A composite conductive powder and conductive silver paste for preparing conductive silver paste

Abstract

This invention discloses a composite conductive powder and conductive silver paste for preparing conductive silver paste, specifically relating to the field of electronic materials technology. The composite conductive powder adopts a double-shell core-shell structure with a silver metal core, a silicon dioxide intermediate coating layer, and a silver nanoparticle self-assembled outer layer, and is treated with ultraviolet light irradiation. The conductive silver paste is based on this composite conductive powder, combined with cerium oxide modified glass powder, graphene nanosheets, thermoplastic polyurethane resin, and divalent acid ester solvent to form a low-temperature environmentally friendly formulation. The conductive silver paste of this invention has a volume resistivity as low as 1.2 × 10⁻⁶. ‑6 With a strength of Ω·cm, a curing temperature reduced to 120℃, and volatile organic compound content meeting environmental protection standards, while tensile strength increased by 50%, it can withstand 500 bending cycles without breakage, and adhesion reaches grade 0 in the cross-cut test. It effectively meets the stringent requirements of high-performance electronic devices for conductive silver paste and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of electronic materials technology, and more specifically, to a composite conductive powder and conductive silver paste for preparing conductive silver paste. Background Technology

[0002] In the field of modern electronics, conductive silver paste is a key material for manufacturing metal electrodes for various electronic components. It is widely used in computer and communication equipment, integrated circuits and communication displays, solar cells, automobile manufacturing and various consumer electronics products. Its cost accounts for 30%-70% of the cost of electronic component materials, and its performance directly affects the technological upgrading and cost control of electronic components.

[0003] Traditional conductive silver paste is generally composed of a conductive silver phase, a binder phase, and an organic carrier (resin + organic solvent). During the printing and sintering process, the volatilization of organic matter not only causes environmental pollution and harms human health, but also often results in the glass phase not having started to melt after the organic matter has volatilized, causing the conductive lines to detach from the carrier and rendering the circuit unusable.

[0004] To meet the demands of electronic devices for high-performance, environmentally friendly, and low-cost conductive silver paste, researchers and industry have conducted numerous explorations. Regarding improving conductivity, some researchers have used a mixture of conductive particles of varying sizes to formulate pastes, attempting to create a denser structure by filling the gaps between larger particles with smaller ones. Others have employed nanoparticles, hoping to improve conductivity through their close packing and lower curing temperature. Still others have mixed metal compounds into granular pastes, utilizing the metal reduced during curing to "weld" the conductive particles, increasing conductive pathways. However, nanoparticles are expensive, and the polymer coating on their surface can increase interparticle contact resistance during low-temperature curing. While micron-sized silver particles with varying sizes are widely used, the random distribution of small particles can easily interfere with the contact between larger particles, affecting conductivity.

[0005] In terms of environmental protection, some technologies have attempted to replace the organic carrier in traditional ohmic silver paste with inorganic binder silicate cement and use water and ethanol mixed in a specific ratio as solvent. Although this reduces pollution to some extent, it is still insufficient to meet the requirements of heat-sensitive flexible substrates and further reduce curing temperature. In terms of adapting to the rapid development of flexible electronic devices, the existing conductive silver paste is difficult to meet the stringent requirements of high flexibility and strong adhesion for materials such as wearable pressure sensor electrode layers and flexible printed circuit boards in terms of mechanical properties such as tensile strength, bending performance and adhesion, thus limiting its application expansion in the emerging field of flexible electronics.

[0006] Based on the above, the present invention provides a composite conductive powder and conductive silver paste for preparing conductive silver paste. Summary of the Invention

[0007] In order to overcome the above-mentioned defects of the prior art, the present invention provides a composite conductive powder and conductive silver paste for preparing conductive silver paste, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a composite conductive powder for preparing conductive silver paste, wherein the composite conductive powder has a double-shell core-shell structure, comprising a silver metal core, a silica intermediate coating layer and a silver nanoparticle self-assembled outer layer, characterized in that: the silver metal core is composed of metallic silver with a particle size of 1-3 μm;

[0009] The silica intermediate coating layer is prepared by the sol-gel method and is uniformly coated on the surface of the silver metal core with a thickness of 5-20 nm.

