Aluminum flat wire three-composite coating process

Abstract

The invention relates to the technical field of aluminum flat wires, and discloses an aluminum flat wire three-composite coating process which comprises the following steps: S1, carrying out surface pretreatment on an aluminum flat wire; s2, the aluminum flat wire is coated with prime paint, the prime paint is modified polyester paint, and first curing treatment is carried out; s3, the bottom-layer coating is coated with a middle-layer coating, the middle-layer coating is heat-resistant polyester paint, and second curing treatment is carried out; and S4, the middle layer coating is coated with a surface layer coating, the surface layer coating is high-weather-resistance polyamide-imide composite paint, and third curing treatment is carried out. Excellent adhesive force is provided through the modified polyester paint at the bottom layer, so that the problem that the aluminum flat wire paint film is easy to crack during bending is solved; the heat-resistant polyester paint in the middle layer improves the voltage resistance of the coating; the high-weather-resistance polyamide-imide composite paint of the surface layer enhances the high temperature resistance, chemical corrosion resistance and weather resistance, so that the comprehensive performance of the coating is remarkably improved, and the high-performance requirement of high-speed machine winding is met.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum flat wires, in particular to a three-composite coating process for aluminum flat wires. Background Art

[0002] In the production of aluminum flat wire, enameled aluminum flat wire serves as a key material for motor windings, and its coating process directly impacts its performance and reliability. Traditionally, the coating process for 200-grade aluminum flat wire utilizes a single-layer coating technique, where an inner layer is coated with a heat-resistant polyester lacquer, and an outer layer is coated with a polyamide-imide lacquer. This process is then baked and cured to produce the 200-grade enameled aluminum flat wire. While this traditional coating process can meet the basic performance requirements of aluminum flat wire to a certain extent, it still has several drawbacks, particularly in terms of coating adhesion, bending resistance, and voltage resistance.

[0003] First, existing coating processes suffer from significant shortcomings in adhesion. Due to the weak bonding between the coating and the aluminum substrate, the coating is prone to cracking when bent or in complex environments. This is particularly true during right-angle bends, where the paint film easily breaks, significantly compromising product performance. Traditional coating processes, in particular, lack sufficient mechanical strength and adhesion for high-speed winding applications, severely impacting the lifespan and electrical performance of the aluminum flat wire.

[0004] Furthermore, the voltage and heat resistance of existing coatings also fail to meet higher standards. Under high temperature and high pressure, conventional coatings on aluminum flat wires can easily lose their original electrical properties and even break down under extreme conditions, impacting the normal operation of the appliance. Furthermore, existing processes have limitations in achieving coating density and weather resistance, resulting in insufficient durability. This is particularly true in humid and high-salt-fog environments, where the coating's protective properties are difficult to maintain over time.

[0005] Based on the above problems, the market performance requirements for coated aluminum flat wires are constantly increasing, especially in high-performance applications of electrical windings, where customers have higher requirements for the adhesion, voltage resistance, heat resistance and weather resistance of the coating.

[0006] Therefore, the present invention proposes a three-composite coating process for aluminum flat wire to solve the shortcomings of the prior art. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention provides a three-composite coating process for aluminum flat wire, which solves the problems of poor paint film adhesion, easy cracking, and insufficient voltage resistance and weather resistance in the existing technology.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A three-composite coating process for aluminum flat wire, comprising the following steps:

[0009] S1. Surface pretreatment of the aluminum flat wire;

[0010] S2. Applying a primer on the aluminum flat wire, wherein the primer is a modified polyester paint, and performing a first curing treatment;

[0011] S3, applying an intermediate layer of paint on the base coating, wherein the intermediate layer of paint is a heat-resistant polyester paint, and performing a second curing treatment;

[0012] S4, applying a topcoat coating on the intermediate coating, wherein the topcoat coating is a highly weather-resistant polyamide-imide composite paint, and performing a third curing treatment;

[0013] The modified polyester paint comprises, by mass, 40 to 60 parts of modified polyester resin, 10 to 20 parts of epoxy resin, 5 to 15 parts of amino resin, 0.5 to 2 parts of surfactant, 1 to 5 parts of nano-silicon dioxide, and 10 to 30 parts of organic solvent;

[0014] The polyamide-imide paint comprises, by mass, 50 to 70 parts of heat-resistant polyester resin, 5 to 15 parts of graphite powder, 2 to 8 parts of calcium fluoride, 1 to 5 parts of zinc oxide, 1 to 3 parts of dispersant, and 10 to 30 parts of organic solvent;

[0015] The high-weather-resistant polyamide-imide paint comprises, by weight, 50-65 parts of polyamide-imide resin, 5-15 parts of polytetrafluoroethylene, 3-10 parts of titanium dioxide, 2-6 parts of nickel-chromium alloy powder, 1-4 parts of rare earth oxide, 0.5-2 parts of nano copper particles, 1-3 parts of hydrophobic additives, and 15-30 parts of organic solvents.

