TEXTILE SURFACES FOR ELECTRICAL INSULATION

Description

Technical field

[0001] The invention relates to a textile surface structure, in particular for the electrical insulation of electrical devices. State of the art

[0002] The use of textile fabrics for the electrical insulation of electrical devices is known from the prior art. For example, textile fabrics are used for the electrical insulation of electric motors, generators, or transformers. In this process, films (e.g., PET, PEN, PI, etc.) are laminated with the corresponding nonwovens, resulting in two- or three-layer laminates with a structure of nonwoven-film or nonwoven-film-nonwoven. The classic technical term for this is DMD (Dacron-Mylard-Dacron). The laminates are then used for insulation in motors / generators / transformers, e.g., as slot insulation, cover plates, field coil insulation, or armature insulation.

[0003] Important requirements for the nonwoven fabric include: good laminating properties, resin absorption, uniformity of fiber distribution and thickness, high smoothness, and the highest possible continuous temperature resistance. The nonwoven fabric can also be used directly, for example, for phase insulation / separation or all-around insulation. In this case, the nonwoven fabric is subsequently coated with a resin, which gives it its electrically insulating properties.

[0004] Key requirements for the nonwoven fabric include: resin absorption and transport, uniform fiber distribution, the highest possible continuous temperature resistance, and sufficient mechanical properties for deformation processes. Another application for such nonwovens is as a carrier for conductive tapes, which are used, for example, in the winding of Roebel rods.

[0005] Important requirements for the nonwoven fabric are: good impregnation behavior, air permeability (through-plane conductivity), the highest possible continuous temperature resistance, and sufficient mechanical properties for winding processes.

[0006] From US Patent 2011 / 0012474 A1, an electrical laminate insulating element for an electrical device is known, comprising a thermoplastic film positioned between, adjacent to, and attached to two nonwoven sheets, each of which consists of polymeric multicomponent fibers. The multicomponent fibers can be core-sheath fibers, in which the high-melting-point polymer forms the sheath and the low-melting-point polymer forms the core of the fiber. In a preferred embodiment, the core consists of the low-melting-point polymer (PET) and the sheath of the high-melting-point polymer (PPS).

[0007] A disadvantage of the described laminate insulation element is its sulfur content. During long-term use, the degradation of sulfur poses a risk of acid and other sulfur compounds forming, leading to corrosion. Therefore, the presence of sulfur is undesirable in electrical insulation. Furthermore, in the case of multi-component fibers, the incompatibility of PPS and PET becomes a factor, complicating the production of, for example, PPS / PET bi-fibers. This necessitates the use of relatively large quantities of PPS or the application of special, and thus complex, core geometries.

[0008] WO 2015 / 049027A1 describes a textile fabric containing at least one layer that includes two different fiber types, each with a different polymer, or that consists of fibers combining both polymers. The cold crystallization temperature of the first polymer is at or below the softening temperature of the second polymer. The textile fabric is produced using a melt spinning process.

[0009] JP H 11 76651A describes a cushioning material comprising a textile fabric, wherein the textile fabric consists of fiber A or fiber B or mixtures thereof, and both fiber A and fiber B contain polyethylene 2,6-naphthalate (PEN). Example 1 describes a fiber B containing PEN in the core and a PEN / PET mixture in the sheath. By using the PEN / PET mixture in the sheath, the melting point of the sheath is lowered below the melting point of the core, allowing the sheath to act as a binding component. The ratio of PEN / PET in the copolymers is 20 / 80 to 80 / 20.

[0010] WO 2006105836 A1 describes a thermally bonded nonwoven fabric containing a low-shrinkage core-sheath bicomponent fiber, wherein the low-shrinkage core-sheath bicomponent fiber consists of a crystalline polyester core and a crystalline polyester sheath with a melting point at least 10°C lower and exhibits a hot shrinkage of less than 10% at 170°C. In a preferred embodiment, the core consists of polyethylene naphthalate (PEN). The nonwoven fabric is used as a filter medium, membrane support nonwoven, and battery separator. It exhibits excellent properties for these applications. However, specifically for electrical insulation, it has the disadvantage of insufficient thermal stability due to the relatively low glass transition temperature of the polyester sheath.

[0011] The invention is therefore based on the objective of providing a textile surface structure for electrical insulation, for example for the electrical insulation of electric motors, generators or transformers, which at least partially eliminates the aforementioned disadvantages.

[0012] The present invention solves the aforementioned problem by means of a textile surface structure according to claim 1, comprising a base body of at least one layer, wherein the at least one layer comprises PEN, copolymers and / or blends thereof as a binding component, wherein the binding component is obtainable by subjecting core / sheath binding fibers, in which the binding fiber sheath polymer contains PEN, copolymers and / or blends thereof, to temperatures above the glass transition temperature of the binding fiber sheath polymer.

[0013] According to the invention, it has been found that core / sheath fibers, in which the sheath comprises PEN, copolymers and / or blends thereof, are ideally suited to provide high-temperature-resistant textile structures for electrical insulation. In the textile structure according to the invention, the PEN, copolymers and / or blends thereof are present as a binding component. This binding component can be in the form of a more or less deformed fiber structure up to a completely fused continuous phase.

