Patent Publication Number: US-2015084231-A1

Title: Thermoplastic fibres with reduced surface tension

Description:
The present invention relates to a process for producing thermoplastic fibres having reduced surface tension and also to products obtainable by the melt-spinning process from these thermoplastic fibres having reduced surface tension, wherein the thermoplastic to be used is admixed with a copolymer of at least one α-olefin and at least one acrylic or methacrylic ester of an aliphatic alcohol, preferably of a 2-ethylhexanol. 
     Products obtained from thermoplastic fibres from the group of polyamides or polyesters within the meaning of the present invention are fibrous nonwoven webs, nonwovens, wovens, threads, yarns, ropes, felts, drawn-loop knits, non-crimp fabrics or formed-loop knits. Fibrous nonwoven webs or nonwovens are preferred products within the meaning of the present invention. A fibrous nonwoven web consists of loosely aggregated fibres yet to be bonded together. The strength of a fibrous nonwoven web is only based on the fibre-inherent adherence. The latter, however, can be influenced by working up. In order that the fibrous nonwoven web may be processed and used, it needs to be consolidated, for which various methods can be employed. Only a fibrous nonwoven web which has been consolidated should be referred to as a nonwoven. This distinction is not made in colloquial language. 
     Nonwovens differ fundamentally from wovens, drawn-loop knits, non-crimp fabrics and formed-loop knits, which are characterized by the laying of the individual fibres or threads in a manner which is determined by the production process. Nonwovens, by contrast, consist of fibres whose positioning can only be described by statistical methods. 
     The fibres in a nonwoven are disposed randomly to each other. Nonwovens are classified inter alia according to the fibre material (the polymer in the case of manufactured fibres, for example), the bonding process, the fibre type (staple fibre or continuous-filament fibre), the fibre fineness and the fibre orientation. The fibres may be deposited in a defined manner in one preferential direction, or they may be in a state of wholly stochastic orientation as in the case of the random-laid nonwoven. 
     When the fibres have no preferential direction in their alignment (orientation), an isotropic nonwoven is concerned. When the fibres are more frequently disposed in one direction than in other directions, this is called anisotropy. 
     Nonwovens are thus textile fabrics where fabric formation is effected not by weaving, formed-loop knitting, drawn-loop knitting or defined laying, but by depositing the fibres with subsequent fixation. Owing to their versatility in use and their comparatively low manufacturing costs, compared with woven and loop-drawingly knitted fabrics, nonwovens continue to enjoy annual growth rates. 
     The advantages of nonwovens reside in a high specific surface area, the production processes allow huge scope for variation in density, fibre size, pore size or thickness and lead to a substantial degree of isotropy in the piece. These advantageous properties allow numerous possible uses in medicine for hygiene products, in particular surgical drapes, sheets, wound coverings, gauze, etc, in the home as wipes of any kind and as decorative cloths, in particular table cloths, serviettes, in the clothing industry as interlinings, for technical applications, in particular insulating mats, covering mats or as filter media in the engine/motor vehicle sector (e.g. oil filters) or as separators in batteries (WO 2009/103537 A1). 
     The surface tension plays a determinative part for many of these applications in that a reduced surface tension may lead, for example, to an increasingly water-repelling behaviour, and this may play an important part for applications in the clothing industry, but also in filter media in the motor vehicle sector. 
     The production of spunbonded nonwovens constitutes a direct combination between the process of spinning and the process of web formation. Not only melt- and dry-spinning processes but also wet-spinning processes are suitable for web formation on the basis of continuous-filament fibres. A multiplicity of fibre-forming polymers are known as a starting material for nonwovens. The continuous-based nonwovens of the present invention are made from thermoplastic polymers from the group of polyamides or polyesters, for example by melt-spinning as so-called meltblown nonwovens. The process of melt spinning is described in EP 0 880 988 A1 or EP 1 473 070 A1 for polyester for example. Polyester nonwovens are described in EP 2 090 682 A1 or EP 2 092 921 A1. The use as a filter medium of polyester nonwovens produced by the meltblown process forms part of the subject-matter of EP 0 466 381 B1. 
     While thermoplastic fibres formed from polyolefins, for example polypropylene or polyethylene fibres, have a relatively low surface tension due to the intrinsically hydrophobic character of polyolefins even without auxiliaries, higher surface tensions are concerned with comparatively more polar thermoplastics, preferably polyamides and polyesters. There are numerous applications where this leads to problems because, although low surface tensions are needed, comparatively high-value polymers such as polyamides or polyesters have to be used, for instance because of insufficient thermal or chemical resistance on the part of polyolefins. This frequently crystallizes into a wish that even comparatively more polar thermoplastics, for example polyamides and polyesters, may be modified to the effect that lower surface tensions are achieved while retaining the familiar advantages such as, for example, heat resistance, mechanical robustness and chemical resistance to oils and motor fuels. 
