Highly conductive copper paste cured under air atmosphere and method of making and using same

Abstract

This invention provides a highly conductive copper paste that cures in an air atmosphere, its preparation method, and its applications, belonging to the field of conductive paste preparation technology. The highly conductive copper paste comprises: 60-80% conductive copper powder; 3-10% polymer resin; 1-3% curing agent; 3-10% first solvent; 1-5% additives; and 7.5-17% particle-free conductive copper ink. The copper salt precursor in the particle-free conductive copper ink is dissolved in the form of copper ions in a mixture of its complexing agent and second solvent. When the highly conductive copper paste is heated and cured in an air atmosphere, the copper ions in the particle-free conductive copper ink are reduced in situ to nano-copper particles, which form welded connections between the conductive copper powder particles, constituting a conductive network composed of micron-sized conductive copper powder and in-situ generated nano-copper weld points. The highly conductive copper paste of this invention has low manufacturing cost, high conductivity, and the potential for room temperature dormancy and heat-triggered decomposition.

Description

Technical Field

[0001] This invention relates to the technical field of conductive paste preparation, and particularly to a highly conductive copper paste that cures in an air atmosphere, its preparation method, and its applications. Background Technology

[0002] Currently, high-performance conductive pastes are key basic materials in advanced manufacturing fields such as photovoltaic solar cells, 5G communication devices, and flexible electronic circuits. Traditional conductive pastes are mainly based on silver paste with excellent conductivity, but with the continued high price of silver, downstream industries are facing severe raw material cost pressures. Therefore, as a key material, conductive pastes urgently need to achieve a technological breakthrough in replacing silver with base metals. Among base metals, copper has conductivity close to that of silver and is much cheaper, giving it a significant economic advantage.

[0003] Traditional air-cured conductive pastes consist of a curing agent, polymer resin, solvent, additives, and conductive powder. To improve conductivity, methods such as increasing copper powder content, surface anti-oxidation treatment of copper powder, and blending different types of copper powder are commonly used. However, these methods have drawbacks to varying degrees: increasing copper powder content leads to increased paste viscosity, affecting printability; copper powder surface treatment processes are complex and easily introduce interface defects, leading to agglomeration or phase separation; copper powder is highly susceptible to oxidation in air, and conventional anti-oxidation coatings are prone to failure during curing, severely affecting conductivity stability.

[0004] Existing technologies also employ liquid-phase reduction to prepare nano-copper particles and mix them with traditional pastes. However, this process requires pre-cleaning and separation, is complex, and results in high contact resistivity (exceeding 50 μΩ·cm) and poor storage stability (resistivity change rate exceeding 15%) after curing in an air atmosphere. Other common air-cured copper paste products have resistivity that is difficult to further reduce, typically remaining between 50-100 μΩ·cm, making it difficult for them to completely replace silver paste in applications requiring high conductivity.

[0005] In view of this, a novel high-conductivity copper paste that cures in an air atmosphere, its preparation method, and its application are proposed to solve all or part of the above problems. Summary of the Invention

[0006] To address at least one of the aforementioned problems and deficiencies in the prior art, embodiments of the present invention provide an air-cured high-conductivity copper paste, its preparation method, and its application. By organically fusing a particle-free conductive copper ink with an air-cured copper paste (compounded conductive copper powder), the copper ions are reduced in situ to nano-copper particles upon heating, achieving a "welding" connection between the micron-sized copper powder and forming a dense conductive network. This results in a resistivity of less than 40 μΩ·cm after air curing, making it a viable alternative to silver paste. Furthermore, through multi-component synergistic antioxidant action, resin physical barrier, and rapid infrared curing, oxidation resistance under air conditions is ensured. Simultaneously, the copper ion-complexing agent coordination achieves a room-temperature "dormant" state and a latent mechanism of heat-triggered decomposition, ensuring that the resistivity change of the paste is less than 5% after storage for more than one year. The high-conductivity copper paste and its preparation method of the present invention avoid the complex process of nanoparticle prefabrication, significantly reducing the paste manufacturing cost, and possessing high conductivity, high stability, and excellent workability. The technical solution is as follows:

[0007] According to one aspect of the present invention, an air-curing highly conductive copper paste is provided. The highly conductive copper paste comprises the following components by total mass percentage:

[0008] Conductive copper powder, 60-80%;

[0009] High molecular weight resin, 3-10%;

[0010] Hardener, 1-3%;

[0011] First solvent, 3-10%;

[0012] Additives, 1-5%; and

[0013] Particle-free conductive copper ink, 7.5-17%;

[0014] Among them, the particle-free conductive copper ink is composed of a copper salt precursor, a complexing agent, and a second solvent. The copper salt precursor is dissolved in the mixed system of the complexing agent and the second solvent in the form of copper ions.

[0015] When the highly conductive copper paste is heated and cured in an air atmosphere, the copper ions in the particle-free conductive copper ink are reduced in situ to nano-copper particles. These nano-copper particles form welded connections between the conductive copper powder particles, forming a conductive network composed of micron-sized conductive copper powder and in-situ generated nano-copper weld points.

[0016] According to another aspect of the present invention, a method for preparing a highly conductive copper paste that cures in an air atmosphere is provided. This preparation method is used to prepare the highly conductive copper paste described above. The preparation method includes:

[0017] Preparation of particle-free conductive copper ink: Mix the complexing agent and the second solvent evenly, add the copper salt precursor, and stir until a clear and transparent copper complex solution is formed. The pH value of the copper complex solution is 7-9.

[0018] Conductive copper powder pretreatment: Conductive copper powder is subjected to alkali washing, acid washing and antioxidant surface coating in sequence, and then dried to obtain pretreated conductive copper powder;

[0019] Preparation of high conductivity copper paste: Mix polymer resin, first solvent and additives, heat to dissolve resin, cool and add curing agent, then add pretreated conductive copper powder in batches, disperse and grind until fineness is less than or equal to 10μm, finally add particle-free conductive copper ink, disperse and degas to obtain high conductivity copper paste.

[0020] In the steps of preparing particle-free conductive copper ink and preparing highly conductive copper paste, the process temperature is controlled to be less than or equal to 30°C in order to maintain the latency of the coordination complex formed by the copper salt precursor and the complexing agent.

[0021] According to another aspect of the present invention, an application of a highly conductive copper paste that cures in an air atmosphere is provided, wherein the highly conductive copper paste is the highly conductive copper paste described in the above-described aspect or is a highly conductive copper paste obtained using the preparation method described in the above-described aspect. This highly conductive copper paste is used in the fabrication of photovoltaic solar cell electrodes, 5G communication device electrodes, flexible electronic circuits, RFID antennas, or printed circuit boards.

