JP2525685B2 - Optical element - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

TECHNICAL FIELD The present invention relates to an optical element used for a light valve, a display device, a light control window, etc., and particularly to changing the orientation of particles by applying an electric field to a dispersion in which anisotropic particles are dispersed in a medium. The present invention relates to an optical element in which the transmittance and reflectance of light are changed.

[Prior art]

Anisotropic particles are dispersed in a medium, and an electric field or magnetic field is applied to the particles to change the orientation of the particles to control the light transmittance, etc. (See, for example, US Pat. No. 1,955,923). In such a case, in order to disperse the particles uniformly in the medium, the composition of the medium is improved (see, for example, Japanese Patent Publication No. 62-40389), or the particles are coated (see, for example, Japanese Patent Laid-Open No. No. 62-232623) is also proposed. FIG. 2 shows a typical example of a conventional optical element using such a principle. As is clear from this figure, the optical element 1 is formed by enclosing a dispersion body 4 in which particles 2 having a shape or optical anisotropy are dispersed in a liquid medium 3 in a cell 5. . The cell 5 is composed of two electrode supporting plates 6 and 6 made of transparent plates, which are opposed to each other with a small space therebetween, and the periphery thereof is sealed by a sealing material 7 serving as a spacer. Transparent electrodes 8 and 8 are provided on the inner surfaces, respectively. In the optical element 1 thus configured, when an electric field of alternating current or pulse wave is applied from the external power source 9 through the electrodes 8 and 8, the orientation of the particles 2 is changed and the light transmittance is changed. That is, when no electric field is applied, many particles 2 are oriented in random directions, and light is absorbed or scattered by the particles 2, so that the optical element 1 is opaque, but an electric field is applied. Then, the particles 2 are oriented in parallel with the electric field, so that light easily passes therethrough and the particles become transparent. Therefore, by using this optical element 1, it is possible to obtain a light valve, various display devices, a dimming window, or the like. In the conventional optical element, the dispersion 4 in which the particles 2 are dispersed in the medium 3 is simply enclosed in the cell 5 as described above.

[Problems to be Solved by the Invention]

By the way, when manufacturing such an optical element 1, it is necessary to inject the dispersion 4 into the cell 5. In that case, the gap between the electrodes 8 of the cell 5 is very small. Moreover, the medium 3 of the dispersion 4 is often a highly viscous one. Therefore, the dispersion 4 cannot be simply injected into the cell 5. Therefore, in the case of the conventional optical element 1, the dispersion 4
It is necessary to use a pressure injection method of pressurizing and injecting, or a reduced pressure injection method of depressurizing and injecting the inside of the cell 5. However, when such a pressure injection method or a reduced pressure injection method is used, it is inevitable that the cell 5 is deformed into a convex shape or a concave shape due to the pressure difference between the inside and the outside. When the cells 5 are thus deformed, the cell gaps are partially different, resulting in color unevenness. Also,
Deformation of the cell 5 may damage the adhesive portion. In order to prevent such deformation of the cells 5, beads are scattered in the cells 5, but if this is done, the beads may cause color unevenness. Further, in the conventional optical element 1, when the cell 5 becomes large, the lower part of the cell 5 swells due to the hydrostatic pressure of the dispersion body 4 enclosed inside, and thus the color unevenness similarly occurs. Furthermore, when the viscosity of the medium 3 is low, the dispersion 4 causes convection due to a slight temperature difference in the cell 5, and the density of the particles 2 locally changes accordingly, which also causes color unevenness. There is a problem that it will occur. Further, in the case where the dispersion 4 is simply enclosed in the cell 5 as in the conventional case, the particles 2 freely move and come into direct contact with the electrode 7, so that the electric field is continuously applied for a long time or turned on / off. When it is repeated, the particles 2 aggregate on the electrode surface to form a spotted pattern, which causes a change in transmittance and uneven color. Due to such a problem, this optical element has not yet been put into practical use, though it is inexpensive. The present invention has been made in view of such circumstances, and an object thereof is an optical type of this type which is less likely to cause color unevenness and aggregation of particles, has excellent durability, and is easy to manufacture. It is to provide an element.

