Composite conductive powder for preparing conductive silver paste and conductive silver paste

Abstract

The invention discloses composite conductive powder for preparing conductive silver paste and the conductive silver paste, and particularly relates to the technical field of electronic materials.The composite conductive powder is of a double-shell core-shell structure composed of a silver metal inner core, a silicon dioxide middle coating layer and a silver nanoparticle self-assembled outer layer and is subjected to ultraviolet irradiation treatment; the conductive silver paste is based on the composite conductive powder and is matched with cerium oxide modified glass powder, graphene nanosheets, thermoplastic polyurethane resin and a dibasic acid ester solvent to form a low-temperature environment-friendly formula. The volume resistivity of the conductive silver paste is as low as 1.2 * 10 <-6 > omega.cm, the curing temperature is reduced to 120 DEG C, the content of volatile organic compounds meets the environmental protection standard, meanwhile, the tensile strength is improved by 50%, the conductive silver paste can bear 500 times of bending circulation without breakage, the adhesive force reaches the level 0 of a cross-cut method, the strict requirement of a high-performance electronic device for the conductive silver paste is effectively met, and the conductive silver paste has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic materials, and more particularly to a composite conductive powder and conductive silver paste for preparing conductive silver paste. Background Art

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

[0003] Traditional conductive silver paste is generally composed of conductive silver phase, adhesive phase, and 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 occurs after the volatilization of organic matter is completed, the glass phase has not yet begun to melt, causing the conductive circuit to fall off from the carrier, resulting in the circuit being scrapped.

[0004] In order to meet the high performance, environmental protection and low cost requirements of electronic devices for conductive silver paste, scientific researchers and the industry have conducted many explorations. In terms of improving conductive performance, they use conductive particles of different sizes to prepare pastes, trying to form a denser structure by filling the gaps between large particles with small particles; or use nano conductive particles, hoping to improve conductivity by virtue of their close stacking and lower curing temperature characteristics; and mix metal compound materials in granular pastes, using the metal reduced from the metal compounds during curing to "weld" the conductive particles and increase the conductive path. However, nano conductive particles are expensive, and the polymer coated on the surface will increase the contact resistance between particles when cured at low temperatures. Although micron-sized silver particles that are mixed with different sizes are widely used, the small particles are randomly distributed, which can easily interfere with the contact between large particles and affect the conductive performance.

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

[0006] Based on the above situation, 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 a conductive silver paste for preparing a conductive silver paste, so as to solve the problems raised in the above-mentioned background technology.

[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 silicon dioxide intermediate coating layer, and a self-assembled outer layer of silver nanoparticles, characterized in that: the silver metal core is composed of metallic silver with a particle size of 1-3 μm;

[0009] The silicon dioxide intermediate coating layer is prepared by a sol-gel method and is evenly 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 50-100 nm, which are coated on the surface of the silicon dioxide intermediate coating layer through light-induced deposition technology to form a three-dimensional conductive network;

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

[0012] Preferably, the method for preparing the silicon dioxide intermediate coating layer comprises:

[0013] The silver metal core is dispersed in a mixed solution of ethyl orthosilicate / ethanol with 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°C for 2-4 hours to form a silver-silicon dioxide core-shell structure.

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

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

[0016] A conductive silver paste is prepared using the composite conductive powder described above and 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 particle size of the glass powder is 1-5 μm;

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

[0020] Thermoplastic polyurethane resin 15%;

[0021] 21.5% dibasic acid ester solvent, which is a mixture 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 Ω·cm, and a conductive film was formed after curing at 120℃ for 20min.

[0023] Preferably, the preparation method of the cerium oxide modified glass powder comprises:

[0024] After mixing glass powder and cerium oxide powder, sintering is carried out at 600-800°C for 2-4 hours. The basic components of the glass powder are 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, have a surface oxygen-containing group content of ≤5%, and form a uniform conductive network in a silver paste after ultrasonic dispersion.

[0026] Preferably, the volatile organic matter content in the dibasic acid ester solvent is ≤50 g / L.

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

[0028] S1. Mixing a thermoplastic polyurethane resin and a dibasic acid ester solvent in a mass ratio of 1:(1.2-1.5), stirring 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 to the carrier solution in step S1 in sequence, and use zirconia balls with a diameter of 3 mm to disperse them by ball milling, 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 at a vacuum degree of -0.1 MPa for 30 min 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 prevent oxidation of the silver nanoparticles, and 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 of ≤100 μm, an electrode layer of a wearable pressure sensor, and an organic solar cell electrode based on a PET substrate.

