Improvements in melt spinning

摘要

A filter bed, for use in melt-spinning apparatus, comprising graded layers of inert granular material, is characterized in that at least some of the finest material comprising the lowermost layer of the bed is moulded into a shape or shapes so that the total filtering interfacial surface of the layer of finest material is greater than the cross-sectional area of the bed, said moulded material being held together by a binding agent which is removed before or during the initial stages of the melt-spinning operation. The moulded shape may be a hollow frustum of a cone, a hollow hemisphere, a cylinder or a rectangular thick-walled box. The inert granular material may be silica sand, iron filings, steel filings or similar metallic substance. The binding agent may be ethylene carbonate or water, either of which is preferably removed from the bed by volatilization. The polymer which will subsequently be filtered through the bed may also be used as the binding agent. As shown, a moulded shape 6 of fine sand in the form of a hollow conical frustum sits on gauze 5 which may be of stainless steel. The space above gauze 5 between the shape 6 and the inside wall of the pack body 2 may be filled with loose fine sand 7 to a depth equal to the wall thickness of the shape 6. Coarser sand 8 may cover fine sand 7 and moulded shape 6, and the core of the latter may be filled with moulded coarse sand 9. Fig. 2 shows a number of smaller moulded shapes 10 of fine graded sand. A further increase in the interfacial surface area may be obtained if the outer surfaces of the moulded shapes 6, 10 are corrugated. Polyethylene terephthalate may be spun through the filter bed into fibres and films.