FILTERING MATERIAL FOR FILTER AND PRODUCTION PROCESS THEREFOR

A first papermaking raw material for an upper layer and a second papermaking raw material for a lower layer are subjected to papermaking so as to form a filtering material with a continuous density gradient from the upper layer to the lower layer. Each of the papermaking raw materials contains natural fibers such as pulp and chemical fibers such as PET. The content of the chemical fibers in the first papermaking raw material is higher than the content of the chemical fibers in the second papermaking raw material. The diameter of the chemical fibers in the first papermaking raw material is larger than the diameter of the chemical fibers in the second papermaking raw material. The thus-obtained filtering material is able to collect a wide size range of particles and is made less susceptible to clogging and longer in life.