Water-Blown Rigid Foams

Abstract

With the scheduled phase out of CFCs near at hand, many companies have been investigating completely water-blown (CO2) rigid foams. Several problems surfaced immediately such as a substantial increase in k-factor, a reluctance for the foaming mass to flow and fill molds properly, and a tendency for the foam to be dimensionally unstable in the density range commonly considered.

Several applications do not require that k-factor be the primary concern. For instance, the insulation provided by some units containing rigid foam is affected by the tightness of the lid to the case, and insulation is required for only a limited, not an extended period of time, as for example, a picnic cooler. In such applications, a water-blown foam provides sufficient insulation and rigidity in the cooler walls to provide a satisfactory result. However, the foam in such cases must be dimensionally stable, i.e., over a period of time in which the cooler may be subjected to a number of heating and cooling cycles, the foam must not shrink, expand, or distort. One method to accomplish this is to use open-celled foam, since the cells contain no trapped gas to exert internal pressure on heating or cause a semi-vacuum on cooling.

At BASF we have uncovered a family of additives which act as cell openers when added to resin formulations. Using standard rigid foam polyols, we have prepared foams with densities as low as 0.90 pcf which show less than 5% dimensional changes when kept at 158°F and 100% R.H. for 28 days. The measured closed cell content can be as low as 3-5%, although foams in the 1.1-1.4 pcf density range were found to be dimensionally stable at closed cell contents as high as 88%.