Insulated cable, method for its manufacture, wrapping tape for the insulation and use of the cable

Abstract

The invention relates to a cable comprising a conductor for conducting electrical current and an insulation, wherein the insulation has a first layer adjacent to the conductor, wherein the first layer adjacent to the conductor covers 50 - 99% of the conductor and leaves the remaining area free, as well as a method for its production and a winding tape for forming the first layer.

Description

[0001] The invention relates to a cable according to the preamble of claim 1 as well as a method for its production, a winding tape therefor and its use.

[0002] Electrical cables are used in many areas, in particular electrical cables are used to transmit electrical energy and to transmit signals.

[0003] It is quite common to group a large number of cables together in cable harnesses, with the cables usually having connectors that are connected to connector housings.

[0004] Particularly in mobile applications, such as in cars, trucks, aircraft or aerospace vehicles, signal or energy-conducting cables are combined in cable harnesses, whereby depending on the function or type of signals, a large number of cables can be combined in one connector housing, with each cable being connected to an electrically conductive connector, so that a large number of cables can be connected at once by joining two connector housings that correspond to each other.

[0005] Of course, such cables must be insulated to prevent short circuits or voltage surges.

[0006] Furthermore, especially in mobile applications, it is important that the cables have a certain degree of robustness against mechanical influences.

[0007] For example, it's well known that cables installed in car bodies can be chafed by sharp edges, especially around body penetrations (holes in the sheet metal). Therefore, it's common practice to design the cable insulation to be robust enough to withstand these mechanical stresses, or to provide the cable harnesses with appropriate protective wrapping.

[0008] Especially in mobile applications, mechanical stress is also caused by vibrations and the corresponding abrasion on hard edges.

[0009] Furthermore, cables, especially in mobile applications, are often subjected to temperature and / or environmental stress. Very high temperatures or large temperature fluctuations can occur, for example, in aerospace vehicles. The insulation, in particular, must therefore withstand both mechanical and thermal stress.

[0010] In addition, it cannot be ruled out that moisture caused by external influences or condensation may also affect cables.

[0011] In summary, electrical cables, whether used for signal or power transmission, must be robust against all possible environmental conditions.

[0012] Additional requirements for such cables may include high chemical resistance, high flexibility, and / or high flammability. On the one hand, the high flexibility facilitates easy installation, while on the other hand, the good bendability of the cables prevents mechanical loads on the connectors.

[0013] In particular, very high voltages and / or currents must be conducted in some cases. The cable insulation must therefore be designed to prevent partial discharge at the operating voltages used, in order to prevent slow decarbonization of the insulation caused by a corona field.

[0014] Another important property of cables is their ease of handling, such as the ability to strip the insulation during connector assembly, but also during maintenance and repair work.

[0015] US 2012 / 0090874 A1 discloses a thin, lightweight, insulated wire comprising a core surrounded by an insulating polymer sheath comprising an inner layer of PTFE for electrical insulation, a middle layer of an aromatic or heterocyclic ring-containing polymer, such as PEEK, for improved mechanical properties such as abrasion resistance and shear strength, and an outer layer of PTFE, which in turn provides electrical and chemical resistance and allows the entire structure to be sintered. The middle layer can flow during sintering and can also form bonds, which can offer additional and unexpected advantages. The preferred thickness of each layer is said to be between 25 and 50 µm.

[0016] The first layer should be a tape wrapped around the conductor or PTFE extruded directly onto the conductor and sintered in situ. This insulating layer should preferably be spirally wound around the core of the conductor, preferably with an overlap of at least 25% to a maximum of 65%, more preferably at least 40% to a maximum of 55%. The layers can be applied individually one after the other or using a laminate, whereby the laminate can consist of two or three layers of insulation. The preferred overlap angle should be between 45 and 55°. The outer PTFE layer should press the entire composite together during sintering and enable a sealed formation, thereby creating outstanding chemical resistance combined with excellent mechanical properties caused by the PTFE layer.

[0017] The sintering temperature should be between 350 and 420°C, with PEEK typically melting at 343°C, so that sintering causes the PTFE to shrink, compacting the entire assembly. Sintering should take place between 30 seconds and 2 minutes, and preferably between 60 and 90 seconds.

[0018] US 10,090,080 B2 discloses an electrical cable for supplying power to an electrical device, comprising at least one conductive core and an insulating sheath arranged around the core, the insulation having a relative dielectric continuity of less than 2 and comprising a first layer that is a polymeric erogen and a second layer that surrounds the first layer and consists of a fluoropolymer. Furthermore, a third layer may be arranged between the conductive core and the first layer and consists of or comprises a fluoropolymer. This is intended to fill any gaps between the first layer and the conductor, particularly in stranded conductors. The fluoropolymer may be PTFE, PFA, ETFE, or FEP. The described cable is intended, in particular, to be used for conducting high voltages in aircraft.

[0019] TE Components markets a highly flexible wire called SHF-260, which is said to be suitable for applications in aircraft, among others. Its flexibility allows it to be installed even in extremely confined spaces without bending or tearing the insulation. This conductor is specifically designed for high-voltage applications and is temperature-stable up to 260°C, and even up to 290°C for short periods. It is said to offer high chemical and liquid resistance, and the insulation is a single- or double-layer extruded fluoropolymer.

[0020] FR2699320 discloses that expanded porous PTFE (ePTFE) exhibits surprisingly higher mechanical strength than conventional PTFE, while its chemical inertness and heat resistance are comparable to those of conventional PTFE. However, its notch strength is similarly poor, as is the case with conventional PTFE.

