Spray and baked coatings

There are two distinct ways of coating a metal surface with a fluoropolymer coating. 

The supply chain for this process can be seen in Fig. 8.11. Electrostatic spray coating or powder coating is a way of applying a dry paint to a surface. Most people have used liquid paints with a brush, a spray can, or even with their fingers. Powder coatings are dry there are no liquid solvents. The dry powder is applied to an item (substrate), then the powder is turned to liquid, usually by melting. The dry powder in its molten state can then flow out to cover the substrate, coalesce, and crosslink. The end result is a painted surface. 

Some parts might need to have a coating thickness less than what other lining processes can provide. These might include valves, tubes, pipes, and impellers. These parts may still need to be protected by a fluoropolymer coating. One of the best references is published by the Powder Coating Institute although other sources are also available. 

Powder coatings are available in FEP, PFA, MFA, ECTFE, ETFE, and PVDF. Typically, a multicoat application is required to achieve a required thickness. The powder size ranges from 1-3.54 milli-inches (25 to 90 microns). 

Powder coating has advantages over liquid coatings, but it also has limits. Most of the advantages 

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Figure 8.11 Supply chain and job sequence for spray and baked coatings.

Typical vessel internals are agitators, baffles, and dip tubes. Agitators and dip tubes are covered by fluo-ropolymer by either coating as explained in Spray and Baked Coatings, (Sec. 8.2.3) or by fluoropoly-mer sheets, typically shrink-wrapped PTFE. Baffles... 

Spray and Baked Dispersion Electrostatic spray FEP (10 mils), PFA (10 0 mils and up to 80 mils when reinforced or filled) PVDF (20-40 mils and up to 90 mils when reinforced with carbon cloth) ETFE (up to 50 mils), FEP (10 mils), PFA (25 0 mils) ECTFE (35-90 mils), PVDF (35 0 mils) Primer and multicoated conventional spray equip Each coat baked Shop only Primer and multicoated Each coat baked Shop only Pressure OK Vacuum OK Pressure OK Vacuum OK 12xl2x 37 12 Visual Spark Visual Spark By hot patching Testing recommended By hot patching Testing recommended... 

Polyimide, aramid Straight organic coatings with high softening points (450-550°C), which are applied by spray and baked low friction characteristics against some resins (for example, PVC) moderate abrasion resistance... 

Spray and baked electrostatic powder coating of fluoropolymers, as described under thin linings, can also be applied as thick linings. One such lining is PVDF and glass, or carbon-fiber fabric. 

The mixture was initially filtered through a 0.2 pm pore diameter teflon filter. It was spin-coated onto a silicon wafer previously sprayed with hexamethyldisilazane and baked for 40 seconds at 90°C and 90 seconds at 110°C, forming a 500 nm resist film. The resist film was exposed to ArF excimer laser light, heat treated for 90 seconds at 110°C, and cooled to ambient temperature. It was then dipped in 2.38% aqueous tetramethylammonium hydroxide solution for 60 seconds for development where it formed a 1 1 line-and-space pattern. The wafer as developed was... 

Coatings can be prepared by hot flocking, in which the heated part is dipped into a fluidized bed of ETFE powder and then is removed to cool. ETFE coatings can also be applied by other powder coating methods (e.g., electrostatically) or by spraying of water- or solvent-based suspensions followed by drying and baking [27],... 

DuPont registered the Teflon trademark in 1945 and released Its first Teflon products a year later. Since then the non-stick coating has become a household staple on kitchen cookware, in baking sprays, and as a stain repellantfor fabrics and textiles. 

A poly(ester-imide) powder is coated on an electrolytic copper foil of 35 my thickness by an electrostatic spray coating machine and baked at 200 °C for 30 min. The substrata obtained is useful for printed circuit board manufacturing [268]. 

The majority of electrocoating installations take the merchandise through two to nine stages of cleaning and phosphating under continuous movement through the electrodip, rinse, and bake, followed by spray coating if so desired. 

A second generation of phenolic dispersions, patented by J. S. Fry (33). involved the post dispersion of phenolic resins in a mixture of water and water-miscible solvents. To conform with air pollution regulations, the solvent was held to 20 volume %, or less, of the volatiles. A heat-reactive phenolic resin dispersion (34) and a phenolic-epoxy codispersion have become commercially available based on the above technology. Supplied at 40-45% solids, these products, which have a small particle size (0.75-1.0 ym), are better film formers than the earlier dispersions. Used alone or in blends with other waterborne materials, corrosion-resistant baking coatings may be formulated for coil coating primers, dip primers, spray primer-surfacers, and chemically resistant one-coat systems. Products of this type are also tackifiers for acrylic latexes, and such systems have been employed as contact, heat seal, and laminating adhesives for diverse substrates. 

MAJOR APPLICATIONS Paints, brushing enamels, and clear varnish. Industrial coatings (spraying, dipping, flow coating, roller coating). Industrial baking finishes. 

The salt water immersion test (SWI) and the standard salt spray (fog) test (SS) were conducted for both ISPCs and control baking enamels applied on bare CRS, iron phosphated B-1000, and BD+P60 panels. The painted coupons of about 1.0 mil dry film thickness cured at 163 C for 15 minutes were X-cut through the film to the substrate and then either immersed in a 3% NaCI solution (SWI test) or subjected to a continuous salt-solution spray in a test chamber (SS test). After a specified duration of testing, the specimens were removed from the salt solution, and the coated surface was immediately dried. A DUCK brand tape (Manco, Inc., Westlake, OH) was applied over the X-cut and then removed, and the protective performance was... 

The chemically resistant coatings, such as the baked phenolics, baked epoxies, and the air-dry epoxy, vinyl, and neoprene coatings, are ideal for minimizing contamination of chanicals handled in steel equipment. They should not be used where 100% protection from corrosion is required. An excellent material for immersion service has been developed that consists of flakes of glass dispersed in a polyester resin. This is applied by spray to a properly prepared surface, and the wet coating is rolled with a paint roller to orient the glass flakes in a plane parallel to the substrate and to provide maximum resistance to chemical attack. 

Uses Conductivity agent for electrostatically sprayed coatings, solv.-based air-dry and baking enamels... 

Uses Used in any type of coating (varnish, stain, solv.- or water-based, bake or air dry enamels) food pkg. coatings Features Exc. weather durability, water repellency, improved salt spray and humidity resist., improved slip and mar resist. min. effect on dirt pick-up, gloss, and clarity preserves integrity of thermoplastic coatings Reguiatory FDA 21CFR 175.300... 

Uses Urea-formaldehyde for highly reactive, rapid drying acid-curable and baking finishes, electrostatic spray finishes, surf, coatings for food containers/pkg. stabilizer, gloss aid for cellulose nitrate lacquers Regulatory Germany approved for food containers and pkg. 

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