A multi-layered, sheet-like silver-coated aluminum powder and its preparation method, and conductive rubber materials.

Abstract

This invention proposes a multi-layered, sheet-like silver-coated aluminum powder, its preparation method, and a conductive rubber material. The multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder, a silica layer, and a silver layer; the silica layer coats the surface of the sheet-like aluminum powder, and the silver layer coats the surface of the silica layer. This invention, employing a multi-layered composite structure design of "aluminum core-silica layer-silver layer," solves the problems of poor aluminum powder stability and easy silver migration, and possesses advantages such as low cost and shear resistance, thus obtaining a novel white conductive filler with high performance, high stability, and high applicability.

Description

Technical Field

[0001] This invention relates to the field of conductive powder materials technology, and in particular to a multi-layered sheet-like silver-coated aluminum powder and its preparation method, as well as conductive rubber materials. Background Technology

[0002] For silver-coated aluminum composite particles, the combined properties of an aluminum core and a silver shell achieve synergistic performance optimization. Aluminum, as a lightweight metal, has a density only about one-third that of copper and possesses excellent electrical and thermal conductivity, ranking fourth among all metals after silver, copper, and gold. Furthermore, a dense alumina passivation film spontaneously forms on the aluminum surface, effectively preventing oxygen from further eroding the internal aluminum matrix, thus significantly improving its oxidation resistance and environmental stability. By coating the aluminum powder with a silver layer, the migration of silver under an electric field can be further suppressed. Therefore, silver-coated aluminum powder becomes an important core-shell functional material. In addition, both aluminum and silver have a face-centered cubic crystal structure, exhibiting good compatibility and bonding strength at the interface.

[0003] Silver-coated aluminum powder, as a new type of high-performance conductive filler developed in recent years, has advantages such as light weight, excellent conductivity, and high strength, but it still has the following problems:

[0004] (1) Environmental stability issues: Aluminum, especially high specific surface area flake aluminum powder, is chemically active and is easily oxidized during processing and storage; although the surface aluminum oxide layer is dense, it will continue to oxidize once it is damaged or under certain conditions, leading to a decrease in conductivity. This is a major drawback for electronic applications that require high reliability.

[0005] (2) Silver migration problem: Although silver coating can suppress silver migration to a certain extent, silver ions may still migrate when the traditional silver-coated aluminum structure is used in a high temperature and high humidity environment for a long time, resulting in short circuit or performance degradation.

[0006] (3) Compatibility with polymer matrix: Ordinary silver-coated aluminum powder has a single surface property, which makes it difficult to combine well with organic polymer matrix such as rubber. It is easy to generate interface defects, resulting in uneven dispersion of filler, unstable conductive network, and easy detachment when the material is under stress, affecting conductivity and mechanical properties. Summary of the Invention

[0007] Based on the technical problems existing in the background art, this invention proposes a multi-structured layered sheet-like silver-coated aluminum powder and its preparation method, as well as a conductive rubber material. It adopts a multi-layered composite structure design of "aluminum core-silicon dioxide layer-silver layer", which solves the problems of poor stability of aluminum powder and easy migration of silver. It has the advantages of low cost and shear resistance, thus obtaining a new type of white conductive filler with high performance, high stability and high applicability.

[0008] The present invention proposes a multi-structured layered flake-shaped silver-coated aluminum powder, comprising: flake-shaped aluminum powder, a silicon dioxide layer, and a silver layer; wherein the silicon dioxide layer coats the surface of the flake-shaped aluminum powder, and the silver layer coats the surface of the silicon dioxide layer.

[0009] In this invention, flake-shaped aluminum powder is selected to achieve high conductivity (high electrical conductivity) with a relatively low filling amount, which has significant advantages over spherical silver-coated aluminum. To solve the oxidation and safety issues of the flake-shaped aluminum core, a dense layer of organosilicon oxide (SiO2) is constructed on the surface of the flake-shaped aluminum powder. X The silica layer completely isolates the reactive aluminum core from the external environment, solving the oxidation problem of high specific surface area aluminum powder during processing, storage, and use. This significantly improves the chemical stability of the material and the operational safety during experiments and production. Simultaneously, to enhance the ability to inhibit silver migration and build a stable conductive path, a silver layer is precisely coated on top of the silica layer. This design completely isolates the conductive silver layer from the aluminum core, not only inheriting the excellent conductivity of silver but also fundamentally blocking direct contact between silver and aluminum, reducing electrochemical corrosion, and thus more effectively inhibiting silver migration and ensuring long-term stability of conductivity.

[0010] Preferably, the surface of the silver layer is further grafted with a coupling agent;

[0011] Preferably, the coupling agent is at least one of titanate coupling agents, zirconate coupling agents, or silane coupling agents.

