| High throwing power cathodic electrophoretic coating and new pretreatment process represent the important development direction of green coating.The high throwing power is good for the interior cavity of the vehicle body,the outer film layer is dense,and the vehicle primer consumption is reduced by nearly 20%.The new film pretreatment mainly refers to the treatment of steel or aluminum surface with a new film such as silanization or ceramic titanium zirconium,which avoids the use of phosphate-containing and heavy metal nickel phosphating process.In this paper,for the development requirements of automotive paint coating,The preparation and process of high throwing power cathodic electrophoretic emulsion were carried out,including two parts content.The first part was about the preparation of epoxy resin modified by polycaprolactone diol with high throwing power.The second part is the research on the matching of high throwi ng power electrophoretic coating and film pretreatment process.?1?Study on the preparation of epoxy resin modified by polycaprolactone diol with high throwing power and emulsion.Using organic hybrid composite resin technology,the modified resin was obtained by using the polycaprolactone diol?PCL?to chain-opening reaction,then respectively by N-methyl diethanolamine?MDEA?and diethanolamine?DEA?to extender chain termination.And the modified epoxy cathodic electrophoretic resin with low amine valu e,higher vitrification temperature and good flexibility were obtained.The relationship between the synthesis process of polyester modified epoxy resin and the throwing power,adhesion and corrosion resistance of coating film were studied by means of FTIR,particle size and zeta potential,centrifugal separation and heat storage experiments,thermogravimetric TG-DSC test,electrochemical test and four-box method.On the other hand,The effects of neutralization degree and neutralizing agent on the stability,conductivity and throwing power of the final emulsion were studied.Finally,the optimal synthesis conditions were determined.The conductivity of the polyester modified cathodic electrophoretic epoxy resin emulsion was obtained after the amine value was 66.7 mgKOH/g,40%neutralization degree,and the ratio of acetic acid to thioglycolic acid was 1.0:0.3 as the composite neutralizer and water dispersion.After electrophoresis curing and other processes,the coating was obtained.The emulsion showed that conductivity was 1269?s/cm,the particle size was 154.6 nm,and the Zeta potential was +57.6 mV.The stable cathodic electrophoresis emulsion was stored.The cathodic electrophoretic coating was subjected to electrochemical polarization curve and AC impedance test?EIS?.The electrophoretic coating had a throwing power of 0.58,the wet film resistance was1.37×108?·cm2,and the corrosion potential(Ecorr)was-0.381 V/SCE.The self-corrosion current density(Icorr)was 1.53?A/cm2,and the mechanical properties of the coating film were improved,and a high-efficiency,high-performance of modified epoxy coating is obtained.The reasons of excellent corrosion resistance,high throwing power and good stability of high throwing power cathodic electrophoretic emulsion were analyzed.?2?Study on the compatibility of high throwing power electrophoretic coating and film pretreatment process.The compatibility of titanium zirconium treatment process and silane composite titanium zirconium treatment process with modified epoxy cathodic electrophoretic coating was studied.The processing time,treatment temperature,washing process and other process parameters of the two kinds of film pretreatment liquids were studied by means of four-box method,electrochemical test and coating performance test.The process parameters and the matching effects of the electrophoretic,corrosion resistance and adhesion of the cathodic electrophoretic coatings in this paper.The results show that the two pretreatment liquids and electrophoretic coatings have good compatibility.After pretreatment and electrophoresis,the throwing power can reach 0.58,the coating film resistance value is 1.05×108?·cm2,and the self-corrosion potential(Ecorr)is-0.171 V/SCE,self-corrosion current density(Icorr)is 1.16?A/cm2.A primer with good corrosion resistance and excellent mechanical properties of the coating film.The low-neutrality low amine value and the thioglycolic acid-containing neutralizing agent were studied in this paper to reduce the dissolution damage of the electrophoretic coating on the conversion coating and improve the compatibility with the film pretreatment process. |
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