In-mold coatings advance on many fronts.

As reported previously, the latest news in in-mold coatings is a one-component topcoating system for thermoset polyester SMC compression molding, which was introduced by Sherwin-Williams Co., Cleveland, at the recent SPI Composites Institute conference (see PT, Jan. '91, p. 37). The company is already known for its vinyl ester-based, one-component in-mold black primer for automotive SMC. The new in-mold topcoats are non-automotive, polyester-based, and eliminate the need for priming. One series of topcoats is aimed primarily at sanitary ware, such as sinks and bathtubs. Another is an exterior durable line, for which applications in recreational equipment and building/construction supplies are in active development.

The topcoats are composed of 100% solids with near-zero volatile emissions. The technology requires a metering and injection machine (sold by firms such as Morrell, Inc., Auburn Hills, Mich.), which is integrated into the SMC molding press. The topcoat reportedly mirrors the gloss level of tool surfaces. (CIRCLE 5)

WORK ON RTM, PULTRUSION 

That's only one of several new in-mold coatings developments in the works at Sherwin-Williams, according to plastics market manager John M. Clifford. The firm is now field testing a new faster curing system for thermosets, which will reduce cure times as much as 30-40%, overcome streaking problems, and offer a broader range of adhesion, according to Clifford.

Besides SMC, Sherwin-Williams is pursuing new markets for its one-component systems in thermoset RTM, where they're said to eliminate the need for gelcoats, and in in-line coating of pultruded profiles for various exterior applications. In pultrusion, the coatings may be applied either inside the main forming die or downstream. Clifford notes that patents are being filed by processors working in this area. (CIRCLE 6)

THERMOPLASTICS & RIM, TOO

What's more, the company also is continuing work on a two-component, polyurethane-based in-mold coating for injection molded thermoplastic components, which may be unveiled later this year, after five years in development (see PT, Sept. '88, p. 81; Feb. '89, p. 14). Like SMC in-mold coatings, this application reportedly does not add to the mold cycle time and has two advantages over spray painting: no solvent emissions and 100% utilization of coating materials.

Clifford emphasizes that the company is not yet ready to entertain customer inquiries on this technology, known as High Pressure Injection In-Mold Coating. Remaining obstacles, Clifford says, are primarily equipment-related. How to achieve efficient color changes is one aspect still being investigated. Sherwin-Williams has worked primarily with RIM machinery from Krauss-Maffei Corp., Florence, Ky.

Clifford sees major thermoplastic opportunities outside of automotive--in off-road vehicles, lawn-and-garden equipment, and business machines. Down the road, EMI shielding may be a potential application. There is also significant automotive potential, such as thermoplastic instrument panels and bumper fascia.

Clifford also says the thermoplastic system, once fully developed, could be applied to thermoset urethane RIM, SRIM and RTM (in applications where cure temperatures are too low for the one-component coatings). Current in-mold technology for RIM involves spraying a solvent paint into the open mold before injection.