CA2483333A1 - Combination twists for paper machine felts and process for the production thereof - Google Patents

Abstract

A base fabric, in particular for use as machine clothing for paper machines or as a textile for other industrial processes, is described. The base fabric comprises at least one combination yarn of filaments which are produced from polyamide and thermoplastic polyurethanes.

Description

Combination twists for paper machine felts and process for the production thereof In machinery used for the production of paper, paperboard, pulp or similar products, the fibrous slurry is partially dewatered by being squeezed either between two press rolls or, in "shoe" presses, between a pressure roll and a press shoe. For economic reasons, it is generally desirable to remove the majority of the water from the fibrous slurry in this press section. In recent decades, intensive research has resulted in the development of entirely new types of felts or fabrics which are suitable for dewatering in the press section of paper machines. It has been possible with the assistance of these new paper machine fabrics to satisfy increasingly stringent requirements far dewatering efficiency.
At the same time, it has also proved possible to achieve a major increase in machine running speeds with the consequence that the search for materials with a major increase in speed after the installation of a new paper machine fabric has intensified.
Other properties, such as running behaviour, resistance to vibration and abrasion resistance also had to be enhanced.
The invention relates to a novel (base) fabric for paper machine felts, in particular press felts with improved properties, in particular with improved elasticity in the felt thickness direction, greater compressibility and improved water absorption capacity during paper production from the beginning to the end of the felt's service life.
The invention is achieved in that, during production of the supporting fabric for the paper machine felt, combination yarns of polyamide and thermoplastic polyurethane filaments, in particular twisted yams of combination twists with to 20 monofilaments of polyamide 6 and/or polyamide 4,6, polyamide 6,10, polyamide 6,12, polyamide 11 or polyamide 12 and 20 to 1 monofilaments produced from thermoplastic polyurethane are used in the warp and/or weft direction instead of twist or individual monofilament yarns composed solely of polyaJnide monofilaments.

Processes for the production of monofilaments of thermoplastic polymers are known in principle from the prior art (c.f. Handbuch der Kunststofftechnik II
[manual of plastics technology II], C. Hawser-Verlag, Munich 1986, pages 295-319).
The Lehrbuch der Papier- and Kartonerzeugung [textbook of paper and paperboard production), VEB-Fachbuchverlag 1987, pages 190 et seq.) contains information about paper production in modern paper machines, for example with regard to sheet formation (forming section), mechanical dewatering (press section) and thermal dewatering (drying section) as well as to smoothing (calendering) and winding.
Fabrics for the sheet forming section mainly consist of polyester monofilaments. In order to increase abrasion resistance, monofilaments based on polyamide monofilaments together with polyester filaments are used as alternating threads in the cross-machine direction of the paper machine.
Press felts in the press section consist of one or more base fabrics needle-punched with nonwoven fabric. These press felts are produced virhzally exclusively from polyamide fibres and polyamide monofilaments, primarily from pure polyamide 6 or also polyamide 6,6 filaments.
Commercial press felts based on polyamide 6 monofilaments offer considerable advantages relative to felts which are possibly also produced from other materials, for example polypropylene/polyester or wool, due to their good abrasion resistance, elevated compressibility and good recovery characteristics after passage through the press nip.
Fabrics for the drying section, which are used in the final section of the paper machine, conventionally consist of polyester monofilaments which are stabilised against hydrolytic degradation, for example by stabilisers such as Stabaxol~
(commercial product, produced by Rheinchemie; Mannheim).
Specifically, the following types of press felts axe known in principle from the prior art.

