Epoxy finishes powder coatings

Powder Coatings. Epoxy-based powder coatings exhibit useful properties such as excellent adhesion, abrasion resistance, hardness, and corrosion and chemical resistance. The application possibilities are diverse, including metal finishing, appliances, structural rebars, pipes, machinery and equipment, furnitures. 

Side and cross members are pretreated by blasting and phosphating. An electrode-posited primer coating follows and is sometimes immediately overcoated with a topcoat based on an air-drying alkyd or epoxy ester, or on an oven-drying alkyd-melamine resin combination. After assembly of the truck, a third layer (i.e., a second topcoat) is applied that serves as a supply finish. These finishes are mostly two-pack acrylic aliphatic isocyanate topcoats. Water-based two-pack systems and powder coatings are the most recent developments. 

Unlike coatings made from thermoplastic powders which require only a visual inspection to see whether the coating is satisfactory, thermosetting powder coatings require additional examination to determine whether the coating has achieved its full physical properties. Simple mechanical tests may be used, as is the practice with conventional paint finishes, but, particularly for epoxy powder coatings, it is normal to use chemical resistance as a criterion for suitability. A common method is to swab the coating continuously for 30 seconds with a cotton wool pad soaked in methyl isobutyl ketone. Any deterioration of... 

Powder coating resin systems (see Fig. 27.2) have been developed to meet specific needs of the metal finishing operations. Epoxies were utilized almost exclusively during the early years of thermosetting powder coatings and continue to be utilized in a range of applications. However, because of the poor outdoor... 

For the AIA-SEM analyses, the raw and clean coal samples were prepared by mixing 2 g of the sample with an epoxy resin and casting into molds 1 in. in diameter. The hardened pellets were polished to reveal a cross section and finished by polishing with 0.3-ym alumina powder. Then the pellets were coated with approximately 500 A of carbon to render sample surfaces electrically conductive for examination in the SEM unit. 

Samples must be solid and may be in almost any form. Thin films, bulk solids, particles, powders, machined pieces, and small objects (including biological specimens) can be analyzed. AU elements from beryllium (Z = 4) to uranium can be determined at concentrations of about 100 ppm or greater. For qualitative analysis, the surface finish of the sample is not important. For quantitative analysis, the surface of the specimen must be flat. A common method for achieving a flat surface for an SEM sample is to embed the sample in epoxy and then carefully polish the hardened epoxy to expose a flat surface of the sample. Calibration standards should have flat surfaces as well, and the composition of the standards should be similar to that of the samples. Alternatively, an FP approach using pure element standards can be used. For nonconductive samples, a thin coating of osmium is deposited on the surface of the sample. 

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