JPH04318814A - Liquid crystal composition - Google Patents

Abstract

PURPOSE:To obtain the light control display element which is low in driving voltage by using high-polymer precursors formed by interposing a methylene chain between a mesogen part and the hetero atom of a polymerized part. CONSTITUTION:At least one kind of the high-polymer precursors formed by interposing one methylene group between the mesogen part (arom. ring part) and the hetero atom of the polymerized part are used for the liquid crystal to be used for the light control display device formed by orienting and dispersing a liquid crystal 5 and a high polymer 4 to each other. The mesogen part is a biphenyl or naphthalene deriv. and the polymerized part is a photosetting type or thermosetting type. The production of the element is executed by forming electrodes 2 and 7 on the flat surfaces of the substrates 1 and 8 and spin coating the surfaces of these substrates with a 2% soln. of polyimide as oriented films 3 and 6, then calcining the coatings. A mixture formed by mixing 4-biphenylmethanol methacrylate and a liquid cupted at 1:10 is sealed into this spacing and is slowly cooled. The liquid crystal/monomer mixture is then oriented and is irradiated with UV rays, by which the transparent element is obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal composition for use in a dimming display element in which a liquid crystal and a polymer are aligned and dispersed.

0002

2. Description of the Related Art In recent years, dimming display elements in which liquid crystals and polymers are mutually dispersed have attracted attention. The operating principle of this dimming display element utilizes the difference in refractive index between liquid crystal and polymer, and when the refractive index matches when an electric field is applied, it exhibits a transparent state.
It is already known that a scattering state occurs when the refractive index differs due to removal of an electric field. On the other hand, we have recently invented a display element with the opposite mode, which transmits light when no electric field is applied and scatters when an electric field is applied. This display element was improved and manufactured as follows so that the liquid crystal and polymer were aligned and dispersed in an orderly manner. First, a polymer precursor and a liquid crystal are mixed and sealed between two substrates having opposing electrodes, at least one of which has been subjected to alignment treatment. At this time, the liquid crystals are aligned along the orientation of the substrate, and at the same time, the polymer precursors are also aligned in the same direction. If ultraviolet polymerization is carried out in this state, a display element with a scattering mode when an electric field is applied is formed. This display element is characterized by better contrast, brightness, and superior threshold characteristics compared to the mode that transmits when an electric field is applied.

0003

[Problem to be solved by the invention] However, this display element requires a high driving voltage, and even a low one requires a voltage of around 12V, so it is difficult to apply it to display elements driven at low voltage such as digital watches and calculators. Met. Furthermore, even if driven at a high voltage, excessive voltage is continuously applied to the low-molecular liquid crystal, which is thought to affect burn-in, heat resistance, reliability, etc., and significantly deteriorate device characteristics. . On the other hand, when considering only low-voltage driving, it is necessary to thin the gap formed when the alignment film surfaces of two substrates face each other (hereinafter referred to as the cell thickness), or reduce the concentration of polymer. Although it is conceivable to do this, the contrast deteriorates and it cannot be said to be a fundamental solution.

Accordingly, an object of the present invention is to lower the driving voltage by using a polymer precursor in which one methylene chain is interposed between the mesogenic part and the heteroatom of the polymerization part.

[0005]

[Means for solving the problem] In a liquid crystal composition used for a dimming display element in which a liquid crystal and a polymer are aligned and dispersed with each other, one methylene chain is interposed between a mesogenic part and a heteroatom of a polymerized part. It is characterized by using at least one type of polymer precursor. Further, the mesogen portion is a biphenyl or naphthalene derivative, and the polymerization portion is a photocuring type or a thermosetting type.

[0006] The details of the present invention will be explained below with reference to Examples.

[0007]

【Example】

(Example 1) This example shows an example in which a photocurable polymer precursor is used. FIG. 1 shows a cross-sectional view of the display element of the present invention. The method for manufacturing the device will be explained. First, the electrode layer 2 and the electrode 7 were formed on the flat surfaces of the substrate 1 and the substrate 8 by a vapor deposition method. Polyimide (JI manufactured by Japan Synthetic Rubber Co., Ltd.) was used as alignment films 3 and 6 on the surfaces of these substrates.
A 2% solution of B) was spin coated at 2000 RPM. These substrates were fired at 150°C. Thereafter, the surface of this alignment film was rubbed in one direction using a bleaching method. The direction of rubbing is 2.
When the two substrates are combined, the rubbing directions are almost parallel. The cell thickness was fixed at 10 μm. In this gap, 4-biphenylmethanol methacrylic acid ester and liquid crystal (LV-R2: manufactured by Roddick) 1:1
0 mixed at 100℃ and slowly cooled to form a liquid crystal/
When the monomer mixture was aligned and irradiated with ultraviolet rays at room temperature, the liquid crystal and polymer phase separated, creating an almost transparent device.

