Process for the production of a lightfast and colorfast composite plastic part

A process for the production of a lightfast and colorfast composite part of cellular plastics by the successive introduction of reaction mixtures into a closed mold with a rigid cavity, such that the first mixture is foamable and is introduced into the cavity, then a second reaction mixture is introduced into the cavity, after the first mixture has at least become resistant to permeation, but is still compressible, such that the second reaction mixture surrounds the first mixture and compresses it, characterized in that

• A. the first reaction mixture comprises aromatic isocyanates having isocyanate contents of from 5 to 50%, by weight:
• one or more compounds with molecular weights of from 32 to 10,000, which contain at least two isocyanate-reactive hydrogen atoms, such that the equivalent ratio of isocyanate to compounds containing isocyanate-reactive hydrogen atoms is from 0.8:1 to 5:1:
• and from 0.1 to 20%, by weight, (based on the reaction mixture), of a blowing agent comprising a compound which releases CO.sub.2 ;
• and
• B. the second reaction mixture comprises aliphatic, cycloaliphatic, or a combination of aliphatic and cycloaliphatic polyisocyanates having isocyanate contents of from 10 to 50%, by weight:
• one or more compounds with molecular weights of from 32 to 10,000, which contain at least two isocyanate-reactive hydrogen atoms, such that the equivalent ratio of isocyanates to compounds containing isocyanate-reactive hydrogen atoms is from 0.8:1 to 5:1;
• and an internal mold release agent selected from the group consisting of polysiloxane, hydroxypolysiloxanes or salts of polysiloxanes containing amino groups with long chain fatty acids.