[0012] In this invention, to improve the interfacial compatibility and bonding strength between flake silver-coated aluminum powder as a filler and the rubber matrix, specific surface modification is performed on the outermost silver surface to introduce functional groups or structures that can interact well with the rubber molecular chains, thereby significantly improving the dispersibility and interfacial bonding force of the silver-coated aluminum powder in the rubber. At the same time, the problems of easy agglomeration and easy detachment of fillers are solved, thus providing conditions for preparing composite conductive rubber materials with stable conductivity and excellent mechanical properties.

[0013] This invention proposes a method for preparing the above-mentioned multi-layered lamellar silver-coated aluminum powder, comprising the following steps:

[0014] S1. Coat the surface of the flake aluminum powder with a silicon dioxide layer to obtain silicon dioxide coated aluminum powder;

[0015] S2. Coat the surface of the aluminum powder with silicon dioxide and then plate it with a silver layer to obtain the flake-shaped silver-coated aluminum powder.

[0016] In this invention, since aluminum itself is chemically reactive and its flake shape has a larger specific surface area than that of a sphere, making it more prone to surface reactions, an organosilicon oxide layer is first coated on the surface of the flake aluminum powder to improve its chemical inertness and experimental safety. A silver layer is then chemically deposited on the outside of this silica oxide layer to form a conductive path. Finally, surface modification treatment is used to enhance the compatibility and dispersion stability of the layer with polymer matrices such as rubber (the application end).

[0017] Preferably, in step S1, the step of "coating the surface of the flake aluminum powder with a silica layer" specifically includes: dispersing the flake aluminum powder in an alcohol solvent, adding an alkyl silicate ester to carry out a hydrolysis reaction, thereby obtaining the silica-coated aluminum powder;

[0018] Preferably, the hydrolysis reaction is carried out under weakly acidic conditions with a pH of 4-5, a reaction temperature of 40-50°C, and a time of 6-8 hours.

[0019] Preferably, the alkyl silicate is at least one selected from methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, or pentyl orthosilicate; and the alcohol solvent is at least one selected from ethanol, isopropanol, or n-butanol.

[0020] Preferably, the amount of the alkyl silicate is 8-12 wt% of the mass of the flake aluminum powder.

[0021] Preferably, in step S2, the step of "plating a silver layer on the surface of the silica-coated aluminum powder" specifically includes: dispersing the silica-coated aluminum powder in water, simultaneously adding a reducing solution and a silver complexing solution, and carrying out a low-temperature reduction reaction under alkaline conditions to obtain the flake-shaped silver-coated aluminum powder;

[0022] Preferably, before dispersing the silica-coated aluminum powder in water, the method further includes sensitizing and activating the silica-coated aluminum powder;

[0023] Preferably, the silica-coated aluminum powder is sensitized with tin chloride solution at a pH of 1.5-2.0, and then activated with palladium chloride solution or silver ammonia solution.

[0024] Preferably, the reducing agent in the reducing agent solution is at least one of sodium borohydride, potassium borohydride, sodium tartrate, or potassium tartrate, and the silver complexing solution includes a silver salt and a complexing agent. The silver salt is at least one of silver nitrate, silver methanesulfonate, or silver iodide, and the complexing agent is at least one of triethylamine, triethanolamine, diethylenetriamine, ethylenediamine, sodium citrate tetraacetate, or ammonia.

[0025] Preferably, the amount of silver salt used is 10-30 wt% of the mass of the silica-coated aluminum powder.

[0026] Preferably, before step S2, the process further includes grafting a chelating agent onto the surface of the aluminum powder coated with silica;

[0027] Preferably, silica-coated aluminum powder is dispersed in a dopamine solution, and thiourea is added to carry out an addition reaction to obtain silica-coated aluminum powder with a surface grafted chelating agent.

[0028] In this invention, the surface of silica-coated aluminum powder is first adhered with polydopamine (PDA). Since the catechol groups on PDA can undergo addition with the amino groups on thiourea, the surface of silica-coated aluminum powder is grafted with chelating groups of dithioimine, which can coordinate and chelate with silver ions, promoting the deposition and reduction of silver ions on the surface of the silica layer, forming a silver shell layer with better bonding and conductivity. When mixed with rubber, it has better conductivity, shear resistance and extrusion resistance.

[0029] Preferably, after step S2, the process further includes dispersing flake-shaped silver-coated aluminum powder in an organic solvent, adding a coupling agent to carry out a coupling reaction, and obtaining silver-coated aluminum powder with a surface-grafted coupling agent.

