Insulated conductor and method of manufacturing same

Abstract

1. An insulated conductor having improved corona resistance, the insulated conductor comprising an electrical conductor capable of having a potential difference applied across it to induce a flow of electric current, the conductor having a surface, and a layer of an insulating polymer compound disposed on said surface, the insulating polymer compound comprising a continuous phase of a polymeric material comprising a polyaryletherketone (PAEK) polymer comprising repeat units of general formula I, where t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2, and the polymeric insulating compound also comprises a dispersed phase of a solid particulate material.

Description

[Technical field]

[0001] The present invention relates to insulated conductors suitable for use as magnet wires in the stators of electric motors and having improved corona resistance, methods of making same, and electrical devices including the insulated conductors. [Background technology]

[0002] Electrically insulating materials, such as polymeric insulators, are widely used in electrical components. Polymers inherently have the advantage that they can be electrically insulating, while at the same time being flexible and resistant to electrical or thermal breakdown.

[0003] Insulated conductors are installed in almost all electrical equipment to conduct electricity without shorting that can be caused by contact of conductors that are not electrically insulated.

[0004] Electrical machines such as electric motors, alternators and generators comprise a stator and a rotor. The stator includes a metal core with electrically insulated wire strands wound through the core to form the stator coils. When an alternating current is passed through the core, a magnetic field is created, which causes the rotor attached to the stator to rotate. The so-called magnet wire must be electrically insulated, and various methods have been proposed to do this. This includes the use of one or more layers of polymeric insulation around a wire of circular or rectangular cross section. Such wires generally have two or more polymeric insulating coatings, for example thermoplastic materials, including thermosetting polymers.

[0005] The development of electric vehicles is creating new technical challenges in this field. As technology develops, higher voltages are required, which in turn requires higher resistance to thermal and electrical stresses. Thus, the requirements for electrical insulators are becoming more and more stringent.

[0006] The technical demands on such insulating materials are therefore very high: the polymer must be electrically insulating, tough, corrosion resistant, processable, and have acceptable high voltage endurance and resistance to voltage-induced breakdown.

[0007] Polyaryletherketones (PAEKs), such as polyetheretherketone (PEEK), are often used as high-performance thermoplastic polymers. PEEK is the material of choice for many commercial applications because, when solidified from the melt, it forms a semi-crystalline solid with excellent mechanical and chemical resistance properties. PEEK melts at approximately 343°C and has a Tg of approximately 143°C.

[0008] US Patent No. 5,399,633 discloses copolymers of PEEK and PEDEK that have a higher than expected degree of crystallinity and can be part of compositions containing fibrous fillers such as glass fibers, carbon fibers, asbestos fibers, silica fibers, alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, boron fibers, fluorocarbon resin fibers and potassium titanate fibers, or non-fibrous fillers such as mica, silica, talc, alumina, kaolin, calcium sulfate, calcium carbonate, titanium oxide, ferrites, clay, glass powder, zinc oxide, nickel carbonate, iron oxide, quartz powder, magnesium carbonate, fluorocarbon resin, graphite, carbon powder, nanotubes and barium sulfate. Such materials can be made as described in Impregnation Techniques for Thermoplastic Matrix Composites, A. Miller and AG Gibson, Polymer & Polymer Composites 4(7), pp 459-481 (1996), EP102158 and EP102159.

[0009] US Pat. No. 5,399,633 discloses a conductor wire covered with a tape, preferably a homogeneous PAEK polymer, for example having a crystallinity of at least 25%.

[0010] However, while such materials have excellent electrical insulation properties, they require additional processing steps to improve their adhesion to common conductor materials such as copper and aluminum, and they do not always provide sufficient resistance to corona formation at the high voltages required for more demanding applications such as high voltage electric motors.

[0011] US Patent No. 5,399,633 discloses an insulated conductor wire having an insulating thermoplastic coating, preferably PAEK, that has been gas plasma treated to remove any oxide layer to improve adhesion of the thermoplastic coating to the wire.

