EP0173221B1 - High-strength polyester yarn and process for its preparation - Google Patents

Abstract

1. An untwisted high-strength polyester yarn for industrial use, wherein the filament-forming substance has a high average molecular weight corresponding to a relative solution viscosity (1.0 g of polymer in 100 ml of dichloroacetic acid at 25 degrees C) of about 1.90 to about 2.20 and the yarn has a heat shrinkage S200 of less than 7%, a degree of elasticity ED20 of at least 90%, a stability quotient SQ of at least 7.5 and a crystallinity of about 57 to about 65%.

Description

The present invention relates to a high-strength, low-shrinkage polyester yarn for industrial use, i. H. the use in particular in the form of twists, fabrics, braids, etc. as reinforcements in technical products such as tarpaulin fabrics, tires, drive belts, conveyor belts, etc., and a manufacturing process for such yarns from high-orientation filaments.

The production of high-strength yarns from polyester filaments is known. According to German Auslegeschrift 1 288 734, the spinning conditions must be chosen for this purpose so that the tensions acting on the solidifying thread are unusually low and the spinning thread is therefore characterized by a very low molecular orientation. Birefringence values of less than 0.003, preferably even less than 0.002, are required. If such filaments are later subjected to high drawing, yarns with high strength can be obtained. The course of the force-elongation curve (KD diagram) of a polyethylene terephthalate yarn for the production of tire cord with the titer dtex 1100 is shown as curve a in FIG. 1. The tenacity of this material is around 76 cN / tex with an elongation at break of 11%. However, such a yarn still has a high thermal shrinkage; at 200 ° C hot air treatment, for example, it is still about 18%. The determination of thermal shrinkage at 200 ° C has become common, since 200 ° C is generally the highest temperature that can occur when coating fabrics made from such yarns. A yarn material that still has a shrinkage of, for example, 18% leads to strong and uncontrollable dimensional changes in such a coating process. It is therefore necessary to reduce the S ₂₀₀ thermal shrinkage from the 18% specified above. This is done in the usual way by thermomechanical shrinking processes, in which the yarns are shrunk under controlled tension. For example, it is possible to heat shrink at 200 ° CS ₂₀₀ to z. B. lower 5%. However, this measure is inevitable with an increase in the maximum tensile strain to z. B. 16% and a decrease in the tenacity of z. B. 76 cN / tex connected to 72 cN / tex.

The maximum tensile strength and maximum tensile strength values are not suitable for sufficiently characterizing the properties of such a yarn. The curve b in the KD diagram of FIG. 1 shows which changes in the physical properties can result after a shrinking process. This curve is the measurement of a commercially available yarn with low shrinkage. From the curve b of Figure 1, the formation of the so-called "shrink saddle" is clearly visible.

The demand for a high initial modulus, low elongation, high degree of elasticity and low shrinkage value can therefore only be met poorly, since all the thermomechanical measures required to lower the thermal shrinkage simultaneously lead to a decrease in the tenacity and to a deterioration in the mechanical properties such as maximum tensile strength expansion, initial modulus and degree of elasticity . So far, one has been forced to compromise. H. shrunk material was used, which had to be overdimensioned in order to achieve the desired values, which are decisive for the dimensional stability, such as the degree of elasticity and the initial modulus. The teaching of German Auslegeschrift 1 288 734 inevitably also requires low spinning speeds, since only under these conditions can the required low tension values be achieved on the freshly spun threads. A low spinning take-off speed means at the same time less conveyance per spinneret. It is known that there is a sharp increase in the conveyance per spinneret with increasing spinning take-off speed, such as e.g. B. is shown in Figure 1 of German Offenlegungsschrift 2 207 849. Attempts to produce high-strength yarns by rapid spinning alone have so far failed due to the low strength and the high elongation at break of yarns produced in this way, which were first described in US Pat. No. 2,604,667.

In German Auslegeschrift 2 254 998 a method is described to first fold and twist high-speed spun threads and then to stretch the cord thread obtained. The necessary excessive twisting of the cord thread before stretching is difficult to apply, the process is too susceptible to faults and therefore has no practical significance.

