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Polyester fibers, their production and their useRelated Patent Categories: Stock Material Or Miscellaneous Articles, Coated Or Structually Defined Flake, Particle, Cell, Strand, Strand Portion, Rod, Filament, Macroscopic Fiber Or Mass Thereof, Rod, Strand, Filament Or Fiber, Coated Or With Bond, Impregnation Or CorePolyester fibers, their production and their use description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070014989, Polyester fibers, their production and their use. Brief Patent Description - Full Patent Description - Patent Application Claims
CLAIM FOR PRIORITY [0001] 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 [0002] 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 [0003] 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. [0004] 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. [0005] 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. [0006] 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. [0007] 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. [0008] Adding fillers to improve the mechanical properties of fibers is known per se. [0009] 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. [0010] 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 .mu.m 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. [0011] 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. [0012] 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. [0013] 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. [0014] 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. [0015] 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. [0016] The present invention further has for its object to provide transparent fibers having high abrasion resistance and excellent dynamic fatigue resistance. SUMMARY OF INVENTION [0017] 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 [0018] 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. [0019] Thickness, as used herein, refers to the smallest extension of the particle along one of its main axes of inertia. 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