WO2000061831A1

WO2000061831A1 - Process for applying metals to plastics and the articles produced thereby

Info

Publication number: WO2000061831A1
Application number: PCT/US2000/009578
Authority: WO
Inventors: Walter H. Strader; Jeffrey L. Gilbert
Original assignee: Price Pfister, Inc.
Priority date: 1999-04-14
Filing date: 2000-04-10
Publication date: 2000-10-19
Also published as: DE10084475T1

Abstract

The present invention relates to a process by which polymeric substrates may be coated with a metal layer to form an article with an outer metal layer such as a high luster faucet. The process involves as its major steps providing a polymeric substrate formed to a desired shape and thermally spraying a metal coating on the surface under certain controlled conditions.

Description

PROCESS FOR APPLYING METALS TO P.LASTICS AND THE ARTICLES PRODUCED THEREBY

BACKGROUND OF THE INVENTION

The present invention relates to a process for applying metals to plastics and, more particularly, to a process of forming articles with metal surfaces including, for example, plumbing fixtures such as faucets. Heretofore, faucets have been manufactured by molding a brass

component, polishing and subsequently electroplating the component to achieve a final decorative product. While decorative faucets are obtained, the products formed by conventional brass molding and electroplating techniques tend to be relatively expensive to manufacture. As such, low cost, high volume production

alternatives are considered desirable.

SUMMARY OF THE INVENTION

The present invention therefore relates to a process for making decorative articles with metal surfaces comprising the steps of : a) providing a polymeric substrate which is shaped to a desired form;

and b) thermally spraying a low temperature metal on the substrate to form a decorative article having a metallic layer.

Depending on the article being formed, the polymeric substrate may be

treated to modify the surface in order to promote adhesion prior to carrying out

the thermal spraying step. Additionally, depending on the application, it may be desirable to apply a base coat to the substrate prior to thermal spraying. Post thermal spraying steps may also be employed such as smoothing and polishing the metal layer, plating the metal layer to form a plated metal layer thereon, and optionally treating the plated layer with a physical vapor deposition step to apply a relatively thin metal nitride layer. The vapor deposited metal nitride layer may provide coloration or alter the coloration of the plated metal layer, and may also provide protection to the plated metal layer.

The surface modification step generally involves roughening the surface to increase the surface area and make the surface more receptive to coating. In some cases, the polymeric substrate as shaped may have a slightly rough or textured surface, such as in the case of a polymeric foamed substrate. The

thermal spraying of the metal layer generally involves a technique such as plasma spraying, flame spraying, kinetic spraying, high velocity oxygen fuel spraying, detonation gun spraying, and arc spraying, among others.

While the process of the present invention may be useful for thermal spray coating an extensive number of polymeric substrates with any one of a number

of low temperature metals or metal alloys depending in large part on processing parameters, the preferred application is for the production of plumbing fixtures and components such as faucets, handles, and spouts; and bathroom and kitchen hardware such as towel bars, towel rings, and accent pieces. The articles produced by the invention not only have a decorative appearance and

aesthetically pleasing feel, but also offer functional advantages over all-metal or

all plastic plumbing fixtures.

More particularly, the process allows for the production of faucets that feel as cold and heavy and exhibit a high luster finish similar to faucets formed by

molding and polishing brass or other all-metal faucets. The process of the invention has the advantages, however, of greater flexibility, greater ease of manufacturing, particularly of more complicated faucet designs, and improved

operation.

Thus, the invention also relates to a faucet or other fixture comprising a polymeric substrate having a roughened surface, a metal layer applied to the roughened surface to provide with fixture with a metal look and feel, and a layer of plating applied to the metal layer to provide the faucet with a high luster finish.

DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a faucet produced by the process of the present invention;

Fig. 2 is a cross-sectional view of the faucet spout of Fig. 1 illustrating the

resulting layers;

Fig. 3 is a perspective view of a production cell utilized to carry out the thermal spraying step of the inventive process;

Fig. 4 is a flow diagram of the process of the present invention; and Fig. 5 is a diagrammatic view of a automated line for the surface

modification steps and thermal spray steps of the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figs. 1 and 2, there is shown a decorative article 10 in the form of a faucet produced by the process of the present invention. The faucet generally includes one or more movable handles 14 and a spout 12 through

which liquid flows. One or both of these components may be coated via the thermal spraying process of the present invention. Referring particularly to Fig. 2, the decorative object 10 includes a pre-formed polymeric substrate 20, a low temperature sprayed metal layer 22 and optionally, but preferably, a plated outer

layer 24. As illustrated in Fig. 3, the initial step 30 of the process involves providing a polymeric substrate which is generally pre-formed to the desired shape of the end product. By shaping the polymeric substrate, it is meant that the underlying object is formed into a desired shape by known plastic forming techniques.

