JP2000122045A - Liquid crystal optical element and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an element which is high in transmittance of a liquid crystal optical element after formation and is excellent in uniformity by subjecting a composition to a heat treatment before curing to execute curing at temperature at which part or the whole of this composition exhibits a liquid crystal phase. SOLUTION: The kinetic property of molecules is enhanced and discontinuous structures are decreased by applying heat energy to the composition after the composition is held between substrates, by which uniformity is enhanced. When the heating temperature is excessively long or when the heating temperature is excessively high, turbidity may occur in some cases. The selection of optimum conditions is made possible by making the time of the heat treatment shorter or making the temperature of the heat treatment lower in such a case. More particularly, the execution of stricter temperature control is needed when the chiral pitch of the composition is small or the spacing between the substrates large. The liquid crystal optical element having the good uniformity and high transmittance may be formed by executing polymn. curing after the heat treatment. The heat treatment temperature is set at the temperature at which part or the whole exhibits the liquid crystal phase when the composition is cured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal optical element which can be used for a light control element, a display element, an optical shutter and the like by controlling the transmission, scattering and reflection states of the element by application / non-application of an electric field.

[0002]

2. Description of the Related Art There has been proposed a transmission-scattering type optical element in which a liquid crystal and a transparent polymer are combined to produce a difference in refractive index between the polymer and the liquid crystal or between the liquid crystals (between minute regions). It is called a liquid crystal / polymer composite element, a liquid crystal / resin composite element, or a dispersion type liquid crystal element. Since this element does not require a polarizing plate in principle, it has low light absorption loss,
A great advantage is that high scattering performance is obtained and the light use efficiency of the entire device is high.

[0003] Taking advantage of this characteristic, it is used for light control glass, optical shutters, laser devices, display devices, and the like. Those in a scattering state when no voltage is applied and in a transparent state when a voltage is applied have been commercialized.

Further, a conventional example 1 (USP 518,876)
0) discloses an element using a liquid crystal and a polymerizable liquid crystal. In Conventional Example 1, since the liquid crystal in the device and the polymerized liquid crystal have the same orientation direction when no voltage is applied, the device exhibits a transparent state when viewed from any direction. When a voltage is applied, the orientation of the liquid crystal in the device is controlled by the electric field, and the orientation of the liquid crystal molecules changes in a minute area in various ways, so that the device exhibits a scattering state.

It has also been disclosed that the contrast ratio is improved by providing a helical structure in the initial alignment by adding a chiral agent. This device is called "anisotropic gel" or "liquid crystal gel". In this conventional example 1, a mesogen monomer having an acryloyl group at the terminal was used.

Further, a conventional example 2 (International Patent Publication WO92 /
19695) also disclosed an element having a similar configuration.
This is an operation mode similar to that of Conventional Example 1, in which a very small amount of polymer is dispersed in a chiral nematic liquid crystal to obtain a transparent state when no voltage is applied and a scattering state when a voltage is applied. This element is P
SCT (Polymer Stabilized Cholesteric
Texture). This Conventional Example 2 also discloses a mesogen monomer having an acryloyl group at the terminal.

[0007]

In the conventional example 1, it was shown that the element was formed by curing the whole composition in a state showing a liquid crystal phase. In the manufacturing method, the uncured composition is sandwiched between the substrates and then cured. Usually, a structure such as a spacer for keeping the gap between the substrates constant is provided between the substrates.

For this reason, foreign matter is present between the substrates, which tends to cause discontinuous portions such as orientation when the composition is injected between the substrates or dropped and spread. When the curable compound is cured, the discontinuous portion is also fixed as it is, so that the transmittance of the device after formation is reduced and the uniformity of the optical characteristics of the device is significantly impaired.

For example, as a method of reducing a discontinuous portion such as an orientation generated when a composition is sandwiched between substrates, a method of reducing a structure such as a spacer which causes a problem or a method of not using a structure at all is used. Can be considered. However, if the means for holding the substrate gap is too reduced, there is a problem that the substrate cannot contact a large area because it cannot support a large area.

The present invention solves these problems and has a high transmittance of a liquid crystal optical element after formation.
An object is to provide an element having excellent uniformity on a substrate surface. Further, since the orientation of the minute regions is uniform, an element suitable for high-density display can be provided.

[0011]

That is, the present invention provides a composition comprising a composition containing a liquid crystal and a curable compound sandwiched between two substrates having electrodes, at least one of which is transparent. Provided is a method for manufacturing a liquid crystal optical element which performs curing at a temperature showing a phase, wherein a heat treatment is performed before curing.

In the above production method, if the temperature at which the entire uncured composition exhibits an isotropic phase is T _C (° C.),
Provided is a method for manufacturing a liquid crystal optical element that performs heat treatment at a temperature of T _C -30 (° C.) or more. Further, in the above-mentioned production method, a method for producing a liquid crystal optical element containing a chiral agent in the composition is provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a technique is employed in which the composition is sandwiched between substrates to increase the mobility of molecules by applying thermal energy to the composition, and to increase the uniformity by reducing discontinuous structures. . Although this structure homogenization method is effective even when the temperature of the entire composition shows an isotropic phase, it is more effective to reduce the discontinuous structure in a shorter time and effectively by heating to a temperature near the temperature showing the isotropic phase. be able to.

If the heating time is too long, or if the heating temperature is too high, cloudiness may occur. In such a case, the optimal condition can be selected by shortening the time of the heat treatment or lowering the temperature of the heat treatment. Particularly, when the chiral pitch of the composition is small or when the gap between the substrates is large, it is necessary to control the temperature more precisely.

By performing polymerization and curing after this heat treatment, a liquid crystal optical element having high uniformity and high transmittance can be formed.

