Nanoscale copper-silver composite stainless steel heating ultralow-resistance slurry

Abstract

The invention belongs to the technical field of conductive paste, and relates to nanoscale copper-silver composite stainless steel heating ultralow-resistance paste. The conductive paste comprises the following components in percentage by mass: 3-6% of glass powder, 15-20% of organic carrier and the balance of silver powder. Wherein the silver powder is a ternary gradient system formed by two Ag-coated Cu composite materials with different particle sizes and flake silver powder; and the glass powder is a multi-element lead-free system containing Li2O, WO3, Al2O3 and V2O5. Through the structural regulation and control of the ternary conductive phase, the synergistic effect of the multi-element glass powder and the optimized compatibility of the organic carrier, after the paste is printed and sintered on a stainless steel substrate, the excellent performance that the sheet resistance is smaller than or equal to 3 m omega / square and the adhesive force is larger than or equal to 16 N / mm < 2 > can be achieved, and the paste has the comprehensive advantages of being rapid in response at the high temperature, stable in long-term work and remarkably reduced in cost.

Description

Technical Field

[0001] This invention belongs to the field of conductive paste technology and relates to a nanoscale copper-silver composite stainless steel heating ultra-low resistance paste. Background Technology

[0002] Conductive pastes, as key functional materials for forming thick-film circuits, are widely used in fields such as heating elements on stainless steel substrates. Currently, the conventional conductive pastes used on stainless steel substrates mainly rely on highly conductive silver-based systems.

[0003] In the existing technology, the design of conductive paste for stainless steel substrates is mainly divided into two categories: (1) single spherical silver powder-based conductive paste, and (2) silver-coated copper powder composite conductive paste. Both of these solutions have significant technical defects and application shortcomings, making it difficult to meet the industrialization requirements of low sheet resistance, high adhesion, excellent temperature resistance and low cost.

[0004] Conventional conductive pastes for stainless steel substrates generally use a single spherical silver powder as the conductive phase, or directly select a composite silver powder formulation with high silver content. Silver powder has excellent conductivity and film-forming properties, making it a classic conductive phase material in the field of conductive pastes. However, this type of formulation has the following problems: the particle packing of single spherical silver powder easily forms a conductive network with high porosity, and the contact sites between particles are limited, resulting in a high sheet resistance of the prepared conductive film layer, which cannot meet the requirements for ultra-low resistance heating films and is difficult to adapt to the high-efficiency heating requirements under low voltage conditions; silver is a precious metal, and the raw material price is high. High silver content formulations directly lead to high production costs of conductive pastes, significantly compressing the profit margin of industrialization and limiting the widespread promotion of heating films for stainless steel substrates.

[0005] To address the issue of excessively high silver powder costs, those skilled in the art have employed a composite conductive paste solution using silver-coated copper powder to partially replace silver powder. This leverages the low-cost nature of copper powder to reduce the amount of precious metals used, while simultaneously preserving the excellent conductivity of the silver phase through the core-shell structure of the silver-coated copper powder. However, in this solution, the particle size distribution between the silver-coated copper powder and the silver powder is prone to imbalance, resulting in a loose internal conductive network and discontinuous conductive paths after the paste film is formed. This not only fails to effectively reduce the sheet resistance of the film but also causes a decrease in conductive stability, making it prone to resistance drift under long-term energized heating conditions.

[0006] In addition, the compatibility of glass powder as a binder phase in conductive paste with stainless steel substrates is insufficient. The softening temperature and expansion coefficient of existing glass powders do not match the stainless steel substrate well. This can lead to poor adhesion between the film and the stainless steel substrate, resulting in film peeling and flaking under thermal cycling and mechanical vibration conditions. Alternatively, it can cause insufficient temperature resistance of the film, leading to softening of the glass phase and crystal phase transformation during high-temperature steady-state heating, resulting in damage to the conductive network and subsequent problems such as a sudden increase in film resistance and heating failure. Summary of the Invention

[0007] To address the problems and deficiencies in the existing technology, this invention provides a nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry.

[0008] On the one hand, the present invention provides a nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry, wherein the conductive slurry is composed of 3%~6% glass powder, 15%~20% organic carrier and the balance silver powder by mass percentage;

[0009] The silver powder is composed of Ag@Cu composite materials with particle sizes of 0.5~2μm and 5~10μm, and flake-shaped silver powder with a particle size of 15~20μm. The glass powder is composed of Bi2O3, B2O3, ZnO, Li2O, WO3, Al2O3 and V2O5; The organic carrier is composed of organic solvent, thickener, surfactant and diluent.

[0010] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the silver powder is composed of 5%~7% 0.5~2μm Ag@Cu composite material, 38%~45% 5~10μm Ag@Cu composite material and the balance 5~20μm flake silver powder.

[0011] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the glass powder is composed of 28%~35% B2O3, 20%~26% ZnO, 3%~8% Li2O, 5%~10% WO3, 3%~7% Al2O3, 2%~6% V2O5 and the balance Bi2O3.

[0012] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the organic carrier is composed of 18%~22% thickener, 0.5%~2% surfactant, 36%~40% diluent and the balance organic solvent.

[0013] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the organic solvent is a mixture of dibutyl phthalate and diethylene glycol butyl ether. The thickener is ethyl cellulose; The surfactant is stearate; The diluent is a mixture of ethanol and terpineol.

[0014] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the mass ratio of dibutyl phthalate to diethylene glycol butyl ether is 1:1. The mass ratio of ethanol to terpineol is 2~4:3~5.

[0015] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the preparation method of the Ag@Cu composite material includes: removing the oxides on the surface of copper powder with a mixed solution of ammonium sulfate and ammonium hydroxide to obtain pretreated copper powder; dispersing the pretreated copper powder in deionized water to obtain a dispersion; adjusting the pH of the dispersion with sodium hydroxide, adding ethylenediaminetetraacetic acid and silver nitrate, stirring and reacting, washing and drying to obtain the Ag@Cu composite material.

[0016] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the concentration of ammonium sulfate in the mixed solution is 10wt%~15wt%, and the concentration of ammonium hydroxide is 5wt%~10wt%.

[0017] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, the pH is 10~12; The stirring reaction is carried out at a temperature of 40-80°C for 60-80 minutes.

[0018] Furthermore, in the nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry provided by the present invention, when the particle size of copper powder is 5~10μm, the molar ratio of copper powder, ethylenediaminetetraacetic acid and silver nitrate is 1:1.6~3.0:1.0~2.0. When the particle size of copper powder is 0.5~2μm, the molar ratio of copper powder, ethylenediaminetetraacetic acid and silver nitrate is 1:3.1~4.7:2.1~3.2.

[0019] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: (1) This invention prepares a conductive phase by combining two Ag@Cu composite materials with flake silver powder of different particle sizes, which effectively reduces the sheet resistance of the heating film layer of stainless steel substrate and is suitable for high-efficiency heating at low voltage of 24V. Under the premise of ensuring conductivity, the amount of precious metals used is greatly reduced, the production cost of slurry is significantly reduced, and both conductivity and economy are taken into account. It solves the problem of mismatch in particle size of silver-coated copper powder, the conductive network is dense, and the conductive stability of the film layer is high.

[0020] (2) The present invention optimizes the glass powder of the binder phase by adding V2O5 and WO3, so that the optimized glass powder formula is highly compatible with the stainless steel substrate, which greatly improves the adhesion and temperature resistance of the film layer, effectively avoids the phenomenon of film layer peeling and high temperature failure, and extends the service life of the product. Detailed Implementation

[0021] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0022] Example 1 This embodiment provides a method for preparing an ultra-low resistance paste for heating stainless steel substrates.

[0023] By weight percentage, the ultra-low resistance slurry described in this embodiment comprises: 80% silver powder, 5% glass powder, and 15% organic carrier; By mass percentage, the silver powder consists of 38% Ag@Cu composite material (5~10μm), 7% Ag@Cu composite material (0.5~2μm) and 55% flake silver powder (15~20μm); The glass powder is composed of 19% Bi2O3, 35% B2O3, 20% ZnO, 5% Li2O, 10% WO3, 5% Al2O3 and 6% V2O5; The organic carrier comprises, by weight percentage: 45% organic solvent (a mixture of dibutyl phthalate and diethylene glycol butyl ether in a mass ratio of 1:1), 18% thickener (ethyl cellulose), 1% surfactant (stearate), and 36% diluent (ethanol and terpineol in a mass ratio of 2:3).

