**5. Conclusions**

Al(OH)3, a widely used filler in solvent-based coatings and BaSO4, a popular filler in both solvent-based coatings and powder coatings, are involved in polyester-epoxy and polyester based ultrafine powder coatings to make comparative investigations.


This experimental study provides valuable information for the application of Al(OH)3 to ultrafine powder coatings. Compared to BaSO4, the use of Al(OH)3 is expected to bring about a better mechanical property and durability of the coating film.

**Author Contributions:** Conceptualization, J.Z. and H.Z.; Methodology, D.C.F.; Software, M.S.Y.; Validation, H.Z., H.Z. and W.L.; Formal analysis, W.L.; Investigation, W.L. and D.C.F.; Resources, H.Z. and Y.S.; Data curation, W.L.; Writing—original draft preparation, W.L. and X.Z.; Writing—review and editing, H.Z. and H.Z.; Visualization, W.L.; Supervision, H.Z.; Project administration, J.Z.; Funding acquisition, H.Z.

**Funding:** This research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), Discovery Grant RGPIN-2018-06256.

**Conflicts of Interest:** The authors declare no conflicts of interest.
