Method of coating a metallic article of merchandise with a protective transparent film of abrasion-resistance material

• US 4,737,252 A
• Filed: 05/21/1984
• Issued: 04/12/1988
• Est. Priority Date: 05/18/1981
• Status: Expired due to Fees

• Current Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Hoffman, Richard A.
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): Leader, William T.
• Application Number:
  US06/612,491
• Time in Patent Office: 1,422 Days
• Field of Search: 204/192 C, 204/192 SP, 204/192 D, 204/192.16, 204/192.26, 204/192.27, 204/192.28, 204/192.29
• US Class Current: 204/192.16
• CPC Class Codes: A44C 27/005 Coating layers for jewellery
• CPC Class Codes: A44C 27/006 Metallic coatings
• CPC Class Codes: C23C 14/025 Metallic sublayers
• CPC Class Codes: C23C 14/0605 Carbon
• CPC Class Codes: C23C 14/0635 Carbides
• CPC Class Codes: C23C 14/0652 Silicon nitride
• CPC Class Codes: C23C 14/081 of aluminium, magnesium or beryllium
• CPC Class Codes: C23C 14/083 of refractory metals or yttrium
• CPC Class Codes: C23C 14/086 of zinc, germanium, cadmium, indium, tin, thallium or bismuth
• CPC Class Codes: C23C 14/10 Glass or silica
• CPC Class Codes: C23C 28/322 only coatings of metal elements only
• CPC Class Codes: C23C 28/345 with at least one oxide layer
• CPC Class Codes: C23C 28/347 with layers adapted for cutting tools or wear applications
• CPC Class Codes: C23C 28/42 characterized by the composition of the alternating layers
• CPC Class Codes: C23C 30/00 Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process C23C26/00, C23C28/00 take precedence
• CPC Class Codes: G04B 37/223 metallic cases coated with a nonmetallic layer

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 SiO₂, SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO₂, 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.

Claims

1. In the manufacture of a metallic article of merchandise that is subjected to frequent human contact during normal usage of the article and is thus exposed to abrasion and/or corrosion damage by such contact and usage, the method of coating said metallic article with a different metal that enhances the aesthetic appeal of the article but is susceptible to such abrasion and/or corrosion damage and then providing the coated surface of the article with a substantially-transparent protective film of a selected non-metallic abrasion-resistant material which does not substantially alter the color or appearance of said coated surface, said selected abrasion-resistant material having a predetermined refractive index, which method comprises;

placing the metallic article in the coating chamber of a radio-frequency type sputtering apparatus along with a quantity of the metal to be deposited on the article and a quantity of an abrasion-resistant material selected from the group consisting of SiO₂, SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO, spinel, and glasses that have a Knoop hardness of over about 400 and consist essentially of mixed oxides,

evacuating said chamber and, after introducing a sputtering gas therein, operating the sputtering apparatus in a first mode such that a sputtered layer of the coating metal is deposited on said article, and

while the metal-coated article is still in the gas-filled coating chamber, operating the sputtering apparatus in a second mode such that a sputtered film of the abrasion-resistant material is deposited over the metal-coated surface of the article,

the duration of the second sputtering operation being so correlated with the refractive index of the abrasion-resistant material that the deposited protective film of abrasion-resistant material is substantially transparent and of a thickness between about 14,000 Angstroms and 40,000 Angstroms, to prevent undesirable discoloration of the coated article due to optical interference effects that would otherwise be produced by incident light rays and thus alter the natural aesthetic appearance of the underlying metallic coating, and to allow adhesion to the article.

2. The method of claim 1 wherein;

said metallic article comprises a piece of jewelry or a wristwatch component that is composed of a base metal and the metal with which it is coated comprises a precious metal, and where the glass that can be used as the protective film is a mixture of oxides selected from the group consisting of SiO₂, Na₂ O, CaO, MgO, Al₂ O₃, K₂ O, B₂ O₃, Li₂ O, and PbO, and has a refractive index in the range of from about 1.4 to about 2.8.

