JP3049779B2 - Liquid crystal optical element and manufacturing method thereof - Google Patents

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 for controlling transmitted light (or reflected light) by a transparent-scattering method or a refracting method, and relates to a display device for displaying characters, figures, etc., and incident light. It is used as an optical shutter, an optical valve, and an optical circuit component for switching an optical path, which controls transmission and blocking of light.

[0002]

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

On the other hand, the method disclosed in JP-T-58-501631 in which a liquid crystal material is encapsulated and dispersed in a polymer does not require a polarizing plate, and thus has the advantage of little light attenuation. . In this disclosed technique, by using the fact that the refractive index of the liquid crystal in the capsule changes depending on the presence or absence of an electric field, the refractive index of the liquid crystal under voltage application is set equal to the refractive index of the polymer, so that under voltage application When the transparent voltage is removed, an optical element that scatters light and becomes opaque is obtained. Similar devices utilizing the change in the refractive index of liquid crystal include liquid crystal dispersed in an epoxy resin (Japanese Patent Publication No. Sho 61-502128) and a liquid crystal dispersed in an ultraviolet curable resin (Japanese Patent Application Laid-Open No. 62-2231). Etc. are known.

[0004]

The above-mentioned conventional liquid crystal optical element can be manufactured by the following method.
A method in which encapsulated liquid crystal is dispersed in a polymer. A method in which a liquid crystal material, a resin, and a common solvent thereof are uniformly mixed, and the liquid crystal material is manufactured by phase separation caused by removing the solvent. A method in which a liquid crystal material and a monomer are uniformly mixed, and the liquid crystal material is produced by phase separation caused by polymerizing the monomer. 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 the liquid crystal optical element is determined by the dispersion state of the liquid crystal. However, in the conventional liquid crystal optical element, since it is impossible to control the interface (dispersion state) between the liquid crystal and the transparent solid material at a high level, there is a problem that scattering of transmitted light cannot be controlled.
Further, in the conventional liquid crystal optical element, even in a state where light is scattered, the amount of light at the central portion is maximized, and only a monotonically decreasing type in which the scattered light intensity depends only on the scattered light angle is obtained. There is a problem that the scattering of light cannot be strengthened.

[0005] It is an object of the present invention to provide a liquid crystal optical element in which the state of scattered light can be set arbitrarily and easily.

[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, the control of the interface between the liquid crystal material and the transparent solid material is performed by controlling the surface of the solid material (mechanical processing or the like). It also has the advantage that it can be easily performed.

[0007] The transparent solid material constituting the liquid crystal optical element of the present invention is in contact with the liquid crystal material at the uneven portions to form 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 having an appropriate refractive index, scattering and refraction of light in a liquid crystal material and a transparent solid material can be changed. For example, when the refractive index of a liquid crystal material under voltage application and the refractive index of a transparent solid material are matched, light goes straight in the state of voltage application, and the light is scattered or refracted in the state of voltage cut off. An optical element is obtained. The combination of such a transparent solid material and a liquid crystal material is as shown in the table below.

[0008]

[Table 1]

[0009]

[0010] The transparent solid material used in the present invention does not necessarily require complete transparency, but has such transparency that light rays do not undergo significant attenuation when passing through the transparent solid material. It is desirable to have 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 have flexibility, elasticity, and flexibility, or may be solid. When the transparent solid material is rigid, it can serve as a substrate for a liquid crystal optical element. The shape of the transparent solid material is not particularly limited, and any shape can be used as long as it can efficiently scatter and refract light. When a structure is formed, a thin film (film) or plate is desirable. In particular, in order to lower the drive voltage, the thickness is desirably 20 μm or less.

As long as it is a transparent solid material having the above-mentioned characteristics, it is not particularly limited, but a polymer material (polymer, plastic) or glass is desirable from the viewpoint of transparency, workability, and the like.