[0030] Preferably, the coupling agent is at least one of titanate coupling agents, zirconate coupling agents, or silane coupling agents;

[0031] Preferably, the amount of the coupling agent is 0.5-1.5 wt% of the mass of the silver-coated aluminum powder.

[0032] The present invention also proposes a conductive rubber material for electronic products, comprising the above-mentioned sheet-like silver-coated aluminum powder or the sheet-like silver-coated aluminum powder prepared by the above preparation method.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] To address the shortcomings of existing conductive fillers, such as silver-coated copper / nickel: high density and cost, which are not conducive to device lightweighting; silver-coated glass microspheres: although lightweight, the glass core material is too rigid and lacks toughness, making it extremely easy to break during shearing or product deformation, resulting in broken conductive paths and poor reliability; spherical silver-coated aluminum: requires a high filling amount to form a conductive network in the matrix, resulting in low conductivity (conduction capacity) and difficulty in achieving high conductivity; carbon black, carbon nanotubes, graphene and other carbon-based materials: only black in color, which cannot meet the application scenarios with specific requirements for material color (such as white or light colors).

[0035] Therefore, this invention provides a multi-layered, sheet-like silver-coated aluminum powder. By selecting sheet-like aluminum substrate, high conductivity (high electrical conductivity) is achieved with a lower filling amount, which has significant advantages compared to spherical silver-coated aluminum. Utilizing the lightweight and ductility of aluminum, it achieves lightweighting and cost reduction compared to silver-coated copper. Compared to silver-coated glass microspheres, it provides good shear strength and toughness, is not easily broken during processing and use, and ensures the integrity of the conductive network. The resulting sheet-like silver-coated aluminum powder is silvery-white, overcoming the limitation that carbon-based conductive fillers can only provide black, and meeting the specific color requirements of electronic products (such as white markings, light-colored coatings, etc.).

[0036] The flake-shaped silver-coated aluminum powder described in this invention exhibits significant advantages in multiple dimensions:

[0037] Compared to silver-coated copper composite powder, aluminum substrate has lower cost and lower density, which is beneficial for achieving lightweight and low cost. Compared to silver-coated glass microspheres (GMB@Ag, where GMB refers to glass microspheres), the aluminum core itself has certain ductility and shear resistance, is not easily brittle, and can provide better mechanical toughness during processing. Compared to spherical silver-coated aluminum powder, the sheet structure can form a more effective conductive network in the matrix, with higher conductivity and better electrical conductivity. Compared to traditional conductive carbon black (CB), carbon nanotubes (CNT) or graphite and other black conductive fillers, this product is silvery-white, which can meet the requirements of light color or specific appearance in some application scenarios.

[0038] The beneficial effects of the flake-shaped silver-coated aluminum powder described in this invention are as follows:

[0039] (1) High stability: The SiO2 layer effectively blocks water and oxygen, prevents aluminum core oxidation, and improves durability; (2) Good conductivity: The sheet-like morphology forms a highly efficient conductive network in the matrix; the silver plating layer of the borohydride system is dense and has high conductivity; (3) Strong compatibility: The coupling agent modification significantly improves its dispersibility and bonding force in polymers such as rubber; (4) Low cost and light weight: The cost of aluminum substrate is much lower than that of copper, and its density is low, which is conducive to lightweighting and cost reduction; (5) Adjustable color: The silver-white appearance can meet the specific needs of light-colored conductive materials.

[0040] In summary, the multi-layered sheet-like silver-coated aluminum powder of the present invention has excellent comprehensive performance and is especially suitable for applications in the electronics industry, high-frequency communication, aerospace and military fields where there are strict requirements for conductivity, color, cost and mechanical properties. Attached Figure Description

[0041] Figure 1 This is a SEM image of the multi-layered, sheet-like silver-coated aluminum powder described in Embodiment 2 of the present invention.

[0042] Figure 2 This is a schematic diagram of the structure of the silica-coated aluminum powder of the surface grafted chelating agent described in Embodiment 3 of the present invention;

[0043] Figure 3 The infrared spectrum of the silica-coated aluminum powder with the surface grafted chelating agent described in Example 3 of this invention is shown. Detailed Implementation

[0044] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0045] Example 1

[0046] A multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer coats the surface of the sheet-like aluminum powder, and the silver layer coats the surface of the silicon dioxide layer.

[0047] The above-mentioned multi-layered lamellar silver-coated aluminum powder is prepared by the following method:

[0048] (1) Pretreatment and dispersion: Place the flake aluminum powder in the reaction vessel, add anhydrous ethanol, and ultrasonically disperse for 30 min to form a uniform suspension. Add a few drops of glacial acetic acid to adjust the pH of the system to 4-5 to obtain an aluminum powder suspension.