[0022] In some embodiments, highly conductive copper paste is printed or coated onto a substrate and then cured by heating in an air atmosphere to form a conductive film or conductive pattern. The heating and curing process uses infrared heating; first, the surface is dried at 100-120°C for 1-2 minutes to evaporate the solvent, and then cured in an infrared heating oven at 200±10°C for 15-30 seconds in an air atmosphere. During the curing process, the complexing agent in the particle-free conductive copper ink and the auxiliary reducing agent in the additives preferentially volatilize or thermally decompose in the initial stage of heating, generating a reducing atmosphere in the local microenvironment of the coating layer, preventing the conductive copper powder from being oxidized.

[0023] The air-cured high-conductivity copper paste, its preparation method, and its application provided by the embodiments of the present invention have at least one or a portion of the following advantages:

[0024] (1) By combining conductive copper powder (micron-sized copper powder main body) with a specific ratio of particle-free conductive copper ink (copper salt precursor solution), the copper ions in the particle-free conductive copper ink are reduced in situ to nano-copper particles during curing heating. The latter form nano "welding points" between the large particles of conductive copper powder to build a dense three-dimensional conductive network. The high load of micron-sized copper powder ensures high filling, and the in situ nano-copper welding points achieve low contact resistance, resulting in a curing resistivity of ≤40μΩ·cm in air atmosphere.

[0025] (2) By performing a specific pretreatment of conductive copper powder by "alkali washing-acid washing-thiol-containing antioxidant coating", the surface oil and oxide layer are effectively removed. At the same time, the coated thiol-containing compound can volatilize or decompose at a curing temperature of ≤300℃, avoiding itself from becoming a high-resistance impurity. Meanwhile, the reducing atmosphere released during its pyrolysis process can also provide active protection for the conductive copper powder, further improving the antioxidant properties and sintering connection effect in the air atmosphere curing environment.

[0026] (3) By selecting specific types of polymer resins, curing agents, solvents (first solvent and second solvent) and additives, these components together ensure the uniform dispersion, construction adaptability and antioxidant performance of the slurry during the curing process; in particular, by selecting polymer resins that are compatible with the polarity of the complexing agent, a resin matrix system that is highly compatible with particle-free conductive copper ink and has a highly efficient synergistic antioxidant function is constructed. While preventing the demulsification and precipitation of ink complexes, the dense cross-linked network formed after curing also acts as a physical barrier to block the penetration of external oxygen and moisture for a long time, thus achieving stable curing in air and long-term storage stability.

[0027] (4) Particle-free conductive copper ink uses copper formate / copper acetate / copper oxalate in a specific ratio as copper salt precursors and oleylamine / 1-amino-2-propanol as complexing agents to form a stable molecular-level complex solution in a specific solvent, giving the slurry excellent "latency"; when stored at room temperature, copper ions are "locked" by the complexing agent and do not react with the system, ensuring storage stability; when air-cured, it is activated and reduced by heat, releasing nano-copper particles to form high-quality solder joints; it simplifies the prefabrication process (no need to prefabricate nano-copper particles) and solves the oxidation and agglomeration problems in nano-copper storage. When stored at room temperature for more than 1 year, the viscosity and resistivity of the slurry change rate are both ≤5%;

[0028] (5) The particle-free conductive copper ink forms a stable coordination complex with organic amines through copper ions, so that copper is uniformly dispersed in the system in ionic form. The particle-free conductive copper ink has a simple composition and does not contain metal particles. It can achieve high stability without the addition of dispersant. The sintering temperature is low (100-200℃), which matches the curing temperature of air-cured conductive copper paste. The coating layer of the cured conductive film / conductive pattern has low impurity content and high conductivity.

[0029] (6) It provides a complete optimized preparation method from particle-free conductive copper ink formulation (ratio control, pH control, low temperature stirring) to conductive copper powder pretreatment (alkali washing-acid washing-coating) to slurry preparation (step feeding, temperature-controlled grinding), as well as curing application process (infrared heating, first low temperature surface drying and then instantaneous high temperature curing); using this preparation method, high conductivity and high storage stability conductive copper slurry products can be stably mass-produced and successfully applied to photovoltaic electrodes, flexible circuits, RFID antennas and other scenarios, solving technical problems such as poor filling of copper powder gaps, copper oxidation, and complex prefabrication process, and achieving cost reduction and efficiency improvement. Attached Figure Description

[0030] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0031] Figure 1 A flowchart illustrating the steps of a method for preparing highly conductive copper paste according to an embodiment of the present invention;

[0032] Figure 2 for Figure 1 The flowchart shown illustrates the specific steps involved in preparing highly conductive copper paste using the method described. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.

[0034] This invention provides an air-curing highly conductive copper paste and its preparation method. The core technical concept lies in organically combining the property of particle-free conductive copper ink, which can be reduced to nano-copper particles to form solder joints during heating, with the formulation system of a curable conductive copper paste, to prepare a highly conductive copper paste with air-curing properties.

[0035] Specifically, the main component of particle-free copper conductive ink consists of a metal precursor (such as copper formate) dissolved in a volatile solvent or organic complexing agent. The copper exists in ionic form and contains no metal particles, achieving high stability without the need for dispersants. The simple composition of particle-free copper conductive ink results in a conductive film / pattern with low impurity content, high conductivity, and stability. Furthermore, its relatively low sintering temperature (between 100-200℃) meets the requirements of most substrates and matches the curing temperature of air-cured conductive copper paste.

[0036] Especially when heat-curing in an air atmosphere, the stability can be further improved through anti-oxidation design. The liquid-phase particle-free copper conductive ink can be fully mixed and wetted with the conductive copper powder in the slurry, forming an active reaction layer on the surface of the conductive copper powder particles. Once triggered by the thermal switch (entering the heat curing process stage), it can be reduced to a nano-metal layer to achieve interconnection between copper particles.

[0037] The high-conductivity copper paste of this invention achieves a resistivity of ≤40μΩ·cm under air atmosphere curing conditions, which can realize cost reduction and performance optimization of "replacing silver with copper" in a variety of application fields (such as photovoltaic solar cell electrodes, 5G communication device electrodes, flexible electronic circuits, RFID antennas, printed circuit boards, etc.).

[0038] See Figure 1 The present invention illustrates the steps of a method for preparing highly conductive copper paste according to an embodiment of the present invention.

[0039] The core of this highly conductive copper paste (paste / paste system) lies in its particle-free conductive copper ink, composed of a copper salt precursor, a complexing agent, and a second solvent, in which copper is uniformly dissolved in ionic form. During curing and heating, the copper ions in the particle-free conductive copper ink are reduced in situ to nano-copper particles within a temperature range of 100-150℃. These fresh, highly active nano-copper particles rapidly form metallurgically bonded connections between the large-sized conductive copper powder particles, thus constituting a highly efficient, low-resistance conductive network composed of a micron-sized conductive copper powder matrix and in-situ generated nano-copper solder joints.

