Paint & Coatings Industry - March 2009 - (Page 38) New Sulfonic Acid Catalysts for Coil Coatings A 120 100 MEK DR 80 60 40 20 0 Initial 7 new class of blocked sulfonic acid catalysts has been developed that promotes the crosslinking reaction of hydroxylfunctional polymers with amino-formaldehyde crosslinking agents such as hexamethoxymethyl melamine, especially in coil coatings. These catalysts are particularly effective in coil primer formulations containing calcium ion exchange anti-corrosive pigments. In addition, the unique deblocking profile of these catalysts provides the so-called snap cure at the desired peak metal temperature, and within the specified time. Introduction Coil coatings are high-performance liquid coatings applied to flat steel and aluminum metal strips before they are fabricated into the final product. Coil coatings are applied in a continuous process at very high line speeds, baked in seconds at very high temperatures and rewound for delivery to the user. The metal strip must then be cut and further fabricated without cracking, chipping or scratching the finish. The process is value added and offers several benefits. It is environmentally friendly, non-polluting and with the ecological advantage of little or no waste. Most lines usually use the exhaust air (containing solvents) from the hoods over the coaters to heat the ovens and hence recycle the residual heat from the oven exhaust. Thus burning the solvent eliminates VOC emissions from coil lines and the fuel value of the solvent is recovered. It offers several technical advantages too, including ease of application and can be applied at speeds of up to 180 meters (600 feet) per minute (fpm) and as fast as 240 meters (800 feet) per minute, at both sides of the metal strip. The faster coating application rate leads to lower labor costs. Film thickness is more uniform as compared to those derived from coating pre-formed parts. The elimination of VOC and HAPs emissions and fire hazards associated with application of these coatings leads to potentially lower insurance cost as well. Thus the manufacturers of the end-use product will not have to deal with VOC concerns, pollution control equipment and paint sludge disposal. Coil coatings on steel and aluminum currently amount to about 36 MM gallons, valued at over $570 MM, with solventborne polyester/melamine being the most widely used. Use for building products contributes to half of the total volume valued at over $280 MM, with overall growth of about 3%/year.1 Major end-use segments include construction, transportation, appliances, furniture, and HVAC (heating, ventilation and air conditioning). Some coil-coated metal application examples include roofing, original siding of mobile homes, garage doors, Venetian blinds, doors and windows, rain gutters and downspouts, passenger cars, vans and light trucks, buses, kitchen counters, cookware, refrigerator boxes, home and office furniture, cabinets, fixtures and shelving, can ends and bodies, tabs and closures, signs and displays. One of the controlling factors for coil coating line speed is the oven dwell time necessary to cure the applied coat- FIGURE 1 | Cure (MEK DR) as a function of oven aging (50 °C). Control Nacure XC-194 14 21 28 Days at 50 ºC Storage FIGURE 2 | Viscosity as a function of oven aging (50 °C). 500 450 400 Viscosity, cPs 350 300 250 200 150 100 50 0 Initial 7 14 Days at 50 ºC 21 28 Control Nacure XC-194 By Ravi Ravichandran, Ram Subrayan and Robert Coughlin | King Industries, Inc., Norwalk, CT 38 MARCH 2009 | W W W . P C I M A G . C O M http://WWW.PCIMAG.COM
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