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A method of encapsulation of inorganic additives with organic materials was developed to improve the fine power flowability and film quality for powder coating. The flowability tests angle of repose (AOR) and avalanche angle (AVA) were conducted for the coating samples to characterize the effectiveness of the encapsulated additives on group C fine powder flowability. The results show that both AOR and AVA are significantly affected by the encapsulating materials, the encapsulating material weight percentage, as well as the total loading ratios of additives added in fine powders. Polyester shows the best performance on the modification of the additive due to the high similarity to host powder coating. AOR/AVA first decreases and then decreases with the encapsulating material weight. An optimum percentage exists at approximately 10%. A similar trend is observed with the additive loading ratio, and the minimal AOR/AVA is obtained at additive loading ratios between 0.5% and 0.8%. The effective surface area coefficient (η) was introduced to improve the adhesion force model to determine the optimum additive loading ratio for various host particle and additive particle sizes, which agrees well with the experimental results.

Fumed silica is one of the most commonly used flow additives in the powder coating industry. To investigate the influence of the properties of fumed silica on powder coatings, three different types of fumed silica, Aerosil R812, R972, and R8200, were selected and introduced to an ultra-high-gloss powder paint by the dry-blending method with preset mixing conditions and times. Their effect on the powder flowability, coating application related properties and film properties were carefully studied. The angle of repose (AOR) and bed expansion height data, which represent the semi-dynamic and dynamic flowability of powders respectively, show a strong flowability enhancement for the powders with additives, and R812 exhibits the best performance compared to 8200 and R972, mainly due to its high hydrophobicity and specific surface area. For the ultra-high-gloss powder paint, all the flow additives cause slight gloss reductions, surface roughness increase and a significant effect on the distinctness of image (DOI). The addition of R972 is beneficial to the transfer efficiency of powders compared with the other two, while the additives impose only a minor influence in the Faraday cage effect. The melting and curing dynamics, i.e., gel time, and inclined plate flow, are not affected by the flow additives.

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.

Powder coating is a coating process that applies the coating materials to a target substrate in dry powder form. As an alternative coating technique to liquid coating technique, powder coating has many advantages, such as environmental friendly, low cost, high efficiency in materials usage. However, problems such as unable to handle ultrafine cohesive powders limit the application of powder coating technology in industry. With a new invention that can effectively fluidize ultrafine powders by enhancing their flowability, a novel electrostatic ultrafine powder coating technique has been developed by our group. Based on this novel technique, many functionalized powder coatings have been created. In this study, electrostatic ultrafine powder coating technique has been utilized to fabricate a polymeric powder coating (PPC) on pure titanium substrates, which contains a bioactive agent, mineral trioxide aggregates (MTA). The study demonstrated that this technique could successfully create MTA enriched polyester powder coating surfaces, that not only have excellent adhesion on pure titanium substrate but also have nano­ topographies and nano-roughness that promote cells growth. Human embryonic palatal mesenchymal stem (HEPM) cells were cultured on PPC coated surfaces and pure titanium surfaces to test the biocompatibility of these surfaces. The results demonstrated that PPC coated surfaces could support the attachment, proliferation and differentiation of HEPM cells, and in some cases, better than pure titanium. Another study was to utilize the same novel fluidization method of fine powders to modify the flowability of glass ionomer cements (GIC) (GC Fuji I®and Ketac-Cem®) for their application in dentinal tubules occlusion by the electrostatic ultrafine powder coating technique. High hydroscopicity was observed for both GIC powders, with Fuji I® taking up water to 2.43 wt% and saturated after 10 hours and with Ketac-Cem® taking up water to 7.37 wt% and saturated after 19 hours. The water absorption decreased the flowability of both Fuji I®and Ketac-Cem® powders. By blending in nano-Al203or nano- lii Si02 or nano-Ti02 as flow additives, the flowability of those GIC powders can be improved. 3.0 wt% of nano A12C>3and 4.0 wt% of nano-Si02were found to be optimal in improving the flowability of dry Fuji I® and Ketac-Cem® powders, while 3.0 wt% of nano Al203 to be effective on improving the flowability of the water-saturated Fuji I ® and Ketac-Cem® powders. Nano Ti02 showed limited effect, with 1.0wt% giving slight improvement in powder flowability. In conclusion, this study demonstrated the potential applications of the novel ultrafine powder flow enhancement technique for orthopaedic and dental implants as well as for dentine tubules occlusion.