EP1961846A2 - Electrically conductive filaments, fabrics made of these filaments and their use - Google Patents

Abstract

The melt-spun thread useful in screen textiles and filter cloths for gas and fluid filters, comprises a thermoplastic polymer, a thermoplastic elastomer block copolymer, and soot particle in the form of aggregates aligned along the longitudinal axis of the thread. The aggregates form electrically conductive paths along the longitudinal axis of the thread. The thread is a core-skin or monofilament and has a modulus of elasticity of 0.1-5.5 GPa and an elastic elongation of greater than 1.5-4%. The aggregates are formed from primary particles connected with each other. The melt-spun thread useful in screen textiles and filter cloths for gas and fluid filters, comprises a thermoplastic polymer, a thermoplastic elastomer block copolymer, and soot particle in the form of aggregates aligned along the longitudinal axis of the thread. The aggregates form electrically conductive paths along the longitudinal axis of the thread. The thread is a core-skin or monofilament and has a modulus of elasticity of 0.1-5.5 GPa and an elastic elongation of greater than 1.5-4%. The aggregates are formed from primary particles connected with each other. The soot particle causes electrical conductivity of the thread of 1.0-10 ->5>Siemens/cm measured in the longitudinal direction of the thread. The core is formed from thermoplastic polymer. The weight ratio of core and skin is 70:30 to 50:50. An independent claim is included for textile surface structure such as fabric.

Description

The present invention relates to filaments having very high electrical conductivities and excellent mechanical properties. These threads, in particular in the form of monofilaments, can be used, for example, in screens or in conveyor belts.

It is known that polyester fibers for technical applications are in most cases subjected to high mechanical and / or thermal stresses during use. In addition, in many cases, exposure to chemical and other environmental influences to which the material must oppose sufficient resistance. For all these loads, the material must have good dimensional stability and constancy of force-elongation properties over as long as possible usage periods. In addition, the material must not be electrostatically charged during processing and during use.

An example of technical applications involving the combination of good mechanical, thermal, chemical and electrical stresses is the use of monofilaments in filters, screens or as conveyor belts. This application requires monofilaments with excellent mechanical properties, such as high initial modulus, tear strength, knot and loop strength, and high abrasion resistance coupled with high resistance to hydrolysis, to withstand the high stresses of their use and to allow sufficient service life of the screens or conveyors guarantee.

In industrial production, such as in the manufacture or processing of papers, filters or conveyor belts are used in processes that occur at elevated temperatures and in hot humid environments. Although polyester-based manmade fibers have proven successful in such environments, when used in humid-hot environments, polyesters are prone to mechanical abrasion in addition to hydrolytic degradation.

In technical applications, abrasion can have a variety of causes. Thus, the sheet forming screen or forming fabric is pulled in paper machines for dewatering suction boxes with the result of increased Siebverschleißes. In the dryer section of the paper machine, screen wear occurs due to differences in speed between the paper web and the screen surface or between the screen surface and the surface of the drying drums. Tissue wear also occurs in other technical fabrics due to abrasion; e.g. in conveyor belts by grinding over fixed surfaces, in filter fabrics by mechanical cleaning and in screen printing fabrics by passing a squeegee over the screen surface.

Multi-ply fabrics are used in the forming fabrics of modern paper machines. In order to achieve the fastest possible dewatering of the paper, vacuum boxes are used on the underside of the sieve to accelerate the dewatering of the paper web by means of negative pressure. The contact surfaces of the edges of these suction boxes with the forming fabric are usually made of ceramic to prevent excessive wear on the suction boxes.

On the other hand, the high production speeds, the friction of the fillers added to the monofilaments and the suction power of the paper machine lead to a high level of wear on the underside of the multilayer Forming screen.

