JP2001209035A - Liquid crystal optical shutter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy saving liquid crystal optical shutter especially dispensing with a polarizing plate and capable of exhibiting excellent characteristics even in low voltage. SOLUTION: The liquid crystal optical shutter having two sheets of conductive substrates and an optical shutter layer supported therebetween is characterized in the following. (1) The optical shutter layer consists of 5-20 wt.% transparent polymer component and 95-80 wt.% liquid crystal component. (2) The liquid crystal component consists of a cholesteric liquid crystal, a chiral smectic C liquid crystal and a nematic liquid crystal and the sum of the cholesteric liquid crystal and the chiral smectic C liquid crystal amounts to 0.05-10 wt.% of the liquid crystal component. (3) The optical shutter layer is constituted of a granular structure in which a transparent polymer thin film consisting of the transparent polymer component wraps the liquid crystal component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy saving type scattering type liquid crystal optical shutter which does not require a polarizing plate.
Further, the present invention relates to a display device using the liquid crystal optical shutter.

[0002]

2. Description of the Related Art Conventionally, as a liquid crystal optical shutter, a TN (twisted nematic) type or an STN (super twisted nematic) type mainly using a nematic liquid crystal has been used. However, these methods use the light-emitting properties (that is, polarized light) of the twisted-aligned liquid crystal, and thus require 1) a polarizing plate, 2) a large energy loss of the light source, and 3).
It requires high-precision control of cell thickness and is not suitable for enlargement of the screen, and has problems such as 4) a narrow viewing angle. In recent years, as a solution to these problems, to provide a large and inexpensive liquid crystal display device with good brightness and contrast,
Research on applying a liquid crystal optical shutter using a polymer-liquid crystal composite system to a display device has been actively conducted.

Most of the polymer-liquid crystal composite liquid crystal optical shutters developed so far use a nematic liquid crystal as a liquid crystal component. In particular, those having a structure in which liquid crystals are dispersed as fine droplets in a polymer matrix (intra-polymer dispersed liquid crystal: J, W. Doane,
NAVaz, BGWu, S. Zumer, Appl. Phys, Lett., 48 , 27 (198
6)) and those having a structure in which a liquid crystal is used as a continuous phase and a polymer is dispersed therein as a three-dimensional network or fine droplets (polymer-dispersed liquid crystal: JP-A-2-28284, JP-A-2-28284). Japanese Patent Application Laid-open No. 55318/55) has been studied.

However, the response speed of the polymer-liquid crystal composite liquid crystal optical shutter using the above nematic liquid crystal is considerably slower than other liquid crystal display devices, and the voltage required for driving is still high.

Recently, a chiral nematic liquid crystal containing 5 to 10% by weight of a cholesteric liquid crystal as a liquid crystal component is used, and the light-shielding ability of a polymer-dispersed liquid crystal optical shutter is enhanced by adding a helical twisting force to the liquid crystal, thereby increasing the contrast. Attempts have been made to increase the ratio and increase the response speed (Japanese Patent Laid-Open No. 4-119320).

However, in this method, although the response speed is considerably improved, the voltage required for driving is rather high, and further improvement is required for practical use.

[0007]

SUMMARY OF THE INVENTION Accordingly, a main object of the present invention is to solve these problems, and in particular, to provide an energy-saving liquid crystal optical shutter which does not require a polarizing plate and can exhibit excellent characteristics even at a low voltage. Is to provide.

[0008]

The present inventor has made intensive studies to solve the problems of the prior art, and as a result, has found that the above-mentioned object can be achieved by employing an optical shutter layer having a specific configuration. Under the heading, the present invention has finally been completed.

That is, the present invention relates to a liquid crystal optical shutter having two conductive substrates and an optical shutter layer supported between these substrates, wherein (1) the optical shutter layer comprises 5 to 20% by weight. Transparent polymer component and 95 to 80
(2) The liquid crystal component is composed of a cholesteric liquid crystal, a chiral smectic C liquid crystal, and a nematic liquid crystal, and the total amount of the cholesteric liquid crystal and the chiral smectic C liquid crystal is 0.05 to 0.05% in the liquid crystal component.
(3) The light shutter layer is constituted by a granular structure in which a transparent polymer thin film made of the transparent polymer component is wrapped around the liquid crystal component. It relates to an optical shutter.