Next, regarding the method of driving the device, an alternating current electric field of 10 KHz and 6 V was applied between two electrodes. 0V was applied when light was transmitted. A transmittance of 80% was obtained. A transmittance of 3% was obtained during light scattering. When a device was similarly made using the conventional photocurable biphenyl derivative 4-phenylphenol methacrylate ester without intervening methylene chains, an AC electric field of 20 V was required to obtain the same transmittance. Therefore, the voltage has been lowered and it has been improved.

[0009] Here, polymer precursors other than those used in this example can also be used. In other words, there is no problem as long as the liquid crystals are aligned in approximately the same direction as the liquid crystal, or even in a different direction, as long as they are aligned in approximately the same direction. Further, as a polymerization site, all functional groups that can be used as a photocurable polymerization site can be used.

[0010] The alignment film used here is not limited to polyimide, and may be of any material, such as polyvinyl alcohol, as long as it has the ability to align liquid crystals. Furthermore, the alignment treatment is effective even if only one side of the substrate is used. When the surfaces of both substrates are subjected to alignment treatment, it is necessary to optimize each orientation direction each time because it is related to the content of the chiral component.

The liquid crystal used here preferably has a refractive index anisotropy Δn as large as possible. Further, a liquid crystal having positive dielectric anisotropy can be used. By using materials whose liquid crystal molecule structure and monomer structure are similar, it is possible to improve the transmittance or reflectance in the transmission state. The optimal content of liquid crystal is 50 to 95% based on the polymer monomer. If the liquid crystal content is less than this, it will not respond to an electric field, and if it is more than this, contrast will not be obtained.

In this example, no chiral component was mixed, but when it was added in the range of 0.1 to 1%, the threshold characteristics were improved. (Example 2) This example shows an example in which a thermosetting polymer precursor is used. A device was manufactured using the same substrate as in Example 1. Here, 4-glycidoxybiphenyl was used as the epoxy resin, and 1
21 (manufactured by Yuka Shell Co., Ltd.) was used. A 1:1 mixture of these and a liquid crystal (LV-R2: manufactured by Roddick) at a ratio of 1.5:8
．． The liquid crystal/polymer precursor mixture was mixed at 100° C. in a ratio of 5 to 5 and then sealed in a substrate and slowly cooled to align the liquid crystal/polymer precursor mixture and left at room temperature for one day to produce an almost transparent element.

Next, regarding the method for driving the device, an alternating current electric field of 10 KHz and 15 V was applied between the two electrodes. 0V was applied when light was transmitted. A transmittance of 80% was obtained. A transmittance of 5% was obtained during light scattering. Conventional thermosetting biphenyl derivatives 1″, 2″ without intervening methylene chains
-epoxyethyl 4-biphenyl ether,
When a device was similarly manufactured, an alternating current electric field of 26 V was required to obtain the same level of transmittance, so the voltage has been lowered, which is an improvement.

The polymer precursor used here can be used without any problem as long as it is aligned in substantially the same direction as the liquid crystal or in a different direction. Moreover, any polymerization site may be used as long as it is thermosettable.

Although two substrates were used in the above embodiment,
It is also possible to form a liquid crystal/polymer layer on one substrate. Further, it is not necessary to form the alignment film on both substrates, and the effect can be exerted even if only one substrate is processed. Further, the cell thickness does not have to be the value shown here, and can be determined depending on the application.

The present invention can be applied not only to the above embodiments but also to displays, light control elements, light valves, light control mirrors, and the like.

[0017]

Effects of the Invention As described above, according to the present invention, one methylene chain is formed between the mesogenic part and the heteroatom of the polymerization part.
By using a polymer precursor with two intervening polymers, it has become possible to produce a dimmable display element with a low driving voltage.

The present invention is a basic technology useful for producing simple matrix type display elements among polymer dispersed liquid crystal elements or liquid crystal dispersed polymer elements, and is also useful for large screen displays such as active matrix type display elements. It is thought that this will also have an effect on the technology that makes it possible.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing a cross section of a dimming display element of the present invention.

[Explanation of symbols]

1 Board 2 Electrode 3 Alignment film 4 Polymer 5 Liquid crystal 6 Alignment film 7 Electrode 8 Board

Claims (4)

[Claims] Claim 1: In a liquid crystal composition used for a dimming display element in which a liquid crystal and a polymer are aligned and dispersed with each other, one methylene chain is inserted between a mesogenic part (aromatic ring part) and a heteroatom of a polymerized part. 1. A liquid crystal composition comprising at least one polymer precursor interposed therein. 2. The liquid crystal composition according to claim 1, wherein the polymerization portion is of a photocurable type. 3. The liquid crystal composition according to claim 1, wherein the polymerization portion is thermosetting. 4. The liquid crystal composition according to claim 1, wherein the mesogenic portion is a biphenyl or naphthalene derivative.