FALSE TWISTING METHOD

Abstract: This invention relates to a high speed false twisting and apparatus, and more particularly to a high speed false twisting method for twisting smoothly yarns at a yarn speed of at least 1,000 m/min and to a high speed false twisting apparatus for conducting smoothly the method. More definitely, when thermoplastic multifilament yarns are false-twisted, false twisting is made with a high number of false twists satisfying the following formula (1) to obtain high quality false-twisted yarns, false twisting is then made at a yarn speed satisfying the following formula (2) to obtain higher productivity and false twisting is further made with a short thread handling length satisfying the following formula (3) in order to obtain high twisting stability. Formula 1: T ≧ 0,24/√A, Formula 2: V ≧ 1,30 x 10⁻³/√A, Formula 3: L ≦ 90/V, where T: number of false twists inserted per meter yarn (n times/m; n is the number of turns of twist), V: yarn speed of false twisting (m/sec), L:length of thread handling from roller for feeding yarn to false twisting zone to twister to which false twist is inserted (m). Symbol A represents the sectional area (m²) of the yarn which is obtained by dividing the size of the yarn (weight per unit length) by the yarn density (weight per unit volume). Furthermore, the false twisting machine of the present invention for practising the false-twisting method includes an apparatus which consists of a feed roller for supplying the yarns at least to the false twisting zone, a heater for bringing steam into direct contact with the yarns, a cooler for bringing water into direct contact with the yarns, a false twister and a delivery roller that are disposed in order named.

Description: The present invention relates to a method of producing a false twist textured yarn according to the preamble of claim 1 and known, for instance, from document GB-A-1 248 089. The method of high speed false twist texturing makes it possible to perform smoothly the false twist texturing at a yarn speed of 1,000 m/min or higher. Up to the present time, in the field of false twist texturing of thermoplastic multi-filament yarns, to improve productivity, development of new manufacturing technologies as described below have been promoted. (1) To attempt to promote labour-saving by making packages of an original yarn for false twist texturing and a textured yarn thereof larger and promoting automation of handling of the package. (2) To attempt to promote energy-saving by developing a heating method, a cooling method etc., with high efficiency. (3) To attempt to promote space-saving by developing a simple and compact installation. Furthermore, recent attempts have been made to achieve an ultrahigh processing at 1,000 m/min or higher. Means used to perform an ultrahigh false twist texturing up to the present time are as follows. (1) A highly-oriented undrawn yarn (POY; Partially Oriented Yarn) is used as a fed original yarn. (2) A longer heater is used in accordance with the heater processing speed. In this case, the heater is a so-called dry hot-plate generally consisting of a heated metal plate with a smooth surface with which a yarn is brought into contact using a heating medium such as "Dowtherm". (3) A yarn-contacting plate made of a metal is used as a cooling device and, in addition, a so-called cooling plate positively cooling the yarn-contacting plate with chilled water is used. (4) A friction-type false twister, capable of twisting with high speed, is used. (5) To suppress ballooning of the yarn, parts where the yarn is freely running are reduced as much as possible. (6) Polishing of yarn path parts such as guides with which the yarns are brought into contact is improved. In particular, US-A-4138840 describes a false twist texturing method in which the yarn is firstly heated and then cooled, in each case using vortices of a fluid which, for heating, may be steam. The draw texturing is carried out at low speed (600 m/min). GB-A-1248089 and JP-A-139838 disclose high speed false twist texturing methods. In the method of GB-A-1248089, the yarn describes a long yarn path along a heating plate, while in that of JP-A-89-139838 the yarn is, during false twisting, firstly heated in a hot fluid, then cooled in a cooled fluid while maintaining the yarn in substantially the same running direction. There is no reference to the respective lengths of the heating and cooling zones. However, when a yarn speed reaches 1,000 m/min or larger, then when using such means as the above, the lengths of the dry hot-plate and cooling plate