[Means for Solving the Problems]

In order to achieve this object, in the present invention, a dispersion in which anisotropic particles are dispersed in a medium is held on a transparent support having continuous fine voids, and the support is used as an electrode in a cell. I am trying to place it between them. This is a first example showing an embodiment of the optical element according to the present invention.
This will be described in more detail with reference to the drawings. As is apparent from FIG. 1, the optical element 10 includes a cell 11 similar to the conventional one. That is, the cell 11 has two electrode supporting plates 12 and 12 made of transparent plates, which are opposed to each other with a small space therebetween, and a spacer 13 around the periphery thereof.
The transparent electrodes 14, 14 are arranged on the inner surface of each electrode support plate 12, 12. In this way, the external power supply 15 applies an electric field of alternating current or pulse wave into the cell 11 through the electrodes 14, 14. Between the electrodes 14, 14 in the cell 11, a transparent support 17 having a large number of continuous fine voids 16, 16 ... In the void 16 of the support 17,
A dispersion 20 in which particles 18 having a shape or optically anisotropy are dispersed in a medium 19 is held. The particles 18 are the same as the conventional ones that are oriented by an electric field, and the medium 19 is also the same as the conventional one that is transparent and electrically insulating. As the support 17, a porous polymeric substance having open cells, a spongy substance, or a fibrous substance such as a glass fiber cloth or a non-woven fabric can be used. The functions required of the support 17 are that light is transmitted, the space 16 has a size capable of accommodating the dispersion 20, the space 16 is continuous without being independent, and both ends thereof are external. Open, electrically insulating so as not to reduce the electric field strength, have sufficient strength to hold the dispersion 20, and cause a chemical reaction with the dispersion 20. It does not alter either the support 17 or the dispersion 20. The support 17 does not necessarily need to be transparent in the air, but may be transparent while the dispersion 20 is held in the voids 16. Alternatively, if it can be made transparent by holding the third liquid, it can be used as a support while holding the liquid. For example, a glass fiber body looks whitish in the air due to diffuse reflection, but becomes transparent because diffuse reflection does not occur when water is impregnated between the fibers. Further, gelatin such as agar is white in a dry state, but becomes transparent when it contains water. Therefore, by using a transparent and electrically insulating liquid instead of water, these can be used as the support in the present invention. Here, transparent means that light is transmitted, and does not mean colorless. Support 17 should not be optically opaque, but need not be colorless.
It may be colored as long as it can transmit light. For example, if a dispersion 20 in which particles 18 that absorb blue light are dispersed is held on a red support 17 and the electric field is turned on / off,
An optical element that changes color between purple and red can be obtained. Further, it is desirable that the support 17 is uniformly transparent, but it is not always necessary depending on the use of the optical element 10. The voids 16 in the support 17 should be larger than the particles 18, but should not be sized to facilitate migration of the dispersion 20. The desirable size of the void 16 depends on the viscosity of the dispersion medium 19, but generally, the average diameter is preferably 5 to 500 times that of the particles 18. Since both ends of the void 16 of the support 17 are open to the outside,
Several methods can be used to hold the dispersion 20 in the voids 16. For example, when the viscosity of the dispersion 20 is low, the support 17 can be impregnated.
When the dispersion 20 has a high viscosity, it can be impregnated under pressure or smeared. In that case, the support 17
If the dispersion and the dispersion 20 are unsuitable, the support 17 may be washed with an acid or an alkali to activate the surface,
A surfactant may be added to the dispersion 20. Also,
Support that has been previously treated to improve familiarity
17 may be used. The support 17 may be sandwiched between the electrodes 14, 14 after holding the dispersion 20 in advance, or the electrodes 14,
It is also possible to disperse the dispersion 20 in the support 17 after the disposition is made between the fourteen. Between the electrode 14 and the support 17 holding the dispersion 20,
As shown in FIG. 1, it is desirable to place an electrically insulating transparent material 21. It is preferable that the substance 21 has an insulating property and a large dielectric constant. Examples of such an insulating substance 21 include inorganic substances such as quartz, silicon nitride, and barium titanate, and polymer compounds such as polystyrene and ethylene tetrafluoride. The insulating substance 21 may be coated on the electrode 14, or a film made of the substance 21 may be simply sandwiched between the electrode 14 and the support 17. The coating method includes
In addition to vapor deposition, sputtering, etc., there are spray coating, brush coating, etc., and an appropriate method can be adopted depending on the type of the substance 21.

