A method for preparing a self-reducing electronic copper paste from waste copper foil

Abstract

The application discloses a method for preparing self-reduction electronic copper paste from waste copper foil, and belongs to the field of high-value utilization of waste metal resources. The method comprises the following steps: sorting and impurity removing, cutting or crushing the waste copper foil, then removing the surface organic residues and electrode residues through heat treatment, then cleaning, drying, mechanical crushing to obtain crude copper powder; melting the crude copper powder through plasma treatment, then spheroidizing and cooling to collect spherical copper powder; mixing organic solvent, organic binder, self-reduction agent and rheological additive to obtain self-reduction organic carrier; mixing the spherical copper powder with the self-reduction organic carrier, and then pre-mixing, grinding, dispersing and defoaming to obtain self-reduction electronic copper paste. The method can solve the problems that impurities and morphology of the waste copper foil cannot meet the requirements of electronic paste during powder preparation, and copper powder is easy to be oxidized, which causes the problem of blocked end-conductive connection of the paste.

Description

Technical Field

[0001] This invention relates to the field of high-value utilization of waste metal resources, specifically to a method for preparing self-reducing electronic copper paste from waste copper foil. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage industries, a large amount of copper foil resources have been generated from retired power batteries, scrapped battery cells, and battery manufacturing by-products. Copper foil is typically used as a negative electrode current collector in lithium-ion batteries, characterized by high copper content, concentrated sources, and large recycling volumes. For new energy battery recycling companies, waste copper foil is simply sorted, briquetted, or smelted and sold as ordinary copper material. The processing flow is relatively short, but the added value of the product is relatively low, making it difficult to fully realize its high-purity copper resource attributes.

[0003] Electronic pastes are widely used in flexible printed circuits, RFID antennas, touch electrodes, photovoltaic cell electrodes, ceramic substrate metallization circuits, and sensor electrodes. Silver paste has excellent conductivity, but its raw material cost is high; copper has better conductivity and cost advantages, therefore copper-based electronic pastes have the potential to replace some silver-based pastes. The performance of copper paste is closely related to the purity, particle size, morphology, dispersibility, and surface oxidation state of the copper powder.

[0004] Plasma powdering or plasma spheroidization technology utilizes high-temperature plasma to rapidly melt metal powder and spheroidize it under surface tension, followed by rapid cooling to obtain spherical metal powder. If waste copper foil is pretreated and pulverized before being used as a raw material for plasma powdering, spherical copper powder suitable for use in electronic pastes can be obtained, thereby realizing the transformation of waste copper foil from low-value-added copper material into functional powder material.

[0005] However, the sources of waste copper foil are complex, and its surface may contain residual binders, separator debris, graphite, electrolyte salts, or foreign metal impurities. Meanwhile, copper powder, especially small-particle copper powder, easily forms an oxide layer in the air. Existing technologies typically require strict passivation, liquid-phase sealing, or inert packaging after powder preparation to reduce the risk of subsequent oxidation; reduction treatment using a reducing atmosphere such as hydrogen can also be employed. However, these methods increase process costs and operational difficulty, and reduction at higher temperatures may cause copper powder to sinter and agglomerate, affecting subsequent slurry dispersion and printing performance. Therefore, it is necessary to propose a method for the high-value utilization of waste copper foil that can leverage the existing raw material conditions of battery recycling companies (i.e., waste copper foil, scrap copper foil, or slit waste obtained from the existing recycling process of new energy battery recycling companies can be used as raw materials and directly enter the subsequent processing flow), and to in-situ control the oxide layer on the copper powder surface at the slurry stage. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing self-reducing electronic copper paste from waste copper foil, which can solve the problems of low added value when waste copper foil is sold directly, difficulty in meeting the requirements of electronic paste due to impurities and morphology when waste copper foil is powdered, and the problem of copper powder being easily oxidized, which leads to obstructed conductive connection at the paste end.

[0007] In one aspect of the invention, a method for preparing self-reducing electronic copper paste from waste copper foil is provided. According to an embodiment of the invention, the method includes the following steps:

[0008] (1) The waste copper foil is sorted and cleaned, cut or crushed, and then the surface organic residue and electrode residue are removed by heat treatment. Then it is cleaned, dried and mechanically crushed to obtain crude copper powder.

