarization axes of the two polarizing plates 9 and 10 is usually the same as the twist angle of the liquid crystal element (the angle between the first direction and the second direction), or the angle between (the polarization axes are parallel) are selected. Usually, the alignment direction of the liquid crystal alignment surface and the polarization axis of the polarizing plate are arranged parallel to or perpendicular to each other. When such a display device performs a normal display when viewed from the first substrate side, it is a reflective display device in which a reflector 11 is disposed on the back surface of the second polarizing plate 9, or a reflective display device in which a reflector 11 is disposed on the back surface of the second polarizing plate 9. A light guide such as an acrylic resin plate or a glass plate having a desired thickness is inserted between the reflector 9 and the reflector 11, and a light source is placed at an appropriate position on the side of the light guide, which is widely used as a nighttime display element. Here, the twist angle is 90 degrees, and the polarization axis crossing angle is 90 degrees.
The principle of display operation of a reflective liquid crystal display device will be explained. Now, when there is no electric field in the liquid crystal layer, external light (ambient light incident on the first polarizing plate 9 of this liquid crystal display element) first passes along the polarization axis of the first polarizing plate 9. The light becomes linearly polarized light and enters the liquid crystal layer 4, but since the liquid crystal molecules are twisted 90 degrees between the layers, when it passes through the liquid crystal layer, the plane of polarization of the polarized light is rotated 90 degrees, and the second polarizing plate 10
Transmit. This light is reflected by the reflecting plate 11, passes through the second polarizing plate 10, the liquid crystal layer 4, and the first polarizing plate 9 in the reverse order as described above, and is emitted to the liquid crystal display device. Therefore, the viewer can observe the polarized light that is incident on the liquid crystal display device, reflected by the reflector, and then outputted from the liquid crystal display device again. In such a display device, when a predetermined voltage is applied to a predetermined selected electrode 6 and an electric field is applied to a predetermined region of the liquid crystal layer, the liquid crystal molecules in that region are aligned along the direction of the electric field. As a result, the optical rotation power of the plane of polarization is lost in that region, and the plane of polarization does not rotate in that region, so that the light polarized by the first polarizing plate 9 is blocked by the second polarizing plate 10. Therefore, the area appears dark to the observer. Therefore, desired display can be performed by applying voltage to desired selected electrodes. In the field-effect liquid crystal display device as described above, it is particularly desirable that the liquid crystal composition used has the following properties. That is, (1) it has good adaptability to the orientation control surface, (2) it can operate in a wide temperature range, and (3) it has good responsiveness even in a wide temperature range, especially at low temperatures. Regarding the first requirement, it is extremely important to control the molecules of the liquid crystal 4 so that they are aligned parallel to each other and in one direction at the interface between the upper and lower plates. This control is performed using SiO
This is done by forming a diagonal vaporized film or by applying a rubbing treatment. In addition, for the second requirement, the minimum requirement is that it be liquid crystal at around normal temperature of 25℃, but in practical terms it should be liquid crystal in the temperature range of -10℃ to +60℃ or higher. A liquid crystal is required. Note that the transition temperature of the predetermined solid/liquid crystal described in the present invention is determined and defined based on the following measurements. Individual liquid crystal single substances and mixed compositions composed of them often exhibit a supercooling phenomenon. In that case, the temperature is sufficiently low (e.g. -40
℃) to measure crystallization, and then the transition temperature at the time of temperature rise was measured using a micro-melting point measuring device, and this was taken as the solid-liquid crystal transition temperature. This second requirement has an extremely important meaning not only in ordinary static driving but also in driving by the so-called time-division driving system. That is, recently, in liquid crystal display devices, particularly in devices that require a large amount of information, such as calculators or matrix displays, it has become essential to adopt a time-division driving method using a voltage averaging method or the like. Low-voltage drive is desirable for calculators, etc., especially 4.5V drive (3 batteries for 1.5V) and 3V drive (battery 1.5V), which can be directly driven by connecting batteries in series.
Low voltage drive such as 1.5V (2 pcs.) is adopted. Since this low-voltage drive connects batteries in series, it does not require a booster circuit, and when combined with C-MOS, the battery life can be maintained at 500 to 2000 hours. However, if such a time-division drive system is adopted, operational constraints that do not occur in the static drive system will exist in principle. In other words, in a time-division display device, it is necessary to prevent crosstalk between picture elements at half-selected points and non-selected points. The voltage averaging method is the most commonly used method for preventing this crosstalk. This method was devised for the purpose of increasing the margin of operation by averaging the crosstalk voltage and increasing the difference from the selection voltage. This method will be explained below with specific examples. Average the crosstalk voltage to 1/3 of the selected voltage,
An example of applying the voltage averaging method using an alternating current drive waveform will be presented. The driving waveform of this method is as shown in the state diagram of FIG. In Figure 3, in the selected state ±
A voltage of V ₀ is applied to the liquid crystal, and a voltage of ±(1/3) V ₀ is applied to the liquid crystal in the half-selected state and non-selected state. At this time, the effective value ν _s1 of the applied voltage applied to the point at which the liquid crystal enters the display state, that is, the display point, is expressed by the following equation. However, N: Duty number. On the other hand, the effective value ν _s2 of the applied voltage applied to the non-display point of the liquid crystal is given by the following equation. ν _s2 = 1/3V ₀ ...(2) Here, in order to put the display point into the display state, ν _s1 ≧V _th with respect to the threshold voltage V _th of the liquid crystal, and there is no crosstalk to the non-display point. In order not to cause ν _s2 ≦
Must be V _th . That is, the conditions for displaying with crosstalk prevented by this driving method are as follows. ν _s2 ≦V _th ≦υ _S1 ...(3) Substituting equations (1) and (2) into equation (3) and rearranging for V ₀ results in the following. Therefore, when V ₀ is changed and the brightness of display points and non-display points is measured, the results are as shown in FIG. The threshold voltage of the liquid crystal converted to V ₀ at the display point and non-display point,
V _th1 and V _th2 exist, and when V _th1 ≦V ₀ ≦V _th2 (5), display that prevents crosstalk is possible.
Note that, according to equation (4), V _th1 and V _th2 can be expressed by the following equations. V _th2 = 3V _th ...(7) Regarding formula (5), to be more precise, the lower limit of the voltage that can be displayed should be the saturation voltage V _sat1 shown in Figure 8, not V _th1 . be. In other words, the _following (8) is the formula for determining the voltage range that allows _display that prevents _crosstalk . It can be said that a device with a larger movable range of V ₀ in equation (8) has a wider operating margin. In the induction of the above equation, ν _s1 ,
ν _s2 Therefore, V _th1 , V _th2 , V _sat1 , etc. have been considered as constant values, but these can change depending on the temperature (T), viewing angle (φ, θ) with respect to the element (Fig. 4), etc. It is. In the explanation of equation (1) or (8), the fourth
I have been considering the visual angle φ = 0 defined in the figure, but
In reality, φ takes values within a certain finite range. There are various factors that determine the operating margin, and these will be explained in order below, but when considering the factors that determine the operating margin, it is convenient to take up the following three factors to see the essence of the problem. It is. (a) Fluctuation of threshold voltage due to temperature (b) Fluctuation of threshold voltage due to angle (c) Sharpness of voltage-luminance characteristics Now, let us explain the relationship between (a) to (c) and the operating margin using the specific measurement method. Clarify quantitatively using examples. The electro-optical characteristics of the time-division drive method were measured by the method shown in FIG. The liquid crystal display device 51 is a luminance meter 52
It is arranged in a constant temperature bath 53 at an angle of 10° to 40° relative to the main body. And for the luminance meter 52
The liquid crystal display device 51 is irradiated with light from a tungsten lamp 54 arranged at an angle of 30 degrees through a heat-absorbing glass filter 55.