[0010] The self-assembled outer layer of silver nanoparticles is composed of silver nanoparticles with a particle size of 50-100nm, which are coated on the surface of the silica intermediate coating layer by photo-induced deposition technology to form a three-dimensional conductive network.

[0011] The composite conductive powder was subjected to a wavelength of 254nm and a power of 50mW / cm. 2 After 10 minutes of ultraviolet irradiation, oxygen vacancies were generated on the surface, and the carrier concentration increased by two orders of magnitude compared with that before treatment.

[0012] Preferably, the method for preparing the silica interlayer includes:

[0013] The silver metal core is dispersed in a mixed solution of tetraethyl orthosilicate / ethanol at a volume ratio of 1:(3-5), and 1-3% ammonia water is added as a catalyst. The mixture is stirred and hydrolyzed at 50-70℃ for 2-4 hours to form a silver-silica core-shell structure.

[0014] Preferably, the method for preparing the self-assembled outer layer of the silver nanoparticles includes:

[0015] Silver-silica core-shell particles were dispersed in a silver nitrate solution with a concentration of 0.1-0.3 mol / L, and glucose was added as a reducing agent. The mixture was irradiated under 365 nm ultraviolet light for 30 min to reduce the silver nanoparticles in situ and allow them to self-assemble on the silica surface. The molar ratio of glucose to silver nitrate was 1:1-1:2.

[0016] A conductive silver paste, prepared using the aforementioned composite conductive powder, comprises the following components by mass percentage:

[0017] Composite conductive powder 60%;

[0018] 3% cerium oxide modified glass powder, wherein cerium oxide accounts for 10-20% of the mass of the glass powder, and the glass powder particle size is 1-5μm;

[0019] Graphene nanosheets: 0.5%, lateral dimensions 0.5-2μm, thickness 1-5 layers;

[0020] 15% thermoplastic polyurethane resin;

[0021] The divalent ester solvent 21.5% is composed of dimethyl succinate, dimethyl glutarate and dimethyl adipate in a volume ratio of 1:1:1;

[0022] The volume resistivity of the conductive silver paste is ≤1.2×10⁻⁶. -6 The Ω·cm is cured at 120℃ for 20 min to form a conductive film.

[0023] Preferably, the method for preparing the cerium oxide modified glass powder includes:

[0024] After mixing glass powder and cerium oxide powder, the mixture is sintered at 600-800℃ for 2-4 hours. The basic composition of the glass powder is silicon dioxide-boron trioxide-lead oxide glass with a mass ratio of 70:20:10.

[0025] Preferably, the graphene nanosheets are prepared by a modified Hummers method, with a surface oxygen group content of ≤5%, and form a uniform conductive network in silver paste after ultrasonic dispersion.

[0026] Preferably, the volatile organic compound content in the divalent ester solvent is ≤50g / L.

[0027] Preferably, the preparation method specifically includes the following:

[0028] S1. Mix thermoplastic polyurethane resin and divalent ester solvent at a mass ratio of 1:(1.2-1.5) and stir at 70°C until completely dissolved to obtain a carrier solution;

[0029] S2. Add composite conductive powder, cerium oxide modified glass powder and graphene nanosheets sequentially to the carrier solution in step S1. Disperse the mixture by ball milling with zirconia balls with a diameter of 3 mm, with a ball-to-material ratio of 3:1, a rotation speed of 500 rpm and a time of 2 h.

[0030] S3. Degas the dispersed slurry under a vacuum of -0.1 MPa for 30 minutes to obtain the conductive silver paste.

[0031] Preferably, in step S2, the ball milling dispersion process is carried out under the protection of an inert gas to avoid oxidation of the silver nanoparticles, wherein the inert gas is nitrogen.

[0032] Preferably, the conductive silver paste is used to prepare flexible electronic devices, which include: a flexible printed circuit board with a thickness ≤100μm, an electrode layer for a wearable pressure sensor, and an organic solar cell electrode based on a PET substrate.