[0014] The use of PEN, copolymers, and / or blends thereof as a binding component is unusual in the industry because these materials generally have a relatively high melting point. However, according to the invention, it has been found that it is possible to use these materials as a binding component even below their melting point if their degree of crystallinity is adjusted to a low level. According to the invention, the binding component can be produced starting from core / sheath binding fibers, where the binding fiber sheath polymer comprises PEN, copolymers, and / or blends of PET with a degree of crystallinity of less than 80%, for example, 0 to 75%, more preferably 0 to 70%, and particularly 0 to 60%. This means that the binding fiber sheath polymer used to produce the binding component preferably has one of the aforementioned degrees of crystallinity.

[0015] A low degree of crystallinity can be easily achieved by using core / sheath binding fibers for the production of the sheet structure according to the invention that are not drawn fibers. This means fibers with a high proportion of amorphous PEN, amorphous copolymers, and / or amorphous blends thereof. Practical tests have shown that these amorphous materials acquire bonding capacity during thermally induced recrystallization even below their melting point (cold crystallization). The cold crystallization temperature is defined as the temperature at which a first exothermic maximum of the free enthalpy occurs. Exothermic refers to an energy release. This process yields core / sheath binding fibers that are therefore suitable for conventional bonding processes in the textile industry, such as calendering.

[0016] A key advantage of using PEN is its exceptionally high thermal and electrical resistance in the product. Furthermore, PEN is highly compatible with a wide range of technically relevant polymers, such as polyesters, making it easy to spin into a core / sheath fiber. This allows for thinner sheath thicknesses. Additionally, the improved interface structure resulting from the polymer compatibility enhances long-term durability. Another advantage of PEN compared to PPS is its sulfur-free composition.

[0017] Because the PEN, copolymers and / or blends thereof are present according to the invention in the sheath of the core / sheath binding fibers used to manufacture the textile fabric, its advantageous properties, in particular its high thermal-electrical resistance and long-term stability, can be utilized particularly well. Furthermore, it can thereby act as protection for the inner fiber component.

[0018] Furthermore, practical tests have shown that the surface structure according to the invention has excellent storage stability, which is manifested, for example, in the fact that the PEN-containing binding component shows almost no deterioration, or even an increase in strength, during thermal storage (see Figs. 1-4Thus, after thermal storage at 160°C for 1 week, the surface structure according to the invention preferably shows a percentage reduction in the maximum tensile force in at least one direction of less than 5%, preferably less than 4%, for example from 0 to 4% and / or an increase in the maximum tensile force in at least one direction of at least 1%, preferably more than 5%, for example from 5 to 100%.

[0019] Without specifying a mechanism according to the invention, it is assumed that the good storage stability is due to the fact that PEN has a comparatively high glass transition temperature. In addition, the degree of crystallinity of the PEN component increases over time, which counteracts destabilization by thermal degradation processes.

[0020] Preferably, the PEN, the copolymers and / or blends thereof in the binder fiber sheath polymer have a cold crystallization temperature in the range of 70 to 200°C, more preferably in the range of 80 to 190°C, most preferably in the range of 90 to 175°C.

[0021] Preferably, the PEN, its copolymers and / or blends thereof have a melting point in the range of 180 to 320°C in the binding fiber sheath polymer and / or in the binding component, more preferably in the range of 210 to 310°C, and most preferably in the range of 230 to 300°C. These polymers are very well suited for thermal bonding.

[0022] According to the invention, the binding component comprises PEN, copolymers, and / or blends thereof. The term "PEN" refers to polyethylene naphthalate. This can be present as a homopolymer, copolymer, and / or blend thereof, with the PEN being the main component in the copolymers and / or blends, namely in a proportion of more than 90 wt.%. Suitable copolymers include, for example, statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, or graft polymers. The copolymers can consist of two, three, four, or more different monomers (terpolymers, tetrapolymers). Particularly preferred comonomers are monomers of the following polymers: aromatic and aliphatic polyesters, aromatic and aliphatic polyamides, aromatic and aliphatic epoxides, aromatic and aliphatic polyurethanes, polysiloxanes, polyacrylates, and polyacrylamides.

[0023] When PEN is used as a blend, preferred further blend components are polymers with a melting point in the range of 180 to 320°C, more preferably in the range of 210 to 300°C, most preferably in the range of 230 to 290°C, and / or with a decomposition point in the range of 210 to 800°C, more preferably in the range of 300 to 750°C, most preferably in the range of 350 to 700°C. Particularly preferred further blend components are the following: aromatic polyesters, aromatic polyamides, polyetheretherketone, poly(p-phenylene-2,6-benzobisoxazole), polyamide-imide, and polyphenylene sulfide.

[0024] When using PEN as a homopolymer, the PEN is preferably present in the binder fiber sheath polymer in a proportion of more than 50 wt.%, more preferably more than 75 wt.%, more preferably more than 90 wt.%, and in particular about 100 wt.%, in each case based on the total weight of the sheath, whereby usual additives such as spinning aids, nucleating additives, matting agents and impurities such as catalyst residues are not to be taken into account.

