Self-skinning foams and the RIM process

A critical factor is the boiling temperature of the blowing agent and its relationship to the temperature of the walls of the mould and of the reacting mixture. There should be sufficient exotherm to vaporise the blowing agent in the centre of the reacting material but the mould walls should be sufficiently cool to 

Advantages of the RIM process over conventional injection moulding 

Disadvantages include the facts that painting of the moulding is often necessary to obtain a good finish, and the difficulty in using any cross-linked waste. 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

Interest in the RIM process appears to have abated somewhat in the 1990s. Nevertheless, nearly 100000 toimes of polyol and polyisocyanate were consumed for this application in the USA alone in 1993. 

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The GMP s process eliminates the use of sheet metal for the skin of the refrigerator door. In this application, the thermoplastic film forms a durable, protective outer skin with a wide choice of color options that are applied directly to the film. In addition more innovations exist apart from the film and thermoplastic interior liner, the doors consist entirely of polyurethane. GMP backs the thermoplastic film with an approximately 4 mm thick layer of the Baydur 110 structural foam polyurethane RIM system from Bayer AG that creates a rigid, dimensionally stable outer shell with no need for sheet metal. Then, GMP fills the space between this shell and the inner liner with insulating polyurethane foam, a rigid, low-density foam. The result is a self-supporting door that satisfies all stability, thermal insulation, and surface finish requirements. 

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