| 摘要 |
<p>A spun-bonded, preferably paper-like, polyolefin sheet or fleece composed of heat and pressure bonded minute polyolefin fibres which is vapour- and gas-pervious but impervious to liquid water and dust, naturally water-resistant and of high tensile and tear strength, is rendered heat-weldable. The material is used for making an applicator for releasing volatile substances, e.g. phosphine derived from metal phosphides at a controlled rate and with complete protection of the contents against liquid water. Excessive local phosphine build-up is avoided. The release rate is controlled by the sheet material itself and by its available surface area. A heat weldable sheet material, in particular for the above purposes, is coated, preferably by powder sprinkle coating with a thermoplastic highly porous heat welding bonding layer, e.g. EVA, melting so much lower (say 30 to 80 DEG C lower) than the polyolefin fibres that a heat welding seam forms before the fibres melt so that the physical properties of the polyolefin fibres and the gas permeability are substantially retained. <IMAGE></p> |