[0033] The technical effects and advantages of this invention are as follows:

[0034] 1. This invention employs a double-shell core-shell structure consisting of a silver metal core, a silicon dioxide intermediate layer, and a silver nanoparticle outer layer. Combined with photoactivation technology, a three-dimensional conductive network is formed, generating oxygen vacancies to increase carrier concentration, resulting in a conductive silver paste with a volume resistivity as low as 1.2 × 10⁻⁶. -6 In addition, the silica coating layer isolates the silver core from oxidation, and combined with cerium oxide modified glass powder, it significantly improves acid and alkali resistance and extends the service life of conductive silver paste.

[0035] 2. This invention uses a composite carrier system of divalent acid ester solvent and thermoplastic polyurethane resin to reduce the curing temperature to 120°C, which is 180°C lower than the traditional process. It is suitable for heat-sensitive flexible substrates, and the content of volatile organic compounds in the solvent meets the standards. While achieving low-temperature and high-efficiency curing, it reduces environmental pollution and energy consumption costs.

[0036] 3. The present invention enhances the tensile strength of conductive silver paste by synergistic enhancement through graphene nanosheets and core-shell structure conductive powder, thereby increasing the tensile strength by 50% and enabling it to withstand 500 bending cycles without breakage. Moreover, combined with a low-viscosity formula and good substrate wettability, its adhesion reaches the cross-cut adhesion test level 0 standard, making it suitable for the manufacture of various flexible electronic devices such as flexible printed circuit boards and wearable sensors, greatly expanding its application scenarios. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating the preparation process of the conductive silver paste of the present invention. Detailed Implementation

[0038] Example 1

[0039] This embodiment provides a composite conductive powder for preparing conductive silver paste, as detailed below:

[0040] The silver metal core is made of metallic silver powder with a particle size of 2μm.

[0041] The silver-silica core-shell structure is obtained by dispersing a silver metal core in a mixed solution of tetraethyl orthosilicate and ethanol at a volume ratio of 1:4, adding 2% ammonia water as a catalyst, and stirring and hydrolyzing at 60°C for 3 hours to form a silica coating layer with a thickness of about 12nm.

[0042] Silver nanoparticles self-assemble outer layer: The above silver-silica core-shell particles are dispersed in a silver nitrate solution with a concentration of 0.2 mol / L, and glucose (the molar ratio of glucose to silver nitrate is 1:1.5) is added as a reducing agent. The mixture is irradiated under 365 nm ultraviolet light for 30 min, so that silver nanoparticles with a particle size of about 80 nm self-assemble on the surface of silica.

[0043] Photoactivation treatment was performed on the above-mentioned composite conductive powder at a wavelength of 254 nm and a power of 50 mW / cm. 2 The ultraviolet light irradiation treatment lasted for 10 minutes.

[0044] This embodiment also provides a conductive silver paste, comprising the following components by mass percentage:

[0045] Composite conductive powder 60%;

[0046] 3% cerium oxide modified glass powder (cerium oxide accounts for 15% of the glass powder mass, the glass powder particle size is 3μm, the basic composition is silicon dioxide-boron trioxide-lead oxide glass, mass ratio 70:20:10);

[0047] 0.5% graphene nanosheets (1 μm lateral dimension, 3 layers thick);

[0048] 15% thermoplastic polyurethane resin;

[0049] Divalent ester solvent (dimethyl succinate, dimethyl glutarate, and dimethyl adipate mixed in a 1:1:1 volume ratio) 21.5%.

[0050] The specific preparation steps are as follows:

[0051] S1. Mix thermoplastic polyurethane resin and divalent ester solvent at a mass ratio of 1:1.3, and stir at 70°C until completely dissolved to obtain a carrier solution;

[0052] S2. Composite conductive powder, cerium oxide modified glass powder, and graphene nanosheets were added sequentially to the carrier solution. The mixture was dispersed by ball milling using zirconia balls with a diameter of 3 mm. The ball-to-material ratio was 3:1, the rotation speed was 500 rpm, and the time was 2 h. The ball milling process was carried out under nitrogen protection.

