CA2291469A1 - Coating - Google Patents

Abstract

An article having deposited on at least a portion of its surface a decorative and protective multi-layer coating comprising at least one nickel layer, a tin-nickel alloy layer, and sandwich layer comprised of layers comprised of titanium or zirconium-titanium alloy alternating with layers comprised of titanium compound such as titanium nitride or zirconium-titanium alloy compound such as zirconium-titanium nitride. The coating provides abrasion and corrosion protection to the underlying substrate and also protects the substrate from attack by chemicals such as acids and bases while being crack resistant and resistant to galvanic corrosion.

Description

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.

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.

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 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 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.

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.

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.

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.

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 (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.

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.
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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 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 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 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.

Claims (14)

1. An article comprising a substrate having on at least a portion of its surface a multi-layer coating comprising:
at least one layer comprised of nickel;
layer comprised of alloy comprised of tin and nickel;
layer comprised of titanium or titanium alloy;
sandwich layer comprised of layers comprised of a titanium compound or a titanium alloy compound alternating with layers comprised of titanium or titanium alloy; and layer comprised of titanium compound or titanium alloy compound.

2. The article of claim 1 wherein said titanium compound is titanium nitride.

3. The article of claim 1 wherein said titanium alloy compound is titanium-zirconium alloy nitride.

4. The article of claim 3 wherein said titanium alloy is titanium-zirconium alloy.

5. The article of claim 1 wherein said at least one layer comprised of nickel is comprised of bright nickel.

6. The article of claim 5 wherein said titanium compound is titanium nitride.

7. The article of claim 5 wherein said titanium alloy compound is titanium-zirconium alloy nitride.

8. The article of claim 7 wherein said titanium alloy is titanium-zirconium alloy.

9. An article comprising a substrate having on at least a portion of its surface a multi-layer coating comprising:
layer comprised of semi-bright nickel;
layer comprised of bright nickel;
layer comprised of alloy comprised of tin and nickel;
layer comprised of titanium or titanium-alloy;
sandwich layer comprised of layers of titanium compound or titanium-alloy compound alternating with layers comprised of titanium or titanium alloy; and layer comprised of zirconium compound or zirconium-titanium alloy compound.

10. The article of claim 9 wherein said titanium compound is titanium nitride.

11. The article of claim 9 wherein said titanium alloy compound is a titanium-zirconium alloy compound.

12. The article of claim 11 wherein said titanium-zirconium compound is titanium-zirconium nitride.

13. The article of claim 11 wherein said titanium alloy is titanium-zirconium alloy.

14. The article of claim 12 wherein said titanium alloy is titanium-zirconium alloy.