JP2004143659A - Sheath-core fiber having high chemical-resistance, electroconductivity and stain repellency, method for manufacturing the same, and usage of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber, especially a monofilament, having a combination of high chemical resistance, thermal stability, good mechanically morphological stability, high tensile strength and antistatic property. <P>SOLUTION: The fiber is a melt-spun fiber having a sheath-core structure and at least 15cN/tex tensile strength, wherein the core material contains a synthetic thermoplastic polymer other than fluoropolymer and the sheath contains at least one melt-spinnable fluoropolymer and particulates comprising an electroconductive material. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to conductive soil-repellent core-sheath fibers, particularly monofilaments, which are particularly useful in industrial woven fabrics.

Fluoropolymers are known to have good thermal stability, good chemical resistance and soil repellency properties. The processing of melt-spinnable fluoropolymers into fibers, multifilaments and monofilaments has already been attempted in order to be able to produce from them textile fabrics for industrial applications having the above-mentioned fluoropolymer properties. . A disadvantage associated with melt-spinnable fluoropolymers is that they are easily entangled. Thus, fibers and filaments formed from this material have low tensile strength and are not shape stable.
Attempts have also been made to combine fluoropolymers with polymers having good mechanical performance characteristics, such as polyethylene terephthalate (hereinafter also referred to as PET). However, it should be noted that in this situation, the fluoropolymer is generally incompatible with the other polymer since it generally does not mix with the other polymer. Thus, the result is often a two-phase mixture in which the fluoropolymer forms three-dimensional islands. Thus, the weight fraction of fluoropolymer that can be added is often limited because the polymer boundary layers have poor adhesion to each other. This property manifests itself as a tendency to tear in the fiber.

Monofilaments composed of PET and random copolymers of ethylene and tetrafluoroethylene (ETFE) have been commercially available for several years. Frequently, these fibers have a low carboxy end group content to stabilize them against hydrolysis and are stabilized with carbodiimides that cap their carboxy end groups. Capping of carboxyl groups by carbodiimides is described, for example, in EP-A-417717 and EP-A-503421.
Industrial fabrics woven from these monofilaments have the mechanical properties of PET filaments predominantly, but in combination with increased hydrolysis resistance and improved soil repellency. Since the fluoropolymer fraction is relatively low, the thermal stability and chemical resistance of these fibers are substantially equivalent to those data for pure PET. However, under mechanical stresses, an increased tendency to tear, for example with the continuous tapping of a fel on a weaving machine, may manifest itself.
However, fibers composed of synthetic polymers and woven fabrics made therefrom have the disadvantage that they are electrostatically charged as a result of friction. BACKGROUND OF THE INVENTION Conductive fibers for producing textiles, such as wovens for industrial or other applications, for example, brushes, have long been a development goal.

DE-A-19826120 discloses a flame-retardant electrically conductive woven fabric containing electrically conductive fibers and flame-resistant non-electrically conductive fibers. The electrically conductive fibers may contain electrically conductive particles such as carbon black or metal particles, be coated with a metal, or be made of an electrically conductive material such as polyaniline. The fiber materials mentioned are polyesters and polyolefins.
DE-U-86 23 879 discloses a yarn for the production of spiral tape encased in a sheath with a layer of curable polymer. This layer contains electrically conductive carbon. Examples of polymers for the sheath layer include melamine resins, epoxy resins, phenolic resins or polyurethanes.
DE-A-3938414 is a high-strength woven fabric formed from artificial fibers incorporated in the warp and weft in the form of electrically conductive fibers, and also containing non-electrically conductive fibers. It has been described. These electrically conductive fibers are composed of polyolefin and contain graphite or carbon black.