[0049] (2) Silica coating: 10 wt% of tetraethyl orthosilicate (TEOS) of flake aluminum powder was mixed with anhydrous ethanol and placed in a constant pressure dropping funnel. The resulting mixture was slowly added dropwise to the aluminum powder suspension, the dropping rate was controlled, and the reaction temperature was maintained at 45°C. After the addition was completed, the mixture was kept warm and stirred for 7 hours to ensure that TEOS was fully hydrolyzed and condensed to form a uniform silica layer on the surface of the aluminum powder. After the reaction was completed, the mixture was aged for 12 hours, filtered, and washed three times with ethanol to obtain silica-coated aluminum powder. The powder was then thoroughly dried in a vacuum drying oven at 80°C.

[0050] (3) Sensitization and activation: Disperse silica-coated aluminum powder in deionized water, add dilute hydrochloric acid to adjust the pH to 1.5-2.0, add SnCl2 solution with a content of 0.075wt%, sensitize for 20min, filter, wash with water, disperse again in water, add PdCl2 dilute solution with a content of 0.12wt%, activate for 10min, so that Pd particles are adsorbed on the surface of aluminum powder as catalytic centers, filter, wash with water, and obtain activated silica-coated aluminum powder;

[0051] (4) Chemical silver plating: Dissolve 20 wt% silver nitrate of silica-coated aluminum powder in deionized water, and slowly add ammonia water while stirring until the initial brown precipitate is completely dissolved to form a transparent silver-ammonia complex solution; dissolve 2.5 times the theoretical amount of potassium borohydride required to reduce silver nitrate in a 1 mol / L NaOH solution cooled in an ice-water bath to obtain a reducing agent solution; disperse the activated silica-coated aluminum powder in deionized water, pour it into a reaction vessel, and adjust the pH of the system to 12- using NaOH solution. 13. Heat the reaction system to 30℃ (strictly control the low temperature to prevent the reaction from being too fast). While stirring vigorously, add the silver ammonia complex solution and the reducing agent solution slowly and simultaneously but separately. Control the dropping rate to ensure that the silver ions are instantly reduced when they reach the powder surface, rather than nucleating themselves in the solution. After the addition is complete, continue to keep the reaction at 30℃ for 1 hour to allow the silver layer to be completely deposited. After the reaction is complete, let it stand and cool, filter it, and wash it repeatedly with deionized water and ethanol until the filtrate is neutral to obtain flake silver-coated aluminum powder. Dry it in a vacuum drying oven at 80℃.

[0052] Example 2

[0053] A multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer coats the surface of the sheet-like aluminum powder, the silver layer coats the surface of the silicon dioxide layer, and the surface of the silver layer is further grafted with a titanate coupling agent.

[0054] The above-mentioned multi-layered lamellar silver-coated aluminum powder is prepared by the following method:

[0055] (1) Pretreatment and dispersion: Place the flake aluminum powder in the reaction vessel, add anhydrous ethanol, and ultrasonically disperse for 30 min to form a uniform suspension. Add a few drops of glacial acetic acid to adjust the pH of the system to 4-5 to obtain an aluminum powder suspension.

[0056] (2) Silica coating: 10 wt% of tetraethyl orthosilicate (TEOS) of flake aluminum powder was mixed with anhydrous ethanol and placed in a constant pressure dropping funnel. The resulting mixture was slowly added dropwise to the aluminum powder suspension, the dropping rate was controlled, and the reaction temperature was maintained at 45°C. After the addition was completed, the mixture was kept warm and stirred for 7 hours to ensure that TEOS was fully hydrolyzed and condensed to form a uniform silica layer on the surface of the aluminum powder. After the reaction was completed, the mixture was aged for 12 hours, filtered, and washed three times with ethanol to obtain silica-coated aluminum powder. The powder was then thoroughly dried in a vacuum drying oven at 80°C.

[0057] (3) Sensitization and activation: Disperse silica-coated aluminum powder in deionized water, add dilute hydrochloric acid to adjust the pH to 1.5-2.0, add SnCl2 solution with a content of 0.075wt%, sensitize for 20min, filter, wash with water, disperse again in water, add PdCl2 dilute solution with a content of 0.12wt%, activate for 10min, so that Pd particles are adsorbed on the surface of aluminum powder as catalytic centers, filter, wash with water, and obtain activated silica-coated aluminum powder;

