Patent Application
20050287316
This invention relates to tarnish resistant compositions and methods of using same. More particularly, this invention relates to materials such as fabrics having at least finely divided colloidal metal particles such as copper or silver particles therein. When used to protect silver and/or gold articles, the compositions and methods of the invention provide superior tarnish resistance.
Copper, nickel, silver and gold containing articles such as jewelry, tableware and the like, tarnish in a short period of time under ordinary conditions of storage. The tarnish is caused by certain gases in the atmosphere such as sulfur containing compounds, hydrogen sulfide gas, halogens, halogen containing vapors and the like, which cause discoloration or tarnish. For example, hydrogen sulfide gas reacts with silver articles to produce a film of silver sulfide on the articles. This film quickly turns into a black coating on the article. This coating is the discoloration known as tarnish.
Some materials and methods have been developed to address the problem include providing a protective coating on the surface of the silver, providing various storage containers, or combinations thereof, to block access of corrosive gases to the articles. However, each of the available materials and methods still suffer significant shortcomings.
It is known to provide a coating of volatile organic corrosion inhibitor (VCI) on articles made of sensitive metals. The VCI, for example, cyclohexamine ammonium benzoate, evaporates, coats the metal to be protected, resulting in corrosion resistance. A limitation to the use of VCI's is that they are unable to maintain efficacy over a sufficiently long period of time. The protection only lasts as long as the corrosion inhibitor continues to evaporate.
U.S. Pat. No. 4,944,916 to Franey discloses a polymeric storage bag, such as polyethylene, that is formed in the presence of a scavenger such as copper or aluminum. When metal articles are placed in the bag the scavenger particles attract the sulfide gases away from the metal article before the sulfides can reach the metal articles. An inherent problem with these metals is that copper reacts somewhat with atmospheric carbon dioxide to form surface carbonates and aluminum immediately reacts with atmospheric oxygen to form surface oxides. These surface coatings impede reaction with sulfide gas and diminish scavenging performance.
It has long been known to store silverware in treated fabrics so as to reduce the formation of tarnish. U.S. Pat. No. 1,766,646 to Grinnell discloses a material impregnated with a silver composition which acts as a scavenger for sulfur containing compounds. The fabric is impregnated by passing fabric through a bath containing silver nitrate solution followed by a bath containing sodium carbonate solution which precipitates the silver onto the fabric. The mechanism of action is as described previously, with the scavenger competing with the metal article for the sulfide so as to preferentially absorb the sulfide before the metal article absorbs it. Silverware stored in the fabric or in boxes lined with such fabric is protected from tarnish to a certain degree.
The inventor has performed experiments duplicating the methods of U.S. Pat. No. 1,766,646 and has found that this technique does not result in an significantly different result than zinc acetate treated fabric. One possible reason for this result is that, during the liquid treatment process with sodium carbonate, the silver particle surface is inactivated by reaction with the carbonate solution.
Additional compounds which have been shown to provide some protection against tarnish include activated carbon, natural and synthetic zeolites, silica gel and activated alumina. However, the protection provided by the known compounds is neither complete nor long lasting. Use of presently available tarnish inhibiting compositions still results in some tarnish, although to a lesser extent than if no protection is used. However, conventional tarnish resistant compositions are also less effective over time. As the scavenger is used up, the tarnish resistant compositions become less effective and ultimately must be replaced.
There is a present and long standing need for compositions that resist tarnish that does not suffer the disadvantages of the prior art. Specifically, it would be advantageous to have a tarnish resistant composition that provides substantially complete tarnish resistance over an extended period of time.
The present invention provides a tarnish resistant composition including a plurality of colloidal metal particles including at least one of colloidal: copper, silver, zinc and nickel particles, and a porous material containing the colloidal particles.
Also provided is a container for storing tarnishable articles, including a plurality of colloidal metal particles including copper and/or silver colloidal particles, a porous material containing the colloidal particles and a solid sided box having one or more interior surfaces lined with the porous material.
