Antioxidant copper powder, preparation method thereof and application of antioxidant copper powder in conductive ink

Abstract

The invention discloses antioxidant copper powder as well as a preparation method and application thereof in conductive ink. The specific process steps are as follows: firstly, dispersing copper powder in alkalescent L-ascorbic acid treating fluid to finish surface modification, and washing and drying to obtain L-ascorbic acid modified antioxidant copper powder; then uniformly mixing and dispersing with a solvent, a film-forming agent and a dispersing agent to prepare stable conductive ink; and finally, coating the conductive layer on a flexible or rigid substrate through silk-screen printing, blade coating or ink-jet printing, and curing or sintering in atmosphere or inert / micro-reducing atmosphere to form a long-term stable conductive pattern and interconnection layer. According to the method, the L-ascorbic acid or the salt thereof and the copper surface are subjected to coordination / chemical adsorption, a CuO-L-ascorbic acid convertible interface layer with the thickness of about 0.5-2.0 nm is formed through in-situ construction, and the interface layer can effectively inhibit oxidation in the storage and printing stages. In the subsequent curing / sintering interconnection process, the interface layer is subjected to desorption and pyrolysis conversion, the residual quantity is low, and particle neck connection and conductive network formation are not hindered.

Description

Technical Field

[0001] This invention relates to the field of conductive ink and metal powder surface treatment technology, specifically to an antioxidant copper powder based on L-ascorbic acid modification, its preparation method and its application in conductive ink, which is particularly suitable as an environmentally friendly conductive material for flexible electronic devices, printed circuits and various sensors. Background Technology

[0002] Conductive inks are functional materials in which conductive particles are dispersed in a film-forming agent and solvent system, and then printed, dried / cured to form conductive patterns. They are widely used in electronic circuits, flexible displays, radio frequency identification (RFID) tags, solar cells, and sensors. These applications place high demands on the volume resistivity, long-term chemical stability, environmental adaptability (temperature and humidity, salt spray, thermal cycling), and cost of conductive inks. Therefore, developing high-performance and cost-effective conductive ink materials has become a key focus of the industry.

[0003] In existing technologies, silver is widely used as a conductive filler due to its excellent conductivity and chemical stability. However, the scarcity and high price of silver resources limit its application in large-scale and cost-sensitive scenarios. Furthermore, the migration of silver ions can lead to device leakage and performance degradation, further increasing reliability risks. Therefore, finding a conductive filler that can replace silver is of great significance.

[0004] Copper has attracted widespread attention due to its conductivity being similar to silver but at a significantly lower cost. However, copper is easily oxidized in air and humid environments to form copper oxide, leading to increased resistance, decreased solderability / sinterability, and shortened device lifespan. Existing technologies for improving copper's oxidation resistance mainly include:

[0005] (1) Chemical reduction or inert / reducing atmosphere treatment: It can inhibit oxidation to a certain extent, but it often requires high temperature or continuous atmosphere control, which is complex and costly.

[0006] (2) Organic molecule surface modification: such as corrosion inhibitors or polymer coating, can delay oxidation, but some systems pose environmental and health risks and have limited durability under high temperature and high humidity conditions (such as 85℃ / 85%RH);

[0007] (3) Inorganic protective coating: such as oxides, nitrides and carbon base layers can improve corrosion resistance, but may affect the formation of necks and conductivity in the subsequent reflow / sintering process, and may lead to high residue.

[0008] L-Ascorbic acid is widely available and environmentally friendly, possessing both reducing and coordinating properties, and has been used for the green preparation and stabilization of precious metal nanomaterials such as gold and silver. Literature also reports the synergistic use of L-ascorbic acid and natural polymers (such as gum arabic) to achieve the preparation and short-term antioxidant effects of nano-copper. However, existing research largely focuses on the nanoparticle generation process and short-term stability. For key issues such as long-term antioxidant properties and environmental adaptability for conductive ink systems, compatibility with different film-forming systems, and low residue and non-neck-binding during reflow / low-temperature sintering, systematic solutions and reproducible parameter windows (such as pH, ionic strength, coverage / thickness, and processing time) are still lacking.

[0009] Based on the above situation, there is an urgent need for a green, simple, and scalable copper powder surface conditioning technology that can impart efficient and verifiable antioxidant capabilities to copper powder under normal atmospheric conditions, achieve low organic residues and good neck conductivity during subsequent printing reflow / sintering processes, and at the same time take into account compatibility with common resin / solvent systems to meet the comprehensive requirements of performance, reliability, cost, and environmental protection for applications such as flexible electronics, smart packaging, photovoltaic interconnection, and sensors. Summary of the Invention

[0010] This invention proposes an antioxidant copper powder based on L-ascorbic acid modification, its preparation method, and its application in conductive inks. Under a controlled chemical window, L-ascorbic acid or its salts are coordinated / chemisorbed onto the copper surface, constructing an in-situ 0.5–2.0 nm CuO—L-ascorbic acid convertible interface layer. This interface layer inhibits oxidation during storage and printing, while exhibiting low residue and not inhibiting particle necking and conductive network formation during reflow / low-temperature sintering. The resulting ink combines long-term environmental stability, good conductivity, and cost advantages, making it suitable for applications such as flexible electronics, smart packaging, photovoltaic interconnects, and sensors.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A method for preparing antioxidant copper powder includes the following steps:

[0013] a) Solution preparation: Dissolve L-ascorbic acid or its salt in a solvent, and then adjust the pH to 8.2-8.8 to obtain a treatment solution containing L-ascorbic acid or its salt;

[0014] b) Copper powder surface modification: Copper powder is dispersed in a treatment solution containing L-ascorbic acid or its salt. Pre-dispersion is performed first, and then stirring is continued at 20-30℃ for 5-15 minutes to allow L-ascorbic acid to coordinate or chemically adsorb onto the surface of copper powder, forming an antioxidant protective layer on the surface of copper powder.

[0015] c) Washing and drying: Centrifuge and filter to collect the solid, wash and dry to obtain L-ascorbic acid modified antioxidant copper powder.

[0016] Preferably, the solvent in step a) is a water-alcohol mixture, wherein the alcohol is one or more of methanol, ethanol or isopropanol, and the water-alcohol volume ratio is 1:0 to 1; the chemical conditions of the treatment solution meet the following requirements: ionic strength of 10 to 50 mM, and L-ascorbic acid or its salt concentration of 0.5 to 5 mM.

[0017] Preferably, the copper powder in step b) is micron-sized copper particles and / or nano-sized copper particles, with a morphology of one or more of spherical, flake, or linear shapes, and a D50 of 0.3–15 μm; the formed protective layer is a CuO-L-ascorbic acid convertible interface layer, with an average thickness of 0.5–2.0 nm on the surface of the copper powder; the coverage of the protective layer, based on specific surface area, is 0.15–0.60 mg·m³. -2 Furthermore, the organic residue after heat treatment at 220℃ for 30 minutes is ≤0.20 wt.%.

[0018] Preferably, the solid collected in step c) is washed 2 to 3 times in sequence with water and ethanol, and then vacuum dried at 40-60°C for 6 to 12 hours.

[0019] Another object of the present invention is to provide an antioxidant copper-based conductive ink, comprising the antioxidant copper powder prepared by the method described above.

[0020] Preferably, the conductive ink comprises: 55-80 wt% antioxidant copper powder, 15-30 wt% solvent, 3-10 wt.% film-forming agent, 0.5-3 wt.% dispersant, and optional additives such as leveling agent (e.g., Silwet L-77), defoamer (e.g., BYK-025), thixotropic agent (e.g., Bentone SD), and sintering accelerator (e.g., sodium persulfate) in a total amount ≤2 wt.%.

[0021] Preferably, the solvent is one or more of ethylene glycol ether, propylene glycol methyl ether, and dimethyl sulfoxide; the film-forming agent is one or more of polyvinyl butyral / formaldehyde or acrylic acid and polyurethane resin; and the dispersant is polyvinylpyrrolidone, polyamide wax, or the commercial dispersant BYK.

[0022] Conductive ink is obtained by mixing and dispersing antioxidant copper powder with solvent, film-forming agent, dispersant and additives.

