Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1999-08-13
2004-12-14
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C134S001000
Reexamination Certificate
active
06830785
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates broadly to the art of rendering and maintaining a surface of a substrate highly hydrophilic. More particularly, the present invention relates to the antifogging art wherein the surface of a transparent substrate such as a mirror, lens and sheet glass is made highly hydrophilic to thereby prevent fogging of the substrate or formation of water droplets. This invention is also concerned with the art wherein the surface of a building, windowpane, machinery or article is rendered highly hydrophilic in order to prevent fouling of, to permit self-cleaning of or to facilitate cleaning of the surface. This invention also relates to a hydrophilifiable member having a surface layer which is capable of having an extremely small contact angle with water, a method for rendering the member hydrophilic, a method for forming a hydrophilifiable surface layer, and a coating composition for forming a hydrophilifiable surface layer.
2. Description of the Prior Art
It is often experienced that, in the cold seasons, windshields and window-glasses of automobiles and other vehicles, windowpanes of buildings, lenses of eyeglasses, and cover glasses of various instruments are fogged by moisture condensate. Similarly, in a bathroom or lavatory, it is often encountered that mirrors and eyeglass lenses are fogged by steam.
Fogging of the surface of an article results from the fact that, when the surface is held at a temperature lower than the dew point of the ambient atmosphere, condensation of moisture in the ambient air takes place to form moisture condensate at the surface.
If the condensate particles are sufficiently fine and small so that the diameter thereof is on the order of one half of the wavelength of the visible light, the particles cause scattering of light whereby window-glasses and mirrors become apparently opaque thereby giving rise to a loss of visibility.
When condensation of moisture further proceeds so that fine condensate particles are merged together to grow into discrete larger droplets, the refraction of light taking place at the interface between the droplets and the surface and between the droplets and the ambient air causes the surface to be blurred, dimmed, mottled, or clouded. As a result, an image viewed through a transparent article such as sheet glass may become distorted, or the reflected image in a mirror may be disturbed.
Similarly, when windshields and window-glasses of vehicles, windowpanes of buildings, rearview mirrors of vehicles, lenses of eyeglasses, or shields of masks or helmets are subjected to rain or water splash so that discrete water droplets are adhered to the surface, their surface is blurred, dimmed, mottled, or clouded, resulting in the loss of visibility.
The term “antifogging” as used herein and in the appended claims is intended to mean broadly the art of preventing or minimizing occurrence of optical trouble resulting from fogging, growth of condensate droplets or adherent water droplets mentioned above.
The antifogging art can significantly affect safety and efficiency in a variety of setting. For example, the safety of vehicles and traffic can be undermined if the windshields, window-glasses or rearview mirrors of vehicles are fogged or blurred. Fogging of endoscopic lenses and dental mouth mirrors may hinder proper and accurate diagnosis, operation and treatment. If cover glasses of measuring instruments are fogged, a reading of data will become difficult.
The windshields of automobiles and other vehicles are normally provided with windshield wipers, defrosting devices and heaters so as to avoid visibility problems, which arise particularly in the cold seasons and under rainy conditions. However, it is not commercially feasible to install this equipment on the side windows of a vehicle, or on the rearview mirrors arranged outside of the vehicle. similarly, it is difficult, if possible at all, to mount such antifogging equipment on windowpanes of buildings, lenses of eyeglasses and endoscopes, dental mouth mirrors, shields of masks and helmets, or cover glasses of measuring instruments.
As is well-known, a simple and convenient antifogging method conventionally used in the art is to apply onto a surface an antifogging composition containing either a hydrophilic compound such as polyethylene glycol or a hydrophobic or water-repellent compound such as silicone. However, the disadvantage of this method is that the antifogging coating thus formed is only temporary in nature and is readily removed when rubbed or washed with water so that its effectiveness is prematurely lost.
Japanese Utility Model Kokai Publication No. 3-129357 (Mitsubishi Rayon) discloses an antifogging method for a mirror wherein the surface of a substrate is provided with a polymer layer and the layer is subjected to irradiation by ultraviolet light, followed by treatment with an aqueous alkaline solution to thereby form acid radicals at a high density whereby the surface of the polymer layer is rendered hydrophilic. Again, however, it is believed that, according to this method, the hydrophilic property of the surface is degraded as time elapses because of adherent contaminants so that the antifogging function is lost over time.
Japanese Utility Model Kokai Publication No. 5-68006(Stanley Electric) discloses an antifogging film made of a graftcopolymer of an acrylic monomer having hydrophilic groups and a monomer having hydrophobic groups. The graftcopolymer is described as having a contact angle with water of about 50°. It is therefore believed that this antifogging film does not exhibit a sufficient antifogging capability.
Isao Kaetsu “Antifogging Coating Techniques for Glass”, Modern Coating Techniques, pages 237-249, published by Sogo Gijutsu Center (1986), describes various antifogging techniques used in the prior art. The author Mr. Kaetsu nevertheless reports that the prior art antifogging techniques, which consist of rendering a surface hydrophilic, suffer from significant problems which must be overcome in reducing them to practice, and, further reports that the conventional antifogging coating techniques seemingly come up against a barrier.
Accordingly, an object of the invention is to provide an antifogging method which is capable of realizing a high degree of visibility in a transparent substrate such as a mirror, lens or glass.
Another object of the invention is to provide an antifogging method wherein the surface of a transparent substrate such as a mirror, lens or glass is maintained highly hydrophilic for an extended period of time.
Still another object of the invention is to provide an antifogging method wherein the surface of a transparent substrate such as a mirror, lens and glass is almost permanently maintained highly hydrophilic.
A further object of the invention is to provide an antifogging coating which has an improved durability and abrasion resistance.
Another object of the invention is to provide an antifogging coating which can be readily applied onto a surface requiring antifogging treatment.
Yet another object of the invention is to provide an antifogging transparent substrate such as a mirror, lens or glass, as well as a method of making such an antifogging transparent substrate, wherein the substrate surface is maintained highly hydrophilic for an extended period of time to thereby provide a high degree of antifogging property for an extended period.
In the fields of architecture and painting, it has been pointed out that growing environmental pollution tends to inadvertently accelerate fouling, contamination or soiling of exterior building materials, including outdoor buildings themselves and the coatings thereon.
In this regard, air-borne grime and dust particles are allowed under fair weather conditions to fall and deposit on roofs and outer walls of buildings. When it rains, the deposits are washed away by rainwater and are caused to flow along the outer walls of the buildings. Furthermore, air-borne grime is captured by rain and is carried onto surfaces (such as
Chikuni Makoto
Fujishima Akira
Hashimoto Kazuhito
Hayakawa Makoto
Kitamura Atsushi
Jones Day
Padgett Marianne
Toto Ltd.
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