Influence of air-cooling time on physical properties of thermoplastic polyester powder coatings

Properties such as the specular gloss, adhesive strength, viscoelasticity, and impact resistance of thermoplastic polyester powder coating film were studied as a function of air-cooling time. Thermoplastic polyester resin is known for the fact that the heating condition has an effect on the degree of crystallinity. We focused on the relationship between the air-cooling time employed in the film preparation process and the degree of crystallinity. The test pieces were dipped into a fluidized polyester powder vessel, and then cooled in air to form the film. We refer to this cooling time in air as the “air-cooling time”. It was found that the degree of crystallinity increased as the air-cooling time increased. As the degree of crystallinity increased, the specular gloss, adhesive strength, viscosity and impact resistance decreased. We therefore found that the improvement in film performance is related to the reduction in the air-cooling time. The importance of this phenomenon is considered in relation to the widespread use of thermoplastic polyester resin. Similar behavior is expected for other polyester powder coatings.

► The effects of air-cooling time on mechanical properties were investigated.
► There was an almost linear relationship between air-cooling time and crystallinity.
► The mechanical properties degraded with increases in crystallinity.
► Crystallinity is controlled by controlling the air-cooling time during coating.
► We achieved excellent performance by optimizing the crystallinity.