[0009] (2) The crude copper powder is melted by plasma treatment, then spheroidized and cooled to obtain spherical copper powder;

[0010] (3) Mix organic solvent, organic binder, self-reducing agent and rheology modifier to obtain self-reducing organic carrier;

[0011] (4) Mix spherical copper powder with a self-reducing organic carrier, and then premix, grind, disperse and degas to obtain a self-reducing electronic copper paste.

[0012] In addition, a method for preparing self-reducing electronic copper paste from waste copper foil according to the above embodiments of the present invention may also have the following additional technical features:

[0013] In some embodiments of the present invention, in step (1): the heat treatment temperature is 250-650℃, and the holding time is 0.2-5h; and / or, the heat treatment atmosphere is one of a low-oxygen atmosphere with an oxygen volume fraction of less than 5%, an inert atmosphere, or a vacuum, wherein the inert atmosphere is one or more of nitrogen, argon, and helium; and / or, the particle size of the coarse copper powder is 1-200μm. The heat treatment temperature is set to 250-650℃ primarily to decompose, carbonize, or remove the adhesive, electrolyte residue, and some organic impurities on the surface of the waste copper foil. If the temperature is too low, the organic residues will not be sufficiently removed; if the temperature is too high, the copper foil is prone to significant oxidation, localized sintering, or increased energy consumption. The holding time is set to 0.2-5h to accommodate waste copper foil from different sources, with different levels of contamination, and of different thicknesses. The selection of low-oxygen atmosphere, inert atmosphere, or vacuum conditions for heat treatment is to reduce the degree of oxidation of copper during the heat treatment process, avoid the formation of an excessively thick oxide layer on the surface of the copper foil, and at the same time ensure the quality of raw materials for subsequent mechanical crushing and plasma spheroidization powdering.

[0014] Specifically, the waste copper foil includes one or more of the following: retired lithium-ion battery negative electrode current collector copper foil, battery production scrap copper foil, copper foil slitting waste, copper foil separated after electrode dismantling, and copper foil obtained from the battery recycling black powder separation process. For copper foil containing obvious separator, aluminum foil, nickel sheet, ferromagnetic impurities, plastic parts, graphite, or electrode active material residues, manual sorting, air separation, magnetic separation, sieving, or density sorting are performed first to reduce foreign matter entrainment in the subsequent powdering process. The sorting and impurity removal includes removing separator debris, aluminum foil, nickel sheet, ferromagnetic impurities, plastic parts, graphite, electrolyte salts, and electrode active material residues. Cleaning includes one or more of the following: deionized water cleaning, ethanol cleaning, alkaline solution cleaning, weak acid solution cleaning, complexation cleaning, or ultrasonic cleaning. Mechanical pulverization includes one or more of the following: shearing pulverization, ball milling, air jet milling, sand milling, disc milling, sieving, or air classification.

[0015] Step (1) aims to transform waste copper foil with complex origins and surface impurities such as binders, graphite, electrolyte salts, and foreign metals into coarse copper powder (particle size 1-200 μm) suitable for subsequent powdering. The principle involves sorting to remove large foreign objects, heat treatment to decompose or carbonize organic residues, cleaning to remove soluble salts and surface residues, and mechanical crushing to convert the sheet-like copper foil into powder. This reduces impurity content, improves raw material uniformity and feedability, and provides a stable precursor for plasma melting and spheroidization.

[0016] In some embodiments of the present invention, in step (2): the plasma treatment is performed using a plasma powder-making device or a plasma spheroidizing device, specifically one of a radio frequency thermal plasma device, a DC plasma device, an inductive plasma device, a plasma atomizing device, or a plasma spheroidizing device; and / or, the plasma treatment is performed in an inert atmosphere or an inert-reducing mixed atmosphere; and / or, the power of the plasma treatment is 10-200kW; and / or, the spherical copper powder is micron-sized, submicron-sized, or nano-sized, with an average particle size of 0.05-20μm. The spherical copper powder is allowed to have a naturally formed trace oxide layer on its surface, and the method does not require strict liquid-phase sealing, inert encapsulation, or separate high-temperature gas-phase reduction of the spherical copper powder as a necessary step.