which have been conventionally used in practice are too short so that the extent of heating-cooling provided is insufficient and the quality level of the conventional textured yarn can not be maintained. In addition, if the dry hot-plate and the cooling plate are made longer to perform sufficient heating, ballooning is generated on a twisted yarn and, moreover, if the length is made longer, it becomes impossible to set the yarn on the devices. In addition, if the yarn speed is increased, ballooning is generated on the twisted yarn, which becomes easily separated from the dry hot-plate and the cooling plate, which results in insufficient heating-cooling. If the texturing speed is increased, the generated ballooning increases yarn breakage until it becomes impossible to maintain stable production. If the productivity is unstable, it is not possible to have cost-down based on speeding up. Therefore, to maintain processing stability while running at high speed, suppression of ballooning may be attempted by making the number of twists smaller than that for texturing at low speed or increasing processing tension, especially twisting tension, but in this case, it is of course impossible to obtain good physical properties of the textured yarn. Taking into consideration problems of high speed false twisting described above, we have made extensive studies and have found that such problems may be solved by utilization of the conditions, in accordance with the present invention, set out below. Thus, the present invention seeks to provide a method of false twist texturing wherein good textured yarn characteristics even when a high speed false twist exceeds 1,000 m/min and stable and high productivity can be maintained. The present invention provides a method of false twist texturing which is performed (a) with a high number of false twists satisfying equation 1 described below to obtain a false twisted textured yarn of high quality, (b) at a yarn speed satisfying equation 2 described below to obtain high productivity and furthermore, (c) using a short yarn path length satisfying equation 3 described below to obtain high processing stability when a thermoplastic multi-filament yarn is false-twisted: T ≧ 0.24/√A V ≧ 1.30 x 10⁻³/√A L ≦ 90/V wherein T is the number of false twists inserted per meter of the yarn (n turns/m; n is the number of turns of the twist); V is the yarn speed of false twist texturing (m/sec); L is a yarn path length from rollers feeding a yarn into the false-twisting zone to a false twister inserting false twist (m); A is the crosssectional area of the yarn (m²), which is obtained by dividing the tex of the yarn (a weight per unit length) by the density of the yarn (a weight per unit volume). A false-twist texturing machine suitable for performing this method could consist of an apparatus having at least feed rollers feeding a yarn into a false-twisting zone, a heating device bringing the yarn into direct contact with steam, a cooling device bringing the yarn into direct contact with water, a false twister and delivery rollers in this order. The best embodiments for practicing the present invention will now be explained in more detail with reference to the accompanying drawings. Figure 1 is a rough sketch illustrating an example of a drawing and false-twisting machine embodying the present invention and Figure 2 is a rough sketch illustrating a drawing and false-twisting machine of a comparative example. Firstly, in order to offer a method of false twist texturing of a thermoplastic multi-filament yarn which allows a false-twist textured yarn of high quality to be obtained, the number of false twists is set at a value of 0.24/√A or larger. In other words, even at a yarn speed of 1,000 m/min or higher, to maintain the same physical properties of a false-twist textured yarn as those of the false-twist textured yarn obtained at a yarn speed of lower than 1,000 m/min, the number of false twists T is set at a value of 0.24/√A or larger. It is set preferably at a value of 0.25/√A or larger, more preferably at a value of 0.26/√A or larger. The value of A can be obtained by calculation from the weight per unit length of the obtained yarn and the specific gravity of the yarn. In addition, the number of false twists T is a value obtained by sampling carefully a false-twisted yarn from the texturing machine while the yarn is textured and measuring it. Secondly, in order to offer a method of false twist texturing of a thermoplastic multi-filament yarn which allows a false-twist textured yarn of high quality and high productivity to