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New technology speeds curing of urethanes.

Sherwin-Williams Co. has introduced a new coating process that it says can speed the curing of high-performance, two-component urethane coatings for wood finishing applications, without baking.

Called the Vapor Injection Cure process (VIC), the new technology uses an amine vapor catalyst to produce a rapid catalytic cure. The process is designed to work with urethanes which contain a blocked accelerator that is activated during the coating application by the amine vapor catalyst.

Sherwin-Williams says it developed VIC in an effort to meet new strict environmental regulations limiting volatile organic compound emissions while balancing quality and productivity considerations. The company says that the VIC process is one answer to these needs in that it allows rapid cure of high-performance, low-VOC coatings to take place at air dry or low-temperature cures.

The VIC process involves a patented two-component urethane chemistry which combines a liquid polyol resin with a cross-linking resin. The process can accommodate all of Sherwin-Williams Polane urethane finishes, which offer chemical, solvent and stain resistance; humidity and water resistance; and mar and abrasion resistance.

Critical to the VIC process is a blocked accelerator contained in wet Polane coatings. The accelerator is unblocked when it comes in contact with an amine vapor catalyst.

Coating material and the amine catalyst are brought together using a portable VIC amine generator, which supplies a predetermined concentration of amine vapor dispersed in an air stream channeled into the spray gun. The coating material and catalyst meet at the point of atomization -- outside the spray gun as the coating is being propelled toward the substrate.

VIC coating characteristics

Depending on film thickness (which can range from 0.5 to 3 or more mils DFT), pencil hardness can be achieved in 15 to 45 minutes with no baking required, the company says.

VIC process coatings can be used on a broad range of substrates including wood, plastic, steel, aluminum and castings. Since dry times are drastically reduced, faster handling is allowed. Other reported advantages of the process include decreased operating energy consumption costs, decreased space requirements for paint curing, reduced rejects caused by uncured paint and reduced recoat/tape time for multiple coats/colors.

Equipment requirements

The VIC process has been designed to be compatible with most conventional air-assisted airless, electrostatic and high-volume-low-pressure spray equipment with minor or no modifications. Modification of electrostatic equipment may be required for some spray guns to accommodate the use of the VIC amine generator. A thorough evaluation is recommended to determine the compatibility of a particular spray gun system before it is used with the amine catalyst. For example, seals utilized in the spray guns should be evaluated for compatibility with dimethlyethonalamine. Some plastic or rubber seals will degrade if they are sensitive to this amine.

Air-assisted airless spray systems have been used long-term with the VIC process. Minor modification of the spray cap may be necessary to increase the amount of atomizing air available to allow sufficient catalytic air to facilitate curing. The air horns may have to be increased in size to permit a higher volume of air to be used with the gun.

With electrostatic spray, in-the-gun air driven turbines which generate the electrical charge should use house air to drive the turbine, not amine-laden air. House air also should be used for actuator switches.

Other equipment required for the VIC process includes a relatively simple amine catalyst generator, which typically can be connected to any existing house air supply. This air serves as the carrier for the amine catalyst, either as atomizing air in the case of conventional air spray and air-atomized electrostatic spray, or as assist-air in the case of air-assisted airless spray.

The amine catalyst generator is a Class I, Division II rated portable generator made of aluminum for light weight and mobility. The generator capacity is 15 to 30 cubic feet per minute of atomizing air, limited to two spray guns. The unit used dried and filtered air available to use at 90 to 120 pounds per square inch.
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Title Annotation:vapor injection cure process
Publication:Wood & Wood Products
Date:Feb 1, 1993
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