Stretched Fluoropolymer

Abstract

The present invention relates to a method for preparing a drawn filament containing at least 80% by weight of a fluoropolymer, the filament having a rectangular cross section with a thickness greater than the width. The raw filament is drawn at a temperature between 70° C. and the Vicat temperature with a draw factor greater than or equal to 3, wherein the drawn filament is cooled to less than 50° C. under full draw load and does not contain a perfluorinated polymer.

Description

[0001] The present invention relates to drawn filaments based on non-perfluorinated fluoropolymers, wherein the filaments are drawn at a temperature between 70°C and the Vicat temperature, and wherein the filaments are cooled to room temperature under full draw load.

[0002] Fiber-reinforced materials are usually based on the use of glass or carbon fibers in polymers. This creates the fundamental problem of compatibility of the fibers with the matrix material and, therefore, the problem of achieving adhesion between the reinforcement and the matrix. This is often a particular problem when thermoplastics are used as the matrix. Furthermore, these materials are not recyclable because it is difficult to remove the fibers.

[0003] The main disclosures in the prior art relate to two methods for stretching polyolefins, such as polyethylene or polypropylene: the melt spinning method (WO 2004 / 028803 A1) and the gel spinning method (WO 2010 / 057982 A1). Polyolefins are easy to stretch at room temperature; due to the exothermic nature of the stretching, the stretching speed chosen here must be relatively low. Stretched polyolefins have the disadvantage that they exhibit very high shrinkage after stretching when processed at elevated temperatures and therefore first have to be balanced at the desired operating temperature. In addition, the mechanical properties of stretched polyolefins are very limited, which limits their use as reinforcing fibers. Particular disadvantages are the lack of thermal stability and the lack of compressive strength (cold formability).

[0004] Omar (Master's thesis: "Processing, morphology and product parameters of PVDF filaments for biomedical applications", August 2008, Institut für Textiltechnik RWTH Aachen, Prof. Dr. Thomas Gries) discloses a stretching procedure applied to PVDF fibers for the production of yarns and textiles; these are stretched up to 2.5 times.

[0005] DE 60024882 T2 discloses a two-stage stretching method for PVDF fibers used to prepare fishing lines. In order to achieve the desired mechanical properties, the fibers are subjected to controlled shrinkage at a temperature of at least 220° C. for a few seconds.

[0006] WO 2013 / 190149 A1 discloses ductile fibers of various thermoplastics, preferably polypropylene and polyethylene, as components known as prepregs. These are understood to be braids of thermoplastic fibers and brittle fibers, in particular carbon fibers. These materials are then preferably pressed or thermoformed in a matrix made of ductile fiber material. This melts the ductile fibers and improves the bonding between the matrix and the brittle fibers.

[0007] The preparation of wholly aromatic polyamide fibers is described in US Pat. No. 3,869,430 A, for example with the trademark (Trademark of DuPont, USA), Poly(terephthalamide) (PPTA, aramid) (trademark of Teijin Lim of Japan).

[0008] EP 0091766 A2 and DE 2304429 A1 describe procedures for stretching perfluoropolymers. The stretching factors obtained in these cases are at most 4.5; attempts to achieve greater stretching lead to fiber breakage. It seems that the stretching procedure improves the mechanical properties of the perfluorinated polymers only to a very limited extent: the elastic modulus after stretching is at most 1228 MPa.

[0009] For the purposes of the present invention, the term "filament" refers to a fiber, film, or tape.

[0010] The film is particularly preferably stretched in more than one direction.

[0011] The term "stretching" refers to a stretching process performed after extrusion by using thermal and mechanical energy.

[0012] It is therefore an object of the present invention to prepare drawn filaments made of fluoropolymers and to provide a simple, non-hazardous and solvent-free process for drawing fluoropolymers.

[0013] This object is achieved by drawn filaments made of non-perfluorinated fluoropolymers, wherein the drawn filaments are cooled under full drawing load.