1 is measured by a brightness meter 52. The drive waveforms in the case of time-division drive 1/3 bias/1/3 duty and 1/2 bias/1/2 duty measured by the method described above are as shown in FIGS. 6 and 7. FIG. 8 shows voltage and brightness characteristics using this waveform. The area is an area that is not lit, and the area is an area where only the selected point is lit. Desired numbers, characters, etc. can be displayed in this area. The area is an area in which all segments are lit and does not serve as a display function. In other words, this is an area where crosstalk occurs. V _th1 is the voltage at the selected point (ON state) at 10% brightness, V _th2 is the voltage at the non-selected (OFF state) point at 10% brightness, V _sat1 is the voltage at the selected point at 50% brightness,
V _sat2 is the non-selection voltage at 50% brightness. The operating margin is defined by the following formula. M (%) = V _th2 (T = 40, φ = 40°, f = 100)
-V _sat1 (T=0, φ=10゜, f=550)/V _th2 (T=40
, φ=40゜, f=100) + V _sat1 (T=0, φ=10゜, f
= 550) × 100 However, T = Temperature (°C) 0° to 40°C φ = Viewing angle (°) 10° to 40° f = Frequency (Hz) 100 to 550Hz Therefore, a wide operating margin means a wide area. It is synonymous with. In this way, time-division driving requires driving within a certain voltage width (margin). Further analysis of the operating margin M expressed by equation (9) reveals that M is determined by the three factors (a) to (c) described above. Each factor is quantitatively defined by the following formula. (a) Temperature characteristics of V _th ΔT ΔT=V _th2 (T=0℃)−V _th2 (T=40℃)/V _th
2 (T=0℃)+V _th2 (T=40℃)×100(%)……(10)
However, the temperature T is in the range of 0° to 40°C, and φ=
Define ΔT as the value at 40° and f=100Hz. (b) Angular dependence of V _th Δφ Δφ=V _th2 (φ=40°)/V _th2 (φ=10°)……(11) However, Δφ is the value at T=40°C and f=100Hz. defined. (c) Sharpness of voltage-luminance characteristics γ γ = V _sat1 /V _th1 ...(12) These three (a) to (c) are the main elements, but in addition to these, the frequency characteristic Δf is generally exist. Δf=V _th1 (f=550)/V _th1 (f=100) (13) However, Δf is defined as the value at T=40°C and φ=40°. Furthermore, for convenience in deriving the equation, a margin α in the voltage averaging method is defined. α=V _th2 /V _th1 (14) Here, by substituting (10) to (14) into equation (9) and rearranging, the operating margin M is given by the following equation. M=1-(γ/Δ)Δf/α・A/1+(γ/Δ
)Δf/α・A……(15) However, A=1−ΔT/1+ΔT Generally, γ, Δ, ΔT, Δf are γ≧1, Δφ≦1,
Takes the value of ΔT≧0, Δf≦1. The operating margin defined here can take various values depending on the liquid crystal material, and a material that can provide a larger margin M is suitable for time-division driving. . As is clear from equation (15), in order to expand the operating margin M, the temperature characteristic ΔT is
approaches 0, the angle dependence Δ, voltage-luminance sharpness γ, and frequency characteristic Δf each decrease to 1.
It is necessary to be close to. In some cases, by introducing a temperature compensation circuit into the device, the influence of the temperature characteristic ΔT can be almost ignored and the operating margin of the device can be expanded. However, providing a temperature compensation circuit inevitably makes the device expensive, so in order to reduce costs, popular products such as calculators are widely used without such extra compensation circuits. It is extremely preferable to use component materials (elements) that allow a sufficient operating margin. Regarding the third requirement, ie, "good responsiveness over a wide temperature range, especially at low temperatures," the method can be derived from the following considerations. The response in twisted nematic mode during time division drive operation is given by the following equation. t _rise ∝1/(8/N+1)・η・d ² /K …(16) t _fall ∝d ² η/K …(17) η is the viscosity, K is the elastic constant, and d is the thickness of the liquid crystal layer .
For K, see equation (61). From the above equation, it can be seen that the response of the liquid crystal is mainly determined by the viscosity of the liquid crystal material. This theoretical formula is said to be in good agreement with actual measurements, and those skilled in the art can easily recognize that responsiveness can be improved by reducing the viscosity of the liquid crystal material. In other words, the key to success or failure in meeting this third requirement lies in finding a liquid crystal material with low viscosity (after satisfying the other first and second requirements, of course). [Problems to be Solved by the Invention] Various materials such as Schiff base type, ester type, biphenyl type, and azoxy type have been proposed as materials for liquid crystal displays, particularly for time-division driving. The azoxy type is a material with good temperature characteristics (small ΔT), that is, there is little variation in threshold voltage due to temperature, and the operating margin M defined earlier is the condition of time-division drive with 1/3 bias and 1/3 duty It can take a large value of 10% or more. Azoxy type liquid crystal is given by the following general formula, It is a material that itself exhibits weak negative dielectric anisotropy. It is usually used in a system mixed with nematic liquid crystal (N _p ) having positive dielectric constant anisotropy. However, this azoxy-type material absorbs a portion of visible light and is colored (yellow), with a maximum absorption of light of 350 nm.
, and the following photochemical reactions occur at wavelengths around this range. That is, a non-liquid crystal substance is produced through a photochemical reaction, and the appearance of this new product changes the color from yellow to red, and generally the electrical resistance of the liquid crystal also sharply decreases. For the above reasons, azoxy nematic liquid crystals must be used with a 500 nm cut filter attached to the device (device) in order to avoid photodegradation effects caused by sunlight or fluorescent lamps. This makes the device (element) complicated. On the other hand, in addition to such materials that are susceptible to photodegradation, liquid crystals such as Schiff base-based, biphenyl-based, and ester-based liquid crystals have been considered as so-called white display materials for application to display devices. Biphenyl-based compounds are not easily disturbed by light, water, oxygen, etc., and are said to be chemically stable.
However, in this material system, only liquid crystal systems with positive dielectric constant anisotropy are known to be room temperature liquid crystals, and negative equivalents are room temperature liquid crystals and there are few practically useful ones. Therefore, there are only a few types of liquid crystal systems that can be constructed as a mixed system using only biphenyl systems, and the positive dielectric constant anisotropy is not particularly large, so it is difficult to adjust the threshold voltage over a wide range. It is difficult to do this by passing it on. In addition, the temperature dependence of the threshold voltage value is large (ΔT is large), and it is generally considered unsuitable for time-division driving. Ester-based liquid crystals have relatively excellent chemical stability, and there are many types of liquid crystal single substances with positive dielectric constant anisotropy and negative dielectric constant anisotropy. However, since the temperature dependence of the threshold voltage value is relatively large and the viscosity is also relatively large, it is generally difficult to meet the second and third requirements. Schiff bases have better physical properties than ester bases, but they are chemically highly hydrolyzable and may not be used unless they are matched to the device configuration, so they cannot be said to be universal. It's something I want. The present invention aims to overcome the drawbacks of the conventional liquid crystal materials, namely, it is stably aligned over a wide temperature range, the threshold voltage value can be set to any voltage value within a wide range, and the temperature dependence of the value is The present invention provides a liquid crystal display device that is characterized by a liquid crystal composition that has a small resistance and a high response speed. Conventionally, a nematic liquid crystal (N _o type liquid crystal) with negative dielectric anisotropy has been used as a base material to meet the second and third requirements of the three requirements above, and an appropriate amount of dielectric constant anisotropy is added to this. Nematic liquid crystals with positive orientation (N _p -type liquid crystals) and/or liquid crystal analogs with positive dielectric constant anisotropy (substances similar to nematic liquid crystals with positive molecular structure, hereinafter referred to as N _p -type liquid crystal analogs) )
The present inventors have discovered that a system to which . [Means for solving the problem] The present inventors newly developed the following general formula [In the formula, R ₁ is n-C _n H _2n+1 , R ₂ is n-C _q
Represents H _2q+1 −O. ] (However, m and q are 1 to 10) It has been discovered that a matrix system consisting of a mixed composition of multiple individual liquid crystals is a matrix system suitable for the above second and third requirements. be. Note that n is a symbol meaning that carbon is a straight chain, and n used in this specification has the same meaning. Further, it is assumed that the bond between the cyclohexane ring carbon and the carbonyl group carbon is an icatorial bond. Among the inventions disclosed in this specification, typical ones are as follows. general formula