The inventor has surprisingly found that use of finely divided particles applied to a porous material provides heretofore unprecedented resistance to tarnish. Although not intending to be limited to any one particular theory of operation, it has been established that the extraordinarily large surface area of the finely divided particles is at least in part responsible for the effectiveness of the compositions of the invention. The large surface area provides much greater reactivity of the colloidal particle with potentially tarnishing agents as compared to known tarnish resistant compositions. This greater reactivity translates into far superior tarnish resistance than is currently available. Furthermore, the greater surface area allows for the superior tarnish resistance to occur for unprecedented extended periods of time without diminishing.
One might assume that colloidal metal particles in dry, fine powder form, would have a tendency to fall off of a fabric surface. Surprisingly, this has not been the case. Although not intending to be limited to any particular theory, it is believed that the particles are so fine that they adhere to or become entrapped among the fibers of the fabric, and can withstand handling, cutting, and the like, without appreciable loss from the fabric.
Compositions of the Invention
The compositions of the present invention include certain colloidal metal particles which have been applied onto a porous material. As used herein, the term “colloidal” refers to fine particles having a high surface area to volume ratio. Preferred colloidal particles have an average diameter of from less than about 0.04 microns to about 2.0 microns. The surface area of such particles ranges from about 10.8 square meters per gram for the smallest particles to about 2.5 square meters per gram for the largest particles, depending upon the particular metal in question. Notably, the surface area increases as diameter of the particles decreases.
A critical aspect of this invention is the very high surface area of the colloidal particles. This surface area dramatically increases the reactivity of the particles in performing their scavenging function. Preferably, a majority of the particles used in the compositions of the invention have an average diameter of less than about 2.0 microns, more preferably less than about 1.5 microns, even more preferably less than about 1.0 microns, most preferably less than about 0.5 microns.
Any colloidal particle that reacts with the sulfur and chlorine containing gases or other tarnish producing gases may be used. Examples of suitable particles include copper, silver, nickel, zinc and/or silver coated copper flake. In a preferred aspect of the invention, the particles are spherical. Additionally, it is preferred that the particles be in elemental form. In a particularly preferred embodiment, the colloidal particles include elemental at least one of copper and silver particles having an average diameter of less than about 2 microns. Most preferably, the colloidal particles are elemental silver particles having an average diameter of less than about 1 micron. Colloidal particles suitable for such use include R&D Copper Powder #10K2 and Silver particles suitable for use include Silver Powder 7000-35, 95, and 450 which are commercially available from Ferro Electronic Material Systems, South Plainfield, N.J.
There are no particular limitations to the amount of colloidal particles contained in the materials. Greater loading of the material will assure better and longer lasting protection. Generally, particles will comprise from about 1% by weight to about 60% by weight of the compositions of the invention. Preferably, the treated material will include at least from about 10% to about 50% by weight more preferably at least about 30% by weight colloidal particles.
The metal colloidal particles will be used alone or in combination. The total weight percent of the particles in the compositions of the invention preferably includes from at least about 50% to about 100% combined copper and/or silver, more preferably from at least about 75% to about 100% combined copper and/or silver, and most preferably at least about 90% combined copper and/or silver, with the balance being made up of elemental colloidal particles of one or more of nickel and zinc. In a preferred aspect of the invention, a majority of the metal particles are colloidal silver, as this metal is less reactive with the atmosphere than is copper, which may form surface carbonates with exposure to carbon dioxide in air, making it less available to react with tarnishing gases such as sulfides.
The metal colloidal particles may be used in combination with other known tarnish inhibiting materials. In a further aspect of the invention, colloidal metal particles are used in combination with zinc acetate, zinc carbonate or the like. The zinc acetate or other similar tarnish inhibiting material may be supplied to a material to be treated in any conventional manner. For example, it is possible to prepare a zinc acetate solution in a bath and to dip coat a porous material such as fabric with the solution.