[0021] US Pat. No. 4,732,626 describes a PTFE that is compressed under pressure and initially expanded using the process described in US Pat. No. 3,953,566. This PTFE is then placed around a conductive wire and heated. The resulting conductor, which is insulated by the compressed PTFE, has the high mechanical strength of PTFE but also offers high resistance to cuts and abrasion.

[0022] Cables for such applications are also known to have a polyimide layer. Such insulation is extremely sensitive to moisture and begins to degrade after absorbing moisture, and this deteriorates even more when exposed to temperature. Therefore, they must be protected from moisture by additional layers of fluoropolymers.

[0023] In practice, it has been shown that such electrical cables, and especially cables containing at least one fluoropolymer layer, tend to shrink during use, especially under the influence of temperature. This can result, for example, in the insulation directly adjacent to the metallic conductor shrinking in the area where the metallic conductor connects to the connector if the adhesion to the conductor surface is too weak, so that voltage flashovers can no longer be ruled out, particularly in high-voltage cables.

[0024] Insulation layers that are extruded or glued directly onto the conductor have been shown to adhere well, but stripping is often not possible or only possible with enormous force, which leads to either the conductor being mechanically deformed during stripping or its surface being damaged and / or insulation residues remaining on the conductor.

[0025] The cutting of the cable insulation during the stripping process must also be carried out in such a way that the conductor and its surface remain mechanically intact in order to ensure the full functionality of the applied conductor coating.

[0026] The object of the invention is to create a cable of the type mentioned above, which has insulation with improved properties. In particular, the aim is to create a cable that meets the requirements of industry standards in terms of its mechanical and thermal properties, as well as its resistance to environmental influences, while also exhibiting as little shrinkage as possible while remaining easy to strip.

[0027] The problem is solved by the features of claim 1. Advantageous further developments are characterized in the dependent subclaims.

[0028] It is a further object to provide a method for manufacturing a cable which achieves improved insulation.

[0029] The problem is solved by the features of claim 13. Advantageous further developments are characterized in the dependent subclaims.

[0030] It is a further object to provide a wrapping tape as the first layer of insulation for such a cable, which enables an insulation structure with improved properties.

[0031] The problem is solved with a winding tape having the features of claim 23.

[0032] Advantageous further training is indicated in the dependent subclaims.

[0033] According to the invention, a cable, particularly a so-called power feeder cable, is created for use under extreme conditions, such as temperatures above 200°C and higher voltages. Furthermore, the cable is polyimide-free, hydrolysis-resistant, abrasion-resistant, and flexible.

[0034] Such multilayer insulation structures containing fluoropolymers tend to shrink irreversibly under the influence of temperature, among other things, in the longitudinal direction, thereby exposing corresponding conductor areas. This is unacceptable for the desired applications, especially in the aviation sector.

[0035] As already explained above, in applications where a PFA layer is extruded or glued directly onto the conductor - which would allow proper and entirely sufficient insulation - it has been found that stripping is no longer possible without further ado.

[0036] According to the invention, an insulation of such a conductor, in particular for use at elevated temperatures and voltages, as well as possibly humid environments, is constructed in at least two layers, wherein a first layer lying against the conductor is a layer which is in particular placed around the conductor or wound around the conductor and which is designed, for example, as a tape, in particular as a so-called winding tape.

[0037] This first winding layer or wraparound layer is made of PTFE. The first winding layer can be made of sintered, expanded PTFE (ePTFE), i.e., a porous PTFE heated above the melting point of PTFE. The first layer can also be made of semiconducting PTFE.

[0038] The thickness of the first layer is 2.5 to 125 µm. In particular, the thickness of the first layer is 12 to 40 µm.

[0039] According to the invention, this first folded or wrapped layer does not completely cover the metallic conductor. This allows a subsequent, particularly extruded, layer to adhere to the conductor. Because there is no full-surface adhesion, the invention enables a compromise between strippability on the one hand and the prevention of shrinkage by partially adhering the second layer directly to the conductor.

[0040] In particular, 1-50% of the conductor surface is uncovered, or 50-99% of the conductor surface is covered. Preferably, 4-20% of the conductor surface is uncovered, or 60-96% of the conductor surface is covered. In particular, 5-15% of the conductor surface is uncovered, or 85-95% of the conductor surface is covered. Further preferably, 10% of the conductor surface is uncovered, or 90% of the conductor surface is uncovered.

[0041] In order to achieve this, the invention provides different, yet equally effective, solutions.

[0042] In a first embodiment, the angle during the wrapping, in particular helical wrapping of the conductor, is selected such that there is a distance between the mutually facing longitudinal edges of the wrapping tape which accordingly corresponds to between 1 and 50% of the width of the wrapping tape between the longitudinal edges.

[0043] The width of the wrapping tape can of course be adjusted accordingly.

[0044] Another possibility according to the invention provides for the wrapping tape to be formed with cutouts across its surface. Such cutouts can be round holes, triangular, square, or polygonal holes, or even elongated slots.

[0045] These can be distributed over the surface of the winding tape, so that, for example, several holes are arranged next to each other or in successive rows.

[0046] Likewise, the slots can be arranged lengthwise, crosswise or diagonally to the longitudinal extent of the winding tape and can be adapted to the desired degree of clearance with regard to the width of the slots, the distance between the slots and the length of the slots.

[0047] The slots can also be comparatively wide and long and only interrupted by bridges between the limiting areas of the winding tape.

[0048] When wound on the conductor, the longitudinal edges of the winding tape can be wound butt-to-end or with a slight overlap if the above-described recesses are provided.

[0049] In the mounted state of the winding tape on the conductor, the slots can also run parallel or inclined with respect to the longitudinal extension of the conductor.

