U.S. patent application number 14/445651 was filed with the patent office on 2014-11-13 for protective coating of silver.
This patent application is currently assigned to BENEQ OY. The applicant listed for this patent is BENEQ OY. Invention is credited to Milja MAKELA, Sami SNECK, Pekka SOININEN.
Application Number | 20140335272 14/445651 |
Document ID | / |
Family ID | 35953681 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140335272 |
Kind Code |
A1 |
MAKELA; Milja ; et
al. |
November 13, 2014 |
PROTECTIVE COATING OF SILVER
Abstract
In the method, silver is protected against tarnishing using an
Atomic Layer Deposition method. In the Atomic Layer Deposition
method, a thin film coating is formed on the surface of silver by
depositing successive molecule layers of the coating material. For
example aluminium oxide (Al.sub.2O.sub.3) or zirconium oxide may be
used as the coating material.
Inventors: |
MAKELA; Milja; (Lahti,
FI) ; SOININEN; Pekka; (Helsinki, FI) ; SNECK;
Sami; (Vantaa, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BENEQ OY |
Vantaa |
|
FI |
|
|
Assignee: |
BENEQ OY
Vantaa
FI
|
Family ID: |
35953681 |
Appl. No.: |
14/445651 |
Filed: |
July 29, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12162051 |
Jul 24, 2008 |
|
|
|
PCT/FI2007/050056 |
Jan 31, 2007 |
|
|
|
14445651 |
|
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Current U.S.
Class: |
427/255.34 ;
427/255.28; 427/255.31 |
Current CPC
Class: |
C23C 16/403 20130101;
C23C 16/405 20130101; C23C 16/45555 20130101; A44C 27/005 20130101;
C23C 16/44 20130101; C23C 16/45525 20130101 |
Class at
Publication: |
427/255.34 ;
427/255.28; 427/255.31 |
International
Class: |
C23C 16/40 20060101
C23C016/40; C23C 16/44 20060101 C23C016/44 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2006 |
FI |
20065082 |
Claims
1. A method for protecting silver products, articles or parts
against tarnish in an atmosphere, the method consisting of applying
a thin coating layer of protective material having a thickness
between 2 nm to 20 nm on at least a part of an outer surface of a
silver product, article or part using an ald (atomic layer
deposition) method to prevent tarnishing of the outer surface of
the silver product, article or part in the atmosphere.
2. The method according to claim 1, wherein applying the thin
coating layer comprises providing at least one layer of metal oxide
using the ALD (Atomic Layer Deposition) method.
3. The method according to claim 2, wherein the metal oxides
comprise aluminum oxide Al.sub.2O.sub.3, titanium oxide TiO.sub.2,
chromium oxide Cr.sub.2O.sub.3, zirconium oxide ZrO.sub.2, indium
oxide In.sub.2O.sub.3, and niobium oxide Nb.sub.2O.sub.5.
4. The method according to claim 1, wherein the thin coating layer
is substantially transparent non-oxide material.
5. The method according to claim 1, further comprising applying a
substantially colorless coating layer on at least a part of the
outer surface of the silver product, article or part.
6. The method according to claim 1, further comprising applying
said thin coating layer at a temperature, which is in a range of 80
to 400.degree. C.
7. The method according to claim 1, wherein the thin coating layer
is produced on a multiple-part silver product after the product is
assembled.
8. The method according to claim 1, wherein the method is applied
to silver jewelry, coins, medals, tableware, ornaments, silver
products, or at least a part of an electronic or electrical
component or other industrial component made of silver or silver
alloys.
9. The method according to claim 1, wherein the method is applied
to products comprising several different materials in addition to
silver.
10. The method according to claim 6, comprising applying said thin
coating layer at a temperature, which is in a range of 120 to
300.degree. C.
11. The method according to claim 6, comprising applying said thin
coating layer at a temperature, which is 200.degree. C.
12. A method for protecting products comprising silver against
tarnish in an atmosphere, the method comprising applying a thin
coating of protective material having a thickness between 2 nm to
20 nm on at least a part of a product using an ALD (Atomic Layer
Deposition) method to prevent tarnishing of the silver of the
product in the atmosphere.
13. A method for protecting silver products, articles or parts
against tarnish in an atmosphere, the method comprising applying a
thin coating of protective material having a thickness between 2 nm
to 20 nm on at least a part of an outer surface of a silver
product, article or part using an ALD (Atomic Layer Deposition)
method to prevent tarnishing of an outer surface of the silver
product, article or part in the atmosphere.