[0017] In some embodiments of the present invention, the inert atmosphere is one or more of argon, nitrogen or helium; the inert-reducing mixed atmosphere is one or more of argon-hydrogen, nitrogen-hydrogen or argon-nitrogen-hydrogen, wherein the volume fraction of hydrogen is 0.5%-15%.

[0018] Step (2) utilizes the high-temperature plasma zone to rapidly melt the coarse copper powder. Under the influence of surface tension, the molten copper droplets tend to become spherical, and after rapid cooling, they solidify to form spherical copper powder. This step transforms irregular coarse copper powder into spherical copper powder (the average particle size of the spherical copper powder is 0.05-20 μm, preferably 0.1-10 μm), improving the sphericity, flowability, packing properties, and dispersibility of the copper powder, making it more suitable for electronic paste preparation and subsequent printing.

[0019] In some embodiments of the present invention, in step (3): the organic solvent is one or more of terpineol, diethylene glycol butyl ether, butyl carbitol acetate, dodecyl alcohol ester, ethylene glycol monobutyl ether, N-methylpyrrolidone, isopropanol or ethanol; and / or, the organic binder is one or more of ethyl cellulose, acrylic resin, polyvinyl butyral, polyvinylpyrrolidone, epoxy resin, phenolic resin or rosin resin; and / or, the self-reducing agent is one or more of formic acid, formate, ascorbic acid, ascorbate, oxalic acid, oxalate, citric acid, glucose, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, rosin amine or organic amine; and / or, the rheology modifier includes one or more of dispersants, thickeners, thixotropic agents, leveling agents, defoamers, antisettling agents, coupling agents or wetting agents.

[0020] Organic solvents are used to dissolve or disperse organic binders and additives, and to adjust the viscosity, volatility, and workability of the slurry. Organic binders are used to improve the film-forming properties, adhesion, and post-printing pattern retention of the slurry. Self-reducing agents are used to release or generate reducing components during drying, curing, or sintering. Formic acid or formate can generate reducing small molecules or reducing intermediates such as H2 and CO under heating and catalysis on the copper surface. Hydroxyl-containing organic compounds such as ascorbic acid and glucose have reducing properties. Polyols such as ethylene glycol, glycerol, and polyethylene glycol can form a reducing environment under heating conditions and participate in the reduction of copper oxide, thereby reducing the CuO / Cu2O oxide layer on the surface of copper powder in situ, converting it into metallic copper, and thus reducing the obstacle of the oxide layer to the conductive connection between copper particles. Rheology modifiers are used to improve the dispersibility, thixotropy, anti-stratification, leveling, and defoaming properties of the slurry.

[0021] Step (3) involves the dissolution, dispersion, and compounding of organic solvents, organic binders, self-reducing agents, and rheology modifiers to form an organic carrier that combines printability and self-reducing functions. This provides a dispersion medium, film-forming system, and in-situ reduction environment for the copper powder, enabling the spherical copper powder to be uniformly dispersed and allowing the slurry to reduce the oxide layer on the surface of the copper powder during subsequent heat treatment.

[0022] In some embodiments of the present invention, in step (4), the spherical copper powder is 70-92 parts by weight, and the self-reducing organic carrier is 8-30 parts.

[0023] In some embodiments of the present invention, the self-reducing organic carrier contains 0.5-10 parts of self-reducing agent, 1-12 parts of organic binder, 0.1-6 parts of rheology modifier, and the remainder is organic solvent.

[0024] Step (4) involves premixing, grinding, dispersing, and degassing to uniformly disperse spherical copper powder in a self-reducing organic carrier, while breaking up soft agglomerates and removing air bubbles inside the paste, resulting in a self-reducing electronic copper paste that is uniformly dispersed, has moderate viscosity, controllable fineness, and stable shape, which can be used for printing or coating.

[0025] In another aspect of the present invention, the present invention provides a method for preparing a self-reducing electronic copper paste from waste copper foil.

[0026] In another aspect of the invention, the invention proposes the application of self-reducing electronic copper paste. According to embodiments of the invention, the self-reducing electronic copper paste is used for screen printing, inkjet printing, gravure printing, blade coating, or dispensing. The formed paste is dried, cured, or sintered at 120-350°C in an atmosphere of air, nitrogen, argon, or a nitrogen-hydrogen mixture. During the drying, curing, or sintering process of the electronic copper paste, the self-reducing agent releases or generates reducing components to perform in-situ reduction of the oxide layer on the surface of the spherical copper powder.

