US20070014989A1

US20070014989A1 - Polyester fibers, their production and their use

Info

Publication number: US20070014989A1
Application number: US11/483,988
Authority: US
Inventors: Hans-Joachim Bruning; Rex Delker
Original assignee: Individual
Current assignee: Teijin Monofilament Germany GmbH
Priority date: 2005-07-16
Filing date: 2006-07-10
Publication date: 2007-01-18
Also published as: EP1743963A1; DE102005033350A1; JP2007023474A

Abstract

Described are fibers comprising aliphatic-aromatic polyester and non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1. The polyester fibers possess excellent bending fatigue resistance, give distinctly reduced abrasion and are useful for producing screens or other industrial fabrics.

Description

CLAIM FOR PRIORITY

This application is based upon German Patent Application No. DE 10 2005 033 350.8, entitled “Polyesterfasern, Verfahren zu deren Herstellung und deren Verwendung”, filed Jul. 16, 2005. The priority of German Patent Application No. DE 10 2005 033 350.8 is hereby claimed and its disclosure incorporated herein by reference.

TECHNICAL FIELD

The present invention concerns polyester fibers having abrasion and high bending fatigue resistance, especially monofilaments useful in screens or conveyor belts for example.

BACKGROUND OF INVENTION

It is known that polyester fibers, especially monofilaments for industrial applications, are in most cases subjected to high mechanical and/or thermal stressors in use. In addition, there are in many cases stressors due to chemical and other ambient influences, to which the material has to offer adequate resistance. As well as adequate resistance to all these stressors, the material has to possess good dimensional stability and constancy of its stress-strain properties over very long use periods.
One example of industrial applications imposing the combination of high mechanical, thermal and chemical stresses is the use of monofilaments in filters, screens or as conveyor belts. This use requires a monofilament material possessing excellent mechanical properties, such as high initial modulus, breaking strength, knot strength and loop strength and also high abrasion resistance coupled with a high hydrolysis resistance in order that it may withstand high stresses encountered in its use and in order that the screens or conveyor belts may have an adequate use life.
Molding compositions possessing high chemical and physical resistance and their use for fiber production are known. Polyesters are widely used materials for this purpose. It is also known to combine these polymers with other materials, for example in order to achieve a specific degree of abrasion resistance.
Industrial manufacturers, such as paper makers or processors, utilize filters or conveyor belts in operations taking place at elevated temperatures and in hot moist environments. Polyester-based manufactured fibers have a proven record of good performance in such environments, but when used in hot moist environments polyesters are vulnerable to mechanical abrasion as well as hydrolytic degradation.
Abrasion can have a wide variety of causes in industrial uses. For instance, the sheet-forming wire screen in papermaking machines is in the process of dewatering the paper slurry pulled over suction boxes, and this results in enhanced wear of the wire screen. At the dry end of the papermaking machine, wire screen wear occurs as a consequence of speed differences between the paper web and the wire screen surface and between the wire screen surface and the surface of the drying drums. Fabric wear due to abrasion also occurs in other industrial fabrics, for instance in transportation belts due to dragging across stationary surfaces, in filter fabrics due to the mechanical cleaning and in screen printing fabrics due to the movement of a squeegee across the screen surface.
Adding fillers to improve the mechanical properties of fibers is known per se.
