Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Jesse Zhu

Abstract

Powder coating is a dry coating technology competing with conventional liquid coatings and offers many benefits such as the elimination of volatile organic compounds, high efficiency of material usage and improved coating durability. However, the rough and thick film surface restricts its wide application. The fine powder coating, which can solve the film quality issues, also has its own limitation: the powder is too cohesive to handle. Although, nanoparticle flow additives can significantly improve the flowability of fine powders, it leads to another obstacle at the same time. Since the inorganic nano additives are not fully compatible with the organic fine powder coating materials during the curing process, the agglomerates formed by nanoparticles can result in film defects such as seeds and pinholes, as well as the reduction of gloss.

A technology of encapsulating polymer resins on the surface of nano silica additive is used for this work. By modifying the surface of the inorganic additives, the compatibility issues are expected to be solved while the effect of additive on flowabilities remains.

The modified additives were prepared by encapsulating commercial nano silica additives with 2 organic materials, polyester or hybrid, in 4 different Resin-to-Encapsulated Additive ratios (R-EA ratios) and evaluated by TEM. The additives were incorporated into fine coating powders in 4 different additive loading ratios (LOAs). All of the 40 samples were tested by flow property measurements to obtain their angle of repose (for semi-static flow property) and avalanche angle (for dynamic flow property). The results show that with a suitable R-EA ratio and additive loading ratio, the powder sample performs better with improved semi-static and dynamic flow properties. And the optimum R-EA ratios and LOAs were suggested for specific applications.

For each powder samples, three panels were sprayed with an electrostatic method and all of the 120 coated panels were evaluated by measuring gloss and the number of seeds on the film surface. Some panels were evaluated by a roughness profiler. The results show that coating films from the samples with modified additives have higher gloss, lower roughness and less seeds on the surface.

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