To improve the abrasion resistance of the underside of the sieve, monofilaments of polyamide, e.g. made of polyamide 6 or polyamide 6.6. Otherwise, monofilaments of polyethylene terephthalate (hereinafter referred to as "PET"), of which the forming wire essentially consists, are predominantly used because of the higher dimensional stability. A proven design is the so-called interchangeable shot on the underside of the sieve: Here, an excess of a polyamide monofilament with the following PET monofilaments is used alternately. This achieves a compromise between abrasion resistance and dimensional stability.

The higher water absorption of the polyamides over PET leads to an extension of the weft wires during operation of the screen. As a result, the Siebränder turn up and the screen is no longer flat in the paper machine. This undesirable effect is called "edge curling".

Numerous developments have tried to replace the polyamide monofilaments with those made of other abrasion-resistant polymers, which are both dimensionally stable and should have a low water absorption.

To mention are monofilaments of PET blends, where 10-40% thermoplastic polyurethane (TPU) has been added (see, eg EP-A-387.395 ). Also, blends of thermoplastic polyester, such as polyethylene terephthalate isophthalate, and thermoplastic polyurethane having melting points of 200 to 230 ° C were used (see, eg EP-A-674.029 ).

Further known from the prior art monofilaments with core-shell structure in which the sheath of a mixture of thermoplastic polyester having a melting point of 200 to 300 ° C, for example PET, and consists of thermoplastic, elastomeric Copolyetherester with selected polyetherdiol assemblies as soft segments, which also have improved abrasion resistance (see, eg EP-A-735.165 ).

Other polyester compositions of crystalline thermoplastic polyester resins, polyester elastomers and sorbitan esters are made DE 691 23 510 T2 known. These are characterized by good moldability, in particular by a good release ability.

From the DE 690 07 517 T2 For example, polyester compositions containing an aromatic polycarbonate, a polyester derived from alkanediol and benzene dicarboxylic acids, and a polyester urethane elastomer or a polyether imide ester elastomer are known. These have improved flow properties while maintaining good mechanical properties.

While these prior art threads provide sufficient abrasion resistance, in many cases the electrical conductivity still leaves something to be desired. Although it has long been known that you can add threads to improve the electrical conductivity carbon black. With the previously known solutions, however, typically only electrical conductivities of up to 10 ^-6 Siemens / cm can be achieved. When using prior art carbon blacks to increase the electrical conductivity has been shown that when stretching the threads produced, the conductive paths formed by the soot are interrupted and thereby a significant reduction in electrical conductivity occurs.

In the WO-A-98 / 14,647 It has been attempted to overcome this drawback by producing a core-sheath filament with a sheath polymer having a lower melting point than the core polymer. After this Stretching the coat is melted, so that the thread shrinks and broken bridges of electrically conductive material can close again. Although this increases the electrical conductivity again; However, the thermal treatment leads to a decrease in the orientation of the molecular chains and thus to a reduction in the strength of the filament.

In the EP-A-1,559,815 a finished thread is coated with a mixture of nano-carbon tubes and a polymer. Since the coated thread is not stretched further, the carbon bridges of the amorphous coating are not ruptured, resulting in very good electrical conductivities.

The object of the present invention is to provide filaments which have excellent electrical conductivity, good mechanical properties and excellent abrasion resistance.

It has now surprisingly been found that threads containing a selected combination of substances have this property profile.

1. a) einen thermoplastischen Polyester,
2. b) ein thermoplastisches elastomeres Block-Copolymer, und
3. c) Ruß- und/oder Graphitteilchen in der Form von entlang der Längsachse des Fadens ausgerichteten Aggregaten, welche entlang der Längsachse des Fadens elektrisch leitfähige Pfade bilden.

The invention relates to melt spun yarns having a modulus of elasticity of 8 to 14 GPa and an elastic elongation of up to 1.5%

1. a) a thermoplastic polyester,
2. b) a thermoplastic elastomeric block copolymer, and
3. c) carbon black and / or graphite particles in the form of aggregates aligned along the longitudinal axis of the filament which form electrically conductive paths along the longitudinal axis of the filament.

