Melt-spun abrasion-resistant monofilaments

The invention relates to melt-spun monofilaments of polyamide, polyester or polypropylene as filament-forming polymers with improved abrasion resistance and their use for producing technical textile materials or use as wire.

BACKGROUND OF THE INVENTION

The processes for producing monofilaments from thermoplastic polymers are known in principle and are described, for example, in Handbuch der Kunststofftechnik II, C Hauser Publishers, Munich 1986, pp. 295-319.

It is further known that the notched bar impact strength of moulded bodies of thermoplastic polymers can be improved by the addition of polyethylene/polypropylene rubber. In known manner the polymer mixtures of thermoplastic polymers and modified polyethylene/polypropylene rubber are granulated and compounded on double-shaft extruders and processed by injection moulding.

To date, few suitable polymer mixtures have become known for the manufacture of monofilaments for technical purposes, such as further processing into press felts for the paper industry, which must in particular have high mechanical strength with respect to abrasion. From US patent specification 5 169 711 it is known that the abrasion resistance of monofilaments of polyethylene terephthalate (PET) can be increased by the addition of thermoplastic polyurethane (TPU).

Monofilaments of polymer mixtures of polyamide, polyphenylene ether and a functionalized elastomer are also known for the manufacture of press felts (see international patent application WO 93/1325 for example).

The abrasion resistance of the monofilaments and hence of the technical fabrics that can be produced from them is improved by the above-mentioned known raw material modifications to only an inadequate extent, and in addition the strength of the monofilaments is reduced.

SUMMARY OF THE INVENTION

The object of the invention is to improve the abrasion resistance and the alternating bending strength of melt-spun monofilaments and their processability to technical fabrics or wire and thereby significantly to prolong the service life of technical fabrics for example.

According to the invention this object is achieved by melt-spun monofilaments for the manufacture of technical wire or technical textile materials, characterized in that they contain

a) 99 to 70 wt. %, preferably from 80 to 95 wt. %, of nylon, polyester or polypropylene as filament-forming polymer,

b) from 30 to 1 wt. %, preferably from 5 to 20 wt. %, of a maleic anhydride modified polyethylene/polypropylene rubber

and additionally

c) up to 3 wt. %, preferably from 0.01 to 3 wt. %, related to the sum of a)+b), of ageing stabilizers, e.g. sterically hindered phenols (SHP), carbodi-imides or aromatic amines, copper salts, particularly those of monovalent copper.

The monofilaments according to the invention are distinguished by a permanently improved abrasion resistance, improved resistance to alternating bending stress and reduced thermo-shrinkage forces.

The invention also provides the use of the monofilaments according to the invention for producing technical textiles, such as fabrics and felts for industry, e.g. grading fabrics, screen printing fabrics, mould screen fabrics and press felts for paper and cellulose fibre manufacture.

The service life of the technical textiles, particularly the mould screen fabrics and press felts for paper and cellulose fibre manufacture, is prolonged by the use of monofilaments according to the invention compared with known monofilaments.

DETAILED DESCRIPTION OF THE INVENTION

The monofilaments according to the invention are produced according to per se known melt extrusion processes. The raw materials are used either as granular mixture and/or as granular/powder mixture or as compounded granules. Attention should be paid to a homogeneous thorough mixing of the components in the melt and hence ultimately in the monofilaments. This is achieved by means of commercially available dynamic mixers after extrusion.

The objective was to increase the notched bar impact strength of the polymers and the transverse stability of the monofilaments obtained from the polymers.

In the monofilaments according to the invention an improvement of the abrasion resistance with an increasing content of maleic anhydride modified polyethylene/polypropylene rubber was surprisingly discovered in wear tests.

Furthermore, a reduction of the thermo-shrinkage forces was unexpectedly achieved with only a small addition of maleic anhydride modified polyethylene/polypropylene rubber, which has a positive effect on the dimensional stability of the fabrics produced from the monofilaments in the thermo-fixing of the fabric.

The invention further provides the use of the monofilaments according to the invention for producing technical textile materials or technical wires, particularly lawnmower wire. The monofilaments according to the invention are preferably used in so-called technical textiles such as fabrics and felts for industry, e.g. grading fabrics, screen printing fabrics, mould screen fabrics and press felts for paper and cellulose fibre manufacture.

Preferred filament-forming thermoplastic polymer for producing the monofilaments is nylon, particularly nylon (PA) 6, 6.6, 6.10, 6.12, 11 and 12, mixtures of the nylon or copolymers thereof. Preferred polyesters are polyethylene terephthalate (PET) or polybutylene terephthalate (PBT).

As additional additives up to 15 wt. %, related to the sum of the components a), b) and c), of plasticizers, e.g. caprolactam for nylon, phenols, arylsulphonyl amides or phthalic acid esters, pigments, e.g. TiO₂, carbon black, dyes, internal lubricants e.g. alkaline earth stearates particularly of Ca or Mg, waxes to increase transparency, such as those based on fatty acid amides, may be added to the mixture according to the invention.

EXAMPLES

Examples 1 to 5 illustrate monofilaments according to the invention, Example 6 a comparative example. A nylon 6 with a relative solution viscosity of η_rel =4.0 (measured in m-cresol at 25° C.) was used as filament-forming polymer (component A). A medium-viscosity semi-crystalline maleic anhydride modified PE/PP rubber was used as modified rubber (component B).

In the examples a product made by EXXON Chemical GmbH with the trade name EXXELOR VA 1803 was used as the PE/PP rubber. The chemical formula is quoted as:

H(C2 H4)X(CH2 CH--CH3)Y(O═COC═OCH═CH)Z H

with the indices X=0.5-0.6, Y=0.5-0.4, Z=0.002. The molecular weight is quoted at 20,000 to 60,000.

