Improved intumescent: Topcoat allows better laminate performance

Wright Composites (Galgorm, Ballymena, Northern Ireland) manufactures composite parts for passenger vehicles, including commercial buses. Parts must not only meet demanding quality and mechanical-performance criteria but also Class 1 British Standard (BS) 476 Part 7 fire retardant (FR) requirements. Historically the company has used Scott Bader Company Ltd.’s (Wollaston, Northamptonshire, U.K.) products, including Crystic Fireguard intumescent topcoat, to ensure fire performance. Applied to a cured laminate surface, the topcoat provides a passive fire barrier that is required on some interior passenger bus parts: Exposed to temperatures of ~200°C/~392°F, the coating, via a chemical reaction, swells and chars, forming a nonflammable layer that insulates the underlying surface and prevents it from burning.

Scott Bader released its improved Crystic Fireguard 75PA Excel topcoat this year, reputed to offer better fire protection and easier handling than the original product and curable to a tack-free state within 30 minutes with a standard methyl ethyl ketone peroxide catalyst. Wright Composites tried it and, says Wright’s general manager, Andy Colhoun, “Because of the Class 1 fire rating performance of Fireguard 75PA Excel, we found we could actually use a Scott Bader Crystic Class 2 laminating resin for our parts, rather than a Class 1 resin.”

The Class 1 resin, which must be highly filled with FR additives, made laminates somewhat brittle, limiting mechanical performance. The Class 2 resin, with less FR filler, is structurally tougher, and with the new topcoat, it meets the Class 1 BS standard. The topcoat withstands direct flame at 700°C/1292°F for more than 60 minutes without the underlying laminate catching fire (see comparison in photos). Colhoun sums up, “Customers benefit from having FR-rated parts with tougher performance capabilities.”