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

[0034] 1. The present invention adopts a double-shell core-shell structure of silver metal core-silicon dioxide middle layer-silver nanoparticle outer layer, combined with light activation treatment technology, to form a three-dimensional conductive network and generate oxygen vacancies to increase the carrier concentration, making the volume resistivity of the conductive silver paste as low as 1.2×10 -6 Ω·cm. 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 the conductive silver paste.

[0035] 2. The present 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. At the same time, the volatile organic compound content of the solvent meets the standard. While achieving low-temperature and high-efficiency curing, it also reduces environmental pollution and energy consumption costs.

[0036] 3. The present invention enhances the conductive silver paste by synergistically enhancing the graphene nanosheets and core-shell structure conductive powder, which increases the tensile strength of the conductive silver paste by 50%, and can withstand 500 bending cycles without breaking. In addition, combined with the low viscosity formula and good substrate wettability, its adhesion reaches the level 0 standard of the cross-hatch method, making it suitable for the manufacture of various flexible electronic devices such as flexible printed circuit boards and wearable sensors, greatly expanding the application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart for preparing the conductive silver paste of the present invention. DETAILED DESCRIPTION

[0038] Example 1

[0039] This embodiment provides a composite conductive powder for preparing conductive silver paste, which is as follows:

[0040] Silver metal core, using metal silver powder with a particle size of 2μm as the core;

[0041] A silica intermediate coating layer was prepared by dispersing a silver metal core in a mixed solution of ethyl orthosilicate and ethanol in a volume ratio of 1:4. Ammonia water accounting for 2% of the solution volume was added as a catalyst, and the mixture was stirred and hydrolyzed at 60°C for 3 hours to form a silica coating layer with a thickness of about 12 nm, thereby obtaining a silver-silica core-shell structure.

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

[0043] The composite conductive powder was photoactivated at a wavelength of 254 nm and a power of 50 mW / cm 2 UV irradiation treatment for 10 min.

[0044] This embodiment also provides a conductive silver paste, which includes the following components weighed in percentage by mass:

[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 3 μm, the basic composition is silicon dioxide-boron trioxide-lead oxide glass, the mass ratio is 70:20:10);

[0047] Graphene nanosheets 0.5% (lateral size 1 μm, thickness 3 layers);

[0048] Thermoplastic polyurethane resin 15%;

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

[0050] The specific preparation steps are as follows:

[0051] S1. Mixing a thermoplastic polyurethane resin and a dibasic acid ester solvent in a mass ratio of 1:1.3, and stirring at 70° C. until completely dissolved to obtain a carrier solution;

[0052] S2. Add composite conductive powder, cerium oxide modified glass powder, and graphene nanosheets to the carrier solution in sequence, and use zirconia balls with a diameter of 3 mm to disperse them by ball milling, with a ball-to-material ratio of 3:1, a rotation speed of 500 rpm, and a time of 2 h. The ball milling process is carried out under nitrogen protection;

[0053] S3. Degas the dispersed slurry at a vacuum degree of -0.1 MPa for 30 minutes to obtain a 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 on a PET substrate and cured at 120°C for 20 min to form a conductive film. The volume resistivity was measured to be 1.0×10 -6 Ω·cm;

[0056] Adhesion: Tested by cross-hatch method, the test result is level 0;

[0057] Acid resistance: When the conductive film is immersed in 5% HCl solution for 24 hours, the weight loss is 0.08%;

[0058] Bending performance: The PET substrate coated with conductive silver paste was subjected to 500 bending cycle tests without any breakage and the tensile strength was 18 MPa.

[0059] Example 2

[0060] This embodiment provides a composite conductive powder for preparing a conductive silver paste. The specific composition is the same as that of Example 1, and the different parameters are as follows:

[0061] Silver metal core, using metallic silver powder with a particle size of 1.5μm;

[0062] The silica intermediate coating layer was prepared by mixing ethyl orthosilicate with ethanol in a volume ratio of 1:3 and ammonia water at a volume ratio of 1% of the solution volume. The solution was hydrolyzed at 50°C for 4 hours with stirring, and the silica coating thickness was about 8 nm.