Further, the present invention relates to a display device using the above-mentioned liquid crystal optical shutter.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The liquid crystal optical shutter of the present invention
A liquid crystal optical shutter having a plurality of conductive substrates and an optical shutter layer supported between these substrates, wherein (1) the optical shutter layer comprises 5 to 20% by weight of a transparent polymer component and 95 to 80% by weight. (2) The liquid crystal component comprises a cholesteric liquid crystal, a chiral smectic C liquid crystal and a nematic liquid crystal, and the total amount of the cholesteric liquid crystal and the chiral smectic C liquid crystal is 0.05 to 10% by weight in the liquid crystal component. (3) The optical shutter layer is characterized in that the transparent polymer thin film made of the transparent polymer component is formed of a granular structure that wraps around the liquid crystal component.

The conductive substrate constituting the liquid crystal optical shutter of the present invention is not particularly limited as long as a voltage can be applied to the optical shutter layer. For example, a transparent conductive substrate obtained by laminating a conductive layer (transparent electrode) made of ITO (Indium Tin Oxide) or the like on a transparent substrate such as glass or resin can be used as the conductive substrate of the present invention. Further, a transparent conductive substrate used in a known liquid crystal display or the like can also be employed. As the transparent conductive substrate, a colorless and transparent substrate may be usually used, and if necessary, a colored and transparent substrate may be used.

In the present invention, an optical shutter layer is supported between the two conductive substrates. The composition of the optical shutter layer substantially consists of a transparent polymer component and a liquid crystal component.
The transparent polymer component is usually about 5 to 20% by weight (preferably 7 to 15% by weight), and the liquid crystal component is usually 95 to 80% by weight.
(Preferably 93 to 85% by weight). When the amount of the transparent polymer component is less than 5% by weight, the polymer component may form a dispersion layer. Further, when the transparent polymer component is 20
If the amount exceeds 10% by weight, the driving voltage may increase.

The liquid crystal component comprises a cholesteric liquid crystal, a chiral smectic C liquid crystal, and a nematic liquid crystal. The cholesteric liquid crystal and the chiral smectic C liquid crystal (hereinafter, both are also collectively referred to as “chiral liquid crystal”).
Is 0.05 to 10% by weight (preferably 0.3 to 1% by weight) in the liquid crystal component. It is well known that even if a little cholesteric liquid crystal is mixed in a nematic liquid crystal, it becomes a cholesteric liquid crystal. In the present invention, a chiral smectic C liquid crystal is added to a cholesteric liquid crystal obtained by adding a cholesteric liquid crystal to a nematic liquid crystal. When the ratio of the chiral liquid crystal is out of the above range, the driving voltage may increase or the response speed may decrease.

The ratio of the cholesteric liquid crystal and the chiral smectic C liquid crystal in the chiral liquid crystal may be appropriately set according to the use and the purpose of use of the final product. Usually, the ratio of the chiral smectic C liquid crystal to 1 mol of the cholesteric liquid crystal is used. It may be 4 mol or less, preferably 0.01 to 2 mol, more preferably 0.01 to 0.5 mol.

In the present invention, since two kinds of liquid crystals, a cholesteric liquid crystal and a chiral smectic C liquid crystal, are used together as a chiral liquid crystal, the driving voltage can be reduced and the light scattering ability based on the polydomain property can be further improved. It is possible to improve. In particular, in the present invention, it is more advantageous to improve the performance that the helical direction of the cholesteric liquid crystal and the helical direction of the chiral smectic C liquid crystal are opposite to each other. For example, when using a cholesteric liquid crystal whose helix direction is clockwise,
A chiral smectic C liquid crystal whose helix direction is counterclockwise may be used. The direction of the helix of these liquid crystals can be confirmed, for example, by preparing a planar texture and observing it with a polarizing microscope.

