Coil member, method for manufacturing same, and armature

Abstract

Provided is a coil member which enables the achievement of weight reduction, loss reduction and the like of a coil. The present invention provides a coil member comprising: a conductor that is composed of an Al base material; and an insulating film that covers at least a part of the conductor. The insulating film has an anodic oxide film that is formed on the Al base material, and the anodic oxide film has a porosity of 20-75% as determined by observing the upper surface thereof. The anodic oxide film has, for example, a film thickness of 20-150 μm. In addition, it is preferable that the anodic oxide film has a main hole that extends substantially in a straight tube shape from the Al base material side, and a sub-hole that is opened to a part of the side wall of the main hole. It is preferable that the insulating film additionally has a resin layer on the anodic oxide film. The resin layer has, for example, a thickness of 1-20 μm. A coil member according to the present invention is, for example, a segment conductor which is inserted into a slot of a stator core of a motor, or the like.

Description

Coil member, manufacturing method thereof, and armature

[0001] The present invention relates to a coil member or the like made of an insulating coated Al-based conductor.

[0002] There are various types of electromagnetic devices that have an armature and a field magnet. A typical example is an electric motor (including a generator). There are various types of electric motors that have a rotor and a stator, such as rotating armature types and rotating field types. There are also inner rotor types in which the rotor rotates on the inner periphery of the stator, and outer rotor types in which the rotor rotates on the outer periphery of the stator. However, all electric motors have in common the fact that they have at least one coil embedded in a core.

[0003] Electric motors installed in vehicles and other moving objects are required to be smaller, lighter, have higher output, and be more efficient (lower loss), etc. To achieve these goals, efforts have been made to improve the coil space factor, reconsider winding methods, and improve the coil wire (materials).

[0004] There is a limit to the improvement that can be made in coils made of continuous conductors. For this reason, coils made of segment conductors have been considered, and the following non-patent literature provides a description of this.

[0005] Masashi Yamamura et al.: Technological Trends in Automotive Motors, Denso Technical Review, vol. 23 (2018)

[0006] JP 2000-349320 JP 2004-59997 JP 2011-117042 JP 2018-44227

[0007] Non-Patent Document 1 relates to a segment conductor made of coated copper wire.

[0008] Patent Documents 1 to 4 all target wiring boards, semiconductor elements, etc., and do not describe coils or the like through which a large current flows in an alternating magnetic field. Patent Documents 1 to 4 simply use a general type of anodic oxide film obtained by electrolysis in a bath of sulfuric acid or oxalic acid as the insulating film.

[0009] The present invention has been made in view of the above circumstances, and has an object to provide a new coil member or the like made of an insulating coated Al-based conductor.

[0010] As a result of extensive research aimed at solving the above problems, the inventors discovered a new anodic oxide film suitable for use as an insulating film for coils. By further developing this finding, the inventors have completed the present invention, which will be described below.

[0011] <<Coil Member>> (1) The coil member of the present invention is a coil member including a conductor made of an aluminum base material (Al base material) and an insulating film covering at least a part of the conductor, the insulating film having an anodized film formed on the Al base material, and the anodized film having a porosity of 20 to 75% as determined by observing the top surface.

[0012] (2) According to the present invention, it is possible to provide a coil that can achieve high insulation (voltage resistance characteristics, insulation life, etc.) or high efficiency (low loss), etc. The reasons for this are considered to be as follows.

[0013] The anodic oxide film of the present invention has a significantly higher porosity than conventional anodic oxide films. An insulating film having such an anodic oxide film has a significantly smaller (relative) dielectric constant, which not only provides excellent insulation but also significantly reduces dielectric loss when AC is applied (see the formula in FIG. 5).

[0014] Furthermore, the highly porous anodic oxide film is highly flexible and is less likely to crack even in high temperature environments, so the insulating film according to the present invention can stably exhibit high insulating properties.

[0015] The present invention may also be understood as a method for manufacturing a coil member. For example, the present invention may be a manufacturing method for obtaining the above-described coil member, comprising an electrolysis step of applying current to an Al base material that has been brought into contact with an electrolytic solution containing phosphoric acid.

