Companies using adhesives are expected to be able to consistently produce an assembly―whether in the flexible packaging, furniture, automotive or construction industry―without differences in the quality of the product manufactured. This is the case for both high-performance structural bonds and applications with lower performance requirements. Polyurethane adhesives can be formulated as a soft flexible polymer or one with high hard segment content with high tensile properties. Without a properly prepared surface to bond, however, the performance will not meet the expectations of the end user.
Having a clean surface is a key requirement to obtain a strong and reliable bond. Users of adhesives may remark that a drop in performance must be due to the adhesive manufacturer providing a sub-standard adhesive. The adhesive company may then go back to its raw material supplier and ask about the quality of polymers or reactive raw materials they have received. However, unexplained bond failures or variability in bond strength can be caused by inconsistent quality of the surface of the substrates being adhered. Coatings also often need a surface pretreatment to achieve optimal performance. They function to improve the long-term durability of a bond, not just initial bond strength. The type of surface preparation or primer depends on the substrates being bonded.