Patent specification US-A-4,323,622 discloses a high-elasticity dewatering felt for use, for example, in papermaking or in cellulose machines, in which the elastic properties of the felt are achieved by incorporating molecular thermoplastic elastomers. Alternatively, a high-molecular, branched urethane-based elastomer material could here be incorporated in order to achieve the desired elasticity. Tn this structure, however, the elasticity is oriented in machine direction and the elastomer material is intended to be capable of extending to at least twice its original length and finally rapidly returning substantially to its original length once the load has been removed from the fabric.
The disadvantages of the prior art according to US-A-4,323,622 are, however, serious. The elevated extension of the material in the paper machine may bring about an unwanted extension of the fabric and likewise of the paper in the machine direction together with contraction thereof in the cross-machine direction.
Such major dimensional changes in the fabric normally result in creasing of the felt and of the paper, which in tum causes breakage of the papex sheet. The term machine direction (MD) is here taken to mean the direction parallel to the motion of the felts in the papermaking machine.
Patent specification US-A-4,533,594 discloses a paper machine felt, in which the mesh layer is a fabric which is in turn formed from yam in the machine direction in .
combination with yarn in cross-machine direction. The crosswise oriented yarns axe here multifilament yams based on nylon, polyester or polyacrylonitrile with a polyurethane coating. The object of said patent specification is to provide a paper machine felt of the butt-on-mesh type in which the mesh fabric exhibits improved resilience. A similar fabric is described in patent specification US-A 4,731,2 1, in which a fabric is obtained from totally encapsulated monofilament yarns. The yarns are coated prior to weaving in order to impart anti-stick characteristics to the fabric.
The coating may be adjusted such that the thickness of the yarn in the machine direction differs from the thickness of the yarn in the cross-machine direction.
The disadvantages of the above-stated prior art according to US-A 4,533,594 are also serious. The coating on the monofilarnents consists of another type of polymer and is only physically bonded around the core filament. The coating is only very weakly chemically bonded. This means that the coating may be deformed or moved on the core filament with a consequent decline in the originally desired properties.
The needling process during production of the papex machine felts is typically very aggressive with regard to this type of coating, which in turn results in the originally desired properties not being retained. In addition to these disadvantages, the coating on the core yarn is only a proportion of the crass-section in the yarn. The actual elastic deformation accordingly occurs in only a small part of the shell, resulting in a smaller elastic effect. The tension/recovery characteristics of a fabric based on this type of yarn thus almost exclusively depend on the properties of the core material.
Patent specification US-A 5,360,518 describes another press fabric with coated yarn which may be used in the press section of a paper machine. It comprises a multilayer structure with a thin paper-contacting surface and an ample underlying layer.
One of two or more layers of woven yarns comprises multicomponent yarns with a plurality of load-bearing strands. The multicomponent yarns may be multifilament or multistrand yarns which are composed of thin polyamide filaments. They may also be polyurethane-coated monofilament yarns and provide the press fabric with a compressible, resilient structure. Die multifilament or multistrand yarns may likewise be polyurethane-coated. The disadvantages of this prior art are comparable with the disadvantages of the fabric known from US-A 4,533,594. It is more readily feasible to achieve a strong coating bond with multifilarnent yarns. However, such a yarn suffers from the same limitations as the above-described monoflament-coated monofilament core yarn. During the frequently repeated pressure phases in the press nip (of the order of several million press operations), the coating is torn off or distorted on the core yam and the originally desired effect declines.
In patent specification US-A-5,194,121, it is attempted to produce a felt with elevated elasticity, recovery and durability with an elastic component in the fibre layer of the felt. However, polyurethane is described as unusable for the needling process which is intended to fasten the fibres to the base fabric. As an alternative solution, it is proposed instead to use a polyamide block copolymer with hard and soft segments.