If the irregularities of the transparent solid material are too small compared to the wavelength of light, the effect of light scattering and refraction cannot be expected. Unevenness can be selected. In particular, when the unevenness of the transparent solid material is manufactured by an optical method or a mechanical method, the control of the unevenness is extremely easy and the accuracy is high. When the transparent solid material is in the form of a thin film or a plate, the irregularities can be formed on only one side, or can be formed on both sides to increase the efficiency of light control.

The method for producing the irregularities of the transparent solid is not limited at all. For example, mechanical methods such as cutting and pressing, processing by a laser beam or the like, and photoreactions used in photoresists are used. Method, a chemical method such as elution with a solvent, or a method of copying a portion having irregularities by a method such as a replica. In any case, the interface between the liquid crystal material and the transparent solid material can be controlled by controlling the surface shape of the solid material, so that it can be controlled with high precision and ease. In particular, the method of copying with 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 having irregularities to evaporate a solvent, or a precursor (monomer) of a transparent solid material is applied to a mold having irregularities, and is 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 liquid crystal compounds or a substance other than the liquid crystal compound. As the liquid crystal material, any of a nematic liquid crystal, a strictic liquid crystal, and a cholesteric liquid crystal may be used, and the dielectric anisotropy may be positive or negative. Since the light beam changes due to the change in the refractive index of the liquid crystal material, the difference between the two refractive indices of the liquid crystal material (the ordinary light refractive index and the extraordinary light refractive index) or the difference in the refractive index between the liquid crystallinity and the isotropic phase. Larger ones are desirable, but not particularly limited.

In the case of a liquid crystal optical element having a layer structure composed of a liquid crystal material and a transparent solid material, each material does not need to be a single layer. You can also stack them.

In the present invention, the light control section made of a liquid crystal material and a transparent solid material needs to be held so that they do not fall apart. The transparent solid material itself may also perform this function, but may be formed of other materials. When the light control unit 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 polymer film.

The liquid crystal optical element of the present invention is driven by applying a voltage, applying a magnetic field, or controlling the liquid crystal phase by temperature.
Although there is a method utilizing a transition of an isotropic phase, etc., a method by applying a voltage is particularly preferable. As an electrode for applying a 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 required to be present on the surface of the substrate, but may be provided directly on or inside the transparent solid material, or may be provided at the interface with the liquid crystal material.

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

In order to use the liquid crystal optical element of the present invention for a projector, the scattered light is reflected on the axis of the incident coin (the direction of the transmitted light).
It is necessary to deviate from the direction by about 5 °, and it is difficult to separate light scattered to an accuracy less than 5 ° from transmitted light (0 °). Therefore, if the interface between the transparent solid and the liquid crystal is formed as irregularities formed by a series of triangles and the slope of the triangle is inclined at an angle of 36 ° or more with respect to the incident light, the direction of the refracted light at the interface changes the direction of the incident light. It can be shifted more than 5 ° 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, the scattered light needs to be shifted by about 5 ° from the direction of the axis of the incident light (the direction of the transmitted light). Is difficult to separate from transmitted light (0 °).
Therefore, the interface between the transparent solid and the liquid crystal is formed as irregularities formed by connecting triangles, and the slopes of the triangles are formed at 36 ° with respect to 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.

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 as to be equal to the half wavelength of the incident light, a transmissive-non-transmissive element can be produced, which can be used as a reflective display device besides a projector. .

[0022]

