JPH05307170A - Liquid crystal electrooptical device - Google Patents

Abstract

PURPOSE:To obtain the electrooptical device of a dispersion type liquid crystal having good transmittability of light when an electric field is not impressed to the device and a high scattering efficiency when the electric field is impressed thereto by using a specific antiferroelectic liquid crystal. CONSTITUTION:The liquid crystal material which exhibits a antiferroelectric property is used as the liquid crystal material to be used for the liquid crystal electrooptical device having a light control layer (composite composed of a liquid crystal and a light transmissive material) between a pair of electrodes. The liquid crystal droplets in the light control layer is produced by a method of injecting a mixture composed of the liquid crystal material and a UV curing resin between substrates and irradiating the resin with UV rays from the substrate surface to cure the resin. The liquid crystal droplets are otherwise formed by preparing a soln. formed by dissolving the liquid crystal and the resin in a solvent and applying the soln. by a spinner method or casting method on the substrate, then gradually evaporating the solvent. The resin is exemplified by polyethylene terephthalate, polyfumarate, polycarbazole, PMMA, etc. The liquid crystal droplets are otherwise produced as liquid crystal capsules by using polyvinyl alcohol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion type liquid crystal electro-optical device having a liquid crystal resin composite in which a liquid crystal material is dispersed in a polymer resin. In particular, it proposes a liquid crystal electro-optical device having high scattering efficiency.

[0002]

2. Description of the Related Art Conventional liquid crystal electro-optical devices of TN type and STN type using nematic liquid crystal are widely known.
It has been put to practical use. Recently, a liquid crystal using a ferroelectric liquid crystal is also known. These liquid crystal electro-optical devices basically sandwich a liquid crystal composition between a first substrate having electrodes and leads on a substrate and a second substrate having electrodes and leads on the substrate. An electric field is applied to the liquid crystal composition by the upper electrode, and the state of the liquid crystal molecule is changed by the anisotropy of the dielectric constant of the liquid crystal material itself or by spontaneous polarization in the case of a ferroelectric liquid crystal, and as a result, the liquid crystal molecule It utilizes the electro-optic effect that accompanies a change in state.

In a TN or STN type liquid crystal electro-optical device, liquid crystal molecules are aligned in the rubbing direction on the contact surfaces of both substrates of the liquid crystal layer by a restricting force by rubbing performed for alignment treatment. The rubbing directions of the upper and lower substrates are displaced so as to be located at 90 ° or 200 ° to 290 °. 90 ° -29 near the middle of the liquid crystal layer
The liquid crystal molecules are arranged spirally so that the energy between the upper and lower molecules located at 0 ° is the smallest. At this time, in the case of the STN type, a chiral substance is mixed with the liquid crystal material as needed.

All of these devices had a polarizing plate and it was necessary to orient the liquid crystal molecules regularly in a certain direction in the liquid crystal electro-optical device. This alignment treatment involves rubbing the alignment film (usually an organic film) with cotton or velvet cloth in a certain direction. Without this treatment, the liquid crystal molecules would not be aligned in a certain direction, and the electro-optical effect of the liquid crystal would be lost. It cannot be used. Therefore, in the structure of the device, a container for holding a liquid crystal material is constituted by a pair of substrates, and the liquid crystal is injected into the container to orient the liquid crystal to utilize its optical effect.

On the other hand, there is known a dispersion type liquid crystal which does not require these polarizing plates or alignment treatment and has a bright screen and good contrast. FIG. 1 shows a schematic view of a dispersed liquid crystal. The dispersion-type liquid crystal sandwiched between the substrates 1 having a light-transmitting property is a solid-state polymer 4 having a light-transmitting property which holds the liquid crystal material 3 in a granular or spongy form to form a light control layer. As a method for manufacturing this liquid crystal device, there is known a method in which an encapsulated liquid crystal material is dispersed in a polymer and the polymer is formed as a thin film on a film or a substrate. Here, gum arabic, polyvinyl alcohol, gelatin, etc. are used as the encapsulating material.

