Vapor catalyst speeds coatings' cure.

An unusual urethane spray coating technology applied primarily to metal finishing since it was developed seven years ago was recently reintroduced by a different supplier and is now being targeted at plastics. The Vapor Injection Cure (VIC) process was developed in the mid 1980s by Ashland Chemical Co., Columbus, Ohio, and purchased two years ago by Sherwin-Williams Co., Cleveland. (see PT, Aug '86, p. 15 and April '87, p. 12). Sherwin-Williams is optimistic about its potential for coating fiber-reinforced plastics. Already, the company says, a few customers are employing it in plastics applications.

Using an amine vapor catalyst to produce an extremely rapid catalytic cure at temperatures between 130 and 140 F, the VIC system has been reported by at least one user to reduce the drying time of a polyurethane enamel on metal from 8 hr to 1 hr. Sherwin-Williams, more conservative estimates put VIC cures 50-60% faster than thermal curing on either metal or plastic. Sherwin-Williams says the VIC process can also speed curing of urethane coatings at room temperature, making it appealing for use with heat-sensitive substrates such as thermoplastics.

The keys to the Polane VIC coating system are a patented, two-component urethane chemistry that uses a special blocked accelerator that becomes unblocked in the presence of the amine vapor catalyst.

Coating material and amine catalyst are joined using a proprietary VIC amine generator. The portable generator disperses a predetermined concentration of amine vapor in an air stream, which is supplied to the spray gun. The coating material and catalyst vapor stream meet at the point of atomization--just outside the spray gun as the coating is being propelled toward the substrate.

Depending on the thickness of the coating, pencil hardness reportedly can be achieved in 15-45 min with no baking.

The VIC system is similar in concept to two other rapid curing systems on the market for plastics uses. One is Ashland's VPC (vapor permeation curing) system, in which the coatings are cured at room temperature in a chamber filled with catalyst vapor (PT, Sept. '82, p. 13 and Sept. '83, p. 15). The other is the Vapocure system, sold by Vapocure Technology Inc., Paterson, N.J., which is also a room-temperature process that cures paint by exposing it to a vaporized catalyst atmosphere. Both have so far found limited use in plastics.

EQUIPMENT NEEDS

Sherwin-Williams says its VIC process is compatible with most conventional, air-assisted airless, electrostatic and HVLP spray equipment. Electrostatic equipment may have to be modified for the spray guns to accommodate the VIC amine generator. However, Sherwin-Williams cautions that each spray equipment system should be evaluated for its compatibility with the amine catalyst because some of the plastic or rubber seals used in the guns degrade when they come in contact with the dimethylethonalamine (DMEA) catalyst. Air-assisted airless systems may have to have their spray caps modified to increase the amount of atomizing air available to ensure sufficient catalytic air is available for curing.

The amine catalyst generator used in the VIC system can be connected to any compressed-air supply, Sherwin-Williams says. The generator itself is rated Class I, Division II. It has a capacity of 15-30 cfm atomizing air, is limited to two spray guns, and can use either dried or filtered air at pressures from 90 to 120 psi. Sherwin-Williams leases the amine generator for $336.76/month on a 60-month lease.

(CIRCLE 19)