[0040] like Figure 1 As shown, the specific implementation process of this preparation method is as follows:

[0041] Step S100: Preparation of particle-free conductive copper ink.

[0042] In one example, the particle-free conductive copper ink of the present invention comprises, by total mass percentage, 5-10% copper salt precursor, 0.5-2% complexing agent, and 2-5% second solvent.

[0043] For example, the copper salt precursor is selected from any one or any combination thereof of copper formate, copper acetate, copper oxalate, copper malonate, copper nitrate, copper citrate, copper neodecanoate, copper β-ketoate (II), and ethylene glycol carboxylates. Copper formate, copper acetate, and copper oxalate are preferred.

[0044] For example, the complexing agent is selected from alkylamines and / or alkanolamines, including any one or any combination thereof, such as oleylamine, butylamine, 1-amino-2-propanol, 2-amino-2-methyl-1-propanol, monoethanolamine, triethanolamine, 1,2-propanediamine, partially etherified amino resins.

[0045] In the process of preparing particle-free conductive copper ink, the operation needs to be carried out at room temperature (usually set at 20-25℃, not exceeding 30℃) in order to obtain a completely dissolved, particle-free, and stably complexed copper precursor solution, ensuring molecular-level compatibility with the resin system and ultimately achieving a latent mechanism for suitable long-term storage of the slurry.

[0046] In one example, the specific operation process is as follows: weigh the complexing agent (0.5-2% by mass, based on the total slurry) and the second solvent (2-5% by mass, based on the total slurry), add them to a glass reactor equipped with mechanical stirring and temperature control, stir at a speed of 300-500 r / min, and stir for 10-15 min until completely dissolved.

[0047] Preferably, the complexing agent is oleylamine or 1-amino-2-propanol, and the second solvent is ethylene glycol butyl ether acetate or diethylene glycol dibutyl ether, to ensure low to medium polarity and avoid strong hygroscopic solvents from damaging the complexing bonds.

[0048] Subsequently, the copper salt precursor (5-10% by weight, based on total slurry) is slowly added (in 3-4 batches, with 5-minute intervals between each batch) to the mixed solution of the complexing agent and the second solvent. Stirring continues at a speed of 400-600 r / min for 30-45 min until the solution is clear and transparent with no solid residue, forming a stable copper complex solution.

[0049] Preferably, the copper salt precursor is copper formate or copper acetate. If copper formate is used, 0.1-0.5% formic acid can be added as an auxiliary reducing agent to promote subsequent in-situ reduction. Optional auxiliary reducing agents such as ascorbic acid or phosphate esters can be added, at a mass ratio of 0.2-0.5% of the total slurry mass, and stirring should continue for 15-20 minutes. After standing for 30 minutes to remove bubbles, a particle-free conductive copper ink is obtained with a viscosity <50 mPa·s. When stored in a sealed container at room temperature, its stability can exceed 12 months.

[0050] The temperature during the entire preparation process is strictly controlled below 30℃ to avoid premature breakage of the complex bonds (latent mechanism aging), while the pH is controlled at 7-9 (a small amount of triethanolamine can be used for adjustment) to prevent the acidic environment from damaging the complex.

[0051] Step S200: Pretreatment of conductive copper powder (usually or preferably compounded conductive copper powder).

[0052] In one example, the conductive copper powder can be a composite mixture of copper powders of any shape, such as nano- or micron-sized spherical powder, flake powder, dendritic copper powder, etc., or any combination thereof. Spherical copper powder is preferred, and the D50 of the spherical copper powder is preferably 0.5-3.0 μm.

[0053] In one example, the pretreatment of conductive copper powder includes three steps in sequence: alkaline washing, acid washing, and surface coating with antioxidants.

[0054] Alkaline washing to remove grease: Immerse the conductive copper powder in a 3-5% sodium hydroxide (NaOH) aqueous solution and clean it for 15-20 minutes with ultrasonic stirring under a constant temperature water bath at 40-50℃. Let it stand for 60 minutes to thoroughly remove grease and organic processing aids adhering to the surface of the conductive copper powder. Subsequently, wash repeatedly with deionized water at 60℃ until the filtrate is neutral, and filter to obtain wet conductive copper powder. The alkaline washing process generally needs to be repeated 2-3 times.

[0055] Acid pickling to remove the oxide layer: Immediately immerse the wet conductive copper powder after alkaline washing in a 1-5% (w / w) dilute sulfuric acid (or dilute hydrochloric acid) solution. At room temperature (25℃), slowly stir mechanically and ultrasonically clean for 10-20 minutes to dissolve the naturally formed primary copper oxide (CuO / Cu2O) layer on the surface of the conductive copper powder, exposing a highly active, fresh pure copper surface. After treatment, filter and quickly wash alternately with deionized water and anhydrous ethanol 2-3 times until neutral. The acid pickling process generally needs to be repeated 2-3 times.

[0056] Antioxidant Surface Coating: The wet conductive copper powder, after being successively alkali-washed and acid-washed to expose its fresh surface, is rapidly transferred to a reaction vessel containing an antioxidant coating agent (e.g., an anhydrous ethanol solution of 1-2% by mass of oleylamine or dodecyl mercaptan). The mixture is mechanically stirred and ultrasonically reacted at 20-40°C for 1-2 hours, allowing the active groups of the antioxidant (such as amino or thiol groups) to tightly bind to the surface of the pure conductive copper powder through chemical bonds (such as Cu-S bonds) or strong physical adsorption. Preferably, the antioxidant is a thiol-containing monomer or compound that is volatile or decomposable below 300°C, such as ethanethiol, isopropanethiol, mercaptoacetic acid, thioglycolate, dodecyl mercaptan, etc.

[0057] Finally, the mixture is filtered and dried in a vacuum drying oven at 40°C for 3-5 hours to obtain pretreated conductive copper powder with high oxidation resistance.

[0058] The above alkaline washing removes surface oil and organic matter, and acid washing removes the surface oxide layer. The antioxidant coating on the surface ensures that the copper powder maintains good antioxidant properties during subsequent storage and slurry preparation.

[0059] Step S300: Preparation of highly conductive copper paste.

[0060] In one example, the high conductivity copper paste of the present invention comprises, by weight percentage of the total paste, the following components: 60-80% conductive copper powder, 3-10% polymer resin, 1-3% curing agent, 3-10% first solvent, 1-5% additives, and 7.5-17% particle-free conductive copper ink (composed of 5-10% copper salt precursor, 0.5-2% complexing agent, and 2-5% second solvent).