[0023] Specific steps for preparing conductive ink:

[0024] a) Premix: Mix all components evenly at a low speed of 50-100 rpm;

[0025] b) High-shear dispersion: 2000-4000 rpm, 30-60 min; if necessary, bead milling (≤200μm glass beads, ≤1 h);

[0026] c) Degassing / Viscosity adjustment: Vacuum degassing for 5-10 minutes; fine-tune viscosity and thixotropy with solvent (to meet the process window requirements of screen printing / inkjet printing, etc.).

[0027] A third objective of this invention is to provide the application of the aforementioned antioxidant copper-based conductive ink in the manufacture of flexible electronics, smart packaging, solar cells, sensors, or chip packaging.

[0028] Preferably, the conductive ink is coated onto a substrate and cured and / or sintered to form a conductive pattern or interconnect layer.

[0029] Preferably, the curing method is one or more of in-furnace curing, laser curing, or microwave curing; the sintering atmosphere is atmospheric, nitrogen, or a mixture containing a small amount of reducing gas; the curing temperature is 80–150°C for 10–30 min; and the sintering temperature is 180–240°C.

[0030] During the curing process, solvent evaporation and resin film formation occur simultaneously. Within the temperature range of 180-240℃, the CuO-L-ascorbic acid interface layer can be transformed or detached without inhibiting the formation of the metal neck conductive network. This ink is compatible with processes including screen printing, blade coating, and inkjet printing (inkjet printing requires control of particle size distribution D90 < 0.5-1.0 μm), etc.

[0031] General formula representation of surface complexation during the preparation of antioxidant copper powder

[0032] Surface complexation:

[0033]

[0034] Among them AscH - / Asc2 - The deprotonated ligand of L-ascorbic acid under weakly alkaline conditions (O,O′enediolate bidentate coordination), "≡" indicates the active site on the copper / copper oxide surface.

[0035] After heat treatment (180-240℃) of the convertible interface layer, partial desorption / pyrolysis occurs:

[0036]

[0037] Beneficial effects:

[0038] Compared with the unmodified copper powder control, the ink of this invention has better resistance retention under humid and hot conditions, lower organic residue after reflow / sintering, better film conductivity uniformity and resin compatibility, and is suitable for large-scale printing and long-term service. Attached Figure Description

[0039] Figure 1 This is a flowchart of Example 1;

[0040] Figure 2 The XRD results of copper powder before and after L-ascorbic acid modification in Example 1 are shown.

[0041] Figure 3 The resistance value of the conductive block made from L-ascorbic acid-modified copper powder in Example 1 after 7 days of storage.

[0042] Figure 4 The images are scanning electron microscope (SEM) images of the sintered samples of L-ascorbic acid modified copper powder before and after storage in Example 1. (a) is before storage, and (b) is after storage. Detailed Implementation

[0043] The present invention will be described in detail below with reference to specific embodiments.

[0044] Example 1

[0045] Step 1: Preparation of L-ascorbic acid modified copper powder

[0046] Preparation process according to Figure 1 As shown, 50g of 800-mesh atomized copper powder was taken, and a treatment solution was prepared: L-ascorbic acid sodium was dissolved in deionized water / ethanol (volume ratio 7 / 3) to a final concentration of 2.0mM, and the pH was adjusted to 8.5±0.2 (ionic strength approximately 20mM) with NaHCO3 (20mM). The copper powder was added to 200mL of the treatment solution, and the mixture was stirred at room temperature (25±2℃) for 10min. During this time, L-ascorbic acid, in the form of ascorbate, coordinated / chemisorbed with the copper surface, while simultaneously undergoing a gentle reduction of a small amount of oxides on the surface, forming a dense and convertible CuO-ascorbic acid interfacial layer. After the reaction, the solid was separated by centrifugation or filtration, washed three times each in the order of "deionized water → ethanol", and dried under vacuum at 50℃ for 12h to obtain L-ascorbic acid-modified antioxidant copper powder (denoted as L-ascorbic acid-Cu).