[0050] Furthermore, the wrapping tape can be wrapped around the conductor not helically but also lengthwise or crosswise, leaving a long gap or radial gaps between the longitudinal edges of the wrapping tape, leaving the conductor exposed in this area. The gap is therefore arranged more or less parallel to the longitudinal extension of the conductor.

[0051] This means that in this case the wrapping tape has a width between the longitudinal edges that is less than the circumference of the conductor.

[0052] In a subsequent step, a second insulating layer is extruded or wound onto the winding tape on the conductor. This is typically a PFA layer, for example. In the area of the cutouts, this PFA layer directly contacts the conductor and can adhere to it.

[0053] To improve adhesion, the second layer can be extruded onto the conductor using a nozzle in such a way that the nozzle compresses or compacts the second layer, thus creating a more intimate contact with the conductor. With a wound outer layer, a sintering step is necessary to bond the individual layers and establish contact with the conductor.

[0054] On the one hand, insulation produced in this way as a two-layer composite can be easily removed from the conductor by providing the PTFE winding tape, as this has a low coefficient of static friction compared to the conductor. On the other hand, the arrangement of the recesses can ensure that shrinkage is prevented by the corresponding static friction forces, because the second layer cannot slide freely on the conductor.

[0055] To further improve the insulation performance, and in particular the protection against external influences, a third layer can be provided, which is wound or extruded onto the second layer. The third layer is preferably made of PTFE, in particular densified PTFE. Such densified PTFE can be manufactured, for example, as described in US Patent No. 4,732,626 or US Patent No. 5,374,473.

[0056] It is necessary to sinter the three-layer composite at the end because this sintering process causes the outermost layer to shrink inward / vertically, pressing the second layer and the first layer against the conductor. During sintering, the second layer softens, and all three layers form a tight bond. This bond prevents excessive shrinkage of the third layer.

[0057] A third PTFE layer also has the advantage, especially if it is a compacted PTFE layer, that it is chemically inert on the one hand, and temperature-resistant and abrasion-resistant on the other.

[0058] The invention is advantageous in that it creates an insulation layer which, with very high flexibility, offers high performance against dielectric strength, abrasion, chemical influences and temperature influences, but on the other hand adheres well to the conductor and thus cannot shrink, and is still easy to strip.

[0059] The invention thus relates in particular to a cable comprising a conductor for conducting electrical current and an insulation, wherein the insulation has a first layer adjacent to the conductor, wherein the first layer adjacent to the conductor covers 50-99% of the conductor and leaves the remaining surface free, wherein the thickness of the first layer is 2.5-125 µm, and wherein a second, extruded or wound insulation layer is arranged around the first insulation layer, which contains PFA (perfluoroalkoxy copolymers) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer).

[0060] A further development provides that the first layer is formed from a winding tape, wherein the winding tape is arranged as a longitudinal wrap or helically or transversely around the conductor.

[0061] A further development provides that at least one gap is formed between the longitudinal edges of the winding tape, which leaves 1 - 50% of the surface of the conductor free.

[0062] A further development provides that the winding tape has a plurality of cutouts (8) across its width, which leave the conductor uncovered.

[0063] A further development provides that 1 - 50% of the surface of the conductor, preferably 4 - 20% of the surface of the conductor, more preferably 5 - 15% of the surface of the conductor and even more preferably 7 - 12% of the surface of the conductor are uncovered.

[0064] A further development provides for the winding tape to be made of PTFE.

[0065] A further development provides that the winding tape is made of sintered, expanded PTFE (ePTFE).

[0066] A further development provides that the winding tape is made of semiconductive PTFE.

[0067] A further development provides that a third insulation layer made of PTFE, in particular compressed PTFE, is arranged around the second, extruded or wound insulation layer.

[0068] A further development provides that the third layer has a thickness of 150 - 400 µm, in particular 230-330 µm.

[0069] A further development provides that the second layer contains a semiconducting compound based on PFA or FEP.

[0070] A further development provides that the second layer has a thickness of 100 - 300 µm, in particular 150-250 µm.

[0071] A further development provides that a further layer with a semiconducting compound based on PFA or FEP is arranged between the first layer and the second layer.

[0072] A further development provides that the third insulation layer is folded lengthwise or wrapped helically or transversely around the second insulation layer.

[0073] A further aspect of the invention relates to a method for producing a cable, in particular for the high-voltage range, wherein a conductor is surrounded by a first insulation layer, wherein the first insulation layer is formed such that 50 - 99% of the surface of the conductor is covered and wherein a second, extruded or wound insulation layer made of PFA (perfluoroalkoxy copolymers), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) or a semiconducting compound based on PFA or FEP is formed around the first insulation layer.

[0074] A further development provides that the first layer is formed from a winding tape, wherein the winding tape is laid as a longitudinal wrap or helically or transversely around the conductor.

[0075] A further development provides that at least one gap is formed between the longitudinal edges of the winding tape, which leaves 1 - 50% of the surface of the conductor free.

[0076] A further development provides that the wrapping tape has a plurality of cutouts across its width, which leave the conductor uncovered in these areas.

[0077] A further development provides that 1 - 50% of the surface of the conductor, preferably 4 - 20% of the surface of the conductor, more preferably 5 - 15% of the surface of the conductor and even more preferably 7 - 12% of the surface of the conductor are left uncovered.

[0078] A further development provides for the use of PTFE for the first insulation layer.

[0079] A further development provides that the first insulation layer is made of sintered, expanded PTFE (ePTFE).

[0080] A further development provides that a third insulation layer made of PTFE, in particular compressed PTFE, is arranged around the second insulation layer.

[0081] A further development provides that the third insulation layer is folded lengthwise or wrapped helically or transversely around the second insulation layer.

[0082] A further development provides that the composite of the conductor and the insulation layers is sintered and in particular is sintered at 350°C to 420°C.

[0083] A further aspect of the invention relates to a wrapping tape for forming an insulation, wherein the wrapping tape has a plurality of continuous cutouts over its surface.

[0084] A further development provides for the winding tape to be made of PTFE (polytetrafluoroethylene).

[0085] A further development provides that the winding tape is made of sintered, expanded PTFE (ePTFE).

[0086] A further development provides that the recesses make up 1 - 50% of the area of the winding band, in particular 4 - 20% of the area of the winding band, preferably 5 - 15% of the area of the winding band and particularly preferably 7 - 12% of the area of the winding band.

[0087] A further aspect of the invention relates to the use of a cable according to one of claims 1-11 in motor vehicles, ships, or aircraft or space vehicles.

[0088] A further aspect of the invention relates to the use of a winding tape according to one of claims 23 to 27 for wrapping conductors to form insulation.

[0089] The invention is explained by way of example with reference to the drawings, which show: Fig. 0a: a cross-section through a cable according to the invention with a two-layer insulation structure, wherein the metallic conductor is monofilament; Fig. 0b a cross-section through a cable according to the invention with a two-layer insulation structure, wherein the metallic conductor is formed from strands; Fig. 1: a cross-section through a cable according to the invention with a three-layer insulation structure, wherein the metallic conductor is monofilament; Fig. 2: a cable according to the invention with a three-layer structure, wherein the metallic conductor is formed from strands; Fig. 3: a view of a metallic conductor formed with a winding tape according to the invention and a gap between the longitudinal edges of the winding tape; Fig. 4: the structure according to Fig. 3 in a plan view; Fig. 5: a further embodiment in which the metallic conductor is wound helically butt-jointed with a winding tape according to the invention with cutouts; Fig. 6: the ladder after Fig. 5 in a plan view; Fig. 7: a further embodiment in which slot-like, offset recesses are arranged in the winding tape; Fig. 8: an arrangement according to Fig. 7 with slot-like recesses which are angled to the longitudinal extension of the winding tape; Fig. 9: a further embodiment in which radial slots are formed by the winding tape in a perspective view; Fig. 10: the embodiment according to Fig. 9 in a plan view; Fig. 11: a graphical representation of the shrinkage of three different samples with different degrees of conductor coverage, wherein samples 1 and 2 are not layers according to the invention; Fig. 12: a table with the samples of Fig. 11; Fig. 13: showing the shrinkage and strippability of five different materials, including three structures according to the invention; Fig. 14: the inventive structure according to Fig. 2 before and after sintering (recess is not visible); Figure 15: the inventive structure according to Fig. 2 after sintering (recess is visible); Fig. 16: an enlarged section of Fig. 15; Fig. 17: the penetration of the insulation layer into the conductor in a commercial product; Fig. 18: the poor severability of reference sample 1; Fig. 19: the conductor damage in reference sample 1; Fig. 20: good severability without conductor damage of sample 3 according to the invention; Fig. 21: a tabular overview of the possible embodiments of the invention.

[0090] The Fig. 0a and Fig. 0b show a highly schematic representation of a first embodiment of the invention. Reference numeral 1 denotes a cable with a metallic conductor 2. The metallic conductor can be solid ( Fig. 0a) or be made of several conductors with a smaller diameter as a stranded wire ( Fig. 0b). The conductor can in principle be made of any conductive material, in particular conductive metal. In particular, the conductor 2 is made of copper or aluminum, whereby the copper or aluminum conductor can have a silver, gold, or nickel coating (not shown).

[0091] Conductor 2 is insulated for electrical insulation and to protect against external influences such as moisture. In the example shown, the insulation has two layers.

[0092] A first layer 3 of insulation is formed around and adjacent to the conductor 2.

[0093] The first layer 3 consists of a fluoropolymer.

[0094] In particular, the first layer consists of PTFE (polytetrafluoroethylene), preferably pre-sintered, expanded PTFE (ePTFE). The main function of this first insulating layer is to mechanically separate the conductor 2 from further applied layers in certain areas. The material selected for the first layer 3 has low static friction with the conductor 2. The first layer is thin. The first layer has a thickness of 2.5–125 µm. In particular, the first layer has a thickness of 12 to 40 µm.

[0095] A second insulating layer 4 is arranged around the first layer 3 of insulation.

[0096] The second layer 4 is an extruded or wound layer containing PFA or FEP, or alternatively a semiconducting compound based on PFA or FEP. In particular, the second layer is an extruded PFA.

[0097] The second layer has a thickness of, for example, 100 - 300 µm, in particular 150-250 µm.

[0098] Preferably, the melting point of the material of the second layer 4 is below that of the first layer 3. Preferably, the melting point of the second layer 4 is 350°C and that of the first layer is above 420°C.

[0099] The material of the second layer serves as a base material in terms of its primary function, allowing it to be broken and peeled off relatively easily during stripping without having to cut completely through it. This reduces the risk of cutting the surface of conductor 2. Although PTFE is difficult to break, the thinness of the first layer allows it to be broken off along with the PFA.

[0100] Another embodiment of the invention with a three-layer insulation is highly schematic in Fig. 1 shown. Fig. 1 shows a cable 1 with a metallic conductor 2. The metallic conductor 2 can also be solid ( Fig. 1) or be made of several conductors with a smaller diameter as a stranded wire ( Fig. 2).

