Metal Finishing Guide Book

2012-2013

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tured. 9. The coatings pose little fire hazard; toxicity is less than solvent-based counterparts. 10.The costs for reducing solvents and cleanup are lower for these coatings than for solvent-based counterparts. 11.Exterior durability is very good. 12.Chemical and solvent resistance are fair to good, but cannot compete with baked or two-component coatings. Disadvantages 1. Generally, these coatings have poorer chemical resistances compared with two-part polyurethanes or baked water-reducible coatings. 2. A three-step equipment cleanup is required: water, solvent,water. 3. The coatings do not meet standards for ���high��� performance in industry, such as heavy-duty maintenance, aerospace, appliance, automotive. 4. The coatings are more sensitive to substrate cleanliness than most solvent systems. 5. The coatings require a greater reaming curve with regard to viscosi ty management than other compliant coatings. 6. Generally, primers do not have as good a salt spray resistance as con ventional solvent-based counterparts. 7. In high humidity areas, the coating must be force dried, or high velocity air must be blown over the part to quickly evaporate the water from the film. It is imperative that the water evaporate before the coalesc ing solvent evaporates. AIR AND FORCE-DRIED ACRYLIC LATEXES Acrylic latex coatings are air- or forced-air dried at temperatures less than 90��C (194��F). Advantages 1. These coatings have very low VOC contents, often less than 240 g/L (1.5 lb/gal), less water. New technologies currently being developed will all but eliminate VOCs. 2. The single package coatings have unlimited pot life as long as they are in covered containers. 3. The coatings air dry rapidly when relative humidity is low. 4. The coatings exhibit excellent resistance to sunlight, demonstrated by retention of gloss, color, and flexibility over long periods of exposure. 5. Generally, the coatings are available in a wide range of colors and all but very high gloss levels. 6. The coatings adhere to most clean surfaces and to most industrial primers. 7. Since water is used for thinning and cleanup, costs are minimized. 8. The coating���s low flammability, offers potentially reduced insurance costs and improved working conditions. 9. The coatings may be applied with most conventional spray equipment, but 185

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