[0027] In another aspect of the present invention, the present invention proposes the application of self-reducing electronic copper paste. According to an embodiment of the present invention, the self-reducing electronic copper paste is used to prepare radio frequency identification antennas, touch electrodes, photovoltaic cell electrodes, ceramic substrate metallization circuits, sensor electrodes, electromagnetic shielding layers or conductive repair materials.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1) Unlike existing technologies that focus on anti-oxidation or deoxidation measures at the powder end, this invention transfers some of the deoxidation function to the slurry system, reducing the reliance on strict liquid-phase sealing, complex passivation, or separate high-temperature reduction treatment at the powder end. The self-reducing agent releases or generates reducing components in the subsequent application process (slurry drying, curing, or sintering) to reduce the trace oxide layer naturally formed on the copper powder surface in situ, thereby reducing the impact of the oxide layer on the conductive connection between copper particles.

[0030] 2) This invention uses waste copper foil generated centrally by battery recycling companies as the copper source, and can convert ordinary waste copper into copper powder and copper paste for electronic paste, thereby increasing the added value of materials.

[0031] 3) The present invention adopts a pretreatment route that combines heat treatment degumming, cleaning and impurity removal and mechanical crushing, which is beneficial for adapting to different sources such as retired battery copper foil, production of edge copper foil and slitting waste.

[0032] 4) The present invention uses plasma melting and spheroidizing to obtain spherical copper powder, which is beneficial to improving powder flowability, packing state and slurry dispersibility.

[0033] 5) The process route of this invention can be integrated with battery recycling, powder processing and electronic paste preparation processes, which facilitates industrial scale-up. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the process flow for preparing self-reducing electronic copper paste from waste copper foil in Embodiment 1 of the present invention.

[0035] Figure 2 This is a scanning electron microscope (SEM) morphology image of the spherical copper powder in Example 1 of the present invention;

[0036] Figure 3 This is a photograph of the actual product after printing and sintering the self-reducing electronic copper paste of Example 1 in Application Example 1 of the present invention;

[0037] Figure 4 This is the X-ray diffraction (XRD) pattern of the conductive layer after sintering electronic copper paste in Comparative Example 1 of the present invention;

[0038] Figure 5 This is the XRD pattern of the conductive layer after sintering the electronic copper paste in Example 1 of the present invention.

[0039] Figure 6 This is a comparison of the XRD patterns of the conductive layers after sintering electronic copper paste in Example 1 and Comparative Example 1 in Application Example 1 of the present invention.

[0040] Figure 7 This is a magnified view (33-42°) of the CuO characteristic peaks in the conductive layer after sintering electronic copper paste in Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] like Figure 1As shown, a method for preparing self-reducing electronic copper paste from waste copper foil includes the following steps:

[0044] (1) Pretreatment of waste copper foil

[0045] Waste copper foil from the negative electrode current collector, obtained during the recycling of new energy batteries, was sorted, impurities removed, and cut. The cut copper foil was then heat-treated in a nitrogen atmosphere at 450℃ for 1.5 hours to remove residual organic binders, separator debris, and some electrode residues. After heat treatment, the foil was washed sequentially with deionized water and ethanol, and then dried at 80℃. The dried copper foil was then sheared, crushed, and sieved to obtain coarse copper powder with a particle size of 1-200 μm.

[0046] (2) Plasma powder making

[0047] Coarse copper powder is fed into a radio frequency thermal plasma powder-making device via a powder feeding device. The working atmosphere is an argon-hydrogen mixture, with hydrogen comprising 5% by volume and argon comprising 95% by volume. The coarse copper powder melts in the high-temperature plasma region and spheroidizes under surface tension. It then enters a cooling and collection zone for rapid cooling, yielding spherical copper powder with an average particle size of approximately 0.6-0.8 μm. Specifically, the melting zone parameters are: radio frequency thermal plasma power 60 kW, powder feeding rate 0.5 kg / h. The cooling zone parameters are: rapid cooling under argon protection, cooling gas flow rate 20 L / min, and maintaining a low-oxygen environment before collection.