FR-A-2 369 360 describes a multi-stage process consisting of spinning sections and subsequent separate multiple drawing stages. In this known process, a polyester material is spun in such a way that the filament obtained is given an "essential orientation". This relatively high orientation is expressed in a birefringence value of the undrawn filaments of 0.009 to 0.07, preferably 0.009 to 0.03. The degree of orientation of these spun filaments is thus of the same order of magnitude as that of the supply yarn used according to the invention. A major difference between the teaching of the citation and the method according to the invention lies in the drawing process. In the process of FR-A-2 369 360, the spun material is reduced to at least 50% z. B. 50 - 80% of its max. Draw ratio stretched. This stretching, which is obviously carried out at a low but not defined temperature, is followed by a multi-stage heat treatment, some stages being carried out with the yarn length being kept constant, others with the yarn being stretched. In this known method too, the total stretching should exceed 90% of the max. Draw ratio. FR-A-2 369 360 is no indication that it is necessary to produce a yarn with the property combinations specified in claim 1 of our present application, in particular high mechanical stability with low heat shrinkage, very specific drawing conditions, defined by a certain stretching area, with a high total stretching.

The process of FR-A-2 369 360 is technically complex because it requires a spinning drawing device and, in addition, a multi-stage drawing device. For technical reasons, it can only spin at relatively low tensile speeds are operated, which not only economically reduces the polyester throughput but also requires special measures in the actual spin stretching area. For example, when coarse titers are spun, it is very difficult to generate the required spin stretching tension, which is why the method is mainly restricted to finer, non-technical titers.

The filaments produced by this known method show improvements over the previously known high-strength filaments made of polyester with regard to their thermal stability, but have the major disadvantage of a relatively low stability against the action of hot water or chemicals. This disadvantage, already mentioned in European patent application 0 080 906 and in Japanese patent application Sho-58-23914, could be due to the relatively low degree of crystallinity, since the possibility of action of the chemicals on amorphous polyethylene terephthalate is considerably greater than on crystalline ones. As explained above and as can be seen from the examples, the method is primarily suitable for the production of fine individual titers, which further increases the sensitivity to chemicals.

The filament material of FR-A-3 369 360 also has a relatively high heat shrinkage, which is a serious disadvantage for technical use, e.g. B. means as a tire cord. It is therefore recommended in this document to optionally carry out a shrinking treatment of the filaments. However, the elasticity of the material increases again, which is also disadvantageous for technical all-round use.

Compared to this prior art, the object of the present invention was to provide a technically simplified process for the production of polyester filaments which do not have the above-mentioned disadvantages of the filaments produced according to FR-A-2 369 360, but on the basis of their combination of properties are suitable for universal use in the technical field.

European patent application 0 089 912 is also intended to work at an increased winding speed of over 1500 m / min. In the application, a method is described with which, by changing the previously used spinning conditions, a spinning fader is obtained at high take-off speed, which leads to high strength after stretching. Although no indication is given in this patent application about the thermomechanical properties of the drawn filaments, it can be expected that the shrinkage values will inevitably be very high due to the drawn-twist method used. As will be explained later, the dwell times in the stretching zone are much too short to achieve extensive fixation.

Japanese patent application Sho-51-53019 shows that stretched polyester threads with a birefringence value of 0.03 or more can be stretched to high-strength threads, which are then subjected to a shrinking treatment. The yarns obtained in this way have a thermal shrinkage at 150 ° C. of less than 2.5%, but their elongations at break are above 15, mostly in the range between 16 and 22%. Just because of the high elongation at break, it can be demonstrated that these threads or yarns have a "shrink saddle", as was shown in curve b of FIG.

According to Japanese patent application Sho-58-46117, pre-oriented threads which have a certain minimum crystallinity are to be subjected to stretching at at least 85 ° C. Despite the use of two-stage drawing in all of the examples according to the invention, the physical values of the threads or yarns thus obtained are relatively poor. These yarns are only intended for areas of application in which a thermal treatment is carried out before the finished articles are manufactured. The patent application mentions the dip process customary in tire cord twists for heat setting and curing the resorcinol / formaldehyde / latex finish. By contrast, the aim of the present invention is high-strength, low-shrinkage and low-stretch polyester filaments for all technical fields of application.

According to Japanese patent application Sho-58-23914, only threads are obtained which have a thermal shrinkage at 175 ° C of 7.0 to 10.0%, their thermal shrinkage at 200 ° C is correspondingly higher. European patent application 0 080 906 by the same applicant also describes a method in which core-shell differences within the filaments are to be avoided. The thermal shrinkage of the freshly obtained threads is also too high. Accordingly, these filaments also do not meet the claims of the present invention since, in order to achieve low shrinkage values, a subsequent thermal treatment process, as already mentioned in Japanese application Sho-58-46117, must also be carried out. This is the dipping process also mentioned in the two patent applications. A test - the treatment of a stretched yarn at 240 ° C. for one minute - is intended to imitate the dipping process and to show that this treatment can reduce the shrinkage of the yarn, which was originally too high.

There was therefore still the task of providing high-strength yarns made of polyester, the thermal shrinkage of which is as low as possible at 200 ° C. and which, moreover, have no "shrink saddle" in their KD curve, i. H. whose elasticity behavior corresponds as far as possible to that of unshrunk threads.

Unter dem Begriff ED₂₀ wird, wie bereits oben definiert, der Elastizitätsgrad bei einer Belastung von 20 cN/tex verstanden, der Wert S₂₀₀ stellt den Thermoschrumpf in Prozent bei 200°C dar und der Wert D₅₄ die Bezugsdehnung bei einer Belastung von 54 cN/tex. Der Verlauf des KD-Diagramms bei den erfindungsgemäßen Garnen gibt Kurvenzug in Fig. 1 wieder.Surprisingly, it has now been found that it is possible to provide such high-strength polyester yarns. These untwisted yarns have a thermal shrinkage of less than 7% at 200 ° C, a degree of elasticity with a load of 20 cN / tex of at least 90% and a stability quotient SO of at least 7.5. The stability quotient SO used to define the yarns according to the invention is a dimensionless parameter. It is calculated using the following formula

As already defined above, the term ED ₂₀ is understood to mean the degree of elasticity at a load of 20 cN / tex den, the value S ₂₀₀ represents the thermal shrinkage in percent at 200 ° C and the value D ₅₄ the reference elongation at a load of 54 cN / tex. The course of the KD diagram for the yarns according to the invention shows the curve in FIG. 1.

Die Dichte d der Fäden kann mit Hilfe einer Gradientensäule bestimmt werden, die Dichte des amorphen Anteils d_a ist mit 1,335 g/ml und die Dichte des kristallinen Materials d_k mit 1,455 g/mi angesetzt worden.The crystallinity of the individual filaments is 56 to about 65%. The yarns preferably consist of polyethylene terephthalate, the thread-forming substance optionally having up to 2% by weight of other comonomer units. Yarns with an S ₂₀₀ thermal shrinkage of less than 3%, preferably less than 2%, are preferred. The same applies to yarns that have a crystallinity of 60% to 63%. The crystallinity is calculated from the density of the threads according to the following equation

The density d of the threads can be determined with the aid of a gradient column, the density of the amorphous portion d _a has been set at 1.335 g / ml and the density of the crystalline material d _k at 1.455 g / ml.

Such yarns are produced according to the invention by stretching polyester yarns which have a pre-orientation corresponding to a birefringence of at least 0.025 and an average molecular weight corresponding to a relative solution viscosity of approximately 1.9 to 2.2. Such threads are subjected to hot drawing, the drawing ratio used being at least 90% of the maximum cold drawing ratio, and the drawing tension in this drawing being between 19 and 23 cN / tex under the selected conditions. Preferred ranges for this yield stress are 20 to 23 cN / tex.

Untwisted yarns have little or no protective twist; for 1100 dtex yarns e.g. B. 60 T / m widely used. These yarns are either used directly as reinforcements, e.g. B. used in coating fabrics or serve as a starting material for threads, z. B. in Re ⁱ fenbau.

High-tenacity yarns usually have a tenacity of more than 65 cN / tex. According to DIN 53 866, the thermal shrink S ₂₀₀ is the relative change in length of a yarn that has shrunk freely for 10 minutes at an air temperature of 200 ° C.