[0047] Step 2: Antioxidant performance test

[0048] L-ascorbic acid-Cu and unmodified copper powder were subjected to accelerated aging at 60℃ and 90% RH for 7 days. Samples were taken for XRD (CuKα) testing, and the quality changes were recorded. The results are as follows: Figure 2 As shown, the unmodified copper powder exhibited significantly enhanced characteristic peaks such as Cu2O (111) and (200), and a significant increase in mass. The L-ascorbic acid-Cu sample maintained a diffraction signal dominated by metallic copper, with a weak Cu2O peak and a significantly reduced mass increase, indicating that L-ascorbic acid modification can effectively inhibit humid heat oxidation.

[0049] Step 3: Preparation of conductive ink

[0050] Weigh 116g of L-ascorbic acid-Cu obtained in step 1, add 60g of ethylene glycol ether, 20g of acrylic resin, and 4g of dispersant polyvinylpyrrolidone (PVP). Premix at low speed (100rpm, 10min), then perform high-energy dispersion / ball milling ≤2h (5000rpm, 20min) to obtain a stable particle size distribution. Subsequently, vacuum degassing is performed to obtain a uniform conductive ink. The resulting ink has a viscosity suitable for screen printing at 25℃ (if inkjet printing is required, the particle size needs to be further controlled to D90 < 0.8-1.0μm, and the solvent and curing should be fine-tuned according to the inkjet window).

[0051] Step 4: Application Testing of Conductive Ink

[0052] The ink from step 3 was screen-printed onto a PET film, pre-dried at 100℃ for 10 min, and cured at 120℃ for 30 min to form a conductive pattern. Three parallel samples were prepared, and their initial sheet resistance was measured to be approximately 50 Ω / sq. After being stored at 60℃ and 90% RH for 7 days, the sheet resistance showed no significant change (or a relative change ≤10%). Figure 3 As shown, L-ascorbic acid-Cu imparts good environmental stability and conductivity retention to the pattern in the actual ink system.

[0053] Step 5: Long-term storage stability test

[0054] The ink from step 3 was stored in a sealed container at room temperature for 6 months, during which its viscosity and electrical properties were periodically monitored. The results showed minimal viscosity drift and no significant change in conductivity. SEM observation of the printed film before and after storage revealed no newly formed oxide morphology. Figure 4 As shown, this further verifies the long-term protective effect of the L-ascorbic acid interface layer on copper powder.

[0055] Example 2

[0056] Step 1: Powder and Processing

[0057] The same batch of atomized copper powder as in Example 1 was used. The treatment solution was prepared as follows: deionized water:ethanol = 4:1 (volume fraction), buffered with Na₂CO₃ to pH 8.5, ionic strength I = 25 mM; 1.5 mM of L-ascorbic acid (AA) was added. The mixture was magnetically stirred at room temperature (25°C) for 8 min, then filtered; washed three times each with deionized water and ethanol; and vacuum dried at 40°C.

[0058] Step 2: Ink Formulation (mass fraction)

[0059] L-Ascorbic acid-Cu 70%; Solvent (propylene glycol methyl ether) 20%; PVB 7%; Dispersant (PVP) 2%; Defoamer 1% (BYK-025). Planetary stirring for 10 min (low speed: 100 rpm, 2 min; high speed: 5000 rpm, 8 min), vacuum degassing for 3 min.

[0060] Step 3: Film formation and heat treatment

[0061] PET substrate, blade coating (wet film approximately 25-30μm), dry film thickness approximately 12±1μm; curing 120℃×15min (air); reflow / sintering 220℃×20min (N2).

[0062] Comparative Example 1

[0063] Conditions: pH 6.5, AA 0.10 mol·L⁻¹ -1 Soak at room temperature for 45 minutes; filter and wash with water; dry at 40°C. All other steps are the same as in Example 1.

[0064] Comparative Examples 2-4

[0065] Only the pH of the treatment solution was changed; I was fixed at 25 mM, AA at 2.0 mM, and treated at 25°C for 10 min; all other aspects were the same as in Example 1. Table 1 shows the comparative results.

[0066] Table 1 Comparison of Examples 1-2 and Comparative Examples 1-4

[0067]

[0068] Comparative Example 1: High concentrations of AA form a thick organic coating under neutral / weakly acidic conditions, which is difficult to remove effectively during reflux, inhibiting metal necking, resulting in high sheet resistance, humid heat deterioration, and decreased adhesion.

