Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 83 of 331

BAKED ALKYDS, MODIFIED ALKYDS AND ACRYLICS Alkyds, modified alkyds and acrylics should be cured using a water-reducible bake at temperatures less than 90°C (194°F). Advantages 1. Coatings are available at VOCs less than 360 g/L (3.0 lb/gal), less water; and some even below 275 g/L (2.3 lb/gal), less water. 2.The coatings have excellent film performance, often equivalent to polyurethanes. 3.The coatings are made for use on metal substrates only due to high temper- ature of bake, except perhaps for high-temperature plastics. 4.There are no pot life limitations; the coatings are a one-component materi- al. 5.Water is the primary solvent. 6.The coatings can be spray applied with standard application equipment. 7. Touch-up and repair is possible, although this should first be con firmed by experimentation. 8.The coatings are available in a wide range of colors and gloss levels, and can be used for texture finishing. 9.The coatings meet industry standards for many top-of-the-line ap plications, such as computers, business machines, lighting fixtures, ap pliances, automotive, coil, etc. 10.The coatings are available as primers and topcoats, although the coating can sometimes be applied directly to metal without the need for a primer. 11. The coatings have a lower fire hazard and lower toxicity than solvent-based systems. 12.Costs are lower for reducing solvents and cleanup. Disadvantages 1. The coatings require a high-temperature oven, 121–204°C (240–400°F), for more than 10 minutes. 2.A larger energy supply (and cost) is required. 3.The coatings are not for use on plastics, and other heat-sensitive sub strates, except perhaps some high-temperature plastics. 4.Performance on porous castings is unreliable due to outgassing, un less special precautions are taken to minimize the problem. 5.Touch-up may require a second bake or use of another air-dry coating. 6.The coatings are not applicable where parts such as machined surfaces have tight dimensional tolerances and cannot tolerate warpage. 7. Surface cleanliness is more critical than for solvent systems. 82

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