Technical Insight 001: Overpaintability of high performance sealants

Today’s demand for higher performance regularly sees dissimilar advanced materials combined to create complex structures, delivering high functionality with aesthetic appeal.

In the automotive and mass transport industries the use of high performance adhesive sealants has grown significantly in recent years, with a technology shift away from mechanical fastenings towards fully bonded structures. The associated weight reductions have a two-fold impact, lowering fuel consumption and raising payloads.

Along with these advances in engineering design, the requirement for high quality livery finishes has increased dramatically with a plethora of fully branded home-delivery vehicles on our roads, servicing the boom in on-line shopping. One big challenge in maintaining the aesthetics of these fleets is the need to seal joints with a colour-matched sealant or indeed to have a sealant that can be successfully over painted.

For the chemists involved in sealant formulation, there is a significant challenge to get the paint to adhere to cured sealant – chemical compatibility between sealant and paint; differing levels of hardness; differing paint application processes and the effect of joint design on sealant bead profile, to name a few. In the building of mass transit vehicles much use is made of high-performance epoxy etch primers in conjunction with epoxy or PU 2-pack top coat finishes. It is very important for vehicle durability that a high level of adhesion is achieved to all substrates, particularly the sealed seams where differing materials join. Paint adhesion failure on the sealed joints will incur significant costs to operators.

The latest generation of seam sealants in the FORMOA range demonstrate very high levels of paint adhesion. To test the adhesion of various paint systems to our adhesives and sealants we use the Cross Hatch Test (DIN EN 2409, ASTM D3002, D3359). This determines the adhesion of a paint to any substrate, in this case the sealant. Each substrate is then given a score to determine the level of paint adhesion to that substrate. Ask us for the results when considering your next order.