Method for imparting tarnish protection or tarnish protection with color appearance to silver, silver alloys, silver films, silver products and other non-precious metals

Abstract

A method of surface coating a metallic object, including removing substantially all of the existing silver sulfide tarnish if present, ultrasonically cleaning the object with immersion in a solvent, uniformly dispersing selected nanoparticles over the surface of the object by sonicating the object in an ultrasonic bath containing the selected nanoparticles. The invention further includes quickly rinsing the object with solvent upon removal from the ultrasonic bath to inhibit formation of large agglomerates, drying the object with a flow of gas, optically inspecting the object for the presence of agglomeration and applying a barrier layer conformal coating and a protective layer conformal coating.

Claims

1. An object, comprising: a substrate; a uniformly dispersed layer of selected nanoparticles directly covering a surface of the substrate; a barrier layer conformal coating overlying the dispersed layer of selected nanoparticles selected from a group consisting of carbides, metals, metal alloys, metal compounds, combinations of organic/inorganic complex compounds and stacks thereof; and a protective layer conformal coating, comprising a polymer layer having a thickness of 3 to 20 microns; wherein the polymer layer comprises parylene.

2. The object claimed in claim 1, wherein the selected nanoparticles include nanoparticles selected from a group consisting of silver nanoparticles, diamond nanoparticles, platinum nanoparticles, silica nanoparticles, and corundum nanoparticles.

3. The object claimed in claim 1, wherein the barrier layer conformal coating is further selected from a group consisting of oxides, oxynitrides and nitrides.

4. The object claimed in claim 1, wherein the thickness is chosen to maintain optical clarity, minimal change in color appearance and adhesion to the underlying barrier layer conformal coating.

5. The object claimed in claim 1, wherein the substrate comprises silver and the uniformly dispersed layer of selected nanoparticles, the barrier layer conformal coating and the protective layer conformal coating inhibit tarnishing of the silver.

6. The object claimed in claim 1, wherein the substrate comprises silver and the uniformly dispersed layer of selected nanoparticles, the barrier layer conformal coating and the protective layer conformal coating present a gold appearance.

7. The object claimed in claim 1, wherein the substrate is selected from a group consisting of silver, silver alloys, silver films, silver products, copper, copper alloys and brass.

8. The object claimed in claim 1, wherein the substrate comprises an article of jewelry.

9. The object claimed in claim 1, wherein the substrate comprises a nonprecious metal.

10. An object, comprising: a substrate; a uniformly dispersed layer of selected nanoparticles covering a surface of the object; a barrier layer conformal coating overlying the dispersed layer of selected nanoparticles selected from a group consisting of carbides, metals, metal alloys, metal compounds, combinations of organic/inorganic complex compounds and stacks thereof; and a protective layer conformal coating; wherein the protective layer conformal coating is selected to be the layer of porous silica and where in the layer of porous silica is embedded with erbium nanoparticles.

11. An object, comprising: a substrate, selected from a group consisting of silver, silver alloys, silver films, silver products and nonprecious metals; a uniformly dispersed layer of selected nanoparticles comprising diamond nanoparticles covering a surface of the substrate; a barrier layer conformal coating overlying the dispersed layer of selected nanoparticles selected from a group consisting of carbides, metals, metal alloys, metal compounds, combinations of organic/inorganic complex compounds and stacks thereof; and a protective layer conformal coating overlying the barrier layer conformal coating, wherein the protective layer conformal coating is selected to be a sol-gel layer and wherein the sol-gel layer comprises Boehmite nanoparticles in a silane dispersant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic depiction of anti-tarnish treatment layers according to an example embodiment of the invention;

(2) FIG. 2 is a flowchart depicting an example method of applying anti-tarnish treatment to an object according to an embodiment of the invention;

(3) FIG. 3 is a flowchart further depicting an example method of applying treatment to an object including dispersing nanoparticles according to an embodiment of the invention of FIG. 2;