[0012] US Patent No. 5,399, 667 discloses insulated electrical conductor wires coated with an intermediate layer of a thermosetting polymer (e.g., PEI) to improve adhesion of a thermoplastic insulating coating (e.g., PEEK). US Patent No. 5,399, 667 discloses further examples of embodiments having a thermosetting enamel intermediate layer. Thus, further improvements in the field of polymeric electrical insulation continue to be important. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2014 / 207458 [Patent Document 2] International Publication No. 2016 / 120592 [Patent Document 3] US Patent Application Publication No. 2019 / 0131037 [Patent Document 4] European Patent No. 2843668 [Patent Document 5] US Patent Application Publication No. 2020 / 0312535 Summary of the Invention [Problem to be solved by the invention]

[0014] It is an object of the present invention to provide an insulated conductor suitable for use as magnet wire in the stators of electric motors and having improved corona resistance, a method for making the same, and an electrical device including the insulated conductor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] In a first aspect, the present invention relates to an insulated conductor having improved corona resistance, wherein the insulated conductor comprises a conductor capable of having a potential difference applied across it to induce a flow of electric current, the conductor having a surface and a layer of an insulating polymeric compound disposed on the surface, the insulating polymeric compound having a continuous phase of a polymeric material comprising a polyaryletherketone (PAEK) polymer comprising repeat units of general formula I: [ka] wherein t1 and w1 independently represent 0 or 1, v1 represents 0, 1 or 2, and the polymeric insulating compound also includes a dispersed phase of solid particulate material.

[0016] It has been found that PAEK polymers containing distributed solid particulate material significantly increase thermal conductivity and improve partial discharge and corona resistance without compromising electrical insulation properties. In addition, such materials have been found to have improved adhesion to copper and aluminum over PAEKs that do not contain any filler material.

[0017] These materials may therefore be used in a wide variety of electrical components and provide excellent electrical insulation properties in high performance applications, particularly but not limited to, as stator windings in electric motors, generators or alternators.

[0018] Insulating Polymer Compounds Preferably, the insulating polymer compound constitutes at least 65% by weight of the polymeric material, more preferably at least 75% by weight, more preferably at least 85% by weight, with the remainder generally being constituted by solid particulate material, as described below.

[0019] Polymer Materials The polymeric material is thermoplastic and comprises at least 50% by weight, more preferably at least 70% by weight, most preferably at least 80% by weight of the PAEK polymer of formula I. The remainder may be provided by copolymers and / or blends with other polymers as described below. When blended with another polymer, such polymer may be selected from the list consisting of polyphenylsulfone, polyetherimide, polyethersulfone, polyphenylene sulfide, polycarbonate, polyester or mixtures thereof.

[0020] PAEK polymers or copolymers, unlike many conventional polymers, can be obtained in either amorphous or crystalline form as a direct result of how the polymer is processed. The glassy or amorphous state can be obtained by rapidly cooling the polymer from the molten state below the Tg, while slow cooling of the polymer from the molten state will result in greater crystallinity in the sample (melt crystallization). Crystalline forms of polymers can also be obtained from the polymer in an amorphous state, for example at room temperature, by heating the polymer to a temperature above the Tg but below the Tm and then cooling to room temperature (cold crystallization), or by holding the polymer at a constant temperature between the Tg and Tm for a period of time and then cooling to room temperature (isothermal crystallization).

[0021] A PAEK polymer in the context of the present invention is one having repeat units of formula 1, [ka] In the formula, t1 and w1 independently represent 0 or 1, and v1 represents 0, 1 or 2.

[0022] The bonds between adjacent phenyl groups are generally predominantly in a "para" 1,4 relationship, as shown in Formula II. [ka] (Formula II)

[0023] However, some percentage of the PAEKs may be in a "meta" 1,3 or an "ortho" 1,2 relationship. As used throughout, unless otherwise specified, the bonds are in the "para" configuration.

[0024] PAEKs, including in particular PEEKs, can be prepared by nucleophilic polycondensation of bisphenols with organic dihalide compounds in the presence of alkali metal carbonates and / or bicarbonates or alkaline earth metal carbonates and / or bicarbonates in a suitable solvent. Such processes are described, for example, in EP 0001879A, EP 0182648A, EP 0244167A and EP 3049457A.

[0025] Preferably, the PAEK has a crystallinity of at least 10%, more preferably at least 20%, however, in some applications, especially when the PAEK is to be extruded, a lower crystallinity, such as less than 25% or even less than 22%, may be advantageous.

