Reaction injection moulded polyurethane products

Both products are made in a similar manner. Release agent is applied to the clean mould surface and allowed to dry. To overcome the problems of poor UV stability and to reduce production costs, a surface coating is sprayed on to the mould surface and allowed to dry. Mould temperature is 40-90°C to speed 

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Not only are these reactions of importance in the development of the cross-linked polyurethane networks which are involved in the manufacture of most polyurethane products but many are now also being used to produce modified isocycuiates. For example, modified TDI types containing allophanate, urethane and urea groups are now being used in flexible foam manufacture. For flexible integral foams and for reaction injection moulding, modified MDIs and carbodi-imide MDI modifications cU"e employed. 

Protection from isocyanate vapours liberated during polyurethane manufacture is usually achieved by installing permanent exhaust ventilation units which either exhaust directly to the atmosphere or pass their exhaust fumes through scrubbers which extract the isocyanate vapour through a sodium carbonate spray tower before atmospheric exhaustion occurs. Continuous vertically positioned exhaust hoods are common where continuous conveyor lines are involved for localized extract situations, vertical down-draught or horizontal extract modes are much safer for operatives, being designed to remove all isocyanate vapour away from an operative s face and body. These latter situations apply particularly in the manufacture of cast-moulded and reaction-injection moulded products. 

The modern polyurethane (PU) foam sole may be regarded as evolving from these processes. Both direct and indirect processes are used. The moulding process is an application of reaction injection moulding (RIM), in which the appropriate chemical reagents are metered via a mixing chamber into the mould, where the polyurethane forms. Clarks process produces microcellular foams but, for some products, separate injections of skin and foam (two-shot process) has been adopted more recently. 

The production of integral foams requires the metering and fast mixing of reactive components and the injection of the resulting mixture into a closed mould. This process is known as reaction injection moulding (RIM). It may be noted that reaction injection moulding is applied mainly to polyurethanes but the process can be used with other systems, e.g. polyamides (see section 10.2.3(d)). 

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