There are no particular limitations to the porous material to which the colloidal particles will be applied so long as the material possesses sufficient porosity to allow the gases of concern to access the colloidal particles located therein, as well as sufficient interstitial spaces within which the colloidal particles reside. Generally, natural or synthetic fabrics that are woven, braided or pressed may be used. The fabric may be substantially uniform throughout or may possess variable porosity. Preferred is a material having a large amount of surface area within the material, for example, flannel. Large surface areas of the material maximize the opportunity for contact of the tarnish producing agents with the anti-tarnish metals continued therein. Non-limiting examples of materials suitable for use in the invention include papers, foams, and the like. The specific material used will be determined by the particular application.
For example, silverware is traditionally kept in either flannel fabric bags tied around the silverware or in solid storage boxes lined with treated fabric. Jewelry is traditionally stored in jewelry boxes that may be lined with a treated fabric to resist tarnish. Alternatively, silverware, jewelry or the like may be stored in a container of any sort with anti-tarnish packets placed in the container. All such applications are envisioned as within the scope and spirit of the invention.
In one aspect of the invention, a storage box is lined with a treated material such as flannel. The storage box may be made of any suitable material and desirably will be of a solid material such as metal, wood or plastic. Referring now to
An alternative storage box is shown in
In another aspect of the invention, a piece of fabric is treated with at least colloidal metal particles and formed into storage bags. Preferably, the fabric is sufficiently thick and dense so as to provide some protection against the stored articles being dented or scratched. Referring now to
In a further aspect of the invention, a drawer liner is provided. Referring now to
An alternative drawer liner is shown in
In a further alternative aspect of the invention, a storage pouch is filled with colloidal particles or is made from fabric loaded with silver particles. Referring now to
Non-limiting examples of suitable fabrics for use in the invention include single or multiple layers of flannel, felt, or velour. For applications involving storage of silverware, flannel is preferred.
Methods of Making the Compositions
The compositions of the invention may be made using any number of conventional techniques. For example, in one aspect of the invention, the colloidal particles are suspended in a liquid suspension and the material to be loaded with the particles is passed through the suspension and later dried. Alternatively, the colloidal particles may be suspended in a concentrated slurry which can be diluted to form a liquid suspension. For example, a concentrated slurry of colloidal silver (85%) dispersed in diethylene glycol monobutyl ether (15%) may be diluted in a quantity of water to form a dip bath for application onto the material to be treated, such as a flannel fabric. Higher concentrations of loading are achieved by multiple passes of the material through the dip bath, by suspending a higher concentration of particles in the suspension or a combination thereof.
Preferably, the suspension contains from about 5% to about 25%, more preferably from about 2% to about 20% of colloidal metal particles by weight of the suspension. Preferably, the suspension is in an aqueous medium. In a preferred aspect of the invention, the material is passed through an aqueous solution of zinc acetate before, during or after being passed through the colloidal particle suspension. Preferably, the solution contains from about 5% to about 25%, more preferably from about 2% to about 20% by weight of zinc acetate.
Use of elemental forms of the colloidal particles allows for other simple methods of making the compositions of the invention. For example, due to the nature and size of elemental colloidal particles, it is possible to simply brush the dry particles onto the surface of the porous material. The particles will become impregnated into the material and remain there indefinitely. Similarly, it is possible to spray the particles onto one or more surfaces of the material using dry colloidal particles or a liquid suspension of the particulates. The brush or spray treated cloth may be pre- or post-treated with zinc acetate. Other methods of making the invention will be apparent to those having ordinary skill in the art and are within the scope of the invention.
The examples of the present invention presented below are provided only for illustrative purposes and not to limit the scope of the invention. Numerous embodiments of the invention within the scope of the claims that follow will be apparent to those of ordinary skill in the art from reading the forgoing text and following examples.
Examples 1 to 5 involve treating a cloth material with a composition of the invention and covering a silver article with the treated material or storing a silver article in a container lined with the treated material. The covered or stored silver articles and controls are exposed in a sealed chamber to a test atmosphere of 100 ppm of ammonium sulfide fumes for five hours. After exposure the silver articles are compared to detect level of tarnish.