[Formula] [In the formula, R ₁ is n-C _n H _2n+1 , R ₂ is n-C _q
H _2q+1 −O] (m and q are integers from 1 to 10)
A compound with the general formula

[Formula] [In the formula,

【ceremony

[Formula] or

[Formula], R ₃ - represents n-C _r H _2r+1 - (r is an integer from 1 to 7)]; and at least one compound represented by the general formula

[Effect]

The present inventors have discovered that nematic liquid crystals with negative dielectric constant anisotropy of the type expressed by the above general formula and their analogues can be used as a useful matrix for a wide liquid crystal temperature range by combining them to form a mixed system. They discovered that it could produce liquid crystals. Furthermore, the present inventors searched for nematic liquid crystals (N _p ) with positive dielectric constant anisotropy and their analogues that could be combined with the above-mentioned parent mixed system,
By combining this with the above matrix, we have found a liquid crystal composition system that is extremely suitable for time-division driving. Furthermore, by further adding N _o type in the above formula (18) and N _p type obtained by the above search, N o type liquid crystal and N _o type liquid crystal that can improve various properties suitable for time-division driving. I was able to find a similar one. [Example] The invention will be described in detail below with reference to Examples. Regarding the matrix composition composed of each liquid crystal element having the structure shown in formula (18), particularly preferable constituent materials are: (However, m, q are integers from 1 to 10.) In equation (19), the (m, q) combinations are (3, 5), (4, 5), (5, 5), (6 ，
5), (4,6), (3,1), (3,2), (3,3
),
(3,4), (3,9), (4,1), (4,2), (
4,
3), (4,4), (4,6), (4,8), (5,1
),
(5,2), (5,3), (5,4), (5,6), (
5,
7) etc. are preferred.