[0016] When the electrolyte contains phosphoric acid, a highly porous anodic oxide film is easily formed. Furthermore, the surface of the anodic oxide film is coated with an insoluble phosphate film, which inhibits natural sealing of the anodic oxide film (hydration reaction with moisture in the atmosphere), and the high porosity of the anodic oxide film is easily maintained. Therefore, the above-described manufacturing method can provide a coil member that not only improves the characteristics of the coil (and thus the electric motor, etc.), but also contributes to ensuring reliability.

[0017] The present invention can also be understood as a coil manufactured using the above-described coil member, an electromagnetic device (e.g., an electric motor) including the coil, a component thereof (e.g., an armature), etc. One example is an armature in which the above-described coil member is inserted into a slot in a core.

[0018] It should be noted that the armature referred to in this specification is not limited to that used in electric motors (including generators). If the armature is used in an electric motor, it may be a stator, a rotor, or both. The electric motor may be a DC motor or an AC motor. The electric motor may also be a synchronous machine or an asynchronous machine (such as an induction machine). For example, the coil member of the present invention may be used in the rotor of an induction machine. The induction machine may be either a squirrel-cage type or a wound type.

[0019] <<Others>> In this specification, "x to y" includes a lower limit x and an upper limit y, unless otherwise specified. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit to establish a new range such as "a to b." Furthermore, in this specification, "α to β μm" means α μm to β μm, unless otherwise specified. The same applies to other unit systems (nm, etc.).

[0020] 1 is an SEM image of the insulating film (anodic oxide film) observed from above. 2 is an SEM image of the upper side of the fractured surface. 3 is an SEM image of the upper side of the fractured surface of the insulating film (anodic oxide film and resin layer). 4 is an SEM image of the lower side (bottom side) of the fractured surface. 5 is a schematic diagram showing the manufacturing process of a stator incorporating segment conductors. 6 is a formula for calculating the dielectric constant (εi) and withstand voltage (V) of the insulating layer.

[0021] The contents described in this specification may apply not only to the product of the present invention but also to the method, as appropriate. One or more components arbitrarily selected from this specification may be added to the components of the present invention. Which embodiment is best depends on the target, required performance, etc.

[0022] <Anodic Oxide Film> (1) Composition The anodic oxide film is mainly composed of aluminum oxide (Al ２ O ３) The anodized film may contain components derived from the composition of the electrolyte. For example, if an electrolyte containing phosphoric acid is used, P, H, etc. may be contained in the anodized film. Furthermore, phosphates (e.g., Al-P-O compounds, Al-P-O-H compounds) may be present near the surface of the anodized film.

[0023] Anodized oxide films differ from plating films (layers) that simply coat the substrate in that they are produced by anodizing, which involves oxidation of the Al substrate itself. Conventional anodized oxide films have a dense, thin barrier layer (active layer) and a porous layer (growth layer) grown on top of it. Typically, the porous layer is mostly composed of approximately straight, tubular micropores (groups) that open to the surface. It is difficult to achieve high porosity with such general anodized oxide films. Note that, as used herein, "approximately α-shaped" refers only to the α-shaped appearance when viewed visually in actual products or micrographs; it does not necessarily have to be ideally linear (e.g., straight) or angular (e.g., right-angled). The same applies to "approximately orthogonal" and other terms. For example, "approximately rectangular" coils typically have more or less rounded corners (corners) at the apexes of their cross sections, and their cross sections rarely have a strict geometrical rectangle.

[0024] (2) Porosity The porosity of the anodic oxide film according to the present invention is, for example, 20 to 75%, 30 to 65%, 40 to 55%, or 43 to 50%. Such a high porosity is not observed in conventional anodic oxide films consisting of a porous layer with columnar pores (cells). An anodic oxide film with high porosity has excellent flexibility and is less likely to crack even when exposed to high-temperature environments. Furthermore, such an anodic oxide film has high voltage resistance and a low dielectric constant. Therefore, it is suitable, for example, for insulating films for conductors (e.g., coil members in an alternating magnetic field) through which high-frequency (e.g., 0.1 to 30 kHz, 1 to 15 kHz) and high-voltage AC currents are passed. A detailed method for calculating the porosity will be described later.

