Method for interlacing yarns

Abstract

The invention relates to a method for tangling multifilament yarns, comprising the steps of providing a multifilament yarn, guiding the multifilament yarn through a first yarn guiding member, guiding the multifilament yarn through an interlacing nozzle, interlacing the yarn by means of compressed air in the interlacing nozzle, guiding the interlaced multifilament yarn through a second yarn guiding member, characterised in that the first and second yarn guiding members are at a maximum distance of seven centimetres from one another, and the compressed air used for interlacing has a pressure of at least 3 bar.

Description

[0001] Process for intermingling yarns

[0002] Description:

[0003] The invention relates to a tangled unsized synthetic filament yarn, in particular a synthetic filament yarn for the production of airbag fabrics and other technical fabrics, with a yarn linear density of 200 - 1 000 dtex.

[0004] Fabrics for the production of airbags must meet a number of very different requirements. In addition to the particularly important, precisely adjusted air permeability, these fabrics must exhibit good aging resistance, high strength, good foldability, and a high degree of flexibility in the event of an impact. In line with the specific requirements placed on the properties of the fabrics, very specific requirements are also placed on the yarns used for these purposes, relating, on the one hand, to their effects on the fabric properties and, on the other, to their processing behavior during fabric production.

[0005] In practice, it proved difficult to meet all the requirements in the manner desired by automobile manufacturers. Therefore, the first airbags were made from coated fabrics. These proved to be less than ideal, not only due to their manufacturing costs but also due to several disadvantages in use.

[0006] The yarns initially used after the increased popularity of uncoated airbag fabrics generally had relatively high yarn and filament deniers. While these fabrics were able to achieve the required air permeability and strength in most cases, they often lacked satisfactory foldability and flexibility.

[0007] The yarns mentioned were almost always used in sized fabric production, and in rare cases, twisted or plied. The weft usually consisted of unsized and untwisted yarns, although twisted yarns were also used in the weft on rare occasions.

[0008] Both twisting and sizing significantly increase the manufacturing costs of the yarn and thus also of the fabric. In addition, the sizing must be removed after fabric production, meaning the fabric must be desized. This process is problematic from both an economic and ecological perspective, as not only are the costs incurred for desizing, but additional costs are also incurred for the treatment of the desizing baths, which is essential for ecological reasons.

[0009] While twisting, which requires roughly a similar cost to sizing, eliminates desizing costs, this process presents another disadvantage: twisted or plied yarns typically produce "grainier" fabrics than untwisted or untwisted yarns. Furthermore, it is more difficult to precisely adjust the desired air permeability when using twisted or plied yarns.

[0010] Improved foldability and flexibility can be achieved by using yarns with a lower linear density of the individual filaments. Such yarns have already been proposed for the production of airbag fabrics.

[0011] As weaving practice shows, processing fine-filament yarns, especially warp yarns, is considerably more difficult than weaving coarse-filament yarns. With fine-filament yarns, the risk of filament breakage and the resulting filament build-up is significantly higher. This can lead to weaving machine downtime and fabric defects. Therefore, it is especially important to apply a sufficient amount of sizing to fine-filament yarns to ensure smooth processing on the weaving machine.

[0012] In the practice of chemical fiber processing, it is known that intermingling the individual filaments, commonly referred to as tangling, can be an alternative to sizing. EP 0 738 793 A1 discloses a yarn whose properties could be significantly improved by intermingling. However, it is not capable of fulfilling the objective underlying the application because it does not allow for the complete omission of sizing and twisting. EP 0 738 793 is incorporated in its entirety by reference into the disclosure of the present application.

[0013] The task was therefore to provide suitable yarns for the production of uncoated airbag fabrics which can be processed into fabrics at low cost without negatively influencing the required fabric properties and which, in addition, result in an improvement in the fabrics produced therefrom compared to the airbag fabrics predominantly used to date, particularly with regard to foldability and flexibility.

[0014] The object is achieved by a method for interlacing multifilament yarns, comprising the steps of providing a multifilament yarn, guiding the multifilament yarn through a first yarn guide element, guiding the multifilament yarn through an interlacing nozzle, interlacing the yarn by means of compressed air in the interlacing nozzle, guiding the interlaced multifilament yarn through a second yarn guide element, characterized in that the first and the second yarn guide element are a maximum of six centimeters apart, that the compressed air used for interlacing has a pressure of at least three bar.

[0015] Polyamide yarns such as polyamide 6.6, polyamide 4.6, and polyamide 6 can be used. However, other fiber types, such as polyester fibers such as polyethylene terephthalate, can also be used. This application is not intended to be limited to a specific fiber type, but rather to encompass all synthetic filament yarns.

[0016] The processed multifilament yarns have yarn linear density of at least 50 dtex, in one embodiment at least 78 dtex, 100 dtex or 200 dtex.

[0017] The processed multifilament yarns have a yarn count of no more than 200 dtex, in one embodiment no more than 500 dtex, 700 dtex or 1000 dtex.