[0016] Preferably, the surface pretreatment of the aluminum flat wire comprises sequentially performing mechanical polishing, alkali cleaning, pickling and hot air drying steps.

[0017] Preferably, the first curing treatment includes four temperature zones, namely 160-280°C, 280-380°C, 380-480°C and 480-520°C, and the treatment time is 2-3 minutes;

[0018] The second curing treatment includes four temperature zones, namely 160-280°C, 280-380°C, 380-480°C and 480-520°C, with a treatment time of 2-3 minutes;

[0019] The third curing treatment includes four temperature zones, which are 160-280° C., 280-380° C., 380-480° C. and 480-520° C., and the treatment time is 2-3 minutes.

[0020] Preferably, the coating of the bottom layer is carried out by felt or dip coating, with a film thickness of 15 to 25 microns;

[0021] The coating of the intermediate layer is carried out in a felt manner, and the coating thickness is 50 to 70 microns;

[0022] The surface layer is coated by atomizing spraying, and the coating thickness is 20 to 30 microns.

[0023] Preferably, after the surface layer is coated, the surface layer is subjected to a high-temperature activation treatment, the temperature of the high-temperature activation is 220 to 260° C., and the time of the high-temperature activation is 2 to 8 minutes.

[0024] Preferably, before coating the intermediate layer, the surface of the bottom layer is subjected to low-pressure plasma treatment, with a treatment frequency of 13.56 MHz, a power of 30 to 100 W, and a treatment time of 20 to 60 seconds.

[0025] Preferably, the hydrophobic additive is nano-silicon particles or fluorosilane-based materials.

[0026] Preferably, the rare earth oxide includes cerium oxide, yttrium oxide or a mixture thereof.

[0027] Preferably, the modified polyester resin is a copolymer of a polyester resin and a polyurethane resin, and the mass ratio of the polyester resin to the polyurethane resin is 4:1 to 2:1.

[0028] Preferably, the heat-resistant polyester resin is a copolymer of a polyester resin and a polyimide resin, and the mass ratio of the polyester resin to the polyimide resin is 5:1 to 3:1.

[0029] The present invention provides a three-composite coating process for aluminum flat wire. It has the following beneficial effects:

[0030] 1. This invention utilizes a synergistically optimized three-composite coating process: a modified polyester basecoat, a heat-resistant polyester middlecoat, and a highly weather-resistant polyamide-imide topcoat. Compared to existing technologies, this coating has improved adhesion and prevents cracking even during small bends or complex right angles. This solves the problem of traditional coatings cracking during bending and effectively meets the requirements of high-speed winding machines.

[0031] 2. This invention utilizes plasma treatment technology to activate the base layer before applying the intermediate layer, enhancing the coating's bond strength. The treated coating achieves a nearly threefold increase in interlayer peel strength and a higher breakdown field strength. Compared to traditional treatment methods, this new approach effectively prevents interlayer peeling and electrical performance degradation, ensuring the coating's reliability in high-voltage environments.

[0032] 3. The present invention uses high temperature to activate the cross-linking reaction during the surface layer curing process to make the structure of the coating more compact. Compared with conventional curing methods, the stability and durability of the coating are significantly improved.

[0033] 4. This invention utilizes a gradient curing design, allowing the base, middle, and top layers to cure layer by layer at different temperatures. This design avoids the problem of residual solvent within the coating, resulting in a denser coating and minimizing porosity. Compared to traditional single-temperature curing schemes, gradient curing effectively reduces micropores in the coating, significantly improving the coating's weather resistance and long-term reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 1 is a flow chart of the coating process of the present invention. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the present specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] In order to better understand the present invention, the above contents are described in detail below in conjunction with specific embodiments.