     Influencing the properties of thermoplastic fibres to be spun by additizing the thermoplastic to be used therefore is described in DE 19 937 729 A1 with regard to breaking strength using polyesters as an example. The additive there is a copolyester containing inter alia acrylic esters or methacrylic esters as monomer units. WO2005/040257 A1 pursues a similar purpose in using ethylene-alkyl acrylate copolymers in polyester films, tapes and melt-spun fibres to improve their mechanical properties such as the tensile strength for example. Copolymer additions above 5% are recited therein as preferable. 
     FR-OS 239 746 and U.S. Pat. No. 3,378,609 describe oleo- and hydrophobizing polyester-based wovens by applying an aqueous emulsion of a fluorinated polymer to the ready-produced woven. EP 0 196 759 A1 describes hydrophobizing individual polyester fibre by endowing the polyester fibres subsequently with a polyoxyalkylene glycol and a fluorine-based water and oil repellent, which have no substantial reactivity with the polyester. 
     WO 2009/152349 A1 describes inter alia hygiene cloths finished with fluorochemicals based on perfluorinated alkyl groups having up to four carbon atoms as repellent additive. Copolymers of such perfluorinated substances with acrylate esters or methacrylate esters are recited by way of example. JP 2003 193331 A describes rubber reinforcement polyester monofilaments finished inter alia with copolymers of ethylene with glycidyl methacrylate. 
     WO 2005/087868 A1 discloses ethylene copolymer modified polyamide products which may be fibres obtained by the melt-spinning process and finished with E/X/Y copolymers where E represents ethylene, X represents inter alia alkyl acrylate and Y represents inter alia glycidyl acrylate, glycidyl methacrylate or glycidyl vinyl ether. 
     WO 2008/083820 A1 finally discloses soft yarns based on polyamide or polyesters which may be finished with softener polymers of ethylene alkyl acrylates. Methyl acrylate, ethyl acrylate and butyl acrylate are listed. 
     These prior art solutions all have the disadvantage that the surface tension change resulting in the oil- and water-repellent behaviour is in each case only realized subsequently in an additional process step by application of auxiliaries to the woven. The subsequent application to the surface entails not only a heightened level of process complexity but also a heightened risk of the auxiliary desorbing or being washed off, which not only weakens the surface effect desired but may also be associated with a problematic contamination of the environment, for example an impurification of the filtrate in the ease of aftertreated filter media. It is also frequently necessary to resort to fluorinated chemicals, which in addition to being very costly also need special consideration with regard to their toxic potential in relation to recovery by incineration for example. 
     The problem addressed by the present invention was therefore that of modifying the polyamide/polyester in advance such that a reduction in surface tension is possible even without aftertreatment of the products produced from the thermoplastic fibre in question and shall be achieved with very low usage of material. The modification should further eschew fluorinated chemicals, be colour neutral and be such that fibre formation itself is not unacceptably impaired. The modification for reducing the surface tension should further be such that auxiliaries added can be limited by virtue of their effectiveness to a use level without decisive, if any, effect on the melt-spinning process. The fibre thus obtained should be variously further processable in that state into products, particularly into fibrous nonwoven webs, nonwovens, wovens, drawn-loop knits, non-crimp fabrics or formed-loop knits having reduced surface tension. 
     The solution to the problem and subject-matter of the present invention is a process for reducing the surface tension of thermoplastic-based fibres or filaments, characterized in that the thermoplastic is additized with at least one E/X copolymer of an α-olefin and a methacrylic or acrylic ester of an unsubstituted aliphatic alcohol, preferably an unsubstituted aliphatic alcohol having 6-30 carbon atoms, more preferably of a 2-ethylhexanol, and the mixture is subsequently spun, preferably by the melt-spinning process. 
     It was found that, surprisingly, additizing the thermoplastics polyamide or polyester with the E/X copolymer to be used according to the present invention is very effective in reducing the surface tension of the corresponding thermoplastic fibres and their descendant products and thus leads, for example, to a water-repellent finish for the thermoplastic-based fibres, preferably the polyamide/polyester fibres, and their descendant products. The copolymer to be used according to the present invention is so effective that a substantial reduction in surface tension is achieved even at very low concentrations, so there is no decisive if any effect on the melt spinning. 
     The process preferably utilizes mixtures for spinning which are based on 99.9 to 10 parts by weight, preferably 99.5 to 40 parts by weight and more preferably 99.0 to 55 parts by weight of at least one thermoplastic and 0.1 to 20 parts by weight, preferably 0.25 to 15 parts by weight, more preferably 0.5 to 10 parts by weight, yet more preferably 0.75 to 6 parts by weight, in particular most preferably 1.0 to 2.0 wt % of the above-defined E/X copolymer. 
     Preference for use as thermoplastic-based fibres is given to fibres based on thermoplastic polymers from the group of polyamides or of polyesters. 
     Particular preference for use as thermoplastic-based fibres from the group of polyamides is given to fibres based on aliphatic polyamides. 
     Particular preference for use as thermoplastic-based fibres from the group of polyesters is given to fibres based on polyalkylene terephthalates. 
