US 3503883 A
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United States Patent US. Cl. 25289 6 Claims ABSTRACT OF THE DISCLOSURE Surfaces of silver, copper and nickel and alloys thereof are protected against tarnish by application of a silver cleaning and/or polishing protective preparation containing a dialkyl disulphide of the formula RSSR, wherein R is an alkyl group having from 8 to 22 carbon atoms. The preparation may be, inter alia, in liquid, paste, cream, dip or solid formor, can be applied to the surface to be protected by impregnating a suitable material such as cloth with the preparation and then wiping the surface with the cloth. The amount of dialkyl disulphide ranges from 0.1% to by weight; amounts as low as 0.5 by weight have been found to be particularly advantageous. The cleaning and/or polishing preparation can contain any of the usual ingredients including descaling, etching, abrasive and polishing agents.
This application is a continuation-in-part of our copending application Ser. No. 481,071, filed Aug. 19, 1965, now abandoned.
The present invention is concerned with protecting noble and coinage metals against disfiguration through the action of the atmosphere. In particular, the present invention comprises preparations which provide long term protection for silver, copper and nickel surfaces against tarnish. We have discovered that the incorporation of a dialkyl disulphide of the formula RSSR, wherein R is an alkyl group having from 8 to 22 carbon atoms in the alkyl chain as a protective medium in any known silver, copper or nickel cleaning and/or polishing preparation provides a high degree of protection to the surface against tarnish. These preparations which can be prepared, inter alia, in liquid, cream, paste, dip and solid form, may also include descaling, etching, abrasive and polishing agents. The dialkyl disulphide may also be applied to the surface to be protected by impregnating a cloth or other suitable material with the preparation and then using the cloth to wipe the surface. Particularly effective results have been achieved when the alkyl group has 12 or more carbon atoms.
United States Patent No. 2,841,501 granted to James G. Murphy, dated July 1, 1958, and re-issued under No. 24,819 one May 3, 1960, describes silver polishes comprising abrasive, powdery material capable of polishing silver together with an anti-tarnish component which is an n-alkane-l-thiol, the alkane being a C1240 straight chain radical.
Our own co-pending United States patent application Ser. No. 377,391, filed June 19, 1964, describes similar polish preparations and protective solutions but which contain as the protective ingredient or medium an ester of a mercapto carboxylic acid with a long chain alkyl group.
It is also known in the art to use short chain dialkyl disulphides as corrosion inhibitors in water systems and for other purposes but there is nothing to suggest any protective property for silver, copper or nickel surfaces against the atmosphere.
According to the present invention application of a dialkyl disulphide of the formula RSSR, wherein R is an alkyl group having from 8 to 22 carbon atoms in the alkyl chain as a protective medium to a silver, copper or nickel surface to be protected, provides tarnish protection over a prolonged period.
Most conveniently, the dialkyl disulphide is applied to the surface by application of a cleaning and/ or polishing preparation containing 0.1% to 50% by weight of the dialkyl disulphide. 0.5% has been found to be an effective amount. Any of the known ingredients presently incorporated in such preparations such as pickling, descaling, etching, abrasive, brightening and polish agents may also be present. In an alternate embodiment, a cloth is impregnated With a cleaning and/or polishing preparation containing the dialkyl disulphide and then the surface to be protected is wiped with the cloth. The preparations of the present invention and the impregnated cloths have been found to be particularly effective in protecting silver surfaces against tarnish.
Among all the many organic sulphur containing compounds which have an afiinity for silver it is surprising that these dialkyl disulphides should be capable of providing an invisible, transparent, colorless layer which protects surfaces against tarnish and is sufliciently robust to withstand the polishing action of an abrasive. A long chain mercaptan introduced into an alcoholic solution of silver nitrate gives a heavy yellow precipitate. Similarly a long chain ester of a mercapto carboxylic acid gives a light white precipitate. With a long chain dialkyl disulphide there is no precipitate at all. Thus it would appear that the dialkyl disulphide behaves quite differently from the other compounds and forms no chemical bond with the silver. The contrary is in fact the case as has been found according to the present invention. The protective effect which is most notable on pure silver surfaces and silver alloy surfaces, sterling, Britannia silver or the like, also occurs to a certain extent on surfaces of copper .or nickel rich in these metals.