[0037] Please see the attached Figure 1 , a three-composite coating process for aluminum flat wire, comprising the following steps:

[0038] S1. Surface pretreatment of the aluminum flat wire;

[0039] S2. Applying a primer on the aluminum flat wire, wherein the primer is a modified polyester paint, and performing a first curing treatment;

[0040] S3, applying an intermediate layer of paint on the base coating, wherein the intermediate layer of paint is a heat-resistant polyester paint, and performing a second curing treatment;

[0041] S4, applying a topcoat coating on the intermediate coating, wherein the topcoat coating is a highly weather-resistant polyamide-imide composite paint, and performing a third curing treatment;

[0042] Surface pretreatment of S1 aluminum flat wire

[0043] Mechanical polishing (120-180 mesh grinding wheel), alkali cleaning (5-15wt% NaOH solution, 30-50°C, 30-90 seconds), acid cleaning and neutralization (5-10wt% HNO3 solution, 30-60 seconds), and hot air drying (60-80°C, 5-10 minutes) are carried out in sequence.

[0044] Mechanical polishing: Physical polishing removes the oxide layer, oil stains and micro burrs on the surface of the aluminum flat wire to form a uniformly rough surface, increase the contact area between the coating and the substrate, and improve adhesion.

[0045] Alkali washing: NaOH solution reacts with the aluminum surface to form soluble aluminates, which remove grease and organic pollutants.

[0046] Acid pickling and neutralization: HNO3 neutralizes the residual alkaline substances and forms a dense oxide film (Al2O3) to avoid secondary oxidation and enhance the chemical bonding ability between the substrate and the coating.

[0047] Hot air drying: removes surface moisture to prevent solvent volatilization during coating, which may increase the porosity of the coating.

[0048] For S2 base coating and first curing

[0049] Coating formula: calculated by mass, it includes 40-60 parts of modified polyester resin, 10-20 parts of epoxy resin, 5-15 parts of amino resin, 1-5 parts of nano-silicon dioxide, 0.5-2 parts of surfactant, and 10-30 parts of organic solvent.

[0050] Coating method: Felt, thickness 20-30 microns.

[0051] Curing conditions: 160-280-380-480-520°C, 2-3 minutes.

[0052] Modified polyester resin: Modified polyester resin is a copolymer of polyester resin and polyurethane resin, with the mass ratio of polyester resin to polyurethane resin being 4:1 to 2:1, which enhances adhesion.

[0053] Epoxy resin: Through the cross-linking reaction between the epoxy group and the hydroxyl group of the polyester resin, a three-dimensional network structure is formed, which improves the hardness and solvent resistance of the coating.

[0054] Amino resin: amino groups form coordination bonds with oxygen atoms in the aluminum matrix oxide film to strengthen the interfacial bonding force.

[0055] Nano-silica: As a nano-filler, it fills the micropores in the coating and reduces internal stress concentration; its surface silanol groups form chemical bonds with the resin to inhibit crack propagation.

[0056] Surfactants (such as alkylsiloxanes): reduce the surface tension of the coating, improve wettability, and make the coating evenly cover the surface of the aluminum substrate.

[0057] For S3 intermediate layer coating and second curing

[0058] Coating formula: Calculated by mass, it includes 50-70 parts of heat-resistant polyester resin, 5-15 parts of graphite powder, 2-8 parts of calcium fluoride, 1-5 parts of zinc oxide, 1-3 parts of dispersant, and 10-30 parts of organic solvent.

[0059] Coating method: electrostatic spraying or roller coating, thickness 50-70 microns.

[0060] Curing conditions: 180-200°C, 15-20 minutes.

[0061] Heat-resistant polyester resin: Heat-resistant polyester resin is a copolymer of polyester resin and polyimide resin. The mass ratio of polyester resin to polyimide resin is 5:1 to 3:1, and it maintains structural stability at high temperatures.

[0062] Graphite powder: The lamellar structure forms a heat conduction path in the coating, quickly dissipating local heat (such as Joule heat generated when current is overloaded) and preventing heat accumulation from causing coating cracking.

[0063] Calcium fluoride: high dielectric constant (ε≈8.4) and low dielectric loss, suppresses electric field concentration and increases breakdown voltage (≥5kV).

[0064] Zinc oxide: As a heat stabilizer, it reacts with the acidic groups in the polyester resin to form zinc salts, which delays the thermal decomposition of the resin.

