Cable with insulation, method for its manufacturing, winding tape for the insulation and use of the cable

Abstract

The invention relates to a cable, having a conductor for conducting electric current and an insulation, wherein the insulation has a first layer in contact with the conductor, wherein the first layer in contact with the conductor covers 50 – 99% of the conductor and leaves the remaining surface uncovered, as well as a method for its manufacture and a winding tape.

Description

[0001] Cable with insulation, method for its manufacture, winding tape for the insulation and use of the cable

[0002] Technical Field

[0003] The invention relates to a cable as well as a method for its manufacture, a winding tape and its use.

[0004] Background

[0005] Electric cables are used in many areas, in particular electric cables are used to transmit electrical energy and to transmit signals.

[0006] It is quite common to combine a plurality of cables in cable harnesses, wherein the cables usually have connectors connected to connector housings.

[0007] In particular in mobile applications, such as in cars, trucks or aerospace vehicles, signal-conducting or energy-conducting cables are combined in cable harnesses, wherein depending on the function or type of signals, a plurality of cables can be combined in a connector housing, wherein each cable is connected to an electrically conductive connector such that a plurality of cables can be connected at once by joining two connector housings that correspond to each other.

[0008] Of course, such cables must be insulated so as to avoid short-circuits or voltage flashovers.

[0009] Moreover, it is important in particular for mobile applications that the cables have a certain robustness against mechanical influences.

[0010] It is, for example, known that cables, when they are laid in car bodies, can be abraded on sharp edges, in particular in the region of body feedthroughs, i.e. holes in the sheet metal. It is therefore known to make the cable insulation itself robust in order to withstand these mechanical stresses or to provide the cable harnesses with appropriate protective wrapping.

[0011] In particular in mobile applications, mechanical stresses are also caused by vibrations and the corresponding abrasion on hard edges. Moreover, cables are often subjected to temperature and / or environmental conditions, in particular in mobile applications. Very high temperatures or large temperature fluctuations can occur, for example in particular in aerospace vehicles. In particular the insulations must be able to withstand both mechanical and temperature loads.

[0012] In addition, it cannot be ruled out that moisture due to external influences or condensation may also affect cables.

[0013] In summary, electric cables, whether used for signal or power transmission, must be designed to be robust against all possible environmental conditions.

[0014] Additional requirements for such cables may include high chemical resistance, a high degree of flexibility, and / or high resistance to flammability. On the one hand, a high degree of flexibility makes the cables easy to lay, while on the other hand, good bendability of the cables prevents mechanical loads on the connectors.

[0015] In particular, very high voltages and / or currents sometimes have to be conducted. The cable insulation must therefore be designed in such a way that partial discharge cannot occur at the voltages used in order to prevent slow decarbonization of the insulation due to a corona field.

[0016] Another important property of cables is easy handling, such as the ability to strip the insulation during connector assembly, but also during maintenance and repair work.

[0017] US 2012 / 0090874 Al discloses a thin, lightweight insulated wire, which has a core, which is surrounded by an insulating polymeric sheath, which has an inner layer of PTFE for electrical insulation, a middle layer of a polymer containing an aromatic or heterocyclic ring, such as PEEK, in order to have improved mechanical properties such as abrasion resistance and shear strength and an outer layer of PTFE, which in turn has electrical and chemical resistance and allows the entire structure to be sintered. The middle layer can flow during sintering on the one hand and form connections on the other, which can provide additional and unexpected advantages. The preferred thickness of each layer should be between 25 and 50 pm.

[0018] The first layer should be a tape wound around the conductor or PTFE extruded directly onto the conductor which is sintered in situ. This insulation layer should preferably be wound in a spiral shape around the core of the conductor, preferably with overlapping of at least 25 to no more than 65%, further preferably of at least 40% to no more than 55%. The layers as a whole can be applied individually one after the other or using a laminate, wherein 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 compress the entire composite during sintering and enable a sealed formation, which results in outstanding chemical resistance in combination with excellent mechanical properties caused by the PTFE layer.

[0019] The sintering temperature should be between 350 and 420°, wherein PEEK typically melts at 343°C such that sintering causes the PTFE to shrink, which compacts the entire structure. Sintering should take place for between 30 seconds and 2 minutes, in particular preferably between 60 and 90 seconds.

[0020] US 10,090,080 B2 discloses an electric cable for supplying power to an electrical device, wherein at least one conductive core should be present and an insulating sheath which is arranged around the core, wherein the insulation has a relative dielectric constant of less than 2 and comprises a first layer which is a polymeric erogen and a comprises a second layer which surrounds the first layer and consists of a fluoropolymer. Furthermore, a third layer can be present which is arranged between the conductive core and the first layer and consists of a fluoropolymer of comprises this. This is intended to fill any gaps between the first layer and the conductor, particularly in the case of stranded conductors. The fluoropolymer can be PTFE, PFA, ETFE or FEP. The cable described is intended in particular for carrying high voltages in aircraft.

[0021] The company TE Components sells a highly flexible wire under the name SHF-260, which is intended to be suitable, inter alia, for applications in aircraft and is very flexible such that it can be laid even in extremely confined spaces without bending or tearing the insulation. In particular, this conductor is intended to be used for high-voltage applications and is temperature-stable up to 260 °C, in the short-term even up to 290 °C. Both the chemical resistance and resistance to fluids is intended to be high, wherein the insulation is intended to be a single or two-layer extruded fluoropolymer.

[0022] It is known from FR2699320 that expanded porous PTFE (ePTFE) has a surprisingly higher mechanical resistance than conventional PTFE whilst the chemical inertness and heat resistance correspond to conventional PTFE. However, the notch resistance is similarly poor as with conventional PTFE.

