Process of melt spinning of a blend of a fibre-forming polymer and an immiscible polymer and melt spun fibres produced by such process

A process of melt spinning a fibre-forming polymer selected from the group consisting of polyethylene terephthalate, polyhexamethylene adipamide or polypropylene at a minimum wind up speed of 2 kilometer per minute, the improvement being that, before melt spinning, there is added to the fibre-forming polymer, between 0.1% and 10% by weight of another polymer which is immiscible in a melt of the fibre-forming polymer, such other polymer having an average particle size of between 0.5 and 3 microns in the melt with the fibre-forming polymer immediately prior to spinning and having an extensional viscosity such that molten spheres of the other polymer, in which form it exists immediately prior to melt spinning, deform into microfibrils during melt spinning there being in the process at least a 20% suppression of wind up speed compared with the process carried out with the same throughput in the absence of the added polymer, the term at least 20% suppression of wind up speed meaning that certain properties of the spun fibre are those that would be obtained from a fibre spun at at least a 20% lower wind up speed, such properties in the case of polyethylene terephthalate including birefringence and extension-to-break, in the case of polyhexamethylene adipamide including extension-to-break and in the case of polypropylene including the true stress at 50% strain.