For the purposes of this description, the term "filaments" generally refers to fibers of finite length (staple fibers), fibers of infinite length (filaments) and multifilaments composed of staple fibers or secondary thereto spun yarns understood. The melt-spun threads are preferably used in the form of monofilaments.

For the purposes of this description, modulus of elasticity is understood to mean the secant modulus of the force-strain characteristic between 0 and 1% elongation.

In the context of this description, elastic elongation is understood as meaning the linear progression of the force-strain characteristic from its origin to the deviation from the linearity. An elastic elongation of 0.5% thus corresponds to a linear course of the force-strain curve from 0% to 0.5% elongation; an elastic elongation of 1.5% therefore a linear curve of the force-elongation characteristic of 0% to 1.5%.

As polyester of component a), thread-forming polyesters according to the invention are used which, after spinning, stretching and, if appropriate, relaxing, give threads with the moduli of elasticity and elastic strains described above.

As a rule, these are polyethylene terephthalate homopolymers or copolymers containing ethylene terephthalate units. These polymers are thus derived from ethylene glycol and optionally further alcohols and terephthalic acid or its polyester-forming derivatives, such as terephthalic acid esters or chlorides.

These thermoplastic polyesters are known per se. Building blocks of thermoplastic copolyesters a) are preferably the abovementioned diols and dicarboxylic acids, or correspondingly constructed polyester-forming derivatives. Primary acid component of the polyesters is terephthalic acid, optionally together with minor proportions, preferably up to 15 mol%, based on the total amount of the dicarboxylic acids, of other aromatic and / or aliphatic and / or cycloaliphatic dicarboxylic acids, preferably with para- or trans-aromatic compounds, such as 2,6-naphthalenedicarboxylic acid or 4,4'-biphenyl-carboxylic acid, and preferably with isophthalic acid and / or with aliphatic dicarboxylic acids, such as with adipic acid or sebacic acid.

In addition to ethylene glycol, suitable dihydric alcohols may be used. Typical representatives thereof are aliphatic and / or cycloaliphatic diols, for example propanediol, 1,4-butanediol, cyclohexanedimethanol or mixtures thereof.

Examples of preferred components a) are copolyesters which, in addition to polyethylene terephthalate units, have further units derived from alkylene glycols, in particular ethylene glycol, and aliphatic and / or aromatic dicarboxylic acids, such as adipic acid, secacic acid or isophthalic acid.

Particularly preferred components a) are polyethylene terephthalate homopolymers or copolyesters containing recurring structural units of the polyethylene terephthalate, repeating structural units of the polyethylene adipate, polyethylene sebacate or especially of the polyethylene isophthalate.

The polyesters of component a) 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)).

Threads of polyesters with a content of free carboxyl groups of less than or equal to 3 meq / kg are preferred.

These preferably contain a means for occluding free carboxyl groups, for example a carbodiimide and / or an epoxide compound.

Such treated polyester yarns are stabilized against hydrolytic degradation and are particularly suitable for use in humid-hot environments, especially in paper machines or as a filter.

The thermoplastic and elastomeric block copolymers of component b) can be of very different types. Such block copolymers are known to the person skilled in the art.

Examples of components b) are thermoplastic and elastomeric polyurethanes (TPE-U), thermoplastic and elastomeric polyesters (TPE-E), thermoplastic and elastomeric polyamides (TPE-A), thermoplastic and elastomeric polyolefins (TPE-0) and thermoplastic and elastomeric styrene Block copolymers (TPE-S).

The thermoplastic and elastomeric block copolymers b) can be composed of a wide variety of monomer combinations. As a rule, these are blocks of so-called hard and soft segments. The soft segments are typically derived from polyalkylene glycol ethers in TPE-U, TPE-E and TPE-A. The hard segments are typically derived from short chain diols or diamines in TPE-U, TPE-E and TPE-A. In addition to the diols or diamines, the hard and soft segments of aliphatic, cycloaliphatic and / or aromatic dicarboxylic acids or diisocyanates are built up.