Various attempts have been made to improve the properties of polyamide and thermoplastic polyurethanes by mixing the polymers during the extrusion process.
Published patent application DE 19 829 928 A2 describes a process for the S production of filament material which comprises a mixture of polyamide and thermoplastic polyurethane. However, the large disparity in melting points of the two polymers results in particular processing problems. The resultant monofilament is lower in strength than conventional polyamide. Moreover, only a slight increase in cross-sectional elasticity is observed. The thermal degradability of the thermoplastic polyurethane may also be very disadvantageous during extrusion if the residence time in the extruder is excessively long.
Patent specification US-A-6,514,386 describes a paper machine felt which is asserted to exhibit excellent elasticity over an extended duration, and which consists of a base fabric and needled nonwoven layer together with a separate film layer with elongate ridges oriented in cross-machine direction. Such a film may be provided in the base fabric or between different layers of the felt. The paper machine felt is consequently capable of running smoothly through the winding section of the paper machine and is comparatively resistant to the fatigue which may occur due to repeated pressing in the press nip.
From the standpoint of felt production, laminating an elastic layer onto a strong base fabric may be a very risky operation as ruckling and unevenness can easily be produced. The edges of the film must be joined, these zones then always being imperfect zones.
Although it could in principle be conceivable to use TPU monofilaments and/or twisted yarns based on TPU monofilaments in the base fabric of press felts, the person skilled in the art would probably initially anticipate severe processing problems as monofilaments based on thermoplastic polyurethanes are highly elastic and highly extensible and moreover exhibit an elevated coefficient of friction. TPU
monofilarnents axe accordingly only processed in relatively large diameters and under tension. Yarns and fabric produced in this manner would exhibit defects _6_ unacceptable to the paper machine industry. Dimensional stability and tension in machine direction and cross-machine direction of the paper machine would not be tolerable. Since the elastic yarns are highly extensible, such a fabric would exhibit low modulus in machine direction and elevated contraction in cross-machine direction. These disadvantages could in part be overcome by laminating such a fabric onto another fabric of polyamide. However, problems would still remain due to the very different tension/recovery characteristics of such a twin base fabric.
Rolling of the fabric edges is for example one result of the mismatch between these opposing base fabrics.
It has surprisingly now been found that the above-described disadvantages of the prior art may largely be avoided if TPU monofilaments are simultaneously processed with one or more polyamide monofilaments and/or polyamide multifilaments to yield industrial base fabrics, in particular if they are first twisted and then woven. It has furthermore surprisingly been found that these combination yarns (twists) based on thermoplastic polyurethane and polyamide monofilaments may be converted into base fabrics or felts virtually in the same manner as conventional pure polyamide yarns.
The present invention provides a base fabric, in particular for use as machine clothing for paper machines or as a textile for other industrial processes, which is characterised in that the base fabric contains at least one combination yarn of polyamide and TPU monofilaments.
The thermoplastic polyurethane (TPU/polyamide (PA)) combination yarns may consist either only of initial twists (with one direction of twist) or of initial and final twists (twists with different direction of twist). The TPU/PA combination yarns may preferably be arranged in the machine direction and/or cross-machine direction of the press felt of the paper machine.
A preferred base fabric is characterised in that the polyamide is selected from the range polyamide 4,6, polyamide 6, polyamide 6,6, polyamide 6,I2, polyamide 6,10, polyaxnide 1 l and polyamide 12, together with copolyaxnides of the stated polymers or selected mixtures of these polyamides.
In a preferred embodiment, the combination yarn is made from straight, i.e.
untwisted filaments of polyamide and thermoplastic polyurethanes.
In a preferred variant of the base fabric, the combination yaxn is produced from at least one part of twisted polyamide filaments and thermoplastic polyurethane filaments.
In a further preferred embodiment of the base fabric, the above-stated combination yarn will comprise a combination of 1 to 10,000 monofilaments of polyamide and to I monofilaments of thermoplastic polyurethanes.
I S Very particularly preferably, the combination yarn for the base fabric is a combination of 1 to 20 monofilaments of polyamide and 20 to 1 monofilaments of thermoplastic polyurethanes.
A particularly preferred base fabric is also one which is characterised in that the 20 monofilaments in the combination yarn (polyamide and/or TPU monofilaments) exhibit a diameter in the range from 0.05 to 2 mm.
One particular advantage of the above-stated base fabric is that it may be produced straightforwardly using existing paper machine manufacturing technology, including .
conventional twisting machines and looms.
Another advantage is that the modulus of elasticity of the polyamide is retained in machine direction and may be combined with the modulus of elasticity of the thermoplastic polyurethane in the thickness direction of the fabric.
It has furthermore been found that press felts produced on the basis of the base fabric according to the invention not only have a greater paper dewatering capacity but also achieve a higher level of dewatering more quickly and retain their _g_ dewatering capacity over a longer period than press felts which have been produced without the stated combination yarns based on TPU/polyamide. It has moreover also been found that paper machine vibration may be further reduced if press felts are used which have been produced with the assistance of the above-stated base fabric.
As a result, less energy is required for the drying step at the end of the papermaking process. Alternatively, the paper machine may be operated at higher speeds with otherwise identical energy consumption.
The TPU/PA polyfilament combination may also be processed in the untwisted state. This may be achieved by simultaneously winding TPU and polyamide monofilaments onto the bobbin after production. Thermoplastic polyurethanes suitable for the production of TPU filaments are any extrusion grades of thermoplastic polyurethane elastomers based both on polyester or polyether grades, preferably with a Shore hardness of 75 to 99 Shore A.
Thermoplastic polyurethane elastomers {TPU) are industrially significant because they exhibit excellent mechanical properties and can be processed by low-cost melt-processing methods. The mechanical properties may be varied over a wide range by using different chemical synthesis components. ~verviews of TPU, their properties and applications may be found in Kunststoffe 68 {1978), pages 819-825 and Kautschuk, Gummi, Kunststoffe 35 (1982), pages 568-584.
TPU are synthesised from linear polyols, usually polyester or polyether polyols, organic diisocyanates and short-chain diols (chain extenders). Catalysts may additionally be added to accelerate the formation reaction. The molar ratios of the synthesis components may be varied over a wide range, by which means it is possible to adjust product properties. Molar ratios of polyols to chain extenders of 1:1 to 1:12 have proved effective, yielding products in the range from 70 Shore A to 75 Shore D. Synthesis of the melt-processable polyurethane elastomers may proceed either stepwise (prepolymer process) or by the simultaneous reaction of all components in a single stage {one-shot process). In the prepolyrner process, a prepolyrner containing isocyanate is formed from the polyol and diisocyanate, the prepolymer being reacted with the chain extender in a second step. TPU may be produced continuously or discontinuously. The best known industrial production processes are the belt process and the extruder process.
Melt-processable polyurethanes usable according to the invention may be obtained by reacting the polyurethane-forming components A) organic diisocyanate, B) linear hydroxyl-terminated polyol with a molecular weight of 500 to 5000, C) diol or diamine chain extenders with a molecular weight of 60 to 500, wherein the molar ratio of NCO-groups in A) to the isocyanate-reactive groups in B) andC)is0.9to1.2.
Organic diisocyanates A) which may, for example, be considered are aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, as are described in Justus Liebigs Anna.len der Chemie, 562, pages 75-136.
The following may specifically be stated by way of example: aliphatic diisocyanates, such as hexamethylene diisocyanate, cycloaliphatic diisocyanates, such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate and 1-methyl-2,6-cyclohexane diisocyanate and the corresponding isomer mixtures, 4,4'-dicyclohexylmethane diisocyanate, 2,4'-dicyclohexylmethane diisocyanate and 2,2'-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures, aromatic diisocyanates, such as 2,4-tolylene diisocyanate, mixtures of 2,4-tolylene diisocyanate and, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 2,2'-diphenylmethane diisocyanate, mixtures of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate, urethane-modified, liquid 4,4'-diphenylmethane diisocyanates and 2,4'-diphenylmethane diisocyanates, 4,4'-diisocyanato-1,2-diphenylethane and 1,5-naphthylene diisocyanate. Preferably used compounds are 1,6-hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane diisocyanate isomer mixtures with a 4,4'-diphenylmethane diisocyanate content of >96 wt.% and in particular 4,4°-diphenylinethane diisocyanate and 1,5-naphthylene diisocyanate. The stated diisocyanates may be used individually or in the form of mixtures with one another.
They may also be used together with up to 15 wt.% (calculated relative to the total quantity of diisocyanate) of a polyisocyanate, for example triphenylmethane 4,4',4"-triisocyanate or polyphenyl-polymethylene polyisocyanates.
Linear hydroxyl-terminated polyols with a molecular weight of 500 to 5000 are used as component B). As a result of their production process, these often contain small quantities of nonlinear compounds and they are consequently often referred to as "substantially linear polyols". Polyester, polyether, polycarbonate diols or mixtures of these are preferred.
Suitable polyether diols may be produced by reacting one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene residue with a starter molecule which contains two active hydrogen atoms in bound form. Alkylene oxides which may be mentioned by way of example are: ethylene oxide, 1,2-propylene oxide, epichlorohydrin and 1,2-butylene oxide and 2,3-butylene oxide. Ethylene oxide, propylene oxide and mixtures of 1,2-propylene oxide and ethylene oxide are preferably used. The alkylene oxides may be used individually, alternately in succession or as mixtures. Starter molecules which may, for example, be considered are: water, aminoalcohols, such as N-alkyldiethanolamines, for example N-methyldiethanolamine, and diols, such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol and 1,6-hexanediol. Mixtures of starter molecule may optionally also be used. Suitable polyether diols are furthermore the hydroxyl group-containing polymerisation products of tetrahydrofuran. Trifunctional polyethers may also be used in proportions of 0 to 30 wt.%, relative to the difunctional polyether, but at most in such a quantity that a melt-processable product is obtained. The substantially linear polyether diols have molecular weights of 500 to $000.
They may be used both individually and in the form of mixtures with one another.