For example, liquid crystal molecules encapsulated with polyvinyl alcohol, if they have a positive dielectric anisotropy in a thin film, will have the long axis of the liquid crystal molecules in the presence of an electric field in the presence of an electric field. When they are arranged so as to be parallel to, and have a refractive index equal to that of the liquid crystal, transparency is exhibited. On the other hand, when there is no electric field, the liquid crystal is not aligned in a specific direction but faces various directions, and therefore the difference in the refractive index of the liquid crystal from the refractive index of the polymer is large, so that light is scattered and the transmission of light is prevented. Hinder,
It becomes cloudy. The change in the transmittance of the liquid crystal electro-optical device with respect to the applied voltage has the relationship shown in FIG. The arrow on the curve in the figure indicates the direction of change in voltage. If the liquid crystal has a negative dielectric anisotropy and the average refractive index of the liquid crystal is the same as that of polyvinyl alcohol, the transparency is exhibited in the absence of an electric field.

The average refractive index will be briefly described here. When the refractive index distribution is measured in a liquid crystal material in a non-electric field state without using any alignment treatment, the relationship shown in FIG. 4 is obtained. can get. In the figure, n _o and n _e respectively indicate the refractive index of the liquid crystal for ordinary light and extraordinary light. The average refractive index is defined as the refractive index n _ave when the distribution intensity is highest in FIG.

On the other hand, in the presence of an electric field, the long axes of the liquid crystal molecules are oriented perpendicularly to the direction of the electric field and a difference in refractive index occurs, so that light is scattered and becomes a cloudy state. Similar results are obtained if the liquid crystal molecules have spontaneous polarization in the direction perpendicular to the long axis of the liquid crystal molecules.
The change in the transmittance of the liquid crystal electro-optical device using such a liquid crystal material with respect to the voltage has the relationship shown in FIG. The dispersion type liquid crystal electro-optical device utilizes the difference between the transparency and the opaque state to provide various information.

As the dispersion type liquid crystal, in addition to such encapsulated ones, a liquid crystal material dispersed in an epoxy resin, or a liquid crystal and a photocurable resin are mixed to obtain a light for curing the resin. There are known ones that utilize the phase separation between liquid crystal and resin by irradiating with, and one in which the liquid crystal is impregnated in a three-dimensionally connected polymer. In the present invention, these are collectively referred to as dispersion type liquid crystal.

Since these dispersion type liquid crystal electro-optical devices do not use a polarizing plate as compared with conventional electro-optical devices such as TN and STN, the light transmittance of the liquid crystal electro-optical device is remarkably high. Specifically, the transmittance of one polarizing plate is about 50%,
In the case of an active matrix that uses it in combination 1
In the STN system, which transmits only about 10% of light, it is about 20%. Therefore, in these cases, efforts are being made to increase the illuminance of the rear illumination and to brighten the screen. On the other hand, in the case of the dispersion type liquid crystal electro-optical device, 50% or more of light is transmitted. This is because the dispersion type liquid crystal device does not need a polarizing plate.
Superiority.

As described above, the dispersive liquid crystal is used between the transparent state and the cloudy state, and a large amount of light is transmitted through the liquid crystal electro-optical device. Therefore, research and development is usually conducted as a transmissive liquid crystal electro-optical device. Has been done. In particular, it has been developed as a projection type liquid crystal electro-optical device among the transmission type.

In this projection type liquid crystal electro-optical device, a liquid crystal electro-optical device panel is arranged on an optical path of light emitted from a light source, and light passing through the panel is projected on a wall surface through a slit having a certain angle. To do. When the liquid crystal molecules have a positive dielectric anisotropy, the liquid crystal of this panel is oriented in various directions in a low electric field region below a threshold value that does not respond to an applied voltage, and is in a clouded state. The light that has entered at this time is scattered after passing through the panel, and the optical path of the light that has entered is greatly widened. Then, since the light scattered by the slit arranged next is cut off, almost no light reaches the wall surface, and a black state is obtained.

On the other hand, when the liquid crystal responds when an electric field is applied and the liquid crystal molecules are aligned parallel to the direction of the electric field, the incident light goes straight without being scattered, and a bright state with high brightness is obtained on the wall surface. .. When the liquid crystal molecules have negative dielectric anisotropy or have spontaneous polarization in a direction perpendicular to the long axis direction of the liquid crystal molecules, the average refractive index of the liquid crystal molecules in the absence of an electric field holds the liquid crystal. Contrary to the case where the liquid crystal molecules have a positive dielectric anisotropy, it is transparent and transmits light when there is no electric field, and becomes opaque when there is an electric field, as long as it matches the refractive index of the polymer resin. Light is scattered and a black state is obtained.