[0025] The binding component can create an adhesive bond between the surface structure.

[0026] According to the invention, the sheet material is preferably a nonwoven fabric. A nonwoven fabric is a structure made of fibers of limited length, continuous fibers (filaments), or cut yarns of any kind and origin, which have been joined together in some way to form a nonwoven (a layer of fibers, a nap of fibers) and bonded together in some way; this excludes the interlacing or entanglement of yarns, as occurs in weaving, knitting, crocheting, lacemaking, braiding, and the manufacture of tufted products. Films and papers are not considered nonwoven fabrics.

[0027] According to the invention, the core / sheath binding fibers used to produce the textile fabric preferably have a core containing a polymer different from the sheath polymer (binding fiber core polymer). When the core / sheath binding fibers are heated, the binding fiber core polymer may or may not bind. The binding fiber core polymer can be partially or completely enclosed by the binding component. The ratio between the binding fiber core and sheath polymers can be freely chosen. Ratios of 90:10 to 10:90 (weight ratio core : sheath in wt.%) have proven particularly advantageous, even more preferably 80:20 to 20:80, even more preferably 80:20 to 30:70, and especially 80:20 to 40:60.

[0028] According to the invention, the binding fiber sheath polymer has a higher melting point than the binding fiber core polymer. The difference in melting temperatures between the binding fiber sheath polymer and the binding fiber core polymer is preferably at least 2.5°C, more preferably at least 5°C, and particularly preferably at least 7.5°C. Polymers with a temperature difference of 2.5 to 200°C, more preferably 5 to 150°C, and particularly preferably 7.5 to 100°C are preferably used. This difference in the melting temperatures of the two polymers results in good temperature stability.

[0029] According to a particularly preferred embodiment, the binding fiber sheath polymer has a glass transition temperature at least 5°C higher than that of the binding fiber core polymer, preferably at least 10°C, and particularly preferably at least 15°C. Polymers with a glass transition temperature difference of 5 to 600°C, more preferably 10 to 500°C, and particularly preferably 15 to 200°C are preferably used.

[0030] The binding fiber core polymer can contain a wide variety of materials. Preferably, the binding fiber core polymer is melt spinnable. More preferably, the binding fiber core polymer is a polyester selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polytetramethylene terephthalate, poly(decamethylene) terephthalate, poly-1,4-cyclohexylene dimethyl terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyglycolic acid, polylactides, polycaprolactones, polyethylene adipates, polyhydroxyalkanoates, polyhydroxybutyrates, poly-3-hydroxybutyrate-co-3-hydroxyvalerates, polytrimethylene terephthalates, vectrans, polyethylene naphthalate, their copolymers, and / or their mixtures. Sheet materials containing the aforementioned polymers are readily recyclable.

[0031] Furthermore, the binding fiber core polymer is most preferably selected from the group consisting of poly(decamethylene) terephthalate, poly-1,4-cyclohexylene dimethyl terephthalate, polybutylene terephthalate, polyethylene naphthalate, preferably polyethylene naphthalate, polybutylene terephthalate, their copolymers, and / or their blends. According to a preferred embodiment, the binding fiber core polymer contains polyethylene terephthalate and / or co-polyethylene terephthalate. Suitable copolymers include, for example, statistical copolymers, gradient copolymers, alternating copolymers, block copolymers, or graft polymers. The copolymers can consist of two, three, four, or more different monomers (terpolymers, tetrapolymers).Particularly preferred comonomers are monomers of the following polymers: aromatic and aliphatic polyesters, aromatic and aliphatic polyamides, aromatic and aliphatic epoxides, aromatic and aliphatic polyurethanes, polysiloxanes, polyacrylates, polyacrylamides.

[0032] Preferably, the proportion of the aforementioned polymers in the binding fiber core polymer is 5 to 100 wt.%, more preferably 50 to 100 wt.% and in particular 75 to 100 wt.%, in each case based on the total weight of the core, whereby usual additives such as spinning aids, nucleating additives, matting agents and impurities such as catalyst residues are not taken into account.

[0033] If a blend is used as the binding fiber core polymer, preferred further blend components are polymers with a melting point in the range of 180 to 320°C, more preferably in the range of 210 to 300°C, most preferably in the range of 230 to 290°C, and / or with a decomposition point in the range of 210 to 800°C, more preferably in the range of 300 to 750°C, most preferably in the range of 350 to 700°C. Particularly preferred further blend components are the following: aromatic polyesters, aromatic polyamides, polyetheretherketone (PEEK), polybenzobisoxazole (PBO), polyamide-imide (PAI), and polyphenylene sulfide (PPS).

[0034] By selecting the appropriate polymers used, the temperature stability and the mechanical properties, in particular the elasticity, deformability and strength of the sheet structure, can be influenced.

[0035] The binding fiber core polymer also preferably has a melting temperature in the range of 180 to 320°C, more preferably in the range of 210 to 300°C, most preferably in the range of 230 to 290°C and / or a decomposition point in the range of 210 to 800°C, more preferably in the range of 300 to 750°C, most preferably in the range of 350 to 700°C.