(4) FIG. 4 is a flowchart further depicting an example method of applying treatment to an object including applying a barrier layer conformal coating according to an embodiment of the invention of FIG. 2;

(5) FIG. 5 is a flowchart further depicting an example method of applying treatment to an object including applying a protective layer conformal coating according to an embodiment of the invention;

(6) FIG. 6 is a flowchart depicting an example method of applying gold appearance to an object according to an embodiment of the invention; and

(7) FIG. 7 is a flowchart further depicting an example method of applying treatment to an object including applying a protective layer conformal coating according to an embodiment of the invention of FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

(8) The invention described here provides a robust process for producing a bio-compatible tarnish prevention treatment for functional and decorative articles of silver and silver alloys including but not limited to other metals such as copper, copper alloys and brass that are also prone to tarnish.

(9) Additionally, the invention described here provides robust processes for converting the appearance of silver, silver alloys, other metals such as brass, cobalt, or plated metals having rhodium or silver platings to the appearance of fine carat gold, rose gold, purple gold etc. without the use of gold. Additionally, the invention described here provides a method for transforming the appearance of silver, silver alloys, other metals such as brass, cobalt, plated metals etc., to achieve the look of fine rhodium platings without the use of rhodium. Additionally, the invention described here can be used for providing a special appearance to metal jewelry such as the look of antique gold.

(10) Filigree gold jewelry is typically very delicate due the requirement for using 22K or higher gold to create the filigree. Generally, filigree gold jewelry tends to have low wear resistance. Further, the invention described here can be used to provide improvement in the surface hardness of metallic objects that has application in areas such as filigree gold jewelry.

(11) The invention also includes processes to prevent tarnish in functional as well as decorative articles of silver and silver alloys, pure silver foils used in specialty jewelry making such as Kundan as well as a process to directly deposit silver onto jewelry components that are used in Kundan jewelry making and rendering the silver film that is deposited to have anti-tarnish properties.

(12) An Example Anti-Tarnish Process for Silver Objects

(13) The process described below provides a step-by-step method for rendering a silver object, such as a decorative silver piece, silver/silver alloy jewelry or silverware used as utensil for serving and eating of food, with a long lasting anti-tarnish property.

(14) Referring to FIG. 2, in one embodiment, the method includes, at reference numeral 20: removing substantially all pre-existing tarnish from the silver article, for example, by using a commercial chemical tarnish remover such as Silver Quick, Hagerty's Silver Dip or any other such chemical agents that reverse the silver sulfide reaction. The removal method uses a chemical reaction to convert the silver sulfide back to silver. Many metals (X) in addition to silver form compounds with sulfur. Some of them have a greater affinity for sulfur than silver does.
3Ag.sub.2S+2X.fwdarw.6Ag+X.sub.2S.sub.3

(15) At 22, the silver article is prepared by subjecting it to a thorough solvent based ultrasonic cleaning process to ensure that the surface is free of organic residues or contamination.

(16) Referring to FIG. 3, at 24, the next step of the method's anti-tarnish treatment involves the use of nano-particles such as nano-silver particles, nano-diamond particles or nano-platinum particles which are dispersed uniformly over the silver article 24a. Silica nano-particles, corundum nano-particles and others may also be utilized. This pre-treatment step improves the adhesion and scratch resistance of the film deposited in the further steps of the process. According to an example method, nano-particles are dispersed in a solvent or water medium and a monolayer of the nano-particles are dispersed over the silver article by immersion of the silver article into the slurry containing the nano-particles under the influence of an ultrasonic bath. 24b.

(17) Sonication is performed in a regular sonic bath for a duration that can be optimized by experimentation based upon the silver substrate's geometry and size. The duration of sonication is derived experimentally by performing the sonication of the silver article to be coated with a dispersion of nano-particles for various durations and examining the resulting layer for uniformity and density of coverage using an analytical technique such as scanning electron microscopy. A ultrasonic bath is a piece of industrial or laboratory equipment that consists of a container, or bath, used for cleaning, or mixing things inserted into the bath, by sending ultrasonic vibrations through the liquid in the bath. There are several commercially available ultrasonic bath systems which operate as various ultrasound frequencies (15-400 kHz).