3. The method of claim 1 wherein said metallic article comprises a component for a wristwatch that is composed of stainless steel or brass and is coated with a layer of gold or gold alloy which is deposited by the first sputtering operation.

4. The method of claim 3 wherein the sputtered layer of gold or gold alloy has a thickness that does not exceed about 5,000 Angstroms, and the protective film of abrasion-resistant material comprises SiO₂ that has a thickness between about 14,000 Angstroms and 40,000 Angstroms.

5. In the manufacture of a metallic article of merchandise which has a surface that enhances the aesthetic appeal of the article but is exposed to the atmosphere and frequent human contact during normal use of the article and is susceptible to abrasion damage and/or tarnishing as a result of such exposure, the method of protecting the surface of said metallic article comprising;

placing the article in the deposition chamber of a sputtering apparatus along with a target composed of a selected non-metallic abrasion-resistant, chemically inert material selected from the group consisting of SiO₂, SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO, spinel, and glasses that have a Knoop hardness of over about 400 and consist essentially of mixed oxides that when sputter-deposited, forms a protective film that is substantially transparent,

orienting the article so that the surface thereof which is to be protected will be exposed to and be coated with sputtered material from said target when the apparatus is operated, and then

operating said apparatus and thereby sputter-depositing a substantially-transparent protective film of the said non-metallic abrasion-resistant material between about 14,000 Angstroms and 40,000 Angstroms thick on the surface of the article, the time period which said apparatus is operated and the thickness of the resulting sputter-deposited substantially-transparent protective film of abrasion-resistant material both being so correlated with the refractive index of said material so that the sputtered film is substantially devoid of undesirable discoloration effects that would otherwise be produced by optical interference of incident light rays which enter the transparent protective film, and so that the sputtered film adhers to the article.

6. The method of claim 5 wherein, the glass that can be used as the protective film is a mixture of oxides selected from the group consisting of SiO₂, Na₂ O, CaO, MgO, Al₂ O₃, K₂ O, B₂ O₃, Li₂ O, and PbO, and has a refractive index in the range of from about 1.4 to about 2.8.

7. The method of claim 5 wherein;

said article is composed of a base metal and the said surface of the article comprises a coating of precious metal which is also susceptible to scratching during normal use of the article, and

said protective film is formed sufficiently abrasion-resistant to permit the precious metal coating to be thinner than the coating which would otherwise have to be employed to avoid exposing the base metal after prolonged use of the article.

8. The method of claim 7 wherein said precious metal coating is composed of gold or a gold alloy and said protective coating is SiO₂.

9. The method of claim 8 wherein said article comprises a piece of jewelry.

10. The method of claim 8 wherein said article comprises a case or bracelet component for a wristwatch.

11. In the manufacture of a metallic article of merchandise that is subjected to frequent human contact during normal usage of the article and is thus exposed to abrasion, corrosion and/or tarnishing by such usage and contact, the method of coating said metallic article with a different metal that enhances the aesthetic appeal of the article but is susceptible to such abrasion damage and degradation and then providing the coated surface of the article with a substantially-transparent protective film of a selected non-metallic abrasion-resistant material which does not substantially alter the color or appearance of said coated surface, said selected abrasion-resistant material having a predetermined refractive index, which method comprises;

placing the metallic article in the coating chamber of a radio-frequency type sputtering apparatus along with (a) a quantity of the different metal to be deposited on the article, (b) a quantity of an abrasion-resistant material selected from the group consisting of SiO₂, SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO, spinel, and glasses that have a Knoop hardness of over about 400 and consist essentially of mixed oxides, from which the protective film is to be formed, and (c) a quantity of a selected metallic primer material which is adapted to enhance the adhesion of the coating metal,

evacuating said chamber and, after introducing a sputtering gas therein, operating the sputtering apparatus in a first mode for a predetermined time such that a coating of sputtered metallic primer material is deposited on said article, and

while the primer-coated article is still in the gas-filled coating chamber, sequentially operating the sputtering apparatus in second and third modes such that a layer of sputtered coating metal and a protective film of sputtered abrasion-resistant material are sequentially deposited over the primer-coated surface of the article,

the duration of the third sputtering operation being so correlated with the refractive index of the abrasion-resistant material that the protective film of sputtered abrasion-resistant material is substantially transparent and of a thickness between about 14,000 Angstroms and 40,000 Angstroms, to prevent undesirable discoloration of the metal-coated surface of the article due to optical interference effects that would otherwise be produced by incident light rays, and to allow adhesion to the article.

