GB973358A - Artificial filaments and spinnerets for their production - Google Patents

Abstract

A spinneret for making hollow artificial filaments suitable for cigarette filters by dry spinning, has one or more orifices the cross-section of which normal to the axis of extrusion is in the shape of a crescent defined by arcs of circles of the same radius, one arc passing through the centre of curvature of the other arc. The spinneret may have orifices both of the crescent shape and of one or more other shapes. The orifices may be arranged in one or more concentric circles in the spinneret face and the orifices of crescent shape may alternate with differently shaped orifices. When the spinneret is used for dry spinning, hollow filaments having the cross-sectional shape of a prolate split-ring with the split in one of the long sides of the ring and thus possessing a high surface to weight ratio may be produced. They do not pack tightly even when mixed with filaments of other cross-sections, so that a bundle of filaments containing a substantial proportion of or consisting wholly of filaments of the above cross-section exhibit a high porosity and are therefore suitable for use in the manufacture of cigarette filters. In an example, 90 bundles each containing 180 filaments produced by dry spinning an acetone solution of a secondary cellulose acetate (through a spinneret having 180 crescent-shaped orifices according to the invention) are joined together into one large bundle and passed through a stuffing box crimper to impart to the bundle an average of about 8 crimps per inch. The crimped tow is opened in a conventional manner, sprayed with 6% of its weight of glycerine triacetate as a plasticizer and formed into a cigarette filter rod which is dried at room temperature for 2 hours to cause adhesion of the filaments to one another at points of contact.