EP1413653B1 - Conductive, soil-resistant core-sheath fibre with high resistance to chemicals, its production process and use - Google Patents

Abstract

A hotmelt spun fiber has a core and a mantle structure having a combined tensile stregnth of at least 15 cN/tex. The core is a synthetic thermoplastic polymer which is not a fluoro-polymer. The mantle is a hotmelt spun fluoropolymer incorporating particles which are electrical conductors. The core is a synthetic thermoplastic polymer esp. polyester. e.g. polyethylenterephthalate or a liquid crystaline polyester. Also claimed is a hotmelt spinning process in which two compatible polymers are selected in which the melting point of the second polymer is at least 20C below that of the first, and in which the two polymers are co-extruded and stretched to achieve the desired tensile strength value.

Description

The present invention relates to conductive soil-repellent core-sheath fibers, in particular monofilaments, which can be used in particular in technical fabrics.

It is known that fluoropolymers have good thermal stability, good chemical resistance and dirt-repellent properties. It has already been attempted to process melt-spinnable fluoropolymers into fibers, multi- and monofilaments in order to produce textile surfaces for technical applications with the above-mentioned properties of fluoropolymers. A disadvantage of melt-spinnable fluoropolymers is the high creep behavior. Fibers and filaments of this material therefore have only low tensile strengths and are not dimensionally stable.

It has also been attempted to combine fluoropolymers with polymers having good mechanical performance properties, e.g. with polyethylene terephthalate (hereinafter also referred to as "PET"). However, it should be noted that fluoropolymers are often incompatible with other polymers and generally do not mix. Thus, a two-phase mixture often arises in which the fluoropolymers form spatial islands. The proportion by weight of fluoropolymer which can be metered in is thus frequently limited, since the boundary layers of the polymers adhere only poorly to one another. In fibers, this property is noticeable as a "splice tendency".

Monofilaments of PET and random copolymers of ethylene and tetrafluoroethylene ("ETFE") have been commercially available for years. Often point these fibers for hydrolysis stabilization have a low carboxyl end group content, and are stabilized to close the carboxyl end groups with carbodiimides. The closure of carboxyl groups by means of carbodiimides is for example in the EP-A-417.717 and EP-A-503.421 described.

Technical fabrics made from these monofilaments have largely the mechanical properties of a PET monofilament, but with increased resistance to hydrolysis and improved soil repellency. Temperature stability and chemical resistance of these fibers correspond substantially to the values of pure PET due to the relatively low proportion of fluoropolymers. However, the increased splice tendency may be noticeable under mechanical loads, e.g. at the Webriets plot.

However, synthetic polymer fibers and fabrics made therefrom have the disadvantage of being able to recharge with static electricity due to friction. Conductive fibers for the production of textile fabrics, such as fabrics for technical use, or for other purposes, e.g. for brushes, have always been the target of numerous developments.

From the DE-A-198 26 120 is a flame-retardant, electrically conductive fabric known which contains electrically conductive and flame-retardant electrically non-conductive fibers. The electrically conductive fibers may include electrically conductive particles such as carbon black or metal particles, metal coatings, or may be made of electrically conductive materials such as polyanilines. As fiber materials polyester and polyolefins are described.

From the DE-U-86 238 79 For example, yarns are known for making spiral tapes coated with a layer of thermosetting polymers. This layer contains electrically conductive carbon. As polymers for the cladding layer, melamine resins, epoxies, phenolic resins or polyurethanes are exemplified.

The DE-A-39 38 414 describes high-strength fabrics of synthetic fibers, which are woven in the form of electrically conductive fibers in warp and weft, and continue to contain electrically non-conductive fibers. The electrically conductive fibers consist of polyolefins and contain graphite or carbon black.

The EP-A-160.320 describes core-shell monofilaments for use in hairbrushes of selected polymers. The core contains nylon or polyester comprising at least 60% by weight of polybutylene terephthalate units. The jacket contains special types of nylon or copolyetherester.

From the DE-U-86/06334 Core sheath fibers are known, the core of thermoplastic material, preferably of polyamide, and their sheath of electrically conductive plastic, preferably of polyamide, which contains soot or metals embedded.

The JP-A-07 / 278.956 describes electrically conductive copolyesters containing mainly polybutylene terephthalate units doped with carbon black. It also describes core-sheath fibers of this material in which the core is made of aromatic polyester.

From the WO-A-98 / 14,647 electrically conductive heterofilaments are known, which may be configured, for example, as core-sheath fibers. As examples of core and sheath polymers, PET and other polyesters or PET / nylon are described.

The WO-A-01 / 20.076 discloses nonwovens with high dielectric constant. As fiber material mixtures of polyvinylidene fluoride and polypropylene are proposed. The resulting products are characterized by a prolonged half-life of electrostatic charges and can be used as electrostatic filters.

The US-A-6,085,061 describes a brush for cleaning electrostatically charged surfaces. As fiber materials core-sheath fibers can be used, the core of which is electrically conductive and whose sheath consists of polyvinylidene fluoride.

From the DE-A-44 12 396 For example, melt-spun undrawn, electrically nonconductive core-sheath fibers whose sheaths contain fluoropolymers are known. The core polymer used is polycarbonate. This fiber is used as an optical fiber and is not suitable because of the low strength for technical textiles, such as technical fabrics. In addition, in the case of an optical waveguide, high reflection at the boundary layer and the lowest possible attenuation of the electromagnetic wave are important. Both properties can only be achieved by using a high-purity coating.

In the JP-A-2001 to 127.218 For example, a semiconducting fiber of a carbon black-containing fluoropolymer will be described. This fiber has no core-shell structure and is used for the production of non-wovens, for example by the melt-blow process. The fiber is not stretched.

The prioritized, not pre-published WO-A-03/004738 describes core-sheath fibers of high strength and good chemical resistance. The sheath of the fibers contains a fluoropolymer. Combinations of PET as core material and PVDF as cladding material are described. This document also discloses in a general way the possibility of adding additives in core or shell. Possible additives include electrically conductive materials.

Based on this prior art, the present invention has the object to combine the performance advantages of the known materials for fiber production without having to accept the disadvantages associated with the use of the individual materials in purchasing.

It is known to the person skilled in the art that adhesion problems usually occur at the boundary layer of two polymers. In particular, this applies to the use of known poorly adhering fluoropolymers with other polymers. Surprisingly, it has been shown that when using one with electric Conductive particles doped fluoropolymers to achieve a very good adhesion with the polymer core.

Another object of the present invention is thus to provide core-sheath fibers with good adhesion between the individual layers.

The present invention thus provides fibers, in particular monofilaments, which combine antistatic properties with high chemical and chemical properties have thermal resistance and good mechanical dimensional stability and high tensile strength.

The invention relates to a melt spun fiber having a core-sheath structure and a tensile strength of at least 15 cN / tex, the core of which contains a melt-spinnable synthetic thermoplastic polymer having a first melting point which is not a fluoropolymer and whose sheath comprises at least one melt-spinnable fluoropolymer having a second melting point , which is at least 20 ° C below the first melting point, and contains particles of electrically conductive material, the amount of which is up to 50 wt.%, Based on the amount of the shell material.

The core thermoplastic synthetic polymers can be of any nature as long as they are melt-spun and impart the fiber with the properties desired for the particular application. Fluoropolymers are not included in the synthetic thermoplastic polymers, although the core may also contain fluoropolymers as the blending component in addition to these polymers.
Examples of synthetic thermoplastic materials are polyolefins such as polyethylene, polypropylene or copolymers containing ethylene and / or propylene units in conjunction with other alpha-olefin units copolymerized therewith, such as alpha-butylene, alpha-pentylene, alpha-hexylene or alpha-octylene; Polyesters such as polycarbonate, aliphatic / aromatic polyesters or wholly aromatic polyesters; Polyamides, such as aliphatic or aliphatic / aromatic polyamides (nylon types) or wholly aromatic polyamides (aramids); or polyether ketones, ie polymers which have at least ether and ketone groups and, as a rule, aromatic divalent radicals, such as phenylene, in the recurring chain, many combinations of these groups being possible, for example PEK, PEEK or PEKK; or polyarylene sulfides, preferably polyphenylene sulfide; or polyether esters, ie polymers which have at least ether and ester groups and, as a rule, aromatic divalent radicals, such as phenylene, in the recurring chain, for example TPE-E; or polyacrylonitrile or polyacrylonitrile copolymers with other ethylenically unsaturated comonomers such as acrylic or methacrylic acid.

Preferably, the core of the core-sheath fibers according to the invention contains polyamides and in particular polyesters.

The thermoplastic polyamides which are preferably used in the compositions according to the invention are known per se.

Examples of these are thread-forming polyamides, such as aliphatic or aliphatic / aromatic polyamides, e.g. Polycaprolactam, poly (hexamethylene-1,6-diaminadipamide), poly (hexamethylene-1,6-diamine-sebacic acid diamide), poly (hexamethylene-1,6-diamine-terephthalic acid diamide) or poly (hexamethylene) -1,6-diamine isopthalsäurediamid); or completely aromatic polyamides, such as poly (phenylene-1,4-diamine-terephthalic acid diamide) or poly (phenylene-1,4-diaminisophthalic acid diamide).

The polyamides used according to the invention usually have viscosity numbers according to DIN 53727 of 120 to 350, preferably 150 to 320 cm ³ / g (measured at 25 ° C in sulfuric acid).

The thermoplastic polyesters and / or aromatic liquid-crystalline polyesters which are particularly preferably used in the compositions according to the invention are known per se.

Examples thereof are fiber-forming polyesters, such as polycarbonate or aliphatic / aromatic polyesters, such as polybutylene terephthalate, polycyclohexanedimethyl terephthalate, polyethylene naphthalate or especially polyethylene terephthalate, but also completely aromatic, liquid crystalline polyesters, such as Polyoxibenzonaphtoat. Building blocks of thread-forming polyesters are preferably diols and dicarboxylic acids, or appropriately constructed oxycarboxylic acids. The main acid constituent of the polyesters is terephthalic acid or cyclohexanedicarboxylic acid, but other aromatic and / or aliphatic or cycloaliphatic dicarboxylic acids may also be suitable, preferably para or trans aromatic compounds, for example 2,6-naphthalenedicarboxylic acid or 4,4'-biphenyldicarboxylic acid , but also p-hydroxy-benzoic acid. aliphatic Dicarboxylic acids such as adipic acid or sebacic acid are preferably used in combination with aromatic dicarboxylic acids.

Typical suitable dihydric alcohols are aliphatic and / or cycloaliphatic and / or aromatic diols, for example ethylene glycol, propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol but also hydroquinone. Preference is given to aliphatic diols having from two to four carbon atoms, in particular ethylene glycol; furthermore preferred are cycloaliphatic diols, such as 1,4-cyclohexanedimethanol.

Preferred thermoplastic polyesters are in particular selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexanedimethanol terephthalate, polycarbonate or a copolycondensate comprising polybutylene glycol, terephthalic acid and naphthalenedicarboxylic acid units.

Further preferred thermoplastic polyesters are aromatic, liquid-crystalline polyesters, in particular polyesters containing p-hydroxybenzoate units.

In particular, in the case of fibers which are to be used in moist-hot environments, as in the case of monofilaments used in paper machines, and which contain polyester as the core component, these polyesters are preferably stabilized against hydrolytic degradation by addition of polyester stabilizers.

Such stabilized fibers show a significant reduction in the level of degradation of the polyester, so that life of monofilaments equivalent to monofilaments based on highly durable fiber materials such as polyarylene sulfides or oxides can be achieved.

Particular preference is given to fibers comprising core-stabilized polyesters, more preferably carbodiimides.

The polyesters used according to the invention usually have solution viscosities (IV values) of at least 0.60 dl / g, preferably from 0.60 to 1.05 dl / g, particularly preferably from 0.62 to 0.93 dl / g ( measured at 25 ° C in dichloroacetic acid (DCE)).

The mantle-forming fluoropolymers may also be of any nature as long as they are melt-spun and have a melting point that is at least 20 ° C below the melting point of the thermoplastic polymer of the core.
The fluoropolymers used in the present invention are poly (fluoroolefin) homopolymers and / or copolymers derived from ethylenically-unsaturated fluorine-containing olefin monomers and other monomers copolymerizable therewith. Such polymers are also known per se.

Examples thereof are melt-spinnable copolymers of tetrafluoroethylene with other alpha-olefins such as ethylene, propylene, butylene, hexylene or octylene.

It is also possible to use homopolymers or copolymers derived from other fluorine-containing monomers, for example from mono-, di- or trifluoroethylene, from vinyl fluoride or in particular from vinylidene fluoride.
Particular preference is given to using melt-spinnable copolymers of tetrafluoroethylene with at least one alpha-olefin, preferably with ethylene.

Very particular preference is given to using polyvinylidene fluoride ("PVDF") as the sheath component.

When spinning polyesters, in particular PET, with PVDF to a bicomponent monofilament in core-sheath structure surprisingly shows a very good core-sheath adhesion.

The invention therefore also relates to a heterafilamentary fiber containing at least two components, wherein the first component is an electrical insulator and a thermoplastic polymer which is not a fluoropolymer and the second component comprises polyvinylidene fluoride.

The particles of electrically conductive material present in the cladding of the melt-spun fiber according to the invention may be of any nature, as long as they impart increased electrical conductivity to the cladding.

These may be particles of carbon, for example carbon fibers, carbon black or graphite; of metals, such as copper, silver, aluminum or iron; of metal alloys, for example of bronze; or of conductive plastics, for example polyanilines or polypyrrole.

The particles may be in any form, for example in fibrous form or in the form of round or irregular particles.

The content of the electrically conductive particles in the cladding should be chosen such that there is a significant increase in the electrical conductivity of the plastic material. Typical amounts are in the range of up to 50% by weight, preferably 2 to 15% by weight, based on the amount of shell material.

Particular preference is given to melt-spun fibers in which the sheath contains between 2% by weight and 15% by weight, in particular between 4% by weight and 9% by weight, of electrically conductive particles.

The core-sheath fibers according to the invention can be present in any desired form, for example as multifilaments, as staple fibers or in particular as monofilaments.

The titer of the core-sheath fibers according to the invention can likewise vary within wide limits. Examples are 100 to 45,000 dtex, in particular 400 to 7,000 dtex.

Particularly preferred are monofilaments.

Particular preference is given to monofilaments whose cross-sectional shape is round, oval or n-shaped, where n is greater than or equal to 3.

The staple lengths of staple fibers can also vary widely, for example between 30 to 70 mm.

The core of the core-sheath fiber according to the invention forms the mechanical support of the fiber, while the sheath mainly determines the performance characteristics, such as antistatic behavior and sliding behavior.

The core used may preferably be a commercially available PET raw material.

For the jacket, a fluoropolymer based on PVDF is particularly preferably used which has been previously processed, in particular with carbon black, into a spinnable mixture.
Weight fraction of the core-forming component A) to the shell-forming component B), based on the total amount of these components, for component A) 50 to 95 wt.%, Preferably 60 to 80 wt.%, And for component B) 50 bis 5% by weight, preferably 40 to 20% by weight.

• i) Auswahl eines ersten Polymeren, das ein schmelzspinnbares synthetisches thermoplastisches Polymer und kein Fluorpolymer ist und das einen ersten Schmelzpunkt aufweist,
• ii) Auswahl eines zweiten Polymeren, das ein schmelzspinnbares Fluorpolymer ist, das einen zweiten Schmelzpunkt aufweist, der wenigstens 20°C unterhalb des ersten Schmelzpunktes liegt, und das Teilchen aus elektrisch leitfähigem Material enthält,
• iii) Koextrusion des ersten Polymeren und des zweiten Polymeren durch eine Heterofilament-Spinndüse bei einer Spinntemperatur oberhalb des ersten Schmelzpunktes, so dass sich eine Bikomponentenfaser mit einem Kern aus dem ersten Polymeren und einem Mantel aus dem zweiten Polymeren ausbildet, und
• iv) Verstrecken des gebildeten Kern-Mantel Filaments zur Vergrößerung der Zugfestigkeit.

The preparation of the core-sheath fibers according to the invention can be carried out by methods known per se.
These procedures include the measures:

• i) selecting a first polymer which is a melt spinnable synthetic thermoplastic polymer and not a fluoropolymer and which has a first melting point,
• ii) selecting a second polymer which is a melt-spinnable fluoropolymer having a second melting point at least 20 ° C below the first melting point and containing particles of electrically conductive material,
• iii) coextrusion of the first polymer and the second polymer through a heterofilament spinneret at a spin temperature above the first Melting point, so that a bicomponent fiber is formed with a core of the first polymer and a shell of the second polymer, and
• iv) stretching the formed core-sheath filament to increase the tensile strength.

