Polyurethane Rigid Foam Systems for Metal-Faced Sandwich Panels for the 1990s

Abstract

Sandwich panels with polyurethane rigid foam cores are important building elements for a wide variety of applications. They are used for the cost effective construction of industrial and commercial buildingsand in many stages of the food chain, including cold storage, cold rooms and refrigerated transport containers and trucks. The blowing agent used in the foam systems has traditionally been CFC-ll. This has contributed to the excellent thermal resistance of the panels but its use will be phased out by the year 2000. Foam systems have been developed based on a wide variety of alternatives. These are designed to suit various national and international CFC phase-out schedules. These include systems based on 100% CO2, HCFC-22, HCFC-123 and HCFC-141b. In all cases the formulations have been based around the particular blowingagent to obtain the best combination of processing, physical and thermal resistance properties. Because the HCFCs are now accepted to be transitional substances with a finite production lifetime, the foam systems based on HCFC-123 and -141b are designed to be “drop-In” replacements for those based on CFC-ll. This means that all changes are incorporated into the foam system rather than into the production process and that thermal resistance with those blowing agents equals that for systems based on CFC-11. These panels have an important structural role to play and, in addition to the retention of foam strength, the adhesion between the foam and facing plays an important role in the overall performance of the panel. The parameters affecting adhesion have been investigated with the alternative systems and optimised processing conditions determined. A family of foam systems has been developed to serve the metal-faced sandwich panel industry through the 1990s.