[0014] The present invention provides a method for preparing a drawn filament comprising at least 80% by weight, preferably 85% by weight, more preferably 90% by weight, still more preferably 95% by weight of a fluoropolymer, in particular consisting of a fluoropolymer, characterized in that

[0015] The filament has a rectangular cross-section with a thickness less than its width,

[0016] wherein the original filaments are stretched with a stretch factor (SF) greater than or equal to 3 at a temperature between 70° C. and the Vicat temperature, the Vicat temperature being determined according to DIN EN ISO 306:2004-10B50,

[0017] wherein the filaments are cooled to below 50° C. under full tensile load,

[0018] No perfluorinated polymers are present.

[0019] The present invention also provides drawn filaments prepared by the process of the present invention.

[0020] The present invention also provides use of the drawn filaments of the present invention for preparing a composite material.

[0021] The present invention also provides the use of the drawn filaments of the present invention for preparing a winding layer.

[0022] One advantage of the drawn filaments of the present invention is that they shrink very little at elevated temperatures, ie they exhibit very little relaxation effect.

[0023] It is also advantageous that the drawn filaments of the invention have a high mechanical stability. The mechanical stability is preferably measured as the breaking stress in the direction of drawing.

[0024] It is also advantageous that the drawn filaments of the present invention have surprising elasticity at relatively high draw factors.

[0025] It is also advantageous that the drawn filaments of the invention have a high mechanical stability, also at elevated temperatures.

[0026] The drawn filaments of the present invention, the composite materials of the present invention comprising the filaments of the present invention, and the preparation and use according to the present invention are described by the following examples, but it is not intended that the present invention is limited to these exemplary embodiments. When referring to ranges, general formulas or compound classes, these include not only the corresponding ranges or compound groups explicitly mentioned, but also all sub-ranges and compound sub-groups that can be obtained by extracting a single value (range) or a compound. If a document is cited for the purpose of this specification, its entire content should be part of the disclosure of the present invention. If percentage data are provided below, unless otherwise stated, these data are all data expressed in weight %. Unless otherwise stated, the percentage data of the composition are based on the entire composition. Unless otherwise stated, the average values ​​provided below are all mass average values ​​(weight average values). When measured values ​​are provided below, unless otherwise stated, these measured values ​​are measured at a pressure of 101325Pa and a temperature of 25°C.

[0027] The scope of protection includes the finished and packaged forms usually used in business for the product of the invention, not only per se, but also possible comminuted forms not defined in the claims.

[0028] The fluoropolymer can be selected from polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-perfluoroalkyl vinyl ether-tetrafluoroethylene copolymer (CPT), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ETFE modified by a third component (tercomponent) such as propylene, hexafluoropropylene, vinyl fluoride or vinylidene fluoride (for example EFEP); in addition, there are copolymers based on vinylidene fluoride, which contain up to 40% by weight of other monomers, such as trifluoroethylene, chlorotrifluoroethylene, ethylene, propylene and hexafluoropropylene.

[0029] The fluoropolymer of the filament of the present invention is not a perfluorinated polymer. The fluoropolymer preferably has hydrogen and fluorine together as substituents on carbon; more preferably, the carbon atoms of the skeleton, i.e. the carbon atoms forming the polymer chain, show a certain degree of hydrogen substitution. More preferably, at least 5mol%, preferably at least 10mol%, 20mol%, 30mol% or 40mol%, and in particular 50mol% of the carbon atoms of the fluoropolymer are substituted by hydrogen; the corresponding upper limit is preferably 90mol%, 80mol%, 70mol%, 60mol%, in particular 50mol%. These content data are particularly preferably based on the carbon atoms of the fluoropolymer skeleton.

[0030] Preferably, the fluoropolymer of the filament of the present invention exhibits branching only at no more than 25% of the backbone carbon atoms; branching occurs when a carbon-carbon bond exists between a backbone carbon atom and another carbon atom. More preferably, the fluoropolymer has branching at no more than 20%, 15%, 10% or 5% of the backbone carbon atoms, and particularly preferably has no branching at the backbone carbon atoms.

[0031] It is further preferred that the fluoropolymer of the filament of the invention contains no ether groups.

[0032] The fluorine-containing polymer of the filament of the present invention is preferably selected from polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (E-CTFE), polychlorotrifluoroethylene (PCTFE), ETFE modified by a third component (such as propylene) or ETFE modified by vinylidene fluoride; in addition, there are copolymers based on vinylidene fluoride, which contain up to 40% by weight of other monomers. PVDF is particularly preferred.

[0033] Preferably, the fluoropolymer is free of solvent.

[0034] The Vicat temperature of the fluoropolymer of the filament of the present invention is preferably at least 80°C, more preferably at least 90°C, still more preferably at least 110°C, particularly preferably at least 125°C, particularly preferably at least 140°C.

[0035] The Vicat temperature is known to the person skilled in the art and is preferably determined in accordance with DIN EN ISO 306:2004-10, B50. The required temperature tolerance is in each case ±5° C.; thus, for a value of 140° C., values ​​of 135° C. to 145° C. are included.

[0036] The width to thickness ratio of the filaments of the present invention is preferably at least 25:1, more preferably at least 50:1, still more preferably at least 100:1, particularly preferably at least 200:1, more particularly preferably at least 300:1, and particularly preferably at least 400:1.

[0037] The stretching temperature is preferably from 70°C to the Vicat temperature [°C], more preferably from 85°C to 5% lower than the Vicat temperature [°C], and particularly preferably from 100°C to 10% lower than the Vicat temperature [°C].

[0038] The filaments of the present invention are prepared by stretching raw filaments at a stretch factor (SF) of preferably greater than or equal to 3, more preferably greater than or equal to 5, and particularly preferably greater than or equal to 10, or more.

[0039] The skilled person is familiar with the determination of the stretch factor. Preferably, the determination is carried out by measuring the length of the original filament before stretching and the length of the filament after stretching. The factor is then calculated by dividing the length after stretching by the length before stretching. The stretch factor is expressed as a value of 1 or greater, or as a corresponding percentage value, wherein the value 1 corresponds to 100%.

[0040] Preferably, starting from a stretch factor of 3.0, the filaments of the invention have a high elasticity; the elasticity is preferably expressed as the modulus of elasticity.

[0041] More preferably, at a stretch factor of 3.0, the elastic modulus of the filaments of the invention has risen to less than twice the value of the unstretched input material, preferably less than 1.5 times said value.

[0042] The increase in the elastic modulus starting from a stretch factor (SF) of 3.0 is more preferably at most 150 MPa, particularly preferably at most 120 MPa, particularly preferably at most 100 MPa, per change in the stretch factor of 1.0.

[0043] In particular, for a stretch factor rising from 3 to 4, the elastic modulus rises by at most 150 MPa, by at most 120 MPa, very particularly by at most 100 MPa.

[0044] Preferably, the filaments of the invention have been stretched in free space, without contact. The area in which the stretching takes place is an area in which the ambient atmosphere is heated, thus, for example, a tube oven or the space between at least two heating plates.

[0045] The filaments of the present invention may be drawn continuously or batchwise.

[0046] Preferred is a static stretching procedure, ie a stretching procedure in which one end of the filament is held stationary, at a speed of 10 mm / min to 200 mm / min, preferably 20 mm / min to 100 mm / min, more preferably 30 mm / min to 80 mm / min.

[0047] The preferred continuous stretching procedure is carried out in a manner providing a low transport speed preferably ranging from 10 mm / min to 3000 mm / min, preferably from 50 mm / min to 2500 mm / min, more preferably from 100 mm / min to 2000 mm / min, even more preferably from 500 mm / min to 1500 mm / min. The speed of the faster running transport unit is calculated by the stretching factor.

[0048] The filaments of the present invention can be stretched by a single stretching procedure or multiple continuous stretching procedures. The latter case always requires the selection of a relatively high stretching temperature. A single stretching procedure is more preferred.