[0023] US 4,732,626 describes PTFE initially expanded according to the method in accordance with

[0024] US 3,953,566 and compressed through pressure. This is then arranged around a conductive wire and heated up. The resulting conductor which is insulated by the compacted PTFE has the high mechanical resistance of PTFE but also a high resistance to cuts and abrasion.

[0025] In addition, cables are known for such applications which have a layer of polyimides. Such insulations are extremely sensitive to moisture and start to degrade after moisture is absorbed, which is made worse by the influence of temperature. They therefore have to be shielded from moisture by additional layers of fluoropolymers.

[0026] In practice, it has been observed that with such electric cables, and in particular cables which have at least one fluoropolymer layer, such layers tend to shrink in use and especially under the influence of temperature. This can, for example, result in the insulation lying directly on the metallic conductor retreating in the region of the connection between the metallic conductor and the connector if the adhesion to the conductor surface is too low such that voltage flashovers can no longer be prevented in particular in the case of high-voltage cables.

[0027] In the case of insulation layers that are extruded or bonded directly onto the conductor, it has been observed that although these generally adhere well, stripping them is often not possible or only with great effort which results in either the conductor being mechanically deformed during stripping or its surface being damaged and / or insulation residues remaining on the conductor.

[0028] The cable insulation must also be cut during the stripping process 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.

[0029] The object of the invention is to create a cable of the type mentioned in the introduction which has insulation with improved properties. In particular, a cable should be created which meets the requirements of industry standards in its mechanical and thermal properties and resistance to environmental influences but also has as little shrinkage as possible with simple stripping.

[0030] Another object is to create a method for manufacturing a cable with which improved insulation is achieved.

[0031] Another object is to create a winding tape as the first layer of insulation for such a cable, which enables an insulation structure with improved properties.

[0032] Detailed description According to the invention, a cable, in particular a so-called power feeder cable, is provided for use in extreme conditions, such as temperatures of over 200 °C and higher voltages. In addition, the cable may be free of polyimides, resistant to hydrolysis and abrasion and may be flexible.

[0033] Such multi-layered structures of insulations which contain fluoropolymers tend to shrink irreversibly under the influence of temperature, inter alia in the longitudinal direction, thereby exposing regions of the conductor. This cannot be tolerated in the desired applications, in particular in the aerospace sector.

[0034] As already mentioned above, in applications in which in particular a PFA layer is directly extruded or bonded onto the conductor, which would enable proper and fully sufficient insulation, it has transpired that stripping is no longer readily possible.

[0035] According to the invention, insulation of such a conductor, in particular for applications at high temperatures and voltages and possibly in humid environments is constructed at least in two layers, wherein a first layer in contact with the conductor is a layer which is in particular placed around the conductor or wound around the conductor, which may be formed, for example, as a tape, in particular as a so-called winding tape.

[0036] This first layer or layer may be made of PTFE. This first layer may be made of sintered expanded PTFE (ePTFE), i.e. porous PTFE heated above the melting point of PTFE. The first layer may also be made of semiconductive PTFE or semiconductive ePTFE.

[0037] The thickness of the first layer may be 2.5 to 125 pm. In particular, the thickness of the first layer may be 12 to 40 pm.

[0038] This first wrapped or wound layer does not fully cover the metallic conductor. This makes it possible for a subsequent, for example extruded layer, to adhere to the conductor. The fact that there is no full-surface adhesion allows a compromise to be reached between the ability to strip the insulation on the one hand and the prevention of shrinkage due to the partial adhesion of the second layer directly to the conductor on the other hand.

[0039] In particular, 1 - 50% of the surface of the conductor is not covered, or 50 - 99% of the surface of the conductor is covered. 4 - 20% of the surface of the conductor may not be covered, or 60 - 96% of the surface of the conductor may be covered. In particular, 5 - 15% of the surface of the conductor may not be covered, or 85 - 95% of the surface of the conductor may be covered. 10% of the surface of the conductor may not be covered, or 90% of the surface of the conductor may be covered.

[0040] To achieve this, the invention provides for different but equally effective solutions.

[0041] In one first embodiment, the angle of the winding, in particular the helical winding of the conductor, is selected such that a gap exists between the longitudinal edges of the winding tape facing one another which accordingly corresponds to between 1 and 50% of the width of the winding tape between the longitudinal edges.

[0042] The width of the winding tape can of course be adapted accordingly.

[0043] Another possibility according to the invention provides that the winding tape is formed with openings over its surface. Such openings can be round, triangular, square or polygonal holes, but also elongated slots.

[0044] These can be distributed over the surface of the winding tape such that, for example, a plurality of holes are arranged next to one another or in successive rows.

[0045] Likewise, the slots can be arranged longitudinally, transversely or diagonally to the longitudinal extension of the winding tape and adapted to the desired degree of opening in terms of the width of the slots, the distance between the slots and the length of the slots.

[0046] The slots can also be comparatively wide and long and only interrupted by bridges between the boundary regions of the winding tape.

[0047] When wound around the conductor, the longitudinal edges of the winding tape can be wound end-to-end or with a slight overlap when the aforementioned openings are provided.

[0048] The slots can also run parallel or inclined relative to the longitudinal extension of the conductor when the winding tape is mounted on the conductor.

[0049] Moreover, the winding tape can be wrapped around the conductor longitudinally or transversely rather than helically such that a long gap or radial gaps remain between the longitudinal edges of the winding tape and the conductor is exposed in this area. The gap is accordingly arranged more or less parallel to the longitudinal extension of the conductor. This means that in this case the winding tape has a width between the longitudinal edges that is less than the circumference of the conductor.

