EP0967306B1 - Monofilament based on polyethylene-2.6-naphthalate - Google Patents

Abstract

Monofilaments based on polyethylene-2,6-naphthalate (PEN) contain 60-99.9 wt% PEN, 0.1-10 wt% liquid crystalline polymer(s) (LCP), 0-15 wt% polybutylene terephthalate (PBT), 0-3 wt% capping agent and optionally other additives. An Independent claim is also included for a process for the production of these monofils by mixing the above components, forming monofilaments from the melt and then cooling and stretching, using extrusion and stretching conditions matched to give monofils with a diameter of 0.08-1.5 mm.

Description

The invention relates to monofilaments based on polyesters, namely Polyethylene-2,6-naphthalate, which liquid-crystalline polymers as admixtures contain, their manufacture and their use in particular for Manufacture of paper machine fabrics.

A monofilament in the sense of the invention is a continuous yarn consisting of a single continuous fiber, generally manufactured without twist, to understand which has a diameter of at least 0.08 mm. It differs of the single filaments or capillaries, which make up a multifilament yarn, especially due to the significantly larger diameter; they also differ Properties and techniques for processing monofilaments in many different ways Regarding the properties and processing methods of multifilament yarns.

Monofilaments are mainly used for the production of technical articles, in particular technically used fabrics, in contrast for multifilament yarns, which are mainly used in the textile industry.

Monofilaments for technical applications are used in most cases subject to high mechanical loads. In addition there are in many cases also thermal and chemical or other loads Environmental influences to which the material has sufficient resistance must oppose. With all these loads, the material must be good Dimensional stability and constancy of the force expansion properties over possible have long periods of use.

When using monofilament in paper machine sieves, especially in four-wire, the press section and the dryer section, high demands are placed on the monofilament material. Not just high starting modules and high ones Tear resistance, but also good knot and loop strength and high Abrasion resistance is required, as well as high resistance to hydrolysis; further the service life of the sieve should be as long as possible.

It is known to manufacture paper machine screens from polyethylene terephthalate monofilaments in the Chain and a combination of polyethylene terephthalate and polyamide 6 or To produce polyamide-6,6 monofilaments in the weft. However, these sieves can have the disadvantage that they are in the course of sieving on the paper machine extend in the direction of travel and must therefore be retightened.

There has been no shortage of attempts to produce synthetic monofilaments for the are suitable for a wide variety of uses, in particular for Manufacture of paper machine screens. Thus, in US Pat. No. 5,169,499 An alternative to polyethylene terephthalate is the use of copolymers based described by 1,4-dimethylcyclohexane, terephthalic acid and isophthalic acid. Although these polymers have good hydrolysis stability, they do show comparatively poor, longitudinal, knot and loop strength.

und 1 bis 15 Mol.-% der wiederkehrenden Struktureinheit der Formel II enthalten, -OC-R²-CO-O-R³-O- worin R¹ ein Rest eines zweiwertigen aliphatischen oder cycloaliphatischen Alkohols ist oder sich von Mischungen derartiger Alkohole ableitet, R² einen Rest einer aliphatischen, cycloaliphatischen oder einkernigen aromatischen Dicarbonsäure darstellt oder sich von Mischungen derartiger Dicarbonsäuren ableitet, R³ eine der für R¹ definierten Bedeutungen annimmt, und die Mengenangaben auf die Gesamtmenge des Polymeren bezogen sind.EP-0 761 847 A2 describes paper machine screens which contain monofilaments from copolymers which contain 85 to 99 mol% of the repeating structural unit of the formula I.

and contain 1 to 15 mol% of the recurring structural unit of the formula II, -OC-R ² -CO-OR ³ -O- wherein R ^{1 is} a radical of a dihydric aliphatic or cycloaliphatic alcohol or is derived from mixtures of such alcohols, R ^{2 is} a radical of an aliphatic, cycloaliphatic or mononuclear aromatic dicarboxylic acid or is derived from mixtures of such dicarboxylic acids, R ^{3 is} one of the meanings defined for R ¹ assumes, and the amounts are based on the total amount of the polymer.