[0049] The filaments of the invention are cooled to below 50° C. after the drawing process. The cooling is preferably carried out slowly, preferably for at least 10 seconds, more preferably for at least 20 seconds, still more preferably for at least 30 seconds, particularly preferably for at least 45 seconds, particularly preferably for at least 1 minute.

[0050] When heated to a temperature below the melting point (relaxation temperature), the drawn filaments of the present invention preferably exhibit only slight shrinkage / relaxation in the direction of tension.

[0051] Preferably, the relaxation temperature is above 25°C and below the melting point, preferably below the stretching temperature.

[0052] The relaxation of the filaments of the present invention is preferably at most 6%, preferably at most 5.5%, more preferably at most 5%, still more preferably at most 4.5%, particularly preferably at most 4%, based on the stretched length.

[0053] Preferably, the filaments of the present invention do not relax under tensile stress.

[0054] Preferably, the length of the stretched filaments of the invention is greater than 5 times the dimension at right angles to the length; preferably, the filaments are so-called continuous filaments. The length of the filaments is always measured in the direction of tension.

[0055] For the purposes of the present invention, the term "filament" refers to a fiber, film, or tape.

[0056] The film is particularly preferably stretched in more than one direction.

[0057] Preferably, the filaments do not have a circular cross-section.

[0058] Single filaments may be used to make composite materials; therefore, preferred composite materials for the belt are laid scrim, woven fabrics such as mats, and hybrid forms.

[0059] The mesh may consist of filaments cut to specific lengths, or of continuous filaments in wound form around, for example, a tube.

[0060] A preferred mesh made of the continuous filaments of the invention is a winding layer around a hollow body, the filaments here preferably being tapes. The winding is preferably unidirectional or multidirectional. The multidirectional winding layer is at an angle relative to the tension direction of the filaments. The angle is preferably in the range of 5° to 120°, more preferably in the range of 30° to 90°, particularly preferably in the range of 15° to 80°. In the case of winding layers around a tube, these winding layers exhibit an inclination relative to the center of the tube. Preferably, different winding layers exhibit different inclinations. The inclination of the winding layer around the tube is preferably designed so that after one rotation, the edges of the layers are flush and abut each other.

[0061] Preferably, no yarn is produced using filaments, wherein the yarn is preferably produced from a plurality of individual filaments by braiding (e.g. plaits and cords) or twisting (e.g. cables); in particular no yarn is produced using filaments having a circular cross section. Example

[0062] Material:

[0063] PVDF: 1006, a trademark of Solvay in the United States

[0064] PVDF: 6008, a trademark of Solvay of the United States

[0065] FEP: NP-20, a trademark of Daikin Industries of Japan.

[0066] method

[0067] DSC:

[0068] Perkin Elmer Diamond, automatic peak identification and integration by method based on DIN EN ISO 11357-1:2010, heating rate 20 K / min.

[0069] Vicat temperature:

[0070] DIN EN ISO 306:2004-10, method B, 50N (load 5kg).

[0071] Example 1a, preparation of sample:

[0072] PVDF (Solef 1006) was extruded using an extruder (Collin E45M) at 260°C, calendered to obtain a tape having a thickness of 650 μm and a width of 35 mm, and cooled to 57°C.

[0073] The take-off speed is 1.4 m / min.

[0074] E 1, * is a sample made of PVDF Solef 1006;

[0075] E 2, * is a sample made of FEP.

[0076] Example 1b, preparation of sample:

[0077] PVDF (Solef 6008) was extruded at 240° C. using an extruder (Collin CE20), calendered to obtain a tape having a thickness of 150 μm and a width of 120 mm, and cooled to 89° C. The take-off speed was 2.1 m / min.

[0078] E 3, * is the sample of Example 1b.

[0079] Example 2, tensile test specimen:

[0080] Method 1:

[0081] The test specimen according to Example 1a was stretched in a tensile testing machine (Zwick, Z101-K) at 10 mm / min at 140° C. Before releasing the tensile load, the test specimen was cooled to below 50° C.