Abbildung 2 zeigt die Abhängigkeit des Elastizitätsgrades von der angewandten Belastung bei einem handelsüblichen schrumpfarmen Garn (Kurve a). Bei dieser Kurve ist ein spontaner Abfall des Elastizitätsgrades ab etwa 10 cN/tex zu beobachten. Zur Beschreibung des elastischen Verhaltens dient in dieser Patentschrift der Elastizitätsgrad bei einer Last von 20 cN/tex, dieser Elastizitätsgrad trägt die Bezeichnung ED₂₀. Bei den erfindungsgemäßen Garnen wird statt dessen eine Abhängigkeit gemäß Kurve b in Fig. 2 gefunden.The degree of elasticity ED ₂₀ is determined according to DIN 53 835. For this purpose, the yarn is loaded in a tensile testing machine up to a defined force limit and then completely relieved. It is determined how high the total elongation at the defined load limit (εges.) And the remaining residual elongation (ε _rest ) is after the yarn is relieved. A wet for the elastic behavior is the elastic expansion ratio (ED) or also called degree of elasticity. This is calculated using the formula

Figure 2 shows the dependence of the degree of elasticity on the applied load for a commercially available low-shrinkage yarn (curve a). In this curve, a spontaneous drop in the degree of elasticity can be observed from around 10 cN / tex. In this patent specification, the degree of elasticity at a load of 20 cN / tex is used to describe the elastic behavior; this degree of elasticity bears the designation ED ₂₀ . Instead, a dependency according to curve b in FIG. 2 is found in the yarns according to the invention.

The reference elongation D _{54 also} serves to characterize the mechanical behavior of the yarn according to the invention in this application. It is the value of the elongation at a load of 54 cN / tex. The value of the load of 54 cN was chosen arbitrarily. It corresponds to about 75% of the tenacity of these yarns and also allows a good statement about the elastic behavior of the yarns, but in particular whether or not there is a "shrink saddle" in the KD diagram of the yarn examined. Of course, the reproduction of the complete force-elongation diagram has the best informative value about the mechanical behavior of an examined yarn, but numerical values are more suitable for comparisons.

Individual points of this diagram are therefore often given in the literature. The maximum tensile force and the maximum tensile force elongation are specified most. As already explained above, however, this information is not very meaningful for high-strength filaments, especially if they have been shrunk. As is known, for example, the elongation at break decreases with increasing draw ratio, but increases again with subsequent shrinkage approval in a thermomechanical process. It is therefore not possible to differentiate by specifying the maximum tensile force expansion, whether it is a high degree of stretching with subsequent shrinkage approval or a low degree of stretching with less or no shrinkage approval. Defective filaments also show lower breaking strengths and thus lower elongation at break. To characterize the elongation properties of a filament, it is therefore better to choose a point on the KD diagram in an area that is not too unsafe due to such influences. In the present case, the reference strain D ₅₄ was selected for characterization. The initial module (also called Young's module), which can mainly be found in Anglo-Saxon literature, and which indicates the slope of the KD line in its initial area, is less suitable for the characterization of high-strength fibers. However, a conclusion about the entire working range of the threads is only possible from the initial module for drawn but not shrunk filaments. As can be seen for example from FIG. 1 curve b, the KD diagram changes in a characteristic way with shrunk filaments. After an initially identical increase in curves a and b, that is to say a corresponding initial module, curve b begins to flatten out from approximately 10 cNltex, which then increases again with high loads and high elongation values. For practical use, the elongation specification is the most important in a point on the KD diagram that is above the shrink saddle, but clearly below the elongation at break.

It has been found that it is possible to use a simple and economical process to produce high-strength, thermally and dimensionally stable and highly elastic filaments which, without further thermal aftertreatment of the textiles produced therefrom, provide the desired properties and are valuable for many areas of use.

A stretching process as described in the following and which can only be carried out with spun fabric having a higher pre-orientation is essential for achieving the claimed filament properties.

Drawing processes are usually defined by specifying drawing conditions and drawing temperatures.

In order to characterize the drawing process according to the invention, the widely used specification of the "drawing temperature" was dispensed with, since such information can hardly be reproduced by third parties without considerable errors, even if information about the dwell time in the drawing zone is made at the same time. It is practically impossible to specify the effective yarn temperature in a heater.

In this text, a minimum draw ratio was defined instead and a range for the draw tension to be achieved.

Maintaining a sufficient dwell time of threads on a heater is of particular importance for technical use, particularly in the case of high-titer filaments. What effect heat transfer can have shows z. B. Aleksandrijskij (Soviet. Contributions to fiber research and textile technology 1971, p. 521). When transferring the heat via heated metal surfaces such. B. heated rollers for the dtex 1100 titer, a dwell time of at least 0.5 seconds is required in order to obtain a constant shrinkage when fixing drawn filaments. When heat is transferred by heated air (convection), the dwell time should be at least 3 seconds (Pakshver, Khimicheskie Volokna, 1983, 1, pp. 59 - 61). In the case of fast spin-stretching processes, such as, for. B. are described in European Patent Application 80 906, for example at 5000 m / min thread speed, the length of contact of the filaments with the hot roller would be 71.7 m with a dwell time of 0.5 seconds. With a usual ten-times looping of a heating godet with a diameter of 20 cm, as is customary in commercial spin-stretching systems, a contact length of less than 6 m is calculated corresponding to a dwell time of less than 0.07 seconds. From these numbers it can be seen that a complete fixation of the threads produced is not possible via a fast spin-stretching process, and the desired low shrinkage properties with low elongation and high elasticity cannot be obtained.