[0025] (3) Main Holes and Sub Holes The highly porous anodized film may have main holes extending in a substantially straight tube shape from the Al substrate side, and sub holes opening in part of the side walls of the main holes. Details of the main holes and sub holes are as follows.

[0026] The main pores are, for example, cylindrical with a bottom extending from the bottom on the Al substrate side to the opening at the top. The pore configuration (shape, size) may vary somewhat along the vertical direction (depth direction, axial direction, or extension direction). The opening diameter of the main pores is, for example, 50 to 1,000 nm, 100 to 500 nm, or 150 to 350 nm. Such opening diameters (also referred to as "opening diameters") are usually significantly larger than conventional columnar pores (cells).

[0027] The sub-holes may, for example, open in a portion of the side wall of the main hole and extend in the horizontal direction (a direction substantially perpendicular to the side wall of the main hole). At least some of the sub-holes may penetrate the side wall of the main hole (connecting adjacent main holes). The distribution of the sub-holes may be uniform or non-uniform along the longitudinal direction of the main hole.

[0028] It is sufficient that there is at least one sub-hole in the field of view when the anodic oxide film is observed from the side.More specifically, it is desirable that there is at least one surface region (1 μm deep × 10 μm wide) containing one or more, three or more, or even five or more sub-holes in the field of view.

[0029] The porosity and opening diameter referred to in this specification are determined based on images (observation images) obtained by microscopic observation of the anodized oxide film. The porosity is the ratio of the pore area (total value) to the total area of ​​the anodized oxide film within the field of view observed from the top surface. The opening diameter is the arithmetic average value of the circle-equivalent diameters of each pore within the same field of view. The porosity and opening diameter are calculated, for example, using image analysis software (Image J). The field of view (evaluation range) of the observation image is not critical, but may be, for example, 5 × 4 μm to 12.7 × 8.8 μm. The presence (number) and shape of subpores may be visually confirmed based on the surface observation image of the anodized oxide film. Of course, they may also be evaluated based on an observation image of a longitudinal cross section of the anodized oxide film (e.g., a cut surface or fracture surface in the film thickness direction). In this case, it is preferable to evaluate the subpores at least in the surface region of the anodized oxide film (e.g., a region 10 μm deep from the outermost surface).

[0030] In this specification, for convenience of explanation, the surface side of the anodic oxide film (the opening side of the main hole) is referred to as the upper side, and the opposite side (the Al substrate side) is referred to as the lower side or bottom side. In addition, the thickness direction of the anodic oxide film is referred to as the vertical direction, and the direction approximately perpendicular to that is referred to as the horizontal direction.

[0031] (4) Film Thickness The thickness of the anodic oxide film is, for example, 20 to 150 μm, 30 to 100 μm, or 35 to 70 μm. The thickness of the anodic oxide film also includes the thickness of the so-called barrier layer. The thickness of the barrier layer is, for example, 10 to 1000 nm, 50 to 500 nm, or 100 to 300 nm. The group of main holes formed on the barrier layer is also referred to as a "porous layer" in this specification, as appropriate.

[0032] The thickness of the anodic oxide film (film thickness) referred to in this specification is measured with a film thickness meter unless otherwise specified. Based on the observed image, the film thickness may be determined as the distance (average value) from the bottom surface of the anodic oxide film (the bottom surface of the barrier layer) to the top surface (the top surface of the porous layer).

[0033] <<Resin Layer>> A resin layer may be formed on the anodized film. The resin layer can prevent the anodized film from adsorbing moisture and increase the withstand voltage of the insulating film.