[Action]

With this structure, the dispersion 20 in which the particles 18 are dispersed is retained in the voids 16 of the support 17. And
Since the voids 16 are minute and have high flow resistance, the dispersion 20 is substantially enclosed in the voids 16. In particular, if the average diameter of the voids 16 is suppressed to 5 to 500 times that of the particles 18, the dispersion 2
0 hardly moves. Moreover, there is almost no pressure difference in the height direction due to the hydrostatic pressure. Therefore, the particles 18 are prevented from moving from their positions. Color unevenness and agglomeration of particles in conventional optical elements are caused by the particles moving over a long distance compared to their size. According to the present invention, since the movement of the particles 18 is prevented as described above, such a defect does not appear. On the other hand, since the voids 16 of the support 17 are larger than the particles 18,
The particles 18 are able to rotate within the void 16. Therefore, when an electric field of an alternating current or a pulse wave is applied through the electrodes 14, 14, a large number of particles 18, 18, ... Are all oriented in parallel to the electric field, that is, in the thickness direction of the cell 11. Since the support 17 holding the dispersion 20 is transparent,
Thereby, light is easily transmitted in the thickness direction, and the optical element 10 becomes transparent. Also, when the application of the electric field is stopped,
The particles 18, 18 ... Orient in random directions by Brownian motion, and the optical element 10 becomes opaque. As described above, the optical element 10 can be manufactured without the operation of injecting the dispersion 20 into the cell 11. Moreover, the shape of the cell 11 is maintained by the support 17 housed in the cell 11. In that case, the support 17 is the cell 11
Since it supports the entire surface, its shape retaining effect is great. Therefore, the cell 11 during manufacture or use
Deformation is reliably prevented. The aggregation of the particles 18 also occurs on the surface of the electrode 14. It is considered that the agglomeration is caused by the particles 18 near the electrode 14 contacting the electrode 14 when the electric field is applied and vibrating only slightly, resulting in the movement of charges. Therefore, the electrode
If the insulating substance 21 is arranged between the support 14 and the support 17,
Such aggregation on the electrode surface can be surely prevented. In that case, if the insulating material 21 has a large dielectric constant, the potential drop in the insulating material 21 can be suppressed to a small level.

