Copper wire with antioxidant protective film on surface and preparation method thereof

Abstract

The invention discloses a copper wire with an anti-oxidation protective film on the surface and a preparation method of the copper wire, and belongs to the technical field of copper wire surface protection treatment. The preparation method provided by the invention comprises the following steps: carrying out acid treatment, water washing and drying on a copper wire to obtain a pretreated copper wire; soaking the pretreated copper conductor in a polyamide acid solution to obtain a pre-coated copper conductor; and performing water spraying or water vapor treatment on the pre-coated copper conductor, and drying to obtain the copper conductor of which the surface is provided with the antioxidant protective film. The method is simple in process and low in cost, the obtained protective film is easy to remove, the oxidation resistance of the copper wire can be remarkably improved, meanwhile, the film has the reversible dissolution characteristic and can be rapidly and thoroughly removed through short-time soaking of absolute ethyl alcohol, the removal process is mild, a copper wire base body is not damaged, and the service life of the copper wire is prolonged. The method is especially suitable for temporary anti-oxidation protection requirements of copper wires in links of production circulation, storage and transportation and the like.

Description

Technical Field

[0001] This invention relates to the field of copper conductor surface protection treatment technology, and particularly to a copper conductor with an antioxidant protective film on its surface and its preparation method. Background Technology

[0002] Copper conductors, with their excellent electrical and thermal conductivity, are widely used in power transmission, electronic devices, communication cables, and automotive wiring harnesses, making them an indispensable basic material in modern electrical systems. However, copper is prone to oxidation and corrosion in natural environments, especially under conditions of high humidity and corrosive media containing sulfides or salt spray. In these conditions, copper oxide and basic copper carbonate rapidly form on the copper surface. This corrosion layer not only darkens the surface color and deteriorates the appearance of the copper conductor, but more importantly, it significantly increases contact resistance, leading to a series of problems such as reduced power transmission efficiency, localized overheating, decreased connection reliability, and signal transmission distortion. In marine environments, chemical plants, or under high temperature and humidity conditions, the corrosion rate of copper conductors accelerates further, severely limiting their service life and threatening the operational safety and stability of the entire electrical system.

[0003] To inhibit the oxidation and corrosion of copper conductors, various surface protection methods have been developed, mainly including metal plating protection, organic coating protection, and chemical passivation. While metal plating, such as tin, silver, and nickel plating, provides good protection, the processes involve electroplating or chemical plating, requiring significant equipment investment and energy consumption. Furthermore, controlling the plating thickness is difficult, potentially negatively impacting subsequent welding or drawing processes. Organic coating protection typically involves dipping or spraying to form a polymer protective film on the copper surface. However, most existing organic coating materials are thermosetting resins, requiring high-temperature curing. This not only results in long processing cycles and high energy consumption but also risks softening or oxidizing the copper substrate during the high-temperature treatment, affecting its mechanical and electrical properties. In addition, some organic protective coatings have insufficient adhesion to the copper substrate, easily leading to defects such as peeling and blistering during storage or transportation, resulting in unstable protective effects.

[0004] Furthermore, the requirements for oxidation protection of copper conductors vary across different stages. In long-term service environments, the protective layer must possess durability and weather resistance; however, during short-term processes such as production, storage, and transportation, the required protective layer only needs to function for several weeks to months and must be easily and thoroughly removable before subsequent processing. However, existing protective technologies often struggle to balance short-term protection with ease of removal. For example, while some coatings offer good protection, removal requires strong acids, strong alkalis, or high-temperature decomposition, resulting in harsh operating conditions that can cause secondary damage to the copper substrate and create environmental burdens such as wastewater treatment. Other methods, due to their thin protective layers or insufficient adhesion, fail to provide adequate protection under conditions of humidity, heat, and salt spray.