[0101] The conductor can in principle be made of any conductive material, in particular conductive metal. In particular, the conductor 2 is made of copper or aluminum, wherein the copper or aluminum conductor can have a silver, gold, or nickel coating (not shown).

[0102] Conductor 2 is insulated for electrical insulation and to protect against external influences such as moisture. In this case, the insulation consists of three layers.

[0103] A first layer 3 of insulation is formed around and adjacent to the conductor 2.

[0104] The first layer 3 consists of a fluoropolymer.

[0105] In particular, the first layer consists of PTFE (polytetrafluoroethylene), preferably pre-sintered, expanded PTFE (ePTFE). The main function of this first insulating layer is to mechanically separate the conductor 2 from further applied layers in certain areas. The material selected for the first layer 3 has low static friction with the conductor 2. The first layer is thin. The first layer has a thickness of 2.5–125 µm. In particular, the first layer has a thickness of 12 to 40 µm.

[0106] A second insulating layer 4 is arranged around the first layer 3 of insulation.

[0107] The second layer 4 is an extruded or wound layer containing PFA or FEP, or alternatively a semiconducting compound based on PFA or FEP. In particular, the second layer is an extruded PFA.

[0108] The second layer has a thickness of, for example, 100 - 300 µm, in particular 150-250 µm.

[0109] Preferably, the melting point of the material of the second layer 4 is below that of the first layer 3. Preferably, the melting point of the second layer 4 is 350°C and that of the first layer is above 420°C.

[0110] The material of the second layer serves as a base material in terms of its primary function, allowing it to be broken and peeled off relatively easily during stripping without having to cut completely through it. This reduces the risk of cutting the surface of conductor 2. Although PTFE is difficult to break, the thinness of the first layer allows it to be broken off along with the PFA.

[0111] A third layer 5 is arranged around the second layer 4.

[0112] The third layer 5 consists of compressed PTFE with a thickness of, for example, 150 - 400 µm, in particular 230-330 µm.

[0113] The compacted PTFE material provides excellent mechanical resistance and also excellent thermal resistance.

[0114] The two- or three-layer structure is sintered together after assembly.

[0115] For this purpose, the entire composite of conductor 2 and layers 3, 4, and 5 is subjected to a temperature treatment above 350°C, in particular between 350°C and 420°C. The sintering temperature and duration should be such that the second layer 4 melts or becomes plastic, but the first and third layers 3, 5 do not melt.

[0116] In Fig. 3 and Fig. 4 shows an embodiment of the first insulation layer on the conductor 2, wherein the conductor 2 appears solid here, but can also be designed as a stranded conductor.

[0117] The first insulating layer 3 is arranged around the conductor, wherein the insulating layer 3 is designed as a wrapping tape and the wrapping tape is wrapped lengthwise around the conductor 2.

[0118] The edges 6 delimiting the winding tape 3 are spaced apart from one another, which means that the width of the winding tape 3 between the longitudinal edges 6 must be smaller than the circumference of the conductor 2. This results in a gap 7 running essentially parallel to the longitudinal extent of the conductor 2, in the region of which the conductor 2 is exposed. The gap 7 has a width dimensioned such that between 1 and 50%, and in particular 4-20%, more preferably 5-15%, and in particular 10%, of the conductor 2 is exposed.

[0119] In a further advantageous embodiment of the winding tape 3 ( Fig. 5, Fig. 6) a pattern of cutouts 8 is arranged on the winding tape 3, distributed across the width.

[0120] The cutouts 8 can, for example, be circular holes. However, the holes do not have to be circular; they can also be triangular, square, polygonal, oval, or formed in some other way. The area share of the cutouts 8 in the surface of the winding tape is 1-50%, in particular 4-20%, preferably 5-15%, and in particular 10% of the total surface of the winding tape, so that the corresponding percentage shares of the surface of the conductor 2 are left free in the area of the cutouts 8. In the embodiment according to the Fig. 5 and Fig. 6 the winding tape is wound helically without a gap between the longitudinal edges 6 and thus butt-wound around the conductor 2.

[0121] Of course, in this case the wrapping tape 3 can also be wound with a slight overlap, and the wrapping tape can also be wound with a butt spacing, whereby the butt spacing is then of course to be added to the clearance area.

[0122] In addition, it is of course also possible to use a winding tape without cutouts 8, in which case the winding tape 3 is then wound with a butt spacing of the longitudinal edges 6, the butt spacing then corresponding to the desired percentage of exposure of the surface of the conductor 2, i.e. 1 - 50%, in particular 4 - 20%, more preferably 5 - 15%, and in particular 10% (not shown).

[0123] A wrapping tape of the embodiment according to Fig. 5 and Fig. Instead of a helical wrapping, the strip 6 can be placed lengthwise around the conductor 2, with the butt edges 6 then abutting against each other, meaning that the width of the wrapping strip 3 corresponds to the circumference of the conductor. Here, too, a distance or gap 7 between the longitudinal edges 6 can, of course, be combined with the recesses 8 to form an exposed surface for the conductor 2.

[0124] Another embodiment is shown in the Fig. 7 and Fig. 8 can be seen.

[0125] Here, the cutouts 8 are designed as slots, with the slots being distributed across the width of the strip. Furthermore, the longitudinal edges 6 can be adjacent to one another or spaced apart from one another, subject to the same conditions as previously mentioned for the other embodiments.

[0126] It is obvious to the person skilled in the art that, if this appears advantageous, a mixture of the shape of the recesses 8, for example round circles, slots, etc., can also be used.

[0127] Even in an embodiment according to the Fig. 7 and Fig. 8, the wrapping tape can of course also be wrapped lengthwise around the conductor 2 and used with or without a gap 7.