Suitable techniques for forming the polymeric substrate include, without limitation, extrusion, casting, compression molding, and conventional injection molding and gas assist injection molding processes.

The polymer utilized to form the substrate may be selected from an extensive list including acetyl polymers and copolymers including, for example and without limitation, polyoxymethylene; acrylonitrile butadiene styrene (ABS) resins, polyamides including nylon 6/6, nylon 6, nylon 6/12, and so on; polycarbonates; polysulfones; polyphenylene sulfides (PPS); polyethersulfones

(PES); polyphenylene oxides, modified (PPO), polyetherimides (PEI),

polyphenylene ethers, including modified polyphenylene ethers such as the 40% mineral filled structural foam product available from General Electric under the tradename NORYL FM 4025; polyesters such as polybutylene terephthalates

and polyethylene terephthalates; polycarbonate/ABS alloys (PC/ABS),

polyphthalamides (PPA); other combinations and alloys of these; polymers such as these may be filled with mineral or fiber fillers, or otherwise modified of improved structural strength. A preferred polymeric material is polybutylene terephthalate, particularly filled polybutylene terephthalate compositions such as a 68% mineral/glass filled PBT available from General Electric under the tradename ENDURAN 7085. In another preferred embodiment, the polymeric material is a structural foam. In particular, it may be desirable to introduce a foaming agent and produce a foamed polymer substrate when gas assist injection molding is used to provide a channel in the polymer article, such as is done to form a water channel in a plumbing fixture such as a faucet. The structural foam may have a surface roughness that promotes adhesion without further surface modification. If desired for aesthetic reasons, a structural foam may be back-filled to increase the weight of the article.

Once the underlying object is pre-formed to the desired shape, the surface of the polymeric object, also referred to herein as the polymeric substrate generally loaded onto a surface preparation station 50 as illustrated in Fig. 50. Once loaded, the polymeric substrate may optionally be modified to promote adhesion as represented in Fig. 3 by box 32. In the case of foamed substrates

it may not be necessary to further modify the surface as the foamed articles may already have a slightly roughened surface. When included, the surface modification step can involve any one of a number of different techniques including, for example, chemical etching, peening, or vapor blasting. A preferred surface modification technique involves wet or dry grit blasting that may utilize

any of various media including, for example, aluminum oxide, silicon carbide, steel shot, ceramics, plastics, sand, glass beads, walnut shells, CO₂ pellets, and diamonds or diamond-like material. Wet grit blasting is generally carried out with a slurry consisting of water and commonly available abrasive particles. The slurry is spray applied to the substrate surface at a pressure in the range of 30- 90 psi. As a result, the surface is prepared and cleaned in the same operation. Dry grit blasting is similar to wet grit blasting but the abrasive particles are not slurried prior to application. The surface modification step is generally carried out in an enclosed hood as designated by reference numeral 52 in Fig. 5.

The next step as denoted at box 34 of Fig. 3, if employed, involves coating the modified or unmodified substrate with a base coat. The base coat may be an epoxy or thermoplastic material conducive for thermal spraying techniques or a metal such as zinc or tin. If utilized, the base coat layer (not shown) is applied

directly to a selected area of the substrate prior to the application of the metal layer shown. Epoxy or other polymeric materials may be applied using conventional spraying equipment. Zinc, tin, or other metals may be applied by thermal spray methods. If applied, the base coat layer will be relatively thin, i.e., having an average thickness of from about 2 mils to about 5 mils, to facilitate adhesion of the low temperature metallic coating of step 36. The base coat layer

(not shown) may be applied in the same enclosed area 54 as the thermally sprayed metallized coating shown in Figs. 3 and 5.

While the thermal spraying step 36 could theoretically include any one of a number of known processes such as plasma vapor deposition and high velocity oxygen fuel (HVOC) spraying, the preferred process involves twin wire arc

spraying. A twin wire arc spraying technique involves feeding two wires through an arc spray gun. One wire is charged positively and the second wire is charged negatively. The two wires impinge to create an electric arc. The arc melts the

wires to form a semi-solid material that forms droplets The metal droplets are propelled from the gun to the substrate with compressed air and can impinge the surface at less than 200°F. The parameters of the process are adjusted so that the droplets will "bite in" the substrate to form an adhering layer but also spread to form a uniform and coalesced layer on the substrate. Among the preferred metals used for the thermal spraying step are zinc, tin, babbitt, pewter, bronze and blends or alloys of these. In twin wire arc spraying an alloy may be deposited by using one wire of one material and a second wire of another material as well as by using wires that are of the desired

alloy. A highly preferred metal is substantially pure zinc wire (+98.0% purity, more preferably 99.99% pure) having a diameter of from about 20 mils to about 100 mils. The metal is deposited in an average thickness for the sprayed metal layer of from about 10 mils to about 50 mils, preferably from about 10 mils to about 30 mils, and more preferably from about 15 mils to about 25 mils, to give

a low porosity metallic layer.