[0014]

As described above, the principle of switching of the dispersion type liquid crystal is that the light incident from the translucent substrate side has a different refractive index in the light control layer and the liquid crystal droplet. The light passes through the inside of the substrate several times, changes the optical path at both interfaces, reaches the opposite substrate surface, and the light is scattered. At that time, the incident light is largely scattered. In order to increase the scattering efficiency in the light control layer at this time, it is desirable that the number of times the resin and the liquid crystal droplets are in contact with each other in the thickness direction of the light control layer. This is because the light scatters each time. Therefore, the scattering efficiency increases as the thickness of the light control layer increases. However, there has been a problem that the substrate spacing, and hence the electrode spacing, becomes large and the drive voltage for switching the light control layer becomes large. For this reason, even if the scattering efficiency is improved, it is impossible to drive the IC and the TFT normally.

In general, in such a liquid crystal electro-optical device, 1) it can be driven at a low voltage, 2) the speed is sufficiently fast, and 3) even when the cell thickness is 2.5 to 10 μm, it is 0.1 ms (100 μs). ) Practical characteristics are required to be able to drive below. Most of the conventional dispersion type liquid crystal electro-optical devices use a liquid crystal material exhibiting nematic property, but in terms of response speed, the above requirements have not been met. A liquid crystal electro-optical device that satisfies these conditions and has a fast optical response that corresponds to moving image display without using a polarizing plate has not been proposed. Dispersion-type liquid crystal electro-optical devices using a developing liquid crystal material have been proposed. However, in the liquid crystal electro-optical device using this ferroelectricity, the liquid crystal material existing between the electrodes has ferroelectricity, so that the piezoelectric effect is exhibited at the time of driving. Specifically, the electric field applied when driving the liquid crystal causes the liquid crystal portion to contract in volume, which causes the substrate to vibrate and emits sound.

Due to the vibration of the substrate, there is a possibility that the liquid crystal electro-optical device in which a pair of substrates are usually bonded together may be broken or otherwise broken. The present invention eliminates many drawbacks as described above,
The contents are described below.

[0017]

In order to solve the above problems, the present invention is used in a liquid crystal electro-optical device having a dimming layer (composite of liquid crystal and translucent material) between a pair of electrodes. It is characterized in that a liquid crystal material exhibiting antiferroelectricity is used as the liquid crystal material, and by this, the response speed of the liquid crystal is increased, and the liquid crystal electro-optical device according to the volume change of the liquid crystal material is used. It is a solution to the problem.

Typical methods for producing liquid crystal droplets in the light control layer of the present invention are the following three types. 1) A mixture of a liquid crystal material and an ultraviolet curable resin in a ratio of 4: 6 to 8: 2 is injected between the substrates, and ultraviolet rays are irradiated from the substrate surface to cure the resin. At the time of irradiation, it is desirable to adjust the temperature of the sample so that it is heated to about 5 to 40 ° C. from the transition temperature of the mixture of liquid crystal and resin from the isotropic phase to the liquid crystal phase. 2) A liquid crystal and a resin may be dissolved in a solvent to prepare a solution, which is applied on a substrate by a spinner method or a casting method, and then the solvent is gradually vaporized to prepare the film. Examples of the resin include polyethylene terephthalate, polyfumaric acid ester, polycarbazole, PMMA and the like. 3) What was made into a liquid crystal capsule using polyvinyl alcohol. In any case, the shape of the liquid crystal droplet is spherical as shown in FIG. The present invention is described below with reference to examples, but the present invention is not limited to these examples and can be applied to a wide range of applications.

[0019]

EXAMPLE First, as shown in FIG. 1, a dispersion type liquid crystal is produced by a normal process. In this embodiment, a dispersion type liquid crystal using an ultraviolet curable resin will be described. An indium-tin oxide film (Indium-Tin-Oxide) 2 which is a light-transmitting conductive film was formed on the light-transmitting substrate 1 by a known vapor deposition method or sputtering method. The film thickness was 500 to 2000. The sheet resistance at this time was 20 to 200 Ω / cm ² . Next, this was patterned by the usual photolithography technique. Next, the first
The second substrate was bonded to the second substrate with an inorganic spacer having a distance of 5 to 100 μm, preferably 7 to 30 μm interposed therebetween under pressure. As a result, it is possible to maintain a cell spacing of approximately the Spessor diameter. Next, the liquid crystal material will be described. The liquid crystal used was an ester-based antiferroelectric liquid crystal having a refractive index of 1.6 and Δn of 0.2. As the uncured photocurable resin, a mixed system of a urethane oligomer having a refractive index of 1.62 and an acrylic monomer was used.