     The thermoplastic polyamides to be spun according to the present invention may be obtained in various ways and synthesized from very different building blocks. In the specific application scenario, they are used alone or in combination with processing aids, stabilizers, polymeric alloying partners, especially elastomers. Also suitable are blends with proportions of other polymers, preferably blends with polyethylene, polypropylene or ABS, in which case one or more compatibilizers may optionally be used. The properties of polyamides can be improved by admixture of elastomers, for example with regard to the breaking strength of, for example, particularly low-viscosity polyamides. The multiplicity of possible combinations provides a very large number of products having a very wide variety of properties. 
     Polyamides are obtainable via a multiplicity of existing procedures involving the use, depending on the desired end product, of different monomeric building blocks, various chain transfer agents to achieve a target molecular weight or else monomers having reactive groups for subsequently intended aftertreatments. 
     Industrially relevant processes for producing polyamides usually proceed via polycondensation in the melt. In this context, polycondensation also comprehends the hydrolytic polymerization of lactams. 
     Preferred polyamides (PA) are partly crystalline polyamides obtainable from diamines and dicarboxylic acids and/or lactams having at least 5 ring members or corresponding amino acids. 
     Possible starting materials include aliphatic and/or aromatic dicarboxylic acids such as adipic acid, 2,2,4-trimethyladipic acid, 2,4,4-trimethyladipic acid, azelaic acid, sebacic acid, isophthalic acid, terephthalic acid, aliphatic and/or aromatic diamines such as, for example, tetramethylenediamine, hexamethylenediamine, 1,9-nonanediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, the isomeric diaminodicyclohexylmethanes, diaminodicyclohexylpropanes, bisaminomethylcyclohexane, phenylenediamines, xylylenediamines, aminocarboxylic acids such as, for example, aminocaproic acid, and the corresponding lactams. Copolyamides of two or more of the monomers mentioned are included. 
     The use of caprolactams is particularly preferred and of ε-caprolactam is very particularly preferred. 
     Particular suitability further extends to most moulding compounds based on nylon-6, nylon-6,6 and other aliphatic and/or aromatic polyamides/copolyamides and having 3 to 11 methylene groups in the polymer chain per polyamide group. 
     The polyamides obtained according to the present invention can also be used in admixture with other polyamides and/or further polymers. 
     The polyamides may include admixtures of customary additives such as, for example, demoulding agents, stabilizers and/or flow assistants. 
     The thermoplastic polyesters to be spun according to the present invention are partly aromatic polyesters with particular preference. 
     Polyesters to be spun with particular preference are selected from the group of derivatives of polyalkylene terephthalates. Polyesters to be spun with very particular preference are selected from the group of polyethylene terephthalates, polytrimethylene terephthalates and polybutylene terephthalates, yet more preferably polybutylene terephthalate and polyethylene terephthalate, most preferably polybutylene terephthalate, or mixtures of these terephthalates. 
     Partly aromatic polyesters are materials comprising aliphatic moieties as well as aromatic moieties. 
     Polyalkylene terephthalates for the purposes of the invention are reaction products of aromatic dicarboxylic acids or of their reactive derivatives, especially dimethyl esters or anhydrides, and aliphatic, cycloaliphatic or araliphatic diols and mixtures of these reactants. 
     Preferred polyalkylene terephthalates are obtainable from terephthalic acid (or its reactive derivatives) and aliphatic or cycloaliphatic diol of 2 to 10 carbon atoms by known methods (Kunststoff-Handbuch, vol. VIII, p. 695 FF, Karl-Hanser-Verlag, Munich 1973). 
     Preferred polyalkylene terephthalates contain at least 80 mol % preferably 90 mol %, based on the dicarboxylic acid, of terephthalic acid radicals and at least 80 mol %, preferably at least 90 mol %, based on the diol component, of ethylene glycol and/or 1,3-propanediol and/or 1,4-butanediol radicals. 
     Preferred polyalkylene terephthalates may besides terephthalic acid radicals contain up to 20 mol % of radicals of other aromatic dicarboxylic acids having 8 to 14 carbon atoms or radicals of aliphatic dicarboxylic acids having 4 to 12 carbon atoms, in particular radicals of phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, 4,4′-biphenyldicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, cyclohexanediacetic acid, cyclohexanedicarboxylic acid. 
     Preferred polyalkylene terephthalates may besides ethylene/1,3-propanediol/1,4-butanediol glycol radicals contain up to 20 mol % of other aliphatic diols havinig 3 to 12 carbon atoms or cycloaliphatic diols having 6 to 21 carbon atoms, in particular radicals of 1,3-propanediol, 2-ethyl-1,3-propanediol, neopentylglycol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 3-methyl-2,4-pentanediol, 2-methyl-2,4-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,2,4-trimethyl-1,6-pentanediol 2-ethyl-1,3-hexanediol, 2,2-diethyl-1,3-propanediol, 2,5-hexanediol, 1,4-di(β-hydroxyethoxy)benzene, 2,2-bis(4-hydroxycyclohexyl)propane, 2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane, 2,2-bis(3-β-hydroxyethoxyphenyl)propane 2,2-bis(4-hydroxypropoxyphenyl)propane (DE-A 25 07 674 (=U.S. Pat. No. 4,086,212), DE-A 25 07 776, DE-A 27 15 932 (=U.S. Pat. No. 4,176,224)). 
     Polyalkylene terephthalates may be branched by incorporation of relatively small amounts of 3- or 4-hydric alcohols or 3- or 4-basic carboxylic acids as described for example in DE-A 19 00 270 (=U.S. Pat. No. 3,692,744). Examples of preferred branching agents are trimesic acid, trimellitic acid, trimethylolethane, trimethylolpropane and pentaerythritol. 
