Research On The Curing Agent Of High Throwing Power Automotive Primer And The Polyol Resins Of Top-coat

Waterborne coatings represents an important development direction of the coatings industry.The synthesis and application on the curing agent of high throwing power automotive electrophoretic primer and the polyol resins of top-coat were studied in this paper,including two parts content.The first part was a study on the blocked isocyanates curing agent of high throwing power electrophpretic primer.The second part was a study on the polyester-acrylic hybrid resin and high gloss two component polyurethane topcoat.(1)Study on the blocked isocyanates curing agent of high throwing power automotive electrophoretic primer.The development of automotive green compact coating technology and thin film pretreatment requires cathodic electrophoretic primers to have higher throwing power,better flatness,and superior electrophoretic film performance.This article synthesized the curing agent of high throwing power automotive electrophoretic primer.Compounded blocked polyisocyanates curing agent was synthesized by physical mixing with IPDI-type blocked polyisocyanate and TMXDI-type blocked polyisocyanate which was synthesized with isophorone diisocyanate,meta-tetramethylxylene diisocyanate,trimethylolpropane,acetyl alcohol surfactants,3,5-dimethylpyrazole,methyl ethyl ketoxime and propylene glycol butyl ether.Cathodic electrophoretic emulsion was prepared with this curing agent and modified epoxy resin.The synthesis process of the compounded blocked polyisocyanate curing agent was determined by chemical titration and FT-IR.Corrosion resistance analysis and crosslink density analysis showed the film was cured by compounded blocked polyisocyanate curing agent which contained 30%TMXDI-type blocked polyisocyanate had high crosslink density and good corrosion resistance.TG and DSC analysis showed that this film had gradient unblock curing behavior and good thermal stability,and heating reduction was about 4.7%;at the same time,SEM test showed that the gradient unblock curing behavior can improve the leveling of the resin and the moisturizing and defoaming functions of acetyl alcohol surfactants can make the coating had good flatness.The particle size distribution test,Zeta potential test,TEM test and four box method test showed that the uniform particle size and structure made electrophoretic emulsion have high dispersion stability and the hybrid blocked polyisocyanate curing agent was fully encapsulated with cationic epoxy resin that made the prepared resin had high throwing power,and the throwing powe was 57%.The study found this blocked isocyanates curing suitable for automotive cathodic electrophoretic primer coating to improve the formation performance of the film.(2)Study on the polyester-acrylic hybrid resin and high gloss two component polyurethane top-coat.The energy crisis required automobiles to use high-performance waterborne coatings that can be cured at low temperatures.The surface coatings for passenger cars and rail transit applications required waterborne two-component polyurethane topcoats to have higher decorative properties such as gloss and to satisfy bubble-free thick-film coating.At this article,the polyester-acrylic hybrid resin and aqueous dispersion was synthesized that used to prepare polyurethane film with isocyanate curing agent.Initiated by BPO,the polyester-acrylic hybrid resin and aqueous dispersions was prepared by grafting a unsaturated polyester resin,which were prepared from ethylene glycol,neopentyl glycol,isophthalic acid and maleic anhydride,onto the solution of acrylic polyol resin,and its high gloss polyurethane film was obtained with isocyanate curing agent.The synthesis process of polyester-acrylic hybrid resin was determined by FT-IR and DSC analysis;at the same time,particle size distribution test and TEM test showed the particle size and structure of aqueous dispersion was uniform and the prepared aqueous dispersion had excellent stability when a 20%unsaturated polyester was added to the solution of the acrylic resin for free radical double bond graft polymerization.Gloss test showed the film had high gloss when the acrylic polyol resin to hybrid was obtained with 1:1 as the molar ratio of hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate,and the film was prepared with 1.5:1 as n(-NCO):n(-OH)value and 4:6 as the curing agent 3900/2655 compounding ratio;at the same time,SEM test,electrochemical analysis and thermal stability analysis showed the film had high crosslink density and good flatness,corrosion resistance and thermal stability,that made be suitable for surface coating of automobiles to obtain high gloss film.