[0005] In summary, existing copper conductor surface anti-oxidation protection technologies still have many shortcomings in terms of process complexity, production cost, protective performance, and coating removability. There is an urgent need to develop a short-term anti-oxidation protection method that is simple in process, low in energy consumption, has good protective effect, and does not affect subsequent processing, so as to meet the actual application needs of copper conductors in the production process. Summary of the Invention

[0006] In view of this, the present invention provides a copper wire with an antioxidant protective film on its surface and a method for preparing the same. The present invention uses polyamic acid solution immersion coating combined with water spraying or steam treatment, omitting the traditional high-temperature imidization step. The process is simple and low-cost, and the resulting protective film is easy to remove, significantly improving the antioxidant performance of the copper wire.

[0007] In a first aspect, the present invention provides a method for preparing a copper conductor with an antioxidant protective film on its surface, comprising the following steps: Pretreated copper wires are obtained by acid treatment, water washing and drying. Pre-treated copper wires are immersed in a polyamic acid solution to obtain pre-coated copper wires; The copper wire with an antioxidant protective film on its surface is obtained by spraying or steaming the pre-coated copper wire with water and then drying it.

[0008] Optionally, the acid treatment is carried out by spraying with a dilute nitric acid solution or a mixed acetic acid-hydrogen peroxide solution; the mass concentration of the dilute nitric acid solution is 3%~20%, and the mass concentration of acetic acid in the mixed acetic acid-hydrogen peroxide solution is 5%~30% and the mass concentration of hydrogen peroxide is 1%~5%.

[0009] Furthermore, the spraying time using dilute nitric acid solution or acetic acid-hydrogen peroxide mixture is 10~180s.

[0010] Optionally, the solvent for the polyamic acid solution is at least one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0011] Optionally, the concentration of the polyamic acid solution is 1~30wt%.

[0012] Optionally, the polyamic acid is prepared by polycondensation reaction of dianhydride monomer and diamine monomer; the dianhydride monomer is selected from at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride; the diamine monomer is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, and 4,4'-diaminodicyclohexylmethane.

[0013] Optionally, the soaking time is 1 to 1000 seconds.

[0014] Optionally, the water temperature used in the water spraying step is 10~40℃, and the water steam treatment temperature is 100~150℃.

[0015] Optionally, the water spray or steam treatment time is 1~600s.

[0016] Secondly, the present invention provides a copper wire with an antioxidant protective film on its surface, which is prepared by the above-described preparation method.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The present invention adopts a process route of immersion in polyamic acid solution combined with water spraying or steam treatment, with solvent displacement-induced physical nucleation precipitation as the core film formation mechanism. Compared with the traditional polyimide coating which requires long-term heat treatment at above 300°C, the method of the present invention can complete film formation in the range of room temperature to 150°C, which significantly reduces energy consumption and equipment requirements, shortens the process flow, and avoids potential damage such as softening and oxidation to the copper conductor substrate caused by high-temperature treatment.

[0018] (2) The protective film formed by the present invention is mainly composed of polyamic acid aggregates, which form a stable structure only through intermolecular hydrogen bonding. There is no irreversible imidization or cross-linking reaction. Therefore, it has both excellent protective performance and convenient removability. On the one hand, the film can effectively block oxygen and moisture, and provide good short-term antioxidant protection for copper wires in a humid and hot environment, meeting the protection needs in the production, storage and transportation process. On the other hand, the film can be quickly and thoroughly removed by short-term soaking and swelling with anhydrous ethanol and gentle wiping. The removal process is gentle, non-corrosive and does not damage the copper wire substrate. It does not affect subsequent welding, drawing and other processing steps, solving the problem that existing protective technologies cannot balance protective effect and easy removal.

[0019] (3) The process steps of the present invention are simple, can be adapted to continuous production lines, have strong controllability of process parameters, stable film quality, low raw material cost, and no high-pollution waste liquid is generated, thus having excellent prospects for industrial-scale application. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1This is a macroscopic image of the copper conductor with an antioxidant protective film on its surface obtained in Embodiment 1 of the present invention; Figure 2 This is a metallographic photograph of the surface protective film of the copper wire with an antioxidant protective film on its surface obtained in Embodiment 1 of the present invention; Figure 3 This is a macroscopic image of the copper conductor with an antioxidant protective film on its surface obtained in Embodiment 2 of the present invention; Figure 4 This is a macroscopic image of the copper conductor with an antioxidant protective film on its surface obtained in Embodiment 4 of the present invention. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] This invention discloses a method for preparing a copper wire with an antioxidant protective film on its surface, comprising the following steps: Pretreated copper wires are obtained by acid treatment, water washing and drying. The pretreated copper wires are immersed in a polyamic acid solution to obtain pre-coated copper wires. The pre-coated copper wire is treated with water spray or steam and then dried to obtain a copper wire with an antioxidant protective film on its surface.

[0024] In the above technical solution of the present invention, the purpose of acid treatment is to remove the naturally formed oxide layer and oil stains and other contaminants on the surface of the copper conductor, and at the same time to form a micro-rough structure or active sites on the copper surface to enhance the wettability and adhesion of the subsequent polyamic acid solution.

[0025] In the above-mentioned technical solution of the present invention, the core purpose of acid treatment is: first, to thoroughly remove the naturally formed oxide layer (CuO, Cu2O), oil, fingerprints and other environmental pollutants on the surface of the copper conductor, exposing a fresh and highly active copper substrate surface; second, to perform gentle and uniform micro-etching on the copper surface to form a nanoscale rough structure, thereby improving the wettability and spreadability of the subsequent polyamic acid solution on the copper surface and enhancing the interfacial adhesion between the protective film and the substrate; and third, to strictly control the degree of corrosion to avoid excessive corrosion leading to a decrease in the dimensional accuracy of the copper substrate and a deterioration in its mechanical properties, while also preventing the occurrence of surface passivation and ensuring the quality of subsequent film formation.

[0026] This invention employs a spray method to apply the acidic medium during acid treatment, avoiding excessive corrosion caused by immersion treatment while ensuring uniform treatment. The preferred acidic medium systems are as follows, which can be flexibly selected based on the diameter, precision requirements, and application scenario of the copper wire: Dilute nitric acid system: A general pretreatment method suitable for copper wires with a conventional diameter (above 0.5 mm), balancing oxidation removal efficiency and micro-etching effect. The mass concentration of the dilute nitric acid solution is 3%~20%, more preferably 5%~15%; the spraying time is 10s~120s, more preferably 20s~60s. Dilute nitric acid within this concentration range can rapidly react chemically with the oxides on the copper surface, thoroughly removing the original oxide layer, while simultaneously performing gentle and uniform micro-etching on the copper substrate, forming a controllable micro-rough interface. This avoids the problem of rapid passivation of the copper surface caused by high-concentration nitric acid, and also avoids the defects of insufficient oxidation removal and low treatment efficiency caused by excessively low concentrations.

[0027] A mild acetic acid-hydrogen peroxide system is suitable for the pretreatment of fine-diameter (0.05mm~0.5mm) high-precision copper wires, with no risk of over-corrosion and superior surface activity. In the mixed solution, the mass concentration of acetic acid is 5%~30%, more preferably 10%~25%; the mass concentration of hydrogen peroxide is 1%~5%, more preferably 2%~4%; and the spraying time is 30~180s, more preferably 60s~120s. In this system, hydrogen peroxide oxidizes trace amounts of elemental copper on the copper surface into copper oxide, which readily reacts with acetic acid. Acetic acid then reacts with copper oxide and cuprous oxide to form water-soluble copper acetate, achieving a mild and thorough removal of the oxide layer. The entire process is free of strong corrosion and passivation effects, and will not damage the mechanical properties of fine-diameter copper wires. The treated copper surface exhibits high activity, and the polyamic acid solution provides excellent wettability.

