At present there are known yarns obtained from ordinary spinnerets and featuring crimp necessary for wool-like fibres and filaments. The crimp is attainable either through the use of two or more components in the filamentary yarn with different shrinking and swelling properties or through asymmetric cooling thereof in a direction normal to its movement.
The known methods of imparting crimp to the filament are rather complicated since they call for special auxiliary contrivances.
There are also known spinnerets with a non-round configuration of the filament-forming holes which make it possible to produce hollow wool-like fibres and filaments with a non-round cross-section featuring certain wool-like properties: low heat conductivity, increased mechanical cohesion of individual fibres, bulk and opticl properties.
For instance, according to USSR Inventor's Certificate No. 286,130, there is known a spinneret for forming chemical hollow wool-like fibres, having a spinning hole made as a slot with a configuration of an open polygon provided with three branches, each being arranged at a right angle to one of the sides of the polygon.
Fibres formed by extrusion through the hole of the known configuration approximate, as to heat conductivity, volume weight and cohesion, natural wool, but the most essential characteristics determining their hygienic properties (capillarity, moisture conductivity) practically do not change. Moreover, fibres spun through the spinneret according to USSR Inventor's Certificate No. 286,130 lack crimp required for wool limitation. The mechanical crimp of the filament rapidly disappears during processing and in use. Therefore, these fibres are used, mainly, as additives to natural wool, their amount in the mixture not exceeding 30 percent. Thus, all chemical fibres and yarns known in the art do not exhibit all the properties inherent in natural wool, such as low heat conductivity, permanent crimp, adequate moisture conductivity, moisture capacity, and bulk.