[0036] In a preferred embodiment of the invention, the sheet structure contains matrix fibers. Unlike the binding component, the matrix fibers are present in a significantly more distinct fiber form. The cores of the core / sheath binding fibers used to produce the sheet structure can function as matrix fibers. However, it is particularly preferred that additional fibers be used as matrix fibers, either in addition to or as an alternative to the cores of the core / sheath binding fibers. The presence of the matrix fibers is advantageous because it increases the overall stability of the sheet structure.

[0037] Preferably, the difference in crystallinity between the sheath of the core / sheath binding fibers and the crystallinity of the matrix fibers before thermal treatment is at least 5%, for example, 5 to 80%, more preferably at least 7.5%, for example, 7.5 to 70%, and particularly at least 10%, for example, 10 to 60%, wherein the crystallinity of the matrix fibers is higher than the crystallinity of the sheath of the core / sheath binding fibers. Core / sheath binding fibers with a low degree of crystallinity can be obtained easily, for example, by melt spinning, which omits a drawing step.

[0038] In a particularly preferred embodiment of the invention, the matrix fibers are configured as core / sheath matrix fibers, comprising a matrix fiber sheath polymer and a matrix fiber core polymer. Preferably, the difference in the degree of crystallinity between the sheath of the core / sheath binding fibers and the degree of crystallinity of the matrix fiber sheath polymer before thermal treatment is at least 5%, for example, 5 to 80%, more preferably at least 7.5%, for example, 7.5 to 70%, and particularly at least 10%, for example, 10 to 60%, wherein the degree of crystallinity of the matrix fiber sheath polymer is higher than the degree of crystallinity of the sheath of the core / sheath binding fibers.

[0039] The matrix fiber sheath polymer can be selected from the same polymers as those described for the sheath polymer of the core / sheath binding fibers used to manufacture the binding component. Similarly, the matrix fiber core polymer can be selected from the same polymers as those described for the core polymer of the core / sheath binding fibers used to manufacture the binding component.

[0040] Preferably the matrix fiber sheath polymer is selected from PEN, copolymers and / or blends thereof and / or the matrix fiber core polymer is made from polyethylene terephthalate and / or co-polyethylene terephthalate.

[0041] In a preferred embodiment of the invention, the proportion of PEN, copolymers and / or blends thereof on the one hand and polyethylene terephthalate and / or co-polyethylene terephthalate on the other hand combined is more than 80 wt.%, preferably more than 90 wt.%, more preferably more than 95 wt.% and in particular more than 97 wt.%, in each case based on the total weight of the base body.

[0042] When PEN is used as a blend and / or copolymer, preferred further blend components, preferred copolymers, and preferred proportions are those already mentioned above with regard to the binding component. The polymers, compositions, and proportions of the core / sheath binding fibers used for the production of the binding component and the core / sheath matrix fibers used for the production of the matrix fibers can be selected independently of one another.

[0043] The polymers of the binder fiber sheath polymer and the matrix fiber sheath polymer can be different. This makes it easy to set different melting ranges. Preferably, according to the invention, the binder fiber sheath polymer and the matrix fiber sheath polymer contain the same polymers, copolymers, or blends, which, however, differ in their crystallinity before thermal treatment, as explained above.

[0044] Maintaining the fiber structure of the matrix fibers during thermal treatment in the production of the sheet structure can be achieved by adjusting the matrix fibers to a higher degree of crystallinity compared to the sheath of the core / sheath binding fibers, as described above.

[0045] The fibers used to produce the sheet structure can be filaments, staple fibers, and / or short-cut fibers. According to the invention, staple fibers and / or short-cut fibers are preferred. Staple fibers and / or short-cut fibers can be produced and laid using a wide variety of known manufacturing processes, for example, carding, airlaid, and wetlaid processes.

[0046] In one embodiment of the invention, the proportion of PEN or its copolymers or blends is 5 to 95 wt.%, preferably 5 to 75 wt.%, and particularly 10 to 60 wt.%, based on the total weight of the sheet structure. It is especially preferred that the PEN or its copolymers be used in a smaller quantity. This is advantageous because the expensive PEN can be used in a material-saving manner to increase the stability of the sheet structure.

[0047] Preferably, the proportion of the binding component is 5 to 75 wt.%, preferably 5 to 65 wt.%, and in particular 10 to 55 wt.%, in each case based on the total weight of the surface structure.

[0048] Preferably, the fiber diameter of the core / sheath binding fibers and the matrix fibers, independently of each other, is in the range of 0.1 to 20 dtex, more preferably in the range of 0.1 to 15 dtex, and particularly preferably in the range of 0.1 to 10 dtex. Further preferably, the length of the core / sheath binding fibers is from 1 to 90 mm and / or the length of the matrix fibers is from 1 to 90 mm, provided they are not in the form of filaments. Since the shape of at least the core / sheath binding fibers can naturally change during thermal treatment, the aforementioned fiber dimensions refer to the state before thermal treatment.