[0050] In a subsequent step, a second insulation layer is extruded or wound around the winding tape located on the conductor. In particular, it may be a PFA layer, for example. In the area of the openings, this layer made of PFA makes direct contact with the conductor and can adhere to it.

[0051] In order to improve adhesion, the second layer can be extruded onto the conductor with a nozzle in such a way that the second layer may be compressed or compacted by the nozzle such that there is closer contact with the conductor. In the case of a wound outer layer, a sintering step is required to connect the individual layers and ensure contact with the conductor.

[0052] Insulation as a two-layer composite manufactured in this way can, on the one hand, be easily removed from the conductor by the provision of the PTFE winding tape as it has a low coefficient of static friction in relation to the conductor; on the other hand, the arrangement of openings can ensure that the corresponding static friction forces prevent shrinkage because the second layer cannot slide freely on the conductor.

[0053] In order to further improve the insulation performance and in particular the protection performance from outside influences, a third layer can be provided which is wound or extruded onto the second layer. The third layer is preferably made of PTFE, for example compacted PTFE. Such compacted PTFE can be produced, for example, as described in US patent no. 4,732,626 or US 5,374,473.

[0054] It is necessary to sinter the three-layer composite at the end because this sintering causes the outermost layer to shrink inwards / vertically and also presses the second layer and also the first layer onto the conductor. During sintering, the second layer softens and all three layers form an intimate bond. This bond prevents excessive shrinkage of the third layer.

[0055] A third PTFE layer also has the advantage, particularly when it is a compacted PTFE layer, that it is chemically inert, temperature-resistant and abrasion-resistant.

[0056] It is advantageous that an insulation layer is created which offers a high level of performance to withstand electrical stress, abrasion, chemical influences and temperature influences with very high flexibility, but on the other hand adheres easily to the conductor and therefore cannot shrink and is nevertheless easy to strip.

[0057] Summary

[0058] The invention thus relates in particular to a cable, having a conductor for conducting electric current and insulation, wherein the insulation has a first layer in contact with the conductor, wherein the first layer in contact with the conductor covers 50 - 99% of the conductor and leaves the remaining surface uncovered, wherein the thickness of the first layer is 2.5-125 pm, and wherein a second, extruded or wound insulation layer containing PFA (perfluoroalkoxy copolymers) or FEP (tetrafl uoroethylene-hexafluoropropylene copolymer) is arranged around the first insulation layer.

[0059] The first layer may be semiconductive, optionally comprise semiconductive PTFE. The thickness of the first layer may be 12 to 40 pm

[0060] The first layer may be formed from a winding tape, optionally wherein the winding tape is arranged as a longitudinal, helical or transverse wrap around the conductor.

[0061] At least one gap may be formed between longitudinal edges of the winding tape, optionally leaving 1 - 50% of the surface of the conductor uncovered.

[0062] The winding tape may have a plurality of openings over its width which leave the conductor uncovered.

[0063] 1 - 50% of the surface of the conductor, 4 - 20% of the surface of the conductor, 5 - 15% of the surface of the conductor or 7 - 12% of the surface of the conductor may be uncovered.

[0064] The winding tape may be made of PTFE.

[0065] The winding tape may be made of sintered, expanded PTFE (ePTFE).

[0066] The winding tape may be made of semiconductive PTFE or semiconductive ePTFE.

[0067] A third layer made of PTFE, optionally compacted PTFE, may be arranged around the second layer which mya be an extruded or wound layer.

[0068] The third layer may have a thickness of 150 - 400 pm, or 230 - 330 pm.

[0069] The second layer may comprise a semiconducting PFA or FEP. The second layer may have a thickness of 100 - 300 pm, or 150 - 250 pm.

[0070] A layer comprising a semiconducting PFA or FEP may be arranged between the first layer and the second layer.

[0071] The third layer may be wrapped longitudinally or wound helically or transversely around the second layer.

[0072] Another aspect of the invention relates to a method for manufacturing a cable, optionally 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 layer comprising PFA (perfluoroalkoxy copolymers), FEP (tetrafl uoroethylene-hexafluoropropylene copolymer) or a semiconducting PFA or FEP is formed around the first insulation layer. The second layer may be an extruded or a wound layer.

[0073] The first layer may be formed from a winding tape, wherein the winding tape is a longitudinal, helical or transverse wrap around the conductor.

[0074] At least one gap may be formed between longitudinal edges of the winding tape, optionally leaving 1 - 50% of the surface of the conductor uncovered.

[0075] The winding tape may have a plurality of openings over its width which leave the conductor uncovered in their regions.

[0076] One 1 - 50% of the surface of the conductor, 4 - 20% of the surface of the conductor, 5 - 15% of the surface of the conductor or 7 - 12% of the surface of the conductor may be left uncovered.

[0077] The first layer may comprise PTFE. The first layer may be made of sintered, expanded PTFE (ePTFE). The first layer may comprise or be made of semiconductive PTFE or semiconductive ePTFE.

[0078] A third layer made of PTFE, optionally compacted PTFE, may be arranged around the second layer.

[0079] The third layer may be wrapped or wound longitudinally, helically or transversely around the second layer. The composite of the conductor and layers may be sintered and optionally may be sintered at

[0080] 350 °C to 420 °C.

[0081] Another aspect of the invention relates to a winding tape for forming insulation, wherein the winding tape has a plurality of continuous openings over its surface.

[0082] The winding tape may be made of PTFE (polytetrafluoroethylene).

[0083] The winding tape may be made of sintered, expanded PTFE (ePTFE).

[0084] The winding tape may be made of semiconductive PTFE or semiconductive ePTFE.

[0085] The openings make up 1 - 50% of the surface of the winding tape, 4 - 20% of the surface of the winding tape, 5 - 15% of the surface of the winding tape or 7 - 12% of the surface of the winding tape.