[0034] The resin layer is preferably a resin with excellent heat resistance and a small (relative) dielectric constant. Such a resin may be a thermoplastic resin or a thermosetting resin. For example, polyimide, polyamideimide, polyesterimide, epoxy, polyvinylformal, polyurethane, or polyester may be used.

[0035] The resin layer is usually thinner than the anodized film. There are no specific restrictions on the thickness, but it may be, for example, 1 to 35 μm, 5 to 30 μm, or 10 to 20 μm. It is preferable that the resin layer does not penetrate deep into the anodized film, leaving voids in the anodized film, thereby ensuring a high porosity. This improves the withstand voltage of the insulating film and reduces dielectric loss. Note that, as long as a high porosity is ensured, a sealing treatment or a sealing treatment may be performed instead of or in addition to the formation of the resin layer.

[0036] The main holes that open to the surface side and the sub-holes on the surface side can improve the adhesion of the resin layer to the anodized film by the anchor effect, etc. Therefore, it is preferable that many larger sub-holes are distributed on the surface side.

[0037] The resin layer is formed on the anodized film by, for example, applying, spraying, dipping, or electrodeposition of an electrical insulating paint (varnish). The drying and curing are performed depending on the type of resin, but for example, heat drying or heat curing is preferable. In other words, a resin coating process is performed in which the resin is applied to the anodized film and then heated. Heating removes moisture and other substances adsorbed on the anodized film.

[0038] The Al substrate may have any composition as long as it has excellent electrical conductivity and does not inhibit the formation of a highly porous anodic oxide film. For example, pure Al (JIS A1000 series, etc.) containing 98 mass % or more, 98.5 mass % or more, 99 mass % or more, or even 99.6 mass % or more of Al may be used as the Al substrate.

[0039] The Al base material may be, for example, an Al alloy or pure Al having a conductivity of 50% IACS (International Annealed Copper Standard) or more, 55% IACS or more, or even 60% IACS or more. "% IACS" refers to annealed standard soft copper (volume resistivity: 1.7241×10 -８ The electrical conductivity is a relative index (ratio) to the electrical conductivity (100% IACS) of Ωm. The Al base material may be, for example, a wrought material or a cast material.

[0040] Anodizing treatment: An anodic oxide film is formed by an electrolysis process in which an electric current is passed through an Al substrate in contact with an electrolyte. By anodizing an Al substrate that has been formed or processed into a desired shape, cracks in the anodic oxide film (insulating film) can be prevented.

[0041] (1) Electrolyte The composition of the electrolyte is not limited as long as it forms an anodic oxide film of the desired shape. The electrolyte may be, for example, an inorganic acid solution (such as an aqueous phosphoric acid solution, an aqueous sulfuric acid solution, or an aqueous chromic acid solution) or an organic acid solution (such as an aqueous oxalic acid solution).

[0042] When an electrolyte containing phosphoric acid is used, the concentration of phosphoric acid may be, for example, 1 to 30%, 2 to 20%, or 3 to 10%. The concentration of the electrolyte referred to in this specification is a mass percentage relative to the total unless otherwise specified. The temperature of the electrolyte (bath temperature) may be, for example, 15 to 80°C, 20 to 60°C, or 25 to 40°C.

[0043] (2) Current Flow The electrolysis process is carried out by, for example, constant current or constant voltage current flow. The current (density) or applied voltage may be changed (fluctuated) during current flow. The electrolysis process may be carried out by direct current, alternating current, or superimposed AC / DC current, which is a combination of an AC component and a DC component. The waveform of the alternating current may be a sine wave, a rectangular wave, a pulse wave, or the like.

[0044] When the electrolysis step is carried out by direct current, a high voltage of, for example, about 30 to 250 V, 40 to 200 V, or even 75 to 175 V may be applied to the Al base material at least temporarily. There is no particular restriction on the counter electrode provided in the electrolytic solution, but typically, a platinum electrode, a graphite electrode, or the like is used.

