JPH04250418A - Liquid crystal optical element and its manufacture - Google Patents

Abstract

PURPOSE:To offer the liquid crystal optical element which can easily and optionally set the state of scattered light. CONSTITUTION:The liquid crystal optical element is formed by providing a liquid crystal material 11 in contact with the uneven surface of an uneven transparent solid material 12. For example, when respective materials are so selected that the refractive index of the liquid crystal material when a voltage is applied is equal to the refractive index of the transparent sold material, light travels straight in the voltage applied state and is scattered in a voltage unapplied state. The scattering state of the light can easily be controlled according to the unevenness of the transparent solid material.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a liquid crystal optical element that manipulates transmitted light (or reflected light) using a transparent-scattering method or a refraction method, and relates to a display device that displays characters, figures, etc., and an incident light It is used as an optical shutter to control transmission/blocking of light, a light valve, and an optical circuit component to switch the optical path.

0002

2. Description of the Related Art Conventionally, liquid crystal display elements of TN type and STN type using nematic liquid crystal have been put into practical use. Since these require a polarizing plate, they are limited in brightness and contrast.

On the other hand, the method disclosed in Japanese Patent Publication No. 58-501631, in which liquid crystal material is encapsulated and dispersed in a polymer, does not require a polarizing plate and has the advantage of less attenuation of light. . This disclosed technology takes advantage of the fact that the refractive index of the liquid crystal in the capsule changes depending on the presence or absence of an electric field, and by setting the refractive index of the liquid crystal under voltage application to be equal to the refractive index of the polymer, When the transparent voltage is removed, an optical element is obtained that scatters light and becomes opaque. Similar elements that utilize changes in the refractive index of liquid crystals include those in which liquid crystals are dispersed in epoxy resin (Japanese Patent Application Publication No. 61-502128) and those in which liquid crystals are dispersed in ultraviolet curing resin (Japanese Patent Application Laid-open No. 62-2231). etc. are known.

0004

The conventional liquid crystal optical element described above can be manufactured by the following method. ■
A method of dispersing encapsulated liquid crystals in polymers. ■Production method by homogeneously mixing liquid crystal material, resin, and their common solvent, and then removing the solvent to produce phase separation. ■A method of manufacturing by uniformly mixing liquid crystal materials and monomers and using phase separation caused by polymerization of the monomers. However, with these manufacturing methods, it is difficult to control the shape and position of the liquid crystal material dispersed in the transparent solid material, and it is impossible to obtain a material whose shape and position are highly controlled. By the way, the scattering state of a liquid crystal optical element is
Determined by the dispersion state of liquid crystal. However, in conventional liquid crystal optical elements, the interface between liquid crystal and transparent solid material (dispersed state)
Since it is impossible to highly control the scattering of transmitted light, there is a problem in that it is not possible to control the scattering of transmitted light. In addition, in conventional liquid crystal optical elements, even when light is scattered, the amount of light is maximized at the center, and only a monotonically decreasing type in which the scattered light intensity depends only on the scattered light angle can be obtained. The problem is that it is not possible to enhance the scattering of

An object of the present invention is to provide a liquid crystal optical element in which the state of scattered light can be arbitrarily and easily set.

[0006]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal optical element comprising a transparent solid material having irregularities and a liquid crystal material provided in contact with the irregularities. In the present invention, since the interface between the liquid crystal material and the transparent solid material is controlled by controlling the surface of the solid material (mechanical processing, etc.), the interface can be controlled with high precision compared to known methods. It also has the advantage of being easy to perform.

The transparent solid material constituting the liquid crystal optical element of the present invention comes into contact with the liquid crystal material at its uneven portions, forming an interface having unevenness. The refractive index of a liquid crystal material changes depending on changes in the alignment state and phase state (liquid crystal phase and isotropic phase) of liquid crystal molecules. By using a transparent solid material with an appropriate refractive index, it is possible to change the scattering and refraction of light in the liquid crystal material and the transparent solid material. For example, if the refractive index of a liquid crystal material under voltage application and the refractive index of a transparent solid material match, light will travel straight when voltage is applied, and will be scattered or refracted when voltage is turned off. An optical element is obtained. Examples of such combinations of transparent solid materials and liquid crystal materials are shown in the table below.

[0008]

[Table 1]

[0009]

[0010] The transparent solid material used in the present invention does not necessarily have to be completely transparent, but must be transparent enough that light rays are not significantly attenuated when passing through the transparent solid material. It is desirable to have Further, the transparent solid material does not need to be colorless, and a colored solid material can be used if necessary. Regarding the solidity of the transparent solid material, it may be flexible, elastic, and malleable, or it may be solid. If the transparent solid material is strong, it can also serve as a substrate for a liquid crystal optical element. The shape of the transparent solid material is not particularly limited, and it can be of any shape as long as it can efficiently scatter and refract light. When forming a structure, it is desirable to have a thin film shape or a plate shape. In particular, in order to lower the driving voltage, the thickness is preferably 20 μm or less.

