Study On The Proparation And Properties Of The Carbon Fiber Conductive Shielding Paper

As the structures of high performance electronic equipments and devices become increasingly more complex, electromagnetic interference (EMI), electromagnetic radiation hazards and compatibility (EMC) have emerged as key issues. Therefore, Electromagnetic materials play a very important role in preventing electromagnetic radiation(EMR), EMI and guaranteeing information safety on such occasions of commerce, polity, national security, and so on.Carbon fiber will be a promised material for electromagnetic shielding because of its predominant characters, for example, good conductivity, light weight, low price (compared with metal fiber) and oxidation resistance. In this study, carbon fiber electromagnetic shielding paper was developed for reducing or preventing EMI, electromagnetic hazards and information leakage. The dispersion properties, papermaking process, mechanic properties, shielding properties and the influential factors of this paper were investigated; and the possibility and approach for manufacturing a higher-SE material were also presented in this paper.The analysises of FT-IR, SEM and titration indicated that there were a few oxygen-containing groups on the carbon fiber surface, and its dispersion was poor, but it could be improved by dispersants and surface treatment. After being nitric acid oxidized, the oxygen-containing groups and the specific surface area increased visibly, and the dispersion of carbon fiber was modified further. The carbon fiber could enhance the tensile index, burst index and tear index of the sheets to some degree within certain content; the conductance of the sheets rested heavily on the carbon fiber content, the more the carbon fiber content was, the higher the conductance the sheets had. The resistance decreased with the basic weight of the sheets increase, and well fited the physics conductive theory and model.The conductive network and the contact resistance had very important effects on the conductance of the conductive shielding paper. Increasing the carbon fibers length could enhance its conductance. Wet pressing, wood fiber beating and its dosage affected the contact resistance greatly. By adjusting the carbon fibers length, wood fiber dosage and papermaking process, conductive network could be optimized, and conductivity could be enhanced.The conductance shielding paper had good shielding effectness(SE), which result from reflection loss and absorption loss. The SE of the sheet increased visibly with the increase of carbon fiber content and the paper thickness. The SE also varied according to different electromagnetic wave frequency. In the frequency range of 600MHz～1.2GHz, the shielding paper had higher SE than that of other frequency. The conductive shielding paper with various SE (30dB～50dB) could be obtained by changing the carbon fiber content and the paper thickness.The effects of adding silver covered copper powder to the carbon fiber paper on the conductance and the SE were not so much as that of coating, and that presented us the possibility and approach for manufacturing a higher-SE paper could be used in different occasions for preventing or reducing EMI, electromagnetic hazards or information leakage.