[0065] Dispersant (such as polyvinyl pyrrolidone): prevents graphite powder and calcium fluoride particles from agglomerating through steric hindrance effect, ensuring coating uniformity.

[0066] For S4 topcoat and third curing

[0067] Coating formula: calculated by mass, it includes 50-65 parts of polyamide-imide resin, 5-15 parts of polytetrafluoroethylene, 3-10 parts of titanium dioxide, 2-6 parts of nickel-chromium alloy powder, 1-4 parts of rare earth oxide, 0.5-2 parts of nano copper particles, 1-3 parts of hydrophobic additive, and 15-30 parts of organic solvent.

[0068] Coating method: Felt, thickness 20-30 microns.

[0069] Curing conditions: 160-280-380-480-520°C, 2-3 minutes.

[0070] Post-processing: infrared irradiation (850-1200 nm, 30-60 seconds).

[0071] Polyamide-imide resin: The main chain contains amide bonds and imide rings, forming a conjugated structure at high temperatures, with a heat resistance of up to 220°C (Class C insulation).

[0072] PTFE: imparts hydrophobicity and chemical resistance (acids, alkalis, solvents) to the coating.

[0073] Titanium dioxide: decomposes organic pollutants through photocatalytic effect (self-cleaning function); ultraviolet light absorption prevents resin photoaging.

[0074] Nickel-chromium alloy powder: High infrared reflectivity reduces thermal radiation absorption and acts as a conductive filler to inhibit static electricity accumulation.

[0075] Rare earth oxides (such as CeO2): Oxygen vacancy defects capture free radicals (such as OH), delaying resin oxidation; react with resin decomposition products (such as CO2) at high temperatures to form stable carbonates, repairing coating microcracks.

[0076] Nano-copper particles: release Cu 2+ The ions destroy bacterial cell membranes (antibacterial rate ≥ 99%) and act as catalysts to promote self-repair reactions.

[0077] Hydrophobic additives (such as fluorosilane): form a low surface energy nanostructure on the coating surface to achieve a superhydrophobic effect (anti-fouling and moisture-proof).

[0078] High temperature activation: selectively excites polar groups in the coating, promotes molecular chain rearrangement and cross-linking, and improves density.

[0079] Plasma treatment: High-energy particles bombard the surface to generate oxygen-containing polar groups, thereby enhancing interlayer chemical bonding.

[0080] Example 1:

[0081] Surface preparation:

[0082] Mechanical polishing: using 180-grit grinding wheel, linear speed 20 m / min, pressure 0.3 MPa, the surface roughness after treatment is 1.0 μm;

[0083] Alkaline washing: 10% mass concentration of sodium hydroxide solution, temperature 40 ° C, ultrasonic treatment for 60 seconds;

[0084] Pickling and neutralization: 8% mass concentration nitric acid solution, soak at room temperature for 45 seconds;

[0085] Hot air drying: 70℃ hot air drying for 2 minutes, residual moisture 0.08%.

[0086] Primer coating and first curing:

[0087] Coating formula (mass parts): 50 parts of modified polyester resin (copolymer of polyester resin and polyurethane resin, mass ratio of 3:1), 15 parts of epoxy resin, 10 parts of amino resin, 3 parts of nano-silica, 1 part of alkyl siloxane surfactant, and 20 parts of xylene solvent.

[0088] Coating method: felt, film thickness 25 microns;

[0089] Curing process: 160~280~380~480~520℃, 2~3 minutes.

[0090] Intermediate coating and second curing:

[0091] Plasma pretreatment: frequency 13.56 MHz, power 60 W, treatment time 40 s;

[0092] Coating formula (mass parts): 60 parts of heat-resistant polyester resin (polyester and polyimide copolymer, mass ratio 4:1), 10 parts of graphite powder, 5 parts of calcium fluoride, 3 parts of zinc oxide, 2 parts of polyvinyl pyrrolidone dispersant, and 25 parts of butanone solvent.

[0093] Coating method: felt, film thickness 60 microns;

[0094] Curing process: 160~280~380~480~520℃, 2~3 minutes.

[0095] Topcoat and third curing:

[0096] Coating formula (mass parts): 60 parts of polyamide-imide resin, 10 parts of polytetrafluoroethylene, 5 parts of titanium dioxide, 4 parts of nickel-chromium alloy powder (80% nickel, 20% chromium), 3 parts of cerium oxide, 1 part of nano-copper particle, 2 parts of fluorosilane hydrophobic additive, and 25 parts of N-methylpyrrolidone solvent.

[0097] Coating method: felt, film thickness 25 microns;

[0098] Curing process: 160-280-380-480-520℃, 2-3 minutes;

[0099] High temperature activation: temperature is 220℃, time is 2 minutes.

[0100] Example 2:

[0101] Surface preparation:

[0102] Mechanical polishing: 180-grit grinding wheel, linear speed 18 m / min, pressure 0.4 MPa, surface roughness 0.9 μm;

[0103] Alkali washing: 8% sodium hydroxide solution, temperature 45 ° C, ultrasonic treatment for 50 seconds;

[0104] Pickling and neutralization: 7% mass concentration nitric acid solution, soak at room temperature for 50 seconds;

[0105] Hot air drying: 75℃ hot air drying for 7 minutes, residual moisture 0.05%.

[0106] Primer coating and first curing:

[0107] Coating formula (mass parts): modified polyester resin (polyester and polyurethane copolymer, mass ratio 3.5:1) 45 parts, epoxy resin 12 parts, amino resin 8 parts, nano-silica 2 parts, alkyl siloxane surfactant 0.8 parts, xylene solvent 18 parts.

[0108] Coating method: dip coating, pulling speed 0.8 m / min, wet film thickness 28 μm;

[0109] Curing process: heating at 165℃ for 14 minutes.

[0110] Intermediate coating and second curing:

[0111] Plasma pretreatment: frequency 13.56 MHz, power 80 W, treatment time 30 seconds;

[0112] Coating formula (mass parts): 55 parts of heat-resistant polyester resin (polyester and polyimide copolymer, mass ratio 3.5:1), 8 parts of graphite powder (particle size 3 microns), 6 parts of calcium fluoride, 2 parts of zinc oxide, 1.5 parts of polyvinyl pyrrolidone dispersant, and 20 parts of cyclohexanone solvent.

[0113] Coating method: electrostatic spraying, voltage 75 kV, wet film thickness 55 μm;

[0114] Curing process: heating at 195℃ for 16 minutes.

[0115] Topcoat and third curing:

[0116] Coating formula (mass parts): 58 parts of polyamide-imide resin, 8 parts of polytetrafluoroethylene, 6 parts of titanium dioxide, 3 parts of nickel-chromium alloy powder (80% nickel, 20% chromium), 2 parts of cerium oxide, 1.5 parts of nano-copper particles, 1.8 parts of fluorosilane hydrophobic additive, and 22 parts of N-methylpyrrolidone solvent.

[0117] Coating method: atomized spray, atomizing pressure 0.7 MPa, wet film thickness 28 microns;

[0118] Curing process: heating at 215℃ for 12 minutes;

[0119] High temperature activation: temperature is 260℃, time is 8 minutes.

[0120] Example 3:

[0121] Surface preparation:

[0122] Mechanical polishing: 180-grit grinding wheel, linear speed 22 m / min, pressure 0.35 MPa, surface roughness 1.1 μm;

[0123] Alkaline washing: 12% sodium hydroxide solution, temperature 35°C, ultrasonic treatment for 70 seconds;

[0124] Pickling and neutralization: 9% mass concentration nitric acid solution, soak at room temperature for 40 seconds;

[0125] Hot air drying: 65℃ hot air drying for 9 minutes, residual moisture 0.06%.

[0126] Primer coating and first curing:

[0127] Coating formula (mass parts): 55 parts of modified polyester resin (polyester and polyurethane copolymer, mass ratio 2.5:1), 18 parts of epoxy resin, 12 parts of amino resin, 4 parts of nano-silica, 1.2 parts of alkyl siloxane surfactant, and 25 parts of xylene solvent.

[0128] Coating method: felt, film thickness 22 microns;

[0129] Curing process: The heating area is divided into four zones, with temperatures of 160-280-380-480-520°C and a curing time of 2-3 minutes.

[0130] Intermediate coating and second curing:

[0131] Plasma pretreatment: frequency 13.56 MHz, power 40 W, treatment time 50 s;

[0132] Coating formula (mass parts): 65 parts of heat-resistant polyester resin (polyester and polyimide copolymer, mass ratio 2.8:1); 12 parts of graphite powder (particle size 8 microns); 4 parts of calcium fluoride; 4 parts of zinc oxide; 2.5 parts of polyvinyl pyrrolidone dispersant; 28 parts of butanone solvent.

