JPS6187778A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a nematic liquid crystal compsn. which has steep voltage- brightness characteristics and a high time- division driving effect, containing two org. compds. CONSTITUTION:A nematic liquid crystal compsn. contains a compd. (A)4 of formula I (wherein R is a 1-10C straight-chain alkyl; R' is a 1-10C straight- chain alkoxyl) and a compd. (B) of formula II (wherein R is as defined above; X is H, F, Cl). The quantity of the compd. of formula I is 50-95w% and the quantity of the compd. wherein the sum of carbon atoms of R and R' is 7 or above, is 30-75wt%. The quantity of the compd. of formula II is 5-25wt%. The compsn. is a liquid crystal at about room temp. and stable chemically and thermochemically, has a relatively low viscosity, little causes changes in voltage-brightness characteristics due to temp. change and visual field change and has steep voltage- brightness characteristics. Hence, a liquid crystal display device having improved high time-division driving characteristics wherein the number of time division scanning lines is 32 or above, can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a field-effect liquid crystal display element, and particularly to a high time division driving type liquid crystal display device.

(Prior Art) In addition to conventional clocks, calculators, etc., liquid crystal display devices have recently been used in large-sized displays capable of displaying a large amount of information, such as portable computers, portable televisions, and various office measuring instruments. Its uses are also beginning to expand. One of the driving methods that can meet these demands is a time-division driving method using a voltage averaging method.Currently, liquid crystal display devices using a high time-division driving method are being 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. For this reason,
Many studies are being conducted to improve the high time division drive performance of display devices by improving liquid crystal compositions.

(Problems to be Solved by the Invention) Customization generally required for liquid crystal compositions used in display devices are (1) liquid crystal over a wide temperature range around room temperature; (2)
Chemically and thermochemically stable; (3) relatively low viscosity; (4) little change in voltage-luminance characteristics due to changes in temperature and visual field; (5) direct pressure-luminance. The characteristics are steep, etc.
When performing high time division driving, customization of (5) is particularly important. This will be explained below using a donmatrix display device as an example.

In Figure 1, there is a striped y on the lower plate, % y2
b y, . . . Ym electrodes (signal electrodes) are placed on the upper plate with a certain gap from the lower plate in the same way as striped X,...
X,,X,...Xn'tJ4 poles (scanning electrodes) are formed, and liquid crystal is present between both electrodes. Characters and figures are displayed by selectively lighting up or turning off the liquid crystal at each intersection of the X and Y electrodes. A certain scanning electrode (XS in the figure)
When 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 on the signal electrodes y, sy, . . . 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 applied to the non-lighting points ■, ■, and ■ other than the lighting point ■.

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. The voltage at the lighting point and the voltage at the non-lighting point have a mutual relationship, and this relationship can be expressed by the following equation.

However, a=σ+1 vo: 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). As is clear from this figure, 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.

A typical voltage-luminance characteristic in a liquid crystal field effect display draws 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 (Vo
It is necessary that the applied effective voltage (Voff) at the non-lighting point be equal to or less than the threshold effective voltage (v-th).

Therefore, Vsat/Vth (=γ)≦Yon/Vof
The relational expression f(α) must be satisfied.

When a liquid crystal composition in which r>α is used, adverse effects on display such as a decrease in display accuracy and occurrence of crosstalk occur. Currently, there are no fixed standards in the industry for determining how much brightness the effective voltage indicates as Vsat or vth.
Generally, the effective voltage when giving a brightness set within the range of 50 to 90% is Vaat (in Figure 3,
The brightness of Vaat is set to 80%. ), brightness 1
The effective voltage when giving a brightness set within the range of 0 to 20% is vth (in Fig. 3).

The brightness of vth is set to 0%. ). In any case, since the α value decreases with the increase in the number of train lines in the 9-time division mentioned above, the γ value must also decrease.

That is, the high time division driving method 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. Ru.

In summary, the object of the present invention is to provide high time-division driveability by using a liquid crystal composition that has not only the characteristics (1) to (4) above, but also the steep voltage-luminance customization described in (5) above. An object of the present invention is to provide a liquid crystal display device having 32 or more time-division scanning lines, which is improved.