[0049] Preferably, the sheet structure contains no further fibers besides the aforementioned matrix fibers and binding components, or further fibers only in a proportion of less than 60 wt.%, for example, from 0 to 60 wt.% and / or from 5 to 60 wt.%. If the sheet structure contains further fibers, these are preferably configured as monofilaments. These also preferably have a melting point or decomposition point of more than 210°C, for example, from 210 to 2000°C, particularly preferably from 220 to 2000°C, and especially from 250 to 2000°C. Furthermore, the further fibers are preferably selected from the group consisting of: polyesters, in particular polybutylene terephthalate; polyamides, in particular polyamide 6.6 (Nylon®); and polyamide 6.0 (Perlon®< )-, meta-aramid, para-aramid; aromatic polyamides, polyvinyl chloride, polyacrylonitrile, polyimide, polyamide-imide, polytetrafluoroethylene (Teflon®< )-, phenolic resin, LCP (Liquid Crystal Polymer), glass, and basalt fibers. Particularly preferred are the following fibers selected from the group consisting of: polyamide, polyp-phenylene terephthalamide, polym-phenylene terephthalamide, polyester fibers, and mixtures thereof. Due to its good mechanical properties, thermal resistance, and cost-effectiveness, polyester, and in particular polyethylene terephthalate, meta-aramid, and / or para-aramid, is especially preferred.

[0050] In a further preferred embodiment of the invention, the textile fabric is characterized by a weight-related tensile strength in the machine direction (MD) of more than 0.25 N / g, for example from 0.25 to 12 N / g, preferably from 0.5 to 10 N / g and particularly preferably from 0.75 to 8 N / g.

[0051] The high tensile strength is advantageous, for example, for using the fabric for sheathing electrical conductors, as a certain degree of strength is necessary for the conductor manufacturing process, in which the materials are applied, for example, as a wrapping. In principle, however, the tensile strengths can be adjusted to preferred values ​​depending on the specific application, for example, from 15 to 800 N and / or from 25 to 700 N and / or from 35 to 600 N, measured according to DIN ISO 9073-3. According to a preferred embodiment of the invention, the textile fabric exhibits the aforementioned high tensile strengths in the machine direction even at small thicknesses, for example, less than 3 mm, such as in the range of 0.02 mm to 2 mm.

[0052] The textile fabric can be manufactured in a wide range of thicknesses. This allows for the use of a customized textile fabric for a variety of electrical insulation applications. Thicknesses according to DIN EN 9073-2 in the range of 0.01 to 2 mm, 0.01 to 1.7 mm, and / or 0.02 to 1.5 mm have proven preferable.

[0053] Such sheet-like structures are particularly easy to process due to their thinness and good deformability.

[0054] The sheet structure according to the invention is suitable for a wide variety of applications, preferably for the production of electrical insulating materials, for example for the electrical insulation of electric motors, generators or transformers, and in particular for the production of (flexible) laminates with films in the core as insulation for, e.g., grooves or cover slides and / or as a layer separator for phase separation. For this purpose, it can be manufactured in a wide variety of forms, for example as a groove lining, a closure, a wedge, a rod, as a wrapping, as a separation layer in ring form or as a bandage in the cable. The sheet structure according to the invention is also particularly suitable for use as a carrier material for conductive tapes.

[0055] For use as a groove lining and / or for insulating electrical conductors, it must be taken into account that the available space is severely limited. Therefore, it is advantageous if the textile surface does not significantly increase the thickness of the laminate.

[0056] In these cases, thicknesses of less than 1 mm, for example between 0.01 mm and 0.07 mm, between 0.02 mm and 0.5 mm, and / or between 0.01 mm and 0.48 mm, are preferred.

[0057] The basis weight can vary widely. Preferably, the textile fabric has a basis weight according to DIN EN 29073-1 of 20 to 400 g / m², preferably of 20 to 300 g / m², and particularly of 30 to 250 g / m². Fabrics according to the invention with such basis weights possess excellent stability.

[0058] Preferably, the textile fabric has an air permeability, measured according to DIN EN ISO 9237, of 5 to 800 l / m²*sec, preferably of 10 to 700 l / m²*sec, and particularly of 15 to 600 l / m²*sec. In terms of weight, this means an air permeability of preferably 0.15 to 200 l / sec*g, preferably of 0.25 to 175 l / sec*g, and particularly of 0.35 to 150 l / sec*g for the fabric according to the invention.

[0059] It has been shown that particularly good impregnation behavior is present at the aforementioned air permeabilities. In a preferred embodiment of the invention, the surface structure according to the invention has a coating and / or impregnation with a resin.

[0060] It is conceivable that the sheet structure has a reinforcing layer, for example a plastic film. This results in a sheet structure with high mechanical strength and low weight.

[0061] According to a preferred embodiment, the sheet structure has a multilayered composition. Preferably, the sheet structure contains at least one further layer in addition to the base body. The further layers could be designed as spunbond nonwoven layers or staple fiber layers. The further layers can differ from one another in their function, manufacturing method, fiber type, polymers they contain, and / or their color.

[0062] It is also conceivable to subject the textile surface structure to subsequent chemical treatment or finishing, such as an anti-pilling treatment, hydrophilization or hydrophobization, an antistatic treatment, a treatment to improve fire resistance and / or to change the tactile properties or gloss, a mechanical treatment such as roughening, sanforizing, sanding or a tumble dryer treatment and / or a treatment to change the appearance such as dyeing or printing.

