| 摘要 |
PROBLEM TO BE SOLVED: To provide a cylindrical filter long in filtration life and excellent in processability when manufactured. SOLUTION: This cylindrical filter is obtained by winding a main filtration nonwoven fabric consisting of a melt blown nonwoven fabric and an auxiliary filtration nonwoven fabric around a porous cylinder so that both fabrics are laminated adjacently to each other. A nonwoven fabric which has the average flow rate pore size larger than that of the main filtration nonwoven fabric and where a melt blown fiber is intermixed with a thermoplastic drawn fiber is used as the auxiliary filtration nonwoven fabric. Otherwise, a wet nonwoven fabric, which has the average flow rate pore size larger than that of the main filtration nonwoven fabric, is not fibrilated substantially and is manufactured by using a fiber which has smaller than 20μm fiber diameter and contains an extra fine fiber having 4μm fiber diameter and an adhered binder fiber having 8μm or larger to smaller than 20μm fiber diameter and the maximum pore size of which is two times or less of the average flow rate pore size, is used as the auxiliary filtration nonwoven fabric.
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