[0045] <<Coil Element>> The specific form (shape or size) of the coil element is not important. The coil element may be a continuous conductor or a segmented conductor. Using segmented conductors improves the flexibility of the coil shape and the space factor. One example of a segmented conductor is a segment conductor inserted into a slot in a core (e.g., a stator core or a rotor core). A segment conductor is connected to another segment conductor at its adjacent ends to form a coil. The ends of such a segment conductor may not be insulating-coated. An insulating film may not be provided at such ends, or the insulating film may be peeled off. The ends are joined (connected) by, for example, welding or fusing. The cross-sectional shape of the segment conductor may be (elliptical) circular, but a rectangular shape (particularly a substantially rectangular shape) improves the space factor.

[0046] Such a segment conductor may be used, for example, in an armature (particularly a stator) of a high-power motor for an electric vehicle (including a hybrid vehicle) or the like.

[0047] Assuming that the segment conductor (SC) to be incorporated into the stator of a motor is to be used, several types of samples were produced by forming an anodized film on the surface of an aluminum substrate (conductive material) with a rectangular cross section, while changing the manufacturing conditions. The present invention will be explained in more detail below with reference to the following specific examples.

[0048] First Example: Constant Current Electrolysis Preparation of Samples (1) Test Piece A test piece (simply referred to as "Al piece") made of pure aluminum (JIS A1050) and having a rectangular cross section (50 mm square x 2 mm thick) was prepared.

[0049] (2) Anodizing Treatment (Electrolysis Step) The Al pieces were subjected to an electrolysis step under the conditions shown in Table 1. An aqueous solution of phosphoric acid, sulfuric acid, or oxalic acid was used as the electrolyte. The concentrations shown in Table 1 are mass ratios to the entire aqueous solution.

[0050] The aluminum pieces were immersed in their entirety in a treatment bath containing an electrolytic solution, and a constant current (density) of direct current was applied to the aluminum pieces as the anode and the stainless steel pieces (JIS SUS304) as the cathode while stirring the electrolytic solution. The current density was 30 mA / cm. ２ The current density was determined by dividing the applied current by the treated area of ​​the Al piece. ２ ) was kept constant by masking a part of the Al piece. Since the applied voltage fluctuates during electrolysis, for reference, the voltage measured 10 minutes after the start of current application is also shown in Table 1.

[0051] After the electrolysis process, the Al pieces were removed from the electrolytic solution, washed thoroughly with distilled water, sprayed with compressed air to remove moisture, and then thoroughly dried in the air. In this way, three types of sample groups A, B, and C shown in Table 1 were obtained. Samples A1, B1, and C1 were Al pieces coated only with an anodic oxide film.

[0052] (3) Formation of Resin Layer (Resin Coating Step) Furthermore, samples were prepared in which two types of resin layers were formed on each anodized film. One was Samples A2, B2, and C2, in which a commercially available non-photosensitive polyimide varnish was spray-coated onto each anodized film (coating step), and then thermally cured by furnace heating (350°C x 1 hour) (thermal curing step) to form Resin Layer 1.

[0053] The other samples were samples A3, B3, and C3, in which a commercially available photosensitive polyimide varnish was spray-coated onto each anodized film (coating step), and then thermally cured by heating in an oven (200°C x 1 hour) (thermal curing step) to form a resin layer 2.

[0054] For comparison, a sample D was also produced in which a resin layer 2 was formed in the same manner on the surface of an Al piece that had not been subjected to anodizing treatment. However, the resin layer 2 of sample D was formed thickly by repeatedly applying photosensitive polyimide varnish.

[0055] The resin layer of each sample was visually inspected for cracks, and the results are shown in Table 1.

[0056] <<Observation and Measurement>> (1) Surface Observation The surfaces (top surfaces) of the anodized films of samples A1, B1, and C1 were observed using a scanning electron microscope (SEM / S-5500 manufactured by Hitachi High-Technologies Corporation). The SEM images are shown in Figure 1.