     It is not advisable to use more than 1 mol % of the branching agent, based on the acid component. 
     Particular preference is given to polyalkylene terephthalates formed solely from terephthalic acid and its reactive derivatives, in particular its dialkyl esters, and ethylene glycol and/or 1,3-propanediol and/or 1,4-butanediol, in particular to polyethylene terephthalate and polybutylene terephthalate, and mixtures of these polyalkylene terephthalates. 
     Preferred polyalkylene terephthalates further include copolyesters formed from at least two of the abovementioned acid components and/or from at least two of the abovementioned alcohol components, particularly preferred copolyesters being poly(ethylene glycol/1,4-butanediol)terephthalates. 
     Polyalkylene terephthalates generally have an intrinsic viscosity of about 0.3 dl/g to 1.5 cm 3 /g, preferably 0.4 dl/g to 1.3 dl/g, more preferably 0.5 dl/g to 1.0 dl/g, all measured in 1:1 (w/w) phenol/o-dichlorobenzene at 25° C. 
     The thermoplastic polyesters which are preferably spun according to the present invention can also be used in admixture with other polyesters and/or further polymers. Very particular preference is given to using polyethylene terephthalate (PET), polypropylene terephthalate or polybutylene terephthalate (PBT) or mixtures thereof, in particular polybutylene terephthalate. 
     Recycled polyesters from post- or pre-consumer recyclates may further also be used alone or mixed, in which case polyester recyclates from bottles, so-called PET copolyesters, are preferred. One example thereof appears to be PET Plus80® from PET Kunststoffrecycling GmbH, Beselich-Obertiefenbach, Germany. 
     Particular preference for use as polyesters in melt spinning is given to poly(C 2-t alkylene)terephthalates containing up to 15 mol % of other dicarboxylic acids and/or diols, in particular isophthalic acid, adipic acid, diethylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, or whichever are the other C 2-t alkylene glycols. Preference is given to polyethylene terephthalate having an intrinsic viscosity (I.V.) in the range from 0.5 to 1.4 dl/g, polypropylene terephthalate having an I.V. of 0.7 to 1.6 dl/g or polybutylene terephthalate having an I.V. of 0.5 to 1.8 dl/g, while polyethylene terephthalate having an intrinsic viscosity (I.V.) in the range from 0.6 to 1.0 dl/g or polybutylene terephthalate having an I.V. of 0.6 to 0.9 dl/g is particularly preferable. 
     To reduce their surface tension, the thermoplastics to be spun according to the present invention contain E/X copolymers of E at least one α-olefin with X a methacrylic or acrylic ester of an unsubstituted aliphatic alcohol. Preferred α-olefins for use as constituent E of the copolymers preferably have between 2 and 10 carbon atoms and may be unsubstituted or substituted with one or more aliphatic, cycloaliphatic or aromatic groups. Preferred α-olefins are selected from the group comprising ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-octene, 3-methyl-1-pentene. Particularly preferred α-olefins are ethene and propene, ethene is very particularly preferable. Mixtures of the described α-olefins are also suitable. 
     The α-olefin content of the E/X copolymer is between 50 and 90 wt %, preferably between 55 and 75 wt %. 
     The E/X copolymer is further defined by the second constituent in addition to the α-olefin. Suitable for use as the second constituent are alkyl or arylalkyl esters of acrylic acid or of methacrylic acid whose alkyl or arylalkyl group is formed from 5-30 carbon atoms and which contains only a minimal if any concentration of reactive functions selected from the group comprising epoxides, oxetanes, anhydrides, imides, aziridines, furans, acids, amines. The alkyl or arylalkyl group may be linear or branched and also contain cycloaliphatic or aromatic groups while also being substituted by one or more ether or thioether functions. Suitable methacrylic or acrylic esters in this context also include those which were synthesized from an alcohol component based on oligoethylene glycol or oligopropylene glycol having only one hydroxyl group and not more than 30 carbon atoms. 
     The alkyl or arylalkyl group of the methacrylic or acrylic ester is preferably selected from the group comprising 1-hexyl, 2-hexyl, 3-hexyl, 1-heptyl, 3-heptyl, 1-octyl, 1-(2-ethyl)hexyl, 1-nonyl, 1-decyl, 1-dodecyl, 1-lauryl or 1-octadecyl. Particular preference is given to unsubstituted alkyl or arylalkyl groups of 6-20 carbon atoms, more preferably 8-20 carbon atoms. Preference is given in particular also to branched alkyl groups which, compared with linear alkyl groups of the same number of carbon atoms, lead to a lower glass transition temperature T G . 
     Of particular preference for the purposes of the present invention are copolymers where the α-olefin is copolymerized with 2-ethylhexyl acrylate. 
     Mixtures of the acrylic or methacrylic esters described are likewise suitable. 
     The acrylic or methacrylic ester content of the copolymer is in the range from 10 to 50 wt %, preferably in the range from 25 and 45 wt %. 
     Especially suitable copolymers are selected from the group of materials which are available from Arkema under the brand name Lotryl® EH, some of which are also used as hot-melt adhesives. 
     The particular preference of the present invention is accordingly for a process for reducing the surface tension of polyester-based fibres or polyamide-based fibres that is characterized in that an E/X copolymer of ethylene and an acrylic ester of an unsubstituted aliphatic alcohol having 6 to 30 carbon atoms, preferably of E ethylene and X an acrylic ester having 6 to 20 carbon atoms, more preferably of E ethylene and X 2ethylhexyl acrylate, is added to the thermoplastic and the mixture is subsequently spun by the melt-spinning process. 