The composition of the liquid crystal and the uncured curable compound is as follows:
It is preferable that the solution is a homogeneous solution after mixing. This composition may be in a liquid crystal phase or an isotropic phase when sandwiched between substrates with electrodes. When it is cured, it is set at a temperature at which a part or the whole shows a liquid crystal phase.

The function of aligning the liquid crystal on the electrode surface can also be imparted by directly polishing the electrode surface of the substrate with electrodes holding the composition, or by rubbing a resin thin film. Thereby, the unevenness when the composition of the liquid crystal and the uncured curable compound is sandwiched can be reduced.

Further, the combination of the orientation directions of the pair of oriented substrates may be parallel, orthogonal, or any other angle, and the angle may be set so as to minimize unevenness when the composition is held.

The electrode gap can be held by a spacer or the like, and is preferably 4 to 50 μm, more preferably 5 to 30 μm.
Is preferred. If the electrode gap is too small, the contrast ratio decreases, and if it is too large, the driving voltage increases.

The substrate supporting the electrodes may be a glass substrate or a resin substrate, or a combination of a glass substrate and a resin substrate. Further, a metal such as aluminum or a dielectric multilayer film may be provided on one of the substrates.

In the case of a film substrate, a substrate with electrodes supplied continuously is sandwiched between two rubber rolls or the like, and a composition of a liquid crystal containing a spacer and dispersed therein and an uncured curable compound is supplied therebetween. Heating and hardening can be performed continuously by sandwiching and high productivity.

In the case of a glass substrate, a small amount of spacers are scattered in the electrode surface, and four sides of the opposed substrate are sealed with sealing agents such as epoxy resin to form sealing cells at two or more locations. One of the cells is immersed in a composition of liquid crystal and an uncured curable compound, and the other is sucked from the other to fill the cell with the composition and cure to obtain a liquid crystal optical element. Also, a normal vacuum injection method can be used. Hereinafter, examples will be described.

[0023]

EXAMPLES (Example 1) Chiral agent (Merck S-
Mixture of 811 and C15 manufactured by Merck in a weight ratio of 1: 1)
95 parts of a cyano-based nematic liquid crystal (BL-009 manufactured by Merck & Co., Ltd.) in which 2.5% by weight was dissolved, 5 parts of an uncured curable compound of the formula (1), and 0.15 part of 2,2-dimethoxy-2-phenylacetophenone Was prepared. When the temperature (T _C ) at which the entire composition became an isotropic phase was measured, it was found to be 10
2 ° C.

[0024]

Embedded image

A pair of substrates obtained by rubbing the composition with a polyimide thin film formed on a transparent electrode in one direction are opposed to each other so that the rubbing directions are orthogonal to each other.
Was injected through a resin bead into a liquid crystal cell produced by laminating epoxy resin printed on four sides with a width of about 1 mm. Discontinuities in orientation occurred during injection.

When this cell was kept in a thermostat set at a temperature of 120 ° C. for 10 minutes, the discontinuous portion accompanying the injection disappeared. Thereafter, with the temperature maintained at 25 ° C., an HgXe lamp having a main wavelength of about 365 nm was used to apply about 3 mW from the upper side.
/ Cm ² , and about 3 mW / cm ² of ultraviolet light from below for 10 minutes to obtain a liquid crystal optical element.

A half-width of about 20 with a center wavelength of 530 nm
transmittance measurement system using a measurement light source of nm (F value of optical system 1)
When the transmittance was measured in 1.5), it was 80.5% without applying a voltage. The appearance after curing was good without any problem in uniformity.

(Example 2) The same conditions and materials as in Example 1 were used except that only the temperature setting condition of the thermostat after the injection was set to 150 ° C for 10 minutes. The non-uniform part after the injection disappeared by the heat treatment, and after the curing, the appearance became uniform, transparent and good. With no voltage applied, the transmittance was 80.5% (center wavelength of measurement = 530 nm).

(Comparative Example 1) The same conditions and materials as in Example 1 were used except that only the temperature setting condition of the thermostat after the injection was set to 50 ° C for 10 minutes. The non-uniform portion after the injection was hardly changed even after the heat treatment, and remained uneven and unsuitable after curing. The transmittance is 7 when no voltage is applied.
It was 9.7% (center wavelength of measurement = 530 nm).

(Comparative Example 2) The same conditions and materials as in Example 1 were used except that only the temperature setting condition of the thermostat after the injection was 200 ° C for 10 minutes. The non-uniform portion after the injection became cloudy due to the heat treatment, and had an opaque inappropriate appearance even after curing. When no voltage was applied, the transmittance was 68.0% (center wavelength of measurement = 530 nm).

[0031]

According to the present invention, it is possible to reduce the non-uniform portion of the uncured composition. As a result, stable production has become possible, and high-quality devices can be continuously produced at a high yield. The present invention is also applicable to various applications within a range that does not impair the effects of the present invention.

Claims (4)

[Claims] 1. A liquid crystal in which a composition containing a liquid crystal and a curable compound is sandwiched between two substrates with electrodes, at least one of which is transparent, and a part or the whole of the composition is cured at a temperature showing a liquid crystal phase. A method for manufacturing a liquid crystal optical element, comprising performing a heat treatment before curing in an optical element manufacturing method. When wherein the temperature of the total composition of the uncured exhibiting an isotropic phase and T _C (℃), the liquid crystal optical element according to claim 1 to heat treatment at T _C -30 (℃) temperatures above Manufacturing method. 3. The composition according to claim 1, further comprising a chiral agent.
Or the method for producing a liquid crystal optical element according to 2. 4. A liquid crystal optical element manufactured by the method according to claim 1, 2 or 3.