[0133] Coating method: felt, film thickness 65 microns;

[0134] Curing process: The heating area is divided into four zones with temperatures of 160-280-380-480-520°C and the curing time is 2-3 minutes.

[0135] Topcoat and third curing:

[0136] Coating formula (mass parts): 62 parts of polyamide-imide resin, 12 parts of polytetrafluoroethylene, 8 parts of titanium dioxide, 5 parts of nickel-chromium alloy powder (80% nickel, 20% chromium), 2.5 parts of cerium oxide, 1.8 parts of nano-copper particles, 2.2 parts of fluorocarbon-modified silane hydrophobic agent, and 28 parts of N-methylpyrrolidone solvent.

[0137] Coating method: felt, film thickness 22 microns;

[0138] Curing process: The heating area is divided into four zones with temperatures of 160-280-380-480-520°C and a curing time of 2-3 minutes;

[0139] High temperature activation: temperature is 230℃, time is 4 minutes.

[0140] Comparative Example 1:

[0141] Compared with Example 1, the difference is that: modified polyester resin (polyester / polyurethane copolymer) is not used in the primer, but ordinary polyester resin (not copolymerized with polyurethane) is used instead, and the other components and process conditions are the same.

[0142] Comparative Example 2:

[0143] Compared with Example 2, the difference is that after the coating of the surface layer, the surface layer is not subjected to infrared radiation activation treatment, and the other components and process conditions are the same.

[0144] Comparative Example 3:

[0145] Compared with Example 3, the difference is that the surface of the bottom layer is subjected to low-pressure plasma treatment before coating the intermediate layer, and the other components and process conditions are the same.

[0146] Experiment 1: Adhesion and right-angle bending test

[0147] Implementation steps:

[0148] Sample preparation:

[0149] Substrate selection and processing: Six standard aluminum flat wire samples (cross-sectional dimensions 2 mm × 10 mm, length 200 mm) were selected, and the six standard aluminum flat wire samples were numbered S1 to S6.

[0150] Coating preparation and application:

[0151] Samples numbered S1 to S3 were coated according to the coating process of Example 1;

[0152] Samples numbered S4 to S6 were coated according to the coating process of Comparative Example 1;

[0153] Six standard aluminum flat wire samples numbered S1 to S6 were cured at room temperature for 24 hours.

[0154] Test method and test frequency:

[0155] Right-angle bending test (IEC61189-3):

[0156] Each aluminum flat wire sample was bent 180° around a cylinder with a diameter of 5 mm;

[0157] The crack density (bars / cm) was observed with a 50x magnifying glass. Each sample was tested three times and the crack density (bars / cm) and crack morphology were recorded.

[0158] The experimental results are shown in Table 1:

[0159] Table 1: Right-angle bending test data

[0160]

[0161]

[0162] The aluminum flat wire coating of Example 1 demonstrated significant advantages in right-angle bend testing. The average crack density in Comparative Example 1 reached 23.3 cracks / cm, with a maximum of 29 cracks / cm. The crack morphology was complex, exhibiting radial branching or a network-like distribution. This failure mode stems from the inability of conventional polyester resins to form hydrogen bonds, resulting in weak interfacial bonding and stress concentration at the coating-substrate interface, leading to rapid crack propagation. For example, the network of cracks in Sample 5 covered the entire surface, indicating that the coating experienced overall brittle fracture during bending.

[0163] The modified polyester resin in Example 1 disperses bending stress through a copolymer of polyester resin and polyurethane resin. The short cracks (<1 mm) in Sample 1 showed no branching, indicating that the cracks were blocked or deflected by the nano-silica (20-40 nm) during propagation. The microcracks at the edges of Sample 3 did not penetrate the coating, further demonstrating the improved toughness of the modified resin.

[0164] Experiment 2: Test on the effect of infrared radiation on the bending performance of the surface layer

[0165] Implementation steps:

[0166] Sample preparation:

[0167] Substrate selection and processing: Six standard aluminum flat wire samples (cross-section 2mm×10mm, length 200mm) were selected and numbered C1 to C6.

[0168] Coating application:

[0169] Samples numbered C1 to C3 were coated according to the coating process of Example 2;

[0170] Samples numbered C4 to C6 were coated according to the coating process of Comparative Example 2;

[0171] Six standard aluminum flat wire samples numbered C1 to C6 were cured at room temperature for 24 hours.