【Example】

Hereinafter, examples in which the optical element according to the present invention was actually manufactured and tested will be described together with comparative examples. (Comparative Example 1) A transparent electrode film (ITO film) was formed on one surface of transparent glass with a thickness of 3 mm.
Was sputter-deposited to a thickness of 2000 angstrom. Prepare two pieces of the glass, face each other with the ITO film inside, and use a DuPont polymer resin mylar with a thickness of 0.1 mm as a spacer and use an epoxy adhesive to create a cell gap of 0.1 mm. A cell was prepared. The outer dimensions of the cell are 50 mm long x 50 mm wide, and the inner dimensions are 40 mm long x 40 mm wide. Join the lead wire to the edge of the ITO film with a conductive adhesive,
The lead wire was connected to a commercial power source of 100 V AC through a switch. On the other hand, 75 parts by weight of Halocarbon Oil # 0.8 / 100 manufactured by Halocarbon Products and 25 parts by weight of a copolymer of neopentyl acrylate and methylol acrylamide were mixed to obtain a mixed solution. Then, using the mixture as a dispersion medium, fine particles of cinchonidine bisulfate periodide as anisotropic particles were added so that the concentration by weight was 0.3%, and the mixture was dispersed for 24 hours with a shaker to obtain a uniform dispersion. A dispersion was obtained. This dispersion was injected into the above cell, and an AC voltage was applied from a commercial power source. The cell was blue, but turned transparent when a voltage was applied. When this state was continued, streaky color unevenness occurred after 50 minutes, and aggregation occurred after 1 hour and 20 minutes, and spots appeared. The size and number of the spots increased with time, and after 3 hours, aggregation occurred on the entire surface of the cell. (Comparative Example 2) Halocarbon manufactured by Halocarbon Products (0.8)
Was mixed with 75 parts by weight of a copolymer of neopentyl acrylate and methylol acrylamide to obtain a mixed solution. The obtained mixed liquid was used as a dispersion medium, and fine particles of anhydrous glycine periodide as anisotropic particles were added to the medium.
3% by weight was added and dispersed. Then, the dispersion liquid was injected into the same cell as in Comparative Example 1. When an AC voltage was applied in the same manner as in Comparative Example 1, color unevenness occurred 2 hours and 5 minutes after the voltage was applied, and the voltage was 2 hours and 50 minutes.
After a minute, spots began to appear. Then, after 4 hours and 40 minutes, aggregation occurred on the entire surface of the cell. (Example 1) Thickness of 0.15 made of long fiber glass having a diameter of 5 to 24 microns
mm glass paper in a vacuum furnace at a pressure of 10 Torr,
After heating at a temperature of 500 ° C for 1 hour to remove the binder,
It was immersed in a dilute hydrochloric acid solution for 1 hour, then washed with water and dried.
Then, the glass paper was cut into a length of 40 mm and a width of 40 mm and impregnated with the dispersion liquid of Comparative Example 1. This glass paper was placed horizontally between two transparent glass plates of 50 mm in length and 50 mm in width which were sputtered with the same ITO film as in Comparative Example 1. At this time, since the dispersion liquid impregnated in the glass paper did not leak, sealing was not performed, and the glass paper was placed on the flat glass plate and then another glass plate was placed on top of it. I put it down. In this state, an alternating voltage of 150 V was applied to keep the electric field strength constant. In this case, color unevenness and aggregation did not occur even after 50 hours had passed since the voltage was applied. (Example 2) The same method and conditions as in Example 1 were used except that the dispersion liquid of Comparative Example 2 was used. Also in this case, color unevenness and agglomeration did not occur even after 50 hours had passed since the voltage was applied. (Example 3) A nonwoven fabric made of long-fiber polyester and having a thickness of 0.15 mm was impregnated with the dispersion liquid of Comparative Example 1 and tested in the same manner and under the same conditions as in Example 1. Even after 50 hours had passed after the voltage of 150 V was applied, color unevenness and aggregation did not occur. Example 4 Quartz was sputter coated on the ITO film of Example 1 to a thickness of 2000 angstroms. Then, other than that, the test was performed under the same method and conditions as in Example 1. In this case, the voltage application was continued for a longer time, but color unevenness and aggregation did not occur even after 100 hours had elapsed after the voltage was applied. In the above description, only a transmissive optical element has been described, but the present invention is not limited to this, and can be used for a reflective optical element.

【The invention's effect】

As is clear from the above description, according to the present invention, the support having continuous fine voids is made to hold the dispersion in which the particles are dispersed, so that the movement of the particles over a long distance is restricted. As a result, it is possible to prevent color unevenness and aggregation due to local changes in particle density. Further, at the time of manufacture, it is only necessary to sandwich the support between the electrodes and it is not necessary to inject the dispersion into the cell, so that the cell can be prevented from being deformed due to the difference in internal and external pressures. Moreover, since the cells are supported from the inner surface by the support, it is possible to prevent the cells from being deformed by an external force or the like. Further, since there is almost no pressure difference in the height direction due to the hydrostatic pressure, it is possible to make the size large. In this way, it is possible to obtain an optical element that can be used for a long time, is easy to manufacture, and is inexpensive.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an optical element according to the present invention, and FIG. 2 is a vertical sectional view showing a conventional optical element. 10 ... Optical element, 11 ... Cell, 14 ... Electrode, 16 ... Void, 17 ... Support, 18 ... Particle, 19 ... Medium, 20 ... Dispersion, 21 ... Insulating material

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-63-303325 (JP, A) JP-A-54-56396 (JP, A) JP-A-56-91223 (JP, A)

Claims (3)

(57) [Claims] 1. A dispersion in which anisotropic particles are dispersed in an electrically insulating medium is enclosed in a thin cell having electrodes arranged on two opposing surfaces, and an electric field is applied through the electrodes. An optical element in which the transmittance or reflectance of light is controlled by changing the orientation of the particles; and the dispersion is an electrically insulating transparent material having continuous voids open at both ends. An optical element, characterized in that the support is held in the voids and the support is placed between the electrodes. 2. The support has an average diameter of 5 to 5 of the particles.
The optical element according to claim 1, which is a porous material or a fibrous material having 500 times as many voids. 3. The optical element according to claim 1, wherein an electrically insulating transparent substance is arranged between the electrode and the support.