Effect of Carbon Black on Adhesion to Plastics in Solventborne 2K Polyurethanes

By Kalpana S. Katti, Marek W. Urban

These studies show that when the pigment volume content (PVC) of carbon black particles in-creases in polyurethanes (PUR), NCO consumption increases, and the extent of H–bonded C=O species near the film-substrate (F–S) interface is enhanced.

During crosslinking, polyurea (PUA) is produced, and its concentration levels near the F–S interface are diminished for unpigmented coatings, whereas for the same system containing carbon black, the PUA formation is enhanced.

Although the presence of carbon black particles at the F–S interface results in diminished adhesion of 2K PUR to acrylonitrile-butadiene-styrene (ABS), adhesion is also affected by the presence of OH and C=O functionalities on ABS, which are potential sites for H— bonding to PUR.

Stronger hydrogen donor affinity of N–H functionalities in PUA as compared to the N–H groups on PUR leads to increased H–bonding in the presence of carbon black. Enhanced intermolecular H–bonding in PUR due to the presence of carbon black particles competes with the F–S interfacial H–bonding that promotes adhesion.