[Table] Table 1 shows the liquid crystal temperature range (MR) of the main N _o simple liquid crystals 4-n-alkyl-cyclohexanecarboxylic acid-trans-4'-alkoxyphenyl esters.
showed that. Furthermore, when these compounds are mixed, a mixed system with a wide MR can be obtained as shown in Table 2.

[Table] The liquid crystal in Table 2 1-1 is approximately
Shows a viscosity of 35 centipoise (CP). On the other hand, known ester liquid crystals whose molecular structure corresponds to the cyclohexane ring substituted in these liquid crystals have approximately 2
The viscosity is twice as high. for example, The viscosity of the mixed system is approximately 70 centipoise (CP) at room temperature.
give. In general, the system of the present invention exhibits a viscosity that is about half that of a typical ester-based liquid crystal containing two benzene rings, and exhibits physical properties that are advantageous for high-speed response. As you can see from the example above, [In the formula, R ₁ is n-C _n H _2n+1 , R ₂ is n-C _q
It is clear that the matrix liquid crystal (N _o ) consisting of a mixed system of H _2q+1 −O] (where m and q are integers from 1 to 10) is a matrix suitable for the third requirement. It is. On the other hand, in these N _o- type liquid crystal systems, Δε=ε‖−, where ε‖ is the dielectric constant in the direction of the director of the nematic liquid crystal, and ε ⊥ is the dielectric constant in the direction perpendicular to the director of the liquid crystal. The value of ε ⊥ is negative and its absolute value is relatively small. for example, The substance shown by has a small dielectric constant and weak electrical polarity, and from the concept of organic chemistry, it is close to a nonpolar solvent. In such a nonpolar solvent, N _p type, for example,

When solutes having large dielectric constants and large anisotropies such as [Formula] are mixed, their mutual compatibility naturally becomes a problem. for example

[Formula] and

The dielectric constant (measured at 22℃) of a mixed system with a 1:2 molar ratio in [Formula] is ε⊥
(1.5kHz) = 25.7, ε ⊥ (1.5kHz) = 7.3, Δε (1.5k
Hz) = 18.4 (measurement frequency is in parentheses), the dielectric constant is large, and its anisotropy is also large. In other words, these solutes belong to a polar group from an organic chemical concept. If such solvents and solutes, that is, non-polar N _o liquid crystal matrix and polar N _p liquid crystals/or N _p liquid crystal analogues, are mixed without careful consideration, the following problems may occur. This can be easily predicted, and the present inventors have already empirically recognized that this fact exists. 1) Phase separation may occur when the proportion of solute ( _NP -type nematic liquid crystal and its analogues) is increased. 2) The lower limit temperature of nematic liquid crystal in a mixed system increases. 3) At low temperatures, it may be difficult to control the alignment of liquid crystal molecules. Specific examples showing these undesirable phenomena are shown below. As the parent N _o type liquid crystal, Using a mixed matrix system (A-1), as an N _p- type liquid crystal, was used. As the orientation control film, SiO oblique evaporation (incident angle 83°) was used. Various amounts of the substance expressed by formula (26) were sealed in a twisted nematic liquid crystal device containing a SiO oblique evaporation film. When this device was placed in a constant temperature bath and the temperature was lowered from room temperature to a low temperature, it was found that some types of orientation abnormalities appeared in some devices. In a device equipped with upper and lower polarizing plates and a reflector, it was observed that part or all of the display section became dark. That is, the arrangement of the liquid crystal molecules has undergone some kind of change from the normal twisted state, and an abnormal alignment has occurred, which is thought to result in a decrease in the ability to control light. Table 3 shows the relationship between the amount of the N _p -type liquid crystal (Formula (26)) added and the orientation abnormality. This table shows the upper limit of the temperature at which the liquid crystal of each composition starts to exhibit alignment abnormalities. In the region where the amount of the N _p -type liquid crystal (Formula (26)) added is small, low-temperature stability is good. The orientation anomaly is approximately N _p
This is most likely to occur when equal amounts of N _o are mixed, and less likely to occur when the amount of N _p -type liquid crystal (formula (26)) is small.

