Our filler, based on polyester and 5 % styrene, is subsequently overpainted with nitrocellulose. After a few days.however, it swells. What would you suggest we can do?
Polyester fillers curing with 5 % styrene should present no curing problems provided sufficient stabilised styrene monomer is present. The first step would be to check whether any polystyrene is present, due to accidental polymerisation of the styrene monomer.
Evidently, crosslinkage is not enough to prevent swelling by the solvent. Here, it might help to modify the polyester resin formulation. For example, the dicarboxylic acid and polyalcohol components could be modified in such a way that curing is unaffected and, above all. Is complete. This can be achieved by incoporating compounds with an allyloxy structure. The use of hydrogenated bisphenol A in the poloyol component has also proved successful. One could also incorporate other unsaturated monomers besides styrene monomer, eg vinyl or acrylic monomers.