Now you see it, now you don’t
PU self-healing coatings utilize polymer memory to repair scratches
Whether from a car wash, runaway shopping cart or an overgrown hedge, cars inevitably get scratched, causing their owners frustration and often costly repairs. Automotive coatings are just one application that can benefit from the inherent self-healing properties offered by the unique chemistry of polyurethane coatings.
Innovative self-healing coatings
In polyurethane (PU) coatings, fixed covalent bonds provide hardness and resistance, while reversible hydrogen bonds impart elastic strength. Thanks to the elastic reversibility of the hydrogen bonds, a crosslinked PU coating has its own "polymer memory”.
When a scratch occurs, the polymer chains are physically displaced. The hydrogen bonds are disconnected and look for new anchors, whereas the fixed chemical bonds are unaffected. The polymer memory effect is triggered by heat, such as when a car sits out in the sun. The added heat causes the bonds to return to their original shape, and the scratch to disappear.
These innovative coatings also display the classic properties associated with polyurethane coatings, including low volatile organic compound (VOC) content and chemical resistance.
The coating system can be tailored for a specific application by varying the molecular structure of the soft segments, the distribution and length of the hard segments, or the molecular weight and degree of chain branching. This is all accomplished by choosing the appropriate polyisocyanate and polyol components.
Raw materials developed by Covestro enhance the coatings’ self-healing properties. Self-healing properties are proven in automotive refinish, OEM clear-coat and plastic clear-coat formulation trials, and are being tested in furniture applications.