| 摘要 |
A process for preparing a web of a thermoplastic polymer, which resembles a non-woven fabric, comprises melt-extruding a film of a foamable composition of the polymer under conditions such that foaming takes place to give a product with closed cells. Thereafter, this product is treated to rupture at least 50% of the closed cells, the said treatment comprising stretching the foamed film, or heating it to cause shrinkage, whilst restraining shrinkage. It is preferred that the extrusion takes place through an annular die, such that it can be expanded by an internally-applied fluid pressure. A fluid-impervious backing which contacts at least a portion of the extruded film permits further rupturing of cells and expansion by restricting the flow of the fluid through the ruptured cells. Suitable apparatus is illustrated in Fig. 1 (not shown), in which 12 is the annular die, the fluid pressure is applied through pipe 16, and 20, 20A are the fluid-impervious backing. The invention is suited to polyvinyls and polyolefines, but any thermoplastic polymer may be used, e.g. polyurethanes, polycarbonates, cellulose acetate, polyamides. Any conventional chemical or physical blowing agents may be used. |