[Table] To prevent such orientation abnormalities and lack of compatibility,
As a method to obtain a more reliable liquid crystal composition,
The present inventors have discovered the following extremely general method. In other words, a non-polar N _o matrix liquid crystal and a polar
In order to increase the compatibility with N _p -type liquid crystals and/or analogues of N _p -type liquid crystals and to obtain a wide MR, a type of N _o -type liquid crystal system other than the above-mentioned N _o is added as a third component. Good. In particular, the third component, N _o type, should be a nematic liquid crystal or a liquid crystal analogue that has electrical polarity in its molecules and negative dielectric anisotropy, in order to meet the above-mentioned favorable properties, i.e., a mixed system. Compatibility can be increased and a wide MR can be obtained. For example, in the mixed system of Schiff base type liquid crystal (N _o liquid crystal) of the system (A-1),
When adding N _p -type liquid crystal (formula (26)), N _o- type liquid crystal and/or N _o- type liquid crystal analog containing a polar group in the molecule as shown in the following example is further added as a third component. be. (However, m and q mean integers from 1 to 10.) As an example, the base N _o type liquid crystal is as follows: and as N _p type to this

[Formula] is added at 13wt%, and as a polar N _o type substance, added. The relationship between the amount of (C-2) added and the liquid crystal temperature range (MR) is shown in FIG. As can be seen from the figure, the liquid crystal temperature range (MR) decreases as the amount of (C-2) added increases, and the decrease in the liquid crystal-liquid transition temperature (N-I point) is relatively small, and as a whole (C-2) decreases as the amount of (C-2) added increases. The addition of -2) gave a favorable result in that the MR was expanded. In the above examples, the effectiveness of the third component was explained using Schiff base type liquid crystal as the parent N _o type, but the same thing is shown in Table 2 for the parent system (N _o type). Mixed system of 4-n-alkyl-cyclohexanecarboxylic acid-trans-4'-alkoxyphenyl ester (Table 2 1-1
It has become clear that this phenomenon occurs even when using ~1-11). In other words, _various types of
When adding N _p -type liquid crystal and/or N _p -type liquid crystal analogue, adding N _o -type liquid crystal and/or N _o -type liquid crystal analogue as the third component explained above will improve the compatibility with the above N _p -type substance. and widen
It became clear that MR could be obtained. Preferred N _o type liquid crystals and/or N _o type liquid crystal analogs as the third component are as follows. (In the above, m and/or q in (28) to (39) are integers from 1 to 10) However, R is CH ₃ -O-CH ₂ CH ₂ -O or CH ₃ -O-(CH ₂ ) ₃ -O (m is an integer from 1 to 9) R is (CH ₂ ) ₂ -CH-O or (CH ₂ ) ₂ -CH(CH ₂ ) ₂ -O (m, q are integers from 1 to 10) R is CH3 _- O-CH2 _- O, CH3 _- O-( _CH2 ) _2- O, _{C2H5 -} O-(CH2 _{) 2-} O, CH3 _- O-( _CH2 ) ₃ -O, _{C3H7 -} O-( _CH2 ) ₂ -O or _{C2H5 -} O-( _CH2 ) ₃ -O R is

[expression] or

【formula】

(m and/or q in (44) to (54) above are 1
~10 integer) (m is an integer from 1 to 10, q is an integer from 1 to 8) (m is an integer from 1 to 12, q is an integer from 1 to 10) (m, q are integers from 1 to 10) (m is an integer from 1 to 18, q is an integer from 1 to 6) (m, q are integers from 3 to 8) (m, q are integers from 1 to 10) When adding each of these substances (27) to (60) or any mixture of these as a third component, the following general rules should be used to determine the amount to be added. A fact or law becomes a guiding principle. In other words, N _p mixed into the base N _o type liquid crystal
The amount of N-type liquid crystal and/or _Np -type liquid crystal analogue is determined by the required operating threshold voltage value of the mixed liquid crystal, and the amount to be mixed and the operating threshold voltage value is determined. The relationship is determined roughly according to the following idea. The amount of the N _o type liquid crystal having a polar group and/or the N _o type liquid crystal analog having a polar group, which is the third component, is also the same as the amount of the above N _p type liquid crystal and/or N _p type liquid crystal. It should be added in proportion to the amount of similar substances mixed. The threshold voltage value (V _th ) of a twisted nematic liquid crystal device is given by the following equation. (4π) ^-1 (ε‖−ε ⊥)V _th ² = π ²・K ₁₁ + (K ₃₃ −2K ₂₂ ) ψ ² ...(61) However, ψ is the twist angle and is usually the value of π/2. I take the. K ₁₁ , K ₂₂ , and K ₃₃ are elastic constants for splay, twist, and bend, respectively. Equation (61) can be easily written as V _th =2π ^3/2・(K/ΔE) ^1/2 ……(61)′ However, Δε=ε‖−ε ⊥ K=K ₁₁ +1/4(K ₃₃ −2K ₂₂ ) ...(61)'' By using a mixture of liquid crystals with different values of Δε, it is possible in principle to obtain a liquid crystal of any Δε.Now, let the dielectric constants of the two liquid crystals A and B be ε‖ ^A ,
Let ε⊥ ^A , ε‖ ^B , ε⊥ ^B and the mixing ratio be A/B=X/1−X. Assuming that the additivity of permittivity holds true, Δε of the mixed system is given as follows. Δε=XΔε ^A +(1+X)Δε ^B =X(Δε ^A −Δε ^B )+Δε ^B ...(62) If additivity also holds for K, then K of the mixed liquid crystal is given as follows. . K=XK ^A +(1-X)K ^B =X(K ^A -K ^B )+K ^B
...(63) Substituting (62) and (63) into (61)′, V _th = 2π ^3/2・√( ^A − ^B ) + ^B /√
( ^A − ^B ) + ^B (64) Here, specific numerical values are applied to each constant and calculation of the threshold voltage value will be exemplified. Δε ^B of N _o- type liquid crystal is −0.3, N _p -type liquid crystal

Let Δε ^A in [Formula] be 25. Also, K ^B =4×10 ^-7 dyne, K ^A =17×
10 ^-7 dyne, equation (64) becomes V _th = 2π ^3/2 √ (13 + 4) 10 ^-7 /√25.3−0.3 ……(64)′. Here, those skilled in the art will easily understand that the values of Δε ^A , Δε ^B , K ^A , and K ^B are not arbitrary, and are values that reflect the physical properties of actual liquid crystals. It's something you get. Figure 10 shows N _p type liquid crystal.