[0026] In a preferred embodiment, the crystallinity of the PAEK material is suitably at least 25% (preferably at least 28%, more preferably at least 30%) over substantially the entire extent of the insulating layer. The crystallinity of the PAEK is preferably substantially constant over the extent of the insulating layer. Preferably, the crystallinity of the PAEK in the layer varies by less than 10%. For example, the minimum and maximum crystallinity of the material in a layer differs by less than 10%. The insulating layer is preferably free of regions with a crystallinity of less than 15% (often referred to as amorphous patches). The crystallinity of the polymeric material described anywhere in the present description may be less than 40%. The insulating layer is preferably homogeneous, preferably homogeneous over its entire extent.

[0027] Crystallinity is measured by DSC, and the onset of Tg is determined by the intersection of a line drawn along the baseline before the transition with a line drawn along the maximum slope obtained during the transition. Tn is the temperature at which the main peak of the cold crystallization exotherm reaches a maximum. Tm is the temperature at which the main peak of the melting endotherm reaches a maximum. The heat of fusion of melting (ΔHm) is obtained by connecting two points where the melting endotherm deviates from a relatively linear baseline. The integrated area under the endotherm as a function of time gives the transition enthalpy of melting (mJ), and the mass-normalized heat of fusion is calculated by dividing the enthalpy by the mass of the sample (J / g). The level of crystallinity (X(%)) is determined by dividing the heat of fusion of the sample by the heat of fusion of a fully crystalline polymer, which for polyetheretherketone is 130 J / g. ISO11357-1 to ISO11357-4 describe the test methods used to determine the above measurements.

[0028] A preferred PAEK is polyetheretherketone (PEEK), where in the repeat unit t1=1, v1=0 and w1=0.

[0029] PAEK, such as PEEK, may also contain other repeat units to form copolymers. Particularly preferred copolymers contain repeat units of PEEK and polyetherdiphenyletherketone (PEDEK). Suitable copolymers of PEEK and PEDEK are disclosed in EP0184458.

[0030] PEDEK is a polymer with the repeating unit: -O-Ph-Ph-O-Ph-CO-Ph- (III)

[0031] PEEK-PEDEK copolymers are disclosed as having chemical resistance and mechanical properties comparable to PEEK, as well as a lower Tm and a Tg value comparable to or higher than PEEK.

[0032] WO2014 / 207458 A1 discloses suitable PEEK-PEDEK copolymers produced by a process comprising polycondensing a mixture of at least one dihydroxybenzene compound and at least one dihydroxybiphenyl compound in a molar ratio of 65:35 to 95:5 with at least one dihalobenzophenone in the presence of sodium carbonate and potassium carbonate, the mole % of potassium carbonate used in the synthesis of the PEEK-PEDEK copolymer by nucleophilic polycondensation being at least 2.5, where the mole % of potassium carbonate is expressed as a percentage of the total number of moles of hydroxy monomers used in the synthesis. The PEEK-PEDEK copolymers of WO2014 / 207458 A1 result in PEEK-PEDEK copolymers with a higher degree of crystallinity compared to those disclosed for the copolymers of EP0184458A.

[0033] Suitable PEEK-PEDEK copolymers are also disclosed in WO 2019 / 186085 A1, which discloses their formation by a specific nucleophilic polycondensation process involving polymerization termination (e.g., using lithium salts) in the presence of reduced amounts of aromatic sulfone solvents and end-capping of the copolymer (to provide the copolymer with specific terminal units), resulting in PEEK-PEDEK copolymers with reduced chain branching and reduced melt viscosity at low shear rates compared to prior art copolymers of comparable molecular weight.

[0034] Also useful copolymers are shown in GB 2108948.7, which discloses a copolymer consisting essentially of repeat units of PEEK and PEDEK, where the PEEK is made up of proportions of PEEK (i.e., in the "para" configuration), mPEEK (i.e., in the "meta" configuration), and oPEEK (i.e., in the "ortho" configuration). A particularly preferred polymer is that provided in Example 19 therein, which is a PEEK-oPEEK-PEDEK copolymer in the ratio 65:15:20, containing 1,2-dihydroxybenzene as a comonomer.

