Depth filter

Abstract

A depth filter is formed by rolling a fiber assembly into a cylinder. The fiber assembly is formed of melt blown fibers formed of a thermoplastic resin A and melt blown fibers formed of a thermoplastic resin B having a lower melting point than the thermoplastic resin A. This depth filter has a gradient where the average fiber diameter of the melt blown fibers formed of the thermoplastic resin A and the average fiber diameter of the melt blown fibers formed of the thermoplastic resin B continuously decrease from the outer circumference toward the inner circumference of the cylinder of the depth filter; and the average fiber diameters of the melt blown fibers formed of the thermoplastic resin A and the melt blown fibers formed of the thermoplastic resin B are decreased from the range of 20 μm to 1 μm to the range of 0.99 μm to 0.1 μm.

Dependencies are inferred from the claim text.