Nano-silver ball for conductive ink and preparation method of nano-silver ball

Abstract

According to the nano-silver ball for the conductive ink and the preparation method, silver salt is dispersed in a dispersing agent, and the types and the addition amount of an added photosensitive reducing agent and a photoreaction auxiliary agent are controlled in a visible light irradiation environment, so that the reduction reaction rate and the silver seed crystal nucleation and growth rate are accurately controlled and regulated; and performing aging treatment to obtain precipitates, namely the nano-silver balls. According to the invention, through visible light with the wavelength of 450nm-620nm, a proper photoreaction auxiliary agent is added in the reaction process while the nano-silver balls are synthesized by utilizing a photocrystallization method, so that the morphology and the size of a nanoscale reaction product are accurately regulated and controlled, and an environment-friendly reagent and proper reaction parameters are selected; precise regulation and control and batch optimization preparation of the particle size and the morphology of the nano-silver are achieved.

Description

Technical Field

[0001] The present invention relates to a technology in the field of nanomaterials, in particular to a nano silver ball for conductive ink and a preparation method thereof. Background Art

[0002] Existing technologies for synthesizing silver nanospheres include: Physical methods employ a top-down preparation approach, using large particles of elemental silver as the raw material. External energy sources such as pressure, high temperature, laser, vacuum, and ultrasound are used to disrupt the original physical structure of the silver, thereby converting the bulk material from large to small particles. This method has a relatively simple process flow, but places high demands on instrumentation and equipment, resulting in high energy consumption. Chemical methods employ a bottom-up strategy, producing nanomaterials through atomic-level manipulation. Specifically, silver salts, reducing agents, and stabilizers are added to the liquid phase, and reduction of the silver salt is achieved under suitable reaction conditions. This method requires less equipment and can control the morphology of the silver nanospheres to a certain extent, but the reducing agents and stabilizers used in the reaction process can pose certain environmental risks. Furthermore, the small size of the silver nanospheres makes agglomeration very likely to occur during the synthesis process, making the large-scale production of uniformly sized and stable silver nanospheres a technical challenge. Summary of the Invention

[0003] The present invention addresses the problems of uneven particle size, difficult to control morphology, easy agglomeration, and high temperature requirements for the synthesis of nanosilver spheres in the prior art. The present invention proposes nanosilver spheres for conductive ink and a preparation method. The nanosilver spheres are synthesized by photocrystallization using visible light with a wavelength of 450nm-620nm, and a suitable photoreaction auxiliary agent is added during the reaction process to achieve precise control of the morphology and size of the nanoscale reaction products. Environmentally friendly reagents and suitable reaction parameters are selected to achieve precise control of the particle size and morphology of the nanosilver and batch optimized preparation.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a method for preparing nano silver spheres for conductive ink. The method comprises dispersing a silver salt in a dispersant, and controlling the type and amount of a photosensitive reducing agent and a photoreaction auxiliary added under visible light irradiation, thereby precisely controlling the reduction reaction rate, the nucleation rate of silver seeds, and the growth rate. The precipitate obtained after aging treatment is the nano silver sphere.

[0006] The silver salt is silver nitrate, silver sulfate, silver acetate, silver trifluoromethanesulfonate, silver methanesulfonate, silver p-toluenesulfonate or silver trifluoromethanethiol.

[0007] The photosensitive reducing agent is titanium dioxide, zinc oxide, vanadium pentoxide, benzoin, 3-hydroxyacetophenone or a combination thereof.

[0008] The photoreaction auxiliary agent is polyvinyl pyrrolidone, ethylenediaminetetraacetic acid, sodium lauryl sulfate, glucose, ethylene glycol, ascorbic acid, potassium sodium tartrate, sodium hypophosphite, xylene, sodium citrate, triethanolamine, KH560 or a combination thereof.

[0009] The mass ratio of the dispersant to the silver salt is 1:10.

[0010] The mass ratio of the photosensitive reducing agent to the silver salt is 1:20.