[0018] The filament linear density of the multifilament yarns used is at least 1 dtex, in one embodiment at least 2 dtex or at least 5 dtex. The filament linear density of the multifilament yarns used is at most 5 dtex, in one embodiment at most 8 dtex or at most 12 dtex.

[0019] In this application, the terms “yarn” and “multifilament yarn” are used synonymously unless otherwise stated.

[0020] Examples of usable yarn types are 235 f 72 with a filament titer of 3.26 dtex (ie 72 individual filaments of 3.26 dtex with a total titer of 235 dtex), 350 f 144 with a filament titer of 2.43 dtex, 470 f 144 with a filament titer of 3.26 dtex, 700 f 140 with a filament titer of 5.0 dtex, 700 f 144 with a filament titer of 4.86 dtex, 700 f 210 with a filament titer of 3.33 dtex and 940 f 280 with a filament titer of 3.36 dtex.

[0021] The polyamide yarns suitable for the production of airbag fabrics have, in one embodiment, a tenacity of at least 60 cN / tex and an elongation of 15-30%. Polyester yarns intended for use in airbag fabrics also have tenacity values ​​above 60 cN / tex, and elongations of 10-25%.

[0022] The yarns used are manufactured using methods commonly used in the chemical fiber industry. Melt spinning processes are typically used to spin filament yarns made of polyamides or polyesters. The desired linear density is adjusted using conventional methods, particularly by controlling the throughput at the spinneret.

[0023] Entangling is also a process commonly practiced in the chemical fiber industry. Terms such as intermingling or intermingling are also common. In the following, the terms "intermingling," "entangling," and "intermingling" are used synonymously.

[0024] The opening length and stability of the interlacing points are controlled by precisely coordinating the geometry of the Tangei nozzle, the tension and speed upon entry into the Tangei nozzle, the introduced air volume, and the air pressure. These process conditions for interlacing depend on the yarn linear density and the finish applied to the yarn and must therefore be coordinated with these parameters. Furthermore, the yarn guidance is of great importance; this should be as tight as possible. This means that the smallest possible distance between the yarn guides ensures a particularly even distribution of the interlacing points. The interlacing nozzle(s) is arranged between the yarn guides.

[0025] The two thread guides are spaced apart by a maximum of six centimeters, in one embodiment by a maximum of five centimeters, four centimeters, three centimeters or two centimeters.

[0026] The yarn guides can be eyelets, hooks, rings, rods, or so-called pigtails. In one embodiment, the yarn not only passes through the yarn guide, but is in contact with the yarn guide in such a way that the yarn's direction is changed or the yarn is mechanically decoupled from the rest of the yarn between the yarn guides.

[0027] It is important for the yarns according to the invention to maintain a certain average opening length of 3 - 8 cm, in one embodiment 4 - 6 cm. Greater average opening lengths do not result in satisfactory processing properties on the weaving machine, as they do not allow sufficient yarn closure and thus satisfactory integration of the break-prone fine individual filaments into the yarn structure is not possible. For example, a broken filament in a warp yarn will usually only be pushed up to the next interlacing point and run with it through the heddle on the loom. If the next interlacing point is far away, a relatively large length of broken filament is created, which is then pushed up and ultimately leads to a thick spot that the heddle can no longer pass through, which can cause yarn breakage.At the same time, there is also the possibility that the broken filament is picked up by the neighboring yarn running in the warp, causing the aforementioned defect in the yarn just as it does in the yarn from which the filament originates: namely, breakages of neighboring yarns due to an obstruction of the passage at the heddle. In this case, we speak of so-called sympathetic breaks, which manifest themselves in the fabric as defects known to weaving experts as "spatulas" or "nests."

[0028] Excessively high average opening lengths can have a similar effect on weft yarns. Filaments protruding from the yarn structure, commonly referred to in weaving practice as "filament losers," are not captured by the rapier, for example, during processing on a rapier weaving machine, and lead to yarn build-up or, as a result, thickening of the yarn.

[0029] The mean opening length is the average distance between the interlacing points in a yarn. The interlacing point, sometimes also referred to as a tangle knot, is a point of interlacing in the yarn at the beginning of which a measurement signal is triggered during the opening length measurement. These interlacing points, which are pre-formed by filament crossings in the yarn, lead to a measurement signal when a certain resistance is applied to the measuring needle due to a corresponding degree of interlacing.

[0030] In addition to the average opening length itself, the range of the opening length is also of great importance. This refers to the variability of the measured opening lengths. The lower the variability, the more evenly distributed the interlacing points are across the yarn. This is advantageous because a very uneven distribution of the interlacing points on the sections where the interlacing points are spaced apart disproportionately far apart can lead to the same disadvantages outlined above for excessively large opening lengths.

[0031] The yarn processing speed is also crucial for the variation in the opening length. It should be noted that a low processing speed generally means a narrower variation, but for reasons of process efficiency, the highest possible processing speed is desirable. In one embodiment, the processing speed for the present process is 2000 meters per minute (mpm) or more, 2500 mpm or more, 3000 mpm or more, or 3500 mpm or more.