[0024] The preparation method of the ultra-low resistance slurry described in this embodiment is as follows: Preparation of 1.5~10μm Ag@Cu composite material (silver-coated copper powder): The oxides on the surface of copper powder (5~10μm) were removed using a mixed solution of ammonium sulfate ((NH4)2SO4, 10wt%) and ammonium hydroxide (NH4OH, 5wt%). After washing, pretreated copper powder was obtained. The pretreated copper powder (3g) was dispersed in 100mL of deionized water to obtain a dispersion. The pH of the dispersion was adjusted to 11 using sodium hydroxide (NaOH), and then 0.11mol of ethylenediaminetetraacetic acid (EDTA) and 0.07mol of silver nitrate (AgNO3) were added. The mixture was stirred at 40℃ for 60min, washed, and dried to obtain the Ag@Cu composite material.

[0025] Preparation of S2.0.5~2μm Ag@Cu composite material: The preparation method of 0.5~2μm Ag@Cu composite material is the same as that of 5~10μm Ag@Cu composite material. The particle size of copper powder (3g) is 0.5~2μm. Due to the increase in the specific surface area of ​​copper powder, the amount of EDTA added is adjusted to 0.15mol and the amount of AgNO3 added is adjusted to 0.10mol.

[0026] S3. Preparation of silver powder and glass powder: Weigh the raw materials according to the above ratio of silver powder and glass powder and mix them thoroughly.

[0027] S4. Preparation of organic carrier: Weigh the raw materials according to the above proportion of organic carrier and stir them thoroughly in a water bath at 60°C to obtain organic carrier.

[0028] S5. Preparation of ultra-low resistance paste: Silver powder, glass powder and organic carrier are mixed evenly and then rolled to obtain ultra-low resistance paste for stainless steel substrates.

[0029] Example 2 This embodiment provides a method for preparing an ultra-low resistance paste for heating stainless steel substrates.

[0030] By weight percentage, the ultra-low resistance slurry described in this embodiment comprises: 77% silver powder, 3% glass powder and 20% organic carrier; By mass percentage, the silver powder consists of 42% Ag@Cu composite material (5~10μm), 5% Ag@Cu composite material (0.5~2μm) and 53% flake silver powder (15~20μm); The glass powder is composed of 28% Bi2O3, 30% B2O3, 20% ZnO, 8% Li2O, 5% WO3, 7% Al2O3 and 2% V2O5; The organic carrier comprises, by weight percentage: 40.5% organic solvent (a mixture of dibutyl phthalate and diethylene glycol butyl ether in a mass ratio of 1:1), 20% thickener (ethyl cellulose), 0.5% surfactant (stearate), and 39% diluent (ethanol and terpineol in a mass ratio of 2:5).

[0031] The preparation method of the ultra-low resistance slurry described in this embodiment is as follows: Preparation of 1.5~10μm Ag@Cu composite material (silver-coated copper powder): The oxides on the surface of copper powder (5~10μm) were removed using a mixed solution of ammonium sulfate ((NH4)2SO4, 15wt%) and ammonium hydroxide (NH4OH, 10wt%). After washing, pretreated copper powder was obtained. The pretreated copper powder (3g) was dispersed in 100mL of deionized water to obtain a dispersion. The pH of the dispersion was adjusted to 12 using sodium hydroxide (NaOH), and then 0.08mol of ethylenediaminetetraacetic acid (EDTA) and 0.05mol of silver nitrate (AgNO3) were added. The mixture was stirred at 60℃ for 80min, washed, and dried to obtain the Ag@Cu composite material.

[0032] Preparation of S2.0.5~2μm Ag@Cu composite material: The preparation method of 0.5~2μm Ag@Cu composite material is the same as that of 5~10μm Ag@Cu composite material. The particle size of copper powder (3g) is 0.5~2μm. Due to the increase in the specific surface area of ​​copper powder, the amount of EDTA added is adjusted to 0.18mol and the amount of AgNO3 added is adjusted to 0.12mol.

