Study On Surface Modification Of Silver Powder And Coatings’ Salt Spray Resistance

Metal conductive coatings can be used in the fields of electromagnetic shielding,antistatic and marine sewage due to their good electrical and mechanical properties.However,because of the excellent electrical conductivity of this type of coating,it is prone to electrochemical corrosion with metal substrates,especially in high humidity and high salt environments.This is because the electrolyte solution is formed when water,air and other corrosive media pass through the coating and reach the substrate,and the different electrode potentials between the metal filler and the substrate cause the system to form a galvanic cell,which accelerates the corrosion between the coating and the substrate,thereby rendering the coating ineffective.Therefore,in order to improve the corrosion resistance of conductive coatings,it is particularly important to use surface modification technology to modify filler particles in conductive coatings to slow the erosion of corrosion particles.Aiming at the problems of the corrosion resistance of metal conductive coatings,this paper takes the surface modification of metal fillers in coatings as the research object,and conducts a series of work closely around the performance characteristics of metal fillers after modification.Based on a systematic study of the molecular structure,micro-morphology,and coating corrosion characteristics of fillers modified with organic compounds containing-SH groups,combined with reaction temperature,addition content,and reaction time,a method for preparing surface-modified metal fillers was proposed.Finally,a conductive coating with excellent conductivity and salt spray resistance was prepared.The main research contents and innovations of this paper are as follows:（1）The reaction mechanism between metal conductive particles and organics was studied.Based on the strong binding between sulfhydryl groups and metals,the surface modification of metal conductive particles with organic compounds containing sulfhydryl groups was clearly performed.Combined with the high environmental resistance of organic terminal functional groups-CF₃,Perfluorodecanethiol was selected as a surface modifier at first.（2）The law of metal conductive particles modified by perfluorodecanethiol was studied.It is concluded that the neutral salt spray resistance of the coating is slightly improved,but the conductivity is significantly decreased.By adjusting the process parameters,it was found that when the amount is 1%of the mass of the metal filler,the modification temperature is 40℃,and the time is 4h,the salt spray resistance of the coating is increased from 20h to 80h,while the volume resistivity is increased from3.16×10^-4Ω?cm to 24.75×10^-4Ω?cm.（3）Due to the low dispersion of the filler caused by the oil-repellent property of the element F,a silane coupling agent KH590,which can significantly improve the compatibility between the filler and the resin,is used as a modifier.After its modification,the neutral salt spray resistance of the coating has been greatly improved,but the conductivity has been significantly reduced.By adjusting the process parameters,it is concluded that when the dosage is 3%,the modification temperature is 50℃,and the time is 4h,the salt spray resistance of the coating can reach 250h,and the resistivity is 11.41×10^-4Ω?cm.（4）Due to the filler aggregation caused by polycondensation of hydrolysate of KH590,dodecyl mercaptan with a terminal functional group of only a long-chain alkyl structure was used as a modifier.After its modification,the neutral salt spray resistance of the coating is greatly improved,and the conductivity is only slightly reduced.When the dosage is 3%,the modification temperature is 60℃,and the time is 8h,the salt spray resistance of the coating can reach 600h,and the resistivity is only 6.73×10^-4Ω?cm.