In Examples 2-5, a scale of 0 to 5 is used to quantitatively rate the degree of tarnish after exposure to the test atmosphere. Grade 0 represents no tarnish. Grades 1 to 5 represents increasing levels of tarnish with 5 being severely tarnished and having black discoloration.
A flannel cloth treated with zinc acetate (i.e., commercially available from Fifield, Inc., Hingham, Mass.), is cut into one square foot sections. The flannel used ranged in weight from about 15 g/ft2 to about 30 g/ft2. Three sections are not further treated. Each of three one foot square sections are evenly brushed with 2 grams of elemental colloidal copper particles (R&D Copper Powder # 10K2 available from Ferro Electronic Material Systems, So. Plainfield, N.J.). The copper used includes 90% of particles having a diameter of less than 1.8 microns. Nine identical untarnished sterling silver alloy plates measuring 1½″×1½″×0.050″ are used in the experiment. As a control, three plates are exposed to the test atmosphere without protection. Three plates are each wrapped in two layers of zinc acetate treated flannel. Three plates are each wrapped in two layers of zinc acetate and colloidal copper particle treated flannel. The silver plates are then exposed to the test atmosphere as described above.
After five hours, visual inspection of the silver plates reveals that the plates exposed to the test atmosphere with no protection are severely tarnished. The three plates wrapped in zinc acetate treated cloth were tarnished, although less severely than the plates with no protection. The three plates wrapped in zinc acetate and colloidal copper particle treated cloth showed no evidence of tarnish.
A flannel cloth treated with zinc acetate (i.e., commercially available from Fifield, Inc., Hingham, Mass.) is cut into one square foot sections. Three sections are not further treated. Each of three one foot square sections are brushed with 2 grams of elemental colloidal silver particles (Silver Powder 7000-35 available from Ferro Electronic Material Systems, So. Plainfield, N.J.). The silver used includes 90% of particles having a diameter of less than 1.0 micron. Nine identical untarnished sterling silver alloy plates measuring 1½″×1½″××0.050″ are used in the experiment. As a control, three plates are exposed to the test atmosphere without protection. Three plates are each wrapped in two layers of zinc acetate treated flannel. Three plates are each wrapped in two layers of zinc acetate and colloidal copper particle treated flannel. The silver plates are then exposed to the test atmosphere as described above.
Results of Example 2 are shown below in Table 1.
As shown in Table 1, after five hours, visual inspection of the sterling silver plates reveals that the plates exposed to the test atmosphere with no protection are severely tarnished. The three plates wrapped in zinc acetate treated cloth were tarnished, although less severely than the plates with no protection. The three plates wrapped in zinc acetate and colloidal silver particle treated cloth showed no evidence of tarnish.
A flannel cloth is cut into one square foot sections. Three sections are not pre-treated. Each of three one foot square sections are brushed with 2 grams of silver coated flakes (Silver Coated Copper Flake—450, available from Ferro Electronic Material Systems, So. Plainfield, N.J.). The silver coated copper flakes used have 90% of particles with a diameter of 18.03 microns. Nine identical untarnished sterling silver alloy plates measuring 1½″×1½″×0.050″ are used in the experiment. As a control, three plates are exposed to the test atmosphere without protection. Three plates are each wrapped in two layers of untreated flannel. Three plates are each wrapped in two layers of flannel treated with silver coated copper flakes. The silver plates are then exposed to the test atmosphere as described above.
Results of Example 3 are shown below in Table 2.
As shown in Table 2, after five hours, visual inspection of the sterling silver plates reveals that the plates exposed to the test atmosphere with no protection are severely tarnished. The three plates wrapped in untreated cloth were also severely tarnished. The three plates wrapped in flannel treated with silver coated copper flakes showed no evidence of tarnish.