     The particular preference of the present invention is accordingly for a process for reducing the surface tension of polyester-based fibres that is characterized in that an E/X copolymer of ethylene and an acrylic ester of an unsubstituted aliphatic alcohol having 6 to 30 carbon atoms, preferably of E ethylene and X an acrylic ester having 6 to 20 carbon atoms, more preferably of E ethylene and X 2-ethylhexyl acrylate, is added to the thermoplastic and the mixture is subsequently spun by the melt-spinning process. 
     The particular preference of the present invention is accordingly for a process for reducing the surface tension of polyamide-based fibres that is characterized in that an E/X copolymer of ethylene and an acrylic ester of an unsubstituted aliphatic alcohol having 6 to 30 carbon atoms, preferably of E ethylene and X an acrylic ester having 6 to 20 carbon atoms, more preferably of E ethylene and X 2-ethylhexyl acrylate, is added to the thermoplastic and the mixture is subsequently spun by the melt-spinning process. The copolymer quantity to be added to the polyamide/polyester mixture to be processed by spinning, for example, was specified above and will be found sufficient in most cases if it is ≧6 wt %. The concentration of the copolymer is preferably chosen from within the range from 0.75 to 6.0 wt % according to the desired take-off speed (&gt;700-1500 m/min) such that the birefringence of the fibre is &lt;3.5·10−3. Fibre birefringences of this type allow draw ratios of 5:1 and ensure the desired high thread tenacities at wind-up speeds of distinctly above 3800 m/min irrespective of the spinning take-off speed of up to 1500 m/min. 
     Customary added substances, preferably dyes, further hydrophobicizing agents, delustrants, stabilizers, antistats, lubricants, branching agents, may safely be added to the thermoplastic-copolymer mixtures of the present invention in amounts of 0.001 to 5.0 wt %. 
     Dyes which may be used with preference are disperse dyes, in particular those based on azo dyes or those based on very finely divided carbon blacks. 
     Delustrants which may be used with preference are microcrystalline anatases having an average particle size [d50] of 0.25 to 0.35 μm, which may also have an organic or inorganic surface treatment. 
     Stabilizers which may be used with preference include, for example, aromatic polycarbodiimides such as, for example, Stabaxol P from Rheinchemie of Mannheim, Germany, but also thermal stabilizers based on organic phosphite derivatives. 
     Antistats which may be used with preference are, in particular, finely divided conductivity-grade carbon blacks or carbon nanotubes. 
     Lubricants which may be used with preference are, in particular, long-chain fatty acids, preferably stearic acid or behenic acid, salts thereof, preferably calcium stearate or zinc stearate, and also ester derivatives thereof, and also low molecular weight polyethylene waxes and/or polypropylene waxes. Montan waxes within the meaning of the present invention are mixtures of straight-chain, saturated carboxylic acids having chain lengths of 28 to 32 carbon atoms. Preferred lubricating and/or demoulding agents are compounds from the group of low molecular weight polyethylene waxes and also from the group of amides or esters of saturated or unsaturated aliphatic carboxylic acids having 8 to 40 carbon atoms with aliphatic saturated amines or alcohols having 2 to 40 carbon atoms. Ethylenebisstearylamide and pentaerythritol tetrastearate (PETS) are very particularly preferable for the purposes of the present invention. Pentaerythritol tetrastearate (PETS) in particular is very particularly preferable. 
     Branching agents which may be used with preference are meltable modified bisphenol A epichlorohydrin resins such as, for example, Araldite GY764CH or Araldite GT7071 from Huntsman of Everberg, Belgium. 
     The copolymer to be used according to the present invention is mixed with the polyamide/polyester matrix polymer by compounding, preferably via mixing elements in an extruder, by using static mixer or via other suitable devices capable of mixing two or more components with each or one another. The melt may optionally also be strand extruded, cooled and pelletized. 
     Masterbatch techniques are also possible, in which case the copolymer is mixed as a concentrate or as a pure substance with the polyester pellets. 
     However, the individual components may also be mixed directly in the spinning or meltblowing installation, in which case the components may be imported as a physical premixture via one feed port or else separately via two or more feed ports. Another practicable possibility is for them to be added to a substream of the matrix polymer which is then admixed to the main stream of the matrix polymer. Advantageously, a defined distribution is established there by the specific choice of mixer and the duration of the mixing operation, before the melt mixture is forwarded through product distribution lines to the individual spinning stations and spinning dies. Mixers having a shear rate of 16 to 128 sec −1  will be found advantageous. In effect, the product formed by multiplying the shear rate (sec −1 ) with the 0.8 th  power of the residence time (in sec) should preferably be 250-2500, more preferably in the range from 350 to 1250. Values above 2500 are generally avoided in order to limit the pressure drop in the pipework lines. For the avoidance of doubt, it may be noted the thermoplastic is herein also referred to using the term polymer. 
     Shear rate herein is defined as the superficial shear rate (sec −1 ) times the mixer factor, the mixer factor being a characteristic parameter of the type of mixer. For Sulzer SMX types, for example, this factor is about 7-8. The superficial shear rate γ computes as per 
     
       
         
           
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     and the residence time as per 
     
       
         
           
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     where 
     F=polymer pump rate (g/min) 
     V 1 =internal volume of empty tube (cm 3 ) 
     R=empty tube diameter (mm) 
     ε=empty-volume fraction (from 0.84 to 0.85 for Sulzer SMX types) 
     δ=nominal density of polymer mixture in melt (about 1.2 g/cm 3 ). 
     Not only the mixing of the polymers but also the subsequent spinning of the polymer mixture is generally carried out at temperatures which, depending on the matrix polymer, are preferably in the range from 5 to 85° C. and more preferably from 30 to 70° C., each above the melting temperature of the matrix polymer. The preferred temperature settings are from 265 to 340° C. for PET and from 225 to 300° C. for nylon-6 and PBT. 
     Fibrous nonwoven webs produced from the thermoplastic to be used according to the present invention are produced in, for example, a meltblown plant. An extruder therein is used to heat the components and bring them to a high pressure. Following optional prefiltration by a suitable filter assembly, the melt is then pressed by the spinning pumps at an accurately metered rate through a spinneret. The polymer exits from the die plate as a fine fibre—also called filament in textile terminology—while still in the molten form. An air stream cools the filament and stretches it while still in the melt. The air stream conveys the filament onto, for example, a conveyor belt constructed as a sieve, or onto a porous drum or onto an incoming substrate such as, for example, paper. Aspiration underneath the sieve belt causes the threads to become fixed. This random-laid sheet of fibre is a fibrous nonwoven web which needs to be consolidated. Consolidation may be effected, for example, by two heated rolls (calender) or by a vapour stream. When a calender is used to effect consolidation, one of the two rolls usually has an engraved pattern consisting of dots, short rectangles or lozenge-shaped dots. The filaments fuse at the points of contact and thus form the nonwoven fabric. Comparatively lightweight nonwoven fabrics are obtainable by this technique (thermobonding) only, while comparatively heavyweight nonwoven fabrics are produced with a second incorporated low-melting polymer by melting the hot-melt adhesive in the course of a pass through a so-called fixing oven and the matrix fibres are usually adhered together at their cross-over points to thereby ensure the tenacities desired for the nonwoven. Consolidation is further possible by the method of hydroentangling, in which jets of water impinge on the still unconsolidated web at water pressures up to 400 bar. 
     The meltblown process is typically operated with the following parameters: 
     fibre diameter 0.1 μm to 20 μm, preferably 1 to 10 μm 
     web width up to 5000-6000 mm 
     air temperature 230 to 400° C., preferably 290° to 370° C. 
     air speed 0.5-0.8 times the speed of sound 
     basis weight 8 to 350 g/m 2 , typically 20 to 200 g/m 2    
     holes in spinneret Ø100 to 500 μm with 1 to 6 holes/mm 
     High-tenacity filaments are preferably produced from the thermoplastic-based mixtures to be used according to the present invention, preferably the polyamide/polyester mixtures, by spinning at take-off speeds of &gt;700 m/min, more preferably in the range from 750 to 1000 m/min, and drawing, heat-setting and winding up at a corresponding speed. This is accomplished using spinning means known per se. 
     High-tenacity polyamide/polyester filaments are typically produced by the melt-spinning process in large direct-melt spinning installations in which the melt is distributed via heated product lines to the individual spinlines and to the individual spinning systems within the spinlines. A spinline is a string or one or more rows of spinning systems, while a spinning system is the smallest spinning unit with a spinhead, which contains at least one spinning die pack including spinning die plates. The melt in such systems is exposed to a high level of thermal stress in residence times up to 35 min. The effectiveness of the copolymer which, according to the present invention, is to be used for reducing the surface tension is not significantly affected as a consequence of the high thermal stability of the copolymer, so even small quantities of the additive, for example ≦2.0% and in many cases even ≦1.5%, are sufficient depending on the desired reduction in the surface tension—despite high thermal stress. 
     The die pack to be used according to the present invention preferably has at least 20, more preferably from 150 to 1500 and even more preferably from 500 to 1000 die holes per metre of die width. Die hole diameters from 0.05 to 1 mm and particularly from 0.3 to 0.5 mm are preferable. 
     Die exit speed is preferably in the range from 1 to 20 m/min, but more preferably from 3 to 10 m/min. The blowing stream of hot air causes the extruded threads to become drawn to preferably from 50 to 800 times their length post die exit, leading to spinning speeds of up to 10 000 m/min. 
     The present invention also relates to the use of at least one copolymer of at least one α-olefin and at least one acrylic or methacrylic ester for reducing the surface tension of thermoplastic-based fibres or filaments, preferably polyester-based fibres or filaments or polyamide-based fibres or filaments, more preferably polyester-based fibres or filaments. 
     The present invention further relates to fibres or filaments having reduced surface tension obtainable by melt spinning thermoplastic-based fibres or filaments additized with at least one copolymer of at least one α-olefin and at least one acrylic or methacrylic ester of an aliphatic alcohol. 
     The present invention also relates to products, preferably fibrous nonwoven webs, nonwovens, wovens, drawn-loop knits, non-crimp fabrics or formed-loop knits, in particular fibrous nonwoven webs or nonwovens, obtainable from reduced surface tension thermoplastic-based fibres of the present invention, preferably polyester-based fibres or filaments or polyamide-based fibres or filaments, each of reduced surface tension, which were additized with at least one copolymer of at least one α-olefin and at least one acrylic or methacrylic ester. 
     It may be noted for clarity that all the definitions and parameters recited hereinabove in general terms or in preferred combinations are encompassed in any desired combinations in the context of the present invention. 
     Generally, the surface tension of fibres can be determined from their wettability with liquids that differ in polarity. A further possible way to determine the surface tension on fibre products obtained according to the present invention involves using a suitable tensiometer to examine the absorption kinetics of a liquid medium (e.g. water or cyclohexane) absorbed by the fibre product. 
    