[0058] (4) Chemical silver plating: Dissolve 20 wt% silver nitrate of silica-coated aluminum powder in deionized water, and slowly add ammonia water while stirring until the initially formed brown precipitate is completely dissolved to form a transparent silver ammonia complex solution; dissolve 2.5 times the theoretical amount of potassium borohydride required to reduce silver nitrate in a 1 mol / L NaOH solution cooled in an ice-water bath to obtain a reducing agent solution; disperse the activated silica-coated aluminum powder in deionized water, pour it into a reaction vessel, and adjust the pH of the system to 1 with NaOH solution. 2-13. Heat the reaction system to 30℃ (strictly control the low temperature to prevent the reaction from being too fast). While stirring vigorously, add the silver ammonia complex solution and the reducing agent solution slowly and simultaneously but separately. Control the dropping rate to ensure that the silver ions are instantly reduced when they reach the powder surface, rather than nucleating themselves in the solution. After the addition is complete, continue to keep the reaction at 30℃ for 1 hour to allow the silver layer to be completely deposited. After the reaction is complete, let it stand and cool, filter it, and wash it repeatedly with deionized water and ethanol until the filtrate is neutral to obtain flake silver-coated aluminum powder. Dry it in a vacuum drying oven at 80℃.

[0059] (5) Surface organic modification: 1 wt% of titanate coupling agent (isopropyltris(dioctylpyrophosphate)titanate) of the flake silver-coated aluminum powder was dissolved in anhydrous ethanol and stirred evenly. The dried flake silver-coated aluminum powder was placed in a dry reaction vessel. Under stirring conditions, the ethanol solution of the coupling agent was slowly added to the flake silver-coated aluminum powder to ensure uniform wetting. The system was heated to 65°C and stirred continuously for 5 hours to allow the coupling agent molecules to fully react with the hydroxyl groups and other groups on the surface of the silver layer to form chemical bonds. After the reaction was completed, the powder was collected by vacuum filtration, washed once with a small amount of anhydrous ethanol to remove the physically adsorbed coupling agent, and dried in a vacuum drying oven at 70°C for 4 hours to obtain the flake silver-coated aluminum powder with surface modification of the coupling agent. Its SEM image is shown in the figure below. Figure 1 As shown.

[0060] Example 3

[0061] A multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer coats the surface of the sheet-like aluminum powder, the silver layer coats the surface of the silicon dioxide layer, and the surface of the silver layer is further grafted with a titanate coupling agent.

[0062] The above-mentioned multi-layered lamellar silver-coated aluminum powder is prepared by the following method:

[0063] (1) Pretreatment and dispersion: Place the flake aluminum powder in the reaction vessel, add anhydrous ethanol, and ultrasonically disperse for 30 min to form a uniform suspension. Add a few drops of glacial acetic acid to adjust the pH of the system to 4-5 to obtain an aluminum powder suspension.

[0064] (2) Silica coating: 10 wt% of tetraethyl orthosilicate (TEOS) of flake aluminum powder was mixed with anhydrous ethanol and placed in a constant pressure dropping funnel. The resulting mixture was slowly added dropwise to the aluminum powder suspension, the dropping rate was controlled, and the reaction temperature was maintained at 45°C. After the addition was completed, the mixture was kept warm and stirred for 7 hours to ensure that TEOS was fully hydrolyzed and condensed to form a uniform silica layer on the surface of the aluminum powder. After the reaction was completed, the mixture was aged for 12 hours, filtered, and washed three times with ethanol to obtain silica-coated aluminum powder. The powder was then thoroughly dried in a vacuum drying oven at 80°C.

[0065] (3) Dopamine hydrochloride at 5 wt% of the mass of silica-coated aluminum powder was added to tris(hydroxymethyl)aminomethane buffer solution and stirred to dissolve, thus obtaining a dopamine solution (pH=8.5). The silica-coated aluminum powder was added to the dopamine solution and stirred for 12 h. After filtration, washing with water, and drying, the intermediate product was dispersed in deionized water. Thiourea at 1 wt% of the mass of silica-coated aluminum powder was added and stirred for 6 h. After filtration, washing with water, and drying, silica-coated aluminum powder with surface grafted chelating agent was obtained, and its structure is shown in the figure. Figure 2 As shown, the infrared spectrum is as follows Figure 3 As shown;

[0066] (4) Chemical silver plating: Dissolve 20 wt% of silver nitrate (by weight of silica-coated aluminum powder with surface grafted chelating agent) in deionized water, and slowly add ammonia water while stirring until the initially formed brown precipitate is completely dissolved to form a transparent silver ammonia complex solution; dissolve 2.5 times the theoretical amount of potassium borohydride required to reduce silver nitrate in a 1 mol / L NaOH solution cooled in an ice-water bath to obtain a reducing agent solution; disperse the silica-coated aluminum powder with surface grafted chelating agent in deionized water, pour it into a reaction vessel, and adjust the volume with NaOH solution. With the pH set at 12-13, the reaction system was heated to 30°C (the low temperature was strictly controlled to prevent the reaction from being too fast). Under vigorous stirring, the silver ammonia complex solution and the reducing agent solution were added dropwise simultaneously but separately. The dropping rate was controlled to ensure that the silver ions were instantly reduced when they reached the powder surface, rather than nucleating themselves in the solution. After the addition was complete, the reaction was continued at 30°C for 1 hour to allow the silver layer to be completely deposited. After the reaction was completed, the mixture was allowed to stand and cool, filtered, and repeatedly washed with deionized water and ethanol until the filtrate was neutral to obtain flake-shaped silver-coated aluminum powder, which was then dried in a vacuum drying oven at 80°C.

[0067] (5) Surface organic modification: Dissolve 1 wt% of titanate coupling agent (isopropyltris(dioctylpyrophosphate) titanate) in anhydrous ethanol and stir evenly. Place the dried flakes of silver-coated aluminum powder in a dry reaction vessel. Under stirring conditions, slowly add the ethanol solution of coupling agent to the flakes of silver-coated aluminum powder to ensure uniform wetting. Heat the system to 65°C and stir continuously for 5 hours to allow the coupling agent molecules to fully react with the hydroxyl groups and other groups on the surface of the silver layer to form chemical bonds. After the reaction is completed, filter and recover the powder. Wash once with a small amount of anhydrous ethanol to remove the physically adsorbed coupling agent. Dry in a vacuum drying oven at 70°C for 4 hours to obtain flakes of silver-coated aluminum powder with surface modification by coupling agent.

[0068] Comparative Example 1

[0069] A multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder and a silver layer; the silver layer coats the surface of the sheet-like aluminum powder, and the surface of the silver layer is further grafted with a titanate coupling agent.

[0070] The above-mentioned multi-layered lamellar silver-coated aluminum powder is prepared by the following method:

[0071] (1) Sensitization and activation: Disperse the flake aluminum powder in deionized water, add dilute hydrochloric acid to adjust the pH to 1.5-2.0, add SnCl2 solution with a content of 0.075wt%, sensitize for 20min, filter, wash with water, disperse again in water, add dilute PdCl2 solution with a content of 0.075wt%, activate for 10min, so that Pd particles are adsorbed on the surface of aluminum powder as catalytic centers, filter, wash with water, and obtain activated aluminum powder;

[0072] (2) Chemical silver plating: Dissolve 20 wt% silver nitrate of flake aluminum powder in deionized water, and slowly add ammonia water while stirring until the initially formed brown precipitate is completely dissolved to form a transparent silver-ammonia complex solution; dissolve 2.5 times the theoretical amount of potassium borohydride required to reduce silver nitrate in a 1 mol / L NaOH solution cooled in an ice-water bath to obtain a reducing agent solution; disperse the activated aluminum powder in deionized water, pour it into a reaction vessel, adjust the pH of the system to 12-13 with NaOH solution, and then... The reaction system was heated to 30℃ (the low temperature was strictly controlled to prevent the reaction from being too fast). Under vigorous stirring, the silver ammonia complex solution and the reducing agent solution were added dropwise simultaneously but separately. The dropping rate was controlled to ensure that the silver ions were instantly reduced when they reached the powder surface, rather than nucleating themselves in the solution. After the addition was completed, the reaction was continued at 30℃ for 1 hour to allow the silver layer to be completely deposited. After the reaction was completed, the mixture was allowed to stand and cool, filtered, and repeatedly washed with deionized water and ethanol until the filtrate was neutral to obtain flake silver-coated aluminum powder, which was then dried in a vacuum drying oven at 80℃.

[0073] (3) Surface organic modification: Dissolve 1 wt% of titanate coupling agent (isopropyltris(dioctylpyrophosphate) titanate) in anhydrous ethanol and stir evenly. Place the dried flakes of silver-coated aluminum powder in a dry reaction vessel. Under stirring conditions, slowly add the ethanol solution of coupling agent to the flakes of silver-coated aluminum powder to ensure uniform wetting. Heat the system to 65°C and stir continuously for 5 hours to allow the coupling agent molecules to fully react with the hydroxyl groups and other groups on the surface of the silver layer to form chemical bonds. After the reaction is completed, filter and recover the powder. Wash once with a small amount of anhydrous ethanol to remove the physically adsorbed coupling agent. Dry in a vacuum drying oven at 70°C for 4 hours to obtain flakes of silver-coated aluminum powder with surface modification by coupling agent.

[0074] Comparative Example 2

[0075] A multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer coats the surface of the sheet-like aluminum powder, the silver layer coats the surface of the silicon dioxide layer, and the surface of the silver layer is further grafted with a titanate coupling agent.

[0076] The above-mentioned multi-layered sheet-like silver-coated aluminum powder was prepared by the preparation method described in Example 3. Except in step (3), 5 wt% of dopamine hydrochloride was added to tris(hydroxymethyl)aminomethane buffer solution and stirred to dissolve to obtain a dopamine solution (pH=8.5). The silica-coated aluminum powder was added to the dopamine solution, stirred and reacted for 12 h, filtered, washed with water, and dried to obtain silica-coated aluminum powder with PDA grafted on the surface.

[0077] Comparative Example 3

[0078] A multi-layered, sheet-like silver-coated aluminum powder comprises: sheet-like aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer coats the surface of the sheet-like aluminum powder, the silver layer coats the surface of the silicon dioxide layer, and the surface of the silver layer is further grafted with a titanate coupling agent.

[0079] The above-mentioned multi-structured layered sheet-like silver-coated aluminum powder was prepared by the preparation method described in Example 3. Except in step (3), where the silica-coated aluminum powder was dispersed in deionized water, 1 wt% of thiourea was added to the silica-coated aluminum powder, and after stirring and reacting for 6 hours, the powder was filtered, washed with water, and dried to obtain silica-coated aluminum powder with thiourea grafted on the surface.

[0080] Performance testing:

[0081] The flake-shaped silver-coated aluminum powder described in Examples 2 and 3 and Comparative Examples 1, 2 and 3, as well as existing Cu@Ag (see “Preparation and Antioxidant Properties of High-Density Silver-Coated Copper Powder”, Kuang Sixiang et al., Marine Electrical Technology, 2025, 45(08):71-76), GMB@Ag (silver-coated glass microspheres, see “Preparation and Performance of Core-Shell Particles of Silver-Coated Glass Microspheres for Electromagnetic Shielding Materials”, Wang Yilong et al., Journal of the Chinese Ceramic Society, 2008, (03):301-305), and CB / CN were used. T (mass ratio 1:1) is used as a conductive filler in conductive rubber materials. The matrix compound is a two-component addition-type liquid silicone rubber (component A: vinyl silicone oil, dimethyl silicone oil, and platinum catalyst in a mass ratio of 10:1.5:0.25; component B: vinyl silicone oil, hydrogen-terminated silicone oil, and methylbutyninol in a mass ratio of 10:3:0.1, component A: component B = 50:50); the additive is a structure control agent (hexamethyldisilazane, HMDS), used to pretreat the filler to improve dispersion.

[0082] The conductive rubber material is prepared by the following method:

[0083] (1) Pretreatment of filler: After the conductive filler is vacuum dried at 80℃ for 4 hours, it is subjected to vapor phase surface treatment with 1wt% HMDS to reduce surface energy;

[0084] (2) Mixing: Place the silicone rubber B component and the same mass fraction (50wt%) of conductive filler in a planetary mixer, stir at low speed for 10 min under vacuum conditions, then stir at high speed for 20 min to ensure that the filler is evenly dispersed, add the A component, and stir at low speed for 5 min to mix evenly.

[0085] (3) Vulcanization molding: Inject the mixed rubber into a standard mold (such as a dumbbell-shaped tensile specimen or a circular resistance test specimen), and use staged vulcanization: stage 1 vulcanization: 100℃×15min; stage 2 vulcanization: 180℃×2min. Prepare at least 5 parallel specimens to ensure the reliability of data statistics.

[0086] The obtained conductive rubber material underwent the performance tests shown in Table 1 below, and the test results are shown in Table 1:

[0087] Test method: The volume resistivity (Ω·cm) of the vulcanized disc sample was measured using a four-probe resistance tester.

[0088] High temperature and high humidity test: The vulcanized disc sample was placed in a constant temperature and humidity test chamber (85℃, 85% RH) for 240 hours. Every 24 hours, it was taken out and cooled to room temperature, and its resistivity change was tested.

[0089] Thermal cycling test: The vulcanized disc sample was placed in a high and low temperature alternating test chamber and 100 cycles were performed, with each cycle consisting of (-40℃×30min→25℃×10min→125℃×30min). The resistivity change before and after the cycle was tested.

[0090] Table 1 Performance Test Results

[0091]

[0092] As can be seen from Table 1, the sheet-like silver-coated aluminum powder described in the embodiments forms a highly efficient two-dimensional conductive network with excellent performance; Cu@Ag has slightly better conductivity, but higher cost and density; GMB@Ag has an isotropic structure with low conductivity and requires a higher filling amount; although CB / CNT forms a network, it has high intrinsic resistance and poor conductivity.