Suitable polyester diols may, for example, be produced from dicarboxylic acids having 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, and polyhydric alcohols. Dicarboxylic acids which may for example be considered are:
aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid and aromatic dicarboxyhc acids, such as phthalic acid, isophthalic acid and terephthalio acid. The dicarboxylic acids may be used individually or as mixtures, for example in the form of a mixture of succinic, glutamic and adipic acids. For the production of polyester diols, it may optionally be advantageous, instead of using dicarboxylic acids, to use the corresponding dicarboxylic acid derivatives, such as carboxylic acid diesters having 1 to 4 carbon atoms in the alcohol residue, carboxylic anhydrides or carboxylic acid chlorides.
Examples of polyhydric alcohols are glycols having 2 to 10, preferably 2 to 6 carbon atoms, such as ethylene glycol, diethyiene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 2,2-dimethyl-1,3-propanediol, 1,3-propanediol and dipropylene glycol. Depending upon the desired properties, the polyhydric alcohols may be used alone or optionally as a mixture. Esters of carbonic acid with the stated diols, in particular those having 4 to 6 carbon atoms, such as 1,4-butanediol or 1,6-hexanediol, condensation products of hydroxycarboxylic acids, for example hydroxycaproic acid and polymerisation products of lactones, for example optionally substituted caprolactones, are furthermore suitable. Preferably used polyester diols are ethanediol polyadipates, 1,4-butanediol polyadipates, ethanediol/1,4-butanediol polyadipates, 1,6-hexanediol/neopentyl glycol polyadipates, 1,6-hexanediol/1,4-butanediol polyadipates and polycaproplactones.
The polyester diols have molecular weights of 500 to 5000 and may be used individually or in the form of mixtures with one another.
Diols or diamines with a molecular weight of 60 to 500, preferably aliphatic diols having 2 to 14 carbon atoms, such as for example ethanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol and in particular 1,4-butanediol are used as the chain extenders C). Diesters of terephthalic acid with glycols having 2 to 4 carbon atoms are, however also suitable, such as for example texephthalic acid bis-ethylene glycol or terephthalic acid bis-1,4-butanediol, hydroxyalkylene ethers of hydroquinone, such as for example 1,4-di(hydroxyethyl)hydroquinone, ethoxylated bisphenols, (cyclo)aliphatic diamines, such as for example isophoronediamine, ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, N-methylpropylene-1,3-diaxnine, N,N'-dimethyl-ethylenediamine and aromatic diamines, such as for example 2,4-tolylenediamine and 2,6-tolylenediamine, 3,5-diethyl-2,4-tolylenediamine and 3,5-diethyl-2,6-tolylenediamine and primary mono-, di-, tri- or tetraalkyl-substituted 4,4'-diaminodiphenylmethane. ?Mixtures of the above-stated chain extenders may also be used. Smaller quantities of triols may additionally be used.
Conventional monofunctional compounds may furthermore be used in small quantities, for example as chain terminators or mould release agents. Alcohols such as octanol and stearyl alcohol or amines such as butylamine and stearylamine may be mentioned by way of example.
In order to produce the TPU, the synthesis components, optionally in the presence of catalysts, auxiliaries and additives, are reacted in quantities such that the equivalent ratio of NCO groups to the total of the NCO-reactive groups, in particular the OH
groups of the low molecular weight diols/triols and polyols is 0.9:1.0 to 1.2:1.0, preferably 0.95:1.0 to 1.10:1Ø
Suitable catalysts according to the invention are known prior art and conventional tertiary amines, such as for example triethylamine, dimethylcyclohexylamine, N-methylinorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo(2.2.2)octane and similar and in particular organic metal compounds such as titanic acid esters, iron compounds, tin compounds, for example tin diacetate, tin dioctoate, tin dilaurate or the dialkyltin salts of aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate or the like.
Preferred catalysts are organic metal compounds, in particular titanic acid esters, iron or tin compounds.
Apart from the TPU components and the catalysts, other auxiliaries and additives may also be added. The following may be mentioned by way of example:
lubricants such as fatty acid esters, the metal soaps thereof, fatty acid amides and silicone compounds, antiblocking agents, inhibitors, stabilisers to counter hydrolysis, the action of light or heat and discoloration, flame retardants, dyes, pigments, inorganic or organic fillers. Further details regarding the stated auxiliaries and additives may be found in the specialist literature, for example J.H. Saunders, K.C. Frisch:
"High Polymers", volume XVI, Polyurethane, parts 1 and 2, Interscience Publishers and 1964, R. Gachter, H. IoiLiiller (eds.): Taschenbuch der Kunststoff Additive [plastics additive handbook], 3rd edition, Hanser Verlag, Munich 1989, or DE-A 29 Ol 774.
Further additives which may be incorporated into the TPU are thermoplastics, for example polycarbonates and acrylonitrile/butadiene/styrene terpolymers, in particular ABS. Other elastomers such as rubber, ethylene/vinyl acetate copolymers, styrene/butadiene copolymers and other TPU may likewise be used. Conventional commercial plasticisers such as phosphates, phthalates, adipates, sebacates and alkylsulfonic acid esters are fiufihermore suitable for incorporation.
The TPU usable according to the invention may be produced continuously by the "extruder" process, for example in a multi-screw extruder. The TPU components A), B) and C) may be apportioned simultaneously, i.e. by the one-shot process, or in succession, i.e. in accordance with a prepolyrner process. The prepolymer may here both be initially introduced batchwise and be continuously produced in one section of the extruder or in a separate, upstream prepolymer unit.
The TPU and polyamide monofilaments are produced as such using production processes which are generally known from the prior art.
The present invention also provides a process for the production of a combination yarn of filaments produced from polyamide and such filaments produced from thermoplastic polyurethanes, in which polyamide and thermoplastic polyurethane monofilaments are delivered to a twisting machine at speeds of 5 to 50 m/min and then twisted at a tension of at Least 0.1 cN/tex, preferably of 0.2 to 4 cN/tex, particularly preferably 0.3 to 0.8 cN/tex, wherein the tension relates to the TPU
monofilaments.