[0048] (3) Preparation of self-reducing organic carriers

[0049] Weigh out 14 parts by weight of terpineol, 3 parts by weight of ethyl cellulose, 1 part by weight of formic acid, 1 part by weight of ascorbic acid and 1 part by weight of dispersant (polyvinylpyrrolidone), and stir in a water bath at 60°C until dissolved evenly to obtain a self-reducing organic carrier.

[0050] (4) Preparation of electronic copper paste

[0051] Weigh 80 parts by weight of spherical copper powder and 20 parts by weight of self-reducing organic carrier, premix them, and then circulate and disperse them through a three-roll mill to obtain self-reducing electronic copper paste.

[0052] Figure 2 The image shows the SEM morphology of the spherical copper powder obtained in step (2). As can be seen from the image, the copper powder after plasma treatment is generally spherical or nearly spherical, indicating that the coarse copper powder can be spheroidized under the action of surface tension after melting in the high-temperature plasma region, and then rapidly cooled to form spherical powder. According to the scale bar in the image, the main particle size is estimated to be about 0.3-0.9 μm, and a small number of larger particles are about 1.0-1.8 μm; the average particle size is estimated to be about 0.6-0.8 μm.

[0053] Example 2

[0054] A method for preparing self-reducing electronic copper paste from waste copper foil differs from Example 1 only in that: in step (1), the heat treatment temperature is 350℃, the holding time is 3h, and the cleaning process combines ultrasonic cleaning with deionized water and rapid rinsing with 0.5% citric acid aqueous solution for 3min; in step (2), a DC plasma spheroidizing device with a power of 50kW and a powder feeding rate of 0.3kg / h is used, the working atmosphere is a nitrogen-hydrogen mixture with a hydrogen gas fraction of 5%, and the cooling medium is nitrogen protection for rapid cooling; in step (3), the self-reducing organic carrier is composed of 14 parts by weight of diethylene glycol butyl ether, 3 parts by weight of acrylic resin, 1.5 parts by weight of ethylene glycol, 1 part by weight of glycerol and 0.5 parts by weight of thixotropic agent (hydrogenated castor oil); the remaining parameters and steps are the same as in Example 1.

[0055] The electronic copper paste obtained by the above method is suitable for coating, dispensing, or forming conductive lines with thicker linewidths. The self-reducing agent produces an in-situ reduction effect on the oxide layer on the surface of the copper powder during subsequent heat treatment, which helps to reduce the obstruction of the oxide layer to conductive connections.

[0056] Example 3

[0057] A method for preparing self-reducing electronic copper paste from waste copper foil differs from Example 1 only in that: in step (1), the waste copper foil is sourced from copper foil scraps and slitting waste generated during battery production, and this type of waste is mechanically crushed after degreasing and drying; in step (2), spheroidization is performed using an inductive plasma device with a power of 80kW and a powder feeding rate of 0.5kg / h, argon is used as the working atmosphere, argon is used as the carrier gas, and argon is used as the cooling medium for rapid cooling under protection; in step (3), the self-reducing agent is selected from the following raw materials in parts by weight: 11.5 parts of terpineol, 2 parts of diethylene glycol butyl ether, 3 parts of polyvinyl butyral, 1 part of ascorbic acid, 0.5 parts of glucose, 1.5 parts of polyethylene glycol, 0.5 parts of dispersant (polyvinylpyrrolidone), and polyvinyl butyral is selected as the organic binder; the remaining parameters and steps are the same as in Example 1.

[0058] The above method can adapt to waste copper foil raw materials from different sources without changing the main process route, and can meet the rheological performance requirements of different printing methods by adjusting the type of self-reducing agent, the type of binder, the solvent system and the grinding conditions.

[0059] The electronic copper paste obtained in Comparative Example 1 and the self-reducing electronic copper paste obtained in Example 1 were tested:

[0060] (1) Fineness test: The electronic copper pastes obtained in Example 1 and Comparative Example 1 were thoroughly stirred. An appropriate amount of paste was placed at the deepest end of the groove of the scraper fineness tester. The scraper was used to scrape from the deep end to the shallow end of the groove at a uniform speed. The position where continuous particles or obvious scratches began to appear in the groove was immediately observed, and the corresponding scale was read as the fineness of the paste. Each group of samples was tested in parallel 3 times, and the average value was taken. The fineness of the self-reducing electronic copper paste of Example 1 was 7.5 μm, and the fineness of the electronic copper paste of Comparative Example 1 was 13.8 μm.