[0093] In this invention, the flake-shaped silver-coated aluminum powder, as a filler, can be uniformly dispersed in the silicone rubber matrix without significant agglomeration. At the same time, the interface between the filler and the silicone rubber matrix is ​​blurred, the bond is tight, and there are no visible gaps or debonding. Cu@Ag, as a filler, disperses well, but its high density makes it prone to slight sedimentation. GMB@Ag suffers from partial debonding (gap) due to the weak bonding between the rigid spheres and the soft rubber matrix. CB / CNT is extremely prone to agglomeration, forming black lumps, and has poor dispersion uniformity.

[0094] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing multi-layered, lamellar silver-coated aluminum powder, characterized in that, Includes the following steps: S1. Coat the surface of the flake aluminum powder with a silicon dioxide layer to obtain silicon dioxide coated aluminum powder; S2. Coat the surface of the aluminum powder with silicon dioxide and then plate it with a silver layer to obtain the flake-shaped silver-coated aluminum powder. Before step S2, the process also includes grafting a chelating agent onto the surface of the aluminum powder coated with silica; Silica-coated aluminum powder was dispersed in a dopamine solution, and thiourea was added to carry out an addition reaction to obtain silica-coated aluminum powder with a surface grafted chelating agent. After step S2, the process also includes dispersing flake-shaped silver-coated aluminum powder in an organic solvent, adding a coupling agent to carry out a coupling reaction, and obtaining silver-coated aluminum powder with surface grafted coupling agent. The multi-layered flake silver-coated aluminum powder comprises: flake aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer coats the surface of the flake aluminum powder, and the silver layer coats the surface of the silicon dioxide layer; a coupling agent is also grafted onto the surface of the silver layer; the coupling agent is at least one of titanate coupling agent, zirconate coupling agent, or silane coupling agent.

2. The method for preparing multi-layered lamellar silver-coated aluminum powder according to claim 1, characterized in that, In step S1, the step of coating the surface of the flake aluminum powder with a silica layer specifically includes: dispersing the flake aluminum powder in an alcohol solvent, adding alkyl silicate ester to carry out a hydrolysis reaction, thereby obtaining the silica-coated aluminum powder; The hydrolysis reaction is carried out under weakly acidic conditions with a pH of 4-5, a reaction temperature of 40-50℃, and a reaction time of 6-8 hours.

3. The method for preparing multi-layered lamellar silver-coated aluminum powder according to claim 2, characterized in that, The alkyl silicate ester is at least one of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate, butyl orthosilicate, or pentyl orthosilicate; the alcohol solvent is at least one of ethanol, isopropanol, or n-butanol. The amount of the alkyl silicate ester is 8-12 wt% of the mass of the flake aluminum powder.

4. The method for preparing multi-layered lamellar silver-coated aluminum powder according to any one of claims 1-3, characterized in that, In step S2, the process of recoating the surface of the silica-coated aluminum powder with a silver layer specifically includes: dispersing the silica-coated aluminum powder in water, simultaneously adding a reducing solution and a silver complexing solution, and carrying out a low-temperature reduction reaction under alkaline conditions to obtain the flake-shaped silver-coated aluminum powder.

5. The method for preparing multi-layered lamellar silver-coated aluminum powder according to claim 4, characterized in that, The reducing agent in the reducing solution is at least one of sodium borohydride, potassium borohydride, sodium tartrate, or potassium tartrate. The silver complexing solution includes a silver salt and a complexing agent. The silver salt is at least one of silver nitrate, silver methanesulfonate, or silver iodide. The complexing agent is at least one of triethylamine, triethanolamine, diethylenetriamine, ethylenediamine, sodium citrate tetraacetate, or ammonia. The amount of silver salt used is 10-30 wt% of the mass of the silica-coated aluminum powder.

6. The method for preparing multi-layered lamellar silver-coated aluminum powder according to claim 1, characterized in that, The amount of the coupling agent is 0.5-1.5 wt% of the mass of the silver-coated aluminum powder.

7. A multi-structured, layered, sheet-like silver-coated aluminum powder prepared by the preparation method according to any one of claims 1-6, characterized in that, It includes: flake aluminum powder, a silicon dioxide layer, and a silver layer; the silicon dioxide layer covers the surface of the flake aluminum powder, and the silver layer covers the surface of the silicon dioxide layer; The surface of the silver layer is also grafted with a coupling agent; the coupling agent is at least one of titanate coupling agent, zirconate coupling agent or silane coupling agent.

8. A conductive rubber material for electronic products, characterized in that, It includes multi-structured layered sheet-like silver-coated aluminum powder prepared by the preparation method according to any one of claims 1-6.

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