[0011] The mass ratio of the photoreaction auxiliary agent to the silver salt is 1:10.

[0012] The dispersion is preferably achieved by ultrasonic stirring to achieve uniform dispersion.

[0013] The wavelength of the visible light is 450nm-620nm.

[0014] The irradiation has a light intensity of 5000-10000 lux and an irradiation time of 20-30 minutes.

[0015] During the reduction reaction, magnetic coupling stirring is continuously performed to ensure that the reactants are evenly mixed.

[0016] The nano silver seeds nucleated in the aging treatment are continuously matured, crystallized, recrystallized, etc. to obtain a precipitate (ie, a reaction product).

[0017] The precipitate is preferably washed by centrifugation or filtration with deionized water or ethanol, repeated three times, the supernatant is poured out, and the solid is placed in a vacuum drying oven or a freeze dryer for drying to obtain a nano silver sphere product with uniform particle size.

[0018] The present invention relates to nano silver balls for conductive ink prepared by the above method, which have excellent conductivity and mechanical properties, are not easily oxidized, and can maintain long-term stability in physical and chemical properties, while having a high specific surface area. Technical Effects

[0019] The present invention introduces visible light during the material synthesis process, uses the photocrystallization method to synthesize nano-silver spheres with uniform particle size, and uses visible light energy to accurately control the reaction rate and product composition, thereby achieving precise regulation of the morphology and size of nano-scale reaction products. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope (SEM) image of the silver nanospheres prepared in the embodiment of the present invention (scale 500 nm);

[0021] Figure 2 This is a scanning electron microscope (SEM) image of the silver nanospheres prepared in the embodiment of the present invention (scale 250 nm);

[0022] Figure 3 This is the X-ray diffraction pattern (XRD) of the silver nanospheres prepared in the embodiment of the present invention. DETAILED DESCRIPTION Example 1

[0023] This embodiment relates to a method for preparing nano silver spheres, comprising:

[0024] 1) Add 500 mg of silver salt or 10 mL of silver salt solution to the dispersant and ultrasonicate for 10-20 minutes (ultrasonic frequency is 25-35 kHz) or magnetically stir at room temperature for 5-30 minutes until the mixture has no obvious particulate matter and ensures uniform dispersion.

[0025] The mass ratio of the dispersant to the silver salt is 1:10.

[0026] The dispersant includes an anionic wetting dispersant (including sodium oleate, magnesium pyrrolidone carboxylate, sodium lauryl polyoxyethylene ether sulfate, sodium lignin sulfonate, etc.), a cationic wetting dispersant (including sodium ammonium polyacrylate, tetrabutylammonium bromide, pyridinium tribromide, etc.), a nonionic wetting dispersant (including polyoxyethylene alkylphenol ether, polyoxypropylene fatty alcohol ether, etc.), a polymer hyperdispersant (including polyvinyl pyrrolidone, acrylate homopolymer, polyaminopropionate, polyethyleneimine multi-chimeric copolymer, etc.), a controlled free radical hyperdispersant (such as silane coupling agent, magnesium hydroxide, aluminum hydroxide, wollastonite, kaolin, etc.). In this embodiment, a cationic wetting dispersant - sodium ammonium polyacrylate is used.

[0027] The dispersant is preferably one of polyvinyl pyrrolidone, sodium citrate, deionized water, ethanol (99.8%) or ethanol aqueous solution.

[0028] The volume ratio of deionized water to ethanol (99.8%) in the ethanol aqueous solution is 1:1 to 10:1.

[0029] The silver salt solution is a silver salt aqueous solution or a silver salt ethanol solution.

[0030] The silver salt is one of silver nitrate, silver sulfate, silver acetate, silver trifluoromethanesulfonate, silver methanesulfonate, silver p-toluenesulfonate, and silver trifluoromethanethiol. In this embodiment, the dispersant is deionized water and the silver salt is silver acetate.

[0031] Step 2) Slowly add a photosensitive reducing agent to the mixed solution in step 1) to perform a reduction reaction to preliminarily generate silver seed crystals. By controlling the type and amount of the photosensitive reducing agent, the reduction reaction rate, seed nucleation and growth rate are regulated, thereby achieving precise control of the size of the nanosilver spheres. This seed nucleation process is carried out under visible light irradiation (wavelength 450nm-620nm), and magnetic coupling stirring is continuously performed during the growth of the crystal nucleus to ensure that the reactants are evenly mixed. During the reaction process, the photosensitive reducing agent absorbs visible light energy to generate free radical ions, and the silver ions generate nanosilver seeds under the action of the free radicals.

[0032] The mass ratio of the photosensitive reducing agent to the silver salt is 1:20. The photosensitive reducing agent is one or more of semiconductor materials with light absorption characteristics such as titanium dioxide, zinc oxide, vanadium pentoxide, benzoin, and 3-hydroxyacetophenone. The visible light irradiation time is 20-30 minutes. In this embodiment, 3-hydroxyacetophenone is selected.

[0033] Step 3) A photoreaction aid is added to the mixed solution in step 2), and the mixture is subjected to continuous magnetic coupling stirring for 10-30 minutes at a stirring speed of 650 rpm under visible light irradiation (wavelength 450 nm-620 nm). After the stirring is completed, the mixture is allowed to stand for 1 hour to undergo an aging treatment. During the aging process, the nucleated nanosilver seeds continue to coarsen and agglomerate, thereby obtaining a precipitate (i.e., the reaction product).

[0034] The mass ratio of the photoreaction auxiliary to the silver salt is 1:10, and the photoreaction auxiliary is any one or a mixture of polyvinyl pyrrolidone, ethylenediaminetetraacetic acid, sodium lauryl sulfate, glucose, ethylene glycol, ascorbic acid, potassium sodium tartrate, sodium hypophosphite, xylene, sodium citrate, triethanolamine, and KH560. The visible light irradiation time is 30 minutes. In this embodiment, ethylenediaminetetraacetic acid is specifically used.

[0035] Step 4) washing and drying the precipitate: The precipitate is washed with a detergent, which can be any one of water, ethanol, or a mixture of the two in any proportion. The number of centrifugal washings is 3 times, and the rotation speed during the centrifugation process is 5000-8000 rpm. The supernatant after the last centrifugation is poured out, and the resulting solid is dried at -50°C to 80°C for 10h to 24h to obtain nanosilver spheres with uniform particle size. The drying method is one of vacuum drying, freeze drying, and supercritical drying. The dried nanosilver spheres are placed in an inert gas (nitrogen or argon) and sealed.

[0036] like Figure 1-Figure 3As shown in FIG, the SEM image of the silver nanospheres prepared in the above embodiment shows that the particle size distribution is relatively uniform and the crystallinity is good. The diffraction peaks are in good agreement with the silver standard card (JCPDS No. 04-0783). The diffraction peaks at 38.12°, 44.28°, 64.43°, 77.47°, and 81.54° correspond to the (111), (200), (220), (311), and (222) crystal planes of elemental silver, respectively.

[0037] Compared with the existing technology, the present invention uses a photosensitive reducing agent to regulate the reduction reaction rate, seed nucleation and growth rate by controlling the type and addition amount of the photosensitive reducing agent; by introducing visible light, nano silver spheres are synthesized using the photocrystallization method, and light energy can accurately control the reaction rate and product composition, thereby achieving precise control of the morphology and size of nanoscale reaction products; by adding a photoreaction auxiliary agent, the electrostatic interaction and steric hindrance effect between the seed crystals generated during the reduction reaction are further enhanced to prevent the occurrence of agglomeration, and the physical and chemical properties of the prepared nano silver spheres can remain stable for a long time.