[0035] In one aspect of the invention, there is provided an insulated conductor assembly having improved corona resistance, wherein the assembly includes a conductor capable of having a potential difference applied across it to induce a flow of electric current, and a layer of an insulating polymer compound is provided over the assembly, the insulating polymer compound comprising polyaryletherketone, PAEK, the PAEK comprising repeating units of the formula: [ka] and The repeat unit of the formula [ka] wherein at least 95 mol % of the repeat units of the copolymer are repeat units of formula (a) and formula (b); The repeat units (a) and (b) have a molar ratio (a):(b) of 55:45 to 80:20; PAEK was also extruded through a tungsten carbide capillary die with a diameter of 0.5 mm and a length of 8.0 mm at 400 °C for 1000 s. -1 Measured using capillary rheometry at shear rates of 0.35-0.55KNsm -2 It has a melt viscosity MV of

[0036] Preferably, the polymeric insulating compound of formula (a):(b) above also comprises a dispersed phase of a solid particulate material. Preferably, the solid particulate material is selected from the group comprising barium sulfate, calcium sulfate, chromium oxide, glass fibre, iron oxide, magnesium carbonate, magnesium oxide, mica, silica, silicon carbide, silicon dioxide (quartz), silicon nitride, sodium silicate, titanium dioxide, talc (e.g. Jetfine™), zinc oxide, zirconia, boron nitride, wollastonite, aluminium nitride or mixtures thereof. Preferably, the solid particulate material is present at a loading level of 0.1-35% by weight, preferably 0.5-30% by weight, more preferably 1-20% by weight. In one embodiment, there is provided an insulated conductor comprising an insulating polymeric compound of formula (a):(b) above comprising substantially 20% by weight of talc. Preferably, the solid particulate material has a d50 of 0.001-50 μm.

[0037] For brevity, the units of formula (a) and formula (b) are referred to herein as PEEK and PEDEK, respectively. In general, the polymer also has the terminal units of the polymer having terminal OH or F groups, which may be the same as the repeat units. However, the method of forming the polymer may include a separate end-capping step upon completion of the polymerization, in which case a separate monomer or reagent may be added as an end-capping agent, whereby the terminal units may be different from the repeat units of the polymer. Such end-capping is well known in the field of nucleophilic polycondensation reactions. In other words, in the polymers of the present invention, 95 mol % or more of all the repeat units present are units of formula (a) and units of formula (b) in a specific molar ratio (a):(b) of 55:45 to 80:20. This can be verified by knowing the number of moles of monomers used in the preparation of the polymer.

[0038] The phenylene moieties in each repeat unit (a) and (b) have 1,4-para bonds to the atoms to which they are attached, which renders the polymeric material essentially crystalline. Preferably, the 1000s -1 And the MV of the PAEK of the first aspect of the present invention measured at 400 ° C. is 0.40 to 0.50 KNsm -2 Preferably, the molar ratio (a):(b) is from 60:40 to 75:25. Preferably, at least 98 mol %, more preferably 99 mol %, of the repeat units of the copolymer are repeat units of formula (a) and formula (b). Most preferably, the polymer consists essentially of repeat units of formula (a) and formula (b).

[0039] In this context, the term "consisting essentially of" means that no other monomers are intentionally included, although some may be present as unavoidable impurities or as end groups.

[0040] Electrical characteristics The inclusion of solid particulate material in the polymeric material surprisingly improves partial discharge and corona resistance while retaining other physical properties that make it suitable for use as an insulator. In one particular embodiment incorporating a talc filler material, the inventors have found a surprising improvement in corona resistance. In such a configuration, it is believed that the thickness of the insulating coating can be reduced, for example, from 200 μm to 100 μm.

[0041] The insulating polymer compound retains its electrical resistivity by virtue of the fact that it is dispersed with solid particulate material, and preferably has a resistivity of at least 10, as measured perpendicular to the surface of the electrical conductor. 10 It has an electrical resistivity of Ω·cm.

[0042] The insulating polymer compound preferably has a dielectric strength (i.e., breakdown voltage) of 90 to 190 kV / mm. The dielectric strength varies depending on the thickness of the material. For example, an insulating coating of about 2 mm has a dielectric strength of less than 50 kV / mm. Conversely, an insulating coating thinner than 2 mm, for example 8 μm, has a breakdown voltage of more than 300 kV / mm.

[0043] The configurations provided by the present invention provide improved corona resistance and longer insulation life in demanding electrical applications, as evidenced, for example, by voltage endurance data.

[0044] Also preferably, the insulating polymer compound has a relative dielectric constant of less than 3.8, preferably less than 3.5, and more preferably less than 3.3.

