Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating
Reexamination Certificate
2001-05-16
2004-10-05
Wong, Edna (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating
Reexamination Certificate
active
06800190
ABSTRACT:
FIELD OF THE INVENTION
The field of invention pertains to coating electroconductive articles to produce colors thereon with a sense of depth and beauty for decorative purposes. In particular, the invention relates to electroplating of such coatings having decorative and functional utility for deposition on numerous electroconductive substrates.
There exists a need for a relatively inexpensive means of plating articles to provide vivid spectral interference thicknesses with greater coverage consistency and reproducibility than exist in the prior art.
BACKGROUND OF THE INVENTION
It is a strong argument that the superior visual appearance of one commodity given the choice between competing brands—is the main factor influencing a consumer's final purchasing decision. Metallic coatings have historically been primarily paint based. Although, with chemical vapor deposition and similar technologies, metallic oxide coatings are finding several new functional and decorative applications. Such coatings can span a vast range of optical phenomenon: Metallic coatings exhibit luster. The coatings exhibit diaphaneity (i.e., they can be opaque or semi-transparent, or transparent). As such, the luster of the metallic coatings can be richly specular or present diffuse illumination from their reflective surfaces. They can display all manner of iridescence, including pearlescence and a more colorful nacreous look. Some metallic coatings exhibit goniochromism (dichromatic reflection) whereby a surface can display distinct color change depending on the angle of the viewer. Metallic coatings may also show temporal properties, such as glitter, glint, and aventurine brilliants. Such phenomena are related to the concept of binocular depth. Human visual perception can sense clarity in these films, as well as “binocular mottle.” This term was coined by Calvin S. McCarny—it is the sense of texture resulting from the reflection of a subsurface through a translucent metallic surface-film.
Prior Art.
Metallic paints suffer from the drawback that they are not as specular as brightly polished or bright electroplated metals. Furthermore, there are inherent difficulties in obtaining paint uniformity over large surface areas in terms of color, thickness and luster. For multiple color applications, there is a need to purchase several different paints, or, if possible, mix new colorant pigments. Many consumer items which are fashioned from metal are painted because of the cost associated with electroplating and the desire to have colorful objects.
The marriage of clear lacquers with electroplated work-pieces is used industrially to cover dissimilar metals, such as zinc die-castings and steel, in order to give the articles the same color tone and luster. In the prior art, it is known to take such work-pieces and apply finely divided bronze and copper metal powders, usually by spraying them on through a pneumatic spray jet in an admixture of lacquer. The painter then applies additional lacquer layers and polychrome dyes (known as polychroming) in order to achieve artistic results, such as an antique bronze finish. Once the article is painted, the underlying electroplated coating is partially visible, giving the article an increased specular metallic reflection. However, such work is tedious, labor intensive and involves both an artistic temperament and a technical understanding of the compatibilities of lacquer types and solvents, and there is the problem of color matching with the dyes.
The coloring of metals dates to ancient times. The discovery of Greek papyri manuscripts at Thebes in the early nineteenth century, believed to be from the sarcophagus of an ancient Egyptian alchemist, discusses, among other topics, the surface coloring of metals. [Lagercrantz, Otto.
Papyrus Graecus Holmiensis
, Upsula, Sweden: Akademiska, Bokhandeln, 1913]. There are a number of methods for depositing oxides on metal surfaces which imbue the metal substrate with light polarized interference colors. The discovery of this phenomenon is often attributed to the physicist Leopoldo Nobili (1784-1835), who conducted his experiments in 1826. He is credited with founding the art of metallochromy. However, the
Edinburgh Philosophical Journal
of 1823 discloses the inventions of Sir John Barton (1771-1834) on the production of “iris metal.”
A metallochrome is defined as a coloring produced by light polarization of a deposited metallic compound. The authors do not wish to be bound by theory. It is believed, however, that the metallic film is to some degree translucent, allowing the transmittance of visible light through the film whereby some of the light is reflected at the film's exterior surface and whereby the remaining light is both partially adsorbed by opaque constituents within the semi-transparent film and reflected at the subsurface [substrate] layer causing the display of spectral colors by the optical interference of both surface and substrate reflections whose wavelengths correspond in hue to the thickness of the film. “Nobili's rings” are a rainbowy formation created by the irregular deposition of peroxide of lead from a bath of lead acetate. [David Fishlock.
Metal Colouring
, Teddington, England: R. Draper, 1962]. Nobili also succeeded in the deposition of cuprous oxide from a bath of copper acetate.
Other pioneers in the art of metallochromy were Fechner and later Elsner, who used zinc compositions. Boettger used a bath of copper and ammonium chloride. M. Puscher used lead acetate and sodium hyposulphite (c. 1869).
The noted physicist Antoine César Becquerel (1798-1878) also experimented with several elements and bath compositions. He is known as one of the founding fathers of the science of electrochemistry. He was the first to make the voltaic pile with constant current, thus ushering in the age of electrodeposition. His research included electroplating and electro-metallochromy.
After its introduction in 1845 at the German Industrial Exposition [Berlin], metallochromy found commercial application for use on toys and watch dials in factories in Nuremberg and Feurth, Bavaria. [“Metallochromy,”
Manufacturer and Builder
, Volume 1, (7), July, 1969, p. 210].
There is little evidence that aqueous bath electroplated and immersion metallochrome coatings have been used in industry after that time. This may be due to the craft tradition of trade secrets. It is believed that the commercialization of metallochrome finishes fail due to the difficult nature of achieving consistent results. The principal drawback of metallochrome coatings is that they were not very durable for most applications. An article of metallochrome jewelry, for example, would wear within a short time period and lose its beauty. Certain metallochromes are subject to galvanic reduction by metals. The coatings are also subject to chemical reduction by acids and lacquer coatings with acidic pH levels and to thermal reduction. Applications for the coloring of more exotic metals by means of light interference will be briefly reviewed:
Certain valve metals may be anodized to produce a dialectric coating exhibiting interference colors, see A. F. Torrisi, “Relation of Color to Certain Characteristics of Anodic Tantalum Films, “
Journal of the Electrochemical Society
, April 1955, 102, (4), pp. 176-180. The reactive metals titanium and niobium may be anodized to produce polychromic effects and is largely used for jewelry applications. Also, anodizing techniques for coloring aluminum by means of light interference are known to the art.
The coloring of zinc is largely accomplished by chemical conversion coatings. In industry, steel is electroplated or hot dip galvanized with zinc, and in order to improve its corrosion resistance, a conversion coating with a chromate containing trivalent or hexavalent chromium, and often silver, is used. The photo-active silver in such conversion coatings has the disadvantage that exposure to ultraviolet light will discolor and diminish the luster. It is costly, in terms of wast
Wilcox Fred T.
Wilcox Steven F.
Deimen James M.
Wong Edna
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