Examples of thermoplastic polyolefins are block copolymers comprising blocks of ethylene-propylene-butadiene and of polypropylene (EPDM / PP) or of nitrile-butadiene and of polypropylene (NBR / PP).

Particularly preferred components b) are thermoplastic and elastomeric styrene block copolymers. Examples of these are block copolymers which have blocks of styrene-ethylene and of propylene-styrene (SEPS) or of styrene-ethylene and of butadiene-styrene (SEBS) or of styrene and of butadiene (SBS).

In the context of this description, thermoplastic block copolymer and elastomeric block copolymer are block copolymers which behave at room temperature comparable to the conventional elastomers, but can be plastically deformed under heat supply and thus exhibit a thermoplastic behavior. These thermoplastic and elastomeric block copolymers have in some areas physical crosslinking points (e.g., minor valence forces or crystallites) that dissolve on heat without the polymer molecules decomposing.

As component c) selected carbon black and / or graphite particles are used. These are carbon blacks or graphites whose primary particles are arranged in the form of aggregates, which preferably have the shape of a tang, in particular having the shape of elongated filaments. The carbon blacks used according to the invention consist of nanoscale primary particles. These are generally spherical and typically have diameters in the range from 10 to 300 nm. Due to the strong anisotropy of the aggregates of carbon black particles or graphite platelets used according to the invention, longitudinally aligned aggregates form during the spinning of the thread, which are electrically conductive along the longitudinal axis of the thread Form paths. In the unstretched thread these aggregates are partially present in a geknäulter form and are stretched by stretching in the thread longitudinal direction, but not torn. In this way, the electrically conductive paths are obtained in the thread.

Particularly preferably used components c) are carbon blacks, which are present in the form of elongate aggregates made up of a plurality of primary particles in contact with one another and the drawn thread has an electrical conductivity of at least 0.5 ^× 10 ^-6 Siemens / cm, preferably at least 1 , 0 * 10 ^-5 Siemens / cm, measured in the longitudinal direction of the thread.

The amounts of components a), b) and c) in the threads according to the invention can be selected within wide limits. The threads typically contain from 20 to 70% by weight of component a), from 15 to 40% by weight of component b) and from 5 to 50% by weight of component c), in each case based on the total mass of the thread.

The combination of components a), b) and c) used according to the invention gives the filaments not only excellent abrasion resistance, but also good textile-technological properties, in particular good dynamic properties and excellent dimensional stability, as well as excellent electrical conductivity.

The components a), b) and c) required for producing the threads according to the invention are known per se, some are commercially available or can be prepared by processes known per se.

The threads according to the invention may contain, in addition to components a), b) and c), further auxiliaries d).

Examples of these are, in addition to the hydrolysis stabilizer already mentioned, processing aids, 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 antioxidants are phosphorus compounds, such as phosphoric acid esters or sterically hindered phenols.

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 threads according to the invention can be in any desired form, for example as multifilaments, as staple fibers, as secondary spun yarns, also in the form of twisted yarns, or in particular as monofilaments.

In a particularly preferred embodiment, the threads according to the invention are present as multicomponent threads. Examples of this are side-on threads or, in particular, core-sheath threads. In the latter, the sheath preferably consists of a composition comprising components a), b), c) and optionally d) and the core consists of a filament-forming polymer which determines the mechanical properties, mainly the strength and elongation at break, of the total filament.

A particularly preferred combination is a core-sheath thread whose core consists of polyester, preferably of polyethylene terephthalate, and whose sheath contains the components a), b), c) and optionally d).

In preferred core-sheath filaments, the weight ratio of core to sheath is 95: 5 to 20:80, preferably 75:25 to 45:55, more preferably 70:30 to 50:50.

The titer of the threads according to the invention can vary within wide limits. Examples are 1 to 45,000 dtex, in particular 100 to 4,000 dtex.

The cross-sectional shape of the threads according to the invention may be arbitrary, for example round, oval or n-cornered, where n is greater than or equal to 3.

The threads of the invention can be prepared by methods known per se.

