Note: Descriptions are shown in the official language in which they were submitted.
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Description
Method for covering copper with patina
[0001] The invention relates to a process for producing a patina on
articles comprising copper or copper alloys and a patination solution
used in this process.
[0002] It is generally known that a greenish layer having, inter alia, a
protective function is formed on the surface of copper parts when they
are exposed to weathering for a long time. This layer is referred to as
copper patina. At our latitudes, it normally takes from ten to fifteen years
for a copper surface to be coated completely with the green layer.
Various methods of shortening this long period of time have been
developed in the past with the objective of imitating or readily producing
a natural patina on copper surfaces.
[0003] Thus, for example, US-3,497,401-A discloses a process and a
reaction solution for producing a patina. Here, a copper part is dipped
into an acidic, aqueous solution comprising potassium chlorate and
copper sulfate at room temperature. US-5,160,381-A, too, describes the
production of a patina on a copper article. In the multistage process
described there, the copper part to be patinated is, after cleaning,
treated with an aqueous solution containing copper, sodium, acetate,
.chloride, sulfate, Hi' and OH- ions. After careful cleaning and drying, the
copper piece is treated in a second process step with an aqueous
solution of copper carbonate, ammonium chloride, copper acetate,
arsenic trioxide, copper nitrate and hydrochloric acid. EP 0 943 701 Al
also concerns the production of a patina, once again by treatment of a
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copper article with an aqueous copper salt solution. This process is
particularly suitable for preoxidized copper surfaces.
[0004] However, the known processes have a number of disadvantages.
Thus, components which are toxic and harmful to health, e.g. the
abovementioned arsenic trioxide, are used in the preparation of some
known patination solutions. For reasons of environmental protection and
for health reasons, it Is desirable to avoid the use of such. constituents.
Other processes have limited applicability. Thus, some processes are
generally less well suited to the patination of untreated copper surfaces,
since they require preoxidation of the copper parts to be patinated.
[0005] In terms of the quality properties, too, both with regard to optical
aspects and with regard to mechanical aspects, many synthetically
produced patina layers display deficiencies. They often have
unsatisfactory adhesion properties, i.e. the artificial protective layer
flakes off even under light mechanical stress.
[0006] It is therefore an object of the invention to provide a process
which avoids the disadvantages of the prior art and solves as many as
possible of the problems indicated.
[0007] It is another object of the invention to provide a process for
patinating articles comprising copper or a copper alloy by means of an
aqueous patination solution containing copper ions, wherein the article is
treated with the patination solution, characterized in that the article which
has been treated in this way is subjected to a maturing process in a
temperature- and humidity-controlled chamber, the maturing process
encompassing the maturing steps
- allowing the treated article to rest at a first rest temperature in the
range from 20 C to 70 C and a first rest atmospheric humidity in the range
from 30% to 90% for a first rest time up to one week
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irrigating the treated article at least once at an irrigation
temperature in the range from 20 C to 70 C and an irrigation atmospheric
humidity in the range from 30% to 95% for an irrigation time up to one day,
and
- allowing the treated article to rest at a second rest temperature in
the range from 20 C to 70 C and a second rest atmospheric humidity in
the range from 30% to 90% for a second rest time up to one week,
wherein the patination solution contains at least one zinc salt.
It is another object of the invention to provide a patinated article
comprising copper or a copper alloy produced by a process as defined
herein.
[0008] In the process of the invention, articles comprising copper or a
copper alloy are treated with a preferably aqueous patination solution
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containing copper ions and subsequently subjected to a maturing
process.
[0009] The maturing process is made up of individual maturing steps
which encompass a choice of atmospheric humidities and temperatures.
The setting and control of the two parameters temperature and
atmospheric humidity can, in particular, readily be carried out in a
temperature- and humidity-controlled chamber provided for this purpose.
[0010] A preferred sequence of maturing steps can be summarized as
follows: the treatment of the article with the patination solution, in
particular the application of the patination solution to the article to be
patinated, is followed by the article being allowed to rest at a first rest
temperature and a first rest atmospheric humidity for a first rest time.
The article is then irrigated at least once at an irrigation temperature and
an irrigation atmospheric humidity for an irrigation time, again followed
by the article being allowed to rest at a second rest temperature and a
second rest atmospheric humidity for a second rest time.
[0011] During the first resting step, the temperature in, in particular, the
temperature- and humidity-controlled chamber is preferably in the range
from 20 C to 70 C, in particular from 25 C to 55 C (first rest
temperature). The atmospheric humidity is preferably in the range from
30% to 90%, in particular from 40% to 50% (first rest atmospheric
humidity). These preferred ranges for temperature and atmospheric
humidity indicated for the first resting phase correspond essentially to
the preferred ranges for the second rest temperature and the second
rest atmospheric humidity.
[0012] During the irrigation step, the temperature in the temperature-
and humidity-controlled chamber is preferably in the range from 20 C to
70 C, in particular from 25 C to 55 C. The atmospheric humidity during
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the irrigation step is preferably maintained 'in the range from 30% to
95%, in particular in the range from 65% to 80%. Irrigation is usually
effected by spraying the treated article with water. This step is preferably
repeated from four to five times at intervals of from 90 minutes to
2 hours.
[0013] The first rest time can be up to one week, but preference is given
to a period of from two to three days. The same applies to the second
rest time. The irrigation time is usually not more than one day, but can
be as short as from 5 to 10 hours.