(18) At 26, the silver article is removed from the slurry and quickly rinsed with a solvent to prevent the formation of large agglomerates.

(19) At 28, the silver article is dried with nitrogen and optical inspection 30 is performed to check for agglomeration that shows up as dark residues.

(20) The silver article with a uniform dispersion of nano-particles is ready for the next step in the anti-tarnish treatment. Referring to FIG. 4, in one embodiment of the invention, at 32, the next step involves applying a barrier layer conformal coating, for example, coating the silver object conformally with thin films of aluminum oxide and titanium oxide (32a). At 32b, various other oxides or combinations of oxide stacks may be applied. Combinations of metal, metal alloys, metal compounds (including but not limited to nitrides, oxides, oxynitrides and carbides) in stacks may be used. Combinations of organic/inorganic complex compounds may also be used. The metals, alloys and metal compounds can be chosen to include metals that show a higher affinity to sulfur than silver. At 32c, conformal coatings of multilayer compounds may be applied by using various vapor-based or liquid immersion techniques such as atomic layer deposition (ALD) techniques, plasma enhanced chemical vapor deposition techniques (PA-CVD), physical vapor deposition techniques (PVD), sol-gel techniques (dip, spray, spin coating methods). According to one embodiment, the thin films of multi-layer compounds are applied at a thickness between 70 nm to 500 nm to minimize a change in optical appearance of the silver article.

(21) Referring to FIGS. 2 and 5, after conformal multi-layer oxides treatment, the silver article or other metallic article is ready for the next step in the inventive anti-tarnish treatment, at 34, applying a protective layer conformal coating. A next step involves the conformal coating of the silver object with a protection layer that is organic in nature or that is inorganic in nature. The protective layer conformal coating provides a barrier to separate the multi-oxide layer from exposure to damage from mechanical wear and tear, chemicals, environment and moisture.

(22) In one embodiment of the invention, referring to FIG. 5, at 34a, a polymer such as Parylene 34b is conformally coated over the multilayer oxide layer. The thickness of the polymer layer is chosen to maintain good optical clarity, minimal change in color appearance and good adhesion to the inorganic layer below it 34c. In one example embodiment, the range of thickness for Parylene conformal coating is between about 3-20 microns. Parylene or its variants demonstrates good thermal stability up to 290 C, excellent crevice penetration, and low coefficient of friction in addition to its excellent barrier properties. The process for deposition of Parylene is known and is typically done by vaporization of a dimer in vacuum followed by heating the dimerized gas and pyrolizing to cleave the dimer to monomeric form followed by deposition of the monomer at room temperature as a transparent polymer film 34d.

(23) In another embodiment of the invention, the silver object with thin multilayer oxides applied is further protected by an inorganic sol gel coating or an organic-inorganic sol gel coating 34e. Sol-Gel processing designates a solid materials synthesis procedure, performed in a liquid and at low temperature (typically T<100 C). The physics and chemistry involved in sol-gel synthesis has been detailed in many reviewed papers as well as in books [10, 11]. The choice of the sol gel chemistry is dependent on the optical properties and annealing temperature of the resulting film. In one embodiment, a titanium dioxide solgel is coated conformally by a dip coating process using a tetraisopropyl-orthotitanate solution and ethanol as a solvent. Other example inorganic sol gel coatings include silica and alumina coatings. Hybrid coatings based on a combination of nanoparticles and solgel to create durable transparent protective film can also be used. One example of such a coating is the use of Boehmite nanoparticles in a silane dispersant.

(24) An Example Anti-Tarnish Process for Thin Silver Films

(25) The process below provides a step-by-step method for imparting tarnish resisting properties to thin films of silver that are deposited on various substrates to impart a functional or decorative property. In one embodiment of the invention, the process is applied for the manufacture of Kundan jewelry in two different ways.