14. The method according to claim 13, wherein the thin coating of
protective material forms an outer surface of the silver product,
article or part to prevent tarnishing of the outer surface of the
silver product, article or part in the atmosphere.
Description
[0001] This application is a continuation of application Ser. No.
12/162,051, filed Jul. 24, 2008, which in turn is a National Phase
of International Application No. PCT/FI2007/050056 filed on Jan.
31, 2007, which claims priority to Finnish Patent Application No.
20065082 filed on Feb. 2, 2006. The disclosures of the prior
applications are hereby incorporated by reference herein in their
entireties.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for coating silver
products, and more particularly to a method according to the
preamble of claim 1 coating silver.
BACKGROUND OF THE INVENTION
[0003] Silver naturally tarnishes in the atmosphere, especially in
the presence of sulphur. Industrial atmospheres and natural
digestive processes are important sources for the tarnishing of
silver. When silver is tarnished, sulphides, oxides or carbonates
are formed on the surface of silver. The tarnishing of silver and
silverware is a problem for example for the utility article,
jewellery and giftware industries as well as to the end users of
the silver products. Tarnishing degrades the appearance of the
product as a layer or spots of black or dark grey colour are
formed. It can be removed but this is usually a laborious process,
and the process may affect the appearance of the product
negatively. Also in technical applications the tarnishing of the
silver reduces the optical properties, such as reflectivity, of
silver and silver products and parts.
[0004] Methods for preventing tarnishing in advance are known in
the prior art. One existing method for preventing tarnishing
comprises using silver alloys that are designed with resistance to
oxidation and involve the mixing of special additives, such as
silicon or germanium, with silver. Another existing method for
preventing tarnishing comprises coating pure silver using rhodium.
One of the problems associated with the above arrangement using
silver alloys is that the method requires all factors to be
carefully controlled during manufacture, like using extremely pure
new metal and accurate temperature control in melting and
annealing. As a result, the manufacturing process and the equipment
to carry out the process are very expensive to set up. The cost is
also prohibitive in the method for coating silver with rhodium.
Further, the rhodium coating has a blue-white shade, and thus a
silver product coated with rhodium may become visually different
from pure silver.
[0005] Other existing methods for preventing tarnishing of silver
comprise coating the finished silver product, article or part with
a method that provides a layer of material on the silver product,
article or part which prevents or restrains tarnishing on the
finished silver product, article or part. These kind of prior art
methods comprise varnishing the silver products. The problem with
these known coating methods is that the coating layer is not
uniform over the whole product or part of the product that has been
coated. The thickness variations in the coating layers over the
silver product cause colour variations, for example due to
interference, or other optical alterations, which are not
preferable. These known methods also produce relatively thick
layers of coating materials on the silver products. This further
has a negative influence on the appearance of a silver product.
Varnish may also yellow and peel off. Thus, the known methods for
preventing tarnishing of a silver product do not provide a uniform
and substantially to human eye invisible coating, but a non-uniform
coating and/or a coating producing discoloration of a silver
product.
BRIEF DESCRIPTION OF THE INVENTION
[0006] An object of the present application is to provide a method
so as to alleviate the above disadvantages. The objects of the
application are achieved by a method according to the
characterizing portion of claim 1. Therefore the present invention
is characterized by applying a thin coating of protective material
on at least a part of the surface of a silver product, article or
part using an ALD (Atomic Layer Deposition) method.
[0007] Preferred embodiments are disclosed in the dependent
claims.
[0008] The term thin layer means in this context a layer having
thickness between 1 nm and 1 .mu.m, preferably between 1 and 100
nm, and most preferably approximately 2-20 nm.
[0009] In the method a thin film coating is deposited on the
surface of a silver object. In the present solution, silver is
coated with one or more molecule layers of aluminium oxide
Al.sub.2O.sub.3. Trimethyl aluminium (CH.sub.3).sub.3Al may be used
as a precursor and water H.sub.2O as an oxygen source. The
thickness of the generated thin film per one ALD cycle is about 0,1
nm and the coating is carried out in a temperature of about
200.degree. C.