(Means for Solving the Problems) For the purpose of the above invention, (1) General formula (I) (wherein R is a linear alkyl group having 1 to 10 carbon atoms,
R' represents a linear alkoxyl group having 1 to 10 carbon atoms. ), and (wherein R is a linear alkyl group having 1 to 10 carbon atoms,
X represents a hydrogen atom, a fluorine atom or a chlorine atom. (2) The total content of the compound represented by the general formula CI) is 5.
0 to 95% by weight, and the total content of compounds in which the sum of the number of carbon atoms of each of R and R' in the compound is 7 or more is 3
(3) The total content of the compound represented by the general formula (II) is 5 to 25% by weight. .

The liquid crystal composition used in the present invention has the above general formula (I) and (
In addition to IF) compounds, threshold voltage,
For the purpose of adjusting the liquid crystal temperature range, viscosity, etc., other nematic liquid crystal compounds may be contained in an appropriate amount within a range that does not impede the object of the present invention. Preferred representative examples of such other nematic liquid crystal compounds include compounds represented by the following general formulas (4) to (4).

(In the above formula (4) to α, R and R' each represent a linear alkyl group having 1 to 10 carbon atoms, and X represents a halogen atom.) Preferred content of the other nematic liquid crystal compounds mentioned above is 0~
It is 35% by weight.

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. Comparative example 2
Shown as The liquid crystal compositions of these two comparative examples are for temporary divisional display (number of scanning lines: 4) with a duty of .

In addition, the following terms written in Tables 1 and 2 have the following meanings.

M, R,: Liquid crystal temperature range △n: Refractive index anisotropy △ε: Military orientation TNx: Nematic phase-isotropic liquid correlation transition temperature T
SN: Smectic phase-nematic phase transition temperature d
: Cell gap 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 r value was calculated from , vth and Vmat. In the measurement, the effective voltage v at which the brightness is 10% at a temperature of 25°C and a viewing angle of 0°
th, and the effective voltage at which the brightness was 50% at a temperature of 25° C. and a viewing angle of 0° was defined as Meat.

These results are listed in the table below.

Table 3 When a liquid crystal display device is driven at constant duty, the equation for the operating margin is α=1196. γ1 of Example 1-75 is all t15 or less, and 11 of Comparative Examples 1 and 2 is 1.21 or more. Therefore, in this example, α〉
γ1 and 9 signals, the duty ratio is sufficient for driving at a duty ratio of 1. Comparative examples 1 and 2 show a sufficient γ value to drive at a duty ratio of 9 duty ratios or higher, and a good display is obtained, whereas Comparative Examples 1 and 2 have α If the display is driven at a duty ratio above, a marked reduction in display contrast and occurrence of crosstalk will occur, making it impossible to obtain a good display.

As is clear from the above results, the liquid crystal composition used in the present invention is significantly improved in r characteristics, which are essential characteristics for high time division driving, compared to the comparative example.

(Effects of the Invention) As explained in detail above, the liquid crystal display device of the present invention uses a nematic liquid crystal composition having steep voltage-luminance characteristics, so it has a unique effect of being excellent in high time-division drivability. 0

[Brief explanation of drawings]

Fig. 1 is a plan view of a dot-to-matrix display device to explain the time-division driving method, Fig. 2 is a chart showing the relationship between the operating margin of the liquid crystal display device and the number of time-division scanning fl, and Fig. 3 is the liquid crystal display device. 2 is a chart showing the relationship between luminance and applied effective voltage. Agent Patent Attorney Katsutoshi Takahashi 11i21 2nd day

Claims (1)

[Claims] 1. Using a nematic liquid crystal composition as a display material 3.
In a liquid crystal display device having a number of time-division scanning lines of 2 or more, the nematic liquid crystal composition has (1) general formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (wherein R is a carbon atom number of 1 to 1) 10 linear alkyl groups,
R' represents a linear alkoxyl group having 1 to 10 carbon atoms. ) and general formula (II) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R is a linear alkyl group having 1 to 10 carbon atoms,
X represents a hydrogen atom, a fluorine atom or a chlorine atom. ) (2) The total content of the compound represented by the general formula (I) is 50 to 95% by weight, and the number of carbon atoms in each of R and R' in the compound is 50 to 95% by weight. The total content of compounds whose sum is 7 or more is 30 to 75% by weight, and (3) the total content of compounds represented by general formula (II) is 5.
~25 weight 5. A liquid crystal display device featuring: