Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02291469 1999-12-02
COATING
Field of the Invention
This invention relates to decorative and protective coatings.
Background of the Invention
It is currently the practice with various brass articles such
as lamps, trivets, candlesticks, faucets, door knobs, door handles,
door escutcheons and the like to first buff and polish the surface
of the article to a high gloss and to then apply a protective
organic coating, such as one comprised of acrylics, urethanes,
epoxies, and the like, onto this polished surface. This system has
the drawback that the requisite buffing and polishing operation,
particularly if the article is of a complex shape, is labor
intensive. Also, the known organic coatings are not as durable as
desired and wear off.
These deficiencies are remedied by a coating containing a
nickel basecoat and a non-precious refractory metal compound such
as zirconium nitride, titanium nitride and zirconium-titanium alloy
nitride. However, it has been discovered that when titanium is
present in the coating, for example, as titanium nitride or
zirconium-titanium alloy nitride, in corrosive environments the
coating may experience galvanic corrosion. This galvanic corrosion
renders the coating virtually useless. It has been surprisingly
discovered that the presence of a tin-nickel alloy layer between
the base nickel layer and the top titanium compound or titanium
alloy compound layer reduces or eliminates galvanic corrosion. A
coating containing a tin-nickel alloy layer between the nickel
basecoat and refractory metal compound top coat is disclosed in
U.S. patent 5,667,904. This coating is comprised of a nickel
layer, a tin-nickel alloy layer, and a top layer comprised of
zirconium compound or titanium compound. While generally quite
excellent, this type of coating has several deficiencies. This
type of coating is not sufficiently resistant to chemical attack.
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It is particularly susceptible to attack by acids and bases.
Another problem is that this type of coating sometimes cracks.
The present invention remedies these deficiencies and provides
a coating which exhibits improved resistance to chemical attack,
resistance to cracking, and resistance to galvanic corrosion.
Summary of the Invention
The present invention is directed to a protective and
decorative coating for a substrate, particularly a metallic
substrate. More particularly, it is directed to a substrate,
particularly a metallic substrate such as brass, having on at least
a portion of its surface a coating comprised of multiple superposed
layers of certain specific types of metals or metal compounds. The
coating is decorative and also provides corrosion, wear and
chemical resistance. In one embodiment the coating provides the
appearance of polished brass with a golden hue, i.e. has a golden-
brass color tone. Thus, an article surface having the coating
thereon simulates polished brass with a gold hue.
A first layer deposited directly on the surface of the
substrate is comprised of nickel. The first layer may be
monolithic, i.e., a single nickel layer, or it may consist of two
different nickel layers such as a semi-bright nickel layer
deposited directly on the surface of the substrate and a bright
nickel layer superimposed over the semi-bright nickel layer.
Disposed over the nickel layer is a layer comprised of a tin and
nickel alloy. Over the tin and nickel alloy layer is a sandwich
layer comprised of layers of titanium or titanium alloy alternating
with a titanium compound or a titanium alloy compound.
The sandwich layer is so arranged that a titanium or titanium
alloy layer is on the tin-nickel alloy layer, i.e., is the bottom
layer, and the titanium compound or titanium alloy compound layer
is the top or exposed layer.
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In another embodiment of the invention disposed over the
titanium compound or titanium alloy compound layer is a layer
comprised of titanium oxide or titanium alloy oxide, or a layer
comprised of the reaction products of titanium or titanium alloy,
oxygen and nitrogen.
Brief Description of the Drawin s
Fig. 1 is a cross-sectional view, not to scale, of the multi-
layer coating on a substrate.
Description of the Preferred Embodiment
The substrate 12 can be any plastic, metal or metallic alloy.
Illustrative of metal and metal alloy substrates are copper, steel,
brass, tungsten, nickel alloys and the like. In one embodiment the
substrate is brass.
A nickel layer 13 is deposited on the surface of the substrate
12 by conventional and well known electroplating processes. These
processes include using a conventional electroplating bath such as,
for example, a Watts bath as the plating solution. Typically such
baths contain nickel sulfate, nickel chloride, and boric acid
dissolved in water. All chloride, sulfamate and fluoroborate
plating solutions can also be used. These baths can optionally
include a number of well known and conventionally used compounds
such as leveling agents, brighteners, and the like. To produce
specularly bright nickel layer at least one brightener from class
I and at least one brightener from class II is added to the plating
solution. Class I brighteners are organic compounds which contain
sulfur. Class II brighteners are organic compounds which do not
contain sulfur. Class II brighteners can also cause leveling and,
when added to the plating bath without the sulfur-containing class
I brighteners, result in semi-bright nickel deposits. These class
I brighteners include alkyl naphthalene and benzene sulfonic acid.
The benzene and naphthalene di- and trisulfonic acids, benzene and
naphthalene sulfonamides, and sulfonamides such as saccharin, vinyl
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and allyl sulfonamides and sulfonic acids. The class II
brighteners generally are unsaturated organic materials such as,
for example, acetylenic or ethylenic alcohols, ethoxylated and
propoxylated acetylenic alcohols, coumarins, and aldehydes. These
class I and class II brighteners are well known to those skilled in
the art and are readily commercially available. They are
described, inter alia, in U.S. Patent No. 4,421,611 incorporated
herein by reference.
The nickel layer 13 can be comprised of a single nickel layer
such as, for example, bright nickel, or it can be comprised of two
different nickel layers such as a semi-bright nickel layer and a
bright nickel layer. In the figures layer 14 is comprised of semi-
bright nickel while layer 16 is comprised of bright nickel. This
duplex nickel deposit provides improved corrosion protection to the
underlying substrate. The semi-bright, sulfur free plate 14 is
deposited by conventional electroplating processes directly on the
surface of substrate 12. The substrate 12 containing the semi-
bright nickel layer 14 is then placed in a bright nickel plating
bath and the bright nickel layer 16 is deposited on the semi-bright
nickel layer 14, also by conventional electroplating processes.
The thickness of the nickel layer 13 is generally in the range
of from about 100 millionths (0.0001) of an inch, preferably from
about 150 millionths (0.00015) of an inch to about 3,500 millionths
(0.0035) of an inch.
In the embodiment where a duplex nickel layer is used, the
thickness of the semi-bright nickel layer and the bright nickel
layer is a thickness effective to provide improved corrosion
protection. Generally, the thickness of the semi-bright nickel
layer 14 is at least about 50 millionths (0.00005) of an inch,
preferably at least about 100 millionths (0.0001) of an inch, and
more preferably at least about 150 millionths (0.00015) of an inch.
The upper thickness limit is generally not critical and is governed
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by secondary considerations such as cost and appearance.
Generally, however, a thickness of about 1,500 millionths (0.0015)
of an inch, preferably about 1,000 millionths (0.001) of an inch,
and more preferably about 750 millionths (0.0075) of an inch should
not be exceeded. The bright nickel layer 16 generally has a
thickness of at least about 50 millionths (0.00005) of an inch,
preferably at least about 125 millionths (0.000125) of an inch, and
more preferably at least about 250 millionths (0.00025) of an inch.
The upper thickness range of the bright nickel layer is not
critical and is generally controlled by considerations such as
cost. Generally, however, a thickness of about 2,500 millionths
(0.0025) of an inch, preferably about 2,000 millionths (0.002) of
an inch, and more preferably about 1,500 millionths (0.0015) of an
inch should not be exceeded. The bright nickel layer 16 also
functions as a leveling layer which tends to cover or fill in
imperfections in the substrate.
Disposed on the bright nickel layer 16 is a layer 20 comprised
of tin-nickel alloy. More specifically, layer 20 is comprised of
an alloy of nickel and tin. The tin-nickel alloy layer has been
surprisingly found to reduce or eliminate galvanic corrosion when
titanium is present in the vapor deposited layers . Layer 20 is
deposited on layer 16 by conventional and well known tin-nickel
alloy electroplating processes. These processes and plating baths
are conventional and well known and are disclosed, inter alia, in
U.S. patent Nos. 4,033,835; 4,049,508; 3,887,444; 3,772,168 and
3,940,319, all of which are incorporated herein by reference. The
tin-nickel alloy layer is preferably comprised of about 50-80
weight percent tin and about 20-50 weight percent nickel, more
preferably about 65°s tin and 35o nickel representing the atomic
composition SnNi. The plating bath contains sufficient amounts of
nickel and tin to provide a tin-nickel alloy of the afore-described
composition.
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A commercially available tin-nickel plating process is the Ni-
ColloyT"' process available from ATOTECH, and described in their
Technical Information Sheet No: NiColloy, Oct. 30, 1994,
incorporated herein by reference.
The thickness of the tin-nickel alloy layer 20 is a thickness
effective to reduce or eliminate galvanic corrosion. This
thickness is generally at least about 10 millionths (0.00001) of an
inch, preferably at least about 20 millionths (0.00002) of an inch,
and more preferably at least about 50 millionths (0.00005) of an
inch. The upper thickness range is not critical and is generally
dependent on economic considerations. Generally, a thickness of
about 2,000 millionths (0.002) of an inch, preferably about 1,000
millionths (0.001), and more preferably about 500 millionths
(0.0005) of an inch should not be exceeded.
Disposed over tin-nickel alloy layer 20 is a sandwich layer 26
comprised of layers 30 comprised of titanium or titanium alloy
alternating with layers 28 comprised of titanium compound or
titanium alloy compound. Such a structure is illustrated in the
figures wherein 26 represents the sandwich layer, 28 represents a
layer comprised of a titanium compound or a titanium alloy
compound, and 30 represents a layer comprised of titanium or
titanium alloy.
The metals that are alloyed with the titanium to form the
titanium alloy or titanium alloy compound are the non-precious
refractory metals. These include zirconium, hafnium, tantalum, and
tungsten. The titanium alloys generally comprise from about 10 to
about 90 weight percent titanium and from about 90 to about 10
weight percent of another non-precious refractory metal, preferably
from about 20 to about 80 weight percent titanium and from about 80
to about 20 weight percent of another refractory metal. The
titanium compounds or titanium alloy compounds include the oxides,
nitrides, carbides and carbonitrides.
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In one embodiment layers 28 are comprised of titanium-
zirconium alloy nitrides and layers 30 are comprised of titanium-
zirconium alloy. In this embodiment the titanium-zirconium alloy
nitride layer has a brass color with a golden hue.
The sandwich layer 26 has a thickness effective to provide
abrasion, scratch and wear resistance and to provide the requisite
color, e.g., a golden hued brass color. Generally layer 26 has an
average thickness of from about two millionths (0.000002) of an
inch to about 40 millionths (0.00004) of an inch, preferably from
about four millionths (0.000004) of an inch to about 35 millionths
(0.000035) of an inch, and more preferably from about six
millionths (0.000006) of an inch to about 30 millionths (0.00003)
of an inch.
Each of layers 28 and 30 generally has a thickness of at least
about 0.01 millionths (0.00000001) of an inch, preferably at least
about 0.25 millionths (0.00000025) of an inch, and more preferably
at least about 0.5 millionths (0.0000005) of an inch. Generally,
layers 28 and 30 should not be thicker than about 15 millionths
(0.000015) of an inch, preferably about 10 millionths (0.00001) of
an inch, and more preferably about 5 millionths (0.000005) of an
inch.
In the sandwich layer the bottom layer is layer 30, i.e., the
layer comprised of titanium or titanium alloy. The bottom layer 30
is disposed on the tin-nickel alloy layer 20. The top layer of the
sandwich layer is layer 28'. Layer 28' is comprised of titanium
compound or titanium alloy compound layer 28' is the color layer.
That is to say it provides the color to the coating. In the case
of titanium-zirconium alloy nitride it is a brass color with a
golden hue. Layer 28' has a thickness which is at least effective
to provide the requisite color, e.g., brass color with a golden
hue. Generally, layer 28' can have a thickness which is about the
same as the thickness of the remainder of the sandwich layer.
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Layer 28' is the thickest of layers 28, 30 comprising the sandwich
layer. Generally, layer 28' has a thickness of at least about 2
millionths, preferably at least about 5 millions of an inch.
Generally a thickness of about 50 millionths, preferably about 30
millionths of an inch should not be exceeded.
A method of forming the sandwich layer 26 is by utilizing well
known and conventional vapor deposition techniques such as physical
vapor deposition or chemical vapor deposition. Physical vapor
deposition processes include sputtering and cathodic arc
evaporation. In one process of the instant invention sputtering or
cathodic arc evaporation is used to deposit a layer 30 of
zirconium-titanium alloy or titanium followed by reactive
sputtering or reactive cathodic arc evaporation to deposit a layer
28 of zirconium-titanium alloy compound such as nitride or titanium
compound such as nitride.
To form sandwich layer 26 wherein the titanium compound and
the titanium alloy compound are the nitrides, the flow rate of
nitrogen gas is varied (pulsed) during vapor deposition such as
reactive sputtering or reactive cathodic arc evaporation between
zero (no nitrogen gas or a reduced value is introduced) to the
introduction of nitrogen at a desired value to form multiple
alternating layers of metal 30 and metal nitride 28 in the sandwich
layer 26.
The number of alternating layers of metal 30 and refractory
metal compound layers 28 in sandwich layer 26 is a number effective
to reduce or eliminate cracking. This number is generally at least
about 4, preferably at least about 6, and more preferably at least
about 8. Generally, the number of alternating layers of refractory
metal 30 and refractory metal compound 28 in sandwich layer 26
should not exceed about 50, preferably about 40, and more
preferably about 30.
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In one embodiment of the invention a layer 34 comprised of the
reaction products of a titanium metal or titanium alloy, an oxygen
containing gas such as oxygen, and nitrogen is deposited onto
sandwich layer 26.
The reaction products of the metal or metal alloy, oxygen and
nitrogen are generally comprised of the metal or metal alloy oxide
and metal or metal alloy nitride. Thus, for example, the reaction
products of titanium, oxygen and nitrogen comprise titanium oxide
and titanium nitride. These metal oxides and metal nitrides and
their preparation and deposition are conventional and well known,
and are disclosed, inter alia, in U.S, patent No. 5,367,285, the
disclosure of which is incorporated herein by reference.
The layer 34 can be deposited by well known and conventional
vapor deposition techniques, including reactive sputtering and
reactive cathodic arc evaporation.
In another embodiment of the invention instead of layer 34
being comprised of the reaction products of titanium or titanium
alloy, oxygen and nitrogen, it is comprised of titanium oxide or
titanium alloy oxide. These oxides and their preparation are
conventional and well known.
Layer 34 containing (i) the reaction products of titanium or
titanium alloy, oxygen and nitrogen, or (ii) titanium oxide or
titanium alloy oxide generally is very thin. It has a thickness
which renders layer 34 non-opaque or translucent or transparent so
that the layer 28 is visible therethrough. It also has a thickness
which is at least effective to provide improved chemical
resistance. Generally this thickness is at least about five
hundredths of a millionth (0.00000005) of an inch, preferably at
least about one tenth of a millionth (0.0000001) of an inch, and
more preferably at least about 0.15 of a millionth (0.00000015) of
an inch. Generally, layer 34 should not be thicker than about five
millionths (0.000005) of an inch, preferably about two millionths
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(0.000002) of an inch, and more preferably about one millionth
(0.000001) of an inch.
Layer 34 can be deposited by well known and conventional vapor
deposition techniques, including physical vapor deposition and
chemical vapor deposition such as, for example, reactive sputtering
and reactive cathodic arc evaporation.
Sputtering techniques and equipment are disclosed, inter alia,
in J. Vossen and W. Kern "Thin Film Processes II", Academic Press,
1991; R. Boxman et al, "Handbook of Vacuum Arc Science and
Technology", Noyes Pub., 1995; and U.S. patent Nos. 4,162,954 and
4,591,418, all of which are incorporated herein by reference.
Briefly, in the sputtering deposition process a refractory
metal (such as titanium or zirconium) target, which is the cathode,
and the substrate are placed in a vacuum chamber. The air in the
chamber is evacuated to produce vacuum conditions in the chamber.
An inert gas, such as Argon, is introduced into the chamber. The
gas particles are ionized and are accelerated to the target to
dislodge titanium or zirconium atoms. The dislodged target
material is then typically deposited as a coating film on the
substrate.
In cathodic arc evaporation, an electric arc of typically
several hundred amperes is struck on the surface of a metal cathode
such as zirconium or titanium. The arc vaporizes the cathode
material, which then condenses on the substrates forming a coating.
Reactive cathodic arc evaporation and reactive sputtering are
generally similar to ordinary sputtering and cathodic arc
evaporation except that a reactive gas is introduced into the
chamber which reacts with the dislodged target material. Thus, in
the case where titanium oxide is the layer 34, the cathode is
comprised of titanium and oxygen is the reactive gas introduced
into the chamber.
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In order that the invention may be more readily understood the
following example is provided. The example is illustrative and
does not limit the invention thereto.
wTnenr r~ ~
Brass faucets are placed in a conventional soak cleaner bath
containing the standard and well known soaps, detergents,
defloculants and the like which is maintained at a pH of 8.9 - 9.2
and a temperature of about 145 - 200°F for 10 minutes. The brass
faucets are then placed in a conventional ultrasonic alkaline
cleaner bath. The ultrasonic cleaner bath has a pH of 8.9 - 9.2,
is maintained at a temperature of about 160 - 180°F, and contains
the conventional and well known soaps, detergents, defloculants and
the like. After the ultrasonic cleaning the faucets are rinsed and
placed in a conventional alkaline electro cleaner bath for about 50
seconds. The electro cleaner bath is maintained at a temperature
of about 140 - 180°F, a pH of about 10.5 - 11.5, and contains
standard and conventional detergents. The faucets are then rinsed
and placed in a conventional acid activator bath for about 20
seconds. The acid activator bath has a pH of about 2.0 - 3.0, is
at an ambient temperature, and contains a sodium fluoride based
acid salt.