[0028] After acid treatment, the copper conductors are immediately rinsed thoroughly with deionized water to completely remove any residual acidic media and reaction products from the surface. This prevents residual acid from causing continuous corrosion to the copper substrate or interfering with the subsequent polyamic acid film formation process. After rinsing, the surface moisture of the copper conductors is quickly dried with clean, high-pressure dry air to obtain clean, highly active pretreated copper conductors. This prevents residual moisture from diluting the polyamic acid solution and affecting the uniformity and adhesion of the coating.

[0029] In this invention, the concentration of the polyamic acid solution affects the thickness and uniformity of the coating: if the concentration is too low, the amount of polyamic acid adhering per unit area is insufficient, resulting in a thin film that is difficult to provide adequate antioxidant protection; if the concentration is too high, the solution viscosity is too high, resulting in poor fluidity and easily leading to uneven coating thickness or surface run marks. In this invention, the concentration of the polyamic acid solution can be selected from 1 to 30 wt%, further from 5 to 20 wt%, and even further from 8 to 18 wt%, for example 10 wt%, 12 wt%, and 15 wt%. The solvent of the polyamic acid solution must be able to completely dissolve the polyamic acid and have no corrosive effect on the copper substrate, while having a suitable evaporation rate to ensure the stability of the solution during immersion. Optional solvents include at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), and dimethyl sulfoxide (DMSO). These solvents are all good solvents for polyamic acid and are miscible with water, which is beneficial for rapid solvent diffusion during subsequent water treatment.

[0030] In this invention, polyamic acid can be prepared by polycondensation of dianhydride monomers and diamine monomers. Different monomer combinations affect the molecular weight, chain rigidity, and final film density and adhesion of the polyamic acid. The dianhydride monomer can be selected from at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride; the diamine monomer can be selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, and 4,4'-diaminodicyclohexylmethane. For example, polyamic acid obtained by polycondensation of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether has high molecular chain regularity and good film density after formation. Using monomer combinations containing flexible ether bonds can improve the flexibility of the film and adapt to the bending requirements of copper wires. In practical applications, a suitable monomer combination can be selected according to the protection requirements and subsequent processing requirements.

[0031] The immersion time of the pretreated copper wires in the polyamic acid solution must ensure that the polyamic acid is fully adsorbed on the copper surface and reaches an appropriate adhesion amount. If the immersion time is too short, adsorption will be insufficient, resulting in a thin or discontinuous coating; if the immersion time is too long, production efficiency will decrease, and an excessively thick coating is prone to stress cracking or peeling during water treatment. Immersion times can be selected from 1 to 1000 seconds, further options include 10 to 300 seconds, and even further options include 20 to 120 seconds, such as 30 seconds, 60 seconds, and 90 seconds. After immersion, the copper wires can be removed from the solution, and excess solution can be drained appropriately; no further cleaning is required.

[0032] In this invention, the core function of water spraying or steam treatment is that water is a poor solvent for polyamic acid, but it is infinitely miscible with organic solvents in the coating (such as N,N-dimethylformamide, N-methylpyrrolidone, etc.). When water comes into contact with the polyamic acid coating, it will rapidly diffuse in both directions, replacing the organic solvent in the coating. This causes the polyamic acid molecular chains to experience a sudden drop in solubility due to the abrupt change in the solvent system, leading to their shrinkage, aggregation, and in-situ precipitation, forming a white solid aggregate that is insoluble in water. This solvent-displacement-induced physical nucleation precipitation is the dominant mechanism for the formation of the white film. Meanwhile, water molecules undergo limited hydrolysis with the residual anhydride groups at the ends of the polyamic acid molecular chains to generate free carboxylic acids. The newly generated free carboxylic acids can provide more hydrogen bonding sites, strengthen the hydrogen bonding association between polyamic acid molecular chains, further improve the structural compactness of the precipitated aggregates, and avoid pinholes and cracking defects during film drying. The free carboxylic acids generated by hydrolysis can also undergo acidolysis with the trace amounts of cuprous oxide and copper oxide remaining on the copper conductor surface after acid washing, removing the residual oxide layer in situ, achieving secondary cleaning of the copper surface, and improving the interfacial adhesion between the film and the copper substrate.