(26) Procedure 1:

(27) As discussed above, Kundan jewelry manufacturing involves the use of silver foil that is cut into shapes and used as a reflective material placed behind the cut glass pieces or rough cut diamonds that are a key component of this jewelry style. The silver foil can be anti-tarnish treated using the procedure above which provides the foil with a conformal anti-tarnish property. The foil can be cut into the desired shapes during the Kundan jewelry manufacturing.

(28) Procedure 2:

(29) The cut glass pieces or rough cut diamond pieces are thoroughly cleaned by using a combination of solvent cleaning steps in a sonication bath. For example, the solvents acetone and isopropyl alcohol may be used.

(30) The cleaned pieces are placed on holders with the flat side exposed. A thin film of pure silver is deposited on the exposed surface using a vapor coating process such as magnetron sputter deposition, evaporation or ion-assisted deposition (IAD). The silver coated pieces are thereafter treated as discussed above in which the nanoparticle dispersion is optional.

(31) In another embodiment of the invention, the deposition of the highly reflective silver layer can be in combination with a high index film such as titanium oxide using multilayer deposition chemistry in the vapor coating process. The multilayer coating chemistry composed of a first layer of silver and a second layer of a high index oxide film results in the formation of a colored reflective surface and has application in the development of colored Kundan cut glass. The resulting colored Kundan cut glass has anti-tarnishing properties by virtue of the second coating layer deposited over the highly reflective silver layer.

(32) An Example Process for Achieving a Gold Appearance

(33) Referring to FIG. 6, in another embodiment, the thin films of multilayer compounds that are deposited on the surfaces of the nanoparticle dispersed silver object are tailored to produce a specific appearance such as gold, rose gold, colored gold, rhodium or other fancy colors. The thickness and composition of the thin film treatment are varied to achieve the exact color appearance desired.

(34) The invention includes a combination process where the gold color is achieved. First, a thin film multilayer stack of oxides/nitrides/oxynitrides is applied 32b. This layer is the first barrier to tarnishing of silver. Second, an organic/inorganic complex of sol gel with compounds that will provide the final color appearance of gold is applied 34. The thickness of the first multilayer stack of oxide/nitride/oxynitrides allows some color development as compared to the treatment disclosed herein where silver is anti-tarnish clear treated. The second protection step 34 using sol gel or Parylene is also modified to allow color development.

(35) If the substrate is silver or a silver alloy, cleaning and tarnish removal is performed as discussed above 20.

(36) The article is then prepared by a thorough solvent based ultrasonic cleaning process to ensure that the surface is free of organic residues or contamination 22.

(37) The disclosed treatment can also be applied to non-silver based objects, in which case the step of removing existing tarnish may not be required. An example is the transformation of brass articles or jewelry to the appearance of fine carat gold using the process described here. Another example of changing the appearance of a decorative object is to use the process described here on gold or gold plated jewelry to produce a look of antique gold.

(38) In another embodiment, the surface of a metallic article such as delicate filigree gold jewelry is subjected to the above described process involving nano-particle dispersion. The nano particles may include nano-diamond or corundum nano-particles and may be followed by a thin film treatment composed of oxide or nitrides or oxynitrides of metals or alloys including but not limited to titanium or titanium-aluminum materials.

(39) According to an example embodiment, a combination process is employed. The gold color is achieved through modification of the above described anti-tarnish process. First the thin film multilayer stack of oxides/nitrides/oxynitrides is made thicker. Second, the organic/inorganic complex of sol gel is modified with compounds that provide the final color appearance of gold. The thickness of the first multilayer stack of oxide/nitride/oxynitrides is such as to allow some color development as opposed to the above described silver anti-tarnish clear treatment. The second protection step using sol gel or Parylene is also modified to allow color development.

(40) Generally, to achieve the gold appearance, the multilayer stack includes but is not limited to aluminum oxide, aluminum oxide/titanium dioxide stack, aluminum oxide/silica stack, aluminum oxide/silicon nitride or oxynitride stack.