In the present embodiment, these materials were mixed and stirred, and ultrasonic waves were applied so that the liquid crystal material was uniformly dispersed. At this time, heating is performed at the same time, and the liquid crystal material is in an isotropic phase (liquid) state and is stirred and ultrasonic waves are added.
It was very effective to disperse the particles uniformly and then lower the temperature to the temperature of the liquid crystal phase.

At a temperature higher than the S _A -I phase transition point of the liquid crystal mixed system, it is injected into the liquid crystal cell formed by the above-mentioned first substrate and second substrate, and the UV irradiation intensity is about 10 to 100 mW / cm ^2. UV irradiation for about 30 to 300 seconds to cure the resin while causing phase separation between the liquid crystal and the resin. As a result, the liquid crystal droplets 3 surrounded by the resin 4 were formed.

The liquid crystal device thus manufactured is
As shown in FIG. 5, the liquid crystal molecules 1 are randomly aligned in the state where no voltage is applied between the electrodes provided on the upper and lower substrates, but the average refractive index of the liquid crystal and the refractive index of the polymer resin are Since the values of are approximately equal, the light is transmitted. Further, when a voltage is applied, due to the spontaneous polarization 2 of the liquid crystal molecule 1, the long axis of the liquid crystal molecule is oriented so as to be nearly perpendicular to the direction of the electric field, as shown in FIG. Since there is a difference in the refractive index from the polymer resin, the light is scattered.

[0023] In this embodiment, the phase sequence of the liquid crystal material used is intended to take _{^{Iso-SmA-SmC * -SmC A}} * -Cry, the transition temperature of Iso-SmA 100
℃, SmA-SmC ^* is 84 ℃, SmC _A ^* is 82 ° C., S
mC _A ^* -Cry is -10. 1 ° C., anisotropy value Δn of the refractive index was about 0.2. The value of spontaneous polarization is 80
It was nC / cm ² . The electro-optical characteristic values of this liquid crystal electro-optical device are shown in Table 1.

[0024]

[Table 1]

The values in Table 1 are at 80 ° C. As can be seen from the value of the transmittance, in the dispersion type liquid crystal using the liquid crystal material exhibiting the antiferroelectricity, the change in the transmittance with respect to the applied voltage has the relationship as shown in FIG. 2 of the conventional dispersion type liquid crystal electro-optical device. However, the result is as shown in FIG. Further, the switching speed of this liquid crystal electro-optical device was obtained in which the corresponding response time was fast, which was different from the case where the liquid crystal material exhibiting nematic property was used. The threshold voltage for driving the liquid crystal at this time required a relatively high voltage as shown in Table 1, but if a liquid crystal material having a larger refractive index anisotropy value is used, the ability to scatter light is high. Since the substrate interval can be made thin, the voltage for actual driving can be set within a general range.

Further, in the present invention, as the liquid crystal material,
Since a liquid crystal material exhibiting antiferroelectricity is used, the volume contraction that occurs due to the electric field applied to the liquid crystal material when the liquid crystal electro-optical device is driven is much less than when a ferroelectric liquid crystal is used. The substrate of the electro-optical device does not vibrate.

Further, in the case of the ferroelectric liquid crystal, even if an electric field is applied, the smectic layer structure taken in the droplets in which the liquid crystal material is dispersed will not be deformed. In the case of antiferroelectric liquid crystal, the smectic layer structure taken in the droplets in which the liquid crystal material is dispersed can be easily deformed by the electric field applied from the outside. A large difference in refractive index can be obtained, and a large contrast value can be obtained when a liquid crystal electro-optical device is formed.

Further, in the present invention, as the liquid crystal material,
Since a liquid crystal material exhibiting antiferroelectricity is used, the threshold characteristic has hysteresis. Therefore, a liquid crystal material exhibiting nematicity or a dispersion type liquid crystal electro-optical device using a liquid crystal material exhibiting ferroelectricity. Unlike the above, it has become possible to realize an electro-optical device having a fast response time and a memory property.