EP-A-160320 describes a hairbrush core-sayamonofilament composed of selected polymers. The core comprises nylon or a polyester comprising at least 60% by weight of polybutylene terephthalate units. The sheath contains a specific nylon grade or copolyetherester.
DE-U-86 / 06334 discloses a core material whose core consists of a thermoplastic polymer, preferably a polyamide, and whose sheath is made of an electrically conductive polymer containing carbon black or metal, preferably polyamide. -Discloses sheath fiber.
JP-A-7-278956 describes an electrically conductive copolyester mainly containing polybutylene terephthalate units and doped with carbon black. It also describes a core-sheath fiber composed of this material and a core-sheath fiber having a core composed of aromatic polyester.

WO 98/14647 discloses, for example, electrically conductive heterofilaments which can be arranged as a core-sheath fiber. Examples described for the core and sheath polymer are PET and other polyesters, or PET / nylon.
WO 01/20076 discloses a non-woven fabric having a high dielectric constant. A mixture of polyvinylidene fluoride and polypropylene has been proposed as a fiber material. The products formed therefrom are notable for their long half-life for charging and can therefore be used as electrostatic filters.
US 6,085,061 describes a brush for cleaning charged surfaces. The fibrous material used can be a core-sheath fiber whose core material is electrically conductive and whose sheath is made of polyvinylidene fluoride.
DE-A-441 396 discloses melt-spun, undrawn, non-electrically conductive fibers whose sheath has a core-sheath structure containing a fluoropolymer. The core polymer used is polycarbonate. Since this fiber is used as an optical fiber, its low strength makes it unsuitable for industrial knitting, for example industrial woven fabric. In addition, important properties of optical fibers are high reflectivity in their boundary layer and very low attenuation of electromagnetic waves. Both of these properties can only be achieved through the use of high purity coatings.
JP-A-2001-127218 describes a semiconductor fiber composed of a fluoropolymer containing carbon black. This fiber does not have a core-sheath structure and is used for producing nonwovens, for example by melt-blow. The fiber has not been drawn.

EP-A-417717 EP-A-503421 DE-A-19826120 DE-U-8623879 DE-A-3938414 EP-A-160320 DE-U-86 / 06334 JP-A-7-278956 WO 98/14647 WO01 / 2076 US 6,085,061 DE-A-44213396 JP 2001-127218 A

It is an object of the present invention to combine the advantages of the performance of known materials for fiber production without incurring the disadvantages associated with the use of those individual materials.
One skilled in the art has found that connectivity problems in the boundary layer between two polymers are common. This is particularly true for the use of known low binding fluoropolymers with other polymers. Surprisingly, it has been found that the use of a fluoropolymer doped with electrically conductive particles can provide very good bonding to the polymer core.
Accordingly, it is a further object of the present invention to provide a core-sheath fiber having good bonding between the individual layers.
Accordingly, the present invention provides fibers, especially monofilaments, which combine the non-charging properties with high chemical resistance, thermal stability, good mechanical shape stability and high tensile strength.

The present invention is a melt-spun fiber having a core-sheath structure and a tensile strength of at least 15 cN / tex, wherein the core comprises a synthetic thermoplastic polymer that is not a fluoropolymer, and the sheath has at least A fiber containing the melt-spinnable fluoropolymer and particles comprising an electrically conductive material.
The synthetic thermoplastic polymers forming the core are freely selectable as long as they are melt spinnable and provide fibers having the desired properties for the particular intended application. Even though the core may contain a fluoropolymer as a blend component, as well as a synthetic thermoplastic polymer, the fluoropolymer is not encompassed by the synthetic thermoplastic polymer.

Examples of synthetic thermoplastic materials are polyethylene, polypropylene or ethylene and / or ethylene in combination with other copolymerized α-olefin units such as α-butylene, α-pentylene, α-hexylene or α-octylene. Or polyolefins such as copolymers containing propylene units; polyesters such as polycarbonate, aliphatic aromatic polyesters or completely aromatic polyesters; aliphatic or aliphatic aromatic polyamides (nylon) or completely aromatic Polyamides, such as polyamides (aramids); or polyether ketones, that is, polymers having at least ether and ketone groups in their repeating chains, and generally aromatic divalent groups such as phenylene. Many combinations of these groups are possible Polymers such as PEK, PEEK or PEKK; or polyarylene sulfides, preferably polyphenylene sulfide; or polyetheresters, ie at least ether and ester groups in their repeating chains, and generally aromatics such as phenylene A polymer having a hydrophilic divalent group, for example TPE-E; or polyacrylonitrile or a polyacrylonitrile copolymer with another ethylenically unsaturated comonomer such as acrylic acid or methacrylic acid.
Preferably, the core-sheath fiber core of the present invention contains a polyamide, especially a polyester.

The thermoplastic polyamides preferably used in the composition of the present invention are known per se.
Examples thereof are aliphatic or aliphatic aromatic polyamides such as polycaprolactam, poly (hexamethylene-1,6-diamineadipamide), poly (hexamethylene-1,6-diaminesebacamide), Poly (hexamethylene-1,6-diamineterephthalamide) or poly (hexamethylene-1,6-diamineisophthalamide); or poly (phenylene-1,4-diamineterephthalamide) or poly (phenylene-1,4) Fiber-forming polyamides, such as other completely aromatic polyamides, such as diamine isophthalamide).
The polyamide used in the present invention conventionally has a DIN 53727 viscosity number of from 120 to 350 cm ³ / g, preferably from 150 to 320 cm ³ / g (measured in sulfuric acid at 25 ° C.).

The thermoplastic polyesters and / or aromatic liquid crystal polyesters more preferably used in the composition of the present invention are known per se.
Examples thereof are polycarbonates or other aromatic polymers such as aliphatic aromatic polyesters, for example polybutylene terephthalate, polycyclohexanedimethyl terephthalate, polyethylene naphthalate or especially polyethylene terephthalate, or polyoxybenzonaphthoate. And a fiber-forming polyester such as The building blocks of the fiber-forming polyester are preferably diols and dicarboxylic acids, or suitably configured hydroxycarboxylic acids. The main acid that is the main acid component of the polyesters is terephthalic acid or cyclohexanedicarboxylic acid, but other aromatic and / or aliphatic or cycloaliphatic dicarboxylic acids, preferably, for example, 2,6- Aromatic compounds in the para- or trans-configuration such as naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid or other p-hydroxybenzoic acid may also be suitable. For example, an aliphatic dicarboxylic acid such as adipic acid or sebacic acid is preferably used in combination with an aromatic dicarboxylic acid.

Typical suitable dihydric alcohols are aliphatic and / or cycloaliphatic and / or aromatic diols such as ethylene glycol, propanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol or other Is hydroquinone. Preferred are aliphatic diols having 2 to 4 carbon atoms, especially ethylene glycol; more preferred are cycloaliphatic diols such as 1,4-cyclohexanedimethanol.
Preferred thermoplastic polyesters are, in particular, polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexane dimethanol terephthalate, polycarbonate, or copolycondensates, such as polybutylene glycol, terephthalic acid. And a copolycondensate containing a naphthalenedicarboxylic acid unit.
More preferred thermoplastic polyesters are aromatic liquid crystalline polyesters, especially polyesters containing p-hydroxybenzoic acid units.
In particular, in the case of fibers used in hot-wet environments such as monofilaments for use in paper machines and containing polyester as a core component, these polyesters are preferably prepared by adding a polyester stabilizer. Stabilized against hydrolytic degradation.

Since such stabilized fibers exhibit a significant reduction in the tendency of the polyester to collapse, a monofilament life equal to the life of a monofilament based on a very stable fiber material such as polyarylene sulfide or oxide is achieved. You.
Particularly preferred are fibers containing stabilized polyester in their core material, particularly preferably carbodiimide.
The polyester used in the present invention is typically at least 0.6 dl / g, preferably 0.60 to 1.05 dl / g, more preferably 0.62 to 0.93 dl / g (25 ° C in dichloroacetic acid). ) (Measured in).
Similarly, the fluoropolymer forming the sheath can be freely selected as long as it can be melt-spun.

The fluoropolymer used in the present invention is a poly (fluoroolefin) homopolymer and / or copolymer derived from ethylenically unsaturated fluorinated olefin monomers and other monomers copolymerizable therewith. Such polymers are likewise known per se.
Examples are melt-spinnable copolymers of tetrafluoroethylene with other α-olefins such as ethylene, propylene, butylene, hexylene or octylene.
However, it is also possible to use homo- or copolymers derived from other fluorinated monomers, for example from mono, di, 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 α-olefin, preferably with ethylene.
Highly preferred is the use of polyvinylidene fluoride (PVDF) as the sheath component.

When spinning polyester, especially PET, together with PVDF to form a composite monofilament of core-sheath structure, it is surprising that very good core-sheath binding is obtained.
Accordingly, the present invention is a heterofilament fiber containing at least two components, wherein the first component comprises a thermoplastic polymer that is an electrical insulator and is not a fluoropolymer, and the second component comprises a polyfluorinated polymer. Heterofilament fibers comprising vinylidene are also included.
The particles composed of electrically conductive material present in the sheath of the melt spun fibers of the present invention are freely selectable as long as they provide a sheath with increased electrical conductivity.
The particles may be composed of carbon, for example, carbon fiber, carbon black or graphite; metal, for example, copper, silver, aluminum or iron; alloy, for example, bronze; or conductive plastic, for example, polyaniline or polypyrrole. Can be.
The particles can be in any desired form, for example in the form of fibers or in the form of spherical or irregular particles.

The level of electrically conductive particles in the sheath should be chosen such that a distinct increase in the electrical conductivity of the polymer material occurs. Typical amounts vary up to 50% by weight, preferably in the range of 2 to 15% by weight, based on the amount of the sheath material.
Particularly preferred are melt-spun fibers wherein the sheath contains 2 to 15% by weight, especially 4 to 9% by weight, of electrically conductive particles.
The core-sheath fibers of the present invention may be present in any desired form, for example as multifilaments, staple fibers or especially monofilaments.
The linear density of the core-sheath fibers of the invention can likewise vary within a wide range. Examples thereof are from 100 to 45,000 dtex, in particular from 400 to 7,000 dtex.
Particularly preferred are monofilaments.
Particularly preferred are monofilaments whose cross-sectional shape is circular, elliptical, or n-gonal where n is 3 or more.
The staple length in the case of staple fibers can likewise vary over a wide range, for example between 30 and 70 mm.
While the core-sheath fiber core of the present invention forms the mechanical strength component of the fiber, the sheath primarily determines performance characteristics such as antistatic performance and smoothness. As the core material, a commercially available PET raw material can be preferably used.
Saya more preferably utilizes a fluoropolymer based on PVDF which has been pre-processed with carbon black and in particular a melt-spinnable mixture.

The weight fraction of the core-forming component A) to the sheath-forming component B) is from 50 to 95% by weight, preferably from 60 to 80% by weight, for component A), based on the total weight of these components. For B) it is 50 to 5% by weight, preferably 40 to 20% by weight.
The core-sheath fiber of the present invention can be produced according to a method known per se.
These methods are:
i) selecting a first polymer that is a synthetic thermoplastic polymer but not a fluoropolymer and has a first melting point;
ii) selecting a second polymer that is a melt-spinnable fluoropolymer containing particles comprising an electrically conductive material and having a second melting point at least 20 ° C below the first melting point;
iii) co-extruding the first polymer and the second polymer through a heterofilament spinneret at a spinning temperature above the first melting point, comprising a core comprising the first polymer and the second polymer; Forming a composite fiber having a sheath consisting of
iv) stretching the manufactured core-sheath filament to increase its tensile strength.

The two polymers or a mixture containing these polymers is preferably dried just before being fed into the extruder, melted in the extruder and filtered through a spin pack. The fluoropolymer is provided with the electrically conductive particles. This is typically accomplished before the fluoropolymer is fed into the extruder, but can also be performed just upstream of the spin pack. Similarly, a masterbatch containing a fluoropolymer and electrically conductive particles can be used.
After the polymer melt is pressed through a heterofilament spinneret, the molten polymer yarn is quenched in a spin bath, for example, a water bath, and then wound up or taken up. The take-off speed is greater than the extrusion speed of the molten polymer, causing the extruded yarn to stretch or draw.

The freshly spun heterofilament yarn thus produced is then preferably subjected to a post-drawing operation, more preferably to a plurality of stages, in particular two or three stages, of a 1: 3通 し 1: 8, preferably 1: 4-1: 6.
After stretching, heat-setting is preferably performed at a temperature of 130-280 ° C; its length is kept constant or shrinkage up to 30% is allowed.
Operating at a melt temperature of 285-315 ° C and a jet draw ratio of 1: 2-1: 6 has been found to be particularly advantageous for the monofilaments of the present invention.
The spinning take-off speed is customarily 10 to 40 m / min.
When the thermoplastic polymer of the core and the fluoropolymer of the sheath are spun into a composite monofilament having a core-sheath structure, it is surprising that a very good core-sheath binding is obtained.
The conductivity of the sheath may be lost during stretching, but is preferably restored by heat treatment above the melting point of the sheath material but below the melting point of the core, thereby inducing shrinkage.
Fluoropolymers that are doped to become conductive primarily determine surface properties. The fibers according to the invention are notable for very good soil repellency, good chemical resistance and electrical conductivity.
Combination with a fluoropolymer results in fibers having improved lubricity as compared to fibers composed of the thermoplastic polymer itself. These fibers exhibit increased soil repellency compared to fibers composed of the thermoplastic polymer itself.

The fibers according to the invention may contain auxiliaries as well as components A) and B). Examples of auxiliaries are processing aids, stabilizers, antioxidants, plasticizers, lubricants, pigments, matting agents, viscosity modifiers or crystallization accelerators.
Examples of processing aids are siloxanes, waxes or long-chain carboxylic acids or their salts, aliphatic, aromatic esters or ethers.
Examples of stabilizers and antioxidants are the above-mentioned polyester stabilizers, phosphorus compounds such as phosphate 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 of the present invention, especially the monofilaments, are preferably used for producing woven fabrics, such as woven fabrics, molded loop knits, stretch loop knits, non-crimped woven fabrics and nonwoven fabrics.
Woven fabrics containing the monofilaments of the present invention are particularly useful for industrial applications as filters, screen printing materials or especially paper machine wires.
The monofilaments of the present invention have good knitting physical properties and are easily processed by weaving. They have the usual shape stability of the thermoplastic polymer forming the core.
Woven fabrics formed from these monofilaments are very useful for industrial fabrics, especially in the filtration of sticky media that also has the risk of charge build-up, ie, especially in solid-gas and solid-liquid filtration.
The present invention relates to the use of fibers for the production of textiles used in environments characterized by severe chemical and / or physical stress, in particular for use as paper machine wires, or for industrial wovens, It also includes, for example, its use in filtration, for making conveyor belts or as a reinforcing ply. In this case, the fibers are used as monofilaments, especially as weft yarns in woven fabrics.

The use of the monofilaments of the invention as paper machine wire can be carried out in a forming section, a compression section or especially a drying section. When used in a drying section, the monofilaments of the present invention are used particularly as spiral wires.
For these applications, the fibers used according to the invention, in particular in the form of monofilaments, typically have a linear density of 10 to 4,500 tex and a modulus of 2.0 to 8.0 N / tex. It has a tenacity of 15 to 50 cN / tex, a breaking elongation of 15 to 45%, and a hot air shrinkage of 1.0 to 20.0%.
The following examples illustrate the invention without limitation.

Core material composed of polyethylene terephthalate and polyvinylidene fluoride containing carbon black-sheath fiber Polyethylene terephthalate (PET) (70% by weight) and conductive carbon black of polyvinylidene fluoride @ 9% by weight (Palmarole EXP 184/14) Extruders characterized as a masterbatch containing: 30% by weight, but with separate temperature controls {PET has a melting temperature of 282 ° C. (core) and PVDF has a melting temperature of 240 ° C. (sheath)} And then spun through a 20-hole spinneret with 1.40 mm diameter holes and a draw speed of 15 m / min to form a core-saya monofilament and drawn twice (first Stretched at 80 ° C. in a water bath, second stretched at 150 ° C. in a hot air duct) and hot air duct Heat set at 205 ° C. The through-stretching ratio was 4.1: 1. The final diameter of the core material-saya monofilament was 0.500 mm.
The resulting core-sayamonofilament had the following properties:
Linear density: 2890 dtex
Strength: 24cN / tex
Hot air shrinkage 10 'at 160 ° C for 10 minutes: 2.5%
Loop tenacity:> 20 cN / tex
Elongation at break: 44%
12cN / texEASL: 8.5%
15cN / texEASL: 13%
Electric resistance (length fixed with a clamp: 10 mm): 8 × 10 ⁵ (Ω)
Electric resistance (length fixed with a clamp: 150 mm): 9 × 10 ⁶ (Ω).

Claims (18)

A melt-spun fiber having a core-sheath structure and a tensile strength of at least 15 cN / tex, wherein the core material comprises a synthetic thermoplastic polymer that is not a fluoropolymer, and the sheath has at least one melt-spinnable fiber. A fiber comprising a fluoropolymer and particles comprising an electrically conductive material. The melt-spun fiber according to claim 1, wherein the synthetic thermoplastic polymer of the core material is polyamide or polyester. The melt-spun fiber according to claim 2, wherein the polyester is polyethylene terephthalate. The melt-spun fiber according to claim 2, wherein the polyester is a liquid crystal polyester. The melt-spun fiber of claim 1, wherein the melt-spinnable fluoropolymer is a copolymer of tetrafluoroethylene and at least one α-olefin. The melt-spun fiber according to claim 1, wherein the melt-spun fusible fluoropolymer is polyvinylidene fluoride. A melt spun fiber according to claim 1, wherein the sheath contains up to 50% by weight of electrically conductive particles. The melt-spun fiber according to claim 6, wherein the sheath contains 2 to 15% by weight of electrically conductive particles. The fiber according to claim 1, wherein the particles comprise an electrically conductive material made of carbon, metal or alloy. The melt-spun fiber according to claim 1, which is a filament. A method for producing a melt-spun core-sheath fiber according to claim 1, comprising:
i) selecting a first polymer that is a synthetic thermoplastic polymer but not a fluoropolymer and has a first melting point;
ii) selecting a second polymer that is a melt-spinnable fluoropolymer containing particles comprising an electrically conductive material and having a second melting point at least 20 ° C below the first melting point;
iii) co-extruding the first polymer and the second polymer through a heterofilament spinneret at a spinning temperature above the first melting point, comprising a core comprising the first polymer and the second polymer; Forming a composite fiber having a sheath consisting of
iv) A method comprising stretching the manufactured core-sheath filament to increase its tensile strength. 使用 Use of the melt-spun core material-sheath fiber according to claim 1 for producing an industrial woven fabric. 13. Use according to claim 12, wherein the industrial woven fabric is a paper machine wire, a filter fabric, a screen printing fabric, a conveyor belt or a reinforcing ply. 6. The melt-spun fiber according to claim 5, wherein the α-olefin is ethylene. A melt spun fiber according to claim 1, wherein the sheath contains 2 to 15% by weight of electrically conductive particles. The melt-spun fiber according to claim 6, wherein the sheath contains 4 to 9% by weight of electrically conductive particles. The melt spun fiber according to claim 9, wherein the carbon is carbon black or graphite. The melt spun fiber according to claim 10, wherein the filament is a monofilament.