[0053] S3. Degas the dispersed slurry under a vacuum of -0.1 MPa for 30 minutes to obtain conductive silver paste.

[0054] The performance of the conductive silver paste prepared in this embodiment is tested below:

[0055] Volume resistivity: Conductive silver paste was coated onto a PET substrate and cured at 120℃ for 20 min to form a conductive film. The measured volume resistivity was 1.0 × 10⁻⁶. -6 Ω·cm;

[0056] Adhesion: Tested using the cross-cut test method, the result was grade 0;

[0057] Acid resistance: The conductive film lost 0.08% of its weight after being immersed in a 5% HCl solution for 24 hours.

[0058] Bending performance: The PET substrate coated with conductive silver paste was subjected to 500 bending cycles and showed no breakage. The tensile strength was 18 MPa.

[0059] Example 2

[0060] This embodiment provides a composite conductive powder for preparing conductive silver paste, with the same composition as in Example 1, but the different parameters are as follows:

[0061] The silver metal core is made of metallic silver powder with a particle size of 1.5μm;

[0062] The intermediate coating layer of silica consists of tetraethyl orthosilicate and ethanol in a volume ratio of 1:3, and ammonia is used at 1% of the solution volume. The mixture is stirred and hydrolyzed at 50°C for 4 hours, and the silica coating layer is about 8 nm thick.

[0063] The outer layer of silver nanoparticles was self-assembled. The concentration of silver nitrate solution was 0.1 mol / L, the molar ratio of glucose to silver nitrate was 1:1, and the silver nanoparticles were irradiated with 365 nm ultraviolet light for 30 min. The particle size of the silver nanoparticles was about 50 nm.

[0064] Photoactivation treatment, same as in Example 1.

[0065] This embodiment also provides a conductive silver paste, with the same component ratios and preparation steps as in Example 1.

[0066] The performance of the conductive silver paste prepared in this embodiment is tested below:

[0067] Volume resistivity: The volume resistivity of the conductive film after curing is 1.1 × 10⁻⁶. -6 Ω·cm;

[0068] Adhesion: Grade 0 in cross-cut adhesion test;

[0069] Acid resistance: After soaking in 5% HCl solution for 24 hours, the weight loss was 0.09%.

[0070] Bending performance: After 500 bending cycles, the tensile strength is 17 MPa.

[0071] Example 3

[0072] This embodiment provides a composite conductive powder for preparing conductive silver paste. The preparation process is the same as in Embodiment 1, but the photoactivation treatment step is omitted.

[0073] This embodiment also provides a conductive silver paste, with the same component ratios and preparation steps as in Example 1.

[0074] The performance of the conductive silver paste prepared in this embodiment is tested below:

[0075] Volume resistivity: The volume resistivity of the cured conductive film is 1.8 × 10⁻⁶. -6 Ω·cm, significantly higher than in Example 1;

[0076] Adhesion: The cross-cut adhesion test result was 1, indicating a decrease in adhesion compared to Example 1.

[0077] Acid resistance: After soaking in 5% HCl solution for 24 hours, the weight loss was 0.2%, which is not as good as that of Example 1;

[0078] Bending performance: Fine cracks appeared after 500 bending cycles, and the tensile strength was 13 MPa.

[0079] As can be seen from Examples 1-2, the composite conductive powder and conductive silver paste of the present invention can achieve good conductivity, adhesion, weather resistance and mechanical properties under different parameters. Example 3, through comparison, highlights the key role of photoactivation treatment in improving the overall performance of conductive silver paste.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite conductive powder for preparing conductive silver paste, wherein the composite conductive powder has a double-shell core-shell structure, comprising a silver metal core, a silica intermediate coating layer, and a silver nanoparticle self-assembled outer layer, characterized in that: The silver metal core is composed of metallic silver with a particle size of 1-3 μm; The silica intermediate coating layer is prepared by the sol-gel method and is uniformly coated on the surface of the silver metal core with a thickness of 5-20 nm. The self-assembled outer layer of silver nanoparticles is composed of silver nanoparticles with a particle size of 50-100nm, which are coated on the surface of the silica intermediate coating layer by photo-induced deposition technology to form a three-dimensional conductive network. The composite conductive powder was subjected to a wavelength of 254nm and a power of 50mW / cm. 2 After 10 minutes of ultraviolet irradiation, oxygen vacancies were generated on the surface, and the carrier concentration increased by two orders of magnitude compared with that before treatment.

