| 摘要 |
PROBLEM TO BE SOLVED: To provide a filter medium in which possibility of incineration corresponding to a future environmental problem is prepared and weight after incineration is very smaller in comparison with a conventional filter medium using glass fiber and uniform formation being a feature in a wet sheet-making method is equipped and pressure drop is small and filtration efficiency and strength are large, and the filter medium does not tear easily and can be singly incorporated into a filter. SOLUTION: The filter medium comprises a web manufactured to sheets through a wet sheet-making method by using aqueous dispersion liquid comprised of extremely fine fiber, a skeletal fiber having average diameter larger than the extremely fine fiber and expandable particles. The expandable particles after foaming treatment form void parts in the layer of the web. The extremely fine fiber desirably is microglass fiber of <=3μm average fiber diameter. Further, at least a part is organic fiber fibrillated to <=1μm fiber diameter.
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