[0045] Preferably, the insulating polymer compound has a resistance to electrical conductor of at least 0.15 Wm2 measured in a direction perpendicular to the surface of the electrical conductor. -1 K -1 , preferably at least 0.2 Wm -1 K -1 , more preferably at least 0.25 Wm -1 K -1 It has a thermal conductivity of

[0046] Thickness The insulating polymer compound may have a dimensional thickness, as defined in a direction perpendicular to the surface of the conductor, suitable for the application. Preferably the polymer material has an average thickness of 2 to 500 μm, more preferably 2 to 300 μm, preferably 10 to 300 μm.

[0047] The thickness of the insulating layer is preferably substantially constant over the extent of the insulating layer. Thus, preferably, the ratio defined as the thickness of the insulating layer at its thinnest point divided by the thickness of the insulating layer at its thickest point is at least 0.8, preferably at least 0.9, more preferably at least 0.95. In one embodiment, the insulating layer is not covered by another material, e.g. another layer.

[0048] Conductor Shape The conductor can be of any shape or form, so long as it is designed to be capable of passing an electric current by applying a potential difference across it in use. Such conductors can be, for example, elongated, planar, or three-dimensional. In either case, the conductor has an outer surface, which can be flat or curved, onto which the insulating polymeric compound of the present invention can be applied.

[0049] The preferred conductor is a wire, e.g., magnet wire, which may have a circular or rectangular or other cross section, e.g., triangular or hexagonal. When the conductor is a wire, the tangential direction of the surface is also parallel to the length of the wire. Other wires may have a geometry tailored for use, for example, with insulating polymer compounds of varying thickness.

[0050] Such wire is particularly useful as magnet wire in electric motors, e.g., as windings around the stator coils. This is particularly beneficial for high performance motors where partial discharge and corona resistance are particularly desirable physical properties.

[0051] Conductor Material The present invention is applicable to a wide range of conductor materials, such as nickel or silver, but preferably the conductor is essentially copper or aluminum. In one embodiment, the conductor may comprise a copper core conductor plated with a suitable material, such as silver or nickel. When the conductor is copper, it is preferably a low-oxygen copper with an oxygen content of less than 30 ppm, more preferably less than 20 ppm.

[0052] particle size The solid particulate materials of the present invention may contain non-spherical particles, and therefore it is important to characterize their size accordingly. A preferred particle size measurement is the Sauter mean particle size, or d3,2, which is the diameter of a sphere having the same surface area to volume ratio as a sample of particles. This measure of particle size takes into account deviations from the shape of spherical particles. For example, non-spherical particles have a larger surface area relative to the size of the particle than spherical particles, and therefore they have correspondingly smaller d3,2 values. Preferably, the solid particulate material has a d3,2 of 0.001 to 50 μm, more preferably 0.005 to 15 μm.

[0053] The d50 is between 0.001 and 50 μm, more preferably between 0.005 and 15 μm. In one configuration, the solid particulate material has a d50 between 0.001 and 50 μm, more preferably between 0.005 and 15 μm.

[0054] Particle Shape In one embodiment of the present invention, the solid particle material is comprised of particles having a length and width such that each particle has an orientation angle between 0 and 90 degrees, where the orientation angle is the angle between the direction of its length and the tangential direction of the surface nearest the particle, and the particles are oriented within the insulating polymer compound such that the number average orientation angle is less than 45 degrees. It has been found that such elongated particles, when aligned with the surface of a conductor, further improve electrical and thermal properties.

[0055] Preferably, the particles are oriented within the insulating polymeric material such that the number average orientation angle is less than 30 degrees, more preferably less than 20 degrees. The more aligned the particles are with respect to the surface of the conductor, the greater the electrical insulating properties of the polymer, while also providing additional technical benefits such as adhesion, corona resistance and thermal breakdown.

[0056] When the particles forming the solid particulate material are significantly non-spherical, they may also be properly characterized by their aspect ratio. Such aspect ratio is the ratio of the particle's maximum length to its minimum width, where the width is perpendicular to the length. Although each particle in a population will have its own aspect ratio due to natural variations, a number average aspect ratio of at least 2:1, more preferably at least 4:1, is preferred.

