JPH0721142B2 - Liquid crystal display element - Google Patents

Description

The present invention relates to a field effect liquid crystal display device having a high time division driving characteristic.

[Prior Art] A twisted nematic (TN) type liquid crystal display element, which is one of the field effect type liquid crystal display elements, is driven by a low voltage, consumes less power, and does not emit light by itself. Has the advantage that the brighter the contrast, the better it is, and because it is a flat display, it has the advantage of being able to miniaturize the entire device, so it has maintained an advantageous position as a display device since 1975, In recent years, calculators and watches have almost replaced the liquid crystal display.

On the other hand, as the field of use of liquid crystal displays and the research and development associated therewith have progressed, the demand for liquid crystal display devices used for large-sized screens has been gradually made, especially in the field of information. For this reason, improvement of liquid crystal materials and research on liquid crystal interfaces have been promoted, and 1 line (1/8 duty drive) ~ 4
Line (1/32 duty drive) liquid crystal display device was put into practical use,
Therefore, it has come to be used in simple word processors, typewriters, and the like. Recently, the demand for larger screens for displays for information has further increased, and the era of practical use of displays for handheld personal computers, computer computers, etc. has entered.

However, the liquid crystal display elements of 8 rows (1/64 duty drive) or 12 rows (1/100 duty drive) used for these displays are displayed at these duty ratios because of high time division drive. There is a problem that the on / off ratio (contrast) between the segment and the segment that is not displayed is inevitably small, and the display quality is degraded. For this reason, the liquid crystal material, the liquid crystal interface, and the like have been continuously improved. However, only small improvements have been made, and there has been a limit in improving the display quality of the liquid crystal display.

To improve such a problem, the twist angle of the nematic liquid crystal molecule helical structure enclosed between a pair of upper and lower electrode substrates facing each other is set to 160 degrees or more, and The present inventors have proposed a liquid crystal display device in which a pair of polarizing plates are arranged with a certain angle offset with respect to the alignment direction of liquid crystal molecules (JP-A-60-50).
No. 511).

According to such a configuration, compared with a liquid crystal display element having a 90-degree twisted structure which is normally used, the falling characteristic due to the voltage transmittance becomes sharp and the time division characteristic is dramatically improved.
It is possible to display from 100 duty drive to 1/200 duty drive.

[Problems to be solved by the invention]

In the above-mentioned conventional example, the 90-degree twisted structure of liquid crystal molecules,
Comparing the liquid crystal display elements having a twisted structure of 0 degree or more, for example, 180 degrees with respect to the characteristics, for example, the angle dependence of the voltage-transmittance characteristic, the liquid crystal display element having the twisted structure of 180 degrees shown in FIG. In comparison with the liquid crystal display element having the 90-degree twist structure shown in FIG. 5, the falling characteristic due to the voltage transmittance is sharp, and the characteristic is obviously improved.
In these figures, θ _{0 to} θ ₅₀ indicate the viewing angle of 0 ° to 50 ° in the observer direction. In such a liquid crystal display device having a 180-degree twist structure, the voltage falling characteristic is steep, so that the voltage difference between the on state and the off state of the voltage during time division driving becomes large, and higher time division driving is possible. It will be possible.

By setting the twist angle in the range of 160 degrees to 230 degrees in this way, the falling characteristics are improved, but even if various liquid crystals are used, the falling characteristics (below (referred to as γ characteristic) is greatly improved.

However, in the liquid crystal display device configured as described above, the relationship between the γ characteristic in the case of a 90 ° twist angle due to the liquid crystal material and the γ characteristic in the case of a twist angle of 160 ° to 230 ° does not show the same tendency. In contrast, a material with a good γ characteristic is better as the elastic modulus ratio (K ₃₃ / K ₁₁ ) is smaller, which is a phenomenon that does not apply to the conventional theory (90 degree twist angle).

An object of the present invention is to provide a liquid crystal display element having a twist angle of 160 degrees to 230 degrees of liquid crystal molecules, which can further improve time division characteristics.

[Means for solving problems]

The present invention provides a nematic liquid crystal composition between translucent electrode substrates.
Enclosed in a twisted orientation within the range of 160 ° to 230 ° and enclosed in the liquid crystal composition of the general formula The liquid crystal material represented by (R = CnH ₂ n ₊₁ ; n = 2 to 7) is 10 to 5
The above-mentioned problems can be solved by adding it in the range of 0 wt%.