[0063] For some applications, it may also be advantageous to subsequently treat the textile fabric with one or more additives, for example by coating it. These additives may be selected from carbonates, in particular calcium carbonate; carbon black, in particular conductive carbon black; graphite; ion exchange resins; activated carbon; silicates, in particular talc; clay; mica; silica; zeolites; chalk; calcium and barium sulfate; aluminum hydroxide; glass fibers and spheres; wood flour; cellulose powder; powdered superabsorbent; perlite; cork or plastic granules; ground thermoplastics; cotton; carbon fibers, in particular ground carbon fibers; and mixtures thereof. The addition of a filler and / or additive can, for example, alter the permeability to liquid and / or air and control the thermal and / or electrical conductivity of the material.To improve the adhesion of the additive and / or filler, an adhesive / binder can be used, for example based on polyvinyl alcohol, polyacrylates, polyurethanes, styrene-butadiene rubber or nitrile-butadiene rubber, polyester, epoxy, polyurethane resins.

[0064] In a preferred embodiment of the invention, the layers in the sheet structure according to the invention, preferably the at least one layer and / or the further layers of the base body, are designed as a nonwoven fabric, woven fabric, knitted fabric, film, foil, fleece, or nonwoven material. This allows a sheet structure with high mechanical strength to be obtained. According to the invention, it is particularly preferred that the at least one layer be designed as a nonwoven material.

[0065] The invention also includes a method for producing the textile fabric according to the invention, comprising the following process steps: Providing core / sheath binding fibers in which the sheath comprises PEN, copolymers and / or blends thereof, forming a layer containing the core / sheath binding fibers, subjecting the layer to temperature, wherein the temperature is above the cold crystallization temperature of the binding fiber sheath polymer, so that a textile fabric is obtained comprising a base body of at least one layer, wherein the at least one layer comprises PEN, copolymers and / or blends thereof as a binding component.

[0066] The first process step comprises providing core / sheath bonding fibers in which the sheath comprises PEN, copolymers, and / or blends thereof. The application of heat to the layer could take place in an oven and / or a calender, in air or an inert atmosphere, or under vacuum. Exemplary temperatures are in the range of 100 to 290°C, preferably from 110 to 280°C. In a preferred embodiment of the invention, pressure treatment takes place simultaneously or subsequently. When using a calender, preferred pressures are line pressures of 20 to 350 N / mm, preferably from 40 to 300 N / mm, and particularly from 50 to 275 N / mm.

[0067] According to the invention, the materials already discussed above with regard to the sheet structure are preferably used as starting materials in the described forms, proportions, etc. Staple fibers (preferably with a length of 1 to 120 mm) and / or continuous fibers (filaments) can be used as core / sheath binding fibers and / or matrix fibers. The core / sheath binding fibers and / or matrix fibers have a density of 0.1 to 50 dtex, more preferably 1.0 to 40 dtex.

[0068] To avoid repetition, reference is made here to the above statements.

[0069] The invention will now be explained in more detail using several examples: Four different surface structures according to the invention will be produced as examples: 1. Production of various flat structures

[0070] First, a fiber mixture is produced from the following fibers in a mixing ratio of 60 : 40 (matrix fiber : core / sheath binding fiber). Matrix fiber:

[0071] Core / sheath fiber (sheath PEN / core PET) Fiber titer: 4.8 dtex Fiber length of 50 mm. Crystallinity PEN: 32% Core / sheath binding fiber for the production of the binding component:

[0072] Core / sheath binding fiber (sheath PEN / core PET) Fiber titer: 10.8 dtex Fiber length of 50 mm. Crystallinity PEN : 17%

[0073] A fiber mat is laid on a carded nonwoven fabric with MD orientation and thermally bonded in a calender with a steel / steel roller configuration at temperatures of 160 to 250°C and line pressures of 50 to 250 N / mm² using pressure and temperature. Precise setting parameters must be adjusted according to the respective production speeds.

[0074] This results in the formation of surface structures 1-4 according to the invention. 2. Measurement of relevant parameters of the surface structures produced under 1.

[0075] Example Weight thickness Maximum tensile strength (weight-related) MD Maximum tensile strain weight-related MD Maximum tensile strength weight-related CD Maximum tensile strain weight-related CD Air permeability per unit weight [g / m²] [µm] [N / g] [%] [N / g] [%] [l / sec*g] Comparison s-example 60 74 3,42 0,35 1,32 0,23 0,50 1 60 70 0,62 0,03 0,32 0,03 4,50 2 60 69 0,78 0,03 0,42 0,03 4,25 3 74 75 0,82 0,03 0,53 0,03 0,96 4 97 96 0,89 0,02 0,57 0,02 0,55 Example Weight thickness Maximum tractive force MD Maximum tensile strain MD Maximum tractive force CD Maximum tensile strain CD Air permeability [g / m²] [µm] [N] [%] [N] [%] [l / m²*sec] Comparative example 60 74 205 21 79 14 30 1 60 70 37 2 19 2 270 2 60 69 47 2 25 2 255 3 74 75 61 2 39 2 71 4 97 96 86 2 55 2 53

[0076] Highly compressed nonwovens were produced in three different weight variants. Example 1 was compressed at 50 N / mm², example 2 with 100 N / mm. The material thickness had a relatively minor impact, and air permeability could only be increased slightly, while the maximum tensile strength (MD) and maximum tensile strength (CD) increased simultaneously. As expected, higher areal weights resulted in higher mechanical strengths and decreasing air permeability. Interestingly, there was no effect on elongation at break. 3. Testing the sheet structures produced under 1. for high-temperature resistance by storage tests at 160°C or 200°C.