[0033] Room temperature water spraying mainly relies on physical nucleation through solvent replacement, resulting in a mild film formation process and easy control over film thickness uniformity, making it suitable for continuous production lines. High temperature steam treatment, on the other hand, significantly accelerates the bidirectional diffusion rate and the reaction kinetics of limited hydrolysis based on solvent replacement, leading to faster film formation and higher film density. Furthermore, the high temperature environment can further enhance the acidolysis reaction efficiency of carboxylic acids and copper oxides.

[0034] Water spraying treatment uses room temperature water, with a selectable temperature range of 10~40℃, and further selectable ranges of 15~30℃, such as 20℃ or 25℃. Room temperature water spraying is suitable for continuous production lines with high production efficiency requirements or where high temperatures are not advisable. Steam treatment uses a high temperature steam environment, with a selectable temperature range of 100~150℃, and further selectable ranges of 110~140℃, such as 120℃ or 130℃. The high temperature steam environment can significantly accelerate the bidirectional diffusion rate of water molecules and good solvents, shorten the phase separation and film formation time, and promote the formation of hydrogen bond networks between polyamic acid molecular chains, resulting in films with higher density and better protective performance. The water spraying or steam treatment time needs to be controlled in conjunction with the polyamic acid solution concentration, coating thickness, and treatment temperature: if the treatment time is too short, the solvent replacement is insufficient, the polyamic acid phase separation is incomplete, the film is discontinuous and lacks density, and the protective effect cannot meet the standard; if the treatment time is too long, the precipitated film may be washed away by the continuous water flow, or the structure may become loose due to excessive water absorption, affecting the protective performance and adhesion. The treatment time can be selected from 1 to 600 s, further selected from 1 to 60 s, and even further selected from 5 to 30 s, for example 10 s, 15 s, 20 s. The short-time steam treatment conditions of 100 to 150 ℃ used in this invention cannot reach the reaction activation energy of polyamic acid ring-closed imidization, and irreversible imidization reaction will not occur. The main body of the film is still polyamic acid aggregate, and the characteristic of convenient subsequent removal is fully preserved.

[0035] The present invention does not impose special restrictions on the drying method after water spraying or steam treatment. For example, it can be air-dried or dried at low temperature. Specifically, it can be dried at 20~40℃ to obtain copper wires with an anti-oxidation protective film on the surface.

[0036] The present invention does not impose any special limitation on the diameter of the copper conductor, which may be, for example, 0.1mm, 0.2mm, 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.8mm, 2.0mm, 2.5mm, 3.0mm, 4.0mm, 5.0mm, 6.0mm, 8.0mm, 10.0mm, or 12.0mm, including but not limited to the examples mentioned above.

