Synergistic Effect Of Nano-carbon Materials On Electromagnetic Shielding Efficiency Of Waterborne Coatings

With the development of modern society,electromagnetic waves,generated from electromagnetic products,cause the harm,trouble and inconvenience.In order to shield electromagnetic waves,electromagnetic shielding coatings have developed.In recent years,to more effectively block the electromagnetic radiation emitted during the use of communication and electronic equipment for the sake of human health and information security,the development of high-performance electromagnetic shielding coatings has become a research hotspotIn this paper,we explore the effect of adding carbon nanomaterials for the improvement of electromagnetic shielding performance of aqueous coatings.Firstly,we optimize the coating formula by comparing the performance of cured coating.Based on above,we add carbon nanomaterials to the coating to obtain the electromagnetic shielding coating and test the shielding effectiveness,and come up with the formula of electromagnetic shielding coating with excellent performance so as to conduct a comprehensive performance study of the painting（coating）.First of all,since the dispersion of inorganic filler in water affects terribly the stability of the basic paint,the method of adding dispersant was selected to achieve the stable dispersion of filler in this experiment.In an effort to study the dispersion of the two inorganic fillers,calcined kaolin（CK）and titanium dioxide,which were mainly used in this experiment,sedimentation test and Zeta potential test were used to explore the dispersion effect of different dispersants on these two dispersive phases in water,and the dispersion mechanism was analyzed by infrared spectrum and molecular structure.The results showed that the suspension time of the two fillers was significantly extended and the absolute value of Zeta potential of CK and titanium dioxide reached 48 m V and 55 m V respectively when sodium hmetaphosphate（SHMP）served as the dispersant,indicating that the electrostatic repulsion of particle surface was enhanced with the assistance of the dispersant,which improved the stability of the dispersion system.Consequently,SHMP was finally selected as the dispersant of paint system.Then by adjusting the proportion of raw materials,the coating and the formula of excellent basic paint were obtained,which laid the foundation for the following electromagnetic shielding coating research.In addition,this paper chose to add three kinds of conductive fillers with different structures（graphene,flake graphite and conductive black）into the formula of basic paint to prepare electromagnetic shielding coating,and then the formula with better shielding effectiness（the electromagnetic shielding coating prepared by graphene and flake graphite）was selected to prepare electromagnetic shielding coating by combining with nano-Fe₃O₄.And the shielding effectiness test is carried out.In this experiment,the dispersant suitable for each conductive filler was first explored through Zeta potential measurement so that the conductive filler could be evenly dispersed in the paint to obtain a coating with better performance.After that,the formula with excellent shielding effectiness was figured out through the cabinet shielding effectiness testing method.The results indicated that the shielding effectiness of the composite coating with 3 wt.%graphene and 2 wt.%nano-Fe₃O₄was so good that the shielding effectiness reaches 28 d B in the frequency range of 15 MHz.While 1 wt.%flake graphite and 2 wt.%nano-Fe₃O₄ were combined to prepare the coating,there appeared the optimal shielding effectiness reaching 34 d B in the frequency range of15 MHz.When the conductive black was used as the conductive filler,the shielding effectiness of the coating in the frequency range between 15 MHz and 450 MHz reached more than 15 d B.Afterwards,the influence law of coating thickness on shielding effectiness under each formula was explored and the shielding mechanism of the coating was analyzed in combination with the microstructure of the coating and the conductive path formed by conductive particles with different structures.By analyzing the crystalline transformation of the coating,the influence on the viscosity of the coating was explored after the conductive filler was added,and the performance of the painting（coating）meets the requirements of the national standard“General Specification for Military Electromagnetic Shielding Coating”（GJB 2604-1996）and the group standard“Waterborne Graphene Electromagnetic Shielding Architectural Coating”（T/CGIA 001-2017）for practical application.