[0172] Test method:

[0173] Right-angle bending test (IEC61189-3):

[0174] Each aluminum flat wire sample was bent 180° around a 5mm diameter cylinder, and the crack density (cracks / cm) was observed with a 50x magnifying glass. Each sample was tested three times and the crack morphology was recorded.

[0175] The experimental results are shown in Table 2:

[0176] Table 2: Right-angle bending test data

[0177]

[0178]

[0179] The infrared irradiation process of Example 2 significantly improves the bending resistance of the surface coating. The average crack density of Comparative Example 2 (non-irradiated) is 20 / cm, and the highest is 24 / cm. The crack morphology is mainly network and radial branches. Actual observations found that there are micropores (2-5μm) inside the non-irradiated coating. When bending, stress is concentrated at the edge of the pores, causing multiple cracks. For example, the network cracks of sample C5 are accompanied by local blistering, indicating that the resin is not completely cross-linked and the residual gas causes a loose structure.

[0180] High-temperature activation increased the crosslink density of the surface layer from 65% to 82%, resulting in a denser resin network. Sample C1 from Example 2 exhibited only short, straight cracks (1-2 mm), which were blocked when they reached the nickel-chromium alloy particles. The branching cracks at the ends of sample C3 were altered by the directional alignment of the alloy particles (guided by the infrared thermal field), which altered the stress transmission path.

[0181] Data fluctuations reflect process sensitivity. The longitudinal cracks (17 cracks / cm) of sample C6 in comparative example 2 are related to the spraying direction. The resin flow leads to local filler enrichment, which temporarily delays crack propagation. The 4 cracks / cm of sample C2 in Example 2 correspond to the uniformly irradiated area, while the 6 cracks / cm of C3 are due to uneven crosslinking due to local temperature deviation (±5°C). Irradiation parameters (such as wavelength stability and temperature uniformity) need to be optimized in actual production, but existing data have clearly demonstrated the key role of infrared irradiation in improving performance.

[0182] Experiment 3: Breakdown Field Strength Measurement

[0183] Implementation steps:

[0184] Sample preparation:

[0185] Substrate selection and processing: Six standard aluminum flat wire samples (cross-sectional dimensions of 2 mm × 10 mm, length of 200 mm) were selected. The six standard aluminum flat wire samples were numbered D1 to D6.

[0186] Coating preparation and application:

[0187] Samples numbered D1 to D3 were coated according to the coating process of Example 3;

[0188] Samples numbered D4 to D6 were coated according to the coating process of Comparative Example 3;

[0189] Six standard aluminum flat wire samples numbered D1 to D6 were cured at room temperature for 24 hours.

[0190] Test method:

[0191] Breakdown field strength test (IEC60243-1):

[0192] The electrode spacing is 1 mm, and the voltage rise rate is 500 V / s;

[0193] The breakdown voltage (kV / mm) was recorded after each sample was tested three times;

[0194] SEM was used to observe the morphology of the breakdown point and analyze the failure mode.

[0195] The experimental results are shown in Table 3:

[0196] Table 3: Breakdown field strength test data

[0197]

[0198]

[0199] The samples in Comparative Example 3, which did not undergo plasma treatment, had an average breakdown field strength of only 3.0 kV / mm, significantly lower than the 6.4 kV / mm in Example 3. Their failure modes were directly related to interfacial defects: Sample D4 suffered from residual bubbles (50 μm in diameter) between the layers, leading to electric field concentration and a breakdown path extending along the bubble's edge; while Sample D5 suffered from insufficient bonding between the intermediate and underlying layers, leading to a breakdown of insulation performance after delamination. A weak interface formed between the untreated aluminum surface oxide layer and the intermediate resin layer, allowing the arc to preferentially propagate along this interface during breakdown (as seen in D6, where the crack extended to the interface).

[0200] The plasma treatment in Example 3 removed surface contaminants through argon ion bombardment, improving the aluminum substrate roughness (Ra) from 0.8 μm to 1.2 μm and increasing the resin penetration and anchoring depth by 50%. The intermediate layer and the underlying layer formed chemical bonds (hydrogen bonds and van der Waals forces), and the diameter of the interfacial bubbles was controlled to within 3 μm. Although sample D1 experienced micropore breakdown due to localized enrichment of expanded graphite (carbon content deviation ±8%), the breakdown field strength still reached 6.3 kV / mm, far exceeding that of Comparative Example 3.