[0128] In another embodiment ( Fig. 9, Fig. 10), the winding tape 3 is laid radially around the conductor 2, wherein the individual windings of the winding tape 3 are spaced from one another by gaps 7, which are each delimited by the longitudinal edges 6 delimiting the winding tape.

[0129] Of course, a wrapping tape with recesses 8 can also be laid in such a way that gaps 7 remain, so that gaps 7 and recesses 8 together form the uncovered surface of the conductor 2.

[0130] The method according to the invention provides for first wrapping a solid or stranded conductor 2 with a winding tape 3, either lengthwise or helically or radially. The conductor used can be a copper or aluminum conductor, whereby the copper or aluminum conductor can be gold-, silver-, or nickel-plated.

[0131] The wrapping tape 3 for the innermost insulating layer, which lies directly on the conductor, is made of PTFE, preferably sintered or pre-sintered ePTFE.

[0132] This winding tape 3, which can be designed with recesses 8 as described above, or can be placed around the conductor 2 with a gap 7, or can be designed with the gap 7 and the recesses 8 and can be wound helically or radially or can be laid lengthwise, is then fed with the conductor 2 to an extrusion or winding device in which a second insulation layer 4 is extruded or wound onto the conductor and the first layer 3.

[0133] The second layer 4 is FEP, PFA, or a semiconducting compound based on PFA or FEB. In the area of the gap 7 and / or the cutouts 8, the second insulation layer 4 contacts the conductor 2 through the cutouts 8 or the gap 7.

[0134] In order to achieve good contact, mechanical pressure can be exerted on the second layer 4 in the plastic state during extrusion or winding, for example by the geometry of the extrusion nozzle or a downstream, temperature-controlled compression nozzle.

[0135] For a three-layer structure, a further layer of a high-strength fluoropolymer, such as compacted PTFE, can then be applied. This third layer 5 is preferably also applied and wound helically in the form of a winding tape around the conductor 2, the first layer 3 lying thereon, and the layer 4 extruded or wound thereon.

[0136] The method according to the invention provides for this three-layer composite to subsequently be subjected to a sintering step. During this sintering step, a temperature above the melting temperature of the second layer 4 is preferably desired; in particular, sintering is carried out at sintering temperatures above 350°C, and in particular 350-420°C.

[0137] According to the invention, this melts the second layer 4. The compressed PTFE material arranged around the second layer 4, in particular wound, shrinks vertically onto the conductor at these sintering temperatures, thereby pressing the material of the second layer 4 onto the first layer 3 and thus the first layer 3 onto the conductor 2, and in the case of a stranded conductor, also into the corresponding interstices between the strands.

[0138] In addition, the material of the second layer 4 is particularly closely connected to the conductor 2 through the gap(s) 7 and the cutouts 8 by this shrinking process of the outermost layer 5.

[0139] Before sintering, the innermost layer 3 has a thickness of, for example, 2.5-125 µm, in particular 12-40 µm. The second layer 4 arranged on the innermost layer has a thickness of 120-350, in particular 170-290 µm. The third compacted PTFE layer 5 applied to the second layer has a thickness of 150-400 µm, in particular 230-330 µm.

[0140] Other thicknesses are of course possible.

[0141] The method according to the invention produces an insulation structure with at least two layers, but in particular with three layers, in which the innermost layer made of PTFE mechanically separates the second layer from the conductor 2 except for the areas in which the second layer with PFA or FEP directly contacts the conductor 2.

[0142] Since the first layer of PTFE has a low coefficient of static friction, this layer, together with the static friction of the material of the second layer 4, combines the properties of shrinkage and strippability in such a way that the shrinkage is greatly reduced or prevented by the adhesion of the second layer 4 to the conductor 2, while the mechanical separation from the conductor 2 takes place on the remaining surface, resulting in easy strippability.

[0143] The sintering process of the densified PTFE material on the outer surface is key in bonding all three materials together and initiating the melting of the second layer, which is pressed into the wire structure or conductor structure.

[0144] It should be noted that the innermost layer 3 made of PTFE does not melt during the sintering process, although it is strongly compressed, it remains mechanically stable and retains its shape and does not continue to adhere to the conductor 2.

[0145] In Fig. Figure 11 shows a graphical comparison of three samples, each having a nickel-plated copper conductor, the conductor having a cross-section of AWG (American Wire Gage) 2 (35mm 2 ) has.

[0146] Samples 1 and 2 are comparison samples in which the first layer is wound with a coverage ratio of 1.2. Sample 1 features a PTFE inner layer with an outer, compacted PTFE layer without any recesses. The shrinkage test shows that the shrinkage, predominantly above 10 mm, is completely outside the target value of less than 3.18 mm. This is due to the very strong thermal shrinkage of the compacted PTFE material.

[0147] Samples 2 and 3 each have three layers, with the innermost layer made of sintered, expanded PTFE, the middle layer of PFA, and the outermost layer of densified PTFE. Sample 2 has no recess in the first layer, while Sample 3 contains a recess according to the invention.

[0148] In Fig. 12 shows the comparison of the three samples in tabular form.

[0149] Such a setup was subjected to the relevant industry-standard tests. For the shrinkage tests, measurements are taken according to "Insulation Shrinkage AS4347 Method 104 / AS22759." The test specimen is held at 290°C for six hours, and then the insulation shrinkage is measured. A 36 cm long insulated conductor is used as the test length, and the insulation shrinkage is not allowed to shrink by more than 3.18 mm per test specimen end.