[0037] This invention also provides a copper conductor with an antioxidant protective film on its surface, prepared by the above-described method. The copper conductor is coated with a dense white film, the main component of which is a polyamic acid aggregate linked by hydrogen bonds. Its chemical structure differs from that of polyimide; it has not undergone high-temperature imidization ring closure and lacks an irreversible covalent cross-linked structure. The film thickness can be controlled by adjusting the polyamic acid concentration, immersion time, and water treatment conditions, and can be selected from 0.1 to 10 μm, more preferably from 0.5 to 5 μm, for example, 1 μm or 2 μm. The film is white in appearance, bonds well to the copper substrate, and effectively blocks oxygen, moisture, and corrosive media, providing excellent short-term antioxidant protection for the copper conductor in humid and hot environments, salt spray conditions, or industrial atmospheres. Meanwhile, the film exhibits excellent removability: immersing the copper conductor coated with the film in ethanol for 5-120 seconds causes the film to swell or partially dissolve, allowing for complete removal with a cloth or non-woven fabric. The removal process is gentle, does not damage the copper substrate surface, and does not affect subsequent welding, drawing, plating, or other processing steps. Testing showed that after removing the protective film, the resistivity of the copper conductor remained essentially unchanged or slightly decreased compared to before treatment, indicating that the protective treatment does not introduce contamination or adversely affect the conductivity of the copper conductor substrate itself. This copper conductor is suitable for temporary anti-oxidation protection during production, storage, and transportation in the fields of power cables, communication cables, and electronic component leads, demonstrating significant industrial practical value.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0039] Example 1 This embodiment provides a method for preparing a copper conductor with an antioxidant protective film on its surface, the steps of which are as follows: (1) A copper wire with a diameter of 2.0 mm was sprayed with 15 wt% nitric acid solution for 20 s, then rinsed with pure water, and then dried with high pressure air to obtain a pretreated copper wire.

[0040] (2) Polyamic acid obtained by polycondensation of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether is diluted with N,N-dimethylformamide to a concentration of 15wt% to obtain a polyamic acid solution.

[0041] (3) Immerse the pretreated copper wire obtained in step (1) into the polyamic acid solution obtained in step (2) for 30 seconds, remove it and drain off the excess solution on the surface to obtain the pre-coated copper wire.

[0042] (4) Spray the pre-coated copper wire obtained in step (3) with room temperature water (25°C) for 10 seconds and let it air dry naturally to obtain a copper wire with an anti-oxidation protective film on the surface.

[0043] like Figure 1 As shown, the copper conductor surface film obtained in this embodiment is uniformly white, dense and defect-free, with a thickness of approximately 1.2 μm. Figure 2 The metallographic image shows the surface protective film of the copper conductor obtained in this embodiment. It can be seen that the protective film is tightly bonded to the copper conductor substrate, with no obvious gaps or delamination. The film has a dense microstructure, with no defects such as pinholes or cracks, and the thickness is uniformly distributed.

[0044] Example 2 This embodiment provides a method for preparing a copper conductor with an antioxidant protective film on its surface, the steps of which are as follows: (1) A copper wire with a diameter of 2.0 mm was sprayed with a mixed solution of acetic acid and hydrogen peroxide for 60 s, wherein the mass concentration of acetic acid was 20% and the mass concentration of hydrogen peroxide was 3%. Then it was rinsed with pure water and the surface was dried with high pressure air to obtain a pretreated copper wire. (2) Polyamic acid obtained by polycondensation of 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine was diluted with N-methylpyrrolidone to a concentration of 20 wt% to obtain a polyamic acid solution. (3) Immerse the pretreated copper wire obtained in step (1) into the polyamic acid solution obtained in step (2) for 20 seconds, remove it and drain off the excess solution on the surface to obtain the pre-coated copper wire. (4) Place the pre-coated copper wire obtained in step (3) in a 120°C water vapor environment for 10 seconds, take it out and dry it at low temperature to obtain a copper wire with an anti-oxidation protective film on the surface.

[0045] like Figure 3 As shown, the thin film on the surface of the copper conductor obtained in this embodiment is white and has a thickness of approximately 0.8 μm.

[0046] Example 3 This embodiment is basically the same as embodiment 1, except that the concentration of polyamic acid in step (2) is 10wt%, the soaking time in step (3) is 60s, and the water spraying treatment time in step (4) is 30s.

[0047] The thin film on the surface of the copper conductor obtained in this embodiment is white and has a thickness of approximately 0.5 μm.

[0048] Example 4 This embodiment is basically the same as embodiment 1, except that in step (4), water vapor at 140°C is used for treatment for 10 seconds.

[0049] The copper conductor surface film obtained in this embodiment is white, with a thickness of approximately 1.5 μm, and the film is more dense, such as... Figure 4 As shown.