The dwell times required for adequate fixation can only be technically achieved if the speed of the yarn or cable to be treated is reduced to a few 100 m / min. Draw frames operating under these conditions for the stretching of incoming threads or yarns can lead to fixed and thermostable filaments. For economic reasons, however, low-shrinkage technical filaments are primarily produced on so-called belt mills, in which a large number of filaments are stretched and shrunk side by side as a sheet between the roller mills. The filaments according to the invention are also preferably produced on such a belt stretching device. The basic structure of such a belt line is shown in FIG. 3.

• Ein Spinnfaden wird bei Raumtemperatur an einer Zugprüfmaschine bei einer Einspannlänge von 100 mm und einer Klemmengeschwindigkeit von 400 m/min gerissen. Daraus ergibt sich
  
  Eine weitere, das Verstreckverfahren definierende Größe ist die Verstreckspannung. Diese ist eine eindeutige Funktion des Verstreckverhältnisses, der Verstrecktemperatur und der Verweilzeit im Streckfeld. Die Verstreckspannung ist der Quotient aus der z. B. mittels eines Tensiometers gemessenen Zugkraft und dem um das eingestellte Verstreckverhäftnis verminderten Titer des Zuliefergarns

As already stated above, the draw ratio for the production of high-strength filaments must be as high as possible in order to achieve the strength inherent in the filaments as completely as possible. According to the invention, the draw ratio is at least 90% of the maximum draw ratio (max. VV), which is determined as follows:

• A spinning thread is torn at room temperature on a tensile testing machine with a clamping length of 100 mm and a clamp speed of 400 m / min. This results in
  
  Another variable that defines the drawing process is the drawing tension. This is a clear function of the draw ratio, the draw temperature and the dwell time in the draw field. The drawing tension is the quotient from the z. B. tensile force measured by means of a tensiometer and the titer of the supply yarn reduced by the set stretching ratio

It has now been found that the drawing tension is very important for the fulfillment of the shrink properties of the finished drawn threads which are desired according to the invention. The internal stresses impressed on the threads by the drawing tension are reproduced by the thermal shrinkage, as can be seen from FIG. FIG. 4 shows the dependence of the shrinkage at 200 ° C. (S ₂₀₀ ) on the drawing tension of a yarn with the final titer of 1100 dtex and a birefringence of 0.0025 (curve a). The same was done with a filament with a double refraction of 0.033 and a max. VV of 90% carried out, which was spun at a winding speed of 3000 m / min. The measured values gave the Curve b in FIG. 4.

In order to obtain a thread with constant elongation properties resulting from the constant draw ratio and the lowest possible thermal shrinkage, efforts will be made to keep the draw tension as low as possible. Since high drawing tensions also more easily lead to the tearing off of individual capillaries, which can make the processing of the filaments into twists and fabrics very difficult, this is another reason to work with the lowest possible drawing tension. In operational practice it has now been shown that drawing tensions in the range between 19 and 23 cN / tex, preferably in the range between 20 and 23 cN / tex, based on the titer of the thread at the end of the drawing zone, lead to optimal results. If the drawing tensions are increased by reducing the temperature or by shortening the dwell time, not only is a higher thermal shrinkage obtained, but the number of capillary breaks also increases. A lowering of the drawing tensions could only be achieved by further increasing the temperature, by slower driving or by lowering the drawing ratio. However, a lowering of the draw ratio must be avoided due to the associated deterioration in the strength values. A slower driving style and thus an increased dwell time in the stretching field will only be successful if the time for complete fixation with the faster driving style was too short. If this was sufficient, a further slowdown does not bring any further reduction in the drawing tension, but only worsens the strength of the thread. An increase in temperature is only possible up to the point at which the maximum tensile force of the filaments or yarn is not yet exceeded at these high temperatures. So there remains only a relatively small area in which the stretching can be carried out optimally. This is in the range between 19 and 23 or 20 to 23 cN / tex given above.

If one now wants to transfer this experience made on spinning threads with low pre-orientation about the dependence of drawing tension, drawing ratio, drawing temperature and dwell time to those with higher pre-oriented spinning threads, one encounters difficulties. If you try to stretch higher pre-oriented spun threads under the temperature and residence time conditions that are optimal for low-oriented spinning threads, stretching ratios that reach 90% of the max. VV have much higher drawing tensions, which then also lead to the difficulties mentioned above. So if you want to get perfect filaments, you are forced to reduce the draw ratio. However, this reduction has the consequence that the thread strengths are significantly reduced and the filaments still have high shrinkage values. Such an effect is clearly visible in the following comparative examples 4 compared to 5 and 12 compared to 13.

It has now surprisingly been found that spun threads with a high degree of pre-orientation can be drawn at such high temperatures at which spun threads with a low degree of pre-orientation can no longer be stretched safely because they tear off. By increasing the temperature during drawing, however, it is again possible to obtain drawing tensions between 19 and 23 or preferably 20 and 23 cN / tex. This significantly increased stretching temperature for the spun threads with higher pre-orientation leads to threads with particularly favorable shrink properties, and again allows a stretching ratio that is at least 90% of the maximum cold stretching ratio (max. VV).

In the method according to the invention, too, the specification of a drawing temperature would not be meaningful, since such data would be, for example, the temperature of the heating medium instead of the only important temperature of the thread. It is not possible to measure the thread temperatures inside a furnace. As soon as the thread leaves the oven, it begins to cool down very quickly. Only by measuring the thread temperature at different distances from the exit from the heating area of the furnace and using the approximation formula given by Kaufmann in "Fiber Research and Textile Technology" 28 (5), pp. 297 - 301 (1977) can you get to the actual thread temperatures at the end of the Close the oven. In the case of a furnace with heated air flowing transversely, it can only be concluded with a sufficiently long dwell time in the furnace that the thread has reached the temperature of the incoming air before leaving the furnace. In the case of an oven which is heated by infrared emitters, measurement is no longer possible at all, since thermal sensors in the oven, even in the vicinity of the thread, assume a different temperature due to the radiation than the threads themselves. However, regulation of the radiation intensity can also be carried out using such sensors how the temperature of the heated air in a furnace can be regulated well. The examples show which temperature settings have to be made in order to achieve corresponding effects and that it is sufficient to specify the drawing tension and the proportion of the maximum drawing ratio achieved in order to characterize the drawing.

FIG. 3 shows a schematic illustration of a preferred device for carrying out the method according to the invention.

The spun yarns Y are drawn off from the bobbins 1 plugged into the creel and fed to the roller mill 2 together as a family of threads. This consists of 5 to 7 heatable rollers, the surface temperatures of which range from 75 to 100 ° C depending on the thread speed. The thread sheet then passes through the heated furnace 3, which completely encloses the thread sheet, and then reaches the roller mill 4, which also has 5 to 7 rollers. The speed of the roller mill 4 is higher by a factor of the stretching than that of the roller mill 2. From here, the threads either arrive directly at the winding 6 or they are previously guided over the roller mill 5, which generally has three rollers.

The furnace can be heated either in such a way that its walls are heated electrically or by means of a liquid heat transfer medium; at the same time, heated air can flow against the threads. Another Version is the heating of the thread sheet with infrared radiators, which are installed in the oven. Another possibility is heating by hot air, which flows across the thread sheet transverse to its direction of travel. If a relaxation process is subsequently connected to the stretching, only the roller mill 4 is heated to a correspondingly high temperature, the shrinkage approval then takes place between the roller mill 4 and the roller mill 5 or between the roller mill 4 and the winding 6. In the latter case, the shrinkage approval must be exact be adjustable between these two units.

Without relaxation, the stretching of highly pre-oriented polyester yarns according to the invention leads to a thermal shrinkage S ₂₀₀ of approximately 6%. These yarns are preferred for use in fabrics that are not heat treated prior to their incorporation into a composite article, such as yarns for Autore ⁱ fen, transmission belts and conveyor belts.