1. i) Extrudieren eines Gemisches enthaltend Komponenten a), b) und c) durch eine Spinndüse,
2. ii) Abziehen des gebildeten Filaments,
3. iii) Verstrecken, und
4. iv) gegebenenfalls Relaxieren des gebildeten Filaments.

A typical manufacturing process comprises the measures:

1. i) extruding a mixture comprising components a), b) and c) through a spinneret,
2. ii) stripping the formed filament,
3. iii) stretching, and
4. iv) optionally relaxing the formed filament.

The production of multi-component threads is analogous. Only here are the spinning masses, which form the different components, melted in different extruders and pressed through a multi-component spinneret.

The composition comprising components a), b), c) and optionally d) is preferably used in the form of a masterbatch.

The threads according to the invention are drawn one or more times during production.

Particularly preferred for the production of the threads as component a) and / or as a component of the core thread, a polyester produced by solid phase condensation is used.

After pressing the polymer melt through a spinneret, the hot polymer filament is cooled, e.g. in a cooling bath, preferably in a water bath, and then wound up or peeled off. The removal speed is greater than the injection rate of the polymer melt.

The yarn produced in this way is then re-stretched one or more times, optionally fixed and wound up, as is known from the prior art for the abovementioned melt-spinnable polymers.

The threads according to the invention are preferably used for the production of textile surface constructions, in particular of woven fabrics, spiral fabrics, laid or knitted fabrics. These textile surface constructions are preferably used in screens.

Textile surface constructions containing the threads according to the invention are likewise the subject of this invention.

The threads according to the invention can be used in all industrial fields. They are preferably used in applications in which increased wear and static electricity due to mechanical stress are to be expected. Examples thereof are the use in screen fabrics and filter cloths for gas and liquid filters, in dry belts, for example for the production of food, in packaging containers or in hoses for conveying small particles. These uses are also the subject of the present invention.

Another use of the filaments of the invention in the form of monofilaments relates to their use as conveyor belts or as components of conveyor belts.

The threads according to the invention can also be used in screens intended for use in paper machines.

These uses are also the subject of the present invention.

The following examples illustrate the invention without limiting it.

Examples: General procedure for the preparation of core-shell monofilaments of Examples 1 to 2

The core component, polyethylene terephthalate ("PET"), was melted in the extruder. The components for the sheath, PET and a masterbatch (Deltacom PET 1917 EC3, Delta Kunststoffe Produktions-und Handelsgesellschaft mbH, Weeze, Germany), made of PET, thermoplastic elastomer, conductive carbon black and additives were mixed and melted in another extruder. The melted spun masses from both extruders were spun, drawn and drawn into a bicomponent 20-hole spinneret with a hole diameter of 1.0 mm at a flow rate of 488 g / min and a take-off speed of 31 m / min into core-shell monofilaments heat-set in the hot-air duct at 255 ° C under heat-shrinkage. The textile technological data of the monofilaments obtained are shown in Table 1.

The PET used was a type with an IV value of 0.72 dl / g.
The masterbatch consisted of 50% by weight of the PET type described above, and 27% by weight of a thermoplastic elastomeric styrene block copolymer, 20% by weight of a conductivity carbon black and 3% by weight of processing stabilizer, lubricant, steric hindered amine and silane. A commercially available antistatic monofilament (Homer AIX from the Albany Group) served as comparison. Table 1 Example 1 ¹⁾ Example 2 ¹⁾ Comparative example tensile strenght 20.8 20.4 13.6 (CN / tex) Modulus of elasticity (GPa) 11.8 10.6 11.8 elastic 1.3 1.4 1.3 Strain (%) Elongation at break (%) 32.5 60.6 31.3 Titre (dtex) 2715 2703 4483 el. resistance 1.6 * 10 ^-5 1.8 * 10 ^-5 6.6 * 10 ^-6 (S / cm) ¹⁾ The products of Examples 1 and 2 differed in heat setting

• Zugfestigkeit gemäß DIN EN/ISO 2062
• Reißdehnung gemäß DIN EN/ISO 2062

The fiber properties were determined as follows:

• Tensile strength according to DIN EN / ISO 2062
• Elongation at break according to DIN EN / ISO 2062

• Das Monofilament wurde unter leichter Vorspannung zwischen zwei Klemmen eingespannt und an zwei Positionen versilbert. An den versilberten Stellen wurden elektrische Klemmen angebracht, die mit einem Widerstandsmessgerät (Metra Hit 15 S; Meßbereich bis 30 MΩ) verbunden waren. Als Klemmenabstand wurden zwischen 10 mm und 300 mm gewählt. Standardmäßig ist ein Klemmenabstand von 100 mm verwendet worden. Gemessen wurde der Widerstand pro cm, also Ω/cm. Der Leitwert ist der reziproke Widerstand für 1 Zentimeter Monofillänge.

The determination of the electrical conductivity was as follows:

• The monofilament was clamped under slight tension between two clamps and silvered at two positions. At the silvered points electrical terminals were attached, which were connected to a resistance meter (Metra Hit 15 S, measuring range up to 30 MΩ). The clamp spacing was chosen between 10 mm and 300 mm. By default, a clamp distance of 100 mm has been used. The resistance was measured per cm, ie Ω / cm. The conductance is the reciprocal resistance for 1 centimeter monofilament length.

Example: R = 620 kΩ / 10 cm corresponds to R = 62 kΩ / cm corresponds to L = 1.6 * 10 ^-5 S / cm.

Claims (11)

Melt-spun yarn having a Young's modulus of 8 to 14 GPa and an elastic elongation of up to 1.5% a) a thermoplastic polyester, b) a thermoplastic elastomeric block copolymer, and c) carbon black and / or graphite particles in the form of aggregates aligned along the longitudinal axis of the filament which form electrically conductive paths along the longitudinal axis of the filament. Thread according to Claim 1, characterized in that component a) is a polyethylene terephthalate homopolymer or a polyethylene terephthalate copolymer which, in addition to polyethylene terephthalate units, has units which are derived from aliphatic, cycloaliphatic or aromatic dicarboxylic acids or their polyester-forming derivatives and from aliphatic or cycloaliphatic dialcohols. Thread according to one of claims 1 or 2, characterized in that component b) is a thermoplastic polyurethane elastomer, a thermoplastic polyester elastomer, thermoplastic styrene block copolymer or a combination of two or more of these components. Thread according to one of claims 1 to 3, characterized in that component b) is a thermoplastic, elastomeric styrene block copolymer, in particular a styrene-butadiene-styrene block copolymer or a styrene-ethylene-butadiene-styrene block copolymer. A thread according to any one of claims 1 to 4, characterized in that component c) is a carbon black which is in the form of elongated aggregates composed of a plurality of primary particles in contact with each other is present in the thread and causes an electrical conductivity of the thread of at least 0.5 * 10 ^-6 Siemens / cm, preferably at least 1.0 * 10 ^-5 Siemens / cm, measured in the longitudinal direction of the thread. Thread according to one of claims 1 to 5, characterized in that the thread is a core-sheath thread whose core is formed of polyester and whose sheath contains components a), b) and c). Thread according to Claim 6, characterized in that the polymer of component a) is a polyester and in that the weight ratio of core and shell is 95: 5 to 20: 80, preferably 75: 25 to 45: 55, in particular 70: 30 to 50 : 50. Thread according to one of claims 1 to 7, characterized in that the thread is a monofilament. Textile surface construction, in particular fabric, comprising threads according to one of claims 1 to 8. Textile surface construction according to claim 9, characterized in that in addition to threads according to one of claims 1 to 8 further threads of polyester, in particular of polyethylene terephthalate. Use of a thread according to one of claims 1 to 8 in textile surface constructions for technical applications, in particular in mesh fabrics and filter cloths for gas and liquid filters, in dry belts, preferably for the production of food, in packaging containers, in hoses for conveying small particles or as conveyor belts or as components of conveyor belts.