[Formula], and the mixing ratio when both N _p and N _o type liquid crystals are mixed using base material 1-4 shown in Example 4 as the N _o type liquid crystal is the value of V _th (static drive). This shows the relationship between The theoretical formula (calculation formula) (64) or (64)′ and the experimental results show good agreement. However, as already explained in detail, the above combination alone is not sufficient in terms of compatibility. Therefore, N _o type as the third component, especially polar N _o type substances (polar N _o type liquid crystal and/or
or N _o type liquid crystal analogue) must be added.
The amount added may be variously adjusted depending on the amount of N _p type liquid crystal and/or N _p type liquid crystal analog. An example of this will be explained in the examples below. General formula of N _o type disclosed in Table 2 etc. [In the formula, R ₁ is n-C _n H _2n+1 , R ₂ is n-C _q
H _2q+1 −O] (where m and q are integers from 1 to 10) The following substance was discovered as an N _p -type liquid crystal and/or an N _p -type liquid crystal analog to be added to the matrix system. . (m in (65) to (78) is an integer from 1 to 10)
Substances such as (65) to (78) are preferable. In addition, the following substances were added to the parent system and good results were obtained. m is an integer from 1 to 8 m is an integer of 1 to 8; X represents halogen F, Br, Cl, I; m is an integer of 1 to 10; X represents halogen F, Br, Cl, I; m is an integer from 1 to 10 m is an integer from 1 to 10

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[Table] As an example (example) of a composition system consisting of the No _- type substance represented by general formula (18) and the third component No _- type substance, it has been found that those shown in Table 4 below are particularly preferable. . Next, a fifth example of a system in which an N _p -type liquid crystal and/or an N _p- type liquid crystal analogue is added to an N _o- based mixed system matrix is shown.
Shown in the table. As seen in Examples 24 to 27, 29, 30, 32, and 33, each mixture system maintains a wide MR around room temperature. All of them form good liquid crystal systems that can be used in display devices. Next _, it will be shown in Examples ( _No. Table 6). In Table 6, tr represents the rising response speed, and tf represents the falling response speed. The most necessary requirements and operating margins for executing time-division driving have already been explained in detail. In the examples shown in Table 6, the composition according to the present invention showed a large operating margin value, and the factors that determine the operating margin value were also shown. For comparison, Table 7 shows evaluation data for conventional materials. In Table 7, 1/3 and 1/3 in *1 are 1/3
Bias, 1/3 duty, 1/2 in *2,
1/2 means 1/2 bias and 1/2 duty. Reflects the compatibility between each composition that makes up the liquid crystal
Examples of MR and responsiveness, which should be emphasized as display characteristics, were also presented. As already shown, the factors that determine the operating margin are determined by the temperature dependence of V _th (ΔT), the angle dependence of V _th (Δφ), and the voltage-luminance rise characteristic (γ) of V _th . These are mainly determined by the liquid crystal itself. However, although it may vary somewhat depending on the element interface, the optical system of the element, etc., in this example, all measurements were performed under almost the same conditions to reflect the characteristics of the liquid crystal itself. It is clear from many experiments that the main factors that affect the operating margin and that reflect the liquid crystal material are the temperature dependence of V _th (ΔT) and the viewing angle dependence of V _th (Δφ). is being used. These factors are controlled by the physical properties of the liquid crystal, especially Δε (Δε‖−ε ⊥) (dielectric constant anisotropy), K (elastic constant), Δn (refractive index anisotropy), etc. Therefore, it is closely related to the molecular structure of liquid crystals. The compatibility of each component of liquid crystal when mixed is reflected in MR. In particular, the crystal-nematic liquid crystal transition point (C-N
This is thought to be reflected in the value of point). Therefore, the MR value is shown for each composition system, and the compatibility is added to each example as a guideline for determining thermodynamic stability as a liquid crystal material. Furthermore, response characteristics essential as display characteristics were measured for each composition system, and are shown below as examples. Generally, in a mixed system of N _o type liquid crystal and N _p type liquid crystal
When the amount of N _p added is increased, V _th decreases, but at the same time, the value of the operating margin M also tends to decrease. Therefore, it is generally extremely difficult to find a liquid crystal that can be driven at low voltage (for example, 3V drive under 1/3 bias, 1/3 duty time-division drive conditions), that is, a liquid crystal that can be driven at low voltage. This is a challenge. Generally, it is said that mass production of devices is extremely difficult unless the value of the operating margin M is 6% or more. Furthermore, in the case of low voltage driving, it is necessary to increase the amount of N _p added, but the N _p type liquid crystal itself
In many cases, they have a high viscosity, which increases the overall viscosity of the mixed system (N _p and N _o ), and often worsens the responsiveness of the system. The present inventors have discovered the following general method as a method and means for avoiding such difficult problems. In other words, as an N _p that reduces V _th , a material that is N _p type like a material with a large Δε, but that reduces the viscosity of the mixed system and therefore improves the response, is used in combination as an N _p type additive system. It is to be.
As an N _p -type material that is particularly effective in lowering V _th , (m is an integer from 1 to 10) etc. are valid. These examples are Example 36,
37, 38, 39, 42, and 43 (Table 6).

Ester-type N _p -type liquid crystals belonging to formula (80) such as [Formula] are effective in lowering V _th and have relatively low viscosity, making them a highly useful combination additive system.

