Лако-красочные материалы — производство

(i) Molecular Weight

This should not be too high, otherwise the flow of the film during deposition will be adversely affected. The film needs to be liquid when it contains pigment and crosslinking agent, and so the resin system needs, in fact, to be quite low molecular weight to bring this about. It needs to be borne in mind that the film when deposited is substantially solvent free, so too high a molecular weight cannot be compensated by increasing the solvent content — changing the vehicle solids of the bath does not make any difference to the solids of the deposited film! Molecular weights in the region of 2000 — 4000 should be aimed for to start but, of course, it may be necessary to modify this if evaluations indicate the need. This corresponds to a viscosity of about 5-10 stokes at 50% solids (although viscosities vary very widely with the solvent).