[0077] The surface structures according to the invention and the comparative example are subjected to storage tests at 160°C and 200°C, respectively. The results are presented in the Figures 1 - 4 shown.

[0078] Comparative storage tests were conducted to demonstrate the improved thermal stability of the nonwoven fabric according to the invention compared to standard polyethylene terephthalate products. A 60 g / m² nonwoven fabric made of 100% PET was used as the comparison material.

[0079] For storage, the samples were die-cut to DIN A4 size and stored in an oven (Memmert, type U30) at 160°C or 200°C with medium air circulation for four weeks. They were stored on the middle shelf of the oven. Three samples per nonwoven type were used per week, resulting in a total of 12 DIN A4 samples per example. A test specimen was die-cut from each DIN A4 sample, and its maximum tensile strength or maximum tensile elongation was determined according to DIN ISO 9073-3. To determine the decrease in properties after storage, the mean value of three individual measurements (per week and variant) was calculated, and the measured value was normalized to the initial value before storage.

[0080] The relative decrease in tensile strength was used as a measure of the thermal stability of the nonwoven fabric. As expected, a significant decrease in tensile strength MD was found in comparison example 1. Comparison example 1 shows a constant loss of tensile strength to as little as 28% of the original value after 4 weeks at 200°C ( Fig. 1-2 The fluctuations visible here are within the measurement accuracy of the stored samples. However, when considering the nonwovens according to the invention, it is surprisingly evident that the tensile strength does not decrease but initially even increases and then remains almost constant. The increases are in the range of 20 to 50%. Comparing the storage temperatures at 160°C with those at 200°C, an acceleration of the processes is observed, as expected according to Ahrenius. This results in a more pronounced decrease in the tensile strength of the PET-based nonwoven. The results are in Figure 1 and 2 depicted.

[0081] Analogous to the maximum tensile strength, the percentage decrease in maximum tensile strength elongation was investigated, i.e., the elongation of the test specimen in percent at failure of the test specimen after measurement of maximum tensile strength according to DIN EN ISO 9073-3. Analogous to the measurement results in the Figure 1 and 2 A significant relative decrease in values ​​is observed in the case of the comparison nonwoven fabric. Elongation decreases to 10% of the original value at a storage temperature of 160°C and to 3% at a storage temperature of 200°C. The decrease is considerably less pronounced in the case of the PEN / PET-based nonwoven fabrics. At 160°C, the elongation decreases to 47–66% of the original value after four weeks, and to 45–60% at a storage temperature of 200°C.

[0082] Based on the presented measurements, it can therefore be concluded that the PEN sheath protects the PET core and thus has a stabilizing effect.

[0083] The results are in Figure 3 and 4 depicted. 4. Measurement method for determining melting points, decomposition points, enthalpies of melting and crystallization, glass transition temperatures and crystallinity

[0084] Glass transition temperatures, melting points, decomposition points, and enthalpies of crystallization and fusion were measured using DSC according to DIN EN ISO 11357-2 (edition: 2014-07). The melting points correspond to the temperatures at the maxima of the endothermic enthalpy of fusion. The exothermic enthalpies of crystallization and the endothermic enthalpies of fusion are derived from the respective integrals of the measurement curves. In all cases, the first heating curve was used to determine the values.

[0085] The degree of crystallinity (K%) can be determined from the ratio of the melting and crystallization enthalpies (“Thermoplastic Materials: Properties, Manufacturing Methods, and Applications”, Christopher C. Ibeh, CRC Press, ISBN: 13:978-1-4200-9384-1, p. 105 ff.) according to: K % = ΔH Schmelz . − ΔH Krist . × 100 % / ΔH Krist . 100 % . calculate. 5. Determination of the enthalpies of crystallization and enthalpies of fusion of the fibers used for the production of the sheet structures of examples 1 to 4

[0086] Testing device: Mettler Toledo Cooling: active liquid nitrogen cooling Purge gas: Nitrogen (N₂ 99.999%) 30 ml / min Crucible: Aluminium 40µl Weight (mg): 8 to 12 Rehearsal preparation: cut with a scalpel Temperature (°C): 25 → 300 / / 300 → 25 / / 25 → 300 Heating rates (K / min): 10 10 10 Waiting times (min): 5 5 5

[0087] To determine the integrals, the minimum between the two crystallization enthalpies was defined as the limit. The procedure was analogous for the fusion enthalpy of the matrix fiber.