2. The composite conductive powder for preparing conductive silver paste according to claim 1, characterized in that: The method for preparing the silica intermediate coating layer includes: The silver metal core is dispersed in a mixed solution of tetraethyl orthosilicate / ethanol at a volume ratio of 1:(3-5), and 1-3% ammonia water is added as a catalyst. The mixture is stirred and hydrolyzed at 50-70℃ for 2-4 hours to form a silver-silica core-shell structure.

3. The composite conductive powder for preparing conductive silver paste according to claim 2, characterized in that: The method for preparing the self-assembled outer layer of the silver nanoparticles includes: Silver-silica core-shell particles were dispersed in a silver nitrate solution with a concentration of 0.1-0.3 mol / L, and glucose was added as a reducing agent. The mixture was irradiated under 365 nm ultraviolet light for 30 min to reduce the silver nanoparticles in situ and allow them to self-assemble on the silica surface. The molar ratio of glucose to silver nitrate was 1:1-1:

2.

4. A conductive silver paste, prepared using the composite conductive powder described in claim 3, characterized in that: By mass percentage, it includes the following components: Composite conductive powder 60%; 3% cerium oxide modified glass powder, wherein cerium oxide accounts for 10-20% of the mass of the glass powder, and the glass powder particle size is 1-5μm; Graphene nanosheets: 0.5%, lateral dimensions 0.5-2μm, thickness 1-5 layers; 15% thermoplastic polyurethane resin; The divalent ester solvent 21.5% is composed of dimethyl succinate, dimethyl glutarate and dimethyl adipate in a volume ratio of 1:1:1; The volume resistivity of the conductive silver paste is ≤1.2×10⁻⁶. -6 The Ω·cm is cured at 120℃ for 20 min to form a conductive film.

5. The conductive silver paste according to claim 4, characterized in that: The preparation method of the cerium oxide modified glass powder includes: After mixing glass powder and cerium oxide powder, the mixture is sintered at 600-800℃ for 2-4 hours. The basic composition of the glass powder is silicon dioxide-boron trioxide-lead oxide glass with a mass ratio of 70:20:

10.

6. The conductive silver paste according to claim 5, characterized in that: The graphene nanosheets were prepared by a modified Hummers method, with a surface oxygen group content of ≤5%, and formed a uniform conductive network in silver paste after ultrasonic dispersion.

7. The conductive silver paste according to claim 6, characterized in that: The volatile organic compound content in the divalent ester solvent is ≤50g / L.

8. The conductive silver paste according to claim 7, characterized in that: Specifically, the preparation methods include the following: S1. Mix thermoplastic polyurethane resin and divalent ester solvent at a mass ratio of 1:(1.2-1.5) and stir at 70°C until completely dissolved to obtain a carrier solution; S2. Add composite conductive powder, cerium oxide modified glass powder and graphene nanosheets sequentially to the carrier solution in step S1. Disperse the mixture by ball milling with zirconia balls with a diameter of 3 mm, with a ball-to-material ratio of 3:1, a rotation speed of 500 rpm and a time of 2 h. S3. Degas the dispersed slurry under a vacuum of -0.1 MPa for 30 minutes to obtain the conductive silver paste.

9. The conductive silver paste according to claim 8, characterized in that: In step S2, the ball milling dispersion process is carried out under the protection of an inert gas to prevent the oxidation of silver nanoparticles. The inert gas is nitrogen.

10. The conductive silver paste according to claim 8, characterized in that: The conductive silver paste is used to fabricate flexible electronic devices, which include: flexible printed circuit boards with a thickness of ≤100μm, electrode layers of wearable pressure sensors, and organic solar cell electrodes based on PET substrates.

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