[0050] Comparative Example 1 The difference between this comparative example and Example 1 is that steps (2) to (4) are not performed, and the pretreated copper wire is used as a blank control.

[0051] Comparative Example 2 This comparative example is basically the same as Example 1, except that step (4) water spraying treatment is omitted, that is, the copper wire is directly dried after being soaked in polyamic acid solution.

[0052] The resulting copper wires were coated with a transparent, viscous polyamic acid coating, but no white film was formed. The coating remained sticky after 24 hours and had poor moisture resistance.

[0053] Comparative Example 3 This comparative example is basically the same as Example 1, except that step (4) is replaced by: placing the pre-coated copper wire in a 280°C oven for heat treatment for 1 hour (traditional high-temperature imidization process).

[0054] An amber-colored polyimide film forms on the surface of the resulting copper conductor. The film is hard and has strong adhesion.

[0055] Comparative Example 4 This comparative example is basically the same as Example 1, except that the concentration of polyamic acid in step (2) is 0.5 wt%.

[0056] The resulting copper conductor has an extremely thin and discontinuous surface film.

[0057] Test case 1. Thin film removal performance test The copper wires prepared in Examples 1-4 and Comparative Example 3 were immersed in anhydrous ethanol. They were removed every 10 seconds to observe the swelling of the film and gently wiped with a non-woven cloth. The time required for complete removal of the film was recorded, and the surface condition of the copper wires after removal was observed. The results are summarized in Table 1.

[0058] Table 1. Statistics on the time required for complete film removal

[0059] As shown in Table 1, the films in Examples 1-4 could be completely removed within 20-60 seconds, and the copper conductor surface was clean and free of residue after removal, with the metallic luster restored. In Example 4, which was treated with water vapor, the film had higher density and tighter hydrogen bonding, allowing for complete removal with a slightly longer soaking time. In contrast, the film in Comparative Example 3 showed no change after soaking in anhydrous ethanol for 10 minutes and could not be removed.

[0060] 2. Moisture and heat resistance test Referring to GB / T 2423.3-2016, the copper wires prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were placed in a constant temperature and humidity chamber at 40℃ and approximately 93% relative humidity. Samples were taken at 24h, 72h, and 150h to observe the surface oxidation, and the area ratio of the oxidized region was observed using an electron microscope. Simultaneously, the protective film on the surface of the sample from Example 1 was removed after 150h, and the surface condition of the copper substrate was observed. The results are shown in Table 2.

[0061] Table 2 Percentage of surface oxidation area after damp heat test for different samples (%) sample 24h 72h 150h Example 1 (without membrane removal) 0 0 0 Example 1 (150h membrane removal) - - 0.8 Comparative Example 1 (bare copper wire) 12 31 45 Comparative Example 2 (Untreated water) 10 28 41 Comparative Example 3 (High-Temperature Imine) 0 0 0 The results showed that the white film on the surface of Example 1 remained intact throughout the 150-hour damp heat test, and the copper conductor showed no oxidation. After removing the film, the oxidized area on the copper substrate surface accounted for only 0.8%, far lower than that of the bare copper conductor. Comparative Example 2, without water treatment, had a coating that offered almost no protection, and the copper conductor was severely oxidized. While the high-temperature imidized film of Comparative Example 3 exhibited excellent protective properties, it could not be easily removed and therefore could not meet the needs of temporary protection.