As illustrated with reference to Fig. 4, the thermal spraying step is typically carried out within a spray cell including a robotic gun, an adjustable platform for part movement, a housing and a computer or control console for inputting the

process parameters to be followed during the thermal spraying step. A fully automated production line such as shown in Fig. 5 would be used for high volume production. Articles would be loaded onto carousels and then sequentially passed through a surface conditioning station and possibly a base coat application station. After surface conditioning, the parts are moved onto a

turntable in a thermal spray station. The metal is applied by a robot spray machine. The part carousels are then unloaded or moved to a belting station for smoothing. After belting, the part can be buffed. Finally, the smoothed parts are moved to a plating operation, and if desired, to a physical vapor deposition station. While the resulting metal layer provides properties such as weight, hardness and a cold feel to the touch, the metal layer may also provide functional properties for certain applications such as anti-friction, anti-wear, and so on.

Once the thermal spraying has been completed, the metal layer may optionally be prepared for carrying out a plating step as will be described in greater detail below. The plating preparation step denoted by reference numeral 38 in Fig. 3 involves degreasing, activating and rinsing the metal layer prior to carrying out the plating step.

The plating step 40 may involve using any one of a number of different plating compositions depending largely upon the composition of the metal layer. The plating layer or layers may vary considerably, depending on the metal layer over which it is applied and the appearance and properties of the finished article desired. For example, a copper-nickel-chromium finish is preferably plated on

a zinc metal layer, whereas a nickel-chrome finish may be plated on a copper metal layer. For example, the copper-nickel-chromium plating over zinc would preferably include a preparing the metal surface by degreasing, activating and rinsing the surface, applying a cyanide copper strike, then plating. In one finish preferred for plumbing fixtures, the metal layer is sequentially plated by first

plating with copper at a thickness of from about 1 mil to about 1.5 mils, then plating with nickel at a thickness of from about 0.4 to about 0.6 mils; and finally plating with chrome (hexavalent chrome) in a thickness of from about 10 microns to about 15 microns.

The total average thickness of the multilayer plating is generally between about 1.5 mils to about 2.0 mils. Lastly, a metal nitride layer may be applied as designated by reference numeral 42 in Fig. 3 by physical vapor deposition techniques to provide

coloration or alter the coloration of the plated metal layer, and to provide protection and durability of the plated metal. Although it is possible to deposit other materials, metal nitrides are preferred. The metal nitride layer is generally at least about 0.1 micron and up to about 1 micron thick, preferably from about

0.2 micron to about 0.5 micron thick. Examples of suitable metals applied by the

physical vapor deposition are, without limitation, zirconium nitride, titanium nitride, aluminum nitride, chromium nitride, and combinations and alloys of these.

To demonstrate one embodiment of the present invention, a four inch center set faucet was produced by molding a substrate from Enduran 7085 PBT,

including approximately 63.0% by volume mineral filler. The resulting substrate

was dry grit blasted with 60 mesh aluminum oxide particles at 60 psi through a VA nozzle. After grit blasting, the substrate was coated with a 0.010" thick base coat of zinc via a twin wire and spray process. Thereafter, the zinc coated substrate was sanded using 320 aluminum oxide and buffed on a cotton sisal

buff wheel. Lastly, the zinc coated substrate was sequentially plated with copper,

nickel and hexavelent chromium to a total thickness of 1.5 mils. The resulting decorative article had a high luster appearance similar to electroplated brass plumbing fixtures. While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.

Claims

1. A process for producing decorative articles comprising the steps of: a) providing a polymeric substrate shaped to a desired form; and b) thermally spraying a low temperature metal onto said substrate to form a decorative article having a metallic layer.

2. The process of Claim 1 wherein said polymeric substrate is

selected from the group consisting of polyoxymethylene; acrylonitrile butadiene styrene (ABS) resins, polyamides, polycarbonates, polyethers, polysulfones, polyphenylene sulfides (PPS), polyethersulfones (PES), polyphenylene oxides, polyetherimides (PEI), polyphenylene ethers, polyphthalamides (PPA) and mixtures thereof.