be achieved, the yarn speed V is set at a value of 1.30 x 10⁻³/√A or larger. In other words, in order to maintain both high productivity and the same good physical properties of a textured yarn as those of a textured yarn manufactured by the conventional low speed texturing, the yarn speed V is set at 1.30 x 10⁻³/√A or larger. It is preferably set at 1.55x 10⁻³/√A or larger, more preferably at 1.81 x 10⁻³/√A or larger. Thirdly, in order to offer a method of false twist texturing of a thermoplastic multi-filament yarn which allows a high texturing stability to be achieved , the yarn path length L from feed rollers feeding a yarn in the false-twisting zone to a false twister inserting false twist is set at a value of 90/V or shorter. In other words, up to the present time, to increase the yarn speed of false twist texturing, a dry hot-plate and a cooling plate, the lengths of which have been extended, have been used. As a result, in commercially available false-twist texturing machines, the total length of the dry hot-plate and the cooling plate is 5 m or longer at the maximum machine speed of 1,200 m/min . Thus, the present invention provides a method in which, to obtain a high texturing stability, a high productivity and good physical properties of a textured yarn by performing false twist texturing of a thermoplastic multi-filament yarn, the yarn path length from feed rollers feeding a yarn in the false-twisting zone to a false twister inserting false twist is restricted. By this method, a stable false twist texturing with a lower tension in comparison with the conventional method, without occurrence of ballooning in the twisted yarn and without yarn breakage can be realized. In this case, the yarn path length L from feed rollers feeding a yarn into the false-twisting zone to a false twister inserting false twist is a value of 90/V or shorter and preferably, a value of 70/V or shorter and more preferably, a value of 50/V or shorter. As described above, in the present invention, by restricting the process conditions to those required by the above relationships governing the number of false twists per meter of a yarn, the yarn speed of false twist texturing, the yarn path length from feed rollers feeding a yarn in the false-twisting zone to a false twister inserting false twist and the actual crosssectional area of a yarn, it is possible to obtain stable productivity and good physical properties of a textured yarn even when the false twist texturing is performed at high speed. In the method of the present invention, heat treatment of a textured yarn is performed in an atmosphere of a high temperature fluid, in particular, steam. If the yarn path length from feed rollers feeding a yarn into the false-twisting zone to a false twister inserting false twist is restricted in a relation to the yarn speed of false twist texturing, it is not possible to obtain good physical properties of a textured yarn without utilizing a heating method which is performed in an atmosphere of a high temperature heating fluid and is accordingly a short time and high efficiency heating method in comparison with the conventional dry hot-plate. As the source of steam, it is especially preferable to use a saturated steam. In addition to the method of heating in the atmosphere of this high temperature heating fluid, it is also possible to use a method of heating by means of infrared heating and dielectric heating in parallel with this method. In addition, the method of heating in an atmosphere of high temperature heating fluid can be used in parallel with other heating methods. Furthermore, in the present invention, it is preferable that cooling of the false-twisted yarn is performed in an atmosphere of a cooling fluid, in particular, water. If the yarn path length from feed rollers feeding a yarn in the false-twisting zone to a false twister inserting false twist is restricted in a relation to the yarn speed of false twist texturing, it is not possible to obtain good physical properties of a textured yarn without utilizing a cooling method which is performed in an atmosphere of a cooling fluid and is accordingly a short time and high efficiency cooling method in comparison with the conventional cooling plate. As cooling fluid, it is especially preferable to use water at room temperature. The method of the present invention is effective at a yarn speed of 1,000 m/min or larger, preferably effective at a yarn speed of 1,200 m/min or larger and more preferably effective at a yarn speed of 1,400 m/min or larger. As a thermoplastic multi-filament yarn used for