Study On Conductive Mechanism And Shielding Property Of EMI Shielding Rubber

For having the demand of both cushion seal and EMI shielding, electromagnetic shielding rubber elastomer takes on the irrepalace effect. In a way reviewing shielding property equals reviewing electric property of materials. Thus for seeking out excellent shielding property, firstly we should focus the respect on improving conductivity of composites. Only based on good conductivity we can adjust integral structure of composites more and scheme out structural complex materials that are provided with higher shielding effectiveness. Through above analysis, electromagnetic shielding complex silicone rubber is looked upon as main subject investigated, and the following aspects are discussed in this paper:The principle of solidification,preparation technics of silicone rubber and the best content of required solidified agent in different conductive fillers and their portions are studied. Results show that the relation between content of solidified agent and filling portions is apparently linear. The best contents of required solidified agent about the complex silicone rubber with N234, HG-CB and Ni powder are acquired in the same way.We class and sum up the conductive mechanisms of complex silicone rubber. Combined with a few conductive fillers studied in this experiment, each conductive mechanism and distributing model is further presented. The fitting experimental results show the above models are very suitable for respective conductive fillers. The experimental results further tell us that for the complex silicone rubber with carbon blacks, HG-CB with higher structure degree are obviously better than N234 (ISAF). But it should be pointed out that the consistency between N234 and basal body is more excellent than HG-CB. Thus, although the consistency between HG-CB and Ni powder can gain better electric property, we choose easily dispersed N234 carbon black to be filled in silicone rubber together with Ni powder.By measuring electrical resistivity of RTV silicone rubber with Ni powder, percolation threshold of Ni-based conductive silicone rubber was confirmed. When N234 was filled in Ni-based conductive silicone rubber, double percolation phenomenon was found other than percolation law. After fitting the experimental results, the reason of double percolation phenomenon was presumed. To shielding effectiveness of high conductive silicone rubber, the result shows that shielding effectiveness can be described well with Schelkunoff theory. The influence of double percolation phenomenon on shielding effectiveness of rubber was investigated.When N234 carbon black is filled in Ni-based conductive silicone rubber, double percolation phenomenon other than percolation law is found after researching conductive mechanism and determining resistivity. Meanwhile we find that double percolation phenomenon has very important effect on shielding effectiveness of the complex silicone rubber after analysing and summing up theoretic value and experimental value. When electrical resistivity of conductive rubber falls from 10-1 Ωcm to 10-2 Ωcm, its shielding effectiveness increases from 50dB to 100dB.The dependence of electrical resistance on the tensile force is derived, which can be expressed in the form of polynomial. Equilibrium resistance increase with tensile augment under loaded condition. Pulling sensitive characteristic of the complex silicone rubber can be looked upon as a method that identifies whether reaching the best content of carbon black. When rubber possess the maximum pulling sensitive characteristic, its electrical conductivity and mechanical property possess the optimal binding site and the best contents of both HG-1B and N234 are determined respectively: 35% and 10%.