Preparation And Properties Of UV-curable Cathodic Electrophoretic Coatings For Metals

Electrophoretic coating has become a popular technology to improve the corrosion resistance and aesthetics of metal parts because of its excellent corrosion resistance and good covering ability.Compared with other processes,electrophoretic process can not only meet the coating of special-shaped metal parts,and the electrophoretic coating used to meet the needs of environmental protection,water as a dispersion medium,no volatile organic compounds(VOCs)emissions,so as to become the upgrading product in the field of metal coating technology.The UV-curable electrophoretic coating for metal has the advantages of common electrophoretic coating,but also can be combined with the advantages of fast UV-curable curing speed and low energy consumption,so it has a broader application prospect.In this thesis,UV curable polyacrylate cathodic electrophoresis resin and UV curable polyurethane acrylate cathodic electrohoresis resin have been synthesized.In the preparation process,the influence of the feed amount of each raw material on the emulsion and paint film was studied.The influence of different ratio on emulsion and paint film was investigated.The type and dosage of photoinitiator,the best dosage of crosslinking agent,leveling agent and wetting agent were analyzed and determined,and the best electrophoretic process conditions were explored.The emulsion and paint film were characterized and tested by FIIR,GPC,TGA,particle size analysis,real time FTIR and other modern testing techniques.The main conclusions are as follows:(1)Polyacrylate prepolymer was prepared from dimethylaminoethyl methacrylate(DMAEMA),methyl methacrylate(MMA),n-butyl acrylate(n-BA)and hydroxyethyl methacrylate(HEMA)as the main ra3-Dimethylamino-1,2-propanediolw materials,and then the semi-closed isocyanate(IPDI-HEA)synthesized by isophorone isocyanate(IPDI)and hydroxyethyl acrylate(HEA)was grafted and unsaturated bond was introduced to prepare a photocurable resin,which was used to prepare cathodic electrophoretic paint.The effects of addition amount of heat initiator and chain transfer agent,dosage of hydrophilic group DMAEMA,dosage of BA and graft ratio of IPDI-HEA on emulsion and paint film were discussed.The UV-curing kinetics of the final formula was studied at 3 wt.%of Darocur1173 and 60 m W/cm~2of he light intensity(365 nm wavelength).The results show that under the conditions of neutralization degree of 100%,solid content of 15%,electrophoresis time of 5 min and flash time of 3 min,the amount of heat initiator and chain transfer agent was 2 wt.%and 0.3 wt.%of acrylate monomer respectively.The hydrophilic group DMAEMA accounted for 12 wt.%of the total monomer.The soft segment account of n-BA monomer is 24 wt.%.When the grafting ratio of IPDI-HEA and HEMA was 0.8:1,the adhesion was good,and the electrophoretic working solution was milky white/blue phase.The emulsion was stable,and the photocuring rate and conversion rate were high.Smooth film,high gloss,high hardness,excellent overall performance;(2)Using IPDI,polytetrahydrofurandiol(PTMG-1000),3-Dimethylamino-1,2-propanediol(DMAD)and HEA as the main raw materials to prepare polyurethane-acrylate prepolymer,and then acid into salt neutralization,to prepare a UV curable cathodic electrophoretic paint.The effects of R value(n(-NCO)/n(-OH))and hydrophilic group content n(DMAD)/n(PTMG-1000)on emulsion and paint film were also discussed.The UV-curing kinetics of the final formula was studied by using 3 wt.%of Darocur1173 and 60m W/cm of light intensity(365 nm wavelength).The results show that under the conditions of neutralization degree of 100%,solid content of 15%,electrophoresis time of 5 min,flash time of 3 min,hydrop Hilic group n(DMAD)/n(PTMG-1000)content of 1.2:1,R value of 1.3,the adhesion is good,the electrophoretic working solution is milky blue phase,the emulsion state is stable.High photocuring rate and conversion rate;Smooth film,high gloss,excellent overall performance;(3)The laboratory synthesis of poly(acrylate and polyurethane-acrylate resin base cathode electrophoresis for distribution,discusses the effect of different ratio of emulsion and film,and type,light initiator concentration,crosslinking agent,leveling agent and the influence of wetting agent and other auxiliaries,eventually electrophoresis process conditions on the emulsion and the influence of the paint film.The results are as follows:(a)The optimized conditions of electrophoresis process were as follows:fixed room temperature at 25?,p H 6.5?7,20 cm of pole spacing,solid content 15 wt.%of electrophoresis liquid,8 min of electrophoresis time and 80 V of electrophoresis voltage;(b)Optimal formulation of the compound resin:the ratio of polyacrylate/polyurethane-acrylate=1:1 was used to prepare the compound resin,and 3 wt.%of photoinitiator 030,10wt.%of cross linking agent TMPTA,0.5 wt.%of leveling agent and 0.5 wt.%of wetting agent were added to the formulation;The obtained film has high curing rate,excellent properties,aging resistance and acid and alkali resistance.