[0062] 3. Resistivity test Referring to GB / T 3048.2-2007, the initial resistivity of the pretreated copper wire in Comparative Example 1 was tested using a DC double-arm bridge and found to be 0.016984 Ω·mm. 2 The resistivity (converted to 20℃) of the final copper wires prepared in Examples 1, 2, and 3 after being stored at room temperature (25℃±2℃) and relative humidity of approximately 50% for 24 hours was measured after removing the protective film. The resistivity of the pretreated copper wire in Comparative Example 1 after being stored under the same conditions for 24 hours was also measured, and the rate of change in resistivity was calculated. The protective film removal method for the copper wires in Examples 1 and 2 was as follows: immersion in anhydrous ethanol for 60 seconds, followed by gentle wiping with a non-woven cloth. The protective film removal method for the copper wires in Comparative Example 3 was as follows: immersion in a 10wt% sodium hydroxide solution at 80℃ for 30 minutes. Each sample was tested 5 times, and the average value was taken. The results are shown in Table 3.

[0063] Table 3 Resistivity test results for different samples sample <![CDATA[Resistivity after storage for 24 h (Ω·mm 2 / m)]]> Rate of change of resistivity (relative to initial resistivity) Example 1 0.016967 (after removing the film) -0.10% Example 2 0.016971 (after membrane removal) -0.08% Comparative Example 1 0.016992 +0.05% Comparative Example 3 0.017123 (after membrane removal) +0.82% The results show that the resistivity of the copper wires obtained in Examples 1 and 2 of this invention decreased slightly after the protective film was removed following 24 hours of storage, indicating that the protective film effectively protected the copper wires, and that the conductivity of the substrate could be restored or even improved after the film was removed. In Comparative Example 3, the resistivity increased after high-temperature imidization and strong alkali removal, indicating that the method caused some damage to the copper wire substrate.

[0064] In summary, this invention forms a dense, white, temporary protective film on the surface of copper conductors through a simple three-step process of "acid pickling-immersion-water treatment." This film possesses excellent short-term antioxidant protection and can be quickly and thoroughly removed by anhydrous ethanol. After removal, the copper conductor surface is clean, and its conductivity is slightly improved without affecting subsequent welding processes. Compared with traditional high-temperature imidized polyimide coatings, this invention's process has extremely low energy consumption, short cycle time, and low cost, and the film's removability has a significant advantage. Compared with untreated or directly stored after acid pickling, this invention provides reliable protection for copper conductors in harsh environments such as humidity and heat, greatly extending the shelf life of copper conductors during circulation and storage.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a copper wire with an antioxidant protective film on its surface, characterized in that, Includes the following steps: Pretreated copper wires are obtained by acid treatment, water washing and drying. The pretreated copper wires are immersed in a polyamic acid solution to obtain pre-coated copper wires. The pre-coated copper wire is treated with water spray or steam and then dried to obtain a copper wire with an antioxidant protective film on its surface.

2. The preparation method according to claim 1, characterized in that, The acid treatment is performed by spraying with a dilute nitric acid solution or a mixture of acetic acid and hydrogen peroxide; the mass concentration of the dilute nitric acid solution is 3% to 20%, and the mass concentration of acetic acid in the mixture of acetic acid and hydrogen peroxide is 5% to 30% and the mass concentration of hydrogen peroxide is 1% to 5%.

3. The preparation method according to claim 2, characterized in that, The spraying time using dilute nitric acid solution or acetic acid-hydrogen peroxide mixture is 10~180s.

4. The preparation method according to claim 1, characterized in that, The solvent for the polyamic acid solution is at least one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide.

5. The preparation method according to claim 1, characterized in that, The concentration of the polyamic acid solution is 1~30wt%.

6. The preparation method according to claim 1, characterized in that, The polyamic acid is prepared by polycondensation reaction of dianhydride monomer and diamine monomer; the dianhydride monomer is selected from at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride; the diamine monomer is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, and 4,4'-diaminodicyclohexylmethane.

7. The preparation method according to claim 1, characterized in that, The soaking time is 1~1000s.

8. The preparation method according to claim 1, characterized in that, The water temperature used in the water spraying step is 10~40℃, and the water steam treatment temperature is 100~150℃.

9. The preparation method according to claim 1, characterized in that, The time for water spraying or steam treatment is 1~600s.

10. A copper wire with an antioxidant protective film on its surface, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 9.

Images