[0011] As long as the transparent solid material has the above-mentioned characteristics, it is not particularly limited, but polymeric materials (polymer, plastic) or glass are preferable due to transparency, workability, etc.

If the unevenness of the transparent solid material is too small compared to the wavelength of light, no light scattering or refraction effect can be expected; You can choose the unevenness. In particular, when the unevenness of a transparent solid material is produced by an optical method or a mechanical method, the control of the unevenness is extremely easy and highly accurate. When the transparent solid material is in the form of a thin film or a plate, unevenness can be formed not only on one side, but also on both sides in order to improve the efficiency of light control.

[0013] The method of manufacturing the unevenness of the transparent solid is not limited in any way, but includes, for example, mechanical methods such as cutting and pressing, processing using laser beams, and photoreactions such as those used in photoresists. There are various methods, such as a chemical method such as elution with a solvent, and a method of copying the uneven portion using a method such as a replica method. In either method, since the interface between the liquid crystal material and the transparent solid material can be controlled by controlling the surface shape of the solid material, it can be easily controlled with high precision. In particular, a method of copying using a replica or the like is suitable for mass production. This method includes
A solution of a transparent solid material is applied to a mold with irregularities and the solvent is evaporated, or a precursor (monomer) of a transparent solid material is applied to a mold with irregularities and polymerized by UV irradiation or heat. There is a way.

The liquid crystal material is not limited to a single liquid crystal compound, but may be a mixture containing two or more types of liquid crystal compounds or substances other than liquid crystal compounds. As the liquid crystal material, any one of nematic liquid crystal, stictic liquid crystal, and cholesteric liquid crystal may be used, and the dielectric anisotropy may be positive or negative. Since the light ray changes due to a change in the refractive index of the liquid crystal material, the difference between the two refractive indexes of the liquid crystal material (ordinary ray refractive index and extraordinary ray refractive index), or the difference between the refractive index between the liquid crystalline and isotropic phases. A large one is desirable, but this is not a particular limitation.

In the case of a liquid crystal optical element in which a liquid crystal material and a transparent solid material have a layered structure, it is not necessary that each material has a single layer, but in order to limit the characteristics of the optical element, these materials may be used in multiple layers. You can also stack them.

[0016] In the present invention, the light control unit made of a liquid crystal material and a transparent solid material must be held so that they do not fall apart. The transparent solid material itself may serve this function, but it can also be made of other materials. When the light control section is in the form of a thin film or a plate, the substrate corresponds to this. The substrate may be made of a rigid material such as glass or metal, or may be made of a flexible material such as a polymeric film.

The liquid crystal optical element of the present invention can be driven by applying a voltage, applying a magnetic field, or changing the liquid crystal phase by temperature.
There are methods that utilize isotropic phase transition, but a method using voltage application is particularly desirable. As the electrode for applying voltage, a transparent electrode such as ITO (indium tin oxide) can be used when transparency is required, and various electrodes can be used when transparency is not required. The position of the electrode is not necessarily on the substrate surface;
It can be provided directly on or inside the transparent solid material, or it can be provided at the interface with the liquid crystal material.

When the liquid crystal optical element of the present invention is used as a reflective type, it is necessary to provide a reflective plate. The reflecting plate can be provided separately from the electrode, but it can also be designed so that the reflecting plate also serves as the electrode.

In order to use the liquid crystal optical element of the present invention for a projector, the scattered light must be aligned with the axis of the incident tip (direction of transmitted light).
It is necessary to deviate from the direction by about 5°, and it is difficult to separate light scattered with less accuracy from transmitted light (0°). Therefore, if the interface between the transparent solid and the liquid crystal is formed with unevenness in the shape of a series of triangles, and the slope of the triangle is tilted at an angle of 36 degrees or more with respect to the incident light, the direction of the refracted light at the interface will be changed from that of the incident light. It can be offset by 5° or more from the axis. However, the refractive index of the transparent solid was 1.5, and the refractive index of the liquid crystal was 1.7.