[0057] Another suitable method for characterizing the solid particulate material is sphericity, defined as the surface area of ​​a sphere having the same volume as the particle divided by the surface area of ​​the particle. Although particles of any sphericity have been found to be beneficial, preferably the solid particulate material has an average sphericity of less than 0.7, more preferably less than 0.6.

[0058] In one embodiment, the solid particulate material may include particles that are substantially symmetrical about a line of symmetry.

[0059] solid particle material A variety of materials can be formed into solid particulate materials, particularly those with high thermal conductivity such as minerals, so long as they have an appropriate particle size. Examples of such materials include calcium sulfate, chromium oxide, glass fiber, iron oxide, magnesium carbonate, magnesium oxide, mica, silica, silicon carbide, silicon dioxide (quartz), silicon nitride, sodium silicate, titanium dioxide, talc (e.g., Jetfine™, including Jetfine 3CA), zinc oxide, zirconia, barium sulfate, boron nitride, wollastonite, and aluminum nitride.

[0060] It has been found that below the minimum amount of solid particulate material the beneficial effects of the invention are minimal, and above a certain amount the beneficial properties of the polymer are diminished. Thus, the solid particulate material is preferably present in the insulating polymeric material at a loading level of 0.1-50% by weight, or 0.1-40% by weight, 0.1-35% by weight, more preferably 0.5-30% by weight, more preferably 1-20% by weight, and most preferably 15-25% by weight. For example, 5% or 10% or 15% titanium dioxide may be present in the PAEK, preferably PEEK. Alternatively, 5% or 10% or 15% barium sulfate may be present in the PAEK, preferably PEEK. In yet another example, 5% or 10% or 15% or 20% by weight talc may be present in the PAEK, preferably PEEK.

[0061] In one preferred embodiment, the insulated conductor comprises an insulating polymeric compound, such as preferably PEEK or preferably the copolymer PEEK-PEDEK mentioned above, and 10-30% by weight of a solid particulate material.

[0062] In one embodiment, the insulated conductor comprises an insulating polymer compound, preferably PEEK, or preferably the copolymer PEEK-PEDEK, and 20% by weight talc.

[0063] In one embodiment, 5% or 10% or 15% barium sulfate may be present in the PAEK, preferably PEEK-PEDEK. In yet another example, 5% or 10% or 15% or 20% or 30% talc may be present in the PAEK, preferably PEEK-PEDEK.

[0064] Additional Layers The polymeric material may be applied directly to the surface of the conductor, but there may also be an additional layer of material between the insulating polymeric material and the conductor. Such an additional layer is often called an enamel layer and may include a further polymer layer, for example a thermosetting polymer layer, such as a fluoropolymer layer or a polyimide layer. Similarly, additional layers may be provided on top of the electrically insulating polymeric compound as required depending on the application of the electrical component.

[0065] Formation method In a second aspect, the present invention relates to a method for making an insulated conductor as described herein, the method comprising: (a) blending ingredients of a flowable polymeric material together with a solid particulate material to form a random blend; (b) shearing the random blend; (c) simultaneously or subsequently laying the blend onto a surface of a conductor.

[0066] In a particularly preferred method of manufacture, the insulated conductors are produced by a process which includes extruding a flowable mass of polymeric material containing the solid particulate material.

[0067] The insulating polymer compound may be prepared prior to application onto the conductor, or it may be formed and deposited directly onto the conductor, for example, in an extrusion process.

[0068] When the insulating polymer compound is prepared before being applied onto the conductor, the insulated conductor of the present invention can be prepared by laying a layer of the insulating polymer compound on the surface of the conductor. For example, when the conductor is a wire, a process of wrapping it with a polymer layer in the manner disclosed in WO2016 / 120592 may be used.

[0069] As previously discussed, the insulated conductors are particularly useful as magnet wires in the stators of electric motors. Thus, in a third aspect, the present invention relates to an electrical device comprising the insulated conductors described herein. For example, such an electrical device comprising the insulated conductors may be an automobile motor assembly. EXAMPLES

[0070] Adhesion Test Samples of PEEK polymer, with a shear viscosity of 90 Pa.s at 400°C, were tested for their adhesion to aluminium, copper, beryllium copper and stainless steel substrates at various levels of solid particulate material. Adhesion was measured by a T-peel test to BS EN ISO 113399.