[0069] Comparative Example 2: pH 5.5 (slightly acidic) Judgment: Insufficient interfacial layer, poor antioxidant and moisture and heat retention.

[0070] Comparative Example 3: pH 7.0 (neutral) judgment: improved compared to pH 5.5, but still not as good as the weakly alkaline window.

[0071] Example 1: pH 8.5 (weakly alkaline) determination: thin and convertible interface layer, sufficient necking, and best overall performance.

[0072] Comparative Example 4: pH 9.2 (alkaline) Judgment: Excessive complexation → thicker interface layer, which is detrimental to electrical conductivity and humidity.

[0073] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0074] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing antioxidant copper powder, characterized in that, Includes the following steps: a) Solution preparation: Dissolve L-ascorbic acid or its salt in a solvent, and then adjust the pH to 8.2-8.8 to obtain a treatment solution containing L-ascorbic acid or its salt; b) Copper powder surface modification: Copper powder is dispersed in a treatment solution containing L-ascorbic acid or its salt. Pre-dispersion is performed first, and then stirring is continued at 20-30℃ for 5-15 minutes to allow L-ascorbic acid to coordinate or chemically adsorb onto the surface of copper powder, forming an antioxidant protective layer on the surface of copper powder. c) Washing and drying: Centrifuge and filter to collect the solid, wash and dry to obtain L-ascorbic acid modified antioxidant copper powder.

2. The method for preparing antioxidant copper powder as described in claim 1, characterized in that, The solvent in step a) is a water-alcohol mixture, wherein the alcohol is one or more of methanol, ethanol or isopropanol, and the water-alcohol volume ratio is 1:0 to 1; the chemical conditions of the treatment solution are: ionic strength of 10 to 50 mM, and L-ascorbic acid or its salt concentration of 0.5 to 5 mM.

3. The method for preparing antioxidant copper powder as described in claim 1, characterized in that, The copper powder mentioned in step b) is micron-sized copper particles and / or nano-sized copper particles, with a morphology of one or more of spherical, flake, or linear shapes, and a D50 of 0.3–15 μm; the formed protective layer is a CuO-L-ascorbic acid convertible interface layer, with an average thickness of 0.5–2.0 nm on the surface of the copper powder; the coverage of the protective layer, based on specific surface area, is 0.15–0.60 mg·m³. -2 Furthermore, the organic residue after heat treatment at 220℃ for 30 minutes is ≤0.20 wt.%.

4. A method for preparing antioxidant copper powder according to any one of claims 1 to 3, characterized in that, The solid collected in step c) is washed 2 to 3 times in sequence with water and ethanol, and then vacuum dried at 40-60℃ for 6 to 12 hours.

5. An antioxidant copper-based conductive ink, characterized in that, The antioxidant copper powder prepared by the method according to any one of claims 1 to 4.

6. The antioxidant copper-based conductive ink according to claim 5, characterized in that, The conductive ink comprises: 55-80 wt% antioxidant copper powder, 15-30 wt% solvent, 3-10 wt.% film-forming agent, 0.5-3 wt.% dispersant, and optionally added leveling agent, defoamer, and thixotropic agent, with a total amount ≤2 wt.%. An antioxidant copper-based conductive ink as described in claim 6, characterized in that the solvent is one or more of ethylene glycol ether, propylene glycol methyl ether, and dimethyl sulfoxide; the film-forming agent is one or more of polyvinyl butyral / formaldehyde or acrylic acid and polyurethane resin; and the dispersant is polyvinylpyrrolidone, polyamide wax, or the commercial dispersant BYK.

7. The application of the antioxidant copper-based conductive ink as described in claim 6 in the manufacturing of flexible electronics, smart packaging, solar cells, sensors, or chip packaging.

8. The application as described in claim 8, characterized in that, The conductive ink is coated onto a substrate and cured and / or sintered to form a conductive pattern or interconnect layer.

9. The application as described in claim 9, characterized in that, The curing method is one or more of in-furnace curing, laser curing, or microwave curing; the sintering atmosphere is argon, nitrogen, or a mixture containing a small amount of reducing gas; the curing temperature is 80-150℃ for 10-30 minutes; and the sintering temperature is 180-240℃.

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