| 摘要 |
PURPOSE:To secure good drain properties for a long time and prepare a filtering medium of superior durability for drainage by bonding a covering layer with a water permeating layer in the longitudinal direction in the form of continuous or intermittent line by means of heat fusion at a lap-joining section on the water permeating layer. CONSTITUTION:In a filter medium A for drainage, a conveying layer consisting of an exterior net 4 constituted of thermal plastic and a water permeating sheet 3 constituted of fiber intertwined sheets and the like is applied outside a water permeating layer 1 as a covering layer of good drain properties in the surface direction constituted of a plurality of superposed comparatively large mesh synthetic resin nets 2. Also, the both ends of said covering layer are lap-joined from the left and right sides on the surface of the water permeating layer 1, and at the lap-joining section 5, said both ends are bonded together in the longitudinal direction in the form of continuous or intermittent line by means of heat fusion such as high-frequency welding or the like. As a result, good drain properties are secured for a long time and the filtering medium A of superior durability can be prepared.
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