[0033] S3. Preparation of silver powder and glass powder: Weigh the raw materials according to the above ratio of silver powder and glass powder and mix them thoroughly.

[0034] S4. Preparation of organic carrier: Weigh the raw materials according to the above proportion of organic carrier and stir them thoroughly in a water bath at 70°C to obtain organic carrier.

[0035] S5. Preparation of ultra-low resistance paste: Silver powder, glass powder and organic carrier are mixed evenly and then rolled to obtain ultra-low resistance paste for stainless steel substrates.

[0036] Example 3 This embodiment provides a method for preparing an ultra-low resistance paste for heating stainless steel substrates.

[0037] By weight percentage, the ultra-low resistance slurry described in this embodiment comprises: 75% silver powder, 6% glass powder and 19% organic carrier; By mass percentage, the silver powder consists of 45% Ag@Cu composite material (5~10μm), 5% Ag@Cu composite material (0.5~2μm) and 50% flake silver powder (15~20μm); The glass powder is composed of 28% Bi2O3, 30% B2O3, 20% ZnO, 8% Li2O, 5% WO3, 7% Al2O3 and 2% V2O5; The organic carrier comprises, by weight percentage: 36% organic solvent (a mixture of dibutyl phthalate and diethylene glycol butyl ether in a mass ratio of 1:1), 22% thickener (ethyl cellulose), 2% surfactant (stearate), and 40% diluent (ethanol and terpineol in a mass ratio of 4:5).

[0038] The preparation method of the ultra-low resistance slurry described in this embodiment is as follows: Preparation of 1.5~10μm Ag@Cu composite material (silver-coated copper powder): The oxides on the surface of copper powder (5~10μm) were removed using a mixed solution of ammonium sulfate ((NH4)2SO4, 12wt%) and ammonium hydroxide (NH4OH, 8wt%). After washing, pretreated copper powder was obtained. The pretreated copper powder (3g) was dispersed in 100mL of deionized water to obtain a dispersion. The pH of the dispersion was adjusted to 10 using sodium hydroxide (NaOH), and then 0.14mol of ethylenediaminetetraacetic acid (EDTA) and 0.09mol of silver nitrate (AgNO3) were added. The mixture was stirred at 80℃ for 80min, washed, and dried to obtain the Ag@Cu composite material.

[0039] Preparation of S2.0.5~2μm Ag@Cu composite material: The preparation method of 0.5~2μm Ag@Cu composite material is the same as that of 5~10μm Ag@Cu composite material. The particle size of copper powder (3g) is 0.5~2μm. Due to the increase in the specific surface area of ​​copper powder, the amount of EDTA added is adjusted to 0.22mol and the amount of AgNO3 added is adjusted to 0.15mol.

[0040] S3. Preparation of silver powder and glass powder: Weigh the raw materials according to the above ratio of silver powder and glass powder and mix them thoroughly.

[0041] S4. Preparation of organic carrier: Weigh the raw materials according to the above proportion of organic carrier and stir them thoroughly in a water bath at 80°C to obtain organic carrier.

[0042] S5. Preparation of ultra-low resistance paste: Silver powder, glass powder and organic carrier are mixed evenly and then rolled to obtain ultra-low resistance paste for stainless steel substrates.

[0043] Comparative Example 1 This comparative example is the same as Example 1, except that the silver powder in this comparative example is only 15~20μm flake silver powder.

[0044] Comparative Example 2 This comparative example is the same as Example 1, except that the 5~10μm Ag@Cu composite material and the 0.5~2μm Ag@Cu composite material in this comparative example are replaced with spherical silver nanoparticles of the same particle size.

[0045] Comparative Example 3 This comparative example is the same as Example 1, except that the glass powder composition (by mass percentage) of this comparative example is 30% Bi2O3, 35% B2O3, 20% ZnO, 5% Li2O, and 10% Al2O3.

[0046] The 304 stainless steel substrate was sequentially ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 20 min, dried at 80°C for 30 min, and then plasma-treated for 4 min. Ultra-low resistivity pastes from Examples 1-3 and Comparative Examples 1-3 were screen-printed onto the pretreated substrate surface. After printing, the substrate was leveled at room temperature for 12 min, pre-dried at 60°C for 30 min and 120°C for 30 min, and then sintered in a muffle furnace. The sintering curve was as follows: heating at 5°C / min to 300°C and holding for 20 min, then heating at 8°C / min to 600°C and holding for 20 min, followed by furnace cooling to room temperature to obtain the stainless steel substrate heating film layer (sample to be tested).

[0047] Sheet resistance was determined according to GB / T 17702-2021, and adhesion was determined according to GB / T17473.4-2008. The test results are shown in Table 1.

[0048] Table 1 Performance test results of ultra-low resistance slurry

[0049] As shown in Table 1, the sheet resistance of Examples 1-3 is all below 3.0 mΩ / □, which is approximately 12-18% lower than that of Comparative Example 1 (using only flake silver powder). These data indicate that introducing Ag@Cu composite materials with different particle sizes as fillers and supports into the conductive phase of this invention can more effectively construct a dense conductive network and reduce the overall resistance. Comparative Example 2 (spherical silver powder of different particle sizes + flake silver powder) shows no significant difference in sheet resistance compared to Examples 1-3, but Examples 1-3 have a lower cost.

[0050] The adhesion of Examples 1-3 is ≥16 N / mm 2 It is higher than the 11 N / mm of Comparative Example 1. 2 Compared to Comparative Example 3, 10 N / mm 2 The above data indicates that although the high Al2O3 content (up to 10%) in the glass powder can improve its strength, the lack of fluxing and activating functions of Li2O and V2O5, as well as the chemical reinforcing effect of WO3, results in insufficient fluidity of the glass powder at the sintering temperature, poor wettability to the stainless steel substrate, and weak interfacial chemical bonding. Ultimately, the glass phase fails to form a dense and strong bonding layer, leading to poor conductive network construction (sheet resistance of 5.18 mΩ / □). In this invention, the synergistic effect of Li2O, V2O5, WO3, and Al2O3 solves the interfacial bonding problem caused by the low surface energy of the stainless steel substrate and the dense passivation layer.

[0051] After welding nickel strip electrodes onto the sample to be tested, it was fixed on a test platform lined with heat-insulating ceramic cotton and driven under a constant voltage of 24.0±0.1V. A FLIR T1040sc infrared thermal imager was used to acquire the full-range temperature distribution of the heated area in real time, with the sampling frequency set to 1Hz.

[0052] During the test, the response time and steady-state surface temperature of the sample under test from room temperature to a stable temperature state were first recorded. Then, the sample under test was continuously operated at rated power (48W) for 500 hours. During this period, heating was paused every 24 hours, and power was restarted after the sample cooled to room temperature. The above steady-state test procedure was repeated, and the steady-state operating temperature and corresponding input power at each time point were recorded. The cumulative power attenuation rate was calculated.

[0053] Table 2. Test results of heating performance of ultra-low resistance slurry

[0054] As shown in Table 2, under a rated voltage of 24V, the steady-state temperature of samples in Examples 1-3 can reach 280-290℃, and it only takes 40-42 seconds to heat up to 200℃, with a power density of 8.8-9.3W / cm³. 2 The heating performance is significantly better than all comparative examples. The above results show that the ternary conductive phase system of "dual-size Ag@Cu composite material + high proportion of flake silver powder" designed in this invention can construct a more dense, low-resistance conductive network with rich conductive paths, thereby significantly improving heating efficiency and response speed; at the same time, the system exhibits good thermal stability and thermal conductivity under high-temperature working conditions, providing a structural basis for efficient and stable electrothermal conversion.