In order to use the liquid crystal optical element of the present invention for a projector, it is necessary for the scattered light to deviate from the axis of the incident light beam (direction of transmitted light) by about 5°, and the light scattered at an angle smaller than that is , it is difficult to separate it from transmitted light (0°). Therefore, the interface between the transparent solid and the liquid crystal is formed with unevenness in the shape of a series of triangles, and the slope of the triangle is 36 degrees to the incident light.
With the above inclination, the direction of the refracted light at the interface can be shifted by 5° or more from the axis of the incident light. However, the refractive index of the transparent solid was 1.5, and the refractive index of the liquid crystal was 1.7.

Furthermore, when the interface between the transparent solid and the liquid crystal is rectangular, the difference in the optical distance between the transparent solid and the liquid crystal is
By controlling the rectangular shape so that it is equal to half the wavelength of the incident light, it is possible to create a transmissive-non-transmissive element, which could be used not only as a projector but also as a reflective display device. .

[0022]

[Examples] The present invention will be specifically explained below with reference to Examples. However, the present invention is not limited to these examples. Example 1 Polymethyl methacrylate (Wako Pure Chemical Industries, Ltd. Cat No.
25290-31 (hereinafter abbreviated as PMMA) was dissolved in chloroform to obtain a 20 wt % PMMA solution. Glass substrate 14 (55 mm x 25 mm) with transparent electrode 13
, onto an ITO section (55 mm x 10 mm), and the solvent was evaporated. A PMMA film 12 was formed on a glass substrate. The membrane was transparent and approximately 20 μm thick. PMMA
The membrane was rubbed in one direction with #180 sandpaper and became white and opaque. This film was examined under a transmission electron microscope (S
When observed with EM), in the direction of rubbing, from several μm to several 1
It was confirmed that countless grooves of 0 μm were formed, resulting in an uneven surface. A nematic liquid crystal material E7 (manufactured by Merck & Co., Ltd.) 11 having positive dielectric anisotropy was poured onto this PMMA film, and another ITO-attached glass substrate 14 was pressed and fixed thereon (see FIG. 1). The obtained liquid crystal optical element was white and translucent. A 330 Hz rectangular alternating current wave was applied between the ITO electrodes, and changes in transmittance in the direction of incident light due to changes in voltage were measured. As a light source, 632.8 nm monochromatic light from a He-Ne laser (GLS5320B manufactured by NEC Corporation) was used. The value 0.5 seconds after changing the voltage was measured as the transmittance. The transmittance was 8% at a voltage of 0V, but it increased with voltage and increased to 72% at 50V.The light scattering state in the low voltage region was not concentrically symmetrical with respect to the center, but was due to the PMMA film. It became stronger in the direction perpendicular to the direction of the groove. 5° to the direction of light incidence
The intensity of scattered light in the tilted direction was measured. The scattering intensity tilted by 5° in the direction perpendicular to the groove decreased from 7% at a voltage of 0 V to 0.6% (50 V) as the voltage increased. on the other hand,
The scattering intensity tilted by 5° in the direction parallel to the grooves was independent of voltage and was 0.3% or less in the range of 0V to 50V.

[0023] The applied voltage is kept constant at 50V, and the frequency is set at 0.
The transmittance was measured by changing the frequency from 1 Hz to 104 Hz. The transmittance was 10% at 0.1 Hz, but increased with frequency (21% at 1 Hz, 48% at 10 Hz) 100
It was 70% at Hz, and almost no change was observed at frequencies above that. Comparative Example 1 A device was produced in the same manner as in Example 1. However, no grooves were formed on the PMMA film. The transmittance was 95% at a voltage of 0V and 96% at a voltage of 50V. Further, at a voltage of 50 V, the transmittance was within the range of 95% to 96% at frequencies of 0.1 Hz to 104 Hz. Comparative Example 2 Similar measurements were carried out on a system in which liquid crystals were dispersed in an epoxy resin, which is known from Japanese Patent Publication No. 61-502128. Epoxy resin adhesive (CEMEDINE SUPER, epoxy-amide type) and liquid crystal E7 were mixed in an amount of 50 wt %. The mixture was sandwiched between glass substrates with ITO, and the thickness was 16 mm.
It was pressed together with a μm spacer film. As the epoxy resin cured, it became white and opaque. Transmittance was measured in the same manner as in Example 1. 2 from 0V to 5V
What was 8% increased to 50V and 92%. Scattered light in the direction of 5° from the direction of incidence of the light beam is from 0V to 50V
However, no change was observed depending on the orientation of the substrate. Example 2 A 20% solution of PMMA prepared in the same manner as in Example 1 was poured onto a frosted glass (designed to be the frosted part of a slide glass manufactured by Matsunami Glass Industries), and the solvent was evaporated. A PMMA film was formed on the frosted glass, making it transparent. When the PMMA film is peeled off from the glass plate, it becomes opaque, and when the unevenness of the frosted glass and its replica was observed using SEM, the existence of irregular unevenness ranging from about 1 μm to several tens of μm was confirmed, indicating that the PMMA film was changed from the frosted glass to the PMMA film. It was confirmed that the unevenness was well copied. The film thickness was approximately 10 μm. Liquid crystal E is placed between the PMMA film and the glass substrate with ITO.
7 and fixed with scissors to produce an optical element with a laminated structure. The layer order was substrate/liquid crystal/PMMA/liquid crystal substrate.

