| 摘要 |
PURPOSE:To extend the life of a filter material, by providing high density parts and low density parts to a filter material in the surface direction in a scattered state and making the density of the filter material low in the upstream side of the flow of a fluid to be filtered and high in the downstream side thereof in the thickness direction of said filter material while forming napped parts on the upstream side surface thereof. CONSTITUTION:Low density parts having voids 2 with a large size and high density parts having small voids are formed to a base material 1 in the surface direction thereof in a scattered state and a density gradient is formed to the base material 1 from the upstream side of the flow of a fluid to be filtered toward the downstream side thereof so as to be changed from 'coarse' to 'dense'. Further, napped parts 3 are formed on the surface of a filter material in the upstream side thereof. By this method, the collection of dust stepwise advances and dust having a smaller particle size is successively collected toward the downstream side by the density gradient in the thickness direction and the formation of a dust cake layer is promoted by napped parts.
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