The reason why excellent characteristics can be obtained by using the above two kinds of liquid crystals (liquid crystal mixture) as chiral liquid crystals is not clear, but a liquid crystal system having a short spontaneous recovery time to a polydomain structure even with a small twisting force. Is formed, it is considered that a response is obtained even at a relatively low voltage as a whole, and a relatively fast response is exhibited.

The nematic liquid crystal, cholesteric liquid crystal and chiral smectic C liquid crystal used in the optical shutter layer of the present invention are not particularly limited, and known or commercially available liquid crystals can be used.

As the nematic liquid crystal, a liquid crystal which has a sufficient electric field response at room temperature, is uniformly mixed when mixed with a prepolymer, and forms an isotropic phase is particularly preferable. As long as such conditions are satisfied, a nematic liquid crystal that is widely used can also be used. For example, biphenyl, phenylcyclohexane, cyclohexylcyclohexane, cyanobiphenyl, cyanophenylcyclohexane, cyanocyclohexylcyclohexane, or a mixture thereof can be used. Among these, cyanobiphenyl-based, cyanophenylcyclohexane-based, and cyanohexylcyclohexane-based, which are particularly excellent in electric field response, are preferable.

As the cholesteric liquid crystal and the chiral smectic C liquid crystal, any liquid crystal having excellent mixing and miscibility with the nematic liquid crystal and capable of imparting a sufficient spiral twisting power to the nematic liquid crystal may be used. Specifically, there is no particular limitation as long as it exhibits a cholesteric phase and a chiral smectic C phase alone at normal temperature, and known or commercially available products can be used. The cholesteric liquid crystal and the chiral smectic C liquid crystal preferably have a relatively non-bulky structure.

The transparent polymer component is not particularly limited as long as it can take a structure that covers a small volume wall surface of the liquid crystal component in a thin film shape in order to sufficiently exhibit the wall effect. From the viewpoint of the manufacturing process, the optical shutter layer in the present invention is a mixture containing the ultraviolet / visible light-polymerizable prepolymer and / or monomer and the liquid crystal component (cholesteric liquid crystal, chiral smectic C liquid crystal, and nematic liquid crystal). Ultraviolet / visible light (wavelength: about 350-4
(00 nm) to polymerize the prepolymer or monomer. By performing such a treatment, a thin film polymer is formed in a state of wrapping the focal conic grain structure of the cholesteric liquid crystal, and the structure (granular structure) in which grains containing polydomains are wrapped in a thin film of the polymer is further improved. Can be obtained reliably.

Therefore, in the present invention, the above prepolymer and / or monomer are mixed with a liquid crystal component to make them compatible with each other, and then polymerized at around room temperature by irradiation of ultraviolet light or visible light, etc., to obtain a high transparency. Molecular components can be suitably used. As such a prepolymer or monomer, those generally known as an ultraviolet / visible light-polymerizable prepolymer or monomer can be used, and for example, acrylic, methacrylic, thioacrylic, and the like are used. it can. More specifically, hydroxyethyl acrylate, phenoxyethyl acrylate, lauryl acrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, polytetramethylene glycol diacrylate, trimethyl propane triacrylate, and the like, or prepolymers thereof Can be used alone or as a mixture. In the present invention, in particular, the glass transition temperature (T _g ) of the polymer after the polymerization is obtained.
Is desirably lower than the operating temperature range. In addition,
The degree of polymerization of the prepolymer may be appropriately set according to the type of the prepolymer, the liquid crystal component and the like to be used.

Other components in the light shutter layer include polymerization initiators such as an acrylic polyfunctional group, benzophenone, and 1-hydroxycyclohexyl phenyl ketone, as well as a chain transfer agent, a dye, a photosensitizer, and a crosslinking agent. Additives can be appropriately mixed as needed.

In the present invention, the optical shutter layer is composed of a granular structure (vesicle or cell) in which the transparent polymer thin film composed of the transparent polymer component wraps the liquid crystal component. That is, in the optical shutter layer in the present invention, a small volume of the liquid crystal component is occupied by a plurality of vesicles (grain) wrapped by the transparent polymer thin film (thin film wall).