[0061] (2) Viscosity test: The electronic copper pastes obtained in Example 1 and Comparative Example 1 were tested using a rotational rheometer. Both sets of samples were tested at the same temperature (25 ℃), using the same measuring fixture (parallel plate measuring fixture with a diameter of 25 mm), measuring gap (1.0 mm), and sample volume (0.5 mL per sample). After loading, the samples were allowed to stand for 60 s, and then subjected to a 100 s test. -1 The shear rate was pre-sheared for 30 s, then allowed to stand for 60 s, and then the shear rate was measured at 10 s. -1 and 100 s -1 The apparent viscosity was measured at 10 s, and the test results were recorded after the reading stabilized. Each group of samples was tested in triplicate, and the average value was taken. The electronic copper paste obtained in Example 1 showed a viscosity of 10 s. -1 and 100 s -1 The apparent viscosities at the shear rates were 48,500 mPa·s and 15,800 mPa·s, respectively, while those of the electronic copper paste obtained in Comparative Example 1 were 62,000 mPa·s and 25,500 mPa·s, respectively.

[0062] (3) Thixotropic test: with a 10 s -1 Apparent viscosity at shear rate and 100 s⁻¹ -1 The ratio of apparent viscosity at shear rate is called the thixotropic index, and the formula is: Thixotropic index = η 10 / η 100 , where η 10 For 10 s -1 Apparent viscosity at shear rate, η 100 For 100 s -1 Apparent viscosity at shear rate. The thixotropic index of the electronic copper paste obtained in Example 1 is 48500 / 15800=3.07, and the thixotropic index of the electronic copper paste obtained in Comparative Example 1 is 62000 / 25500=2.43.

[0063] (4) Static stability test: Take the same volume of electronic copper paste from Example 1 and Comparative Example 1 respectively, put them into transparent graduated containers of the same specifications, seal them, and let them stand for 24 h under the same temperature conditions. After standing, measure the height h of the upper clear liquid or obvious stratification area and the total height H of the paste, and calculate the stratification rate after standing for 24 h according to "stratification rate = h / H × 100%". Set up 3 parallel samples for each group of samples and take the average value. The stratification rate of the electronic copper paste obtained in Example 1 after standing for 24 h was 4.2%, and the stratification rate of the electronic copper paste obtained in Comparative Example 1 after standing for 24 h was 11.5%.

[0064] Comparative Example 1

[0065] A method for preparing electronic copper paste without self-reducing agent is basically the same as that in Example 1, except that: formic acid and ascorbic acid are not added in step (3), and the self-reducing organic carrier is adjusted to an organic carrier without self-reducing agent. Specifically, 16 parts of terpineol, 3 parts of ethyl cellulose and 1 part of dispersant (polyvinylpyrrolidone) are weighed according to the weight, and stirred until uniform to obtain an organic carrier without self-reducing agent; the rest of the copper powder preparation process, organic binder, rheology modifier, weight ratio of spherical copper powder to organic carrier, premixing, grinding and dispersing, degassing and subsequent printing, drying / curing / sintering conditions are the same as in Example 1.

[0066] Application Example 1

[0067] The electronic copper pastes prepared in Example 1 and Comparative Example 1 were used for screen printing. Specifically, the printing parameters were: screen printing, squeegee angle 45°, squeegee speed 50 mm / s, and static leveling for 5 min after printing; the screen material was stainless steel mesh with a mesh count of 325; and the printing substrate was polyimide film. The printed paste was dried and sintered in a nitrogen atmosphere. The drying parameters were 80°C for 10 min; the sintering parameters were heating to 220°C and holding for 30 min in a nitrogen atmosphere at a heating rate of 5°C / min, finally obtaining the printed conductive layer. Example 1 and Comparative Example 1 used the same printing pattern, screen, and printing process conditions. The linear test pattern had a linewidth of 200 μm and a length of 20 mm, and the sheet resistance test area was 20 mm × 20 mm. After sintering, the thickness of the conductive layer was measured using a surface profilometer. Five measurements were taken at different locations on each sample. The average thickness test results were as follows: the average thickness of the conductive layer after sintering in Example 1 was 10.2 μm, and in Comparative Example 1 it was 10.5 μm.

