Foamed self-skinning

Molds for PUR Integral Skin Foams (Self-Skinning Foams)... 

The article describes the process of producing expanded polypropylene foam parts with a solid integral skin on one side, citing a bicycle helmet moulded from BASF s Neopolen EPP bead, as an illustration. The self-skinning EPP process reqnires some modification of standard beadmoulding equipment, needing an extra steam chamber. Automotive interior trim is a potential application for the process. 

The passive protection of pedestrians from car front ends can be considerably improved, compared with present day conventional constructions, by the use of a PE foam core with a PU self-skinning foam jacket for this car component. The values achievable with such a flexible front end as well as the effects on a dummy representing a pedestrian are investigated for an impact speed of 45 km/h. 3 refs. 

J. L. Throne, Note on the Mechanical Strength of Self-skinning Foams, J. Cell. Plast., 8, 208-210 (1972). 

Integral-skin foam is referred to as self-skinning foam or self-skiimed foam. The foams have high-density skin layers and low-density cores. The overall densities vary in the range of about 200 to 1,100 kg/m (12 to 70 px f). 

The glass transition temperature lies considerably above the temperature of use with rigid foams and considerably below the temperature of use with flexible foams. The cellular structure may be open, closed, or mixed. All cells are open to each other with open cellular structures. In contrast, each cell is sealed off or encapsulated from the other cells by a plastic wall in closed-cell structures. Structural foams are foams with a dense outer skin and an interior of lower density they are also called integral foams or self-skinning foams. In contrast to normal foams syntactic foams do not directly enclose the gas but contain small hollow bodies of glass, ceramics, or plastics which are under vacuum or are filled with a gas. 

The water-isocyanate reaction forming carbon dioxide is commonly used to form open-cell flexible foams. Trichlorofluoromethane (TCFM) is a physical blowing agent relying on heat from the urethane reaction exotherm to boil this is used to form rigid closed-cell foams and most self-skinned moulded products. There is considerable concern over the effect of fluorocarbons on the Earth s ozone layer, and suitable replacements are actively being sought. 

Figure 11.7 Range of in-mould coated, semi-rigid, self-skinned PU foam mouldings. By permission of Marley Foam, Sheller Clifford and Bridgtown Industries...

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