The average diameter of the above structure may be appropriately set depending on the use of the final product, the kind of the transparent polymer component, and the like, but is usually about 1 to 10 μm, preferably 1 to 3 μm.
It is. By setting within this range, the contrast ratio can be improved, and particularly excellent responsiveness and the like can be exhibited. The average diameter in the present invention is a value obtained by observing a granular structure with a polarizing microscope or a scanning electron microscope, and arithmetically averaging the longest diameters of 50 randomly selected granular structures.

The thickness of the optical shutter layer in the present invention is not particularly limited, and can be appropriately determined according to the purpose and application of a desired device. From the standpoint of response and the like, it is usually about 3 to 60 μm. Preferably, the thickness is 5 to 15 μm. The thickness can be adjusted with a known spacer.

The liquid crystal optical shutter according to the present invention can be manufactured, for example, as follows. First, a nematic liquid crystal is diluted with a chiral liquid crystal, mixed well, a prepolymer and optional components are added, and mixed and stirred. The resulting mixture is inserted between two transparent conductive substrates set at a predetermined interval using a spacer, and the prepolymer is photopolymerized by irradiating ultraviolet / visible light through the substrates, thereby forming a polymer thin film. Is formed at the same time as the liquid crystal component is precipitated, and finally a granular structure in which the liquid crystal component is wrapped in the polymer thin film is obtained. In this way, an opaque light shutter layer is formed.

In this case, the order of blending each component in the optical shutter layer is not particularly limited. In the case of the above example, the chiral liquid crystal and the nematic liquid crystal are mixed, but in some cases, three types of liquid crystals may be mixed simultaneously.

The conditions for forming the above-mentioned granular structure may be appropriately set according to the type of the monomer or prepolymer used, the type of the liquid crystal component, the desired size of the granular structure, and the like. In particular, the temperature at which the granular structure is formed is usually 0.
It is desirable to set it to about 90 ° C.

The liquid crystal light shutter of the present invention can be applied to a light shutter portion of a known transmission type or non-transmission type display device. That is, other than using the liquid crystal optical shutter of the present invention, the display device of the present invention can employ known components as they are. For example, a backlight, a light reflecting plate, a color filter, a condenser lens, and the like can be used as necessary. However, a polarizing plate is not required.

In use, the same usage method as that of a known liquid crystal optical shutter may be used. For example, a power supply, a switch, or the like can be wired so that power can be supplied to the two conductive substrates, and the optical shutter can be opened and closed by turning on / off the power supply.

[0032]

The liquid crystal optical shutter of the present invention has a structure in which a transparent polymer thin film has a structure in which vesicles wrapping a small volume of chiral liquid crystal are stacked, and the polymer thin film is like a cell membrane. It can be called a cell wall type liquid crystal optical shutter. The structure is shown in FIG. The optical shutter layer supported (sandwiched) by the ITO coated glass (3), which is a transparent conductive substrate, is filled with a number of granular structures. Each granular structure (grain) is a polymer thin film (7)
And a chiral liquid crystal (5). Each granular structure has a number of domains separated by domain boundaries (6), and each elementary cholesteric liquid crystal (4)
Are distributed in large numbers.

In this polymer cell wall type liquid crystal optical shutter, when the power is turned off (when no voltage is applied), as shown in FIG. 1, the cholesteric focal conic texture (elemental cholesteric liquid crystal is oriented in various directions). Incident light due to strong turbidity of texture)
Is shut off. On the other hand, when the power is turned on (when no voltage is applied),
As shown in FIG. 2, the liquid crystal molecules are homeotropically aligned to transmit light.

In particular, when the power is turned off, as described above, the liquid crystal phase has a focal conic polydomain structure unique to cholesteric liquid crystal. Therefore, even if the vesicles are not fine, only the nematic liquid crystal is used. Shows a remarkable light scattering property as compared with (i.e., contributes to the state where the shutter is closed). As a result, in the present invention, the display contrast ratio can be improved by using a polymer having high transparency without particularly adjusting the refractive indices of the polymer component and the liquid crystal component.

