JPS62148924A - Liquid crystal light quantity modulating element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal light quantity modulating element having a high response speed and a high contrast ratio by subjecting a liquid crystal composition having a high twisting property to twisting orientation between a pair of transparent electrode substrates. CONSTITUTION:A pair of transparent electrode substrates are subjected to the surface treatment where liquid crystal molecules are oriented in a certain direction, and these substrates are arranged to face each other, and the liquid crystal composition which is adjusted to have 90 deg.-180 deg. natural twisting orientation with a thickness set by the gap between transparent electrode substrates is oriented twistingly at 90 deg. between transparent electrode substrates. Rotating materials are added more than adjustment of a normally used twisted nematic liquid crystal to obtain the liquid crystal composition having a high twisting property. The fall response speed of this element is hardly affected by an applied voltage and a frequency, and the element is driven sharply by voltage modulation or frequency modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a light amount modulation element using a twisted nematic field effect liquid crystal display element.

(B) Prior Art A light amount modulation element is an application of the electro-optic effect exhibited by liquid crystals to the field of optoelectronics. This takes advantage of the property that the alignment of liquid crystal molecules changes when an electric or magnetic field is applied to a part of the liquid crystal, and it is used as a liquid crystal optical system that combines the optical rotation of the liquid crystal's helical structure and the action of the electric field with a polarizing plate. Often used.

Conventionally, such liquid crystal light shutters have been manufactured using a nematic liquid crystal, a cholesteric liquid crystal, a chiral nematic liquid crystal, or other optically active compound as a rotational substance, and a small amount of jl (0,1 to 0.
(approximately 2%) to form twisted nematic liquid crystal, which is further rubbed and held between a pair of upper and lower transparent electrode substrates so that the alignment direction is twisted at 90°. In this case, the natural twist pitch of the liquid crystal is about 50 to 300μ, and the long pitch liquid crystal is set sufficiently larger than the liquid crystal cell thickness (in other words, the liquid crystal has a natural twist orientation of less than 90° at the above thickness). ) were common.

(c) Problems to be solved by the invention The optical shutter using such a liquid crystal cell has an applied voltage of 0N.
-The response speed to OFF, that is, the slow rise time to applied voltage ON and the slow fall time to applied voltage OFF, considerably narrows the scope of its use as a shutter.

Among these, the rise time can be controlled to some extent by the applied voltage, but the fall time is difficult to control by the applied voltage, and shortening this time is an issue. In other words, as shown by curve (A) in Figure 2, the roundness of the fall time is derived from the large bounding of transmittance seen at the beginning of the fall, and this bounding varies depending on the applied voltage and frequency. This makes it difficult to achieve sharp and stable driving. For example, when multiplex driving is performed, the driving waveform varies depending on the lighting pattern, resulting in the problem that the fall response speed varies depending on the lighting pattern. Therefore, it is necessary to reduce the bounding and shorten the response time.However, factors related to force response speed are closely related to factors related to contrast ratio, and if one is emphasized, the other is sacrificed.

This invention was made in view of this situation, and by selecting the twist pitch of the liquid crystal, the fall time can be shortened while maintaining a sufficient contrast ratio, and the amount of light can have an appropriate response speed as a shutter. The present invention aims to provide a modulation element.

(d) Means for Solving the Problems Thus, according to the present invention, a pair of transparent electrode substrates, each of which has been subjected to a surface treatment that orients liquid crystal molecules in a certain direction, are arranged facing each other, and the distance between the transparent electrode substrates is A liquid crystal light amount modulation characterized in that a liquid crystal composition prepared such that the natural twisted orientation of the liquid crystal at a set thickness is more than 90° and 180° or less is twisted 90° between the transparent electrode substrates. An element is provided.

The most distinctive feature of this invention is that a liquid crystal composition with a higher twisting property than the conventional one is twisted by 90° and oriented between a pair of transparent electrode substrates that have been subjected to the above-described predetermined alignment treatment. As a result, it is possible to obtain a liquid crystal light amount modulating element having a faster response speed (Nyatta effect) and contrast ratio than the conventional one.

The highly twisted liquid crystal composition used in this invention can be obtained by adding a larger amount of rotational substance than when preparing twisted nematic liquid crystals that are normally used in this field.

The term "natural twisted orientation (or natural twisted pitch)" as used in this invention refers to the twisted orientation (or twisted pitch) that the liquid crystal composition itself has, which is not regulated by rubbing treatment.

Liquid crystal compositions used in liquid crystal cells such as liquid crystal optical shirts are
The greater the twisted orientation, the more the applied voltage is turned off.
On the other hand, as the orientation increases, domains are more likely to occur, and on the other hand, the contrast ratio must be kept constant (several 10 to several 100), so the above conditions are satisfied. The liquid crystal composition used in this invention has a natural twist orientation of 90° at a thickness determined by the distance between the pair of transparent electrode substrates.
Those prepared at a temperature exceeding 180° are suitable.
Preferably, the angle is 120° or more and 160° or less. In other words, the natural twist pitch of the prepared liquid crystal composition is suitably 2 times or more and less than 4 times the intended liquid crystal cell thickness, and more preferably 225 to 3 times.