12. The method of claim 11 wherein said metallic primer material is a material selected from the group consisting of titanium, chromium, nickel and a Nichrome alloy.

13. The method of claim 11 wherein;

said metallic article is composed of a base metal, the different metal with which it is coated comprises a precious metal, and the protective film is a glass,

where the glass that can be used as a protective film is a mixture of oxides selected from the group consisting of SiO₂, Na₂ O, CaO, MgO, Al₂ O₃, K₂ O, B₂ O₃, Li₂ O, and PbO, and has a refractive index in the range of from about 1.4 to about 2.8 and

the sputtering apparatus is sequentially operated in said three modes for predetermined periods of time such that the thickness of the precious metal coating is less than 100,000 Angstroms, and the thickness of the primer-metal coating is from about 50 Angstroms to 400 Angstroms.

14. The method of claim 13 wherein;

said base metal comprises stainless steel,

said primer-metal coating is composed of titanium and has a thickness of about 200 Angstroms, and

the precious metal coating comprises a layer of sputtered gold or a gold alloy that has a thickness in the range of from about 2,500 to 5,000 Angstroms.

15. In the manufacture of a metallic article of merchandise that is subjected to frequent human contact during normal usage of the article and is thus exposed to abrasion and/or corrosion damage by such usage and contact, the method of protecting the surface of said metallic article from such abrasion and/or corrosion damage during use without materially altering the color or appearance of said surface, which method comprises;

placing the metallic article in the deposition chamber of a sputtering apparatus along with (a) a first target composed of a selected non-metallic inert material which has a thermal expansion coefficient smaller than that of the metallic article, is selected from the group consisting of SiO₂, SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO, spinel and glasses that have a Knoop hardness of at least about 400 and consist essentially of mixed oxides, and is adapted to form a sputter-deposited protective film of controlled thickness that is abrasion-resistant and substantially colorless and transparent and (b) a second target composed of another selected non-metallic inert material that has a thermal expansion coefficient greater than that of the protective film material and less than that of the metallic article and is also adapted to form a sputter-deposited layer that is substantially colorless and transparent,

evacuating said chamber and, after introducing a sputtering gas therein, operating the sputtering apparatus in a first mode such that a sputtered layer of material from the second target is deposited on the metallic article and thereby provides a buffer layer which is substantially colorless and transparent and reduces thermally-induced stresses caused by the difference in the thermal expansion coefficients of the metallic article and the protective film material, and

while the metallic article is still in the gas-filled coating chamber, operating the sputtering apparatus in a second mode such that a sputtered protective film of material from the first target is deposited over the said buffer layer,

the operation of the sputtering apparatus being of such duration that the combination of the deposited buffer layer plus protective film of abrasion-resistant material is substantially transparent and of a thickness between about 14,000 Angstroms and 40,000 Angstroms, to prevent undesirable discoloration effects due to optical interference produced by incident light rays, to provide the desired protection against abrasion and/or corrosion damage when the metallic article is in use, and to allow both to adhere to the article.

16. The method of claim 15 wherein said metallic article is plated with a precious metal coating prior to the sequential sputter-deposition operations, the glass that can be used as the protective film is a mixture of oxides selected from the group consisting of SiO₂, Na₂ O, CaO, MgO, Al₂ O₃, K₂ O, B₂ O₃, Li₂ O, and PbO, and has a refractive index in the range of from about 1.4 to about 2.8, and where the protective film is a glass, the second target material, providing the buffer layer is a material selected from the group consisting of SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO, spinel and glasses that have a Knoop hardness over about 400 and are a mixture of oxides selected from the group consisting of SiO₂, Na₂ O, CaO, MgO, Al₂ O₃, K₂ O, B₂ O₃, Li₂ O, and PbO, and have a refractive index in the range of from about 1.4 to about 2.8.