[0010] In experiments desired results have been achieved by
depositing about 3 nm coating of Al.sub.2O.sub.3 on a silver
product by using 30 ALD cycles with successive pulses of trimethyl
aluminium (TMA) and water. Thicker coatings have also been tested
to determine the relation between the color of the coating and the
thickness of the coating. Another good thickness range is found be
about 70 nm range. This thickness may be achieved by depositing
about 70 nm coating of Al.sub.2O.sub.3 on a silver product by using
700 ALD cycles with successive pulses of TMA and water. An
advantage of the present solution is that it is possible to produce
a thin coating, which effectively prevents silver from tarnishing
without altering the appearance of the silver product. Also the
optical properties of the silver will remain substantially
unaltered. Thus the coating passivates the silver surface. The
coating generated by the method is thin, dense, smooth and
substantially colourless, and it precisely follows conformally the
shapes, also three dimensional shapes, of the silver object without
thickness variations in the coating. By means of the present
solution, a stable, uniform and attractive coating may be achieved.
The generated coating is compatible with foodstuffs. The
consumption of the coating material is low, and thus coating costs
may be reduced. The thickness of the coating layer may be
controlled by varying the number of molecule layers in the coating.
The coating process is not sensitive to minor changes in the
process parameters, and thus the repeatability of the method is
good. This thin layer is sufficient for preventing the tarnishing
of the silver, but does not affect the appearance of the silver
product, as the conventional coating methods. The coating may be so
thin that human eye cannot se it. Such a uniform layer is not
possible to be provided on a three dimensional object for example
with CVD method (Chemical Vapour Deposition) or PVD (Physical
Vapour Deposition) method, since the coating process may not be
controlled in such a detail as with ALD method. CVD and other
similar methods also require that the coated object have to be
rotated for providing coating material over the whole surface of
the three dimensional object.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the following, the invention will be described in greater
detail by means of preferred embodiments with reference to the
accompanying drawings, in which
[0012] FIG. 1 is a schematic representation of the coating process
of silver with aluminium oxide according to the solution of the
present application;
[0013] FIG. 2 is a schematic representation of the structure of the
coating according to the solution of the present application.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Silver naturally tarnishes in the atmosphere, especially in
the presence of sulphur. Industrial atmospheres and natural
digestive processes are important sources for the tarnishing of
silver. When silver is tarnished, sulphides, oxides or carbonates
are formed on the surface of silver. Tarnishing degrades the
appearance of the product as a layer or spots of black or dark grey
colour are formed. Also in technical applications the tarnishing of
the silver reduces the optical properties, such as reflectivity, of
silver and silver products and parts. For preventing the tarnishing
of surfaces of a silver product a thin coating may be provided on
the surfaces of the silver product. The coating should be
sufficiently thin for preventing the change of the appearance of
the silver product, but sufficiently thick to provide good
passivation and/or protection against tarnishing. This kind of thin
coating may be applied on the surfaces of a silver product
preferably by using Atomic Layer Deposition (ALD).
[0015] Atomic Layer Deposition is a thin film technique that allows
thin film coatings that have a nanoscale thickness to be
manufactured. ALD technique may also be called ALC (Atomic Layer
Coating) technique or ALE (Atomic Layer Epitaxy) technique. The ALD
is based on a gas phase process where primary compounds are
typically evaporated and pulsed into a reaction chamber separately.
A thin film is generated when the material obtained from the
reaction between the primary compounds is deposited on the surface
to be coated. The material is deposited on the surface such that
successive layers of molecule level are deposited one by one. This
may be called "growing" of the material. Thin film materials
obtained by means of the ALD technique include, for example, metal
oxides and metal nitrides.
[0016] In the Atomic Layer Deposition method, a thin film coating
is formed on the surface of silver by depositing successive
molecule layers of one or more coating materials.
[0017] According to the solution of the present application, the
ALD technique is adapted to coating an object comprising silver. In
the present solution, the object comprising silver is coated with a
coating comprising aluminium oxide Al.sub.2O.sub.3. However, any
colourless metal oxide, such as zirconium oxide ZrO.sub.2, titanium
oxide TiO.sub.2, chromium oxide Cr.sub.2O.sub.3, indium oxide
In.sub.2O.sub.3, niobium oxide Nb.sub.2O.sub.5, or any other
material obtainable by the ALD technique may also be used.
[0018] FIG. 1 illustrates an embodiment of the present solution
showing the coating of a silver surface S with aluminium oxide
Al.sub.2O.sub.3. The coating is built up of molecule layers of
aluminium oxide. FIG. 1 shows a situation where trimethyl aluminium
(CH.sub.3).sub.3Al and water H.sub.2O are used as primary
materials. If silver were coated with ZrO.sub.2, for example,
ZrCl.sub.4 and H.sub.2O might be used as primary materials.