[0032] In one embodiment, the nozzle has at least one or at least two outlet openings. In one embodiment, the yarn is passed between the outlet openings of the nozzle.

[0033] Various measurement methods are known in the chemical fiber and textile industries for measuring the opening length, the results of which are not always comparable. The values ​​stated here were determined exclusively using the Rothschild Automatic Yam Entanglement Tester, Type R-2072.

[0034] All types of swirl nozzles known to those skilled in the art can be used as swirl nozzles. In one embodiment, the swirl nozzle has a diameter of a maximum of four millimeters, a maximum of three millimeters, a maximum of two millimeters, or a maximum of one millimeter. In one embodiment, it can be a double nozzle, also known to those skilled in the art as a "tandem nozzle."

[0035] When measuring with this device, the yarn to be tested is pre-tensioned using two hysteresis brakes so that the yarn tension at the entrance to the actual measuring section is 1.8 cN / tex. After a pre-travel length, the yarn is grasped and spread by two yarn guides, after which a measuring needle pierces the thread. Once an adjustable peak tension, the so-called trip level, is reached, a measuring signal is triggered, the length of yarn passed through in the meantime is determined by an electronic counting relay and recorded in a memory. The yarn is then automatically pulled further and the measuring cycle begins again. In the interest of determining easily reproducible values, it is advisable to carry out 200 individual measurements to determine the opening length and to calculate the arithmetic mean and median value from these.

[0036] The application further relates to a yarn produced by a method according to one or more of the preceding claims, wherein the median value of the opening length of the yarn is at most 55 millimeters and the mean value of the opening lengths is not more than 10%, preferably not more than 7% larger, even more preferably not more than 5% larger than the median value.

[0037] In this application, the mean is understood to be the arithmetic mean of a set of numbers. The median is understood to be the measured value that, in an ascendingly sorted set of numbers, forms the value that is exactly in the middle if the number of numbers is odd. If the number of numbers in a set is even, the set is sorted in ascending order to determine the median, and the median is then determined as the arithmetic mean of the two middle values. Examples

[0038] Multifilament yarns made of polyethylene terephthalate with 96 individual filaments and a total linear density of 550 dtex were interlaced at various pressures and distances between the yarn guides. Figures 1 and 2 show box plots of the measured opening lengths at 80 and 120 cN needle thread tension. The shaded boxes indicate the area containing 50% of the measured opening lengths. Figure 1 shows the values ​​at a needle thread tension of 80 cN, and Figure 2 shows the values ​​at a needle thread tension of 120 cN. The measurements were carried out using a Rothschild interlacing nozzle. A Rothschild Automatic Yam-Entanglement Tester, Type R-2072, was used to measure the opening lengths.

[0039] A Tangle Jet P20 swirling nozzle was used, operating with a continuous air stream. The nozzle has two 2-millimeter diameter holes through which the thread is passed.

[0040] The turbulences were carried out under the following conditions:

[0041] • 4.3 cm distance between the thread guides, 3 bar pressure

[0042] • 4.3 cm distance between the thread guides, 4 bar pressure

[0043] • 4.3 cm distance between the thread guides, 5 bar pressure

[0044] • 3 cm distance between the thread guides, 3 bar pressure

[0045] • 3 cm distance between the thread guides, 4 bar pressure

[0046] • 3 cm distance between the thread guides, 5 bar pressure

[0047] • 2.5 cm distance between the thread guides, 5 bar pressure

[0048] It was found that the dispersion of the measured opening lengths was particularly small when the distance between the thread guides was as small as possible and the pressure was as high as possible. Furthermore, it was found that the median and mean values ​​converged as the distance between the thread guides was reduced and the pressure increased. Table 1 lists the mean and median values ​​found.

Claims

Process for intermingling yarns Claims:

1. A method for tangling multifilament yarns, comprising the steps of a. providing a multifilament yarn, b. guiding the multifilament yarn through a first yarn guide, c. guiding the multifilament yarn through an interlacing nozzle, d. interlacing the yarn by means of compressed air in the interlacing nozzle, e. guiding the interlaced multifilament yarn through a second yarn guide, characterized in that - the first and second thread guide organs are a maximum of seven centimetres apart, - the compressed air used for swirling has a pressure of at least 3 bar.

2. Method according to claim 1, wherein the first and the second thread guide member are a maximum of six, preferably a maximum of five, more preferably a maximum of four centimeters apart.

3. The method according to claim 1 or 2, wherein the pressure of the compressed air is at least 3.5, preferably at least 4, more preferably 4.5, particularly preferably at least 5 bar.

4. Method according to one or more of the preceding claims, wherein the processing speed of the yarn is at least 2000, preferably at least 2500, more preferably at least 3000, particularly preferably at least 3500 m / min.

5. Method according to one or more of the preceding claims, wherein the thread guide members are hooks, eyelets, pigtails or rods.

6. Yarn produced by a process according to one or more of the preceding claims, wherein the median value of the opening length of the yarn is at most 55 millimeters and the mean value of the opening lengths is not more than 10%, preferably not more than 7%, even more preferably not more than 5% greater than the median value.

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