In a preferred process, the polyamide monofilaments consist of polyamide 4,6, polyamide 6, polyamide 6,6, polyamide 6,12, polyamide 6, I 0, polyamide 11 and polyamide 12 or selected copolymers or mixtures of these polyamides.
In a further, particularly preferred process, the TPU monofilaments are fed at a defined feed tension to the delivery unit of a twisting machine and then twisted with the polyamide filaments.
A further preferred process is characterised in that the defined feed tension of the TPU monofilaments is produced by means of an additional TPU delivery unit, wherein the TPU delivery unit has a lower delivery speed than the PA
monofilament delivery unit.
The following Examples illustrate the advantages of the invention with regard to the combination yarns without limiting the invention as such.

Examples Description of the twisting operation Twist characteristics:
The initial twist of the monofilaments consists of at least one TPU
monofilament and at least one polyamide monofilament and/or a polyamide multifilament. At least two of these initial twists are twisted together in order to form the twisted yarn (final twisting), which is processed by weaving.
Production of a twisted PA/TPU combination yarn:
The TPU monofilaments must be fed with a defined delivery tension to the delivery unit of the twisting machine and are then delivered into the twisting machine with the polyamide monofilaments and twisted. TPU monofilament is produced and PA
monofilament is taken from a yarn reel.
Both monofilaments are fed to a common bobbin, wherein the winding speed is 2Q determined by the delivery speed of the PA monofilament. Since the TPU
monofilament is delivered at a lower speed, it receives a certain feed tension relative to the PA monofilament.
An Alma Saurer model AZB-T twisting machine was used to produce the initial twist and for the subsequent twisting steps.