[0019] In step 1-1, the surface S is exposed to gas comprising
trimethyl aluminium, in which case a layer of trimethyl aluminium
molecules (CH.sub.3).sub.3Al is formed on the surface S. In step
1-2, the residual gas has been removed, and the layer comprising
trimethyl aluminium molecules (CH.sub.3).sub.3Al remains on the
surface S. In step 1-3, the surface S has further been exposed to
water H.sub.2O. In the reaction between trimethyl aluminium
(CH.sub.3).sub.3Al and water, aluminium oxide Al.sub.2O.sub.3 is
formed. The reaction proceeds stepwise, and also other compounds
may be formed, such as aluminium hydroxide AlOH and methane
CH.sub.4. During the reaction, aluminium oxide Al.sub.2O.sub.3 is
deposited on the surface S. Step 1-4 shows a situation where
unreacted trimethyl aluminium (CH.sub.3).sub.3Al and eventual other
compounds have been removed, and there is a layer of aluminium
oxide Al.sub.2O.sub.3 deposited on the surface S.
[0020] The thin film coating of the present solution is obtained by
growing of the material. This is carried out by repeating the steps
1-1 to 1-4 of FIG. 1 several times such that successive layers of
aluminium oxide molecules are deposited on the surface S. The
thickness of the coating may be controlled by varying the number of
molecule layers.
[0021] FIG. 2 illustrates a situation where the coating on the
surface S of silver comprises four molecule layers of aluminium
oxide Al.sub.2O.sub.3. In reality, the number of successive layers
of aluminium oxide Al.sub.2O.sub.3 may be other than four.
[0022] In the coating process, usually a coating that is as thin as
possible is desirable such that it will still be sufficiently thick
in order to have the desired properties. According to the present
solution, the thickness of the coating is preferably within the
range of 1 nanometre to 1 micrometer, more preferably within the
range of 5 to 200 nanometres, most preferably about 10 nanometres.
The thickness of the coating may be adjusted by varying the number
of the molecule layers of the coating material.
[0023] Experiments have shown, that the one preferable thickness
range is between 1 and 15 nm. The yellowish appearance increases as
the thickness of the coating increases (in range 0 to 50 nm) being
very disturbing as the thickness of the coating is 20 nm or more.
On the other hand the protective and/or passivating effect of the
coating gets better as the thickness of the coating increases.
Therefore, the thickness of the coating should be a compromise
between the protection against tarnishing and the appearance of the
silver product.
[0024] Another good thickness range is reached when the
interference of the thin coating starts to intensify the blue
color. Thus the blue color effect produced by the coating makes it
brighter to the human eye. This kind of effect may be produced with
aluminum oxide deposited with ALD on a silver product when the
thickness of the coating is in range about 60 to 90 nm. In this
case also the passivation and/or protective effect of the coating
is good. The blue interference appears as a series also when the
thickness of the coating is increased, but then also other colors
may appear depending on the angle of view of the product and
furthermore the processing of the silver product becomes slower and
more expensive.
[0025] The above mentioned effect may also be achieved with other
colourless or substantially colourless materials or coatings in
addition to aluminium oxide. The preferable thickness ranges vary
according to material, because of the differences in the refractive
index of the materials.
[0026] The lower of the mentioned thickness ranges (1-15 nm)
requires ability to make very uniform and thin coatings as well as
a low refractive index for the coating material. This is because of
the fact that the yellowish appearance becomes a dominant feature
before a sufficient thickness for the passivation and protection is
achieved when materials having high refractive index are used.
Aluminium oxide has proved to be one suitable material for
providing thin uniform coatings to prevent tarnishing of a silver
product when ALD is used. For example, when zirconium oxide is
used, the appearance of a silver product becomes too yellowish
before the sufficient passivation level is reached. A thin coating
is preferable for the silver product. Then a material having low
refractive index may be used. On the other hand, if excellent
passivation is required and thus the thickness of the coating must
be increased. In this case a material having higher refractive
index may be used for achieving desired result, since the desired
result may be achieved with thinner coating compared to material
having lower refractive index.
[0027] The solution of the present application is based on the idea
of protecting silver against tarnish by coating it using ALD
(Atomic Layer Deposition) method. ALD is suitable for a precise
production of very thin coatings. As a method ALD is also very
suitable for commercial production requirements. The scalability
and versatility of ALD makes an attractive method for producing
coatings in industrial production.
[0028] Experiments have shown that the growth produced by ALD
starts as columns and not until the coating is approximately 3 nm
in thickness it is sufficiently uniform and unbroken for preventing
the surface of a silver product from tarnishing. On the other hand,
when aluminium oxides are used as coatings, the surface of a silver
product starts to look yellowish already when the thickness of the
coating is 10 nm. Therefore, as optically more coarse material is
chosen the thickness of the coating may be larger, but when
optically more dense material is chosen the thickness of the
coating should be decreased for preventing the yellowish appearance
of the product. Some of the materials may even produce a yellowish
appearance for the product when the thickness of the coating is not
even sufficient for producing a uniform and unbroken coating.
