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December 7, 1998

5 Min Read
Coating system brightens PC performance outdoors

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Guzzini Engineering's PC/UP treatment can be done in line with a molding operation. Treated parts can be packed and shipped with no curing time.

An Italian company has a solution to a frustrating problem with polycarbonate: the yellowing that UV rays cause in PC material in outdoor applications. Guzzini Engineering's solution is a coating system. Tests comparing coated to uncoated PC light fixtures have shown virtually no yellowing or reduction in light transmission in the treated parts (see charts, below). Meanwhile, untreated parts had a 13 to 14 percent reduction in light transmittance. The system offers production advantages as well: The curing time needed is brief enough that the system runs in line, and a minimal level of solvents and other volatiles makes it significantly more environmentally and operator friendly than traditional paint systems.

Though it is a factor in any outdoor application, UV-induced yellowing of PC is most often associated with outdoor lighting globes, which is the entry point for Guzzini, a division of Acrilux Guzzini SpA, a high-volume producer of a broad spectrum of light covers, including the outdoor PC type. Guzzini Engineering emerged from the in-house mechanical engineering, moldmaking, and machine building activities of Acrilux to become an independent business supplying mold components, nozzles, and now, in-line paint systems. This coating system, called PC/UP, has been in operation at Acrilux for five years and is now being offered commercially worldwide. The coating material used in the system is an acrylic-based proprietary formula supplied by CHR Lechler of Como, Italy.

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Aesthetics is a minor IssueThe fact that PC outdoor lighting fixtures will be influenced by UV rays over time has not prevented them from gaining a solid share of that market. Given that PC's toughness solves such major problems as longevity and resistance to vandalism and its lightness makes it easier and safer to handle than glass, its share of the outdoor lighting market has grown to nearly 30. Lighting design engineers normally calculate a light loss factor (LLF) into their illumination plans to compensate for the light cover becoming less efficient over time. The LLF includes the fixture getting dirty, and in the case of PC fixtures, they factor in a value for the UV-induced yellowing. The LLF with a PC fixture is generally around .7 and equates to the 13 to 14 percent transmittance loss mentioned previously. The use of PC/UP products permits a significant reduction in the LLF.

To compensate for the LLF, the lighting designer has to specify proportionately more wattage. Thus, the light consumes more electricity than actually needed to illuminate the specified area. How much more? About 16 percent, and that needs to be placed in a larger perspective.

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Lighting takes 20 to 25 percent of the electricity used by industrialized countries. Outdoor lighting takes 20 to 30 percent of that share. Fixtures with PC globes and covers constitute a 20 to 30 percent share of the total outdoor lighting or about 156 billion kWh of electricity. Because about 16 percent of that is wasted due to light transmittance loss, around 12 million tons of coal or 47 million barrels of oil are wasted generating that power. Coal and oil, not to mention the energy generating plant itself, cost money. Much of the outdoor lighting is for public spaces such as roadways, which means a sizeable share of this cost is ultimately paid by you. Electrical use is steadily growing and outdoor lighting along with it. North American electrical consumption is due to rise from a 1995 total of 3.6 billion kWh to 4.7 billion in the year 2010, but the growth is worldwide.

The products made using PC/UP technology have other advantages beyond the improved resistance to UV-induced yellowing and resultant light transmittance loss. The brilliance of the molded item remains more constant over time because the coating improves resistance to surface deterioration. The harder surface is more abrasion resistant. Normal PC is rated HB and PC/UP is 5H using the pencil test according to ASTM D3363-74. Chemical resistance is close to that of PMMA. The owner of the light will have reduced maintenance because less dirt adheres to the surface. As we well know, all of these advantages amount to little if the production system needs too much space, requires heavy environmental protection, adds too much time to the production cycle, or simply costs too much to buy and/or operate. Guzzini, by virtue of being close to its parent company's manufacturing operations, included these requirements in the design specification of the PC/UP system.

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The cost of a system depends largely on the item or items to be coated. If the product is a 10-by-10-by-5-inch PC enclosure, we would be talking about a few thousand dollars. For lighting globes up to 600 mm (23.4 inches) in diameter, the cost would be around $200,000. Process costs are about $.0006/sq cm ($.000093/sq in) for coating globes and less for flatter shapes. VOCs (volatile organic compounds), such as aromatics and esters that keep coatings in solution until vaporized in convection curing ovens, are minimized in this system. There is no need for VOC incinerators. The electricity used for the entire system is less than that used for curing in conventional ovens. Perhaps best of all, the short curing time means the coating can take place in line with a molding operation, as is done at Acrilux, and parts can be packed and shipped at the end of the line without a curing time. The total system space can be 75 to 90 percent less than that occupied by a coating operation that calls for curing and VOC incinerators.

Guzzini has only recently begun marketing the PC/UP system. Product samples were on display in the GE Plastics stand at the recently concluded K'98 trade fair in Dusseldorf, Germany.

Contact Information
Guzzini Engineering, Div. Acrilux SpA
Recanati, Italy
Andrea Guzzini
Phone: +39 (071) 75891
Fax: +39 (071) 7574373

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