New spray-coating processes for plastic powder.
PLASMA SPRAYING COMPOSITES
A plasma-spray process to deposit thermoplastic powders--with or without fillers or reinforcements--onto a variety of surfaces in either an indoor spray shop or at an outdoor job site is available from Applied Polymer Systems, Inc., Boynton Beach, Fla. The company also has developed specially formulated powder-coating materials for use with the process.
The patented technology, called Hyper-Spray, can be used in various applications from aircraft coatings to heat shielding and composite coatings in automobiles, APS says. It reportedly eliminates problems of sagging and running that can result from fluidized-bed and electrostatic powder coatings.
The coating materials developed by APS include nylons, polyesters, polyethylene, PTFE and various copolymers that can be used alone or in combinations. The powders can also be used as a matrix for metal-, ceramic- or carbon-filled composites. The coating materials are formulated to obtain the proper wetting of the substrate surface, ensuring a high-quality finish and a durable coating. Coatings can be sprayed onto substrates such as fiberglass composites, aluminum, steel, rubber, concrete and wood, as well as onto other thermoplastics and thermosets. The pigments used for coloring the coating materials all have high resistance to heat and sunlight, APS says.
Hyper-Spray's ability to be used outdoors marks the first time a technology has been developed for this application, the company says. Previously, polymer coatings of this kind could only be applied in an indoor spray plant by either electrostatic spraying and oven baking, or by hot dipping.
The company says the system works along the same lines as spray painting, except the thermoplastics set very quickly and will not drip or run. In the process, argon gas passing through an electric arc loses one of its electrons and becomes an extremely hot plasma. As the gas leaves the internally water-cooled plasma generator in the gun, powdered thermoplastic materials are introduced into the stream. The thermoplastic becomes molten and is projected at subsonic speeds against the surface being coated. The impact of individual particles against the surface at high speeds causes thermal and mechanical energy to be transferred to the substrate, producing enough force to stimulate interatomic bonding. Substrate temperatures should be above 50 F to reduce thermal shock.
APS says spray rates as high as 25 lb/hr can be achieved using this system manually; and rates as high as 50 lb/hr can be attained when spraying with an automatic articulator. Metal substrates must be grit-blasted to roughen and remove oxides from the surface. Surfaces of plastic or composite substrates need only be wiped to remove oils or waxes, the company says. When spraying on an area previously coated, the high-velocity molten material fuses on contact with the existing coating.
The APS equipment system is a self-contained unit mounted on a portable skid. The closed-loop, integrated system includes a computer-controlled remote pendant with touchscreen operation. The IBM-compatible computer has a 30-megabyte hard disk for material and parameter storage.
APS is licensing the technology to processors as well as leasing the equipment. It also does in-house spray coating and contract R&D. The company charges $20/lb for what it calls standard coating material formulations. Non-standard coatings are priced based on the specifications and properties desired. APS's lab development fee is $3500/day. The annual cost of a process license varies, depending on how many years the user takes the license for. A one-year license runs $150,000/yr. Two years are priced at $135,000/yr; three years, $125,000/yr; and four years cost $110,000/yr. A license beyond four years runs $50,000/yr, the company says. (CIRCLE 6)
FLAME SPRAYING A NEW WAY
An unusual portable powder-spray technology, developed by Texas inventor James Reimer, is being readied for big-time commercial applications. In particular, the company is excited about developmental work with elastomeric powders and other polyolefin materials, believed to be a first, that can withstand temperatures up to 350 F.
In June, principles of Wagner & Brown of Midland, Texas, bought a majority interest in Reimer's small start-up business, Plastic Flamecoat Systems, League City, Texas. With its new financial backing, Plastic Flamecoat is upgrading lab facilities and hiring marketing staff and polymer consultants, says Wagner & Brown's Paul Luckett.
Plastic Flamecoat's technology has been used locally for painting bridges, oil rigs and metal parts for about four years. The technology uses a patented (method and equipment) hopper and applicator gun, costing under $10,000 and adaptable for remote or assembly line usage, the company says. A propane and air flame is the heat source; compressed air is the powder propellant. Powdered thermoplastic is melted as it passes through the propane flame and flows onto the surface to be coated at rates of 60-400 sq ft/hr, Luckett says.
Melted powder is applied in a single thick (8-10 mil) coat to many surface materials such as plastic, metal, rubber or concrete--emitting "zero VOCs and no toxic or hazardous fumes of any kind," Reimer says. No mixing chambers are needed, and equipment can be cleaned with an air hose. The only operator safety equipment needed is a dust mask, the company says.
Plastic Flamecoat grinds and colors its own proprietary coating powders with 400-600% elongation, using Du Pont adhesive resins such as Nucrel ethylene methacrylic acid (EMAA), Surlyn EMAA ionomer, and EVA, which are sprayed at 150-170 F.
The first areas of commercial interest to Plastic Flamecoat are metal corosion-protection applications, such as on railcars. But Reimer says anti-abrasion coatings for plastic parts like electronic circuit boards are being tested. Other possible plastics-coating applications include steering-gear boxes, hydraulic cylinders, and pumps, which are assembled from both metal and plastic components. Where now the metal parts are individually coated before assembly, with Plastic Flamecoat's system, the entire assembly part can be coated at once.
Coating of automotive exterior trim and plastic bumpers does not now appear to be a suitable application for the process, because it doesn't make a Class A finish. "Orange-peel" effects have been the limitation. (CIRCLE 7)
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|Date:||Oct 1, 1991|
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