A light control glass containing a light control suspension was first invented by Edwin Land, and the light control glass is in the form of a structure in which a liquid-state light control suspension is inserted between two of transparent conductive substrates having a narrow gap therebetween (see, for example, Patent Documents 1 and 2). According to the invention by Edwin land, the liquid-state light control suspension inserted between the two transparent conductive substrates is such that when an electric field is not applied, as a result of the Brownian motion of light control particles that are dispersed in the suspension, most of the incident light rays are reflected, scattered or absorbed by the light control particles, and only a very small portion is transmitted.
That is, the extent of transmission, reflection, scattering or absorption can be determined on the basis of the shape, nature and concentration of the light control particles dispersed in the light control suspension, and the amount of light energy irradiated. When an electric field is applied to a light control window which uses a light control glass having the above-described structure, an electric field is formed in the light control suspension through the transparent conductive substrates, and the light control particles that exhibit a light control function cause polarization and are arranged in parallel to the electric field. Then, light is transmitted between light control particles, and eventually, the light control glass becomes transparent. However, such an initial light control apparatus had problems in practical use, such as the aggregation of the light control particles inside the light control suspension, sedimentation due to their own weights, color phase change due to heat, changes in the optical density, deterioration caused by ultraviolet ray irradiation, difficulties in keeping up the gap between the substrates and in the injection of the light control suspension into the gap, and others. Accordingly, it was difficult to put the light control apparatus to practical use.
Robert L. Saxe, F. C. Lowell, and R. I. Thompson have respectively disclosed light control windows making use of light control glasses for which the initial problems of light control windows, namely, the aggregation and sedimentation of light control particles, changes in the optical density, and the like have been compensated (see, for example, Patent Documents 3 to 9). In these patented inventions, those initial problems are solved by using a liquid-state light control suspension, which includes needle-shaped light control crystal particles, a suspending agent for dispersing crystal particles, a dispersion control agent, a stabilizer and the like, and preventing the sedimentation of light control particles by matching the densities of the light control particles and the suspending agent to be almost equal, while preventing the aggregation of the light control particles by adding a dispersion control agent to increase the dispersibility of the light control particles.
However, since even these light control glasses also have a structure in which a liquid light control suspension is encapsulated in a gap between two transparent conductive substrates as in the case of conventional light control glasses, there is a problem that, in the case of the manufacture of large-sized products, uniform encapsulation of the suspension in the gap between the two transparent conductive substrates is difficult, and a swelling phenomenon in the lower part is likely to occur due to the difference in the hydraulic pressure between the upper part and the lower part of the product. Furthermore, when the gap between the substrates is changed due to the external environment, for example, the pressure of wind, the optical density is changed as a result, so that the color phase becomes inhomogeneous. Further, there is a problem that the sealing material in the peripheral area for holding a liquid between the transparent conductive substrates is destroyed, and the light control material leaks out. In addition, unevenness occurs in the response time as a result of deterioration by ultraviolet ray, and a decrease in the voltage between the peripheral areas and the center of the transparent conductive substrates.
As a method of improving this, there has been suggested a method of mixing a liquid light control suspension with a solution of a curable polymer resin, and producing a film by using a phase separation method based on polymerization, a phase separation method based on solvent volatilization, a phase separation method based on temperature, or the like (see, for example, Patent Document 10).
Furthermore, in a space surrounded by the light control glasses used heretofore, since the transparent conductive resin substrates used in the glasses have small surface resistivity and low radio wave transparency, there is a problem that television sets, mobile telephones, remote control devices utilizing radio waves, and the like may not function adequately.