Abstract: Based on needle-punching process, compound filters are prepared with PAN pre-oxidized fiber as their raw material, and then coat the compound filter material with PTFE foam. This paper investigates the influence of the coating on the appearance, air permeability, tensile property, pore size distribution and filtering quality of the filter material. Results indicate that the PTFE membrane was formed on the surface of the filter after coating; the air permeability and pore size of the filter decreased significantly, while the tensile property had no obvious change; the filtration efficiency of the coated filter to different sized particles increased significantly, of which the filtration efficiency for effective purification of particles with diameter above 25 μm reached up to 98.11%; and as the PTFE coating formed a film on the filter, which made the dust hard to enter deep inside the filter and easily removed from the surface, the residual resistance of the filter after cleaning decreased and the cleaning cycle extended. At high temperature, the filtration efficiency of the coated filter in initial and stabilization stage was as high as 99.955 6% and 99.915 8%, respectively.

Key words: PAN pre-oxidized fiber; foam coating; pore size; filtration efficiency