The Filament Bundle

The pneumatic deposition of the filament bundles onto the moving belt results in formation of the web. A pneumatic gun uses high pressure air to move the filaments through a constricted area of lower pressure but higher velocity, as in a venturi tube. Pneumatic jets used in spunbonded production have been described (17,24). Unfortunately, the exceUent filament uniformity coming out of the spinnerette is lost when the filaments are consoHdated going through a gun. 

Filament yams are twisted for two reasons. One is to supply certain esthetic characteristics such as touch, drapability, and elasticity. The other more fundamental reason is to provide physical integrity to the filament bundle so that it can be warped, woven, and knitted without excessive breakage or fraying of individual filaments. 

Increasing twist in a cord further reduces filament buckling by increasing the extensibility of the filament bundle. 

The hot filaments are cooled by blowing air through the filament bundle and are combined together into a tow band, which is deposited into a can. The fibre thickness is determined by the wind-up speed of the denier setter . Spin draw finish is applied as an aid to subsequent processing. 

All the known methods for spunbond fabrication with spin extruders process the chips into a melt, which is then guided by means of spinning heads with internal melt piping systems and spinning pumps and extruded through the spinnerets (with different round, rectangular cross sections) to the filaments. Following the filament path, the main takeup ways to obtain the filament bundle are [163, 164] ... 

After the filament bundle has been spread in the laying system (e.g., electrostatic system, gas dynamic stream, laying jets and blades, elliptic oscillators, multilaying with cross-moving directions), one obtains a warp to form a fabric with defined properties (spaee weight, width, edge width, individual titer, and thiekness of the fleece, etc.) and therefore defined end uses (eovers for baby diapers, heavy geotextiles, ete.). 

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