    
     EXAMPLES 
     The reduction in the surface tension of materials obtained according to the present invention is demonstrated quantitatively on injection-moulded plates, which serve as model system for exact determination of surface tension, and qualitatively on fibrous nonwoven webs obtained by the meltblown process. 
     Determination of Reduced Surface Tension on Injection-Moulded Plates: 
     To exemplify the surface tension reduction described in the present invention, corresponding moulding compounds were prepared first. For this, the individual components were mixed in a twin-screw extruder (ZSK 26 Mega Compounder from Coperion Werner &amp; Pfleiderer (Stuttgart, Germany)) at temperatures between 250 and 285° C., strand extruded, cooled to the point of pelletizability, and pelletized. After drying (generally 2-6 h at 80° C. in a vacuum drying cabinet), the pellets were processed into test specimens. 
     The test specimens (rectangular plates measuring 60*40*4 mm or 150*105*1.0 mm) for the tests reported in tables 1 and 2 were produced on an Arburg 320-210-500 type injection-moulding machine at a melt temperature of about 260° C. and a mould temperature of about 80° C. 
     The surface tension of the rectangular plates obtained from the materials produced according to the present invention was determined in accordance with DIN ISO 8296 using test inks in a simple and reproducible manner. 
     The surface tensions to DIN ISO 8296 are generally not comparable to the values obtained according to ASTM D 2587-84. Surface tension values are reported in nN/m (=dyn/cm). 
     The test method is based on the assessment of the degree to which the polymer surface of the test specimen is wetted by inks having different surface tensions. The applicator attached to the bottle closure is dipped into the test ink, brushed against the bottle rim and used to apply the ink without delay to the in-test surface. Stroke length should be at least 100 mm. The behaviour of the stroke edge is assessed over a length of 90%, so minimal inhomogeneities are not considered. If the ink stroke contracts within less than two seconds, the measurement must be repeated with an ink of lower surface tension until the edges persist for two seconds. If the ink stroke remains unchanged for more than two seconds, the measurement must be repeated with inks of higher surface tension until the two seconds are achieved. The value indicated on the bottle then corresponds to the surface energy of the test plate. The test must be carried out under 23/50 standard conditions, i.e. at an air temperature or 23° C.+/−2° C. and relative humidity of 50%+/−10%. 
     The present tests were carried out with test inks from Softal Electronic GmbH, (see Softal Report No. 108), Hamburg, Germany. 
     Determination of Surface Tension on Fibrous Nonwoven Webs: 
     To reduce the surface tension on thermoplastic fibres in the manner of the present invention, a meltblown apparatus was used to produce fibrous nonwoven webs having a basis weight of about 55 g/m 2 . The tests were carried out with the melt temperature at about 275° C. and the hot-air stream at about 360° C. The ratio between melt throughput and air volume flow was chosen so as to obtain an average fibre thickness of about 1 μm from a die diameter of 300 μm. The fibrous nonwoven webs described in the inventive and comparative examples differ only in the particular polymer compositions used, all other parameters and hence nonwoven parameters such as basis weight, pore size, fibre orientation and fibre thickness being kept the same for each pair of inventive and comparative examples. 
     For a qualitative assessment of surface tension, a droplet of water was applied to the fibrous nonwoven web. Rapid wetting of the web with the droplet of water indicates a high level of surface tension (hydrophilic behaviour), while a retained droplet shape on the surface suggests a low level of surface tension. To achieve further differentiation, an air stream was applied to the droplet. If the droplet leaves behind a trail in the form of a film of water, it can be qualitatively summarized that the surface tension is comparatively high; if the droplet moves across the fibrous nonwoven web without leaving behind a visible trail of water, a comparatively low level of surface tension can be summarized (see table 3). 
     The following were used in the tests: 
     component A1: linear polybutylene terephthalate (Pocan® B600 from Lanxess Deutschland GmbH, Leverkusen, Germany) having an intrinsic viscosity of about 69 cm 3 /g (measured in 1:1 phenol:1,2-dichlorobenzene at 25° C.) 
     component A2: linear polybutylene terephthalate (Pecan® B1300 from Lanxess Deutschland GmbH, Leverkusen, Germany) having an intrinsic viscosity of about 94 cm 3 /g (measured in 1:1 phenol:1,2-dichlorobenzene at 25° C.) 
     component A3: PET copolymer having an intrinsic viscosity of about 80 cm 3 /g (PETplus 80 from PET Kunststoffrecycling GmbH, Beselich-Obertiefenbach, Germany) 
     component A4: nylon-6 (Durethan® B40F from Lanxess Deutschland GmbH, Leverkusen, Germany) 
     component B1: copolymer of ethene and 2-ethylhexyl acrylate having an ethene fraction of 63 wt % and an MFI of 550 (Lotryl® 37 EH 550 from Arkema, Puteaux, France) [CAS No. 26984-27-0] 
     component B2: Lotryl® 35 BA 320: copolymer of ethene and n-butyl acrylate having an ethene fraction of 65 wt % and an MFI of 320 (Lotryl® 35 BA 320 from Arkema, Puteaux, France) [CAS No. 25750-84-9] 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Surface tension reduction in polyester fibres as modelled with injection-moulded plate [60 × 40 × 4 mm] 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Example 
                 Comp. 1 
                 Inv. 1 
                 Inv. 2 
                 Comp. 2 
                 Inv. 3 
                 Inv. 4 
                 Comp. 6 
                 Comp. 5 
                 Comp. 3 
                 Inv. 6 
                 Comp. 4 
                 Inv. 7 
                 Inv. 8 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 component A1 
                 [%] 
                 100 
                 99 
                 96 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 component A2 
                 [%] 
                   
