EP0283831B1 - Process for producing yarns by melt-spinning polyethylene terephthalate - Google Patents

Abstract

Process for producing yarns by melt-spinning polyethylene terephthalate (PETP) wherein solid PETP is melted in one operation and the molten PETP is extruded through spinneret holes and solidified to form a spun product which is drawn to form a yarn, characterised by the following conditions: a) the solid PETP has a relative viscosity between 1.8 and 2.1, b) prior to spinning the PETP is mixed with 0.1-0.8 % by weight of a bisketeneimine, c) the molten PETP is taken off the spinneret holes at a speed of from 1500 to 4000 m/min, and d) the resulting spun product, without intermediate winding, is drawn with a draw ratio of from 1.5 to 4.0, the draw ratio being chosen in such a way that the final speed of the yarn is not more than 6000 m/min.

Description

The invention relates to the production of yarns by melt spinning solyethylene terephthalate, hereinafter abbreviated to PETP, solid PETP being melted in a single operation, pressed through nozzle openings, solidified and drawn into a yarn.

Such a method is known and is used, for example, for the production of yarns for technical applications, for example for the reinforcement of rubber articles such as car tires.

Yarns used in car tires should preferably have a high modulus (HM) and low shrinkage (LS). The yarns produced in accordance with the invention are referred to below as HMLS yarns.

The HMLS yarns produced according to the invention can be processed in a known way to reinforcing cords for tires and this cord can, according to a likewise known method, be provided with an adhesive, a so-called "dip", whereby a "dipped cord" is obtained.

The dipped cord which is obtained from the HMLS yarns produced according to the invention has a low hot air shrinkage (HAS / hot air shrinkage) in the range from 3.5 to 1.5%. HMLS yarns with the properties mentioned can be produced in a known manner by spinning PETP at a speed of approximately 4000 m / min to form a roving with a high degree of orientation, which then has to be stretched approximately twice. This known method has the disadvantage that it cannot be carried out in one operation, since in this case the winding speed at the end of the process should be at least 6000 m / min. Such winding speeds place high demands on the winding units in large production units. Therefore, a two-step procedure is used in practice. First, the spun yarn is wound up at a speed of approximately 4000 m / min, after which the wound yarn is stretched in a separate operation.

To carry it out in a one-step process, a lower spinning speed in the range between 3500 and 4000 m / min would have to be selected in order to be able to stretch and wind the roving thus obtained in such a way that a speed of 6000 m / min is not exceeded.

At the usual relative viscosity of the polymer of approx. 2, the roving has a too low pre-orientation, so that the desired HMLS properties cannot be achieved in a one-step process.

• a) das feste PETP hat eine relative Viskosität (nach der nachfolgend beschriebenen Art bestimmt) zwischen 1,8 und 2,1,
• b) vor dem Spinnen wird das PETP mit 0,1-0,8 Gew.-% eines Bis-ketenimin, nachfolgend kurz BKI genannt, gemischt,
• c) das erschmolzene PETP wird von den Düsenöffnungen mit einer Geschwindigkeit zwischen 1500 und 4000 m/min abgezogen, und
• d) das erzielte gesponnene Produkt wird ohne Zwischenaufwicklung mit einer Verstreckungsrate von 1,5 bis 4,0 verstreckt, wobei die Verstreckungsrate derart gewählt wird, daß die Endgeschwindigkeit des Garns höchstens 6000 m/min beträgt.

The object of the present invention is therefore to provide a method of the type mentioned at the outset with which HMLS yarns can be produced in a one-step process. This object is achieved in a process for the production of yarns by melt spinning polyethylene terephthalate (PETP), solid PETP being melted in one operation, the melted PETP being extruded through spinnerets and being solidified to form a web which is drawn into a yarn. that the following conditions are met:

• a) the solid PETP has a relative viscosity (determined in the manner described below) between 1.8 and 2.1,
• b) before spinning, the PETP is mixed with 0.1-0.8% by weight of a bis-ketenimine, hereinafter referred to as BKI for short,
• c) the melted PETP is withdrawn from the nozzle openings at a speed between 1500 and 4000 m / min, and
• d) the spun product obtained is drawn without intermediate winding at a drawing rate of 1.5 to 4.0, the drawing rate being selected such that the final speed of the yarn is at most 6000 m / min.

If higher viscosities in the range between 1.8 and 2.1 are used, heating the spinnerets or the spinning device is advantageous.

The addition of a BKI in the amount mentioned above results in a higher spinning orientation for the spun product, as a result of which the drawn yarn has the desired HMLS properties.

The addition of BKI in the PETP before spinning is known per se from US Pat. No. 3,692,745. According to the method described there, BKI is added to the PETP in order to reduce the concentration of the carboxyl groups of the PETP, with the aim of greater chemical stability. Nothing is mentioned in this patent of the spinning conditions mentioned under c and d, nor is there any indication that an HMLS yarn can be produced using a combination of steps a to d. According to the US patent mentioned, BKI can be added to the polymer, for example, by adding powdered BKI to PETP grains (so-called breading). BKI can also be added to the previously melted polymer. The preferred BKI is N, N'- bis (diphenylvinylidene) p-phenylenediimine, which is easy to prepare and gives good results. BKI other types can be used such as N, N'-bis (Diphenylvinyliden) -4,4 -bis (diphenylvinyliden) -hexamethylendiimin _{'-diphenyimethan} diimine, and N, _N'.

The speed at which the polymer is drawn off from the spinnerets is between 1500 and 4000 m / min depending on the relative viscosity and the desired properties of the end product. At low take-off speeds, a slightly higher draw ratio (e.g. by 4.0) is usually required in the last operation than at a higher take-off speed.

The yarns produced according to the invention have the above-mentioned HMLS properties. They also have better thermal and chemical stability than yarns with HMLS properties that were spun without BKI. The high spinning speed that is generally required in HMLS games leads to an open structure that is sensitive to chemical attacks and high temperatures. This sensitivity decreases with the addition of BKI.

The parameters used such as titer (linear density), modulus, strength, 5% LASE (Load At Specified Elongation), elongation at break and hot air shrinkage at 180 _° C are determined in accordance with ASTM D885-M-1979. Deviating from these regulations, the hot air shrinkage, HAS, is measured at 180 _° C and with a preload of 1 cN / tex.

Relative viscosity

It is determined by dissolving 1 g of PETP by heating in 100 g of metacresol. The flow time t _{1 of} the subsequent solution is measured using a capillary tube with an inner diameter of 1.25 mm at 25 _° C. The flow time to of the metacresol without PETP is measured under the same conditions. The relative viscosity is the ratio t ₁ to to.

Examples

The starting point is PETP grains which have the relative viscosity given in the table below. These grains are dusted with the specified amount of N, N'-bis (diphenyl vinylidene) p-phenylenedimine. They are then melted at 290 _° C and extruded through a heated spinneret plate having 140 holes with a diameter of 400 _Ji m. After leaving the spinning plate, the threads are drawn off at a speed vi, as indicated in the table. They are cooled with air at room temperature. The threads are passed over godets and then drawn by winding at a speed _V2 as indicated in the table. The threads have the properties mentioned in the table under "Yarn". A tire cord with dtex 1100 (Z 472) x 2 (S 472) is produced in a known manner with the yarn obtained. The untreated cord is then dipped in two dip baths to improve the adhesion with the elastomeric material. The properties of the dipped cord are also shown in the table. The dipping of the cord according to the invention in two baths takes place in a way known per se. Here, the cord is passed through a first bath for applying a pre-dip and then through a second bath for applying the main dip in a continuous process. Between the first and second baths, the cord is dried for 60 seconds at 240 ° C and a tension of 10N. After the main dip has been applied, ie after leaving the second bath, the cord is dried again for 120 seconds at 220 ° C. and a tension of 4.5 N.

Bei den Vergleichsbeispielen 1 und 3 wurde kein BKI verwendet. Es handelt sich also um Beispiele, die außerhalb der Erfindung liegen und werden deshalb Vergleichsbeispiele genannt.The compositions of the immersion baths are the same as in the example of EP-A 201 114.

No BKI was used in Comparative Examples 1 and 3. These are examples that lie outside the scope of the invention and are therefore called comparative examples.

In Comparative Example 1, the speeds v _i and v _{2 were used} in a one-step process, as is still the case in industrial production. With otherwise satisfactory properties, the hot air shrinkage (HAS) of the immersed cord is too high, namely 3.7%.

In comparative example 3 (without BKI additive), the product achieved is very good, but a winding speed of 6900 m / min was required. This speed can be used for a short time on a laboratory scale, but cannot be achieved on an industrial scale and in an economically justifiable manner.

According to Examples 2 and 4, yarns with inherent switching are obtained which are comparable to those of the yarns from Comparative Example 1. The favorable influence of the method according to the invention can be seen in the dipped cord. The hot air shrinkage (HAS) of the cord in Examples 2 and 4 is significantly lower than in Comparative Example 1. Such a positive effect is also achieved in Comparative Example 3, although, as mentioned above, it was necessary to work at an undesirably high speed v ₂ that is not feasible in practice. In addition, the already favorable HAS value of Example 4 exceeds the value of Comparative Example 3.

Claims (2)

1. A method of producing yarn by melt spinning of polyethylene terephthalate (PETP), in which solid PETP is melted in one step and the molten PETP is extruded through spinnerets and solidified into a spun material which is drafted to form a yarn, characterised by the following conditions:

a) the solid PETP has a relative viscosity between 1.8 and 2.1;

b) before spinning, the PETP is mixed with 0.1 to 0.8 wt.% of a bis-ketene imine;

c) the molten PETP is drawn from the spinnerets at a speed of 1500 to 4000 m/min, and

d) the resulting spun material, without intermediate winding, is drafted at a drafting rate of 1.5 to 4.0, the drafting rate being chosen so that the final speed of the yam is not more than 6000 m/min.

2. A method according to claim 1, characterised in that the bis-ketene imine is an N,N'-bis (diphenyl vinylidene)p-phenylene diimine.