A flannel cloth is cut into one square foot sections and treated as described above in Example 2. Nine identical U.S. silver fifty cent pre-1965 coins polished to a mirror finish are used in the experiment. As a control, three coins are exposed to the test atmosphere without protection. Three coins are each wrapped in two layers of untreated flannel. Three coins are each wrapped in two layers of flannel treated with colloidal silver particles. The coins are then exposed to the test atmosphere as described above.
Results of Example 4 are shown below in Table 3.
As shown in Table 3, after five hours, visual inspection of the silver coins reveals that the coins exposed to the test atmosphere with no protection are severely tarnished. The three coins wrapped in zinc acetate treated flannel showed significant tarnish. The three coins wrapped in flannel treated with zinc acetate and ultra-fine silver particles showed no evidence of tarnish.
Six identical untarnished sterling silver plates and six U.S. fifty cent coins as described above are used in the experiment. As a control, three plates and three coins are exposed to the test atmosphere without protection. Three plates and three coins are each placed in a hinge closed wooden storage box having a top and bottom lining of flannel treated with colloidal silver (Silver Powder 7000-35 available from Ferro Electronic Material Systems, So. Plainfield, N.J.). The box is closed and placed in the test chamber along with the three plates and coins that are unprotected and exposed to the test atmosphere as described above
Results of Example 5 are shown below in Table 4.
As shown in Table 4, after five hours, visual inspection of the silver plates and coins reveals that the coins and plates exposed to the test atmosphere with no protection are severely tarnished. The silver plates and coins in the wooden box containing silver treated flannel showed no evidence of tarnish. Accordingly, even when the tarnishable objects are not entirely wrapped in the treated fabric, the compositions of the invention still work to prevent tarnish.
Examples 6 to 9 involve treating a cloth material with a known weight of a composition of the invention and exposing the treated cloth to a test atmosphere to totally saturate the treated cloth. The change in the weight of the cloth material is used to quantify the amount of sulfide gas that may be successfully scavenged from the atmosphere by the composition.
In each of Examples 6 to 9, untreated flannel squares (approximately 4″×4″) were weighed. Colloidal copper or silver particles were brushed lightly onto the surface of the flannel and the cloth so treated was weighed. The difference in these measurements represents the weight of particles added to the cloth. The treated cloth was then exposed to a test atmosphere of 100,000 ppm of sulfide gas for five (5) days to assure reaction was complete, i.e., all particles were coated with sulfide. The exposed cloth was then weighed to measure the amount of sulfide adsorbed onto the treated cloth. This measurement was then compared to the original weight of the particles to determine the percent increase in weight due to sulfide adsorption. The percent increase represents the percentage of its total weight that the compounds of the present invention absorbed. Results of Examples 6 to 9 are tabulated below in Table 5.
This example provides the useful life of a jewelry chest lined with a treated cloth based on a baseline concentration of sulfide gas in the atmosphere of 1 ppb using the amount of sulfide gas that may be successfully scavenged as determined in Examples 6, 8 and 9.
Dimensions of a conventional jewelry chest are approximated at 32 cm long, 20 cm wide and 15 cm high, for a volume of 9600 cm3 or approximately 10 liters. Assuming the jewelry box is opened 400 times a year (at least twice a day) and all of the air in the box is exchanged during opening of the box, the air in the chest is expected to change by about 8000 liters per year or 20 liters per day.
For the purposes of this example, the ambient concentration of sulfide gas is 1 ppb under standard conditions of temperature and pressure (20° C. and 760 mmHg). Accordingly, 1 liter of air weighs 1.3 grams and includes 1.3×10−9 grams of sulfide. Based on the aforementioned assumptions, the useful lifetime of a conventional jewelry chest is calculated as that number of times that the jewelry chest may be opened and still possess particles available for absorption of corrosive gases. The results of Example 10 are tabulated below in Table 6.
It is clear from the results in Table 6 that the adsorption of corrosive gas is increased as surface area of particles increases. Furthermore, a jewelry chest lined with cloth treated with compositions of the invention can be expected to last indefinitely. This represents a great improvement over currently available tarnish resistant compositions and articles using same.
Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to be limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.
