Depth filter

Abstract

Provided is a depth filter which has the absolute property of filtration and the removing performance of gel even for particles to be removed having a reduced particle diameter, and is excellent in liquid permeability. This depth filter comprises an outer layer, a pre-filtration layer, and a precision filtration layer arranged in this order with respect to the filtration direction. The outer layer is formed by winding an outer layer nonwoven fabric containing a high-melting-point resin and a low-melting-point resin multiply. The nonwoven fabrics to be wound are thermally bonded by the low-melting-point resin, and the average fiber diameter continuously decreases with respect to the filtration direction. The precision filtration layer is a laver in which a precision filtration laver nonwoven fabric having an average fiber diameter of less than 300 nm is wound multiply. The pre-filtration layer is a laver in which a pre-filtration layer nonwoven fabric having an average fiber diameter of 300 nm or more and less than 1000 nm is wound multiply, and an average fiber diameter is constant or decreases stepwise with respect to the filtration direction.

Dependencies are inferred from the claim text.