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

[0064] Photoactivation treatment is the same as in Example 1.

[0065] This embodiment also provides a conductive silver paste, the proportions of the components are the same as those in Example 1, and the preparation steps are the same.

[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 Ω·cm;

[0068] Adhesion: Cross-hatch test: Grade 0;

[0069] Acid resistance: immersion in 5% HCl solution for 24 hours, weight loss 0.09%;

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

[0071] Example 3

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

[0073] This embodiment also provides a conductive silver paste, the proportions of the components are the same as those in Example 1, and the preparation steps are the same.

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

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

[0076] Adhesion: The cross-hatch test was grade 1, and the adhesion was lower than that of Example 1;

[0077] Acid resistance: After immersion in 5% HCl solution for 24 hours, the weight loss was 0.2%, and the acid resistance was not as good as that of Example 1.

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

[0079] It can be seen from Examples 1-2 that 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, while Example 3, by comparison, highlights the key role of photoactivation treatment in improving the comprehensive performance of conductive silver paste.

[0080] The above description is only 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 in the scope of protection 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 silicon dioxide intermediate coating layer, and a self-assembled outer layer of silver nanoparticles, characterized in that: The silver metal core is composed of metallic silver and has a particle size of 1-3 μm; The silicon dioxide intermediate coating layer is prepared by a sol-gel method and is evenly 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 50-100 nm, which are coated on the surface of the silicon dioxide intermediate coating layer through light-induced deposition technology to form a three-dimensional conductive network; The composite conductive powder is subjected to a wavelength of 254 nm and a power of 50 mW / cm 2 After 10 minutes of ultraviolet irradiation treatment, oxygen vacancies were generated on the surface and the carrier concentration increased by 2 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 preparation method of the silicon dioxide intermediate coating layer comprises: The silver metal core is dispersed in a mixed solution of ethyl orthosilicate / ethanol with 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°C for 2-4 hours to form a silver-silicon dioxide 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 silver nanoparticles comprises: Silver-silica core-shell particles were dispersed in a 0.1-0.3 mol / L silver nitrate solution, glucose was added as a reducing agent, and the solution was irradiated under 365 nm ultraviolet light for 30 minutes to reduce the silver nanoparticles in situ and 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 according to claim 3, characterized in that: Calculated 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 particle size of the glass powder is 1-5 μm; Graphene nanosheets 0.5%, lateral size 0.5-2 μm, thickness 1-5 layers; Thermoplastic polyurethane resin 15%; 21.5% dibasic acid ester solvent, which is a mixture 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 Ω·cm, and a conductive film was formed after curing at 120℃ for 20min.

5. The conductive silver paste according to claim 4, wherein: The preparation method of the cerium oxide modified glass powder comprises: After mixing glass powder and cerium oxide powder, sintering is carried out at 600-800°C for 2-4 hours. The basic components of the glass powder are silicon dioxide-boron trioxide-lead oxide glass with a mass ratio of 70:20:

10.

6. The conductive silver paste according to claim 5, wherein: The graphene nanosheets are prepared by an improved Hummers method, with a surface oxygen-containing group content of ≤5%, and form a uniform conductive network in a silver paste after ultrasonic dispersion.

7. The conductive silver paste according to claim 6, wherein: The volatile organic matter content in the dibasic acid ester solvent is ≤50 g / L.

8. The conductive silver paste according to claim 7, wherein: Specifically include the following preparation methods: S1. Mixing a thermoplastic polyurethane resin and a dibasic acid ester solvent in a mass ratio of 1:(1.2-1.5), stirring at 70° C. until completely dissolved, to obtain a carrier solution; S2. Add composite conductive powder, cerium oxide modified glass powder and graphene nanosheets to the carrier solution in step S1 in sequence, and use zirconia balls with a diameter of 3 mm to disperse them by ball milling, 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 at a vacuum degree of -0.1 MPa for 30 min to obtain the conductive silver paste.

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

10. The conductive silver paste according to claim 8, wherein: The conductive silver paste is used to prepare flexible electronic devices, which include: a flexible printed circuit board with a thickness of ≤100 μm, an electrode layer of a wearable pressure sensor, and an organic solar cell electrode based on a PET substrate.

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