[0057] (2) Observation of Fracture Surfaces The longitudinal cross sections (coating cross sections) on the surface side of each sample were similarly observed using an SEM. SEM images of samples A1, B1, and C1 are shown together in Figure 2. SEM images of samples A2, B2, and C2 are shown together in Figures 3A and 3B (collectively referred to as "Figure 3"). Figure 3A shows the top side of the coating, and Figure 3B shows the bottom side.

[0058] Based on each SEM image, the presence or absence of sub-holes (horizontal holes) in the region 1 μm deep from the outermost surface of the anodic oxide film (surface layer region) was visually confirmed. The results are also shown in Table 1.

[0059] (3) Film Thickness The thickness of the anodic oxide film and resin layer formed on the surface of each sample was measured using an eddy current film thickness meter (SWT-9200 manufactured by Sanko Electronics Laboratory Co., Ltd.). The measurements were carried out after the electrolysis process and after the resin coating process. The thickness of the resin layer was calculated by subtracting the thickness of the former from the thickness of the latter. The film thicknesses obtained are also shown in Table 1.

[0060] (4) Relative Dielectric Constant The relative dielectric constant of the coating (insulating layer) of Samples A1, A2, B1 and C1 was determined as follows, and the results are shown in Table 1.

[0061] The capacitance between the upper electrode (Cu plate: φ8.5 mm) placed on the coating of each sample and the lower electrode consisting of an Al piece (anodized specimen) was measured using an LCR meter (IM3536 / 3531Z manufactured by Hioki E.E. Corporation) at 24°C and 30% RH (relative humidity).

[0062] The upper electrode was placed at five different locations (arbitrarily) and the measurement was repeated to determine the average capacitance (C [F]). Using this average value, the relative permittivity (ε ｒ ) was calculated. C = ε ｒ ・ε ０ (S / t) ε ０ : Dielectric constant of vacuum (= 8.854 x 10 -１２ F / m) S: Area of ​​upper electrode [m ２ ] t : electrode spacing [m] The electrode spacing was measured by the above-mentioned method. For sample A2, the total thickness of the anodized film and resin layer 1 was used.

[0063] <<Voltage Withstanding Test>> Samples A3, B3, C3 and D were subjected to the following voltage withstanding test.

[0064] Using a variable frequency withstand voltage test power supply (DAC-WT-25 manufactured by Soken Denki Co., Ltd.), a sinusoidal voltage (800 V, 1 kHz) was applied between a spherical electrode (φ20 mm) placed on the coating of each sample and an Al piece (anodized test piece). The test environment was 30°C x 50% RH (relative humidity). After the start of the test (voltage application), the time until the breaking current exceeded 50 mA was measured and defined as the dielectric breakdown life. The results are also shown in Table 1.

[0065] <Image Analysis> The porosity and opening diameter (pore diameter) of the anodic oxide films of Samples A1, B1, and C1 were determined by analyzing the SEM images (see FIG. 1). The specific calculation method is as follows.

[0066] (1) Porosity The SEM image, which was adjusted to include 10 or more main pores in one field of view, was converted to 8 bits using ImageJ (free software) and then binarized to extract pores that were open (opened) on the surface. After processing each pore with the Watershed Algorithm, the pores with an opening area of ​​100 nm were extracted. ２ The total opening area of ​​the pores was calculated. The ratio of this total to the total area of ​​the field of view was defined as the porosity. In this example, the field of view for sample A1 was 1280 nm × 890 nm, and the field of view for samples B1 and C1 was 640 nm × 445 nm.

[0067] (2) Opening diameter The maximum diameter (maximum length) of each of 10 randomly selected main pores in the SEM image used to measure the porosity was measured, and the arithmetic average value was taken as the opening diameter. The same operations (analysis and measurement) were performed on five SEM images for both the porosity and the opening diameter. The average values ​​of the five SEM images thus obtained are also shown in Table 1.

[0068] <Evaluation> (1) Anodic Oxide Film As can be seen from Table 1, the anodic oxide film (sample A1) formed by applying a high voltage in an electrolyte containing phosphoric acid had significantly larger porosity and opening diameter than the other samples B1 and C1.