[0061] For example, the curing agent is selected from any one or any combination thereof of blocked isocyanates, phthalates, silane coupling agents, modified dicyandiamides, and amino resins. Blocked isocyanates (unblocking temperature 120-180°C) are preferred, with the addition of modified dicyandiamides or amino resins (1-3% added) to provide crosslinking and improve oxidation resistance.

[0062] For example, the polymer resin is a thermoplastic or thermosetting resin, selected from polyurethane, phenoxy resin, polyester resin, phenolic resin, acrylic resin, epoxy resin, polycarbonate resin, alkyd resin, amino resin, etc.

[0063] Preferably, the polymer resins selected are alcohol-soluble epoxy resin and polyurethane resin (added at 3-8%). On one hand, these two resins, after film formation, not only provide excellent flexibility and substrate adhesion, but more importantly, their molecular chain backbone contains a certain amount of polar groups such as hydroxyl or amine groups. These groups have extremely excellent physical compatibility with the organic amine complexing agents used in particulate-free conductive copper inks, ensuring that the copper salt precursor is uniformly dispersed in the resin system without demulsification or precipitation. On the other hand, by combining 1-2% phenolic resin or acrylic resin, the crosslinking density, heat resistance, and oxygen barrier (antioxidant) capacity of the resin system can be further enhanced at high temperatures (>200℃).

[0064] It is important to note that in the formulation design of slurry systems, the use of strongly acidic resins or high-acid-value resins containing a large number of free carboxyl groups must be strictly avoided. The reason is that a strongly acidic environment will disrupt the coordination bonds formed between the copper salt precursor and the amine complexing agent, causing the complex to dissociate prematurely, become unstable, or even produce irreversible precipitation, thereby severely compromising the latent stability of the slurry during long-term storage and the final conductive bonding effect.

[0065] For example, the first solvent is selected from two or more combinations of ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, dimethyl succinate, dimethyl glutarate, diacetone alcohol, dipropylene glycol methyl ether, diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, dipropylene glycol butyl ether, 3-methoxyethyl acetate, methyl 3-methoxypropionate, and propylene carbonate. Preferably, low- to medium-polarity alcohol ether solvents, such as ethylene glycol butyl ether acetate, diethylene glycol dibutyl ether, and diethylene glycol butyl ether acetate, are used. Strongly hygroscopic solvents should be avoided to prevent affecting the stability of the copper salt precursor.

[0066] For example, the additives, depending on the requirements of air-cured copper paste, may include dispersants, antioxidants, adhesion promoters, thixotropic agents, and auxiliary reducing agents. Among these, dispersants are preferably phosphate esters or acrylic esters, which can effectively prevent copper powder sedimentation and copper salt precursor agglomeration. Antioxidants are preferably volatile or decomposable monomers or compounds containing thiol groups at temperatures below 300°C (such as ethanethiol, isopropanethiol, mercaptoacetic acid, mercaptoacetic acid esters, dodecanethiol, etc.), phosphate esters, acrylate phosphate esters, and related derivatives. Auxiliary reducing agents are preferably ascorbic acid, formic acid, and phosphate esters as complexing reducing agents to promote the uniform reduction of copper salt precursors.

[0067] See Figure 2 The specific steps and flow chart for preparing highly conductive copper paste are shown.

[0068] In one example, the preparation process of the highly conductive copper paste is divided into three stages: resin matrix preparation, copper powder dispersion, and addition of particle-free copper conductive ink. The total solid content is ≥65%, ensuring that the gaps between the conductive copper powder are filled by in-situ nano-copper to form a dense conductive network. The specific operation process is as follows:

[0069] Step S310: Preparation of resin matrix.

[0070] In one example, polymer resin (3-10%, preferably 50% each of alcohol-soluble epoxy resin and polyurethane resin), solvent (3-10%, preferably ethylene glycol butyl ether acetate and diethylene glycol dibutyl ether), and additives (1-5%, including dispersants, thixotropic agents, and antioxidants) are added to a high-speed disperser (800-1200 r / min). The mixture is heated to 70-80°C and stirred for 20-30 min until the polymer resin is completely dissolved, forming a transparent homogeneous solution. After cooling to room temperature (≤30°C), 1-3% of curing agent (mainly blocked isocyanate + auxiliary curing agents: modified dicyandiamide, amino resin, etc.) is added, and stirring continues for 15-20 min to ensure that the unsealing temperature matches the subsequent curing requirements.

[0071] Step S320: Copper powder dispersion.

[0072] In one example, pretreated conductive copper powder (60-80% by weight, preferably 0.5-3.0 μm spherical mixed copper powder with D50, and already undergone alkali washing-acid washing-mercapto / oleylamine coating) is added in batches and dispersed in a high-speed disperser at a low speed of less than 500 r / min for 30 min. The pretreated conductive copper powder is added in 2-3 batches, with each batch spaced 10 min apart. It is then transferred to a three-roll mill (80-100 μm gap) and milled 2-3 times until the fineness is ≤10 μm, and filtered through a 500-mesh sieve. This process ensures that the temperature is controlled at ≤40℃ to prevent premature evaporation of the coating agent.

[0073] Step S330: Add particle-free copper conductive ink.

[0074] Slowly add the particle-free conductive ink prepared in step S100 (5-10% copper salt precursor + 0.5-2% complexing agent + 2-5% second solvent by total mass), using a centrifugal disperser at 700-900 r / min for 1-3 min (the particle-free conductive ink can be added in 2-3 batches during the operation to avoid local over-concentration). Then, grind it 1-2 times with a three-roll mill, filter, and degas under vacuum for 10-15 min to obtain the finished high-conductivity copper paste with a viscosity of 10-500 Pa·s at room temperature. After adding the particle-free conductive ink, the temperature needs to be controlled to ≤30℃ to ensure that the copper salt precursor is in a "dormant" state (ensuring long-term storage potential) and to avoid excessive shearing that could damage the complex.

[0075] The high conductivity copper paste of the present invention can achieve excellent curing conductivity in an air atmosphere, mainly due to the unique multi-component synergistic antioxidant, resin barrier mechanism and curing mechanism in the paste system.