[0086] Another aspect of the invention relates to the use of a cable according to the present application in motor vehicles, ships, or aerospace vehicles.

[0087] Another aspect of the invention relates to the use of a winding tape according to the present application for winding around conductors to form insulation.

[0088] Short description of the drawings

[0089] Figure 0a: shows a cross-section of a cable according to the invention with a two-layer insulation structure, wherein the metallic conductor is monofilament;

[0090] Figure 0b: shows a cross-section of a cable according to the invention with a two-layer insulation structure, wherein the metallic conductor is formed from strands;

[0091] Figure 1: shows a cross-section of a cable according to the invention with a three-layer insulation structure, wherein the metallic conductor is monofilament;

[0092] Figure 2: shows a cable according to the invention with a three-layer structure, wherein the metallic conductor is formed from strands;

[0093] Figure 3: shows a view of a metallic conductor, which is formed with a winding tape according to the invention and a gap between the longitudinal edges of the winding tape;

[0094] Figure 4: shows the structure according to Figure 3 in a top view; Figure 5: shows another embodiment in which a winding tape in accordance with the invention having openings is wound helically end-to-end around a conductor;

[0095] Figure 6: shows the cable according to Figure 5 in a top view;

[0096] Figure 7: shows another embodiment in which the slot-like, staggered openings are arranged in the winding tape;

[0097] Figure 8: shows an arrangement according to Figure 7 with slot-like openings, which are angled to the longitudinal extension of the winding tape;

[0098] Figure 9: shows another embodiment in which radial slots are formed by the winding tape in a perspective view;

[0099] Figure 10: shows the embodiment according to Figure 9 in a top view;

[0100] Figure 11: is a graphical representation of the shrinkage of three different samples with different degrees of coverage of the conductor, wherein samples 1 and 2 are not layers according to the invention;

[0101] Figure 12: is a table which is continued in Figure 12 showing different cables and their properties;

[0102] Figure 13: is a continuation of Figure 12;

[0103] Figure 14: shows the structure according to the invention according to Figure 2 before and after sintering (openings are not shown);

[0104] Figure 15: shows the structure according to the invention according to Figure 2 after sintering (openings are shown);

[0105] Figure 16: shows an enlarged section of 15;

[0106] Figure 17: shows penetration of the insulation layer into the conductor in a commercial product;

[0107] Figure 18: shows comparative sample 1 being difficult to cut;

[0108] Figure 19: shows the conductor damage in comparative sample 1; Figure 20: shows the sample 3 according to the invention being easy to cut without conductor damage;

[0109] Figure 21: shows a summary table of the possible embodiments of the invention.

[0110] Figures 0a and Ob show a first embodiment of the invention in a highly schematic manner. A cable is designated by reference numeral 1 and has a metallic conductor 2. The metallic conductor can be solid (Figure 0a) or made of a plurality of smaller diameter conductors as a stranded wire (Figure Ob). The conductor can, in principle, consist of any conductive material, in particular conductive metal. In particular, the conductor 2 consists of copper or aluminium, wherein the copper or aluminium conductor can have a silver, gold or nickel coating (not shown).

[0111] The conductor 2 is provided with insulation for the purpose of electrical insulation and protection against outside influences such as moisture. In the example shown, the insulation has two layers.

[0112] A first layer 3 of the insulation is formed around the conductor 2 and in contact therewith.

[0113] The first layer 3 may consist of a fluoropolymer.

[0114] In particular, the first layer may comprise or consist of PTFE (polytetrafluoroethylene), optionally pre-sintered, expanded PTFE (ePTFE). The first layer may comprise or consist of semi- conductive PTFE or semiconductive ePTFE. The main function of this first layer involves mechanically separating the conductor 2 from further applied layers in certain areas. However, a second layer will be able to attach to the conductor through openings in the first layer. The material selected for the first layer 3 has low static friction with the conductor 2. The first layer may be made from a semiconductive material, for example semiconductive PTFE or semiconductive ePTFE. The first layer has a thickness of 2.5 - 125 pm. In particular, the first layer may have a thickness of 12 to 40 pm. The first layer 3 comprises openings through which the second layer 4 can attach to the conductor 2. These opening are shown in Figure 0a at the bottom of the conductor and in Figure Ob at the top left corner of the conductor.

[0115] A second layer 4 is arranged around the first layer 3 of the insulation.

[0116] The second layer 4 may be an extruded or wound layer comprising PFA or FEP, or otherwise may be a semiconducting PFA or FEP. In particular, the second layer may be an extruded PFA. The second layer may have a thickness of, for example, 100 - 300 pm, or 150 - 250 pm.

[0117] The melting point of the material of the second layer 4 may be below the one of the first layer 3. The melting point of the second layer 4 may be 350 °C and / or the one of the first layer may be above 420 °C.

[0118] In terms of its main function, the material of the second layer may be a kind of base material, wherein the material can be broken and stripped relatively easily during stripping without having to cut completely through it. This reduces the risk of cutting into the surface of the conductor 2. Although PTFE is difficult to break, it can be broken off together with the second layer, for example a PFA layer, due to the low thickness of the first layer.

[0119] Another embodiment of the invention having a three-layer insulation is shown in Figure 1 in a highly schematic manner. Figure 1 shows a cable 1 with a metallic conductor 2. The metallic conductor 2 can be solid (Figure 1) or made of a plurality of smaller diameter conductors as a stranded wire (Figure 2).

[0120] The conductor can, in principle, consist of any conductive material, in particular conductive metal. The conductor 2 may comprise or consist of copper or aluminium, wherein the copper or aluminium conductor can have a silver, gold or nickel coating (not shown).