[0069] 1 and 2, the anodized oxide film of sample A1 had large main pores extending in a generally straight tube shape from the Al piece (Al substrate) side, as well as numerous thin sub-pores that penetrated into the side walls of the main pores. Furthermore, as is clear from FIGS. 3A and 3B, the sub-pores were larger in the upper layer region (1 μm deep) than in the lower layer region (bottom side, barrier layer side), and their density tended to increase from bottom to top. This unique morphology was not observed in the anodized oxide films of the other samples.

[0070] (2) Resin Layer As shown in Table 1, no cracks were observed in the resin layers of Samples A2 and A3. On the other hand, cracks were observed in the resin layers of Samples B2, B3, C2, and C3.

[0071] During the thermal curing treatment of the resin layer, thermal stress due to the difference in thermal expansion coefficients acts between the Al pieces and the anodized film, which is thought to cause cracks in the anodized film to propagate to the resin layer.

[0072] The anodized films of samples A2 and A3 have not only large porosity and large diameter main pores but also sub-pores on the side walls. Such anodized films are highly flexible and therefore less likely to crack even when exposed to high temperatures, resulting in excellent crack resistance.

[0073] (3) Adhesion: As can be seen from Figure 3, the resin layer of sample A2 penetrated into the surface of the anodized film (to a depth of about 1 μm) and was retained in the main and sub-holes. This condition was hardly observed in the anodized films of the other samples.

[0074] The SEM image in Figure 3 shows the tensile fracture surface. A portion of the resin layer of sample A2 remained on the anodized film even after fracture. On the other hand, the resin layers of samples B2 and C2 were not in close contact with the anodized film and peeled off entirely from the anodized film upon fracture.

[0075] 3A and 3B, the resin layer only engaged with the top of the anodized film and did not penetrate (penetrate) to the bottom. This is thought to be why sample A2 exhibited the low (relative) dielectric constant (high insulating properties) described below, along with the high adhesiveness of the resin layer.

[0076] (4) Relative dielectric constant As shown in Table 1, the relative dielectric constant of sample A1 was approximately 30 to 40% smaller than that of samples B1 and C1. This is thought to be because the porosity of the anodic oxide film of sample A1 was greater than that of the other samples. The relationship between porosity and the relative dielectric constant of the anodic oxide film (insulator) can also be explained by AS Windeler's formula. The relationship between the relative dielectric constant and the withstand voltage can be understood from Dakin's formula. The sources of each formula shown in Figure 5 are as follows: [1] Windeler, AS, “Polyethylene Insulated Telephone Cable”, The Bell System Technical Journal, Vol. 32, No. 5 (1953), pp. 1245-1256. [2] Dakin, TW, Philofsky, HM, Divens, WC, “Effect of electric discharges on the breakdown of solid insulation”, Transactions of the American Institute of Electrical Engineers, Part 1: Communication and Electronics, Vol.73, No.2(1954), pp.155-162.

[0077] Sample A2, which had a resin layer formed on the anodized oxide film of sample A1, had a dielectric constant that was about 40 to 50% lower. This is thought to be because the moisture adsorbed on the anodized oxide film was desorbed by the heating (thermal curing treatment) during the formation of the resin layer, and the resin layer prevented moisture from penetrating the anodized oxide film.

[0078] Thus, it was found that an insulating film with a low dielectric constant can be formed on an Al-based conductor by forming a resin layer using a high-viscosity varnish or the like on a highly porous anodic oxide film. Based on these results, it is preferable that the dielectric constant of the insulating film be, for example, 5 or less, 4 or less, 3.5 or less, 3 or less, or 2.5 or less.

[0079] (5) Voltage Withstand Characteristics As shown in Table 1, sample A3 had a significantly longer dielectric breakdown life than samples B3, C3, and D, demonstrating high voltage withstand characteristics. The endurance test for sample A3 was terminated because the interrupting current did not exceed 50 mA even after 8,278 minutes (approximately 5.75 days). It was also found that a coating consisting of an anodized oxide film and a resin layer, such as sample A3, exhibited significantly better insulation durability than a single-layer polyimide film, such as sample D. Incidentally, it is believed that sample B3 did not exhibit any insulation properties at all due to cracks in the coating.