3. The process of Claim 2 wherein said polyethers include modified polyphenylene ethers.

4. The process of Claim 2 wherein said polyesters are selected form the group of polybutylene terephthalates and polyethylene terephthalates.

5. The process of Claim 1 wherein said low temperature metal is selected from the group consisting of zinc, tin, babbit, pewter, bronze, and alloys

thereof.

6. The process of Claim 1 wherein said metallic layer has an average thickness of between about 10 mils to about 50 mils.

7. The process of Claim 1 further comprising the step of metal plating said metallic layer.

8. The process of Claim 7 wherein said metal plating includes the sequential application of at least two different metals.

9. The process of Claim 8 wherein said metal plating has an average thickness of between about 1.5 mils to about 2.0 mils.

10. The process of Claim 7 wherein said metal plating includes a metal selected from the group consisting of copper, nickel, chromium and alloys

thereof.

11. The process of Claim 7 further comprising the step of applying a

metal nitride layer to said metallic plating.

12. The process of Claim 11 wherein said metal nitride layer is applied

by physical vapor deposition.

13. The process of Claim 11 wherein said metal nitride is selected from the group consisting of zirconium nitride, titanium nitride, aluminum nitride, chromium nitride, and combinations thereof.

14. The process of Claim 11 wherein said metal nitride layer has an average thickness of between about 0.1 microns to about 1.0 microns.

15. The process of Claim 1 wherein said polymeric substrate is modified to promote adhesion prior to thermally spraying said low temperature metal.

16. The process of Claim 15 wherein said polymeric substrate is modified by chemical etching, peening, vapor blasting, wet grit blasting or dry grit blasting.

17. The process of Claim 1 wherein said polymeric substrate is coated with a base coat prior to the thermal spraying step.

18. The process of Claim 17 wherein said base coat is selected from epoxies, zinc, tin, babbit, pewter, bronze, and alloys thereof.

19. An article produced by the process of Claim 1.

20. A process for producing a decorative plumbing fixture comprising

the steps of: a) providing a polymeric substrate shaped to a desired form; b) optionally, modifying the surface of said substrate; c) optionally, applying a base coat to said substrate; d) thermally spraying a low temperature metal onto said substrate; e) preparing said thermally sprayed coating for metal plating; and f) metal plating said thermally sprayed coating.

21. The process of Claim 20 wherein said polymeric substrate is selected from the group consisting of polyoxymethylene; acrylonitrile butadiene styrene (ABS) resins, polyamides, polycarbonates, polyethers, polysulfones, polyphenylene sulfides (PPS), polyethersulfones (PES), polyphenylene oxides, polyetherimides (PEI), polyphenylene ethers, polyphthalamides (PPA) and

mixtures thereof.

22. The process of Claim 20 wherein said polyethers include modified polyphenylene ethers.

23. The process of Claim 20 wherein said polyesters are selected form

the group of polybutylene terephthalates, polyethylene terephthalates and mixtures thereof.

24. The process of Claim 20 wherein said low temperature metal is selected from the group consisting of zinc, aluminum, tin, copper, stainless steel, nickel, chrome, bronze, and alloys thereof.

25. The process of Claim 20 wherein said metallic layer has an average thickness of between about 10 mils to about 50 mils.

26. The process of Claim 20 wherein said metallic layer has an

average thickness of between about 10 mils to about 50 mils.

27. The process of Claim 20 wherein said metal plating includes the sequential application of at least two different metals.

28. The process of Claim 20 wherein said metal plating has an average thickness of between about 1.5 mils to about 2.0 mils.

29. The process of Claim 20 wherein said metal plating includes a metal selected from the group consisting of copper, nickel, chromium and alloys

thereof.

30. The process of Claim 30 wherein said metal nitride layer is applied by physical vapor deposition.

31. The process of Claim 30 wherein said metal nitride layer is applied by physical vapor deposition.

32. The process of Claim 30 wherein said metal nitride is selected from the group consisting of zirconium nitride, titanium nitride, aluminum nitride, chromium nitride, and combinations thereof.

33. The process of Claim 30 wherein said metal nitride layer has an

average thickness of between about 0.1 microns to about 1.0 microns.

34. The process of Claim 20 wherein said polymeric substrate is

modified by chemical etching, peening, vapor blasting, wet grit blasting or dry grit blasting.

35. The process of Claim 20 wherein said base coat is selected from epoxies, zinc or tin.

36. An article produced by the process of Claim 20.

37. A decorative article comprising: a polymeric substrate formed to a desired shape; a thermally sprayed intermediate metallic layer applied to said polymeric

substrate; and a metal plating layer applied to said intermediate metallic layer.