Thermal spray: Better performance for less

Nov. 22, 2001
Engineered coatings and advanced processing methods help push performance limits for metal and plastic components. Here are design guidelines and processing tips that will help extend the life or improve the aesthetics of that new design.

Brian Griffith
Decorative Coatings Product Manager
Enthone OMI Inc.
West Haven, Conn.

Edited by Jean M. Hoffman

ABS plastic handheld shower fixture is coated with a satin nickel finish called Pearlbrite by Hansgrohe Inc., Alpharetta, Ga.

A plating process called Udique puts a decorative finish on plastics used in automotive name plates and interior and exterior trim. Many Udique plated plastics also meet the End of Life vehicle directive for recyclability.

New developments in plating chemistries have led to more durable coatings for plastics that are stronger as well. Especially companies in the automotive, telecom, and kitchen and bath fixture businesses are increasingly using plastics to replace metals as a way to reduce weight and cost.

Coatings suppliers and platers are shortening production processes and perfecting chemistries to better coat acrylonitrile butadiene styrene (ABS), ABS/PC (polycarbonate), and other engineering resins.

More traditional "long-line" plating processes have been in place for years with palladium-based colloidal chemistry as the industry benchmark. While this process is currently in wide use successfully, there are a few inherent drawbacks. First, it's a relatively timeconsuming process. Second it needs multiple surface preparation, activation, and metallization steps.

However, recent directives such as End of Life Vehicle (ELV) are coming into effect globally. They are forcing manufacturers to find ways of removing copper from traditional plating processes. The goal is to reduce waste and promote recycling.

One avenue in this effort is newer ionic palladium processes that eliminate copper. They also reduce the size of the equipment needed and speed plating throughput for plastic parts.

Other noncopper coating chemistries include those used in a nickelbased monometal plating process called Monolith. The technique applies a highly decorative finish to a variety of plastics without using the traditional combination of copper, nickel and chromium. It is said to make more durable parts which stand up better during thermocycling. The ionic palladium processes also reportedly reduce overall system investments by 15 to 20% and produce parts that more easily recycle.

"The big push now is to replace metal components with ‘heavy' plastics," says Chuck Wolitski, general manager of Quaker City Plating in Los Angeles. Manufacturers in the plumbing fixture business, he continues, want plastics not only to look good and perform well, but also feel substantial to the consumer. Injection molding makes possible complex shapes that assemble easily, while improving aesthetics and functionality.

Plating — the next generation
New direct-plate systems are not only suitable for ABS and ABS/PC but also for many new engineering plastics. The engineered resins are good candidates for metallization because they are strong and withstand high temperatures without distortion.

Leading edge "short-line" processes currently in field tests plate directly onto substrates without using electroless chemistries. These direct-plate systems, such as Enthone's Plato, use a conventional chrome-sulfuric etch to render the plastic surface hydrophilic. This creates bonding sites for maximum adhesion. Next the surface is activated with a nonpalladium, metal complex which lets the plastic be directly electroplated with nickel. This eliminates several processing steps.

The deposited nickel is the foundation for subsequent high-performance decorative finishes. This technique has been used on items ranging from electronic components and housings to automotive trim, faucets, and showerheads. The Plato system, for example, is said to reduce the overall plating process by as much as 60% when compared to ionic palladium. And with the elimination of the palladium activation, it also reduces the need for waste treatment.

Performance is still key
New coating processes are gaining a reputation for being economical and friendly to the environment. An example comes from the auto industry, where tests evaluated nickel-chromium plated components for exterior exposure. CASS (copper-accelerated saltspray) testing simulates service conditions in the laboratory. Early testing standards were generally set for components to meet or exceed 22 hr. Current standards call for up to 66 hr of exposure. But new plating processes now let components exceed 100 hr of testing before deterioration is apparent. Some OEMs are pushing for a standard of 200 hr.

"The consumer continues to demand a variety of specialty coatings beyond traditional chrome finishes," says Kevin Wynschenk, plating manager at Hansgrohe Inc., one of Europe's leading kitchen and bath fixture makers. "Pearlbrite — satin nickel, matte, and dull finishes are very popular in our business. The challenge is to make these new combinations of chemistries and cosmetic finishes perform better while meeting not only our standards, but UL and CSA standards as well."

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