Coating processes – With pretreatment of the base
Reexamination Certificate
1997-12-01
2001-05-15
Pianalto, Bernard (Department: 1762)
Coating processes
With pretreatment of the base
C427S314000, C427S374200, C427S376100, C427S383500, C427S398100, C427S399000
Reexamination Certificate
active
06231925
ABSTRACT:
This invention relates in general to a process for adhering precious metal to vitreous objects, and in particular to a process in which the outer skin of the vitreous object is made plastic and caused to bond to applied precious metal.
BACKGROUND OF THE INVENTION
Precious metal adhesion to glass is involved in a number of industrial and aesthetic applications. Optical and infrared reflectors and lenses can be made to reflect and/or transmit different wavelengths depending upon the particular precious metal film applied. Often such films are also applied in patterns utilizing their ability to conduct electricity. Finally, precious metals, especially gold, have many decorative uses in glass and crystal objects.
U.S. Pat. No. 3,266,912, assigned to Engelhard Corporation, describes a family of products known as “liquid bright golds”. These are varnish-like precious metal preparations containing organic compounds combined with flux components which are based on organic metal compounds. The flux components act as an adhesion promoter. On a smooth glass ceramic surface, a high gloss metal film forms after firing in a high temperature oven or annealer. This film has a gold or other precious metal content of 6 to 15%. Such compounds are used in a number of aesthetic and industrial applications in a relatively straightforward application of precious metal to glass. However, the products have some disadvantages. The organic compounds and flux agents essential to such solutions are environmentally toxic. Moreover, the presence of such agents in the fired film or coating compromise the aesthetic and physical properties of such films. The fluxes discolor when applied to certain types of glasses. This causes the color of the precious metal coating to have two tones; depending upon whether one is viewing the film from the surface of the vitreous substrate or through the actual substance the film is applied to. Furthermore, the liquid bright films have a distinct plated look as the gold is formed on the top and not absorbed or melted into the surface of the vitreous substances. From a material efficiency viewpoint, the relatively low precious metal content of such films degrades the electrical, thermal, and optical properties of the films.
U.S. Pat. No. 4,837,052 describes a technology which involves sandwiching a layer of deposited gold between an inner coating of gold-chromium and an outer protective polymer overcoat. In this process, adhesion to the vitreous substrate is achieved through the application first of gold-chromium. Pure gold is then applied to the layer of gold coating but is very complex, requiring three applications. Moreover, successful adhesion is only achieved through the application of a polymer foreign substance.
A third approach to achieving precious metal adhesion is; described in U.S. Pat. No. 2,950,996. This technology involves; combining gold resinates and vitreous substances together in one compound. This mixture is applied to the vitreous surface. Upon firing, the mixture forms a combination gold/vitreous compound which adheres to the vitreous surface as well as to the gold particles suspended in the composition. This technique is effective for many technical applications but also has shortcomings. Particularly, the film is never 100% gold. Moreover, only gold resinates may be used, these compounds limiting the appearance and physical characteristics of the adhered precious metal. Finally, the vitreous substances must have low melting points relative to the glasses they are coated upon, in order that the contour of the coated glass does not distort. Currently, such low melting glasses contain lead. This prevents the use of such coatings in functional glassware.
SUMMARY OF THE INVENTION
The present invention involves the adhesion of precious metal to glass without the use of any foreign material or substances. After the substrate is coated or otherwise contacted with precious metal, the substrate itself is utilized as the means of permanently adhering the precious metal. In particular, the outer or peripheral skin of the coated glass substrate in contact with the metal is superheated to a temperature at which the skin is in a plastic state. A change in viscosity then takes place, allowing a molecular bond to form between the precious metal and the substrate. The superheating phase is accomplished by rapidly applying high-intensity heat to the surface of the precious metal. By conduction through the metal, heat is transmitted to the peripheral surface or skin of the substrate, until lowering of the viscosity of the skin effects adhesion between the metal and the substrate. This superheating process is completed relatively quickly in order to prevent overeating of the entire cross-section of the substrate and resultant change in shape and contour as well as to avoid negatively affecting the state of the precious metal through melting or vaporization.
This process allows precious metal to glass adhesion without additional fluxes or other chemical agents, allowing the formation of a 100% pure coating of precious metal. Gold in any mesh size or composition may be adhered to glass including gold powder, chips, and/or sheets. Moreover, the molecular bond created is quite strong and wear-resistant.
The vitreous substrate may be any one of a variety of substances, including ceramic, quartz, soda-lime qlasses, lead glasses, and boro-silicate and potasium-based glasses. The metal may be any one of several such as gold, silver, platinum, palladium or alloys containing gold, silver, platinum or palladium.
REFERENCES:
patent: 2880552 (1959-04-01), Whitehurst
patent: 2950996 (1960-08-01), Place, Sr. et al.
patent: 3266912 (1966-08-01), Murphy
patent: 3904782 (1975-09-01), Pomerantz
patent: 4401726 (1983-08-01), Gnanamuthu
patent: 4684446 (1987-08-01), Charles et al.
patent: 4837052 (1989-06-01), Lorimer
patent: 5677014 (1997-10-01), Ohnishi et al.
Fish & Richardson P.C.
Pianalto Bernard
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