The temperature, time and stress conditions of the thermal treatment then determine the properties of the fabrics with regard to shrinkage and elongation. Even after this further thermal treatment, the materials according to the invention prove to be superior to those known hitherto. The finished finished fabrics also have more favorable shrinking, stretching and elasticity properties than the previously known ones and exceed them in thermal and dimensional stability. In addition, it has been shown that, compared to the materials known hitherto, a shorter time of exposure to heat is possible in order to maintain the final properties of the finished materials. This means that the thermal aftertreatment of the textiles can take place under milder conditions with shorter residence times, which is also advantageous in terms of strength.

With some technical articles, such as. B. heated hoses, PVC-coated fabrics and others, this shrinkage is still too high, since these reinforcing materials are directly vulcanized or coated without further thermal pretreatment. Here it is necessary to use filaments with even lower shrinkage. This is obtained when the roller mill 4 of the drawing line has a surface temperature of more than 200 ° C. and the threads are allowed to shrink in a controlled manner between the roller mill 4 and the roller mill 5 or between the roller mill 4 and the winding 6.

If you let threads from spun fabric with a low pre-orientation or threads that have a higher pre-orientation but have not been stretched according to the invention shrink, it is necessary to let these threads relax more in order to achieve a low thermal shrinkage at 200 ° C. of about 2 to 3% to come. This has the previously mentioned consequences that the elongation increases sharply and the degree of elasticity decreases.

In the yarns produced according to the invention, a high degree of elasticity is retained even after relaxation, which is also reflected in a high stability quotient SO. The yarns of the invention are suitable both for use in threads for z. B. the production of tires, etc., which are thermally treated again in the latexing, and - with a re-axing stage downstream of the stretching stage - for the use of PVC-coated fabric, etc. The following examples are intended to explain the process in detail. It can be seen that the filaments according to the invention are obtained only if the conditions of the process according to the invention are observed. Unless otherwise stated, percentages and parts are by weight.

Examples The spun fabric used for the stretching tests described below was produced according to known technology as described below.

The polyethylene terephthalate granules used for Examples 1 to 7 and 12 to 14 showed a relative solution viscosity in dichloroacetic acid of 2.120. In Examples 8 and 9, a material with a relative solution viscosity of 1.990 and for Example 10, a material with a relative solution viscosity of 2.308 was used. The relative solution viscosity was usually determined on solutions of 1.0 g of the polymer in 100 ml of dichloroacetic acid at 25 ° C. by measuring the transit times of the solution through a capillary viscometer and by determining the transit time of the pure solvent under the same conditions. The polyethylene terephthalate granules used were melted using an extruder, fed to a spinning pump and spun using a spin pack. The nozzle plate in the spin pack each had 100 holes with a diameter of 0.45 mm each. The threads emerging from the spinnerets were reheated in the case of the raw materials with relative solution viscosity 2.120 and 2.308 by a device located below the spinneret plate, as described in German Patent 2 115 312, and then with air at 26 ° C. and a speed of Blown transversely at 0.5 m / sec. Two such spun threads were fed together to a preparation device, provided with a spinning preparation and drawn off and spun on at the speeds indicated in the examples. Depending on the pre-orientation of the spun fabric, the threads were then drawn under different conditions and on different drawing systems and partially shrunk. The stretching devices differed by the type of stretching furnace.

In the examples, "IR" is understood to mean a heating channel in which the threads have been heated by ceramic infrared radiators, and "air" is understood to mean an oven in which the threads are heated by hot air flowing transversely. In both cases, the specified temperatures refer to the temperatures of the sensors. In the "IR" oven the sensors were about 15 mm above the thread sheet, in the "Air" oven they were attached below the thread sheet and indicated the temperature of the heated air before this strikes the coulter.

Example 1 specifies the way of drawing a strand with low pre-orientation. The specified temperature could not be increased further, otherwise the thread would break. In Example 5, the same drawing conditions with regard to residence time and temperature as in Example 1 were used, but the feed yarn had a high degree of preorientation. A comparison of the values compiled in the table below shows that, owing to the high degree of preorientation, the shrinkage is slightly lower and the stability quotient is slightly higher than in Example 1, the progress compared to the thread of Example 1, which is also well fixed, is not great. The values of Example 4, however, show that by increasing the sensor temperature by 20 ° C., a thread with significantly reduced shrinkage could be obtained, which would surely meet all of the claims. In example 6, the temperature of the heater was raised to that of example 4, but the residence time was halved by doubling the working speed. This measure led to a sharp increase in the drawing tension, the values for the shrinkage and stability quotient are clearly outside the claimed ranges. This example shows how important it is to comply with the required drawing conditions, because otherwise, despite the high pre-orientation of the spun fabric which reduces the shrinkage, only a yarn is obtained which is even inferior to the classic threads or yarns in terms of thermal stability. In Examples 8 and 10, the drawing conditions according to the invention are applied to spun threads with high pre-orientation. However, the thread-forming substances used have different average molecular weights corresponding to different relative solution viscosities.