Claims

1. Textile sheet structure comprising a main body of at least one ply, wherein the at least one ply comprises polyethylene naphthalate (PEN), copolymers and / or blends thereof as a binding component, wherein the PEN in the copolymers and / or blends is the main component and is present in a fraction of more than 90% by weight, wherein the binding component is obtainable by subjecting core / sheath binder fibres, in which the binder fibre sheath polymer contains PEN, copolymers and / or blends thereof, to temperatures above the glass transition temperature of the binder fibre sheath polymer, wherein the binding component is producible starting from core / sheath binder fibres in which the binder fibre sheath polymer comprises PEN, copolymers and / or blends of PEN having a degree of crystallinity of less than 80%, characterized in that the binder fibre sheath polymer has a higher melting point than the binder fibre core polymer.

2. Textile sheet structure according to Claim 1, characterized in that the binding component is present in a form ranging from a more or less deformed fibre structure up to a completely fused continuous phase.

3. Textile sheet structure according to Claim 1 or 2, characterized in that the binding component is producible starting from core / sheath binder fibres in which the binder fibre sheath polymer comprises PEN, copolymers and / or blends thereof having a degree of crystallinity of 0% to 75%, even more preferably of 0% to 70% and in particular of 0% to 60%.

4. Textile sheet structure according to one or more of the preceding claims, characterized in that the sheet structure after thermal storage at 160°C for 1 week exhibits a percentage reduction in the ultimate tensile strength in at least one direction of less than 5%, preferably of less than 4%, for example of 0% to 4% and / or an increase in the ultimate tensile strength in at least one direction of at least 1%, preferably of more than 5%, for example of 5% to 100%.

5. Textile sheet structure according to one or more of the preceding claims, characterized in that the PEN, the copolymers and / or blends thereof in the binder fibre sheath polymer have a cold crystallization temperature in the range from 70 to 200°C, more preferably in the range from 80 to 190°C, most preferably in the range from 90 to 175°C.

6. Textile sheet structure according to one or more of the preceding claims, characterized in that the PEN, the copolymers and / or blends thereof in the binder fibre sheath polymer and / or in the binding component have a melting temperature in the range from 180 to 320°C, more preferably in the range from 210 to 310°C, most preferably in the range from 230 to 300°C.

7. Textile sheet structure according to one or more of the preceding claims, characterized in that the quantitative ratio between binder fibre core polymer and binder fibre sheath polymer is from 90:10 to 10:90 (weight ratio core:sheath in % by weight), even more preferably from 80:20 to 20:80, even more preferably from 80:20 to 30:70 and in particular from 80:20 to 40:60.

8. Textile sheet structure according to one or more of the preceding claims, characterized in that the difference of the melting temperatures of the binder fibre sheath polymer and the binder fibre core polymer is at least 2.5°C, preferably at least 5°C, preferentially at least 7.5°C.

9. Textile sheet structure according to one or more of the preceding claims, characterized in that the sheet structure comprises matrix fibres, wherein the difference of the degree of crystallinity between the sheath of the core / sheath binder fibres and the degree of crystallinity of the matrix fibres before the thermal treatment is at least 5%, for example from 5% to 80%, even more preferably from at least 7.5%, for example from 7.5% to 70% and in particular from at least 10%, for example from 10% to 60%.

10. Textile sheet structure according to one or more of the preceding claims, characterized in that the matrix fibres are embodied as core / sheath matrix fibres, comprising a matrix fibre sheath polymer and a matrix fibre core polymer.

11. Textile sheet structure according to one or more of the preceding claims, characterized in that the matrix fibre sheath polymer is selected from the same polymers, copolymers and / or blends as the binder fibre sheath polymer and / or the matrix fibre core polymer is selected from the same polymers, copolymers and / or blends as the binder fibre core polymer.

12. Textile sheet structure according to one or more of the preceding claims, characterized in that the fraction of PEN, copolymers and / or blends thereof and polyethylene terephthalate and / or co-polyethylene terephthalate taken together is more than 80% by weight, preferably more than 90% by weight, even more preferably more than 95% by weight and in particular more than 97% by weight, based in each case on the total weight of the main body.

13. Textile sheet structure according to one or more of the preceding claims, characterized in that the fraction of the PEN, its copolymers and / or blends is from 5% to 95% by weight, preferably from 5% to 75% by weight, in particular from 10% to 50% by weight, based in each case on the total weight of the sheet structure.

14. Use of a textile sheet structure according to one or more of the preceding claims for producing electrical insulating materials, for example for the electrical insulation of electric motors, generators or transformers, in particular for producing (flexible) laminates with films in the core as insulation for e.g. slots or slot liners, as carrier material for conductive tapes and / or as a ply separator for phase separation.

15. Process for producing a textile sheet structure according to one or more of Claims 1 to 13, comprising the following process steps: - providing core / sheath binder fibres in which the sheath comprises PEN, copolymers and / or blends thereof, - forming a ply containing the core / sheath binder fibres, - subjecting the ply to temperature, wherein the temperature is above the cold crystallization temperature of the binder fibre sheath polymer, to give a textile sheet structure which comprises a main body of at least one ply, wherein the at least one ply comprises PEN, copolymers and / or blends thereof as a binding component.