Predaration And Fluorine Enrichment Behavior Of Flriorinated Polyester Applied In Powder Coating

Polyester powder coating is a kind of thermosetting powder coating which has been widely used in the outdoor environment. It has many excellent properties such as environment friendly, good weather stability and durability, convenient transport and storage. However, the common polyester powder coating is often affected by moisture and water-soluble corrosion agents, which lead to the deterioration of mechanical properties, decline of durability and service life of cured coatings. Therefore, it is important to improve the hydrophobicity and oleophobicity of the common polyester powder coating.In this study, fluorine was introduced into the polyester powder coating in order to improve the hydrophobicity and oleophobicity of cured coatings. Meanwhile, the fluoroalkyl groups, exhibiting lower surface tension compared to other groups, have the higher tendency to migrate toward the air/coating interface. Thus, only a very small amount of fluorine is needed to improve the hydrophobicity and oleophobicity of coating surface.The fluorinated polyester with octafluoropentyl pendent segments (OFPE) and the fluorinated polyester with hexadecafluorononyl pendent segments (HFPE) were synthesized in the phthalic anhydride/epichlorohydrin reaction system. The structure of fluorinated polyester was characterized with1H-NMR and19F-NMR. The wettability of water and oil on the cured coating was investigated by contact angle meter. The results showed that the contact angles of water and diiodomethane on the cured coatings increased with the increase of the fluorine content. The X-ray photoelectron spectroscopic (XPS) analysis showed that the fluoroalkyl groups had enriched on the coating surface. Besides, the enrichment degree of fluoroalkyl groups on the coating surface increased with the increase of the length of fluoroalkyl groups at first, and then remained almost constant. The argon bombarding analysis showed that the fluoroalkyl groups were preferentially arranged and concentrated nanometers near the coating surface.In order to improve the enrichment degree of fluoroalkyl groups on the coating surface and increase the utilization of fluorine, the fluoroalkyl-modified polyester (PE-Fn) was synthesized by the reaction of polyester resin and fluorinated isocyanate and was used as additives in the polyester powder coating. The structure of PE-Fn was characterized with1H-NMR and19F-NMR. The wettability of the cured coatings with PE-Fn as additives was investigated by contact angle meter. The results showed that the introduction of an extremely low concentration of fluorinated additives into polyester powder coatings led to a significant increase in the contact angles of water and diiodomethane. The X-ray photoelectron spectroscopic (XPS) was used to investigate the enrichment behavior of fluoroalkyl groups on the coating surface. The takeoff angle of XPS was changed in order to investigate the fluorine distribution along film-thickness direction. The results showed that a gradient of fluorine existed from the surface to bulk of the cured coatings. The topological structure of the cured coatings was recorded by an atomic force microscope (AFM) and the results revealed that there are strong surface segregation of fluoroalkyl groups. Besides, the introduction with a small amount of fluorine into polyester powder coating can improve the acid resistance, alkali resistance, boiling water resistance and pollution resistance of cured coatings, but it had little effect on the pencil hardness and adhesion of cured coatings.