Influence of matting on the properties of powder epoxy-polyester coatings

摘要

Polymer matrix of hybrid powder coatings is a mixture of epoxy oligomere and polyester. Matting agent is 4,5-dihydro-2-phenyl-1H-imidazole-1,2,4,5-benzatetracarboxylat, which serves as an acid curing agent for the epoxy oligomere. The rate of interaction of the crosslinking agent carboxyl groups with the epoxy is higher than the rate of interaction of the same group with polyester, since the catalytic action of the imidazole ring, having a basic character and in salt form associated with pyromellitic acid. In addition, interaction of the low-molecular acid with oligomere is higher due to greater mobility than units of high-molecular compound, which is characterized by certain acid value. Matting realizes by of advanced formation crosslinked epoxy polymer by matting agent. This polymer is incompatible with epoxy-polyester polymer formatted later. Depth curing for model systems with different content of matting agent is defined to study the effect of matting agent for curing epoxy-polyester compositions by extraction of films using Soxhlet extractor. It can be concluded that cure depth of coatings decreases with increase the content of the matting agent. It may be due to the fact that by increasing the content of the matting agent increases the proportion of linear epoxy oligomere, which can partially dissolve in acetone at Soxhlet apparatus extraction. Ultramicroscopic studies have shown that polymer aggregates, which incompatible with epoxy-polyester matrix, formed and have a crystalline structure. The crystalline nature of the formed epoxy polymer particles confirmed by matte coatings micrographs in polarized light (Figure 1). The surface topography is formed by aggregates composed of single crystals polyepoxide.