Regarding the response speed, the rise time (τ _r ) in the liquid crystal optical shutter of the present invention corresponds to the time required for forcibly aligning molecules by an electric field.
Higher voltages tend to be shorter. On the other hand, the fall time (τ _d ) corresponds to the time required for the spontaneous recovery of the polydomain structure, and thus is determined mainly by the number of cholesteric liquid crystal (chiral liquid crystal) growth sites generated on the polymer wall surface. (Related to the interaction between the polymer and the liquid crystal interface).

If the twisting force of the chiral liquid crystal is increased, τ _d can be reduced, but on the other hand, a strong force is required for the rise involving the collapse of the cholesteric structure, so that the driving voltage is increased. That is, the speeding up of τ _{r and} the speeding up of τ _d are in a mutually contradictory relationship in the magnitude of the torsional force of the chiral liquid crystal and the driving voltage.

Under such a relationship, the liquid crystal optical shutter of the present invention adjusts the introduction of the wall surface of the polymer component and controls the torsional force of the chiral liquid crystal to achieve an optimum state. Higher response speed can be realized with a driving voltage that is extremely low.

[0038]

According to the liquid crystal optical shutter of the present invention, in the driving voltage 3～12V, rise time (tau _r) is 2~10ms (ms: m sec), fall time (tau _d) is 6~14ms , Maximum contrast ratio (T ₁₀₀ /
T ₀ ) (T ₁₀₀ : transmittance when voltage is applied (%), T ₀ : minimum transmittance (that is, transmittance when no voltage is applied) (%) 60
Excellent performance of 0 or more can be obtained. this is,
Conventional polymer-liquid crystal composite type liquid crystal optical shutter is several tens of volts
Is much lower than that required, and the response speed is almost the same or higher than that of the conventional device even at a low drive voltage. This also indicates that the need for a polarizing plate can be greatly contributed to energy saving.

Also, by including a chiral liquid crystal as a liquid crystal component, the maximum contrast ratio is considerably improved as compared with about 2 to 14: 1 obtained when only a conventional nematic liquid crystal is used. Thus, a high-performance liquid crystal optical shutter and a highly reliable display device can be provided.

Further, since the liquid crystal optical shutter of the present invention does not require a polarizing plate, an alignment film (alignment treatment / rubbing), etc., it is very advantageous in that the manufacturing process can be shortened and the cost can be reduced.

The liquid crystal optical shutter of the present invention is useful for transmissive or non-transmissive display devices such as spatial light modulators, dimmers, large-screen projection displays, large-screen television displays, and personal computer displays. It is also expected to be applied in various fields such as laser printer optical shutters.

[0042]

EXAMPLES The present invention will be described below in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

The measurement of the electro-optical characteristics of each device manufactured in the examples and comparative examples was performed by the following method. A function generator "1920A" (manufactured by NF) was used as a power supply, and a light source of 15A was used.
Using a 0 W (100 V) halogen lamp, a parallel light beam obtained by using a lamp house for a halogen lamp and a white light filter for a microscope is incident on a sample placed at a distance of 40 cm from the filter with a light beam having a diameter of 5 mm and transmitted through the sample. The amount of light passing through a slit having a width of 5 mm at a distance of 10 cm from the sample was evaluated by a photodetector.

The maximum contrast ratio (T ₁₀₀ / T ₀ ) was calculated by obtaining the ratio between the maximum transmittance (T ₁₀₀ ) when a voltage was applied and the transmittance (T ₀ ) when no voltage was applied under the above conditions. . The rise time (τ _r ) and fall time (τ _d ) were measured using a “digital storage oscilloscope” (Iwatsu, 40 MHz) with a rectangular wave having a frequency of 500 Hz.

