| 摘要 |
PURPOSE:To obtain an electret filter low in pressure loss and having high collection efficiency, by laminating a fibrous sheet having high surface charge density constituted of fine fibers and a fibrous sheet having low surface charge density constituted of thick fibers. CONSTITUTION:Surface layer parts 2, 4 are constituted of thick fibers to lower surface charge. Each thick fiber has a thickness of 1d or more and the surface charge density thereof is pref. below 1X10<-10>C/cm<2> and the wt. thereof is set to 300g/m<2> or less. By this surface layer parts, large dust is collected and the adhered dust is prevented from re-scattering. Fine dust passing through the surface layer parts is collected by a layer constituted of fine fibers and having a small void size and high surface charge density. Each fine fiber has a fineness of below 1d and the surface charge density thereof is 1X10<-10>C/cm<2> or more and the wt. thereof is pref. 80g/m<2> or less. By this constitution, dust is collected with high collection efficiency, As for the sheet having low surface charge density, a non-electret one may be used. |