[0076] First, the multi-component synergistic antioxidant mechanism, namely the in-situ protection mechanism of the nano-copper particles, involves the following: During the initial heating phase of the curing process in air (e.g., between 100℃ and 150℃), low-boiling-point complexing agents (such as short-chain amines) and auxiliary reducing agents (such as ascorbic acid and formic acid) in the slurry system preferentially volatilize or undergo thermal decomposition. This process generates a strong reducing atmosphere (e.g., generating H2 and CO) in the local microenvironment of the conductive film or conductive pattern coating, effectively consuming the oxygen that permeates from the air and constructing a regional protective atmosphere around the conductive copper powder, preventing the conductive copper powder, as the main component, from being oxidized. Simultaneously, the copper salt precursor begins to decompose within this temperature range, and the nano-copper layer generated by in-situ reduction possesses extremely high fresh surface activity, enabling it to rapidly undergo metallurgical bonding or sintering with the surrounding large-sized conductive copper powder particles. Once this tight "soldering" network is formed, it significantly reduces the specific surface area of ​​the copper powder particles exposed to air, fundamentally blocking the possibility of subsequent oxidation at high temperatures.

[0077] Secondly, the physical barrier effect of the resin system: The polymer resins (such as phenolic resin and cross-linked epoxy / polyurethane resin) in the slurry system are cross-linked under the action of the curing agent, and after curing, they form a dense three-dimensional polymer network structure. This structure not only gives the conductive film coating or conductive pattern coating excellent adhesion, but also acts as a strong physical barrier, effectively blocking the penetration of external oxygen and moisture into the interior of the conductive coating, thereby ensuring the long-term antioxidant stability of the copper conductive network inside the conductive coating in the air.

[0078] Furthermore, infrared heating is used to achieve curing in an air atmosphere. Leveraging the instantaneous heating characteristic of infrared, the exposure time of the slurry system in the air atmosphere at high temperatures is shortened. Infrared heating primarily uses radiation to raise the temperature; far / mid-infrared rays directly irradiate the surface of the slurry system, are absorbed, and converted into heat. Infrared thermal efficiency is above 85%, energy is concentrated, and the required process temperature can be reached within 10-30 seconds to complete the curing of the conductive film or conductive pattern.

[0079] Furthermore, the "hybrid" slurry system of the present invention combines component compatibility with the potential for long-term storage in its microstructure design.

[0080] Compatibility Mechanism: There is no chemical conflict between the organic complexing agents (such as oleylamine and alkanolamine) in the slurry and the polymer resin (such as alcohol-soluble epoxy resin). By selecting medium- to low-polarity alcohol ether solvents (such as diethylene glycol dibutyl ether and ethylene glycol butyl ether acetate), the polarity of the system is adjusted, allowing the copper salt precursor complex to be uniformly dispersed and dissolved in the resin matrix at the molecular level. This homogeneous system effectively avoids macroscopic phase separation, ensuring that during curing, the in-situ reduced nano-copper can be distributed extremely uniformly in the gaps between all micron-sized large copper powder particles, forming a dense, dead-angle-free conductive network.

[0081] Latent mechanism: Under room temperature storage conditions, copper ions in the copper salt precursor are firmly "encased" in the cage-like structure of the complex by the organic amine complexing agent through strong coordination bonds, and are in a "dormant" state. They do not spontaneously react with the resin, curing agent, or large copper powder particles in the slurry system. This ensures that the viscosity of the slurry remains stable for more than one year at room temperature, and the resistivity change does not exceed 5%. Only when the slurry is printed and placed in a heating device for baking (i.e., triggering the "thermal switch", for example, the temperature rises to above 120°C), the heat energy forces the complex bonds of the complex to break, and the complex decomposes, releasing copper ions / precursors with extremely high chemical activity. Then, under the action of the reducing ligands of the copper salt precursor itself and the auxiliary reducing agent, it is rapidly reduced in situ to nano-metallic copper with high surface energy, thereby instantly completing the "in-situ welding" between large copper powder particles.

[0082] Furthermore, the "hybrid" high-conductivity copper paste of the present invention avoids problems such as phase separation, oxidation and agglomeration of pre-made nanoparticles; compared with pure precursor copper ink, it can increase the solid content by more than 60%, can be used to prepare paste systems with high metal loading, is easy to form thick films, and is suitable for screen printing.

[0083] Compared with existing technologies, the high-conductivity copper paste of this invention does not require the pre-preparation of copper nanoparticles, greatly simplifying the process and eliminating the need for additional cleaning / separation. The conductive copper powder particles in the paste system themselves constitute the main body of the conductive network, with the copper salt precursor accounting for only 5-10% and existing in ionic form, thus avoiding oxidation or agglomeration like copper nanoparticles. Through mixing and compounding, direct in-situ reduction not only improves the conductivity of the copper paste but also further reduces the cost of copper paste preparation.

[0084] In one example, after the highly conductive copper paste is prepared, the curing process uses infrared heating: after screen printing (thickness 20-30μm), it is first surface dried at 100-120℃ for 1-2 minutes (for solvent evaporation), and then cured in an infrared heating oven at 200±10℃ for 15-30 seconds in an air atmosphere.

[0085] During the curing process, the complexing agent and auxiliary reducing agent in the particle-free conductive copper ink preferentially volatilize or thermally decompose in the early stage of heating, generating a reducing atmosphere in the local microenvironment of the coating layer to prevent the conductive copper powder from being oxidized.

[0086] The present invention is further illustrated below through three specific embodiments (Examples 1-3) and a comparative example. The copper paste preparation process in each embodiment was strictly carried out according to the above preparation steps. The pretreatment conditions for the conductive copper powder in all embodiments were uniform: alkaline washing was performed using 3% NaOH, ultrasonicated at 45℃ for 20 min × 2 times; acid washing was performed using 2% H2SO4, ultrasonicated at room temperature for 15 min × 2 times; coating was performed using a 1.5% dodecyl mercaptan + 0.5% oleylamine ethanol solution, reacted at 40℃ for 1.5 h. Performance testing was conducted according to GB / T 17463 (resistivity four-probe method), and viscosity was measured using a Brookfield DV2T, 25℃, No. 14 rotor, 35 r.

[0087] Example 1:

[0088] Example 1 mainly demonstrates high copper powder loading, for example, for the preparation of photovoltaic electrodes, with a target resistivity ≤25μΩ·cm.

[0089] Slurry system components (by mass percentage):

[0090] Blocked isocyanate curing agent 2.0%;

[0091] Alcohol-soluble epoxy resin (E-44) + polyurethane resin (1:1) 6.0%;

[0092] Spherical copper powder (ratio: D50 3μm / D50 0.5μm=2 / 1, pretreatment) 73.0%;

[0093] First solvent (ethylene glycol butyl ether acetate: diethylene glycol dibutyl ether = 1:1) 6.0%; adjuvants (phosphate ester dispersant 2% + dodecyl mercaptan antioxidant 1%) 3.0%;

[0094] In addition, the particle-free conductive copper ink contains the following components: 8.0% copper formate, 1.2% oleylamine complexing agent, and 0.8% ethylene glycol butyl ether acetate.

[0095] Example 2:

[0096] Example 2 mainly demonstrates copper powder loading, for example, for use in flexible circuits, with a target resistivity of ≤30μΩ·cm, highlighting flexibility.

[0097] Slurry system components (by mass percentage):

[0098] Blocked isocyanate + modified dicyandiamide (2:1) 1.5%;

[0099] Polyurethane resin + phenolic resin (8:2) 7.0%;

[0100] A mixture of spherical and flake copper powders (ratio: D50 2.0μm, 7:3, pretreated) yielded 68.0% of the product.

[0101] First solvent (diethylene glycol dibutyl ether: dipropylene glycol butyl ether = 2:1) 8.0%;

[0102] Additives (acrylic acid dispersant 1.5% + thioglycolic acid antioxidant 2% + ascorbic acid reducing agent 0.5%) 4.0%;

[0103] In addition, the particle-free conductive copper ink contains the following components: 7.0% copper acetate, 1.5% 1-amino-2-propanol complexing agent, and 3.0% diethylene glycol dibutyl ether.

[0104] The preparation process is carried out according to the above steps. After adding the particle-free conductive copper ink, it is centrifuged and dispersed for an additional 20 minutes to enhance compatibility.

[0105] Example 3:

[0106] Example 3 mainly demonstrates low copper powder loading, for example, for use in RFID antennas, highlighting its storage stability (latency mechanism) and meeting the requirements of scenarios with strict shelf-life requirements.

[0107] Slurry system components (by mass percentage):

[0108] Blocked isocyanate + amino resin (3:1) 2.5%;

[0109] Alcohol-soluble epoxy resin + phenoxy resin (7:3) 5.0%;

[0110] Spherical copper powder (D50 0.8μm, pretreated) 65.0%;

[0111] First solvent (ethylene glycol ethyl ether acetate: propylene carbonate = 1:1) 9.0%;

[0112] Additives (phosphate ester dispersant 2.5% + isopropanethiol antioxidant 1.5%) 4.0%;

[0113] In addition, the particle-free conductive copper ink contains the following components: copper oxalate 9.0%, triethanolamine complexing agent 0.8%, and diethylene glycol dibutyl ether 4.7%.

[0114] The preparation process is carried out according to the above steps, and the temperature of the resin system during the dissolution stage is precisely controlled at 73-78℃.

[0115] The combination of copper oxalate and triethanolamine results in high complex strength and better room temperature latency, while phenolic-assisted cross-linking further enhances the oxygen barrier effect.

[0116] Comparative example:

[0117] In the comparative example, no particle-free conductive copper ink was added; only traditional conductive copper powder was used.

[0118] Using the same formulation design as in Example 1, only the particle-free conductive copper ink quantum component was removed and the first solvent was replenished.

[0119] Measurements showed that the resistivity of the comparative slurry after curing in air was >100 μΩ·cm, and the storage change was >100%, demonstrating the key role of the in-situ reduction and synergistic anti-oxidation mechanism of the particle-free conductive copper ink in the high-conductivity copper paste of this invention.

[0120] The performance test results of the above embodiments and comparative examples are shown in Table 1:

[0121] Table 1 Performance test results of Examples 1-3 and comparative examples

[0122]

[0123] Further verification through Examples 1-3 above reveals that the mechanism for achieving ultra-low resistivity (8.5 μΩ·cm in Example 1) is essentially a composite design of a "hybrid system" (micron-sized conductive copper powder + in-situ reduced nano-copper solder joints). Compared to the comparative example, the copper salt precursor in the particle-free conductive copper ink undergoes thermal decomposition to generate highly active nano-copper in situ. These nano-copper particles fill the gaps between the micron-sized conductive copper powder, significantly reducing the contact resistance between copper particles.

[0124] Meanwhile, the excellent storage stability of the slurry relies on the stable coordination design of its components. In Examples 2 and 3, the resistivity change after long-term storage was less than 5%. The selection of components such as copper oxalate, triethanolamine (Example 3), or copper acetate, 1-amino-2-propanol (Example 2)—which can form stable complexes—allows copper ions to be "locked in" at room temperature. Simultaneously, the preparation process strictly controls the temperature to ≤30°C to prevent premature breakage of coordination bonds. The comparative example, lacking this mechanism, exhibited drastic resistivity changes (exceeding 500%) during long-term storage.

[0125] Furthermore, the slurry possesses multi-layered antioxidant protection: the first layer (transient gas phase protection) is formed during the initial stage of heat curing, when complexing agents and auxiliary reducing agents (such as ascorbic acid) volatilize / decompose, consuming oxygen and generating a localized reducing atmosphere; the second layer (pretreatment with antioxidant surface coating) is formed, where mercapto-containing compounds such as dodecyl mercaptan and isopropanethiol can form a decomposable protective layer on the surface of conductive copper powder; the third layer (physical barrier) is formed after curing, where the optimized resin system (such as the alcohol-soluble epoxy / polyurethane + auxiliary crosslinking of Example 1) forms a dense network that prevents the penetration of oxygen and moisture in the later stages.

[0126] The comparative examples further demonstrate that without the conductive bridging of in-situ generated nano-copper solder joints, the intrinsic oxidation resistance and physical contact of micron-sized conductive copper powder cannot achieve high conductivity. Furthermore, without the "latent" mechanism of locking copper ions through complexing agents, even with pretreated copper powder, a suitable resin system, and a curing agent, the problem of continuous performance degradation of conventional copper paste during storage cannot be solved.

[0127] In one example, the highly conductive copper paste of the present invention can be widely used in the fabrication of photovoltaic solar cell electrodes, 5G communication device electrodes, flexible electronic circuits, RFID antennas, or printed circuit boards. In use, the highly conductive copper paste of the present invention is screen-printed or coated onto a substrate and cured by infrared heating in an air atmosphere.

[0128] For example, the infrared heating curing process includes: first, surface drying at 100-120°C for 1-2 minutes to evaporate the solvent, and then curing in an infrared heating oven at 200±10°C for 15-30 seconds in an air atmosphere.

[0129] During the curing process, the complexing agent and auxiliary reducing agent in the particle-free conductive copper ink preferentially volatilize or thermally decompose in the early stage of heating (100-150℃), generating a reducing atmosphere in the local microenvironment of the coating layer to prevent the conductive copper powder from being oxidized.

[0130] Specifically, the organic amine complexing agents (such as oleylamine) and auxiliary reducing agents (such as ascorbic acid) in the particle-free conductive copper ink preferentially volatilize or thermally decompose, instantaneously generating a reducing protective atmosphere such as hydrogen and carbon monoxide within tiny areas inside the coating layer, consuming the infiltrated oxygen. Simultaneously, the high temperature causes the particle-free conductive copper ink complex to decompose rapidly, releasing copper ions that are in situ reduced to nano-copper, which quickly establishes a "welded" connection with micron-sized conductive copper powder particles. This process significantly shortens the exposure time of copper in a high-temperature, oxygen-rich environment, overcoming the problem of copper's easy oxidation during sintering in air. Finally, the dense three-dimensional network formed by the cross-linking of the cured polymer resin acts as a physical barrier, encapsulating the entire copper conductive network, ensuring its oxidation resistance and stability during long-term use while retaining the excellent conductivity and oxidation resistance after curing.

[0131] For example, in photovoltaic solar cell electrode applications, the formulation system of Example 1 can achieve a resistivity as low as 8.5 μΩ·cm, meeting the conductivity requirements of high-efficiency cells. It mainly employs a combination design of high copper powder solid content + copper formate precursor + a blend of two copper powder particle sizes + rapid infrared curing. Copper formate exhibits high low-temperature decomposition activity; combined with high solid content and instantaneous heating, it achieves superior conductivity.

[0132] For example, in flexible electronic circuit applications, the formulation system of Example 2 can be used to balance flexibility and conductivity (resistivity 27 μΩ·cm). It mainly employs a combination design of polyurethane resin matrix + ascorbic acid-assisted reduction + alkanolamine complexing agent (compatible with resin hydroxyl groups). Polyurethane provides flexible crosslinking points, and the alkanolamine complexing agent is highly compatible with the resin matrix, ensuring uniform distribution of in-situ nano-solder joints and maintaining good electrical connectivity even when bent.

[0133] For example, in RFID antenna applications, the formulation system of Example 3 can achieve excellent storage stability while ensuring sufficient conductivity (resistivity 36 μΩ·cm). It mainly employs a strong complexing agent (triethanolamine) + highly reactive curing agents such as amino resins + volatile low-molecular-weight antioxidants. Emphasis is placed on the thermal stability of the ligands to achieve long-term and stable "dormant" conditions at room temperature, combined with efficient crosslinking and high-temperature release of antioxidants for high-temperature protection.

[0134] The air-cured high-conductivity copper paste, its preparation method, and its application provided by the embodiments of the present invention have at least one or a portion of the following advantages:

[0135] (1) By combining conductive copper powder (micron-sized copper powder main body) with a specific ratio of particle-free conductive copper ink (copper salt precursor solution), the copper ions in the particle-free conductive copper ink are reduced in situ to nano-copper particles during curing heating. The latter form nano "welding points" between the large particles of conductive copper powder to build a dense three-dimensional conductive network. The high load of micron-sized copper powder ensures high filling, and the in situ nano-copper welding points achieve low contact resistance, resulting in a curing resistivity of ≤40μΩ·cm in air atmosphere.

[0136] (2) By performing a specific pretreatment of conductive copper powder by "alkali washing-acid washing-thiol-containing antioxidant coating", the surface oil and oxide layer are effectively removed. At the same time, the coated thiol-containing compound can volatilize or decompose at a curing temperature of ≤300℃, avoiding itself from becoming a high-resistance impurity. Meanwhile, the reducing atmosphere released during its pyrolysis process can also provide active protection for the conductive copper powder, further improving the antioxidant properties and sintering connection effect in the air atmosphere curing environment.

[0137] (3) By selecting specific types of polymer resins, curing agents, solvents (first solvent and second solvent) and additives, these components together ensure the uniform dispersion, construction adaptability and antioxidant performance of the slurry during the curing process; in particular, by selecting polymer resins that are compatible with the polarity of the complexing agent, a resin matrix system that is highly compatible with particle-free conductive copper ink and has a highly efficient synergistic antioxidant function is constructed. While preventing the demulsification and precipitation of ink complexes, the dense cross-linked network formed after curing also acts as a physical barrier to block the penetration of external oxygen and moisture for a long time, thus achieving stable curing in air and long-term storage stability.

[0138] (4) Particle-free conductive copper ink uses copper formate / copper acetate / copper oxalate in a specific ratio as copper salt precursors and oleylamine / 1-amino-2-propanol as complexing agents to form a stable molecular-level complex solution in a specific solvent, giving the slurry excellent "latency"; when stored at room temperature, copper ions are "locked" by the complexing agent and do not react with the system, ensuring storage stability; when air-cured, it is activated and reduced by heat, releasing nano-copper particles to form high-quality solder joints; it simplifies the prefabrication process (no need to prefabricate nano-copper particles) and solves the oxidation and agglomeration problems in nano-copper storage. When stored at room temperature for more than 1 year, the viscosity and resistivity of the slurry change rate are both ≤5%;

[0139] (5) The particle-free conductive copper ink forms a stable coordination complex with organic amines through copper ions, so that copper is uniformly dispersed in the system in ionic form. The particle-free conductive copper ink has a simple composition and does not contain metal particles. It can achieve high stability without the addition of dispersant. The sintering temperature is low (100-200℃), which matches the curing temperature of air-cured conductive copper paste. The coating layer of the cured conductive film / conductive pattern has low impurity content and high conductivity.

[0140] (6) It provides a complete optimized preparation method from particle-free conductive copper ink formulation (ratio control, pH control, low temperature stirring) to conductive copper powder pretreatment (alkali washing-acid washing-coating) to slurry preparation (step feeding, temperature-controlled grinding), as well as curing application process (infrared heating, first low temperature surface drying and then instantaneous high temperature curing); using this preparation method, high conductivity and high storage stability conductive copper slurry products can be stably mass-produced and successfully applied to photovoltaic electrodes, flexible circuits, RFID antennas and other scenarios, solving technical problems such as poor filling of copper powder gaps, copper oxidation, and complex prefabrication process, and achieving cost reduction and efficiency improvement.

[0141] While some embodiments of the present general inventive concept have been shown and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A highly conductive copper paste that cures in an air atmosphere, characterized in that, The highly conductive copper paste comprises the following components by weight percentage: Conductive copper powder, 60-80%; High molecular weight resin, 3-10%; Hardener, 1-3%; First solvent, 3-10%; Additives, 1-5%; and Particle-free conductive copper ink, 7.5-17%; in The particle-free conductive copper ink is composed of a copper salt precursor, a complexing agent, and a second solvent. The copper salt precursor is dissolved in the mixed system of the complexing agent and the second solvent in the form of copper ions. When the highly conductive copper paste is heated and cured in an air atmosphere, the copper ions in the particle-free conductive copper ink are reduced in situ to nano-copper particles. The nano-copper particles form welded connections between the particles of the conductive copper powder, forming a conductive network composed of micron-sized conductive copper powder and in-situ generated nano-copper weld points.

