Process and reaction solution for producing a patina

Details Process and reaction solution for producing a patina Process and reaction solution for producing a patina

1999-03-05

2001-01-23

Klemanski, Helene (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Metal-depositing composition or substrate-sensitizing...

C106S031060, C106S031950, C427S256000, C427S123000, C427S282000, C427S307000, C427S328000, C427S349000, C427S383100, C427S405000

Reexamination Certificate

active

06176905

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and a reaction solution for producing a patina on surfaces of objects made of copper or a copper alloy.
2. Description of Related Art
When exposed to air, copper surfaces develop a thin green protective layer of basic copper compounds. This protective layer is called patina. It can sometimes take several decades for natural patina to form, depending on the environmental influences. To imitate this natural patina, which often only forms over long periods of time, one uses artificial patination, for example, by applying soluble copper salts or ammonium salts. In the case of imitated patina, basic copper compounds are applied as colored pigments having organic or inorganic film formers to a copper surface.
However, the known reaction solutions do not always have the desired effect as far as layer quality and coloration are concerned. It is also sometimes costly to handle and store these reaction solutions. Therefore, their suitability is limited for industrial production of a patina at the factory or for use at a construction site. Also, when some of these reaction solutions are used on pre-oxidized or partially already patinated copper surfaces, for example, to repair damaged patina, there is the risk of irregular layer formation or coloration.
SUMMARY OF THE INVENTION
It is an object of the present invention to devise a process for producing a mechanically stable patina on preferably pre-weathered copper surfaces, the produced patina exhibiting a reduced copper solubility, and being able to interact with the atmosphere, as is the case with natural patina. It is a further object of the present invention to achieve an improved reaction solution for producing a patina on copper surfaces, which will also be easier to handle and store.
These and other objects of the invention are achieved by a process for producing a patina on a surface of an object made of copper or a copper alloy, comprising the steps of cleaning the surface and thereafter applying to the surface a reaction solution containing an aqueous solution of copper salts and salts of inorganic acids. The surface is then allowed to dry while being protected from atmospheric influences. The invention also provides a reaction solution for producing a patina on a surface of an object made of copper or a copper alloy, the reaction solution comprising an aqueous solution of a copper salt and a salt of an inorganic acid.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, a reaction solution containing an aqueous solution of copper salts and salts of inorganic acids is applied to the surface of a copper object after the surface is cleaned. The copper object, treated in this manner, is then allowed to dry, while being protected from the effects of the environment.
The drying is usually an air-drying, which is continued until the patina has fully hardened. The patina produced according to this process is mechanically stable and exhibits only a low copper solubility. The time required for producing the patina is comparatively short.
Preferably, the produced patina is provided with a transparent protective coat of varnish. For this purpose, a two-component water-base varnish containing rubber is preferably used. The varnish is colorless. Prior to the application, the varnish is prepared with a hardener. The ratio of hardener to varnish is usually 1:4. Preparation time is maximally 20 minutes. The ready-mixed varnish is then applied to the patina, preferably using a spraying device. After the drying phase, the varnish is fully cured and can be exposed to weathering. Depending on the prevailing environmental conditions (temperature, air humidity, etc.), the drying phase can take 15 to 24 hours.
The varnish coat applied in accordance with the present invention has the following properties and advantages, in particular:
The varnish coat is transparent and mat. It does not change the optical properties of the underlying patina.
The varnish coat can be treated with cleaning solutions. Accordingly, any stains, such as sprayed-on graffiti, can be removed by using special cleaning solutions without leaving any residues and without damaging the patina.
The varnish coat allows water vapor to penetrate by diffusion. This permits the underlying patina to continue to interact with the atmosphere.
The varnish coat has a strengthening effect on the underlying patina surface. As a result, the patinated copper objects can be mechanically worked [shaped], e.g., bent or folded, without causing the patina to flake off.
In another embodiment, the invention is a reaction solution containing an aqueous solution of copper salts and salts of inorganic acids. The reaction solution produces a patina on surfaces of objects made of copper or a copper alloy.
The reaction solution according to the present invention combines two different principles to produce patina. On the one hand, the reaction solution contains reactive components in the form of salts of inorganic acids, which react with the copper oxides of the patinated surfaces to form basic copper compounds. The rate of this reaction step depends on the weathering conditions. Furthermore, the solution already contains the copper compounds, which are produced in these reactions, in the form of copper salts as a kind of colored pigments. For this reason, a very good color perception is already achieved immediately upon application. The natural patina, which otherwise often forms only over long periods of time, is imitated in a short period of time. The subsequent chemical reaction intensifies the color perception and strengthens the entire patina layer.
Best results are achieved with the reaction solution according to the present invention when it is applied to a pre-oxidized or partially already patinated copper surface. For this reason, the surfaces of the copper objects should be pretreated accordingly. The copper surface can be pre-oxidized or pre-patinated at the factory. However, it is also possible for the copper surface to have a patina layer that has naturally formed by weathering. A copper surface, which has not been pretreated, should be exposed to natural weathering for approximately two months or longer.
Following a surface pretreatment of this kind, the treatment using the reaction solution according to the present invention can be carried out.
By applying the reaction solution to a pre-oxidized or partially already patinated copper surface, it is possible to produce the patina, either on the spot or at the factory. Copper surfaces, which are not completely green-patinated, or damaged patina layers, also obtain a uniform patina layer by applying the reaction solution according to the present invention. Depending on the composition of the reaction solution, one can vary the coloring of the patina to be produced, and otherwise adapt it to the particular surroundings.
The reaction solution according to the present invention is characterized by simple processing and handling. The application to the copper surfaces can be carried out using a brush, roller or spraying device.
The reaction solution can be stored at ambient temperature over a long period of several months without detrimental ageing effects.
Copper salts, which are well-suited for use in the aqueous reaction solution, are copper(I) carbonate, copper(II) carbonate, copper(I) chloride, copper(II) chloride, copper(II) sulphate, copper acetate, copper nitrate or mixtures thereof. Advantageous concentrations range from 5 to 500 g/l.
Preferably used reactive components are sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, sodium chloride, potassium chloride, ammonium chloride, sodium sulphate, sodium hydrogensulphate, potassium sulphate, potassium hydrogensulphate, or mixtures thereof. The concentrations of these salts of inorganic acids also range preferably from 5 to 500 g/l.
The reaction solution according to the present invention can be changed in its

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