Powder Coated Tough - Spring 2008 - (Page 27) cure, or minor post-cure, would elimcessful emergence of today’s therinate the need for expensive recovery mosetting thin film decorative and and return systems with quick color protective ES powder technology. change becoming a simple task of The first U.S. auto body ES powder just cleaning the tip of the gun. The top coat attempt, based on a theradvantages could be significant, mosetting polyester-melamine binder including possible select replacement system, was made by Ford. While it of air-dry liquid coating applications. matched the flow and smoothness of Meanwhile, unsuccessful efforts the then-applied liquid top coats, A system known as the twin air belt offered highly consis- were made to develop a multicolorupon cure it exuded methanol pintent downdraft airflow across the entire bottom of the holing in the coating film, which booth. Unfortunately, it proved difficult to operate if not powder gun for instant color change maintained properly. with a quick cleaning hose as well as proved a detriment along with poor a deflectorless spray gun—the latter shelf stability (blocking) and spraying also designed for rapid color change difficulties (impact fusion) because of plus elimination of impact fusion and In the course of conducting this powder’s low Tg (glass transition better faraday penetration. The conresearch on the limitations of corona temperature). cept of commercializing the deflectorAlso Nissan’s, GM’s and Ford’s and tribo charging systems, Dr. John less gun is still under consideration other early attempts at top coating Hughes of the University of trucks and auto bodies with pigmentSouthampton, U.K., reported the need today. Early research was also directed at ed ES acrylic powders never took off, for electrostatic optimization of the primarily because of the inability to powder itself similar to that developed improving powder recovery with one such system known as the twin air belt match the “flop” of the existing liquid for electrophotocopier powder toners. with highly consistent downdraft airmetallic top coats, representing a good One such consideration was the flow across the entire bottom of the share of the automotive market. eNexus patented induction charging booth as an important benefit. concept involving conventional powUnfortunately, it proved difficult to ders tailored with antistatic and other Application & Recovery operate if not maintained properly. additives for lower optimum resistiviEquipment The first filter cartridge collector ty. Adequate capital investment, An effort to overcome the early corona booths were then commercialized in charging guns’ faraday cage limitations though, was not obtained to continue the mid-1970s, providing 99.9% powresearch and scale-up for commercialfor penetrating recess areas was the der recovery for maximum material patented Dynacoat Electrogasdynamic izing this concept. utilization. technology, which failed to continualA unique development was the The next-generation cartridge colly deposit uniform thickness powder Selectro plasma spray gun designed to lector booths incorporated roll-away coatings on complex- shaped parts. deliver thermosetting and functional filter collector modules along with the Eliminating the faraday cage effect, powders through the exterior periphcapability for spraying multiple colors tribo guns are currently used for select ery (400-450°F) of a plasma zone but applications, including nylon powfailed to deposit smooth coating films using dedicated-color modules, while still maintaining exceptionally high ders, but their effective charging effiat desired curing rates on large area material utilization. Emphasis next ciency is susceptible to changes in metal substrates such as on the interihumidity and temperature and to the or tanks of supertankers. Research also moved to electrostatic gun control technology with the introduction of types of transport tubing material. included coating the interior of aluselectable cascade voltage multiplier Today’s improved corona charging minum and steel cans. This process guns and recovery systems effectively may still have merit if enough funding load lines, each developed for a specific powder coating application chalis devoted to the proper plasma gun coat a wide range of parts, including lenge. This smart controls technology development. To be able to convert recess areas with most existing large helped provide optimum coating covvolume conventional powders. powder to a liquid spray and instant www.powdercoating.org 27 Courtesy ITW Gema http://www.powdercoating.org
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