The present invention will be described below in detail with reference to examples. However, the invention is not limited to these examples. Example 1 Polymethyl methacrylate (Cat No. manufactured by Wako Pure Chemical Industries, Ltd.)
25290-31: PMMA) was dissolved in chloroform to obtain a 20 wt% PMMA solution. The glass substrate 14 with the transparent electrode 13 (55 mm × 25 mm, I
(TO section 55 mm × 10 mm) to evaporate the solvent. A PMMA film 12 was formed on a glass substrate.
The film was transparent and had a thickness of about 20 μm. PMMA
Rubbing the film in one direction using sandpaper # 180 turned white and opaque. When this film was observed with a transmission electron microscope (SEM), it was confirmed that countless grooves of several μm to several tens of μm were formed in the rubbing direction, and the surface was uneven. A nematic liquid crystal material E7 (manufactured by Merck) 11 having a positive dielectric anisotropy is formed on the PMMA film.
Then, another glass substrate 14 with ITO was pressed and fixed thereon (see FIG. 1). The obtained liquid crystal optical element was white and translucent. A rectangular alternating wave of 330 Hz was applied between the ITO electrodes, and the change in transmittance in the incident light beam direction with the change in voltage was measured. As a light source, 632.8 nm monochromatic light of a He-Ne laser (GLS5320B manufactured by NEC) was used. The value at 0.5 seconds after changing the voltage was measured as the transmittance. The transmittance is 8 at a voltage of 0 V.
%, But increased with the voltage and increased to 72% at 50 V. The light scattering state in the low voltage region is not concentrically symmetric with respect to the center but in a direction perpendicular to the direction of the groove of the PMMA film. I was getting stronger. The scattered light intensity in a direction inclined by 5 ° with respect to the light incident direction was measured. The scattering intensity inclined by 5 ° in the direction perpendicular to the groove decreased from 7% at a voltage of 0 V to 0.6% (50 V) with an increase in the voltage. On the other hand, the scattering intensity inclined by 5 ° in the direction parallel to the groove was 0.3% or less in the range of 0 V to 50 V without depending on the voltage.

The applied voltage is fixed at 50 V, and the frequency is set to 0.1.
The transmittance was measured while changing from 1 Hz to 10 ⁴ Hz. The transmittance was 0.1% at 0.1 Hz, but increased with frequency (21% at 1 Hz and 48% at 10 Hz).
It became 70% at 0 Hz, and hardly changed at frequencies higher than 0 Hz. Comparative Example 1 An element was prepared in the same manner as in Example 1. However, no groove was formed in the PMMA film. The transmittance at a voltage of 0 V was 95%, and the transmittance at a voltage of 50 V was 96%. At a voltage of 50 V, the transmittance was in the range of 95% to 96% at a frequency of 0.1 Hz to 10 ⁴ Hz. Comparative Example 2 The same measurement was carried out for a system in which liquid crystal was dispersed in an epoxy resin known in Japanese Patent Publication No. Sho 61-502128. An epoxy resin-based adhesive (Cemedine Super, epoxy-amide based) and liquid crystal E7 were mixed at 50 wt% each. The mixture was sandwiched between glass substrates with ITO and had a thickness of 1
It was pressed together with a 6 μm spacer film. As the epoxy resin cured, it became white and opaque. The transmittance was measured in the same manner as in Example 1. What was 28% from 0V to 5V increased to 50V, 92%. The scattered light in the direction of 5 ° from the incident direction of the light beam is 0 V to 50 °.
V decreased from 4% to 0.3%, but no change due to the orientation of the substrate was observed. Example 2 A 20% solution of PMMA prepared in the same manner as in Example 1 was applied to frosted glass (specified by a frosted part of a slide glass manufactured by Matsunami Glass Industry) to evaporate the solvent. A PMMA film was formed on the frosted glass and became transparent. When the PMMA film is peeled off from the glass plate, it becomes opaque, and the unevenness of the frosted glass and its replica is observed by SEM. It was confirmed that the transfer of the irregularities was good. The thickness was about 10 μm. A liquid crystal E is placed between a glass substrate with ITO and a PMMA film.
7 was fixed together with scissors to produce an optical element having a laminated structure. The order of the layers was substrate / liquid crystal / PMMA / liquid crystal substrate.

