The dream of self-healing coatings where scratches simply disappear has come true in applications as varied as car paintwork and office furniture. Raw materials from Bayer MaterialScience form the basis for these self-healing polyurethane coatings.
Memory effect
Polyurethanes make excellent raw materials for coatings since they offer both strength and elasticity: fixed covalent bonds for hardness and resistance, reversible hydrogen bonds for elastic strength. Thanks to the elastic reversibility of the hydrogen bonds, a crosslinked polyurethane 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 network is now in a state of fixed tension. The built-in memory effect is triggered by an input of heat, which sets the whole tensed-up system in motion again. As the polymers relax, the hydrogen bonds reposition themselves in the original formation and the scratch disappears. It's a bit like us humans when an infrared lamp or heat rub helps us to relax and relieve muscular tension. How exactly does that work in practice? Watch this short video.
Flexible product chemistry
The urethane or urea structures in an elasticized polyurethane coating are the essential precondition for this self-healing effect irrespective of how the structure is built up:
2K or 1K technology
Solventborne, solvent-free or waterborne
Crosslinking via NCO-OH or UV-curing technology
Self-healing coating applications
One of the first chapters in the self-healing success story was written in the automotive industry. After all, car-drivers have been longing for scratch-resistant paintwork for many years. More recently, self-healing coatings have also been successfully applied in other areas, such as office furniture.
Urethane acrylates are basic binders for very effective UV-curing self-healing coatings. Monomer-free urethane acrylates are especially suitable since they allow the highest degree of formulation freedom. For more information please see the presentation "Self-healing UV-coatings"
Moreover, the article "Self-healing 2-component polyurethane coatings - the next generation". contains very detailed information about the various self-healing polyurethane technolgies.
Examples for polyurethane raw materials with self-healing properties:
