Conductive paste and method for preparing antioxidant copper powder in conductive paste

Abstract

The present invention discloses a conductive paste, comprising the following raw materials in percentage by mass: 60-90% antioxidant copper powder, 1-30% thermosetting resin, 0.1-5% curing agent, 0.5-5% additive, and 0.1-10% diluent; the antioxidant copper powder is one or more combinations of micro-nano flake or spherical copper powder organically coated by a hydrothermal method, with an average particle size of 0.1-5 μm. In the present invention, a hydrothermal method is used to coat the copper powder with organic matter, so that the surface of the copper powder and the organic matter can be well combined to form a dense organic film layer. At the same time, the high temperature and high pressure liquid phase environment can make the organic matter uniformly form a protective layer on the surface of the copper powder and the surface wrinkle area. The selected organic matter contains carboxylic acid or hydroxyl groups. The organic matter and the surface of the copper powder are not only physically bonded but also chemically bonded. The protective film layer formed in this way can effectively prevent the action of oxygen on the copper powder, achieving a good antioxidant effect. At the same time, the protective film layer in the slurry is not easily destroyed by the components in the slurry, ensuring that the slurry still maintains excellent antioxidant properties after curing.

Description

Technical Field

[0001] The present invention relates to the field of anti-oxidation copper powder conductive paste, and in particular to a conductive paste and a method for preparing the anti-oxidation copper powder in the conductive paste. Background Art

[0002] Conductive paste is one of the most fundamental and key materials in the modern electronics industry and a core functional material in electronic devices. Conductive paste is widely used in various electronic components, including chip resistors, chip capacitors, chip inductors, thick-film integrated circuits, and semiconductor packaging. It is widely used in mobile communications, the Internet of Things, aerospace, solar photovoltaics, automotive electronics, LED lighting, flexible electronics, and other fields.

[0003] Conductive pastes typically consist of a conductive phase, a binder phase, and an organic vehicle, which are thoroughly mixed and dispersed to form a uniform paste. Specific application processes (such as screen printing, spray coating, or 3D printing) are used to form specific circuits. Conductive properties are achieved through high-temperature sintering or low-temperature curing. The conductive phase is typically composed of micro- or nanopowders of gold, silver, palladium, platinum, copper, aluminum, nickel, tungsten, molybdenum, or graphite. The binder phase is categorized as either a glass binder (high-temperature sintering) or a resin binder (low-temperature curing) depending on the metallization process. Low-temperature curing conductive pastes, also known as resin conductive pastes, are typically used for substrates that cannot tolerate high temperatures and require conductive bonding. Low-temperature curing, antioxidant conductive pastes typically consist of a paste composed of metal powder, thermoplastic or thermosetting resin, reactive or inactive organic solvents, surfactants, and thixotropic agents. The conductive film layer is formed using screen printing and then cured at 150-250°C.

[0004] With the rapid development of flexible electronics, low-temperature curing silver electronic pastes are widely used and developed. However, the high price of silver contributes to the high cost of components. Copper and silver have similar resistivities and are approximately one-hundredth the price of silver. However, copper is more susceptible to oxidation in air than silver, forming cupric oxide and cuprous oxide, significantly reducing its conductivity. Copper micro- and nanopowders are commonly used as the conductive phase in electronic pastes. Copper powders, due to their small particle size and large surface area, are more susceptible to oxidation. Therefore, effectively addressing the oxidation resistance of copper powder is a key technology in electronic pastes. A relatively mature technology involves coating copper with silver, which ensures good conductivity and slows copper powder oxidation, but this remains costly. Coating copper powder with organic polymers can also slow copper oxidation to a certain extent, but the organic matter in the electronic paste often dissolves, exposing the copper powder and allowing it to oxidize. Therefore, the antioxidant treatment of copper powder and the electronic paste formulation technology have a significant impact on the conductivity and oxidation resistance of copper electronic pastes. Summary of the Invention

[0005] The object of the present invention is to provide a conductive paste.

[0006] The present invention also provides a method for preparing oxidation-resistant copper powder in a conductive paste.

[0007] The innovation of the present invention lies in that the antioxidant copper powder in the present invention has excellent conductive properties and antioxidant properties when used in conductive paste. The conductive paste in this patent can be better suitable for flexible circuits, RFID devices, MLCC soft terminals and HJT photovoltaic cells, etc.

[0008] To achieve the above-mentioned object of the invention, the technical solution of the present invention is: a conductive paste, characterized in that it comprises the following raw materials in percentage by mass: 60-90% of antioxidant copper powder, 1-30% of thermosetting resin, 0.1-5% of curing agent, 0.5-5% of additive, and 0.1-10% of diluent;

[0009] The antioxidant copper powder is one or more combinations of micro-nano flake or spherical copper powder organically coated by a hydrothermal method, and has an average particle size of 0.1-5 μm.

[0010] Furthermore, the thermosetting resin is one of a blocked polyurethane prepolymer and an epoxy resin mixture, or a mixture of the two.

[0011] Furthermore, the thermosetting resin is a mixture of a blocked polyurethane prepolymer and an epoxy resin mixture, and the mass ratio of the blocked polyurethane prepolymer to the epoxy resin mixture is 4:1 to 1:4.

[0012] Furthermore, the blocked polyurethane prepolymer is a diisocyanate (MDI) blocked by methyl ethyl ketone oxime (C3H7NO) and extended by a polyester diol, the average molecular weight of the polyester diol is 300-3000, and the molar ratio of the polyester diol to the diisocyanate (MDI) is 3:1-1:3; the epoxy resin mixture is a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin, the mixing mass ratio is 1:2-2:1, the viscosity is 1000-1500 Pa·s, and the epoxy equivalent is 160-170.

[0013] Furthermore, the curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:1 to 100:10, wherein the latent curing agent is any one or more mixtures of 2-phenyl-4-methylimidazole (2P4MZ), 1-cyanoethyl-2-ethyl-4-methylimidazole trimellitate (2E4MZ-CNS), 2,4-diamino-6[2'-methylimidazole-(1')]ethyl-S-triazine triisocyanate adduct (2MA-OK), 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ), 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ), 1-cyanoethyl-2-phenyl-4,5-bis(cyanoethylmethyl)imidazole (2PHZ-CN), etc.; the curing accelerator is any one or more mixtures of dibutyltin dilaurate, stannous octoate, bismuth laurate, bismuth isooctanoate, boron trifluoride ethylamine, etc.

[0014] Furthermore, the additive is any one or more mixtures of polyamide wax, oleic acid, n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and polyether-modified polysiloxane.

[0015] Furthermore, the diluent is any one or more mixtures of diethylene glycol butyl ether acetate, propylene glycol phenyl ether, alcohol ester dodecahydrate, polyethylene glycol diglycidyl ether, and hexahydrophthalic acid diglycidyl ester.

[0016] A method for preparing oxidation-resistant copper powder in a conductive paste, characterized by comprising the following steps:

[0017] (1) One or more combinations of micro-nano flake or spherical copper powders are immersed in a 5-18 mol / L formic acid solution at a speed of 400-500 rpm for 30 min, and the solution is filtered to obtain treated copper powder;

[0018] (2) adding the organic coating agent solution to the treated copper powder, and using an emulsifier at 10,000-20,000 rpm to emulsify and coat for 3-5 minutes to obtain an emulsified coated copper powder solution;

[0019] (3) transferring the emulsified coated copper powder liquid into a high-pressure reactor, placing the high-pressure reactor in an oven at 150-200°C for 4-24 hours, and performing hydrothermal coating to obtain a hydrothermal coated copper powder liquid;

[0020] (4) The hydrothermal coated copper powder solution was filtered to remove the supernatant, and the solution was washed with deionized water until the resistivity of the washing solution was ≥18MΩ to obtain water-washed copper powder, which was then placed in a freeze dryer for freeze drying to obtain antioxidant copper powder.

[0021] Furthermore, in step (1), the mass ratio of the copper powder to the formic acid solution is 1:2, and in step (2), the mass ratio of the organic coating agent to the copper powder is 0.1:1 to 20:1.

[0022] Furthermore, the organic coating agent is ascorbic acid (C6H8O6), malic acid (C4H6O5), succinic acid (C4H6O4), lactic acid (CH3CH(OH)COOH), tartaric acid (C4H6O6), benzoic acid (C6H5COOH), adipic acid (C6H 10 O4), glucose (C6H 12 O6), salicylic acid (C7H6O3), acrylic acid (CH2=CHCOOH), decanoic acid (C 10 H 20 O2), citric acid (C6H8O7), lauric acid (C 12 H 24 O2), octanoic acid (C8H 16 O2), nonanoic acid (C9H 18 O2), oleic acid (C 18 H 34 O2), linoleic acid (C 18 H 32 O2), phytic acid (C6H 18 O 24 P6), coumaric acid (C9H8O3), p-hydroxybenzoic acid (C7H6O3), vanillic acid (C8H8O4), salvia miltiorrhiza acid (C 26 H 22 O 10 ) etc.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention adopts a hydrothermal method to coat copper powder with organic matter, so that the surface of the copper powder and the organic matter can be well combined to form a dense organic film layer. At the same time, the high temperature and high pressure liquid phase environment can make the organic matter evenly form a protective layer on the surface of the copper powder and the surface wrinkle area. The selected organic matter contains carboxylic acid or hydroxyl groups. The organic matter and the surface of the copper powder are not only physically combined but also chemically bonded. The protective film layer formed in this way can effectively prevent the action of oxygen and copper powder, achieving a good antioxidant effect. At the same time, the protective film layer in the slurry is not easily destroyed by the components in the slurry, ensuring that the slurry still maintains excellent antioxidant properties after curing. The selected organic coating agent has a small molecular weight, and the organic film layer formed after dehydration and drying is thin, which ensures the conductive properties of the copper powder.

[0025] 2. The present invention utilizes a thermosetting resin, curing agent, and additives as the organic phase, achieving excellent screen-passing performance. The cured film is dense and smooth, exhibiting strong substrate adhesion and excellent flexibility. The epoxy resin mixture with a viscosity of 1000-1500 mPa·s facilitates the slurry's slurrying and adhesion properties. The blocked polyurethane prepolymer imparts excellent film flexibility. The curing accelerator can appropriately lower the curing temperature of the blocked polyurethane prepolymer. The curing agent's good latency facilitates storage of the slurry.

[0026] 3. The antioxidant copper powder and conductive paste of the present invention are suitable for curing in the range of 120~200℃, which can meet the application of different substrates. After being fully mixed with the conductive powder, the organic matter can fully coat the conductive powder, achieving good rheological properties, improving printing accuracy, and excellent filling effect. During the curing process, the blocked polyurethane prepolymer self-polymerizes and the blocked polyurethane prepolymer-epoxy copolymerizes to form a polymer, achieving excellent flexibility of the film layer. The polymer is coated on the surface of the conductive powder to form a dense cured film layer. At the same time, the polymer forms a good bond with the substrate. The cured organic matter cross-links to form a polymer-copper-polymer composite conductive chain, and the conductive performance of the slurry is guaranteed. The retention of the polymer further enhances the oxidation resistance of the slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of resistivity and oxidation resistance evaluation.

[0028] Figure 2 It is a screen printing diagram of resistivity and oxidation resistance electrode.

[0029] Figure 3 It is a printed screen pattern for adhesion strength. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings.

[0031] Example 1: A conductive paste comprising the following raw materials in percentage by mass: 60% of the antioxidant copper powder of Example 6, 30% of a thermosetting resin, 2% of a curing agent, 5% of an additive, and 3% of a diluent;

[0032] The antioxidant copper powder is a micro-nano flaky copper powder organically coated by a hydrothermal method, with an average particle size of 0.1~5μm.

[0033] The thermosetting resin is a blocked polyurethane prepolymer.

[0034] The blocked polyurethane prepolymer is a polyester diol-chain-extended diisocyanate (MDI) blocked with methyl ethyl ketone oxime (C3H7NO) dissolved in a high-boiling-point solvent. The average molecular weight of the polyester diol is 300-3000, and the molar ratio of polyester diol to diisocyanate (MDI) is 3:1.

[0035] The curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:1, the latent curing agent is 2-phenyl-4-methylimidazole (2P4MZ), and the curing accelerator is dibutyltin dilaurate.

[0036] The additive is polyamide wax.

[0037] The diluent is diethylene glycol butyl ether acetate.

[0038] Example 2: A conductive paste comprising the following raw materials in percentage by mass: 90% of the antioxidant copper powder of Example 7, 1% of a thermosetting resin, 0.1% of a curing agent, 0.5% of an additive, and 8.4% of a diluent;

[0039] The antioxidant copper powder is a micro-nano spherical copper powder organically coated by a hydrothermal method, with an average particle size of 0.1~5μm.

[0040] Thermosetting resin is an epoxy resin mixture.

[0041] The epoxy resin mixture is a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin, with a mixing mass ratio of 1:2, a viscosity of 1000-1500 Pa·s, and an epoxy equivalent of 160-170.

[0042] The curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:5, the latent curing agent is 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate (2E4MZ-CNS), and the curing accelerator is stannous octoate.

[0043] The additive is oleic acid.

[0044] The diluent is propylene glycol phenyl ether.

[0045] Example 3: A conductive paste comprising the following raw materials in percentage by mass: 68% of the antioxidant copper powder of Example 6, 15% of a thermosetting resin, 5% of a curing agent, 2% of an additive, and 10% of a diluent;

[0046] The antioxidant copper powder is a micro-nano flaky copper powder organically coated by a hydrothermal method, with an average particle size of 0.1~5μm.

[0047] The thermosetting resin is a mixture of a blocked polyurethane prepolymer and an epoxy resin mixture, and the mass ratio of the blocked polyurethane prepolymer to the epoxy resin mixture is 4:1.

[0048] The end-capped polyurethane prepolymer is a polyester diol-extended diisocyanate (MDI) blocked with methyl ethyl ketone oxime (C3H7NO) dissolved in a high-boiling-point solvent. The average molecular weight of the polyester diol is 300-3000, and the molar ratio of polyester diol to diisocyanate (MDI) is 1:2. The epoxy resin mixture is a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin in a mixing ratio of 1:1, with a viscosity of 1000-1500 Pa·s and an epoxy equivalent weight of 160-170.

[0049] The curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:10, the latent curing agent is 2,4-diamino-6[2'-methylimidazole-(1')]ethyl-S-triazine triisocyanate adduct (2MA-OK), and the curing accelerator is bismuth laurate.

[0050] The additive is n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0051] The diluent is alcohol ester dodecahydrate.

[0052] Example 4: A conductive paste comprising the following raw materials in percentage by mass: 75% of the antioxidant copper powder of Example 8, 18.9% of a thermosetting resin, 3% of a curing agent, 3% of an additive, and 0.1% of a diluent;

[0053] The antioxidant copper powder is a combination of micro-nano flake or spherical copper powder organically coated by a hydrothermal method, with an average particle size of 0.1~5μm.

[0054] The thermosetting resin is a mixture of a blocked polyurethane prepolymer and an epoxy resin mixture, and the mass ratio of the blocked polyurethane prepolymer to the epoxy resin mixture is 1:2.

[0055] The end-capped polyurethane prepolymer is a polyester diol-extended diisocyanate (MDI) blocked with methyl ethyl ketone oxime (C3H7NO) dissolved in a high-boiling-point solvent. The average molecular weight of the polyester diol is 300-3000, and the molar ratio of polyester diol to diisocyanate (MDI) is 1:3. The epoxy resin mixture is a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin in a mixing ratio of 2:1, with a viscosity of 1000-1500 Pa·s and an epoxy equivalent weight of 160-170.

[0056] The curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:8, the latent curing agent is 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ); the curing accelerator is any one or more mixtures of bismuth isooctanoate, boron trifluoride ethylamine, etc.

[0057] The additive is polyether-modified polysiloxane.

[0058] The diluent is polyethylene glycol diglycidyl ether.

[0059] Example 5: A conductive paste comprising the following raw materials in percentage by mass: 65% of the antioxidant copper powder of Example 8, 23% of a thermosetting resin, 4% of a curing agent, 4% of an additive, and 4% of a diluent;

[0060] The antioxidant copper powder is a combination of micro-nano flake or spherical copper powder organically coated by a hydrothermal method, with an average particle size of 0.1~5μm.

[0061] The thermosetting resin is a mixture of blocked polyurethane prepolymer and epoxy resin.

[0062] The thermosetting resin is a mixture of a blocked polyurethane prepolymer and an epoxy resin mixture, and the mass ratio of the blocked polyurethane prepolymer to the epoxy resin mixture is 1:4.

[0063] The end-capped polyurethane prepolymer is a polyester diol-chain-extended diisocyanate (MDI) blocked with methyl ethyl ketone oxime (C3H7NO) dissolved in a high-boiling-point solvent. The polyester diol has an average molecular weight of 300-3000, and the molar ratio of polyester diol to diisocyanate (MDI) is 1:1. The epoxy resin mixture is a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin in a mixing ratio of 3:2-2:1, a viscosity of 1000-1500 Pa·s, and an epoxy equivalent weight of 160-170.

[0064] The curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:3, the latent curing agent is any one or more mixtures of 2-phenyl-4-methylimidazole (2P4MZ), 1-cyanoethyl-2-ethyl-4-methylimidazole trimellitate (2E4MZ-CNS), 2,4-diamino-6[2'-methylimidazole-(1')]ethyl-S-triazine triisocyanate adduct (2MA-OK), 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ), 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ), 1-cyanoethyl-2-phenyl-4,5-bis(cyanoethylmethyl)imidazole (2PHZ-CN), etc.; the curing accelerator is any one or more mixtures of dibutyltin dilaurate, stannous octoate, bismuth laurate, bismuth isooctanoate, boron trifluoride ethylamine, etc.

[0065] The additive is any one or more mixtures of polyamide wax, oleic acid, n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane and polyether modified polysiloxane.

[0066] The diluent is any one or more mixtures of diethylene glycol butyl ether acetate, propylene glycol phenyl ether, alcohol ester dodecahydrate, polyethylene glycol diglycidyl ether, and hexahydrophthalic acid diglycidyl ester.

[0067] Example 6: A method for preparing antioxidant copper powder in a conductive paste, comprising the following steps:

[0068] (1) The micro-nano flaky copper powder was immersed in a 5 mol / L formic acid solution at 400 rpm for 30 min, and the solution was filtered to obtain the treated copper powder. The mass ratio of the copper powder to the formic acid solution was 1:2.

[0069] (2) adding the organic coating agent solution to the treated copper powder, and using an emulsifier at 10,000 rpm for 3 minutes to emulsify and coat the copper powder to obtain an emulsified coated copper powder solution, wherein the mass ratio of the organic coating agent to the copper powder is 0.1:1, and the organic coating agent is ascorbic acid (C6H8O6);

[0070] (3) transferring the emulsified coated copper powder liquid into a high-pressure reactor, placing the high-pressure reactor in an oven at 150° C. for 4 h, and performing hydrothermal coating to obtain a hydrothermal coated copper powder liquid;

[0071] (4) The hydrothermal coated copper powder solution was filtered to remove the supernatant, and the solution was washed with deionized water until the resistivity of the washing solution was ≥18MΩ to obtain water-washed copper powder, which was then placed in a freeze dryer for freeze drying to obtain antioxidant copper powder.

[0072] Example 7: A method for preparing antioxidant copper powder in a conductive paste, comprising the following steps:

[0073] (1) The micro-nano spherical copper powder was immersed in a 10 mol / L formic acid solution at 450 rpm for 30 min, and the solution was filtered to obtain the treated copper powder;

[0074] (2) Adding the organic coating agent solution to the treated copper powder, and using an emulsifier at 15000 rpm for 4 minutes to emulsify and coat the copper powder to obtain an emulsified coated copper powder solution. The mass ratio of the organic coating agent to the copper powder is 10:1, and the organic coating agent is malic acid (C4H6O5);

[0075] (3) transferring the emulsified coated copper powder liquid into a high-pressure reactor, placing the high-pressure reactor in an oven at 180°C for 10 hours, and performing hydrothermal coating to obtain a hydrothermal coated copper powder liquid;

[0076] (4) The hydrothermal coated copper powder solution was filtered to remove the supernatant, and the solution was washed with deionized water until the resistivity of the washing solution was ≥18MΩ to obtain water-washed copper powder, which was then placed in a freeze dryer for freeze drying to obtain antioxidant copper powder.

[0077] Example 8: A method for preparing antioxidant copper powder in a conductive paste, comprising the following steps:

[0078] (1) The copper powder of micro-nano flake or spherical combination is immersed in 18 mol / L formic acid solution at 500 rpm for 30 min, and the solution is filtered to obtain the treated copper powder;

[0079] (2) Adding the organic coating agent solution to the treated copper powder, and using an emulsifier at 20,000 rpm for 5 minutes to emulsify and coat the copper powder to obtain an emulsified coated copper powder solution. The mass ratio of the organic coating agent to the copper powder is 20:1, and the organic coating agent is succinic acid (C4H6O4);

[0080] (3) transferring the emulsified coated copper powder liquid into a high-pressure reactor, placing the high-pressure reactor in an oven at 200°C for 24 hours, and performing hydrothermal coating to obtain a hydrothermal coated copper powder liquid;

[0081] (4) The hydrothermal coated copper powder solution was filtered to remove the supernatant, and the solution was washed with deionized water until the resistivity of the washing solution was ≥18MΩ to obtain water-washed copper powder, which was then placed in a freeze dryer for freeze drying to obtain antioxidant copper powder.

[0082] Example 9: Referring to Example 8, the organic coating agent is ascorbic acid (C6H8O6), malic acid (C4H6O5), succinic acid (C4H6O4), lactic acid (CH3CH(OH)COOH), tartaric acid (C4H6O6), benzoic acid (C6H5COOH), adipic acid (C6H 10 O4), glucose (C6H 12 O6), salicylic acid (C7H6O3), acrylic acid (CH2=CHCOOH), decanoic acid (C 10 H 20 O2), citric acid (C6H8O7), lauric acid (C 12 H 24 O2), octanoic acid (C8H 16 O2), nonanoic acid (C9H 18 O2), oleic acid (C 18 H 34 O2), linoleic acid (C 18 H 32 O2), phytic acid (C6H 18 O 24 P6), coumaric acid (C9H8O3), p-hydroxybenzoic acid (C7H6O3), vanillic acid (C8H8O4), salvia miltiorrhiza acid (C 26 H 22 O 10 ) etc.

[0083] Comparative Example 1: Referring to Example 1, the antioxidant copper powder was replaced with micro-nano flaky copper powder without surface coating.

[0084] Comparative Example 2: Referring to Example 2, the antioxidant copper powder was replaced with micro-nano spherical copper powder without surface coating.

[0085] Comparative Example 3: Referring to Example 1, 50% of the antioxidant copper powder was replaced with micro-nano flaky copper powder without surface coating.

[0086] Comparative Example 4: Referring to Example 2, 50% of the antioxidant copper powder was replaced with micro-nano spherical copper powder without surface coating.

[0087] The antioxidant copper powders of Examples 6 to 8, the micro-nano flaky copper powder without surface coating, and the micro-nano spherical copper powder without surface coating were tested for resistivity and TGA weight gain according to the following method. The results are shown in Table 1.

[0088] Resistivity: Weigh 1 ± 0.1 g of copper powder and place it in a cylindrical mold with a diameter of 6 mm and a height of 10 mm. Press the sample under a pressure of 5 MPa. Use a four-wire resistance meter to measure the resistance, and calculate the resistivity according to formula (1).

[0089] Formula (1)

[0090] Where, is the resistivity in Ω·cm; R is the resistance in Ω; h is the sample height in cm; d is the bottom diameter of the sample in cm; and π is the ratio of the diameter of the circle to the circumference of the circle. Generally, the lower the resistivity of a sample, the better.

[0091] (2) TGA weight gain: Weigh 0.1±0.01g of copper powder and place it in a 0.4ml alumina crucible. In an air atmosphere, heat the temperature from room temperature to 200℃ at a rate of 5℃ / min, then hold the temperature for 60min. Calculate the weight gain ratio of the sample. Generally, the lower the sample weight gain ratio, the better the sample's antioxidant properties.

[0092] Table 1 Performance test results of hydrothermal coated copper powder in Examples 1 to 12

[0093] <![CDATA[Resistivity (×10 -4 Ω·cm )]]> TGA weight gain (%) Example 6 65.33 2.32 Example 7 1.63 0.38 Example 8 21.39 0.76 Comparative Example 1 1783.54 12.2 Comparative Example 2 1552.81 16.4

[0094] The conductive pastes prepared in Examples 1 to 4 and Comparative Examples 1 to 4 were tested for viscosity, resistivity, anti-oxidation resistivity, and adhesion strength according to the following methods. The results are shown in Table 2.

[0095] (1) Viscosity: Stir the sample evenly with a mixing knife. Take a small amount of the sample and place it in a small sample adapter. Place it in a 25℃ water bath for 10 minutes. Use a Brookfield HBT rotational viscometer with a 14# rotor and rotate it at 10 rpm for 1 minute to read the viscosity data. Viscosity affects the printing properties of the conductive paste. Too low viscosity can easily cause edge diffusion and paste leakage. Too high viscosity can cause edge burrs and printed adhesive. The viscosity of the conductive paste is usually required to be 30-100 Pa·s to meet screen printing requirements.

[0096] (2) Resistivity: Stir the sample evenly with a slurry knife, take a small amount of the sample, and Figure 2 The wire mesh shown in (a) is used to make Ag electrodes on alumina substrates ( Figure 1 As shown in (b), using Figure 2 (b) Screen printed copper conductive paste ( Figure 1 After printing, allow to level naturally for 3 to 5 minutes, pre-cure at 120°C for 10 minutes, and cure at 200°C for 30 minutes to ensure the thickness of the cured film is 10 to 25 μm. Figure 1 The average resistivity is calculated by formula (2) on the silver electrode in (b):

[0097] (2)

[0098] Where, is the average resistivity, in units of Ω·cm ; Is a single resistor, the unit is Ω ; w is the electrode width, in units of cm; l is the electrode length, in units of cm, h i is the electrode thickness, in units of cm;i=1,2…n;n For the measurement quantity, take n = 4. It is generally desired that the resistivity of the film layer is as small as possible.

[0099] (3) Stir the sample evenly with a mixing knife, take a small amount of the sample, and Figure 2 The wire mesh shown in (a) is used to make Ag electrodes on alumina substrates (( Figure 1 As shown in (b), using Figure 2 (b) Screen printed copper conductive paste ( Figure 1 After printing, allow to level naturally for 3 to 5 minutes, pre-cure at 120°C for 10 minutes, and cure at 200°C for 30 minutes to ensure the thickness of the cured film is 10 to 25 μm. Figure 1 The resistance value of the silver electrode in (b) is tested, and the average resistivity is calculated by formula (2): Place the electrode sheet in a 60℃ blast oven, take it out after 1000h, test the resistance value, and calculate the resistivity after vulcanization according to formula (2): Formula (3) is used to calculate the change rate of sulfurized resistance.

[0100] (3)

[0101] Where, is the rate of change of antioxidant resistance; is the initial resistivity of the electrode, in units of Ω·cm ; is the resistivity after oxidation, in units of Ω·cm It is generally desired that the resistivity change of the film layer be as small as possible.

[0102] (4) Adhesion: Stir the sample evenly with a mixing knife, take a small amount of the sample, and use Figure 3 The screen pattern shown is a 2.5mm x 2.5mm pattern printed on an alumina substrate. After printing, allow the pattern to level naturally for 3-5 minutes. A 2mm x 2mm aluminum oxide square is then bonded to the electrode. Pre-curing is performed at 120°C for 10 minutes, followed by curing at 200°C for 30 minutes, ensuring a cured film thickness of 10-15μm. The adhesion strength of the slurry is tested using a thrust tester. Adhesion strength is a characteristic of the product's bond to the substrate, and generally, the higher the adhesion strength, the better.

[0103] Table 2 Performance of conductive pastes of Examples 1 to 4 and Comparative Examples 1 to 4

[0104] Viscosity (Pa·s) <![CDATA[Resistivity (×10 -4 Ω·cm )]]> Oxidation resistance change rate (%) <![CDATA[Adhesion strength (N / mm 2 )]]> Example 1 58.3 12.74 10.95 11.3 Example 2 82.9 0.91 1.47 10.5 Example 3 98.1 1.15 1.53 8.6 Example 4 106.4 1.02 3.12 7.4 Comparative Example 1 79.2 785.51 19.29 9.1 Comparative Example 2 79.2 1088.43 13.72 6.3 Comparative Example 3 77.6 348.19 16.86 8.7 Comparative Example 4 75.4 213.62 11.37 8.2

[0105] As shown in Tables 1 and 2, the electrode layers produced from the antioxidant copper powder and conductive paste of the present invention exhibit excellent resistivity, low oxidation resistance change rate, and good adhesion strength. The copper powders hydrothermally coated in Examples 6-8 exhibit superior oxidation resistance compared to uncoated micro-nano flaky copper powders and uncoated micro-nano spherical copper powders. The conductive pastes produced in Examples 1-4, compared to Comparative Examples 1-4, have suitable viscosities that meet screen printing requirements. The pastes exhibit good resistivity, oxidation resistance, and adhesion strength, meeting the requirements of electronic circuits for various applications.

[0106] The embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A conductive paste, characterized in that: The invention comprises the following raw materials in percentage by mass: 60-90% of antioxidant copper powder, 1-30% of thermosetting resin, 0.1-5% of curing agent, 0.5-5% of additive, and 0.1-10% of diluent; The antioxidant copper powder is one or more combinations of micro-nano flake or spherical copper powders organically coated by a hydrothermal method, with an average particle size of 0.1 to 5 μm. The preparation method of the antioxidant copper powder comprises the following steps: (1) One or more combinations of micro-nano flake or spherical copper powders are immersed in a 5-18 mol / L formic acid solution at a speed of 400-500 rpm for 30 min, and the solution is filtered to obtain treated copper powder; (2) adding the organic coating agent solution to the treated copper powder, and using an emulsifier at 10,000-20,000 rpm to emulsify and coat for 3-5 minutes to obtain an emulsified coated copper powder solution; (3) transferring the emulsified coated copper powder liquid into a high-pressure reactor, placing the high-pressure reactor in an oven at 150-200°C for 4-24 hours, and performing hydrothermal coating to obtain a hydrothermal coated copper powder liquid; (4) filtering the hydrothermal coated copper powder solution to remove the supernatant, washing with deionized water until the wash solution resistivity is ≥18 MΩ to obtain washed copper powder, and freeze-drying the washed copper powder in a freeze dryer to obtain antioxidant copper powder; The organic coating agent is ascorbic acid (C6H8O6), malic acid (C4H6O5), succinic acid (C4H6O4), lactic acid (CH3CH(OH)COOH), tartaric acid (C4H6O6), benzoic acid (C6H5COOH), adipic acid (C6H 10 O4), glucose (C6H 12 O6), salicylic acid (C7H6O3), acrylic acid (CH2=CHCOOH), decanoic acid (C 10 H 20 O2), citric acid (C6H8O7), lauric acid (C 12 H 24 O2), octanoic acid (C8H 16 O2), nonanoic acid (C9H 18 O2), oleic acid (C 18 H 34 O2), linoleic acid (C 18 H 32 O2), phytic acid (C6H 18 O 24 P6), coumaric acid (C9H8O3), p-hydroxybenzoic acid (C7H6O3), vanillic acid (C8H8O4), salvia miltiorrhiza acid (C 26 H 22 O 10 ) or more combinations thereof.

2. The conductive paste according to claim 1, characterized in that The thermosetting resin is one of a blocked polyurethane prepolymer and an epoxy resin mixture or a mixture of the two.

3. The conductive paste according to claim 2, characterized in that The thermosetting resin is a mixture of a blocked polyurethane prepolymer and an epoxy resin mixture, and the mass ratio of the blocked polyurethane prepolymer to the epoxy resin mixture is 4:1 to 1:

4.

4. The conductive paste according to claim 3, characterized in that The blocked polyurethane prepolymer is a polyester diol-chain-extended diisocyanate (MDI) blocked with methyl ethyl ketone oxime (C3H7NO) dissolved in a high-boiling-point solvent, wherein the polyester diol has an average molecular weight of 300-3000 and a molar ratio of polyester diol to diisocyanate (MDI) of 3:1-1:

3. The epoxy resin mixture is a mixture of bisphenol A epoxy resin and bisphenol F epoxy resin in a mixing mass ratio of 1:2-2:1, a viscosity of 1000-1500 Pa·s, and an epoxy equivalent weight of 160-170.

5. The conductive paste according to claim 1, characterized in that The curing agent is a mixture of a latent curing agent and a curing accelerator in a mass ratio of 100:1 to 100:10, wherein the latent curing agent is any one or more mixtures of 2-phenyl-4-methylimidazole (2P4MZ), 1-cyanoethyl-2-ethyl-4-methylimidazole trimellitate (2E4MZ-CNS), 2,4-diamino-6[2'-methylimidazole-(1')]ethyl-S-triazine triisocyanate adduct (2MA-OK), 2-phenyl-4,5-dihydroxymethylimidazole (2PHZ), 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ), and 1-cyanoethyl-2-phenyl-4,5-bis(cyanoethylmethyl)imidazole (2PHZ-CN); and the curing accelerator is any one or more mixtures of dibutyltin dilaurate, stannous octoate, bismuth laurate, bismuth isooctanoate, and ethylamine boron trifluoride.

6. The conductive paste according to claim 1, characterized in that The additive is any one or more mixtures of polyamide wax, oleic acid, n-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and polyether-modified polysiloxane.

7. The conductive paste according to claim 1, characterized in that: The diluent is any one or more mixtures of diethylene glycol butyl ether acetate, propylene glycol phenyl ether, alcohol ester dodecahydrate, polyethylene glycol diglycidyl ether, and hexahydrophthalic acid diglycidyl ester.

8. The conductive paste according to claim 1, characterized in that The mass ratio of the copper powder to the formic acid solution in the step (1) is 1:2, and the mass ratio of the organic coating agent to the copper powder in the step (2) is 0.1:1 to 20:1.

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