JPS63293525A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a display device capable of resisting temperature change without increasing the additional quantity of rotatory polarization substances by adding plural kinds of polarization substances having the same polarization characteristics and different temperature factors in the induced inherent pitch of the liquid crystal to the liquid crystal. CONSTITUTION:Nematic phase liquid crystal 2 having spiral structure with 180-270 deg. twisting angle and positive dielectric anisotropy is sealed between substrates 1 mounting electrodes 12 and orientation films 13 on their insides and polarizers 3 are arranged on the pront and behind of respective substrates 1. Thereby, the inherent pitch of the liquid crystal 2 having spiral structure can have a temperature factor corresponding to the display device and its polarization characteristics obtained from plural polarization substances have the same direction at least and do not increase the necessary quantity of the substances to obtain the prescribed pitch. Thus, display with high display quality can be obtained for high dark division driving and large screen display.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a liquid crystal display device which is subject to severe temperature changes or is susceptible to local deterioration, and is particularly suitable for large screen display.

Prior Art A field-effect type liquid crystal display is formed by giving a nematic phase liquid crystal having positive cage anisotropy a helical structure. Although this spiral structure requires a constant pitch depending on the display, the liquid crystal itself also has a specific pitch t, and the two are perfectly matched. ! If the thread collapses, temperature changes or drive signals may cause alignment defects that result in undesirable displays, and the twist angle of the helical structure may become 18.
If it exceeds 0 degrees, a reverse domain (display defect due to a reverse helical structure) will occur.

Now, the characteristic pitch of liquid crystal in such a helical structure is disclosed in Japanese Patent Application Laid-open No. 55-7350 and Japanese Patent Application Laid-open No. 60-107.
It is often obtained by adding an optically active substance to an otic liquid crystal, as disclosed in Japanese Patent No. 020.

In this case, the unique pitch is due to the addition of an optically active substance.
Generally, it shows a large temperature dependence due to direct factors such as The tendency is for the natural pitch to increase as the temperature rises (as the spiral stretches, the total natural pitch is (
+) with a polar concentration coefficient). A change in the natural pitch can be detected as a change in the threshold value ('Qh) when driving the liquid crystal display, and as the natural pitch increases, it decreases to the threshold value. FIG. 5 shows an example of a display device with a large twist angle (220 degrees twist) as shown in the above-mentioned publication, and typically has a value of 10 to 20 ff1V/"CO plexiformation"4.

This temperature dependence of the characteristic pitch is caused by changes in temperature conditions during display, and when high time division driving is used for large screen displays, there is little margin for this, but heat is transmitted locally during display. This is not preferable because it will cause significant contrast fluctuations and domain formation.

Two attempts have been made in recent years to reduce the concentration coefficient of the characteristic pitch. One example is the combination of a dextrorotatory optically active substance and a levorotatory optically active substance as shown in Japanese Patent Publication No. 60-29090, and the rate of change in temperature yL can be reduced to 1/2 to 115 times that of the conventional method. However, as mentioned earlier, since the optically active substance gives the liquid crystal its characteristic pitch, the amount of the optically active substance is too large to balance dextrorotation and levorotation and give the desired pitch. . This is undesirable because it significantly reduces the responsiveness to electric fields. Another attempt was to improve the optically active substance itself; for example, in 1986, at the Japan Society of Applied Physics, an optically active substance for nematic liquid crystals with a concentration coefficient of H polarity was introduced. However, this is not exactly desirable either. This is because the concentration coefficient of the characteristic pitch is affected by the display device, and considering the volumetric expansion coefficient t due to the temperature of the liquid crystal itself, it is better to have a polarity slightly ←) with the temperature coefficient a of the characteristic pitch. Melt.

In particular, as in the two previously mentioned publications, the twist angle of the helical structure is large, ranging from 180 degrees to 270 degrees, and in displays with a display mode that utilizes the birefringence of liquid crystal, there are severe restrictions on the layer thickness of the liquid crystal. , ←) When matching is performed at room temperature using a liquid crystal with a polar concentration coefficient of , ←), a mismatch occurs at low temperatures and a reverse domain occurs.

C) Problems to be solved by the invention The present invention has been made in consideration of the above-mentioned points, and the concentration coefficient of the characteristic pitch of the liquid crystal is adapted to the display device without extremely increasing the amount of optically active substance added. This provides a liquid crystal display that is resistant to temperature changes.

