Compositions: coating or plastic – Coating or plastic compositions – Polishes
Patent
1983-11-09
1985-12-31
Hayes, Lorenzo B.
Compositions: coating or plastic
Coating or plastic compositions
Polishes
252101, 252102, 252142, 252541, C09G 118
Patent
active
045618950
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a non-abrasive metal polish or cleaning agent for objects, particularly for cleaning and shining household objects and ornaments, which objects have surfaces of copper, silver or chromium or of any alloy which is comprised predominantly of any of these metals, either separately or together.
Objects which have copper, silver or chromium surfaces and which are exposed to contaminated air, for example air in large built-up areas or industrial areas, or in the vicinity of such areas, quickly become coated with a discoloring film of various reaction products. At first, this film dulls the surfaces of the objects, and then changes their color to a darker hue.
It has long been usual to polish household objects having copper and silver surfaces and also different chromium-coated objects, with one abrasive-containing polish or the other, the discoloring film being worn away to a greater or lesser extent, often together with a relatively substantial layer of the actual surface metal. In addition to an abrasive, these polishes often contain dissolving agents, such as ammonia water or carboxylic acid. For example, SE-C-167770 describes a polish or cleaning agent in paste form in which the dissolving agent is sulphuric acid and which also contains a thiourine substance, which is said to act as a reductant which facilitates removal of oxide films. In SE-C-196019 there is described a polish in which the dissolving agent used is carbonic acid. This gives the polish a better effect, especially on silver surfaces, which grow dull when using polishes based on sulphuric acid. One serious disadvantage with carbonic-acid based polishes, is that the metal surfaces must be rubbed vigourously, particularly in the case of heavily tarnished surfaces.
In recent years polishes of the aforementioned kind have been proposed which lack any form of abrasive and which, in liquid form, are applied to the metal surfaces and there left for a certain length of time, whereafter the polish is rinsed from the surfaces with water, optionally together with a detergent. One such liquid polish, which is based on phosphoric acid, is today sold for polishing silver surfaces. According to the treatment prescribed, the silver surfaces are first immersed in the polish solution, and then removed and rinsed. One disadvantage with this polish is that if highly polished, relatively resistant surfaces are desired, it is restricted to silver surfaces. Another, more serious disadvantage is that the length of time over which the object is immersed is critical, since excessive immersion times have negative secondary effects, which mainly manifest themselves in the form of irregular surface finishes. By polish is meant in this case a shine-improving agent requiring no abrasive. Another commercially available polish of this kind, intended for copper, is based on oxalic acid in combination with a detergent. This polish has a limited use, and can only be used satisfactorily on copper surfaces which are only slightly discolored.
It has now been found to produce a metal cleaning agent which is capable of producing highly polished surfaces while escaping the disadvantages and limitations associated with known polishes of this kind. The invention is based on the surprising synergistic effect obtained when the dissolving agent used in the cleaning agent or polish is nitric acid and when an inhibiting component of thiourea thereof is present at the same time, in a weight surplus relative to the acid. The polish according to the invention is characterized in that it comprises an aqueous solution containing 1-3% by weight nitric acid and 5-10% by weight of thiourea or a derivative thereof. The amount of nitric acid above is calculated as 100% HNO.sub.3, and hence the amount of nitric acid charged must be adapted to the concentration of the acid. Thus, in order to obtain the desired concentration, 20 ml of concentrated nitric acid must be added to 1000 ml of water.
At nitric acid concentrations beneath about 1% by weight, the dissolving effect
REFERENCES:
patent: 2132511 (1938-10-01), Hentrich et al.
patent: 3196113 (1965-07-01), Ponchel
patent: 3228816 (1966-01-01), Kendall
patent: 4397753 (1983-08-01), Czaja
Hayes Lorenzo B.
Ljungman Nils H.
Yarbrough Amelia B.
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