[0201] Data fluctuations reflect process sensitivity. The slightly higher breakdown field strength of D6 in Comparative Example 3 (3.2kV / mm) may be due to accidental good interface contact, but it cannot change the overall degradation trend; the carbonization of D2 edge in Example 3 (6.7kV / mm) is related to the coating thickness deviation (±2μm), and the spraying uniformity needs to be optimized. In actual production, although plasma treatment increases costs (about 0.5 yuan / piece), the breakdown performance is improved by 113%, which can avoid the risk of batch recalls due to insulation failure of motor windings.

[0202] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A three-composite coating process for aluminum flat wire, characterized in that: The following steps are involved: S1. Surface pretreatment of the aluminum flat wire; S2. Applying a primer on the aluminum flat wire, wherein the primer is a modified polyester paint, and performing a first curing treatment; S3, applying an intermediate layer of paint on the base coating, wherein the intermediate layer of paint is a heat-resistant polyester paint, and performing a second curing treatment; S4, applying a topcoat coating on the intermediate coating, wherein the topcoat coating is a highly weather-resistant polyamide-imide composite paint, and performing a third curing treatment; The modified polyester paint comprises, by mass, 40 to 60 parts of modified polyester resin, 10 to 20 parts of epoxy resin, 5 to 15 parts of amino resin, 0.5 to 2 parts of surfactant, 1 to 5 parts of nano-silicon dioxide, and 10 to 30 parts of organic solvent; The heat-resistant polyester paint comprises, by mass, 50 to 70 parts of heat-resistant polyester resin, 5 to 15 parts of graphite powder, 2 to 8 parts of calcium fluoride, 1 to 5 parts of zinc oxide, 1 to 3 parts of dispersant, and 10 to 30 parts of organic solvent; The high-weather-resistant polyamide-imide paint comprises, by weight, 50-65 parts of polyamide-imide resin, 5-15 parts of polytetrafluoroethylene, 3-10 parts of titanium dioxide, 2-6 parts of nickel-chromium alloy powder, 1-4 parts of rare earth oxide, 0.5-2 parts of nano copper particles, 1-3 parts of hydrophobic additives, and 15-30 parts of organic solvents.

2. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The surface pretreatment of the aluminum flat wire comprises the steps of mechanical polishing, alkali cleaning, pickling and hot air drying in sequence.

3. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The first curing treatment includes four temperature zones, namely 160-280°C, 280-380°C, 380-480°C and 480-520°C, with a treatment time of 2-3 minutes; The second curing treatment includes four temperature zones, namely 160-280°C, 280-380°C, 380-480°C and 480-520°C, with a treatment time of 2-3 minutes; The third curing treatment includes four temperature zones, which are 160-280° C., 280-380° C., 380-480° C. and 480-520° C., and the treatment time is 2-3 minutes.

4. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The bottom layer is coated by felt or dip coating, with a film thickness of 15 to 25 microns; The coating of the intermediate layer is carried out in a felt manner, and the coating thickness is 50 to 70 microns; The surface layer is coated by atomizing spraying, and the coating thickness is 20 to 30 microns.

5. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: After the surface layer is coated, the surface layer is subjected to a high-temperature activation treatment, wherein the temperature of the high-temperature activation is 220 to 260° C., and the time of the high-temperature activation is 2 to 8 minutes.

6. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: Before coating the intermediate layer, the surface of the bottom layer is subjected to low-pressure plasma treatment, with a treatment frequency of 13.56 MHz, a power of 30 to 100 W, and a treatment time of 20 to 60 seconds.

7. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The hydrophobic additive is nano-silicon particles or fluorosilane-based materials.

8. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The rare earth oxide includes cerium oxide, yttrium oxide or a mixture thereof.

9. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The modified polyester resin is a copolymer of a polyester resin and a polyurethane resin, and the mass ratio of the polyester resin to the polyurethane resin is 4:1 to 2:

1.

10. The three-composite coating process for aluminum flat wire according to claim 1, characterized in that: The heat-resistant polyester resin is a copolymer of a polyester resin and a polyimide resin, and the mass ratio of the polyester resin to the polyimide resin is 5:1 to 3:1.

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