Patent GB-578238-A (GB)
Title: Improvements in or relating to the production of tapered artificial filaments
IPC: H04B1/08
Filed: 1944-04-28
Abstract: Artificial filaments having uniformly recurring symmetrically tapered portions which can be cut into bristles of uniform size and shape, are obtained by extruding a molten organic material from which filaments capable of being cold drawn can be formed, at a constant rate through a spinneret across an air gap into a liquid cooling bath, and directly withdrawing the filaments in accordance with a repetitive schedule of linear rates comprising a period of acceleration, a period of deceleration of greater <PICT:0578238/IV/1> duration than that of acceleration and a period of uniform withdrawal at the minimum rate.  The filaments are preferably formed from synthetic linear polyamides such as those derived from diamines and dicarboxylic acids or amide-forming derivatives of dibasic carboxylic acids, and those derived from polymerizable amino acids or amide-forming derivatives thereof, for example, esters and lactams. The polyamides may contain groups other than the amide groups, e.g. ester groups.  Mixtures of polyamides and interpolyamides may also be used, and the term "polyamide" is inclusive of such polymers as those derived from glycol and a diisocyanate or a diisothiocyanate. Numerous suitable polyamides are specified, among which the superpolyamide hexamethylene sebacamide or hexamethylene adipamide alone or in admixture with phenol-formaldehyde resin is stated to be suitable for the manufacture of paint brush bristles. Filament-forming polymer is melted by grid 11, fed by screw pump 12 to the spinneret 13 and extruded across an air gap, the width of which is preferably less than one inch, into cooling bath 16 containing water or other inert liquid.  The filament 15 is withdrawn from bath 16 by pinch p  rolls 19 and 20, of which 19 is driven, the roll 20 being held against or geared to 19.  The periodic tapering of the filament is accomplished by regularly and uniformly varying the angular velocity of the pinch rolls 19, 20.  This is effected by imparting predesigned non-uniform angular motion, by means of cam 33 and arms 34 and 32, to the annular member of a planetary gear train housed at 23 by which the pinch rolls are driven.  The rotational speed of the pinch roll 19 is thus alternately accelerated and decelerated by imparting a small angular rotation alternately clockwise and counterclockwise to the annular gear housed at 23. To obtain symmetrically tapered filaments, the period of decelaration must be greater than that of acceleration and a period of constant rate of withdrawal must be included in the schedule of withdrawal, the shape of the cam being adapted accordingly.  With any one cam 33 means may be provided to vary the gradient of the filament taper, to vary the volume of material contained in the unit length of filament between successive points of maximum diameter, or to vary the unit length without change in volume per unit length and by using a cam of appropriate shape filaments having tapers of various kinds, e.g. wedge-shaped, convex, concave or combinations thereof, or filaments having tapered sections alternate with untapered sections may be obtained.  A weighted roller 61 free to move in a vertical direction, serves to tension the filament as it leaves the rolls 19, 20.  If desired, the grid 11 and pump 12 may be jacketed.  The various parts of the apparatus are preferably driven from a single source of power, in order that their synchronization may be preserved.  The filaments may be coloured by adding a pigment to the polymer or to the polymer-forming reactants or the filaments may be dyed. Specifications 461,236 and 535,263 are referred to.