Claims (13)

1. A base fabric, in particular for use as machine clothing for paper machines or as a textile for other industrial processes, characterised in that the base fabric comprises at least one combination yarn of filaments produced from polyamide and thermoplastic polyurethanes.

2. A base fabric according to claim 1, characterised in that the polyamide is selected from the range polyamide 4,6, polyamide 6, polyamide 6,6, polyamide 6,12, polyamide 6,10, polyamide 11, polyamide 12, copolamides of the above-stated polyamides or selected mixtures of these polyamides.

3. A base fabric according to one of claims 1 to 2, characterised in that the combination yarn is made from smooth (untwisted) filaments of polyamide and thermoplastic polyurethanes.

4. A base fabric according to one of claims 1 to 2, characterised in that the combination yarn is produced from at least one twisted filament fraction of polyamide or thermoplastic polyurethane filaments.

5. A base fabric according to one of claims 1 to 4, characterised in that the combination yarn comprises a combination of 1 to 10,000 monofilaments of polyamide and 20 to 1 monofilaments of thermoplastic polyurethane.

6. A base fabric according to claim 5, characterised in that the combination yarn comprises a combination of 1 to 20 monofilaments of polyamide and 20 to 1 monofilaments of thermoplastic polyurethane.

7. A base fabric according to one of claims 1 to 6, characterised in that the monofilaments in the combination yarn have a diameter of the order of magnitude of 0.05 to 2 mm.

8. A process for the production of combination yarn from filaments, produced from polyamide and thermoplastic polyurethanes, characterised in that the polyamide and thermoplastic polyurethane monofilaments are fed to a twisting machine at a speed of 5 to 50 m/min and are then twisted together at a tension of the TPU monofilaments of at least 0.1 cN/tex, preferably of 0.2 to 4 cN/tex, particularly preferably of 0.3 to 0.8 cN/tex.

9. A process according to claim 8, characterised in that the polyamide monofilaments are produced on the basis of polyamide 4,6, polyamide 6, polyamide 6,6, polyamide 6,12, polyamide 6,10, polyamide 11 and polyamide 12 or selected mixtures or copolyamides of these polyamides.

10. A process according to one of claims 8 or 9, characterised in that the TPU
monofilaments are delivered to the twisting machine at the defined delivery tension of the delivery unit and are then twisted with the polyamide filaments.

11. A process according to one of claims 8 to 10, characterised in that the defined feed tension of the TPU monofilaments is produced with the assistance of an additional TPU delivery unit, the TPU delivery unit having a lower delivery speed than the PA monofilament delivery unit.

12. A process according to one of claims 8 to 11, characterised in that the defined delivery tension of the TPU monofilaments is produced by the tension-controlled roller take-off of the filaments from the TPU bobbin.

13. A process according to one of claims 8 to 11, characterised in that the defined delivery tension of the TPU monofilaments is produced by common parallel winding of the TPU monofilaments together with the polyamide monofilaments onto a bobbin which serves as a delivery bobbin for the twisting machine.