[Action]

In the present invention, the general formula By adding the liquid crystal material represented by (R = CnH ₂ n ₊₁ ; n = 2 to 7), the falling characteristic becomes more steep.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

It has been generally considered that a liquid crystal material having the best γ characteristic at a 90-degree twist angle is a liquid crystal material containing a pyrimidine-based material having a small elastic modulus ratio (K ₃₃ / K ₁₁ ). As an example, as shown in FIG. 1, at a 90 degree twist angle, the pyrimidine-based material A of Merck Co., which is indicated by a circle, is also indicated by an X mark, which is a PCH of Merck.
Such a tendency becomes clearer as the elastic modulus ratio (K ₃₃ / K ₁₁ ) becomes smaller than that of the system material B. In the figure, ▲ γ ^{10 °} _{80% -20%} ▼ on the vertical axis means the γ characteristic (voltage falling characteristic), which is the voltage ratio between the transmittance 80% and 20% at a viewing angle of 10 degrees. ) Is shown. On the other hand, 180
In the case of the degree twist angle, as shown in FIG. 2, the method of the pyrimidine-based material A having a small elastic half ratio (K ₃₃ / K ₁₁ ) has a lower γ characteristic than the PCH-based material B. As described above, in the case of the twist angle of 160 degrees to 230 degrees, the idea so far does not hold, and the PCH-based material B exhibits good γ characteristics. Next, with a twist angle of 160 to 230 degrees, for example, a twist angle of 180 degrees, various materials are used with the voltage ▲ Vth ^{10 °} _50% ▼ at which the transmittance at the viewing angle 10 is 50% as a parameter, for example, pyrimidine-based materials The γ characteristics of the materials, the PCH-based materials indicated by X and the biphenyl-based materials indicated by △ are measured,
As a result of the comparison, it has been clarified that the PCH-based material indicated by x has the best γ characteristic.

Hereinafter, the present invention will be described in detail with reference to specific examples.

Introduction General formula for Np liquid crystal materials Table 1 shows an example of data showing the improvement situation of time division characteristics by adding (R = CnH ₂ n ₊₁ , n = 2 to 7) in the range of 10 to 50 wt% together with the data showing each liquid crystal material. To raise.
As the liquid crystal interface for evaluating these liquid crystal materials, an alignment film formed by rubbing the surface of the translucent electrode substrate on which the electrode is formed is used.

The liquid crystal materials shown in Examples 1, 2 and 3 were each added with chiral liquid crystal S811 (manufactured by Merck Ltd.) in the range of 0.5 to 0.6 wt%.

As is clear from Table 1 above, in the specific examples 1, 2 and 3, the general formula By adding the PCH-based liquid crystal material represented by (R = CnH ₂ n ₊₁ ; n = 2 to 7), as is clear from comparison with FIG. 2, ▲ γ ^{10 °} _{80% -20%} ▼ The time-sharing characteristics have been improved significantly.

〔The invention's effect〕

As described above, according to the present invention, the nematic liquid crystal composition is twisted and aligned between the transparent electrode substrates in the range of 160 ° to 230 °, and the nematic liquid crystal composition has the general formula The liquid crystal material represented by (R = CnH ₂ n ₊₁ ; n = 2 to 7) is 10 to 5
Addition in the range of 0 wt% has an extremely excellent effect that the γ characteristic is significantly improved and a liquid crystal display element having an excellent high time division characteristic can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the ratio of the elastic coefficients of the pyrimidine-based liquid crystal material A and the PCH-based liquid crystal material B at the 90-degree twist angle and the γ characteristic, and FIG. 2 is the pyrimidine-based liquid crystal materials A and PC.
FIG. 3 is a diagram showing the relationship between the elastic coefficient ratio and the γ characteristic at the 180-degree twist angle of the H-based liquid crystal material B. FIG.
FIG. 4 is a diagram showing the relationship between the voltage and the γ characteristic at a degree twist angle, and FIG. 4 is the voltage of a liquid crystal display device having a 180 degree twist structure.
FIG. 5 is a characteristic diagram showing the angle dependency of the transmittance characteristic, and FIG. 5 is a characteristic diagram showing the angle dependency of the voltage-transmittance characteristic of a liquid crystal display device having a 90-degree twist structure.

Claims (1)

[Claims] 1. A nematic liquid crystal composition is twisted and oriented within a range of 160 ° to 230 ° and enclosed between translucent electrode substrates,
The liquid crystal composition has the general formula The liquid crystal material represented by (R = CnH ₂ n ₊₁ ; n = 2 to 7) is 10 to 5
A liquid crystal display device characterized by being added in an amount of 0 wt%.