JPH0357952B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a liquid crystal composition suitable as a material for use in a field effect liquid crystal display element, particularly a display element using a high time division driving method. (Prior Art) A liquid crystal display element includes: In addition to conventional clocks, calculators, etc.
In recent years, its use has begun to expand to larger displays capable of displaying more information, such as portable computers, portable televisions, and various office measuring instruments. One of the drive methods that meets these requirements is a time-division drive method using voltage averaging.
Liquid crystal display elements using a high time-division driving method have begun to be put on the market. Accordingly, there has been a demand for liquid crystal compositions that are compatible with high time division drive systems, but many conventional compositions are not compatible with this system. (Problems to be Solved by the Invention) Characteristics generally required of liquid crystal compositions used in display elements are: (1) being liquid crystal over a wide temperature range around room temperature; (2) chemical and thermal resistance; Chemically stable, (3) relatively low viscosity, (4) little change in voltage-brightness characteristics due to changes in temperature and visual field, (5) steep voltage-brightness characteristics. , etc., but when performing high time division driving, especially (5)
characteristics are important. This will be explained below using a dot matrix display element as an example. In Figure 1, striped Y ₁ on the lower plate,
_{Similarly ,} striped _{X 1 ,} ,
A liquid crystal is placed between both electrodes. To display text and graphics, the liquid crystal at each intersection of the X and Y electrodes is selectively turned on.
Or do it with the lights off. When a certain scanning electrode (X ₃ in the figure) is selected, a display signal of lighting or non-lighting is simultaneously applied to all pixels on that electrode according to the signal to be displayed from the signal electrodes Y ₁ , Y ₂ ...Ym. . That is, the combination of voltage pulses applied to the scanning electrode and the signal electrode turns on or off the intersection of both electrodes. Therefore, for example, voltage is also applied to non-lighting points other than the lighting points. A high effective voltage is applied to the lighting point, and a low effective voltage is applied to the non-lighting point, and the voltage difference creates a lighting and non-lighting state, and displays characters, figures, etc. There is a mutual relationship between the voltage at the lighting point and the voltage at the non-lighting point, and this relationship can be expressed by the following equation. Effective voltage applied at lighting point

[Formula] Effective voltage applied at non-lighting point

[Formula] Operating margin However, a=√+1 V ₀ : Drive power supply voltage a: Bias ratio N: Number of time-division scanning lines FIG. 2 is a diagram showing the relationship between the number of time-division scanning lines (N) and the operating margin (α). It is clear from this figure that α asymptotically approaches 1 as N increases.
That is, in the high time division driving method, the voltage difference between the lighting point and the non-lighting point becomes extremely small. Typical voltages in liquid crystal field effect displays
The brightness characteristics draw a curve as shown in FIG. In order to obtain a good display using the time division drive method, the effective voltage applied to the lighting point (Von) must be set to the saturation effective voltage (Vsat).
Voltage above, applied effective voltage at non-lighting point (Voff)
needs to be a voltage below the threshold effective voltage (Vth). Therefore, Vast/Vth (=γ)≦
The relational expression Von/Voff(α) must be satisfied. When a liquid crystal composition in which γ>α is used, a decrease in display density and an adverse effect on display after the occurrence of crosstalk occur. Currently, there is no fixed standard in the industry regarding how much brightness the effective voltage indicates as Vsat or Vth, but in general, the brightness is 50~
Vsat is the effective voltage when giving a certain brightness set within the range of 90% (in Figure 3, the brightness of Vsat is 80%)
is set to . ), Vth is the effective voltage when giving a certain brightness set within the brightness range of 10 to 20%.
(In FIG. 3, the brightness of Vth is set to 10%.) In any case, as mentioned above,
Since the α value decreases as the number of time-division scan lines increases, the γ value must also decrease. That is,
The high time division driving system requires a liquid crystal composition with a small γ value, in other words, a liquid crystal composition whose brightness changes sharply with a slight change in applied voltage, as shown by the dotted line in FIG. In some liquid crystal cells filled with a liquid crystal composition having a small refractive index anisotropy Δn, interference colors of light appear on the display surface. To prevent this, there are methods to widen the cell gap, and methods to increase Δn of the entire composition by adding another liquid crystal with a large Δn, but these methods sometimes This results in deterioration of responsiveness, deterioration of time-division drivability, etc. In summary, an object of the present invention is to provide a liquid crystal composition that has not only the characteristics (1) to (4) above, but also the steep voltage-luminance characteristic (5) above. Another object of the present invention is to have large refractive index anisotropy;
An object of the present invention is to provide a liquid crystal composition that does not generate interference colors of light on the display surface of a cell when filled into a cell. (Means for solving the problem) The purpose of the above invention is to: (a) General formula (In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms, and R' represents a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxyl group having 1 to 10 carbon atoms. ) (hereinafter referred to as compound (1)), (b) general formula (In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms, and R' represents a linear alkoxyl group having 1 to 10 carbon atoms.) (hereinafter referred to as compound (2)). ) and (c) general formula (In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms, and X represents a hydrogen atom, a fluorine atom, or a chlorine atom.) (hereinafter referred to as compound (3)) and the general formula (In the formula, R is a linear alkyl group having 1 to 10 carbon atoms,