Component C) is a commercially available ageing stabilizer IRGANOX 1098 from Ciba Geigy, a sterically hindered phenol of formula (I) ##STR1## N,N'-hexamethylene-bis-(3,5-di-tert.-butyl-4-hydroxy-hydrocinnamic amide).

The concentrations of component A) were varied between 98.25 wt. % and 84.5 wt. %, and of component B) between 1.25 wt. % and 15 wt. %. The concentration of component C) was left constant at 0.5 wt. %.

Components A), B) and C) were degassed as granules and/or granule/powder mixture according to the desired concentration ratio on a single-screw extruder under vacuum, then melted at 270° C. and then mixed together in a dynamic mixer so that components A), B) and C) were mixed together homogeneously and in a finely dispersed manner.

The monofilaments were then produced in per se known manner on a monofilament spin/stretch unit. To do this, from a device for the melt-spinning of monofilaments the filament-forming polymer melt was spun off for cooling purposes into a water bath at 20 to 30° C., then stretched 3.5-fold in hot water at 80° C. and in hot air at 150° C. and finally fixed in hot air at 210° C.

Example 6 shows a nylon monofilament with no maleic anhydride modified PE/PP rubber, only of stabilized polyamide 6 (η_rel =4.0) for comparison with the monofilaments according to the invention according to Examples 1 to 5. Production was similar to the spinning process described above.

The results of Examples 1 to 6 are summarized in Table 1.

Abrasion Measuring Method

In the examples the abrasion tests were carried out on the test rods produced from the monofilaments using Messrs Einlehner's abrasion tester AT 2000 in calcium carbonate/water suspension.

Used as wear body was a ceramic strip rotary body comprising 16 circularly arranged round rods of Al-oxide ceramic with surface-ground, screen-touching outer side. The arrangement approximately corresponds to the open and closed surfaces of a flatbox in a paper machine. The material loss of the particular test screen is determined from the difference between abraded and non-abraded screen surface as weight and thickness loss.

                                  TABLE 1__________________________________________________________________________Examples 1 to 6    Comp. B                                        Weight loss    Comp. A    Maleic anhydride            Comp. C      Count                             Max. tensile                                   Hot air                                         Boil                                             Mass  of screenEx. Nylon 6    modified PE/PP            Sabilizer                 Dia.                     Count                         strength                             elongation,                                   shrinkage at                                         shr.                                             loss through                                                   sample throughNo. wt. %    rubber wt. %            wt. %                 mm  dtex                         cN/tex                             %     150° C.,                                         %   abrasion,                                                   abrasion,__________________________________________________________________________                                                   mg1   98.25    1.25    9.5  0.218                     431 34.26                             54.77 5.60  9.6 66    1.92   97   2.5     0.5  0.218                     430 34.50                             58.04 5.50  8.8 62    1.93   94.5 5       0.5  0.212                     405 32.44                             55.45 5.20  8.6 57    1.64   89.5 10      0.5  0.216                     413 28.19                             53.00 5.00  8.6 53    1.35   84.5 15      0.5  0.213                     397 25.82                             56.56 4.70  8.5 47    16   99.5 0       0.5  0.215                     420 37.02                             62.26 5.80  9.2 70    2__________________________________________________________________________

Table 2 shows further Examples 7 to 10 in which a hydrolysis-stabilized high-molecular polyethylene terephthalate (PET) with a maleic anhydride modified polyethylene/propylene rubber (EXXELOR VA 1803) and a hydrolysis stabilizer (STABAXOL P100) was used instead of polyamide.

                                  TABLE 2__________________________________________________________________________Examples 7 to 10    Comp. A      Comp. B                            Weight loss    Polyethylene      Maleic anhydride              Comp. C   Count      Mass  of screen    terephthalate,      modified PE/PP              Stabilizer,                   Diameter                        strength                            Max. tensile                                   loss through                                         sample throughEx. No.    wt. %  rubber, wt. %              wt. %                   mm   cN/tex                            elongation, %                                   abrasion μm                                         abrasion, wt.__________________________________________________________________________                                         %7   95.5   2.5     2    0.218                        35.3                            33.5   80    2.58   93     5       2    0.218                        32.4                            33.1   76    2.39   88     10      2    0.212                        34.1                            35.2   74    1.910  98     0       2    0.216                        32.40                            37.9   90    2.9__________________________________________________________________________

Table 3 reports the properties of technical wire (lawnmower wire) produced from unstabilized copolyamide (nylon 6: nylon 6.6 content=82:18 wt. %) with a maleic anhydride modified polyethylene/polypropylene rubber. In tests under practical conditions the length loss, for example, was determined according to the concrete edge impact test. The length loss decreases with an increasing content of maleic anhydride modified rubber.

                                  TABLE 3__________________________________________________________________________Examples 11 to 14Comp. B                                Standard                                             Length lossComp. AMaleic anhydride        Comp. C           Count        flexural                                             after                                                    Mowing onnylon 66/-modified PE/PP        Stabilizer,              Diameter,                    Count tensile                          strength,                                Max. tensile                                       strength                                             edge impact                                                    natural stone18, wt. %rubber, wt. %        wt. % mm    force, daN                          cN/tex                                elongation, %                                       N/mm2                                             test,                                                    in__________________________________________________________________________                                                    cm85   15      0     2.400                          7.0    980   20      0     2.400                          4.0    775   25      0     2.392 61.9  12.70 51.60  19.33 2.0    5100   0      0     1.987 147.0 41.8  25.3   68.3  Wire breaks                                                    12.0                                             off completely__________________________________________________________________________