EP0579083A1 - Method of drawing heated yarns, thereby obtained polyester yarns and their end uses - Google Patents

Abstract

There is described a particularly gentle and fast process for heating and drawing yarns passing contactlessly through a heating apparatus at high speed. The process comprises the measures of: i) preheating a heat transfer gas to a temperature which is above the desired yarn temperature, and ii) feeding the preheated heat transfer gas into the yarn duct so that it impinges essentially perpendicularly on the moving yarn along a length such that the yarn heats up to the desired elevated temperature within the heating apparatus, the length of the impingement zone being such that continuous removal of the boundary layer by the impinging heat transfer gas ensures that the yarn comes into direct contact with the heat transfer gas and thus heats up very rapidly, and iii) tensioning the yarn moving contactlessly through the heating apparatus in such a way that it undergoes drawing as it passes through said heating apparatus. The invention further relates to polyester fibres having the following properties: a tenacity index TI equal to or greater than 50 and a molecular orientation MO equal to or greater than 20 or a compliance COM equal to or less than 12 and a storage modulus index SMI equal to or greater than 100, where TI = a1 <*> T - a2 <*> BE - a2 <*> S, MO = a3 <*> SS - a2 <*> BE - a2 <*> S, COM = a2 <*> BE + a2 <*> S - a4 <*> CAO, and SMI = a1 <*> T - 4 <*> (a2 <*> BE + a2 <*> S) + A4 <* CAO + a3 <*> SS - a2 <*> DC, in which a1 = 1 <*> (tex/cN), a2 = 1 <*> (1/%), a3 = 10 <*> (sec/km) and a 4 = 10 <*> (1/%), T is the tenacity in cN/tex, BE is the breaking extension in %, S is the shrinkage in % measured at 200 DEG C in a through-circulation oven, SS is the speed of sound in km/sec measured at 25 DEG C, CAO is the crystallite axial orientation in % expressed by the Hermann orientation function, and DC is the degree of crystallisation in % measured by the method of the density gradient column. The polyester fibres of the invention can be used in particular for reinforcing plastics or for producing dimensionally stable textile fabrics.

Description

The present invention relates to a new method by means of which high-speed yarns can be heated quickly, gently and uniformly over the cross section to a desired elevated temperature, polyester fibers of high strength, high modulus and low shrinkage, which can be produced by the method according to the invention, and the Use of these fibers as reinforcing materials or for the production of textile fabrics.

Heating processes play a major role in the production and processing of yarns; A large number of heating methods and heating devices are therefore already known.

These methods and devices can be distinguished, for example, by the type of heat input. It is customary to supply the heat by means of heat transfer media, such as, for example, by means of heated liquids or gases, by contacting the thread. It is also customary to transfer the heat by means of radiation from heated surfaces or by means of contact with heated surfaces.

Also in a number of processing processes of high-speed yarns, e.g. heating is required when stretching or fixing. It is generally known that the heat should be supplied as quickly and gently as possible in such processes.

As is known, the speed of heat transfer essentially depends on the temperature gradient between the heat supplier and the object to be heated. Around To achieve the fastest possible heat transfer, one usually chooses the highest possible overtemperature of the heating medium. Too high an excess temperature leads to overheating of parts of the yarn bundle, such as single filaments hanging out or loops. The demands for the fastest possible and at the same time gentle treatment are therefore contrary.

From DE-A-3,431,831 a process for drawing polyester yarns is known in which drawing is carried out on a belt line. The process is carried out at reduced speeds. Details of the heating of the running yarns cannot be found in this document.

A heating chamber for running yarns is known from EP-A-114,298, in which the threads are treated with saturated water vapor of more than 2 bar. The heating chamber is characterized by a special type of sealing of the yarn inlet and outlet, with which a good sealing effect is achieved, which allows simple threading and with which the operating state can be set quickly after threading. According to the description, the heat transfer takes place primarily through condensation of the saturated steam on the yarn in the heating chamber, as a result of which a high uniformity of the treatment temperature is achieved. The yarn emerging from the heating chamber therefore generally contains condensed water which evaporates again in the subsequent steps. The treatment temperature in this heating chamber cannot be varied easily since it corresponds to the temperature of the saturated steam.

