Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-04-07
2001-09-11
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S213000, C428S214000, C428S216000, C428S312200, C428S312600, C428S316600, C428S318400, C428S319100, C428S412000, C428S428000, C428S448000, C428S451000
Reexamination Certificate
active
06287683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anti-fogging coating which can prevent fogging of an optical substrate caused by moisture, and optical parts obtained by applying the anti-fogging coating to optical substrates such as lenses, prisms and mirrors.
2. Related Background Art
The reason why various kinds of optical substrates typified by lenses and mirrors in optical instruments fog up is that moisture in the air adheres thereto in the form of fine waterdrops because their surface humidity is lowered to a dew point or lower, and so light is diffusely reflected. Accordingly, it is considered that the fogging can be prevented by preventing the formation of waterdrops on the surface of the substrate. As such anti-fogging methods, for example, the following four factors have come to be considered. (A) Adjustment of wetting; (B) impartment of water-absorbing property; (C) impartment of water repellency; and (D) adjustment of humidity by heating.
Although various methods have been attempted as yet, all the attempts are insufficient. It is now practiced to adjust humidity of the surface of an optical substrate by heating, thereby producing an anti-fogging effect on lenses of copying machines, rear windshields for automobiles and high-grade dressing tables. However, such a method involves many problems. For example, since a power source is required, its application fields are limited, and accidents such as fires may happen.
In order to offset the above demerits, there have been developed films formed of an anti-fogging coating composition comprising a high water-resistant organic polymer containing a surfactant. This anti-fogging coating composition is so designed that a film made hydrophilic by the surfactant and polyether polyol absorbs moisture to exhibit anti-fogging property, and in the case where the moisture exceeds the critical point of water absorption of this film, wetting is adjusted by the surfactant contained to maintain good transparency. However, since the surfactant easily dissolves in water to run out, the anti-fogging properties and strength of the film are markedly lowered.
There have been further proposed anti-fogging coating films formed mainly of an organic substance having polyvinyl alcohol or a polymer of hydroxyethyl methacrylate as a main component (for example, Japanese Patent Application Laid-Open No. 55-110201). However, such a film has low hardness and abrasion resistance, and poor weathering resistance.
As known water-absorbing substances, there are natural polymers including starch type polymers such as hydrolyzates of starch-acrylonitrile graft polymers, and cellulosic polymers such as cellulose-acrylonitrile graft polymers; and synthetic polymers including polyvinyl alcohol type polymers such as crosslinked polyvinyl alcohol, acrylic polymers such as crosslinked sodium polyacrylate, and polyether type polymers such as crosslinked polyethylene glycol diacrylate.
When one of these substances is coated and formed into a film for use as an anti-fogging film for the purpose of preventing fogging, the lastingness of its effect is markedly improved compared with the case of the surfactant. When the water-absorbing substance is used for the anti-fogging film, however, the anti-fogging properties thereof tends to be impaired when an anti-reflection layer formed of a substance having a low refractive index or a protective layer is coated thereon.
When the water-absorbing substance is made into a thin film and its optical thickness [(geometrical thickness, d)×(refractive index, n)] is adjusted to an odd number times a quarter of the target wavelength whose reflection is to be prevented, thus using it as an anti-reflection film, the film tends not to attain sufficient anti-fogging properties because the thickness of the water-absorbing film is too thin.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an anti-fogging coating having an excellent anti-fogging effect.
Another object of the present invention is to provide an anti-fogging coating having excellent film strength and abrasion resistance.
A further object of the present invention is to provide an anti-fogging coating having an anti-reflection effect.
A still further object of the present invention is to provide an optical part provided with any of the above-described anti-fogging coatings.
The above objects can be achieved by the present invention described below.
According to the present invention, an anti-fogging coating formed on the surface of an optical substrate is provided, wherein the anti-fogging coating comprises a water-absorbing film and a porous film in the order near to the surface of the substrate.
According to the present invention, an optical part having an anti-fogging coating on the surface of an optical substrate is also provided, wherein the anti-fogging coating comprises a water-absorbing film and a porous film in the order near to the surface of the substrate.
In short, the anti-fogging effect of the anti-fogging coating according to the present invention is as follows. When water vapor near the surface of the anti-fogging coating is in a supersaturated state due to environmental conditions, water vapor adsorbed on the surface of the anti-fogging coating forms nuclei of droplets without undergoing reevaporation. Molecules of water in the atmosphere collide with the nuclei, and the nuclei grow. When droplets grow to a certain extent, they are absorbed in the interior of the porous film through fine pores (ducts). The water absorbed by the porous film reaches the water-absorbing film situated further inside and is fixed thereto. The anti-fogging effect of this coating lasts to the limit of water absorption power of the water-absorbing film. The limit of water absorption power means a state that the water absorption of the water-absorbing film reaches saturation. The water absorption power of the water-absorbing film is in proportion to the density of hydrophilic groups in the film and the thickness of the film.
The water absorption properties required of the porous film is reduced by the absorbing capacity of the water-absorbing film. As a result, latitude in selection of a material usable in the formation of the porous film is widened, so that a porous film having excellent strength and abrasion resistance can be formed with ease.
Further, even when the reflectance of an optical substrate, for example, a glass lens becomes higher in the case where the water-absorbing film is formed on the substrate and flare and ghost are caused in an optical instrument, the reflectance of the substrate can be lowered by presetting the optical thickness of the porous film so as to have an anti-reflection effect.
REFERENCES:
patent: 3895155 (1975-07-01), Shukuri et al.
patent: 5404073 (1995-04-01), Tong et al.
patent: 5976680 (1999-11-01), Ikemori et al.
patent: 0716051 (1996-06-01), None
patent: 0782015 (1997-07-01), None
patent: 0798272 (1997-10-01), None
patent: 55-110201 (1980-08-01), None
patent: 96-18918 (1996-06-01), None
Patent Abstracts of Japan, vol. 11, No. 335 (P-632) 05/87 for JP 62-118301.
Patent Abstracts of Japan, vol. 15, No. 184 (P-1200) 02/91 for JP 03-41402.
Hatakeyama Hideyuki
Itoh Susumu
Shimura Shoichi
Ukuda Hideo
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nakarani D. S.
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