(41) After conformal multi-layer oxides treatment, the article is ready for the next step in creating a gold appearance. The next step involves the conformal coating of the substrate object with a protection layer. In one embodiment of the invention silver nanoparticles in porous silica are added to the sol gel to contribute to the appearance of gold.

(42) In one embodiment of the invention, a polymer such as Parylene is conformally coated over the multilayer oxide layer to a range of thickness between about 3-20 microns.

(43) In another embodiment of the invention, the object that has been conformally coated with thin multilayer oxides is further protected by an inorganic sol gel coating or an organic-inorganic sol gel coating as discussed above.

(44) Specific Example of Method for Achieving Gold Appearance

(45) All pre-existing tarnish is removed from a silver substrate by procedures discussed above 20.

(46) The silver article is prepared by solvent based ultrasonic cleaning process to ensure that the surface is free of organic residues or contamination 22.

(47) Nanoparticles are dispersed onto the surface of the silver article as discussed above. The nanoparticles are selected from nano-silver particles, nano-diamond particles, nano-platinum particles, silica nano-particles and corundum nano-particles. The nano-particles are dispersed uniformly over the silver article 24.

(48) According to the method, nano-particles are typically dispersed in a solvent or water medium and a monolayer of the nano-particles can be dispersed over the silver article by immersion of the silver article into the slurry containing the nano-particles under the influence of an ultrasonic bath.

(49) Sonication is performed in a regular sonic bath for a duration that can be optimized by experimentation based upon the substrate's geometry and size. The duration of the sonication is derived experimentally by performing the sonication of the silver article to be coated with a dispersion of nano-particles for various durations and examining the resulting for uniformity and density of coverage using an analytical technique such as scanning electron microscopy.

(50) The article is removed from the slurry and quickly rinsed with a solvent to prevent the formation of large agglomerates 26.

(51) The silver article is dried with nitrogen 28 and optical inspection is performed to check for agglomeration that shows up as dark residues 30.

(52) Next, a layer of aluminum oxide is deposited 32 using IAD (ion assisted deposition) or ALD (atomic layer deposition) to thickness at least 70 nm.

(53) Next, a layer of porous silica embedded with silver nano particles is deposited 34f. This layer is deposited with silver nano particles in the size range 20-50 nm 34g using sol-gel synthesis. In this example 34h tetraethylorthosilicate (TESO) and Polyacrylic acid (PAA) in acid media are used as synthesis materials in which are dispersed the silver nano-particles.

(54) Last, the silver article is annealed in an N2-H2 reducing atmosphere at 450 C 34i.

(55) It is expected that the creation of other colors can be achieved by using other types of nano particles in the silica sol gel layer. For example, it is expected that the appearance of pink gold can be created using Erbium nano particles 34j.

(56) The invention also includes an object including the layers created by the various treatments disclosed in this application.

(57) The invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the forgoing description to indicate the scope of the invention.

REFERENCES

(58) 1. L. Gal-Or, 4th Santa Fe Symposium on Jewelry Manufacturing Technology (1990), p. 19. 2. H. Royal, 4th Santa Fe Symposium on Jewelry Manufacturing Technology (1990). P. 37. 3. R. M. Enick, U.S. Pat. No. 6,183,815 (2001). 4. T. D. Burleigh, Corrosion, V. 56 (2002), p. 49. 4. E. W. Salmon, 12th Santa Fe Symposium on Jewelry Manufacturing Technology (1998), p. 363. 6. Ullman's Encyclopedia of Industrial Chemistry, V. A24 (1993), p. 148. 7. [1]: CAL-IN Technology Transfer, LLC 8. Protective coating of Silver, Makela, Milja et al., US Patent Appl. 20090004386 9. Brinker, C. J.; Scherer, G. W. Sol-Gel Science. The Physics and Chemistry of Sol-Gel Processing, Academic Press, New York, 1990. 10. Pierre, A. C. Introduction to Sol-Gel Processing, Kluwer, Boston, 1998.