[0150] The measurement of shrinkage after thermal shock is carried out according to the "Thermal Shock AS4347 method 805 / ASTM D 3032-21" test. This measurement involves four temperature cycles, each lasting 60 minutes. The material is heated to 260°C and held for 30 minutes, then cooled to -55°C within 2 minutes and held there for 30 minutes.

[0151] The shrinkage of the insulation is then measured, whereby the test specimen length is 150 cm and the insulation must not shrink by more than 3.18 mm per test specimen end.

[0152] The ability to strip the insulation depends on two factors: the ability to cut through the insulation and the ability to peel it off.

[0153] The strippability test is carried out according to the "Wire Insulation Stripping AS22759 paragraph 3.7.3" test setup. The entire insulation of the wires covered by this standard must be easily removed using conventional stripping tools / knives, without damaging the conductor when the knives cut through the insulation. The Pressmaster Oden tool from Pressmaster was used for the stripping.

[0154] For a quantitative assessment of strippability, a pull-off force measurement of insulation was used according to the Adhesion of Inner Conductor ESA / SCC 3902 Method 9.13 method. 150 mm long samples are prepared, with 75 mm of insulation being pulled off using a pull-force device, and the maximum force required is measured. The stripping force of the wires must be properly measured and recorded. Since there are no tools and acceptance criteria specified in a MIL specification for wires larger than American Wire Gage (AWG) size 10 (6 mm 2 ), a relative comparison is preferred here in order to be able to make a statement about the ease of stripping.

[0155] Sample 2, with an overlap of 20% and without cutouts, shows good stripping properties and the shrinkage values in the insulation shrinkage test are still acceptable, but the shrinkage in the temperature shock test is no longer within the required limits.

[0156] The inventive design of sample 3 with 10% cutouts showed a significantly improved shrinkage behavior, with a shrinkage of only 0.5 mm in the shrinkage test at 290°C for six hours and of only 1.2 mm after thermal shock, while at the same time providing good strippability.

[0157] Fig. 13 shows a comparison table. Sample 4 corresponds to sample 1 from Fig. 11 and sample 5 is constructed according to sample 3. Only the conductor has a different cross-section of AWG (American Wire Gage) 6 (16mm 2). Compared to sample 5, samples 6 and 7 feature an aluminum conductor and a larger clearance (20%), respectively, and FEP as the second layer material instead of PFA. The table also shows a commercially available product from Tyco Electronics, which also features an AWG 6 copper conductor (nickel-plated) with a modified PFA insulation layer extruded onto it.

[0158] This shows that samples 5 to 7 (with cutouts) all have a shrinkage behavior that is below the required maximum limits and can be easily stripped without damaging the conductor.

[0159] The shrinkage behavior of comparison sample 4 (without cutouts) is not sufficient, and the insulation cannot be stripped.

[0160] While the commercially available product also has acceptable shrinkage behavior, it does not have the required strippability.

[0161] In Fig. 14 shows an inventive structure before and after sintering in an enlarged sectional view.

[0162] You can see the strands of the conductor and the first layer of sintered ePTFE wrapping tape wrapped around them. A PFA layer is extruded onto this wrapping tape, and a wrapping tape made of compacted PTFE is wrapped around this layer.

[0163] The left image shows an unsintered structure, the right image a sintered one. It can be seen that the first layer is comparatively thin and in the right image Fig. 14 rests on the strands of conductor 2. Sintering shrinks the outermost densified PTFE material, which generally has a very high thermal shrinkage capacity. This compresses the material of the middle layer, in this case the PFA material, toward the conductor, thereby also forcing the ePTFE material of the first layer into the strands.

[0164] In Fig. 15 and Fig. The cutouts are visible in Figure 16. In the area of the cutouts, the material of the middle layer, such as the PFA material, is pressed into the conductor or into the gaps between the individual stranded wires.

[0165] Tests conducted by the applicant have shown that stranded conductors are not a prerequisite for good adhesion. Since even a solid conductor has a surface microstructure due to its manufacturing process, it is clearly sufficient to anchor it after sintering to ensure good shrinkage resistance of the entire structure.

[0166] However, sintering also bonds the three layers or the materials of the three layers together.

[0167] However, due to the low static friction of the PTFE layer directly on the conductor, very good insulation stripping can be achieved using conventional tools. The invention therefore offers the advantage of combining the inherently contradictory goals of strippability on the one hand and internal shrinkage on the other in an excellent way.

[0168] In contrast, Fig. 17, that in the commercially available product without an inner PTFE layer, the PFA material of the second / outer layer penetrates and adheres between the strands over the entire circumference and stripping is therefore no longer possible.

[0169] Poor stripping, especially cut-through, is common in the Fig. 18 and Fig. 19, which shows a section through Sample 1, which has both an inner PTFE insulation layer and an outer densified PTFE insulation layer on the conductor. Due to their mechanical properties, the PTFE layers, especially densified PTFE, could not be broken off and had to be cut through completely. Although the two-layer insulation layer is easily peeled off once cut, a great cutting depth is required to cut through it. Fig. 18 shows remaining insulation connections on the conductor, although a greater cutting depth has already been reached and the conductor surface has already been damaged. Fig. Figure 19 shows the damaged strands of the conductor when the cutting depth is even greater to remove the remaining insulation connections.

[0170] Fig. Figure 20, in turn, shows that with the inventive structure of Sample 3, good severability can be achieved without damaging the conductor. The second layer, in the form of PFA, only needs to be cut through a portion of its thickness. The remainder can then be broken off. The comparably thin PTFE inner layer can be broken off and peeled off together with the PFA layer.

