Preparation And Characterization Of Electroactive Cathodic Electrophoretic Coatings

Cathodic electrophoretic coatings can produce flat,controllable,uniform and high adhesion coating on the surface of the substrate without damaging the metal by virtue of its unique external electric field deposition method.Therefore,it has been a research hotspot in the field of metal protective coatings.With the development of metal devices,it is very meaningful to prepare cathodic electrophoretic coatings with high anticorrosion performance.Among the many methods to improve the corrosion resistance of the coating,polyaniline and its derivatives have become the focus of attention in the field of metal anticorrosive materials because of their characteristic electrical activity,better environmental stability,lower production cost and so on.The related achievements are too numerous to enumerate.It is of great significance to combine the advantages of cathodic electrophoretic coatings with polyaniline and its derivatives to prepare high performance anticorrosive coatings.However,during the construction process of cathodic electrophoretic coatings,due to the electrolysis of water,the high pH in the vicinity of the coated object will drive the de-doping of polyaniline and its derivatives and then lose their electrical activity,which limits its application.In order to solve the problem of reducing electrical activity of polyaniline in high pH environment,it is an effective method to dope polyaniline with conductive material carbon nanotubes.The ? bond on the surface of carbon nanotubes can transfer electrons to the conjugated structure of polyaniline,thereby maintaining the electrical activity of polyaniline under high pH conditions.In addition,the use of oligoanilines with similar electrical activity as polyaniline but with a lower molecular weight and a clearer structure is more useful for improving dispersibility and studying the corrosion resistance of coating.Therefore,in this paper,through the doping effect of carbon nanotubes on tetraaniline,an electroactive hybrid cathode electrophoretic coatings with high pH applicability was prepared and applied to the field of metal corrosion protection.The specific research content is divided into the following two parts:1.Preparation of electroactive hybrid cathode electrophoretic coatings by physical blending method.Firstly,tetraaniline(TANI)was prepared with 4-aminodiphenylamine(4-ADPA)and oxidant ammonium persulphate(APS).The molecular weight was about 365.Secondly,using the same process again,only adding carbon nanotubes(CNTs)during the preparation process allows 4-ADPA to be polymerized in situ on the surface of the CNTs to prepare a tetraaniline /carbon nanotubes(TC)composite material.Then the structure and properties of the composites were characterized.Thirdly,the resin for cathodic electrophoretic coatings were prepared with 2-(dimethylamino)ethyl methacrylate(DMAEMA),N-(hydroxymethyl)acrylamide(NMA),2-hydroxyethyl methacrylate(HEMA),2-ethylhexyl acrylate(EHA)and styrene(St).The electroactive hybrid cathodic electrophoretic coatings were prepared by dispersing the TC composite material into the resin and emulsifying with water.Fourthly,the electroactive coating were prepared on the surface of metal substrate under the deposition condition of 70 V and 1 min and the curing process of 160 ? and 30 min.Finally,the corrosion resistance and corrosion products of the coating were studied.The results shown that: TANI was aggregated on the on the surface of CNTs by ?-? interaction.When the mass ratio of CNTs to TANI was 1:2,the composite material exhibits the best electrical activity.It can also show good redox activity even under the condition of pH = 9.When the addition of the composite was 3% of the mass of the polymer,the composite was well dispersed in the coating,and the coating shown good mechanical properties.The results of electrochemical and salt spray tests shown that the coating with composite materials exhibited the best anticorrosion performance.2.Preparation of electroactive hybrid cathode electrophoretic coatings by Chemical grafting method.Firstly,in this chapter,based on the previous chapter,using isophorone diisocyanate(IPDI)as a "bridge",TANI was grafted into polymers for electrophoretic coatings to prepare electroactive resin PT.And its structure and grafting rate were studied.Secondly,the electroactive hybrid cathodic electrophoretic coatings was prepared by dispersing CNTs in the resin and emulsifying with water.Thirdly,electrophoretic deposition technology was used to prepare electrophoretic coatings on the surface of metal substrates.The deposition voltage was controlled at 70 V,the deposition time was 1 min,and the curing process was 160 ? for 30 min.Finally,the anticorrosion performance of the coatings were studied,and the corresponding anticorrosion mechanism of the coatings were put forward.The results shown that: TANI was successfully grafted into polymer.When the grafting rate was 3%,the adhesion was still 0 grade.When the grafting ratio continued to increase,the adhesion started to decrease.When the amount of CNTs added was 1% of the mass of the polymer,well-dispersed CNTs can be observed under the 3D display microscopes.According to the test results of cross section SEM and water contact angle of the coatings,they were shown that CNTs can effectively fill the internal defects of the coating and make the coating more compact.The results of electrochemical and salt spray tests shown that the coating grafted with TANI and added with CNTs had the best anticorrosion performance.Combined with the test results of EDS and XRD,it was proved that the coating grafted with TANI and introduced into CNTs can form a passivation layer on the metal surface and improve the corrosion resistance of the substrate.