[0014] As mentioned above, the patination solution used is a solution
containing copper ions whose preferred composition will be described in
more detail below. Furthermore, it should be emphasized that it is
particularly preferred that the article to be patinated is cleaned and/or
has its surface roughened before application of the patination solution.
Any grease or oil residues and other contaminants present on the
surface can have an adverse effect on the adhesion of the patina
formed. This is countered, in particular, by chemical degreasing and/or
blasting of the surface to be patinated with broken glass spheres. As an
alternative, it is also possible to use, for example, an eccentric grinder or
a belt grinder.
[0015] The article to be patinated is, if appropriate after an optional
25, pretreatment of the type indicated, subjected to the maturing process,
preferably by transferring it to the previously mentioned temperature-
and humidity-controlled chamber. It is not absolutely necessary, but
preferred, for the app)ication of the patination solution to be carried out in
the chamber.
[0016] The patination solution is preferably applied in finely divided form,
particularly preferably sprayed on. The temperature (preferably in the
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temperature- and humidity-controlled chamber) is preferably in the range
from 30 C to 70 C, in particular from 40 C to 55 C, during this
application. The patination solution is usually applied in at least two,
preferably in four or five, treatment steps, in particular at intervals of
about 1 hour.
[0017] It has surprisingly been found that, in contrast to classical
processes for the patination of copper parts which consist essentially of
a single or multiple treatment with an aqueous copper salt solution and a
subsequent air drying step, the use of a maturing process, in particular
in a temperature- and humidity-controlled chamber, offers' great
advantages, in particular in respect of the optics and the quality of the
patina produced. The artificial patina formed gives a uniform and
intensive color impression.
[0018] An after-treatment of the freshly patinated surface can optionally
be carried out. It is possible either to lighten or darken the surface. If
appropriate, the surface can also be sealed since the unsealed patina
can sometimes react further under natural weathering influences.
[0019] The process indicated is preferably provided for the patination of
copper plates, strips or shingles. However, it can in principle also be
applied to all shaped parts or articles comprising copper or copper
alloys. Partial patinations of shaped parts such as roof guttering are also
.25 possible. Thus., for example, in the case of roof guttering the bead
region
can be strongly patinated while the outside of the water channel is only
oxidized. This results in the visual impression that the copper piece has
been exposed to atmospheric influences for years and decades. Such
effects are frequently used in the optical structuring of new buildings, but
in particular in the restoration or repair of relatively old listed buildings
in
order to obtain the overall historic impression.
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[0020) Further features possessed by the patina produced by the
process of the invention are a good resistance to mechanical stress and
excellent adhesion properties.
[0021] These positive properties can also be attributed to the patination
solution which is preferably used and is likewise subject matter of the
present invention. It consists of an aqueous solution in which a copper
salt, preferably copper nitrate, is present in a proportion of up to 20% by
weight, in particular in a proportion of from 3% by weight to 5% by
weight. It is preferred that a zinc salt, in particular zinc chloride, is
additionally present in the solution, preferably in a proportion of from
0.1% by weight to 5% by weight, in particular in a proportion of from
0.2% by weight to I% by weight. Furthermore, the solution can contain
various chloride and carbonate additives, In particular sodium chloride,
ammonium chloride, calcium chloride and ammonium carbonate. The pH
of the patination solution is preferably in the basic range, in particular in
the slightly basic range of pH 7 - 10.
[0022] Among the components present in the patination solution of the
invention, the zinc salt desires particular emphasis. It has surprisingly
been found that the addition of zinc salts has a positive effect on the
adhesion properties of the patina formed. In addition, such an addition
results in a lighter greenish appearance.
[0023] Finally, the invention encompasses the patinated article comprising
copper or a copper alloy itself. After conclusion of the maturing process, the
article is coated with a green-turquoise patina containing copper ions and
preferably also zinc ions. The patina usually has a thickness of from 0.02
mm to 0.06 mm, in particular from 0.03 mm to 0.05 mm.
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[0024] Further features of the invention can be derived from the following
examples. Here, the features and properties presented can in each case
either be realized alone or in a combination of a plurality thereof.
Example
[0025] To produce the patination solution, the following components are
dissolved in one liter of water:
40 g of copper(II) nitrate
_ 3 g of zinc chloride
8 g of calcium chloride
2 g of sodium chloride
- 20 g of ammonium chloride
[0026] The temperature- and humidity-controlled chamber has a base
area of about 3 x 2.5 M. A copper sheet whose surface has been
thoroughly ground by means of an eccentric grinder and is free of
grease and other contaminants is placed in the temperature- and
humidity-controlled chamber. The temperature in the temperature- and
humidity-controlled chamber is set to 50 C. At this temperature, the
patination solution is sprayed four times at intervals of in each case
one hour onto the surface of the copper piece. During the subsequent
first rest time, the temperature is maintained at about 45 C. The
atmospheric humidity is regulated to about 45%. After allowing the
copper sheet to rest for three days, the treated copper part is irrigated a
number of times. It is sprayed with water a total of five times at intervals
of in each case 90 minutes. The atmospheric humidity in the
temperature- and humidity-controlled chamber during this time is about
75%, and the temperature is, as in the case of the treatment with
patination solution, about 50 C. The parameters atmospheric humidity
and temperature are subsequently reduced again to 45% and 45 C,
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respectively, and the copper sheet is allowed to rest for a further 3 days.
The patination is then concluded. The copper sheet is coated absolutely
uniformly by the artificial protective layer.