[0071] Machine settings: Instron 2736-015, peel speed: 50mm / min, Peel elongation: 200 mm, load cell: 30 KN.

[0072] Insulating polymer compounds were prepared in which the polymer compound was a first PAEK (PEAK1) having a shear viscosity of 90 Pa.s at 400° C., or a second PEAK (PEAK2) having a lower melting point and a shear viscosity of 117 Pa.s at 400° C. The PAEK2 comprised the PEEK PEDEK copolymer described above.

[0073] Polymers were prepared without any solid particulate material, with 20% by weight talc (Jetfine™) and / or 15% by weight glass particles.

[0074] The polymer films were prepared according to the following protocol.

[0075] An aluminium frame was cut to 150 x 150mm. Both sides of the frame were coated with Frekote™ to prevent the plastic from sticking to the frame or holder and the frame was sandwiched between two further aluminium sheets, each of which was also coated with Frekote on the inside. The hot press was heated to 400°C. 10g of polymer was weighed and placed in the centre of the frame. The sandwich within the frame was then placed between two metal plaques to hold the sample in place. This was then pressed for 4 minutes with no pressure. After 4 minutes the sample was pressed with 5 tonnes of pressure for a further 2 minutes. The sample was then removed from the hot press and quenched in water to rapidly cool.

[0076] How to prepare a T-shaped peel sample The hot press is heated to 400°C. Metal samples are cut into 75x200mm strips and pretreated accordingly. The pressed polymer film is cut into 75x150mm strips. The film is then sandwiched between two pretreated metal strips leaving a 50mm tab on the end to grab with the Instron grips. The sample is then placed between two 200x200mm aluminum sheets to prevent spilling onto the press. The sample is then placed onto two metal plaques. The sample is pressed for 2 minutes without pressure. Once complete, the sample is again removed from the press and quenched. The samples need to be further cut into 25x200mm sample sizes, resulting in triplicate samples for each metal, compound and surface treatment.

[0077] The results are shown in Tables 1 to 4 below. [Table 1] [Table 2] [Table 3] [Table 4]

[0078] From these results, it is clear that the talc filler has a distinct effect on adhesion, and it appears to improve adhesion most dramatically when the metal is shot blasted or acid etched. Since the surface area of ​​the conductor is increased by both of these techniques, it makes sense that the talc with the plated structure would improve adhesion because it has a larger surface area and the plating can better align with the surface and get a more intimate contact at the metal-polymer interface. This supports a physical key-type bond onto the metal surface.

[0079] Advantageously, the addition of a filler, such as talc, can lower the coefficient of thermal expansion (CTE), reducing the stress at the interface between the metal and the PAEK, thus maintaining good adhesion.

[0080] Voltage endurance test This involves placing a piece of film between two electrodes and measuring the time to failure when applying, for example, 2.83 kVrms at 1 kHz. The test system used consists of a 5 kV transformer that can be driven at frequencies between 400 Hz and 2 kHz, producing a sinusoidal voltage with a maximum output of 5 kVrms. A series resistor is used to limit the maximum current that can flow at the time of sample failure. The voltage is then sent to the test electrodes through a voltage divider that is used to monitor the system voltage during the test, and finally to a high voltage relay. A high voltage relay is used to isolate the power supply to the failed sample. The electrodes on either side of the film sample are separated by the thickness of the film (a polished 50 mm base electrode and a polished 25 mm top electrode with a 1 mm radius of curvature on its edges).

[0081] The PEEK unfilled film referenced in Table 5 had a shear viscosity of about 291 Pa.s according to ISO 11443. [Table 5]

[0082] All filled films exhibited longer life than those without any solid particulate material.

[0083] Theory suggests that the particle mixture inhibits mechanical erosion (thinning) of the insulating layer under corona discharge, thus extending voltage endurance life (Table 5).

[0084] Breakdown Voltage The dielectric breakdown voltage was evaluated by applying the IEC 60851-5 method to the magnet wire. A coating of a compound containing 86% by weight of PEEK and 14% by weight of talc was used with a coating thickness of 100 microns, and 11 kV was applied to the wire.

