Coatings update: high solids coatings

An interesting article by Bauer and Briggs has described a means for predicting flow properties of high solids coatings formulated with and without flow control agents. The flow properties were studied, starting with spray application and continuing through until curing. The solvent content in the coating film was measured by high performance liquid chromatography as a function of time after spray. A kinetic model was used to determine the increase in molecular weight and correspondingly in viscosity during cross‐linking. The rheological behaviour of the polymer solutions, which contained a polymeric microparticle flow control agent was measured. Also, models were developed to calculate the sheer stress as a function of sheer rate for different coatings, and these were related to the concentration of the flow control agent. Finally, all of the above data were used to calculate the sag of coatings as a function of time after spray with and without flow control agents. Although the addition of a flow control agent reduces sag during baking, it also tends to inhibit levelling. Also, the appearance of the high solids coating containing the flow control agent is more sensitive to film thickness than are low solids coatings.