The transmittance of the manufactured optical element was measured in the same manner as in Example 1. In terms of voltage dependence of transmittance,
It was almost constant at 20% up to 10 V, but rose rapidly from 10 V and reached 89% at 50 V (see FIG. 2). In the frequency dependence at a voltage of 50 V, the transmittance is 21% (0.1 Hz) to 88% (10 ² to 10%) as well as the frequency.
10 ⁴ Hz). These changes in transmittance are
It was stable irrespective of the direction of change in voltage and frequency, and also in repeated measurements. Comparative Example 3 An element was prepared and measured in the same manner as in Example 1, except that a transparent (flat) glass was used instead of the frosted glass. When the voltage is changed from 0V to 50V, the frequency is 0.1
The change in transmittance when changing from 10 Hz to 10 ⁴ Hz was 97 to 98% and 96 to 98%, respectively. Example 3 An optical element was prepared and measured in the same manner as in Example 2 except that E8 (manufactured by Merck) was used as a liquid crystal instead of polystyrene (manufactured by Wako Pure Chemical, molecular weight: 1600-1800) instead of PMMA. The transmittance increases from 9% (0 V) to 7 with the voltage.
It increased to 9% (50V). Examples 4 and 5 Devices were prepared and measured in the same manner as in Example 1 except that a polyvinyl chloride adhesive (for Cemedine Vinyl) and an epoxy resin adhesive (Cemedine High Super 5) were used instead of the PMMA solution. . The voltage dependence of transmittance is 40% (0 V) to 93% (50 V) and 41%, respectively.
(0 V) to 77% (50 V). Example 6 A PMMA film having irregularities on both surfaces was formed by turning the PMMA film obtained by the method of Example 2 upside down and pressing it against a frosted glass to which a small amount of chloroform had been applied. As in Example 2, each layer of liquid crystal / PMMA / liquid crystal was sandwiched and fixed between two substrates. The transmittance varied from 9% (0 V) to 81% (50 V) with the voltage. Example 7 An optical element was manufactured using two PMMA films obtained in the same manner as in Example 1, and measurement was performed. The order of the layers 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 of Example 1 was manufactured, and no voltage was applied.
The change in transmittance with temperature was measured. Liquid crystal material (E
The transmittance which was 96% at about 70 ° C. or higher where 7) changed to an isotropic phase was 17% at a temperature lower than 70 ° C. The transmittance when the measurement was repeated was equal to these values. Example 9 A transparent electrode made of ITO was attached to the flat side (opposite to the frosted glass) of the PMMA film formed in the same manner as in Example 2 by a sputter coating method. An element having a three-layer structure (substrate / liquid crystal / PMMA) in which a liquid crystal and the above-mentioned PMMA film were stacked on a glass substrate with ITO was prepared. When the transmittance was measured in the same manner as in Example 1, the transmittance was changed from 15% when no voltage was applied to 70% at 50V.

As described above, the present invention provides a novel liquid crystal optical element, and comprises a liquid crystal optical element composed of a transparent solid material having irregularities and a liquid crystal material.
Provided is an optical element which can control irregularities at a solid-liquid crystal interface with high precision and easily. Therefore, the present invention can be widely applied to display device optical shutters (light valves), optical circuits, and the like.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one 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 the liquid crystal optical element of the present invention.

[Explanation of symbols]

 Reference Signs List 11 liquid crystal material 12 transparent solid material 13 transparent electrode 14 glass substrate

Claims (3)

(57) [Claims] 1. A transparent solid material having irregular irregularities and a liquid crystal material provided in contact with the irregularities, and the refractive index difference between the transparent solid material and the liquid crystal material is changed. A liquid crystal optical element which scatters or refracts light at an interface. 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 has transparency. 3. Scattering of transmitted light having irregular irregularities
And a liquid crystal material provided in contact with the unevenness of the transparent solid material, and by changing the refractive index difference between the transparent solid material and the liquid crystal material, light is scattered or dispersed at these interfaces. A method for producing a liquid crystal optical element to be refracted, comprising applying a solution of a transparent solid material or a precursor of a transparent solid material onto irregularities of another solid material having irregularities and solidifying the solid surface. To capture the irregularities in the previous period,
A method for manufacturing a liquid crystal optical element in which the obtained transparent solid material and a liquid crystal material are laminated.