EP0071206A2 - Method of plying and drawing spun yarns - Google Patents

Abstract

High-twist, low-shrinkage and non-snarly yarns or threads are produced by imparting high twist to partially oriented filaments having a yield stress of above 7.5 cN/tex and then subjecting them to a subsequent drawing at room temperature of preferably 5 to 20 %.

Description

The invention relates to a method for producing high-twisted, low-shrinkage and low-twist yarns or twists by twisting and stretching pre-oriented yarns.

For economic reasons, false-twisted polyester yarns are largely manufactured from so-called pre-oriented yarns, which are produced by using high spinning take-off speeds. On the other hand, smooth polyester yarns are still made to a large extent from little pre-oriented spun fabric.

From CH-PS 601 518 it is already known to twisted and fixed, i.e. to produce heat-treated yarns from pre-oriented yarns, the spinning take-off speed being from 3000 to 5000 m / min, corresponding to drawing ratios from 1: 1.6 to 1: 1.2. The yarns are twisted, stretched and, for example, thermally fixed at 200 ° C. Such a twisted, twisted yarn has a low thermal shrinkage and is twisted, i.e. it shows no curl tendency.

The use of temperatures of 200 ° C usually means a very large amount of energy. The threads of each individual twisting point must be passed through separate heaters, whose energy losses are extremely large. It is estimated that less than 1 per mille of the heating power of each individual heater is transferred to the running thread or thread. The remaining energy heats up the work area in which this machine is located. Such workrooms are common air-conditioned, which means that the heating energy must be destroyed again via the air conditioning system, and so on. Energy costs.

To improve this conventional hot twisting process with individual twisting points and individual heaters, EP-OS 20 285 describes a hot twisting device with a common heater over which a large number of yarns are guided as a narrow band. With such a measure, energy savings of more than a power of ten can be achieved compared to driving with individual heaters. But heaters are also needed here, e.g. work together for 20 spindle positions. But even with this energy-saving version, only a very small fraction of the heating energy used is used to heat the threads; in this case, too, the main amount of heating energy is given off to the surrounding space.

DE-OS 29 00 799 already describes a method in which the drawing and twisting of yarns in the balloon of double-wire twisting spindles can be carried out without the use of a heater in the drawing and twisting. Polyester yarns, for example, which are obtained with a winding speed of 2560 to 4100 m / min are suitable as insert yarns. However, the yarns are stretched irregularly in the balloon of the twisting spindle and therefore show orientations that change over their length, which can be seen, for example, in different dyeability. In addition, however, it is necessary in this process to subject the yarns obtained to a heat treatment under tension following the stretching and twisting carried out without the action of temperature. The necessary temperatures are stated at 70 to 240 ° C. In the examples, a temperature of 220 ° C was always maintained. The procedure according to this document also points again a high energy expenditure through the use of heaters. If the heat treatment of the twisted and drawn threads is omitted, no usable yarns are obtained. In this context, DE-OS speaks of a cardboard-like appearance of such yarns. In addition, such threads have an alternating orientation along their length, which is shown, for example, in an uneven coloring.

It was therefore still the task to find a process for producing high-twist, calmed yarns by twisting and stretching threads or yarns, in which, if possible, the use of heating energy can be completely dispensed with.

Surprisingly, it has now been found that when using pre-oriented yarns that can no longer be drawn under the balloon tension of a conventional double-twist machine, the disadvantages of the method according to DE-OS 29 00 799 described above can no longer be observed, provided that this emerges from the double-wire twister Yarn is then subjected to drawing at room temperature.

A stretching in the balloon of a double-wire twisting machine at normal spindle speeds no longer takes place if the yield stress of the insert yarns is above approximately 7.5 cN / tex. The feed yarns should preferably have a yield stress of 8 to 10 cN / tex when carrying out the process according to the invention.

Yield tension is understood to mean the yarn tension (tensile force divided by initial titer) at which the force-elongation diagram deviates from the initially linear course, i.e. in which the attacking forces generally no longer lead to a reversible but an irreversible change in length of the threads.

The beginning of the irreversible change in length is often difficult to see. Instead, however, it is possible to use the height of the minimum of the force-strain curve as a value for the flow force. Such a minimum is usually observed after the linear rise and a certain overshoot in the floating point as a horizontal branch of the curve. In this area there is an increase in length without increasing the force. With a high degree of pre-orientation of the yarns, this minimum can only be identified as a turning point or kink in the curve, but the flow force can be determined in any case.

The required minimum yield stress of more than about 7.5 cN / tex is achieved on conventional spinning systems at spinning take-off speeds of over 4100 m / min. The preferred range from 8 to 10 cN / tex corresponds to the spinning take-off speeds of approximately 4300 to 5000'm / min in conventional spinning systems and conventional titers for textile applications. As already explained above, yield stress values below about 7.5 cN / tex result in a partially irregular stretching in the twisting process of the double-wire twisting machine. The upper limit of the pre-orientation of the insert yarns largely results from the spinning behavior of the threads. When using _" conventional spinning systems, spinning take-off speeds of more than 5000 m / min usually lead to strong fluffy yarns.

In order to increase the flow resistance of the twisted yarns and to reduce the elongation at break and the tendency to curl, post-stretching of the twisted yarns is necessary. This post-stretching is generally between 5 and 20%. A high post-stretching also requires an increase in the twist applied to the insert yarn, given the given twist of the finished yarn. Usually, the stretching ratio will be kept so small that the tendency to curl is just kept low enough for the respective area of application.

In a preferred embodiment of the method, turning and post-stretching take place in succession in one device.