Commercially available mercaptans have a most unpleasant smell which makes them domestically unacceptable without a strong disguising odor such as Wintergreen. Mercaptans are much less stable than dialkyl disulphides having a corresponding number of carbon atoms in the alkyl chain and consequently are more toxic both before and after use. Metal ware cleaned with preparations according to the invention and according to the prior art often retains on the surface a small amount of the polishing preparation. Such ware may be cutlery or a teapot which may come into contact with food-stuffs. The instability of a mercaptan and the extended shelf-life of silver cleaning preparations containing it means that in order to have an active proportion of mercaptan in the preparation when the container is almost exhausted, it is necessary to use a comparatively high proportion in the original preparation. The lowest elfective proportion in an ordinary silver polish is 0.2%. Thus owing to the instability of the mercaptan the polish as manufactured has to contain 2%. With a dialkyl disulphide it is possible to use as little as 0.5%, which provides a substantial economic advantage. A similar advantage is obtainable in connection with the other kinds of protective preparations described herein.
Exemplary kinds of polish preparations which are suitable for carrying the dialkyl disulphide are liquid polishing preparations, polishing pastes or creams, emulsion polishes, and solvent based polishes, as well as polishing powder, polishing powder impregnated cloths, and solid polishes in block form. Metal protective solutions com- Polishing Protective medium, medium,
Kind of composition percent percent Other main ingredient Liquid polish 5-50 01-20 180% alcohol.
Polish paste, 10-70 0. 1-20 150% detergent. Emulsion polish 5-50 1-20 5-00% hydrocarbon. Solvent based p 5-50 0 1-20 30-90% hydrocarbon. Polishing powder. 50-99 1-50 Liquid preparation 0 1-50 50-99.9% alcohol.
Dip soluti0n 0. 1-50 01-40% emulsifien Dip solutiom. 0. 1-50 50-99.9% solvent. Solid pOllSll -80 0. 1-20 10-60% higher fatty acid.
1 Balance largely water.
In order to make up a preparation according to the invention the dialkyl disulphide protective medium may simply be mixed with the polishing medium but is generally melted and then added to an alcohol. The resulting mixture can then be incorporated with the other intended ingredients of the preparation. For the preparation of a polish, the polishing medium is added to the alcohol solution and stirred in vigorously to give a viscous mixture. If a liquid polish is to be produced water is then added in small additions possibly with more polishing powder and stirring. A surface active agent may be added if desired to improve the covering power of the material.
The exact number of carbon atoms in the long chain alkyl groups in protective media used according to the invention does not greatly vary the protective properties so long as there are at least 8 carbon atoms and preferably at least 14 or 16 carbon atoms in the alkyl chain. Short chain dialkyl disulphides may actually hasten the tarnish of a silver surface in the atmosphere. While 22 carbon atom chains have been indicated as the practical upper range, effective protection is provided by long chain dialkyl disulphides and chains in excess of 22 can also be utilized. The selection of any particular chain length is made on the basis of considerations such as price and commercial availability, as the protective effectiveness of the long chain compounds varies only slightly. Distearyl, dipalmityl (dihexadecyl) disulphides have been found to be particularly effective.
The following examples illustrate the invention; the proportions of the constituents being by weight.
EXAMPLE 1 A liquid polishing preparation suitable for use on surfaces containing silver, copper or nickel contains the following substances in admixture:
Percent Polishing powder: diatomaceous earth Ethyl alcohol 20 Distearyl disulphide 0.5
Water up to 100%.
In making up this preparation the distearyl disulphide is melted and is then added to the alcohol. Sufiicient of the polishing powder is then added with vigorous stirring until a fairly viscous mixture is obtained. Stirring is continued with a high shear action, some water is added, and then alternate additions of polishing powder and water are made until the mixture is complete. The resultant mixture has a dispersion of disulphide on the surface of the polishing powder which is in turn homogeneously dispersed in the aqueous alcoholic liquid.