[0038] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for preparing nano silver balls for conductive ink, characterized in that: By dispersing silver salt in a dispersant and controlling the type and amount of the added photosensitive reducing agent and photoreaction auxiliary under visible light irradiation, the reduction reaction rate, silver seed nucleation and growth rate are precisely controlled and regulated, and the precipitate obtained after aging treatment is nano-silver spheres; The silver salt is silver nitrate, silver sulfate, silver acetate, silver trifluoromethanesulfonate, silver methanesulfonate, silver p-toluenesulfonate or silver trifluoromethanethiol; The photosensitive reducing agent is titanium dioxide, zinc oxide, vanadium pentoxide, benzoin, 3-hydroxyacetophenone or a combination thereof; The photoreaction auxiliary agent is polyvinyl pyrrolidone, ethylenediaminetetraacetic acid, sodium lauryl sulfate, glucose, ethylene glycol, ascorbic acid, potassium sodium tartrate, sodium hypophosphite, xylene, sodium citrate, triethanolamine, KH560 or a combination thereof.

2. The method for preparing nano silver balls for conductive ink according to claim 1, wherein: The mass ratio of the dispersant to the silver salt is 1:10; The mass ratio of the photosensitive reducing agent to the silver salt is 1:20; The mass ratio of the photoreaction auxiliary agent to the silver salt is 1:

10.

3. The method for preparing nano silver balls for conductive ink according to claim 1, wherein: The wavelength of the visible light is 450nm-620nm; The irradiation has a light intensity of 5000-10000 lux and an irradiation time of 20-30 minutes.

4. The method for preparing nano silver balls for conductive ink according to claim 1, wherein: The precipitate is preferably washed by centrifugation or filtration with deionized water or ethanol, repeated three times, the supernatant is poured out, and the solid is placed in a vacuum drying oven or a freeze dryer for drying to obtain a nano silver sphere product with uniform particle size.

5. The method for preparing nano silver balls for conductive ink according to any one of claims 1 to 5, wherein include: Step 1) 500 mg of silver salt or 10 mL of silver salt solution was added to the dispersant and ultrasonicated at a frequency of 25-35 kHz for 10-20 minutes or magnetically stirred at room temperature for 5-30 minutes until the mixture had no obvious particulate matter, ensuring uniform dispersion; The dispersant is a cationic wetting and dispersing agent - sodium ammonium polyacrylate; The dispersant is deionized water, and the silver salt is silver acetate; Step 2) slowly adding a photosensitive reducing agent to the mixed solution in step 1) to perform a reduction reaction to initially generate silver seed crystals; by controlling the type and amount of the photosensitive reducing agent, the reduction reaction rate, seed nucleation, and growth rate are regulated, thereby achieving precise control of the size of the silver nanospheres; the seed nucleation process is carried out under visible light irradiation with a wavelength of 450nm-620nm, and magnetic coupling stirring is continuously performed during the growth of the crystal nuclei to ensure uniform mixing of the reactants; The photosensitive reducing agent is 3-hydroxyacetophenone; step 3) adding a photoreaction aid to the mixed solution in step 2), and subjecting the mixed solution to continuous magnetic coupling stirring for 10-30 minutes at a stirring speed of 650 rpm under visible light irradiation of a wavelength of 450 nm to 620 nm. After the stirring is completed, the solution is allowed to stand for 1 hour for aging treatment; during the aging process, the nucleated nanosilver seeds are continuously coarsened and agglomerated, thereby obtaining a precipitate; The photoreaction auxiliary agent is ethylenediaminetetraacetic acid; Step 4) washing and drying the precipitate: The precipitate is washed with a detergent, which may be water, ethanol, or a mixture of the two in any proportion; the precipitate is centrifuged three times at a speed of 5000-8000 rpm; the supernatant after the final centrifugation is discarded, and the resulting solid is dried at -50°C to 80°C for 10 to 24 hours to obtain silver nanospheres with uniform particle size; the drying method may be vacuum drying, freeze drying, or supercritical drying; and the dried silver nanospheres are sealed under inert gas.

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