2. The high conductivity copper paste according to claim 1, characterized in that, The conductive copper powder is at least one of pretreated spherical copper powder, flake copper powder, and dendritic copper powder. The pretreatment includes sequential alkaline washing, acid washing, and antioxidant surface coating, wherein... Alkaline washing removes surface oil and organic matter. The surface oxide layer is removed by acid pickling. The antioxidant is a thiol-containing compound that is volatile or decomposable at 300°C or less, and the thiol-containing compound includes any one or any combination of ethanethiol, isopropanethiol, mercaptoacetic acid, mercaptoacetic acid ester, and dodecanethiol.

3. The high conductivity copper paste according to claim 1, characterized in that, The curing agent is any one or any combination of blocked isocyanates, phthalates, silane coupling agents, modified dicyandiamides, and amino resins. The polymer resin is any one or any combination thereof from alcohol-soluble epoxy resin, polyurethane resin, phenolic resin, phenoxy resin and acrylic resin. The first solvent is a medium-to-low polarity alcohol ether solvent, which includes any one or any combination thereof of ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol dibutyl ether, diethylene glycol butyl ether acetate and dipropylene glycol butyl ether; The adjuvants include dispersants, antioxidants, and auxiliary reducing agents, wherein the dispersant is a phosphate ester or acrylic acid compound, and the auxiliary reducing agent is any one or any combination of ascorbic acid, formic acid, and phosphate ester compounds.

4. The high conductivity copper paste according to claim 3, characterized in that, The resin system formed by the polymer resin includes polar groups that can participate in the heat curing reaction under air atmosphere and / or provide a dense barrier effect. These polar groups are polarly compatible with the complexing agent in the particle-free conductive copper ink. The polymer resin consists of an alcohol-soluble epoxy resin and / or polyurethane resin as the resin body, and is supplemented with phenolic resin or acrylic resin at a mass percentage of 10-30% of the total resin mass of the resin system to improve the crosslinking density and oxygen barrier capacity of the resin system at a high temperature of 200°C or higher.

5. The high conductivity copper paste according to claim 1, characterized in that, The particle-free conductive copper ink comprises the following components by total mass percentage: Copper salt precursor, 5-10%; Complexing agent, 0.5-2%; The second solvent, 2-5%; of which The copper salt precursor is any one or any combination of copper formate, copper acetate, copper oxalate, copper malonate, copper nitrate, copper citrate, copper neodecanoate, copper β-keto acid (II), and ethylene glycol carboxylates. The complexing agent is an alkylamine and / or an alkanolamine, including any one or any combination thereof of oleylamine, butylamine, 1-amino-2-propanol, 2-amino-2-methyl-1-propanol, monoethanolamine, triethanolamine, 1,2-propanediamine and partially etherified amino resins.

6. The high conductivity copper paste according to any one of claims 1-5, characterized in that, The highly conductive copper paste has latency: Under room temperature storage conditions, the copper ions in the copper salt precursor form a coordination complex with the complexing agent. The coordination complex is in a dormant state and does not react with the polymer resin, curing agent and conductive copper powder. When in use, when the heating and curing temperature is greater than or equal to the trigger temperature, the coordination complex undergoes thermal decomposition, releasing copper ions and reducing them in situ to nano-copper particles; The high conductivity copper paste, when stored at room temperature for more than one year, exhibits a viscosity and resistivity change rate of less than or equal to 5%.

7. The high conductivity copper paste according to claim 6, characterized in that, The resistivity of the highly conductive copper paste is less than or equal to 40 μΩ·cm after being heated and cured in air.

8. A method for preparing a highly conductive copper paste that cures in an air atmosphere, the method being used to prepare a highly conductive copper paste according to any one of claims 1-7, characterized in that, The preparation method includes: Preparation of particle-free conductive copper ink: Mix the complexing agent and the second solvent evenly, add the copper salt precursor, and stir until a clear and transparent copper complex solution is formed, wherein the pH value of the copper complex solution is 7-9; Conductive copper powder pretreatment: Conductive copper powder is subjected to alkali washing, acid washing and antioxidant surface coating in sequence, and then dried to obtain pretreated conductive copper powder; Preparation of high-conductivity copper paste: A polymer resin, a first solvent, and additives are mixed, heated to dissolve the resin, cooled, and then a curing agent is added. The pretreated conductive copper powder is then added in batches, dispersed, and ground until a fineness of less than or equal to 10 μm is achieved. Finally, the particle-free conductive copper ink is added, dispersed, and degassed to obtain the high-conductivity copper paste. In the steps of preparing particle-free conductive copper ink and preparing highly conductive copper paste, the process temperature is controlled to be less than or equal to 30°C to maintain the latency of the coordination complex formed by the copper salt precursor and the complexing agent.

9. The preparation method according to claim 8, characterized in that, The steps for preparing the highly conductive copper paste include: Mix the polymer resin, the first solvent and the additives, and stir at 70-80℃ until the polymer resin is completely dissolved to form a homogeneous resin matrix solution. After cooling to ≤30℃, add the curing agent and stir evenly. The pretreated conductive copper powder was added in batches to the homogeneous resin matrix solution, and then slowly stirred and dispersed at ≤40℃ and milled 2-5 times with a three-roll mill until the fineness was ≤10μm. Slowly add particle-free copper conductive ink, disperse it at ≤30℃, and then perform three-roll milling and vacuum degassing 1-3 times to obtain the high conductive copper paste with a total solid content greater than or equal to 65% and a viscosity of 10-500 Pa·s at room temperature.

10. Application of a high-conductivity copper paste cured in an air atmosphere, wherein the high-conductivity copper paste is the high-conductivity copper paste according to any one of claims 1-7 or the high-conductivity copper paste obtained by the preparation method according to claim 8 or 9, characterized in that, The highly conductive copper paste is used to prepare photovoltaic solar cell electrodes, 5G communication device electrodes, flexible electronic circuits, RFID antennas, or printed circuit boards. The highly conductive copper paste is printed or coated onto a substrate and then cured by heating in an air atmosphere to form a conductive film or conductive pattern. The heat curing process uses infrared heating. First, the solvent is evaporated by surface drying at 100-120℃ for 1-2 minutes. Then, it is cured in an infrared heating oven at 200±10℃ for 15-30 seconds in an air atmosphere. During the curing process, the complexing agent and auxiliary reducing agent in the particle-free conductive copper ink preferentially volatilize or thermally decompose in the early stage of heating, generating a reducing atmosphere in the local microenvironment of the coating layer to prevent the conductive copper powder from being oxidized.

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