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142 Paints i3 Coatings improve the adhesion of the metallic layer. Frequently, the base coat is 100% solids UV-curable paint that is spray-applied. Conven- tional solvent-based paints are used only if required by the product specifications. UV-curable paints offer an advantage over the more conventional air-dry or bake-dry paints in that they sig- nificantly reduce energy require- ments. Depending on the product specifications, the top coat may vary from solvent-borne urethanes to UV-curables. Rainey concedes that problems still exist with UV-curable topcoats in view of their poor adhesion to the metal film. Improving the performance standards of low-polluting top coats is just one of the challenges that Varian Associates hopes to solve in the coming decade. Varian’s Florence plant, which opened late in 1980, will apply a metallic finish using the sputtercoating technique to appliances, furniture and plumbing compo- nents fabricated of plastic. The types of plastic to be coated at the new plant will centre mainly on acrylonitrile-butadiene-styrene (ABS) plastics and some poly- propylene plastics. Varian As- sociates has demonstrated that other sputterable plastics include polystyrene, nylon, phenylene- oxide-based resin, polycarbonate, acrylic, thermoplastic, acetal and p~lyurethane.~~ According to Rainey, sputtercoating economics might not be as good today as more conventional painting methods, but it is gener- ally competitive with electroplating. Unlike electroplating which is a proven technology, sputtercoating is a newcomer to the finishing world. Rainey speculates that in five years, sputtercoating will be two times cheaper than electroplating.39 Unlike electroplating, which requires complex and costly pretreatment steps to prepare the substrate for plating, the sputtercoating process is relatively simple. Powder Coating In the powder coating process, specially formulated fusible paint Small parts in the load zone, background is the spray booth and far right hand side background Is the oven. Cabinets - upside down on the conveyor at the unload zone. powder is applied to the object to be coated and fused to its surface by heat curing in an oven. At most modem installations, powder is applied by an electrostatic spray method to keep the powder on the surface of the target object until it can be fused. Because powder coatings are 10Wo solids, they ,. present no solvent emission problems during curing. Another significant low-pollution aspect of powder coatings is that they are easily recycled. Operating costs are lower than for conventional liquid paint lines because of reduced material, labour and energy req~irements.~~
I I Moyer Diebel (Jordan, Ontario) has recently upgraded the small paint line at its vending machine manufacturing plant. In a spirit of modernization, Moyer Diebel chose an automated powder coating operation. “We were very hesitant when we first considered going to powder because it represented some- thing of a leading edge technology. Being on the leading edge is not a very comfortable position tobe in,” says George Perdue, vice presi- dent of manufacturing. According to Perdue, the capital cost of the automated powder system and the automated conventional liquid system were vir- tually the same. At the time of the installation, Moyer Diebel paid $280,000 for its new powder line manufactured by Interrad Inter- national, about $5,000 less than for a liquid paint line. The real savings result from the reduced energy consumption, reduced material costs, and reduced maintenance costs. The powder system is costing Moyer Diebel about 15% less in operating costs than a comparable liquid system?’ At Moyer Diebel, the majority of parts coated are steel. Some aluminum and stainless steel parts are coated as well. Before the ‘ parts can be coated, they must be washed to permit proper adhesion of the paint. Steel parts usually have a thin protective film of oil on the surface which must be re- moved before painting. Since the company installed its powder line, the previous four-stage washing system has been reduced to a three-stage process. Perdue says, “We were sur- prised to find that the powder coating stuck on easier and with less cleaning. The upshot is that it is cheaper to pre-clean surfaces to be powder-coated because fewer cleaning cycles are needed.” For Moyer Diebel, reducing the total volume of wastewater gener- ated by reducing the number of cleaning cycles is a significant benefit. The company’s rural loca- tion means that no sewer is avail- able to accept their wastewater. The wastewater from the washing Process is recycled for re-use as washwater. Sludge and residual Manual dry powder electrostatic spray gun. Dry powder electrostatic touch-up booth on automatic appliance line. Twin air bell powder booth and reclaim unit. wastewater are hauled away by a disposal company. Once the parts have been moved automatically through the three- stage wash system and dry-off oven, the parts are ready to pass through an enclosed spray booth. E E m U C J - 0 c 2 m s s U m - B C Paints & Coatings 743 Several spray guns automatically spray coat the part with a posi- tively charged powder, allowing the powder to adhere to the metal until baking. A manual touch-up using hand operated electrostatic guns follows immediately to coat inaccessible areas. The excess powder that does not adhere to the object falls to the bottom of the paint booth onto a moving belt. The belt carries the excess powder to a vacuum system which collects and transports the overspray to the filter units. Once the overspray has been filtered to remove dirt, metal bits and clumps of paint, the powder is returned to the feed hopper for ~e-use.~“ Only 40 to 50% of the powder sprayed stays on the target object, however the highly efficient overspray recycle system means that almost all of the 5000 pounds of powder used each month is actu- ally used in coating the parts. “Because the recovery rate of overspray is about 99 percent, we don’t accumulate barrels of paint sludge,” says Perdue. The powder-coated parts are then moved to a gas-fired oven which cures the paint for a durable finish. Although powder baking requires an oven temperature of 400” to 425”F, about 20°F higher than for a liquid system, the overall energy efficiency is much higher.42 According to Perdue, the new powder line requires 35% less energy than a conventional system. “We used to have to exhaust hot air from our baking ovens because it was laden with solvents,” says Perdue. “Now we get excellent energy conservation because the hot oven air is filtered and recycled immediately instead of exhausted. The energy savings are especially tremendous in the winter.” There is no doubt in Perdue’s mind that the economics of powder are best for those applications that do not need many colour changes. Powder coating technology does have a relatively wide range of application, particularly in the appliance industry, the outdoor furniture industry, or as a base coat in the automotive industry. Colour change takes about three hours to accomplish. This is done
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