The monofilaments described there are characterized by valuable properties off, however, they are regarding the splicing behavior and the transverse strengths still room for improvement.

US Pat. No. 5,692,938 describes monofilaments based on Polyethylene terephthalate described which admixtures of liquid crystalline Contain polymers. The monofilaments described there show an improved Abrasion resistance and are particularly suitable for the production of Suitable for paper machine screens.

However, the distribution of the liquid-crystalline polymers in the is problematic Polyethylene terephthalate, since the liquid crystalline polymers tend to to be distributed in a droplet shape in the matrix, which among other things in a reinforced Expresses tendency to splicing. This has been known for a long time Problem and others tried to solve by a method like that in the US PS 5,171,778, namely by processing a mixture of Polyalkylene terephthalate, a liquid crystalline polyester and a poly (O) -or - (N) -epoxyalkyl-substituted cyclic amide, imide or imidate, especially triglycidyl isocyanurate.

Aside from the fact that the processing of such reactive mixtures has problems is an indication of processing such mixtures into monofilaments in not found in this patent.

There is therefore still a need for monofilaments with improved ones Properties that can be used for a variety of technical purposes.

The object of the invention is therefore to provide monofilaments which in particular have an improved transverse strength and a high modulus own and are largely stable to hydrolysis.

This object is achieved by monofilaments according to claim 1.

In the claims 2 to 7 are particularly advantageous embodiments reproduced the monofilament according to the invention.

Another object of the invention is a method for manufacturing such monofilaments according to claim 8.

Another object of the invention is the use of inventive monofilaments or monofilaments produced according to the invention claims 9 to 13.

The monofilaments according to the invention can be produced in the following way happened:

The starting products, namely polyethylene-2,6-naphthalate and that liquid crystalline polymer and optionally polybutylene terephthalate and Closure agents and other additives are used immediately before spinning dried, preferably by heating in a dry atmosphere Vacuum. These raw materials are mixed together homogeneously and then in an extruder at a melt temperature of 270 to 320 ° C, preferably 290 to 305 ° C, melted, filtered in a spin pack and through a Spinneret spun.

After leaving the spinneret, the melt threads come out (Monofilament) cooled in a spinning bath at a water temperature of approx. 70 ° C (quenched) and wound or pulled at a rate that is greater than the spray speed of the melt. The spinning delay is 1: 1.5 to 1: 6.0, preferably 1: 3 to 1: 5, the spin draw speed 5 to 30 m / min, preferably 10 to 20 m / min.

The spun thread (monofilament) thus produced is subsequently stretched, preferably in several stages, in particular one, two or three stages post-stretched, with a total stretch ratio of 1: 4 to 1: 8, preferably 1: 5 to 1: 7 and then at temperatures of 190 to 250 ° C. heat-set, preferably 200 to 230 ° C.

The mechanical properties such as Initial module, maximum tensile force, maximum tensile force elongation, but also that Loop strength and knot strength as well as shrinkage are affected become. Of course, the titer of the resulting monofilament also depends on of stretching. The delivery rate and stretching are thus in line voted that the resulting monofilaments at the end a diameter of have at least 0.08 mm. According to the invention, diameters of For example, 0.08 to 1.5 mm can be set.

The polyethylene-2,6-naphthalate used generally has one Molecular weight of 25,000 to 30,000 g / mol corresponding to a relative Viscosity from 1.80 to 1.90, measured as a 1 w / v% solution in di-chloroacetic acid.

By adding sealing agents, it is possible to remove the end groups of the to use used polyester and thus stabilize the polymer. This is particularly advantageous if the monofilaments produced for the production of Paper machine screens or paper machine fabrics are used, so high demands are placed in particular on the hydrolysis stability.

By adding polybutylene terephthalate, it is possible to use mechanical To improve properties such as knot strength even further. The used Polyethylene terephthalate generally has a molecular weight of 25,000 to 30,000 g / mol corresponding to a relative viscosity of 2.0 to 2.3, measured as a 1 w / v% solution in di-chloroacetic acid.