[Formula] (belongs to formula (69)) is a material with a large Δε and a high N-I point (98℃), and is an effective _Np substance in keeping the N-I point of the mixed system high. (Examples 42, 43). Figure 11 shows

Consists of [expression] In the mother system,

The N-I point and V _th (threshold voltage) when [Formula] is added are shown. It was also found that biphenyl-based substances exist as _Np -type substances that are effective in reducing the viscosity described above (formulas (74), (75), and (76)). As shown in Examples 34 and 35, the response time tr showed a value of 200 ms or less. This is due to other N _p substances (formula (80)), Examples 36 and 37 (formula (65))
This is an excellent value compared to Examples 38 and 39. Like the biphenyl type, it is a thinning agent that can improve response and is an N _p substance. (m is an integer from 1 to 10) was found to be extremely effective. This point will be discussed in more detail later. Generally, the addition of a non-liquid crystal substance (liquid crystal-like substance) tends to lower the liquid crystal-liquid transition temperature (N-I point) (Example 37,

[Formula] does not exhibit nematic liquid crystallinity). This decrease in the N-I point often results in a deterioration (increase) in ΔT. In Example 37, the N-I point is as low as 50°C. This value is clearly lower than the other examples (34 to 39). In addition, ΔT is 18.5, which is abnormally large compared to other examples. As is clear from equation (15), an increase in ΔT leads to a decrease in M (operating margin) (in Example 37, M is a small value of 3.5). The present inventors have proposed the following formula (84) as a substance (additive) that is effective for preventing such a decrease in the N-I point, preventing an increase in ΔT, and ultimately increasing the value of the operating margin (M). We found two types of substances with formula (79). These substances were used in the N _o type matrix liquid crystals shown in Examples 1 to 11 (Table 2) and Examples 12 to 22 (Table 4), Example 23 (Table 5), and Example 28 (Table 5). ), Example 31 (Table 5), etc., when added to the base liquid crystal, etc., the effect is extremely remarkable. Its effectiveness is shown in Examples 40 and 41,
Addition of a small amount of a substance belonging to the general formula (84) is extremely effective in keeping the N-I point at a high value and in reducing ΔT. The similar role played by the substance represented by formula (79) will be explained based on Examples. Examples 53 and 54 (systems to which the substance represented by formula (79) is added) and Example 52 (formula (79)
Comparison with Example 58 (system in which the substance represented by formula (79) was added) and Example 57 (system in which the substance represented by formula (79) was added). As is clear from the comparison with the non-containing system), the increase in the N-I point of these additives
The effect of reducing ΔT is obvious. In Example 40, N _p -type substance

[Formula] (component effective for reducing V _th ) and By combining these, we have found a device that maintains a wide MR and has an operating margin of M=12 (%). Example 50 is effective for lowering V _th

[Formula] (N _p ) is effective for reducing viscosity.

[Formula] (N _p ) and the above-mentioned equation that is effective for increasing the N-I point and decreasing ΔT. This is an example of a combination of The present inventors have discovered a new composition system with a general formula [In the formula, R ₁ is n-C _n H _2n+1 , R ₂ is n-C _q
H _2q+1 −O] (where m and q are integers from 1 to 10) (where m is an integer of 1 to 10). This will be explained using an example. Examples 44, 45, 46, and 47 are based on the parent system shown in Example 23. and (where m is an integer of 1 to 10) This relates to a composition containing an N _p type mixed system of cyclohexane phenyl and cyclohexane biphenyl (see Example 44).
A notable feature is that the response becomes better as the amount of added increases. Moreover, the second excellent feature is that the operating margin (M) is maintained at a high level of about 10 to 12 (%). Maintaining this high margin is due in part to the relative
It is thought that taking a large value of 0.9 to 0.88 close to 1.00 is a factor, and the parent system (4-n-alkyl-cyclohexanecarboxylic acid-trans-4'-
Optical properties that show a favorable effect on electro-optical properties of a mixed system of an N _o type matrix (based on an alkoxyphenyl ester) and an N _o type mixture of a cyclohexane phenyl system and a cyclohexane biphenyl system (This suggests that it has a refractive index (n) and refractive index anisotropy (Δn). Another factor for maintaining a high operating margin is the increase in the N _p type mixing ratio. Also, the value of ΔT does not increase and remains at a nearly constant level of 8.0 to 8.6.In general, an increase in other N _p- type components often results in an increase in ΔT (see Example
34 and 35, 42 and 43 are comparative examples). Examples 52 to 58 show the composition system of the present invention that is most suitable for 1/3 bias, 1/3 duty, and 3V drive.
It was shown to. The characteristics of the system shown in these examples are N _p
Effective as a type material for lowering V _th (ester cyano type) and the aforementioned cyclohexane biphenyl (formula (77)) and cyclohexane biphenyl (formula (79)). Example 55, 56, 58), which shows a high level, and the response time (tr, 25°C) also shows a good value of around 200ms. These comprehensively excellent characteristics are extremely preferable for application to time-division drive devices. Examples 59 to 62 further contain a N _o type liquid crystal in the matrix (N _o type matrix mainly composed of 4-n-alkyl-cyclohexanecarboxylic acid-trans-4'-alkoxyphenyl ester) (see Example 50). As, are added to form an N _p- type liquid crystal.

