Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Jesse Zhu, Dr. Hui Zhang

Abstract

Traditional powder coating provides poor coating appearance. Fine powder coating can overcome this drawback since the smaller powder particles lead to much smoother finish. Nevertheless, fine powder has been experienced to cause more application problems. This study investigated fine powder coatings from different aspects and it provided solutions to solve these application problems.

The investigation on fine powders conducted by this study concluded that the medium particle size and D10 was not suitable for the flowability characterization of fine powder coatings. Instead, an index which represented the particle size distribution could correlate with the flowabilities of the fine powder coatings much better.

In addition, several processing methods were developed for the production of fine powder coatings. The experiments disclosed that the revised designs of the cyclone and the grinder could obtain narrower particle size distribution of the powder coatings, which was desired. In addition, other performances of the processes were not sacrificed.

The spraying method of powder coatings was also investigated in this study. The additional moisture on the surfaces of the fine powder particles was found to reduce the resistivity of the powder so as to enhance the transfer efficiency during the corona spraying. On the other hand, a new spray gun design with alternative charging pattern could reduce the Faraday Cage effect during corona spraying of fine powders. In addition, it also showed large potential on improving the transfer efficiency of coarse powders.

Finally, new processing techniques for functional powder coatings were developed. Utilization of dry blended catalysts could solve the problems of pre-curing and short shelf life associated with the conventional low-cure powder coatings. Other than that, the complicated heat-blending process for processing metallic color powder coatings can be replaced by a new bonding technique with utilization of liquid bonder. The strong bond between powder particles and metallic pigments provided by this new technique can solve the recyclability problem of the metallic color powder coatings during spraying.

The discoveries from the thesis study contribute to further understandings of powder coatings. This study also provides useful suggestions for future developments of powder coating technologies.

Available for download on Saturday, June 30, 2018


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