Stacy M. Trey, Kamyar Alavi, Mikael Lundstrom, Daniel Ståhlberg, Mats Johansson

Sheet molded compound (SMC) is a highly filled, glass fiber reinforced, thermoset material used in trim and body panel automotive parts. When SMC-substrates are coated with conventional thermally cured paints, inherent porosity and entrapped volatiles of the substrate result in popping (“paint pops”) defects. UV-curable primers provide an order of magnitude reduction of paint defects in SMC coatings, but typically have poor adhesion. The present study investigates a dual-cure approach to address both the popping defect problem and the poor adhesion of UV-curable primers. An initial UV-curing will seal the SMC-surface and subsequent thermal cure will improve the adhesion.

A series of di- and triacrylate resins is studied, showing the effect of resin functionality and resulting degree of cure shrinkage on the adhesion of the coatings to SMC substrates. The effect of resin functionality and isocyanate content (0-5 wt%) on cure shrinkage is determined by the dynamic shear modulus and film thickness, measured by a dynamic torsional rheometer. Gelation kinetics and equilibrium conversion are also examined as a function of temperature and functionality of the resins. The in-plane stress of the films is measured independently by the bilayer beam bending technique and compared to predicted values calculated from the storage modulus and the thickness contraction after gelation. The present study demonstrates that a UV-primer can solve several of the present problems with SMC-coatings as well as impart the key parameters in the design of such a primer system.

Dr. Stacy Trey received her B.S. in Chemistry at the State University of New York at Oswego in 2002.  She then graduated with her Ph.D. in Polymer Science and Engineering in 2007 from The University of Southern Mississippi where her area of study was the synthesis and characterization of polyurethane poly(ethylene glycol) hydrogel films and microgels.  After graduating she worked for 3 months at the startup company Ablitech Inc. in Hattiesburg, Mississippi where she synthesized small molecules for application in polymer materials for biomedical applications.

She is now at The Royal Institute of Technology as a post-doc for Mats Johansson in the Coatings Technology Group of the Fiber and Polymer Technology department where she is working in the area of acrylate and thiol-ene UV curable films.  More specifically within these areas, the adhesion modification of acrylate coatings with isocyanate and thiol additives for use as primers on sheet molded composites.  Additionally work has begun on the addition of ene and acrylate functionalized dendrimers into thiol-ene crosslinked films and the resulting structure-property relationship.