Device for spinning materials forming threads

Abstract

An apparatus comprises a spinning head connected to a feeder for the melt, a spinneret assembly which is held in the spinning head and comprises a spinning bore and which spins a melt monofilament, a plate which is located below the spinning head and which comprises a Laval nozzle arranged in a fixed geometrical relationship. Between plate and spinning head a closed first space is formed provided with a supply of gas and below the plate a second space is provided. The throughput of the melt per spinning bore, the temperature of the melt and the pressure in the first and second spaces are adjusted in such a way that the spun melt monofilament after leaving the Laval nozzle before solidification thereof attains a hydrostatic pressure which is greater than the gas pressure surrounding it, such that the thread bursts and splits into a plurality of fine threads.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application is a continuation-in-part of U.S. patent application Ser. No. 10 / 030,202 which is a continuation of copending International Application No. PCT / EP00 / 05703 filed Jun. 21, 2000 which designates the United States, and claims priority to German application no. 199 29 709.6 filed Jun. 24, 1999.TECHNICAL FIELD OF THE INVENTION [0002] The present invention relates to a device for spinning materials forming threads, from melts or solutions at temperatures above the ambient temperature. BACKGROUND OF THE RELATED TECHNOLOGY [0003] Microthreads of this kind, but usually microfibres of finite length, have for many years been made by a hot-air spun-blown method, the so-called melt-blown method, and today there are different apparatuses for this. A common feature of all of them is that, in addition to a row of melt holes—several rows parallel to each other have also become known—hot air which draws the threads escapes. By mixing with ...

AI Technical Summary

Benefits of technology

[0028] The advantage of the present invention lies in that, in a simple and economical manner, very fine threads within a range of well below 10 μm, mainly between 2 and 5 μm, can be produced, which in the case of pure drawing for example by the melt-blow method can be accomplished only with hot gas (air) jets heated above melting point, and so requires considerably more energy. Moreover, the threads are not damaged in their molecular structure by excessive temperatures, which would lead to reduced strength, with the result that they can then often be rubbed out of a textile structure. Another advantage lies in that the threads are endless or quasi-endless and cannot protrude from a textile structure such as a non-woven fabric and come away as fuzz. The apparatus for carrying out the method according to the invention is simple. The spin holes of the spinneret can be larger and so less susceptible to breakdowns, and the Laval nozzle cross-section in its precision does not need the narrow tolerances of the lateral air slots of the melt-blown method. For a given polymer one need only coordinate the melt temperature and the pressure in the chamber with each other, and with a given throughput per spin hole and the geometrical position of the spin holes relative to the Laval nozzle splitting occurs.

[0029] By way of the fact that the device comprises a spinneret with at least two plate-like parts arranged over one another, e.g. the lower part with the nozzles, and electrical heating conductors are arranged in the region of the boundary surface of the at least two plate-like parts in a manner such that they surround the distribution conduits and compensate heat losses to the outside, one achieves a uniform heating of the melt and essentially no waste heat is dissipated to the outside.

[0030] It is particularly advantageous for the distribution conduits to comprise melt channels and at least one melt distribution space which are incorporated (machined) into at least one boundary surface, or are arranged in the region of the boundary surface. With longer paths of the spinning material melts, the problem exists that dead corners arise in the spinneret where the melt does not flow or no optimal conduits with regard to flow technology having a uniform resistance and a uniform melt distribution are present. If the distribution conduits are provided in the region of the boundary surface of the second plate-like parts, then the melt conduits, disregarding the supply and discharge conduits, are completely accessible on manufacture and may thus be checked with regard to the nature of the surface and dead corners.

[0031] The electrical heaters are essentially applied parallel to the melt conduits or melt channels and melt distribution space and surround them in their entirety. At the same time one uses tubular heating conductors which are applied pressed into fittingly calibrated grooves or inserted into the grooves, wherein the grooves in the region of the respective boundary surfaces are incorporated (machined) into the plate-like part or parts.

[0032] It is particularly advantageous for further electrical heating conductors, for increasing the temperature of the melt, to be arranged in the region of the spinning bores, i.e. essentially perpendicular to their longitudinal directions. By way of these measures the melt, before exit from the spinneret, is heated again to higher temperatures, wherein this heating is only effected over a short path so that the thread result is improved and the melt is not thermally damaged, which would have a negative effect on the subsequent mechanical properties of the thread and thus of the nonwoven or yarn. This increased heating is realized by way of groove heating or heating cartridges. In one advantageous manner, the device according to the invention may be used with the methods and means as are disclosed in DE 199 29 709 C1 and WO 02 / 05 2070 A2. Here, on the one hand it is a question of an as uniform as possible heating of the spinneret over the width if spunbond nonwovens are to be manufactured, since all temperature differences are noticeable due to the changes in viscosity of the exit flow quantity from the individual spinning bores and thus unequal web or nonwoven weights result over the web width. In order to distribute a polymer melt, the temperature should not be too high and thus the viscosity should not be too low. On the other hand however with regard to the requirements of this method with which a melt monofilament is converted into a multifilament of individual threads by way of splicing, the melt must exceed a certain temperature so that a splicing also indeed takes place. The device according to the invention may however also be applied to other spinning methods.

Problems solved by technology

By mixing with the colder ambient air, there is cooling and solidification of these threads or fibres, for often, usually of course undesirably, the threads break.

The disadvantage of this melt-blown method is the high expenditure of energy to heat the hot air flowing at high speed, a limited throughput through the individual spinning nozzles or spinning bores (even though these have been set increasingly closer together in the course of time, down to a spacing of below 0.6 mm with 0.25 mm in hole diameter), that with thread diameters of less than 3 μm breaks occur, which leads to beads and protruding fibres in the subsequent textile composite, and that due to the high air temperature necessary to produce fine threads the polymers are thermally damaged well above the melt temperature.

They are expensive, operationally susceptible and tedious to clean.

An overheating of the liquid spinning materials in order to compensate the losses at the supply conduit to the spinnerets and at these nozzles is generally ruled out since the spinning materials do not tolerate being molecularly degraded too greatly.

The expense with regard to heat transfer medium heaters is considerable, in particular with vaporous media which otherwise are quite favourable, where the condensation product must be led back to the heat source in an expensive manner.

A fire hazard and even an explosion hazard sometimes exist with these media.

An air gap always exists between the spinneret to be heated and the heating housing in which it is installed, which accordingly needs to be overcome technically by way of an accordingly higher temperature of the heater housing, thus with more energy expense.

Here, particularly large heat losses may also occur on account of the known chimney effects.

In particular with long spinnerets, as are required for spunbond nonwoven manufacturing methods, here in particular the melt-blown method, the heating in this manner is unequal in a waved manner over the length of the spinnerets, which although capable of being alleviated by way of a suitably greater mass of the spinneret, however on account of this leads to an increased material expense and an extended pre-heat time of the spinneret before this may begin with the production.

The expense for the individually, perpendicularly introduced heating cartridges is also considerable.

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