不同导电填料对防静电涂层温度-电阻效应的影响

Influence of Different Conductive Fillers on the Temperature-resistance Effect of Antistatic Coatings

箭体外表面防静电涂层通常既需承受一定的温度又需防静电性能,此时涂层的表面电阻率变化规律即温度-电阻效应,对防静电涂层的研制、开发及应用有着重要的意义。以有机硅改性丙烯酸为成膜物,通过选取典型的非金属导电填料—导电炭黑和金属导电填料—镍粉和银粉,制备一系列不同导电填料含量的防静电涂层,研究导电填料的种类和含量对防静电涂层温度电阻效应的影响。研究结果表明:导电填料的种类及含量对防静电涂层的温度-电阻效应影响显著。基于体积膨胀理论,导电炭黑涂层体系随温度升高而体积膨胀,导电网络被阻断,表面电阻率随温度的升高而增大,但其正温度系数(PTC)效应不显著,PTC强度仅为1.24,且导电炭黑含量与其PTC强度呈负相关;镍粉涂层体系的PTC效应显著,PCT强度高达10^(6),且镍粉含量与其PTC强度也呈负相关;银粉涂层体系则在渗流阈值前PTC效应显著,PTC强度为4.58,而渗流阈值后则几乎不表现PTC效应。制备了含导电炭黑和镍粉的复合导电填料涂层体系,其PTC强度较纯镍粉涂层体系大大降低,可为箭体外表面防静电涂料的设计提供新的思路。

Antistatic coatings on the surface of arrows are often subjected to certain heating environments;therefore,their antistatic performance should be retained with increasing temperature,and the content of conductive fillers should be as low as possible.Thus,the variation in the surface resistance of the antistatic coating,namely,the temperature-resistance effect,is significant for the development and application of antistatic coatings for arrows and for obtaining antistatic coatings with appropriate surface resistance,even at a certain high temperature.First,an amorphous organic silicone-modified acrylic polymer was utilized as the film former of the antistatic coating to avoid interference from the crystallization structures of the film former.Typical non-metallic conductive fillers,i.e.,conductive carbon black,and two types of conductive metal fillers,i.e.,nickel and silver powders,were selected to prepare various antistatic coatings.Subsequently,the influence of the type and content of conductive fillers on the temperature-resistance effect of the antistatic coating,as well as the corresponding changes in microstructures and mechanisms,were investigated by observing the changes in the surface resistance with increasing temperature and the microstructures from SEM graphs after the heating process.The results showed that the type and content of the conductive filler significantly influenced the temperature-resistance effect of the antistatic coating.Two typical theories corresponding to the two types of behaviors for different antistatic coatings were demonstrated:the volume expansion theory and stress model theory.For the conductive carbon black coating system,the positive temperature coefficient(PTC)effect was observed but was not significant,with a PTC strength of only 1.24.This can be attributed to the volume expansion theory.Here,the conductive network was blocked when the volume of the film former in the coating system expanded with increasing temperature,which was also observed from the changes in the microstructures,but the degree of volume expansion was limited.Moreover,increasing the content of fillers weakened the impact of the volume expansion,which led to a lower PTC strength with increasing content of conductive carbon black.Meanwhile,the percolation threshold had an important effect on the temperature resistance effect.The PTC effect of the silver powder coating system was significant because of the volume expansion theory before the percolation threshold,where the PTC strength was 4.58,and the PTC effect could be neglected after the percolation threshold because the limited volume expansion of the film former could not destroy the effective conductive network after the percolation threshold.Based on stress model theory,the PTC effect of the nickel powder coating system was significant,with a PTC strength of up to 10^(6).Here,the sudden stress increased with increasing temperature,leading to changes in the conductive filler position and the subsequent destruction of the conductive network.In addition,the nickel powder content was negatively correlated with the PTC strength,which also indicated that a higher filler content results in more conductive network chains.Furthermore,based on the above results,a coating system containing both conductive carbon black and nickel powder was prepared,whose PTC strength was significantly lower than that of the pure nickel powder coating system,but the surface resistance was much lower than that of the conductive carbon black coating system.An appropriate mixture and percolation threshold may provide important guidance for the design of antistatic coatings for rockets.