| Currently the antistatic coatings were broadly used in aircraft industry, electronic industry and military industry. Filled antistatic coating is one of the most important kind of antistatic coatings as the result of its simple processing technology, low manufacture cost and excellent mechanical properties. In order to achieve good antistatic properties, a very large amount of fillers must be added to form a conductive path in the coatings. However the amount of common powder fillers are usually too large to damage the mechanical properties. As one kind of the conductive fillers, carbon fiber has many advantages, such as low weight, high conductivity,low additive amount and so on. But the high dielectric constant and dielectric loss restrict range of its use. Our issue produced proper low-temperature- carbonaceous -fibers (LTCFs) that dielectric properties are superior and the conductivity can be controlled. At the same time, we produced antistatic composite coating based on resilient polyurethane resin.We researched on the influence of carbonization process on the volume resistivity of LTCFs. Analysis and testing technologies such as elemental analyzer (EA), fourier transform infrared spectrum(FTIR), X-ray diffraction(XRD) were used to characterize the structure of the carbonaceous fibers. The results show that the inner structure of fibers become more and more compact and the degree of crystallinity become higher and higher as the carbonization temperature rising; The volume resistivity of LTCFs from 600℃ to 900℃ can be controlled in 103～10-2Ω·cm; The appropriate extended holding time help volume resistivity of LTCFs decreased. We analyzed the influence of different pre-oxidation process on the volume resistivity of LTCFs, and found that the influence of pre-oxidation process decreased with the increase of the carbonization temperature. Thirdly, we compared the different volume resistivity of wet spinning fiber, dry jet spinning fiber and electrostatic spinning fiber. Finally we explored the influence of carbonization temperature on dielectric properties and the rule of impact.The surface resistivity of coatings is mainly effected by volume resistivity, fibers’ length, mass content of LTCFS. The lower the volume resistivity is, the lower the surface resistivity of the coating after complete conductive path formed will be; It will be easier for fibers to form a complete conductive path as the length is longer. With the content of carbon fibers increasing, the coating suddenly begins to be conductive and then goes into permeability transition area. After that, the surface resistivity decreased slowly when continue to add fibers. By comparing the surface resistivity of coatings tested under different voltage, we proves the existence tunnel effect and the field emission effect in the carbon fiber composite coatings. At the same time, we found the advantage of carbon fiber composite coatings which is "cutting-edge effect", through comparing conductive properties of composite coatings with different fillers.Homogenization dispersion of short fibers in matrix is the key to prepare the network antistatic coating. Through researching on the effects of dispersing time and ultrasonic time on the dispersion, we found that the best method is combining high speed stirring and low-speed mixing:first scattered at a speed of 800 r/min for 5 min; then stir 20 min at a speed of 2000 r/min; shot fibers can be dispersed at a good degree. Using quality dispersion coefficient β to describe degree of dispersion. The results show that it is easy to obtain homogenization dispersion system when the fibers’ length is less than 4 mm. The content of short fibers is the key to the homogenization dispersion of surface resistivity; in order to guarantee the uniformity, fiber content should be avoid less than permeability transition area. In addition, this topic discusses the influences of resin viscosity and solvent treatment on the degree of dispersion. |
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