Further, in the present specification, the dispersed liquid crystal material is described as a droplet and is represented by a circle or a circular shape in the drawings. The shape is not limited, and the same effect can be expected even if the resin corresponding to the white part of the photograph exists between the substrates in a three-dimensional mesh pattern and the liquid crystal is held in the cavity corresponding to the black part of the dust. .. In addition to these, a dichroic dye or the like may be added to form a guest-host type liquid crystal electro-optical device.

[0030]

With the structure of the present invention, it is possible to provide a dispersion type liquid crystal electro-optical device which has a good light transmittance in the absence of an electric field and a large scattering efficiency when an electric field is applied in the dispersion type liquid crystal electro-optical device. I was able to realize it.

Compared with the case of using the TN liquid crystal that has been known so far, the present invention has a switching speed of 400 μs or less even if the interelectrode spacing has a thickness of 5 to 10 μ. It is less than 20 times faster, and since the liquid crystal material uses an antiferroelectric liquid crystal, the spontaneous polarization is as large as 80 nC / cm ^2, and as a result, the molecules given to the liquid crystal are forcibly driven there even under the same electric field. The strength to try is great.
As a result, it was possible to provide a high switching speed even when the electric field strength was low, that is, the liquid crystal cell was thick and the voltage was low.

In the conventional ferroelectric liquid crystal electro-optical device with a polarizing plate, the cell thickness was extremely thin, 1.3 to 2.3 μm. However, since the thickness is too small, shorts are generated between the upper and lower substrate electrodes due to dust or the like, which poses a problem in practical use. When this is set to 2.5 to 10 μm, for example, 5 μm, the occurrence rate of this short circuit decreases and the electric field strength between the substrates decreases, but a switching speed of 500 μsec or less could be obtained.

Further, in the conventional dispersion type liquid crystal electro-optical device using the liquid crystal material exhibiting nematic property, there is no hysteresis in the threshold characteristic and there is no storage function of the displayed contents. However, in the present invention, since the liquid crystal material exhibiting antiferroelectricity is used, the threshold value when the electric field is applied to change from the scattering state to the transmitting state becomes 9.5 V / μm, while the electric field is applied. Therefore, the threshold value when the non-applied state is changed from the scattering state to the transmission state is 5.5 V / μm, and clear hysteresis occurs in the threshold characteristic, so that the display content can be stored.

Further, since no polarizing plate is used, a bright liquid crystal display with little light loss can be obtained. In other words, the background color is milky white, creating a liquid crystal panel that looks like paper. It was able to reproduce a display that looked as if it were a printed matter.

[Brief description of drawings]

FIG. 1 is a schematic view of a dispersion type liquid crystal electro-optical device.

FIG. 2 shows a change in transmittance of a dispersion type liquid crystal electro-optical device with respect to a voltage when a liquid crystal material having a positive dielectric anisotropy is used.

FIG. 3 is a graph showing a change in transmittance of a dispersion type liquid crystal electro-optical device with respect to a voltage when a liquid crystal material having negative dielectric anisotropy or a liquid crystal material having spontaneous polarization in a direction perpendicular to a long axis of liquid crystal molecules is used. Indicates.

FIG. 4 shows a schematic view of a refractive index distribution of liquid crystal.

FIG. 5 shows a schematic view of alignment of liquid crystal molecules of a dispersion type liquid crystal electro-optical device when no electric field is applied.

FIG. 6 shows a schematic view of alignment of liquid crystal molecules of a dispersion type liquid crystal electro-optical device when an electric field is applied.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Shimizu 398 Hase, Atsugi City, Kanagawa Prefecture, Semiconducting Energy Laboratory Co., Ltd. In-house

Claims (2)

[Claims] 1. A pair of substrates having electrodes, at least one of which has translucency, and a dimming layer supported between the substrates, the dimming layer being transparent to an antiferroelectric liquid crystal material. A liquid crystal electro-optical device characterized by having a crystalline substance. 2. A smectic liquid crystal having electrodes, at least one of which has a pair of translucent substrates and a dimming layer supported between the substrates, the dimming layer exhibiting antiferroelectricity. Having a material and a transparent substance, it transmits incident light to the light control layer when no electric signal is applied to the light control layer, and scatters incident light to the light control layer when an electric signal is applied. Characteristic liquid crystal electro-optical device.