[0082] Method 2:

[0083] Endless specimens according to Example 1a were provided on reels and stretched on a continuously running machine (Retech drawing machine) at a material feed rate of 4 rpm and a tension rate not exceeding 32 rpm to obtain a stretch factor (SF) of 8. The stretching temperature was 140°C.

[0084] Method 3:

[0085] The specimens according to Example 1a were stretched at 10 mm / min in a tensile testing machine (Zwick, Z101-K) at 100° C., 120° C. and 140° C. Before releasing the tensile load, the specimens were cooled to below 50° C. The tensile specimens produced in this way were clamped again in the machine and stretched again at a speed of 10 mm / min at 100° C., 120° C. and 140° C.

[0086] Table 2 lists the results.

[0087] Method 4:

[0088] Endless specimens according to Example 1b were provided on reels and stretched on a continuously operating machine (Retech wire drawing machine) at a material feed rate of 1.5 m / min and a variable tension rate to achieve different stretch factors (SF). The stretching temperature was 120°C.

[0089] Table 3 gives the results.

[0090] Method 5:

[0091] Endless specimens according to method 4 (stretched at SF=6) were provided on reels and stretched on a continuously running machine (Retech wire drawing machine) at a feed rate of 1.5 m / min and variable tension rate to obtain different stretch factors (SF). The stretching temperature was 120°C.

[0092] Table 4 gives the results.

[0093] Example 3a, mechanical testing:

[0094] Tensile test

[0095] Dumbbell specimens (specimen type 1BA) according to DIN 527-2:2012 were punched out of the stretched (method 1) strips; the tensile test resulted in no change in thickness.

[0096] The tensile strength was tested using a test device from Zwick at a temperature of 23° C. and a relative humidity of 50%. Test speed=10 mm / min, clamping length=120 mm, measurement length of incremental gauge=75 mm.

[0097] The results are shown in Table 1 and Figures 1 and 2.

[0098] The result is the arithmetic mean of 3 samples.

[0099] Example 3b, mechanical test:

[0100] Tensile test

[0101] The tensile strength according to DIN 527-2:2012 was measured from the stretched (methods 4 and 5) tapes; the thickness resulting from the tensile test was not changed.

[0102] The tensile strength was tested using a test device from Zwick at a temperature of 23° C. and a relative humidity of 50%. Test speed = 60 mm / min, clamping length = 100 mm.

[0103] The results are shown in Table 4.

[0104] The result is the arithmetic mean of 3 samples.

[0105] Table 1: Results of the tensile test according to Example 3a at T = 23°C

[0106]

[0107] Table 2: Results of tensile tests performed according to Example 2, Method 3

[0108]

[0109] Table 3: Results of tensile tests according to Example 2, Method 4

[0110]

[0111] Table 5: Results of tensile tests according to Example 2, Method 5

[0112]

[0113] Table 4: Results of tensile tests according to Example 3b

[0114]

Claims

1. A method for preparing a drawn filament comprising at least 85% by weight of a fluoropolymer, characterized in that The drawn filament has a rectangular cross-section with a thickness less than a width, wherein the original filament is stretched with a stretching factor greater than or equal to 5 at a temperature between 70° C. and the Vicat temperature, the Vicat temperature being determined according to DIN EN ISO 306:2004-10B50, The stretched filaments are cooled to below 50°C under full stretch load. There are no perfluorinated polymers present, The stretched filaments have a width to thickness ratio of at least 25, The fluorine-containing polymer is selected from polyvinylidene fluoride (PVDF) and a vinylidene fluoride-based copolymer containing up to 40% by weight of other monomers.

2. The process for preparing drawn filaments according to claim 1, wherein the Vicat temperature of the fluoropolymers is at least 80°C.

3. A drawn filament produced according to the method of claim 1 or 2, wherein the drawn filament has a width to thickness ratio of at least 25.

4. Use of the drawn filaments as claimed in claim 1 or 2 or the drawn filaments as claimed in claim 3 for preparing a composite material.

5. Use of the drawn filaments as claimed in claim 1 or 2 or the drawn filaments as claimed in claim 3 for producing a wrapping layer.

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