Gel Particles in Polyurethane Paints

Gel Particles in Polyurethane Paints

We are having problems with our metal-finish paints based on polyurethanes. After stoving, the paint film is marked by particle agglomerates. Can you suggest a reason for this?

The reason for this defect is evidently the presence of gel-particles formed by partial separation of the blocking component in the isocyanate, which then reacts prematurely with the polyhydroxyl compounds by crosslinkage.
Since this phenomenon may be caused by a number of different factos, it would seem advisable to check the whole fomiulation if one does not use an isocyanate with a stably bonded blocking agent- but there are probably technical reasons why this cannot be done.

lt is a well known fact that catalysts contained in such formulations exert a major influence upon the temperature at which the decomposition reactions takes place. Such catalysts include tertiary amines and organotin compounds. Here it might be advisable to consider an alternative product. The metallic pigment paste also,

however, influences the film forming reaction, the reason here being the solvent composition, which should contain only a small percentage of aromatic solvents. Gel permeation chromotography and infra-red analysis would quickly provide important information on the subject, but is relatively expensive to carry out.




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