In Examples 7 and 9, a method was used in which a shrinking process took place after the stretching. In both cases, despite the very low thermal shrinkage of the yarn material, the elasticity is still practically 100% present and the claimed stability quotient is also exceeded.

Beispielen 11 bis 13 wurde ein Verstreckofen mit quer anströmender Luft benutzt. Auch hier zeigt sich wiederum, daß erst durch eine Erhöhung der Verstrecktemperatur, die diesmal vermutlich auch die Temperatur des Fadens am Ende des Streckfeldes sein könnte, ein erfindungsgemäßer Faden erhalten werden kann. Eine Erhöhung der Verstrecktemperatur im Beispiel 11 auf 250°C führte zu einem ständigen Reißen der Fäden. Auch bei 245°C rissen einzelne Fäden ab, andere zeigten jedoch sehr viele Kapillarbrüche. Im Beispiel 11 wurde ein wenigvororientiertes Zuliefergarn eingesetzt, das nur eine Doppelbrechung von 0,0033 aufwies.On the other hand, if, as shown in Examples 2 and 3, an attempt is made to apply this method to a spun thread with low pre-orientation, the thermal shrinkage of the yarn material is much higher in Example 2 than in Example 7, with the same degree of elasticity. A further relaxation, as in the example 3 shows, lowers the value of the thermal shrink a little, but this does not reach the low values of Examples 7 and 9. On the other hand, the reference elongation at 54 cN / tex, which has risen to a very high value, and the Degree of elasticity ED ₂₀ , which has dropped sharply, to the formation of a clear "shrink saddle" in the KD diagram. Example 14 shows that if the pre-orientation is increased by increasing the take-off speed to a birefringence, which is still below the claimed size of 0.025, an improvement in the thermal stability is achieved, since the drawing temperature has already been increased somewhat. However, the claimed ranges of the physical values of the yarns could not be reached. Both

Examples 11-13 used a cross-flow air stretching oven. Here, too, it is again shown that an inventive thread can only be obtained by increasing the drawing temperature, which this time could presumably also be the temperature of the thread at the end of the drawing field. An increase in the drawing temperature in Example 11 to 250 ° C. led to the threads continuously tearing. Individual threads broke even at 245 ° C, but others showed a large number of capillary breaks. In Example 11, a slightly pre-oriented supply yarn was used that only had a birefringence of 0.0033.

Claims (6)

1. An untwisted high-strength polyester yarn for industrial use, wherein the filament-forming substance has a high average molecular weight corresponding to a relative solution viscosity (1.0 g of polymer in 100 ml of dichloroacetic acid at 25°C) of about 1.90 to about 2.20 and the yarn

has a heat shrinkage S₂₀₀ of less than 7 %,

a degree of elasticity ED₂₀ of at least 90 %,

a stability quotient SO of at least 7.5 and

a crystallinity of about 57 to about 65 %.

2. The yarn as claimed in claim 1, wherein the filamentforming substance comprises a polyethylene terephthalate which may contain up to 2 % by weight of other comonomer units.

3. The yarn as claimed in claim 1 or 2, which has a heat shrinkage S₂₀₀ of less than 3 %, preferably less than 2 %.

4. The yarn as claimed in any of the preceding claims, which has a crystallinity of about 60 to 63 %.

5. A process for preparing a yarn as claimed in any of the preceding claims, which comprises subjecting a polyester feed yarn of high preorientation corresponding to a birefringence of at least 0.025 and an average molecular weight corresponding to a relative viscosity (1.0 g of polymer in 100 ml of dichloroacetic acid at 25 °C) of about 1.9 to about 2.20 to a drawing operation at a draw ratio of at least 90 % of the maximum cold stretching ratio and operating at such a high temperature that a drawing tension between 19 and 23 cNltex can be maintained.

6. The process as claimed in claim 5, wherein the drawing tension is 20 to 23 cN/tex.

Images