Лако-красочные материалы — производство

Two types of isocyanate compounds, differing greatly in their reac­tivity, coating performance and cost, are (a) aromatic isocyana­tes and (b) aliphatic isocyanates. Aromatic isocyanates have much higher reactivity with active H-compounds than aliphatic isocya­nates. Polyurethane coatings based on aromatic isocyanates suffer from poor resistance to sunlight exposure (poor UV resistance), poor gloss retention and significant discoloration and chalking ten­dency upon exterior exposure. Aliphatic isocyanates have excellent resistance to exterior exposure and discoloration and therefore are preferred candidates for polyurethane coatings designed for high performance exterior applications. However, their substantially high cost restricts their use in some applications.

Isocyanate compounds are supplied in both monomeric as well as polymeric forms. The monomeric isocyanates are generally low MW liquid difunctional materials and are used as primary building blocks. Due to their greater toxicity, they must be handled very carefully, and generally, free monomer content is restricted in the

final products. Figure 2.61 shows some examples of isocyanate com­pounds used for paint and coating applications.