The transmittance of the produced optical element was measured in the same manner as in Example 1. Regarding the voltage dependence of transmittance,
It remained almost constant at 20% up to 10V, but rose rapidly from 10V to 89% at 50V (see Figure 2). Regarding the frequency dependence at a voltage of 50 V, the transmittance increases from 21% (0.1 Hz) to 88% (102 ~
104 Hz). These changes in transmittance were stable regardless of the direction of change in voltage and frequency, and even in repeated measurements. Comparative Example 3 A device was produced and measured in the same manner as in Example 1 except that transparent (flat) glass was used instead of frosted glass. When the voltage is changed from 0V to 50V, the frequency is 0.1
The changes in transmittance when changing from Hz to 104 Hz were 97-98% and 96-98%, respectively. Example 3 An optical element was prepared and measured in the same manner as in Example 2, except that polystyrene (manufactured by Wako Pure Chemical Industries, Ltd., molecular weight 1600-1800) was used instead of PMMA, and E8 (manufactured by Merck) was used as the liquid crystal. The transmittance increases with voltage from 9% (0V) to 7
It increased to 9% (50V). Examples 4 and 5 Elements were prepared and measured in the same manner as in Example 1, except that the PMMA solution was replaced by a polyvinyl chloride adhesive (for Cemedine Vinyl) and an epoxy resin adhesive (Cemedine High Super 5). . The voltage dependence of transmittance is 40% (0V) to 93% (50V) and 41%, respectively.
(0V) to 77% (50V). Example 6 The PMMA film obtained by the method of Example 2 was turned over and pressed against frosted glass coated with a small amount of chloroform, thereby creating a PMMA film having irregularities on both sides. As in Example 2, the liquid crystal/PMMA/liquid crystal layers were sandwiched and fixed between two substrates. The transmittance varied with voltage from 9% (0V) to 81% (50V). Example 7 An optical element was manufactured using two PMMA films obtained in the same manner as in Example 1, and measurements were performed. The layer order was substrate/liquid crystal/PMMA/liquid crystal/PMMA/liquid crystal/substrate. The transmittance varied from 10% (0V) to 41% (50V). Example 8 An optical element similar to that in Example 1 was produced, no voltage was applied,
Changes in transmittance due to temperature changes were measured. Liquid crystal material (E
The transmittance of 7) was 96% at temperatures above about 70° C., where it changes to an isotropic phase, and was 17% at temperatures below that temperature. The transmittance of repeated measurements was also equal to these values. Example 9 A transparent electrode made of ITO was attached to the flat side (opposite the frosted glass) of a PMMA film prepared in the same manner as in Example 2 by sputter coating. An element having a three-layer structure (substrate/liquid crystal/PMMA) was prepared by stacking a liquid crystal and the above PMMA film on a glass substrate with ITO. When the transmittance was measured in the same manner as in Example 1, the transmittance was 15% when no voltage was applied, but it changed to 70% at 50V.

[0025]

As described above, the present invention provides a novel liquid crystal optical element, and by constructing the liquid crystal optical element from a transparent solid material having irregularities and a liquid crystal material, the solid-liquid crystal interface can be improved. To provide an optical element whose unevenness can be easily controlled with a high density. Therefore, the present invention can be widely used in display device optical shutters (light valves), optical circuits, etc.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an example of a liquid crystal optical element of the present invention.

FIG. 2 is a diagram showing an example of a voltage-transmittance curve of a liquid crystal optical element of the present invention.

[Explanation of symbols]

11 Liquid crystal material 12 Transparent solid material 13 Transparent electrode 14 Glass substrate

Claims (3)

[Claims] 1. A liquid crystal optical element comprising a transparent solid material having irregularities and a liquid crystal material provided in contact with the irregularities. 2. The liquid crystal optical element according to claim 1, wherein the liquid crystal material and the transparent solid material are held between two substrates, at least one of which is transparent. 3. Coating a solution of a transparent solid material or a precursor of a transparent solid material onto the irregularities of another solid material having irregularities and solidifying the same, thereby copying the irregularities on the surface of the transparent solid material, A method for manufacturing a liquid crystal optical element by laminating the obtained transparent solid material and a liquid crystal material.