Folded thermoplastics-impregnated filter paper - sealed at edges by roughening and pressing thermoplastics

摘要

An edge seal for a zig-zag folded, thermoplastics impregnated filter paper, formed by compacting the edges of the filter paper block and utilizing the impregnating thermoplastics as the sealing adhesive is given in the parent patent. In the present patent the zigzag edges are upset by pressure applied onto the plane of the edges. The edges are also pref. roughened in this region. Embossed corrugations may be produced in the paper to act as spacers between successive folds. The whole folded paper may finally be fitted above all four sides into a frame. Improved sealing, esp. at the folded edges is obtd.