Accordingly, the thickness of the substantially invisible coating
produced by ALD may differ depending on the materials used such
that the coating on a silver product is sufficient for producing a
uniform and unbroken coating, but sufficiently thin for preventing
discoloration of a silver product. Here, the optical dense is
influenced, in addition to the refraction index, by reflectance
factors, boundaries, imaginary components etc.
[0029] The temperature used in the coating process depends on the
material properties. In many cases, it is advantageous to use a
relatively high temperature. A high temperature allows molecules to
evaporate readily, and a coating having a sufficiently good quality
is obtained. According to the present solution, the coating
temperature is preferably within the range of 80 to 400.degree. C.,
more preferably within the range of 120 to 300.degree. C., most
preferably about 200.degree. C.
[0030] Aluminum oxide process functions at least in a temperature
range 100 to 250.degree. C., and part even in a temperature range
20 to 300.degree. C. These relatively low temperature ranges enable
the coating for preventing tarnishing to be deposited after
possible gemstones are planted and/or assembly solder joints or
other assembly steps are conducted. Thus, all surfaces may be
protected and there is no need to touch the surfaces with tools.
The low temperature also enables rapid processing of the silver
products using these low temperatures, which also makes treatment
more simple and advantageous.
[0031] According to another embodiment of the present solution only
a part of an object or a surface is coated.
[0032] According to yet another embodiment of the present solution,
the method is applied together with one or more protecting methods
other than the method described herein. In that case, the use of
silver alloys that are resistant to oxidation, for example, may be
applied.
[0033] According to yet another embodiment of the present solution,
the method is applied to coating silver-plated objects.
[0034] According to yet another embodiment of the present solution,
the method is applied to coating silver alloys.
[0035] According to yet another embodiment of the present solution,
the method is applied to coating objects or surfaces comprising
bronze, copper and/or brass. In other words this same method may be
used to coat also other metals so that the appearance of the metal
is not influenced.
[0036] The method enables objects of various shapes to be coated.
Thus it may be applied to coating jewels, ornaments, tableware,
etc., as well as various industrial components.
[0037] It should be noted that the use of aluminium oxide is not
necessarily required by the present solution; any other coating
material obtainable by the ALD technique, such as titanium oxide
(TiO.sub.2), tantalum oxide (Ta.sub.2O.sub.5) and/or zirconium
oxide (ZrO.sub.2), may also be used. Different coating materials
may be used simultaneously. The obtained coating should have the
desired properties and it should be compatible with the metal to be
coated such as silver. Instead of (CH.sub.3)Al, also other
compounds may be used as precursors, such as aluminium chloride
AlCl.sub.3 and/or triethyl aluminium (CH.sub.3CH.sub.2).sub.3Al.
Instead of water, also other compounds, such as hydrogen peroxide
H.sub.2O.sub.2, ozone O.sub.3, etc may be used as the oxygen
source. The choice of the coating material may depend on the
application. For example, tableware or jewellery may require a
biocompatible coating layer. An example of a biocompatible coating
material is aluminium oxide Al.sub.2O.sub.3. Reactions illustrated
in FIG. 1 may occur in different order and also other reactions
and/or steps may be carried out.
[0038] It is also possible to provide a coating having nanolaminate
structure using ALD with two or more different coating materials.
Then protective material is applied on the surface of a silver
product such that one or more successive molecule layers are
deposited and then another protective material is applied on the
surface of a silver product such that one or more successive
molecule layers are deposited. This may be continued until a
predetermined coating thickness is achieved. It is also possible
use three or more different materials in the mentioned successive
manner. This provides a coating comprising two or more layers of
two or more protective materials.
[0039] The applied coating is generally so thin that it is
invisible to human eye. The method may therefore be applied to
silver jewellery, coins, medals, tableware, ornaments or the like
silver products. The method may also be applied to products
comprising several different materials in addition to silver.
Furthermore, the method according to the present invention may be
applied to at least part of an electronic or electrical component
or other industrial component made of silver or silver alloys.
[0040] It will be obvious to a person skilled in the art that as
technology advances, the inventive concept can be implemented in
various ways. The invention and its embodiments are not limited to
the examples described above but may vary within the scope of the
claims.
* * * * *