US 4,517,217 A · Protective coating means for articles such as gold-plated jewelry and wristwatch components

Abstract

The surface of a metal article which is exposed to the atmosphere and abrasion during normal use of the article is protected from scratches and/or corrosion during such use by a thin transparent abrasion-resistant film of an inert non-metallic material such as SiO.sub.2, SiC, Si.sub.3 N.sub.4, TiO.sub.2, MgO, Al.sub.2 O.sub.3, Ta.sub.2 O.sub.5, Nb.sub.2 O.sub.5, GeO.sub.2, spinel and selected colorless glass compositions. The protective film is preferably deposited by RF-sputtering techniques and undesirable coloration of the article by optical interference effects from incident light rays is avoided by properly correlating the film thickness with the refractive index of the particular material used to form the film. The invention permits the use of thinner gold plating on such items as articles of expensive jewelry and bracelets and cases for fine wristwatches without detracting from the quality, durability or appearance of the merchandise. Alternative embodiments in which several films of various selected non-metallic inert materials are combined to form composite protective coatings that provide additional cost and manufacturing advantages are also disclosed along with methods for sputter-depositing the protective films in the proper thicknesses to avoid optical discoloration effects, either on articles that have been previously plated with gold or which have been provided with a sputter-deposited layer of gold by sequentially operating the sputtering apparatus.

Claims19

Dependent claims

In combination with an article of manufacture that is composed of metal and has a metallic surface which enhances the aesthetic appeal of the article but is susceptible to abrasion damage and/or environmental degradation such as corrosion and tarnishing, said article being of a type that is subjected to frequent human contact during normal usage of the article and is thus exposed to additional surface damage by such contact and usage,

an adherent coating that protects said article from such abrasion damage and degradation without materially altering the natural pleasing appearance of the metallic surface, said coating consisting essentially of a thin substantially transparent film of a sputter-deposited non-metallic inert material that has;
a Knoop hardness in the range of from about 400 to about 2500 and is thus of sufficient hardness to be abrasion-resistant, and
a refractive index in the range of from about 1.4 to about 2.8,
said protective film having a thickness that is in the range of from about 14,000 to about 40,000 Angstroms and is also so correlated relative to the refractive index of the non-metallic inert material comprising said film that the film, in addition to being substantially transparent, is (a) substantially devoid of discoloration due to interference effects that otherwise would be produced by incident light rays and thus alter the natural aesthetic appearance of the underlying metallic surface of the article, and (b) is of sufficient thickness to protect the metallic surface of the article from abrasion damage and degradation when in use and subjected to frequent human contact.

1 more element

Dependencies are inferred from the claim text.

Protective coating means for articles such as gold-plated jewelry and wristwatch components

Life of this patent

Protective coating means for articles such as gold-plated jewelry and wristwatch components

Life of this patent

Abstract

Claims19