The twist pitch is adjusted by the amount of the rotational substance added, and the rotational substance used is one known in the art, such as an optically active compound such as cholesteric liquid crystal or chiral nematic liquid crystal.

Specific examples of these optically active compounds and the rotational properties of these optically active compounds obtained with respect to nematic liquid crystal are shown below.

CH30 (left rotation) (4-(2-methylbutoxy)benzoic acid-
4゛-cyanophenyl ester), CH3 (left rotation) (4-(2-methylbutoxy)-4°-cyanobiphenyl), CH9 (right rotation) (4-(2-methylbutyl)-4゛- Preferred examples include Cl CH300C113 (left-handed rotation), H3COOCH3 (left-handed) OCH3 (right-handed), C130 (right-handed), Cy71T-5-OCOCJ+7 (left-handed), and cholesteryl nonanoate. Can be mentioned. Note that the above neR represents CH2Cl, (Jl(CH3)CH2-).

Materials and methods other than those described above used in this invention may be those known in the art.

(E) Function The liquid crystal composition prepared to have a natural twist orientation in the above range of 90° or more is used in a liquid crystal cell set to have a 90° twist orientation, so that the liquid crystal composition in the cell has a natural twist orientation of 90° or more.
Since the spring stress caused by being forced into a twisted orientation is stored, the twisting disappears and is recovered quickly when the electric field is turned on and off.

The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereby.

(F) Embodiment FIG. 1 is an explanatory diagram showing the main part of an embodiment of the liquid crystal light amount modulation element of the present invention. In this figure, a liquid crystal light amount modulation element (1) consists of a pair of opposing transparent glass substrates (2),
(2), a liquid crystal composition (5) filled between them, and a spacer (6) for enclosing this liquid crystal composition, (6)
A liquid crystal cell (7) consisting of a polarizing plate (8), (8
).

The liquid crystal composition (5) sealed in the cell is liquid crystal Z
Cholesteryl nonanoate (Eastman Kodak) or CB-15 (Merck) as an optically active substance was added to L1169/+ (Merck & Co.) or ZLI]565 (Merck & Co.) in the proportions shown in the table below. It is a twisted nematic liquid crystal that has been adjusted to be narrow.

At this time, the cell thickness of the liquid crystal cell is adjusted to 5μ, and transparent electrodes M are provided on the opposing surfaces of both glass substrates (2).
(3) and a transparent insulating film (4) are laminated in this order, and the surface of the transparent insulating film (4) is subjected to a rubbing treatment to regulate the liquid crystal composition to have a 90° twisted orientation.

When the relationship between the transmittance and the falling response time of the liquid crystal light amount modulating element manufactured as described above was measured, the results shown by the curve (A) in FIG. 2 were obtained.

The curve (B) in FIG. 2 is a comparative example of a 90° twisted nematic alignment liquid crystal cell ( These are the results of measuring the above relationship under the same conditions as above using a conventional liquid crystal cell.

From the above results, in the liquid crystal light amount modulation element of the present invention, the bounding of transmittance seen at the beginning of the falling response curve is smaller than that of the conventional one (Fig. 2 W2→W
1) It has a sharp response speed with a shortened fall response time.

(g) Effects of the Invention The liquid crystal light amount modulating element of the present invention uses a liquid crystal composition prepared to have higher twisting properties than conventional ones in a liquid crystal cell subjected to 90° twist alignment treatment, and the falling response speed is high. It becomes less susceptible to the effects of voltage and frequency, and can be driven more sensitively by voltage modulation and frequency modulation.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the essential parts of an embodiment of the liquid crystal light amount modulation element of the present invention, and FIG. 2 is a graph diagram showing the relationship between the transmittance and the falling response time of the element of the present invention together with a comparative example. be. (])---Liquid crystal light amount modulation element, (2)---Glass substrate, (3)---Transparent electrode film, (4)
...Transparent insulating film, (5) ...Liquid crystal composition, (6) ...Spacer, (7) ...
Liquid crystal cell, (8) Polarizing plate. Kei Beak 4! I-

Claims (1)

[Claims] 1. A pair of transparent electrode substrates, each of which has been subjected to a surface treatment that orients liquid crystal molecules in a certain direction, are placed facing each other, and the natural twisted orientation of the liquid crystal at the thickness set by the distance between the transparent electrode substrates exceeds 90°. A liquid crystal light amount modulating element characterized in that a liquid crystal composition prepared to have an angle of 180 degrees or less is twisted at 90 degrees between the transparent electrode substrates.