| 摘要 |
PROBLEM TO BE SOLVED: To obtain a filter medium with a coarse-dense structure by laminating nonwoven cloth with a specified average fiber diameter to nonwoven cloth treated thermally under pressure and further treating both nonwoven clothes under a lower pressure than the pressure at which the nonwoven cloth is thermally treated so that these nonwoven clothes are formed in a single piece. SOLUTION: Nonwoven cloth A is a melt blow nonwoven cloth, and the average fiber diameter of the fiber is 0.1-10μm, preferably 0.5-5μm. Nonwoven cloth B is made of the same material as the nonwoven cloth A, and if polypropylene fiber is used, it is thermally treated at 40-100 deg.C, more preferably 50-80 deg.C, and at a linear pressure of 30-300kg/cm, more preferably 50-200kg/cm. In addition, both nonwoven clothes A, B are laminated together, and this laminate is treated at a linear pressure of 5-50kg/cm, preferably at 10-30kg/cm under lower linear pressure conditions than those of the nonwoven cloth B when manufactured. If both nonwoven clothes A, B are bonded together into a single piece by the adhesion of their fibers, the nonwoven cloth A is not so densely textured as the nonwoven cloth B, so that the former is of a coarser texture than the latter to provide a filter medium with a difference in coarseness.
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