false twist texturing by a method of the present invention, no specific restriction exists and any yarn that can be false-twist textured is applicable. In particular, the method is especially suitable for application to polyester fibers and polyamide fibers. In addition, false twist texturing methods embodying the invention include not only methods wherein a drawn yarn and a yarn spun at about 5,000 m/min or higher (OSP yarns; One-Step Process yarns based on high-speed spinning) is false-twist textured, but also methods wherein an undrawn yarn and a highly oriented undrawn yarn (POY) is drawn and false-twisted. Next, a false-twist texturing machine suitable for carrying out a method of the present invention will be described. Such an apparatus has at least feed rollers feeding a yarn in a false-twisting zone, a heating device bringing the yarn into direct contact with steam, a cooling device bringing the yarn into direct contact with water, a false twister and delivery rollers, in this order. The false-twist texturing machine is operable at high speed, offers excellent texturing stability and is capable of providing a textured yarn of good quality by providing at least feed rollers feeding a yarn into a false-twisting zone, a heating device bringing the yarn into direct contact with steam, a cooling device bringing the yarn into direct contact with water, a false twister and delivery rollers, in this order, when performing false twisting of a thermoplastic multi-filament yarn. Namely, in a method embodying the present invention, in order to obtain stable productivity and good physical properties of a textured yarn when a thermoplastic multi-filament yarn is false-twist textured, a heating device bringing the yarn with a fast heat-transmitting speed into direct contact with steam and a cooling device bringing the yarn with a fast cooling speed into direct contact with water, are used, the free zone from feed rollers feeding the yarn into a false-twisting zone to a twister inserting false twist is minimised as much as possible and the length of the yarn path from feed rollers feeding the yarn into the false-twisting zone to the twister inserting false twist is made as short as possible. The false-twist texturing machine can realize a stable false twist texturing with a low tension in comparison with the conventional one, without occurrence of ballooning in the twisted part and without yarn breakage. In addition, physical properties of the obtained textured yarn are excellent. A method embodying the present invention may be carried out using a false-twist texturing machine with high speed, affording stable productivity and a textured yarn having good physical properties by means of a heating device bringing a yarn into direct contact with steam and fitted with a yarn path sealing part from which hardly any steam leaks out of the device. The pressure of steam used in the heating is ordinarily higher than atmospheric pressure. The heating device consists of a heating cylinder furnished with a seal mechanism defining an inlet and an outlet orifice for a yarn to be heated in such a way that steam with a pressure higher than the atmospheric pressure does not leak from the heating device. If the seal mechanism were not provided, steam would leak roughly along the yarn path and disturb the yarn in the false-twisting zone and as a result, it would be impossible to perform stable false twist texturing. In addition, if the seal mechanism were not provided, a remarkably large amount of steam would flow out of the heating device fed with steam and uniform and stable heating would not result and a textured yarn having good physical properties would not be obtained. A method embodying the present invention may be carried out using a false-twist texturing machine providing high speed and stable productivity and a textured yarn having good physical properties by means of a cooling device bringing a yarn into direct contact with water in the false-twist texturing machine and fitted with a sealing part from which hardly any water leaks out of the device. The cooling device consists of a water bath with a seal mechanism at an inlet and an outlet for a yarn to be cooled in such a way that water etc., hardly leaks from the cooling device. If the seal mechanism were not provided, water would be taken out of the cooling device by the yarn running through it and any lubricant or polymer or oligomer produced by decomposition of the polymer released from the yarn accompanied by water would be scattered by rotation of the yarn in the false-twisting zone out of