To improve the stability of the suspension, bentonite A may be incorporated in the proportion of about 2 to 4% by forming a gel with part of the water. This gel may be added to the viscous mixture aforesaid before the addition of water thereto.
EXAMPLE 2 A polishing paste for metal surfaces as aforesaid is made up as follows:
Percent Polishing powder 20 Detergent paste 40 Dipalmityl disulphide 0.5
Water up to In preparing the paste the disulphide is first warmed with an equal weight of detergent paste and the resulting liquid is added to the dry ingredients whilst being stirred. The formation of the stiff paste ensures homogenising of the final product. Afterwards the liquid content is added slowly while the mixture is stirred.
EXAMPLE 3 An emulsion for metal surfaces as aforesaid is made up from the following ingredients:
Parts Dimyristyl disulphide 1 Hydrocarbon solvent 30 Anionic surfactant: sodium alkyl benzene sulphonate 8 Diatomaceous earth 15 Water 46 The emulsion polish is prepared substantially as in the Example '1 above.
EXAMPLE 4 A solvent based paste polish (as opposed to a water based paste polish such as in Example 2) is made up from the following ingredients:
Percent Distearyl disulphide 1 Diatomaceous earth 15 Alcohol 4 Hydrocarbon solvent 68 Gelling agent 12 The disulphide is dissolved in the hydrocarbon solvent together with the gelling agent and thoroughly mixed. The alcohol is then added and homogeneously mixed. Finally the diatomaceous earth is stirred into the mixture.
EXAMPLE 5 A cleaning and polishing powder for use on metal surfaces as aforesaid comprises the following:
Grams Polishing powder: kieselguhr 98 Distearyl disulphide 62 These constituents are thoroughly blended by grinding.
The resulting preparation may be used as such or may be incorporated into a suitable polishing cloth or braid, for example.
EXAMPLE 6 preparation suitable for treating metal surfaces as above mentioned by immersion therein or for adding in a small proportion to various kinds of baths as in Example 6 is made up of the following constituents:
Parts Distearyl disulphide 3 Ethoxylated fatty alcohol (fatty alcohol/ ethylene oxide condensate) 3 Water 94 EXAMPLE 8 A dipping solution of organic solvent type suitable for usein similar manner to Examples 6 and 7 is prepared by dissolving distearyl disulphide in a hydrocarbon solvent in the proportion of 2% distearyl disulphide to 98% solvent.
EXAMPLE 9 A solid polishing composition suitable for mechanical application comprises the following:
Parts Higher fatty acid (stearic acid) 19 Microcrystalline wax 8 Triethanolamine 1 Polishing powder: Tripoli powder 80 Dilauryl disulphide 12 3. A preparation according to claim 1, wherein the dialkyl disulphide is distearyl disulphide.
4. A new article of manufacture for use on surfaces of silver, copper, nickel, or alloys thereof to prevent tarnish which comprises a cloth material impregnated with a preparation containing as the essential active ingredient from 0.1% to by weight of a dialkyl disulphide of the formula RSSR, wherein R is alkyl of 8 to 22 carbon atoms.
5. A prepartion according to claim 1, wherein R is alkyl of 12 to 22 carbon atoms.
6. A method of providing prolonged protection against tarnishing to surfaces of silver, copper, nickel or alloys thereof which comprises applying to such surfaces a dialkyl disulphide of the formula RSSR, wherein R is alkyl having 8 to 22 carbon atoms in an amount sufficient to inhibit tarnish.
References Cited UNITED STATES PATENTS 3,352,695 11/1967 Iaciofano 1065 2,326,837 2/1943 Coleman 252142 2,841,501 7/1958 Murphy 106--3 3,062,612 11/1962 Boucher 21--2.5 3,248,235 4/1966 Pryor et a1. 106-3 LEON D. ROSDOL, Primary Examiner W. SCHULZ, Assistant Examiner U.S. Cl. X.R.