[0085] Beneficially, the magnet wire did not break under the above conditions. In doing so, the applicant has demonstrated that the present invention provides improved voltage endurance when comparing filled and unfilled PAEK-based materials without compromising other important electrical properties. Additionally, the present composition demonstrates improved adhesion of filled PAEK compounds to conductors compared to unfilled PAEK materials. Enabling high levels of adhesion to, for example, copper conductors is commercially attractive as it helps ensure the longevity of the insulation system by minimizing the risk of delamination. Conversely, disadvantageously, it is known to use enamel as an interface to promote adhesion, but this can crack or cause embrittlement after exposure to heat.

Claims

1. 1. An insulated conductor having improved corona resistance, the insulated conductor comprising an electrical conductor capable of having a potential difference applied across it to induce the flow of current, the conductor having a surface and a layer of an insulating polymer compound disposed on the surface, the insulating polymer compound having a continuous phase of a polymeric material comprising a polyaryletherketone (PAEK) polymer comprising repeating units of general formula I: 【Chemical 1】 wherein t1 and w1 independently represent 0 or 1, and v1 represents 0, 1, or 2, and the polymeric insulating compound also includes a dispersed phase of solid particulate material.

2. 10. The insulated conductor of claim 1, wherein t1=1, v1=0, and w1=0, forming a polyetheretherketone (PEEK).

3. 3. The insulated conductor of claim 1 or 2, wherein the polymeric material has a crystallinity of less than 25%.

4. 3. The insulated conductor of claim 1 or 2, wherein the polymeric material has a crystallinity of at least 25% and less than 40%.

5. 1. An insulated conductor assembly having improved corona resistance, the insulated conductor assembly including a conductor capable of having a potential difference applied across it to induce a flow of current, an insulating polymer compound provided on the insulated conductor assembly, the insulating polymer compound comprising polyaryletherketone (PAEK), the PAEK having a formula 【Chemistry 2】 Repeating units of and formula 【Chemistry 3】 is a copolymer comprising repeat units of wherein at least 95 mole percent of the repeat units of the copolymer are of formula (a): and a repeat unit of formula (b), the repeat units (a) and (b) have a molar ratio (a):(b) of 55:45 to 80:20; Also, PAEK was extruded through a tungsten carbide capillary die with a diameter of 0.5 mm and a length of 8.0 mm at 400°C for 1000 s. －１ 0.35 to 0.55 KNsm as measured using capillary rheometry at a shear rate of －２ 1. The insulated conductor assembly of claim 1, wherein the insulated conductor assembly has a melt viscosity MV of

6. 3. The insulated conductor of claim 1 or 2, wherein the solid particulate material is selected from the group comprising barium sulfate, calcium sulfate, chromium oxide, glass fiber, iron oxide, magnesium carbonate, magnesium oxide, mica, silica, silicon carbide, silicon dioxide (quartz), silicon nitride, sodium silicate, titanium dioxide, talc (e.g., Jetfine™), zinc oxide, zirconia, boron nitride, wollastonite, aluminum nitride, or mixtures thereof.

7. 3. An insulated conductor according to claim 1 or 2, wherein the solid particulate material is present at a loading level of from 0.1 to 35% by weight, preferably from 0.5 to 30% by weight, more preferably from 1 to 20% by weight.

8. 8. The insulated conductor of claim 7, wherein the insulating polymer compound comprises PEEK and 15-25% by weight of talc, preferably 20% by weight of talc.

9. 3. The insulated conductor of claim 1 or 2, wherein the solid particulate material has a d50 of 0.001 to 50 μm.

10. 3. The insulated conductor of claim 1 or 2, wherein the insulating polymer compound has an average thickness of 2 to 500 μm, preferably 2 to 300 μm.

11. 3. The insulated conductor of claim 1 or 2, wherein the conductor is a wire which may have a circular or rectangular cross section.

12. 12. The insulated conductor of claim 11, wherein the wire is magnet wire wound around a stator coil of an electric motor, alternator, or generator.

13. 3. The insulated conductor of claim 1, wherein the polymeric material is applied directly to a surface of the conductor.

14. A method for producing an insulated conductor according to claim 1 or 2, comprising: (a) blending ingredients of a flowable polymeric material together with said solid particulate material to form a random blend; (b) shearing the random blend; (c) simultaneously or subsequently laying the blend on a surface of a conductor.

15. 15. The method of claim 14, wherein step (c) is carried out simultaneously by an extrusion process.

16. An electrical device, such as a motor assembly of an automobile, comprising an insulated conductor according to claim 1 or 2.

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