17. The method of claim 15 wherein said buffer layer is composed of a glass-like material.

18. In the manufacture of a metallic article of merchandize that is subjected to abrasion damage during normal use which progressively degrades the aesthetic appearance and quality of the article, the method of coating said metallic article with a composite coating which automatically restores the aesthetic appearance of the article during the course of such use and resulting abrasion and consists essentially of a plurality of overlapping alternately-arranged thin films of (a) a metal that enhances the aesthetic appearance of the metallic article and (b) a selected non-metallic material which is substantially transparent in thin-film form and is also of sufficient hardness to constitute an abrasion-resistant material, said films being of such thickness that they are adapted to be worn away sequentially by abrasion during normal usage of the article, which method comprises;

placing the metallic article in the coating chamber of a sputtering apparatus along with a quantity of the metal to be deposited on the article and a quantity of said non-metallic abrasion-resistant material selected from the group consisting of SiO₂, SiC, Si₃ N₄, TiO₂, MgO, Al₂ O₃, Ta₂ O₅, Nb₂ O₅, GeO, spinel and glasses that have a Knoop hardness over about 400 and consist essentially of mixed oxides,

evacuating said coating chamber and, after introducing a sputtering gas therein, sequentially operating the sputtering apparatus in first and second modes for predetermined times such that a thin film of sputtered metal of predetermined thickness is first deposited on said article and then coated with a thin film of sputtered non-metallic abrasion-resistant material which is also of predetermined thickness,

the operation of the sputtering apparatus in said second mode being of such duration that the film of sputtered non-metallic abrasion-resistant material is not only substantially transparent but is also substantially colorless and thus protects the underlying film of sputtered metal without substantially altering the aesthetic appearance of the sputtered metal film, and then

repeating the sequential operation of said sputtering apparatus in said first and second modes for said predetermined times until a predetermined number of overlapping alternately-arranged thin films of sputtered metal and adherent, substantially colorless and transparent protective thin films of sputtered non-metallic abrasion-resistant material are deposited on the metallic article and thus form said composite coating.

19. The method of claim 18 wherein the sequential operation of the sputtering apparatus is repeated up to twenty times so that a total of from 4 to 40 overlapping and alternately-arranged films of sputtered metal and sputtered non-metallic abrasion-resistant material are deposited on the metallic article.

20. The method of claim 18 wherein the operation of the sputtering apparatus in said first and second modes is so correlated with the sputtering yields of the metal to be deposited and the said non-metallic abrasion-resistant material that the thickness of each of the sputter-deposited thin films is less than about 100 Angstroms.

21. The method of claim 18 wherein;

the abrasion resistant material is a glass,

said metal to be deposited comprises a precious metal and the glass that can be used as the abrasion resistant material is a mixture of oxides selected from the group consisting of SiO₂, Na₂ O, CaO, MgO, Al₂ O₃, K₂ O, B₂ O₃, Li₂ O, and PbO, and has a refractive index in the range of from about 1.4 to about 2.8.

22. The method of claim 18 wherein the operation of the sputtering apparatus in said first and second modes is so correlated with the sputtering yields of the precious metal and the said non-metallic abrasion-resistant material that each of the sputter-deposited thin films of precious metal is of substantially uniform thickness and each of the sputter-deposited thin films of said non-metallic abrasion-resistant material is also of substantially uniform thickness and thicker than the respective precious metal films.

23. The method of claim 22 wherein the sputtering yield-duration correlation is such that thickness of each of the precious metal films does not exceed about 50 Angstroms and the thickness of each of the non-metallic abrasion-resistant films does not exceed about 100 Angstroms.

24. The method of claim 23 wherein;

the precious metal is platinum, silver, gold or a gold alloy, and

the metallic article is composed of a base metal that is coated with a primer material which promotes the adhesion of the first sputter-deposited film of precious metal.