Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 174 of 331

velop sprayable UV products. By the late 1980s the UV market matured sufficiently to justify the develop- ment costs of safer UV raw materials. Only as recently as the early 1990s were research efforts undertaken to inves- tigate the underpinning principles and complications of spray applying sol- ventless, 100% solids, liquid, and UV-curable coatings. In the technology's infancy, UV processing was referred to as "radiation" or "rad- cure" technology. This came back to haunt the budding UV industry because the layman factory worker interpreted radiation to mean the type of radiation as- sociated with nuclear radiation. UV radiation is simply light radiation and is by no means the type of radiation associated with nuclear (radioactive) materials. UV processing received heightened scrutiny over the last 30 years, which has resulted in remarkably good record in terms of health, safety, and economic benefits. The health and safety record has been so favorable that in Septem- ber of 1996 UV-curable resins (acrylates) were removed as a group from the U.S. EPA's list of suspected carcinogens. This had the effect of spurring on re- search efforts to design, develop,and market new UV-curable raw materials. Cor- respondingly, the formulator's arsenal of raw materials have grown dramat- ically, which has in turn increased the latitude to design products with specific properties. THE PROCESS UV light energy triggers or powers a desired chemical reaction that converts a 100% solids (liquid), UV-curable, coating into a solid. The industrial con- vention of designating a liquid coating as 100% solids indicates the near to- tal absence of volatile solvents in the coating formulation. The near total absence of volatile solvents eliminates the traditional reliance on evaporation to form a dry film. Eliminate drying time and conversion of a wet coating into a dry finish occurs in a matter of seconds. No flash-off or drying time im- mediately translates into dramatically increased production speeds for the user along with attendant and significant secondary and tertiary economic and lo- gistical benefits. Green plants and flowers naturally use UV light to power their internal chem- ical reaction known as photosynthesis, which is the atmospheric source of life sus- taining oxygen. Plants derive their energy directly from UV light — the same type of UV light used in industrial UV processing. UV light is just beyond the blue end of the visible spectrum for humans. The UV band (400–190 nm) is divided into three primary bands designated: UVA, which lies between 440 and 320 nm (also known as black-light); UVB, which lies between 320 and 280 nm (also known as erythermal UV),and; UVC, which lies between 280 and 180 nm (also known as actinic UV or ger micidal UV). UVC is generally used to sterilize operating rooms and food-handling facili- ties. The odd, pale blue lights seen in restaurant kitchen areas and hospitals are germicidal UV lights. UVC causes sunburns to human eyes and skin. Overexpo- sure of eyes to UV light causes very uncomfortable irritation, identical to that as- sociated with arc welding. This condition is completely reversible, leaving the vic- 173

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