In addition to the components already mentioned, the mixture to be spun can still contain other additives. So of course Catalyst residues resulting from polycondensation, such as antimony trioxide and tetraalkoxy titanates. Processing aids or Lubricants such as siloxanes can also be used.

The monofilaments can also be inorganic or organic pigments or Matting agents contain stabilizers, especially flame retardants like corresponding phosphorus compounds.

The processing of the monofilaments according to the invention can be carried out in a conventional manner happen, so the monofilaments on conventional wide weaving machines too Paper machine screens are woven. The monofilaments according to the invention can also with other monofilaments such as polyamide monofilaments or Polyethylene terephthalate monofilaments are processed together.

The table below shows the production parameters and properties of monofilaments according to the invention.

Claims (13)

1. Monofilaments based upon polyethylene-2,6-naphthalate containing 60 to 99.9 % by weight of polyethylene-2,6-naphthalate, 0.1 to 10% by weight of one or more liquid-crystal polymers, 0 to 15 % by weight of polybutyleneterephthalate and 0 to 3 % by weight of a end-group capping agent together with other additives if required
2. Monofilaments in accordance with claim 1, characterised in that they contain 0.5 to 7, preferably 1 to 5 % by weight of liquid-crystal polymers, 3 to 12, preferably 4 to 11 % by weight of polybutyleneterephthalate and 0.15 to 2.25 % by weight of end-group capping agent.
3. Monofilaments in accordance with claim 1 or 2, characterised in that they contain 0.4 to 1, preferably 0.45 to 0.6 % by weight of monocarbodiimide as a end-group capping agent.
4. Monofilaments in accordance with claim 1 or 2, characterised in that they contain 0.15 to 2.25, preferably 0.75 to 1.8% by weight of polycarbodiimide as a end-group capping agent.
5. Monofilaments in accordance with at least one of the patent claims 1 to 4, characterised in that they contain a mixture of monocarbodiimide and polycarbodiimide as end-group capping agent.
6. Monofilaments in accordance with at least one of claims 1 to 5, characterised in that they contain as the liquid-crystal polymer a polycondensation product based upon p-hydroxybenzoic acid and 2.6-hydroxynaphthoic acid.
7. Monofilaments in accordance with claim 6, characterised in that the polycondensation product is constructed of 70 to 80, preferably 72 to 74 mol.% of p-hydroxybenzoic acid and 20 to 30, preferably 26 to 28 mol.-% of 2,6-hydroxynaphthoic acid.
8. Procedure for the manufacture of monofilaments in accordance with one or more of claims 1 to 7, characterised in that polyethylene-2,6-naphthalate, one or more liquid-crystal polymers together with, if required, polybutyleneterephthalate, end-group capping agents and other additives are mixed together, formed into monofilaments by melting whereby after leaving the spinning nozzle the monofilaments are cooled and stretched in such a manner that the extrusion and stretching are so balanced with respect to one another that monofilaments are produced which have a diameter of between 0.08 and 1.5 mm.
9. Use of the monofilaments in accordance with at least one of claims 1 to 7 or manufacture by a procedure in accordance with claim 8 for the manufacture of wire cloth or filters.
10. Use of the monofilaments in accordance with at least one of claims 1 to 7 or manufacture by a procedure in accordance with claim 8 for the manufacture of paper-machine "wires" or paper-machine "wire" cloths.
11. Use of the monofilaments in accordance with at least one of claims 1 to 7 or manufacture by a procedure in accordance with claim 8 for the reinforcement of elastomers.
12. Use of the monofilaments in accordance with at least one of claims 1 to 7 or manufacture by a procedure in accordance with claim 8 for the manufacture of conveyor belt fabrics.
13. Use in accordance with claim 9 or 12 for the manufacture of conveyor belt fabrics, "wire"cloths or filters for the food-stuffs industry.