Example 1 10% by weight of a 60:40 (weight ratio) mixture of hydroxyethyl acrylate and phenoxyethyl acrylate
And a cholesteric liquid crystal "C-15" (manufactured by Merck, spiral direction is counterclockwise (-)) and a ferroelectric liquid crystal "CS-2003" (Chisso Corporation, spiral direction showing a chiral smectic C phase) Clockwise (+)) 1: 0.2
(Molar ratio) 90% by weight of a liquid crystal component obtained by diluting with a nematic liquid crystal “5CB” (manufactured by Merck) was mixed sufficiently so that the mixture was 0.4% by weight in the liquid crystal component. The above mixture is inserted between two ITO-coated transparent conductive glass substrates with a spacing of 7.5 μm set by a polyimide film spacer, and a parallel beam of ultraviolet and visible light is emitted from a high-pressure mercury lamp of 100 W at room temperature 22 ° C. Irradiation was performed for 5 minutes at a position 30 cm from the lens to cause polymerization. The size of the optical shutter layer formed between the two substrates is about 1c.
It was mx 1 cm, and the structure in the optical shutter layer was observed with an electron microscope. As a result, it was recognized that a polydomain focal conic grain structure was formed.
The size of the grains was about 2 μm on average, and it was confirmed that there was some distribution. When the electro-optical characteristics of this device were measured at a room temperature of 20 ° C., the maximum contrast ratio (T ₁₀₀ / T ₀ ) was 700 or more at a driving voltage of 8 V, and τ _r = 2.
2 ms, τ _d = 7.3 ms were obtained.

Comparative Example 1 10% by weight of a 60:40 (weight ratio) mixture of hydroxyethyl acrylate and phenoxyethyl acrylate
And the nematic liquid crystal "5" such that the cholesteric liquid crystal "C-15" (manufactured by Merck) accounts for 20% by weight of the liquid crystal component.
Liquid crystal component 90 obtained by dilution with "CB" (manufactured by Merck)
% By weight. Two ITOs with the spacing set to 7.5 μm by a polyimide film spacer
The above mixture was inserted between the coated transparent conductive glass substrates, and ultraviolet light was applied at room temperature 22 ° C. using a 100 W high-pressure mercury lamp.
A parallel light beam of visible light was irradiated at a position 30 cm from the light-emitting side lens for 5 minutes to polymerize the polymer component. The size of the optical shutter layer formed between the two substrates is about 1 cm x
1 cm. When the electro-optical characteristics of this device were measured at a room temperature of 20 ° C., a maximum contrast ratio (T ₁₀₀ / T ₀ ) of 300 and τ _r = 10.6 were obtained at a driving voltage of 6 V.
ms, τ _d = 15 ms.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the operation principle (when no voltage is applied) of a liquid crystal optical shutter of the present invention.

FIG. 2 is a schematic diagram of the operation principle (when voltage is applied) of the liquid crystal optical shutter of the present invention.

Claims (5)

[Claims] 1. A liquid crystal optical shutter comprising two conductive substrates and an optical shutter layer supported between these substrates, wherein (1) the optical shutter layer has a high transparency of 5 to 20% by weight. (2) The liquid crystal component is composed of a cholesteric liquid crystal, a chiral smectic C liquid crystal and a nematic liquid crystal, and the total amount of the cholesteric liquid crystal and the chiral smectic C liquid crystal is 0% in the liquid crystal component. 0.05 to 10% by weight,
(3) The liquid crystal optical shutter, wherein the optical shutter layer comprises a granular structure in which the transparent polymer thin film made of the transparent polymer component wraps the liquid crystal component. 2. The liquid crystal optical shutter according to claim 1, wherein the helical direction of the cholesteric liquid crystal and the helical direction of the chiral smectic C liquid crystal are opposite to each other. 3. The liquid crystal optical shutter according to claim 1, wherein the average diameter of the granular structure is 1 to 10 μm. 4. An ultraviolet / visible light-irradiating ultraviolet-visible light is applied to a mixture containing a cholesteric liquid crystal, a chiral smectic C liquid crystal and a nematic liquid crystal. The liquid crystal optical shutter according to claim 1, wherein the monomer is polymerized. 5. A display device using the liquid crystal optical shutter according to claim 1.