[0055] After 500 hours of continuous operation at rated power, the samples in Examples 1-3 exhibited a power attenuation rate of only 4%-5%, demonstrating excellent long-term operational stability, which was superior to all comparative examples. Comparative Example 1 (flake silver powder only) showed a power attenuation rate of 38%, indicating that the conductive network lacking Ag@Cu composite material filling was more prone to structural degradation under long-term thermal stress. The Ag@Cu composite material's filling effect optimized the initial conductive network and suppressed relaxation or breakage of the conductive pathways due to thermal expansion differences. Comparative Example 2 (spherical silver powder + flake silver powder) showed a power attenuation rate of 11%, indicating that the high surface energy of nano-silver in the pure silver conductive phase easily leads to excessive growth of sintering necks or particle agglomeration under long-term high temperatures, thereby degrading the conductive network. In contrast, the Ag@Cu structure in this invention, with its copper core, to a certain extent inhibited excessive surface diffusion and migration of the silver layer, improving the stability of the microstructure. Comparative Example 3 (glass powder without V2O5 and WO3) showed a power attenuation rate as high as 86%. The glass powder system, lacking the key functional components V2O5 and WO3, could not maintain stable adhesion to the stainless steel substrate and provide antioxidant protection for the conductive phase at high temperatures. Due to the lack of necessary low-temperature fluidity and chemical bonding strength in its glass phase, the interfacial bonding was weak and the encapsulation was inadequate. Under long-term thermal-oxygen coupling, the conductive network rapidly oxidized and deteriorated, accompanied by interfacial failure.

[0056] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry, characterized in that, The ultra-low resistance slurry, by weight percentage, consists of 3% to 6% glass powder, 15% to 20% organic carrier, and the balance silver powder; The silver powder is composed of Ag@Cu composite materials with particle sizes of 0.5~2μm and 5~10μm, and flake-shaped silver powder with a particle size of 15~20μm. The glass powder is composed of Bi2O3, B2O3, ZnO, Li2O, WO3, Al2O3 and V2O5; The organic carrier is composed of organic solvent, thickener, surfactant and diluent.

2. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 1, characterized in that, The silver powder consists of 5%~7% 0.5~2μm Ag@Cu composite material, 38%~45% 5~10μm Ag@Cu composite material, and the balance 5~20μm flake silver powder.

3. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 1, characterized in that, The glass powder consists of 28%~35% B2O3, 20%~26% ZnO, 3%~8% Li2O, 5%~10% WO3, 3%~7% Al2O3, 2%~6% V2O5 and the balance Bi2O3.

4. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 1, characterized in that, The organic carrier consists of 18%~22% thickener, 0.5%~2% surfactant, 36%~40% diluent and the balance organic solvent.

5. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 1, characterized in that, The organic solvent is a mixture of dibutyl phthalate and diethylene glycol butyl ether; The thickener is ethyl cellulose; The surfactant is stearate; The diluent is a mixture of ethanol and terpineol.

6. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 5, characterized in that, The mass ratio of dibutyl phthalate to diethylene glycol butyl ether is 1:1; The mass ratio of ethanol to terpineol is 2~4:3~5.

7. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 1, characterized in that, The preparation method of the Ag@Cu composite material includes: removing the oxides on the surface of copper powder with a mixed solution of ammonium sulfate and ammonium hydroxide to obtain pretreated copper powder; dispersing the pretreated copper powder in deionized water to obtain a dispersion; adjusting the pH of the dispersion with sodium hydroxide, adding ethylenediaminetetraacetic acid and silver nitrate, stirring and reacting, washing and drying to obtain the Ag@Cu composite material.

8. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 7, characterized in that, The concentration of ammonium sulfate in the mixed solution is 10wt%~15wt%, and the concentration of ammonium hydroxide is 5wt%~10wt%.

9. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 7, characterized in that, The pH is 10-12; The stirring reaction is carried out at a temperature of 40-80°C for 60-80 minutes.

10. The nanoscale copper-silver composite stainless steel heating ultra-low resistance slurry according to claim 7, characterized in that, When the particle size of copper powder is 5~10μm, the molar ratio of copper powder, ethylenediaminetetraacetic acid and silver nitrate is 1:1.6~3.0:1.0~2.0; When the particle size of copper powder is 0.5~2μm, the molar ratio of copper powder, ethylenediaminetetraacetic acid and silver nitrate is 1:3.1~4.7:2.1~3.2.

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