Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2000-06-30
2001-11-27
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S282000, C216S105000
Reexamination Certificate
active
06322636
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of artificially forming patina on copper products, and more particularly to a method of artificially and rapidly forming uniform patina on copper product surfaces without causing environmental problems.
Patina formed on the surfaces of copper products advantageously prevents oxidization and corrosion of copper products and inhibits mold from growing on their surfaces. Another advantage of patina formed on the surfaces of copper products is decorative coloring, improving the appearance of copper products. Such advantages are appreciated in various copper works in fine arts, industrial arts, sculptures, monuments, architectures (particularly roofs and decorations) and the like having patina uniformly formed on their surfaces. Patina has also lately been used for various researches such as the creation of aseptic conditions by patina, medical applications of patina, hygienic applications of patina such as utilization of antibacterial effects, the influence of patina on plants and animals, etc.
Conventionally known as the artificial formation of patina on copper surfaces are electrolytic methods and acid application methods. In the electrolytic methods as exemplified in Japanese Patent Laid-Open No. 64-4493, a copper anode is eroded in an electrolytic solution, an electrolytic reaction causing patination on the surface of the copper anode. The electrolytic methods are, however, encountered with such problems that they are not suitable for or cannot be applied to large-scale copper products, particularly outdoor constructions such as monuments and architectures because it is difficult to process such copper products in an electrolytic solution.
In the acid application methods as exemplified in Japanese Patent Laid-Open No. 62-99547, an artificial patination solution composed mainly of hydrochloric acid and acetic acid is applied to copper products to cause patination. In these methods, however, the operations tend to be dangerous for workers, involving risks of generating acid gases detrimental to the environment. Furthermore, for processing copper products such as bronze statutes and architectures of temples and shrines often designated as cultural assets, the acid application methods cannot be used because acids may damage copper products.
For the above-mentioned reasons, neither the electrolytic methods nor the acid application methods can be used in processing outdoor constructions and large-scale copper products.
It is, thus, an object of the present invention to provide a method of artificially and rapid forming uniform patina on surfaces of copper products such as outdoor constructions and large-scale copper products without causing environmental problems.
SUMMARY OF THE INVENTION
As a result of intense research in view of the above object, the inventor has found that by blowing sodium hydrogen carbonate powder onto a surface of a copper product to remove rust and other deposits therefrom while finely roughening the surface so that copper ion is easily dissolved away from the copper surface; and by sprinkling sodium hydrogen carbonate powder onto the surface of the copper surface after wet with water spray, thereby causing sodium hydrogen carbonate powder to deposit thereon, copper ion generated from the surface of the copper product is subjected to reaction to form patina thereon; and that by repeating the steps of wetting the copper product surface with water spray and sprinkling sodium hydrogen carbonate powder thereto, the more rapid and uniform patination can be achieved. The present invention has been completed based on these findings.
Therefore, the method of artificially forming patina on a surface of a copper product according to the present invention comprises the steps of blowing or blasting sodium hydrogen carbonate powder onto a surface of a copper product to clean and finely roughen the surface of the copper product; wetting the surface of the copper product with water, and sprinkling sodium hydrogen carbonate powder onto a wet surface of the copper product.
It is preferable to use granular sodium hydrogen carbonate powder having an average particle diameter raging from 10 &mgr;m to 300 &mgr;m and having a Mohs hardness of about 2.5. Following the step of roughening the surface of the copper product, the step of wetting the surface with water spray and the step of sprinkling sodium hydrogen carbonate powder onto the wet surface of the copper product are preferably repeated a plurality of times to rapidly achieve uniform patination. The copper surface wet with a sodium hydrogen carbonate aqueous solution is preferably covered with a porous sheet such as paper, woven fabrics or non-woven fabrics to ensure uniform patination.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[1] Sodium Hydrogen Carbonate Powder
Sodium hydrogen carbonate powder to be blown onto a surface of a copper product is required to have 1) a particle diameter enabling the sodium hydrogen carbonate particles to collide with the copper surface at a proper speed and (2) a hardness enabling the particles to roughen the copper surface finely. It is, therefore, preferable to use sodium hydrogen carbonate powder in the form of granules of agglomerated sodium hydrogen carbonate fine particles, granules having comparatively large size and porosity, such that the granules can be partially destroyed when colliding with the copper surface.
The sodium hydrogen carbonate powder in the form of granules preferably has an average particle diameter of 10-300 &mgr;m. When the granular sodium hydrogen carbonate powder has an average particle diameter of smaller than 10 &mgr;m, it is too light in weight, whereby it is likely that the granular hydrogen carbonate powder blown with the compressed air does not collide with the copper surface at a sufficient speed and may be scattered before colliding with the copper surface. With such insufficient collision speed and energy, oxides, deposits, mold, etc. will not be sufficiently removed from the surface of the copper product, while failing to roughen the surface finely enough. On the other hand, the granular sodium hydrogen carbonate powder particle having a diameter of larger than 300 &mgr;m will not be blown uniformly onto the surface of the copper product, resulting in likelihood of excessive roughening or damaging of the surface. A more preferable average particle diameter of the granular sodium hydrogen carbonate powder is in the range of 50-150 &mgr;m, and further preferably 75-100 &mgr;m.
The hardness of the granular sodium hydrogen carbonate powder is preferably about 2.5 in Mohs hardness. The sodium hydrogen carbonate powder in the form of granules having a Mohs hardness of much smaller than 2.5 will be finely destroyed into pieces on collision with the surface of the copper product, resulting in failure to remove oxides and other deposits from the surface of the copper product and to roughen the surface finely. The granular sodium hydrogen carbonate powder having a Mohs hardness of much lager than 2.5, on the other hand, will cause damage on the surface of the copper product. The permissible range of the Mohs hardness of the granular sodium hydrogen carbonate powder is 2-3.
[2] Blowing Sodium Hydrogen Carbonate Powder
To blow or blast granular sodium hydrogen carbonate powder onto the surface of the copper product, it is preferable to introduce the powder into a flow of compressed air and blow the powder-including compressed air through a nozzle of a blowing device. To blow granular sodium hydrogen carbonate powder, a dry process or a wet process may be employed.
In the dry process, only compressed air is used for blowing granular sodium hydrogen carbonate powder without using water. Employing this process, the energy of the granular sodium hydrogen carbonate powder colliding with the surface of the copper product can be the largest, thereby achieving fine roughening of the surface effectively. Because the blown granular sodium hydrogen carbonate powder is scattered a
Browdy and Neimark
Oltmans Andrew L.
Sheehan John
The Hiraoka Environmental Science Laboratory
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