[0080] From the above, it has been confirmed that the anodic oxide film according to the present invention has a high porosity and a unique morphology, which contributes to high adhesion to a resin layer, a low (relative) dielectric constant, high withstand voltage characteristics, etc. Such an anodic oxide film is suitable for an insulating film or an underlayer of an Al-based conductor.

[0081] <Segment Conductor> As an example of the coil wire of the present invention, a segment conductor 1 forming an armature coil is shown in FIG.

[0082] The segment conductor 1 is made by coating an Al-based conductor 2, which is a wire rod with a rectangular cross section formed into a substantially U-shape, with an insulating film 3 consisting of the above-mentioned anodic oxide film 31 and resin layer 32. However, each end 12 of the segment conductor 1 is not insulated. Such ends may be formed by masking the Al-based conductor or by immersing it in an electrolyte, or by partially peeling off an insulating film that has already been formed.

[0083] The segment conductors 1 are inserted into slots a of the motor's stator core C. The number of slots that one segment conductor 1 spans and the number of segment conductors inserted into one slot are adjusted by the number of poles of the stator core, the winding method of the coil, etc.

[0084] The end of the segment conductor 1 inserted into the stator core C is joined to the end of another adjacent segment conductor 1. Examples of joining methods include welding by laser irradiation and fusion by resistance heating.

[0085] In this way, a stator S is obtained in which the coil L is provided on the stator core C. A motor equipped with such a stator has a high coil space factor and is lightweight, and its insulating film has a low dielectric constant and a high withstand voltage, so it has low loss, good efficiency, and high reliability.

[0086]

[0087] REFERENCE SIGNS LIST 1 Segment conductor (coil member) 2 Al-based conductor 3 Insulating film 31 Anodic oxide film 32 Resin layer C Stator core L Coil S Stator

Claims

1. A coil member comprising a conductor made of an aluminum base material (referred to as "Al base material") and an insulating film covering at least a portion of the conductor, the insulating film having an anodized film formed on the Al base material, and the anodized film having a porosity of 20-75% as determined by observing the top surface.

2. The coil member according to claim 1, wherein the anodic oxide film has a thickness of 20 to 150 μm.

3. The coil member according to claim 1, wherein said anodic oxide film has a main hole extending in a substantially straight tube shape from said aluminum base side and a sub-hole opening in a part of a side wall of said main hole.

4. A coil member according to claim 3, wherein the main hole has an opening diameter of 50 to 1000 nm.

5. The coil member according to claim 3, wherein at least a portion of said sub-hole penetrates a side wall of said main hole.

6. The coil member according to claim 1, wherein the insulating film further comprises a resin layer on the anodic oxide film.

7. The coil member according to claim 6, wherein the resin layer is thinner than the anodized film.

8. The coil member according to claim 6, wherein said resin layer is made of polyimide, polyamideimide, polyesterimide, epoxy, polyvinylformal, polyurethane or polyester.

9. The coil member according to claim 1, wherein the Al base contains 98 mass % or more of Al based on the entire base.

10. The coil member according to claim 1, which is a segment conductor inserted into a slot in the core.

11. The coil member according to claim 10, wherein the ends of the segment conductors are not insulated.

12. The coil member according to claim 10, wherein the segment conductor has a cross section that is substantially rectangular.

13. A manufacturing method for producing the coil member according to any one of claims 1 to 12, comprising an electrolysis step of passing a current through the Al base material which has been brought into contact with an electrolyte containing phosphoric acid.

14. The method for manufacturing a coil member according to claim 13, further comprising a resin coating step of applying resin onto the anodic oxide film and heating the resin.

15. An armature comprising a coil member according to any one of claims 10 to 12 inserted into a slot in a core.

16. The armature of claim 15, wherein said segment conductors are connected between adjacent ends.

17. The armature of claim 16 which is a stator.

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