A PVC-free mastic sealer has been developed as a recyclable, environmental friendly material. Core-shell structure type acrylic resin was selected to replace PVC resin for its compatibility with the plasticizer in the formulation. The required mechanical properties could not be achieved by simple replacement of the PVC resin with the equivalent amount of acrylic resin. Therefore, we investigated a change in the synthetic rubber component of the sealer to increase strength. As a result, we found that the addition of an SBR rubber with high tearing strength provided the mastic sealer with high strength and high elasticity properties. The fluidity and contamination properties were improved by changing 42% of the calcium carbonate to a surface-treated calcium carbonate and using an inorganic vulcanization catalyst. This provided the PVC-free mastic sealer with the same performance properties as the conventional mastic sealer. Improving the adhesion to aluminum was required due to the increasing application of aluminum for automobile body panels. We focused on the adhesion performance of the sealer to the aluminum stamping oil in the development. Improved adhesion properties to the aluminum was achieved with a solvent that had a low molecular weight of 170. As a result of the formulation study, we achieved a PVC free mastic sealer of approximately 30% lower in cost than the conventional PVC sealer, which can be used on both aluminum and steel body panels.
Article of Honda R&D Technical Review Vol.16 No.1 (153 - 158)