Patent ID: 6749753
Filing Date: 2004-06-15
Classification: B01D,Y10T

Abstract:
A cylindrical filter of a high accuracy composed of non-woven fibrous agglomerates and comprising at least three layers of a pre-filtration layer, a precision filtration layer, and a support layer disposed in the direction of filtration, said pre-filtration layer being formed with a non-woven fibrous agglomerate prepared by a melt-blow process, and the diameter of all or part of the fibers constituting said non-woven fibrous agglomerate in said pre-filtration layer becomes gradually smaller toward the direction of filtration, said precision filtration layer comprising one or more non-woven fibrous agglomerates, and the diameter of fibers which account for 10% by weight or more of the fibers in said one or more non-woven fibrous agglomerates in the precision filtration layer being smaller than the diameter of the fibers having a smallest diameter in said pre-filtration layer, and said support layer being formed with a non-woven fibrous agglomerate in which at least a part of the fibers are bonded by heat treatment, and the diameter of the fibers constituting said non-woven fibrous agglomerate in said support layer is larger than the diameter of the fibers in said precision filtration layer, wherein the diameter of all or part of the fibers constituting said non-woven fibrous agglomerate in said support layer becomes gradually larger toward the direction of filtration.