[0121] The conductor 2 is provided with the insulation for the purpose of electrical insulation and protection against outside influences such as moisture. In Figures 1 and 2, the insulation has three layers.

[0122] A first layer 3 of the insulation is formed around the conductor 2 and in contact therewith and comprises openings (shown in Figure 1 towards the bottom and in Figure 2 at the top left).

[0123] The first layer 3 may consist of a fluoropolymer.

[0124] In particular, the first layer may consist of PTFE (polytetrafluoroethylene), optionally pre-sintered, expanded PTFE (ePTFE). The main function of this first layer involves mechanically separating the conductor 2 from further applied layers in certain areas. However, a second layer will be able to attach to the conductor through openings in the first layer. The material selected for the first layer 3 should have low static friction with the conductor 2. The first layer may be made from a semiconductive material, for example semiconductive PTFE or semicon- ductive ePTFE. The first layer has a thickness of 2.5 - 125 pm. In particular, the first layer has a thickness of 12 to 40 pm. A second layer 4 is arranged around the first layer 3 of the insulation.

[0125] The second layer 4 may be an extruded or wound layer containing PFA or FEP, or otherwise a semiconducting PFA or FEP. In particular, the second layer may be an extruded PFA.

[0126] The second layer may have a thickness of, for example, 100 - 300 pm, or 150 - 250 pm.

[0127] The melting point of the material of the second layer 4 may be below that of the first layer 3. The melting point of the second layer 4 is may be 350 °C and / or the one of the first layer may be above 420 °C.

[0128] In terms of its main function, the material of the second layer may be a kind of base material, wherein the material can be broken and stripped relatively easily during stripping without having to cut completely through it. This reduces the risk of cutting into the surface of the conductor 2. Although PTFE is difficult to break, it can be broken off together with the second layer (which may be a PFA layer) due to the low thickness of the first layer.

[0129] A third layer 5 is arranged around the second layer 4 as shown in Figures 1 and 2.

[0130] The third layer 5 may consist of compacted PTFE and / or may have a thickness of, for example, 150 - 400 pm, in particular 230 - 330 pm.

[0131] Compacted PTFE material provides outstanding mechanical resistance and also excellent thermal resistance.

[0132] The two- or three-layer cable may be sintered after joining.

[0133] For this purpose, the entire composite consisting of the conductor 2 and the layers 3, 4 and 5 may be subjected to a heat treatment above 350 °C, in particular 350 °C to 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.

[0134] Figures 3 and 4 show an embodiment of the first insulation layer on the conductor 2, wherein the conductor 2 is solid. However, the conductor may also be formed as a stranded conductor.

[0135] The first layer 3 is arranged around the conductor, wherein the first layer 3 is formed as a winding tape and the winding tape is wrapped lengthwise around the conductor 2. The edges 6 delimiting the winding tape 3 are spaced apart from one another when wrapped around the conductor, 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 substantially parallel to the longitudinal axis of the conductor 2. In this region the conductor 2 is exposed. The gap 7 has a width which is such that between 1 and 50%, 4 - 20%, 5 - 15% or 10% of the conductor 2 is exposed.

[0136] In another advantageous embodiment of the winding tape 3 (Figures 5, 6), a pattern of openings 8 is distributed over the width and length of the winding tape 3.

[0137] The openings 8 may, for example, be round holes as shown in Figures 5 and 6. However, the holes do not have to be circular, they may also be triangular, square, polygonal, oval or have any other shape. The surface area of the openings 8 as a proportion of the surface area of the winding tape may be 1 - 50%, 4 - 20%, 5 - 15% or 10% of the overall surface of the winding tape such that the corresponding percentage of the surface area of the conductor 2 is left uncovered in the region of the openings 8. In the embodiment according to Figures 5 and 6, the winding tape is helically wound around the conductor 2 without a gap between the longitudinal edges 6 and thus end to end.

[0138] Of course, the winding tape 3 may also be wound with an overlap in this case, and the winding tape may also be wound with a gap between the longitudinal edges 6 of the winding tape. In this case, the gap between the longitudinal edges then adds to the uncovered area of the conductor by the first layer.

[0139] Alternatively, a winding tape without openings 8 may be used, so that the winding tape 3 is then wound such that a gap between the longitudinal edges 6 is created. This gap then corresponds to the desired percentage of exposure of the surface of the conductor 2 when the first layer is present. The area of the conductor that is left uncovered may be 1 - 50%, 4 - 20%, 5 - 15 %, or 10%.

[0140] A winding tape, such as the one of the embodiment according to Figures 5 and 6 may also be laid lengthwise around the conductor 2 instead of a helix-like wrapping, wherein the longitudinal edges 6 may be abutting each other, which means that the width of the winding tape 3 corresponds to the circumference of the conductor. Alternatively, a space or gap 7 between the longitudinal edges 6 may be combined with the openings 8 to form the uncovered surface of the conductor 2. Another embodiment is shown in Figures 7 and 8.

[0141] The openings 8 are formed as slots, wherein the slots are distributed over the width and length of the tape, herewith this winding tape it is also possible that the longitudinal edges 6 may either be in contact with each other or spaced apart as mentioned above for the other embodiments.

[0142] It is self-evident to a person skilled in the art that, if this appears expedient, a mixture of the shapes of the openings 8, for example circles, slots etc., may also be used.

[0143] Alternatively to the embodiment shown in Figures 7 and 8, the winding tape may be wrapped lengthwise around the conductor 2 either with the longitudinal edges abutting or forming a gap.

[0144] In another embodiment (Figures 9, 10), the winding tape 3 is placed radially around the conductor 2, wherein the individual windings of the winding tape 3 are spaced apart with gaps 7, which are each delimited by the longitudinal edges 6 delimiting the winding tape. This means that there is not a continuous winding tape but multiple rings of winding tape which are not abutting each other in order to form a gap between the different rings of winding tape.

[0145] Alternatively, a winding tape with openings 8 may be used in this way so that the total uncovered area of the conductor is the sum of the openings in the winding tape and the space between adjacent rings of winding tape.

[0146] The method according to the invention includes a winding tape 3 first being wrapped around a solid or stranded conductor 2 either longitudinally or wound around it helically or radially. The conductor may be a copper or aluminium conductor, wherein the copper or aluminium conductor may be coated with gold, silver or nickel.

[0147] The winding tape 3 for the first layer, which is in direct contact with the conductor, may consist of PTFE, preferably sintered or pre-sintered ePTFE. The winding tape 3 for the first layer may consist of semiconductive PTFE or semiconductive ePTFE.

[0148] This winding tape 3 as described above, may then be placed around the conductor 2 in any of the configurations mentioned above. This combination of the conductor and the first layer may then fed to an extrusion or winding device, in which a second layer 4 is extruded or wound onto the conductor and the first layer 3. The second layer 4 may comprise FEP, PFA or a semiconducting PFA or FEP. In the region of the gap 7 and / or the openings 8, the second layer 4 makes contact with the conductor 2 through the openings 8 and the gap 7 or gaps 7.

[0149] In order to achieve good contact, mechanical pressure may be exerted on the second layer 4 in the plastic state during extruding or winding, for example by the geometry of the extrusion nozzle or a downstream, temperature-controlled compression nozzle.

[0150] For a three-layer structure, another layer of high-strength fluoropolymer such as compacted PTFE may then be placed around the second layer of the cable comprising a conductor and a two layer insulation. This third layer 5 may also be 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.

[0151] The method according to the invention may then include subjecting this three-layer composite around the conductor to a sintering step. In this sintering step, a temperature above the melting temperature of the second layer 4 may be used; in particular, sintering may be carried out at sintering temperatures above 350 °C and in particular 350 - 420 °C.

[0152] As a result, the second layer 4 is melted. The for example compacted PTFE material of the third layer 5 may shrink radially 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 fillers between the strands.

[0153] In addition, this shrinking process of the third layer 5 bonds the material of the second layer 4 also to the conductor 2 through the gap(s) 7 and / or the openings 8.

[0154] Prior to sintering, the first layer 3 may have, for example, a thickness of 2.5 - 125 pm, or 12 to 40 pm. The second layer 4 arranged on the first layer may have a thickness of 120 - 350, or 170 - 290 pm. The third layer 5 which may be compacted PTFE and is applied to the second layer may have a thickness of 150 400 pm, or 230 - 330 pm.

[0155] The method for manufacturing a cable produces an at least two-layer, but alternatively a three- layer insulation structure, in which the first layer, which may be made of PTFE, separates the second layer from the conductor 2 apart from the regions of the openings in the first layer through which the second layer, which may be made of PFA or FEP, makes direct contact with the conductor 2. As the first layer, which may be made of PTFE, and therefore has a low coefficient of static friction, this first layer, together with the static friction and adhesion of the material of the second layer 4, combines the properties of shrinkage and ability to strip 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 fact that the mechanical separation from the conductor 2 takes place on the remaining surface makes it easy to strip the insulation.

[0156] The sintering process of the for example compacted PTFE material of the third layer is key in bonding all three layers together and in initiating the melting of the second layer, which is pressed into the wire structure or conductor structure through the openings of the first layer.

[0157] It should be noted that the first layer 3 which may be made of PTFE, does not melt during the sintering process, is highly compressed, but remains mechanically stable and retains its shape and also does not further adhere to the conductor 2.

[0158] Figure 11 is a graph showing a comparison of three samples i, which all have a nickel-coated copper conductor (NCC), wherein the conductor has a cross-section of AWG (American Wire Gauge) 2 (35mm2).

[0159] Samples 1 and 2 are comparative samples in which the first layer is wound with a degree of overlap (1.2 = 20% overlap). In sample 1, a PTFE inner layer is present with an outer compacted PTFE layer without openings. The shrinkage test shows that the shrinkage of more than 10 mm is completely outside the target of less than 3.18 mm. This is the result of the very high level of thermal shrinking of the compacted PTFE material.

[0160] Samples 2 and 3 respectively have three layers in which the innermost layer is formed from sintered, expanded PTFE, the middle layer from PFA and the outermost layer from compacted PTFE. Sample 2 has no openings or gaps in the first layer (1.2 = 20% overlap), wherein in sample 3 10% of the conductor are not covered by the first layer (0.9 = 10% not covered). Samples 1 to 3 are also shown in Figure 12 with regard to shrink, thermal shrinkage after temperature shock, pull out-force, detachability and severability.

[0161] The different sample cables were subjected to the tests that are relevant in the industry. The measurement according to "Insulation Shrinkage AS4347 Method 104 1 AS22759" is used for the shrinkage tests. The test sample is held at 290 °C for six hours and the shrinking of the insulation is then measured, wherein a 36 cm long insulated conductor is used as test length and its insulation may not shrink more than 3.18 mm, per test sample end. The measurement of shrinkage after thermal shock is measured according to "Thermal Shock AS4347 method 805 I ASTM D 3032-21". In this measurement, four temperature cycles are run in which each cycle lasts for 60 minutes, in which the material is heated to 260 °C and held for 30 minutes and then cooled to -55 °C within 2 minutes and held there for 30 minutes.

[0162] The shrinking of the insulation is then measured, wherein the test sample length here is 150 cm and its insulation may not shrink more than 3.18 mm, per test sample end.