the cooling device. Some of these scattered substances would adhere or accumulate on the yarn path part. As the yarn is brought into contact with this accumulation of parts of machinery in the yarn path, this would tend to cause yarn breakage, so that it would be impossible to perform a false twist texturing with high speed and reliability. The yarn path length from feed rollers feeding a yarn into a false-twisting zone to a twister inserting false twist is restricted at 2 m or shorter in the false-twist texturing machine. Thus, when the yarn travels at high speed in the false twist texturing device, there is a need to extend the lengths of the heating and cooling devices placed between the feed rollers feeding the yarn into the false-twisting zone and the twister inserting false twist, so that the yarn path length from the feed rollers to the false-twister is also extended as a whole. However, due to the long yarn path, movements of rotation and running of the yarn in the false-twisting zone become unstable and as a result, the yarn produces ballooning and stable texturing may become impossible. Therefore the length of the yarn path is restricted at 2 m or shorter to perform stable movements of rotation and running of the yarn in the false-twisting zone. In a method embodying the present invention, a normal operation can be performed effectively at a yarn speed on the delivery rollers of 1,000 m/min or larger in the false-twist texturing machine. Preferably, the method is effective at a yarn speed of 1,200 m/min or higher and more preferably, the method has greater effectiveness at a yarn speed of 1,400 m/min or higher. The false-twister of the false-twist texturing machine is not specially restricted, but a triaxial circumscribed frictional twister and a belt type frictional twister are preferably used. Practical examples will be described below, with reference to the accompanying drawings. Figure 1 is a rough sketch illustrating an example of a drawing and false-twisting machine for carrying out a method embodying the present invention and Figure 2 is a rough sketch illustrating a drawing and false-twisting machine for carrying out a comparative method. In these figures, 1 is a package; 2 is a pair of feed rollers; 3 is a dry hot-plate; 4 is a seal mechanism; 5 is a heat-treating device with a high temperature fluid; 6 is a cooling device with a cooling fluid; 6' is a cooling plate; 7 is a belt type frictional twister; 8 is a pair of delivery rollers; 9 is a driving roller for winding; Y is a highly oriented undrawn yarn; P is a textured yarn. The Example and Comparative Examples described below are performed by means of apparatus outlines of which are illustrated in these figures. Example 1 Using a polyester multi-filament yarn with a birefringence Δn of 0.037, an elongation of 180%, a round crosssection, 15,44 tex (139 denier) and 36 filaments, an ultrahigh speed false-twist texturing with a speed of 2,000 m/min was performed by means of the drawing and false-twisting machine illustrated in Figure 1. In addition, in the machine, saturated steam was used as a high temperature fluid for the heat-treating device and water was used as a cooling fluid for the cooling device. Conditions: Yarn speed on delivery rollers = 2,000 m/min Surface speed on the twister belt = 3,000 m/min Speed of the feed rollers = 1,064 m/min Temperature of the dry hot-plate = 220°C Length of the dry hot-plate = 0.5 m Temperature in the steam heat-treating device = 213°C (Pressure of saturated steam = 20 kgf/cm²G) Length of the steam heat-treating device = 1 m Temperature of water in the cooling device = 28°C Draw ratio = 1.88 Twisting tension just before the twister = 44 g Number of false twists per unit length just before the twister = 3,300 turns/m Length of the yarn path between the feed rollers in the false-twisting zone and the false-twister = 2 m Comparative Examples 1 and 2 By means of the drawing and false-twisting machine based on the conventional technology and illustrated in Figure 2, a false-twist texturing was performed under the same conditions as Example 1 except that L = 5 m (in Comparative Example 1) and V = 10 m/sec (in Comparative Example 2). Various physical properties of the false-twist textured yarns obtained by Example 1 and Comparative Examples 1 and 2 were shown in Table 1. Crimp recovery ratio, one of the properties shown in the table was obtained on the samples pretreated under the following conditions based on the test method JIS L1090. (1) An initial load of 2 mg/tex(denier) per an indicated tex(denier) was applied on a small