The two polymers or mixtures containing these polymers are preferably dried immediately before being fed into the extruder, melted in the extruder and filtered through a spin pack. The fluoropolymer is provided with the electroconductive particles. This is usually done before the delivery of the fluoropolymer to the extruder, but can also take place immediately before the spin pack. It is also possible to use masterbatches comprising the fluoropolymer and electrically conductive particles.

After compressing the polymer melts through a heterofilament spinneret, the molten polymer filament is cooled in a spin bath, for example a water bath, and then wound or drawn off. The removal speed is greater than the injection rate of the polymer melt and thus causes a stretching of the formed thread.

The heterofilament spun yarn produced in this way is then preferably subjected to a post-drawing, more preferably in several stages, in particular a two- or three-stage post-drawing, with a total draw ratio of 1: 3 to 1: 8, preferably 1: 4 to 1: 6.

After stretching preferably followed by a heat-setting, with temperatures of 130 to 280 ° C are used; while working at a constant length or a shrinkage of up to 30% is allowed.

It has proved to be particularly advantageous for the monofilaments according to the invention when working at a melt temperature in the range from 285 to 315 ° C. and at a spinning draw of from 1: 2 to 1: 6.

The spinning take-off speed is usually 10 to 40 m per minute.

When spinning the thermoplastic polymer of the core and the fluoropolymer of the shell to a bicomponent monofilament core-sheath structure surprisingly shows a very good core-shell adhesion.

The conductivity of the jacket may be lost during stretching, but may be restored by a heat treatment and the shrinkage caused thereby, preferably above the melting point of the jacket material but below the melting temperature of the core.

The conductively doped fluoropolymer mainly determines the surface properties. The fibers of the invention are characterized by very good dirt repellency, good chemical resistance and electrical conductivity.

The combination with the fluoropolymer results in fibers with improved slip properties compared to pure thermoplastic polymer fibers. These fibers show increased soil repellency compared to pure thermoplastic polymer fibers.

The fibers according to the invention may contain auxiliaries in addition to the components A) and B). Examples include processing aids, stabilizers, antioxidants, plasticizers, lubricants, pigments, matting agents, viscosity modifiers or crystallization accelerators.

Examples of processing aids are siloxanes, waxes or longer-chain carboxylic acids or their salts, aliphatic, aromatic esters or ethers.

Examples of stabilizers and antioxidants are the polyester stabilizers already mentioned above, phosphorus compounds such as phosphoric acid esters or carbodiimides.

Examples of pigments or matting agents are organic dye pigments or titanium dioxide.

Examples of viscosity modifiers are polybasic carboxylic acids and their esters or polyhydric alcohols.

The fibers according to the invention, in particular the monofilaments, are preferably used for the production of textile fabrics, such as fabrics, knitted fabrics, crocheted, laid and nonwovens.

Textile fabrics comprising monofilaments according to the invention are particularly suitable for technical applications, such as for filters, as screen printing materials or in particular as paper machine screens.

The monofilaments according to the invention have good textile-physical properties and can be easily interwoven. The fabrics have the usual dimensional stability of the core forming thermoplastic polymers.

Fabrics made of these monofilaments are excellently suited for technical fabrics, in particular in the filtration of aggressive media, which are also at risk of electrostatic charge; i.e. especially in the solid-gaseous and solid-liquid filtration.

The invention also relates to the use of the fibers for making fabrics used in environments of high chemical and / or physical stress, in particular as paper machine fabrics or as technical fabrics, e.g. used in filtration, for the production of conveyor belts or as reinforcing inserts. Here the fibers are used as monofilaments and in particular as weft threads in the fabric.

The use of the monofilaments according to the invention as papermaking fabrics may take place in the forming section, the press section or, in particular, in the dryer section respectively. In the dryer section, the monofilaments according to the invention are used in particular as spiral sieves.

For these applications, the fibers used according to the invention, in particular in the form of monofilaments, usually have a titer range of 10 to 4500 tex, a modulus of elasticity of 2.0 to 8.0 N / tex, a tenacity of 15 to 50 cN / tex Elongation at break of 15 to 45% and hot air shrinkage at 180 ° C of 1.0 to 20.0%.