[0068] like Figure 3 As shown, the self-reducing electronic copper paste of Example 1 can form a relatively complete conductive pattern after screen printing, drying / curing / sintering. This result supports the basic application of the paste in printing and forming.

[0069] The performance of the conductive layers after printing and sintering the electronic copper paste prepared in Example 1 and Comparative Example 1 was tested:

[0070] (1) XRD test. The conductive layers prepared using the electronic copper paste of Example 1 and Comparative Example 1 were subjected to XRD test. The test results are as follows: Figure 4-7 As shown, both Example 1 and Comparative Example 1 conductive layers prepared with electronic copper paste exhibit obvious characteristic peaks of metallic Cu. The CuO-related diffraction peaks in the conductive layer prepared with electronic copper paste in Example 1 are weak; the conductive layer prepared with electronic copper paste in Comparative Example 1 shows more obvious CuO characteristic peaks at approximately 35.5° and 38.7°, indicating that the CuO residue in the conductive layer after sintering in Example 1 is relatively low.

[0071] (2) Oxygen content test. An oxygen-nitrogen-hydrogen analyzer was used to determine the oxygen content using the inert gas melting-infrared absorption method. Before testing, a blank crucible was used for blank calibration, and a standard sample with an oxygen content range similar to that of the sample to be tested was used to calibrate the instrument. Test procedure: An appropriate amount of sample was weighed and placed in a graphite crucible. Under inert carrier gas protection, high-temperature melting was performed. The oxygen in the sample reacted with the graphite to generate carbon monoxide and carbon dioxide, which were carried by the carrier gas into the infrared detector for quantitative analysis. The conductive layers prepared in Example 1 and Comparative Example 1 were tested in three parallel trials, and the average value was taken as the final oxygen content. Test results: The oxygen content of the conductive layer after sintering in Example 1 was 0.86 wt.%, and the oxygen content of the conductive layer after sintering in Comparative Example 1 was 1.74 wt.%.

[0072] (3) Sheet resistance test: The sheet resistance test was performed using a four-probe sheet resistance tester. The sheet resistance test area of ​​the conductive layer was 20 mm × 20 mm. The test steps were as follows: After the printed and sintered conductive pattern was cooled to room temperature, a test area without obvious broken lines, bubbles, or contamination was selected. The four-probe probe was used to contact the surface of the conductive layer. At least 5 points were tested at different locations on the same sample, and the average value was taken as the sheet resistance result. The sheet resistance of the conductive layer after printing and sintering the electronic copper paste in Example 1 reached 2.3 mΩ / □, while the average sheet resistance of the conductive layer after sintering in Comparative Example 1 was 8.9 mΩ / □. The relative standard deviation of the sheet resistance of the conductive layer after sintering in Example 1 was 6.4%, while the relative standard deviation of the sheet resistance of the conductive layer after sintering in Comparative Example 1 was 18.7%. This indicates that the self-reducing agent in Example 1 can produce an in-situ reduction effect on the oxide layer on the surface of the copper powder during the drying, curing, or sintering process of the paste, reducing the obstacle of the oxide layer to the conductive connection between copper particles, thereby improving the conductivity, and the conductivity uniformity after sintering is also better.

[0073] (4) Printed line width and graphic integrity test. In the printing test, the designed line width was 200 μm and the length was 20 mm. The actual line width of the conductive layer after sintering in Example 1 was 212 μm, with a line width deviation of 6.0%; the actual line width of the conductive layer after sintering in Comparative Example 1 was 238 μm, with a line width deviation of 19.0%. The number of broken lines / pinholes in the conductive layer after sintering in Example 1 was 1.2 per cm. 2 In Comparative Example 1, the number of broken wires / pinholes in the conductive layer after sintering was 5.8 per cm. 2 The relative standard deviation of sheet resistance of the conductive layer after sintering in Example 1 was 6.4%, while that in Comparative Example 1 was 18.7%. These results indicate that Example 1 exhibits better slurry dispersion, higher continuity of printed patterns, and better linewidth retention.

