【作者】 李鹏；

【导师】 刘顺华；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 对于既有缓冲密封要求,又要确保电磁波屏蔽的场合来说,橡胶弹性体电磁波屏蔽材料具有不可替代的作用。而在某种程度上对复合材料屏蔽性能的考察就是对材料电性能的考察。所以要想获得好的屏蔽性能着眼点首先就应放在对复合材料导电性的提高上。只有以良好的导电性为基础才可能进一步对复合材料的整体结构进行调整,设计出具有更高屏蔽效能的结构复合材料。鉴于此,本文以电磁波屏蔽用复合型硅橡胶为主要研究对象,就以下各方面开展了研究工作: 研究了复合型硅橡胶的固化原理,硅橡胶的制备工艺以及在不同导电填料和填充份数下所需固化剂的最佳用量。结果表明:固化剂的用量与填料份数之间呈一定的线性关系,用同样的方式分别获得了N234、HG—CB及Ni粉填充复合型硅橡胶所需固化剂的最佳用量。 对复合型硅橡胶的导电机理进行了分类和总结,并结合本实验所研究的几种导电填料给出了其各自的导电机理和分布模型,从而对实验结果进行了很好的拟合,发现上述模型均适合于其各自的导电填料。实验结果告诉我们,对于碳黑填充复合型硅橡胶来说,具有高结构度的华光碳黑要明显好于中超耐磨碳黑N234。但有一点需要指出的是,N234与基体的结合,换句话说与基体的相容性要好于HG-CB。因此,在接下来与Ni粉的结合填充时,选择了较易分散的N234型碳黑,尽管HG-CB型碳黑与Ni粉的结合会获得更好的导电性。 通过对镍粉填充RTV硅橡胶的电阻率的测量确定了镍基导电硅橡胶的渗滤值点。在此基础上添加不同含量的炭黑,发现了有别于渗滤规律的二次渗滤现象。根据导电机制模型推测了二次渗滤现象产生的原因,并对实验结果进行了拟合。同时针对高导电硅橡胶的屏蔽性能,发现可用Schelkunoff理论较好地描述其屏蔽效果。结合二次渗滤现象,分析了其对屏蔽性能的影响。 在镍基导电橡胶的基础上填充N234型碳黑,经导电机理研究与电阻率测定发现了有别于渗滤规律的二次渗滤现象。同时通过理论计算、并对实验结果进行分析总结,最终发现二次渗滤现象对复合型硅橡胶的屏蔽效能有着极为重要的影响。当橡胶电阻率从10^-1Ωcm降到10^-2Ωcm时,其屏蔽值从50dB提高到100dB以上。 可用二次多项式来描述阻值随拉力的变化过程,在受载情况下平衡阻值随拉力的增加而增大。可将复合型硅橡胶的拉敏特性作为识别其是否达到最佳炭黑填充量的一种方法,当橡胶具有最大的拉敏特性时,其导电性与力学性能具有最佳的结合点。由此可得出N234与HG—1B的最佳填充量分别为:35%和10%。更多还原

【Abstract】 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%.更多还原