2) Means for solving all problems In the present invention, a plurality of types of optically active substances are added which have the same direction of optical rotation characteristics as liquid crystals and different concentration coefficients of the inherent pitches of the liquid crystals, and particularly preferably. This is a liquid crystal having a helical structure with a twist angle of 180 to 270 degrees, to which an optically active substance having a different polarity of the concentration coefficient of the intrinsic pitch is added.

e) Effect: As a result, the characteristic pitch of a liquid crystal having a shirazen structure can have a concentration coefficient suitable for the display device, and since the optical rotation characteristics are at least the same in the direction of a plurality of optically active substances, a predetermined characteristic pitch can be obtained. The amount required to obtain i is not large.

f) Example Figure 1 is a cross-sectional view of the liquid crystal display used in the present invention, and the peaks are j.
is a substrate having an electrode α2... and an alignment film (131 (13) on the inner surface of a glass plate (111a11), (2) is held between the substrate (1) (υ, and has a torsion angle of 180 degrees to 270 degrees).
It is a nematic phase liquid crystal with a positive dielectric anisotropy ak and a helical structure of 1. Such a liquid crystal display is often used as a display by arranging polarizers 131 (31k) at the front and rear.

'I'N-4005' manufactured by Chisso N was used as a nematic phase liquid crystal raw material with positive dielectric anisotropy t, and a blur angle of 22
A detailed explanation will be given by taking as an example a case where a threshold value (V-1; h) t- is measured for a frame frequency of 100 Hz as a characteristic pitch parameter using a display device with a 0 degree liquid crystal layer thickness of 6 μm.

Cholesteryl nonanonate (ON)', which has a polar concentration coefficient of (+) and a levorotatory optical rotation, was prepared as the first optically active substance. In order to use this first optically active substance alone in the above-mentioned display, 0Nit7 weight percent is added to TN-4003, and as a result, the threshold value for 0 to 50°C is ! The alteration rate was +15Pnv7C. As the second optically active substance, TDV-001 (Dainippon Ink & Chemicals Co., Ltd.
R) was prepared.

Similarly, when using this optically active substance alone, 58% by weight of TDV-001 was added to TN-4005, and the threshold temperature change rate was 11jV/''Q.However, in this case, -30 A reverse domain was generated at 1 minute at °C.

These first and second optically active substances are mixed in a large number of combinations AC,
The mixed optical rotator was added to TN-4003 so that the pitches matched at room temperature.As a result, the characteristics shown in Figure 2 were obtained. A good friend. For example, the temperature change rate of the threshold box is set to 2-+-'rPIV/'OK based on the volume of the display, d/Δn, etc., and when tied, use the ratio of 0H60%TDV-001Q4096, and the liquid crystal display is small, etc. The threshold temperature change rate at'
i+3mV/"If you want to set OK, QN, 30%TDV
This shows that it is sufficient to use -001,70%.

In this way, multiple optically active substances are used, but even if only the type of cholestyryl nonanate is (g)polar levorotatory, there are a number of different temperatures for the specific pitch at which it ferments into liquid crystals, and H3 -0OH-CnH2n+1 A levorotatory optical substance consisting of a compound having the structural formula t-V is (
c) Since it has various concentration coefficients of polarity, it is possible to match the concentration coefficient of a predetermined specific pitch by appropriately combining all of these.

g) Effects of the Invention As described above, since the spiral structure can be matched over a wide temperature range, a high-quality display can be obtained using a liquid crystal display even in a place with a poor temperature environment or in a poor usage method. In addition, since it does not adversely affect the field effect characteristics of the liquid crystal, it is particularly effective for high time division driving, large screen display, etc.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid crystal display used in the present invention, FIG. 2 is a characteristic diagram of the present invention, and FIG. 3 is a temperature characteristic diagram of a conventional liquid crystal display.

Claims (2)

[Claims] (1) In a field-effect liquid crystal display having a nematic phase liquid crystal with positive dielectric anisotropy, in which the liquid crystal molecules form a helical structure in the absence of an electric field and are sandwiched between two substrates, the liquid crystal A liquid crystal display characterized in that a plurality of types of optically rotating substances are added which give the same direction of optically rotating property to the liquid crystal but have different concentration coefficients of the intrinsic pitch induced in the liquid crystal. (2) The twist angle of the helical structure of the liquid crystal is 180 to 2
70 degrees, and the optically rotating substance is added to the liquid crystal with different polarities (+) and (-) of the temperature coefficient of the intrinsic pitch induced in the liquid crystal.