[0163] The ability to strip is dependent on two factors: the ability to cut the insulation and removability.

[0164] The measurement of the ability to strip is tested 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 with conventional stripping devices / knives without damaging the conductor when the insulation is cut by the knives. The "Pressmaster Oden" tool from Pressmaster was used to strip the insulation.

[0165] A measurement of the stripping force of insulations was used for a quantitative classification of the ability to strip according to the "Adhesion of Inner Conductor ESA / SCC 3902 Method 9.13" method. 150 mm long samples are prepared here, wherein 75 mm of the insulation is stripped with a tensile force device and the maximum force required for this is measured. The stripping force of the wires must be measured and recorded. As there are no tools and acceptance criteria specified in an MIL specification for wires larger than American Wire Gauge (AWG) size 10 (6mm2), a relative comparison is preferred here in order to be able to make a statement about the ability to strip.

[0166] Figures 11 and 12 show different cables and their properties. Samples 1 to 3 of Figure 12 correspond to samples 1 to 3 of Figure 11.

[0167] Although sample 2, with an overlap of 20% and without openings or gaps in the first layer, demonstrates a good ability to be stripped and the shrinkage values in the "Insulation Shrinkage Test" are still acceptable, the shrinkage in the temperature shock test is no longer within the required limits.

[0168] The embodiment of sample 3, with 10% of the conductor uncovered, shows a considerably improved shrinkage behaviour, with a shrinkage of only 0.5 mm in the shrinkage test at 290°C for six hours and only 1.2 mm after thermal shock, with good ability to be stripped at the same time.

[0169] Sample 4 is structured according to sample 1, and sample 5 is structured according to sample 3. Only the conductor has a different cross-section of AWG (American Wire Gauge) 6 (16mm2) in both. Compared to sample 5, samples 6 and 7 (see Figures 12 and 13) have an aluminium conductor. Sample 6, in addition, has the conductor uncovered by the first layer at 20% while sample 7 leaves the conductor uncovered by 10%. Samples 7 has FEP as the material of the second layer, instead of PFA. The table also shows a commercially available product from Tyco Electronics, which also comprises an AWG 6 copper conductor (nickel-coated) on which a modified PFA insulation layer is extruded.

[0170] It can be seen here that samples 5 to 7 (with a first layer comprising gaps / openings) all have a shrinkage behaviour below the upper limits and are easy to strip without damage to the conductor.

[0171] The shrinkage behaviour of comparative sample 4 (the first layer fully covers the conductor) is not adequate, and it is not easy to strip without conductor damaging.

[0172] Sample 8 comprises a three layer insulation having as the first layer a semiconductive PTFE that leaves 20% of the conductor uncovered, a second semiconductive PFA layer covered by a PFA Layer and as the third and outer layer a densified PTFE layer. As shown in Figure 13 this cable has the acceptable shrinkage behaviour and ease of stripping.

[0173] Sample 9 of Figure 13 shows the effect of a PFA layer as the first layer which covers the conductor fully. Whilst the shrinkage properties are as desired, pull-out force is very high and detachability very difficult. These examples show that the amount of uncovered conductor allows for the control of shrink and detachability.

[0174] Whilst the commercially available product also has an acceptable shrinkage behaviour, it does not have the required ease of stripping.

[0175] Figure 14 shows a structure according to the invention before and after sintering in an enlarged sectional view.

[0176] It shows the strands of the conductor and a first layer made of a sintered ePTFE winding tape placed around it. A PFA second layer is extruded onto the first layer and a winding tape made of compacted PTFE as the third layer is wound around the second layer. The left-hand image shows an unsintered structure and the right-hand image a sintered one. It can be seen that the first layer is comparatively thin and in the right-hand image of Figure 14 rests on the strands of the conductor. As a result of sintering, the third compacted PTFE layer, which generally has a very high thermal shrinking capacity, shrinks. As a result, the material of the second layer, in this case the PFA material, is compressed towards the conductor and thereby also presses the ePTFE material of the first layer into the strands of the conductor.

[0177] The openings are shown in Figures 15 and 16. In the region of the openings, the material of the second layer, i.e for example the PFA material, is pushed into the conductor or also into the fillers between the individual strands of the conductor.

[0178] The tests carried out by the applicant have shown that stranded conductors are not a prerequisite for good adhesion. As a solid conductor also has a superficial microstructure, which is caused by the manufacturing process, this superficial microstructure is obviously sufficient for anchoring of the first and second layer to take place after sintering and thus ensures good shrinkage resistance of the entire structure.

[0179] However, as a result of sintering, the two or three layers or the materials of these layers are also bonded together.

[0180] However, due to the low static friction of the PTFE layer, which is directly located on the conductor, very good stripping can be achieved with conventional tools. The cables of the present application therefore combine favourable properties of ease of stripping on the one hand and internal shrinkage on the other, which are in themselves contradictory in an excellent way.

[0181] In contrast, Figure 17 shows that with the commercially available product without an inner PTFE layer, the PFA material of the second / outer layer penetrates and adheres between the strands of the conductor over the entire circumference and the ability to strip is thus no longer ensured.

[0182] Figures 18 and 19 show in a sectional view of sample 1, difficult stripping, in particular difficult cutting, of a PTFE firstlayer and a compacted PTFE second layer. The PTFE layers could not be broken off due to their mechanical properties, in particular the compacted PTFE, and therefore had to be completely severed. Although the two-layer insulation can easily be stripped once it has been severed, a large cutting depth must be used in order to sever the insulation. Figure 18 shows remaining insulation on the conductor, although a relatively high cutting depth was reached and the conductor surface was already damaged by the cut. Figure 19 shows the damaged strands of the conductor with an even greater cutting depth in order to remove the remaining insulation. Figure 20 in turn shows that the cable of sample 3 which is according to the invention is easy to cut without conductor damage. The second layer which is made of PFA only has to be cut through part of its thickness. The remainder can then be broken off. The comparatively thin PTFE first layer can be torn off and removed together with the PFA layer.

