EP0225347B2 - Polyester yarn and method for preparing it - Google Patents

Abstract

The method for producing dimensionally stable, low-shrinkage, chemically modified industrial polyester yarns by melt spinning at speeds of 1000 to 4000 m/min. utilizes a copolymer containing at least 85 percent by weight polyethylene terephthalate units and comonomers. During polyester production to lower the thermal shrinkage one or more conformationally fixed linear difunctional comonomers are added to the polymer melt. These difunctional comonomers have the general formula, X'-R-X, where R is an unsaturated linear alkyl group having from three to ten carbon atoms or a cycloalkyl or aromatic group with 6 or more carbon atoms, and X and X' are, independently, OR' or CPPR'', and R'=H or an alkyl group and, independently, R'' is also H or an alkyl group.

Description

The invention relates to a chemically modified polyester yarn and a method for producing the same.

The production of low-shrinkage polyester threads, which are also high-strength and low-stretch for technical purposes, is known. For example, CH-A-513 992 describes a process for spinning, drawing and heat setting in one operation. In addition to heat setting, up to 1% by weight of branching components are also used to reduce the shrinkage. The branching components listed not only hinder the stretching of the thread, but also reduce the strength and the modulus and thus the dimensional stability. This process results in a thermal shrinkage of more than 7% measured at 160 ° C with a breaking strength of at most 80 cN / tex with a titer of about 1100 dtex. However, a yarn with such a high tendency to shrink no longer meets the requirements for the dimensional stability of a tire. Here, the breaking strength, thermal shrinkage and initial module (Young's module) must be coordinated with one another within certain limits.

However, a method for producing chemically modified, quickly spun threads is also known (DE-B-1266992). In this process, however, only the coloring properties are described by adding chain branching agents or crosslinking agents such as polyols in amounts of 0.1 to 1.0 mol%.

According to EP-A-0 169 415, dimensionally stable, low-shrinkage polyester yarns are also obtained, but this requires higher intrinsic viscosities of at least 0.9 dl / g. Neither values for dimensional stability nor initial moduli can be found in the publication, from which the dimensional stability could be calculated together with the strength and the thermal shrinkage.

It has now been found that the dimensional stability of a tire can be expressed by a key figure if the essential parameters such as elongation at break or strength (Ft), initial modulus (Mo) and thermal shrinkage (TS) are kept within certain limits. To evaluate a dimensionally stable yarn with low shrinkage and high initial modulus (LSHM), the following key figure is suggested:

So far it has not been possible to achieve a low shrinkage with a given reference elongation or strength (Ft) and a high initial modulus in a mechanical-thermal way.

The object of the invention is to provide a yarn with a high initial modulus and a low shrinkage, in particular with a high dimensional stability (DS).

zugefügt, wobei R eine gesättigte oder nicht gesättigte lineare Alkylgruppe von C₃ bis C₁₀ oder ein Cykloalkyl- oder aromatischer Rest mit 6 oder mehr Kohlenstoffatomen, X OR', und/oder COOR" und n gleich 2 bedeuten, dabei ist R' gleich H, CO-Alkyl oder eine Alkylgruppe mit 1 oder mehr Kohlenstoffatomen und R" gleich H oder Alkyl ist, und dass die Comonomere in die Polymerisationsschmelze vor der Polykondensation zugegeben werden.The object is achieved according to the characterizing part of claim 1. To reduce thermal shrinkage, one or more difunctional comonomers with the general formula: $${\text{R - (X)}}_{\text{n}}$$

added, where R is a saturated or unsaturated linear alkyl group from C ₃ to C ₁₀ or a cycloalkyl or aromatic radical having 6 or more carbon atoms, X OR ', and / or COOR "and n is 2, where R' is the same H, CO-alkyl or an alkyl group with 1 or more carbon atoms and R "is H or alkyl, and that the comonomers are added to the polymerization melt before the polycondensation.

The copolyester can be prepared in a customary manner either by direct condensation of ethylene glycol and terephthalic acid or by transesterification of dimethyl terephthalate with ethylene glycol and subsequent polycondensation of the diglycol terephthalate initially formed. The comonomer together with the monomers before the transesterification. Esterification phase or added to the mixture before the polycondensation phase.

Difunctional, conformationally fixed comonomers have proven to be particularly suitable for reducing thermal shrinkage and simultaneously increasing the dimensional stability DS.

Conformationally fixed is to be understood as meaning atomic frameworks whose arrangement or types of bonds are suitable for keeping the relative position of the above-mentioned functions relative to one another constant within certain limits.

However, these difunctional compounds must be used in concentrations of 1 to 10% by weight, based on the polyester.

Comonomers of aromatic diols are also suitable, such as hydroquinone, 2-chlorohydroquinone _, 2,5-dichlorohydroquinone, 2,3,5-trichlorohydroquinone, 2-methylhydroquinone, 2,3-dimethylhydroquinone, 2,5-dimethylhydroquinone, 2,3,5 -Trimethylhydroquinone. 2,3,5,6-tetramethylhydroquinone, 4,4'-dihydroxybiphenyl, 2,6-naphthalenediol, 1,5-naphthalenediol or their derivatives such as hydroquinone diacetate. 2-chlorohydroquinone diacetate, 2,3,5-trichlorohydroquinone diacetate, 2-methylhydroquinone diacetate, 2,5-dimethoxyhydroquinone diacetate, 2,3,5-trimethylhydroquinone diacetate, 4,4'-diacetoxybiphenyl, 2,6-diacetoxynaphthalene, 1,5-diacetoxynaphthalene.

Aromatic hydroxycarboxylic acids such as 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 5-hydroxy-1-naphthoic acid, in particular acetyl compounds and alkyl esters such as methyl 4-hydroxybenzoic acid, methyl 6-hydroxy-2-naphthoate, 4-acetoxybenzoic acid can also be used according to the invention.

Of the difunctional rigid and aromatic comonomers, hydroquinone diacetate or methyl 4-acetoxybenzoate have proven to be the best.

The polyester yarn produced by the process according to the invention is characterized by a code number DS of ≧ 31135. The prerequisite is that Ft is in the range of 50 cN / tex and 80 cN / tex, preferably from 60 cN / tex to 80 cN / tex. At the same time, a Young's module of 1000 cN / tex to 1400 cN / tex, preferably 1200 cN / tex to 1300 cN / tex, is stipulated, and a thermal shrinkage TS of 1 to 3%.

The process is to be explained in more detail using examples.

Polyester is understood to mean a polymer of at least 85% by weight of terephthalate and ethylene glycol units. To produce the copolyester, 6.1 kg of ethylene glycol and 10 kg of dimethyl terephthalate are placed in an autoclave. 4 g of crystallized manganese acetate are added as the transesterification catalyst. The mixture is heated to 230 ° C. for 2.5 hours, during which the methanol released and the excess of glycol are distilled off under normal pressure. The following substances are added in succession at 230 ° C.: 3 g of phosphorous acid and 3.5 g of antimony trioxide. When heating up to 280 ° C, the pressure is reduced to below 0.5 mbar. The comonomer according to the invention is added directly into the polymer melt before the polycondensation. Depending on the type of comonomer, the vacuum is broken after 3.5 to 5 hours by introducing nitrogen, the polymer melt is discharged from the autoclave, for example in the form of a cable, cooled and the solidified polymer is cut. The intrinsic viscosity, measured at 25 ° C in a mixture of phenol / tetrachloroethane 1: 1 (according to H. Frind, Faserforschung (1954), page 296) is approximately 0.67 dl / g. The granules are then dried in a tumble dryer under a vacuum of 0.5 mbar, first at 150 ° C. for 2 hours, then after a few hours at 235 ° C. to an IV. Which is between 0.80 and 1.00, after-condensed and dry stored. The post-condensation time depends on the type of comonomer and the achievable vacuum and is up to 30 hours.

For spinning, the dry granulate is processed on a known spinning machine for processing high-viscosity polyesters and drawing high-strength multifilament yarns. The polyester melted at a temperature of about 285 to 310 ° C is extracted from the spinneret with e.g. 192 continuous filaments pressed in a known manner, regularly cooled, converged, provided with a preparation and wound up or directly drawn.

The undrawn yarn is drawn and wound up several times on hot aggregates in several stages. The spinning and especially the drawing can, at different speeds, respectively. integrated or in the split process. The heat transfer during drawing takes place via an iron, hot rollers or an oven, where the thread is oriented and fixed in a crystallized manner. The longitudinal tension under which the thread material is held is sufficient to prevent shrinkage during each stage of the heat treatment and to cause repeated stretching. During this process, the thread material is given a breaking strength of at least 65 cN / tex and the elongation at break, measured at 25 ° C. on the conditioned thread at an elongation rate of 2.7% D / s, is 8 to 15%, preferably 9 to 12%.

In the copolyester according to the invention, the thermal shrinkage (TS) is 1 to 3% (measured at 190 ° C.). The shrinkage values were determined using a thermomechanical analyzer (thermofilter from TEXTECHNO / Mönchengladbach). The thread is first pretreated with a preload of 0.4 cN / dtex for 1 minute at 235 ° C and then the shrinkage of the cooled thread is monitored at a heating rate of 20 K / min. The clamping length is 10 cm and the shrinkage value at the desired temperature is e.g. 190 ° C determined from the curve.

The module is determined from the steepness of the force-elongation curve in the initial area as follows: The filament is stretched at a clamping length of 500 mm with a force expansion measuring device (company ZWICK type 1474) at a speed of 2.5 cm / min and the force is registered until it reaches 2 cN. In this area of the filaments according to the invention, the force expansion function (apart from a very small thrust piece) is very linear. You now create a tangent to the curve and can calculate the force extrapolated to 100% elongation from the steepness. This force value divided by the titer of the filament bundle is taken as the initial module [cN / dtex] or [cN / tex].