The following example illustrates the invention without limiting it.

Core-sheath fibers of polyethylene terephthalate and polyvinylidene fluoride containing carbon black

The components polyethylene terephthalate ("PET") (70% by weight) and polyvinylidene fluoride (as masterbatch containing 9% by weight of conductive carbon black; Palmarole EXP 184/14; 30% by weight) were melted in two extruders with separate temperature control (PET at 282 ° C.) C melting temperature (core material) or PVDF at 240 ° C melting temperature (sheath material) and spun through a 20-hole spinneret with a hole diameter of 1.40 mm and a take-off speed of 15 m / min to a core-sheath monofilament, stretched twice ( first drawing in a water bath at 80 ° C., second drawing in the hot air channel at 150 ° C.) and heat-setting in the hot-air channel at 205 ° C. The total drawing was 4.1: 1. The final diameter of the core-sheath monofilament was 0.500 mm.

The core-sheath monofilament obtained had the following properties: titres 2890 dtex strength 24 cN / tex HLS (hot air shrink 10 'at 160 ° C) 2.5% loop strength > 20 cN / tex elongation 44% BZD (reference strain at 12 cN / tex): 8.5% BZD (reference strain at 15 cN / tex): 13% EGG. Resistance (10 mm clamping length): 8 * 10 ⁵ (ohms) EGG. Resistance (150 mm clamping length): 9 * 10 ⁶ (ohms)

Claims (13)

1. A melt-spun fiber having a core-sheath structure and a tensile strength of at least 15 cN/tex whose core contains a melt-spinnable synthetic thermoplastic polymer having a first melting point which is not a fluoropolymer and whose sheath contains at least one melt-spinnable fluoropolymer having a second melting point at least 20°C below the first melting point and particles composed of electroconductive material whose amount is up to 50% by weight, based on the amount of the sheath material, and where the core is 50 to 95% by weight and the sheath is 50 to 5% by weight, based on the total amount of core and sheath.
2. The melt-spun fiber of claim 1, wherein the synthetic thermoplastic polymer of the core is a polyamide and especially a polyester.
3. The melt-spun fiber of claim 2, wherein the polyester is a polyethylene terephthalate.
4. The melt-spun fiber of claim 2, wherein the polyester is a liquid-crystalline polyester.
5. The melt-spun fiber of claim 1, wherein the melt-spinnable fluoropolymer is a copolymer of tetrafluoroethylene with at least one alpha-olefin, preferably ethylene.
6. The melt-spun fiber of claim 1, wherein the melt-spinnable fluoropolymer is a polyvinylidene fluoride.
7. The melt-spun fiber of claim 1, wherein the sheath contains 2 to 15% by weight of electroconductive particles.
8. The melt-spun fiber of claim 6, wherein the sheath contains between 2% by weight and 15% by weight and especially between 4% by weight and 9% by weight of electroconductive particles.
9. The melt-spun fiber of claim 1, wherein the particles composed of electroconductive material consist of carbon, metals or metal alloys and are especially carbon black or graphite.
10. The melt-spun fiber of claim 1 which is a filament, especially a monofilament.
11. A process for preparing the melt-spun core-sheath fiber of claim 1, comprising the measures of:

    i) selecting a first polymer which is a melt-spinnable synthetic thermoplastic polymer and not a fluoropolymer and which has a first melting point,

    ii) selecting a second polymer which contains particles composed of electroconductive material whose amount is up to 50% by weight, based on the amount of the sheath material, and which is a melt-spinnable fluoropolymer which has a second melting point at least 20°C below the first melting point,

    iii) coextruding the first polymer and the second polymer through a heterofilament spinneret at a spinning temperature above the first melting point to form a bicomponent fiber having a core composed of the first polymer and a sheath composed of the second polymer and

    iv) drawing the produced core-sheath filament to increase the tensile strength.
12. The use of melt-spun core-sheath fibers of claim 1 for producing industrial wovens.
13. The use of claim 12, wherein the industrial woven is a paper machine wire, a filter cloth, a screen printing cloth, a conveyor belt or a reinforcing ply.