GB-A-759,374 describes the production of artificial fibers and films having improved mechanical properties. The claimed process is characterized by the use of very finely divided metal oxides in the form of aerosols. The particle size shall be not more than 150 nm. Viscose, polyacrylonitrile and polyamides are mentioned as examples of polymers.
EP-A-1,186,628 discloses a polyester raw material comprising finely dispersed silica gels. The individual particles have diameters of up to 60 nm and aggregates, if present, are not more than 5 μm in size. The filler is said to lead to polyester fibers having improved mechanical properties, improved color and improved handleability. The reference is unforthcoming about applications for these polyester fibers.
U.S. Pat. No. 6,544,644 (which corresponds to WO-A-01/02,629) describes monofilaments useful, inter alia, in papermaking machines. The description part refers mainly to polyamide monofilaments; polyester raw materials are also mentioned in very general terms. The monofilaments described are characterized by the presence of nanoscale inorganic materials. These provide enhanced resistance to abrasion. Platelets are described as well as spherical particles. The non-spherical particles described are nanoclays, i.e., layered particles. These can be treated with swelling agents, such as phosphonium or ammonium compounds, so that the layered assemblies wholly or partly dissolve to form particles less than 10 nm thick in one dimension. In the case of platelet-shaped particles, this reference thus mentions either the use of layered particles whose layered structure has only incompletely dissolved, if at all, so that aggregates below 100 nm in thickness are present, or whose layered structure has completely dissolved, in which case particles having thicknesses below 10 nm are present. Exfoliated montmorillonites are mentioned in this reference as one example of these platelets.
The use of layer-shaped and platelet-shaped nanoparticles, so-called nanoclays, in polyester spinning dopes has shown that in general, there are problems with the spinning. Either the spinning dopes cannot be processed at all, or special measures have to be taken if a fiber is to be produced at all. If, on the other hand, nanoparticles lacking sufficient thickness are used, it has been determined that the fibers formed do not have satisfactory textile-technological properties. It is believed that the high fraction of interfaces due to these very small particles in the polymer has a disruptive effect on the drawing stage, so that polymer chains are insufficiently aligned after the drawing operation. This has an adverse effect on the mechanical properties, for example the strength, of the fiber.
The use of nanoscale fillers can lead to fibers having improved mechanical properties. In general, however, the addition of fillers leads not only to the desired improvement in some properties but at the same time also to a deterioration in others.
It has now been found that, surprisingly, selected polyester raw materials comprising certain nanoscale fillers possess distinctly improved abrasion resistance compared with unmodified polyester raw materials without their dynamic fatigue resistance, expressed by the bending fatigue resistance, being significantly reduced by the use of a filler; in fact, it may even be increased. This performance profile was observed on selected polyester raw materials.
Proceeding from this prior art, the present invention has for its object to provide filled polyester fibers which, as well as excellent abrasion resistance, possess dynamic fatigue resistances which are equivalent to or even superior than those of unfilled polyester fibers.
The present invention further has for its object to provide transparent fibers having high abrasion resistance and excellent dynamic fatigue resistance.

SUMMARY OF INVENTION

This invention provides fibers comprising aliphatic-aromatic polyester and non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1.

DETAILED DESCRIPTION

The invention is described in detail below with reference to several embodiments and numerous examples. Such discussion is for purposes of illustration only. Modifications to particular examples within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to one of skill in the art. Terminology used herein is given its ordinary meaning consistent with the exemplary definitions set forth immediately below.
Thickness, as used herein, refers to the smallest extension of the particle along one of its main axes of inertia.
Aspect ratio, as used herein, is the quotient along the largest extension of the particle along one of the main axes of inertia to the smallest extension of the particle along one of the main axes of inertia; that is, the aspect ratio is the quotient formed from the largest length of the particle (along one of the main axes of inertia) to the thickness of the particle.
Preference is given to polyester fibers having a free carboxyl group content of not more than 3 meq/kg.
These polyester fibers comprise an agent to cap free carboxyl groups, for example a carbodiimide and/or an epoxy compound.
Polyester fibers thus endowed are stabilized to hydrolytic degradation and are particularly suitable for use in hot moist environments, especially in papermaking machines or as filters.
Any fiber-forming polyester can be used as long as it comprises aliphatic and aromatic groups and is formable in the melt. Aliphatic groups are herein also to be understood as meaning cycloaliphatic groups.
These thermoplastic polyesters are known per se. Examples thereof are polybutylene terephthalate, polycyclohexanedimethyl terephthalate, polyethylene naphthalate or especially polyethylene terephthalate. Building blocks of fiber-forming polyesters are preferably diols and dicarboxylic acids or appropriately constructed oxyl carboxylic acids. The main acid constituent of polyesters is terephthalic acid or cyclohexanedicarboxylic acid, but other aromatic and/or aliphatic or cycloaliphatic dicarboxylic acids may be suitable as well, preferably para- or trans-disposed aromatic compounds, for example 2,6-naphthalenedicarboxylic acid or 4,4′-biphenyldicarboxylic acid, and also isophthalic acid. Aliphatic dicarboxylic acids, such as adipic acid or sebacic acid for example, are preferably used in combination with aromatic dicarboxylic acids.
Useful dihydric alcohols typically include aliphatic and/or cycloaliphatic diols, for example ethylene glycol, propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol or mixtures thereof. Preference is given to aliphatic diols which have two to four carbon atoms, especially ethylene glycol; preference is further given to cycloaliphatic diols, such as 1,4-cyclohexanedimethanol.
Preference is given to using polyesters comprising structural repeat units derived from an aromatic dicarboxylic acid and an aliphatic and/or cycloaliphatic diol.
Preferred thermoplastic polyesters are especially selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexanedimethanol terephthalate, or a copolycondensate comprising polybutylene glycol, terephthalic acid and naphthalenedicarboxylic acid units.
The polyesters used according to the present invention typically have solution viscosities (IV values) of not less than 0.60 dl/g, preferably of 0.60 to 1.05 dl/g and more preferably of 0.62-0.93 dl/g (measured at 25° C. in dichloroacetic acid (DCE)).
The nanoscale fillers used according to the present invention endow polyester fibers with excellent abrasion resistance without adversely affecting the dynamic properties, expressed by the bending fatigue resistance.
The fillers used according to the present invention are specific non-layered platelet-shaped particles. These are selected from the group consisting of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides.
A further characteristic property of these fillers is their shape. The particles are not spherical but platelet shaped. Their thickness is not more than 100 nm, preferably not more than 80 nm and in particular in the range from 20 to 60 nm. A further characteristic property of these fillers is their aspect ratio, i.e., the ratio of the largest extension of the particle on one of the main axes of inertia to the smallest extension of the particle along one of the main axes of inertia. The aspect ratio is not more than 20:1. Layered fillers, such as phyllosilicates (so-called nanoclays), montmorillonites for example, are not wanted in this invention, since their use not only disrupts the processing of the fibers but also did not lead to any significant improvement in properties being observed.
Typically, the nanoscale non-spherical oxides used according to the present invention are oxides of metals of group IIa of the periodic table, preferably oxides of magnesium, of calcium or of strontium, or oxides of metals of group IIIb of the periodic table, preferably oxides of aluminum, of gallium or of indium, or oxides of metals of group IVa of the periodic table, preferably oxides of titanium, of zirconium or of hafnium, or oxides of metals of group IIIa of the periodic table, preferably oxides of scandium or of yttrium or oxides of metals or semimetals of group IVb of the periodic table, preferably oxides of silicon, of germanium or of tin.
Instead of oxides, the corresponding hydroxides can also be used, or else mixed crystals formed from different metal oxides, for example Al₂O₃*2SiO₂(mullite).
Typically, the nanoscale non-spherical carbonates used according to the present invention are carbonates of metals of group IIa of the periodic table, preferably carbonates of magnesium, of calcium or of strontium.
Typically, the nanoscale non-spherical carbides used according to the present invention are carbides of metals of group IIIb of the periodic table, preferably carbides of aluminum, of gallium or of indium, or carbides of metals or semimetals of group IVb of the periodic table, preferably carbides of silicon, of germanium or of tin.
Typically, the nanoscale non-spherical nitrides used according to the present invention are nitrides of metals of group IIIb of the periodic table, preferably nitrides of aluminum, of gallium or of indium, or nitrides of metals or semimetals of group IVb of the periodic table, preferably nitrides of silicon, of germanium or of tin.
Particular preference is given to using nanoscale non-spherical aluminum oxide, aluminum nitride, silicon dioxide, zirconium dioxide, silicon carbide, silicon nitride, yttrium oxide or calcium carbonate.
Very particular preference is given to using nanoscale non-spherical aluminum oxide or calcium carbonate.
The polyester raw materials filled and needed to produce the fibers of the present invention can be produced in various ways. For instance, polyester and filler, and also if appropriate further additives, can be mixed in a mixing assembly, for example in an extruder, by melting the polyester, and the composition is then fed directly to the spinneret die or the composition is granulated and spun in a separate step. The pellet obtained may, if appropriate, also be spun as a masterbatch together with additional polyester. It is also possible to add the nanoscale fillers before or during the polycondensation of the polyester.
Suitable nanoscale non-spherical fillers are commercially obtainable. For example, the DP 6096 product (calcium carbonate in ethylene glycol) from Nano Technologies, Inc., Ashland, Mass., USA can be used.
The level of nanoscale non-spherical filler in the fiber of the present invention can vary within wide limits, but is typically not more than 5% by weight, based on the mass of the fiber. The level of nanoscale spherical filler is preferably in the range from 0.1% to 2.5% by weight and in particular in the range from 0.5% to 2.0% by weight.
The identities and amounts of the components a) and b) are preferably chosen so that transparent products are obtained. Unlike polyamides, the polyesters used according to the present invention are notable for transparency. It has been determined that, surprisingly, the nanoscale non-spherical fillers have no adverse effect on transparency. By contrast, the addition of just about 0.3% by weight of non-nanoscale titanium dioxide (delusterant) causes the fiber to turn completely white.
It has further been determined that, surprisingly, the abrasion resistance of the fibers according to the present invention can be still further enhanced by the addition of polycarbonate. The amount of polycarbonate is typically up to 5% by weight, preferably in the range from 0.1% to 5.0% by weight and more preferably in the range from 0.5% to 2.0% by weight, based on the total mass of the polymers.
Fibers are in the context of this description to be understood as meaning any desired fibers.
Examples thereof are filaments or staple fibers which consist of a plurality of individual fibers, but are monofilaments in particular.
The polyester fibers of the present invention can be produced by conventional processes.
The present invention also provides a process for producing the above-defined fibers, the process comprising the measures of:

- i) mixing polyester pellet with non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1,
- ii) extruding the mixture comprising polyester and non-layered platelet-shaped particles through a spinneret die,
- iii) withdrawing the resulting filament, and
- iv) optionally drawing and/or relaxing the resulting filament.
  The present invention also provides a process for producing the above-defined fibers, the process comprising the measures of:
- i) feeding an extruder with polyester pellet mixed before or during the polycondensation with polyester pellet with non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1,
- ii) extruding the mixture comprising polyester and non-layered and platelet-shaped particles through a spinneret die,
- iii) withdrawing the resulting filament, and
- iv) optionally drawing and/or relaxing the resulting filament.

Preferably, the polyester fibers of the present invention are subjected to single or multiple drawing in the course of their process of production.
It is particularly preferable to produce the polyester fibers using a polyester produced by solid state condensation.
The polyester fibers of the present invention can be present in any desired form, for example as multifilaments, as staple fibers or especially as monofilaments.
The linear density of the polyester fibers according to the present invention can likewise vary within wide limits. Examples thereof are 100 to 45 000 dtex and especially 400 to 7000 dtex.
Particular preference is given to monofilaments whose cross-sectional shape is round, oval or n-gonal, where n is not less than 3.
The polyester fibers according to the present invention can be produced using a commercially available polyester raw material. A commercially available polyester raw material will typically have a free carboxyl group content in the range from 15 to 50 meq/kg of polyester. Preference is given to using polyester raw materials produced by solid state condensation; their free carboxyl group content is typically in the range from 5 to 20 meq/kg and preferably less than 8 meq/kg of polyester.
However, the polyester fibers of the present invention can also be produced using a polyester raw material which already comprises the nanoscale non-layered platelet-shaped filler. The polyester raw material is produced by adding the filler during the polycondensation and/or to at least one of the monomers.
After the polyester melt has been forced through a spinneret die, the hot strand of polymer is quenched, for example in a quench bath, preferably in a water bath, and subsequently wound up or taken off. The takeoff speed is greater than the ejection speed of the polymer melt.
The polyester fiber thus produced is subsequently preferably subjected to an afterdrawing operation, more preferably in a plurality of stages, especially to a two- or three-stage afterdrawing operation, to an overall draw ratio in the range from 3:1 to 8:1 and preferably in the range from 4:1 to 6:1.
Drawing is preferably followed by heat setting, for which temperatures in the range from 130 to 280° C. are employed; length is maintained constant, slight after-drawing is effected or shrinkage of up to 30% is allowed.
It has been determined to be particularly advantageous for the production of the polyester fibers of the present invention to operate at a melt temperature in the range from 285 to 315° C. and at a jet stretch ratio in the range from 2:1 to 6:1.
The takeoff speed is customarily 10-80 m per minute.
The polyester fibers of the present invention, as well as nanoscale non-layered platelet-shaped filler, may comprise further auxiliary materials.
Besides the hydrolysis stabilizer already mentioned, examples of further auxiliaries are processing aids, antioxidants, plasticizers, lubricants, pigments, delusterants, viscosity modifiers or crystallization accelerants.
Examples of processing aids are siloxanes, waxes or long-chain carboxylic acids or their salts, aliphatic, aromatic esters or ethers.
Examples of antioxidants are phosphorus compounds, such as phosphoric esters, or sterically hindered phenols.
Examples of pigments or delusterants are organic dye pigments or titanium dioxide.
Examples of viscosity modifiers are polybasic carboxylic acids and their esters or polyhydric alcohols.
The fibers of the present invention can be used in all industrial fields. They are preferably employed for applications where increased wear due to mechanical stress is likely. Examples thereof are the use in screens or conveyor belts. These uses likewise form part of the subject matter of the present invention.
The polyester fibers of the present invention are preferably used for producing sheetlike structures, in particular woven fabrics used in screens.
A further use for the polyester fibers of the present invention in the form of monofilaments concerns their use as conveyor belts or as components of conveyor belts.
Particular preference is given to uses for the fibers of the present invention in screens which are wire screens and intended for use in the dry end of papermaking machines.
These uses likewise form part of the subject matter of the present invention.
The present invention further provides for the use of non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness not more than 100 nm and an aspect ratio of not more than 20:1, for producing fibers, especially monofilaments, having high abrasion resistance.
The examples which follow illustrate the invention without limiting the invention in any way.

GENERAL OPERATING METHOD FOR INVENTIVE EXAMPLE 1

Polyethylene terephthalate (PET) and if appropriate hydrolysis stabilizer were mixed in an extruder, melted and spun through a 20 hole spinneret die having a hole diameter of 1.0 mm at a feed rate of 488 g/min and a takeoff speed of 31 m/min to form monofilaments, triply drawn to draw ratios of 4.95:1, 1.13:1 and 0.79:1 and also heat-set in a hot air duct at 255° C. with shrinkage being allowed. The overall draw ratio was 4.52:1. Monofilaments having a diameter of 0.25 mm were obtained.
The PET used was a type having an IV value of 0.72 dl/g, to which 0.04% by weight of nanoscale Al₂O₃of 50 nm had been added.
The hydrolysis stabilizer used was a carbodiimide (Stabaxol® 1, from Rheinchemie).

GENERAL OPERATING METHOD FOR COMPARATIVE EXAMPLES 1 AND 2

Monofilaments were produced as described in the operating method for Inventive Example 1. Different PET raw materials were used but no nanoscale fillers. A type having IV value of 0.72 dl/g was used in Comparative Example 1 and a type having IV value of 0.9 dl/g in Comparative Example 2.
Fiber properties were determined as follows:

- Tensile strength to DIN EN/ISO 2062
- Breaking extension to DIN EN/ISO 2062
- Hot air shrinkage to DIN 53843

Squirrel cage test: conducted using a rotatable metallic abrader having metal bars mounted on a drum rotating at a constant speed of rotation. The monofil was mounted on this abrader using a constant pretension. The number of rotations to filament breakage is measured.
The table which follows summarizes the properties of the monofilaments.

Hot air

Fiber Tensile Breaking shrinkage Squirrel

Example diameter strength extension at 200° C. cage test

No. [mm] [cN/tex] (%) (%) (cycles)

Inv. 1 0.25 31.5 37.8 10.8 7503

Comp. 1 0.254 31.2 37.2 11.0 1249

Comp. 2 0.25 33.3 41.0 4.4 7342
While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references including co-pending applications discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference, further description is deemed unnecessary.

Claims

1. A fiber comprising aliphatic-aromatic polyester and non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1.

2. The fiber according to claim 1 wherein the polyester comprises structural repeat units derived from an aromatic dicarboxylic acid and an aliphatic and/or cycloaliphatic diol, especially polyethylene terephthalate repeat units alone or combined with other structural repeat units derived from alkylene glycols and aliphatic dicarboxylic acids.

3. The fiber according to claim 1 wherein the aliphatic-aromatic polyester has a free carboxyl group content of not more than 3 meq/kg.

4. The fiber according to claim 3 comprising a hydrolysis stabilizer for blocking free carboxyl groups, preferably at least one carbodiimide and/or at least one epoxy compound.

5. The fiber according to claim 1 wherein the non-layered platelet-shaped particles are not more than 80 nm and in particular from 20 to 60 nm in thickness.

6. The fiber according to claim 1 wherein the non-layered platelet-shaped particles are oxides of magnesium, of calcium, of strontium, of aluminum, of gallium, of indium, of titanium, of zirconium, of hafnium, of scandium, of yttrium, of silicon, of germanium, of tin or mixed oxides of these metals or semimetals.

7. The fiber according to claim 1 wherein the non-layered platelet-shaped particles are carbonates of magnesium, of calcium or of strontium.

8. The fiber according to claim 1 wherein the non-layered platelet-shaped particles are carbides of aluminum, of gallium, of indium, of silicon, of germanium or of tin.

9. The fiber according to claim 1 wherein the non-layered platelet-shaped particles are nitrides of aluminum, of gallium, of indium, of silicon, of germanium or of tin.

10. The fiber according to claim 1 wherein the non-layered platelet-shaped particles are selected from the group consisting of aluminum oxide, aluminum nitride, silicon dioxide, zirconium dioxide, silicon carbide, silicon nitride, yttrium oxide or calcium carbonate.

11. The fiber according to claim 10 wherein the non-layered platelet-shaped particles are selected from the group consisting of aluminum oxide or calcium carbonate.

12. The fiber according to claim 1 whose content of non-layered platelet-shaped particles is in the range from 0.1% to 5% by weight and preferably in the range from 1% to 2% by weight, based on the mass of the fiber.

13. The fiber according to claim 1 which, as well as the aliphatic-aromatic polyester, comprises from 0.1% to 5% by weight and preferably from 0.5% to 2% by weight, based on the total mass of the polymers, of polycarbonate.

14. The fiber according to claim 1 which is transparent.

15. The fiber according to claim 1 which is a monofilament.

16. The fiber according to claim 1 incorporated into a screen or conveyor belt.

17. The fiber according to claim 1 incorporated into a wire screen intended for use in the dry end of papermaking machines.

18. A process for producing the fibers according to claim 1, the process comprising the steps of:

i) mixing polyester pellet with non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1,

ii) extruding the mixture comprising polyester and non-layered platelet-shaped particles through a spinneret die,

iii) withdrawing the resulting filament, and

iv) optionally drawing and/or relaxing the resulting filament.

19. The process according to claim 18 wherein the polyester fiber is subjected to single or multiple drawing.

20. The process according to claim 18 wherein the polyester fiber is produced using a polyester produced by solid state condensation.

21. A process for producing the fibers according to claim 1, the process comprising the steps of:

i) feeding an extruder with polyester pellet mixed before or during the polycondensation with polyester pellet with non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1,

iii) withdrawing the resulting filament, and

iv) optionally drawing and/or relaxing the resulting filament.

22. In a process for making polyester monofilament, the improvement comprising providing high abrasion resistance by incorporating a non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1.