Method and device for producing substantially endless fine threads
View Patent ↗The invention relates to a method and a device for producing substantially endless fine threads from polymer solutions, especially spinning material for lyocell, wherein the spinning material is spun from at least one spinning hole or a spinning slot. The spun thread or film is drawn by high-speed accelerated gas flows using a Laval nozzle whose narrowest cross-section is located beneath the point where the spinning material exists. The threads are arranged on a strip in the form of a non-woven or are taken up in the form of a yarn and are subsequently separated in spinning baths by means of solvents.
1. A method for producing endless fine threads from a spinning material made of cellulose dissolved in a solvent, in which the dissolved cellulose is spun from at least one spinning orifice and the spun thread is drawn by gas flows which are constantly accelerated to a high speed by means of a Laval nozzle, the gas flow in the region of the fiber formation being substantially laminar, at least one of the temperature of the spinning material, the temperature of the thread exiting from the spinning orifice, the pressure before the Laval nozzle and the pressure after the Laval nozzle is controlled such that the thread reaches a pressure in its interior before solidifying which is greater than the gas pressure surrounding it, in such a manner that the thread splits and fans out into a multiplicity of fine threads, whereby in the drawing region water or steam is injected in order to start coagulation.
2. The method according to claim 1 wherein the maximum of the speed of the gas flow is beneath the outlet of the spinning material from the spinning orifice.
3. The method according to claim 1 wherein the gas flows drawing the thread are at ambient temperature or at a temperature which is conditioned by their production and supply.
4. The method according to claim 1 wherein the chamber after the Laval nozzle is at ambient pressure or, in the case of further processing of the threads, is at a pressure somewhat above ambient pressure which is required for the further processing.
5. The method according to claim 1 wherein the ratio of the pressures in the chamber above and below the Laval nozzle when using air is selected between 1.02 and 3, dependent upon the throughput and temperature of the spinning material.
6. The method according to claim 1 wherein the spinning material in the region of the outlet position and/or the thread exiting from the spinning orifice is heated.
7. The method according to claim 1 wherein a multiplicity of threads is spun and if necessary fanned out, which threads are laid out into a non-woven fabric or are further processed into yarns.
8. The method according to claim 1 wherein the pressure ratios before and after the Laval nozzle are set such that the gas flow in the Laval nozzle reaches speeds up to and above the speed of sound.
9. The method according to claim 1 wherein threads spun from a cellulose solution are laid out in a dry place and subsequently guided through a precipitation bath.
10. The method according to claim 1 wherein, in the drawing region of the threads, water or steam is injected in order to control the binding of the threads to each other into a non-woven fabric.
11. The method according to claim 1 wherein the cellulose content is less than about 13% by weight.