The faucets are then rinsed and placed in a bright nickel
plating bath for about 12 minutes. The bright nickel bath is
generally a conventional bath which is maintained at a temperature
of about 130 - 150°F, a pH of about 4.0 - 4.8, contains NiS04,
NiCL2, boric acid, and brighteners . A bright nickel layer of an
average thickness of about 400 millionths of an inch is deposited
on faucets. The bright nickel-plated faucets are rinsed twice and
placed in a tin-nickel plating bath for about 7 '-~ minutes . The
bath is maintained at a temperature of about 120 - 140°F and a pH
of about 4.5 - 5Ø The bath contains stannous chloride, nickel
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chloride, ammonium bifluoride, and other well-known and
conventional complex wetting agents. A tin-nickel layer of an
average thickness of about 200 millionths of an inch is deposited
on the surface of the bright nickel layer. The nickel and tin-
nickel plated faucets are thoroughly rinsed in deionized water and
then dried.
The electroplated faucets are placed in a cathodic arc
evaporation plating vessel. The vessel is generally a cylindrical
enclosure containing a vacuum chamber, which is adapted to be
evacuated by means of pumps. A source of argon gas is connected to
the chamber by an adjustable valve for varying the rate of flow of
gas.
A cylindrical zirconium-titanium alloy cathode is mounted in
the center of the chamber and connected to negative outputs of a
variable D.C. power supply. The positive side of the power supply
is connected to the chamber wall. The cathode material comprises
zirconium and titanium.
The electroplated faucets are mounted on spindles, 16 of which
are mounted on a ring around the outside of the cathode. The
entire ring rotates around the cathode while each spindle also
rotates around its own axis, resulting in a so-called planetary
motion which provides uniform exposure to the cathode for the
multiple faucets mounted around each spindle. The ring typically
rotates at several rpm, while each spindle makes several
revolutions per ring revolution. The spindles are electrically
isolated from the chamber and provided with rotatable contacts so
that a bias voltage may be applied to the substrates during
coating.
The vacuum chamber is evacuated to a pressure of about 5x10-3
millibar and heated to about 150°C.
The electroplated faucets are then subjected to a high-bias
arc plasma cleaning in which a (negative) bias voltage of about 500
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volts is applied to the electroplated faucets while an arc of
approximately 500 amperes is struck and sustained on the cathode.
The duration of the cleaning is approximately five minutes. Argon
gas is introduced at a rate sufficient to maintain a pressure of
about 3x10-2 millibars. A layer of zirconium-titanium alloy having
an average thickness of about 4 millionths of an inch is deposited
on the tin-nickel plated faucets during a three minute period. The
cathodic arc deposition process comprises applying D.C. power to
the cathode to achieve a current flow of about 500 amps,
introducing argon gas into the vessel to maintain the pressure in
the vessel at about 1x10-2 millibar, and rotating the faucets in a
planetary fashion described above.
After the zirconium-titanium alloy layer is deposited the
sandwich layer is applied onto the zirconium-titanium alloy layer.
A flow of nitrogen is introduced into the vacuum chamber
periodically while the arc discharge continues at approximately 500
amperes. The nitrogen flow rate is pulsed, i.e. changed
periodically from a maximum flow rate, sufficient to fully react
the zirconium and titanium atoms arriving at the substrate to form
zirconium-titanium alloy nitride compound, and a minimum flow rate
equal to zero or some lower value not sufficient to fully react
with all the zirconium-titanium alloy. The period of the nitrogen
flow pulsing is one to two minutes (30 seconds to one minute on,
then off). The total time for pulsed deposition is about 15
minutes, resulting in a sandwich stack with 10 layers of thickness
of about one to 1.5 millionths of an inch each. The deposited
material in the sandwich layer alternates between fully reacted
zirconium-titanium alloy nitride compound and zirconium-titanium
metal alloy (or substoichiometric ZrTiN with much smaller nitrogen
content).
After the sandwich layer is deposited, the nitrogen flow rate
is left at its maximum value (sufficient to form fully reacted
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zirconium-titanium alloy nitride compound) for a time of five to
ten minutes to form a thicker "color layer" on top of the sandwich
layer. After this zirconium-titanium alloy nitride layer is
deposited, an additional flow of oxygen of approximately 0.1
standard liters per minute is introduced for a time of thirty
seconds to one minute, while maintaining nitrogen and argon flow
rates at their previous values. A thin layer of mixed reaction
products is formed (zirconium-titanium alloy oxy-nitride), with
thickness approximately 0.2 to 0.5 millionths of an inch. Finally
the arc is extinguished at the end of this last deposition period,
the vacuum chamber is vented and the coated substrates removed.
While certain embodiments of the invention have been described
for purposes of illustration, it is to be understood that there may
be various embodiments and modifications within the general scope
of the invention.
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