[0171] Fig. Figure 21 shows a summary table of the possible embodiments of the invention with the different possible layer arrangements. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2012 / 0090874 A1

[0015] US 10,090,080 B2

[0018] FR 2699320

[0020] US 4,732,626 [0021, 0055] US 3,953,566

[0021] US 5,374,473

[0055] Cited non-patent literature

[0000] Thermal Shock AS4347 method 805 / ASTM D 3032-21

[0150] Wire Insulation Stripping AS22759 paragraph 3.7.3

[0153] Adheson of Inner Conductor ESA / SCC 3902 Method 9.13

[0154]

Claims

[1] Cable, comprising a conductor (2) for conducting electrical current and an insulation, wherein the insulation has a first layer (3) lying on the conductor (2), wherein the first layer (3) lying on the conductor covers 50 - 99% of the conductor and leaves the remaining surface free, wherein the thickness of the first layer is 2.5-125 µm, and wherein a second, extruded or wound insulation layer (4) is arranged around the first insulation layer (3), which contains PFA (perfluoroalkoxy copolymers) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer). [2] Cable according to claim 1, characterized by that the thickness of the first layer is 12 to 40 µm. [3] Cable according to claim 1 or 2, characterized by that the first layer is formed from a winding tape (3), wherein the winding tape is arranged as a longitudinal wrap or helically or transversely around the conductor. [4] Cable according to one of the preceding claims, characterized by that at least one gap (7) is formed between longitudinal edges (6) of the winding tape (3), which gap leaves 1 - 50% of the surface of the conductor free. [5] Cable according to one of the preceding claims, characterized by that the winding tape has a plurality of cutouts (8) across its width, which leave the conductor uncovered. [6] Cable according to one of the preceding claims, characterized by that 1 - 50% of the surface of the conductor, preferably 4 - 20% of the surface of the conductor, more preferably 5 - 15% of the surface of the conductor and even more preferably 7 - 12% of the surface of the conductor are uncovered. [7] Cable according to one of the preceding claims, characterized by that the winding tape (3) is made of PTFE. [8] Cable according to one of the preceding claims, characterized by that the winding tape (3) is made of sintered, expanded PTFE (ePTFE). [9] Cable according to one of the preceding claims, characterized by that a third insulation layer (5) made of PTFE, in particular compressed PTFE, is arranged around the second, extruded or wound insulation layer (4). [10] Cable according to one of the preceding claims, characterized by that the second layer contains a semiconducting compound based on PFA or FEP. [11] Cable according to one of claims 1 to 10, characterized by that between the first layer (3) and the second layer (4) a further layer with a semiconducting compound based on PFA or FEP is arranged. [12] Cable according to claim 9, characterized by that the third insulation layer (5) is folded lengthwise or wrapped helically or transversely around the second insulation layer (4). [13] Method for producing a cable, wherein a conductor (2) is surrounded by a first insulation layer (3), wherein the first insulation layer (3) is formed such that 50 - 99% of the surface of the conductor (2) is covered and wherein a second, extruded or wound insulation layer (4) made of PFA (perfluoroalkoxy copolymers), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) or a semiconducting compound based on PFA or FEP is formed around the first insulation layer (3). [14] Method according to claim 13, characterized by that the first layer (3) is formed from a winding tape (3), wherein the winding tape is laid as a longitudinal wrap or helically or transversely around the conductor (2). [15] Method according to claim 13 or 14, characterized by that at least one gap (7) is formed between longitudinal edges (6) of the winding tape (3), which gap leaves 1 - 50% of the surface of the conductor (2) free. [16] Method according to one of claims 13 to 15, characterized by that the winding tape (3) has a plurality of cutouts (8) across its width, which leave the conductor (2) uncovered in their areas. [17] Method according to one of claims 13 to 16, characterized by that 1 - 50% of the surface of the conductor, preferably 4 - 20% of the surface of the conductor, more preferably 5 - 15% of the surface of the conductor and even more preferably 7 - 12% of the surface of the conductor is left uncovered. [18] Method according to one of claims 13 to 17, characterized by that PTFE is used for the first insulation layer (3). [19] Method according to one of claims 13 to 18, characterized by that the first insulation layer (3) is made of sintered, expanded PTFE (ePTFE). [20] Method according to one of claims 13 to 19, characterized bythat a third insulation layer (5) made of PTFE, in particular compressed PTFE, is arranged around the second insulation layer (4). [21] Method according to one of claims 13 to 20, characterized by that the third insulation layer (5) is folded lengthwise or wrapped helically or transversely around the second insulation layer (4). [22] Method according to one of claims 13 to 21, characterized by that the composite of the conductor and the insulation layers (3,4,5) is sintered and in particular is sintered at 350°C to 420°C. [23] Wrapping tape for the formation of an insulation, wherein the wrapping tape has a plurality of continuous recesses (8) over its surface. [24] Wrapping tape according to claim 23, characterized by that the winding tape is made of PTFE (polytetrafluoroethylene). [25] Wrapping tape according to one of claims 23 or 24, characterized bythat the winding tape (3) is made of sintered, expanded PTFE (ePTFE). [26] Wrapping tape according to one of claims 23 to 25, characterized by that the cutouts make up 1 - 50% of the area of the winding tape, in particular 1 - 40% of the area of the winding tape, preferably 2 - 20% of the area of the winding tape and particularly preferably 5 - 15% of the area of the winding tape and even more preferably 7 - 12% of the area of the winding tape. [27] Use of a cable according to any one of claims 1-13 in motor vehicles, ships, or aircraft or space vehicles. [28] Use of a winding tape according to one of claims 23 to 26 for wrapping conductors to form insulation.

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