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[Formula] or

Represents [formula]. ) (hereinafter referred to as compound (4)) A nematic liquid crystal composition containing at least one compound selected from the group consisting of: In addition to the above-mentioned compounds (1) to (4), the liquid crystal composition of the present invention has a threshold voltage, liquid crystal temperature range, viscosity, etc., in order to meet various required characteristics such as driving voltage, driving temperature range, and response speed. Other nematic liquid crystal compounds may be contained in an appropriate amount for the purpose of adjusting the temperature within the range that does not impair the purpose of the present invention. Suitable representative examples of such other nematic liquid crystal compounds include the following general formula:
Compounds (5) to (14) can be mentioned. (In the above formulas (5) to (14), R and R' each represent a linear alkyl group having 1 to 10 carbon atoms.) The preferred blending ratio of each component constituting the liquid crystal composition of the present invention is , Compound (1) 10-45% by weight,
Compound (2) 20-55%, total of compounds (3) and (4) 5-35
℃, other nematic liquid crystal compounds 0-25%. In order to clarify the present invention more specifically, Examples will be shown below. For comparison, a phenylcyclohexane liquid crystal composition that is widely used as a low viscosity liquid crystal composition is used as Comparative Example 1, and a biphenyl liquid crystal composition that is widely used as a liquid crystal composition that has large refractive index anisotropy. Liquid crystal compositions obtained by excluding compound (1) from the compositions of Example 1 and Example 3 are shown as Comparative Example 3 and Comparative Example 4, respectively. The liquid crystal compositions of these four comparative examples are 1/2 to 1/4
This is for duty temporary divided display (number of scanning lines is 2 to 4). In addition, the following terms written in the table have the following meanings. MR: Liquid crystal temperature range △n: Refractive index anisotropy △ε: Dielectric constant anisotropy T _NI : Nematic phase - isotropic liquid phase transition temperature T _SN : Smectic phase - nematic phase transition temperature

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[Table] The liquid crystal compositions of the above examples and comparative examples were filled into three types of display cells with different cell gaps, and the threshold effective voltage (Vth) and saturation effective voltage (Vsat) of each cell were measured. The γ value was calculated from Vth and Vsat, and the maximum number of time-division scanning lines (N _nax ) was further calculated from the calculated γ value. In the measurement, the temperature was 25℃ and the viewing angle was
The effective voltage that gives 10% brightness at 0° is Vth, and the temperature is 25
The effective voltage at which the brightness is 80% at °C and viewing angle of 0° is defined as Vsat. These results are listed in the table below. In the table, d represents the cell gap.

[Table] As is clear from the above results, the liquid crystal composition of the present invention has significantly improved γ characteristics, which are essential characteristics for high time division driving, compared to the comparative example, and the optical interference color on the cell display surface has been significantly improved. It has sufficient refractive index anisotropy to prevent the occurrence of. (Effects of the Invention) As explained in detail above, the liquid crystal composition of the present invention has steep voltage-luminance characteristics, so it has excellent high time-division drivability and does not cause interference colors of light to occur on the cell display surface. It has a unique effect.

[Brief explanation of drawings]

Figure 1 is a plan view of a dot matrix display element to explain the time-division driving method, Figure 2 is a chart showing the relationship between the operating margin of a liquid crystal display element and the number of time-division scanning lines, and Figure 3 is a diagram of a liquid crystal display element. It is a chart showing the relationship between luminance and applied effective voltage.

Claims (1)

[Claims] 1 (a) General formula (In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms, and R' represents a linear alkyl group having 1 to 10 carbon atoms or a linear alkoxyl group having 1 to 10 carbon atoms.) A compound represented by (b) general formula (In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms, and R' represents a linear alkoxyl group having 1 to 10 carbon atoms.) and (c) a compound represented by the general formula (In the formula, R represents a linear alkyl group having 1 to 10 carbon atoms, and X represents a hydrogen atom, a fluorine atom, or a chlorine atom.) (In the formula, R is a linear alkyl group having 1 to 10 carbon atoms, and [Formula] represents [Formula] [Formula] [Formula] or [Formula].) A nematic liquid crystal composition containing at least one compound.