Preparation And Modification Of The Cationic Acrylate Resins For Cathodic Electrophoretic Coating

Presently,energy saving and low toxicity had become the development trend of paint.In comparision with solvent paint,electrodeposition coating as a kind of waterborne coatings had lower VOC.In addition,high efficiency,high automation and film properties of good corrosion resistance and appearance don’t exist in other water-based coatings.However,the anodic electrodeposition coating has same drawbacks such as anodic dissolution,ionic contamination and discoloring,which could be avoided by cathodic electrodeposition coating with good corrosion resistance.Acrylic resin shows excellent weather resistance,chemical resistance and solvent resistance,good gloss appearance performance,small pigment reactivity,broad source about monomers.Used for a basic resins of cathodic electrodeposition paint,acrylic acid with decorative performance of color shallow and high gloss had broad prospects in the metal decoration market.However,as a decorative coating,corrosion resistance of acrylic resin is relatively poor,so the study on modification of resin needs to be done.In this paper,cationic acrylic resin was synthesised by methyl methacrylate(MMA),styrene(St),butyl acrylate(BA),hydroxypropy methacrylate(HPMA)and2-(dimethylamino)ethyl methacrylate(DMAEMA)through solution polymerization,and neutralizated with acetic acid.FT-IR analysis showed that all the monomers participate in the polymerization.The glass transition temperature of the resin,which was measured by DSC,was 11.5 ℃.The optimal synthetic conditions are the following:mass ratio of hard monomer to soft monomer is 3:2.The dosage of HPMA and DMAEMA is 20wt% and 15wt%,respectively.The content of azodiisobutyronitrile(AIBN)for initiator is 2wt%.The reaction temperature and time is90℃ and 5.5h,respectively.The neutralization degree of acetic acid is 80% and the solid content of resin is about 60%.Trimer TDI,which was used as the curing agent,was mixed with the acrylic resin in water to electrodeposition coating liquid.The optimal ratio of n(OH):n(NOC)was 1:1.2,and the solid content of paint liquid was about 10%.The pH value of coating and its conductivity were measured.The tinplate aselectrophoretic cathode plate was electrodeposited under the conditions of voltage for60 V and the time for 80 s.The hardness of film was 2H.The adhesion force,which was measured by the method of circle,was 1.The resistance to impact strength was 50cm·kg.The film was formed through heating and cross-linking under the conditions of temperature of 160℃ and the time of 30 min.Organic fluorine modification,organic silicon modification and synergy modification of fluorine and silicone for cationic acrylic resin with the solid content of resin for 68wt% were synthesised by introducing hexafluorobutyl methacrylate(HFMA)and vinyltriethoxysilane(VTES)to the process of free radical polymerization of acrylic resin.FT-IR analysis confirmed that fluoride and silicon group had been introduced into the polymer molecular chain.The modified acrylic resin was prepared for electrodeposition paint in the same way,and film was formed through heating and cross-linking.The properties of the coating such as the pencil hardness,adhesion,acid and alkali resistance,contact angle between paint film with water and water absorption are measured.The effects of different content of fluoride and silicon on the properties of resin and coating were studied.It confirmed that the resin had favorable water solubility,and acid and alkali resistance of film was enhanced obviously when the content of organic fluorine was 12wt%.The contact angle between film and water was improved form 88.4o to 101.4o and the water absorption of resin was reduced from 22.45wt% to7.36wt%.When the content of organic silicon was 6wt%,the water solubility of resin was feasible and acid-alkali resistance of film was improved observably.The contact angle between film and water was increased from 88.4o to 101.4o and the water absorption of resin was decreased to 7.36wt%.Organic fluorine and silicon synergy modified cationic acrylic resin had better corrosion resistance than that of the single fluorine modification or silicon modification.Finally,organic fluorine monomer content was 7-8wt% and organic silicon monomer content was about 4-5wt% for collaborative modification of acrylic resin.The acid resistance and alkali resistance of the modified coating were more than 7 days and 96 h,respectively.The contact angle was more than98o.The synthetic acrylic resin and silicon and fluorine modified resin were used asbinders to prepare the electrodeposition paint.Factors,which have an influence on the the stability of the electrodeposition coating and its particle size and the performance of the film in the process of electrodeposition and baking cross-linking,was studied.It showed that electrodeposition coating can be prepared under the mixing condition that the rotationl speed of the dispersion machine was 900 r/min and the mixed time was 40 min.In this case,the coating had the small size distribution coefficient and the stability of coating was good.When the content of pigments was in the range of 3.83 and4.54wt%,the electrodeposition conditions was that the electrodeposition voltage was80 V and the time was 30 s.The baking conditions were that the bake temperature was160℃ and the bake time was 30 min.In this case,the film thickness was in the range of10μm and 20μm and the gloss,hardness and smoothness of the film were good.