[0183] Figure 21 shows a summary in table form of the possible embodiments of the invention re- garding the different layer arrangements.

Claims

Claims1. A cable, having a conductor (2) for conducting electric current, and an insulation, wherein the insulation has a first layer (3) in contact with the conductor (2), wherein the first layer (3) covers 50 - 99% of the surface of the conductor and leaves the remaining surface uncovered, wherein the thickness of the first layer (3) is 2.5-125 gm, and wherein a second, extruded or wound insulation layer (4) containing PFA (perfluoroalkoxy copolymers) or FEP (tetrafl uoroethylene-hexafluoropropylene copolymer) is arranged around the first insulation layer (3).

2. The cable of claim 1, wherein the first layer (3) is semiconductive, optionally wherein the first layer (3) comprises semiconductive PTFE or semiconductive ePTFE.

3. The cable according to any one of Claim 1 or Claim 2, wherein the thickness of the first layer is 12 to 40 pm.

4. The cable according to any one of Claims 1 to 3, wherein the first layer (3) is formed from a winding tape, wherein the winding tape is arranged as a longitudinal, helical or transverse wrap around the conductor.

5. A cable according to claim 4, wherein at least one gap (7) is formed between longitudinal edges (6) of the winding tape (3), which leaves 1 - 50% of the surface of the conductor uncovered.

6. A cable according to any one of claims 4 or 5, wherein the winding tape has a plurality of openings (8) over its width and / or length which leave the conductor uncovered.

7. A cable according to one of the preceding claims, wherein 1 - 50% of the surface of the conductor, 4 - 20% of the surface of the conductor, 5 - 15% of the surface of the conductor or 7 - 12% of the surface of the conductor is not covered by the first layer.

8. A cable according to any one of claims 4 to 7, wherein the winding tape (3) comprises PTFE, optionally wherein the winding tape comprises semiconductive PTFE.

9. A cable according to any one of claims 4 to 7, wherein the winding tape (3) comprises sintered, expanded PTFE (ePTFE), optionally semiconductive ePTFE.

10. A Cable according to one of the preceding claims, wherein the insulation comprises a second layer (4) and optionally wherein the second layer (4) comprises semiconducting PFA or FEP.

11. A cable according to one of the preceding claims, wherein the insulation comprises a third layer (5) comprising PTFE, optionally compacted PTFE, and wherein the third layer (5) is arranged around the second layer (4), which optionally is an extruded or wound layer.

12. A cable according to any one of Claims 1 to 11, wherein a further layer is arranged between the first layer (3) and the second layer (4) and optionally wherein this further layer comprises semiconducting PFA or FEP.

13. A cable according to Claim 11, wherein the third layer (5) is wrapped longitudinally or wound helically or transversely around the second layer (4).

14. A method for manufacturing a cable, wherein a conductor (2) is surrounded by a first layer (3), wherein the first layer (3) is formed such that 50 - 99% of the surface of the conductor (2) is covered and wherein a second layer (4) comprising PFA (perfluoroalkoxy copolymers), FEP (tetrafl uoroethylene-hexafluoropropylene copolymer) or a semiconducting PFA or FEP is located around the first layer (3).

15. The method according to Claim 14, wherein the first layer (3) is formed from a winding tape, wherein the winding tape is a longitudinal, helical or transverse wrap around the conductor (2).

16. The method according to Claim 14 or 15, wherein at least one gap (7) is formed between longitudinal edges (6) of the winding tape of the first layer (3), which leaves 1 - 50% of the surface of the conductor (2) uncovered.

17. The method according to any one of Claims 14 to 16, characterized in that the winding tape (3) of the first layer has a plurality of openings (8).

18. The method according to any one of Claims 14 to 17, wherein 1 - 50% of the surface of the conductor, 4 - 20% of the surface of the conductor, 5 - 15% of the surface of the conductor or 7 - 12% of the surface of the conductor is left uncovered.

19. The Method according to any one of Claims 14 to 18, wherein the first layer (3) comprises sintered, expanded PTFE (ePTFE), semiconductive PTFE or semiconductive ePTFE.

20. The method according to any one of Claims 14 to 19, wherein a third layer (5) comprising PTFE, optionally compacted PTFE, is arranged around the second layer (4).

21. The method according to any one of Claims 14 to 20, wherein the third layer (5) is wrapped longitudinally, helically or transversely around the second layer (4).

22. The method according to one of Claims 14 to 21, wherein the composite of the conductor and the first to third layers (3, 4, 5) is sintered and optionally is sintered at 350 °C to 420 °C.

23. Winding tape for forming insulation, wherein the winding tape has a plurality of openings (8) over its surface.

24. Winding tape according to Claim 23, wherein the winding tape comprises PTFE (polytetrafluoroethylene), optionally semiconductive PTFE.

25. Winding tape according to any one of Claims 23 or 24, wherein the winding tape comprises sintered, expanded PTFE (ePTFE) or semiconductive ePTFE.

26. Winding tape according to any one of Claims 23 to 25, the openings make up 1 - 50% of the surface of the winding tape, 1 - 40% of the surface of the winding tape, 2 - 20% of the surface of the winding tape, 5 - 15% of the surface of the winding tape or 7 - 12% of the surface of the winding tape.

27. Use of a cable according to any one of Claims 1 - 13 in motor vehicles, ships, or aerospace vehicles.

28. Use of a winding tape according to one of Claims 23 to 26 for winding around conductors to form insulation.

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