                   
                   
                 100 
                 97 
                 94 
                 97 
                 94 
                   
                   
                 50 
                 48.5 
                 47 
               
               
                 component A3 
                 [%] 
                   
                   
                   
                   
                   
                   
                   
                   
                 100 
                 97 
                 50 
                 48.5 
                 47 
               
               
                 component B1 
                 [%] 
                   
                   
                 1 
                 4 
                   
                 3 
                 6 
                   
                   
                 3 
                   
                 3 
                 6 
               
               
                 component B2 
                 [%] 
                   
                   
                   
                   
                   
                   
                   
                 3 
                 6 
               
               
                 surface tension 
                 [mN/m] 
                 38 
                 36 
                 30 
                 40 
                 30 
                 30 
                 34 
                 30 
                 36 
                 30 
                 36 
                 30 
                 30 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Surface tension reduction in polyamide fibres as modelled with injection- 
               
               
                 moulded plate [150 × 105 × 1 mm] 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Example 
                 Comp. 5 
                 Inv. 9 
                 Inv. 10 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 component A4 
                 [%] 
                 100 
                 99 
                 95 
               
               
                   
                 component B1 
                 [%] 
                   
                 1 
                 5 
               
               
                   
                 surface tension 
                 [mN/m] 
                 54 
                 36 
                 &lt;34 
               
               
                   
                   
               
            
           
         
       
     
     A high value indicates a high level of surface tension and hence indicates hydrophilic behaviour, whereas the material becomes increasingly hydrophobic with decreasing surface tension value. The examples show that the surface tension can only be reduced down to a limit of 30 mN/m in that the value of 30 mN/m represents a point of saturation. In the prior art (component B2 in Comparative Example 5) this limit is only achieved with 6 wt % of copolymer of ethylene and butyl acrylate. When only 3 wt % are used, the surface tension can only be reduced down to 34 mN/m. A comparison between the surface tensions of component B1 and component B2 shows that component B1, a copolymer of ethylene and 2-ethylhexyl acrylate, delivers a very low surface tension of just 30 mN/m even if used at a very low dosage level of, for example, 3 wt %. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Surface tension reduction on nonwoven polyester webs 
               
            
           
           
               
               
               
               
            
               
                 Example 
                 Comp. 1 
                 Inv. 1 
                 Inv. 2 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 component A1 
                 [%] 
                 100 
                 99 
                 98 
               
               
                 component B1 
                 [%] 
                   
                  1 
                  4 
               
               
                 behaviour of water 
                   
                 droplet wets the 
                 droplet scarcely wets 
                 droplet scarcely wets 
               
               
                 droplet on web 
                   
                 surface and spreads 
                 the surface and persists 
                 the surface and persists 
               
               
                   
                   
                   
                 as an almost spherical shape 
                 as an almost spherical shape 
               
               
                 behaviour of water 
                   
                 droplet wets the surface 
                 droplet can be blown 
                 droplet can be blown 
               
               
                 droplet on web after 
                   
                 so severely that it is virtually 
                 away, but leaves a readily 
                 away without leaving behind a visible 
               
               
                 application of air stream 
                   
                 impossible to blow away 
                 visible trail of water 
                 water residue on the web surface 
               
               
                   
               
            
           
         
       
     
     The fact that the adherence of the water droplet decreases severely with increasing concentration of component B1 is indicative of the severely decreasing wettability of the web with water and thus indicates the surface tension reduction in the polyester films used for the web. Just one 1 wt % of component B1 is sufficient for it to achieve a decisive increase in hydrophobicity.