This shows that it is possible to obtain a nematic liquid crystal with a wide MR by using a liquid crystal mixed with [Formula]. In particular, as shown in Examples 59, 60, and 61, the solid-liquid crystal transition point (C
-N point) was discovered. Examples 63 to 66 contain N _p- type substances in the parent system. This shows that by adding each substance, a composition having a wide MR and a high operating margin can be obtained. Examples 67 and 68 It is also related to Liquid crystal has a very wide MR, and has a parent system (N-I point 60
℃), the N-I point increases by 17℃.
Generally, liquid crystals with three benzene rings have a high viscosity.
Response speed suddenly decreases. However, this The viscosity of liquid crystal is lower than that of other materials with three benzene rings;
℃)) has no adverse effect on the response. Therefore, adding it to this matrix is very effective and tends to increase the operating margin (ΔT decreases by adding it). Based on the examples shown in Examples 34 to 68 above, the following conclusions can be made as a general method for devising a mixed liquid crystal with good time division drive characteristics. As for _Np , which reduces V _th , there are materials with large Δε (this is defined as N _p ^s ), and materials that are N _p type like N _p ^s , but suppress or reduce the increase in viscosity of the mixed system, but A substance that improves responsiveness (this is defined as N _p ^w ) is added as an N _p type additive.
The mixed system obtained when used in combination with N _p ^s or N _p ^w has good time-division drive characteristics, and in particular, both reduction in V _th and good response are maintained. It has been found that formulas (65) to (73), formula (80), formula (81), and formula (83) exist as N _p ^s type substances. In addition, as N _p ^w type substances, formulas (74) to (78),
We found that equation (84) exists. Furthermore, the addition of N _p ^s and N _p ^w is effective in lowering V _th and improving response, but it also lowers the N-I point of the mixed system, lowering the operating temperature range, or increasing ΔT. This may lead to deterioration of operating characteristics and time-division drive characteristics. To prevent such a decrease in the N-I point and an increase in ΔT,
Furthermore, we have found two types of substances, formula (84) and formula (79), which are effective in increasing the value of the operating margin (M). These substances have three ring structures in their molecules, have a high N-I point, and belong to positive N _p type substances with relatively weak dielectric constants. We have found that adding a small amount of a substance with these properties (defined as N _p ^wl ) is generally effective in improving the operating margin. The composition ratios of the mixed liquid crystal according to the present invention described in Table 6 (parts 1 to 5) explained above can be summarized as follows. A: Substance of formula (18) B: N _o type substance other than A C: N _p ^s type substance D: N _p ^w type substance and N _p ^wl type substance (1) Good in combination of substances A, B, and C A mixed liquid crystal composition consisting of 40 to 90 mol% of A, 0 to 40 mol% of B, and 10 to 35 mol% of C is used as a composition that provides good time-division drive characteristics.(2) A good combination of substances A, B, and D A mixed liquid crystal comprising 40 to 90 mol% of A, 0 to 30 mol% of B, and 10 to 40 mol% of D as a composition that provides time-division drive characteristics. (3) A composition that provides good time-division drive characteristics in the combination of substances A, B, C, and D: 28 to 59.4 mol% of A, 12 to 29.6 mol% of B, 6 to 25 mol% of C, and 5 to 40 mol%. A mixed liquid crystal consisting of mol% of D.

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[Table] As is clear from Table 7, the conventionally used azoxy liquid crystal can have a margin of 10% or more. However, as mentioned above, this material system requires a filter because of its extremely low chemical stability against light, and is not preferred because it is yellow. White materials include biphenyl and ester phenylcyclohexane nematic liquid crystals. These materials, such as ester-based materials, are suitable in a sense for low-voltage driving, but they have high viscosity and slow response. Phenylcyclohexane-based nematic liquid crystals have low viscosity and high-speed response. However, as is clear from Table 7, each system has a small operating margin and is unsuitable as a material for time-division driving. On the other hand, the material according to the present invention is a white material and has a sufficiently large operating margin necessary for time-division driving. Furthermore, regarding the first requirement that a liquid crystal material should possess, which cannot be forgotten in practical terms, ``good adaptability to alignment control films,'' the present inventors

〔Effect of the invention〕

As is clear from the above description, the present invention relates to a liquid crystal represented by general formula (18), a compound represented by general formula (74) or general formula (77), and a compound represented by general formula (65). This is a time-division drive liquid crystal display device in which a nematic liquid crystal material containing Examples 50, 51, 52 to 58 and 68) have characteristics suitable for low voltage driving.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of a liquid crystal display device to which the present invention relates, Fig. 2 is a configuration diagram showing the alignment state of liquid crystal molecules, and Fig. 3 is a voltage averaging method (1/3 bias).
A state diagram showing an example of time-division drive waveforms, Fig. 4 is a diagram showing the definition of viewing angle, Fig. 5 is an explanatory diagram of the electro-optic characteristic measuring device, Fig. 6 is 1/3 bias, 1/3 duty drive Waveforms, Figure 7 shows the drive waveform of 1/2 bias and 1/2 duty, Figure 8 shows the brightness-voltage characteristics when time-division driving is performed, and Figure 9 shows the Schiff base.
N _o type substance in N _o type and N _p type mixed system Figure 1 shows the relationship between the amount of addition and the liquid crystal temperature range.
Figure 0 is a diagram showing an example of the relationship between the mixing ratio of the N _o type material and the N _p type material and the threshold voltage value related to the present invention, and Figure 11 is a diagram showing an example of the relationship between the mixing ratio of the N o type material and the N p type material and the threshold voltage value, and Figure 11 is a diagram showing an example of the relationship between the mixing ratio of the N _o type material and the N _p type material and the threshold voltage value. It is a figure which shows an example when adding. 1... Upper plate, 2... Lower plate, 5... Liquid crystal, 6...
Electrode, 8, 9...Polarizing plate, 51...Liquid crystal display element.

Claims (1)

[Claims] 1 General formula [Formula] [In the formula, R ₁ represents n-C _n H _2n+1 , R ₂ represents n-C _q
Represents H _2q+1 −O (m and q are integers from 1 to 10)]
A compound of the general formula [Formula] [where [Formula] represents [Formula] or [Formula], and R ₃ − represents n-C _r H _2r+1 − (r is an integer from 1 to 7). ] and the general formula [Formula] [wherein R ₄ − represents n−C _s H _2s+1 − (s is an integer of 1 to 5]]
1. A time-division drive liquid crystal display device comprising a nematic liquid crystal containing at least one of the compounds represented by the following formula sandwiched between a pair of opposing electrodes.