The invention will be explained in more detail by means of examples, the results of which are summarized in the table.

example 1

300 g of hydroquinone diacetate (3% by weight, based on the polyester) were used as comonomer together with the other two starting materials, ethylene glycol and dimethyl terephthalate. The other conditions corresponded to the general procedure described. After 2 hours of transesterification, 6.3 liters of methanol had developed and after another 30 minutes 1.1 liters of glycol. The following polycondensation lasted 4 hours 50 minutes, the copolyester having an IV of 0.70 dl / g and a melting point of 254 ° C. After a post-condensation of 28 hours at 235 ° C, an IV of 0.90 dl / g was reached.

Some properties of the resulting yarns are set out in Table 1, with a model thread made with 14 fibrils.

Example 2

300 g of 4-acetoxybenzoic acid were used as comonomer in the same manner as in Example 1. After 2 hours, 3.7 l of methanol resulted and after a further 30 minutes also 1.1 l of glycol. After 4 hours 30 minutes the IV reached 0.65 dl / g and the melting point was 248 ° C. After a further condensation of 28 hours, an IV of 0.80 dl / g was reached. The table shows the yarn properties.

Example 3

100 g of 2-butene-1,4-diol were used as comonomer in the same manner as in Example 1. After 2.5 hours, 3.7 l of methanol were released, and after a further 30 minutes, 1.5 l of glycol. The polycondensation lasted 4 hours and an IV of 0.68 dl / g or a melting point of 253 ° C. was reached. After a post-condensation of 28 hours, the IV was 0.97 dl / g.

Example 4 (Comparative example)

The procedure corresponds to that of Examples 1 to 3 but without using a comonomer. After 2 hours, 3.4 liters of methanol or 1 liter of glycol developed after a further 30 minutes. The polycondensation lasted 3 hours 50 minutes. The polymer had an IV of 0.70 dl / g and a melting point of 255 ° C. After a post-condensation of 25 hours, the IV was 0.99 dl / g. The properties of the yarns are set out in Table 1 as Example 4.

The measurement results of the examples are shown in the curves of the single figure. The ordinate gives the dimensional stability with the dimension cN ² / tex ² and the abscissa the spinning speeds in m / min.

The best dimensional stability of 48280 cN ² / tex ^{2 is} shown in Example 2 with a thermal shrinkage of 1.75% at a spinning speed of 3000 m / min.

The yarns produced by the process according to the invention are preferably suitable as yarns with low shrinkage and high Young's modulus (LSHM) for the production of tire cord fabrics and other technical applications such as for drive belts and seat belts.

Claims (7)

1. Chemically modified polyester yarn characterised by a dimensional stability DS ≥ 31,135 cN²/tex² while at the same time the tenacity is 50 - 80 cN/tex, the initial modulus 1,000 to 1,400 cN/tex and the heat shrinkage at 190°C 1.0 to 3.0 % and having an intrinsic viscosity of 0.75 to 0.85 dl/g.
2. Process for producing dimensionally stable, low shrinkage, chemically modified industrial polyester yarns by melt spinning at speeds of 3000 to 4000 m/min using a copolymer which contains at least 85% by weight of polyethylene terephthalate units and comonomers, having an intrinsic viscosity of 0.75 to 0.85 dl/g and a total linear density of at least 500 dtex, characterised in that there are added during polyester synthesis, in an amount of 1 to 10% by weight based on the polyester, one or more difunctional and conformationally fixed comonomers of the general formula: $${\text{R - (X)}}_{\text{n}}$$

   

   where R is a saturated or unsaturated linear alkyl group of C₃ to C₁₀ or a cycloalkyl or aromatic radical of 6 or more carbon atoms, X is OR' and/or COOR'', n is 2, R' is H, CO-alkyl or an alkyl group of 1 or more carbon atoms, and R'' is H or alkyl and that the comonomers are added to the polymerisation melt prior to polycondensation.
3. Process according to Claim 2, characterised in that the comonomers used are unsaturated aliphatic diols or derivatives thereof or unsaturated aliphatic hydroxycarboxylic acids or derivatives thereof.
4. Process according to Claim 2, characterised in that the comonomers used are aromatic diols or derivatives thereof and/or aromatic hydroxycarboxylic acids or derivatives thereof.
5. Process according to Claim 2, characterised in that the unsaturated aliphatic diol is 2-butene-1,4-diol.
6. Process according to Claim 2, characterised in that the derivatives are acetyl compounds and/or alkyl esters.
7. Process according to Claim 5, characterised in that the acetyl compound is hydroquinone diacetate or methyl 4-acetoxybenzoate.

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