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- Trey, Stacy. M., et al.
(author)
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Effects of dual cure and surface treatments on coating adhesion to different SMC substrates
- 2009
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In: Plastics, rubber and composites. - : Informa UK Limited. - 1465-8011 .- 1743-2898. ; 38:2-4, s. 131-137
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Journal article (peer-reviewed)abstract
- Sheet moulded compound (SMC) is a highly filled, glass fibre 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 (UVP) provide an order of magnitude reduction of paint defects in SMC coatings, but typically have poor adhesion. The present study investigates a series of UVPs, showing the effect of resin functionality and isocyanate additive content on the adhesion of the coatings to SMC substrates. The SMC formulation is also considered regarding how variables such as surface chemistry, morphology, surface area and degree of post-mould emissions affect UVP adhesion. The present study reveals the crucial factors involved in achieving adhesion including the importance of low post-mould emissions, high surface areas, glass fibre and other oxygen moieties on the surface, and improved wetting of the surface.
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| 2. |
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| 3. |
- Trey, Stacy M., et al.
(author)
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Dual cure (UV/thermal) primers for composite substrates-Effect of surface treatment and primer composition on adhesion
- 2009
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In: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 64:4, s. 489-496
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Journal article (peer-reviewed)abstract
- It can be concluded by the Study of UV primer formulations on sheet molding compound (SMC) substrates that all studied formulation parameters affect adhesion. Moreover, the dual cure approach can result in acceptable adhesion of UV primers on SMC substrates if the coating procedure and composition are well designed. Adhesion of UV cure primers as determined by the cross-cut test is significantly improved in formulations containing solvent. This is a result of enhanced wetting and interaction of the solvent with the SMC Substrate, confirmed by contact angle and gravimetric swelling studies. Furthermore, sanded SMC surfaces demonstrated superior UV primer adhesion. This results from the increased surface area of the topography, confirmed by CSLM and the exposure of more oxygen moieties such as pigments and silanols at the air-substrate interface as confirmed by AFM and XPS, The UV films have a higher modulus with increasing resin functionality and resulting cross-link density which correlated with reduced adhesion in formulations without an added isocyanate functional UV monomer. This indicates that cure shrinkage may play a role in the adhesion of UV cure primers and will be investigated further. Also, the added adhesion that an isocyanate functional UV monomer provides results in a significant increase in the glass transition temperature (T-g) giving a glassier film at room temperature.
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| 4. |
- Trey, Stacy M., et al.
(author)
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Effects of thiol additives on urethane acrylate UV primers for SMC applications
- 2009
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In: Progress in organic coatings. - : Elsevier BV. - 0300-9440 .- 1873-331X. ; 64:2-3, s. 238-246
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Journal article (peer-reviewed)abstract
- 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 (UVP) provide an order of magnitude reduction of paint defects in SMC coatings, but typically have poor adhesion. Mercaptan polymers have a long history, dating back to 1928. of use in adhesives and sealant applications. The present study investigates a series of UVPs, showing the effect of resin functionality and thiol functional additive content on the adhesion of the coatings to SMC substrates. The SMC formulation is also considered when evaluating UVP adhesion, regarding variables such as surface chemistry, morphology, and surface area. The present study brings to light how adhesion of acrylate UVP can be enhanced with mercaptan moieties in additive amounts. The effect is most apparent on SMC substrates that have been treated to expose inorganic fillers as opposed to untreated surfaces of polyester. Additionally annealing the films boosts adhesion, but only in thiol containing formulations. This is a result of the decrease in T(g)s and modulus of the films with the addition of mercaptans, thus providing better contact with the substrate in comparison to non-thiol containing formulations.
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