The effect of TiO2, pigmentation on the hydrolysis of amino resin crosslinked epoxy can coatings

Abstract

Pigmented (TiO2), amino resin crosslinked coatings, designed for applications in can coatings’ internal lacquers, were formulated, characterized, applied, and cured. Three grades of a pigmentary form of TiO2 were characterized in terms of their particle size, their particle morphology, their zeta potential, and their moisture retention behavior. Epoxy coatings that were crosslinked using one of several, different amino crosslinkers were prepared. The effect of the presence of the TiO2 pigments on the hydrolysis of the cured coatings was monitored via the controlled retorting of the coatings. The different grades of TiO2 pigment were selected, to establish whether or not they could be used interchangeably with respect to hydrolysis and to melamine release. Also, the effects of the aging of the fluid coatings on the amount of melamine released from the coatings (after curing and retorting) were monitored. Storage under laboratory conditions for 2, 20, and 40 weeks was used for this purpose. The TiO2 pigment contributed significantly to the hydrolysis behavior of the epoxy coatings in that their presence substantially reduced the amount of melamine released and the extent of crosslinker hydrolysis. Typical results show that excluding the TiO2 pigment particles from the formulation results in there being 50% more hydrolysis of the crosslinker to melamine. With respect to the melamine release and crosslinker hydrolysis, the different grades of the pigment gave similar results.