The swirl calming or reduction of the curling tendency is necessary to ensure trouble-free processing of the Ensure yarn. For example, in the case of yarns which are not sufficiently twisted, especially when warping, torn yarns, especially between the payout spool and the first thread brake, are wound around the payout spool in such a way that a restart is only possible with a great deal of work.

For a rough assessment of whether a yarn is curling, you can put a loop of yarn together in a manual test and assess the formation of the first curl. This measuring principle was standardized in the following way.

A thread or yarn 100 cm long is clamped with 2 clamps. One of these clamps is moved by motor in the direction of the other clamp and the loop or loop that forms is observed. If the lower end of the loop turns over and a curl forms, the motor drive of the clamp is stopped and the distance between the two clamps is read. A high value read means that the first curl has already jumped in at a large distance between the leg ends, a corresponding yarn has a large curl tendency. A small distance indicates a low curling tendency, the leg ends of the loop forming could be brought together far.

A tendency to curl of less than 12 cm has proven to be sufficient for threads that are to be processed on conventional warping gates.

Another advantage of the method according to the invention lies in the low shrinkage values of the insert yarns, which are already around 4-5%. Due to the cold post-stretching required according to the invention, the shrinkage values increase only slightly.

The starting yarn is usually obtained in the form of a cylindrical bobbin during rapid spinning and can either be presented in this form to a twisting machine - usually a double wire twisting machine - or beforehand in another form, e.g. into the shape of a cop. These steps are not essential to the invention, they are mainly determined by economic factors.

To further clarify the invention, an embodiment of the method according to the invention will be described with reference to the figure.

A cylindrical spinning bobbin 1 is placed on the double wire spindle 2 and the yarn is turned up in a conventional manner. The balloon thread guide 3 is followed by two delivery mechanisms 4 and 5, between which the twisted yarn is stretched at room temperature. The twisted and drawn yarn is wound up in the winding machine 6 and represents a ready-to-sell twisted yarn that is low in shrinkage and has a low twist. The twisting and drawing process according to the invention yields yarns which correspond to yarns both in thermal shrinkage and in curl tendency (as a measure of the twist calming), as could only be obtained in the prior art by thermal treatment of twisted yarns. As stated above, this thermal treatment is associated with high energy costs. In contrast to this, the method according to the invention can be carried out with the least investment - the twisting machine only has to be extended by one stretching zone.

As the following examples show, the process according to the invention results in yarns which meet the usual quality standards in the uniformity of the yarn properties even surpass. Another advantage of the yarns produced according to the invention is their high dye absorption, which is due to the high spin draw required (cf. Jacob and Schröder in "Chemical fibers / textile industry" 1980, pp. 114-119, 228-232, for example Fig. 10). The method according to the invention is particularly suitable for yarns made from polyethylene terephthalate, but can also be used for yarns made from other high polymers.

example 1

Die Fadenzugkraft im Ballon bei einer Spindeldrehzahl von 6850 U/min lag bei etwa 50 cN und in der Verstreckzone zwischen 85 und 105 cN je nach dem angewandten Verstreckverhältnis.Fast spinning yarns made of polyethylene terephthalate were processed on a double wire machine type DD 39 from Barmag, Barmer Maschinenfabrik AG. The original yarn was obtained at a winding speed of 4300 m / min on cylindrical bobbins. The textile technology data of the starting yarn and the yarns obtained, depending on the post-stretching used, are summarized in the table below. For comparison, the values of a commercially available yarn of comparable titer were included in this table, in which the twisting was carried out by a thermal process. The initial titer of the master yarn was dtex 122 f 40 matt. With the help of the double wire twisting machine 650 twists / m Z were applied. The comparison yarn had a titer of dtex 110 f 48 Z 650 glossy.

The thread tension in the balloon at a spindle speed of 6850 rpm was about 50 cN and in the drawing zone between 85 and 105 cN depending on the drawing ratio used.

At the warping gate, a curling tendency of less than 12 cm was considered sufficient, so that a stretching of 6% in the present case can be regarded as sufficient.

Example 2

Aus dieser Tabelle ergibt sich, daß bei einem Zwirn von 400 T/m bereits eine Nachverstreckung von 6 % als ausreichend angesehen werden kann, während bei 9 % Nachverstreckung die Kringelneigung bereits vollständig beseitigt ist, während zur Drallberuhigung bei einem Zwirn von 1000 T/m zumindest 14 % Nachverstreckung erforderlich sind.In the same way as in Example 1, a polyester multifilament yarn was used as the master yarn for a combined twisting and drawing process. The DD 39 from Barmag was again used as a double wire machine. The winding speed of the spun threads was 4900 m / min, the starting titer dtex 118 f 40 matt. Various series of tests were carried out, the yarn being subjected to a twist of 1000 turns / m and in another case 400 turns / m. In both cases, the post-drawing was varied. The results obtained have been summarized in the table below, in which the further textile data of the spun yarn submitted were also recorded.

From this table it follows that with a twist of 400 T / m a post-stretching of 6% can already be regarded as sufficient, while with 9% post-drawing the curling tendency is already completely eliminated, while for twisting with a twist of 1000 T / m at least 14% post-stretching is required.

Claims (3)

1. A process for producing high-twisted, low-shrinkage and low-twist yarns or twists by twisting and stretching pre-oriented yarns, characterized in that the yarns have a yield stress of more than 7.5 cN / tex and are then subjected to post-stretching at room temperature. 2. The method according to claim 1, characterized in that the yield stress of the master yarns is 8 to 10 cN / tex. 3. Process according to claims 1 and 2, characterized in that the post-stretching is 5 to 20%.

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