hank. (2) The hank on which the initial load was hanged was then immersed in hot water at 98 ±1°C for 20 min. (3) The immersed hank was taken out of hot water and the initial load was removed. The hank was left standing for about 12 hr or longer in an ordered standing condition so as not to put the hank into disorder to bring it to a water equilibrium condition. (4) The length ℓ when the initial load of 2 mg/tex(denier) per tex(denier) was applied on this yarn and the length ℓ₁ when a load of 0.1 g per denier was additionally applied on this initial load were measured and the crimp recovery ratio was obtained by the following equation. In addition, crimp generating stress (g) was measured under the following conditions by means of a crimp tester manufactured by Rothshild Co., Ltd. Yarn speed: 16 m/min Initial tension: (0.1 g/denier) 0.011 g/tex Overfeed ratio: 4% Heater temperature: 150°C As clearly shown in Table 1, a false-twist textured yarn obtained by Example 1 exhibited each of strength, elongation, crimp recovery ratio and crimp generating stress superior to those for a false-twist textured yarn obtained by Comparative Example 1 and the same yarn physical properties as those of Comparative Example 2 which was the conventional low speed condition. In addition, in Example 1, no yarn breakage and fluff were generated and the operation was stabilized. Many fluffs were produced in the false-twist textured yarn in Comparative Example 1 and yarn breakage occurred very frequently and as a result, it was impossible to perform stable texturing. On the other hand, in Comparative Example 2, good yarn physical properties were obtained and the operation was stable, but the productivity was remarkably low and it was impossible to obtain high productivity based on high speed false twisting which was the purpose of the present invention. By means of the method of false twist texturing of the present invention as described above, a high speed false twist texturing with a yarn speed of 1,000 m/min or higher is practicable at a low tension in comparison with the conventional technology and is achievable smoothly. Moreover, it is possible to obtain a textured yarn with good physical properties under conditions such that no yarn breakage and fluff generation occur and the operation is stable. Example 1 Comparative Example 1 Comparative Example 2 L (m) 2.0 5.0 5.0 V (m/sec) 33.3 33.3 10.0 T (n times/m) 3300 3300 3300 A (m²) 6.0 x 10⁻⁹ 6.0 x 10⁻⁹ 6.0 x 10⁻⁹ Tensile Strength g/tex (g/d) 0.55 (5.0) 0.46 (4.2) 0.55 (5.0) Elongation (%) 17.8 14.1 20.1 Crimp Recovery Ratio (%) 31.0 16.0 31.5 Crimp Generating Stress (g) 1.95 1.35 1.90

Claims: A method of producing a false twist textured yarn, which method comprises the steps of passing the yarn (Y), at a travelling speed of 1,000 m/min or more, through a false twisting zone provided between a nip defined by a pair of yarn feed rollers (2) and a false twister (7), while the yarn (Y) is in the false twisting zone, heating the yarn (Y) by contacting the yarn (Y) with steam in a steam heater (5), and thereafter, and while the yarn (Y) is still in the false twisting zone, cooling the yarn (Y) by contacting the yarn (Y) with water in a water cooler (6), characterized in that, in combination (a) the number of false twists is sufficiently high to satisfy the equation T ≧ 0.24/√A (b) at the travelling speed of 1,000 m/min or more, the cross-sectional area of the yarn (Y) is sufficiently low to satisfy the equation V ≧ 1.30 x 10⁻³/√A and (c) the yarn path length between the nip defined by the pair of yarn feed rollers (2) and the false twister (7) is so short as to satisfy the equation L ≦ 90/V wherein, in each equation (1), (2) and (3), T is the number of false twists inserted per meter of the yarn (n times per meter, where n is the number of turns); V is the travelling speed of yarn (Y) (m/sec); L is the yarn path length between the nip defined by the pair of yarn feed rollers (2) and the false twister (7) (m); and A is the cross-sectional area (m²) of the yarn, calculated by division of yarn tex (weight per unit length) by yarn density (weight per unit volume). A method according to claim 1, wherein the yarn is passed through the false twisting zone at a travelling speed of 1,400 m/min or more. A method according to claim 1 or claim 2, wherein the yarn path through the false-twisting zone has a length of 2 m or shorter.

Inventors: NEGISHI TAKAO, UENO NOBORU, NEGISHI, TAKAO, UENO, NOBORU
Applicants: TORAY INDUSTRIES, TORAY INDUSTRIES, INC.
Application year: 1989
Main classification: D02G1
IPC codes: D02G1