CURING STUDY AND OPTIMIZATION OF A POLYURETHANE-BASED MODEL PAINT COATED ON SHEET MOLDING COMPOUND PART II: DRYING DEFECTS RELATED TO CURING CONDITIONS

ABSTRACT

This study deals with the bubbling phenomenon which appears in some drying conditions on paint films applied as thin layers on SMC substrates. The bubbles and craters origin can be due either to reactions which may occur at the interface paint / SMC either to inadequate drying conditions which affect the polymerization reaction (gelation, viscosity) and the solvent vaporization.

Firstly, we reported data describing the solvent interaction with the SMC substrate - namely the contact angle, the interfacial tension, the absorption kinetics and the sorption isotherms - and the relationship between the bubbling defects and the numerous process variable (operating conditions, paint formulation and support properties).

Then, we gathered experimental data concerning the influence of different parameters (state and type of substrate, temperature, heating mode, film thickness. paint formulation, etc.) on the bubbling phenomenon and we tried to establish some quantitative interpretation. It proved that this defect was mainly due to the SMC heterogeneity expressed by the porosity of this composite material.