A heating device for a crimping machine is known from EP-A-193,891. This device has a thread guide tube which is heated on its outer circumference and which is arranged vertically or obliquely. To improve the heat transfer to the running yarn, an air nozzle is placed on the yarn inlet side of the thread guide tube, through which fresh air is blown into the thread tube. This device is intended to make the heat treatment more effective. The actual heating of the fresh air takes place only in the heating device itself. With this heating device none can Heat treatment can be carried out at constant temperatures, since the air in the thread guide tube has an undefined temperature.

DE-A-2,927,032 discloses a device for texturing yarns, in which these are heated directly in thread channels through which warm air flows. The thread channels are fed with the warm air and are connected to a suction pipe. The device is characterized by a special arrangement of the supply and discharge lines for the hot air and the heating device for the hot air; Furthermore, inlet and outlet connections are provided on the thread channels for the supply and removal of the yarns. With the arrangement described, an accurate temperature control and a large temperature equality within the device is to be achieved. The yarns are directly surrounded by an even flow of hot air, which results in an even heating of the yarns at constant temperature and air speed. The device requires the used hot air to be drawn off via a separate suction pipe.

From DE utility model 83 12 985 a device for texturing yarns is known, in which a heating device is provided in which warm air heats a running yarn in a thread channel. The device is characterized by the special type of air guidance in the thread channel, which in each case has a flow line between at least two return lines for the warm air. The device is intended to achieve the lowest possible temperature drop in the thread channel between its inlet and outlet. Similar to an injector nozzle, the yarn is hit at one point by the hot air and then the yarn and air move together or in opposite directions, the air losing temperature.

From GB-A-1,216,519 a method for heating a thermoplastic yarn is known, using a device designed as a contact heater. In this method, a continuously moving yarn is passed through a thread channel designed as a capillary. The inner diameter of the thread channel is chosen so that fluids are not within this channel can move freely, but there is a sealing effect due to the capillary nature of the thread channel. In this thread channel a pressurized heating fluid, for example air, superheated steam or saturated steam, is introduced so that it can move along the direction of yarn together with the yarn through the heating channel and plasticize the yarn by contact. Due to the construction of this device, it can be assumed that a strong temperature gradient builds up along the yarn running direction in the thread running channel and that, due to the small amounts of heating fluid in the capillary of the thread channel, a temperature of the heating fluid must be used which is far above the desired yarn temperature.

From DE-PS-967,805 a method and an apparatus for fixing running yarns when generating false twist are known. The method involves the contactless movement of a surface-moistened and twisted yarn through a heating device that contains hot air. The false twist is fixed using a high relative movement between the hot air and the moving yarn. According to the description, the process is designed so that a high temperature gradient is formed between the hot air and the yarn; The moistening of the surface then serves the purpose of protecting the yarn from thermal damage.

From DE-AS-1,908,594 a device for the heat treatment of relaxed synthetic yarns is known, in which a yarn is passed through a hollow heating cylinder. At the yarn inlet there is an injector which is operated with a primary gas stream from heating gas and which is designed as an annular nozzle, and an additional inlet for a secondary gas stream. The device is characterized in that the additional inlet for the secondary gas flow is arranged in such a way that this flow, viewed in the direction of movement of the yarn, meets the primary gas flow behind the injector opening in the heating cylinder. With the device, the formation of eddies in the heating cylinder is to be avoided and the quality of the treated yarns is to be improved. The risk of vortex formation is because the primary gas flow is relatively high Speed enters the heating cylinder and slows down there.

From DE-A-2,347,139 a method for texturing thermoplastic yarn is known, which involves fixing the twisted yarn by means of hot steam which is passed through the heating device at the speed of sound. The heating medium is also supplied here at the yarn inlet point of the heating device by means of an annular nozzle. The process is characterized by high productivity. The yarn is heated by contact with a comparatively small mass of the turbulent, fast-flowing steam, which steam has a higher temperature than the desired end temperature of the running yarn.

Finally, a yarn heater with a heated yarn run is known from DE-A-3,344,215. This heater is characterized in that it contains means by which a heated medium in the area of the yarn inlet strikes a yarn moving along this yarn path. The heating medium is also supplied here by means of an annular nozzle. With the heater, the heating output is to be increased, so that shorter heaters can be used than previously customary. Details of the temperature profile in the thread channel cannot be found in this publication.

With these known methods of heating yarns, either no high-speed yarns are used or, in the case of high-speed yarns, high excess temperatures of the heating unit are sometimes set in order to achieve the desired temperatures on the running yarn with short dwell times, or heating devices are obtained in the thread channel Larger temperature gradients, since turbulence of the heating medium occurs, for example. Inevitably, the heating takes place unevenly from outside to inside into the yarn or into the yarn bundle. The quality of the treated yarns or yarn bundles thus generally leaves something to be desired. It is generally found that rapid and increased heating can lead to a decrease in strength or to uneven dye absorption in the yarn, since Parts of the yarn bundle are heated unevenly.

Other previously known heating methods, in which the yarn in the thread channel is heated as uniformly as possible, require special guidance of the heating medium and can be implemented only with great effort.

The object of the present invention was to provide a simple method for drawing heated free-running yarns, in which said yarns are heated as gently and uniformly as possible.

It has now surprisingly been found that high-speed yarns can be gently heated and stretched to a desired elevated temperature without contact by a heating device.

• i) Vorerwärmen eines Wärmeüberträgergases auf eine Temperatur, die oberhalb der gewünschten Garntemperatur liegt,
• ii) Zuführen des vorerwärmten Wärmeüberträgergases in den Fadenkanal, so daß dieses im wesentlichen senkrecht auf das laufende Garn entlang einer solchen Länge einströmt, daß sich das Garn innerhalb der Erhitzungsvorrichtung auf die gewünschte erhöhte Temperatur erwärmt, und wobei die Länge der Anblaszone so gewählt wird, daß durch ständiges Wegreißen der Grenzschicht durch die Anströmung des Wärmeüberträgergases das Garn direkt mit diesem in Kontakt kommt und somit eine sehr rasche Aufheizung des Garns erfolgt, und
• iii) Spannen des berührungslos durch die Erhitzungsvorrichtung laufenden Garns in einer solchen Weise, daß dieses beim Durchlaufen durch besagte Erhitzungsvorrichtung eine Verstreckung erfährt.

The method according to the invention comprises the following measures:

• i) preheating a heat transfer gas to a temperature which is above the desired yarn temperature,
• ii) supplying the preheated heat transfer gas into the thread channel so that it flows essentially perpendicularly to the running yarn along a length such that the yarn within the heating device heats up to the desired elevated temperature and the length of the blowing zone is chosen so that by continuously tearing away the boundary layer due to the flow of the heat transfer gas, the yarn comes into direct contact with it and thus the yarn heats up very quickly, and
• iii) tensioning the yarn running contactlessly through the heating device in such a way that it undergoes drawing as it passes through said heating device.

In the method according to the invention, the yarn is blown over a certain length with a uniformly heated heat transfer gas, so that the heat transfer process takes place more by moving the heat transfer gas (Convection) than by heat transfer using temperature gradients. Through this type of blowing, the adhering air boundary layer, which counteracts the heat transfer due to its insulating effect, is blown away over a longer yarn path and the heated heat transfer gas can release its heat quickly and evenly to the yarn. The temperature of the heat transfer gas only needs to be a little above the yarn temperature, because most of the heat is transported by convective air movement and only a small part by temperature differences. This convective type of heat transfer is very efficient and overheating of the yarn material is avoided, so that gentle and uniform heating is achieved.
In the context of this invention, the term “yarn” is understood to mean all endless threads, that is to say both multifilament yarns and staple fiber yarns or monofilaments. Depending on the area of application, yarn titres of 50 to 2500 dtex are customary, preferably yarn titres of 50 to 300 dtex (for textile applications) and 200 to 2000 dtex (for technical applications).
The term "fiber" is understood in the context of this invention as a generic term in its broadest meaning, for example as yarn or as staple fiber. With regard to the fiber-forming material, the method according to the invention is not subject to any restrictions. Both yarns made of inorganic material, for example glass, carbon or metal yarns, and yarns made of organic material, for example yarns based on aliphatic or aromatic polyamide, polyester, in particular polyethylene terephthalate, or polyacrylonitrile can be used.

In the context of this invention, the term “high-speed” usually means speeds of more than 300 m / min, preferably 400 to 6000 m / min, in particular 400 to 3000 m / min; this information relates to the speed when leaving the heating device.

Any gases that are inert to the yarn to be heated under the respective treatment conditions can be used as the heat transfer gas are. Examples of such gases are nitrogen, argon or in particular air. The gases can also contain additives, for example a certain moisture content; however, the moisture content must not be so high that a significant condensation takes place on the yarn in the heating device.

The heat transfer gas can be preheated in any conventional way; for example by contact with a heat exchanger, passing through heated pipes or by direct heating via heating coils. The temperature of the preheated heat transfer gas is above the yarn temperature desired in the individual case; the heat transfer gas is preferably heated to temperatures up to 20 ° C. above and care is taken to ensure that there is no appreciable drop in temperature between the preheating and the actual heating of the yarn.

The heated heat transfer gas can be introduced into the thread running channel at any point. Preferably, the heat transfer gas is fed to the thread run channel in such a way that it can come into contact with the yarn along the entire thread run channel. The length of the blowing zone is preferably more than 6 cm, in particular 6 to 200 cm. In the event that the heating device is integrated in a stretching step, the length of the blowing zone is preferably 6 to 20 cm. In the event that the heating device is integrated in a fixing step, the length of the blowing zone is preferably 6 to 120 cm, in particular 6 to 60 cm.

The heat transfer gas is preferably conducted into the thread running channel perpendicularly to the direction of yarn travel, the heat transfer gas being entrained on the one hand by the running yarn and leaving the heating device together with the running yarn via the yarn exit opening, and on the other hand moving against the yarn travel direction and leaving the heating device via the yarn entry opening.

In a preferred embodiment, the heat transfer gas is in the middle Part of the thread running channel is blown perpendicularly onto the yarn from small openings for a length of about 1/4 to 1/2 of the channel length and escapes in and against the direction of the yarn from the thread running channel. In a likewise preferred modification of this embodiment, cross-blowing with suction on the opposite side takes place.

The contacting of the heat transfer gas in the heating device with the running yarn has to take place under such conditions that the yarn inside the heating device heats up to the desired elevated temperature and the heat transfer gas in the heating device cools down very little.

A number of measures are available to the person skilled in the art, by means of which these specifications can be set. For example, it is possible to allow relatively large masses of heat transfer gas to flow through the thread channel per unit time compared to the yarn mass that moves through the thread channel per unit time, so that despite the effective and rapid heat transfer to the thread, there is only a slight cooling of the heat transfer gas. In contrast to blowing on practically one point of the moving yarn, blowing along a certain zone results in a particularly intensive interaction of the heating gas with the yarn, since the boundary layer between the yarn and the surrounding medium in this zone is constantly torn away. In this way it is possible to achieve an effective heating of the yarn even with only a slight change in the temperature of the gas. The control of the temperature profile of the heat transfer gas can also be controlled by selecting the heat capacity of the gas or by the flow rate of the gas in a manner known per se.

In particular, it is possible to control the heating power by means of individual point or group control so that a predetermined temperature prevails on the thread by one or more sensors in the vicinity of the yarn regulating the heating power by means of a control circuit. Because the time constant of electronic control loops is below of 1 second, start-up processes can thus be regulated very quickly, so that the proportion of lead goods that lie outside the desired specifications is reduced, and loss wrap or switching to salable bobbins are thus eliminated.

The temperature of the heat transfer gas in the heating device generally changes only insignificantly under the operating conditions; i.e. this gas does not undergo any appreciable change in temperature when it passes through the heating device. This can be achieved by suitable insulation of the gas-carrying parts of the device.

A particular advantage is to be seen in the fact that the temperature control described above can ignore the heat losses between the heating device and the yarn, because the heating device is controlled according to the temperature close to the yarn. As a result, the expensive wall heating in the air duct between the heating device and the yarn can be avoided. Even fluctuations in the insulation effect from place to place can be compensated for by this type of regulation.

It is considered a particular advantage of the drawing process according to the invention that fibers with increased strength and high dimensional stability can be produced. The upper limit of the temperature of the heat transfer gas is less critical in the method according to the invention, since the compact yarn does not immediately follow the hot gas temperature because of its heat content. It is therefore also possible to work with temperatures of the heat transfer gas that are higher than the melting temperature of the yarn material.

Dabei bedeuten:

X_L =

Gasdurchsatz in Nm³/h (Nm = Normkubikmeter)

v =

Garngeschwindigkeit in m/min

fd =

Garntiter in dtex

c_pf=

Wärmekapazität des Garnmaterials in kJ/Kg * K

q_L =

Dichte des Wärmeüberträgergases in kg/m³

c_pl=

Wärmekapazität des Wärmeüberträgergases in kJ/Kg * K

Bevorzugte X_L-Werte für ein bestimmtes Garnmaterial und Wärmeüberträgermaterial bewegen sich im Bereich der durch die obige Formel errechneten Werte bis zum Vierfachen dieses Wertes. Ein üblicher X_L-Wert beläuft sich auf 2,2 Nm³/h.An x _L value, which should preferably be exceeded, is used to estimate a suitable value for the throughput of the heat transfer gas through the heating device. This value x _L can be calculated using the following formula:

${\text{X}}_{\text{L}}{\text{= 1.5 * 10⁻⁵ * (v * fd * c}}_{\text{pf}}{\text{) / (q}}_{\text{L}}{\text{* c}}_{\text{pl}}\text{).}$

Here mean:

X _L =

Gas throughput in Nm³ / h (Nm = standard cubic meter)

v =

Yarn speed in m / min

fd =

Yarn titer in dtex

c _pf =

Heat capacity of the yarn material in kJ / Kg * K

q _L =

Density of the heat transfer gas in kg / m³

c _pl =

Heat capacity of the heat transfer gas in kJ / Kg * K

Preferred X _L values for a specific yarn material and heat transfer material are in the range of the values calculated by the above formula up to four times this value. A common X _L value is 2.2 Nm³ / h.

In a particularly preferred variant, the process according to the invention can be used in the production of high-strength multifilament yarns, preferably based on polyester, in particular based on polyethylene terephthalate.

In the case of polyethylene terephthalate multifilaments, the drawing / fixing temperature controlled by the temperature of the heat transfer gas is usually selected in the range from 160 to 250 ° C., preferably from 210 to 240 ° C. The drawing tension is usually 1.5 to 3.0 cN / dtex, preferably 2.3 to 2.8 cN / dtex, based on the final titer.

Polyester multifilament yarns stretched and fixed in this way surprisingly have a strength that is about 5 to 10 cN / tex higher than polyester multifilament yarns that have been drawn using conventional heat sources.

Unexpectedly, polyester fibers which have been drawn in one step by the process according to the invention (for example drawing between delivery and take-off godets with an intermediate heating device) show a very high level Degree of fixation and a very high degree of crystallization, have low residual shrinkage values and thus high dimensional stability. After the single-stage stretching, these fibers can be used industrially as low-shrink fibers and have a shrinkage of less than 8% at 180 ° C.

In order to produce low-shrink polyester fibers by conventional methods, a second process step is necessary, in which part of the shrinkage is let out at high temperature. Because of the decrease in thread orientation during shrinking, these threads are susceptible to post-stretching in the further processing process. In contrast, the polyester fibers produced according to the invention already have low shrinkage values with the highest orientation of the molecules. Subsequent expansion is then practically no longer possible. The fibers obtainable in this way can be characterized by strength index FI and molecular orientation MO or by compliance NG and storage module index SP.

$\text{MO = a₃ * SG - a₂ * D - a₂ * S,}$

$\text{NG = a₂ * D + a₂ * S - a₄ * KAO, und}$

$\text{SP = a₁ * F - 4 * (a₂ * D + a₂ * S) + A₄ * KAO + a₃ * SG - a₂ * KG,}$

worin a₁ = 1 * (tex/cN), a₂ = 1 * (1/%), a₃ = 10 * (sec/km) und a₄ = 10 * (1/%) bedeuten, F die Feinheitsfestigkeit in cN/tex, D die Höchstzugkraftdehnung in %, S der Schrumpf in % bei 200°C im Umluftofen gemessen, SG die Schallgeschwindigkeit in km/sec gemessen bei 25°C, KAO die Kristallit-Achsen Orientierung in % ausgedrückt durch die "Hermannsche Orientierungs-Funktion" und KG den Kristallisationsgrad in % gemessen nach der Methode der Dichte-Gradienten-Säule bedeutet.The invention therefore also relates to polyester fibers, in particular multifilaments, obtainable by the drawing process according to the invention, which are characterized by the following properties: strength index FI greater than or equal to 50, in particular from 58 to 65, and molecular orientation MO greater than or equal to 20, in particular from 25 to 35 , or by resilience NG of less than or equal to 12, in particular from 2 to 8, and memory module index SP of greater than or equal to 100, in particular from 115 to 150, or by a combination of the parameters FI, MO, NG and SP in the ranges specified above , in which

$\text{FI = a₁ * F - a₂ * D - a₂ * S,}$

$\text{MO = a₃ * SG - a₂ * D - a₂ * S,}$

$\text{NG = a₂ * D + a₂ * S - a₄ * KAO, and}$

$\text{SP = a₁ * F - 4 * (a₂ * D + a₂ * S) + A₄ * KAO + a₃ * SG - a₂ * KG,}$

where a₁ = 1 * (tex / cN), a₂ = 1 * (1 /%), a₃ = 10 * (sec / km) and a₄ = 10 * (1 /%), F is the tenacity in cN / tex, D the maximum tensile force elongation in%, S the shrinkage in% at 200 ° C measured in a convection oven, SG the speed of sound in km / sec measured at 25 ° C, KAO the crystallite axes Orientation expressed in% by the "Hermann orientation function" and KG means the degree of crystallization in% measured by the density gradient column method.

The quantities on which the above definitions for FI, MO, NG and SP are based are determined as follows:
The tenacity F and the maximum tensile strain D are determined in accordance with DIN 53834.

The shrinkage S is triggered by heat treatment in a forced air oven at 200 ° C. and a dwell time of 5 minutes and then measured under a load that corresponds to the weight of 500 meters of the starting yarn.

The speed of sound SG is measured at a load of 1 cN / dtex using a dynamic modulus tester PPM-5 from Morgan & Co./Massachusetts USA.

The degree of crystallization KG is determined from the density according to the two-phase model, assuming 1.331 g / cm³ for the density of the amorphous phase and 1.455 g / cm³ for the density of the crystalline phase. The density is measured using the gradient method in zinc chloride / water.

ausgedrückt. Gemessen wird die azimutale Intensitäts-Verteilung des (-1,0,5) Reflexes von Polyethylenterephthalat und daraus nach der oben angegebenen Formel f_c errechnt. Die Röntgen-Untersuchungen wurden mit Hilfe des Röntgen-Diffraktomerters D 500 (Siemens) nach der Methode von Biangardi, Schriftenreihe "Kunststoff-Forschung" 1, TU-Berlin, durchgeführt.The crystallite axis orientation KAO is made possible by the "Hermann orientation function" ${\text{f}}_{\text{c}}\text{= 1/2 * (3 * <cos² (theta)> - 1)}$

expressed. The azimuthal intensity distribution of the (-1,0,5) reflex of polyethylene terephthalate is measured and from it calculated according to the formula f _{c given} above. The X-ray examinations were carried out using the X-ray diffractometer D 500 (Siemens) according to the method of Biangardi, publication series "Kunststoff-Forschung" 1, TU Berlin.

The polyester fibers according to the invention can advantageously be used in all those areas in which high-strength, high-modulus and low-shrinkage fibers Find use.

The polyester fibers of the invention are preferably used as reinforcing materials for plastics or for the production of textile fabrics, such as woven, knitted or knitted fabrics.

A preferred area of application of the polyester fibers according to the invention relates to their use as reinforcing materials for elastomers, in particular for the production of vehicle tires or conveyor belts.

Another preferred use of the polyester fibers according to the invention relates to the production of dimensionally stable textile fabrics, such as tarpaulins.

The following examples describe the invention without limiting it. The values for FI, MO, NG and SP given in these examples were determined using the definitions given above and the measurements described for F, D, S, SG, KAO and KG. Viscosity data in the following examples relate to the intrinsic viscosity, measured on solutions of the polyester in o-chlorophenol at 25 ° C.

Examples 1 to 7:

Tab Ic Bsp.-Nr. FI MO NG SP 1 60,2 28,6 7,605 122,535 2 58 28 6,609 120,511 3 63,8 28,4 6,723 125,487 4 60,2 32,6 3,993 136,287 5 59,1 27,8 6,041 122,849 6 61,4 33,4 3,193 138,727 7 46,5 17 14,047 81,363 Polyethylene terephthalate (PET) is melt-spun in the usual way and stretched over a single-stage drafting system consisting of delivery and withdrawal godets. Examples 1 to 6 describe embodiments in which the heating device according to the invention is used, while example 7 relates to a commercially available high-strength and high-modulus PET thread which has been produced without the heating device according to the invention. The following Tables Ia, Ib and Ic show the process conditions and the properties of the threads obtained.

Tab Ic E.g. no. FI MO NG SP 1 60.2 28.6 7,605 122.535 2nd 58 28 6,609 120.511 3rd 63.8 28.4 6,723 125.487 4th 60.2 32.6 3,993 136,287 5 59.1 27.8 6,041 122.849 6 61.4 33.4 3,193 138.727 7 46.5 17th 14,047 81,363

The results in Table Ic are shown graphically in FIGS. 1 and 2.

Claims (20)

A method for drawing and heating yarns running fast without contact by means of a heating device, comprising the steps: i) preheating a heat transfer gas to a temperature which is above the desired yarn temperature, ii) supplying the preheated heat transfer gas into the thread channel so that it flows essentially perpendicularly to the running yarn along a length such that the yarn within the heating device heats up to the desired elevated temperature and the length of the blowing zone is chosen so that by continuously tearing away the boundary layer due to the flow of the heat transfer gas, the yarn comes into direct contact with it and thus the yarn heats up very quickly, and iii) tensioning the yarn running contactlessly through the heating device in such a way that it undergoes drawing as it passes through said heating device. A method according to claim 1, characterized in that the thread channel is additionally heated. A method according to claim 1, characterized in that nitrogen, argon or in particular air is used as the heat transfer gas. A method according to claim 1, characterized in that the heat transfer gas is applied to this yarn in the heating device substantially along the entire path of the yarn. A method according to claim 1, characterized in that the heat transfer gas flows radially from the outside inwards onto the running yarn. A method according to claim 1, characterized in that the heat transfer gas in the central part of the thread running channel is blown from small openings perpendicular to the yarn over a length of about 1/4 to 1/2 of the channel length and escapes in and against the yarn running direction from the thread running channel. Method according to one of claims 1 to 6, characterized in that the heating power is controlled by individual point or group control so that a predetermined temperature prevails on the yarn by one or more sensors in the vicinity of the yarn regulating the heating power via a control circuit. A method according to claim 1, characterized in that the throughput of the heat transfer gas through the heating device is at least x _L in Nm³ / h, X _L according to the formula

${\text{x}}_{\text{L}}{\text{= 1.5 * 10⁻⁵ * (v * fd * c}}_{\text{pf}}{\text{) / (q}}_{\text{L}}{\text{* c}}_{\text{pl}}\text{).}$

is calculated and v = yarn speed in m / min, fd = yarn titer in dtex, c _pf = heat capacity of the yarn material in kJ / (kg * K), q _L = density of the heat transfer gas in kg / m³, and c _pl = heat capacity of the heat transfer gas in kJ / (kg * K) means. A method according to claim 8, characterized in that the throughput of the heat transfer gas through the heating device is chosen between x _L and 4 * x _L. A method according to claim 1, characterized in that the yarn is a multifilament yarn based on polyester, in particular based on polyethylene terephthalate, that the heat transfer gas is preheated to a temperature of 160 to 250 ° C, and a draw tension of 1.5 to 3.0 cN / dtex, preferably 2.3 to 2.8 cN / dtex, based on the final titer. A method according to claim 1, characterized in that the drawing of the yarn is carried out in one step. Polyester fibers, in particular multifilaments, with a strength index FI of greater than or equal to 50 and a molecular orientation MO of greater than or equal to 20, wherein

$\text{FI = a₁ * F - a₂ * D - a₂ * S, and}$

$\text{MO = a₃ * SG - a₂ * D - a₂ * S,}$

where a₁ = 1 * (tex / cN), a₂ = 1 * (1 /%) and a₃ = 10 * (sec / km) mean F the tenacity in cN / tex, D the maximum tensile strength elongation in%, S the shrinkage in % measured at 200 ° C in a convection oven and SG means the speed of sound in km / sec measured at 25 ° C. Polyester fibers, in particular multifilaments, with a resilience NG of less than or equal to 12 and a storage module index SP of more than or equal to 100, wherein

$\text{NG = a₂ * D + a₂ * S - a₄ * KAO, and}$

$\text{SP = a₁ * F - 4 * (a₂ * D + a₂ * S) + A₄ * KAO + a₃ * SG - a₂ * KG,}$

where a₁ = 1 * (tex / cN), a₂ = 1 * (1 /%), a₃ = 10 * (sec / km) and a₄ = 10 * (1 /%), F is the tenacity in cN / tex, D the maximum tensile force elongation in%, S the shrinkage in% measured at 200 ° C in a convection oven, SG the speed of sound in km / sec measured at 25 ° C, KAO the crystallite axis orientation in% expressed by the "Hermann orientation function" and KG means the degree of crystallization in%, measured by the density gradient column method. Polyester fibers, in particular multifilaments, according to claims 12 and 13 with a strength index FI of greater than or equal to 50, a molecular orientation MO of greater than or equal to 20, a compliance NG of less than or equal to 12 and a storage module index SP of greater than or equal to 100, wherein FI, MO, NG and SP have the meanings defined in claims 12 and 13. Polyester fibers according to one of Claims 12 to 14, characterized in that FI is 58 to 65, MO is 25 to 35, NG is 2 to 8 and SP is 115 to 150. Polyester fibers according to one of claims 12 to 15, characterized in that the polyester is polyethylene terephthalate. Use of polyester fibers according to one of claims 12 to 16 as reinforcing materials for plastics or for the production of textile fabrics. Use of polyester fibers according to claim 17 as reinforcing materials for elastomers. Use of polyester fibers according to claim 18 for the manufacture of vehicle tires or conveyor belts. Use of polyester fibers according to claim 17 for the manufacture of dimensionally stable textile fabrics, in particular tarpaulins.

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