Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-09-24
2001-02-06
Mai, Huy (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S267000, C359S274000
Reexamination Certificate
active
06185034
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an electrochromic device utilizing an electrochromism and, more particularly, to an electrochromic device capable of preventing occurrence of a photochromism without adding (or with addition of only a small amount of) an ultraviolet radiation stabilizing agent.
An electrochromic device utilizing an electrochromism is used, for example, for a dimming mirror including a dimming rearview mirror, and also for a dimmer. Electrochromism is a general term for denoting phenomenon in which color of a material is changed upon application of voltage to the material. A substance which exhibits such phenomenon is called an electrochromic material. Representative electrochromic materials include, e.g., tungsten oxide (WO
3
) as an inorganic material and viologen as an organic material. In all of the electrochromic materials, moving of electrons upon application of voltage causes coloring and bleaching reactions.
Most of electrochromic materials present a photochromism. The photochromism is a phenomenon according to which a certain material in a state of solid or solution changes its color by irradiation of light (ultraviolet radiation or a short wavelength visible radiation) thereon and returns to an original color in a dark place. As the photochromism progresses, an electrochromic material is deteriorated and decomposed and, as a result, remains in a color-changed state and fails to return to the original state. As to the mechanism of the photochromism, it is considered that, in the case of an inorganic compound such as WO
3
, irradiation of light exceeding its band gap (in WO
3
, the band gap is 3.2 eV, i.e., 388 nm or below) brings electrons in the material to an excited state and thereby starts the coloring reaction. In the case of an organic compound, this phenomenon is considered to take place due to photoisomerization caused by movement of hydrogen atoms upon irradiation of light, generation of free radicals by dissociation and cleavage of a ring etc.
FIG. 2
shows an infrared absorption spectrum of WO
3
before and after a weather resistance test (sunshine weather -o- meter) for 300 hours. It will be seen that, by irradiation of ultraviolet radiation, the W=O bond has disappeared and WO
3
thereby has been destroyed. The photochromism is a phenomenon which should be avoided for the electrochromic device in which coloring and bleaching are controlled by application of voltage.
As a prior art electrochromic device which prevents occurrence of the photochromism, there is an electrochromic device disclosed in U.S. Pat. No. 5,140,455. In this electrochromic device, the photochromism can be prevented by dispersing an ultraviolet radiation stabilizing agent in an electrochromic solution and thereby absorbing ultraviolet radiation irradiated from outside.
The ultraviolet radiation stabilizing agents includes, for example, salicylic acid type ultraviolet radiation stabilizing agents such as phenyl salicylate, p-tert-butyle phenyl salicylate and p-octylphenyl salicylate; benzophenone type ultraviolet radiation stabilizing agents such as 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone; benzotriazole type ultraviolet radiation stabilizing agents such as 2-(2′-hydroxy-5′-methylphenyl) benzotriazole and 2-(2′-hydroxy-5′-tert-butylpheny) benzotriazole; and cyanoacrylate type ultraviolet radiation stabilizing agents such as 2-ethylhexyl-2-cyano-3,3′-diphenylacrylate and ethyl2-cyano-3,3′diphenylacrylte.
For effectively preventing the photochromism by adding the ultraviolet radiation stabilizing agent in an electrolyte or electrochromic solution, it is necessary to add a large amount of the ultraviolet radiation stabilizing agent. Since, however, the ultraviolet radiation stabilizing agent is colored per se, this method has the disadvantage that addition of a large amount of the ultraviolet radiation stabilizing agent impairs the tone of color of the electrochromic device.
FIG. 3
shows reflectance spectra of a sample A in which 1 weight % of ultraviolet radiation stabilizing agent was added to the structure of
FIG. 10
to be described later (without the provision of the photocatalytic layer and hydrophilic layer) and a sample B in which the ultraviolet radiation stabilizing agent was not added to the same structure. In the sample A, the reflectance below 490 nm is significantly reduced by the addition of the ultraviolet radiation stabilizing agent and the tone of color of the sample A thereby is impaired. For securing a sufficient effect of the ultraviolet radiation stabilizing agent, about 5 weight % of the ultraviolet radiation stabilizing agent is required.
It is, therefore, an object of the invention to provide an electrochromic device which has solved the above described problem of the prior art and is capable of preventing occurrence of the photochromism without adding (or with addition of only a small amount of) an ultraviolet radiation stabilizing agent.
SUMMARY OF THE INVENTION
For achieving the above described object of the invention, there is provided an electrochromic device comprising: transparent substrates, an electrochromic layer provided between said transparent substrates, said electrochromic layer containing no ultraviolet radiation stabilizing agent or containing less than 1 weight % of ultraviolet radiation stabilizing agent, and a transparent photocatalytic layer performing a photocatalytic reaction formed on the front surface of a front side substrate of said transparent substrates. In this specification, the term “electrochromic layer” designates an entire layer provided between opposite electrodes of two transparent substrates and includes, for example, a laminate of a film of an electrochromic material and an electrolyte, and an electrochromic solution in which an electrochromic material is dissolved or dispersed.
According to the invention, the photocatalytic layer formed on the front surface side of the device (the frontmost layer or a layer near to the frontmost layer) absorbs ultraviolet radiations and, therefore, the photochromism of the electrochromic material is inhibited. Accordingly, the necessity for adding an ultraviolet radiation stabilizing agent can be obviated (or if added, only a small amount will suffice) and impairing of the tone of color of the electrochromic device can thereby be prevented. Further, the photocatalytic layer decomposes and removes dirt deposited on the surface of the electrochromic device and, therefore, the surface of the device can be kept clean. The photocatalytic layer may be made of a photocatalytic substance only or may be made as a layer in which a photocatalytic substance and other material are mixed together.
In one aspect of the invention, there is provided an electrochromic device comprising transparent substrates, an electrochromic layer provided between said transparent substrates, said electrochromic layer containing no ultraviolet radiation stabilizing agent or containing less than 1 weight % of ultraviolet radiation stabilizing agent, a transparent photocatalytic layer performing a photocatalytic reaction formed on the front surface of a front side substrate of said transparent substrates, and a transparent porous inorganic hydrophilic layer formed on the front surface side of said transparent photocatalytic layer.
According to the invention, occurrence of the photochromism is prevented by the provision of the photocatalytic layer and, in addition, the surface of the device becomes hydrophilic by the provision of the porous inorganic hydrophilic layer and deposition of a waterdrop can thereby be prevented. Further, since dirt which is deposited inside of pores of the porous inorganic hydrophilic layer and blocks the pores is decomposed and removed by the photocatalytic layer, the hydrophilic property of the device can be maintained. The photocatalytic layer may be made of a film comprising, for example, TiO
2
and the porous inorganic hydrophilic layer may be made of, for example, a porous SiO
2
film.
A refle
Kikuchi Hideyuki
Nakamura Masatoshi
Mai Huy
Murakami Corporation
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