Hi
To make a PU coating on steel substrate, I mixed PU & 5% cross-linker of it and followed sonication, mechanical stirrer. After that I poured the mixture on steel substrate, leveled it and heated at 60C but the coating on the substrate appears as crack.
What is the problem of not forming uniform coating on the steel substrate?
You may be required to add some interfacial adhesive to reduce interfacial tension between the polymer and steel. Crosslinker would only stiffen the polymer by strengthening the interchain linking but it would not help much in enhancing adhesiveness of polymer on steel.
Dear Amit Roy
Two major issues come to my mind regarding your problem. First, you should be very careful about the heating and especially coaling rate of the coated steel substrate. Since the coating and the substrate have got different thermal expansion coefficients, you should heat and cool your specimen very gradually avoiding thermal stresses.
The other vital parameter is shrinking factor of PU+cross-linking agent, you should consider it in the curing process and chose a cross-linker which leads to minimum shrinkage in the cured coating.
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