Rapid UV/thermal curing of waterborne difunctional-group melamine resin coating and its excellent functionality

Abstract

Melamine resin coatings (MF coatings) are usually cured by thermal curing (TC) or acid/ thermal curing (ATC) method. That exists some defects such as operation cumbersomely, curing slowly, easy to shrink and brittle, etc., which hinders the practical applications of MF in the field of painting. In this paper, a waterborne melamine resin oligomer (dMFO) with a difunctional structure (allyl group and hydroxymethyl group) was designed and prepared. The gelation of the dMFO can quickly accomplish and obtain a cured MF coating with excellent functionality by the “UV/thermal “curing method. The results show that when the dosage of photoinitiator 1-hydroxy-cyclohexyl-phenyl ketone (Pi184) is 3 % relative to the mass of dMFO, the MF coating can be cured in about 11 min. The tensile strength of the coating reaches 8.24 MPa, the impact resistance height is 180 mm, the adhesion is up to 5.51 MPa, the pencil hardness is 5H, the water contact angle can reach 113°, the water resistance exceeds 14 h, and the limiting oxygen index is 30.87 %. The MF coating was prepared from dMFO displays excellent characteristics such as structural toughness, self-hydrophobicity, and intrinsic flame retardancy. In addition, the MF coating also has good self-cleaning performance, anti-corrosion property, and chemical corrosion resistance. The analysis suggests that the MF coating has an in-situ interpenetrating network structure (IPN) formed by the interpenetration of thermoplastic segments and thermosetting network structures. The effective synergy between the molecular chain segments of these two structures facilitates the structural optimization and performance enhancement of the MF coating. The work presented in this paper has laid a key technical foundation for the large-scale application of MF coatings, which holds promising prospects for industrial application and significant commercial value.