[0074] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the present invention, and all such modifications or additions should fall within the protection scope of the present invention.

Claims

1. A method for preparing self-reducing electronic copper paste from waste copper foil, characterized in that, Includes the following steps: (1) The waste copper foil is sorted and cleaned, cut or crushed, and then the surface organic residue and electrode residue are removed by heat treatment. Then it is cleaned, dried and mechanically crushed to obtain crude copper powder. (2) The crude copper powder is melted by plasma treatment, then spheroidized and cooled to obtain spherical copper powder; (3) Mix organic solvent, organic binder, self-reducing agent and rheology modifier to obtain self-reducing organic carrier; (4) Mix spherical copper powder with a self-reducing organic carrier, and then premix, grind, disperse and degas to obtain a self-reducing electronic copper paste.

2. The method for preparing self-reducing electronic copper paste from waste copper foil according to claim 1, characterized in that, In step (1): The heat treatment temperature is 250-650℃, and the holding time is 0.2-5h; And / or, the atmosphere for the heat treatment is one of a low-oxygen atmosphere with an oxygen volume fraction of less than 5%, an inert atmosphere, or a vacuum; And / or, the particle size of the coarse copper powder is 1-200 μm.

3. The method for preparing self-reducing electronic copper paste from waste copper foil according to claim 1, characterized in that, In step (2): The plasma treatment is carried out using a plasma powder-making device or a plasma spheroidizing device. And / or, the plasma treatment is performed in an inert atmosphere or an inert-reducing mixed atmosphere; And / or, the power of the plasma treatment is 10-200kW; And / or, the average particle size of the spherical copper powder is 0.05-20 μm.

4. The method for preparing self-reducing electronic copper paste from waste copper foil according to claim 3, characterized in that: The inert atmosphere is one or more of argon, nitrogen, or helium; the inert-reducing mixed atmosphere is one or more of argon-hydrogen, nitrogen-hydrogen, or argon-nitrogen-hydrogen, wherein the volume fraction of hydrogen is 0.5%-15%.

5. The method for preparing self-reducing electronic copper paste from waste copper foil according to claim 1, characterized in that, In step (3): The organic solvent is one or more selected from terpineol, diethylene glycol butyl ether, butyl carbitol acetate, dodecyl alcohol ester, ethylene glycol monobutyl ether, N-methylpyrrolidone, isopropanol or ethanol; And / or, the organic binder is one or more of ethyl cellulose, acrylic resin, polyvinyl butyral, polyvinylpyrrolidone, epoxy resin, phenolic resin or rosin resin; And / or, the self-reducing agent is one or more of formic acid, formate, ascorbic acid, ascorbate, oxalic acid, oxalate, citric acid, glucose, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, rosin amine, or organic amine; And / or, the rheology modifier includes one or more of the following: dispersant, thickener, thixotropic agent, leveling agent, defoamer, antisettling agent, coupling agent, or wetting agent.

6. The method for preparing self-reducing electronic copper paste from waste copper foil according to claim 1, characterized in that: In step (4), by weight, the spherical copper powder is 70-92 parts and the self-reducing organic carrier is 8-30 parts.

7. The method for preparing self-reducing electronic copper paste from waste copper foil according to claim 6, characterized in that: In the self-reducing organic carrier, the self-reducing agent is 0.5-10 parts, the organic binder is 1-12 parts, the rheology modifier is 0.1-6 parts, and the remainder is an organic solvent.

8. A self-reducing electronic copper paste prepared by the method for preparing self-reducing electronic copper paste from waste copper foil as described in any one of claims 1-7.

9. The application of the self-reducing electronic copper paste according to claim 8, characterized in that: The self-reducing electronic copper paste is used for screen printing, inkjet printing, gravure printing, scraping, or dispensing.

10. The application of the self-reducing electronic copper paste according to claim 8, characterized in that: The self-reducing electronic copper paste is used to prepare radio frequency identification antennas, touch electrodes, photovoltaic cell electrodes, ceramic substrate metallization circuits, sensor electrodes, electromagnetic shielding layers, or conductive repair materials.

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