| 摘要 |
PURPOSE:To enhance dust removing efficiency without increasing pressure loss, by bringing a dry unwoven car filter element to an electret system. CONSTITUTION:A synthetic fiber layer in which the mixing ratio of low m.p. polyester easily brought to an electret state is successively increased from the upstream layer side to the downstream layer side thereof or the unwoven fiber layer obtained by preliminarily applying mechanical bonding treatment to said fiber layer is heated to 150-180 deg.C and, in this state, treatment is performed within a gap of 5mm. at voltage of 10kV for about 5min. As the polyester fiber to be used, three kinds respectively having a high m.p. of 250-260 deg.C, a medium m.p. of 200-230 deg.C and a low m.p. of 150-180 deg.C are used. In this case, an unwoven fabric obtained by a method wherein three kinds of card webs wherein a high m.p. one is gradually reduced while medium and low m.p. ones are increased from the upstream layer side to the downstream layer side are laminated and the formed laminate is subjected to needle punching processing and heat treatment at 150 deg.C may preferably be used.
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